Formation mechanism of incubation layers in the initial stage of microcrystalline silicon growth by PECVD

The incubation layers in microcrystalline silicon films (\muc-Si:H) are studied in detail. The incubation layers in \muc-Si:H films are investigated by bifacial Raman spectra, and the results indicate that either decreasing silane concentration (SC) or increasing plasma power can reduce the thickness of incubation layer. The analysis of the in-situ diagnosis by plasma optical emission spectrum (OES) shows that the emission intensities of the SiH*(412 nm) and H_\alpha (656nm) lines are time-dependent, thus SiH*/H_\alpha ratio is of temporal evolution. The variation of SiH*/H_\alpha ratio can indicate the variation in relative concentration of precursor and atomic hydrogen in the plasma. And the atomic hydrogen plays a crucial role in the formation of \muc-Si:H; thus, with the plasma excited, the temporal-evolution SiH*/H_\alpha ratio has a great influence on the formation of an incubation layer in the initial growth stage. The fact that decreasing the SC or increasing the plasma power can decrease the SiH*/H_\alpha ratio is used to explain why the thickness of incubation layer can reduce with decreasing the SC or increasing the plasma power.