The document summarizes research on chemical vapor deposition of ruthenium thin films using tricarbonyl(1,3-cyclohexadiene)Ru(0) as the precursor. Key findings include: (1) NMR analysis showed the likely decomposition reaction is (C6H8)Ru(CO)3 → H2 + C6H6 + 3CO, with a low activation energy of 17 ± 7 kJ/mol, enabling low-temperature deposition. (2) Films were crystalline at all deposition temperatures and exhibited a compact microstructure. Texture was determined by growth conditions rather than thermodynamic driving forces. (3) Contrary to surface science studies, the 1,3

1. Chemical Vapor Deposition of Ruthenium
Teresa S. Spicer, PhD, PMP
teresa.s.spicer@gmail.com
http://www.linkedin.com/in/teresaspicer
• 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

2. Outline
Introduction
Problem Statement
Experiments
Results
Key Findings

3. Introduction

4. Integrated circuits have created a vital industry and
enabled the telecommunications revolution
Global Semiconductors Market Value, $ billion, 2004-2013(e)
350 9
J 8
Market value (USD billions)
300
7
250 J
J J 6
J
% Growth
200 5
J
150 4
J
3
100 J
J 2
50
1
0 0
2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Source: Datamonitor
Image from http://www.textually.org/
Semiconductor industry plays an important role in globalization,
and therefore also in shaping our collective future.

5. Miniaturization drives integrated circuit development
and applications
Image from http://tunicca.wordpress.com/2009/07/21/moores-law-the-effect-on-productivity/

6. Materials and thin film processing are key to
miniaturization
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
In order to continue miniaturization,
thin films of new materials are required.

7. As devices shrink in area, conformal deposition
becomes a new challenge
} ttop
The ideal: completely conformal (uniform), fast coating.
Conformality = (ttop/tbottom)·100%
} tbottom
Conformal coating.
The problem: the hole ‘clogs’ at the top - pinch-off.
Pinch-off.
The impractical compromise: grow slowly so that the
hole doesn’t have time to pinch off.
Conformal coating, but slow growth.
An opportunity exists to find a process that is fast
but retains the uniformity of the coating.

8. DRAMs and interconnects need conformal Ru
deposition
Future dynamic random access memories
• Ru is electronically like Pt, which was used in initial
research
• Unlike Pt, Ru etches easily in mass production
Kim, K., and Lee, S. Y., Microelectronic Engineering, 2007. 84: p. 1976-1981.
Seed layer for electrodeposition filling of copper
• Cu electroplates onto Ru
• Ru adheres better to the TaN underneath than Cu ECD Ru seed
layer
Cu
Moffat, T.P., et al., J. Electrochem.Soc., 2006. 153(1): p. C37-C50.

9. Synthetic inorganic chemistry and materials
engineering are required for new CVD processes
Synthetic inorganic
Materials engineering
chemistry
Conception and synthesis of new
CVD of films from precursor
CVD precursor candidates
Process hypothesis
development
Synthesis of modified precursor Measurement of film properties
Development of novel growth processes and chemistry
are needed to develop good CVD processes.

10. Problem Statement

11. Ruthenium catalyzes decomposition of organic
ligands even at low temperatures
Common case Desired case
H H
H H
H H
C C C
Ru Ru
Example:
1. Cyclohexadiene → benzene + H2
2. Benzene → surface hydrocarbons
All MOCVD Ru precursors are susceptible
to severe carbon incorporation.

12. Due to this difficulty, Ru MOCVD growth rates are
generally low
Resistivity Growth Rate Conformality Grows on
Molecule C%
(μΩ·cm) (nm/min) 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 ? ✕
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.

13. Surface science suggests choosing an appropriate
ligand set can minimize ligand decomposition
• Low benzene coverages inhibit benzene
Desired case decomposition on Ru1
• CO does not dissociate readily on Ru2
• When CO and benzene are co-adsorbed:
O O O
‣ CO acts as a spacer between the
C C C benzene molecules3
‣ CO halves the saturation benzene
Ru coverage3
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
Ligands that result in CO and benzene co-adsorbed on Ru may
circumvent the catalytic decomposition.

14. Tricarbonyl(1,3-cyclohexadiene)Ru(0) is expected to
give benzene and CO co-adsorbed on the surface
Expected Consequences:
• Very low carbon incorporation
• Conformal growth due to siteblocking
H
H
O O O O
C C C C
Ru
Ru
1,3-cyclohexadiene and CO as Ru ligands could naturally give
clean and conformal deposition.

15. Experiments

16. Ru films were deposited and analyzed on several
different substrates
Deposition in vacuum chamber Substrates
➡ In-situ ellipsometer monitors growth
Amorphous oxides: SiO2, Corning 7059 glass
➡ Precursor at ambient temperature FCC semiconductor crystal: Si(100)
➡ No carrier gas Cubic ionic crystal: KBr
Hexagonal covalent crystal: Al2O3(0001)
Phase and microstructure Resistivity and composition
• X-ray diffraction • 4-point probe
• Scanning electron microscopy • Auger electron spectroscopy*
• Atomic force microscopy* • X-ray photoelectron spectroscopy*
• Transmission electron microscopy* • Time-of-flight elastic recoil detection analysis
Reaction and kinetic studies
• Reaction product identification • Conformality and sticking coefficient
determination
* Select films

17. Results

18. Reaction products were analyzed with NMR
Condensation of reaction
products
• Film deposition run in specialty glassware
• Products captured in chilled NMR tube

19. The likely decomposition reaction is
(C6H8)Ru(CO)3 → H2 + C6H6 + 3CO
1H NMR Spectrum of Reaction Products
CHCl3 (solvent)
H2O (present initially)
Benzene
Missing 1,3-cyclohexadiene peaks
7 6 5 4 3 2 1 PPM
Toluene multiplets
(synthesis solvent) Toluene methyl group
(synthesis solvent)

20. The activation energy is 17 ± 7 kJ/mol
500°C 400°C
Growth rate: 2 - 24 nm/min
Decomposition temperature: 80°C
300°C
Precursor pressure: 0.030 mTorr
200°C
The low activation energy of the decomposition
reaction makes low-temperature deposition possible.

21. The Ru films are crystalline at all temperatures
200°C
500°C
Typical amorphous material
At both high and low growth temperatures,
the films show clear crystallinity.

22. The microstructures are compact
Ru film
Ru film
SiO2
Si substrate
Si substrate
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.

23. At low temperatures, kinetics rather than driving
forces determine both microstructure and texture
For Ru
Zone I: RT - 500 ºC
Zone II: 500 ºC - 1030 ºC
Zone III: 1030 ºC - 2334ºC
H
H
O O O O
C C C C
Ru
Ru
Energy minimization does not play a large role in low-
temperature ( > 500 ºC for Ru) texture.

24. ation of any in-plane textureintensity of reection i a reasonable oriented sample. In most case
was not possible in in a randomly
The films exhibit c-plane fiber texture at low
me for any of the films tried.more than one preferred orientation. (0 0 0 1) was the most preferr
Pole figure intensities were too low
information. However, the out-of-planein almostwasfilms grown at temperatures below 350 C
orientation texture all quantified ◦
temperatures
g texture coefficients for each resolved reflection. Texture 350 C. The overall degree of textu
prominence diminished above ◦
re defined as[123, 124] films, σ, was computed from a close analogue to the standard dev
Texture coefficients: Overall degree of texture:
Ii N
N I0 (Ci − Ci0 )2
Ci = N I , σ = (3.1) ,
i=1
i
i=1
N
I0
is the texture coefficient for reflection CiN is theare defined as in equation 3.1 and Ci0 is the te
where i, and N number of
}
• Increasing texture in thicker compared toi, and i0 is the
sidered, Ii is the intensity incoeffcient of a peak in aIrandomly oriented film. As can quickly be
film of reection
thinner films
eection i in a randomly orienteddenition, σ is zero cases,randomly texture forms during of 1 o
The
the sample. In most for a lms had oriented film. σ values
• Texture of T modulated films determined by
ne preferred orientation. (0 0 0 1) was the most preferred thickening
final growth temperature
n almost all films grown at temperatures below 350 ◦ C, while its 39
diminished above 350 ◦ C. The overall degree of texture in the
computed from trends on all substrates standard deviation Role of substrate minimal
• Same σ a close analogue to the as
N
below T*=0.24
• (0001) fiber texture(Ci − Ci0 )
2
σ= , (3.2)
N Two different formation
• (1122), (0001), and (1011) preferred
i=1
mechanisms
orientations above
and N are defined as in equation 3.1 and Ci0 is the texture

25. The films can grow on many materials types
The films grow readily on several oxides and silicon.

26. The films grow very well on oxides
2 µm
32s Growth at 300°C
on thermally grown SiO2
1 µm
Root-mean-square roughness:
1.3 nm
~2300 nuclei/µm2
0 µm
0 µm 1 µm 2 µm
The films start growing very quickly and evenly on oxides.

27. Contrary to expectation, the 1,3-CHD ligands
decompose to carbon fragments
TOF - ERDA Elemental Composition Catalytic activation of C-C bonds likely occurs
H
H
H H
C C C
Ru
The adsorption behavior seen in surface science studies does
not prevent ligand decomposition in a CVD process.

28. Traditional CVD has a high reaction probability
Traditional CVD O
(at high temperatures) C
O
Ru C C
C C O
O O
C
C O
C
C
O
Ru
O
Ru
O
Traditional CVD often leads to pinch-off.

29. If the incoming molecules do not stick or react
where they first land, conformality is possible
High sticking probability Low sticking probability
Precursor Nearly conformal
Precursor The deposited
atoms quickly molecules bounce coverage.
molecules react
cause pinch-off. off the walls into
or stick nearly
the trench.
instantly
If the incoming molecules don’t stick immediately, coatings are
more likely to be uniform.

30. Conformality was measured using a macrotrench
experiment
Conformality and sticking
coefficient determination
Silicon
• Film grown in macrotrench at 0.50 mTorr
Ta foil
• Conformality directly calculated from Silicon
thickness profile
• Sticking coefficient and growth rate
dependence on pressure calculated
Cross-section → thickness profile

31. The process is very conformal due to siteblocking
Temperature: 300°C
~90% Pressure: 0.5 mTorr
~75% GR on flat surface: 10 nm/min
Simulations1:
75% conformality in a macrotrench
90% conformality in a closed hole
1 Yang, Y.; Jayaraman, S.; Kim, D.Y.; Girolami, G. S.;
Abelson, J. R., Chem. Mat. 2006, 18, 21, 5088-5096.
As predicted, the conformality of the process is good
and the sticking coefficient is low.

32. Key Findings

33. 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

34. Acknowledgements
Dr. Charles Spicer, UNCC
Dr. Bong-Sub Lee, UIUC
Kristof Darmawikarta, UIUC
Dr. Angel Yanguas-Gil, UIUC
Dr. Mauro Sardela, UIUC
Nancy Finnegan, UIUC (Ret.)
Dr. Tim Spila, UIUC
Dr. 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