The Role of Native Oxide Layers in the Patterning of InP by Ga Ion Beam Writing and Ion-beam-assisted Cl sub 2 Etching.

We have studied the mechanism of increased etch rate induced in InP substrates by focused Ga ion implantation and Cl sub 2 etching. We cannot account for the depth of surface steps formed in this process with a purely kinetic mechanism. The preferential etching of implanted areas is attributed instead to local modification or removal of native oxides from the surface of InP. The thin oxide layer effectively protects the substrate and inhibits Cl sub 2 etching. Consistent with the thermodynamic prediction, a cleaned InP (100) surface is etched by Ca sub 2 (5x10 sup (-4) Torr) with a rate of approximately 1000angstroms/min at 200C. Surface steps as deep as 3microns have been reproducibly prepared using an oxide mask believed to be approximately 20angstroms thick. In the etching process, any substrate damage caused by the Ga beam writing is completely removed. The oxide mask, which can be patterned on a very fine scale by energetic particle bombardment, provides a new avenue for in-situ processing of InP.