Low pressure chemical vapor deposition of silicon nitride using the environmentally friendly tris(dimethylamino)silane p
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Low pressure chemical vapor deposition of silicon nitride using the environmentally friendly tris(dimethylamino)silane precursor R. A. Levy, X. Lin, and J. M. Grow New Jersey Institute of Technology, University Heights, Newark, New Jersey 07102-1982
H. J. Boeglin and R. Shalvoy Olin Chemicals Research, Cheshire, Connecticut 06410 (Received 24 August 1995; accepted 26 January 1996)
This study investigates the use of the environmentally benign precursor tri(dimethylamino)silane (TDMAS) with NH3 to synthesize silicon nitride films by low pressure chemical vapor deposition. The growth kinetics are investigated as a function of deposition temperature, total pressure, and NH3yTDMAS flow ratios. The deposits are found to be essentially stoichiometric and to contain ,5 at. % carbon when appropriate NH3 concentrations are present. The films are found in all cases to be amorphous and highly tensile. For optimized processing conditions, values of the refractive index are close to those reported for Si3 N4 . The film density is observed to increase with higher deposition temperatures up to 800 ±C and then decrease due to the onset of gas phase nucleation effects. This behavior is readily reflected in the etch rate of those films. FTIR spectra reveal the presence of hydrogen even at high deposition temperatures (900 ±C). Hardness and Young’s modulus of the films are seen to increase with higher deposition temperatures, reaching saturation values near 20 and 185 GPa, respectively, above 800 ±C.
I. INTRODUCTION
Silicon nitride films offer an attractive combination of properties reflected in their high electrical resistivity, high dielectric breakdown field, chemical stability, good diffusion barrier characteristics, and superior mechanical strength. These properties render such films useful in a wide range of applications involving insulation, isolation, passivation, and etch masking of semiconductor devices.1 The high optical and x-ray transmission of silicon nitride also makes the films useful as membrane material in x-ray masks.2 Low pressure chemical vapor deposition (LPCVD) is an ideal method of synthesizing high quality silicon nitride films because of the excellent step coverage, high throughput, and uniformity that it provides.3 Current CVD processes rely on the use of silane or chlorosilanes as sources for silicon.4 –7 Such precursors are either hazardous or highly corrosive. Recently, the use of the environmentally benign silicon precursor, ditertiarybutylsilane (DTBS), has been used for synthesizing LPCVD silicon nitride films.8 Results of this study revealed that although these films were found to be essentially stoichiometric, they contained a relatively high concentration of carbon (,10%). In an attempt to synthesize such films with a minimal carbon concentration, this study investigates the use of tri(dimethylamino)silane (TDMAS) as a silicon precursor. The presence of direct single Si–N bonds and the J. Mater. Res., Vol. 11, No. 6, Jun 1996
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