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An investigation of two industrially cast quasi-monocrystalline silicon blocks revealed a high dislocation density originating at intersections between the seed crystals. This may be ascribed to three different generation mechanisms. Firstly, a dislocation cell structure was observed in the seed crystals, probably as an effect of poor surface preparation of the seeds. Furthermore, clusters of dislocations form around contact points in the interface between two neighbouring seeds. At contact points, the two monocrystalline silicon seeds plastically deform and sinter together. Dislocation rosettes form as a result of an indentation mechanism at high temperatures. A third mechanism acts at the bottom surface, where dislocation clusters also form by indentation of contact points between the seed and the crucible. Since dislocations forming in the seeds will continue into the growing ingot, it is crucial to depress the dislocation formation in the seeds. |
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