Characterization of in-depth cavity distribution after thermal annealing of helium-implanted silicon and gallium nitride

Abstract

Single-crystalline silicon wafers covered with sacrificial oxide layer and epitaxially grown gallium nitride layers were implanted w ith high-fluence helium ions (2 -610 16 cm −2 ) at energies of 20-30 keV. Thermal annealings at 650-1000 °C, 1 hour were performed on the Si samples and rapid thermal annealings at 900-1150 °C, 60-180 sec under N2 were performed on the GaN samples. The as-implanted samples and the near-surface cavity distributions of the annealed samples were investigated with variable angle spectroscopic ellipsometry. In-depth defect profiles and cavity profiles can be best described with multiple independent effective medium sublayers of varying ratio of single-crystal/void. The number of sublayers was chosen to maximize the fit quality without a high parameter cross-correlation. The dependence of the implantation fluence, oxide layer thickness and annealing temperature on the cavity distribution was separately investigated. The ellipsometric fitted distributions were compared and cross-checked with analyses of transmission electron micrographs where the average surface cavity was determined sublayer by sublayer. The in-depth profiles were also compared with simulations of He and vacancy distributions.