Spectroellipsometric characterization of SIMOX with nanometre-thick top Si layers

Abstract

The size dependence in optical properties of the top Si layer of SIMOX (separation by implanted oxygen) structures has been studied by spectroscopic ellipsometry. The ellipsometric parameters Ψ and Δ were measured in the spectral range from 230–800 nm in air. The sample structure analyzed is [top SiO 2]/[top Si]/[buried SiO 2]/[Si substrate]. By using the bulk dielectric functions, the thickness of the top SiO 2, top Si, and buried SiO 2 layers have been determined by the SIMPLEX method. The best fit to the data was realized by applying a fluctuating thickness model for the buried SiO 2 layer. The fluctuating thickness model is found to yield a much better fit than a model including an EMA interface roughness layer. Furthermore the MDF (model dielectric function) developed by Adachi was applied for the nanometre (nm) thick top Si layers in order to improve the fitting. As a result, a size dependence in the dielectric functions of the nm thick top Si layers was observed.