Surface modified quartz glass crucible, and its modification process
A surface modified quartz glass crucible and a process for modifying the crucible includes a layer of a metal oxide on the whole or a part of the inside and/or outside of the crucible, and baking it. At least an inside surface of the crucible is coated with a said metal oxide of magnesium, calcium, strontium or barium. The coated layer of the crucible does not abrade easily and provides a high dislocation free ratio of silicon single crystals pulled by using the crucible.
1. A process for making a surface modified glass crucible, comprising:
coating at least the inside surface of a glass crucible with a liquid solution comprising a metal salt, which is one or more salts of metals selected from the group consisting of magnesium, calcium, strontium, and barium, to obtain a crucible having at least a coated inside surface,
drying said crucible having a coated inside surface to thermally decompose the metal salt and to produce a transparent coated layer of a metal oxide baked on said surface of said crucible,
baking said dried, coated crucible at a temperature higher than a thermal decomposition temperature of the metal salt to obtain a baked, coated crucible, wherein the baked, coated crucible is not devitrified, and wherein the dried coating liquid is baked on at a temperature of from 600 to 1200° C., for 10 to 120 minutes, without polysilicon in the crucible, and
washing the baked crucible with water and drying,
wherein the baking is carried out before silicon is melted in the dried, coated crucible.
2. The process of claim 1 , wherein the metal salt is one or more organic acid salts of magnesium, calcium, strontium, or barium.
3. The process of claim 2 , wherein the organic acid salt is a carboxylate.
4. The process of claim 3 , wherein the carboxylate has the formula CnH 2n+1 COO, where n is an integer of 3 to 7.
5. The process of claim 4 , wherein the carboxylate is derived from n-butyric acid, or methyl butyric acid, iso-valeric acid, 2-ethyl butyric acid, 2,2-dimethyl butyric acid, 3,3-dimethyl butyric acid, 2,3-dimethyl butyric acid, 3-methyl pentanoic acid, 1,4-methyl pentanoic acid, 2-ethyl pentanoic acid, 3-ethyl pentanoic acid, 2,2-dimethyl pentanoic acid, 3,3-dimethyl pentanoic acid, 2,3-dimethyl pentanoic acid, 2-ethyl hexanoic acid, or 3-ethyl hexanoic acid.
6. The process of claim 1 , wherein the solution comprises from 0.01 to 15 weight % of the metal based on the amount of a metal oxide formed by the baking.
7. The process of claim 1 , wherein the solution comprises from 0.5 to 10 wt. % of the metal based on the amount of a metal oxide formed by the baking.
8. The process of claim 1 , wherein the baking is carried out at a temperature of from 700 to 1200° C., without polysilicon in the crucible.
9. The process of claim 1 , wherein the solution comprises an organic solvent selected from the group consisting of an ester, an alcohol, a ketone, a hydrocarbon and mixtures thereof.
10. The process of claim 9 , wherein the solvent is toluene.
11. The process of claim 1 , wherein the glass crucible is a quartz glass crucible.
12. The process of claim 1 , wherein the silicon is polysilicon.
13. The process of claim 1 , wherein the glass crucible is a quartz glass crucible, the silicon is polysilicon, the metal salt is a carboxylate acid salt, the baking is carried out at a temperature of from 600 to 1200° C. without polysilicon in the crucible, and the solution comprises an organic solvent.
14. The process of claim 1 , further comprising
coating the solution on at least a portion of the outside surface of the crucible.
15. The process of claim 1 , further comprising:
adding silicon to the crucible after washing,
heating the crucible containing silicon to melt the silicon, and
pulling a single crystal of silicon from the molten silicon.
16. The process of claim 1 , wherein the coating includes spraying an organic solvent solution of the metal salt onto the crucible.
17. The process of claim 16 , wherein the coating liquid comprises the metal salt in an amount of from 0.1-1 wt. % calculated as the oxide and the baking is carried out at a temperature of from 850 to 1,200° C., without polysilicon in the crucible.
18. The process of claim 16 , wherein the organic solvent is toluene.
19. The process of claim 16 , wherein the baking is carried out at a temperature of from 600 to 1200° C., without polysilicon in the crucible and the coating liquid has from 0.01 to 1 wt. % of a barium carboxylate calculated as the oxide.
20. The process of claim 19 , wherein the strength of the coated, baked layer according to JIS 5,600.5-4 does not show scratching when marked with a pencil of hardness 6 H.
21. The process of claim 19 , wherein the baked, coated layer of the metal oxide is not substantially changed after washing.
22. The process of claim 1 , wherein the baked, coated layer of the metal oxide has a crystal layer thickness of from 60-130 μm.
23. The process of claim 1 , wherein the baked, coated layer of the metal oxide has a crystal layer thickness of from 80 to 130 μm.
24. The process of claim 1 , wherein the baked, coated layer of metal oxide has a crystal layer thickness of from 110-130 μm.
25. The process of claim 1 , wherein the metal salt is 2-ethylhexanoic barium.