Compression Tests of Heat-Treated Czochralski-Grown Silicon Crystals

Compression tests are performed on dislocation-free Czochralski silicon crystals subjected to isothermal annealing at 800 °C and two-step annealing at 800 plus 1050 °C. Good correlation is obtained between the decrement of the upper yield stress σu and the increment of the etch pit density in the crystals. From the observation of inner defect structures by transmission electron microscope possible dislocation sources are discussed with regard to the stress-field around SiO2 precipitates. Among some types of thermally induced defects, rapidly grown SiO2 precipitates accompanying strong stress fields or prismatic dislocation loops are found to act as the dislocation nucleation centers. By the stress-relaxation tests, the locking effect of dislocations by dissolved oxygen atoms is confirmed for oxygen-rich Si crystals independently of the magnitude of σu.