Mechanisms of defect formation and growth during thermal ramping and annealing in oxygen implanted silicon-on-insulator material

The development of defects in high-dose oxygen implanted silicon-on-insulator (SIMOX) material during thermal ramping and annealing was directly studied by weak beam and high resolution electron microscopy. The ramping and annealing cycle was simulated by annealing a series of samples for 2 h at temperatures from 700 to 1250°C. Short stacking faults, 10-30 nm lenght, are present in as-implanted material in the superficial silicon layer with some extending to the wafer surface from small, near-surface precipitates. During annealing from 900 to 1100°C the near-surface precipitates grow and generate additional stacking faults, some of which grow downward through the superficial silicon layer toward the buried oxide. At higher annealing temperatures the near-surface precipitates dissolve, but stacking faults are stabilized by the wafer free surface and by precipitates near the buried oxide. Lateral dislocation segments also from between precipitates near the buried oxide during thermal ramping. At the latter stages of high temperature annealing, precipitates and lateral pinned dislocations are incorporated into the buried oxide, but defects running through the superficial silicon layer are stabilized by the wafer surface and by the buried oxide, resulting in a high defect density of 10⁹ cm^-2. Techniques for processing SIMOX for defect density reduction are discussed in terms of the role of the defect formation mechanisms.