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

Abstract

The exposure of Ta filaments to a pure NH 3 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 SiH 4 and NH 3 atmosphere (under SiN x deposition conditions) the filaments are hardly affected. Only at the “cold” parts near the electrical contact SiN x deposition on the Ta filaments is observed. X-ray diffraction patterns and cross-section microscope images reveal that in a CH 4, H 2 and NH 3 ambient the TaC 0.275N 0.218 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 Ta 2C phases.