Directional solidification of large pure silicon ingot

摘要

Process is for directional solidification of silicon as an ingot (30) in a bottomless metallic cold wall crucible (9) with an ingot-supporting cooling body (11) which is lowered relative to the crucible in accordance with further silicon supply and the solidification rate. The novelty is that: (a) a coarsely crystalline to monocrystalline seed, which initially closes the crucible (9) and which is superficially melted by the silicon melt, is placed in surface contact with the cooling body (11); and (b) the cooling body (11) is withdrawn, together with the seed (25) and the already solidified part of the ingot (30), from the crucible (9). Equipment for carrying out the above process comprises a furnace chamber (1) containing a bottomless metallic cold wall crucible (9), a heating system (7, 10, 20) and a device for vertical withdrawal of a directionally solidified silicon ingot (30), the novelty being that the withdrawal device consists of a cooling body (11) which closes the horizontal internal cross-section of the crucible (9) and which has a horizontal upper seating surface (24) on which a plane-parallel silicon seed (25) is placed.