ANISOTROPIC PHOTOETCHING OF III-V SEMICONDUCTORS .2. KINETICS AND STRUCTURAL FACTORS

Three kinetic ranges are defined for the photoetching of semiconductors. In these ranges, either the light intensity, the reduction rate of the oxidizing agent, or the solubility or removal of semiconductor oxidation products is rate limiting. The discussion of photoetching kinetics includes the dependence of the etch rate on time or etched depth, width of the structure, and wavelength of the light. The shape of the etched holes depends on the light intensity distribution. This influence can be both direct, via photocarrier generation, and induced, via photogalvanic effects. The latter factor also limits lateral broadening during anisotropic photoetching. Some practical conclusions are drawn for the cases of etching by light projection and for uniform illumination of a masked pattern. The main results are summarized in a table, which contains quantiative data on n-GaAs in H2O2/H2SO4 as an example.