Method of manufacturing a vitreous silica crucible having a transparent layer, bubble-containing layers, and a semi-transparent layer in its wall
A method of manufacturing of a vitreous silica crucible includes: fusing silica powder under a reduced pressure of −50 kPa or more and less than −95 kPa to form a transparent vitreous silica layer as an inner layer; fusing silica powder under a reduced pressure of 0 kPa or more and less than −10 kPa to form a bubble-containing vitreous silica layer as an intermediate layer; and fusing silica powder under a reduced pressure of −10 kPa or more and less than −50 kPa to form a semi-transparent vitreous silica layer as an outer layer.
1. A method of manufacturing of a vitreous silica crucible for pulling a silicon single crystal, wherein the crucible has a wall comprising, from an inner surface toward an outer surface of the crucible, a transparent vitreous silica layer having a bubble content rate of less than 0.5% and having an OH group concentration of 30 ppm or less, a first bubble-containing vitreous silica layer having a bubble content rate of 1% or more and less than 50%, a semi-transparent vitreous silica layer having a bubble content rate of 0.5% or more and less than 1.0% and having an OH group concentration of 35 ppm or more and less than 300 ppm, and a second bubble-containing vitreous silica layer having a bubble content rate of 1% or more and less than 50%; wherein the first bubble-containing vitreous silica layer comprises an impurity-containing vitreous silica layer to which impurities are added acting as nuclei when turning the vitreous silica into crystalline silica in a high temperature environment, wherein a concentration of impurities in the impurity-containing vitreous silica layer is 20 ppm or higher and is higher than that in the neighboring layers; and wherein the total thickness of the first and second bubble-containing vitreous silica layers is 50% or less of the thickness of the wall,
said method comprising the processes of: forming a silica powder layer on an inner surface of a rotating mold; fusing the silica powder layer, followed by solidifying, to form a vitreous silica layer constituting the vitreous silica crucible, wherein
first, the silica powder layer is fused in a predetermined thickness under a reduced pressure of −50 kPa or more and less than −95 kPa with reference to atmospheric pressure to form the transparent vitreous silica layer, then the silica powder layer is fused in a predetermined thickness under a reduced pressure of 0 kPa or more and less than −10 kPa with reference to atmospheric pressure to form the first bubble-containing vitreous silica layer, then the silica powder layer is fused in a predetermined thickness under a reduced pressure of −10 kPa or more and less than −50 kPa with reference to atmospheric pressure to form the semi-transparent vitreous silica layer, and then the silica powder layer is fused in a predetermined thickness under a reduced pressure of 0 kPa or more and less than −10 kPa with reference to atmospheric pressure to form the second bubble-containing vitreous silica layer.
2. The method of claim 1 , wherein temperature for forming the semi-transparent vitreous silica layer is 1600 deg. C. to 2600 deg. C.
3. A method of manufacturing a silicon ingot comprising the processes of: obtaining silicon melt by melting polycrystalline silicon in a crucible manufactured by a method of claim 1 , dipping an end of a seed crystal to the silicon melt, pulling a silicon ingot by pulling the seed crystal while rotating it, and thereafter recharging and melting polycrystalline silicon, and pulling another silicon ingot.
4. The method of claim 3 , wherein Ba is added to the silicon melt.