Growth determination in the solidification of a crystalline material

1. A method of producing a crystalline material comprising the steps of:

i) providing a crystal growth apparatus comprising a chamber and a hot zone within the chamber, the hot zone comprising at least one heating system, at least one heat removal system, and a crucible containing at least solid feedstock;

ii) heating the solid feedstock in the crucible with the heating system to form a liquid feedstock melt;

iii) removing heat from the hot zone with the heat removal system to form a partially solidified melt comprising solidified crystalline material submerged in remaining liquid feedstock;

iv) determining an amount of solidified crystalline material in the partially solidified melt with at least one laser positioned at a height above the crucible by measuring a surface height of the remaining liquid feedstock with the laser, calculating a density of the partially solidified melt from the measured surface height, and comparing the density of the partially solidified melt to a density of the liquid feedstock, a density of the solidified crystalline material, or both; and

v) further solidifying the partially solidified melt to form the crystalline material.

2. The method of claim 1 , wherein the crystal growth apparatus is a directional solidification furnace.

3. The method of claim 1 , wherein the heat removal system comprises a helium-cooled heat exchanger positioned beneath the crucible.

4. The method of claim 1 , wherein the heat removal system comprises insulation positioned around the hot zone having at least one section vertically movable within the chamber.

5. The method of claim 1 , wherein the method further comprises the step of determining a rate of solidification by determining the amount of solidified crystalline material in the partially solidified melt with the laser over a desired time period.

6. The method of claim 5 , wherein the crystal growth apparatus further comprises at least one control system connected to the heating system, the heat removal system, or both, the control system being configured to control the step of removing heat from the hot zone by comparing the determined rate of solidification to a target rate of solidification.

7. The method of claim 1 , wherein the laser has an output detected by at least one sensor.

8. The method of claim 7 , wherein the output is detected by at least one specular light sensor.

9. The method of claim 7 , wherein the output is detected by at least one diffuse light sensor.

10. The method of claim 1 , wherein the laser is positioned outside the chamber.

11. The method of claim 10 , wherein the laser has on output directed through a port in the chamber positioned above the crucible, the output being reflected off of the remaining liquid feedstock back through the port to a detector.

12. The method of claim 10 , wherein the laser has an output directed through a first port in the chamber positioned above the crucible, the output being reflected off of the remaining liquid feedstock melt back through a second port in the chamber positioned above the crucible to a detector.

13. The method of claim 1 , wherein the solid feedstock comprises alumina.

14. The method of claim 13 , wherein the crystalline material is sapphire.

15. The method of claim 1 , wherein the solid feedstock comprises silicon, and wherein the laser has an output detected by a specular light sensor.

16. The method of claim 15 , wherein the crystalline material is silicon.

17. The method of claim 15 , wherein the crystalline material is monocrystalline silicon.