Temperature effects on the structure of polycrystalline silicon films by glow-discharge decomposition using SiH4/SiF4

Polycrystalline silicon (poly-Si) films were prepared on glass substrates by the plasma-enhanced chemical vapor deposition method using SiH4/SiF4 mixtures as a function of deposition temperature, Td, from 150 to 400°C, and the structural properties were investigated. In addition, the effects of addition of H2 to the SiH4/SiF4 gas were also examined. The crystallinity and grain size of Si films with added were found to have maximum values at around Td = 250-300°C. However, poly-Si films without H2 addition contain numerous microvoids, and exhibit easy O contamination, and their crystallinity monotonically increased with Td. The change in the SiH and SiH2 bond density with H2 addition was consistently interpreted in terms of this model. As a result, H2 addition at low Td was suggested to suppress O contamination and improve the crystalline quality. By contrast, H2 addition at high Td is likely to deteriorate crystalline quality. The results were discussed in terms of fluorine and hydrogen chemistry.