Anisotropy in Hydrogenated Silicon Thin Films

We investigated spatial non-uniformity and optical anisotropy in hydrogenated silicon thin films using infrared spectroscopy and other techniques. The films ranged in morphology from amorphous to micro-crystalline, as determined by Raman spectroscopy and X-ray diffraction (XRD). Trace element analysis of the films was carried out using secondary ion mass spectrometry (SIMS). We used polarized attenuated total reflection (ATR) measurements together with Fourier transform infrared (FTIR) spectroscopy to investigate anisotropy in the Si-H covalent bonding structure of the films, and also to detect oxide impurity phases present at certain sites in some samples. The FTIR-ATR measurements were performed using a germanium (Ge) contact microprobe with a 100-micron sampling area, as well as on films deposited on standard crystalline Si and Ge ATR substrates. The Ge contact ATR microprobe enabled relatively interference-free measurements of the IR spectra of a-Si:H and μc-Si:H films deposited on conductive substrates such as stainless steel and transparent conductive oxides, and is also sensitive to the spatial distribution of oxide precipitates in the films. This measurement is difficult or impossible using transmission or reflection IR spectroscopy.