DEGRADATION-FREE ELECTRON-CYCLOTRON RESONANCE PLASMA-ETCHING OF INP

We report the first demonstration of featureless surface morphology on InP plasma etched in CH4/H2/Ar electron cyclotron resonance (ECR) discharges. At a plasma composition of 5 CH4/17 H2/8 Ar it is necessary to limit the microwave input power to less-than-or-equal-to 150 W in our reactor in order to achieve smooth etching. At microwave powers above this value, we observe increasingly rough surfaces. This is ascribed to faster removal of phosphorus than indium because of an imbalance of active hydrogen (removing P as PH3) to methyl radicals (which are the active species in forming the In etch product). The addition of Ar to the discharge enhances the etch rate by a factor greater-than-or-equal-to 3 compared with CH4/H2 alone, indicating that some additional degree of ion bombardment is necessary with this gas chemistry even under ECR conditions. Degradation of the InP photoluminescence as a result of plasma etching at bias voltages less than 150 V can be completely quenched by the addition of PCl3 to the discharge. This provides a phosphorus partial pressure during the etch, maintaining the stoichiometry of the InP surface.