Etch rates and surface chemistry of GaAs and AIGaAs reactively ion

The etch rates of GaAs and Al,Ga] _xAs (x = 0.09-1) in C2H6/H2 were investigated as a function oftime 0-12 min), gas flow rate (5-25 seem), total pressure (4-30 mTorr), plasma power density (0.56-1.32 W em2 ), and percentage ofC2H 6 in the discharge (1O%-50%). The etch rates are constant with time, and decrease with increasing Al content in the AIGaAs. The maximum etch rates occur at 25% by volume C2H., in H2 and increase linearly with increasing power density. Increasing the total pressure at constant gas composition reduces the etch rates by approximately a factor of 2 between 4 and 30 mToH. The etched surfaces have smooth morphologies for C2H 6 concentrations less than 40% of the total gas volume. A layer of subsurface dislocations approximately 40 A deep were observed in GaAs by transmission electron microscopy for the highest-power density discharges, while the surfaces for all samples are As-deficient to a depth of 30 A after reactive ion etching. Polymer deposition is not significant for CZH6 volumes less than 40% of the total gas volume.