Wafer construction for making single-crystal semiconductor device
 Seed crystals are made in a region of a polycrystalline layer on a substrate by melting the region and then cooling it so that it solidifies from one end to the other in a first direction and outwardly toward the edges in a second direction normal to the first direction. The desired cooling pattern is established by providing a thermal layer under the polycrystalline layer, which thermal layer is used to provide different rates of heat conduction therethrough in different parts of the thermal layer. A large, single-crystal device can be made by providing an operating layer of polycrystalline material in contact with the seed, melting the operating layer and recrystallizing it so that its solidification proceeds from the seed. The thermal layer can be used to ensure the desired direction of resolidification by providing different rates of heat conduction therethrough in different parts of the thermal layer. 
Sony Corporation
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Setsuo Akikazu Yoshinori Akashi
Usui Shibata Hayafuji Sawada