CVD of Silicon Nitride Plate from HSiCl 3 -NH 3 -H 2 Mixtures
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CVD OF SILICON NITRIDE PLATE FROM HSiCl
3
J. W. LENNARTZ AND M. B. DOWELL Union Carbide Coatings Service Corporation, Parma, OH 44130
-NH 3 -H 2 MIXTURES 12900 Snow Road,
ABSTRACT Preferred conditions for deposition of thick c-Si 3 N4 plate from HSiCl 3 -NH 3 -H 2 on the vertical surfaces of a lowpressure, hot-wall CVD reactor were identified by means of a designed experiment. The design included the range of temperatures 1300OC-1500 0 C, pressures 0.5-2.0 Torr, and residence times 0.01-1.0 sec. The vertical deposition surfaces received a viscous, laminar flow of well mixed, thermally equilibrated reactants. Plates 0.05-0.5 mm thick were produced on multiple vertical substrates 350 cm 2 in area at deposition rates 5-70 pm/hr. Plates 0.5-4.0 mm thick were produced on horizontal substrates at deposition rates of 60120 um/hr. When NH3 flows in stoichiometric excess, deposition rates on vertical surfaces increase approximately linearly with the flow rate of HSiCI 3 but depend little on temperature, as would be expected if the reaction proceeds under mass transport control with product depletion. Multiple correlation analyses show that thickness variations in the deposit are reduced by increasing the temperature and decreasing the gas residence time. CVD silicon nitride plate produced under the optimized conditions exhibits theoretical density and is free of pores and cracks. It exhibits a columnar morphology in which the and crystallographic directions are oriented preferentially normal to a surface, which consists of well-defined trigonal facets 10-50 um across. Crystallite sizes determined by Xray line broadening range from 0.06-1.0 um. This CVD plate is gray and contains approximately 0.5 w/o C and 0.5 w/o 0 as principal impurities. INTRODUCTION Silicon nitride is well recognized as an important engineering ceramic. Its high hardness, chemical inertness, resistance to creep and thermal shock, and strength at high temperatures recommend its use in advanced turbines. Its high electrical resistivity and dielectric strength find use in electrical insulators, including some in integrated circuits. Silicon nitride sputtering targets and crucibles for growth of low-oxygen single crystals are two uses which require relatively thick sections free from metallic impurities. The chemical vapor deposition process is of interest for producing such articles.
Mat. Res. Soc. Symp. Proc. Vol. 250. @1992 Materials Research Society
162
CVD silicon nitride has been described previously 1- 4 as have some of its uses. 5 A statistical optimization approach to production of thick CVD silicon nitride from HSiCI 3 , NH3 and N2 has been reported. 6 We now report preferred conditions for deposition of thick CVD Si 3 N4 plate from HSiCl 3 -NH 3 -H 2 gas mixtures on vertical, non-impingement surfaces, by use of a similar method. EXPERIMENTAL Experiments were carried out in low-pressure CVD reactor as depicted introduced into the reaction chamber nozzle, the annulus of which carries overall reaction is 3 HSiCI
3
(g)
+ 4 NH3 (g) = Si
3
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