Evidence for Cathodic Protection of Crystallographic Facets from GaAs Etching Profiles

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Abstract
Etching experiments were carried out on partially masked single crystals in alkaline solutions in which the dissolution rate of all crystal planes is diffusion‐controlled. Etching could be rate determined in two ways. In the first case, mass transport of OH− ions to the surface determined the rate of the anodic partial reaction and also the etch rate. This resulted in rounded profiles at the semiconductor/resist edge as expected for diffusion limited etching. In the second case, mass transport limited reduction of the oxidizing agent determined the dissolution rate. Etching at the resist edge was now, surprisingly, anisotropic and faceted profiles were observed. On the basis of electrochemical measurements with these etchants it is concluded that a local galvanic element can be formed between crystallographic facets. As a result, certain facets may be cathodically protected and consequently etch more slowly than the corresponding free crystal plane.

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