Precipitates caused by prolonged high-temperature annealing in floating zone silicon wafer grown from Czochralski single-crystal rod

The behavior of precipitates in a floating zone silicon crystal produced from a Czochralski single-crystal ingot has been studied. Large precipitates of α-Si₃N₄ crystal, having a dimension of about 2 μm, were formed at the mid-depth in the wafer by annealing at a high temperature in an ambient N₂ (70%)+O₂ (30%) atmosphere. The number of precipitates detected by cross-sectional X-ray topography increased with increasing annealing time. Because preannealing accompanying silicon oxidation in an ambient Ar+O₂ atmosphere prevented the precipitates formation, interstitial silicon is considered to eliminate the origin of precipitate.