Gettering by Overpressurized Bubbles Induced by High-Energy-He-Implantation In Silicon

摘要

Silicon samples were implanted with He ions at 1.6 MeV using doses ranging from 1 x 10~(16) cm~(-2) to 1x10~(17)cm~(-2) with different fluxes (0.4μA/cm~2 - 2.0μA/cm~2) and annealed at high (1000℃) and low temperatures (800℃). The implantation induced-defect structure and their distribution in the depth of the sample were studied by cross section electron microscopy (XTEM). An unexpected consequence of the flux on the defect population and density was found solely for 2x10~(16) cm~(-2), which is the upper threshold to get nano-bubbles at such large implantation depth. Nuclear Reaction Analysis (NRA) were performed to measure the ratio of He remaining in the bubbles as a function of time and temperature anneal. Some samples were gold or nickel diffused at temperatures ranging from 870℃ to 1050℃ prior to He implantation. The gettering efficiency of the implantation-induced defects was measured by secondary ion mass spectroscopy (SIMS), after a high temperature getter annealing. SIMS profiles exhibit a shape and a width closely related to the presence of the defects (observed by XTEM) which are very efficient sinks for all kinds of metal impurities. The bubbles were found to be more efficient traps than the dislocation loops.