Surface reaction control in digital etching of GaAs by using a tunable UV laser system: reaction control mechanism in layer-by-layer etching

In order to achieve ideal atomic layer etching, surface reaction control in the digital etching of the GaAs/Cl2 using a tunable UV laser beam, is investigated, and an etching mechanism is proposed. From the time-of-flight measurements, laser-stimulated desorption of unreacted Cl2 and GaCl3 is observed in two wavelength regions (α) below 210 nm and (β) 245–250 nm, when (100) oriented n-type GaAs is used, and these desorption regions depend on the dopant and the orientation of the GaAs wafer. The model proposed for digital etching is photodissociation of physisorbed chlorine on GaAs with diffusion of negatively charged Cl into GaAs, which explains the experimental results well. The model suggests that the adsorbed Cl2 effectively contributes to etching when the laser beam, without photodissociation, is used, and ideal atomic layer etching is expected to be achieved under these conditions.