Spectroscopic ellipsometry characterisation of solid phase crystallisation of silicon thin films obtained by LPCVD

This work investigated the low and high temperature solid phase crystallisation (SPC) on silicon thin films prepared by low-pressure chemical vapour deposition. Silicon thin films were deposited by low-pressure chemical vapor deposition (LPCVD) on oxidized silicon substrates, from silane decomposition. The deposition temperatures use in our experiment have been 500, 530, 550, 590 and 615°C and the pressure values were 20, 53 and 100 Pa. Spectroscopic ellipsometry (SE) was used in order to point out the phase transition of as-deposited and annealed LPCVD silicon from amorphous to crystalline state via a mixed phase. The dependence of the structural parameters on the deposition parameters has been investigated. A better characterization of the polysilicon layer is achieved by using the following optical model: c-Si/SiO₂+voids/c-Si+a-Si+voids/SiO₂+c-Si+a-Si+voids. This optical model for LPCVD silicon films gives the possibility of extracting information about optical, surface roughness and microstructural properties. The SE results were in good agreement with the X-ray diffraction (XRD) measurements. SE has proved an improved sensitivity to microstructural changes in the as-deposited and annealed LPCVD silicon compared with other structural characterization methods like XRD.