Invited) Swirl Defects in Silicon Crystals

The current understanding of microdefects in a striated distribution (swirls) in dislocation-free crystals is reviewed with focusing on their formation mechanism. In float-zoned crystals, their formation is due to clustering of self-interstitials and/or impurity segregation which depend upon both growth conditions and cooling processes. A model for the origin of self-interstitials is proposed which is based on the in-situ X-ray topographic observation that liquid drops are formed inside of crystals by superheating and microdefects are generated by their solidification. A systematic presentation of the swirl formation is attempted in the basis of this model, in contrast with other models of the non-equilibrium incorporation of interstitials at the growth interface and the predominant equilibrium existence of interstitials near the melting point. For Czochralski-grown crystals, the nucleation center of oxygen precipitates is discussed in comparison with the swirl formation of float-zoned crystals.