Reactive-fast-atom beam etching of GaAs using Cl₂ gas

GaAs dry etching using reactive-fast-atom beam etching to obtain an etched mirrorlike surface is investigated. An etch rate of 0.1-0.6 μm/min is obtained when Cl₂ gas is used, which is 50-100 times faster than when Ar gas is used. The etch rate ratio between GaAs and photoresist AZ-1350J is more than 30. As a result, a trench with a depth of more than 10 μm and a width of less than 2 μm is easily fabricated under the etch conditions of a Cl₂ gas pressure of 5-6.5×10^-2 Pa, an accelerate voltage of 1.5-1.8 kV, and a substrate temperature of about 100 °C. The radiation damage caused by this etching is very small, and it is similar to that caused by wet chemical etching, in spite of the relatively higher accelerator voltage. The thickness of an induced damage layer is only 150 Å. It is found that the radiation damage induced by reactive-fast-atom beam etching decreased with an increase of the etch rate. It is confirmed that vertical, smooth, damage-free etching can be easily attained with reactive-fast-atom beam etching.