Recovery of silicon from kerf silicon waste
A process for the recovery of silicon includes providing silicon-containing solids recovered from a silicon manufacturing process, said recovered silicon-containing solids being substantially free of semiconductor dopants; converting the recovered silicon-containing solids into gaseous silicon forms; subjecting to purification by minimal distillation; collecting the gaseous silicon forms as a condensed liquid of silicon-containing compounds; and utilizing the silicon-containing compounds for silicon deposition.
1. A method of converting kerf silicon waste to high purity silicon comprising:
selecting kerf silicon waste to be converted to high purity silicon, wherein the kerf silicon waste comprises silicon powder having an average particle size in the range of 1-10 microns and about 5 to 35 wt % silicon carbide impurities, wherein said silicon powder comprises less than 1 wt % metallic and nonmetallic impurities;
converting said silicon powder into halosilanes with a mixture of hydrogen chloride and hydrogen gas between 200-250° C., wherein substantially all of said silicon carbide impurities remain unreacted;
separating said halosilanes from said unreacted silicon carbide impurities; and
converting the separated halosilanes to high purity silicon, wherein the high purity silicon is at least a photovoltaic-grade silicon.
2. The method of claim 1 , further comprising separating impurities from the kerf silicon waste to obtain a silicon enriched powder, wherein said separating impurities from the kerf silicon waste comprises one or more of:
(a) reducing the carrier fluid from the kerf silicon waste;
(b) reducing metallic impurities from the kerf silicon waste;
(c) reducing the abrasive content from the kerf silicon waste;
(d) reducing oxidized material from the kerf silicon waste; and
(e) washing and drying the kerf silicon waste.
3. The method according to claim 1 , wherein the process is performed primarily in a bed reactor.
4. The method according to claim 1 , wherein the halosilanes are decomposed in a silicon deposition process to deposit polysilicon or a silicon thin film.
5. The method according to claim 1 , wherein the kerf silicon waste comprises high purity silicon, residual wire saw slurry and wire saw material.
6. The method according to claim 5 wherein the residual wire saw slurry comprises a liquid carrier and an abrasive.
7. The method according to claim 6 , wherein the liquid carrier is selected from the group consisting of polyethylene glycol, water and oil and mixtures thereof.
8. The method according to claim 6 , wherein the abrasive is selected from the group consisting of silicon carbide and diamond and mixtures thereof.
9. The method according to claim 5 , wherein the residual wire saw material is selected from the group consisting of iron, steel, stainless steel, brass coated iron, brass coated steel, brass coated stainless steel, or a combination of these.
10. The method according to claim 1 , further comprising submitting the halosilanes to a distillation process to remove non-volatile and volatile impurities.
11. The method of claim 10 , wherein the non-volatile impurities comprise metal halide-containing impurities and silicon carbide.
12. The method according to claim 11 , wherein the non-volatile impurities comprise metal halides and the metal halides are separated in a filter bed.
13. The method according to claim 1 , further comprising washing the kerf silicon waste with water to remove water soluble impurities of the kerf silicon waste.
14. The method according to claim 1 , further comprising washing the kerf silicon waste from oil-based wire saw process with an organic liquid extractant to remove oil.
15. The method according to claim 1 , further comprising reducing magnetic metallic impurities in the kerf silicon waste by a magnetic separation system.
16. The method according to claim 1 , further comprising reducing metallic impurities in the kerf silicon waste by treating with acid to dissolve the metals.
17. The method according to claim 1 , further comprising reducing the abrasive content of the kerf silicon waste by a density-based process.
18. The method according to claim 17 , wherein the density-based process is selected from the group consisting of centrifugation, flotation and momentum-based separation techniques.
19. The method according to claim 1 , further comprising washing the kerf silicon with the abrasive content with hydrofluoric acid to reduce oxidized silicon.
20. The method according to claim 19 , wherein the hydrofluoric acid washed kerf silicon is washed with high purity water to remove hydrofluoric acid from the silicon.
21. The method according to claim 2 , wherein the kerf silicon waste is dried in an inert gas environment.
22. The method of claim 1 , wherein the halosilanes comprise chlorosilanes.
23. The method according to claim 22 , wherein the silicon powder is hydrochlorinated to form chlorosilanes.
24. The method according to claim 22 , wherein the chlorosilanes comprise trichlorosilane and trichlorosilane is purified by distillation process to remove non-volatile and volatile impurities.
25. The method of claim 24 , wherein distillation to remove volatile impurities comprises separation of the trichlorosilane from dichlorosilane and tetrachlorosilane.
26. The method of claim 22 , wherein the chlorosilanes comprise trichlorosilane and the method further comprising:
submitting the trichlorosilane to redistribution reactions to enrich the product in silicon content.
27. The method of claim 26 , further comprising converting the silicon enriched product into the high purity silicon.
28. The method according to claim 27 , wherein the silicon enriched product is decomposed in a silicon deposition process to deposit polysilicon or a silicon thin film.
29. The method of claim 1 , wherein the kerf silicon waste comprises silicon particles having an average particle size in the range of 1-10 microns, about 5-10 weight % SiC; and
less than 1 wt % metallic and nonmetallic impurities, and
wherein the surface of the silicon particles is substantially free of oxides.
30. A method of producing polysilicon comprising:
selecting kerf silicon waste to be converted to high purity silicon, wherein the kerf silicon waste comprises silicon powders having an average particle size in the range of 1-10 microns and about 5 to 35 wt % silicon carbide impurities, wherein said silicon powder comprises less than 1 wt % metallic and nonmetallic impurities;
converting said silicon powders into trichlorosilane with hydrogen chloride and hydrogen gas between 200-250° C., wherein substantially all of said silicon carbide impurities remain unreacted;
separating said trichlorosilane from said silicon carbide impurities; and
converting said trichlorosilane to polysilicon, wherein said polysilicon is at least photovoltaic-grade polysilicon.
31. The method of claim 30 , further comprising:
submitting the trichlorosilane to redistribution to form silane gas.
32. The method of claim 30 , wherein the trichlorosilane is subjected to one distillation purification process.
33. The method of claim 30 , wherein no distillation step is employed.
34. The method of claim 30 , wherein the polysilicon is a solar grade polysilicon.
35. The method of claim 30 , wherein the polysilicon is an electronics grade polysilicon.
36. The method of claim 30 , wherein the trichlorosilane is subjected to two distillation purification processes.