Patent Application
20200369549
The present invention relates to a carbon electrode, and relates to a method for manufacturing a quartz glass crucible using the carbon electrode.
Conventionally, a silicon single crystal used as a substrate for a single crystal semiconductor material has been manufactured by the so-called Czochralski method in which a polycrystalline silicon is melted in a quartz glass crucible and this is grown as a crystal on a seed crystal to manufacture the silicon single crystal. There are several types of the quartz glass crucible used in the above-described manufacturing method depending on manufacturing methods, but practically, a translucent quartz glass crucible obtained by a method for manufacturing a quartz glass crucible by charging silicon dioxide powder (raw quartz powder) along an inner surface of a hollow mold that can be rotated and heating the silicon dioxide powder to melt by an arc discharge using a carbon electrode while rotating the mold has been used. The translucent quartz glass crucible has advantages of many bubbles being dispersed to make the distribution of heat uniform, and being stronger compared to other crucibles so that a crucible of any size can be manufactured.
Conventionally, there has been a problem that even when a silicon single crystal is grown using the translucent quartz glass crucible, crystallization becomes unstable in the process and crystallization rate (the proportion of polycrystal that becomes a single crystal) is decreased. A cause for this includes the fact that a sublimation component of the silicon dioxide which is a starting material condenses and falls to form a microbubble aggregate which undergoes thermal expansion and partially delaminates the inner surface, and the delaminated quartz fragment is mixed into the melted silicon. In order to solve such a problem, a method for manufacturing a quartz glass crucible having a thick transparent layer by heating the inner surface of the crucible to melt to form a transparent layer, or by scattering molten silicon dioxide powder to form the thick transparent layer has been suggested. However, neither of the above-described manufacturing methods can eliminate microbubble aggregates sufficiently, and a silicon single crystal cannot be pulled with a favorable crystallization rate with the quartz glass crucibles. In addition, in the above-described heat-melting process, the inner surface of the obtained crucible is contaminated by selective evaporation/condensation of silicon dioxide and trace impurities contained therein or by scattering, etc. of ash content that accompanies wearing of the carbon electrode, and even when a high-purity starting material is used, it is not possible to fabricate a corresponding inner surface. For this reason, sufficient effect for suppressing crystal defects cannot be obtained even when a high-purity starting material is used.
The method for manufacturing a quartz glass crucible disclosed in Patent Document 1 has been suggested in order to solve these problems. This method is a method for manufacturing a quartz glass crucible by supplying silicon dioxide powder to a rotatable top-open mold, forming a silicon-dioxide-powder-charged layer along the inner surface of the mold, then heating to melt from the inside, and in the method, heat-melting is performed by covering the opening of the mold with a lid having two or more holes and the heat-melting is performed while ventilating the high-temperature gas atmosphere inside the mold through the holes.
Patent Document 1: Japanese Unexamined Patent Application Publication No. H08-026759
When a quartz glass crucible is manufactured, silica fume that is generated by raw silica being melted adheres to a carbon electrode and agglomerates, and thus falls on an inner surface of the quartz glass crucible. If the ratio of the part where this fallen material melted and solidified as it was to the inner surface area of the crucible is large, silicon single crystal pulling performance (single crystallization rate, etc.) is degraded.
In recent years, as the diameter of manufactured quartz glass crucibles become larger, 24 inches, 28 inches, and 32 inches (1 inch is 2.54 cm), electric power for melting has become high-powered, and silica fume generated while melting has increased, and for this reason, it has become impossible to prevent fallen material due to agglomerated silica fume sufficiently only by the method of Patent Document 1.
The present invention has been accomplished in view of the above circumstances, and an object thereof is to provide a carbon electrode that can suppress agglomeration of silica fume on the carbon electrode while manufacturing a quartz glass crucible.
To solve the above problem, the present invention provides 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.
The inventive carbon electrode can inhibit the agglomeration of silica fume that adheres to the carbon electrode during arc melting by having a concave pattern or a convex pattern formed in at least a range of 50 mm to 130 mm in a longitudinal direction as described. 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. In this manner, agglomeration of silica fume while manufacturing the quartz glass crucible can be suppressed.
In this event, preferably, 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 direction×20 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.
Such concave portions or convex portions make it possible to more effectively inhibit the agglomeration of silica fume that adheres to the carbon electrode.
Furthermore, at least one of a groove and a projection can be formed as the at least one of the concave pattern and the convex pattern.
As described, the concave pattern or the convex pattern can be, as specific shapes, a groove or a projection.
Furthermore, in the inventive carbon electrode, a screw groove can be formed as the at least one of the concave pattern and the convex pattern, and a depth of the screw groove can be 2.0 mm or more and 10.0 mm or less, and a pitch of the screw groove can be 1.0 mm or more and 10 mm or less.
The agglomeration of silica fume that adheres to the carbon electrode can also be inhibited by forming such a screw groove.
Furthermore, the present invention provides a method for manufacturing a quartz glass crucible including 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 any carbon electrode described above to melt the raw quartz powder formed into the crucible shape.
The inventive carbon electrode can inhibit the agglomeration of silica fume that adheres to the carbon electrode during arc melting as described above. 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. Therefore, by the inventive method for manufacturing a quartz glass crucible, agglomeration of silica fume while manufacturing the quartz glass crucible can be suppressed.
The inventive carbon electrode can inhibit the agglomeration of silica fume that adheres to the carbon electrode by having a concave pattern or a convex pattern formed in at least a range of 50 mm to 130 mm from an end portion in a longitudinal direction. 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. In this manner, agglomeration of silica fume while manufacturing the quartz glass crucible can be suppressed. In this manner, a quartz glass crucible having a quartz glass crucible inner surface with uniform characteristics can be provided. Accordingly, using such a quartz glass crucible, a single crystal can be manufactured with a good yield and productivity.
Hereinafter, the present invention will be described more specifically with reference to the drawings.
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.
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.
Examples of concave patterns and convex patterns for the inventive carbon electrode are shown in
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
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 direction×20 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 direction×20 mm in the circumferential direction of the carbon electrode shown schematically in
Furthermore, in the embodiments of
Examples of concave portions or convex portions with a ring shape are shown in
Another different embodiment of the present invention is shown in
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.
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.
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.
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.
(Common conditions of the Examples and the Comparative Examples)
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 mm2 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.
A carbon electrode in the embodiment shown in
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.
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.
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 direction×20 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.
A carbon electrode in the embodiment shown in
As shown in Table 2, adhesion acceptability was acceptable (excellent) in Example 2-1.
A carbon electrode in the embodiment shown in
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 mm×20 mm was an area ratio within the range of 10% or more and 90% or less, and adhesion defect occurrence rate was particularly excellent.
A carbon electrode in the embodiment shown in
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 mm×20 mm was an area ratio within the range of 10% or more and 90% or less, and adhesion defect occurrence rate was particularly excellent.
A carbon electrode in the embodiment shown in
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2018-019591 | Feb 2018 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/001172 | 1/17/2019 | WO | 00 |
