Backscattering and electron microscopy study of mega-electron volt gold implantation into silicon

Abstract

Rutherford backscattering spectrometry and cross-section transmission electron microscopy have been used to study implantation of MeV Au+ ions into silicon. Measured range (Rp) and straggle (ΔRp) values for MeV Au+ implanted silicon are found to be consistently larger than values predicted by trim simulations. The magnitude of the discrepancies are such that the differences cannot be attributed to implantation effects alone. We conclude that the trim computer program does not accurately predict Rp and ΔRp values for MeV Au+ implantation into crystalline Si. Experimental results show that for low-current low-energy implants a single Gaussian Au profile is achieved. Low-power implants produce a single band of damage consisting of simple point defects. High-current high-energy implants lead to the creation of more complex defect structures such as dislocation networks; these arise as a result of dynamic beam recrystallization. Multiple layers of precipitation are observed in silicon implanted with MeV Au+ ions in those samples where dynamic recrystallization occurred. Precipitation occurs as a result of the local Au concentration exceeding the solid-solubility during beam-induced recrystallization. Different mechanisms operate in conjunction to cause anomalous Au motion which results in formation of multiple precipitate layers. A first mechanism has the implanted Au segregating into a densely defected region; when the concentration exceeds the local solid solubility Au precipitates out of the matrix. A second mechanism has motion of Au along dislocations in a network; the diffusing Au reaches a dislocation-node where it exceeds the local threshold for precipitation and the Au therefore precipitates. Enhanced Au diffusion is dependent upon the magnitude of dynamic recrystallization occurring during the implantation.