Effects of Oxygen Precipitation on Minority Carrier Lifetime in Silicon Crystals

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Abstract
Infrared (IR) absorption measurements of the interstitial oxygen concentration [O] for two-step annealed wafers, with reverse recovery time Trr and capacitance relaxation time Ts measurements on processed devices, have been used to investigate the influence of oxygen on the minority carrier lifetime (τ) in a Czochralski-grown silicon crystal. Measurements of Trr and Ts show a strong dependence on the axial distribution of the initial interstitial oxygen concentration and on the concentration of precipitated oxygen. For a two-step anneal at 800°C and 1050°C for 16 h, the maximum average lifetimes of 4 µs and 180 µs are obtained from Trr and Ts respectively in wafers with an initial oxygen concentration [O]i ⋍ 1.3 × 1018 cm−3, where oxygen precipitation is minimal. Minimum lifetime values of 0.31 μs and 10 μs for the same respective measurements are obtained for wafers with [O]i ≥ 1.8 × 1018 cm−3, where oxygen precipitation dominates. The experimental results indicate that oxygen precipitation is the dominant mechanism contributing to the degradation of minority carrier lifetime. The detection of an SiO2 phase in the infrared spectrum and the detection of precipitate platelets in these wafers subsequent to the two-step anneal provide additional supporting evidence of a direct relation between oxygen precipitation and minority carrier lifetime degradation.