Impurity redistribution in EFG

Abstract

Numerical solutions of convective and diffusive transport equations in the melt contained by the EFG capillary die are presented for a two-dimensional model of EFG of silicon ribbon. Die geometry is shown to influence convective impurity transport in melt supplying the interface region during growth. Nonuniformity in the component of melt velocity parallel to the growth interface gives rise to impurity redistribution across the width of the ribbon. Enhancement of impurity levels above those of the bulk melt is associated with regions of low velocity, depletion of levels with regions of high velocity. The degree of redistribution varies with growth speed and the interface segregation and liquid diffusion coefficients of the impurity species. The close relation between redistribution patterns and die geometry suggests levels of certain impurities in preselected regions of the ribbon may be controlled by die design.