Crystallization behavior of semiconducting materrials from Undercooled Melts

在过去的几十年里，硅一直是最重要的工业材料之一。在此期间，电子工业一直在努力增加铸锭的尺寸，以降低芯片生产的成本。然而，直径越大，对加工基材的工厂和设备的投资就越高。最近，有人提出了一个具有挑战性的想法，可以降低成本；即在小的球形硅晶体表面安装集成电路。然而，这种球形单晶的生长技术还有待发展。本研究在可控过冷条件下，采用无容器加工技术对硅的过冷液滴进行结晶。从界面形貌的角度将生长速率与过冷度分别划分为IA、IB、II和III三个区域。在过冷度小于40k的IA区，观察到多面（III）面和锯齿状的波状边缘面。薄板晶体在40K至100K过冷的IB区分支成多个板。在过冷度为100K ~ 200K的II区，观察到有规则排列的多面枝晶，而在过冷度超过200K的III区，观察到有不规则排列的枝晶。假设界面的形态变化为边缘平面的三维失稳，理论上估计直径为5mm的试样从I区过渡到II区的临界过冷度为100 K。理论处理预测临界过冷度将取决于样品尺寸，即样品尺寸越小，模具临界过冷度越大。在区域I温度下播种的样品是具有大晶粒的准单晶，除了观察到孪晶和裂纹的小区域。结果表明，如果使用较小的样品，例如直径为2或3毫米的样品，可以生长出单晶。少

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