POLYCRYSTALLINE SILICON INGOT, PREPARATION METHOD THEREOF, AND POLYCRYSTALLINE SILICON WAFER

• US 20150056123A1
• Filed: 03/28/2013
• Published: 02/26/2015
• 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
• Granted Patent: US 9,562,304 B2
• Time in Patent Office: Days
• US Class Current: 423/348
• 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 preparation method of a polycrystalline silicon ingot. The preparation method comprises: providing a silicon nucleation layer at the bottom of a crucible, and filling a silicon material above the silicon nucleation layer; heating the silicon material to melt same, adjusting the thermal field inside the crucible to make the melted silicon material to start crystallization on the basis of the silicon nucleation layer; and when the crystallization is finished, performing annealing and cooling to obtain a 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. Further disclosed are a polycrystalline silicon ingot obtained through the preparation method and a polycrystalline silicon wafer made using the polycrystalline silicon ingot as a raw material.

Claims

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

providing a nucleating source of silicon material layer at the bottom of a crucible, and feeding silicon onto the nucleating source of silicon material layer;

melting the silicon by heating, and regulating thermal field in the crucible to grow crystals from molten silicon on the base of the nucleating source of silicon material layer;

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

2. The method for preparing polycrystalline silicon ingot according to claim 1, 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;

melting the silicon in the crucible to form molten silicon by heating;

when solid-liquid interface formed by molten silicon and unmelted silicon is close to the bottom of the crucible, regulating thermal field to achieve supercooled state to grow crystals from molten silicon on the base of the unmelted silicon;

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

the unmelted silicon is the nucleating source of silicon material layer.

3. The method for preparing polycrystalline silicon ingot according to claim 2, 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.

4. The method for preparing polycrystalline silicon ingot according to claim 1, 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 one or more of crushed monocrystalline silicon, crushed polycrystalline silicon and 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 is just in or deep into the layer of crushed silicon, 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.

5. The method for preparing polycrystalline silicon ingot according to claim 4, 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.

6. The method for preparing polycrystalline silicon ingot according to claim 4, 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.

7. The method for preparing polycrystalline silicon ingot according to claim 1, comprising:

(1) providing nucleating source at the bottom of the crucible to form a nucleating source layer;

the nucleating source is silicon powder;

(2) providing molten silicon above the nucleating source layer;

the step of providing molten silicon above the nucleating source layer is;

feeding solid silicon onto the nucleating source layer, melting the silicon by heating the crucible, so that the molten silicon is provided on the surface of the nucleating source layer;

or heating solid silicon in another crucible to prepare molten silicon, followed by pouring the molten silicon into the crucible with nucleating source layer, so that the molten silicon is provided on the surface of the nucleating source layer;

(3) controlling the temperature inside the crucible, the temperature raising along the direction perpendicular to the bottom of the crucible to form temperature gradient, making the molten silicon nucleating and forming crystals by using the nucleating source, then obtaining polycrystalline silicon ingot.

8. The method for preparing polycrystalline silicon ingot according to claim 7, wherein in step (1), the step of providing nucleating source is applying the nucleating source at the bottom of the crucible, or laying the nucleating source at the bottom of the crucible.

9. The method for preparing polycrystalline silicon ingot according to claim 7, wherein particle size of the nucleating source is in a range of 0.1 nm-1 cm.

10. The method for preparing polycrystalline silicon ingot according to claim 7, wherein during the nucleation and crystallization process of step (3), degree of supercooling is controlled to be in a range of from −

1K to −

30K.

11. The method for preparing polycrystalline silicon ingot according to claim 1, comprising:

(1) laying a microcrystalline nucleating source layer at the bottom of the crucible, the microcrystalline nucleating source layer is microcrystalline silicon and/or amorphous silicon;

thickness of the microcrystalline nucleating source layer is a first height;

the microcrystalline nucleating source layer is the nucleating source of silicon material layer;

(2) feeding silicon onto the microcrystalline nucleating source layer, melting the silicon to form molten silicon by heating, when solid-liquid interface formed after the silicon is melted completely is just in or deep into the microcrystalline nucleating source layer, regulating thermal field to achieve supercooled state to grow crystals from the molten silicon on the base of the microcrystalline nucleating source layer;

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

12. The method for preparing polycrystalline silicon ingot according to claim 11, when solid-liquid interface formed after the completely melted silicon is deep into the microcrystalline nucleating source layer and the height 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 the molten silicon on the base of the microcrystalline nucleating source layer.

13. The method for preparing polycrystalline silicon ingot according to claim 12, when solid-liquid interface formed after the silicon is melted completely is deep into the microcrystalline nucleating source layer and the height 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 the molten silicon on the base of the microcrystalline nucleating source layer.

14. The method for preparing polycrystalline silicon ingot according to claim 11, wherein the first height is in a range of 1-150 mm.

15. The method for preparing polycrystalline silicon ingot according to claim 1, comprising:

(1) randomly laying seed crystals with unlimited crystal orientation at the bottom of crucible to form a layer of seed crystals, the layer of seed crystals is the nucleating source of silicon material layer

(2) providing molten silicon above the layer of seed crystals, controlling the temperature at the bottom of the crucible below melting point of the seed crystals, making the layer of seed crystals not completely melted;

(3) controlling the temperature inside the crucible, the temperature raising along the direction perpendicular to the bottom of the crucible to form temperature gradient, making the molten silicon growing above the seed crystals, the molten silicon inheriting the structure of the seed crystals, then obtaining polycrystalline silicon ingot.

16. The method for preparing polycrystalline silicon ingot according to claim 15, wherein the seed crystals in step (1) are materials from the top or the end of silicon ingot, materials from the edge of silicon ingot, defective silicon, crushed fragment of single crystals or finely crushed silicon.

17. The method for preparing polycrystalline silicon ingot according to claim 15, wherein the seed crystals in step (1) are single crystals or polycrystals.

18. A polycrystalline silicon ingot prepared by the method as claimed in claim 1.

19. A polycrystalline silicon wafer, wherein the polycrystalline silicon wafer is obtained by sectioning, slicing and cleaning the polycrystalline silicon ingot as claimed in claim 18.