Vacancy-related microdefects responsible for the formation of oxidation-induced stacking faults with ring-shaped distribution (R-OSFs) in Czochralski-grown Si

Abstract

Thermal oxidation of large-sized Si wafers often results in the formation of a ring-shaped distribution of oxidation-induced stacking faults (the so-called R-OSF). A related phenomenon is the formation of annular bands of reduced oxygen precipitation in Si wafers heat-treated around . It is generally thought that these microdefect patterns are due to a local excess in self-interstitials established in growing crystals. Recently we have reported a model describing the formation of R-OSFs, which includes the premise that the grown-in vacancy-related microdefects ( defects) serve as nucleation centres for R-OSFs. The R-OSFs are found to emerge in those regions where the concentration of low-temperature centres for oxygen precipitation is locally reduced as a consequence of vacancy depletion. Here we report experiments that allow the determination of point-defect species involved in the formation of R-OSF nucleation centres during crystal growth. The selective interaction of {221}/{221} twin boundaries with native point defects is used for discriminating vacancies and self-interstitials. Dislocation-free Si tetracrystals grown under conditions that ensure transitions from the self-interstitial to vacancy defects are examined. The etching features of the {221}/{221} twin boundaries, which separate tetracrystals into four grains, differ between the vacancy and interstitial regions. The type and distribution of grown-in and thermally induced microdefects as well as the etching patterns developing at the twin boundaries suggest that it is vacancies rather than self-interstitials that are responsible for the formation of R-OSF nucleation centres in growing crystals.