Formation of Nickel Silicide from Direct-Liquid-Injection Chemical-Vapor-Deposited Nickel Nitride Films Zhefeng Li, a Roy G. Gordon, a, * ,z Huazhi Li, b Deo V. Shenai, b and Christian Lavoie c a Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA b Dow Electronic Materials, North Andover, Massachusetts 01845, USA c IBM, Thomas J. Watson Research Center, Yorktown Heights, New York 10598, USA Smooth, continuous, and highly conformal nickel nitride  NiN x  films were deposited by direct liquid injection DLI–chemical vapor deposition CVD using a solution of bisN, N'-di-tert-butylacetamidinatonickelII in tetrahydronaphthalene as the nickel Ni source and ammonia  NH 3  as the coreactant gas. The DLI-CVD NiN x films grown on HF-last 100 silicon and on highly doped polysilicon substrates served as the intermediate for subsequent conversion into nickel silicide NiSi, which is a key material for source, drain, and gate contacts in microelectronic devices. Rapid thermal annealing in the forming gas of DLI-CVD NiN x films formed continuous NiSi films at temperatures above 400°C. The resistivity of the NiSi films was 15  cm, close to the value for bulk crystals. The NiSi films have remarkably smooth and sharp interfaces with underlying Si substrates, thereby producing contacts for transistors with a higher drive current and a lower junction leakage. Resistivity and synchrotron X-ray diffraction in real-time during annealing of NiN x films showed the formation of a NiSi film at about 440°C, which is morpho- logically stable up to about 650°C. These NiSi films could find applications in future nanoscale complementary metal oxide semiconductor devices or three-dimensional metal-oxide-semiconductor devices such as Fin-type field effect transistors for the 22 nm technology node and beyond. © 2010 The Electrochemical Society. DOI: 10.1149/1.3388721 All rights reserved. Manuscript submitted December 23, 2009; revised manuscript received March 15, 2010. Published April 28, 2010. Metal silicides such as TiSi 2 and CoSi 2 have been commonly used as the contacts to the source, drain, and gate of complementary metal oxide semiconductor CMOS devices by the microelectronics industry. 1,2 As the dimensions of microelectronic circuits are being reduced, TiSi 2 has increased resistance at narrow linewidths  250 nm due to the low nucleation density of the low resistance C54-TiSi 2 phase, 3 whereas CoSi 2 was mainly limited by void for- mation in narrow polysilicon gates  50 nm, which cause a dras- tic rise in resistance and by its very difficult formation on SiGe substrates. 4 To avoid the above problems, NiSi was investigated for the salicidation process because NiSi has many advantages includ- ing low resistivity 14  cm, low silicon consumption, low formation temperature, and no resistivity degradation in very narrow lines. 5 The silicon consumption in NiSi can be decreased by about 30% compared to TiSi 2 and CoSi 2 . The low formation temperature of NiSi not only reduces the thermal budget but also limits dopant deactivation in shallow junctions. The NiSi films also have much smoother interfaces compared to films of TiSi 2 and CoSi 2 because the formation of NiSi is controlled by diffusion, whereas the forma- tion of TiSi 2 and CoSi 2 is nucleation controlled. Such smooth inter- faces could play an important role in the reduction of device leakage. 6 NiSi has usually been made by annealing of sputtered or ther- mally evaporated Ni films on silicon. 7 As device sizes shrink, the step coverage of these physical-vapor-deposited Ni films inside nar- row features is not expected to be adequate for use in future CMOS devices with closely spaced gate stacks or three-dimensional struc- tures such as Fin-type field effect transistors. 8 Chemical vapor depo- sition CVD and atomic layer deposition ALD methods have been investigated to overcome this problem. Ni films prepared by metal- lorganic CVD methods, however, always incorporated a high con- tent of impurities such as carbon. 9 CVD metal films deposited from some precursors also suffered from poor step coverage due to the limited volatility of the precursors. 10 Surface reactions of other pre- cursors are too fast to allow a high step coverage. 11 ALD of Ni films should provide high step coverage. Most ALD processes for Ni first deposited nickel oxide  NiO x  and subse- quently reduced the oxide to Ni by annealing the films with H 2 at a high temperature. 12 The introduction of oxygen during NiO x depo- sition caused oxidation of the underlying silicon surface and there- after agglomeration of the films during annealing unpublished re- sults. The ALD of Ni films by reduction of nickel bisl- dimethylamino-2-methyl-2-butanolate, Ni dmamb 2 , with molecular hydrogen  H 2  was investigated for the formation of NiSi. 13 A significant amount of carbon is distributed in the film, partly forming a Ni 3 C phase. Such carbon contamination can de- grade the film quality of NiSi by increasing sheet resistance and by forming NiSi with nonuniform thickness. Our group had previously deposited Ni films by ALD using the precursor bisN, N'-diisopro- pylacetamidinatenickelII and H 2 . 14 These ALD films were, how- ever, not practical for industrial applications because of the low thermal stability of the precursor and the low growth rate 0.04 Å/cycle of the Ni films. Direct liquid injection DLI–chemical vapor deposition CVD is a very attractive deposition method because DLI has the advan- tage of accurate delivery of high partial pressure of the precursor vapor. By using suitable solvents, solutions of solid precursors can be vaporized by DLI. 15 The high concentration of the precursor vapor during deposition is a key factor for achieving conformal step coverage and high growth rates. In this study, we employed a more stable metallorganic precursor, bisN, N'-di-tert-butylacetamidina- tonickelIINi MeC N t Bu 2  2  for DLI-CVD of NiN x as an inter- mediate for the formation of NiSi. We deposited NiN x films instead of pure Ni as the intermediate for NiSi formation because the incor- poration of nitrogen into nickel has been shown to increase the thermal stability of NiSi and the electrical performance of transistors made using it. 16 The processes for DLI-CVD of NiN x were de- scribed in detail elsewhere. 17 The step coverage of the NiN x films inside deep holes with an aspect ratio of about 80:1 is nearly 100%. Rapid thermal annealing RTA of NiN x films with thickness 20 nm at 450°C yielded continuous NiSi films. For thinner NiN x films, initial steps of in situ annealing with H 2 at 160°C and capping with 10 nm thermally evaporated Ti were employed to prevent oxy- gen diffusion and film agglomeration so that continuous NiSi films having smooth and sharp interfaces with silicon could be achieved even for Ni thickness less than 6 nm. * Electrochemical Society Active Member. z E-mail: gordon@chemistry.harvard.edu Journal of The Electrochemical Society, 157 6 H679-H683 2010 0013-4651/2010/1576/H679/5/$28.00 © The Electrochemical Society H679 Downloaded 29 Apr 2010 to 128.103.93.202. Redistribution subject to ECS license or copyright; see http://www.ecsdl.org/terms_use.jsp