Nonlinear temperature dependence of the refractive index of polycrystalline silicon films and the influence of microstructural disorder

摘要

The optical properties of thin films are known to be affected by microstructural inhomogeneities. In this paper we study, using ellipsometry, the influence of microstructural disorder on the refractive index at 632.8 nm and on its dependence on temperature in the range 300ndash;700 K in the case of thin noncrystalline lowhyphen;pressure chemicalhyphen;vapor deposition silicon films. It is found that films with large amorphous component have a behavior distinct from that shown by polycrystalline films. In particular, both the refractive indexnand the thermohyphen;optic coefficientdn/dTat room temperature have larger values for amorphous films than for polysilicon films. Furthermore, the thermohyphen;optic coefficientdn/dTis found to vanish at about 500 K in the case of highly noncrystalline films.