Growth of high-quality multicrystalline Si ingots using noncontact crucible method

Conventional crystal growth methods using silica crucibles cannot control the stress caused by expansion due to the solidification of the Si melt because crucible walls made of silica have insufficient flexibility to reduce the stress. In the case of crystal growth using a silicon nitride crucible, it was reported that an ingot can be more easily released from the crucible. A noncontact crucible method was proposed using conventional silica crucibles that reduces the stress and number of dislocations in Si multicrystalline ingots. We used the present method to grow wafers with only twin boundaries. An ingot with several grains and twin boundaries was realized using a crucible that had not been coated with Si3N4 particles. Several important characteristics were reported such as the presence of a low-temperature region in the Si melt, the possibility of growing large ingots with a diameter close to the crucible diameter, the minority carrier lifetime, the distribution of dislocations, the O concentration and the effect of Si3N4 particles on the crystal structure. Dislocations were almost undetectable in a large area of the cross section when a necking technique was used for the seed growth. The O concentration in ingots grown using crucibles coated with Si3N4 particles was lower than that in an ingot grown using a crucible without a coating of Si3N4 particles. A large ingot with a diameter of 25 cm was obtained using a crucible with a diameter of 33 cm.

► Ingots with large areas which had only twin boundaries were obtained by the noncontact crucible method.
► The largest ingot with the diameter of 25 cm was obtained using a small crucible with 33 cm diameter.
► Regions with a low minority carrier lifetime disappeared using the necking technique except for the stringlike region.
► An ingot with several grains and twin boundaries was realized using a crucible not coated with Si3N4 particles.
► Dislocations were very low in large areas of the ingot.