Method for preparing polycrystalline silicon ingot

• US 10,227,711 B2
• Filed: 11/21/2016
• Issued: 03/12/2019
• Est. Priority Date: 04/01/2012
• Status: Active Grant

• Current Assignee: Jiang Xi Sai LDK Solar High-Tech Co., Ltd.
• Original Assignee: Jiang Xi Sai LDK Solar High-Tech Co., Ltd.
• Inventors: Hu, Dongli, He, Liang, Wan, Yuepeng, Lei, Qi, Chen, Hongrong, Zhang, Tao, Zhong, Dejing
• Primary Examiner(s): Zimmer, Anthony J
• Application Number:
  US15/357,707
• Publication Number:
  US 20170167051A1
• Time in Patent Office: 841 Days
• CPC Class Codes: C30B 11/00 Single-crystal growth by normal freezing or freezing under temperature gradient, e.g. Bridgman-Stockbarger method C30B13/00, C30B15/00, C30B17/00, C30B19/00 take precedence; under a protective fluid C30B27/00
• CPC Class Codes: C30B 11/003 Heating or cooling of the melt or the crystallised material
• CPC Class Codes: C30B 11/006 Controlling or regulating
• CPC Class Codes: C30B 11/02 without using solvents C30B11/06 takes precedence
• CPC Class Codes: C30B 11/04 adding crystallising materials or reactants forming it in situ to the melt
• CPC Class Codes: C30B 11/14 characterised by the seed, e.g. its crystallographic orientation
• CPC Class Codes: C30B 28/06 by normal freezing or freezing under temperature gradient
• CPC Class Codes: C30B 29/06 Silicon
• CPC Class Codes: H01L 29/04 characterised by their crystalline structure, e.g. polycrystalline, cubic or particular orientation of crystalline planes characterised by physical imperfections H01L29/30
• CPC Class Codes: H01L 29/16 including, apart from doping materials or other impurities, only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/03682 including only elements of Group IV of the Periodic Table
• CPC Class Codes: H01L 31/182 Special manufacturing methods for polycrystalline Si, e.g. Si ribbon, poly Si ingots, thin films of polycrystalline Si
• CPC Class Codes: Y02E 10/546 Polycrystalline silicon PV cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

Disclosed is a method for preparing polycrystalline silicon ingot. The preparation method comprises: coating inner wall of the crucible with a layer of silicon nitride, followed by laying a layer of crushed silicon and feeding silicon in the crucible; the crushed silicon is laid in random order, and the layer of crushed silicon forms a supporting structure having numerous holes; melting the silicon to form molten silicon by heating, when solid-liquid interface reach the surface of the layer of crushed silicon or when the layer of crushed silicon melt partially, regulating thermal field to achieve supercooled state to grow crystals; after the crystallization of molten silicon is completely finished, performing annealing and cooling to obtain polycrystalline silicon ingot. By adopting the preparation method, a desirable initial nucleus can be obtained for a polycrystalline silicon ingot, so as to reduce dislocation multiplication during the growth of the polycrystalline silicon ingot.

Claims

1. A method for preparing polycrystalline silicon ingot, comprising:

coating inner wall of the crucible with a layer of silicon nitride, followed by feeding silicon from the bottom to the top of the crucible;

the step of feeding silicon further comprises laying a layer of crushed silicon at the bottom of the crucible in advance, the crushed silicon is laid at the bottom of the crucible in random order, and the layer of crushed silicon forms a supporting structure having numerous holes, the crushed silicon is non-crystalline silicon;

melting the silicon in the crucible to form molten silicon by heating, when solid-liquid interface formed by molten silicon and unmelted silicon reach the surface of the layer of crushed silicon or when the layer of crushed silicon melt partially, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon;

after the crystallization of molten silicon is completely finished, performing annealing and cooling to obtain polycrystalline silicon ingot.

2. The method for preparing polycrystalline silicon ingot according to claim 1, wherein size of the crushed silicon is in a range of 0.1 μ

m-10 cm, thickness of the layer of crushed silicon is in a range of 0.5 cm-5 cm.

3. The method for preparing polycrystalline silicon ingot according to claim 1, wherein size of the crushed silicon is in a range of 0.1 cm-10 cm.

4. The method for preparing polycrystalline silicon ingot according to claim 1, wherein during melting process, when the layer of crushed silicon melt partially and the height of the solid-liquid interface to the bottom of the crucible is greater than or equal to 1 mm, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon.

5. The method for preparing polycrystalline silicon ingot according to claim 4, wherein during melting process, when the layer of crushed silicon melt partially and the height of the solid-liquid interface to the bottom of the crucible is greater than or equal to 5 mm, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon.

6. The method for preparing polycrystalline silicon ingot according to claim 1, wherein during melting process, when 25%˜

40% of the layer of crushed silicon is melt, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon.

7. The method for preparing polycrystalline silicon ingot according to claim 1, wherein during melting process, the position of solid-liquid interface formed by molten silicon and unmelted silicon is detected at 0.2-1 hour intervals.

8. The method for preparing polycrystalline silicon ingot according to claim 1, wherein the step of regulating thermal field is regulating heating power to lower the temperature at a speed of 2-500 K/min.

9. The method for preparing polycrystalline silicon ingot according to claim 1, wherein a layer of chunk heat conductor is further laid between the layer of crushed silicon and the bottom of the crucible.

10. The method for preparing polycrystalline silicon ingot according to claim 9, wherein the chunk heat conductor is chunk silicon or chunk graphite.

11. The method for preparing polycrystalline silicon ingot according to claim 10, wherein the chunk silicon is one or more of chunk monocrystalline silicon, chunk polycrystalline silicon and chunk noncrystalline silicon.

12. The method for preparing polycrystalline silicon ingot according to claim 9, wherein thickness of the layer of chunk heat conductor is in a range of 1 cm-2 cm.

13. A method for preparing polycrystalline silicon ingot, comprising:

coating inner wall of the crucible with a layer of silicon nitride, followed by feeding silicon from the bottom to the top of the crucible;

the step of feeding silicon further comprises laying a layer of crushed silicon at the bottom of the crucible in advance, the crushed silicon is laid at the bottom of the crucible in random order, and the layer of crushed silicon forms a supporting structure having numerous holes, the crushed silicon is one or more of crushed monocrystalline silicon and crushed polycrystalline silicon, and size of the crushed silicon are in a range of 0.1 μ

m-1 cm;

melting the silicon in the crucible to form molten silicon by heating, when solid-liquid interface formed by molten silicon and unmelted silicon reach the surface of the layer of crushed silicon or when the layer of crushed silicon melt partially, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon;

after the crystallization of molten silicon is completely finished, performing annealing and cooling to obtain polycrystalline silicon ingot.

14. The method for preparing polycrystalline silicon ingot according to claim 13, wherein thickness of the layer of crushed silicon is in a range of 0.5 cm-5 cm.

15. The method for preparing polycrystalline silicon ingot according to claim 13, wherein during melting process, when the layer of crushed silicon melt partially and the height of the solid-liquid interface to the bottom of the crucible is greater than or equal to 1 mm, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon.

16. The method for preparing polycrystalline silicon ingot according to claim 13, wherein during melting process, when 25%˜

40% of the layer of crushed silicon is melt, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the layer of crushed silicon.

17. The method for preparing polycrystalline silicon ingot according to claim 13, wherein during melting process, the position of solid-liquid interface formed by molten silicon and unmelted silicon is detected at 0.2-1 hour intervals.

18. The method for preparing polycrystalline silicon ingot according to claim 13, wherein the step of regulating thermal field is regulating heating power to lower the temperature at a speed of 2-500 K/min.

19. The method for preparing polycrystalline silicon ingot according to claim 13, wherein a layer of chunk heat conductor is further laid between the layer of crushed silicon and the bottom of the crucible, the chunk heat conductor is chunk silicon or chunk graphite.

20. The method for preparing polycrystalline silicon ingot according to claim 19, wherein the chunk silicon is one or more of chunk monocrystalline silicon, chunk polycrystalline silicon and chunk noncrystalline silicon, and thickness of the layer of chunk heat conductor is in a range of 1 cm-2 cm.