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

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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.