Abstract
An anisotropic and low damage cryogenic etching of Si0.7Ge0.3/Si strained-layer superlattices by an ArF (193 nm) excimer laser assisted Cl2 gas was demonstrated. At low temperatures, photo-assisted etching can provide a better etching rate and largely improved the surface morphology and quality. Raman shift spectroscopy results show that the strain relaxation in the etched region was increased with laser power density. And the strain relaxation was obviously improved in the low power density and low temperature etching conditions. As comparing the secondary ion mass spectrometry(SIMS) depth profile, Ge segregation still previals in photo-assisted etching with excimer laser. However the segregation can be effectively suppressed by low power photo-assisted cryogenic etching with fewer energy transmitted to the etched materials so that the composition of superlattice could remain the same after the etching process. Taking advantage of using the Schottky barrier diodes structures, it was demonstrated that the Schottky barrier height have inverse relation to laser power density and sample temperature. The photo-assisted cryogenic etching (PAC) was proved to be a low damage dry etching technique. Furthermore, the mask issue of photo-assisted etching had been systematically researched and a satisfactory result had been obtained.