chemical vapor deposition of ruthenium
DESCRIPTION
Summary of my doctoral research on ruthenium chemical vapor deposition.TRANSCRIPT
• Doctoral research performed at the Department of Materials Science and Engineering at the University of Illinois at Urbana-Champaign, in collaboration with chemistry students in Dr. Gregory S. Girolami’s research group
• Submitted to Chemistry of Materials for publication, published in doctoral thesis in October 2009
Amount of assumed background knowledge and information:
Assumed knowledge areas: Basic chemistry and physics knowledge, chemical nomenclature, ball and stick structures, the basics of chemical vapor deposition as a technique, siteblocking and surface populations, basic crystal systems, conformality, mobilities, structure zone diagrams, familiarity with a variety of materials and chemical characterization techniques and ability to interpret the raw data from them
Chemical Vapor Deposition of Ruthenium
Teresa S. Spicer, PhD, [email protected]://www.linkedin.com/in/teresaspicer
Outline
Introduction
Key Findings
Problem Statement
Experiments
Results
Introduction
Integrated circuits have created a vital industry and enabled the telecommunications revolution
Semiconductor industry plays an important role in globalization, and therefore also in shaping our collective future.
Global Semiconductors Market Value, $ billion, 2004-2013(e)
Source: Datamonitor
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Image from http://www.textually.org/
Miniaturization drives integrated circuit development and applications
Image from http://tunicca.wordpress.com/2009/07/21/moores-law-the-effect-on-productivity/
Materials and thin film processing are key to miniaturization
In order to continue miniaturization, thin films of new materials are required.
2007: 30 new materials introduced into 45-nm node1
1 A Thorough Examination of the Electronic Chemicals and Materials Markets, Businesswire, August 15, 2007 Image from http://www.intel.com/pressroom/kits/45nm/photos.htm
❝The implementation of high-k and metal materials marks the biggest change in transistor technology
since the introduction of polysilicon gate MOS transistors in the late
1960s.❞Gordon Moore, Intel Co-Founder, regarding two of the 30
new materials introduced in 2007
As devices shrink in area, conformal deposition becomes a new challenge
Pinch-off.
Conformal coating.
Conformal coating, but slow growth.
The ideal: completely conformal (uniform), fast coating.
Conformality = (ttop/tbottom)·100%
The problem: the hole ‘clogs’ at the top - pinch-off.
The impractical compromise: grow slowly so that the hole doesn’t have time to pinch off.
An opportunity exists to find a process that is fast but retains the uniformity of the coating.
} ttop
} tbottom
DRAMs and interconnects need conformal Ru deposition
ECDCu
Ru seedlayer
Kim, K., and Lee, S. Y., Microelectronic Engineering, 2007. 84: p. 1976-1981.
Moffat, T.P., et al., J. Electrochem.Soc., 2006. 153(1): p. C37-C50.
Future dynamic random access memories
Seed layer for electrodeposition filling of copper
• Ru is electronically like Pt, which was used in initial research
• Unlike Pt, Ru etches easily in mass production
• Cu electroplates onto Ru
• Ru adheres better to the TaN underneath than Cu
Synthetic inorganic chemistry and materials engineering are required for new CVD processes
Conception and synthesis of new CVD precursor candidates
CVD of films from precursor
Measurement of film properties
Process hypothesis development
Synthesis of modified precursor
Development of novel growth processes and chemistryare needed to develop good CVD processes.
Synthetic inorganic chemistry
Materials engineering
Problem Statement
Ru
HH
C C
H
C
H
All MOCVD Ru precursors are susceptible to severe carbon incorporation.
Ruthenium catalyzes decomposition of organic ligands even at low temperatures
HH
Ru
Example: 1. Cyclohexadiene → benzene + H2
2. Benzene → surface hydrocarbons
Common case Desired case
Molecule C % Resistivity (μΩ·cm)
Growth Rate (nm/min)
ConformalityGrows on
previous layer?
(C6H6)Ru(C6H8)1 <1% - 2% 12-24 ? ? ✓
(1,5-COD)Ru(C7H9)2 1% - 3% ? 0.28 ? ✓
Ru(EtCp)2 3,4 ? ~7-150 ? ? ✓
RuCp(i-PrCp)5 ? 12-13 7.5-20 ? ✕
Due to this difficulty, Ru MOCVD growth rates are generally low
1 Choi, J., et al. Japanese Journal of Applied Physics, 2002. 41(11B): p. 6852-6856; Schneider, A., et al., Chemical Vapor Deposition, 2007. 13(8): p. 389-395. 2 Schneider, A., et al. Chemical Vapor Deposition, 2005. 11(2): p. 99-105. 3 Aoyama, T. and K. Eguchi. Japanese Journal of Applied Physics, Part 2 (Letters), 1999. 38(10A): p. 1134-6.4 Matsui, Y., et al. Electrochemical and Solid-State Letters, 2002. 5(1): p. C18-C21.5 Kang, S.Y., et al. J. Electrochem. Soc., 2002. 149(6): p. C317-C323.
Advances in Ru MOCVD need to be precursor chemistry-driven.
Surface science suggests choosing an appropriate ligand set can minimize ligand decomposition
Ligands that result in CO and benzene co-adsorbed on Ru may circumvent the catalytic decomposition.
Desired case• Low benzene coverages inhibit benzene
decomposition on Ru1
• CO does not dissociate readily on Ru2
• When CO and benzene are co-adsorbed:
‣ CO acts as a spacer between the benzene molecules3
‣ CO halves the saturation benzene coverage3Ru
C
O
C
O
C
O
1 Jakob, P. Doctoral Dissertation, Teknische Universität München, 1989.2 Jakob, P. nd Menzel, D. Surf. Sci. 210, 1988, 503-530.3 Heimann, P. A. et al, Surf. Sci. 210, 1989, 282-300
Tricarbonyl(1,3-cyclohexadiene)Ru(0) is expected to give benzene and CO co-adsorbed on the surface
Ru
HH
C
O
C
O
C
O
RuC
O
Expected Consequences:
1,3-cyclohexadiene and CO as Ru ligands could naturally give clean and conformal deposition.
• Very low carbon incorporation
• Conformal growth due to siteblocking
Experiments
Deposition in vacuum chamber➡ In-situ ellipsometer monitors growth➡ Precursor at ambient temperature➡ No carrier gas
Ru films were deposited and analyzed on several different substrates
Substrates
Amorphous oxides: FCC semiconductor crystal:Cubic ionic crystal:Hexagonal covalent crystal:
SiO2, Corning 7059 glassSi(100)KBrAl2O3(0001)
* Select films
• Reaction product identification • Conformality and sticking coefficient determination
Reaction and kinetic studies
Resistivity and composition
• 4-point probe
• Auger electron spectroscopy*
• X-ray photoelectron spectroscopy*
• Time-of-flight elastic recoil detection analysis
Phase and microstructure
• X-ray diffraction
• Scanning electron microscopy
• Atomic force microscopy*
• Transmission electron microscopy*
Results
Reaction products were analyzed with NMR
Condensation of reaction products
• Film deposition run in specialty glassware
• Products captured in chilled NMR tube
Benzene
CH
Cl 3
(sol
vent
)
Toluene methyl group(synthesis solvent)
H2O
(pre
sent
initi
ally
)
Toluene multiplets(synthesis solvent)
1H NMR Spectrum of Reaction Products
Missing 1,3-cyclohexadiene peaks
The likely decomposition reaction is (C6H8)Ru(CO)3 → H2 + C6H6 + 3CO
1234567 PPM
The low activation energy of the decomposition reaction makes low-temperature deposition possible.
200°C
300°C
400°C500°CGrowth rate: 2 - 24 nm/minDecomposition temperature: 80°CPrecursor pressure: 0.030 mTorr
The activation energy is 17 ± 7 kJ/mol
The Ru films are crystalline at all temperatures
200°C500°C
At both high and low growth temperatures, the films show clear crystallinity.
Typical amorphous material
The microstructures are compact
206 nm Ru on SiO2, 350°C 216 nm Ru on Si, 460°C
The lack of the usual visible gaps or holes in the films helps improve resistivity.
Ru film
SiO2
Ru film
Si substrateSi substrate
At low temperatures, kinetics rather than driving forces determine both microstructure and texture
Energy minimization does not play a large role in low-temperature ( > 500 ºC for Ru) texture.
For RuZone I: RT - 500 ºCZone II: 500 ºC - 1030 ºCZone III: 1030 ºC - 2334ºC
Ru
HH
C
O
C
O
C
O
RuC
O
The films exhibit c-plane fiber texture at low temperatures
• Increasing texture in thicker compared to thinner films
• Texture of T modulated films determined by final growth temperature
The texture forms during thickening
Role of substrate minimal
Two different formation mechanisms
• Same σ trends on all substrates
• (0001) fiber texture below T*=0.24
• (1122), (0001), and (1011) preferred orientations above
3.2 Experimental
3.2.1 Texture characterization
In order to gain insight into the possible mechanisms of texture formation andevolution in CVD films grown at low temperatures from 1, films were grownto similar thicknesses at different temperatures on an epitaxially matched[84]crystalline substrate (sapphire), a non-epitaxial crystal (Si ( 0 0 1 )), and anamorphous substrate (thermally grown SiO2).
Standard 2 θ–ω X–ray diffraction (XRD) and glancing angle X–raydiffraction (GAXRD) patterns were collected on a Philips X’Pert 2 systemusing Cu Kα radiation in order to determine the out-of-plane texture. GAXRDat a constant glancing angle of 1◦ relative to the crystal planes most nearlyparallel to the surface was performed in addition to standard 2 θ–ω scans.Glancing angle measurements eliminate peaks due to the substrate becausethe X-ray beam enters the substrate only to a small extent, and also gives agreater signal to noise ratio because the beam interacts with a larger volumeof film. Nanodiffraction patterns of films directly deposited onto SiOx
membranes were taken with a JEOL 2010 F transmission electron microscopein nanobeam mode. The morphology and microstructure were studied byexamining cross-sections of films in a Hitachi S–4700 scanning electronmicroscope.
Quantification of any in-plane texture was not possible in a reasonableamount of time for any of the films tried. Pole figure intensities were too lowto give clear information. However, the out-of-plane texture was quantifiedby calculating texture coefficients for each resolved reflection. Texturecoefficients are defined as[123, 124]
Ci =N Ii
I0�Ni=1
IiI0
, (3.1)
where Ci is the texture coefficient for reflection i, N is the number ofreections considered, Ii is the intensity in film of reection i, and Ii0 is theintensity of reection i in a randomly oriented sample. In most cases, lms hadmore than one preferred orientation. (0 0 0 1) was the most preferredorientation in almost all films grown at temperatures below 350 ◦C, while itsprominence diminished above 350 ◦C. The overall degree of texture in thefilms, σ, was computed from a close analogue to the standard deviation as
σ =
����N�
i=1
(Ci − Ci0)2
N, (3.2)
where Ci and N are defined as in equation 3.1 and Ci0 is the texturecoeffcient of a peak in a randomly oriented film. As can quickly be seen fromthe denition, σ is zero for a randomly oriented film. σ values of 1 or above are
39
3.2 Experimental
3.2.1 Texture characterization
In order to gain insight into the possible mechanisms of texture formation andevolution in CVD films grown at low temperatures from 1, films were grownto similar thicknesses at different temperatures on an epitaxially matched[84]crystalline substrate (sapphire), a non-epitaxial crystal (Si ( 0 0 1 )), and anamorphous substrate (thermally grown SiO2).
Standard 2 θ–ω X–ray diffraction (XRD) and glancing angle X–raydiffraction (GAXRD) patterns were collected on a Philips X’Pert 2 systemusing Cu Kα radiation in order to determine the out-of-plane texture. GAXRDat a constant glancing angle of 1◦ relative to the crystal planes most nearlyparallel to the surface was performed in addition to standard 2 θ–ω scans.Glancing angle measurements eliminate peaks due to the substrate becausethe X-ray beam enters the substrate only to a small extent, and also gives agreater signal to noise ratio because the beam interacts with a larger volumeof film. Nanodiffraction patterns of films directly deposited onto SiOx
membranes were taken with a JEOL 2010 F transmission electron microscopein nanobeam mode. The morphology and microstructure were studied byexamining cross-sections of films in a Hitachi S–4700 scanning electronmicroscope.
Quantification of any in-plane texture was not possible in a reasonableamount of time for any of the films tried. Pole figure intensities were too lowto give clear information. However, the out-of-plane texture was quantifiedby calculating texture coefficients for each resolved reflection. Texturecoefficients are defined as[123, 124]
Ci =N Ii
I0�Ni=1
IiI0
, (3.1)
where Ci is the texture coefficient for reflection i, N is the number ofreections considered, Ii is the intensity in film of reection i, and Ii0 is theintensity of reection i in a randomly oriented sample. In most cases, lms hadmore than one preferred orientation. (0 0 0 1) was the most preferredorientation in almost all films grown at temperatures below 350 ◦C, while itsprominence diminished above 350 ◦C. The overall degree of texture in thefilms, σ, was computed from a close analogue to the standard deviation as
σ =
����N�
i=1
(Ci − Ci0)2
N, (3.2)
where Ci and N are defined as in equation 3.1 and Ci0 is the texturecoeffcient of a peak in a randomly oriented film. As can quickly be seen fromthe denition, σ is zero for a randomly oriented film. σ values of 1 or above are
39
Texture coefficients: Overall degree of texture:
}
The films can grow on many materials types
The films grow readily on several oxides and silicon.
The films grow very well on oxides
~2300 nuclei/µm2
1 µm 2 µm
1 µm
0 µm
2 µm
0 µm
32s Growth at 300°C on thermally grown SiO2
Root-mean-square roughness:1.3 nm
The films start growing very quickly and evenly on oxides.
Contrary to expectation, the 1,3-CHD ligands decompose to carbon fragments
The adsorption behavior seen in surface science studies does not prevent ligand decomposition in a CVD process.
TOF - ERDA Elemental Composition Catalytic activation of C-C bonds likely occurs
Ru
HH
C C
H
C
H
Traditional CVD has a high reaction probability
Traditional CVD (at high temperatures)
Ru
C
O
C
O
CO
Traditional CVD often leads to pinch-off.
Ru
C
O
C
O
C
OC
O
CO
C
O
Ru
If the incoming molecules do not stick or react where they first land, conformality is possible
If the incoming molecules don’t stick immediately, coatings are more likely to be uniform.
The deposited atoms quickly
cause pinch-off.
High sticking probability Low sticking probability
Precursor molecules react or stick nearly
instantly
Precursor molecules bounce off the walls into
the trench.
Nearly conformal coverage.
Conformality was measured using a macrotrench experiment
Conformality and sticking coefficient determination
• Film grown in macrotrench at 0.50 mTorr
• Conformality directly calculated from thickness profile
• Sticking coefficient and growth rate dependence on pressure calculated
Cross-section → thickness profile
SiliconTa foilSilicon
~90%~75%
Temperature: 300°CPressure: 0.5 mTorrGR on flat surface: 10 nm/min
As predicted, the conformality of the process is good and the sticking coefficient is low.
The process is very conformal due to siteblocking
1 Yang, Y.; Jayaraman, S.; Kim, D.Y.; Girolami, G. S.; Abelson, J. R., Chem. Mat. 2006, 18, 21, 5088-5096.
Simulations1:
75% conformality in a macrotrench
90% conformality in a closed hole
Key Findings
Chemical Vapor Deposition of Ruthenium
• Facile reaction
• CO does not stop catalytic dehydrogenation of 1,3-CHD
• The ligands on the surface cause siteblocking, which makes the process very conformal
Acknowledgements
Dr. Charles Spicer, UNCCDr. Bong-Sub Lee, UIUC
Kristof Darmawikarta, UIUCDr. Angel Yanguas-Gil, UIUC
Dr. Mauro Sardela, UIUCNancy Finnegan, UIUC (Ret.)
Dr. Tim Spila, UIUCDr. Richard Haasch, UIUC
Subhash Gujrathi, Université de Montreal
Research supported by NSF grant DMR-0420768
Film characterization was carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of
Energy under grant DEFG02-91-ER45439