Mechanism to form ring-like distributed oxidation-induced stacking fault bands through relaxing thermal stress during stopping the growth in CZ silicon crystals

Abstract

This paper aims to study the mechanism to form ring-like distributed oxidation-induced stacking fault (R-OSF) bands in CZ silicon. In this experiment, pulling crystals was stopped during the growth, and the crystals were held for predetermined periods contacting the melt while the seed rotation and converse crucible rotation were maintained. Then, the crystals were detached from the melt and cooled rapidly to freeze the defect distribution. In CZ crystals during the growth, high-temperature mass (crystalized silicon) is transferred upward from the growth interface with the crystal pulling. The top of the crystals is directly cooled by the cooling water chamber, while the peripheral part is heated by the radiation from the heater through the gap under the heat shield and the radiation from the melt surface. Thus, the temperature of the upper center part becomes lower than that of the peripheral part, and isotherms in the crystal form U-shape. When the growth is stopped, the crystals also stop raising the “high-temperature mass” from the growth interface. Thus, cooling rapidly proceeds from the center upper part to the growth interface, and the U-shape isotherms fall downward. When the temperature of a region along a U-shaped isotherm decreases to around 1000 ℃, and a temperature gradient exceeding a certain threshold also forms vertically to the U-shaped isotherm, a thermal stress (expansion stress) is applied from the high-temperature side part to the low-temperature center part. At this time, oxygen precipitates, the nuclei of the R-OSFs, are presumably generated there to relax the thermal stress. Although some researchers have presumed that the R-OSF band is a vacancies (Vs)/interstitials (Is) boundary formed at a temperature near the melting point, the results of this study contradict their presumption.