CHEMICAL-VAPOR-DEPOSITION OF TUNGSTEN CARBIDES ON TANTALUM AND NICKELSUBSTRATES

Tungsten carbide films have been deposited by low-pressure chemical va pour deposition from a WF6/H-C3(8)/H-2 mixture on Ta and Ni substrates . Single-phase WC films could be deposited on Ta in a broad vapour com position range at 900 degrees C. A mixture of WC and W2C was deposited in the temperature range 700-850 degrees C, while an amorphous film w as obtained at 650 degrees C. The temperature behaviour suggests that deposition of carbon is a limiting factor in the growth process. The d eposition process on Ta could be separated into two parts: a fast subs trate reduction step of WF6 leading to the formation of metallic W fol lowed by a slower formation and deposition of WC. The growth behaviour on Ta was also affected by tantalum carbides at the film-substrate in terface. A different growth behaviour was observed on Ni. It was found that several eta-carbides (i.e. Ni2W4C and Ni6W6C) were formed during a fast initial growth stage. Later on, the eta-carbides reacted with carbon under the formation of WC and free Ni particles. It was also fo und that the carbon deposition rate on Ni substrates was higher than o n Ta. This was explained by a catalytic process where Ni particles on the film surface favoured carbon deposition.