Heat-treatment behavior of microdefects and residual impurities in CZ silicon crystals

Abstract

Thermal behavior of both microdefects and residual impurities in pulled silicon wafers has been studied, using x-ray diffraction and infrared absorption techniques. Several tens of wafers from different suppliers have been investigated after heat treatments at temperatures between 450 and 1250 °C. The results separate the wafers into two categories. In some wafers (category I), interstitial oxygen content is significantly decreased by heat treatments at temperatures between 650 and 800 °C. A high microdefect density is induced by heat treatment at a high temperature around 1050 °C. On the other hand, only slight oxygen reduction and defect introduction by heat treatments occur in other wafers (category II). Conversion from the category I to the category II wafers and vice versa are successfully performed by adding an appropriate preannealing. It is proposed that the wafer category depends on both the carbon content and thermal history of the crystal in addition to the oxygen content.