Effect of thermal history on oxygen precipitates in Czochralski silicon annealed at 1050 °C

The precipitation of oxygen in bulk Czochralski silicon wafers subjected to single-step isothermal, two-step (low-high), two-step (high-high), and three-step (high-low-high) annealing is studied by means of infrared spectroscopy and by preferential etching. Comparisons are made with transmission electron micrographs obtained on similar wafers. With the same amount of precipitated oxygen, the IR spectra near 1230 cm−1 and the precipitate morphology are different for samples that undergo different thermal cycles. For the single-step and three-step annealed samples, platelet precipitates are the dominant defect type and a peak is observed at 1230-cm−1. For the two-step annealed samples, the majority defects are polyhedral precipitates and stacking faults, no platelet precipitates are found and the 1230-cm−1 peak is absent. It is believed that the stacking faults generated during two-step annealing have a strong effect in converting the oxygen precipitate morphology from platelets to polyhedra. A model is proposed to explain this phenomenon according to the coarsening concept.