Growth mechanism of polycrystalline silicon using silane gases by LPCVD

Abstract

The growth of Si films on Si or $SiO_2$ substrates is of immense interest in Si device technology. For the last application, glass substrates must be used limiting the temperature at which the silicon layers are formed around 600℃, the softening point of glass. Devices with suitable characteristics have been obtained using chemical vapor deposition (CVD), e-beam evaporation, or molecular-beam epitaxy (MBE) of polysilicon films. CVD of Si as a technique to obtain thin film structures is very important, since films of high purity or films of controlled content can be easily obtained. Pyrolysis of silane gases at pressures lower than that of atmospheric pressure chemical vapor deposition (APCVD) resuls in partially or totally polycrystalline silicon films of different textures, namely, a ＜111＞ or ＜311＞ preferred orientation, depending on the temperature of deposition. The microstructure and growth mechanisms of as-deposited polysilicon and mixed-phase silicon films deposited on glass substrates by infra-low pressure chemical vapor deposition (ILPCVD) and low pressure chemical vapor deposition (LPCVD) using 20% $Si_2H_6$/He gas, and 20% $SiH_4/H_2$ have been investigated by X-ray diffraction (XRD) pattern, Raman spectroscopy, and cross-section transmission electron microscopy (XTEM). The deposition temperature and pressure were in the range of 560℃ ~ 600℃ and below 10 mTorr, respectively, in ILPCVD. In LPCVD the deposition temperature and pressure were 600℃ and below 110 mTorr, respectively. In as-deposited polysilicon, there are two kinds of competing factor in crystal growth, crystal growth rate and difficulty of extinguishments. At moderate deposition temperature, the difficulty of extinguishments dominate in the case of columnar growth at higher pressures. Thus ＜220＞ columnar growth results. In the case of columnar growth at higher temperatures, faster crystal growth dominates and ＜100＞ crystal growth appears at higher pressures where nucleation density is high...