Modifications of He implantation induced cavities in silicon by MeV silicon implantation

Doppler broadening spectroscopy (DBS) coupled to a slow positron beam has been used to investigate the formation of He-cavities in the presence of high vacancy concentrations in Cz-Si (1 1 1). Si samples were first implanted with MeV Si ions in order to create a damaged Si layer. DBS measurements show the presence of divacancy (SV2/SSilattice=1.052,WV2/WSilattice=0.83) from the surface up to 4.2 μm depth with a concentration higher than 1018 cm−3. The thickness of this damaged layer was confirmed by spreading resistance measurements. In the second step, samples were implanted with 50 keV 3He with fluence of 1016 cm−2. DBS results show that the apparent divancancy concentration decreases at 3He implantation depth ∼435 nm due to 3He passivation of vacancies that occurs during the implantation process. After 900 °C annealing, large defects are detected at depth up to 2 μm and (S, W) values suggest the detection of cavities at the implantation depth. We also report the possible presence of impurity complexes. The formation of these complexes is attributed to the gettering of metallic impurities present in the Si sample.