System and method for crystal growing
To reduce the heat input to the bottom of the crucible and to control heat extraction independently of heat input, a shield can be raised between a heating element and a crucible at a controlled speed as the crystal grows. Other steps could include moving the crucible, but this process can avoid having to move the crucible. A temperature gradient is produced by shielding only a portion of the heating element; for example, the bottom portion of a cylindrical element can be shielded to cause heat transfer to be less in the bottom of the crucible than at the top, thereby causing a stabilizing temperature gradient in the crucible.
1. A system for growing crystals from a liquid in a crucible, the system comprising:
a support structure to support the crucible from below;
a heat exchanger movable with respect to the support structure to extract heat from the support structure;
at least one heading element to heat the crucible; and
a movable shield movable relative to the at least one heating element and the crucible over a range of positions between the at least one heating element and the crucible.
2. The system of claim 1 , further comprising a controller to independently control the movement of the heat exchanger, the output of the heating element, and the position of the movable shield.
3. The system of claim 1 , wherein the support structure includes a graphite support block.
4. The system of claim 1 , wherein the heating element includes a plurality of electrical heating elements positioned to the side of the crucible.
5. The system of claim 1 , wherein the heat exchanger includes insulation that is movable away from the support structure such that the movement away from the support structure causes a loss of heat from the support structure.
6. The system of claim 5 , further comprising a controller to independently control the movement of the heat exchanger and the movable shield.
7. The system of claim 6 , wherein the controller causes the heat exchanger to move away from the support structure, and thereafter causes the movable shield to be moved to a position between the at least one heating element and the crucible.
8. The system of claim 1 , further comprising an outer housing for enclosing the heating elements, the housing having a floor and having one or more openings in the floor through which the movable shield is moved.
9. The system of claim 1 , wherein the crucible holds a crystal that is at least about 300 kg.
10. A system for growing crystals from a liquid in a crucible, the system comprising:
a support structure to support the crucible from below, the crucible being in a stationary position during the growing of crystals;
at least one heating element positioned laterally with respect to the crucible to heat the crucible;
a housing for enclosing the crucible and the support structure and having a floor under the crucible; and
a movable shield movable relative to the at least one heating element and the crucible over a range of positions between the at least one heating element and to crucible, the shield extending through the floor of the housing.
11. The system of claim 10 , wherein the support structure includes a graphite support block.
12. The system of claim 10 , wherein the crucible hold a crystal that is at least about 300 kg.
13. The system of claim 10 , wherein the heating element includes a plurality of electrical heating elements positioned to the side of the crucible.