Apparati for fabricating thin semiconductor bodies from molten material
A pressure differential can be applied across a mold sheet and a semiconductor (e.g. silicon) wafer (e.g. for solar cell) is formed thereon. Relaxation of the pressure differential can allow release of the wafer. The mold sheet may be cooler than the melt. Heat is extracted through the thickness of the forming wafer. The temperature of the solidifying body is substantially uniform across its width, resulting in low stresses and dislocation density and higher crystallographic quality. The mold sheet can allow flow of gas through it. The melt can be introduced to the sheet by: full area contact with the top of a melt; traversing a partial area contact of melt with the mold sheet, whether horizontal or vertical, or in between; and by dipping the mold into a melt. The grain size can be controlled by many means.
1. An apparatus for fabricating a semi-conductor body, the apparatus comprising:
a. means for retaining a molten semi-conductor material, having a surface;
b. a porous mold, comprising a forming surface;
c. means for providing a differential pressure regime such that pressure at at least a portion of the forming surface is less than pressure at the molten material surface;
d. means for contacting the forming surface to the molten material for a contact duration such that, for at least a portion of the contact duration,
the differential pressure regime is provided
such that a body of semi-conductor material, solidifies upon the forming surface; and
means for detaching the solidified body from the forming surface.
2. The apparatus of claim 1 , further comprising means for providing a functional material between the forming surface and the molten material.
3. The apparatus of claim 1 , further comprising means for controlling nucleation of grain growth.
4. The apparatus of claim 1 , further comprising means for controlling directionality of grain growth.
5. The apparatus of claim 1 , further comprising means for maintaining at least a portion of the forming face at a temperature below a melting point of the semiconductor material.
6. The apparatus of claim 1 , further wherein the mold has a spatially varied thickness.
7. The apparatus of claim 1 , further comprising means for providing a pressure differential that varies spatially with respect to the forming surface.
8. The apparatus of claim 1 , further wherein the mold has spatially varied thermal insulation.
9. The apparatus of claim 1 , the forming surface comprising a spatially varied texture.
10. The apparatus of claim 1 , further wherein the mold has a spatially varied thermal diffusivity.
11. The apparatus of claim 1 , further comprising means for providing area-specific temperature profile at the forming face.
12. The apparatus of claim 1 , further comprising means for providing a crystal seed at a location upon the forming surface that would first contact the molten material.
13. The apparatus of claim 1 , further comprising means for suppressing oscillatory motion of the surface of the molten material.
14. The apparatus of claim 1 , further comprising at least one baffle in the molten material.