Method of manufacturing silica glass crucible for pulling silicon single crystals
The disclosed is a method of manufacturing a silica glass crucible for pulling silicon single crystals. In the method, reduced pressure is imparted from the inner surface to the outer surface of a crucible-shaped molded product and the crucible-shaped molded product is arc-fused while rotating the same to form a silica glass crucible with a transparent layer on the inner surface side and a bubble layer on the outer surface side. The inner surface of the wall portion of the silica glass crucible is fused a second time by arc fusion to cause bubbles present in the transparent layer of the inner surface of the wall portion to be displaced toward the bottom portion of the inner surface of the wall portion. The inner surface of the bottom portion of the silica glass crucible is fuse a second time by arc fusion to cause bubbles present in the transparent layer of the inner surface of the bottom portion to be displaced toward the periphery of the inner surface of the bottom portion. Either the step of displacement toward the bottom portion or the step of displacement toward the outer periphery is inverted first.
1. A method of manufacturing a silica glass crucible for pulling silicon single crystals comprising:
feeding a quartz starting material powder into a rotating mold and forming a crucible-shaped molded product;
imparting reduced pressure from the inner surface to the outer surface of the crucible-shaped molded product and arc-fusing the crucible-shaped molded product while rotating the product to form a silica glass crucible with a transparent layer on the inner surface side and a bubble layer on the outer surface side;
fusing a second time by arc fusion the inner surface of the wall portion of the silica glass crucible to cause bubbles present in the transparent layer of the inner surface of the wall portion to be displaced toward the bottom portion of the inner surface of the wall portion; and
fusing a second time by arc fusion the inner surface of the bottom portion of the silica glass crucible to cause bubbles present in the transparent layer of the inner surface of the bottom portion to be displaced toward the periphery of the inner surface of the bottom portion; and
wherein either said fusing the second time by arc fusion the inner surface of the wall portion or the said fusing the second time by arc fusion the inner surface of the bottom portion is performed first to obtain a silica glass crucible in which bubbles are accumulated in the corner portions of the transparent layer formed on the inner surface of the wall portion and the inner surface of the bottom portion, and wherein the bubbles accumulated in the corner portions of the transparent layer are removed.
2. The method of manufacturing of claim 1 , wherein in said fusing the second time by arc fusion the inner surface of the wall portion, the rotational speed of the silica glass crucible is made lower than the rotational speed during arc fusion of the crucible-shaped molded product, and the temperature when fusing the silica glass crucible a second time is made higher than the temperature during arc fusion of the crucible-shaped molded product.
3. The method of manufacturing of claim 1 , wherein the rotational speed during arc fusion of the crucible-shaped molded product is set so that the gravitational acceleration exerted on the crucible-shaped molded product is 1.3 G or greater, and the rotational speed of the silica glass crucible in said fusing the second time by arc fusion the inner surface of the wall portion is set so that the gravitational acceleration exerted on the silica glass crucible is less than 1.3 G.
4. The method of manufacturing of claim 1 , wherein in said fusing the second time by arc fusion the inner surface of the bottom portion, the rotational speed of the silica glass crucible is made greater than the rotational speed during arc fusion of the crucible-shaped molded product, and the second fusion temperature of the silica glass crucible is made higher than the temperature during arc fusion of the crucible-shaped molded product.
5. The method of manufacturing of claim 1 , wherein the rotational speed during arc fusion of the crucible-shaped molded product is set so that the gravitational acceleration exerted on the crucible-shaped molded product is 1.7 G or less, and the rotational speed of the silica glass crucible in said fusing the second time by arc fusion the inner surface of the bottom portion is set so that the gravitational acceleration exerted on the silica glass crucible exceeds 1.7 G.
6. The method of manufacturing of claim 1 , wherein the second fusing by arc fusion is conducted at a temperature of about 2,000° C.±200° C.
7. The method of manufacturing of claim 1 , wherein the removal of the bubbles is conducted by grinding, etching, or secondary fusing.
8. The method of manufacturing of claim 7 , wherein the secondary fusing of the ground or etched surface conducted after grinding or etching to render the surface smooth.
9. The method of manufacturing of claim 7 , wherein the grinding is conducted with a sand blaster or a grinder.
10. The method of manufacturing of claim 7 , wherein the etching is conducted with hydrofluoric acid.
11. The method of manufacturing of claim 7 , wherein the secondary fusing is conducted by inclining an electrode toward the corner portions.
12. The method of manufacturing of claim 1 , wherein said imparting reduced pressure is applied during at least part of the arc fusion process.