Apparatus for processing a melt

1. An apparatus for processing a melt, comprising:

a crucible configured to contain the melt, the melt having an exposed surface that is separated from a floor of the crucible by a first distance;

a crucible heater disposed below the floor of the crucible and configured to deliver a heat flow to maintain the melt at or above a melting temperature of the melt; and

a submerged heater comprising a heating element and a shell disposed between the heating element and the melt, wherein the heating element does not contact the melt,

the heating element being disposed at a second distance with respect to the exposed surface of the melt that is less than the first distance, wherein the submerged heater is disposed above the crucible heater.

2. The apparatus of claim 1 , wherein the heating element comprises graphite that is coated with silicon carbide and the shell comprises fused silica.

3. The apparatus of claim 2 , wherein the heating element is surrounded by the melt.

4. The apparatus of claim 1 , wherein the melt is composed of silicon and the shell comprises fused silica.

5. The apparatus of claim 1 , wherein the submerged heater is configured to deliver a heat flow of greater than 50 W/cm 2 to the exposed surface.

6. The apparatus of claim 1 , wherein the submerged heater is elongated along a first direction parallel to the exposed surface.

7. The apparatus of claim 6 , wherein the heater has a heater width along the first direction of at least 15 cm.

8. The apparatus of claim 1 , further comprising a drive configured to move the submerged heater along a vertical direction that is perpendicular to the exposed surface.

9. The apparatus of claim 8 , wherein the submerged heater comprises a movable cap structure comprising:

a movable portion having a contact surface in contact with the melt and an outer surface that is in contact with the heating element; and

a fixed portion that forms part of a crucible wall of the crucible.

10. The apparatus of claim 1 , wherein the submerged heater comprises an upper region that forms a portion of a crucible wall of the crucible and is disposed closer to the exposed surface of the melt than the floor of the crucible, and wherein the heating element is disposed outside of the crucible wall.

11. A system for controlling heat flow within a melt, comprising:

a crucible configured to contain the melt, the melt having an exposed surface that is separated from a floor of the crucible by a first distance;

a submerged heater configured to contact the melt, the submerged heater comprising a heating element and a shell that is disposed between the heating element and the melt, wherein the melt does not contact the heating element,

the heating element being disposed at a second distance with respect to the melt that is less than the first distance, wherein the submerged heater is configured to deliver heat to a region of the exposed surface at a first heat flow rate;

a crucible heater disposed below the floor of the crucible and configured to deliver a third heat flow to maintain the melt at or above a melting temperature of the melt, wherein the submerged heater is disposed above the crucible heater; and

a crystallizer configured to remove heat from the region of the exposed surface at a second heat flow rate greater than the first heat flow rate.

12. The system of claim 11 , wherein the submerged heater comprises a graphite heating element that is encased by a fused silica shell.

13. The system of claim 11 , further comprising a crucible heater disposed below the floor of the crucible and configured to deliver a third heat flow to maintain the melt at or above a melting temperature of the melt.

14. The system of claim 11 , wherein the melt is composed of silicon and the shell portion is composed of fused silica.

15. The system of claim 11 , wherein the submerged heater is configured to deliver a heat flow of greater than 50 W/cm 2 to the exposed surface.

16. The system of claim 11 , wherein the crystallizer is configured to form a leading edge of a crystalline sheet along a first direction, and wherein the submerged heater is elongated along the first direction.

17. The system of claim 11 , further comprising a drive configured to move the submerged heater along a vertical direction that is perpendicular to the exposed surface.

18. A method to process a melt comprising

arranging the melt in a crucible; the melt having an exposed surface and lower surface that is in contact with a floor of the crucible, the exposed surface being separated from the lower surface by a first distance;

directing a first heat flow from a crucible heater disposed below the crucible to the exposed surface; and

directing a heat flow from a heating element of a submerged heater into a region of the exposed surface of the melt when the heating element is disposed at a second distance from the exposed surface that is less than the first distance,

wherein the melt does not contact the heating element, and wherein the submerged heater is disposed above the crucible heater.

19. The method of claim 18 , wherein the submerged heater comprises a fused silica shell that surrounds the heating element and contacts the melt, wherein the melt is silicon, the method further comprising:

directing the heat flow to into the region of the exposed surface at a first heat flow rate;

and removing heat from the region of the exposed surface at a second heat flow rate greater than the first heat flow rate.