Reversibility of silicidation of Ta filaments in HWCVD of thin film silicon

If tantalum filaments are used for the hot wire chemical vapour deposition (HWCVD) of thin film silicon, various types of tantalum silicides are formed, depending on the filament temperature.Under deposition conditions employed for device quality amorphous and microcrystalline silicon (Twire ≈ 1750 °C) a Ta5Si3 (as determined by XRD) shell is formed around the Ta core. After 8 h of accumulated deposition time this shell has a thickness of around 20 μm. Upon annealing of the filament in vacuum at 2100–2200 °C the tantalum silicide shell becomes thinner, while a Ta layer is reappearing at the surface of the wire. After 4 h of annealing the silicide is completely removed, whereas the total diameter of the wire has not significantly changed. The resistance of the filament has been monitored and after the annealing procedure, it completely recovered to that of a fresh wire. This regeneration procedure greatly helps to avoid frequent replacement of the filaments.