Reflectance spectra of plasma etched silicon

Abstract

Plasma etching of oxide on silicon using fluorine ion bombardment results in the formation of an amorphous fluorosilyl (SiFx) layer on the surface of the crystalline silicon. Consequently, all reflectance spectra of plasma etched oxide on silicon wafers are very well fitted by a stack consisting of oxide on modified amorphous silicon on silicon. This model fit wafers having an oxide layer of nonzero thickness and wafers that were overetched. Use of such a model in a thin film reflectometer allows the accurate determination of the oxide thickness, measurements which were previously very inaccurate. Examples of such spectra and their analysis are presented together with the results of electron spectroscopy for chemical analysis and mechanical profilometer measurements.