Effect of ammonia on Ta filaments in the hot wire CVD process

The exposure of Ta filaments to a pure NH3 ambient in a hot wire chemical vapour deposition (HWCVD) reactor affects the resistance of the wires. For filament temperatures below 1950 °C the resistance increases over time, which is probably caused by in-diffusion of N atoms. Using the filaments in a mixed SiH4 and NH3 atmosphere (under SiNx deposition conditions) the filaments are hardly affected. Only at the “cold” parts near the electrical contact SiNx deposition on the Ta filaments is observed. X-ray diffraction patterns and cross-section microscope images reveal that in a CH4, H2 and NH3 ambient the TaC0.275N0.218 phase is formed on the surface of the filament. Annealing of these filaments at 2000 °C causes the TaC0.275N0.218 structure to separate into Ta and Ta2C phases.