POLYCRYSTALLINE SILICON MASS AND PROCESS FOR PRODUCING POLYCRYSTALLINE SILICON MASS

• US 20120175613A1
• Filed: 07/21/2010
• Published: 07/12/2012
• Est. Priority Date: 09/16/2009
• Status: Abandoned Application

• Current Assignee: Shin-Etsu Chemical Company Limited
• Original Assignee: Shin-Etsu Chemical Company Limited
• Inventors: Netsu, Shigeyoshi, Okada, Junichi, Kume, Fumitaka
• Application Number:
  US13/496,693
• Publication Number:
  US 20120175613A1
• Time in Patent Office: Days
• US Class Current: 257/49
• 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: C01B 33/037 Purification by zone-melting C30B13/00
• CPC Class Codes: C30B 23/00 Single-crystal growth by condensing evaporated or sublimed materials
• CPC Class Codes: C30B 29/06 Silicon

Abstract

The present invention provides a clean and high-purity polycrystalline silicon mass having a small content of chromium, iron, nickel, copper, and cobalt in total, which are heavy metal impurities that reduce the quality of single-crystal silicon. In the vicinity of an electrode side end of a polycrystalline silicon rod obtained by the Siemens method, the total of the chromium, iron, nickel, copper, and cobalt concentrations is high. Accordingly, before a crushing step of a polycrystalline silicon rod 100, a removing step of removing at least 70 mm of a polycrystalline silicon portion from the electrode side end of the polycrystalline silicon rod 100 extracted to the outside of a reactor is provided. Thereby, the polycrystalline silicon portion in which the total of the chromium, iron, nickel, copper, and cobalt concentrations in a bulk is not less than 150 ppta can be removed.

Claims

1. A polycrystalline silicon mass, wherein a sum of concentrations of chromium, iron, nickel, copper, and cobalt impurities detected from a bulk is not more than 150 ppta.

2. The polycrystalline silicon mass of claim 1, wherein the sum of the concentrations of the impurities is not more than 100 ppta.

3. The polycrystalline silicon mass of claim 1, wherein the sum of the concentrations of the impurities is not more than 75 ppta.

4. The polycrystalline silicon mass of claim 1, wherein the concentrations of impurities are measured by an inductively coupled plasma mass spectrometry (ICP-MS) method.

5. The polycrystalline silicon mass of claim 1, wherein a surface of the polycrystalline silicon mass is coated with a silicon oxide film.

6. The polycrystalline silicon mass of claim 1, wherein

the sum of the concentrations of the impurities is not more than 75 ppta, and a surface of the polycrystalline silicon mass is coated with a silicon oxide film.

13. The polycrystalline silicon mass of claim 6, which is suitable for multi pulling up to 10 single-crystal silicon ingots by a CZ method in one batch.

14. The polycrystalline silicon mass of claim 2, wherein a surface of the polycrystalline silicon mass is coated with a silicon oxide film.

7. A process for producing a polycrystalline silicon mass, the process comprising:

vapor depositing silicon on a core wire to obtain a polycrystalline silicon rod, one end of the core wire being connected to a first electrode and the other end thereof being connected to a second electrode;

extracting the polycrystalline silicon rod to an outside of a reactor;

removing at least 70 mm of a polycrystalline silicon portion from an electrode side end of the polycrystalline silicon rod extracted to the outside of the reactor; and

crushing the polycrystalline silicon rod into polycrystalline silicon masses.

8. The process of claim 7, wherein at least 155 mm of the polycrystalline silicon portion from the electrode side end is removed.

9. The process of claim 7, wherein the extracting comprises covering a surface of the polycrystalline silicon rod with a bag-like member.

10. The process of claim 9, wherein an opening of the bag-like member that covers the surface of the polycrystalline silicon rod is sealed after the polycrystalline silicon rod is extracted to the outside of the reactor.

11. The process of claim 9, wherein the bag-like member is a polyethylene bag.

12. The process of claim 7 further comprising, after the crushing, a washing comprising

oxidation treating with ozone water to coat a surface of the polycrystalline silicon mass with a silicon oxide film.

15. The process of claim 7, wherein the washing comprises:

prewashing, etching, oxidation treating, and drying.

16. The process of claim 15, wherein the prewashing is performed in water.

17. The process of claim 15, wherein the etching is performed in a mixed solution comprising hydrofluoric acid, hydrogen peroxide, and water.

18. The process of claim 15, wherein the etching is performed in a mixed solution comprising hydrofluoric acid and nitric acid.

19. The process of claim 18, wherein the etching removes at least 20 μ

m from a surface of the polycrystalline silicon mass.

20. The process of claim 15, wherein the drying is performed in clean warm air or in a vacuum.