Comparative analysis of amorphous silicon and silicon nitride multilayer by spectroscopic ellipsometry and transmission electron microscopy

Amorphous silicon (a-Si) and silicon nitride (SiN) films were prepared on polished silicon wafers by radio frequency sputtering using silicon target in argon and nitrogen plasma. The process described here is simple and well suited for fabricating multilayer structures of films with different refractive indices. Optical models were developed to analyze the spectroscopic ellipsometry data measured on the multilayer structure. The dielectric functions of amorphous silicon and silicon nitride were modeled by the Tauc-Lorentz oscillator model and by the Cauchy dispersion model, respectively. A thick a-Si layer was prepared and measured to establish appropriate initial refractive index data for evaluation of measurements on multilayer stacks. The parameters of layers with identical materials in the layer stack were coupled to decrease the number of fitted model parameters. Refractive index spectra of a-Si and SiN as well as thicknesses of the multilayer structure were calculated from one measurement. The results of the ellipsometric analysis are in good agreement with transmission electron microscopy data