Photochemical etching of GaAs with Cl2 induced by synchrotron radiation

The quality and efficiency of etching at room temperature is determined in the wavelength range from 105 nm to 300 nm by replicating a mask on a GaAs(100) wafer and by wavelength selection of synchrotron radiation with filters and a monochromator. A good anisotropy and selectivity is found for Cl₂ pressures from 10^–2 mbar up to 1.5 mbar, but above 3 mbar the selectivity is lost. Efficiencies for stimulation of the chlorination reaction and for desorption are separated and an optimal efficiency for stimulation of about 100 removed Ga and As atoms per photon is obtained around a wavelength of 122 nm at 1.5 mbar. Growth of reaction products on the surface occurs for short wavelengths and transport processes through layers up to a thickness of 350 nm are relevant. The efficiency and quality of etching can be improved by additional desorption with long wavelengths especially with lasers.