Structural evolution of a Ta-filament during hot-wire chemical vapour deposition of Silicon investigated by electron backscatter diffraction

Abstract

In this study we investigate the structural changes of a burnt-out tantalum filament that was operated at typical hydrogenated nanocrystalline silicon synthesis conditions in our hot-wire chemical vapour deposition chamber. Scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and for the first time electron backscatter diffraction showed that various silicides form preferentially along the length of the filament. At the cooler filament ends the TaSi2 phase forms, encapsulating a Ta inner core. The tantalum rich Ta5Si3, Si3Ta5 and Ta2Si phases however formed in addition to TaSi2 at the centre regions. Cracks and porosity were found throughout the length of the filament. The microstructure evolution of the aged tantalum filament is discussed based on a model comprising hydrogen damage and the reactions between the hot tantalum filament surface and silicon containing radicals. Possible effects of the well-known hydrogen treatment steps on filament degradation are also discussed.