Effect of ion implantation on mechanical strength of silicon wafers

Abstract

We have investigated the effects of the secondary defects caused by ion implantation on wafer strength. The change in wafer strength with the ion dose has been examined after implanting phosphorus or (BF2)+ ions into wafers with and without heat treatment. Ion implantation defects have been observed using transmission electron microscopy after ion implantation with and without subsequent annealing. The three-point bending tests carried out with the ion implanted samples show that the upper yield stress, which represents wafer strength, gradually decreases with the increasing dose in the case of phosphorus ions and rapidly decreases in the case of (BF2)+ ions due to the formation of secondary defects. In addition, the strength of the wafers with a low oxygen concentration is lower than that of the wafers with a high oxygen concentration. However, the rate of decrease in wafer strength with increasing ion dose is not affected by the oxygen concentration; it only depended on the implanted element.