Polycrystalline silicon mass and process for producing polycrystalline silicon mass

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.

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.   
     
     
         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. 
 
     
     
         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. 
     
     
         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 μm 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.