Characterization of Si nano-polycrystalline films at the nanometer level using resonant Raman scattering

Abstract

We have measured a resonant Raman scattering from polycrystalline silicon (poly-Si) films with thicknesses of 24–381nm at the depth resolution of approximately 5nm and found that poly-Si films are under compressive stress. The main Raman peak in poly-Si films tends to shift to a higher frequency as the thickness of the underlayer of the silicon dioxide (SiO2) film becomes greater. From this result, it has been considered that the compressive stress becomes larger with an increase in the thickness of the underlayer of the SiO2 film. We have tried to separate the observed Raman shifts into those caused by the crystallite size effect and those caused by stress in the poly-Si films. We did this using the resonant Raman scattering technique and calculation by the phonon confinement model. It has been found that the crystallite size obtained from the Raman measurement roughly agrees with the size obtained from the x-ray measurement. This result suggests that the phonon-dispersion curve does not change significantly under the compressive stress of 102MPa order.