new single source precursors for mocvd of tungsten ... · laurel leigh reitfort a dissertation...
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NEW SINGLE SOURCE PRECURSORS FOR MOCVD OF TUNGSTEN CARBONITRIDE THIN FILMS
By
LAUREL LEIGH REITFORT
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
2008
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To my mom and dad
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ACKNOWLEDGMENTS
First, I thank my advisor, Professor Lisa McElwee-White. She is always an inspiration and
has been a pleasure to work for. Her patience, support and encouragement have meant so much
to me and will never be forgotten. I would also like to thank Dr. Khalil Abboud. He has been a
wonderful mentor and support system during my graduate studies.
There are not enough words to thank my parents and family for all of their love, support,
patience, and understanding. For this I will ever be grateful. I also acknowledge Ahmet Baysal,
Delmy Diaz, Ewa Hughes, Karen Lyle, Shannon Skoog, Ece Unur, and Marie Correia for their
love, friendship, and never ending encouragement.
I thank Dr. Sylvia Montesinos, Dr. Barbara Welsch, and Dr. Beree Darby for the countless
conversations and time they put forth to help me endure graduate school.
The McElwee-White group members, present and past, have been a pleasure to work with
and learn from. I also thank Professor Joe Templeton and Dr. Jeff Cross for introducing me to
research and encouraging me to pursue graduate school.
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TABLE OF CONTENTS page
ACKNOWLEDGMENTS ...............................................................................................................3
LIST OF TABLES...........................................................................................................................7
LIST OF FIGURES .........................................................................................................................9
ABSTRACT...................................................................................................................................11
CHAPTER
1 INTRODUCTION ..................................................................................................................13
Thin Films...............................................................................................................................13 Thin Film Deposition Techniques ..........................................................................................13
Physical Vapor Deposition ..............................................................................................13 Chemical Vapor Deposition ............................................................................................14
Film Characterization .............................................................................................................16 X-ray Diffraction (XRD).................................................................................................16 X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES)....16 Four Point Probe..............................................................................................................17
Use of Thin Films in Microelectronics...................................................................................19 Materials Used in Microelectronics.................................................................................19
Interconnect metal ....................................................................................................19 Interlayer dielectrics (ILD).......................................................................................20 Diffusion barriers .....................................................................................................21
Metal Nitride Precursor Design.......................................................................................23 Co-reactant precursors..............................................................................................24 Amido/imido precursors...........................................................................................25 Azolate precursors....................................................................................................28 Guanidinate and amidinate precursors .....................................................................28 Hydrazido precursors ...............................................................................................29
Precursor Screening ................................................................................................................30
2 SYNTHESIS AND CHARACTERIZATION OF Cl4(RCN)W(NCH2CH=CH2) (R = Me or Ph) AS A PRECURSOR FOR MOCVD OF WNXCY .......................................................31
Metal Imido Compounds ........................................................................................................31 Synthesis of the W(VI) Allylimido Precursor ........................................................................32 Characterization of 3a.............................................................................................................33
X-ray Crystallographic Study of Cl4(CH3CN)W(NCH2CH=CH2) (3a)..........................33 Mass Spectrometry ..........................................................................................................36 Film Growth ....................................................................................................................38 Film Composition............................................................................................................39
X-ray diffraction.......................................................................................................39
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Auger electron spectroscopy ....................................................................................42 Effect of the Imido N-C BDE on Film Growth. .....................................................................44 Conclusions.............................................................................................................................47 Experimental Procedure..........................................................................................................47
General (Precursor Synthesis). ........................................................................................47 Synthesis of WOCl4 .................................................................................................48 Synthesis of Cl4(CH3CN)W(NCH2CH=CH2) (3a) ..................................................48
Mass Spectrometry ..........................................................................................................49 Crystallographic Structural Determination of 3a ............................................................49 Film Growth Studies........................................................................................................50
3 EXPERIMENTAL AND COMPUTATIONAL COMPARISON OF PRECURSOR DECOMPOSITION................................................................................................................52
CVD Precursor Decomposition Pathways..............................................................................52 NMR Line Shape Analysis .....................................................................................................52 Dissociation of Acetonitrile in Cl4W(NiPr)(NCCH3) .............................................................53 Loss of Chlorine During Deposition.......................................................................................55 Dissociation of the W-N(imido) and N(imido)-C Bonds in 1a-3a.........................................57 Conclusions.............................................................................................................................60 Experimental Procedure for NMR Kinetics of Acetonitrile Exchange in 2 ...........................61
4 SYNTHESIS, CHARACTERIZATION, AND FILM DEPOSITION OF AN ISOPROPYL GUANIDINATO MOCVD PRECURSOR .....................................................62
Metal Guanidinate Compounds ..............................................................................................62 Use of Guanidinates in Thin Film Deposition........................................................................63 Results and Discussion ...........................................................................................................63
Precursor Synthesis .........................................................................................................63 Precursor Screening.........................................................................................................66
Thermogravimetric analysis .....................................................................................66 Mass spectrometry....................................................................................................68
Film Deposition from 4 ...................................................................................................70 Film growth ..............................................................................................................70 Film composition......................................................................................................70 XRD of films............................................................................................................72 Film growth rate (X-SEM).......................................................................................73 Film resistivity..........................................................................................................74 Diffusion barrier testing ...........................................................................................75 Conclusions ..............................................................................................................77
Experimental Procedure..........................................................................................................78 General Procedure ...........................................................................................................78
Synthesis of W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4) .....................................................78 Crystallographic Structure Determination of 4. ..............................................................79 Mass Spectrometry ..........................................................................................................80 Thermogravimetric Analysis ...........................................................................................80 Film Growth Studies........................................................................................................80
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5 SYNTHESIS OF TUNGSTEN IMIDO GUANIDINATO HYDRIDE COMPLEXES.........82
Transition Metal Hydrides......................................................................................................82 Synthesis and Characterization of Transition Metal Hydride MOCVD Precursors...............82
Synthesis..........................................................................................................................82 Characterization...............................................................................................................83
NMR spectroscopy...................................................................................................83 X-ray crystallography...............................................................................................86 Thermogravimetric analysis .....................................................................................88 Mass spectrometry data............................................................................................90
Conclusion ..............................................................................................................................91 Experimental Procedures ........................................................................................................92
General Procedures..........................................................................................................92 Synthesis of W2(NiPr)2[iPrNC(NMe2)NiPr]2(H2)(µ-H)2 (5).................................92 Synthesis of W2(NCy)2[iPrNC(NMe2)NiPr]2(H2)(µ-H)2 (6). ...............................93 Synthesis of W2(NPh)2[iPrNC(NMe2)NiPr]2(H2)(µ-H)2 (7). ................................93
X-ray Crystallography .....................................................................................................94 Mass Spectrometry ..........................................................................................................95 Thermogravimetric Analysis ...........................................................................................95
APPENDIX
A CRYSTALLOGRAPHY DATA FOR 3a ..............................................................................96
B KINETICS DATA FOR 1 ......................................................................................................99
C STRUCTURAL CHARACTERIZATION FOR 5 ...............................................................100
LIST OF REFERENCES.............................................................................................................117
BIOGRAPHICAL SKETCH .......................................................................................................130
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LIST OF TABLES
Table page 2-1 Crystal data and structure refinement for Cl4(CH3CN)W(NCH2CH=CH2) (3a). .................35
2-2 Selected bond distances (Å) and angles (degrees) for Cl4(CH3CN)W(NCH2CH=CH2) (3a)....................................................................................................................................36
2-3 Summary of relative abundances for positive ion EI and negative ion NCI mass spectra of tungsten imido complexes Cl4(CH3CN)W(NCH2CH=CH2) (3a). ...............................37
2-4 Comparison of deposition behavior for 1a,b-3a,b. ...............................................................45
3-1 Calculated bond lengths (Å) and bond angles (°) for complexes 1-3....................................58
3-2 Calculated bond dissociation enthalpy for the N1-C and W-N1 bonds in 1a-3a and 1a′-3a′......................................................................................................................................59
4-1 Crystal data and structure refinement for 4. ..........................................................................64
4-2 Selected bond distances (Å) and angles (°) for compound 4.................................................66
4-3 Molar flow rates of reactants in the CVD reactor ..................................................................80
5-1 Selected bond distances (Å) and angles (°) for compound 5.................................................88
A-1 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 3a.........................................................................................................................96
A-2 Bond lengths [Å] and angles [°] for 3a...............................................................................97
A-3 Anisotropic displacement parameters (Å2x 103) for 3a. ..................................................98
A-4 Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 3a.......................................................................................................................................98
B-1 Rates for the acetonitrile exchange of complex 1. ................................................................99
C-1 Crystal data and structure refinement for 5.........................................................................101
C-2 Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5..........................................................................................................................102
C-4 Anisotropic displacement parameters (Å2x 103) for 5.....................................................113
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C-5 Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for 5........................................................................................................................................114
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LIST OF FIGURES
Figure page 1-1 Electronic transitions involved in XPS and AES. .................................................................17
1-2 Four point probe. ...................................................................................................................18
1-4 Device layers in an integrated circuit. ...................................................................................20
1-5 Early precursors for TiNx deposition developed by Gordon and co-workers. ......................26
2-1 Bonding in metal imido complexes. ......................................................................................32
2-2 Synthesis of tungsten imido precursors. ................................................................................33
2-3 Thermal ellipsoids diagram of the molecular structure of Cl4(CH3CN)W(NCH2CH=CH2) (3a). ..............................................................................34
2-4 Schematic diagram of CVD system.161,162 .............................................................................39
2-5 XRD spectra for films grown with 3a,b on Si (100) in a H2 atmosphere .............................41
2-6 Change in XRD pattern with deposition temperature for films grown from 3a,b on Si (100) in a H2 atmosphere. ..................................................................................................42
2-7 Comparison of W, N, C and O content in the films grown from 1a,b, 2a,b and 3a,b. Data are from AES measurements after 2.0 minutes sputter. ............................................44
2-8 Variation of apparent activation energy (Ea) for film growth from Cl4(R'CN)W(NR) (1a,b, R = iPr; 2a,b, R = Ph; 3a,b, R = allyl) with the N−C bond energies of the corresponding amines R-NH2 as models for the imido N-C bonds. .................................46
3-1 Effect of exchange rates on NMR line shapes.......................................................................53
3-2 Complexes 1-3. ......................................................................................................................58
3-3 Comparison of nitrogen content in the films grown from 1-3 (AES). ..................................60
4-1 Resonance forms of the guanidinate anion............................................................................62
4-2 Thermal ellipsoids diagram of the molecular structure of 4..................................................65
4-3 TGA curves of compound 4 ..................................................................................................68
4-4 PCI mass spectra of compound 4. .........................................................................................69
4-5 Composition of films deposited from 4 and 1 on Si (100) substrate at different deposition temperature as determined by AES after 0.5 min of sputtering .......................71
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4-6 XRD patterns for films deposited on Si (100) substrate from 4. ............................................72
4-7 X-SEM images for films grown from 4.................................................................................74
4-8 Arrhenius plot of log of film growth rate vs. inverse temperature for deposition from 1 and 4 on a Si(100) substrate...............................................................................................74
4-9 Change in film resistivity with deposition temperature for films grown on Si (100) from 4 and 1a,b..................................................................................................................75
4-10 AES depth profiles of Cu (100 nm)/ WNxCy (50 nm)/Si (100) stack for WNxCy film deposited at 450 °C and annealed in vacuum for 30 min.. ................................................76
5-1 Synthesis of tungsten imido/guanidinato/hydride complexes 5-7. ........................................83
5-2 1H NMR spectrum of 5 in THF-d8.........................................................................................85
5-3 Thermal ellipsoid diagram of the molecular structure of 5. . ................................................87
5-4 TGA data for 5. Weight % and Derivative (Weight %) vs. Temperature. ...........................89
5-5 Comparison of TGA data for complexes 4 and 5. .................................................................90
5-6 PCI mass spectrum of compound 5. ......................................................................................91
C-1 Heteronuclear Multiple Bond Coherence (gHMBC) NMR spectrum of Hydride Dimer 5........................................................................................................................................100
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Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy
NEW SINGLE SOURCE PRECURSORS FOR MOCVD OF TUNGSTEN CARBONITRIDE THIN FILMS
By
Laurel L. Reitfort
May 2008
Chair: Lisa McElwee-White Major: Chemistry
Tungsten carbonitride (WNxCy) thin films were produced from the single-source
precursors Cl4(L)W(NCH2CH=CH2) (L = PhCN or MeCN). The compound
Cl4(NCMe)W(NCH2CH=CH2) was characterized by 1H and 13C NMR spectroscopy, and X-ray
crystallography. Mass spectrometry was performed to determine possible fragmentation
pathways of the precursors. Deposited films were characterized by X-ray diffraction and Auger
electron spectroscopy. This allowed for comparison of the film growth properties to those using
the previous precursors (Cl4(L)W(NR), R = iPr or Ph). Comparison of the three precursors
provided a strong correlation between the imido N−C bond dissociation energy and the
activation energy of film deposition.
MOCVD growth of tungsten nitride (WNx) and WNxCy thin films has been reported from
the complex Cl4(CH3CN)W(N iPr). NMR kinetics of acetonitrile exchange in solution verified
that dissociation of the acetonitrile ligand should be facile for the family of precursors
[Cl4(CH3CN)W(NR), R = iPr, CH2CH=CH2, or Ph] in the temperature range used for film
growth (>450 °C). These data are compared to computational studies of the compounds.
A solution of the tungsten imido guanidinato complex W(NiPr)Cl3[iPrNC(NMe2)NiPr] in
benzonitrile was used to deposit WNxCy thin films by chemical vapor deposition (CVD) in the
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temperature range 400 to 750 °C. The resulting films were composed of tungsten, nitrogen,
carbon and oxygen as determined by Auger electron spectroscopy (AES). X-ray photoelectron
spectroscopy (XPS) results indicated that no chlorine impurity was present in the film. The
properties of thin films deposited were compared to those from the isopropyl imido complex,
Cl4(RCN)W(NiPr) (R= CH3, Ph), to provide insight into the effect of imido and guanidinato
ligands on film properties.
New WNxCy precursors incorporating imido, guanidinato, and hydride moieties were
synthesized. Compounds were characterized by 1H and 13C NMR spectroscopy, X-ray
crystallography, mass spectrometry, and thermogravimetric analysis (TGA). The
characterization data were used to predict possible fragmentation pathways in film deposition.
Variable temperature NMR studies were done on bridging hydride complexes to demonstrate
fluxionality of hydrogens.
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CHAPTER 1 INTRODUCTION
Thin Films
Thin films are deposited layers with high surface to volume ratio, which vary from the
bulk material of the substrate on which they lie. They typically vary in thickness from a few
atomic layers to several micrometers. Thin film deposition is used in a wide variety of
applications, including semiconductor devices, industrial coatings, flat panel displays, disk
drives, and inks. The growth in this area of science has lead to an increase in the development of
new thin film deposition and processing techniques. In addition to new thin film technologies,
development of new materials is a rapidly growing area of research.1,2
Thin Film Deposition Techniques
Physical Vapor Deposition
Physical vapor deposition (PVD) is a film deposition process where atoms or molecules of
a material are vaporized from a solid or liquid source, transported through a vacuum or low
pressure gaseous environment, and condensed on a substrate. In PVD the source material does
not undergo a chemical reaction to form the film, only a phase change. Methods of PVD include
vacuum deposition or vacuum evaporation, sputter deposition, and ion plating. In vacuum
deposition the source is vaporized by boiling or sublimation, transported, and condensed to a
solid film on the substrate surface. Ion plating involves ionizing the material to be deposited and
applying an electric field to accelerate the impingement energy on the substrate, modifying the
deposition process and the properties of the deposited film. The source material can be deposited
using various methods such as evaporation, sputtering, or other vaporization sources.2 The most
widely utilized method of PVD is sputter deposition. In this method thin films are formed when
atoms or molecules are physically ejected from a source by energetic particle bombardment,
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leading to the ejected atoms or molecules condensing on a substrate as a thin film. Some
advantages to sputter deposition include easily controllable film thickness, compatibility with
most inorganic materials, less hazardous by-products, and utilization in large scale deposition
applications. PVD also has disadvantages such as line-of-sight deposition leading to poor
conformality in small device features, low rates of deposition, and introduction of impurities into
the substrate.2-5
Chemical Vapor Deposition
Chemical vapor deposition (CVD) is the formation of a film on a surface from a volatile
precursor (vapor or gas), as a consequence of one or more chemical reactions. The precursor can
break down by thermal decomposition in order to deposit the desired film. This form of
deposition can be useful in a variety of applications including electronics, optoelectronics, and
optical and protective coatings. The advantages of CVD include the ability to uniformly coat
complex components, high purity and variety of chemical compositions of deposited films,
relatively high deposition rates, and potential selective area deposition.6
A number of chemical reactions can occur under CVD conditions including thermal
decomposition, oxidation, reduction, hydrolysis, carbidization and ammonolysis. In thermal
decomposition a precursor breaks down into its elements and uses only one precursor gas. A
reduction reaction occurs when the desired element gains one or more electrons and lowers its
oxidation state. This reaction is used in reduction of metal halides to deposit pure metals; co-
reduction reactions where more than one element is reduced to deposit binary materials; as well
as use of metals such as zinc, cadmium, magnesium, sodium, and potassium as reducing agents
for metal halides. Oxidation and hydrolysis reactions are used in CVD for metal oxide
deposition. In these reactions O2, CO2, or O3 is used as an oxygen source along with a metal
halide. Carbidization and ammonolysis allow for deposition of metal carbides and nitrides.
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Typical precursors for these reactions again utilize metal halides and either hydrocarbons or
ammonia respectively. In the ammonolysis reactions N2 and H2 can be used in place of
ammonia. CVD has the capability of synthesizing simple to complex materials with ease at low
temperatures.7
There are several variations of CVD such as metal-organic CVD (MOCVD), plasma-
enhanced CVD (PECVD), low pressure CVD (LPCVD), and aerosol assisted CVD (AACVD).
MOCVD incorporates the use of an organometallic precursor, PECVD utilizes plasma to
enhance decomposition and reaction, and in LPCVD the reaction chamber is below atmospheric
pressure. To avoid the necessity of using a highly volatile precursor AACVD can be used. In
this method of deposition a liquid or dissolved solid precursor is transported to the substrate as
an aerosol generated by a nebulizer. Another variation of CVD is Atomic Layer Deposition
(ALD). ALD is a surface controlled reaction process that works by subsequent, self-limiting
surface reactions to attain controlled atomic-level deposition. A growth cycle in ALD proceeds
in the following manner:
1. Introduction of the first precursor that will react with the surface until all reactive sites are consumed. This step involves chemisorption of the precursor or formation of relatively strong chemical bonds.
2. Purge of the reaction chamber with a nonreactive gas to remove excess of the first precursor. The physisorbed molecules, which have weak van der Waals interactions, are removed.
3. Introduction of the second precursor which reacts with the initial deposited layer.
4. A final purge of the reaction chamber.8
Due to the cyclic nature of this process, control of film thickness is extremely accurate. Also,
since the introduction of precursors is separate, gas phase reactions are avoided. Some other
advantages to ALD include ease of scale-up, good conformality, and reproducibility.3,4,7,9
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Film Characterization
Characterization of deposited films is an important aspect of thin film deposition. It allows
for quantitative analysis of the composition, thickness, and performance. Some common thin
film characterization techniques include X-ray diffraction (XRD) for structure determination;
Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) to determine
elemental composition, impurities, and chemical states; and four point probe to determine
resistance.
X-ray Diffraction (XRD)
XRD utilizes an incident beam of X-rays focused on a sample; the atomic planes of a
crystal cause the beam of X-rays to interfere as they exit the crystal. The beam is diffracted by
the crystalline phases according to Bragg’s law:
λ = 2d •sinθ
(where λ = wavelength of X-rays, d is the spacing between planes in the atomic lattice, and θ is
the angle between the incident ray and the scattering planes). Diffraction occurs only when the
conditions of Bragg’s Law are satisfied. From the diffraction pattern the crystalline phases can
be identified and structural properties of the film can be measured.10
X-Ray Photoelectron Spectroscopy (XPS) and Auger Electron Spectroscopy (AES)
XPS and AES are both based on the photoelectric effect. The photoelectric effect is when
incident light causes the emission or ejection of electrons from a surface of a metal. In XPS a
sample is irradiated with X-ray photons and if of sufficient energy, electrons are emitted from the
inner-shell orbitals of the sample. The kinetic energy of the ejected photoelectrons is measured
and allows direct identification of the elements present in the thin film by calculating the binding
energy with the following equation:
KE = hν – BE - Φ
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(where KE is the kinetic energy of emitted photoelectron, hν is the X-ray photon energy, BE is
the binding energy of the ejected photoelectron, and Φ is the spectrophotometer work function).
Small variations in the kinetic energy of the ejected photoelectrons also allow determination of
the chemical state of the elements present in the sample.4
Once a photoelectron has been emitted, an outer shell electron can fill the vacant site. In
order to maintain an energy balance, a photon (or Auger electron) can be expelled from an outer
shell. In AES the kinetic energy of the Auger electron is measured in a similar manner to XPS.
Information gathered from AES can allow determination of the elemental composition and the
chemistry of the surfaces of samples. Figure 1-1 illustrates the difference between XPS and
AES.4,10
Figure 1-1. Electronic transitions involved in XPS and AES.
Four Point Probe
The four point probe is used to determine the sheet resistivity and bulk resistance of thin
films. In this technique four thin collinear tungsten wires are used to contact a sample. Current
is applied through the two outer probes, and the voltage between the two inner probes is
measured (Figure 1-2). When the probes are placed with equivalent spacing then the following
equation is applicable:
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(where ρ is resistivity, s is the distance between each probe, t is the thickness of the thin film, V
is the voltage measured, and I is the current flowing through the two outer probes). These
equations give the bulk resistivity.
Figure 1-2. Four point probe.
To determine the sheet resistance of a thin film the latter of the two equations would be
used and both sides would be divided by t giving the following equation:
The sheet resistance is the preferred measurement for thin films since it disregards the geometry
of the material and is purely a representation of the deposited material.4,10
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Use of Thin Films in Microelectronics
Gordon Moore, co-founder of Intel corporation, made the prediction on April 19, 1965 that
component density and performance of integrated circuits would double every year.11 Ten years
later, in 1975, Moore gave a speech at the International Electron Devices Meeting where he
revised this prediction to doubling every two years.12 In order to compensate for extreme
downsizing of electronic devices, new materials are being investigated to increase signal speed
and provide more diverse functions. Thin films play an important role in integrated circuits as
interlayer dielectric material (ILD), diffusion barriers, metal interconnects and semiconductors.
Materials Used in Microelectronics
Many materials can be used for the various device layers in multi-layered structures of
integrated circuits. New materials are constantly being developed and researched to improve the
ever changing technologies. Some of these materials include metal oxides, transition metal
nitrides and carbides, and pure transition metal thin films.
Interconnect metal
A major development in this field is the replacement of aluminum by copper in integrated
circuits.1,13 The use of copper metallization has allowed for a decrease in interconnect size due
to its lower resistivity and higher melting point (1.7-2.0 µΩ-cm, 1084 °C) compared to
aluminum (2.7-3.0 µΩ-cm, 660 °C).5 While copper metallization allows for greater performance
and reliability, it also introduces several challenges for integration purposes, such as limited
processing methods, high diffusivity into silicon, and low adhesion to SiO2. A solution to the
latter two challenges is the use of a diffusion barrier layer that will prevent the diffusion of the
copper into the silicon and promote adhesion of copper (Figure 1-4).
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Figure 1-4. Device layers in an integrated circuit. a) Without diffusion barrier, b) With diffusion barrier
Interlayer dielectrics (ILD)
Low-κ dielectrics are used to electrically insulate conducting metal lines. Requirements of
this material include a low dielectric constant (or low-κ, where κ is a reference value for silicon
dioxide, SiO2 of 3.9 eV); good adhesion to silicon, metals, and silicides; thermal stability; and
lack of moisture and metallic impurities. Another role that the ILD material must play is either
as a getter or a barrier to mobile ions such as Na+. Due to the widespread use of copper as the
metallization material of choice, finding a compatible low-κ dielectric material to lower the
signal delay in a device is of great importance. Lowering the density of the ILD films by
introducing pores helps to greatly reduce the dielectric constant of these films. The main types
of ILD materials are silsesquioxane (SSQ) based, silica based, organic polymers, and amorphous
carbon.4,5,14,15
High-κ dielectric materials are used in metal-oxide-semiconductor field effect transistor
(MOSFET) as gate dielectrics. In the past SiO2 was used due to the thermodynamically stable
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Si-SiO2 interface; it also has good electrical insulation and interfacial bonding properties.
However, as the thickness of this layer continues to decrease the SiO2 will be unable to act as an
insulator. Electrical current will leak across the dielectric material and the capacitor will
discharge. In order to circumvent this problem, new materials with a high-κ value are being
investigated to replace SiO2. Important properties of a replacement material include permittivity,
thermodynamic stability, film morphology, interface quality, compatibility with current or new
materials used in devices and their processing, and reliability. Other oxides such as ZrO2, HfO2,
and La2O3 are being considered for this application. These materials have high κ values
(between 25-30 eV) and high Eg (band gap) values (4.3-5.8 eV) compared to the values of SiO2
where κ = 3.9 eV and Eg = 8.9 eV. The main focus for the replacement of SiO2 is on Hf-based
dielectrics such as HfO2 and HfSiO4.14,16,17
Diffusion barriers
A material must meet several requirements to be considered for use in a diffusion barrier
layer. The material should prevent diffusion of copper into silicon, have low resistivity, and
allow for low temperature deposition to prevent damage to previously deposited device layers
(Figure 1-4). Transition metal nitrides such as TiNx,18-22 TaNx,18,19,23-26 and WNx27-34 have been
used extensively as barrier materials.35 In the past, TiNx has been used as a diffusion barrier for
aluminum.1,36 This poses a problem when it comes to diffusion barrier applications with copper
metallization. TiNx has a columnar type structure, allowing for ease of copper diffusion along
the grain boundaries into the silicon layer.37-39 Another issue that is presented with the use of
TiNx barriers and copper is the diffusivity of copper in TiN.38
Tantalum nitride has been shown to provide a good barrier, but has some general
problems. There are several phases of tantalum nitride including Ta2N, TaN, Ta5N6, Ta4N5, and
Ta3N5.40 In CVD the nitrogen source is usually either NH3 or N2, which is used in excess. Due
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to the excess nitrogen atmosphere the favored phases are those rich in nitrogen (TaN and Ta3N5).
While resistivities of most of the TaxNy phases range from 100 µΩ cm to 800 µΩ cm; Ta3N5 has
a resistivity of 6 Ω cm, an attribute ideal for an insulator instead of a diffusion barrier.40,41 Most
depositions obtaining TaxNy films ideal for diffusion barrier applications require high
temperatures, leading to damage to previously deposited device layers. However, deposition at
the lower temperatures results in Ta3N5 films. In order to avoid deposition of Ta3N5 a strong
reducing agent is required to obtain the Ta+3 oxidation state.42 Another issue with tantalum
nitride is the low adherence to copper, making a Ta/TaN bilayer necessary.1 Typically tantalum
nitride is deposited by sputtering, resulting in amorphous and conductive films.43 As mentioned
previously, the line-of-sight deposition leads to unsatisfactory coverage of detailed device
features. Some tantalum nitride films have been deposited using CVD giving more conformal
films, but resulting in films with higher resistance.44
Tungsten nitride films have also demonstrated excellent growth and barrier
characteristics.45-48 Advantages of this material include migration of nitrogen to the grain
boundaries preventing diffusion of copper, increased adhesion to copper, and facile chemical
mechanical polishing after deposition. As WNx was being studied as a suitable diffusion barrier
material, it was discovered that WNxCy, with resistivities of about 350 µΩ cm, could be
deposited by ALD and the precursor system of WF6, NH3, and triethyl boron at temperatures as
low as 350 °C.46,47,49-52 This was an important discovery because while thin films of WNx have
been deposited at low temperatures, usually the resistivity is higher at the lower deposition
temperatures.53 Therefore, WNxCy is a good candidate as a ternary material for diffusion barrier
applications.
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Metal Nitride Precursor Design
A useful precursor for CVD must possess a few characteristics such as a low vapor
pressure in order to be transferred to the substrate, facile decomposition at low temperatures, and
should not be reactive in the gas phase.54 There are two types of precursor systems that can be
used in CVD: a co-reactant precursor system and a single source precursor. A co-reactant
precursor system consists of multiple precursors each containing one element of the desired film.
A single source precursor incorporates multiple elements of the desired film in one compound.
Use of organometallic compounds for single source precursors has become a popular choice.
These precursors can be synthesized to possess desired characteristics such as increased volatility
and clean decomposition pathways. Some ligands of interest for use in organometallic precursors
include amides,55,56 imides,57 azolates,58,59 amidinates,60 and guanidinates.61-66 Each of these
ligands has a specific advantage; all take advantage of direct metal nitrogen bonds. This is
especially implicit with imides, which possess a strong M-N double bond. Azolates, a nitrogen
analogue to the highly utilized cyclopentadienyl (Cp) ligand, were used in an effort to increase
volatility of the compounds. Amidinates and guanidinates are used to enhance thermal stability
of the precursors while the –R groups increase volatility. Use of organometallic precursors also
allows for compounds with predetermined stoichiometries to be assembled prior to deposition.
While synthesis of organometallic compounds is a well established field, precursor design forces
one to examine possible decomposition pathways of the designed molecule.
Previously co-reactant systems were utilized for deposition of metal nitride thin films.
Precursors such as metal halides and metal carbonyls along with NH3 or N2 were the systems of
choice. As deposition chemistry has evolved, use of single source metal-organic precursors has
developed into a major area of research.
24
Co-reactant precursors
Examples of co-reactant precursor systems used to deposit metal nitride or metal
carbonitride thin films are shown in the list below.
• WCl6 + NH367,68
• W(CO)6 + NH368-71
• WF6 + NH329,72-75
• WF6 + N2 + H276-79
• WF6 + NH3 + Et3B46,47,49-52
• TaCl5 + N2 + H2 + Ar25,40
Initial attempts at deposition of WNx using the WF6/NH3 precursor system produced WF6 • 4NH3
and never deposited the desired film even at high temperatures.29 In attempts at lowering the
activation energy, H2 gas was added to this system to react with fluorine from WF6, producing an
activated intermediate, which would in turn react with NH3. While incorporation of the H2 gas
allowed for successful deposition of tungsten nitride, it was necessary to closely monitor the
molar ratios of the precursors. If too much hydrogen was used then WF6 was reduced too
quickly and pure tungsten metal films were produced. However, if too little hydrogen was used
deposition of WNx films was very slow. Another issue with the WF6 + NH3 precursor system is
the production of HF as a byproduct. HF can react with NH3 to form the solid byproducts, NH4F
and/or NH4HF, providing a source of unwanted particles in the deposited films as well as etching
the silicon substrate.29
In order to avoid issues that arose with the WF6 + NH3 system, several groups began
looking at the N2/ H2/WF6 precursor system.76-79 The N2 gas was used as a source of nitrogen,
while the H2 gas was used as a method to remove fluorine from WF6. These deposition methods
utilized PECVD systems in attempts at lowering the deposition temperatures. While thin films
25
of WNx can be deposited by this method, residual fluorine in the films could cause issues with a
device. Tsai and co-workers showed that most of the residual fluorine can be removed using
rapid thermal annealing (RTA).76 While this provides a means of producing thin films of WNx
the high temperature required during RTA could damage previously deposited layers in a device.
Amido/imido precursors
Development of organometallic precursors for metal nitride deposition began as an effort
to circumvent problems associated with the metal halide co-reactant precursor systems. Early
organometallic precursors for deposition of metal nitride thin films utilized homoleptic alkyl
amide metal complexes, Ti(NR2)4 (R = alkyl or aryl).56,80-85 Sugiyama and co-workers first used
Ti(NR2)4 (R = Me, Et) with N2, H2, or Ar atmosphere to investigate metal nitride deposition in
1975.80 While these precursors deposited TiNx, the films also contained carbon and oxygen
contamination. In 1990, Gordon and co-workers reinvestigated the use of these precursors to
deposit TiNx films. Not only did they take a second look at the Ti(NR2)4 (R = Me, Et)
precursors, they developed a new set of precursors for comparison (Figure 1-5). Films deposited
from the precursors with dialkylamido ligands contained carbon contamination that was both
organic and Ti-bound in nature, while films deposited with cyclic amido ligands contained
exclusively organic carbon. This finding led implied that in the dialkylamido precursors β-
hydrogen activation leads the decomposition pathway; while in the cyclic amido precursors,
homolytic Ti-N bond cleavage gives way to decomposition.82,84
Also investigated was deposition of TaNx using Ta(NMe2)526 and ammonia. Films
deposited from this precursor system were the nitrogen-rich dielectric, Ta3N5. Several studies
have claimed to use Ta(NEt2)5 as a precursor for TaNx films.43,80,86 However, it has been shown
that Ta(NEt2)5 is not stable at moderate temperatures and decomposes into
Ta(EtNCHCH3)(NEt2)3 and (Et2N)3Ta=NEt.87 Most likely the reports of deposition with
26
Ta(NEt2)5, described results from using a mixture of Ta(EtNCHCH3)(NEt2)3 and (Et2N) 3Ta=NEt
to deposit TaNx. Nonetheless, this mixture has been successful at depositing TaNx thin films.23,88
The films deposited from this system showed evidence of Ta3N5, and had high carbon
contamination. Taking advantage of the imido bond in (Et2N) 3Ta=NEt, Chiu and co-workers
developed the precursor (Et2N) 3Ta=NtBu.89 Development of the more stable tBu analogue takes
advantage of the strong imido bond strength and helps to eliminate lack of reproducibility from
the previous mixture. TaNx thin films were deposited from (Et2N) 3Ta=NtBu at temperatures
ranging from 450 °C to 650 °C, with resistivities as low as 920 µΩ cm at 650 °C. Films
deposited at 600 °C had low carbon and oxygen contamination.
Figure 1-5. Early precursors for TiNx deposition developed by Gordon and co-workers.82
Continuing to take advantage of the strong metal-nitrogen imido bond strength, several
WNx precursors were developed.90-92 Chiu and co-workers did extensive deposition studies using
the precursor bis(tert-butylimido)bis(tert-butylamido)tungsten.53,90,93-95 Taking into
27
consideration the high carbon content resulting from β-hydrogen decomposition pathways in the
dialkylamido complexes, the ligands in this precursor were chosen to eliminate this option. Films
with resistivities of 620-8000 µΩ cm were grown at deposition temperatures ranging from 450 to
650 °C.53 Volatile by-products were identified as isobutylene (Me2C=CH2) and MeCN, when
using argon; and under hydrogen carrier gas tBuNH2, NH3, and HCN were also detected. Gas
evolution was evident, although unidentifiable. H2, N2, and methane are all possible gases that
could be released from the system. Possible decomposition pathways leading to these products
include γ-H activation yielding isobutylene and β-methyl eliminations leading to MeCN and
methane generation. Under H2 conditions a methyl group could be stripped from acetonitrile,
then react with surface hydrogen to form HCN. The remaining -NH2 and =NH groups from
isobutylene elimination could react with surface hydrogen to generate NH3, N2, and H2. Due to
these decomposition pathways a significant amount of carbon is left in the deposited films.90,94
Similar studies were also performed with a molybdenum analogue of this precursor.96 Other
precursors investigated in this family include W(NtBu)2(NEt2)2 and W(NtBu)2(NMe2)2.91,92,97,98
In the W(NtBu)2(NEt2)2 precursor, an extra species was detected in thermal decomposition
studies. β-Hydrogen elimination of the diethylamido group leads to formation of EtN=CHMe,
an inaccessible pathway in the -NHtBu analogue.91,98 These studies gave great insight to the
chemistry involved in organometallic precursor decomposition.
Another class of imido precursors is Cl4W(NR)(NCR´) (R = iPr, Ph or CH2CH=CH2; R´ =
Me or Ph).33,57,99 This series of studies demonstrated deposition of WNxCy thin films and
illustrated a strong correlation between the bond dissociation energy of the N-C bond of the
imido ligand and the activation energy for deposition.57 This will be discussed in more detail in
later chapters.
28
In a similar fashion several titanium imido precursors, [TiCl2(NR)(L)n] (R = alkyl or aryl
group and L = various N bound ligands) have been synthesized.100 Of these precursors,
[TiCl2(NtBu)(py)3] seemed to be the best single source precursor. Comparison of films from
[TiCl2(NR)(L)n] showed that the presence of bulky imido substituents and chelating ligands
allowed for high oxygen and carbon content in the films. Taking advantage of an all nitrogen
coordination sphere, TiNx films were deposited using precursors of [Ti(NMe2)2(N3)2]n and
[Ti(NMe2)2(N3)2(py)2].101 The silyl imido complexes [NbCl3(NSiMe2Ph)(NH2SiMe2Ph)]2 and
[TaCl3(NSiMe3)(NC5H3Me2-3,5)2]2 were also successful precursors for deposition of niobium
and tantalum nitride thin films respectively.102 Analysis of the films showed little to no silicon,
carbon, or chlorine contamination, indicating that the elimination of R3SiCl is a facile process.
Azolate precursors
The β-diketonate and cyclopentadienyl (Cp) ligands are prevalent in MOCVD
precursors.103-109 It has been shown that early transition metal complexes with η2-pyrazolate
ligands have similar structural and chemical characteristics to metal-diketonate and Cp
complexes.110,111 The structural and chemical similarities, along with elimination of oxygen from
the ligand, make metal azolate compounds interesting as MOCVD precursors. Winter and co-
workers have synthesized pyrazolato, triazolato, and tetrazolato as single source precursors.112-119
The structural and thermal properties of these compounds have been investigated, but few have
been used for actual film deposition. Some of the precursors synthesized include
Mo(NtBu)2(tBu2pz)2, W(NtBu)2(tBu2pz)2, Ti(tBu2pz)3(PhCN4) and Nb(tBu2pz)3(PhCN4)2, which
appear to have optimal volatility and thermal stability necessary for MOCVD precursors.115,118
Guanidinate and amidinate precursors
In recent years, there has been great interest in guanidinate and amidinate ligands for use in
organometallic precursors. The tunability of the organic groups of these compounds can enhance
29
the volatility of the precursors. More about the specific ligand structure will be discussed in
Chapter 4. A number of transition metal and lanthanide amidinate compounds of the form
[M(R´NC(R)NR´)n]x (R´ = iPr, tBu, R = Me, tBu) using Ti, V, Mn, Fe, Co, Ni, Cu, Ag, and La
have been investigated structurally and thermally for use as MOCVD precursors.120 Using the
[Cu(sBu-amidinate)]2 precursor, copper thin films with low carbon and oxygen contamination
and low resistivities were successfully deposited.121
Several transition metal guanidinato complexes have been synthesized and investigated as
single source MOCVD precursors.122-125 The tungsten guanidinato complexes,
[W(NtBu)2(NMe)(iPrN)2CNMe2] and [W(NtBu)2(H)(iPrN)2CNMe2] with ammonia as a
co-reactant, were used to deposit WNx thin films.63 Lack of ammonia in the deposition
atmosphere produced low nitrogen content films, while use of ammonia reduced carbon
contamination. Films grown from the dimethyl amide precursor had lower carbon contamination
than the hydride precursor. TaNx thin films were successfully deposited with a similar
compound, [Ta(NtBu)(NMeEt)(NiPr)2C(NMeEt)], in the absence of ammonia.126 Use of
W(NiPr)Cl3[iPrNC(NMe2)NiPr] in deposition of WNxCy will be discussed in Chapter 4.
Hydrazido precursors
In co-reactant precursor systems, hydrazine was used as a nitrogen source and a strong
reducing agent in deposition of metal nitride thin films. Using hydrazine as a co-reactant
allowed for a significant deposition temperature decrease.127 In efforts to increase the nitrogen
content in metal nitride thin films and take advantage of the strong reducing nature of hydrazine,
a series of metal hydrazido compounds have been synthesized for MOCVD precursors. This
ligand has been utilized for several different transition metals such as Ga,128 In,128 Ta,129-131
Ti,132,133 Nb,130,131 Hf,129,133 Zr,129,133 Mo,130 and W.130,134 The compounds [Ta(N-
30
tBu)(NMe2)2(tdmh)] and Cl4W(NNMe2)(NCCH3) were successfully used to deposit TaNx and
WNxCy, respectively.129,134
Precursor Screening
Screening of MOCVD precursors is necessary in determining the suitability of a
compound for use in deposition. X-ray crystallography can be used to examine the bonding in a
complex. Identifying the strong and weak bonds can give insight to possible decomposition that
may occur during deposition. Mass spectrometry has been used as a means of precursor
screening to identify the most favorable fragmentation pathways.135,136 Care has to be taken in
the comparison between the ionic mass spectrometry fragmentations versus thermal
decomposition during CVD. Thermogravimetric analysis (TGA) can also give useful
information for precursor selection. Vapor pressure, temperatures of sublimation, and
decomposition characteristics can be interpreted from the TGA data.60,124,125,137 Isothermal
studies can also help predict the stability of precursors.
This work presents the synthesis of various WNxCy precursors. The precursors are
screened by several analytical methods to determine applicability for deposition. The precursors
are used for depositing WNxCy thin films, which are characterized and tested as use for diffusion
barriers in integrated circuits. NMR kinetics experiments were also studied to gain insight into
decomposition pathways.
31
CHAPTER 2 SYNTHESIS AND CHARACTERIZATION OF Cl4(RCN)W(NCH2CH=CH2) (R = Me OR Ph)
AS A PRECURSOR FOR MOCVD OF WNXCY
Metal Imido Compounds
There are two limiting types of metal-imido (NR2-) bonds, which are characterized by the
M-N-C bond angle. The hybridization of the nitrogen and the M-N bond order affect the
structure of the imido ligand. Figure 2-1 A shows an sp2 hybridized nitrogen which forms a M-N
double bond consisting of one σ-bond and one π-bond. The lone pair in the N(sp2) orbital
contributes to a bent M-N-R configuration. This type of imido bond is considered a 4e- donor
and is identified by a M-N-R bond angle ≤140 °C. Most imido bonds have an sp hybridized
nitrogen where the nitrogen lone pair is in a p orbital. (Figure 2-1 B) If the environment around
the metal does not allow for back donation from the nitrogen lone pair then the M-N bond order
is two with a nearly linear M-N-R bond angle, and the imido ligand is considered a 4e- donor.
When back donation into a metal d orbital is possible then an M-N triple bond is formed and
contributes greatly to the linear M-N-R bond angle. This structure is considered a 6e-
donor.138,139 (Figure 2-1 C)
Transition metal complexes that incorporate imido moieties (NR2-) have multiple
applications. Some uses of transition metal imido compounds where the imido ligand is
involved in the reaction include amination,140 hydroamination,141 and transfer of imido groups
onto tertiary phosphines and isocyanides.142-144 Examples in which the imido ligand is simply a
spectator ligand used to stabilize the compound include olefin metathesis catalysts,145 alkene
dimerization and polymerization,146,147 C-H bond activation,148 and alkene cyclopropanation.149
More recently many transition metal imido complexes have been utilized in MOCVD of metal
nitride thin films, making use of the strong metal nitrogen bond to remain intact during the
deposition process.
32
Figure 2-1. Bonding in metal imido complexes. A) Bent, B) Linear, C) Linear.139
Synthesis of the W(VI) Allylimido Precursor
Synthesis of new single source precursors for deposition of WNxCy has recently become an
area of significant interest. Specifically, tungsten imido complexes are of interest due to the
strong W-N multiple bonds that are predicted to stay intact during deposition which in turn will
aid in incorporating nitrogen in the deposited films. The previously synthesized precursors
Cl4(RCN)W(NiPr) (1a, R = CH3; 1b, R = Ph)33,150 and Cl4(RCN)W(NPh) (2a, R = CH3; 2b, R =
Ph)151 (Figure 2-2) were developed to investigate the effect of varying the bond dissociation
energy of the alkyl/aryl-imido bond on the deposited films. In a continuation of this study,
Cl4(RCN)W(NCH3H5) (3a, R = CH3; 3b, R = Ph) was synthesized, characterized, and used to
deposit thin films of WNxCy.57
In designing these precursors it was proposed that the strong tungsten imido bond would
withstand the CVD process while the loosely coordinated acetonitrile fragment would dissociate
easily, use of the H2 carrier gas would eliminate the chlorine as HCl, and the alkyl group would
dissociate from the imido substituent to deposit WNx films.33 In addition by varying the imido
R-group the optimal properties for WNx deposition could be determined. Varying the N-C(alkyl)
or N-C(aryl) bond dissociation energy is important because this bond must be cleaved during the
CVD process.57
33
Figure 2-2. Synthesis of tungsten imido precursors.
Precursor 3 was synthesized by a metathesis reaction, in which tungsten oxychloride is
refluxed with allyl isocyanate in heptanes to form the dimer [Cl4W(NCH2CH=CH2)]2. The target
complexes 3a,b are formed by addition of a coordinating solvent, either acetonitrile or
benzonitrile. Allyl imido complex 3a can be synthesized in relatively high yields of 60-70%.
The compound is a bright orange crystalline powder that is extremely air and moisture sensitive.
Characterization of 3a
X-ray Crystallographic Study of Cl4(CH3CN)W(NCH2CH=CH2) (3a)
The results of single crystal structure determination of complex 3a appear in Figure 2-3
and Tables 2-1 and 2-2. As has been previously reported for analogous tungsten imido
complexes,152,153 the overall geometry at the tungsten center is octahedral with the imido and
acetonitrile ligands located in a trans orientation with respect to each other. The alkene carbons
of the allyl moiety are disordered and for brevity, only one set of positions [C(2)' and C(3)'] will
be discussed.
34
Figure 2-3. Thermal ellipsoids diagram of the molecular structure of Cl4(CH3CN)W(NCH2CH=CH2) (3a). Thermal ellipsoids are plotted at 50% probability. The disordered carbon positions C(2) and C(3) of the allyl moiety are omitted for clarity.
The W≡N bond length of the related chloroimido complex Cl4(CH3CN)W(NCl) has been
reported as 1.72(1) Å.152 This value is somewhat longer than the W-N(1) distance of 1.687(9) Å
observed for 3a, reflecting the electronic differences in the chloroimido vs. alkylimido ligands.
The W≡N bond length of Cl4(THF)W(NC6H4CH3-p)153 (1.711(7) Å) compares more favorably
with that of 3a, as expected for an alkylimido complex. The W-N distance for the nitrile ligand
(2.28(1) Å) as well as the W-Cl bond lengths (2.350(3) and 2.316(3) Å) of Cl4(CH3CN)W(NCl)
are consistent with the analogous distances for 3a.
To my knowledge, only one other allylimido tungsten compound, as well as several
molybdenum complexes containing the NCH2CH=CH2 ligand have been reported, including the
W(IV) compound, [WCl2(PMePh2)2(CO)(NCH2CH=CH2)],154 and the Mo(V) compound
35
Cl3(OPPh3)2Mo(NCH2CH=CH2).155 Much like [WCl2(PMePh2)2(CO)(NCH2CH=CH2)] and
Cl3(OPPh3)2Mo(NCH2CH=CH2), 3a has a C(2)'-C(3)' distance (1.36(3) Å) which is consistent
with the presence of a double bond between these atoms. Furthermore, the C(3)'-C(2)'-C(1)
angle of 120(2)° confirms the presence of sp2 hybridized carbons at C(2) and C(3).
Table 2-1. Crystal data and structure refinement for Cl4(CH3CN)W(NCH2CH=CH2) (3a).
Empirical formula C5 H8 Cl4 N2 W Formula weight 421.78 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P21 Unit cell dimensions a = 6.1482(7) Å α = 90°. b = 7.4742(8) Å β = 95.089(2)°. c = 12.3697(13) Å γ = 90°. Volume 566.18(11) Å3 Z 2 Density (calculated) 2.474 Mg/m3 Absorption coefficient 11.097 mm-1 F(000) 388 Crystal size 0.12 x 0.09 x 0.04 mm3 Theta range for data collection 1.65 to 27.50°. Index ranges -6≤h≤7, -8≤k≤9, -15≤l≤15 Reflections collected 3692 Independent reflections 2287 [R(int) = 0.0442] Completeness to theta = 27.50° 98.6 % Absorption correction Integration Max. and min. transmission 0.6624 and 0.3050 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 2287 / 1 / 112 Goodness-of-fit on F2 1.047 Final R indices [I>2sigma(I)] R1 = 0.0372, wR2 = 0.0883 [1939] R indices (all data) R1 = 0.0469, wR2 = 0.0936 Absolute structure parameter 0.44(4) Largest diff. peak and hole 1.818 and -1.413 e.Å-3
R1 = ∑(||Fo| - |Fc||) / ∑|Fo|
wR2 = [∑[w(Fo2 - Fc2)2] / ∑[w(Fo2)2]]1/2
S = [∑[w(Fo2 - Fc2)2] / (n-p)]1/2
w = 1/[σ2(Fo2)+(m*p)2+n*p], p = [max(Fo2,0)+ 2* Fc2]/3, m & n are constants.
36
Table 2-2. Selected bond distances (Å) and angles (degrees) for Cl4(CH3CN)W(NCH2CH=CH2) (3a)a
W-N(1) 1.687(9) W-Cl(4) 2.351(9) W-N(2) 2.308(8) N(1)-C(1) 1.508(17) W-Cl(1) 2.339(10) C(1)-C(2)' 1.51(2) W-Cl(2) 2.317(8) C(2)'-C(3)' 1.36(3) W-Cl(3) 2.324(9) N(2)-C(4) 1.130(12) C(1)-N(1)-W 167(2) N(1)-W-N(2) 175.8(15) N(1)-W-Cl(2) 90.6(8) N(2)-W-Cl(2) 86.0(7) N(1)-W-Cl(3) 93.6(7) N(2)-W-Cl(3) 84.0(6) Cl(2)-W-Cl(3) 88.7(4) C(4)-N(2)-W 175(3) N(1)-W-Cl(1) 102.4(8) N(2)-W-Cl(1) 81.1(7) C(2)'-C(1)-N(1) 114.2(21) C(3)'-C(2)'-C(1) 120(2) Cl(3)-W-Cl(1) 90.18(13) N(2)-C(4)-C(5) 178(2)
aThe structure of 3a exhibits disorder in the carbon atoms C(2) and C(3) of the allyl moiety. Data for one set of olefinic carbon atoms [C(2)' and C(3)'] are included. Data for the alternative set [C(2) and C(3)]can be found in Appendix A.
Mass Spectrometry
Previously mass spectrometric fragmentation patterns of CVD precursors and their
probable decomposition pathways have shown a strong association.156,157 Realizing that gas
phase ionization and thermal decomposition are different processes, there seems to be a strong
correlation between the fragmentation patterns in mass spectrometry and the resulting film
deposition properties. Previous studies have shown that mass spectrometry of the tungsten imido
precursors Cl4(CH3CN)W(NiPr) (1a) and Cl4(CH3CN)W(NPh) (2a) affords qualitative insights
into their CVD behavior.33,151,158 Therefore mass spectrometry of the precursor complexes was
used as a preliminary screening technique to postulate possible fragmentation pathways before
beginning CVD experiments. Results of a mass spectrometric study of the allylimido complex
3a follow (Table 2-3).
Table 2-3 summarizes the major fragment ions observed in the positive ion electron-impact
(EI) and negative ion electron-capture chemical ionization (NCI) spectra of 3a. As with the
isopropyl and phenyl imido complexes 1a and 2a, no molecular ion was detected with either
37
method. Instead the highest mass envelopes in the EI and NCI spectra occurred at m/z 346 and
381, corresponding to [Cl3W(NCH2CH=CH2)]+ and [Cl4W(NCH2CH=CH2)]- respectively. The
[Cl3W(NCH2CH=CH2)]+ fragment was also the base peak of the EI spectrum. A high abundance
(95%) peak at m/z 41 corresponds to both acetonitrile [CH3CN]+ and the allyl fragment
[CH2CH=CH2]+ from the imido moiety.
Table 2-3. Summary of relative abundances for positive ion EI and negative ion NCI mass spectra of tungsten imido complexes Cl4(CH3CN)W(NCH2CH=CH2) (3a).
EI Fragments NCI Fragments m/z Abundancea [Cl3W(NCH2CH=CH2)]+ 346 100 [Cl4W]+ 326 34 [Cl3WNH]+ 306 12 [Cl3W]+ 291 58 [Cl2W]+ 256 27 [CH3CN]+ or [CH2CH=CH2]+ 41 95 [Cl4W(N CH2CH=CH2)]- 381 5 [Cl4WN]- 340 100
aRelative abundances were adjusted by summing the observed intensities for the predicted peaks of each mass envelope and normalizing the largest sum to 100%
Importantly, the base peak of the NCI spectrum corresponds to the mass envelope of the
nitrido fragment [Cl4WN]- (m/z = 340). A small amount of the protonated nitrido complex
fragment [Cl3WNH]+ was detected in the EI spectrum, but at low relative abundance (~12%).
The observation of the fragments [Cl3WNH]+ and [Cl4WN]- indicates that the critical imido N-C
bond is broken under ionization conditions. The lack of any molecular ion in either mass
spectrum is consistent with the nitrile ligand being labile. As observed with precursors 1a and
2a, the EI spectrum of the allylimido complex 3a also exhibited fragments corresponding to loss
of the imido nitrogen. Accordingly, mass envelopes at m/z 256 (27% abundance) and 291 (58%
abundance) are assigned to the fragments [Cl2W]+ and [Cl3W]+ respectively.
Relative to the isopropyl and phenyl imido precursors 1a and 2a, the allyl complex 3a
shows some similarities and important differences. In each case, the base peak of the EI
38
spectrum corresponds to the loss of CH3CN and one chloride ligand (i.e., [Cl3W(NR)]+). The
abundance of the protonated nitrido fragment [Cl3WNH]+ in the EI spectrum of the allylimido
complex 3a was only about 12% as compared to the 78% relative abundance of the same mass
envelope in the spectrum of the isopropyl imido precursor 1a. Strikingly, this fragment is not
observed at all in the EI spectrum of the phenyl precursor. Additionally, the fragment
corresponding to the loss of the nitrile ligand (i.e., [Cl4W(NR)]-) was observed in the NCI spectra
of all three precursors. Interestingly, this fragment was the base peak for the NCI spectrum of
the phenyl precursor 2a. In contrast, the nitrido fragment [Cl4WN]- was the base peak in the NCI
spectra of the isopropyl and allyl complexes 1a and 3a, while this mass envelope only accounted
for 4% relative abundance in the spectrum of 2a. To the extent that the facile cleavages under
mass spectrometric conditions are also facile under CVD conditions, one would expect higher
nitrogen content in films from 1a and 3a.
The greater abundance of the nitrido fragment [Cl4WN]- in the NCI spectra of 1a and 3a
relative to 2a indicates that the N-C bond of the imido ligand is more easily broken for the allyl
and isopropyl imido precursors than for their phenyl imido analogue. This conclusion is
supported by the absence of [Cl3WNH]+ in the EI spectrum of 2a and its presence in the spectra
of 1a and 3a. These data correlate well with the homolytic C-N bond dissociation energies
reported for the corresponding amines (cf. CH2=CHCH2NH2 = 73 kcal/mol, iPrNH2 = 84
kcal/mol, and PhNH2 = 105 kcal/mol).159,160
Film Growth1
To overcome the low volatility of precursors 1-3, a nebulizer was incorporated into the
delivery system to for deposition of WNxCy.33 The precursors were dissolved in benzonitrile (7.5
1 Film growth and film characterization were done by Omar Bchir.
39
mg/mL) and injected into the nebulizer via syringe. A vibrating quartz plate converts the
dissolved precursor into an aerosol that is carried through the system with a hydrogen carrier gas
to the heated impinging jet. The precursor is then deposited on a silicon substrate that rests on a
heated graphite susceptor (Figure 2-4). After deposition was complete, the films typically had a
smooth, shiny metallic surface, with colors ranging from gold to black, depending on deposition
temperature.
Figure 2-4. Schematic diagram of CVD system.161,162
Film Composition
X-ray diffraction
The X−ray diffraction (XRD) spectra in Figure 2-5 indicate amorphous and polycrystalline
film deposition from complexes 3a,b at 450 and 650 °C, respectively. The polycrystalline film
has peak locations consistent with polycrystalline β −WNxCy. Four characteristic peaks are
evident, indicating that no preferred crystal orientation was present in the films. Primary
Graphite Susceptor
Note: Not to Scale
Dissolved Precursor from Syringe Pump
Precursor “Aerosol”
Thermocouple
Gate Valve (for sample loading)
Sight Glass
Water Cooled Flange
To Vacuum Pump
RF Coils
Quartz Tube
Impinging Jet
Cable to Power Supply
Vibrating Quartz Plate
Carrier Gas to Nebulizer
1/16” Plastic Tubing
Cold Trap
Heated Transfer Tube
40
reflections at 37.18 and 43.33 2θ degrees are consistent with (111) and (200) β −WNxCy growth
planes, while additional reflections at 62.88 and 74.88 2θ degrees indicate (220) and (311)
planes, respectively.
Figure 2-6 shows the evolution of film crystallinity with deposition temperature. For
deposition at and below 525 °C, the characteristic β −WNx peaks are not observed. At 550 °C, a
broad peak appears near 37.63 2θ degrees, indicating polycrystalline β −WNxCy (111) growth.
As the deposition temperature increases to 575 °C, this peak sharpens and a broad peak at 44.08
2θ degrees appears, indicating β −WNxCy (200) growth. The peaks sharpen further as the
temperature approaches 650°C, indicating polycrystalline grain growth. Some of the films
displayed two additional peaks at 32.98 and 61.63 2θ degrees, representing Si (200) Kα and Si
(400) Kβ radiation, respectively. Broad peaks emerge at 63.33 and 75.43 2θ degrees for growth
at 650 °C, indicating β −WNxCy (220) and (311) growth. Since the formation of polycrystalline
films is highly undesirable for diffusion barrier applications, the ability to grow amorphous films
by deposition with this precursor below 550 °C is significant.
The film crystallization for growth at 550 °C with 3a,b can be compared to samples grown
at 500 and 525 °C from 1a,b and 2a,b, respectively. The maximum deposition temperature for
films deposited from 3a,b was 650 °C, as compared to 700 and 750 °C for 1a,b and 2a,b,
respectively. For all three precursors, deposition above the respective maximum growth
temperature resulted in formation of uncharacterized black particles on the substrate and
susceptor, which subsequently compromised film quality.
41
Figure 2-5. XRD spectra for films grown with 3a,b on Si (100) in a H2 atmosphere. a) 450 °C b) 650 °C c) Standard powder diffraction plots for β−WN0.5 and β−WC0.6
42
Figure 2-6. Change in XRD pattern with deposition temperature for films grown from 3a,b on Si (100) in a H2 atmosphere.
Auger electron spectroscopy
Auger results in Figure 2-7 indicate that tungsten, nitrogen, carbon and oxygen were
present in the films deposited from 3a,b, while chlorine was not detected. The lowest carbon
level, 6 at.%, occurs at the lowest deposition temperature of 450 °C. The carbon content
increases with deposition temperature from 6 to 38 at.% between 450 and 600 °C and then levels
off. As in the case for films grown from 1a,b and 2a,b, the overall trend in carbon content for
films grown from the allylimido complexes 3a,b reflects the increasing tendency of the
hydrocarbon groups present in the precursor ligands and the solvent to decompose with
increasing deposition temperature.163
Carbon levels in the films from 3a,b were slightly higher than those from 1a,b for most
deposition temperatures, and significantly higher than those from 2a,b (Figure 2-7). The fact
that films from 2a,b contained lower levels of both nitrogen and carbon than those from 1a,b or
43
3a,b suggests that the phenylimido moiety is more likely to dissociate intact than the
isopropylimido or allylimido fragments, consistent with the higher N−C bond strength in the
phenylimido group.
The nitrogen content in films grown at 450 °C was 4 at.%, and this rose to a maximum of
11 at.% for deposition at 500 °C. Above 500 °C, the nitrogen levels decrease, dipping to 2 at.%
at 650 °C. The higher nitrogen levels at lower temperature reflect the stability of the W−N
multiple bond in the precursor molecule, which likely endures at deposition temperatures up to
500 °C, inhibiting release of nitrogen into the gas phase during deposition. The drop in nitrogen
above 500 °C may indicate decomposition of the W−N multiple bond in the gas phase and/or
increased nitrogen desorption from the film (to form N2 gas) at higher temperature.164
Oxygen contamination resulted from post−growth exposure of the film samples to air, as
demonstrated by incremental AES sputtering, which showed a steady decrease in oxygen levels
with increasing depth into the films. The oxygen concentration was highest at 450 °C, reaching
16 at.%, and decreased slightly to 11 at.% at 525 °C. Amorphous films deposited below 550 °C
had low density and high porosity, which allowed substantial amounts of oxygen to penetrate
into the film lattice. As the deposition temperature was increased to 550 °C, the oxygen content
dropped sharply to 4 at.%. This observation is consistent with crystallization of the film in this
temperature range. As the film crystallizes, its microstructure becomes denser, thereby
inhibiting post−growth oxygen diffusion into the lattice.165,166 As the deposition temperature
increased above 550 °C, the oxygen concentration dropped further, reaching a steady level near 3
at.% at the highest deposition temperatures. This resulted from further film densification (by
polycrystal grain growth) and increased carbon levels at higher deposition temperature, which
stuff the grain boundaries and block diffusion of oxygen into the films.
44
Figure 2-7. Comparison of W, N, C and O content in the films grown from 1a,b, 2a,b and 3a,b. Data are from AES measurements after 2.0 minutes sputter.
Effect of the Imido N-C BDE on Film Growth.
In terms of their expected decomposition chemistry, the most significant difference
between the isopropylimido complexes 1a,b, the phenylimido complexes 2a,b, and the
allylimido complexes 3a,b is the respective dissociation energies of the N−C bond in the imido
ligand. Using the corresponding primary amines as organic model compounds, the N−C bond of
complex 3a,b should be approximately 11 kcal/mol weaker than the analogous bond in 1a,b and
32 kcal/mol weaker than that in 2a,b.159 Since cleavage of this bond is necessary for deposition
45
of WNx, one would expect there to be differences in deposition behavior (Table 2-4) for the three
precursors.
Table 2-4. Comparison of deposition behavior for 1a,b-3a,b.
Precursor Deposition Temp. Range (°C)
Deposition Rate (Å/min)
Ea (eV) Ref.
Cl4(PhCN)W(NCH2CH=CH2), 3a,b 450−650 5−10 0.15 ±0.13 57 Cl4(PhCN)W(NiPr), 1a,b 450−700 10−27 0.84 ±0.23 33 Cl4(PhCN)W(NPh), 2a,b 475−750 2−21 1.41 ±0.28 99
The Ea for film deposition varied significantly for the three precursors, following a trend
consistent with the strength of the imido N−C bond. Film deposition from 2a,b, which possesses
the strongest imido N−C bond, yielded the highest value for Ea (1.41 eV), while that from 1a,b
yielded an intermediate value (0.84 eV). Deposition from 3a,b, which has the weakest N−C
bond, yielded the lowest Ea (0.15 eV), which is well below the typical activation energy range
for CVD growth in the kinetic regime (0.5 to 1 eV).167 A plot of the Ea values for deposition
with the three precursors against the N−C bond strengths for the analogous amines is linear
(Figure 2-8), with a goodness of fit (R2) of 0.96. The linear relationship suggests that cleavage
of the N−C imido bond is the rate-determining step in film growth from the 1a,b, 2a,b and 3a,b
complexes. The strength of the bond in 3a,b is so low, though, that film growth borders on being
mass-transfer controlled. While the typical film growth temperature dependence168 in the mass-
transfer controlled region is ~T1.7−1.8, the temperature dependence for film growth from 3a,b was
slightly higher (~T2.1), indicating that the rate-determining step for film growth from 3a,b has a
very weak kinetic barrier. Imido moieties with higher N−C bond energies, such as those in 1a,b
and 2a,b, present a substantial kinetic constraint on film growth at lower temperature.
46
Figure 2-8. Variation of apparent activation energy (Ea) for film growth from Cl4(R'CN)W(NR) (1a,b, R = iPr; 2a,b, R = Ph; 3a,b, R = allyl) with the N−C bond energies of the corresponding amines R-NH2 as models for the imido N-C bonds. Error bars reflect the uncertainty in film thickness measurement from XSEM images
The strength of the N−C imido bond also has a strong effect on the amount of nitrogen
incorporated into the film. If the N−C imido bond strength is relatively high, as with the
phenylimido complexes 2a,b, the imido group has a greater tendency to dissociate as an intact
ligand via cleavage of the W−N bond, which leaves the films deficient in nitrogen. If the bond
strength is relatively low, as with 1a,b and 3a,b, the alkyl group cleaves from the nitrogen more
easily, leading to higher nitrogen levels in the film. It is interesting to note that unlike
compounds 1a,b and 2a, allylimido complex 3a gives conflicting information on the facility of
N-C bond cleavage in its mass spectra. The [Cl4WN]- ion is the base peak in the NCI spectrum
of 3a while the ion corresponding to loss of the allyl moiety in the EI spectrum, [Cl3WNH]+, is
47
present in only 12% abundance. Although the reason for this behavior is not clear, it may be an
indicator of unanticipated difficulty in clean N-C cleavage under CVD conditions as well.
Conclusions
Comparison of the film growth properties of 3a,b to those of 1a,b and 2a,b allowed
evaluation of the effect of the imido N−C bond dissociation energy on film growth and
properties. Films deposited from 2a,b were deficient in nitrogen compared to those from 1a,b
and 3a,b, consistent with a tendency of the stronger imido N−C bond of 2a,b to result in
dissociation of intact NPh fragments during deposition. Accordingly, an optimal window for
N−C imido bond energy appears to exist in these precursors. If the energy of this bond is too
high (as in 2a,b), the W−N bond cleaves, leaving the films very deficient in nitrogen. If the bond
energy is too low (as in 3a,b), N−C bond cleavage may occur in the gas phase, leading to side
reactions that consume precursor before it reaches the substrate surface. A moderate N−C imido
bond energy (as in 1a,b) combines a substantial growth rate and better nitrogen retention during
low temperature growth with greater likelihood of N−C imido bond cleavage (relative to 2a,b).
In practical terms, films grown from isopropylimido complexes 1a,b are superior to those
from phenylimido complexes 2a,b for barrier applications because material produced from 1a,b
can be deposited at a lower minimum temperature (450 °C), contains more nitrogen, and has a
lower sheet resistance.151 Moreover, the isopropylimido precursor 1a,b appears to be preferable
to the allylimido precursor 3a,b, due to higher growth rate and nitrogen content at their mutual
lowest deposition temperature (450 °C).
Experimental Procedure
General (Precursor Synthesis).
Standard Schlenk and glovebox techniques were employed in the synthesis of
Cl4(CH3CN)W(NCH2CH=CH2) (3a). Allyl isocyanate was purchased from Aldrich and used
48
without further purification. Anhydrous heptane was purchased from Aldrich in a Sure-SealTM
bottle and used as received. All other solvents were purchased from Fisher and passed through
an M. Braun MB-SP solvent purification system prior to use. The benzonitrile complex
Cl4(PhCN)W(NCH2CH=CH2) (3b) was not isolated, but was produced in situ by the substitution
of the acetonitrile ligand of 3a with benzonitrile, which was utilized as the solvent for the
deposition experiments (vide infra). NMR solvents were degassed by three freeze–pump–thaw
cycles and stored over 3Å molecular sieves in an inert atmosphere glove box. 1H and 13C NMR
spectra were recorded on VXR 300, or Inova 500 spectrometers. In cases where assignments of
1H or 13C NMR resonances were ambiguous, 13C-1H HMQC experiments were used. Elemental
analyses were performed by Robertson Microlit (Madison, NJ).
Synthesis of WOCl4
WOCl4 was prepared by the following modification of a literature procedure.169 Inside the
glovebox, 26.17 g of WCl6 (0.06598 mol) was suspended in a 500 mL Schlenk flask in excess
methylene chloride (approx. 350 mL). Freshly distilled Me3SiOSiMe3 (10.71 g, 0.06598 mol)
was added dropwise to the vigorously stirring suspension. The reaction mixture continued to stir
vigorously for 1 hour during which the color changed from a deep red to a bright orange color.
The flask was then removed from the box and the solvent was removed in vacuo on a Schlenk
line. The orange solid was then washed several times with dry hexane to yield clean WOCl4
(21.00 g, 93%).
Synthesis of Cl4(CH3CN)W(NCH2CH=CH2) (3a)
In a glove box, tungsten oxychloride (1.229 g, 3.597 mmol) was slurried in a solution of
allyl isocyanate (0.366 g, 4.41 mmol) in heptane (60 mL) in a sealed Chemglass 350 mL heavy
wall pressure vessel with a Teflon bushing. The vessel was removed from the glovebox and the
mixture was heated for 36 h at 110 °C. The solvent was removed from the resulting dark red
49
solution on a vacuum line. The reddish brown residue was dissolved in a minimal amount of
CH3CN (approximately 10 mL). The resulting solution was stirred for two hours and the solvent
removed under reduced pressure. The resulting brown residue was washed with 5 x 10 mL of
toluene and the extracts concentrated to approximately 5 mL. Hexane was added to precipitate
the product. The orange-brown solid was filtered and washed with hexane to afford 0.974 g (64
% yield) of the imido complex. 1H NMR (CDCl3) δ 7.55 (ddd, J = 1.5, 1.4, 5.6 Hz, 2H,
NCH2CHCH2); 6.07 (tdd, J = 5.6, 10.2, 17.1 Hz, 1H, NCH2CHCH2); 5.73 (dtd, J = 0.6, 1.5, 17.1
Hz, 1H, NCH2CHCH2); 5.60 (dtd, J = 0.6, 1.4, 10.2 Hz, 1H, NCH2CHCH2); 2.50 (s, 3H,
CH3CN). 13C NMR (CDCl3, δ): 129.7 (CH2CHCH2N); 121.9 (CH2CHCH2N); 118.9 (CH3CN);
68.3 (CH2CHCH2N); 3.5 (CH3CN). mp 148-152 °C (dec.). Anal. Calcd for C5H8N2Cl4W: C,
14.24%, H, 1.91%, N, 6.64%. Found: C, 14.51%, H, 1.86%, N, 6.43%.
Mass Spectrometry
All mass spectral analyses were performed using a Finnigan MAT95Q hybrid sector mass
spectrometer (Thermo Finnigan, San Jose, CA). Electron ionization (EI) was carried out in
positive ion mode using electrons of 70 eV potential and a source temperature of 200 °C.
Negative ion electron capture chemical ionization (NCI) used methane as the bath gas at an
indicate pressure of 2 x 10-5 Torr, an electron energy of 100 volts and a source temperature of
120 ˚C. All samples were introduced via a controlled temperature probe with heating and
cooling enabling temperature control down to 35 ˚C. The mass resolving power (m/Δm) was
5000 full width-half maximum (FWHM).
Crystallographic Structural Determination of 3a
Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD
area detector and a graphite monochromator utilizing MoKα radiation (λ = 0.71073 Å). Cell
50
parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was
collected using the ω-scan method (0.3° frame width). The first 50 frames were remeasured at
the end of data collection to monitor instrument and crystal stability (maximum correction on I
was < 1 %). Absorption corrections by integration were applied based on measured indexed
crystal faces.
The structure was solved by the Direct Methods in SHELXTL6,170 and refined using full-
matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms
were calculated in ideal positions and were riding on their respective carbon atoms. The C2-C3
moiety is disordered and was refined in two parts (the other part being C2'-C3' with their site
occupation factors dependently refined. Atom C1 is apparently also disordered but to a lesser
extent than the C2-C3 moiety. It could not be resolved and was refined in the final model as not
disordered. A total of 112 parameters were refined in the final cycle of refinement using 1939
reflections with I > 2σ(I) to yield R1 and wR2 of 3.72% and 8.83%, respectively. Refinement
was done using F2.
Film Growth Studies2
The solid precursor 3a was dissolved in benzonitrile at a concentration of 7.5 mg/mL,
loaded into a syringe and pumped into a nebulizer. Operation of the nebulizer was described
previously.158 Experiments were conducted in a custom-built vertical quartz cold wall CVD
reactor system. P-type boron doped Si (100) substrates with resistivity of 1-2 Ω-cm were used
for the film growths. Growths were conducted for a fixed time period of 150 minutes at
temperatures ranging from 425-675 °C. The system was maintained at vacuum by a mechanical
2 Film growth and characterization was done by Omar Bchir.
51
roughing pump, with the operating pressure fixed at 350 Torr. Hydrogen (H2) carrier gas was
used for the depositions.
Film structure was examined by X-ray diffraction (XRD) on a Philips APD 3720,
operating from 5-85 2θ degrees with Cu Kα radiation. Film composition was determined by
Auger electron spectroscopy (AES) using a Perkin-Elmer PHI 660 Scanning Auger Multiprobe,
while film sheet resistance was measured with an Alessi Industries four-point probe. Film
thickness was estimated by cross-sectional scanning electron microscopy (X-SEM) on a JEOL
JSM-6400, with growth rate calculated by dividing film thickness by deposition time.
52
CHAPTER 3 EXPERIMENTAL AND COMPUTATIONAL COMPARISON OF PRECURSOR
DECOMPOSITION
CVD Precursor Decomposition Pathways
In CVD, understanding decomposition pathways from precursor to deposited material is of
vital importance. Many parameters have to be considered when deconvoluting these pathways.
Not only are solution phase reactions possible, but due to the high temperatures new reactions
should also be considered. While it has been shown that mass spectrometry data can give some
insight into decomposition pathways, they are not conclusive since the mass spectrometry does
not involve thermal degradation of the neutral compound.156,157 Other methods to investigate the
decomposition of metal imido precursors during film deposition have been employed, such as
thermal desorption spectroscopy and temperature programmed reaction spectroscopy.94,98 After
determination of the deposition byproducts, possible decomposition pathways can be inferred.
Experimental and computational studies can help confirm these studies.
NMR Line Shape Analysis
Dynamic chemical processes have a large effect on NMR spectra. Analysis of these
spectra can lead to determination of rate constants (k) and activation parameters. The rate
constant of a reaction has a strong effect on NMR spectra. For example, in the exchange of
NCCH3 in Cl4W(NiPr)(NCCH3), the bound and free NCCH3 will have different chemical shifts
depending on the experimental parameters. If the exchange of NCCH3 is slow then two sets of
resonances with moderately sharp peaks will be apparent. For fast exchange of the NCCH3, a
single sharp peak will be evident at the weighted average of the chemical shifts from the peaks
evident at slow exchange. Intermediate exchange leads to coalescence of the peaks, forming a
single broad peak that can disappear into the baseline.171 (Figure 3-1)
53
Figure 3-1. Effect of exchange rates on NMR line shapes.
Dissociation of Acetonitrile in Cl4W(NiPr)(NCCH3)
In design of the Cl4W(=NR)(NCCH3) (R = iPr, Ph, CH2CH=CH2) precursors, it was
proposed that the NCCH3 ligand would dissociate readily under CVD conditions due to the
strong trans effect of the imido ligand. The trans influence of a ligand is its effect on the strength
of the bond trans to it in a coordination compound.172 In turn the strong trans influence is often
connected to a strong trans effect, which is the effect of a ligand on the rate of substitution for the
trans ligand. Therefore the NCCH3 ligand should readily dissociate based on these
considerations. Previously mass spectrometry was used to illustrate facile dissociation by the
lack of an m/z value of the molecular ion for complexes 1-3.33,57,99 Use of solution phase NMR
kinetics to determine the activation energy for NCCH3 dissociation confirms the ease of this step
in the precursor decomposition. The experimental results are then compared to DFT calculations
for further insight.
To obtain experimental values for the activation energy of CH3CN dissociation from
complex 1, 1H NMR kinetics were used to study the exchange of the acetonitrile ligand with free
CH3CN in CDCl3 solution. Upon lowering the temperature to -20˚C, both bound and free
acetonitrile could be detected in the 1H NMR spectra. As the temperature was raised, the bound
and free acetonitrile signals coalesced. The exchange rate, k, was determined by line shape
54
analysis in the temperature range -6 to 34 °C. The value of k at each temperature can be
calculated from the following equations based on the line shape:
• Fast Exchange:
• Coalescence:
• Intermediate Exchange:
• Slow Exchange:
(k = exchange rate, ν = peak frequency, h = peak-width at half-height, e = with exchange, o =
without exchange).173-177 Both the Arrhenius and Eyring equations define the relationship
between temperature and reaction rate. Since the Arrhenius equation applies strictly to gas
reactions, the Eyring equation is used to calculate the activation energy of the exchange. The
linear form of the Eyring equation is as follows:
(where k = rate constant, T = temperature, R = universal gas constant, ΔH‡ = activation enthalpy,
ΔS‡ = activation entropy, kB = Boltzmann’s constant, and h = Planck’s constant).178-180 Using the
slope of the plot of ln(k/T) vs. 1/T, ΔH‡ is calculated to be 18.52 ± 0.14 kcal/mol and from the y-
intercept ΔS‡ is 15.8 ± 0.5 cal/mol•K for the exchange of acetonitrile in 3a (Figure 3-1).
Calculating ΔG‡ from:
The value of ΔG‡ at temperatures within the film growth range indicate a loss of acetonitrile is
kinetically accessible. Since the first order kinetics of the process are consistent with a
55
dissociative mechanism for the exchange process, those values correspond to ΔH‡ and ΔS‡ for
loss of CH3CN from isopropylimido complex 1. The calculated value for ΔH° is 10.2
kcal/mol.181 Given that the experimental values were obtained in solution while the calculated
values are for a gas phase process, the agreement between them is reasonable.
1/T
0.0032 0.0033 0.0034 0.0035 0.0036 0.0037 0.0038
ln(k
/T)
-4
-3
-2
-1
0
1
2
1/T vs ln(k/T) regression line
Figure 3-1. Plot of ln(k/T) vs. 1/T for acetonitrile exchange in complex 1.
Loss of Chlorine During Deposition
Based on previous RGA (residual gas analyzer) data, during deposition of the imido
precursor 1 with H2 carrier gas, the only detected decomposition product containing chlorine was
HCl.99,163 When using N2 as the carrier gas, H2 and HCl are still detected, leading to the
conclusion that H2 produced during deposition or surface bound H2 still reacts with chlorine
present.163 Another interesting observation is the lack of the reductive elimination product, Cl2, a
process that has been observed in a solution reactions of dichlorotellurium(IV) complexes, which
reductively eliminate chlorine to yield the corresponding tellurium(II) complexes.182 It has also
been shown that thermolysis of cis-PtL2Cl4 (L = pyridine, γ-picoline) can reductively eliminate
56
Cl2 to yield trans-PtL2Cl2.183 There was also no evidence of chlorine in the deposited films
within the detection limits of AES (ca. 1 at%). These data lead us to believe the removal of Cl
from the precursor as HCl is an efficient process and piqued curiosity about the mechanistic
pathways from the imido compounds 1a-3a to HCl. For assessment of the chemistry of 1-3
following loss of the labile acetonitrile ligand, their coordinatively unsaturated derivatives
Cl4W(NiPr) (1a), Cl4W(NPh) (2a), and Cl4W(NCH2CH=CH2) (3a) were used for DFT
calculations.181
In order to produce HCl during deposition, involvement of H2 is probable. Mechanistic
pathways to react H2 with organometallic compounds include oxidative addition, coordination of
H2 followed by transfer of an acidic proton, and σ-bond metathesis. The d0 electron count
eliminates oxidative addition from consideration. DFT calculations have shown coordination of
H2 through a σ-bond in early electron poor transition metals,184 however, no such transition state
was found for complexes 1a-3a.181 This leaves the σ-bond metathesis pathway, which is
favorable for d0 transition metal complexes reacting with H2.185 This reaction takes place by
ligand exchange through a four-centered transition state forming a metal hydride and HCl. DFT
calculations of this intermediate were performed and showed the formation of the metal hydride
and HCl to be endothermic with an activation energy of approximately 37 kcal/mol.181 Under
normal conditions this value may seem high, but under CVD reaction conditions using high
temperatures (450 to 750 °C) and high flux of H2, this endothermic process appears to be a viable
pathway. This appears to be the first reported σ-bond metathesis of a metal chloride with H2 to
form a metal hydride and HCl. Calculations for further removal of chlorines showed the
activation energy for σ-bond metathesis was consistently less than that for reductive elimination.
57
Dissociation of the W-N(imido) and N(imido)-C Bonds in 1a-3a
Loss of the alkyl or aryl fragments in complexes 1-3 is also necessary for deposition of
WNxCy. A strong correlation between the bond dissociation energy of the N-C bond in the
corresponding amine and the activation energy of deposition for compounds 1-3 has been
demonstrated previously.57 Based on this a conclusion could be drawn that cleavage of the
N(imido)-C bond is before or during the rate determining step. A computational study was
done to further understand the bonding in the imido moiety and its effect on precursor
decomposition under CVD conditions. As seen in Figure 3-2 and Table 3-1, bonding in the
phenylimido moiety shows conjugation between the phenyl and imido nitrogen, while the longer
C-N(imido) bonds in the iPr and allylimido moieties reflect the saturated carbon. This also has
an effect on the W-N(imido) bond distance, where the W-N(Ph) is longer as a result of the
stronger C(sp2)-N bond, but the W-N(iPr) and W-N(allyl) have shorter W-N(imido) bonds.
(Table 3-1) The Wiberg bond indices were also calculated for complexes 1-3. As expected the
N-C(phenyl) bond index in 2 (1.1243) is higher than those of N-C(alkyl) for 1 and 3 (0.9763 and
1.0090 respectively). Also the Wiberg bond index for the W-N(imido) bond in 2 (1.8864) is
lower than those of 1 and 3 (2.0412 and 2.0079 respectively).181
58
Figure 3-2. Complexes 1-3.
Table 3-1. Calculated bond lengths (Å) and bond angles (°) for complexes 1-3.
1 (iPr) 2 (Ph) 3 (CH2CH=CH2) Calc.c Calc.c Calc.c Exp.b W-Cla 2.377 2.380 2.375 2.333 W-N1 1.715 1.738 1.716 1.687(9) W-N2 2.347 2.262 2.342 2.308(8) C-N1 1.428 1.363 1.425 1.508(17) Cl-W-N1a 98.1 95.9 98.1 97.4 W-N1-C 179.6 180.0 177.7 167(2)
aAverage value for the four equivalent chlorides. bExperimental values from the X-ray crystal structure of 3.57 cCalculations done by Yong Sun Won.
The bond dissociation energy of W-NCCH3 was calculated using both the acetonitrile
free Cl4WNR (1a-3a) and the previously mentioned Cl3HW(NR) (1a´-3a´) intermediates (Table
3-2). While the calculated bond lengths of the N-C(iPr) and N-C(CH2CH=CH2) were similar, the
corresponding calculated bond dissociation energies reflect the stability of the organic radical
formed upon homolysis. Hence, the general trend for N-C(alkyl, aryl) cleavage is parallel to
59
that of the bond dissociation energy of the corresponding amine. In using the hydride
intermediate the W-N(imido) bond strength increases, while the N-C weakens making cleavage
of the alkyl or aryl groups more favorable.
Table 3-2. Calculated bond dissociation enthalpy for the N1-C and W-N1 bonds in 1a-3a and 1a′-3a′.a
Compound BDE (N1-C) (kcal/mol)
BDE (W-N1) (kcal/mol)
1a (iPr) 98.4 88.2 2a (Ph) 121.3 80.0 3a (CH2CH=CH2) 82.7 86.4 1a′ (iPr) 90.2 94.5 2a′ (Ph) 107.5 85.6 3a′ (CH2CH=CH2) 70.4 93.1
aCalculations done by Yong Sun Won.
The computational data indicate a strong correlation between the W-N(imido) and
N(imido)-C bond strengths to the nitrogen content in the films (Figure 3-3). At lower
temperatures, films deposited from complexes 1a and 2a, with the stronger W-N(imido) bonds
have higher nitrogen content in the film than the films deposited from 3a with a weaker W-
N(imido) bond, leading to the conclusion that the W-N(imido) multiple bond can withstand the
lower deposition temperatures. At temperatures above 500 °C, the nitrogen content in the films
decreases despite the precursor used for deposition indicating possible decomposition of the W-
N(imido) multiple bond. As mentioned previously the weaker W-N(imido) bond in 3a is also
reflected in mass spectrometry data from the lack of the [Cl4WN]- ion. Comparison of
computational results and experimental data illustrates that computational work can be utilized as
a means of precursor screening.
60
Figure 3-3. Comparison of nitrogen content in the films grown from 1-3 (AES).57 Conclusions
Experimental kinetics, DFT calculations and statistical thermodynamics were compared to
evaluate reaction pathways for precursor decomposition during growth of WNx films from the
isopropylimido complex Cl4(CH3CN)W(NiPr) (1), the phenylimido complex
Cl4(CH3CN)W(NPh) (2), and the allylimido complex Cl4(CH3CN)W(NCH2CH=CH2) (3). The
computational results and experimentally determined activation parameters are consistent with
facile dissociation of the acetonitrile ligand (CH3CN) from 1-3 in the temperature range used for
CVD. Computational study of reaction of the coordinatively unsaturated complexes 1a-3a with
H2 located possible transition states for chloride loss via σ-bond metathesis with hydrogen to
yield HCl, the experimentally observed chlorine-containing product in the reactor effluent.
Finally, through qualitative and quantitative theoretical analyses for N(imido)-C and W-
61
N(imido) bonds, nitrogen content in the films grown from 1-3 is linked to calculated bond
dissociation energies.
Experimental Procedure for NMR Kinetics of Acetonitrile Exchange in 2
Compound 1 was prepared as previously described.186 The sample for the exchange study
was prepared in the dry box, by dissolving complex 1 and an equivalent amount of acetonitrile in
CDCl3. The 1H NMR spectrum of this sample at -20 oC displayed the signals for 1 [δ (ppm) 7.14
(hp, 1H), 2.58 (s, 3H) 1.70 (d, 6H)] together with free acetonitrile (2.11 ppm) in a ratio of 1:3.
The exchange of 1 with acetonitrile in the solution was monitored by 1H NMR in the temperature
range -54 to 34 oC. The exchange rate k (see Appendix A) was determined by lineshape analysis
in the temperature range -6 to 34 oC. A plot of ln(k/T) vs. 1/T afforded the activation enthalpy
(18.52 ± 0.14 kcal/mol) and entropy (15.8 ± 0.5 cal/mol•K) for the exchange of acetonitrile by 1.
(Figure 3-1)
The NMR spectra were recorded on a Varian Inova at 500 MHz for proton, equipped
with a 5 mm indirect detection probe, with z-axis gradients. The variable temperature spectra
were recorded on automation. To achieve temperature stability, for each temperature step of 2
ºC, a preacquisition delay of 1500 s was followed by shimming on the lock level. The spectra
were collected in 16 transients, with an acquisition time of 5 seconds. No relaxation delay and no
apodization were used. The actual temperature was measured by running a standard of methanol
under the same conditions. The simulation of the spectra with exchange was done using
gNMR.187
62
CHAPTER 4 SYNTHESIS, CHARACTERIZATION, AND FILM DEPOSITION OF AN ISOPROPYL
GUANIDINATO MOCVD PRECURSOR
Metal Guanidinate Compounds
In the past decade, use of the guanidinato ligand in organometallic chemistry has
developed greatly.188,189 Metal guanidinate compounds have been used in a variety of
applications including catalysts for polymerization reactions and as nitrogen rich precursors for
MOCVD of metal nitride thin films.63,65,137,190-193 There are two resonance forms of the
guanidinate ligand. (Figure 4-1) The electronic flexibility of this ligand makes it compatible
with a range of transition metals and lanthanides in various oxidation states.194-197 Resonance
form A of the guanidinate ligand is essentially considered an amidinate ligand with an amino
substituent. (Figure 4-1) Whereas, contribution from the diamide resonance form B increases the
ligand’s compatibility with electron deficient metal ions due to the increased π-donor ability.
Guanidinates are stronger donors than amidinates, and therefore increase the electron density on
the metal and reduce its ability to be oxidized, an advantage for CVD precursors. Evaluation of
bond lengths in the crystal structures of coordination compounds bearing guanidinate moieties
can help determine which resonance form is the major contributor.
Figure 4-1. Resonance forms of the guanidinate anion.
The first metal guanidinate compounds were synthesized by Lappert et al. in 1970 by
insertion of a carbodiimide into a zirconium or titanium amide bond.198 Since then several other
63
metal guanidinate complexes have been synthesized by this method.124,125,199 Another route to
synthesize metal guanidinates is the use of the lithium guanidinate salt in a salt metathesis
reaction.62,63,123,196,200 One of the advantages of this route is the ability to isolate the guanidinate
salt for characterization before further use.
Use of Guanidinates in Thin Film Deposition
Transition metal guanidinate and amidinate complexes have been used to deposit materials
such as TiCxNy, Fe, Co, Ni, Cu, and TaN by CVD and/or ALD.61,125,201 The volatility of metal
guanidinate complexes makes them ideal precursors for MOCVD. Also, the bidentate ligand
makes these compounds more stable over time. We recently synthesized a series of guanidinate
and amidinate derivatives of precursors 1-3.62 Thermogravimetric analysis and mass
spectrometry were used as a means of screening the new precursors. WNxCy thin films were
deposited using W(NiPr)Cl3[iPrNC(NMe2)NiPr], 4, the guanidinato derivative of 1. The film
properties obtained from 4 are compared to those from Cl4(RCN)W(NiPr) (R = CH3, Ph) (1a,b)
to assess the effect of the guanidinato ligand. The WNxCy films were also evaluated as diffusion
barriers by coating them with PVD Cu and annealing the Cu/WNxCy/Si stack in vacuum at
different temperatures.
Results and Discussion
Precursor Synthesis
The tungsten guanidinate complex 4 was synthesized by reacting the imido complex
W(NiPr)Cl4(OEt2) with the lithium guanidinate salt, Li[iPrNC(NMe2)NiPr]. In attempts to
improve the synthesis of the guanidinate complexes, an alternate solvent system was used. The
lithium guanidinate was synthesized in hexane at 0 °C and used in situ.62,192,202 The
W(NiPr)Cl4(OEt2) complex was dissolved in toluene, cooled to -78 °C, and the lithium
guanidinate salt was added dropwise. The reaction mixture was warmed to room temperature,
64
and stirred overnight to afford compound 4 as an amber solid in 37% yield without the need for
recrystallization. The 1H and 13C NMR spectra of complex 4 display an inequivalence between
the substituents of the chelating guanidinate nitrogens, leading to the assignment as the mer-
isomer.
Table 4-1. Crystal data and structure refinement for 4.
Complex 4 Empirical formula C12H27Cl3N4W Formula weight 517.58 Temperature (K) 173(2) Wavelength (Å) 0.71073 Crystal system Triclinic Space group P-1 Unit cell dimensions a = 8.4844(7) Å α= 93.063(2)° b = 8.8717(8) Å β= 101.094(2)° c = 14.8556(13) Å γ = 116.862(2)° Volume (Å3) 966.23(15) Z 2 Density (Mg/m3) 1.779
Absorption coefficient (mm-1) 6.389 F(000) 504 Crystal size (mm3) 0.06 x 0.05 x 0.01 Theta range for data collection (°) 1.42 to 24.60 Index ranges -9≤h≤9 -9≤k≤9 -16≤l≤16 Reflections collected 6201 Independent reflections (Rint) 2732 (0.0465) Completeness to θ = 24.60 (%) 83.6 Absorption correction Integration Max. and min. transmission 0.9390 and 0.6490 Data / restraints / parameters 2732 / 1 / 189 Goodness-of-fit on F2 0.935 R1a 0.0361 wR2b 0.0502 Largest diff. peak and hole/e.Å3 0.757 and -0.694
aR1 = ∑(||Fo| - |Fc||) / ∑|Fo| bwR2 = [∑[w(Fo2 - Fc2)2] / ∑[w(Fo2)2]]1/2
S = [∑[w(Fo2 - Fc2)2] / (n-p)]1/2 w= 1/[σ2(Fo2)+(m*p)2+n*p], p = [max(Fo2,0)+ 2* Fc2]/3.
65
Figure 4-2. Thermal ellipsoids diagram of the molecular structure of 4. Thermal ellipsoids are
drawn at 40% probability and hydrogens have been omitted for clarity.
Single crystals suitable for X-ray diffraction were obtained from 4, and the structure was
determined. Crystal data and structure refinement for this complex can be found in Table 4-1.
Compound 4 adopts a distorted octahedral geometry as shown in the ORTEP representation of 4
(Figure 4-2). The tungsten-chlorine bond distances are on the order of 2.38 Å, which is within
the expected range for tungsten(VI)-chlorine bonds.203 The W-N(3) bond length of 1.702(4) Å
and the W-N(3)-C(10) bond angle of 168.4(8) are consistent with the values previously reported
for other W(VI) imido complexes that are expected to have strong conjugation of the N lone
pairs into empty metal d orbitals.153,204 The W-N(2) bond length is 1.961(4) Å, while the W-
N(1) bond length is 2.247(4) Å. The elongated bond length of the latter is consistent with the
strong trans influence of the imido ligand.172 The C(1)-N(4), C(1)-N(1) and C(1)-N(2) bond
distances in the guanidinate ligand are 1.373(6), 1.294(6), and 1.399(6) Å, respectively. All of
these bond distances are roughly in the range for C(sp2)-N(sp2) bonds (ca. 1.36 Å).205 This is an
66
indication of lone pair donation from N(4) to C(1) and electron delocalization involving all three
nitrogens of the chelating ligand. A sum of 357.6° for the three bond angles about N(4) is
consistent with the sp2 hybridization necessary for conjugation. A list of selected bond lengths
and angles for 4 is given in Table 4-2.
Table 4-2. Selected bond distances (Å) and angles (°) for compound 4
Bond Bond Length (Å) Bond Bond Angle (°) W-N1 2.247(4) N1-W-N3 163.23(18) W-N2 1.961(4) N2-W-Cl3 155.81(13) W-N3 1.702(4) Cl1-W-Cl2 167.30(5) W-Cl1 2.3752(15) N2-W-N3 101.44(19) W-Cl2 2.3819(16) N1-W-N2 61.88(16) W-Cl3 2.3833(14) W-N1-C1 90.3(3) C1-N2 1.399(6) N1-C1-N2 107.8(4) C1-N1 1.294(6) W-N2-C1 100.0(3) C1-N4 1.373(6) W-N3-C10 168.4(8)
Precursor Screening
Thermogravimetric analysis
TGA experiments run with a heating rate of 10˚C/min from 25˚C to 900˚C resulted in a
residual mass of 43% which was constant above 400˚C (Figure 4-3a). Examination of the
derivative plot (Figure 4-3b) reveals an inflection point corresponding to onset of a
decomposition process around 237 ˚C. At 237 °C the residual mass is 77% corresponding to loss
of an isopropyl group and two chlorines or complete loss of the guanidinato ligand. A second
inflection point appears at 315 °C and 49% residual weight %, after which additional weight loss
is slow. Loss of an isopropyl group, three chlorine atoms, and fragmentation of the guanidinato
ligand, leaving a bisimido complex, correspond to 49% residual mass. Isothermal studies of 4 at
120˚C for 180 minutes are depicted in Figure 4-2c. The thermal behavior of 4 strongly
resembles that of the tantalum guanidinato complexes [Ta(NR1R2)iPrNC(NR1R2)NiPr2(NtBu)]
(R1, R2 = methyl, ethyl), which have been demonstrated to be CVD precursors to TaN.125
67
a.
b.
68
c.
Figure 4-3. (a) TGA curve of compound 4 recorded at a heating rate of 10˚C/min under nitrogen; (b) First derivative of TGA curve a.; (c) Isothermal study of compound 4 at 120˚C under nitrogen.
Mass spectrometry
A relationship has previously been established between the mass spectrometric
fragmentation of precursors and the decomposition pathways during the CVD process.157,206 In
comparing these two processes, one must be careful, since mass spectrometry involves a gas
phase ionization process while the precursor undergoes a thermal degradation process during
CVD.157 However, previous research has shown that mass spectral data are useful for screening
CVD precursors.57,99,207
69
Figure 4-4. PCI mass spectra of compound 4.
Mass spectra were obtained for 4 using positive ion electron-capture chemical ionization
(PCI). In contrast to precursors 1-3,57,99,207 the molecular ion for 4 could be observed (m/z 518).
The base peak of the PCI spectrum corresponds to loss of a chlorine (m/z = 481). Also present is
a peak at m/z 446 (37% abundance) which corresponds to the molecular ion with loss of two
chlorines. Facile elimination of the chlorines in the PCI spectrum is consistent with the lack of
chlorine in the films deposited by these precursors. (Figure 4-4)
70
Film Deposition from 43
Film growth
Films were deposited from precursor 4 at temperatures as low as 400 °C. Films grown
with precursor 4 were generally smooth and had a shiny metallic surface with film color varying
from golden at low deposition temperature to shiny black at high deposition temperature.
Film composition
Figure 4-5 shows AES results for films deposited with precursors 4 and 1a,b using H2 as
co-reactant. The AES spectra indicated the presence of tungsten, nitrogen, carbon, and oxygen
for films deposited with precursor 4. Even though precursor 4 bears chloride ligands, no
chlorine was detected in the film by X-ray photoelectron spectroscopy (spectra not shown).
For films deposited with 4 above 450 °C, the tungsten concentration gradually decreases
until 700 °C, reflecting an increase in carbon content as the deposition temperature rises. The
nitrogen content of films deposited with precursor 4 has a higher nitrogen content than 1 for
films deposited at 400 °C and 450 °C. Then the nitrogen content of the film decreases as
deposition temperature is increased from 450 to 650 °C. The variation of nitrogen content in the
films is likely influenced by several factors, including nitrogen volatilization, competition
between carbon and oxygen for bonding with tungsten sites, and precursor decomposition
pathways and rates.
Both carbon and oxygen were detected in significant amounts in all films. The carbon
content of film deposited with precursor 4 decreases from 400 °C to 450 °C and then
continuously until 700 °C. In a previous study using Cl4(CH3CN)W(NiPr) (1), it was
demonstrated that the extent of carbon incorporation depended upon the solvent (1,2
3 Film growth and film characterization were done by Hiral Ajmera.
71
dichlorobenzene or benzonitrile).163 Ligand decomposition and possible precursor reactions with
the solvent could also contribute to increased carbon content. The oxygen content of film
deposited with 4 decreases as the temperature increases. Possible sources of oxygen
incorporation include an oxygen bearing impurity in the reactants, post growth exposure of the
film to air, residual oxygen in the reactor and a leak in the system. While both precursor
impurities and reactor residual gas can result in oxygen incorporation in the film, the bulk of the
oxygen is believed to diffuse into the film upon post growth exposure to the atmosphere. The
change in film density with deposition temperature is believed to affect the oxygen diffusion and
resultant change in oxygen content with deposition temperature.
Figure 4-5. Composition of films deposited from 4 and 1 on Si (100) substrate at different deposition temperature as determined by AES after 0.5 min of sputtering
72
XRD of films
Figure 4-6. XRD patterns for films deposited on Si (100) substrate from 4.
Figure 4-6 shows the XRD patterns for films deposited with 4 between 400 and 750 °C
deposition temperature. XRD spectra for films deposited at 400 and 450 °C show no peaks
attributable to the film. The absence of WNxCy peaks in these two spectra suggests that films
deposited at 400 and 450 °C are X-ray amorphous. The XRD pattern for the film deposited at
500 °C shows onset of crystallinity as evidenced by the two broad peaks at 37.74 and 44.40°.
These peaks lie between the standard peak position of β-W2N [37.74 2θ for (111) phase and
43.85 ° 2θ for (200) phase and β-W2C [37.74 2θ for (111) phase and 43.85 ° 2θ for (200) phase,
indicating the presence of either the solid solution β-WNxCy or a physical mixture of β-W2N and
β-W2C.208 Films deposited at 550, 600, and 650 °C show evidence of increased crystallinity with
73
four peaks observed at approximately 37.50, 43.70, 63.55 and 75.05°, corresponding to (111),
(200), (220) and (311) phases of β-WNxCy respectively. The (111) peaks become sharper at
higher deposition temperature, suggesting an increase in grain size.
Film growth rate (X-SEM)
The growth rate for films grown from 4 was determined from the measured film thickness
(X-SEM) divided by deposition time. Figure 4-7 shows X−SEM images for films grown at 450
and 650 °C. The growth rate varied from 3 Å/min to 24 Å/min, with the lowest growth rate
observed at 400 °C and highest growth rate observed at 700 °C. Figure 4-8 shows Arrhenius
plots of growth rate for deposition from 4 and 1a,b in the presence of hydrogen. The growth rate
for films deposited with 4 is lower than that for films deposited with 1a,b between 400 and 650
°C. The Arrhenius plot for 4 shows that film growth between 400 and 600 °C is ‘surface
reaction limited’ with a change to ‘mass transfer limited’ between 600 and 750 °C. While the
‘mass transfer limited’ growth regime usually exhibits a small positive slope in an Arrhenius
plot, 4 shows a small negative slope between 600 and 750 °C. This is consistent with
homogenous decomposition of the precursor above 600 °C, resulting in a slight decrease in
growth rate in the ‘mass transfer limited’ growth regime for 4. While the transition from
‘surface reaction limited’ growth to ‘mass transfer limited’ growth occurs between 550 and 600
°C for 1a,b, 4 shows the same transition at 600 °C. An activation energy for film growth using 4
of 0.54 eV was calculated from the Arrhenius equation, which is significantly lower than 0.84 eV
activation energy reported for 1a,b.33 The value of activation energy for 4 is within the typical
values between 0.5 and 1.0 eV observed for CVD growth in the ‘surface reaction limited’
regime.167
74
Figure 4-7. X-SEM images for films grown from 4 at a) 450 °C b) 650 °C
Figure 4-8. Arrhenius plot of log of film growth rate vs. inverse temperature for deposition from
1 and 4 on a Si(100) substrate
Film resistivity
Film resistivity was calculated using:
tR s=ρ
where ρ is film resistivity in Ω−cm, Rs is sheet resistance in Ω/ (measured by 4−point probe)
and t is film thickness in cm (measured from X−SEM). Figure 4-9 shows film resistivity at
different deposition temperature for films grown with precursors 4 and 1a,b. For depositions
with 4 the resistivity ranges from 980 μΩ−cm to 6857 μΩ−cm. The film with the lowest
resistivity of 980 μΩ−cm was grown at 450 °C. The low resistivity at this temperature is thought
75
to be due to higher tungsten content and lower carbon and nitrogen content of the film. Between
450 and 600 °C deposition temperature, the film resistivity gradually increases, which is
attributed to a decrease in tungsten content of the film and an increase in amorphous nitrogen and
carbon in the film as observed by AES.
Comparison of resistivity for films deposited with 4 and 1a,b reveals that while the
lowest resistivity obtained with 1a,b is 750 μΩ−cm at 450 °C, the lowest resistivity obtained
with 4 is 980 μΩ−cm at 450 °C. The resistivity of films deposited with 1a,b increases
throughout the deposition temperature, whereas the resistivity of films deposited with 4 shows a
steep increase between 450 and 600 °C followed by a decrease in resistivity between 600 and
750 °C.
Figure 4-9. Change in film resistivity with deposition temperature for films grown on Si (100) from 4 and 1a,b
Diffusion barrier testing
To determine the effectiveness of diffusion barrier deposited with 4, barrier films deposited
at 450 and 500 °C were coated with 100 nm PVD Cu. The thickness of films deposited at 450
was 45 nm. The Cu/barrier/Si stack was annealed in vacuum at temperatures ranging from 200
76
to 600 °C for 30 min to determine the temperature at which Cu diffuses through the barrier film
into the Si substrate. After annealing, three-point AES depth profile was used to detect copper
diffusion.
Figure 4-10. AES depth profiles of Cu (100 nm)/ WNxCy (50 nm)/Si (100) stack for WNxCy film
deposited at 450 °C and annealed in vacuum for 30 min at (a) 200 (b) 400 (c) 500 and (d) 600 °C.
Figure 4-10 shows the depth profile for post-anneal Cu/WNxCy/Si stack for WNxCy films
deposited from 4 at 450 °C. For an anneal at 200 °C for 30 min, the Cu-WNxCy interface is
similar to that for films with no anneal, suggesting that no bulk copper diffusion occurred. As
the anneal temperature is increased to 400 °C, there is slight mixing of the Cu/WNxCy interface,
77
however the copper has not diffused through the barrier film. For 500 °C anneal, there is further
diffusion of Cu in the WNxCy film, but the barrier film is able to prevent complete diffusion of
Cu through it. At 600 °C annealing temperature, there is complete diffusion of copper through
the barrier film. Intermixing is also observed for the WNxCy/Si interface. The depth profiling
shows that 45 nm barrier film of WNxCy deposited with 4 at 450 °C is able to prevent bulk Cu
diffusion when annealed at 500 °C for 30 min.
Conclusions
It has been demonstrated that the mixed imido guanidinato complex
W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4) can be used in an aerosol assisted CVD system to deposit
WNxCy thin films. A comparison of the effects of imido and guanidinato ligands on film
properties is presented by comparing the film composition, crystallinity, growth rate and
resistivity of films deposited with 4 and Cl4(RCN)W(NiPr) (R = CH3, Ph) (1a,b).
For 4, the lowest growth temperature at which films could be obtained is 400 °C. AES
spectra showed presence of tungsten, nitrogen, carbon and oxygen in this material. When
compared with films grown with 1a,b, the films grown with 4 have a higher C/W ratio and
almost similar N/W ratio. The oxygen content of films deposited with 4 is also significantly
lower than that for films deposited with 1a,b, especially at lower deposition temperature. The
lowest growth temperature for 4 is 50 °C lower than that for 1a,b. For both 4 and 1a,b, films
grown are crystalline at and above 500 °C deposition temperature. From the diffusion barrier
application standpoint, films deposited with 4 at 450 were able to prevent copper diffusion after
annealing at 500 °C for 30 min in vacuum. Since the film deposited from 4 at 450 °C is
amorphous, has lowest resistivity of 980 μΩ−cm and can prevent Cu diffusion after annealing at
500 °C, films deposited from 4 at 450 °C might be the best candidate for diffusion barrier
application.
78
Experimental Procedure
General Procedure
Unless otherwise stated, reactions and manipulations were performed in an inert
atmosphere (N2) glovebox or using standard Schlenk techniques. All reaction solvents were
purified using an MBraun MB-SP solvent purification system prior to use. NMR solvents were
degassed by three freeze–pump–thaw cycles and stored over 3Å molecular sieves in an inert-
atmosphere glove box. 1H and 13C NMR spectra were recorded on Mercury 300, Gemini 300 or
VXR 300 spectrometers using residual protons of deuterated solvents for reference. Infrared
spectra were recorded as mineral oil mulls on NaCl plates on a Perkin Elmer Spectrum One FT-
IR spectrometer. UV/Visible spectra were recorded on a Shimadzu UV-1650 UV-Visible
spectrophotometer. TGA analysis was carried out using a Perkin-Elmer TGA7
thermogravimetric analyzer under nitrogen with a heating rate of 10˚C/min (Sample size ≈ 2
mg). Lithium dimethylamide and 1,3-diisopropylcarbodiimide were used as purchased from
Aldrich. W(NiPr)Cl4(OEt2) complexes were prepared by the method of Schrock.209
Synthesis of W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4)
W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4) was prepared by modification of a literature
procedure.62 Lithium dimethylamide was dissolved in 40 ml of hexane. The solution was cooled
to 0 °C, after which diisopropylcarbodiimide was added dropwise. The solution was stirred for 2
hours while warming to room temperature forming the Li[iPrNC(NMe2)NiPr] salt. The ligand
was added dropwise to a solution of Cl4W(NiPr)(OEt2) dissolved in 30 ml of toluene at -78 °C.
This stirred and allowed to warm to room temperature overnight with exclusion of light. Solvent
was removed in vacuo and the product was extracted with diethylether. The ether was removed
in vacuo to yield clean 4 as a dark amber powder. 1H NMR (300 MHz, C6D6): δ 1.23 (d, 6H, J
= 6 Hz, CH(CH3)2), 1.38 (d, 6H, J = 7 Hz, CH(CH3)2), 1.70 (d, 6H, J = 6 Hz, CH(CH3)2), 2.14 (s,
79
6H, N(CH3)2), 4.08 (septet, 1H, CH(CH3)2), 4.39 (septet, 1H, CH(CH3)2), 5.31 (septet, 1H,
WNCH(CH3)2). 13C NMR (C6D6): δ 23.3, 23.4, 25.4, 40.1 (N(CH3)2), 50.4 (CH(CH3)2), 53.8
(CH(CH3)2), 66.8 (WNCH(CH3)2), 164.7 (N3C). IR (cm-1): 2925 (s), 2854 (s), 1607 (w), 1461
(m), 1377 (m), 1278 (w). UV/Vis [Ether, λmax/nm (ε/M-1cm-1)]: 251 (1800), 309 (2800), 392
(1500). Anal. Calcd. for WC12H27N4Cl: C, 27.85; H, 5.26; N, 10.83. Found: C, 28.14; H, 5.52;
N, 10.52.
Crystallographic Structure Determination of 4.
Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD
area detector and a graphite monochromator utilizing MoKα radiation (λ = 0.71073 Å). Cell
parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was
collected using the ω-scan method (0.3° frame width). The first 50 frames were re-measured at
the end of data collection to monitor instrument and crystal stability (maximum correction on I
was < 1 %). Absorption corrections by integration were applied based on measured indexed
crystal faces.
The structure was solved by the Direct Methods in SHELXTL6,170 and refined using full-
matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms
were calculated in ideal positions and were riding on their respective carbon atoms. The
isopropyl moiety on N1 is disordered and is refined in two parts with their site occupation factors
dependently refined. A total of 189 parameters were refined in the final cycle of refinement
using 2299 reflections with I > 2σ(I) to yield R1 and wR2 of 2.64% and 4.87%, respectively.
Refinement was done using F2.
80
Mass Spectrometry
Mass spectral analyses were performed using a ThermoScientific DSQ mass spectrometer
equipped with a direct insertion probe (DIP) that was held at 50 °C for 1 minute and then heated
up to 280 °C at 30 °/min during the sample analysis. Ion source temperature was 150 °C with
methane gas at 0.5 mL/min.
Thermogravimetric Analysis
TGA analysis was carried out using a Perkin-Elmer TGA7 thermogravimetric analyzer
under nitrogen with a heating rate of 10˚C/min (Sample size ≈ 2 mg).
Film Growth Studies4
Film deposition was done in a vertical cold-wall CVD (chemical vapor deposition) reactor.
The reactor configuration has been described previously.99 The solid precursor 4 was dissolved
in benzonitrile at a concentration of 9.0 mg/mL. The deposition was carried out at atmospheric
pressure for a period of 150 min and the growth temperature was varied from 400 to 750 °C.
Table 4-3 provides the molar flow rate of reactants used in the MOCVD reactor.
Table 4-3. Molar flow rates of reactants in the CVD reactor
Reactant Molar flow rate (mol/min) H2 24.09 10−× W(NiPr)Cl3[iPrNC(NMe2)NiPr] 51.16 10−× Benzonitrile (solvent) 46.47 10−×
Film crystallinity was examined by X-ray diffraction (XRD) using a Phillips APD 3720
system. Cu Kα radiation, generated at 40 kV and 40 mA (1.6 kW), was used for the XRD
analysis. The XRD patterns were taken between 5 and 85 degrees 2θ with step size of 0.05
degree/step. Film composition was determined by Auger electron spectroscopy (AES) using a
Perkin-Elmer PHI 660 Scanning Auger Multiprobe. A 5 kV acceleration voltage and 50 nA 4 Film growth and film characterization were done by Hiral Ajmera.
81
beam current was used for the Auger analysis with a beam diameter of 1 μm. The sample
surface was cleaned by sputter etching for 30 sec using Ar+ ions. The etch rate for the sputtering
was calibrated at 100 Å/min using tantalum oxide standard. No WNxCy standard, however, was
available. XPS spectra were taken using monochromatic Mg Kα radiation with the X-ray source
operating at 300 W (15 kV and 20 mA). The sample surface was sputter etched for 15 min using
Ar ions to remove surface contaminants. The etch rate for the XPS system was calibrated at 10
Å/min using a tantalum oxide standard. The pass energy used for XPS multiplex measurement
was 35.75 eV and the step size of scans was 0.1 eV per step.
The film thickness was measured by cross-sectional scanning electron microscopy (X-
SEM) on a JEOL JSM-6400. The sheet resistance of the deposited films was measured using an
Alessi Industries four-point probe. To test diffusion barrier quality, the WNxCy films were
transferred in air to a multi-target sputter deposition system (Kurt J. Lesker CMS-18) where 100
nm thick Cu films were deposited. The base pressure of the system was 10-6 Torr and deposition
was done at 5 mTorr with Ar used as sputter deposition gas. The forward sputtering power for
Cu target was 250 W and the film growth rate was 240 Å/min. Annealing of the Cu/WNxCy/Si
stacks was also done in the sputter system at base pressure of 10-6 Torr.
82
CHAPTER 5 SYNTHESIS OF TUNGSTEN IMIDO GUANIDINATO HYDRIDE COMPLEXES
Transition Metal Hydrides
Transition metal hydrides have played an important part in the development of
organometallic chemistry.210-212 The first transition metal hydride, H2Fe(CO)4, was reported in
1931.213 Since then the area of transition metal hydrides has grown extensively. Metal hydrides
are typically very reactive complexes that can take part in various transformations such as
deprotonation,214 hydride transfer and insertion,215,216 and hydrogen atom transfer.217 Along with
these various transformations, metal hydrides play an important role in catalytic cycles and as
olefin polymerization intermediates.218-220 In addition to these applications, transition metal
hydrides, such as [(Me2NCH2CH2)C5H4]GaH2,221 [(Me2NCH2CH2)C5H4]AlH2,221 and
[W(NtBu)2(H)(iPrN)2CNMe2],63 have been of interest for use as single source precursors for
MOCVD.
Hydrogen can bond to a metal as a terminal hydride, bridging hydride (µ2-H), capping
hydride (µ3-H), or as a dihydrogen ligand (η2-H2).171,222 The most common metal hydride
complexes include a terminal hydride, while many complexes of the other types are known.
Metal hydrides can be synthesized using a variety of pathways including protonation,223
hydriding,224,225 hydrogen atom transfer,226,227 oxidative addition of H2,228 and ligand
decomposition.229,230 This chapter will discuss the synthesis and characterization of metal
hydride complexes to be used as single source precursors for MOCVD.
Synthesis and Characterization of Transition Metal Hydride MOCVD Precursors
Synthesis
Recently, metal imido and guanidinato complexes have been of interest for use as single
source precursors in MOCVD.61,63,123-125 Advantages of these ligands include strong nitrogen
83
interactions with the metal center and tunable alkyl groups to adjust the volatility of the
compounds. In attempts at producing a WNxCy precursor lacking chlorine, several tungsten
precursors with an imido/guanidinato/hydride ligand set were synthesized.
To a solution of W(NiPr)Cl3[iPrNC(NMe2)NiPr] (4) dissolved in THF, two equivalents of
LiBEt3H was added drop-wise at room temperature.62 Effervescence was observed and upon
completion the solvent was removed in vacuo. The product was extracted with hexane and upon
removal of solvent a bright yellow solid of the dimer W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(µ-H)2
(5) remained in 66% yield. Bright yellow crystals were easily grown from a concentrated
solution of 5 in pentane at -30 °C. A similar procedure was used to synthesize the cyclohexyl (6)
and phenyl (7) imido adducts of 5 (Figure 5-1). However, attempts at obtaining crystals of these
complexes were unsuccessful.
Figure 5-1. Synthesis of tungsten imido/guanidinato/hydride complexes 5-7.
Characterization
NMR spectroscopy
Investigation of 5 by 1H NMR shows one septet at 4.04 ppm for the imido isopropyl group
and one septet at 3.84 ppm for the guanidinato isopropyl groups integrating in a 2:4 ratio,
respectively. The doublets for the isopropyl groups are displayed at 1.12 and 1.23 ppm
84
integrating to 12 and 6 protons, respectively. The methyl groups for the guanidinato ligands are
present as a singlet at 2.81 ppm integrating to 6 protons. Absence of any observable hydride
peaks in the NMR at room temperature led to the measurement of variable temperature NMR
spectra. Lowering the temperature to -53 °C revealed peaks at 11.43 and 3.18 ppm. The hydride
peaks were identifiable by their tungsten satellites with a coupling constant of 1JW-H = 61.2 Hz
for the peak at 11.43 ppm. This downfield shift represents the terminal hydrogens in compound
5, while the peak at 3.18 ppm is from the bridging hydride. These peaks are not visible at room
temperature because they are exchanging too fast on the NMR time scale to be detected. The IR
spectrum shows an absorption band at 1871 cm-1, which is in the range for terminal W-H
stretching frequencies.63,171,231 (Figure 5-2)
a)
85
b)
Figure 5-2. 1H NMR spectrum of 5 in THF-d8. a) Room temperature, b) -53 °C.
Compound 6 shows four overlapping doublets from 1.11 ppm to 1.22 ppm. This indicates
that compound 6 does not contain the same symmetry as compound 5. Protons from the
cyclohexyl group show up as a series of broad multiplets from 2.20-1.75 ppm and 1.68-1.41.
The methyl groups from the NMe2 group in the guanidinato backbone are at 2.85 and 2.81 ppm
while the methine protons from the isopropyl and cyclohexyl group show up as two septets at
3.84 and 4.06 ppm. The hydride peak is visible at room temperature at 12.71 ppm with a
average coupling constant of 1JW-H = 52.5 Hz.
In compound 7 the hydride peak is apparent at 14.81 ppm in benzene-d6 with a coupling
constant of 51.5 Hz. The phenyl group is seen as several multiplets at 6.92-7.00, 7.16-7.23, and
7.48-7.60 ppm. The methine protons from the isopropyl groups appear as a septet at 3.79 ppm,
while the methyl protons from NMe2 are seen at 2.29 and 2.32 ppm. Again for compound 7, the
terminal protons from the isopropyl groups appear as two overlapping doublets at 1.33 and 1.37
86
ppm. The low temperature 1H NMR spectrum of 7 in THF-d8 shows hydride peaks at 12.31 ppm
with a coupling constant of 61.3 Hz and at 14.17 ppm with a coupling constant of 53.1 Hz. A
crystal structure will be necessary to elucidate the structures of compounds 6 and 7, but attempts
to crystallize these compounds have not been successful thus far.
X-ray crystallography
The molecular structure of 5 in the solid state as obtained from single-crystal X-ray
diffraction studies is shown in Figure 5-3. The hydrides were found in the difference Fourier
maps and refined without constraints. The X-ray structure of compound 5 shows two bridging
hydrides and two terminal hydrides and adopts a highly distorted octahedral geometry around
tungsten. A list of select bond lengths and angles is given in Table 5-1. The imido ligand in
compound 5 has less triple bond character than that of compound 4, evident by the longer W-N
bond lengths (W1-N1, 1.733(4) Å; W2-N5, 1.746(4) Å) as compared to 1.720(3) Å for compound
4.62 Also supporting the lower bond order in compound 5 is the less linear angle of W1-N1-C2
(162.7(3)°) and W2-N5-C14 (166.1(3) deg) than that of the imido ligand in compound 4
(174.0(3)°). The guanidinato ligands in compound 5 demonstrate more electron delocalization
between the chelating nitrogens than in compound 4. This is apparent by the more equivalent
N3-C1 (1.317(6) Å), N4-C1 (1.384(6) Å), N7-C13 (1.335(5) Å), and N8-C13 (1.384(6) Å) in the
guanidinato ligands in compound 5. These values show bond lengths between that of a C-N
single bond (ca. 1.47 Å) and a C-N double bond (ca. 1.25 Å), demonstrating a partial double
bond character across the chelating nitrogen atoms. This is in contrast to compound 4 where the
corresponding guanidinato bond lengths of 1.399(6) Å and 1.294(6) Å show less electron
delocalization. Another structural characteristic that supports the electron delocalization present
in the guanidinato ligand of 5 is the W-N bond lengths which show more symmetric coordination
87
of the tungsten with bond lengths of 2.147(3), 2.127(4), 2.157(3), and 2.118(4) Å compared to
those in compound 5 (2.247(4) and 1.961(4) Å).
Figure 5-3. Thermal ellipsoid diagram of the molecular structure of 5. Thermal ellipsoids are drawn at 40% probability, and the hydrogens not attached to the metal have been omitted for clarity.
When comparing compound 5 to compound 4, we know that the guanidinato ligand has an
overall charge of -1. If the guanidinato ligand in compound 5 has a -1 charge in its binding to
the metal then tungsten would be in the W5+ oxidation state with a d1 electron configuration,
causing the compound to be paramagnetic. However, analysis of the NMR spectra indicated that
5 is a diamagnetic complex. An explanation for the diamagnetic character of 5 is that the
guanidinato ligand has its major resonance forms represented in Figure 4-1b, where there is a -2
charge at the metal as opposed to the -1 charge in complex 4. Taking into consideration the
difference in bond lengths in the guanidinato ligand between complex 4 and 5, a -2 charge on the
guanidinato ligand at the metal in complex 5 is a reasonable assumption. If the resonance
88
structure is the guanidinato(2-), then the tungsten in complex 5 would be in a W6+ oxidation state
with a d0 electron configuration yielding a diamagnetic complex. A dianionic guanidinato ligand
can function as a diamido ligand, with π delocalization or Y-conjugation throughout the CN3
backbone. The average W-N(guanidinato) bond length is 2.14 Å, which is longer than typical
tungsten dimethyl amide bond lengths of 2.05-2.07 Å indicating single bonds between the W-
N(guanidinato) in complex 5.232 The guanidinato ligand binds to the tungsten in complex 5
through the two nitrogens forming a planar four-membered metallacycle (N3-C1-N2, N3-W1-N2
dihedral angle = 1.1°). The average C1-N4-(C11, C11´, C12, C12´) bond angle is 121.9°
indicating an sp2 hybridized nitrogen (N4). This is very interesting due to the lack of
guanidinato (2-) ligands in the literature compared to guanidinato(1-) and neutral ligands.189 A
complete listing of bond angles and bond lengths is shown in Appendix C.
Table 5-1. Selected bond distances (Å) and angles (°) for compound 5.
Thermogravimetric analysis
Thermogravimetric analysis of 5 was also carried out (Figure 5-4). Compared to TGA data
of 4, decomposition seems to be a much cleaner process for compound 5. Compound 5 starts to
lose mass around 125 °C as compared to about 165 °C for compound 4. A comparison of the
Bond Length (Å) Bond Length (Å) Bond Angle (°) W1-H1 1.71(5) N2-C1 1.324(6) N2-C1-N4 124.7(5) W1-H3 1.71(6) N3-C1 1.317(6) N3-C1-N4 126.1(5) W1-H4 1.96(5) N4-C1 1.384(6) N3-C1-N2 109.2(4) W1-N1 1.733(4) W1-H3-W2 42(2) W1-N2 2.147(3) W1-H4-W2 38.9(14) W1-N3 2.127(4) W1-W2 2.6332(3) W2-H2 1.58(4) N6-C13 1.330(6) N6-C13-N7 109.3(4) W2-H3 1.78(6) N7-C13 1.335(5) N6-C13-N8 128.2(4) W2-H4 1.66(5) N8-C13 1.384(6) N7-C13-N8 122.4(4) W2-N5 1.746(4) W2-N6 2.157(3) W2-N7 2.118(4)
89
TGA data from compounds 4 and 5 is shown in Figure 5-5. The first inflection point is at 169 °C
at 84% which corresponds to loss of several isopropyl and methyl fragments. The second
inflection point occurs at 328 °C and 60% corresponding to further loss of isopropyl and methyl
groups and possible guanidinato fragmentation. The mass loss seems to be complete around
52% which could correspond to W2N (380 g/mol) with 12% carbon incorporation.
Figure 5-4. TGA data for 5. Weight % and Derivative (Weight %) vs. Temperature.
90
Figure 5-5. Comparison of TGA data for complexes 4 and 5.
Mass spectrometry data
Fragmentation patterns in mass spectrometric data of CVD precursors have shown a strong
relationship with likely decomposition pathways during the CVD process.156,157 Acknowledging
the difference between gas phase ionization and thermal decomposition processes, there seems to
be a strong correlation between the fragmentation patterns in mass spectrometry and the resulting
film deposition properties. Previous studies have shown that mass spectrometry of the tungsten
imido precursors Cl4(CH3CN)W(NiPr) (1a) and Cl4(CH3CN)W(NPh) (2a) affords qualitative
insights into their CVD behavior.33,151,158 Therefore mass spectrometry of the precursor 5 was
used as a preliminary screening technique.
Mass spectral data were obtained for 5 using positive ion electron-capture chemical
ionization (PCI). In contrast to precursors 1-3,57,99,207 but similar to complex 4,62 a mass
envelope for the molecular ion for 5 could be observed (m/z 826), which was overlapping the
91
mass envelope for loss of H2 (m/z 824). These were the base peak of the PCI spectrum. Also
evident is a peak at m/z 698 with 32% abundance, corresponding to loss of a methyl group and
fragmentation of one of the guanidinato ligands to form a bisimido coordination sphere on one of
the tungstens. The guanidinato fragment that was lost to give m/z of 698 is seen at m/z 113,
[C6H13N2]+, with a 6% abundance. (Figure 5-6)
Figure 5-6. PCI mass spectrum of compound 5.
Conclusion
New potential single source precursors for MOCVD of WNxCy have been synthesized.
The compounds synthesized incorporate strongly bound nitrogen ligands and eliminate chlorine
through the use of hydride ligands, a significant advantage in a CVD precursor. TGA data shows
an onset of decomposition for complex 5 at a lower temperature than 4. X-ray crystallography
and NMR spectroscopy allowed for detailed analysis of bonding in compound 5.
92
Experimental Procedures
General Procedures
Unless otherwise stated, reactions and manipulations were performed in an inert
atmosphere (N2) glovebox or using standard Schlenk techniques. All reaction solvents were
purified using an M. Braun MB-SP solvent purification system prior to use. NMR solvents were
degassed by three freeze–pump–thaw cycles and stored over 3Å molecular sieves in an inert-
atmosphere glove box. 1H and 13C NMR spectra were recorded on Mercury 300, Gemini 300 or
VXR 300 spectrometers using residual protons of deuterated solvents for reference. Infrared
spectra were recorded as pure compound on a Perkin Elmer Spectrum One FT-IR spectrometer.
LiBEt3H (1 M in THF) was used as purchased from Aldrich. W(NiPr)(iPrNC(NMe2)NiPr)Cl3,
W(NCy)(iPrNC(NMe2)NiPr)Cl3, and W(NPh)(iPrNC(NMe2)NiPr)Cl3 were prepared by the
method used to synthesize 4 in Chapter 4 of this work.62
Synthesis of W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(µ-H)2 (5).
W(NiPr)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1 M solution of
LiBEt3H in THF was added dropwise at room temperature. Upon addition of LiBEt3H,
effervescence was observed; when addition was complete the solution had turned emerald green.
When effervescence was complete, the solvent was removed in vacuo. As solvent was removed
the color changed from green to brown. The product was extracted with hexane giving a yellow
solution. The hexane was removed in vacuo to give W2(NiPr)2[iPrNC(NMe2)NiPr]2H2(µ-H)2
(5) in a 66 percent yield. Recrystallization from a concentrated solution of 5 in pentane at -30 °C
yielded pure 5 as yellow crystals. Where assignments of 1H or 13C NMR resonances were
ambiguous, 13C-1H HMBC experiments were used to elucidate them (Appendix C). 1H NMR
(300 MHz, room temperature, THF-d8): δ ppm 1.12 (24 H, d, J = 6.41 Hz), 1.23 (12 H, d, J =
6.41 Hz), 2.81 (12 H, s), 3.84 (4 H, septet, J = 6.31 Hz), 4.04 (2 H, septet, J = 6.38 Hz). 1H
93
NMR (300 MHz, -53 °C, THF-d8): δ ppm 1.01 (6 H, d, J = 5.5 Hz), 1.11 (12 H, q, J = 5.8 Hz),
1.22 (18 H, t, J = 5.8 Hz), 2.83 (6 H, s), 3.18 (t, WH, 1JW-H = 55.3 Hz, 1JH-H = 6.7 Hz), 3.84 (4
H, septet, J = 5.8 Hz), 4.04 (2 H, septet, J = 6.2 Hz), 11.43 (s, WH, 1JW-H = 61.2 Hz, 1JH-H =
6.7 Hz). 13C NMR (300 MHz, THF d8): δ ppm 25.45 (NCHCH3), 27.46 (NCHCH3, imido),
39.91 (N(CH3)2), 46.64 (NCHCH3), 61.96 (NCHCH3, imido), 172.91 (NCN). IR (cm-1): 3392
(s), 2965 (s), 2928 (m), 2861 (m), 1871 (w), 1627 (m), 1536 (m), 1452 (m), 1413 (m), 1300 (m),
1198 (m), 1063 (m), 750 (s).
Synthesis of W2(NCy)2[iPrNC(NMe2)NiPr]2H2(µ-H)2 (6).
W(NCy)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1M solution of
LiBEt3H in THF was added dropwise at room temperature. Upon addition of LiBEt3H
effervescence was observed; when addition was complete the solution had turned emerald green.
When effervescence was complete, the solvent was removed in vacuo. The product was
extracted with hexane giving a bright emerald green solution. The hexane was removed in vacuo
to give W2(NCy)2[iPrNC(NMe2)NiPr]2H2(µ-H)2 (6) in a 61 percent yield. Attempted
recrystallization of 6 was unsuccessful. 1H NMR (300 MHz, THF- d8): δ 1.10-1.23 (multiple d,
28H, CH(CH3)2, CH2) , 1.41-1.64 (br, 8H CH2), 1.75-2.01 (br, 8H, CH2), 2.81 (s, 6H, N(CH3)2),
2.85 (s, 6H, N(CH3)2), 3.84 (septet, 2H, WNCH), 4.06 (septet, 2H, WNCH), 12.71 (s, WH, 1JW-H
= 52.5 Hz). 13C NMR (300 MHz, THF-d8): δ 24.5, 25.1, 25.37, 25.41, 25.64, 25.66 (CH2),
26.6, 26.3, 27.00, 27.3 (N(CH3)2), 35.5, 35.7, 37.7, 40.1, 40.5 (CH(CH3)2), 46.8, 48.9,
49.0(CH(CH3)2), 69.3, 71.5 (WNC), 170.3, 172.9 (N3C).
Synthesis of W2(NPh)2[iPrNC(NMe2)NiPr]2H2(µ-H)2 (7).
W(NPh)(iPrNC(NMe2)NiPr)Cl3 was dissolved in 20 mL of THF. A 1M solution of
LiBEt3H in THF was added drop wise at room temperature. Upon addition of LiBEt3H
94
effervescence was observed, when addition was complete the solution had turned brown. When
effervescence was complete, the solvent was removed in vacuo. The product was extracted with
hexane giving an orange solution. The hexane was removed in vacuo to give
W2(NPh)2[iPrNC(NMe2)NiPr]2H2(µ-H)2 (7) in a 55 percent yield. Attempted recrystallization
of 7 was unsuccessful. 1H NMR (300 MHz, C6D6): δ 1.33, 1.37 (two d, 24H, CH(CH3)2), 2.29,
2.32 (two s, 12H, N(CH3)2), 3.79 (septets, 4H, WNCH), 6.92-7.00 (m, 2H, CH), 7.16-7.23 (m,
4H, CH) 7.48-7.60 (m, 4H, CH), 14.81 (s, WH). 1JW-H = 51.5 Hz). 1H NMR (300 MHz, -56 °C,
THF-d8): δ 12.31 (t, WH, 1JW-H = 61.3 Hz, 1JH-H = 6.8 Hz), 14.17 (s, WH, 1JW-H = 53.1 Hz).
13C NMR (300 MHz, THF-d8): δ 39.95, 40.43, 42.24, (CH(CH3)2, CH(CH3)2, N(CH3)2), 122.54,
125.74, 128.40, 128.82, 129.65, 129.83, (CH, WNC), 191.10, (N3C).
X-ray Crystallography
Data were collected at 173 K on a Siemens SMART PLATFORM equipped with A CCD
area detector and a graphite monochromator utilizing MoKα radiation (λ = 0.71073 Å). Cell
parameters were refined using up to 8192 reflections. A full sphere of data (1850 frames) was
collected using the ω-scan method (0.3° frame width). The first 50 frames were re-measured at
the end of data collection to monitor instrument and crystal stability (maximum correction on I
was < 1 %). Absorption corrections by integration were applied based on measured indexed
crystal faces.
The structure was solved by the Direct Methods in SHELXTL6,170 and refined using full-
matrix least squares. The non-H atoms were treated anisotropically, whereas the hydrogen atoms
were calculated in ideal positions and were riding on their respective carbon atoms. A total of
324 parameters were refined in the final cycle of refinement using 22106 reflections with I >
2σ(I) to yield R1 and wR2 of 2.69% and 6.67%, respectively. Refinement was done using F2.
95
The toluene molecule was disordered and could not be modeled properly, thus program
SQUEEZE,233 a part of the PLATON233 package of crystallographic software, was used to
calculate the solvent disorder area and remove its contribution to the overall intensity data.
Mass Spectrometry
Mass spectral analyses were performed using a ThermoScientific DSQ mass spectrometer
equipped with a direct insertion probe (DIP) that was held at 50 °C for 1 minute and then heated
up to 280 °C at 30 °/min during the sample analysis. Ion source temperature was 150 °C with
methane gas at 0.5 mL/min.
Thermogravimetric Analysis
TGA analysis was carried out using a TA Instruments TGA Q5000 V3.3 Build 250
thermogravimetric analyzer. The sample was run under nitrogen using the hi-res dynamic
method with a heating rate of 40˚C/min from 25 °C to 700 °C (Sample size = 6.353 mg).
96
APPENDIX A CRYSTALLOGRAPHY DATA FOR 3a
Table A-1. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 3a. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
x y z U(eq) W 3673(1) 8599(10) 2535(1) 49(1) N1 5066(15) 8370(40) 1429(7) 70(6) N2 1708(12) 8700(50) 4039(6) 44(2) Cl1 5703(14) 10782(10) 3533(7) 76(3) Cl2 1187(11) 6445(7) 1876(6) 59(2) Cl3 5635(13) 6364(9) 3495(7) 68(3) Cl4 1046(15) 10783(8) 1997(7) 79(3) C1 6430(20) 8580(40) 484(10) 93(5) C2 5470(60) 9880(60) -410(30) 66(9) C3 3800(60) 8730(120) -1180(30) 80(10) C2' 5130(30) 8860(50) -592(16) 65(7) C3' 3020(30) 8270(30) -748(16) 53(5) C4 665(13) 8640(50) 4747(7) 44(3) C5 -633(17) 8530(50) 5692(8) 52(3)
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Table A-2. Bond lengths [Å] and angles [°] for 3a.
Bond Length (Å) or Angle (°) W-N1 1.687(9) W-N2 2.308(8) W-Cl2 2.317(8) W-Cl3 2.324(9) W-Cl1 2.339(10) W-Cl4 2.351(9) N1-C1 1.508(17) N2-C4 1.130(12) C1-C2' 1.51(2) C1-C2 1.55(4) C2-C3 1.59(6) C2'-C3' 1.36(3) C4-C5 1.476(14) N1-W-N2 175.8(15) N1-W-Cl2 90.6(8) N2-W-Cl2 86.0(7) N1-W-Cl3 93.6(7) N2-W-Cl3 84.0(6) Cl2-W-Cl3 88.7(4) N1-W-Cl1 102.4(8) N2-W-Cl1 81.1(7) Cl2-W-Cl1 167.0(3) Cl3-W-Cl1 90.18(13) N1-W-Cl4 103.1(7) N2-W-Cl4 79.1(6) Cl2-W-Cl4 88.14(11) Cl3-W-Cl4 163.0(3) Cl1-W-Cl4 89.2(4) C1-N1-W 167(2) C4-N2-W 175(3) C2'-C1-N1 114.2(12) C2'-C1-C2 30.9(16) N1-C1-C2 114.8(17) C1-C2-C3 106(4) C3'-C2'-C1 120(2) N2-C4-C5 178(2) Symmetry transformations used to generate equivalent atoms.
98
Table A-3. Anisotropic displacement parameters (Å2x 103) for 3a. The anisotropic displacement factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 .
U11 U22 U33 U23 U13 U12 W 31(1) 79(1) 38(1) -1(1) 2(1) -1(1) N1 53(5) 115(16) 41(4) 1(8) 1(4) 51(11) N2 35(3) 51(7) 47(4) 13(12) 3(3) 8(10) Cl1 58(5) 101(7) 65(5) 18(5) -10(4) -30(5) Cl2 40(3) 86(5) 51(3) -8(3) 9(2) -14(3) Cl3 52(4) 94(7) 58(5) 2(5) -4(3) 22(4) Cl4 87(5) 69(5) 73(4) 7(3) -30(4) 0(4) C1 69(8) 146(13) 67(7) -6(16) 17(7) 75(13) C4 35(4) 53(6) 45(5) -21(12) 1(4) 14(12) C5 52(5) 58(7) 48(5) -8(15) 13(4) 19(14) Table A-4. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for
3a.
x y z U(eq) H1B 6628 7394 154 112 H1A 7896 9024 761 112 H1B' 7403 9632 623 112 H1A' 7373 7516 438 112 H2 5816 11109 -492 80 H3B 3577 7498 -1024 96 H3A 3011 9267 -1789 96 H2' 5774 9445 -1165 78 H3B' 2371 7687 -177 63 H3A' 2207 8450 -1429 63 H5A -750 7281 5915 78 H5B -2097 9017 5497 78 H5C 85 9229 6294 78
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APPENDIX B KINETICS DATA FOR 1
Table B-1. Rates for the acetonitrile exchange of complex 1.
T (°C) k (sec-1) 1/T ln(k/T) -5.6 11.2 0.00374 -3.17343 -3.4 15.0 0.00371 -2.88948 -1.9 20.2 0.00369 -2.59740 0.4 25.5 0.00366 -2.37284 2.6 33.3 0.00363 -2.11397 4.8 43.8 0.00360 -1.84784 6.9 57.6 0.00357 -1.58148 8.9 73.7 0.00355 -1.34212 10.8 93.3 0.00352 -1.11301 12.8 119.0 0.00350 -0.87673 14.8 151.0 0.00347 -0.64554 16.8 191.0 0.00345 -0.41747 18.7 241.0 0.00343 -0.19148 20.7 305.0 0.00340 0.03721 22.7 382.0 0.00338 0.25553 24.6 474.0 0.00336 0.46492 26.5 544.0 0.00334 0.59630 28.5 684.0 0.00331 0.81866 30.4 854.0 0.00329 1.03435 32.4 943.0 0.00327 1.12692 34.3 1100.0 0.00325 1.27472
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APPENDIX C STRUCTURAL CHARACTERIZATION FOR 5
Figure C-1. Heteronuclear Multiple Bond Coherence (gHMBC) NMR spectrum of Hydride Dimer 5.
101
Table C-1. Crystal data and structure refinement for 5. Identification code llr8 Empirical formula C24 H58 N8 W2 Formula weight 826.48 Temperature 173(2) K Wavelength 0.71073 Å Crystal system Monoclinic Space group P2(1)/n Unit cell dimensions a = 9.2735(9) Å α = 90°. b = 24.545(2) Å β = 98.950(2)°. c = 14.7551(2) Å γ = 90°. Volume 3317.6(6) Å3 Z 4 Density (calculated) 1.655 Mg/m3 Absorption coefficient 6.953 mm-1 F(000) 1624 Crystal size 0.17 x 0.09 x 0.09 mm3 Theta range for data collection 1.62 to 27.50°. Index ranges -9≤h≤12, -27≤k≤31, -19≤l≤19 Reflections collected 22106 Independent reflections 7583 [R(int) = 0.0563] Completeness to theta = 27.50° 99.8 % Absorption correction Integration Max. and min. transmission 0.6063 and 0.2981 Refinement method Full-matrix least-squares on F2 Data / restraints / parameters 7583 / 12 / 324 Goodness-of-fit on F2 1.028 Final R indices [I>2sigma(I)] R1 = 0.0269, wR2 = 0.0667 R indices (all data) R1 = 0.0340, wR2 = 0.0694 Largest diff. peak and hole 1.550 and -0.921 e.Å-3 R1 = ∑(||Fo| - |Fc||) / ∑|Fo|
wR2 = [∑[w(Fo2 - Fc2)2] / ∑[w(Fo2)2]]1/2
S = [∑[w(Fo2 - Fc2)2] / (n-p)]1/2
w= 1/[σ2(Fo2)+(m*p)2+n*p], p = [max(Fo2,0)+ 2* Fc2]/3, m & n are constants.
102
Table C-2. Atomic coordinates ( x 104) and equivalent isotropic displacement parameters (Å2x 103) for 5. U(eq) is defined as one third of the trace of the orthogonalized Uij tensor.
x y z U(eq)
W(1) 1425(1) 992(1) 7347(1) 29(1) W(2) 2585(1) 1791(1) 8408(1) 31(1) N(1) 701(5) 472(2) 7930(3) 50(1) N(2) 452(4) 998(1) 5928(2) 34(1) N(3) 2619(4) 680(2) 6341(3) 60(1) N(4) 1686(6) 668(2) 4724(3) 70(1) N(5) 1449(5) 2356(1) 8448(2) 45(1) N(6) 4127(4) 1690(1) 9650(2) 35(1) N(7) 4803(4) 1993(2) 8396(2) 44(1) N(8) 6737(4) 1739(2) 9580(3) 50(1) C(1) 1597(5) 777(2) 5634(3) 45(1) C(2) 221(8) 148(2) 8646(3) 82(2) C(3) -1198(19) -47(5) 8449(9) 68(3) C(4) 1395(18) -378(5) 8733(8) 68(3) C(3') -1630(30) 108(8) 8336(13) 68(3) C(4') 700(20) -344(7) 8940(11) 68(3) C(5) 3811(6) 291(3) 6373(6) 96(3) C(6) 5147(13) 617(6) 6590(11) 101(3) C(7) 3589(12) -175(5) 7103(10) 101(3) C(6') 5075(18) 332(8) 7156(15) 101(3) C(7') 3330(17) -222(7) 6030(13) 101(3) C(8) -632(7) 1342(2) 5377(3) 63(2) C(9) 499(7) 1949(2) 5504(3) 58(1) C(10) -1784(19) 1439(6) 5624(11) 58(1) C(9') -600(10) 1932(3) 5562(5) 58(1) C(10') -2242(9) 1101(3) 5593(6) 58(1) C(11) 314(15) 481(6) 4095(10) 56(2) C(12) 2863(13) 774(4) 4244(7) 56(2) C(11') 810(20) 458(10) 4083(17) 56(2) C(12') 3380(20) 663(6) 4615(12) 56(2) C(13) 5270(5) 1806(2) 9241(3) 39(1) C(14) 247(6) 2740(2) 8348(3) 61(2) C(15) 807(10) 3290(2) 8045(4) 97(3) C(16) -381(7) 2799(3) 9244(5) 78(2) C(17) 4171(5) 1314(2) 10433(3) 43(1) C(18) 4266(6) 723(2) 10147(4) 59(1) C(19) 2858(6) 1424(3) 10907(4) 66(2) C(20) 5637(6) 2347(2) 7862(3) 54(1) C(21) 5085(9) 2924(3) 7869(5) 88(2) C(22) 5508(7) 2144(3) 6887(4) 71(2) C(23) 7671(6) 1438(3) 9030(4) 77(2) C(24) 7308(6) 1797(2) 10550(3) 61(2)
103
Table C-3. Bond lengths [Å] and angles [°] for 5.
Bond Length (Å) or Angle (°)
W(1)-N(1) 1.733(4) W(1)-N(3) 2.128(4) W(1)-N(2) 2.147(3) W(1)-C(1) 2.611(4) W(1)-W(2) 2.6332(3) W(1)-H(1) 1.70(5) W(1)-H(3) 1.71(6) W(1)-H(4) 1.96(5) W(2)-N(5) 1.746(4) W(2)-N(7) 2.118(4) W(2)-N(6) 2.156(3) W(2)-C(13) 2.600(4) W(2)-H(2) 1.58(4) W(2)-H(3) 1.78(6) W(2)-H(4) 1.66(5) N(1)-C(2) 1.446(6) N(2)-C(1) 1.325(6) N(2)-C(8) 1.460(6) N(3)-C(1) 1.317(6) N(3)-C(5) 1.456(7) N(4)-C(11') 1.26(2) N(4)-C(1) 1.384(6) N(4)-C(12) 1.414(10) N(4)-C(11) 1.524(16) N(4)-C(12') 1.607(19) N(5)-C(14) 1.451(6) N(6)-C(13) 1.330(6) N(6)-C(17) 1.474(5) N(7)-C(13) 1.336(5) N(7)-C(20) 1.471(6) N(8)-C(13) 1.384(6) N(8)-C(24) 1.454(6) N(8)-C(23) 1.473(7) C(2)-C(4') 1.336(18) C(2)-C(3) 1.388(17) C(2)-C(4) 1.681(17) C(2)-C(3') 1.71(2) C(2)-H(2A) 1.0000 C(2)-H(2B) 1.0000 C(3)-H(3A) 0.9800 C(3)-H(3B) 0.9800 C(3)-H(3C) 0.9800 C(4)-H(4A) 0.9800
104
Table C-3. Continued.
C(4)-H(4B) 0.9800 C(4)-H(4C) 0.9800 C(3')-H(3'A) 0.9800 C(3')-H(3'B) 0.9800 C(3')-H(3'C) 0.9800 C(4')-H(4'A) 0.9800 C(4')-H(4'B) 0.9800 C(4')-H(4'C) 0.9800 C(5)-C(7') 1.404(16) C(5)-C(6) 1.467(14) C(5)-C(6') 1.516(17) C(5)-C(7) 1.606(17) C(5)-H(5A) 1.0000 C(5)-H(5B) 1.0000 C(6)-H(6A) 0.9800 C(6)-H(6B) 0.9800 C(6)-H(6C) 0.9800 C(7)-H(7A) 0.9800 C(7)-H(7B) 0.9800 C(7)-H(7C) 0.9800 C(6')-H(6'A) 0.9800 C(6')-H(6'B) 0.9800 C(6')-H(6'C) 0.9800 C(7')-H(7'A) 0.9800 C(7')-H(7'B) 0.9800 C(7')-H(7'C) 0.9800 C(8)-C(10) 1.205(17) C(8)-C(9') 1.473(9) C(8)-C(10') 1.682(11) C(8)-C(9) 1.8139 C(8)-H(8A) 1.0000 C(8)-H(8B) 1.0000 C(9)-H(9A) 0.9800 C(9)-H(9B) 0.9800 C(9)-H(9C) 0.9800 C(10)-H(10A) 0.9800 C(10)-H(10B) 0.9800 C(10)-H(10C) 0.9800 C(9')-H(9'A) 0.9800 C(9')-H(9'B) 0.9800 C(9')-H(9'C) 0.9800 C(10')-H(10D) 0.9800 C(10')-H(10E) 0.9800 C(10')-H(10F) 0.9800 C(11)-H(11A) 0.9800
105
Table C-3. Continued.
C(11)-H(11B) 0.9800 C(11)-H(11C) 0.9800 C(12)-H(12A) 0.9800 C(12)-H(12B) 0.9800 C(12)-H(12C) 0.9800 C(11')-H(11D) 0.9800 C(11')-H(11E) 0.9800 C(11')-H(11F) 0.9800 C(12')-H(12D) 0.9800 C(12')-H(12E) 0.9800 C(12')-H(12F) 0.9800 C(14)-C(16) 1.532(8) C(14)-C(15) 1.536(9) C(14)-H(14A) 1.0000 C(15)-H(15A) 0.9800 C(15)-H(15B) 0.9800 C(15)-H(15C) 0.9800 C(16)-H(16A) 0.9800 C(16)-H(16B) 0.9800 C(16)-H(16C) 0.9800 C(17)-C(18) 1.515(7) C(17)-C(19) 1.521(7) C(17)-H(17A) 1.0000 C(18)-H(18A) 0.9800 C(18)-H(18B) 0.9800 C(18)-H(18C) 0.9800 C(19)-H(19A) 0.9800 C(19)-H(19B) 0.9800 C(19)-H(19C) 0.9800 C(20)-C(21) 1.508(8) C(20)-C(22) 1.510(7) C(20)-H(20A) 1.0000 C(21)-H(21A) 0.9800 C(21)-H(21B) 0.9800 C(21)-H(21C) 0.9800 C(22)-H(22A) 0.9800 C(22)-H(22B) 0.9800 C(22)-H(22C) 0.9800 C(23)-H(23A) 0.9800 C(23)-H(23B) 0.9800 C(23)-H(23C) 0.9800 C(24)-H(24A) 0.9800 C(24)-H(24B) 0.9800 C(24)-H(24C) 0.9800 N(1)-W(1)-N(3) 111.4(2)
106
Table C-3. Continued.
N(1)-W(1)-N(2) 110.63(14) N(3)-W(1)-N(2) 60.50(15) N(1)-W(1)-C(1) 114.70(16) N(3)-W(1)-C(1) 30.13(15) N(2)-W(1)-C(1) 30.37(14) N(1)-W(1)-W(2) 114.08(12) N(3)-W(1)-W(2) 118.33(12) N(2)-W(1)-W(2) 130.21(8) C(1)-W(1)-W(2) 130.22(9) N(1)-W(1)-H(1) 93.8(16) N(3)-W(1)-H(1) 137.9(15) N(2)-W(1)-H(1) 79.6(15) C(1)-W(1)-H(1) 109.0(15) W(2)-W(1)-H(1) 76.8(16) N(1)-W(1)-H(3) 102(2) N(3)-W(1)-H(3) 90(2) N(2)-W(1)-H(3) 142(2) C(1)-W(1)-H(3) 117(2) W(2)-W(1)-H(3) 42(2) H(1)-W(1)-H(3) 118(3) N(1)-W(1)-H(4) 153.0(14) N(3)-W(1)-H(4) 88.5(14) N(2)-W(1)-H(4) 94.8(14) C(1)-W(1)-H(4) 91.8(14) W(2)-W(1)-H(4) 38.9(14) H(1)-W(1)-H(4) 82(2) H(3)-W(1)-H(4) 59(2) N(5)-W(2)-N(7) 114.01(17) N(5)-W(2)-N(6) 112.72(14) N(7)-W(2)-N(6) 61.15(13) N(5)-W(2)-C(13) 120.76(15) N(7)-W(2)-C(13) 30.77(14) N(6)-W(2)-C(13) 30.70(13) N(5)-W(2)-W(1) 114.73(12) N(7)-W(2)-W(1) 118.43(10) N(6)-W(2)-W(1) 125.10(9) C(13)-W(2)-W(1) 124.32(9) N(5)-W(2)-H(2) 94.9(15) N(7)-W(2)-H(2) 140.5(14) N(6)-W(2)-H(2) 83.6(14) C(13)-W(2)-H(2) 111.3(14) W(1)-W(2)-H(2) 66.7(14) N(5)-W(2)-H(3) 155(2) N(7)-W(2)-H(3) 87(2) N(6)-W(2)-H(3) 89(2)
107
Table C-3. Continued.
C(13)-W(2)-H(3) 84(2) W(1)-W(2)-H(3) 40(2) H(2)-W(2)-H(3) 75(2) N(5)-W(2)-H(4) 101.7(17) N(7)-W(2)-H(4) 87.2(17) N(6)-W(2)-H(4) 140.1(17) C(13)-W(2)-H(4) 113.1(17) W(1)-W(2)-H(4) 48.1(16) H(2)-W(2)-H(4) 114(2) H(3)-W(2)-H(4) 64(2) C(2)-N(1)-W(1) 162.7(3) C(1)-N(2)-C(8) 124.9(4) C(1)-N(2)-W(1) 94.6(3) C(8)-N(2)-W(1) 134.1(3) C(1)-N(3)-C(5) 126.4(4) C(1)-N(3)-W(1) 95.7(3) C(5)-N(3)-W(1) 133.5(5) C(11')-N(4)-C(1) 132.7(10) C(11')-N(4)-C(12) 99.2(10) C(1)-N(4)-C(12) 128.1(6) C(11')-N(4)-C(11) 15.8(11) C(1)-N(4)-C(11) 118.6(6) C(12)-N(4)-C(11) 112.8(6) C(11')-N(4)-C(12') 116.9(10) C(1)-N(4)-C(12') 107.8(7) C(12)-N(4)-C(12') 26.7(5) C(11)-N(4)-C(12') 132.5(7) C(14)-N(5)-W(2) 166.1(3) C(13)-N(6)-C(17) 124.2(4) C(13)-N(6)-W(2) 93.4(2) C(17)-N(6)-W(2) 132.2(3) C(13)-N(7)-C(20) 125.5(4) C(13)-N(7)-W(2) 95.0(3) C(20)-N(7)-W(2) 137.2(3) C(13)-N(8)-C(24) 122.1(4) C(13)-N(8)-C(23) 119.3(4) C(24)-N(8)-C(23) 115.8(4) N(3)-C(1)-N(2) 109.2(4) N(3)-C(1)-N(4) 126.1(5) N(2)-C(1)-N(4) 124.7(5) N(3)-C(1)-W(1) 54.2(2) N(2)-C(1)-W(1) 55.0(2) N(4)-C(1)-W(1) 179.4(4) C(4')-C(2)-C(3) 90.8(9) C(4')-C(2)-N(1) 127.5(12)
108
Table C-3. Continued.
C(3)-C(2)-N(1) 115.2(6) C(4')-C(2)-C(4) 26.1(8) C(3)-C(2)-C(4) 109.4(7) N(1)-C(2)-C(4) 102.0(7) C(4')-C(2)-C(3') 107.7(10) C(3)-C(2)-C(3') 17.0(7) N(1)-C(2)-C(3') 104.3(7) C(4)-C(2)-C(3') 126.0(8) C(4')-C(2)-H(2A) 101.3 C(3)-C(2)-H(2A) 110.0 N(1)-C(2)-H(2A) 110.0 C(4)-C(2)-H(2A) 110.0 C(3')-C(2)-H(2A) 104.0 C(4')-C(2)-H(2B) 105.2 C(3)-C(2)-H(2B) 112.4 N(1)-C(2)-H(2B) 105.2 C(4)-C(2)-H(2B) 112.1 C(3')-C(2)-H(2B) 105.2 H(2A)-C(2)-H(2B) 4.8 C(2)-C(3)-H(3A) 109.5 C(2)-C(3)-H(3B) 109.5 H(3A)-C(3)-H(3B) 109.5 C(2)-C(3)-H(3C) 109.5 H(3A)-C(3)-H(3C) 109.5 H(3B)-C(3)-H(3C) 109.5 C(2)-C(4)-H(4A) 109.5 C(2)-C(4)-H(4B) 109.5 H(4A)-C(4)-H(4B) 109.5 C(2)-C(4)-H(4C) 109.5 H(4A)-C(4)-H(4C) 109.5 H(4B)-C(4)-H(4C) 109.5 C(2)-C(3')-H(3'A) 109.5 C(2)-C(3')-H(3'B) 109.5 H(3'A)-C(3')-H(3'B) 109.5 C(2)-C(3')-H(3'C) 109.5 H(3'A)-C(3')-H(3'C) 109.5 H(3'B)-C(3')-H(3'C) 109.5 C(2)-C(4')-H(4'A) 109.5 C(2)-C(4')-H(4'B) 109.5 H(4'A)-C(4')-H(4'B) 109.5 C(2)-C(4')-H(4'C) 109.5 H(4'A)-C(4')-H(4'C) 109.5 H(4'B)-C(4')-H(4'C) 109.5 C(7')-C(5)-N(3) 112.3(7) C(7')-C(5)-C(6) 141.0(9)
109
Table C-3. Continued.
N(3)-C(5)-C(6) 105.2(7) C(7')-C(5)-C(6') 119.9(12) N(3)-C(5)-C(6') 118.4(7) C(6)-C(5)-C(6') 43.2(10) C(7')-C(5)-C(7) 62.3(10) N(3)-C(5)-C(7) 108.2(7) C(6)-C(5)-C(7) 115.7(10) C(6')-C(5)-C(7) 72.6(11) C(7')-C(5)-H(5A) 48.4 N(3)-C(5)-H(5A) 109.2 C(6)-C(5)-H(5A) 109.2 C(6')-C(5)-H(5A) 129.2 C(7)-C(5)-H(5A) 109.2 C(7')-C(5)-H(5B) 100.3 N(3)-C(5)-H(5B) 100.3 C(6)-C(5)-H(5B) 61.6 C(6')-C(5)-H(5B) 100.3 C(7)-C(5)-H(5B) 150.5 H(5A)-C(5)-H(5B) 52.6 C(5)-C(6)-H(6A) 109.5 C(5)-C(6)-H(6B) 109.5 H(6A)-C(6)-H(6B) 109.5 C(5)-C(6)-H(6C) 109.5 H(6A)-C(6)-H(6C) 109.5 H(6B)-C(6)-H(6C) 109.5 C(5)-C(7)-H(7A) 109.5 C(5)-C(7)-H(7B) 109.5 H(7A)-C(7)-H(7B) 109.5 C(5)-C(7)-H(7C) 109.5 H(7A)-C(7)-H(7C) 109.5 H(7B)-C(7)-H(7C) 109.5 C(5)-C(6')-H(6'A) 109.5 C(5)-C(6')-H(6'B) 109.5 H(6'A)-C(6')-H(6'B) 109.5 C(5)-C(6')-H(6'C) 109.5 H(6'A)-C(6')-H(6'C) 109.5 H(6'B)-C(6')-H(6'C) 109.5 C(5)-C(7')-H(7'A) 109.5 C(5)-C(7')-H(7'B) 109.5 H(7'A)-C(7')-H(7'B) 109.5 C(5)-C(7')-H(7'C) 109.5 H(7'A)-C(7')-H(7'C) 109.5 H(7'B)-C(7')-H(7'C) 109.5 C(10)-C(8)-N(2) 120.8(8) C(10)-C(8)-C(9') 75.1(9)
110
Table C-3. Continued.
N(2)-C(8)-C(9') 118.3(5) C(10)-C(8)-C(10') 32.6(8) N(2)-C(8)-C(10') 104.2(4) C(9')-C(8)-C(10') 107.7(5) C(10)-C(8)-C(9) 109.4(9) N(2)-C(8)-C(9) 94.6(3) C(9')-C(8)-C(9) 34.9(4) C(10')-C(8)-C(9) 141.8(3) C(10)-C(8)-H(8A) 120.9 N(2)-C(8)-H(8A) 108.8 C(9')-C(8)-H(8A) 108.8 C(10')-C(8)-H(8A) 108.8 C(9)-C(8)-H(8A) 95.8 C(10)-C(8)-H(8B) 110.3 N(2)-C(8)-H(8B) 110.3 C(9')-C(8)-H(8B) 118.3 C(10')-C(8)-H(8B) 94.2 C(9)-C(8)-H(8B) 110.3 H(8A)-C(8)-H(8B) 15.0 C(8)-C(9)-H(9A) 109.5 C(8)-C(9)-H(9B) 109.5 H(9A)-C(9)-H(9B) 109.5 C(8)-C(9)-H(9C) 109.5 H(9A)-C(9)-H(9C) 109.5 H(9B)-C(9)-H(9C) 109.5 C(8)-C(10)-H(10A) 109.5 C(8)-C(10)-H(10B) 109.5 H(10A)-C(10)-H(10B) 109.5 C(8)-C(10)-H(10C) 109.5 H(10A)-C(10)-H(10C) 109.5 H(10B)-C(10)-H(10C) 109.5 C(8)-C(9')-H(9'A) 109.5 C(8)-C(9')-H(9'B) 109.5 H(9'A)-C(9')-H(9'B) 109.5 C(8)-C(9')-H(9'C) 109.5 H(9'A)-C(9')-H(9'C) 109.5 H(9'B)-C(9')-H(9'C) 109.5 C(8)-C(10')-H(10D) 109.5 C(8)-C(10')-H(10E) 109.5 H(10D)-C(10')-H(10E) 109.5 C(8)-C(10')-H(10F) 109.5 H(10D)-C(10')-H(10F) 109.5 H(10E)-C(10')-H(10F) 109.5 N(4)-C(11)-H(11A) 109.5 N(4)-C(11)-H(11B) 109.5
111
Table C-3. Continued.
H(11A)-C(11)-H(11B) 109.5 N(4)-C(11)-H(11C) 109.5 H(11A)-C(11)-H(11C) 109.5 H(11B)-C(11)-H(11C) 109.5 N(4)-C(12)-H(12A) 109.5 N(4)-C(12)-H(12B) 109.5 H(12A)-C(12)-H(12B) 109.5 N(4)-C(12)-H(12C) 109.5 H(12A)-C(12)-H(12C) 109.5 H(12B)-C(12)-H(12C) 109.5 N(4)-C(11')-H(11D) 109.5 N(4)-C(11')-H(11E) 109.5 H(11D)-C(11')-H(11E) 109.5 N(4)-C(11')-H(11F) 109.5 H(11D)-C(11')-H(11F) 109.5 H(11E)-C(11')-H(11F) 109.5 N(4)-C(12')-H(12D) 109.5 N(4)-C(12')-H(12E) 109.5 H(12D)-C(12')-H(12E) 109.5 N(4)-C(12')-H(12F) 109.5 H(12D)-C(12')-H(12F) 109.5 H(12E)-C(12')-H(12F) 109.5 N(6)-C(13)-N(7) 109.3(4) N(6)-C(13)-N(8) 128.2(4) N(7)-C(13)-N(8) 122.4(4) N(6)-C(13)-W(2) 55.9(2) N(7)-C(13)-W(2) 54.2(2) N(8)-C(13)-W(2) 169.8(3) N(5)-C(14)-C(16) 111.2(5) N(5)-C(14)-C(15) 108.2(5) C(16)-C(14)-C(15) 111.0(4) N(5)-C(14)-H(14A) 108.8 C(16)-C(14)-H(14A) 108.8 C(15)-C(14)-H(14A) 108.8 C(14)-C(15)-H(15A) 109.5 C(14)-C(15)-H(15B) 109.5 H(15A)-C(15)-H(15B) 109.5 C(14)-C(15)-H(15C) 109.5 H(15A)-C(15)-H(15C) 109.5 H(15B)-C(15)-H(15C) 109.5 C(14)-C(16)-H(16A) 109.5 C(14)-C(16)-H(16B) 109.5 H(16A)-C(16)-H(16B) 109.5 C(14)-C(16)-H(16C) 109.5 H(16A)-C(16)-H(16C) 109.5
112
Table C-3. Continued.
H(16B)-C(16)-H(16C) 109.5 N(6)-C(17)-C(18) 112.2(4) N(6)-C(17)-C(19) 108.8(4) C(18)-C(17)-C(19) 112.5(4) N(6)-C(17)-H(17A) 107.7 C(18)-C(17)-H(17A) 107.7 C(19)-C(17)-H(17A) 107.7 C(17)-C(18)-H(18A) 109.5 C(17)-C(18)-H(18B) 109.5 H(18A)-C(18)-H(18B) 109.5 C(17)-C(18)-H(18C) 109.5 H(18A)-C(18)-H(18C) 109.5 H(18B)-C(18)-H(18C) 109.5 C(17)-C(19)-H(19A) 109.5 C(17)-C(19)-H(19B) 109.5 H(19A)-C(19)-H(19B) 109.5 C(17)-C(19)-H(19C) 109.5 H(19A)-C(19)-H(19C) 109.5 H(19B)-C(19)-H(19C) 109.5 N(7)-C(20)-C(21) 110.1(4) N(7)-C(20)-C(22) 110.2(4) C(21)-C(20)-C(22) 109.9(5) N(7)-C(20)-H(20A) 108.9 C(21)-C(20)-H(20A) 108.9 C(22)-C(20)-H(20A) 108.9 C(20)-C(21)-H(21A) 109.5 C(20)-C(21)-H(21B) 109.5 H(21A)-C(21)-H(21B) 109.5 C(20)-C(21)-H(21C) 109.5 H(21A)-C(21)-H(21C) 109.5 H(21B)-C(21)-H(21C) 109.5 C(20)-C(22)-H(22A) 109.5 C(20)-C(22)-H(22B) 109.5 H(22A)-C(22)-H(22B) 109.5 C(20)-C(22)-H(22C) 109.5 H(22A)-C(22)-H(22C) 109.5 H(22B)-C(22)-H(22C) 109.5 N(8)-C(23)-H(23A) 109.5 N(8)-C(23)-H(23B) 109.5 H(23A)-C(23)-H(23B) 109.5 N(8)-C(23)-H(23C) 109.5 H(23A)-C(23)-H(23C) 109.5 H(23B)-C(23)-H(23C) 109.5 N(8)-C(24)-H(24A) 109.5 N(8)-C(24)-H(24B) 109.5
113
Table C-3. Continued.
H(24A)-C(24)-H(24B) 109.5 N(8)-C(24)-H(24C) 109.5 H(24A)-C(24)-H(24C) 109.5 H(24B)-C(24)-H(24C) 109.5
Symmetry transformations used to generate equivalent atoms: Table C-4. Anisotropic displacement parameters (Å2x 103) for 5. The anisotropic displacement
factor exponent takes the form: -2π2[ h2 a*2U11 + ... + 2 h k a* b* U12 ]
U11 U22 U33 U23 U13 U12 W(1) 31(1) 24(1) 31(1) -4(1) -2(1) 0(1) W(2) 33(1) 28(1) 31(1) -8(1) 1(1) 0(1) N(1) 64(3) 36(2) 40(2) 9(2) -20(2) -15(2) N(2) 46(2) 28(2) 26(2) -2(1) 3(1) -1(1) N(3) 43(2) 65(3) 69(3) -42(2) -1(2) 10(2) N(4) 97(4) 63(3) 58(3) -28(2) 40(3) -17(3) N(5) 59(2) 34(2) 38(2) -11(1) -3(2) 5(2) N(6) 38(2) 34(2) 31(2) -5(1) 3(1) -9(1) N(7) 45(2) 54(2) 32(2) -8(2) 2(2) -13(2) N(8) 31(2) 68(3) 50(2) -9(2) -1(2) -2(2) C(1) 51(3) 36(2) 51(3) -23(2) 20(2) -12(2) C(2) 147(6) 52(3) 35(2) 10(2) -24(3) -50(4) C(3) 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(4) 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(3') 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(4') 98(8) 54(4) 49(3) 22(3) 6(3) -21(5) C(5) 36(3) 110(6) 139(6) -93(5) -1(3) 10(3) C(6) 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(7) 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(6') 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(7') 58(3) 91(6) 138(8) -63(5) -34(5) 33(4) C(8) 115(5) 45(3) 26(2) 3(2) 1(3) 32(3) C(9) 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(10) 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(9') 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(10') 70(3) 43(2) 55(3) 10(2) -5(3) 17(3) C(11) 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(12) 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(11') 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(12') 86(6) 50(3) 34(2) -7(2) 18(4) -6(4) C(13) 40(2) 41(2) 34(2) -11(2) -1(2) -8(2) C(14) 66(3) 60(3) 51(3) -20(2) -15(2) 26(3) C(15) 171(8) 63(4) 61(4) 22(3) 33(4) 60(5) C(16) 68(4) 70(4) 101(5) -19(3) 25(4) -5(3)
114
Table C-4. Continued.
C(17) 44(2) 44(2) 38(2) 1(2) -1(2) -9(2) C(18) 72(4) 39(3) 62(3) 5(2) 1(3) 2(2) C(19) 73(4) 76(4) 54(3) 10(3) 23(3) -10(3) C(20) 50(3) 73(3) 38(2) -3(2) 5(2) -21(3) C(21) 134(7) 58(4) 82(4) -8(3) 46(4) -32(4) C(22) 92(5) 84(4) 43(3) -5(3) 28(3) -9(4) C(23) 50(3) 112(5) 71(4) -16(4) 13(3) 7(3) C(24) 44(3) 88(4) 48(3) 0(3) -7(2) -18(3) Table C-5. Hydrogen coordinates ( x 104) and isotropic displacement parameters (Å2x 10 3) for
5.
x y z U(eq) H(1) -10(50) 1417(19) 7390(30) 51(13) H(2) 1610(40) 1393(17) 8900(30) 32(11) H(3) 3030(70) 1120(20) 8060(40) 100(20) H(4) 2450(50) 1687(19) 7290(30) 49(13) H(2A) 350 359 9233 98 H(2B) 373 385 9203 98 H(3A) -1884 259 8419 101 H(3B) -1382 -300 8931 101 H(3C) -1330 -236 7857 101 H(4A) 2389 -244 8933 101 H(4B) 1343 -556 8134 101 H(4C) 1137 -640 9182 101 H(3'A) -2062 471 8362 101 H(3'B) -2037 -136 8758 101 H(3'C) -1861 -35 7710 101 H(4'A) 160 -467 9422 101 H(4'B) 1743 -323 9186 101 H(4'C) 551 -602 8427 101 H(5A) 3780 122 5754 116 H(5B) 4289 428 5854 116 H(6A) 5181 888 6107 152 H(6B) 6000 377 6628 152 H(6C) 5152 801 7179 152 H(7A) 2692 -378 6884 152 H(7B) 3513 -7 7696 152 H(7C) 4424 -424 7173 152 H(6'A) 5725 628 7034 152 H(6'B) 5618 -13 7211 152 H(6'C) 4700 405 7729 152 H(7'A) 3208 -217 5358 152 H(7'B) 2394 -308 6227 152 H(7'C) 4053 -499 6266 152
115
Table C-5. Continued.
H(8A) -571 1283 4714 76 H(8B) -792 1218 4724 76 H(9A) 1401 1880 5254 86 H(9B) 739 2043 6156 86 H(9C) -31 2251 5171 86 H(10A) -2396 1112 5556 86 H(10B) -2279 1733 5248 86 H(10C) -1615 1551 6270 86 H(9'A) -1571 2054 5659 86 H(9'B) -317 2127 5037 86 H(9'C) 109 2009 6112 86 H(10D) -2363 723 5381 86 H(10E) -3037 1324 5271 86 H(10F) -2265 1115 6255 86 H(11A) -545 557 4386 84 H(11B) 375 89 3982 84 H(11C) 229 678 3510 84 H(12A) 2497 953 3660 84 H(12B) 3336 429 4125 84 H(12C) 3572 1011 4615 84 H(11D) -190 492 4219 84 H(11E) 1046 71 4025 84 H(11F) 882 646 3507 84 H(12D) 3962 821 5164 84 H(12E) 3524 878 4076 84 H(12F) 3699 287 4538 84 H(14A) -541 2606 7858 74 H(15A) 1210 3241 7475 145 H(15B) 1571 3428 8525 145 H(15C) -1 3551 7944 145 H(16A) -741 2445 9418 117 H(16B) -1187 3061 9157 117 H(16C) 384 2929 9730 117 H(17A) 5069 1399 10879 51 H(18A) 5120 674 9839 88 H(18B) 3381 625 9726 88 H(18C) 4359 490 10692 88 H(19A) 2841 1810 11075 99 H(19B) 2925 1200 11462 99 H(19C) 1961 1333 10491 99 H(20A) 6688 2340 8148 64 H(21A) 5173 3054 8504 132 H(21B) 4058 2936 7584 132 H(21C) 5663 3158 7526 132 H(22A) 5871 1769 6887 107
116
Table C-5. Continued.
H(22B) 6088 2377 6542 107 H(22C) 4483 2154 6598 107 H(23A) 7193 1424 8390 116 H(23B) 7827 1067 9270 116 H(23C) 8613 1624 9065 116 H(24A) 6614 2004 10852 92 H(24B) 8243 1991 10621 92 H(24C) 7453 1435 10831 92
117
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BIOGRAPHICAL SKETCH
Laurel Reitfort was born in 1979 in Raleigh, North Carolina where she was raised. She
attended high school at Ravenscroft School and after graduated in 1997. She continued her
studies at The University of North Carolina at Chapel Hill where she received her B.S. in
Chemistry in December 2001. In her final year in Chapel Hill Laurel was introduced to the
world of research in Professor Joe Templeton’s group which motivated her to attend graduate
school She worked at Research Triangle Institute from October 2001 until July 2002. In August
2002 Laurel moved to Gainesville, Fl to pursue her Ph.D. in chemistry at the University of
Florida. She started research in Professor Lisa McElwee-White’s group in Spring of 2003 and
graduated in the Spring of 2008.