Dependence of Mechanical Strength of Czochralski Silicon Wafers on the Temperature of Oxygen Precipitation Annealing

Dependence of mechanical strength of Czochralski silicon (CZ-Si) wafers on the temperature of oxygen precipitation annealing has been studied both experimentally and theoretically. Thermal stress was applied to CZ-Si wafers after oxygen precipitation annealing at 1100°C or 1000°C after preannealing at 800°C. The warpages and the densities of slip dislocations in the wafers annealed at 1100°C are much higher than those in the wafers annealed at 1000°C, nevertheless each precipitate density is almost equal. Transmission electron microscopy observations of the 1100°C samples showed that both platelet and polyhedral precipitates were generated, but very few of these precipitates actually generated punched-out dislocations. In contrast, in the 1000°C samples, only platelet precipitates were generated, many of which generated punched-out dislocations. Further studies showed that slip dislocations formed only from platelets which did not punch out dislocations, i.e., slip dislocations formed only in the 1100°C samples. The mechanism of the generation of slip dislocation by oxide precipitates is discussed with calculated results of the system energy change due to slip dislocation generation.