LARGE AREA ION BEAM ASSISTED ETCHING OF GaAs WITH HIGH ETCH RATES AND CONTROLLED ANISOTROPY.

Ion beam assisted etching (IBAE) is a dry etching technique in which the sputter etching component of an argon ion beam and the chemical etching component supplied by a Cl//2 gas flux are independently controlled. This technique has been used to obtain anisotropic etching of GaAs with minimal surface damage over areas of a few square millimeters. The results reported here are achieved with an improved IBAE system designed to etch considerably larger areas. The system accurately and uniformly delivers reactive gas flux to the sample giving uniform etching rates over the 2-cm-diam area exposed to the ion beam. When the sample is exposed to high reactive gas fluxes, etching rates of 5 to 10 mu m/min are obtained, making etched through-holes in GaAs wafers realizable. Control of the ion beam collimation and the reactive gas flux allow for accurate control of undercutting, making submicrometer etched structures in GaAs with aspect ratios greater than 35:1 easily obtainable. Damage studies of the ion beam assisted etched GaAs surfaces shows a low trap density in the range of 10**1**3 cm** minus **3. The improved system uses two gas jets to supply the chemically reactive flux and a liquid N//2 cooled shroud to trap the unused reactive gas. The absolute reactive flux impinging on the sample is determined with a capacitance manometer and the ion beam collimation is controlled by varying the ion gun to sample distance.