Abstract. Structural investigations of thin films of SiC, SiC with free silicon and various titanium silicides (TiSi 2, TiSi and TisSi3) are described. The crystal phases have been identified using X-ray diffractometry. The growth of reaction products from surface reactions between silicon and deposited titanium can be observed. ExperimentalThe hot wall type CVD reactor is shown schematically in Fig. 2. It consist of following components: furnace unit, gas supply and waste * Dedicated to Professor Dr. rer.nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday ** To whom correspondence should be addressed elimination. SiC and SiC(Si) polycrystalline layers were deposited from a gas mixture of CH3SiCI3-H 2 Ar gas mixture at temperature range of 900 to 1000 ~ on graphite substrates. The graphite substrates (5 mm diameter, 20ram long) were located in the central part of the horizontal reaction tube which was heated from the outside. The phases of the deposites was identified by X-ray diffraction analysis. The chemical composition and crystal structure of CVD-SiC are strongly influenced by the H2/CH3SiC13 ratio (c 0 and the temperature. Silicon carbide with codeposited silicon was obtained by using a high H2/CH3SiC13 ratio (c 0 [3]. This codeposited silicon was subsequently converted to other compounds. Elemental titanium served as reagent for the formation of different titanium silicides. This titanium was prepared by chemical vapor deposition from a TiCI4-H2-Ar gas mixture at 950 ~ X-ray Diffraction MeasurementsThe structural investigations of these multicomponent silicon carbide/titanium silicide layers were hard to examine. The deposited layers are thin (weak signals, strong carbon signals) and owned a rough surface.The measurements were obtained on a Siemens D 5000 X-ray diffractometer following the various configurations indicated in Fig. 3. The deposited samples were fastened on a sample holder of silicon (slanting cut through a single crystal) in a Bragg-Brentano arrangement. The system was interfaced with a PC for programming and data acquisition. The data were readily transportable to a graphic program (e.g. diffrac AT) for subsequent analysis. Results and DiscussionA X-ray diffraction diagram of a SiC(Si) layer is shown in Fig. 4. We could percieve three different compounds, large signals of the substrate-reflection of graphite and weak signals from fine crystallined silicon carbide and silicon. X-ray diffraction diagrams showed that the deposited compounds were cubic SiC (3C-type) and cubic silicon. SiC was preferred grown in 111-orienta-

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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...