Photoelectron and infrared spectroscopy of semi-insulating silicon layers

X-ray induced photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and electron microprobe analysis (EMA) were used to study semi-insulating polycrystalline silicon layers obtained by chemical vapor deposition from SiH4 and N2O gases. A mean ''bulk'' oxygen concentration determined by EMA ranged from 16 to 50 at. %. Photoelectron spectra excited by Mg K alpha and Al K alpha radiation were used to find surface composition and bonding information of as-received layers. Beneath the native oxide with a stoichiometry close to the SiO2, there is a heterogeneous material consisting of silicon (Si-Si) and silicon oxide (Si-O) regions. A drop in the Si 2p peak position differences with the mean bulk oxygen concentration indicates a differential charging of the silicon islands surrounded by a silicon oxide phase. A spectral band of an asymmetric Si-O-Si stretching vibration mode around 1030 cm(-1) was used to characterize the samples. An assumption that the samples were a homogeneous alpha-SiOx phase leads to a mean oxygen content much higher than that determined by the EMA technique. On the other hand, oxygen concentration deduced from the number of (Si-O) bonds, calculated by the normalized integrated absorption intensity, were very close to the results of EMA. This leads us to the conclusion that the samples consist of two phases, alpha-SiOr and Si. The values of the refractive index obtained by the spectrophotometric method from reflectance spectra and the results of XPS measurements strongly support the two-phase model. (C) 1997 American Institute of Physics.