Crystallization behavior of semiconducting materrials from Undercooled Melts

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Over the past several decades silicon has been one of the most important industrial materials. In this period, electronics industries have strived to increase the size of ingots in order to lower the cost of chip production. The larger the diameter, however, the higher the amount of investments in plants and equipment for processing the substrate has to be. Recently, a challenging idea that will reduce the cost has been proposed ; that is to mount integrated circuit on the surface of small spherical silicon crystal. However, the technique of growing such spherical single crystals needs to be developed. In the present study, the crystallization from the unedercooled drop of silicon was carried out by means of techniques of containerless processing under the controlled undercooling. The measured growth rate vs. undercooling was categorized into three regions, IA, IB, II and III, respectively, from the point of the interface morphology. A thin plate crystal whose interface consisted of bo … More th faceted (III) plane and wavy edge plane like saw-tooth was observed in the region IA where the undercooling is less than 40 K. The Thin plate crystal branched to several plates in the region IB where the undercooling from 40K to 100K. In the region II where the undercolling is from 100K to 200K, regularly arrayed faceted dendrite was observed, whereas irregularly arrayed dendrite was observed in the region III where the undercooling is beyond 200K. Assuming the morphological change of the interface as the three-dimensional destabilization of the edge plane, the critical undercooling for the transition from region I to region II was theoretically estimated as 100 K for the samples whose diameter is 5mm. The theoretical treatment predicts that the critical undercooling will depend on the sample size, that is, the smaller the sample size, the larger die critical undercooling. The sample seeded at temperatures in the region I is a quasisingle crystal with a large grain, except a small area where twinning and a cracking are observed. The result suggests that a single crystal could be grown, if a smaller sample, for instance, 2 or 3mm in diameter, were used. Less