New precipitate morphology in heat treated CZ Si wafers

Abstract

The morphological forms of the precipitates and other defects in the heat-treated oxygen-containing CZ silicon have been extensively documented, but little information concerning the morphology as a function of the position in the ingot has been reported. Recent studies, using high resolution analytical electron microscopy, have shown that plate type precipitates observed in the seed end of the silicon ingot were amorphous and contain oxygen. We have carried out a detailed TEM study of the precipitate morphology in the heat-treated wafers cut from the seed, middle, and tang regions of the CZ ingot. The interstitial oxygen concentrations in the as grown Si were 2.1×1018cm−3, 1.6×10−18cm−3, and 1.5×1018cm−3in the seed, middle and tang regions, respectively. Initial carbon was below IR detectability limit, but was higher in the tail than seed, based on segregation coefficients. The wafers were subjected to two-step anneals: 1. 0-16 hrs., 800°C in nitrogen and 2. 16 hrs., 1050°C in dry oxygen.