The invention relates to a polysilicon
ingot casting method with low defect and high output and a thermal field structure thereof. The thermal field structure comprises a
thermal insulation cover
system, a
crucible system, split resistance heaters, a support part and a cooling device, wherein the three heaters are independently and separably controlled to lower
energy consumption to the maximum degree and bring convenience for regulating a
crystal growth interface, thereby obtaining an evener
crystal growth interface, improving
crystal quality and solving the later-stage cooling problem of the
crystal growth because of the increase of the height of the
ingot casting. A support block with the unique design and a cooling device are combined to realize the purpose of local cooling, so that the local position on the bottom of a
crucible generates cold spots at the early stage of the
crystal growth;
nucleation is carried out firstly to reduce
nucleation spots, and lateral
temperature gradient is obtained to provide the necessary condition for the lateral growth of the crystal
nucleus; crystalline grains are enlarged to reduce a crystal boundary to the large extent; and microdefects, such as
dislocation and the like, are lowered.