Thickness estimation of silicon-on-lnsulator by means of the fourier transform of bilinearly transformed infrared reflectance data

Abstract

Knowledge of film thickness is essential for device design in silicon-on-insulator technology. A new thickness estimation technique, based on the calculation of the spatial frequencies of bilinearly transformed infrared reflectance data in a spectral window, is introduced. The assignment of dominant spectral peaks in the power spectral density curve to the optical thickness of the silicon, silicon dioxide and the combined layer, is also presented. Examples for silicon-on-silicon dioxide with the silicon layer ranging in thickness between 1000 nm and 50 nm, with fixed oxide thickness, are presented. Thickness values of both layers to better than a few percent accuracy, were obtained for silicon layers down to 100 nm and with reduced accuracy for layers as thin as 50 nm.