High rate hot-wire chemical vapor deposition of silicon thin films using a stable TaC covered graphite filament

We grow silicon films by hot-wire/catalytic chemical vapor deposition using a new filament material: TaC-coated graphite rods. The filaments are 1.6mm diameter rigid graphite rods with ~30μm thick TaC coatings. Whereas heated W or Ta wire filaments are reactive and embrittle in silane (SiH4), the TaC/graphite filament is stable. After >2h of exposure to SiH4 gas at a range of filament temperatures, the full length of a TaC/graphite filament retains its shiny golden color with no indication of swelling or degradation. In comparison, a W wire exposed to SiH4 under the same conditions becomes swollen and discolored at the cold ends, indicating silicide formation. Scanning electron microscopy images of the filament material are nearly identical before and after SiH4 exposure at 1500–2000°C. This temperature-independent chemical stability could enable added control of the gas phase chemistry during deposition that does not compromise the filament lifetime. The larger surface area of the 1.6mm diameter TaC coated graphite filament (compared to the 0.5mmW filament) allows for a ~2× increase in the deposition rate of Si thin films grown for photovoltaic applications.