Oxygen precipitate precursors and low temperature gettering processes. II. DLTS analysis of deep levels associated to oxide precipitates

Abstract

In this paper we report a systematic investigation the nature and energy levels of traps generated during the segregation in oxygen of silicon wafers submitted to a two-step annealing sequence, the first of which is carried out at 470°C and the second at temperatures ranging from 600 to 800°C. The investigation was carried out by using DLTS (deep level transient spectroscopy) and optical DLTS at temperatures ranging from liquid He to room temperature. The main result of our work was the discovery of clear correlations between the annealing sequence and the concentration and nature of traps. In fact, a spectrum of shallow levels was found in samples presenting a high density of thermal donors (TD), whose intensity decreases as soon as the density of TD decreases. Also, the precipitation of oxygen as an (amorphous) oxide, presenting an average size of 2 nm, is associated to the presence of traps which are assigned in literature to dislocations in samples submitted to deformation. In our case, dislocations originate from interstitials ejected during the segregation of the oxide phase, which is known to be a volume exigent process.