PLASMA-ASSISTED CHEMICAL VAPOR-DEPOSITION WITH TITANIUM AMIDES AS PRECURSORS

One possible way of reducing the high deposition temperatures required for conventional chemical vapour deposition (CVD) is the application of metal-organic compounds; a second is the excitation of the precursors in a glow discharge. In the production of wear-resistant coatings such as TiN in a low temperature plasma-assisted CVD process, the use of TiCl4 can cause corrosion as well as producing coatings of undesirably low hardness. To avoid these problems, the application of a metal-organic precursor and plasma enhancement of the CVD process were combined in this investigation. Two titanium amides, Ti(N(CH3)2)4 and Ti(N(C2H5)2)4, both liquids with sufficient volatility, were used together with hydrogen and argon in a d.c. glow discharge at a total pressure of approximately 1 mbar. The temperature of the steel substrates during deposition was varied from 200 to 500-degrees-C. It was established by means of glow discharge optical spectrometry and X-ray diffraction that titanium carbonitride coatings were obtained. The morphology of the Ti(C,N) layers was examined by scanning electron microscopy. Up to a temperature of 400-degrees-C fine-grained polycrystalline layers were observed whose hardness measured more than 2000 HV. At 500-degrees-C thermal decomposition of the metal-organic compounds by a homogeneous reaction became dominant and reduced the quality of the coating.