Method for the purification of a semiconductor material by application of an oxidation-reduction reaction

Abstract

A method for the purification of a semiconductor material, the method comprising the steps of: a) the oxidation at an anode, which is placed in an anodic electrolyte, of a solid semiconductor material to be purified by application of one or more ionic compounds; b) the reduction at a cathode, which is placed in a cathodic electrolyte, of one or more compounds obtained in step a), to a purified, solid semiconductor material where one or more ionic compounds are also formed; where the one or more ionic compounds that are formed in step b) are applied in step a) and the anode and cathode are mutually connected for electron transfer. The formed ionic compounds are purified externally. The present method can for example be applied for the purification of silicon.

1 - 17 . (canceled) 
   
   
       18 . A method for the purification of a semiconductor material by application of an oxidation-reduction reaction, characterized in that the method comprises the steps of:
 a) the oxidation of an anode placed in an electrolyte, which anode is and of a semiconductor material containing one or more contaminations, the electrolyte having one or more ionic compounds present, and the ionic compounds reacting with the semiconductor material and the one or more impurities to form one or more compounds according to formula I:
   AX z H (y-z)′   (I) 
   where   A=ion of semiconductor   X=halogen ion   H=hydrogen   y=valence of A   z=Integer greater than or equal to 1   and one or more associated reaction products,   b) the addition of the one or more compounds of formula I, obtained in step a), to a cathode placed in an electrolyte and carrying out the reduction there to form purified semiconductor material on the cathode, the reduction also leading to formation of one or more ionic compounds;   where the one or more ionic compounds formed in step b) are returned to step a) and where the anode and cathode are mutually connected for electron transfer.   
   
   
       19 . A method according to  claim 18 , where the method comprises an additional step c) which is carried out after step a) and before step b) where step c) comprises two sub steps c1) and c2) namely
 c1) the extraction of the one or more compounds according to formula I and the one or more associated reaction products from the electrolyte;   c2) the separation of the one or more compounds according to formula I from the one or more associated products.   
   
   
       20 . A method according to  claim 19 , where in step c2) the one or more compounds according to formula I are separated to a purity of greater than or equal to 99.99% (4N), preferably 99.9999% (6N). 
   
   
       21 . A method according to  claim 18 , where silicon is applied as the semiconductor material in step a). 
   
   
       22 . A method according to  claim 21 , where MG silicon (metallurgical purity) is applied as the semiconductor material in step a). 
   
   
       23 . A method according to  claim 18 , where the material of the cathode is selected from the group consisting of silicon, carbon silver, molybdenum, platinum, tungsten and one or more combinations thereof. 
   
   
       24 . A method according to  claim 23 , where silicon of a purity of greater than or equal to 99.99% (4N), preferably 99.9999% (6N) is applied as the cathode. 
   
   
       25 . A method according to  claim 18 , where a core of an inert material, enclosed in a mantle of the semiconductor material, is applied as anode. 
   
   
       26 . A method according to  claim 18 , where the electrolyte in which the anode has been placed, is equal to the electrolyte in which the cathode has been placed. 
   
   
       27 . A method according to  claim 26 , where the electrolyte is a combination of NaCl and KCl, preferably a eutectic mixture of NaCl and KCl. 
   
   
       28 . A method according to claim,  18 , where a membrane is applied that is permeable to the one or more ionic compounds that are formed in step b), the membrane being present between the electrolyte in which the anode is placed and the electrolyte in which the cathode is placed. 
   
   
       29 . A method according to  claim 28 , where a ceramic membrane is applied as membrane. 
   
   
       30 . A method according to  claim 26 , where a capture electrode is applied which is connected to an external voltage source, the capture electrode having a potential that is equal to or higher than that of the cathode, where the capture electrode has been placed in the electrolyte between the anode and cathode. 
   
   
       31 . A method according to  claim 19 , where in step b) additionally one or more compounds according to formula I are added. 
   
   
       32 . A method according to  claim 18 , where the reduction is carried out at a temperature of at least 400° C., preferably at least 470 C. 
   
   
       33 . A method according to  claim 18 , where an external voltage source is applied to apply a difference of potential between the anode and the cathode, the difference of potential being selected between 0.01 V and the standard reduction potential of the electrolyte. 
   
   
       34 . A method according to  claim 26 , where the electrolyte is forced to flow from the cathode to the anode and vice versa.