Growth structure of SiOx films deposited on various substrate particles by PECVD in a circulating fluidized bed reactor

Thin SiOx films were deposited on salt and silica gel particles by plasma enhanced chemical vapor deposition (PECVD). A microwave plasma source was integrated in the riser tube of a circulating fluidized bed (CFB) reactor. The CFB reactor provided high deposition rates and good precursor conversion efficiency. The cross-section of the coated particles was analyzed by means of scanning electron microscopy (SEM). The films deposited on smooth salt crystals revealed a dense and coherent film morphology. However, dust particles on the substrate surface caused nodular defects. In contrast on silica gel particles no continuous film could be deposited, but a columnar growth structure was observed. Both growth structures are caused by geometric shadowing effects, which is the dominant growth mechanism at the given deposition conditions.