Process for producing purified silicon

Abstract

Provided is a process for producing a purified silicon by cutting off a crude silicon region, without determining the aluminium concentration in a directionally-solidified silicon. In the process of the invention, a standard solidification fraction (f 0 ) satisfying the following formula (1) and formula (2) is obtained from the predetermined maximum level of aluminium concentration (C 10max ), the temperature gradient (T) and the solidification speed (R), and the directionally-solidified silicon is cut at the part having a solidification fraction (f) in the solidification step corresponding to f 0 . k = { K 1 × Ln  ( R ) + K 2 } × { K 3 × exp  [ K 4 × R × ( K 5 × C 2 + K 6 ) ] } × { K 7 × T + K 8 } - K 9 ( 1 ) [wherein k is a coefficient selected from a range of from 0.9 times to 1.1 times the effective aluminium partitioning coefficient k′, as obtained so as to satisfy the following formula (2): C 10max =k′×C 2 ×(1− f 0 ) k′−1   (2), (k′ is an effective aluminium partitioning coefficient, C 2 is the aluminium concentration of the starting silicon material melt)].

1 . A process for producing a purified silicon by using a silicon melt as a starting material, comprising:
 a step of solidifying an aluminium-containing starting silicon material melt by cooling in a mold under a unidirectional temperature gradient (T (° C./mm)) condition to give a directionally-solidified silicon containing a purified silicon region having an aluminium concentration (C (ppm)) not higher than the predetermined maximum level of aluminium concentration (C 10max  (ppm)) and a crude silicon region having an aluminium concentration (C) higher than the predetermined maximum level of aluminium concentration (C 10max ), and   a step of cutting off the crude silicon region from the obtained directionally-solidified silicon to give a purified silicon having an aluminium concentration (C) not higher than the predetermined maximum level of aluminium concentration (C 10max ),   wherein, in the step of cutting off the crude silicon region, the directionally-solidified silicon is cut at a part corresponding to a standard solidification fraction (f 0 ) obtained from the predetermined maximum level of aluminium concentration (C 10max ) and the temperature gradient (T) and the solidification speed (R (mm/min)) in cooling the starting silicon material melt and satisfying the following formula (1) and formula (2), thereby cutting off the crude silicon region; the standard solidification fraction (f 0 ) indicates the ratio of the purified silicon region having an aluminium concentration (C (ppm)) not higher than the predetermined maximum level of aluminium concentration (C 10max  (ppm)), to the whole of the directionally-solidified silicon, and 0≦f 0 ≦1;   
     
       
         
           
             
               
                 
                   k 
                   = 
                   
                     
                       
                         { 
                         
                           
                             
                               K 
                               1 
                             
                             × 
                             
                               Ln 
                                
                               
                                 ( 
                                 R 
                                 ) 
                               
                             
                           
                           + 
                           
                             K 
                             2 
                           
                         
                         } 
                       
                       × 
                       
                         { 
                         
                           
                             K 
                             3 
                           
                           × 
                           
                             exp 
                              
                             
                               [ 
                               
                                 
                                   K 
                                   4 
                                 
                                 × 
                                 R 
                                 × 
                                 
                                   ( 
                                   
                                     
                                       
                                         K 
                                         5 
                                       
                                       × 
                                       
                                         C 
                                         2 
                                       
                                     
                                     + 
                                     
                                       K 
                                       6 
                                     
                                   
                                   ) 
                                 
                               
                               ] 
                             
                           
                         
                         } 
                       
                       × 
                       
                         { 
                         
                           
                             
                               K 
                               7 
                             
                             × 
                             T 
                           
                           + 
                           
                             K 
                             8 
                           
                         
                         } 
                       
                     
                     - 
                     
                       K 
                       9 
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     [in formula (1), k is a coefficient selected from a range of from 0.9 times to 1.1 times the effective aluminium partitioning coefficient k′, as obtained so as to satisfy the following formula (2):
     C   10max   =k′×C   2 ×(1 −f   0 ) k′−1    (2), 
 K 1  means a constant selected from a range of 1.1×10 −3 ±0.1×10 −3 , 
 K 2  means a constant selected from a range of 4.2×10 −3 ±0.1×10 −3 , 
 K 3  means a constant selected from a range of 1.2±0.1, 
 K 4  means a constant selected from a range of 2.2±0.1, 
 K 5  means a constant selected from a range of −1.0×10 −3 ±0.1×10 −3 , 
 K 6  means a constant selected from a range of 1.0±0.1, 
 K 7  means a constant selected from a range of −0.4±0.1, 
 K 8  means a constant selected from a range of 1.36±0.01, 
 K 9  means a constant selected from a range of 2.0×10 −4 ±1.0×10 −4 , 
 R means a solidification speed (mm/min), 
 T means a temperature gradient (° C./mm)], 
 
     [in formula (2), C 10max  means the predetermined maximum level of aluminium concentration (ppm) in purified silicon, C 2  means the aluminium concentration(ppm) in the starting silicon material melt, and f 0  means the standard solidification fraction]. 
   
   
       2 . The process according to  claim 1 , wherein the predetermined maximum level of aluminium concentration (C 10max ) is from 1/1000 times to 3/100 times the aluminium concentration (C 2 ) of the starting silicon material melt.