Methods for producing crucibles with a reduced amount of bubbles
View Patent ↗Methods for producing crucibles for holding molten material that contain a reduced amount of gas pockets are disclosed. The methods may involve use of molten silica that may be outgassed prior to or during formation of the crucible. Crucibles produced from such methods and ingots and wafers that are produced from crucibles with a reduced amount of gas pockets are also disclosed.
1. A process for producing a crucible for holding molten silicon, the crucible having a base and one or more sidewalls, the process comprising:
forming a composition comprising molten silica and a fining agent to prevent bubble formation, the fining agent selected from the group consisting of arsenic oxide, antimony oxide, KNO 3 , NaNO 3 , NaCl, a fluoride salt, a sulfate salt, and any combination thereof in a vessel;
discharging the composition comprising molten silica and the fining agent from the vessel into a mold or onto a mandrel;
applying a force to the composition comprising molten silica to thereby mold the molten composition into the shape of (1) a crucible having a base and one or more sidewalls, (2) a plate or (3) a tube; and
cooling the molten composition to solidify the composition, wherein when the molten composition is molded into the shape of a plate or a tube, the plate or tube is shaped into the form of a crucible having a base and one or more sidewalls.
2. The process as set forth in claim 1 wherein the molten composition is molded into the shape of a crucible, the composition being molded by pouring the composition into a mold.
3. The process as set forth in claim 1 wherein the molten composition is molded into the shape of a crucible, the composition being molded by pouring the composition over a mandrel and shaping the composition into the form of a crucible.
4. The process as set forth in claim 1 wherein the molten composition is annealed after the force is applied to the composition comprising molten silica, which molds the molten composition into the shape.
5. The process as set forth in claim 1 wherein the source of silica is melted by heating the source of silica to a temperature of at least about 1700° C.
6. The process as set forth in claim 1 wherein the source of silica is melted by heating the source of silica to at least its softening point.
7. The process as set forth in claim 6 wherein the softening point is about 1683° C.
8. The process as set forth in claim 1 wherein the crucible is cooled to below the strain point, wherein the instantaneous cooling rates at temperatures above the strain point are less than about 1° C./min.
9. The process as set forth in claim 8 wherein the strain point occurs between about 1000° C. to about 1200° C.
10. The process as set forth in claim 1 wherein the molten composition is molded in to the shape of a plate, the method further comprising heating the plate while the plate is shaped into the form of a crucible.
11. The process as set forth in claim 1 wherein the molten composition is molded in to the shape of a tube, the tube having an end portion that is shaped to form the base of the crucible.
12. The process as set forth in claim 1 wherein the molten composition comprises at least about 10 wt % silica.
13. The process as set forth in claim 1 wherein the source of silica is quartz sand, quartz powder, reclaimed glass or cullet.
14. The process as set forth in claim 1 wherein the crucible contains less than about 70 bubbles with a diameter of at least about 14 μm per cm 3 .
15. The process as set forth in claim 1 wherein the crucible is substantially free of bubbles with a diameter of at least about 14 μm.
16. The process as set forth in claim 1 wherein at least about 75% of the bubbles in the crucible have a nominal diameter of less than about 14 μm.
17. The process as set forth in claim 1 wherein the crucible has a thickness of at least about 6 mm.
18. The process as set forth in claim 1 wherein the molten composition comprises at least about 95 wt % silica.
19. A process for producing a crucible for holding molten material, the crucible having a base and one or more sidewalls, the process comprising the following steps in order:
discharging molten silica from a vessel into a mold or onto a mandrel;
applying a force to the molten silica to thereby mold the molten silica into the shape of (1) a crucible having a base and one or more sidewalls, (2) a plate or (3) a tube;
annealing the shaped molten silica at a temperature between about 1400° C. and about 1600° C.; and
cooling the molten composition to solidify the composition, wherein when the molten composition is molded into the shape of a plate or a tube, the plate or tube is shaped into the form of a crucible having a base and one or more sidewalls.
20. The process as set forth in claim 19 wherein the anneal is performed for at least about 60 minutes.