Trans-projected-range effect in proximity gettering of impurities in silicon

Abstract

Deep gettering layers have been formed in n-type Si wafers by high-energy ion implantation of Si +, P +, Ge + and As + and subsequent annealing. The samples have then been contaminated with Cu by implanting the impurity into the back face and performing an additional thermal treatment. The resulting copper depth profiles measured by secondary ion mass spectrometry show strong gettering of Cu well beyond the projected ion range R P and formation of a separate gettering band therein. We call this phenomenon the “trans- R P effect”. It has been observed for both the P and As implants, but not for the Si and Ge implants. This effect indicates the presence of a significant amount of defects much deeper than R P . The size of these defects is below the resolution limit of our transmission electron microscopy analysis and we suggest that they are small interstitial clusters. Their gettering ability is higher than that of the extended defects at R P as the amount of Cu atoms gettered beyond R P is much greater than that in the implanted gettering layer. A mechanism for the defect formation and clustering in the trans- R P region is proposed, and an explanation for the differences in the results for the P and As implants is given.