Apparatus for forming crystalline sheet from a melt

1. An apparatus for drawing a crystalline sheet from a melt, comprising:

a crucible configured to contain the melt and having a dam structure, the melt comprising an exposed surface having a level defined by a top of the dam structure; a support apparatus disposed within the crucible and having an upper surface, wherein the crystalline sheet is maintained flush with the exposed surface of the melt when drawn over the support apparatus, wherein the upper surface of the support apparatus is disposed below the crystalline sheet and parallel to the exposed surface of the melt, wherein the support apparatus comprises:

a fixed portion extending from a bottom of the crucible; and

an adjustable portion, the adjustable portion defining the upper surface of the support apparatus, wherein the adjustable portion is movable from a first position where the upper surface is disposed at a first level with respect to the top of the dam structure, to a second position where the upper surface is disposed at a second level with respect to the top of the dam structure.

2. The apparatus of claim 1 , wherein the melt comprises aluminum oxide and the crystalline sheet comprises sapphire.

3. The apparatus of claim 1 , wherein the adjustable portion is in contact with the fixed portion in the first position and second position.

4. The apparatus of claim 1 , wherein the fixed portion has a first contact surface defining a first angle of inclination with respect to a horizontal, wherein the adjustable portion has a second contact surface in contact with the first contact surface and disposed at the first angle of inclination, and wherein the upper surface of the support apparatus is parallel to the horizontal.

5. The apparatus of claim 1 , wherein the support apparatus comprises a refractory metal.

6. The apparatus of claim 1 , further comprising a gas jet disposed downstream of the dam structure directing a stream of gas to the melt adjacent the dam structure.

7. The apparatus of claim 6 , the gas jet generating a first curvature of a meniscus between the melt and support apparatus different than a second curvature of the meniscus between the melt and support apparatus when the gas jet is not present.

8. An apparatus for growing a crystalline sheet from a melt, comprising:

a crucible configured to contain the melt and having a dam structure, the melt having an exposed surface defined by a top of the dam structure;

a crystallizer disposed above the melt to remove heat in a cooling zone from the exposed surface of the melt, wherein a leading edge of the crystalline sheet forms at the exposed surface in the cooling zone, the crystalline sheet having an initial sheet thickness; and

a support apparatus disposed within the crucible beginning and ending downstream of the crystallizer and having an upper surface, wherein the crystalline sheet is maintained flush with the exposed surface of the melt when drawn over the support apparatus, wherein the upper surface of the support apparatus is parallel to the exposed surface of the melt.

9. The apparatus of claim 8 , wherein the melt comprises aluminum oxide and the crystalline sheet comprises sapphire.

10. The apparatus of claim 8 , wherein the support apparatus comprises:

a fixed portion extending from a bottom of the crucible; and

an adjustable portion, the adjustable portion defining the upper surface of the support apparatus, wherein the adjustable portion is movable from a first position where the upper surface is disposed at a first level with respect to the top of the dam structure, to a second position where the upper surface is disposed at a second level with respect to the top of the dam structure.

11. The apparatus of claim 10 , wherein the adjustable portion is in contact with the fixed portion in the first position and second position.

12. The apparatus of claim 10 , wherein the fixed portion has a first contact surface defining a first angle of inclination with respect to a horizontal, wherein the adjustable portion has a second contact surface in contact with the first contact surface and disposed at the first angle of inclination, and wherein the upper surface of the support apparatus is parallel to the horizontal.

13. The apparatus of claim 8 , wherein the support apparatus comprises a refractory metal.

14. The apparatus of claim 8 , further comprising a melt-back heater directing heat through the upper surface of the support apparatus to partially melt the crystalline sheet when the crystalline sheet is drawn over the support apparatus.

15. The apparatus of claim 14 , the melt-back heater disposed below a section of the crucible adjacent the support apparatus.

16. An apparatus for drawing a crystalline sheet from a melt, comprising:

a crucible configured to contain the melt and having a dam structure, the melt comprising an exposed surface having a level defined by a top of the dam structure;

a support apparatus disposed within the crucible and having an upper surface, wherein the crystalline sheet is maintained flush with the exposed surface of the melt when drawn over the support apparatus; and

a melt-back heater directing heat through the upper surface of the support apparatus to partially melt the crystalline sheet when the crystalline sheet is drawn over the support apparatus, wherein the support apparatus comprises:

a fixed portion extending from a bottom of the crucible; and

an adjustable portion, the adjustable portion defining the upper surface of the support apparatus, wherein the adjustable portion is movable from a first position where the upper surface is disposed at a first level with respect to the top of the dam structure, to a second position where the upper surface is disposed at a second level with respect to the top of the dam structure.