Quantitative Analysis of Microsegregation in Silicon Grown by the Czochralski Method

Abstract

Quantitative microsegregation analysis was carried out on Sb‐doped silicon crystal pulled from the melt. Interference by thermal convection in the melt, invariably present in silicon growth at commonly used rates of pulling and seed rotation, was eliminated by introducing severe thermal asymmetry in the growth system. Interface demarcation was employed for the determination of the microscopic growth rates and spreading resistance measurements for obtaining composition profiles. For growth under forced convection conditions it was shown that the microsegregation behavior is controlled by the microscopic growth rate and is adequately accounted for by the Burton, Prim, and Slichter (BPS) model based on steady‐state segregation. The small deviations from steady‐state segregation were manifested as solute redistribution transients associated with the periodic growth rate variations (slight phase shift between dopant concentration and microscopic growth rate). For growth under thermal convection conditions, the microscopic growth rate is modulated by convective temperature fluctuations in the melt, but it does not control the microsegregation behavior because under these conditions the diffusion boundary layer thickness undergoes significant fluctuations. Accordingly, the BPS model, which assumes a constant diffusion boundary layer thickness, was found to be inapplicable to microsegregation in silicon grown under thermal convection.