Bulk properties of very large diameter silicon single crystals

Abstract

It has been experimentally found that it will be difficult to grow 300 mm or larger diameter crystals with similar quality as for 200 mm or smaller diameter crystals. This phenomenon can be understood within the frame of the Voronkov theory in which the value of the parameter V/ G ( V=pull rate, G=temperature gradient at the growth interface) determines which type of defect forms in the growing crystal. Due to fundamental technological constraints, the pull rate of silicon single crystals has to be reduced as the diameter increases. For crystal diameters beyond 300 mm, the reduction of pull rate is so large, that V/ G( r) ( r=radial position) can probably no longer be kept above the critical value C crit=1.34×10 −3 cm 2 K −1 min −1 over the entire crystal volume by the present growth technology. As a result, the defect behavior of the silicon bulk changes. The aggregation of defects is now dominated by excess Si interstitials instead of vacancies and, hence, L-pits (dislocation loops) are observed instead of microvoids. Unless new methods for the suppression of L-pits can be developed, this will seriously challenge the use of polished wafers in very large diameter device manufacturing lines, as L-pits can severely damage the device performance. A promising solution to the defect problem appears to be p+p− epi wafers.