METHOD FOR PRODUCING MONOCRYSTALLINE METAL OR SEMI-METAL BODIES
First Claim
1. A method for producing a monocrystalline metal or semi-metal body by directional solidification, comprising the steps of:
- melting a semi-metal or metal raw material in a melting crucible to form a melt or introducing a semi-metal or metal melt into the melting crucible,directional solidification of the melt under the action of a temperature gradient pointing in a vertical direction and from the upper end of the melting crucible to the lower end thereof to form the monocrystalline metal or semi-metal body,prior to the introduction of the semi-metal or metal raw material or of the melt into the melting crucible, completely covering the bottom of the melting crucible with a thin monocrystalline seed crystal plate layer having a crystal orientation parallel to the vertical direction of the melting crucible; and
keeping the temperature of the bottom of the melting crucible at a temperature below the melting temperature of the raw material or of the melt in order to prevent melting of the seed crystal plate layer in any case down to the bottom of the melting crucible;
in which method;
the thin monocrystalline seed crystal plate layer comprisesa) a plurality of thin monocrystalline seed crystal plates of the same size arranged directly adjoining one another in order completely to cover the bottom of the melting crucible orb) an integral monocrystalline seed crystal plate in which at least one dislocation line is formed, which divides the individual monocrystalline seed crystal plate into seed crystal plate sub-portions of the same size; and
the monocrystalline metal or semi-metal body is divided by sawing along at least one sawing line extending in parallel with the crystal orientation into a plurality of monocrystalline metal or semi-metal bodies;
whereinthe start of the respective sawing line is selected in such a way that said start is defined by the edge of a seed crystal plate or by a respective dislocation line within the integral monocrystalline seed crystal plate.
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Accused Products
Abstract
The invention relates to the production of bulky monocrystalline metal or semi-metal bodies, in particular of a monocrystalline Si ingot, using the vertical gradient freeze (VGF) method by directional solidification of a melt in a melting crucible having a polygonal basic shape.
According to the invention, the entire bottom of the melting crucible is completely covered with a thin seed crystal plate made of the monocrystalline semi-metal or metal. Throughout the procedure, the bottom of the melting crucible is kept below the melting temperature of the semi-metal or metal in order to prevent melting of the seed crystal plate.
Monocrystalline ingots produced in this way are distinguished by a low average dislocation density of for example less than 105 cm−2, allowing the production of very efficient monocrystalline Si solar cells.
46 Citations
15 Claims
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1. A method for producing a monocrystalline metal or semi-metal body by directional solidification, comprising the steps of:
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melting a semi-metal or metal raw material in a melting crucible to form a melt or introducing a semi-metal or metal melt into the melting crucible, directional solidification of the melt under the action of a temperature gradient pointing in a vertical direction and from the upper end of the melting crucible to the lower end thereof to form the monocrystalline metal or semi-metal body, prior to the introduction of the semi-metal or metal raw material or of the melt into the melting crucible, completely covering the bottom of the melting crucible with a thin monocrystalline seed crystal plate layer having a crystal orientation parallel to the vertical direction of the melting crucible; and keeping the temperature of the bottom of the melting crucible at a temperature below the melting temperature of the raw material or of the melt in order to prevent melting of the seed crystal plate layer in any case down to the bottom of the melting crucible; in which method; the thin monocrystalline seed crystal plate layer comprises a) a plurality of thin monocrystalline seed crystal plates of the same size arranged directly adjoining one another in order completely to cover the bottom of the melting crucible or b) an integral monocrystalline seed crystal plate in which at least one dislocation line is formed, which divides the individual monocrystalline seed crystal plate into seed crystal plate sub-portions of the same size; and the monocrystalline metal or semi-metal body is divided by sawing along at least one sawing line extending in parallel with the crystal orientation into a plurality of monocrystalline metal or semi-metal bodies;
whereinthe start of the respective sawing line is selected in such a way that said start is defined by the edge of a seed crystal plate or by a respective dislocation line within the integral monocrystalline seed crystal plate. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A monocrystalline silicon wafer, produced by sawing from a silicon ingot produced by directional solidification, comprising the steps of:
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melting a semi-metal or metal raw material in a melting crucible to form a melt or introducing a semi-metal or metal melt into the melting crucible, directional solidification of the melt under the action of a temperature gradient pointing in a vertical direction and from the upper end of the melting crucible to the lower end thereof to form the monocrystalline metal or semi-metal body, prior to the introduction of the semi-metal or metal raw material or of the melt into the melting crucible, completely covering the bottom of the melting crucible with a thin monocrystalline seed crystal plate layer having a crystal orientation parallel to the vertical direction of the melting crucible; and keeping the temperature of the bottom of the melting crucible at a temperature below the melting temperature of the raw material or of the melt in order to prevent melting of the seed crystal plate layer in any case down to the bottom of the melting crucible; in which method; the thin monocrystalline seed crystal plate layer comprises a) a plurality of thin monocrystalline seed crystal plates of the same size arranged directly adjoining one another in order completely to cover the bottom of the melting crucible or b) an integral monocrystalline seed crystal plate in which at least one dislocation line is formed, which divides the individual monocrystalline seed crystal plate into seed crystal plate sub-portions of the same size; and the monocrystalline metal or semi-metal body is divided by sawing along at least one sawing line extending in parallel with the crystal orientation into a plurality of monocrystalline metal or semi-metal bodies;
whereinthe start of the respective sawing line is selected in such a way that said start is defined by the edge of a seed crystal plate or by a respective dislocation line within the integral monocrystalline seed crystal plate; said monocrystalline silicon wafer having a dislocation density (etch pit density;
EPD) of less than 105 cm−
2.
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Specification