Quartz glass crucible and method for producing the same
A quartz glass crucible including bottom, curved, and straight body portions, where the quartz glass crucible includes an outer layer including opaque quartz glass containing bubbles, and an inner layer including transparent quartz glass, the outer layer fabricated from different types of raw material powder, the outer layer having regions sectioned by bubble content densities, and bubble content densities of two outer layer adjacent regions, when d a (pcs/mm 3 ) is defined as content density of a region “a” having a greater content density, and d b (pcs/mm 3 ) is defined as content density of a region “b” having a smaller content density, a difference D=(d a −d b )/d b between content densities of the two regions is 10% or more.
1. A method for producing a quartz glass crucible having an outer layer comprising an opaque quartz glass containing bubbles therein, and an inner layer comprising a transparent quartz glass, the quartz glass crucible comprising (i) a bottom portion, (ii) a straight body portion having a substantially cylindrical shape, and (iii) a curved portion between the straight body portion and the bottom portion, the method comprising the steps of:
supplying a raw material powder of the outer layer into a rotating mold to form, on an inner surface of the mold, a powder layer to be the outer layer of the quartz glass crucible; and
fabricating the outer layer by heat-melting the powder layer,
wherein
the powder layer is formed using a same type or two or more different types of raw material powder as the raw material powder of the outer layer,
when the powder layer is formed, a difference is made in a rotational rate of the mold so that the powder layer is sectioned into two or more regions according to the rotational rate of the mold,
two or more regions sectioned by content densities of the bubbles are fabricated in the outer layer by heat-melting the powder layer sectioned into the two or more regions, wherein regarding bubble content densities of two adjacent regions of the outer layer, when d a (pcs/mm 3 ) is defined as a bubble content density of a region “a” having a greater content density of the bubbles, and d b (pcs/mm 3 ) is defined as a bubble content density of a region “b” having a smaller content density of the bubbles, a difference D=(d a −d b )/d b between the bubble content densities of the two adjacent regions is 10% or more, and
the rotational rate of the mold is changed in a position corresponding to the straight body portion of the quartz glass crucible so that a boundary where the difference D between the bubble content densities is 10% or more is located in the straight body portion.
2. The method for producing a quartz glass crucible according to claim 1 , wherein the powder layer is fabricated using the two or more different types of raw material powder, and
the two or more regions of the powder layer according to the rotational rate of the mold each contains the different types of raw material powder so that the regions sectioned by the content densities of the bubbles are each fabricated from the different types of raw material powder.
3. The method for producing a quartz glass crucible according to claim 1 , wherein at least a part of the powder layer is formed to have a plurality of sub-powder-layers differentiated by a difference in raw material powder in a thickness direction.
4. The method for producing a quartz glass crucible according to claim 2 , wherein at least a part of the powder layer is formed to have a plurality of sub-powder-layers differentiated by a difference in raw material powder in a thickness direction.
5. The method for producing a quartz glass crucible according to claim 1 , wherein the quartz glass crucible is a quartz glass crucible for pulling a single crystal silicon for pulling a single crystal silicon from a silicon melt held in the quartz glass crucible.
6. The method for producing a quartz glass crucible according to claim 2 , wherein the quartz glass crucible is a quartz glass crucible for pulling a single crystal silicon for pulling a single crystal silicon from a silicon melt held in the quartz glass crucible.
7. The method for producing a quartz glass crucible according to claim 1 , wherein when the powder layer is formed, the difference in the rotational rate of the mold is made so that the difference D between the bubble content densities of the two adjacent regions is 16.3% or more.
8. The method for producing a quartz glass crucible according to claim 1 , wherein when the powder layer is formed, the difference in the rotational rate of the mold is made so that the difference D between the bubble content densities of the two adjacent regions is 37.2% or more.
9. The method for producing a quartz glass crucible according to claim 1 , wherein when the powder layer is formed, the difference in the rotational rate of the mold is made so that the difference D between the bubble content densities of the two adjacent regions is 46.5% or more.