Investigation of silicon contamination of Ta filaments used for thin film silicon deposition

After extensive utilisation of tantalum (Ta) catalyst filaments for hot wire chemical vapor deposition (HWCVD) of thin silicon films a strong degradation takes place. A high concentration of silicon was found not only on the surface but also in the bulk of the tantalum filament. Visual microscopic investigations, Secondary Ion Mass Spectrometry (SIMS), X-ray Diffraction (XRD) and Energy Dispersive X-ray Analysis (EDX) indicate appearance of various silicides and formation of thick silicon layer (> 50 μm) on the filament surface. The high-power backscattered scanning electron microscopy (SEM BSE) and optical microscopic analysis of the filament cross section reveal a complicated, non-uniform structure of filaments after use. By XRD a recrystallisation of tantalum kernel was detected. The EDX analysis indicates that silicides on the filament surface have the highest concentration of Si.