Investigation of the tantalum catalyst during the hot wire chemical vapor deposition of thin silicon films

After extensive utilization of tantalum (Ta) catalyst filaments for hot wire (HW) CVD of silicon films we found a high amount of silicon not only at the surface but also in the bulk of the tantalum catalyst (up to 8%). The amount of silicon accumulation in the bulk depends on the concentration of silane in the process gas. SIMS investigation indicates a silicide/silicon formation on the surface and significant diffusion of silicon into the bulk of the catalyst. This silicon contamination changes the filament resistance and seems to be the reason for rather short lifetime of the filament, which is a serious concern for the HWCVD deposition technology. Annealing of the filament by direct current (DC) at high temperature in vacuum enables to drastically reduce the silicon content (silicides) in a surface region of about 2–3 μm. However, it cannot remove the thick silicon deposits (> 10 μm) from the filament surface. In order to decrease the silicon content in the tantalum catalyst and the silicon formation on the filament surface we used alternating current (AC) (13.5 MHz) to heat the filament. Due to the “skin” effect of the radio frequency (RF) current the silicon indiffusion and the formation of silicon deposits on the surface are suppressed.