A total concentration fixed-grid method is used in this article to model the three-dimensional diffusion-controlled wet chemical etching. A total concentration is defined as the sum of the unreacted and the reacted etchant concentrations. The governing mass diffusion equation based on the total concentration includes the interface condition. The reacted concentration of etchant is a measure of the etch-front position. With this approach the etchfront can be found implicitly. For demonstration purposes, the finite-volume method is used to solve the resulting set of governing equations with initial and boundary conditions. The effect of mask thickness on the etchfront surface evolution is studied. The condition at which a three-dimensional etching is converted into two-dimensional is also presented.
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