Grown-in microdefects, residual vacancies and oxygen precipitation bands in Czochralski silicon

Abstract

A model of multi-step vacancy aggregation in dislocation-free silicon crystals is analyzed. In this model, voids are first nucleated (normally just below 1100°C). The vacancy loss to voids is retarded below some characteristic temperature (about 1020°C) as the vacancies become bound by oxygen into O 2V complexes. These remaining vacancies control nucleation of oxide particles on further cooling. Some vacancies survive even this stage and control nucleation of oxygen clusters at still lower temperature (around 700°C). The oxygen clusters are major precipitation nuclei during subsequent heat treatments. It is through residual vacancies that the oxygen precipitation behavior is closely related to the grown-in microdefects (voids and particles). The microdefect properties and the residual vacancy concentration ( C res ) are computed in dependence of the starting vacancy concentration ( C 0 ). The C res (C 0) function is of a twin-peak type which results in a banded precipitation pattern if C 0 decreases gradually either in radial or axial direction. The model accounts for complicated (strongly banded) precipitation patterns, particularly those observed in halted and quenched crystals.