CO₂ Laser-induced Surface Oxidation and Etching of Si and Si₃N₄

Abstract

A 30 W CO₂ laser was used to perform localized etching on Si and Si₃N₄ coated with an aqueous KOH solution. According to Fourier transform infrared reflection absorption spectrometry, the surface of Si coated with an aqueous KOH solution is oxidized by CO₂ laser beam irradiation, but the spectrum is different from one oxidized without chemical enhancement by KOH. Surface photo voltages which depend on the energy level and the density of surface electron states were measured in order to characterize the oxidized Si surfaces formed with chemical enhancement by KOH. Local density of electron states of model oxidized Si surface structures were calculated using the recursion method and semi-empirical tight-binding theory, and the mechanism of the etching process was investigated. The following results were obtained. The oxidized surface layer has a higher density of defects than one formed without enhancement by KOH. Accordingly, the atomic binding energy in the oxidized layer is decreased, and low power laser etching can be possible.