Stress studies in EFG. Quarterly progress report, October 1-December 31, 1983

Abstract

Stress analysis at Harvard University has examined the implication of non-zero interface stresses on model predictions. Stress distributions at distances greater than about 1 mm from the interface are shown to be independent of the interface stress at high creep intensities, and the predictions based on zero initial stress can be used with confidence. Numerical models for growth dynamics developed at MIT are compared with experimental data on t-V relationships and on interface shape obtained from impurity redistribution in aluminum-doped 10 cm wide ribbon. Comparison of primary creep responses in FZ (floating zone) and CZ (Czochralski) silicon above 1200/sup 0/C using four-point bending indicates that oxygen has a significant influence on the creep rate. Both the strain rate and resulting dislocation densities generated in FZ silicon are an order of magnitude higher than for the CZ material at comparable applied stress levels. A fiber optics probe suitable for temperature measurement during sheet growth has been constructed and tested. Study of the feasibility of using laser interferometric techniques for residual stress measurements has continued at the University of Illinois. The method has been successfully applied to CZ silicon, and is being evaluated for use with EFG ribbon.