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Low-Temperature-Induced Oxygen Precipitation Retardation Phenomenon in Czochralski Silicon-Effect of High-Temperature Preannealing and Other Related Phenomena

Two-step (low-high) and three-step (high-low-high) annealing experiments were systematically carried out on silicon wafers with both high and low carbon content to study the oxygen precipitation behavior under different thermal cycles. In the two-step anneal, the low-temperature step (750°C for 0-128 h) is for SiO2 precipitate nucleation and the high-temperature step (1050°C for 0-40 h) is for SiO2 precipitate growth. In the three-step anneal, a short wet oxidation cycle precedes the two-step anneal. The thermal history was found to have a great influence on the oxygen microdefects and precipitate morphology, as well as on the carbon reduction behavior. Oxygen precipitation retardation was observed after moderate annealing at low temperature for the two-step-annealed samples. This retardation did not occur in the three-step-annealed samples. It is tentatively concluded that the nuclei of the rodlike defects, which can grow at low temperature but dissolve at high temperature, play a dominant role in the phenomena observed in the two-step anneal.