THE INFLUENCE OF NATIVE OXIDE LAYERS OF INP ON THE SHAPE OF ETCHING PROFILES AT RESIST EDGES

Profile etching experiments made on InP in solutions of Br2-HBr revealed that the profile shape is strongly dependent on the resist orientation and on whether SiO2 or photoresist is used as a mask. It was found that the local etch rate of the (111)In crystallographic planes can be significantly enhanced near the resist edges. In the extreme case the dissolution rate was found to be controlled by Br2 diffusion in solution which resulted in rounded profiles. A model is proposed which can account for this apparently anomalous etching behavior. The anisotropic etching of thin surface layers is essential in this model. Experimental results can be explained if it is assumed that native oxide layers covering the monocrystalline InP substrates play this role. The local etching kinetics of crystallographic facets and, consequently, the profile shape are strongly determined by the lateral etch rate of these oxide layers.