Silica-glass crucible and production method thereof
The present invention relates to a silica-glass crucible for pulling up single-crystal silicon therefrom by Czochralski method (CZ method) or for melting an optical-glass, which includes a crystallization promoter, and method of producing the silica-glass crucible in which a raw-material silica powder including Al and Ca at a specific molar concentration ratio is molded.
1. A silica-glass crucible, comprising:
a bottom part;
a bottom corner formed around the bottom part;
a lateral part extending upward from the bottom corner; and
Al and Ca,
wherein:
the silica-glass crucible has a crucible upper-end region at an end of the lateral part opposite the bottom corner;
the crucible upper-end region is a region extending from an upper end of the crucible downward to a distance therefrom of 5 mm or longer but not longer than a distance of a sum of an upper-end wall thickness and 10 mm;
the crucible upper-end region has the wall thickness of 10-18 mm;
the crucible upper-end region has a two-layer structure comprising an opaque outer layer comprising a natural-material-derived silica glass and a transparent inner layer comprising a natural-material-derived silica glass or a synthetic-material-derived silica glass; and
the silica-glass crucible has a structure comprising at least three layers comprising, from a lower end of the crucible upper-end region, an outer layer comprising a crystallization-promoter-containing silica glass, an opaque interlayer which is continuously formed from the opaque outer layer of the crucible upper-end region, and the transparent inner layer.
2. The silica-glass crucible according to claim 1 , wherein the crystallization-promoter-containing silica glass comprises Al and Ca, has an aluminum concentration of 9-20 wt ppm and a calcium concentration of 0.1-0.6 wt ppm, and has a molar concentration ratio (Al/Ca) between Al and Ca in a range of 15≤Al/Ca≤200.
3. The silica-glass crucible according to claim 1 , having a four-layer structure comprising an opaque outer layer comprising a natural-material-derived silica glass superposed on an outer surface of the outer layer comprising the crystallization-promoter-containing silica glass.
4. The silica-glass crucible according to claim 1 , wherein the crucible upper-end region further has a three-layer structure comprising the two-layer structure and a first outer layer made of silica glass that does not contain a crystallization promoter, and
from the lower end of the crucible upper-end region, the structure comprises at least four layers comprising the at least three layers and a second outer layer, made of crystallization-promoter-containing silica glass, disposed on an outer side of the first outer layer.