The occurrence of slip bands, due to stresses, in large-diameter Czochralski-type wafers was studied by means of computer simulation. Two types of stress were produced in the circular wafers. These were thermal stresses that arose from radial temperature variations, and gravitational stresses that were due to the bending moment that was caused by the weight of the wafer itself. Because 200mm-diameter wafers were common, slip-bands that were generated by gravitational stresses were studied as elongated slippages along <110> directions. These were in addition to those that were due to thermal stresses. By using a simplified model, resolved shear stresses that were due to gravity were calculated for a 300mm-diameter wafer. On the basis of a previously proposed thermo-elastic model, curves of the critical stresses which were required in order to cause the multiplication slip of dislocations were obtained as a function of the density of micro-defects which acted as nucleation sites for dislocation multiplication. By comparing the gravitational stresses and the critical stresses, estimates were made of the conditions which were required in order to suppress slip bands in wafers that were more than 300mm in diameter. The conditions which were required to suppress slip dislocations that were due to thermal stresses were also predicted.

H.Shimizu, D.Sudou, T.Satoh, S.Saitou: Materials Transactions, 1997, 38[1], 69-77