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 b y the plasma-enhanced chemical vapor deposition method using SiH4/SiF4 mixt ures as a function of deposition temperature, T-d, from 150 to 400 degrees C, and the structural properties were investigated. In addition, the effect s of addition of H-2 to the SiH4/SiF4 gas were also examined. The crystalli nity and grain size of Si films with added were found to have maximum value s at around T-d = 250-300 degrees C. However, poly-Si films without H-2 add ition contain numerous microvoids, and exhibit easy O contamination, and th eir crystallinity monotonically increased with T-d. The change in the SiH a nd SiH2 bond density with H-2 addition was consistently interpreted in term s of this model. As a result, H-2 addition at low T-d was suggested to supp ress O contamination and improve the crystalline quality. By contrast, H-2 addition at high T-d is likely to deteriorate crystalline quality. The resu lts were discussed in terms of fluorine and hydrogen chemistry.