Ellipsometric study of the optical properties of silicon-based Si:SiO2 composite thin films under different annealing temperatures

In our work, silicon and silica composite films were prepared by using a magnetron sputtering method, and the samples were annealed in the temperature range between 200 degrees C and 600 degrees C. After annealing, the samples were investigated by spectroscopic ellipsometry (SE), and the SE spectra were measured in the range of 1.5 eV similar to 4.5 eV with a dual-rotating-element ellipsometer. In order to investigate the microstructure information of the film by fitting the SE spectra using the effective-medium approximation (EMA), we modeled the whole film by using a multilayer optical model including a surface oxide layer, a composite layer, and substrate layer. We used different mixtures to describe the composite layer, and finally we found that a mixture of amorphous silicon (a-Si), polycrystalline silicon (p-Si), and silicon dioxide had the best fit to the SE spectra. Whereafter, we studied the dependences of the surface roughness, the layer structure, and the composition on the different annealing temperatures and found that with increasing annealing temperature, the surface oxide layer grew in thickness, the silicon dioxide maintained its volume fraction, and a-Si transferred to p-Si.