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

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 degrees C). The vacancy loss to voids is retarded below some characteristic temperature (about 1020 degrees C) as the vacancies become bound by oxygen into O2V 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 degrees 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. (C) 1999 Elsevier Science B.V. All rights reserved.