Microstructural and optical properties of LPCVD polysilicon films

Silicon thin films were deposited by low-pressure chemical vapor deposition (LPCVD) on oxidized silicon substrates, from silane decomposition. The deposition temperatures used in our experiment have been 500, 530, 550, 590 and 615°C and the pressure values was 20, 53 and 100 Pa. The microstructure and the surface roughness of as-deposited films were investigated by X-ray diffraction (XRD), spectroelipsometry (using the Bruggemann-Effective Medium Approximation with a multilayer model) and AFM techniques. Three different models, Tauc, Cody and Wemple-Di Domenico were used to estimate the values of the optical gap. The results show the influence of the microstructure on the physical and optical properties of as-deposited LPCVD silicon films. It is pointed out that polycrystalline silicon thin films can be obtained by LPCVD technique below 550°C.