Trapping of gold by nanocavities induced by H+ or He++ implantation in float zone and Czochralski grown silicon wafers

Abstract

In silicon, implantation of He++ or H+ ions and subsequent annealing can lead to the formation of nanocavities below the implanted surface of the wafers. These nanocavities, which behave as trapping sites for metallic impurities, can be located near the devices in integrated circuits in order to induce a proximity gettering. In this article, we investigate, in float zone (FZ) and Czochralski (Cz) wafers, the trapping of gold by nanocavities formed by implantation of He++ or H+ ions at 250 keV and at a dose of 3×1016 cm−2 followed by subsequent annealing(s) at 750 °C for 1 h. Deep level transient spectroscopy profiles show that substitutional gold concentration decreases near the cavity band in FZ and Cz samples. Gold profiles obtained by secondary ion mass spectroscopy show that there is a strong trapping of gold in the cavity band in all samples. In the case of He++ implanted wafers, this trapping also occurs in the region between the implanted surface and the cavities, and the higher the oxygen concentration, the higher this trapping is. This could be explained by a higher density of implantation induced defects in He++ implanted samples and by the formation of oxygen-vacancy complexes in this region. In H+ implanted samples, the hydrogen passivation of such defects reduces their efficiency as trapping sites. The results suggest that gold trapping is related to gold precipitation which could inject self-interstitials in the bulk and then decreases the substitutional gold concentration near the cavity band even though there is a constant source of gold atoms in our experiments.