Profile broadening of high dose germanium implants into (100) silicon at elevated temperatures due to channeling

(100) Silicon wafers were implanted with 120 keV germanium ions at substrate temperatures up to 600 °C. The germanium profile was monitored together with the crystalline fraction of the implanted silicon by Rutherford backscattering spectroscopy channeling in the 〈100〉 direction. Extensive profile broadening was seen with elevated temperature implants accompanied by a peak shift of 50 nm away from the surface for the highest temperature implant at 600 °C. A germanium tail was also seen extending deeper than 300 nm for this implant together with a reduction in the peak germanium concentration of more than 60% when compared with similar implants at room temperature. Radiation enhanced diffusion and enhanced sputtering are ruled out as causes for the profile broadening. Instead we demonstrate channeling along the 〈100〉 direction to be the cause of both the observed broadening and the increase in the peak depth. This was confirmed by eliminating such profile broadening in a sample implanted at 600 °C by tilting the implant away from major axial and planar channels. Positron annihilation spectroscopy was used to monitor the profile of open volume defects in the implanted material. Data from this analysis show that a defect concentration of greater than 1016/cm3 extends to a depth of ≈1.2 μm for 1×1014 Ge/cm2 at room temperature. A higher concentration of such defects appear deeper for similar implants at 450 °C. These deep open volume defects can be eliminated by using tilted implants through an amorphous 0.5 μm SiO2 mask layer. Their formation is consistent with germanium ion channeling during the initial stages of room temperature implantation and extensive channeling for elevated temperature implantation.