Amorphous and crystalline oxide precipitates in oxygen implanted silicon

Abstract

We studied precipitation of oxygen in the region below the buried oxide of a silicon-on-insulator structure formed by high-dose implantation of oxygen. Underneath the oxide layer there is first a region containing amorphous precipitates, spherical in shape. At greater depth, platelike precipitates of the monoclinic silica phase coesite are observed on {113} silicon planes. The lower interface of the buried oxide is very rough compared to the upper interface. The morphology of the implanted structure is attributed to intrinsic point defects. In particular it is proposed that a high concentration of self-interstitials occurs below the oxide as soon as it becomes a continuous layer. This leads to a large reduction of the oxidation rate in this region. Oxidation then only occurs above the buried oxide, reducing the thickness of the superficial silicon film.