STRUCTURAL AND OPTICAL-PROPERTIES OF MICROCRYSTALLINE SILICON FILMS DEPOSITED BY PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION

Abstract

Hydrogenated microcrystalline (mu c) silicon films were prepared by plasma enhanced chemical vapour deposition using an Ar-diluted SiH4 gas at various deposition conditions. The substrate temperature and RF power were varied from 150 to 400 degrees C and from 10 to 120 W, respectively. Structure and microstructure were examined by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. Hydrogen bonding and optical properties were investigated by FTIR spectra and UV transmission spectra. The crystal fraction of the films increased as the deposition temperature decreased and RF power increased. More definite columnar morphology was developed with increasing crystal fraction. The existence of mu c-Si above a critical RF power ( > 30 W) suggests that SiH2 radical in plasma plays an important role for the formation of columnar morphology and mu c-Si. IR absorption analysis showed that the SiH2/SiH bonding ratio in the silicon films increased as the crystal fraction increased. The UV absorption coefficient of the films became smaller as the deposition temperature and RF power increased.