chemical vapor deposition of ruthenium

• 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, PMPteresa.s.spicer@gmail.comhttp://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