Carburizing of tantalum by radio-frequency plasma assisted chemical vapor deposition

Tantalum carbide (TaC) has great potential as an alternative to tantalum an d tantalum oxide for applications requiring thermal stability and corrosion resistance. In this study TaC layers were produced by inductive rf plasma- assisted chemical vapor deposition that combines diffusion with chemical va por deposition. The maximum temperature of the tantalum substrates measured during a 6 h processing time was 900 degrees C using Ar-CH4 or Ar-CH4-H-2 gas mixtures. The microstructure of the layers was characterized by X-ray d iffraction and Auger electron spectroscopy, and the mechanical properties w ere studied by micro- and nanoindentation and by microscratch techniques. A close correlation among the carburizing parameters, the microstructure, th e mechanical behavior of the layers, and the corrosion resistance was found . The best performing films, several mu m thick, consisting of TaC phase wi th the highest hardness (similar to 25 GPa), were obtained under the follow ing conditions: input power of 1400 W, pressure of 40-60 mbar, and substrat e located at the center of the rf coil. The effect of gas composition, gas pressure, and substrate temperature on the layer composition, the TaC/Ta2C phase ratio, and the mechanical characteristics and chemical stability is p resented and discussed. A mechanism of carburizing of tantalum in an induct ive rf plasma is proposed. (C) 2000 American Vacuum Society. [S0734-2101(00 )10504-4].