Study of Surface Processes in the Digital Etching of GaAs

Surface processes in GaAs digital etching using alternating incidence of Cl radicals and a low energy Ar ion beam are discussed. For Cl feed time greater than 0.3 s, etching of GaAs does not proceed for short Ar ion irradiation times. This etching delay time is about 3 and 7 s for Cl feed time of 0.5 and 0.7 s, respectively. After etching starts, the etch rate increases and finally saturates during Ar ion irradiation. Since the same saturation value was obtained for Cl feed times between 0.5 and 0.7 s, digital etching involves a self-limiting mechanism. Rate equation analysis can explain these unique characteristics of digital etching on the assumption that physisorbed Cl layers prevent the sample surface from etching during short Ar ion irradiation times.