The effect of thermal history during crystal growth on oxygen precipitation in Czochralski-grown silicon

Abstract

The effect was studied of crystal growth conditions on oxygen precipitation in silicon crystals with uniform oxygen distribution and concentration of (1.1-1.2)*1018 cm-3. Following annealing at 800-1000 degrees C X-ray topographs were obtained and the concentration of precipitated oxygen was measured. The results show that the process of formation of oxygen precipitation centres during crystal growth has several stages and intrinsic point defects play a decisive role in all these stages. The type of dominating intrinsic point defects, their concentration, the crystal cooling rate at the stage of grown-in microdefect formation and the duration of low-temperature stage are all critical. A qualitative model for the formation of oxygen precipitation centres is proposed which takes into account the crystal cooling curve, type of intrinsic point defects, their concentration and distribution in the crystal volume. Depending on the crystal growth conditions different types of oxygen precipitation centres may arise. In the case of the 'interstitial' regime ( xi < xi t, where xi =V/G0, V is crystal growth rate, G0 is longitudinal temperature gradient near the interface, xi t=3.3*105 cm2 s-1 K-1) these are grown-in-B defects. In crystals grown in the 'vacancy' regime ( xi > xi t) centres of two kinds may coexist: high-temperature oxygen microprecipitates (grown-in A' defects) and low-temperature centres. Nucleation of A' defects occurs at 1150-1000 degrees C (depending upon the crystal pulling rate), the low-temperature centres are formed in the range 760-610 degrees C. The low-temperature centres have been found to depend on the high-temperature ones. The dependence is hypothesized to be due to vacancy supersaturation established at the onset of the low-temperature stage.