Theoretical study of the impact of stress on the behavior of intrinsic point defects in large-diameter defect-free Si crystals

For the development of the crystal pulling process for 450 mm-diameter defect-free Si crystals, it is important to evaluate the impact of thermal stress on intrinsic point defect behavior during crystal growth. In this study, we evaluated the impact of thermal stress between -30 MPa (tensile) and 30 MPa (compressive), which covers the complete range of stress levels that can be expected in mass production for 450 mm-diameter crystals, on the so-called Voronkov criterion. This criterion predicts the dominant point defect based on a critical pulling speed over axial temperature gradient ratio. The internal pressure dependencies of both the formation and the migration enthalpies of intrinsic point defects were obtained with a density functional theory study, and it was found that assuming internal stress only, the thermal stress shifts the growing Si crystal towards more vacancy-rich under compressive and towards more self-interstitial-rich under tensile stresses. Also Si crystals containing interstitial clusters and heavily doped crystals were studied to evaluate the effect of thermal and dopant-related stresses on the intrinsic point defect formation and diffusivity. It was concluded that the experimentally observed increase in the number of interstitial clusters and the increase in the concentration of self-interstitials in heavily doped Si cannot be explained by the thermal and/or dopant-related stresses. (C) 2012 Elsevier B.V. All rights reserved.