Growth of multicrystalline Si ingots using noncontact crucible method for reduction of stress

Stress control is necessary when preparing high-quality multicrystalline Si ingots using crucibles because crystal defects such as dislocations are mainly generated by stress in the ingots. Conventional crystal growth methods using crucibles cannot control the stress caused by expansion due to the solidification of the Si melt. We proposed a noncontact crucible method using conventional crucibles that reduces the stress in Si multicrystalline ingots. In this method, nucleation occurs on the surface of a Si melt using seed crystals, and crystals grow inside the Si melt without touching the crucible walls. Then, the ingots continue to grow while being slowly pulled upward to ensure that the crystal growth remains in the low-temperature region. The diameter and solidification ratio of the ingots can be controlled by reducing the melt temperature in the low-temperature region and by varying the product of the temperature reduction from the melting point of Si and the total growth time, respectively. A Si ingot with a diameter of 21 cm and a solidification ratio of 83% was obtained in a crucible with a diameter of 30 cm. We have confirmed that ingot growth in a crucible is feasible, during which the ingot does not come in contact with the crucible walls.