Influence of substrate temperature on morphology of SiOx films deposited on particles by PECVD

Thin SiOx films were deposited on silica gel particles by plasma enhanced chemical vapor deposition (PECVD), using hexamethyldisiloxane (HMDSO) as a monomer. The deposition process was conducted in a circulating fluidized bed (CFB) reactor with a microwave plasma source integrated in the riser tube. Thin films were deposited at different substrate particle temperatures to investigate the influence on the growth structure. After the deposition process the fracture cross sections of the coated particles were analyzed by means of scanning electron microscopy (SEM). According to the well-known structure zone model (SZM) the deposition conditions correspond to the zone 1 growth regime where geometric shadowing effects are dominant. In addition, the primary particles on the surface of the silica gel particles acted as nucleation sites. Thus no dense and coherent film was deposited, but a pronounced nodular growth structure could be observed. However, increasing the surface diffusion rate reduced the effect of the geometric shadowing. Therefore, the number of nodules was decreased at elevated substrate temperatures.