CARBON ELECTRODE AND METHOD FOR MANUFACTURING QUARTZ GLASS CRUCIBLE

Abstract

A carbon electrode used for an arc discharge for manufacturing a quartz glass crucible, wherein at least one of a concave pattern and a convex pattern is formed on a surface of the carbon electrode in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from an end portion where the arc discharge takes place. Consequently, a carbon electrode that can suppress agglomeration of silica fume on the carbon electrode while manufacturing a quartz glass crucible is provided.

Claims

1-5. (canceled)

6. A carbon electrode used for an arc discharge for manufacturing a quartz glass crucible, wherein at least one of a concave pattern and a convex pattern is formed on a surface of the carbon electrode in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from an end portion where the arc discharge takes place.

7. The carbon electrode according to claim 6, wherein at least one of a plurality of concave portions and a plurality of convex portions are formed as the at least one of the concave pattern and the convex pattern, and a depth of the concave portions or a height of the convex portions is 2.0 mm or more and 10.0 mm or less, and with a surface of the carbon electrode not having the concave portions or the convex portions formed as a reference surface, the at least one of the concave portions and the convex portions are present in an area ratio of 10% or more and 90% or less in any range of 20 mm in the longitudinal direction20 mm in a circumferential direction of the carbon electrode within the at least the range of 50 mm to 130 mm in the longitudinal direction of the carbon electrode.

8. The carbon electrode according to claim 6, wherein at least one of a groove and a projection is formed as the at least one of the concave pattern and the convex pattern.

9. The carbon electrode according to claim 7, wherein at least one of a groove and a projection is formed as the at least one of the concave pattern and the convex pattern.

10. The carbon electrode according to claim 6, wherein a screw groove is formed as the at least one of the concave pattern and the convex pattern, and a depth of the screw groove is 2.0 mm or more and 10.0 mm or less, and a pitch of the screw groove is 1.0 mm or more and 10 mm or less.

11. The carbon electrode according to claim 7, wherein a screw groove is formed as the at least one of the concave pattern and the convex pattern, and a depth of the screw groove is 2.0 mm or more and 10.0 mm or less, and a pitch of the screw groove is 1.0 mm or more and 10 mm or less.

12. The carbon electrode according to claim 8, wherein a screw groove is formed as the at least one of the concave pattern and the convex pattern, and a depth of the screw groove is 2.0 mm or more and 10.0 mm or less, and a pitch of the screw groove is 1.0 mm or more and 10 mm or less.

13. The carbon electrode according to claim 9, wherein a screw groove is formed as the at least one of the concave pattern and the convex pattern, and a depth of the screw groove is 2.0 mm or more and 10.0 mm or less, and a pitch of the screw groove is 1.0 mm or more and 10 mm or less.

14. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 6 to melt the raw quartz powder formed into the crucible shape.

15. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 7 to melt the raw quartz powder formed into the crucible shape.

16. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 8 to melt the raw quartz powder formed into the crucible shape.

17. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 9 to melt the raw quartz powder formed into the crucible shape.

18. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 10 to melt the raw quartz powder formed into the crucible shape.

19. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 11 to melt the raw quartz powder formed into the crucible shape.

20. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 12 to melt the raw quartz powder formed into the crucible shape.

21. A method for manufacturing a quartz glass crucible comprising the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the carbon electrode according to claim 13 to melt the raw quartz powder formed into the crucible shape.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a schematic view showing examples of concave patterns and convex patterns for the inventive carbon electrode.

[0021] FIG. 2 is a schematic view for explaining an area ratio in a region where a concave pattern or a convex pattern is present on the inventive carbon electrode.

DESCRIPTION OF EMBODIMENTS

[0022] Hereinafter, the present invention will be described more specifically with reference to the drawings.

[0023] The inventive carbon electrode is a carbon electrode used for an arc discharge for manufacturing a quartz glass crucible. The quartz glass crucible manufactured using the inventive carbon electrode is particularly suitable as a quartz glass crucible used as a quartz glass crucible for pulling a single crystal silicon, but is not limited thereto, and the inventive carbon electrode can be used for manufacturing a quartz glass crucible for other uses. The inventive carbon electrode has at least one of a concave pattern and a convex pattern formed on a surface of the carbon electrode in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from an end portion where the arc discharge takes place.

[0024] At least one of a plurality of concave portions and a plurality of convex portions are preferably formed as the at least one of the concave pattern and the convex pattern. Of course, both a concave portion and a convex portion may be formed. Furthermore, at least one of a groove and a projection is preferably formed as the at least one of the concave pattern and the convex pattern.

[0025] Examples of concave patterns and convex patterns for the inventive carbon electrode are shown in FIG. 1 (a) to (e).

[0026] FIG. 1 (a) is noted as concave line, and this is an embodiment in which the carbon electrode has a plurality of concave portions on the surface, and the plurality of concave portions are formed as a plurality of ring-shaped grooves. In addition, FIG. 1 (b) is noted as convex line, and this is an embodiment in which the carbon electrode has a plurality of convex portions on the surface, and the plurality of convex portions are formed as a plurality of ring-shaped projections.

[0027] The depth of the concave portions or a height of the convex portions is preferably 2.0 mm or more and 10.0 mm or less. That is, in the example of FIG. 1 (a), the depth of the grooves (the depth of the concave portions) is preferably 2.0 mm or more and 10.0 mm or less. In the example of FIG. 1 (b), a height of the projection (the height of the convex portions) is preferably 2.0 mm or more and 10.0 mm or less. Agglomeration of silica fume that adheres to the carbon electrode can be inhibited more effectively with such concave portions or convex portions.

[0028] Furthermore, with a surface of the carbon electrode not having the concave portions or the convex portions formed as a reference surface, the at least one of the concave portions and the convex portions are preferably present in an area ratio of 10% or more and 90% or less in any range of 20 mm in the longitudinal direction20 mm in a circumferential direction of the carbon electrode within the at least the range of 50 mm to 130 mm in the longitudinal direction of the carbon electrode. That is, the at least one of the concave portions and the convex portions are preferably present in an area ratio of 10% or more and 90% or less in the range of 20 mm in the longitudinal direction20 mm in the circumferential direction of the carbon electrode shown schematically in FIG. 2. The width of the groove and the interval between the grooves shown in FIG. 1 (a) can be set so as to satisfy this area ratio. The width of the convex portions and the interval between the convex portions shown in FIG. 1 (b) can also be set thus.

[0029] FIG. 1 (c) and FIG. 1 (d) are different embodiments of the present invention. FIG. 1 (c) is noted as concave circle, and this is an embodiment in which the carbon electrode has a plurality of concave portions on the surface, and the concave portions are formed as hemispherical dents. In addition, FIG. 1 (d) is noted as convex circle, and this is an embodiment in which the carbon electrode has a plurality of convex portions on the surface, and the convex portions are formed as hemispherical projections. As in FIGS. 1 (a) and (b), the depth of the concave portions is preferably 2.0 mm or more and 10.0 mm or less in the example of FIG. 1 (c), and the height of the convex portions is preferably 2.0 mm or more and 10.0 mm or less in the example of FIG. 1 (d).

[0030] Furthermore, in the embodiments of FIG. 1 (c) and (d) too, the at least one of the concave portions and the convex portions are preferably present in an area ratio of 10% or more and 90% or less in the range of 20 mm in the longitudinal direction20 mm in the circumferential direction of the carbon electrode shown schematically in FIG. 2. This area ratio can be satisfied by appropriately setting the concave portion diameter and the shortest distance between the concave portions shown in FIG. 1 (c). In addition, this area ratio can be satisfied by appropriately setting the convex portion diameter and the shortest distance between the convex portions shown in FIG. 1 (d).

[0031] Examples of concave portions or convex portions with a ring shape are shown in FIGS. 1 (a) and (b), and concave portions or convex portions with a hemispherical shape in FIGS. 1 (c) and (d), but the shapes of the concave portions or the convex portions are not limited thereto. Moreover, each of the shapes may be combined.

[0032] Another different embodiment of the present invention is shown in FIG. 1 (e). In this embodiment, a screw groove is formed as the at least one of the concave pattern and the convex pattern. In this case, the depth of the screw groove (that is, the height of the screw thread) is preferably 2.0 mm or more and 10.0 mm or less, and the pitch of the screw groove is preferably 1.0 mm or more and 10 mm or less. Note that in this embodiment with the screw groove formed, the shape of the screw portion such as the shape of the screw thread is not particularly limited. For example, a cross-sectional shape of the screw thread can be a triangle (that is, the top of the screw thread is configured to be a line) as shown in FIG. 1 (e). In addition, the cross-sectional shape of the screw thread can be a trapezoid (that is, the top of the screw thread is flat). Similarly, the shape of the bottom of the screw thread is also not particularly limited.

[0033] If there are no concave portions or convex portions on a carbon electrode, part of a silica powder is vaporized while being melted when manufacturing a quartz glass crucible, and silica fume that is cooled on the carbon electrode is deposited on the carbon electrode. In the present invention, the agglomeration of silica fume that adheres to the carbon electrode can be inhibited by adding, as described above, concavities or convexities in a range of 50 mm to 130 mm from the end of the carbon electrode where silica fume is liable to be deposited. The growth-inhibited silica fume is light in weight, and therefore, is discharged outside the system by an arc gas flow blowing up from inside the crucible and does not fall into the quartz glass crucible. During arc melting, deposition of silica fume is automatically suppressed since the carbon electrode end where the arc discharge takes place has a high temperature. Therefore, there is no necessity for concavities or convexities in a range of 50 mm from the electrode end. However, concavities or convexities may also be present in the range of 50 mm from the electrode end. In addition, regarding the electrode further up than 130 mm from the end, the deposition of the adhered silica fume is small compared to the electrode 50 mm to 130 mm from the end, and since the electrode further up than 130 mm is close to the exhaust port or the like at the time of arc discharge, the silica fume is easily discharged outside the system. Therefore, there is no necessity to form concavities or convexities. However, concavities or convexities may also be present in this range.

[0034] In addition, the present invention can be applied not only to a carbon electrode with a round bar shape having an almost constant diameter, but also to a carbon electrode having part of the diameter larger than other regions, etc.

[0035] The present invention also provides a method for manufacturing a quartz glass crucible using the above-described carbon electrode. This method for manufacturing a quartz glass crucible includes the steps of: preparing raw quartz powder which is to be a starting material for the quartz glass crucible to form into a crucible shape, and performing an arc discharge using the inventive carbon electrode described above to melt the raw quartz powder formed into the crucible shape. Since there are few defects on the surface of a quartz glass crucible thus obtained, the quartz glass crucible is suitable for manufacturing a single crystal.

EXAMPLE

[0036] Hereinafter, the present invention will be described more specifically with reference to Examples of the present invention and Comparative Examples, but the present invention is not limited to these Examples, and there is no doubt that various modifications can be carried out unless deviating from the technical concept of the present invention.

[0037] (Common conditions of the Examples and the Comparative Examples)

[0038] A quartz glass crucible with a diameter of 32 inches (approximately 81 mm) was manufactured by an arc discharge method using a round-bar-shaped carbon electrode with a diameter of 57.3 mm, and the quartz glass crucible was evaluated. When the total surface area of a plurality of silica fumes that fell into the manufactured crucible was 50 mm.sup.2 or more, this was defined as an adhesion defect, and the adhesion defect occurrence rate was investigated. An adhesion defect occurrence rate of 4% or less was determined as acceptable. In particular, an adhesion defect occurrence rate of 2% or less was determined as acceptable (excellent). An adhesion defect occurrence rate of more than 4% was determined as unacceptable. In addition, a case where formation of the arc was insufficient or unstable was evaluated as having a somewhat defective arc.

Examples 1-1 to 1-9

[0039] A carbon electrode in the embodiment shown in FIG. 1 (a) was fabricated. Ring-shaped grooves were formed on the round-bar-shaped electrode. The number of ring-shaped grooves (concave portions), the positions of the grooves (the distances from the electrode end), the intervals between the grooves, the width of the grooves, and the depth of the grooves were as shown in Table 1. The ratio (%) of the concave portions taking up the range of 20 mm20 mm shown in FIG. 2 is as shown in Table 1. Examples 1-1 to 1-9 are all examples in which the grooves were formed in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. A quartz glass crucible was manufactured using this carbon electrode.

Comparative Examples 1-1 to 1-3

[0040] In Comparative Example 1-1, no grooves were formed, and a round-bar carbon electrode with no other concavities or convexities formed was used. In Comparative Examples 1-2 and 1-3, grooves were formed, but the grooves were formed in parts that were not in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. The formed grooves were as described in Table 1.

TABLE-US-00001 TABLE 1 Ratio (%) of concave portions Number of Positions of taking up ring-shaped grooves: Interval 20 mm Adhesion grooves distance from between Width of Depth of 20 mm range defect Adhesion (concave electrode grooves grooves grooves (within range of occurrence accept- portions) end (mm) (mm) (mm) (mm) 50 mm to 130 mm) rate (%) ability Arc Example 4 50-52, 70-72, 18 2 2 10 1.3 Acceptable Favorable 1-1 90-92, 110-112 (excellent) Example 4 50-52, 70-72, 18 2 10 10 1.1 Acceptable Favorable 1-2 90-92, 110-112 (excellent) Example 8 50-52, 60-62, 8 2 2 20 1.0 Acceptable Favorable 1-3 70-72, 80-82, (excellent) 90-92, 100-102, 110-112, 120-122 Example 4 52-70, 72-90, 2 18 2 90 1.5 Acceptable Favorable 1-4 92-110, 112-130 (excellent) Compa- No No No 0 0 5.7 Unaccept- Favorable rative grooves grooves grooves able Example 1-1 Example 2 70-72, 110-112 38 2 2 0-10 3.0 Acceptable Favorable 1-5 Example 2 50-89, 91-130 2 39 2 90-100 3.5 Acceptable Favorable 1-6 Example 4 50-52, 70-72, 18 2 15 10 3.1 Acceptable Somewhat 1-7 90-92, 110-112 defective Example 4 50-52, 70-72, 18 2 1 10 3.5 Acceptable Favorable 1-8 90-92, 110-112 Example 3 10-12, 30-32, 18 2 2 0-10 3.0 Acceptable Favorable 1-9 50-52 Compa- 3 10-12, 25-27, 13 2 2 0 5.5 Unaccept- Favorable rative 40-42 able Example 1-2 Compa- 4 140-142, 160-162, 18 2 2 0 5.5 Unaccept- Favorable rative 180-182, 200-202 able Example 1-3

[0041] As shown in Table 1, adhesion acceptability was acceptable in every case in Examples 1-1 to 1-9, where the grooves were formed in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion where the arc discharge takes place.

[0042] In particular, in Examples 1-1 to 1-4, the depth of the grooves was 2.0 mm or more and 10.0 mm or less, and the area ratio of the grooves taking up the range of 20 mm in the longitudinal direction20 mm in the circumferential direction of the carbon electrode was 10% or more and 90% or less, and adhesion acceptability was particularly excellent. In Example 1-7, arc formation was somewhat unstable, but an adhesion reduction effect was obtained.

Example 2-1

[0043] A carbon electrode in the embodiment shown in FIG. 1 (b) was fabricated. Ring-shaped convex portions were formed on the round-bar-shaped electrode. The number of ring-shaped convex portions, the positions of the convex portions (the distances from the electrode end), the intervals between the convex portions, the width of the convex portions, and the height of the convex portions were as shown in Table 2. The ratio (%) of the convex portions taking up the range of 20 mm20 mm shown in FIG. 2 is as shown in Table 2. Example 2-1 is an example in which the convex portions were formed in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. A quartz glass crucible was manufactured using this carbon electrode.

TABLE-US-00002 TABLE 2 Ratio (%) of convex portions Positions of Interval taking up Number of convex portions: between Width of Height of 20 mm Adhesion ring-shaped distance from convex convex convex 20 mm range defect adhesion convex electrode portions portions portions (within range of occurrence accept- portions end (mm) (mm) (mm) (mm) 50 mm to 130 mm) rate (%) ability Arc Example 4 50-52, 70-72, 18 2 2 10 1.3 Acceptable Favorable 2-1 90-92, 110-112 (excellent)

[0044] As shown in Table 2, adhesion acceptability was acceptable (excellent) in Example 2-1.

Examples 3-1 and 3-2

[0045] A carbon electrode in the embodiment shown in FIG. 1 (c) was fabricated. Concave portions which were hemispherical dents were formed on the round-bar-shaped electrode. The concave portion diameter, the positions of the concave portions (the distances from the electrode end), the shortest distance between the concave portions, and the depth of the concave portions were as shown in Table 3. The ratio (%) of the concave portions taking up the range of 20 mm20 mm shown in FIG. 2 is as shown in Table 3. Examples 3-1 and 3-2 are examples in which the concave portions were formed in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. A quartz glass crucible was manufactured using this carbon electrode.

TABLE-US-00003 TABLE 3 Ratio (%) of Shortest concave portions Positions of distance taking up Concave concave portions: between Depth of 20 mm Adhesion portion distance from concave concave 20 mm range defect Adhesion diameter electrode portions portions (within range of occurrence accepta- (mm) end (mm) (mm) (mm) 50 mm to 130 mm) rate (%) bility Arc Example 10 55-65, 75-85, 10 2 19.6 1.5 Acceptable Favorable 3-1 95-105, 115-125 (excellent) Example 5 57.5-62.5, 15 2 4.9 3.3 Acceptable Favorable 3-2 77.5-82.5, 97.5-102.5, 117.5-122.5

[0046] As shown in Table 3, adhesion acceptability was acceptable in each case in Examples 3-1 and 3-2. In particular, in Example 3-1, the ratio of the concave portions taking up a range of 20 mm20 mm was an area ratio within the range of 10% or more and 90% or less, and adhesion defect occurrence rate was particularly excellent.

Examples 4-1 and 4-2

[0047] A carbon electrode in the embodiment shown in FIG. 1 (d) was fabricated. Convex portions which were hemispherical projections were formed on the round-bar-shaped electrode. The convex portion diameter, the positions of the convex portions (the distances from the electrode end), the shortest distance between the convex portions, and the height of the convex portions were as shown in Table 4. The ratio (%) of the concave portions taking up the range of 20 mm20 mm shown in FIG. 2 is as shown in Table 4. Examples 4-1 and 4-2 are examples in which the convex portions were formed in at least a range of 50 mm to 130 mm in a longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. A quartz glass crucible was manufactured using this carbon electrode.

TABLE-US-00004 TABLE 4 Ratio (%) of Shortest convex portions Positions of distance taking up Convex convex portions: between Height of 20 mm Adhesion portion distance from convex convex 20 mm range defect Adhesion diameter electrode portions portions (within range of occurrence accept- (mm) end (mm) (mm) (mm) 50 mm to 130 mm) rate (%) ability Arc Example 10 55-65, 75-85, 10 2 19.6 1.3 Acceptable Favorable 4-1 95-105, 115-125 (excellent) Example 5 57.5-62.5, 15 2 4.9 3.8 Acceptable Favorable 4-2 77.5-82.5, 97.5-102.5, 117.5-122.5

[0048] As shown in Table 4, adhesion acceptability was acceptable in each case in Examples 4-1 and 4-2. In particular, in Example 4-1, the ratio of the convex portions taking up a range of 20 mm20 mm was an area ratio within the range of 10% or more and 90% or less, and adhesion defect occurrence rate was particularly excellent.

Examples 5-1 to 5-8

[0049] A carbon electrode in the embodiment shown in FIG. 1 (e) was fabricated. A screw groove was formed in at least the range of 50 mm to 130 mm in the longitudinal direction of the carbon electrode from the end portion of the carbon electrode where the arc discharge takes place. The height of the screw thread (the depth of the screw groove), the position of the screw formation (the distance from the electrode end), and the pitch of the screw thread were as shown in Table 5. A quartz glass crucible was manufactured using this carbon electrode.

TABLE-US-00005 TABLE 5 Position of screw Adhesion Height of formation: defect screw thread distance from Pitch occurrence Adhesion (mm) electrode end (mm) (mm) rate (%) acceptability Arc Example 2 50-130 1 1.1 Acceptable Favorable 5-1 (excellent) Example 10 50-130 10 1.3 Acceptable Favorable 5-2 (excellent) Example 2 50-130 10 1.4 Acceptable Favorable 5-3 (excellent) Example 1 50-130 2 2.7 Acceptable Favorable 5-4 Example 15 50-130 10 3.6 Acceptable Somewhat 5-5 defective Example 2 50-130 0.5 3.5 Acceptable Favorable 5-6 Example 10 50-130 15 3.6 Acceptable Favorable 5-7 Example 2 50-130 15 3.3 Acceptable Favorable 5-8

[0050] As shown in Table 5, adhesion acceptability was acceptable in each case in Examples 5-1 to 5-8. In particular, Examples 5-1 to 5-3 are examples in which the depth of the screw groove was 2.0 mm or more and 10.0 mm or less and the pitch of the screw groove was 1.0 mm or more and 10 mm or less, and adhesion acceptability was particularly excellent. In Example 5-5, arc formation was somewhat unstable, but an adhesion reduction effect was obtained.

[0051] It should be noted that the present invention is not limited to the above-described embodiments. The embodiments are just examples, and any examples that have substantially the same feature and demonstrate the same functions and effects as those in the technical concept disclosed in claims of the present invention are included in the technical scope of the present invention.