Production and characterization of nitrided CVD-SiC films

Abstract

Abstract. Silicon Carbide (SIC) and SiC with free silicon [SiC(S0] thin films were prepared by chemical vapor deposition (CVD) using a CH3SiC13-H2-Ar gas mixture at a temperature of 1223 K. Afterwards these layers were gas nitrided in an ammonia-hydrogen-argon mixture at 1273 K. The solid product is an extremely thin film of silicon nitride on SiC or SiC(Si)-basic layers. These ultra thin silicon nitride films were investigated by glow discharge optical spectroscopy (GDOS) and x-ray photoelectron spectroscopy (XPS). The thickness of the layers was determined to a maximum value of 30 nm.Key words: silicon nitride, thermal nitridation, SiC, GDOS, XPS.Crystalline silicon nitride ceramics, obtained by reacting-sintering or hot-pressing techniques, are known for their chemical inertness, high temperature strength, high electrical resistivity, good thermal shock resistance, and extreme hardness [1].The development of new ceramic matrix composites (CMC), for instance silicon nitride matrix and SiCcoated carbon fibres, is a topical problem in materials research. Optimum adhesion has been obtained between fibres and matrix, when the surface composition of the coated layer and the matrix composition are of the same nature. This paper will report on deposited nitride thin films obtained by reacting SiC(s) or SiC(Si) (s) and NH3 at a temperature of 1273K. It is known, that passing nitrogen or ammonia over solid silicon substrates heated to 1573K results in extremely thin nitride layers, owing to the high efficiency of the material as a diffusion mask [2]. * Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday ** To whom correspondence should be addressed ExperimentalThin films of SiC or SiC(Si) on carbon substrates were used in this work. The thickness of the layers was about 5 pm. These layers were prepared by chemical vapor deposition in a CH3SiCI3-H 2 Ar gas mixture. The layer composition was dependent on the deposition parameters, especially the temperature and the hydrogen-trichloromethylsilane ratio (c~) in the gas phase. The content of free silicon increased by high Hz/CH3SiC13 ratios. For a Ha/CH3SiC13 ratio of 6 only SiC was obtained in the temperature range of 1173 to 1273 K. For a higher H2/CH3SiC13 ratio, SiC with codeposited silicon was found. For the nitridation experiments SiC-layers (T= 1223K, ~=3) and SiC(Si)-layers (T= 1223K, ~= 18) were selected. The method of production has been exactly described elsewhere [3].These layers were subsequently nitrided in an NH 3 H 2 Ar atmosphere. The experimental conditions are summarized in Table 1.The horizontal hot-wall type CVD or nitridation reactor is shown schematically in Fig. 1. The reaction chamber was a quartz tube of 48 mm in diameter. The purification of gaseous compounds (Ha, Ar) of oxygen and steam were carried out in a commercial purification apparatus. Ammonia was used as a high-purity gas (99.9995%).Photoelectron spectra were taken with an ESCALAB Mk II spectrometer and GDOS depth profiles were measured wit...