PHOTOELECTRON AND INFRARED-SPECTROSCOPY OF SEMIINSULATING SILICON LAYERS

X-ray induced photoelectron spectroscopy (XPS), Fourier transform infr ared spectroscopy, and electron microprobe analysis (EMA) were used to study semi-insulating polycrystalline silicon layers obtained by chem ical vapor deposition from SiH4 and N2O gases. A mean ''bulk'' oxygen concentration determined by EMA ranged from 16 to 50 at. %. Photoelect ron spectra excited by Mg K alpha and Al K alpha radiation were used t o find surface composition and bonding information of as-received laye rs. Beneath the native oxide with a stoichiometry close to the SiO2, t here is a heterogeneous material consisting of silicon (Si-Si) and sil icon oxide (Si-O) regions. A drop in the Si 2p peak position differenc es with the mean bulk oxygen concentration indicates a differential ch arging of the silicon islands surrounded by a silicon oxide phase. A s pectral 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) bo nds, calculated by the normalized integrated absorption intensity, wer e very close to the results of EMA. This leads us to the conclusion th at the samples consist of two phases, alpha-SiOr and Si. The values of the refractive index obtained by the spectrophotometric method from r eflectance spectra and the results of XPS measurements strongly suppor t the two-phase model. (C) 1997 American Institute of Physics.