METHOD OF MAKING LARGE SURFACE AREA FILAMENTS FOR THE PRODUCTION OF POLYSILICON IN A CVD REACTOR

• US 20110271718A1
• Filed: 07/20/2011
• Published: 11/10/2011
• Est. Priority Date: 04/28/2006
• Status: Active Grant

• Current Assignee: Advanced Material Solutions, LLC
• Original Assignee: GT Solar
• Inventors: Servini, Adrian, Wan, Yuepeng, Parthasarathy, Santhana Raghavan, Khattak, Chandra P., Chartier, Carl
• Granted Patent: US 8,647,432 B2
• Time in Patent Office: Days
• US Class Current: 65/437
• CPC Class Codes: C01B 33/035 by decomposition or reduction of gaseous or vaporised silicon compounds in the presence of heated filaments of silicon, carbon or a refractory metal, e.g. tantalum or tungsten, or in the presence of heated silicon rods on which the formed silicon is deposited, a silicon rod being obtained, e.g. Siemens process
• CPC Class Codes: C23C 16/24 Deposition of silicon only
• CPC Class Codes: C23C 16/4418 Methods for making free-standing articles C23C16/01 takes precedence
• CPC Class Codes: C23C 16/458 characterised by the method used for supporting substrates in the reaction chamber
• CPC Class Codes: Y10T 117/10 Apparatus
• CPC Class Codes: Y10T 117/102 for forming a platelet shape or a small diameter, elongate, generally cylindrical shape [e.g., whisker, fiber, needle, filament]
• CPC Class Codes: Y10T 117/1024 for crystallization from liquid or supercritical state
• CPC Class Codes: Y10T 117/1032 Seed pulling
• CPC Class Codes: Y10T 117/104 Means for forming a hollow structure [e.g., tube, polygon]

Abstract

A method for making a large surface area silicon filament for production of bulk polysilicon by chemical vapor deposition (CVD) includes melting silicon and growing the filament from the melted silicon by an EFG method using a shaping die. The cross sectional shape of the silicon filament is constant over its axial length to within a tolerance of 10%. In embodiments, a plurality of identical and/or dissimilar filaments are grown simultaneously using a plurality of shaping dies. The filaments can be tubular. Filament cross sections can be annular and/or can include outwardly extending fins, with wall and/or fin thicknesses constant to within 10%. Filaments can be doped with at least one element from groups 3 and 5 of the Periodic Table. The filament can have a length equal to a length of a specified slim rod filament, and a total impedance not greater than the slim rod impedance.

Claims

1. A method for making large surface area filaments usable in a CVD reactor for the production of polysilicon, the method comprising:

heating silicon in a silicon melt pool to a molten state; and

growing a silicon structure with said silicon in said molten state by an EFG method with a shaping die, said silicon structure having a uniform cross sectional shape over an axial length, all dimensions of said cross sectional shape being constant over said axial length to within a tolerance of 10%.

2. The method of claim 1, wherein the silicon melt pool is contained within a crucible, the crucible being made of one of graphite and quartz.

3. The method of claim 1, wherein the shaping die comprises graphite or quartz.

4. The method of claim 1, wherein the method further includes crystallizing silicon out of the shaping die.

5. The method of claim 1, wherein growing a silicon structure with said silicon in said molten state by an EFG method with a shaping die includes simultaneously growing a plurality of silicon structures with a plurality of shaping dies.

6. The method of claim 5, wherein the plurality of silicon structures have substantially identical cross sectional shapes.

7. The method of claim 5, wherein the plurality of silicon structures includes a plurality of cross sectional shapes.

8. The method of claim 1, wherein said die includes a multi-cavity die.

9. The method of claim 1, wherein the cross sectional shape of the silicon structure includes outwardly projecting fins, the thicknesses of the fins being constant along the axial length of the silicon structure to within a tolerance of 10%.

10. The method of claim 1, wherein the silicon structure is tubular.

11. The method of claim 10, wherein the cross sectional shape of the silicon structure is annular, and the wall thickness of the annular shape is constant about its circumference to within a tolerance of 10%.

12. The method of claim 11, wherein the outer diameter of the annular cross sectional shape is between 20 mm and 100 mm, and the wall thickness is between 1 mm and 6 mm.

13. The method of claim 11, wherein the outer diameter of the annular cross sectional shape is between 40 mm and 80 mm, and the wall thickness is between 1.75 mm and 6 mm.

14. The method of claim 11, wherein the outer diameter of the annular cross sectional shape is about approximately 50 mm, and the wall thickness is about approximately 2 mm.

15. The method of claim 11, wherein the outer diameter of the annular cross sectional shape is at least 20 mm, and the ratio of the wall thickness to the outer diameter of not greater than one fourth.

16. The method of claim 1, wherein the silicon is doped with at least one element from one of groups 3 and 5 of the Periodic Table.

17. The method of claim 1, wherein the silicon structure has an axial length equal to an axial length of a specified solid rod silicon filament, and the silicon structure has a total impedance less than or equal to a total impedance of the solid-rod silicon filament.