Numerical prediction of the etched profile in pyrolytic laser etching of silicon and gallium arsenide

Abstract

A quasi-static two-dimensional heat conduction analysis is used to deduce the geometrical profile of a cavity pyrolytically etched on isotropic silicon and GaAs substrates by a stationary CW argon ion laser with a Gaussian intensity profile. The nonlinear problem is solved using the numerical finite element method. Starting with a substrate having a flat surface, the numerical routine progressively removes regions of the substrate to model the actual etching action. Multiple reflections of the laser beam in the etched cavity are also modeled assuming that the substrate surface is perfectly diffused. Laser etching experiments performed on a silicon substrate in a CCl4 gas ambient are used to verify the numerical routine. Comparison between the experimental and the numerical results indicates that the desorption of SiCl2 radicals is probably responsible for the final etched profile obtained. Numerical results are also compared with the experimental data obtained from previous works carried out on a GaAs substrate.