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

A model of multi-step vacancy aggregation in dislocation-free silicon cryst als is analyzed, In this model, voids are first nucleated (normally just be low 1100 degrees C). The vacancy loss to voids is retarded below some chara cteristic 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 sta ge and control nucleation of oxygen clusters at still lower temperature (ar ound 700 degrees C). The oxygen clusters are major precipitation nuclei dur ing subsequent heat treatments. It is through residual vacancies that the o xygen precipitation behavior is closely related to the grown-in microdefect s (voids and particles). The microdefect properties and the residual vacanc y 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 r esults 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 q uenched crystals. (C) 1999 Elsevier Science B.V. All rights reserved.