The effect of growth rate, diameter and impurity concentration on structure in Czochralski silicon crystal growth

Abstract

It is demonstrated that maximum growth rates of up to 80% of the theoretical limit can be attained in Czochralski grown silicon crystals while maintaining single crystal structure. Attaining the other 20% increase is dependent on design changes in the grower to reduce the temperature gradient in the liquid while increasing the gradient in the solid, a formidable task. The conclusions of Hopkins et al. on the effect of diameter on the breakdown of structure at fast growth rates are substantiated. Copper was Utilized as the test impurity. At large diameters (>7.5 cm), concentrations of greater than 1PPM copper were attained in the solid (45000 ppm in the liquid) without breakdown at maximum growth speeds. For smaller diameter crystals, the sensitivity of impurities is much more apparent. For solar cell applications, impurities will limit cell performance before they cause crystal breakdown for fast growth rates of large diameter crystals (R.H. Hopkins et al., J. Crystal Growth 42 (1977) 493).