Apparatus for forming crystalline sheet from a melt

Abstract

An apparatus for drawing a crystalline sheet from a melt. The apparatus may include a crucible configured to contain the melt and having a dam structure, where the melt comprises an exposed surface having a level defined by a top of the dam structure. The apparatus may further include 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 may include 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.

What is claimed is: 
     
         1 . A method of growing a crystalline sheet from a melt, comprising:
 forming the crystalline sheet on an exposed surface of a melt in a crucible having a dam structure, the exposed surface defined by a top of the dam structure;   measuring a first position of a surface of the crystalline sheet with respect to the exposed surface;   placing an upper surface of a support apparatus at a first level based on the first position; and   drawing the crystalline sheet along a first direction over the upper surface of the support apparatus wherein the crystalline sheet is maintained flush with the exposed surface.   
     
     
         2 . The method of  claim 1 , 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 placing the upper surface at the first level comprises moving the adjustable portion along the first direction from a first position to a second position while the adjustable portion is in contact with the fixed portion. 
   
     
     
         3 . The method of  claim 2 , wherein the fixed portion has a first contact surface defining a first angle of inclination with respect to 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. 
     
     
         4 . The method of  claim 1 , further comprising directing heat through the support apparatus to the crystalline sheet during the drawing, wherein a portion of the crystalline sheet disposed over the support apparatus melts back. 
     
     
         5 . A method of growing a crystalline sheet from a melt, comprising:
 forming the crystalline sheet on an exposed surface of a melt in a crucible;   drawing the crystalline sheet in a first direction along the exposed surface and over an upper surface of a support apparatus;   arranging the upper surface of the support apparatus at a first level when the crystalline sheet has a first thickness; and   moving the upper surface of the support apparatus from the first level to a second level when the crystalline sheet has a second thickness,   wherein the second level is closer to the exposed surface of the melt, and wherein the second thickness is less than the first thickness.   
     
     
         6 . The method of  claim 5 , 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 moving the upper surface of the support apparatus from the first level to the second level comprises moving the adjustable portion along the first direction from a first position to a second position while the adjustable portion is in contact with the fixed portion. 
   
     
     
         7 . The method of  claim 6 , wherein the fixed portion has a first contact surface defining a first angle of inclination with respect to 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. 
     
     
         8 . The method of  claim 5 , wherein the drawing the crystalline sheet along the first direction comprises drawing the crystalline sheet over a dam structure, the dam structure having a top that defines the exposed surface of the crystalline sheet. 
     
     
         9 . The method of  claim 8 , further comprising arranging a gas jet downstream of the dam structure, and directing a stream of gas from the gas jet to the melt, adjacent the dam structure. 
     
     
         10 . The method of  claim 9 , 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. 
     
     
         11 . The method of  claim 5 , further comprising
 measuring a first position of a surface of the crystalline sheet with respect to the exposed surface, wherein the arranging the upper surface of the support apparatus at the first level is based upon the measuring the first position.   
     
     
         12 . The method of  claim 5 , the forming the crystalline sheet comprising:
 positioning a crystallizer above the exposed surface of the melt, upstream to the support apparatus; and   removing heat from the exposed surface through the crystallizer, wherein a leading edge of the crystalline sheet forms at the exposed surface in a cooling zone.   
     
     
         13 . The method of  claim 5 , further comprising:
 directing heat from a heater to the crystalline sheet through the support apparatus, wherein a portion of the crystalline sheet is melted back during the drawing of the crystalline sheet.   
     
     
         14 . The method of  claim 13 , wherein a thickness of the crystalline sheet is reduced from the first thickness to the second thickness during the drawing, and wherein a roughness of the crystalline sheet is reduced during the drawing. 
     
     
         15 . The method of  claim 5 , wherein the crystalline sheet is maintained flush with the exposed surface of the melt during the drawing. 
     
     
         16 . The method of  claim 5 , wherein the melt comprises aluminum oxide and the crystalline sheet comprises sapphire. 
     
     
         17 . The method of  claim 5 , wherein the support apparatus comprises a refractory metal. 
     
     
         18 . A method of growing a crystalline sheet from a melt, comprising:
 removing heat from an exposed surface of the melt through a crystallizer, wherein a leading edge of the crystalline sheet forms at the exposed surface;   drawing the crystalline sheet over an upper surface of a support apparatus;   directing heat from a heater to the crystalline sheet through the support apparatus, wherein a portion of the crystalline sheet is melted back and a reduction in thickness of the crystalline sheet takes place during the drawing the crystalline sheet; and   adjusting a position of the upper surface of the support apparatus to accommodate for the reduction in thickness.   
     
     
         19 . The method of  claim 18 , 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 moving the upper surface of the support apparatus from the first level to a second level comprises moving the adjustable portion along the first direction from a first position to a second position while the adjustable portion is in contact with the fixed portion. 
   
     
     
         20 . The method of  claim 18 , wherein the adjusting comprises:
 arranging the upper surface of the support apparatus at a first level when the crystalline sheet has a first thickness; and   moving the upper surface of the support apparatus from the first level to a second level when the crystalline sheet has a second thickness,   wherein the second level is closer to the exposed surface of the melt, and wherein the second thickness is less than the first thickness.