Control of the morphologies or profiles produced by localized etching of structures has assumed increasing importance with the current emphasis being placed on microdefinition and surface relief optimization for monolithic circuits. To obtain a better understanding of the complex anisotropic etching behavior observed in , the morphologies produced by various acidic hydrogen peroxide solutions were evaluated. The degree and nature of the anisotropy is shown to vary extensively and systematically with the etchant composition. Both highly anisotropic and essentially isotropic etching may be obtained by selection of the appropriate etchant composition.