Structural and morphological changes in low temperature annealed LPCVD Si layers

In this paper we present the morphological and structural properties of the low pressure chemically vapor deposited (LPCVD) silicon-films after annealing at 600°C for 26 hours in nitrogen, in comparison with the properties of as-deposited layers. For the films found in the poly-crystalline state after deposition (i.e. those prepared at temperatures below and above 550°C), XRD spectra have indicated a supplementary (111) diffraction peak after annealing. In addition, from XRD data, we obtained a dependence of grain size of annealed Si layers on initial CVD conditions. The spectroellipsometry (SE) and Ultra-Violet (UV) spectroscopy have indicated an important increase of the crystalline/amorphous silicon ratio for all annealed films. The signature of initial CVD conditions in optical properties investigated by SE and UV was found only for as-deposited Si films. From AFM measurements we have found that the surface roughness has increased by annealing, with a higher value for the annealed films, whic h were in the poly-crystalline state, immediately after deposition. In connection to our earlier results we bring here further support (by SE and UV data) for the crystalline state detected in as-deposited LPCVD films prepared at temperatures as low as 500°C. The value of the amorphous fraction present in the as-deposited film can explain the structural changes of the LPCVD Si films after annealing, as a function of initial CVD conditions.