Methods and Apparatus for Recovery of Silicon and Silicon Carbide from Spent Wafer-Sawing Slurry

Abstract

Methods, systems, and apparatus are disclosed herein for recovery of high-purity silicon, silicon carbide and PEG from a slurry produced during a wafer cutting process. A silicon-containing material can be processed for production of a silicon-rich composition. Silicon carbide and PEG recovered from the silicon-containing material can be used to form a wafer-saw cutting fluid. The silicon-rich composition can be reacted with iodine containing compounds that can be purified and/or used to form deposited silicon of high purity. The produced silicon can be used in the photovoltaic industry or semiconductor industry.

1 . A process for recovering silicon comprising:
 (a) separating iron-containing particles from a cutting slurry using at least one physical separation device, thereby producing a slurry product;   (b) removing liquid from said slurry product, thereby producing a powder mixture of silicon carbide and silicon;   (c) providing said powder mixture to a first vessel containing silicon tetra-iodide, thereby producing a vapor comprising silicon di-iodide; and   (d) providing said vapor comprising silicon di-iodide to a second vessel, wherein said deposited silicon is formed from the silicon di-iodide.   
     
     
         2 . The process of  claim 1  further comprising purifying and recycling remaining silicon tetra-iodide from said second vessel. 
     
     
         3 . The process of  claim 1  further comprising e) recovering said iron-containing particles from step a). 
     
     
         4 . The process of  claim 1  further comprising f) adding a carrier gas to said first vessel in step d) to adjust the flow rate of the vapor-gas mixture. 
     
     
         5 . The process of  claim 1  further comprising recovering silicon carbide particles from said first vessel. 
     
     
         6 . The process of  claim 1  further comprising recovering at least one of glycol, oil or water from said slurry product. 
     
     
         7 .- 27 . (canceled) 
     
     
         28 . A method for forming silicon, comprising:
 (a) providing iodine and a mixture of silicon carbide and silicon to a first vessel to form a vapor comprising silicon tetra-iodide and/or silicon di-iodide in the first vessel, wherein said mixture is recovered from silicon saw kerf;   (b) providing said vapor comprising silicon tetra-iodide and/or silicon di-iodide to a second vessel; and   (c) forming, under vacuum, silicon and iodine (I 2 ) from the silicon tetra-iodide and/or silicon di-iodide in the second vessel.   
     
     
         29 . The method of  claim 28 , wherein the pressure of said second vessel is substantially less than atmospheric pressure. 
     
     
         30 . The method of  claim 28 , wherein the first vessel is operated at a temperature from about 600° C. to 900° C. 
     
     
         31 . The method of  claim 28 , wherein the second vessel is operated at a temperature from about 900° C. to 1300° C. 
     
     
         32 . The method of  claim 28 , further comprising purifying and recycling remaining silicon tetra-iodide from said second vessel. 
     
     
         33 . The method of  claim 28 , further comprising recovering silicon carbide particles from said first vessel. 
     
     
         34 . The method of  claim 28 , wherein said silicon in (c) has a purity of at least about 99.9999%. 
     
     
         35 . The method of  claim 28 , wherein, in (c), said silicon is deposited onto granules in said second vessel. 
     
     
         36 . The method of  claim 28 , further comprising, prior to (a):
 removing iron-containing particles from said silicon saw kerf to produce a slurry product; and   removing liquid from said slurry product to produce said mixture of silicon carbide and silicon.   
     
     
         37 . The method of  claim 36 , further comprising recovering said iron-containing particles. 
     
     
         38 . The method of  claim 28 , further comprising recovering silicon carbide particles from said first vessel. 
     
     
         39 . The method of  claim 28 , further comprising recovering at least one of glycol, oil or water from said slurry product.