A diffusion/chemical reaction model for HE etching of LPCVD phosphosilicate glass sacrificial layers

Abstract

The authors deal with the etching of LPCVD phosphosilicate glass (PSG) sacrificial layers by solutions of hydrofluoric acid (HF). A diffusion/chemical reaction model has been derived assuming one-component steady-state diffusion, one-dimensional geometry, no effect of heat of reaction, and a constant diffusion coefficient. The model fits the experimental data successfully with physically reasonable diffusion coefficients for concentrated HF solutions (3-5*10/sup -5/ cm/sup 2//s). The chemical reaction kinetics have been described experimentally with a non-first order reaction rate expression. Experimental studies using an etching test structure are reported for the effect of channel width, the use of low-stress nitride and polysilicon as the channel structural material, several etchants (including: HF, BHF and surfactant HF), and external agitation. The oxide etch process shifts from reaction-controlled to diffusion-controlled as the etch channel develops. >