JP2008162840A - Method for producing quartz glass crucible - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a quartz glass crucible whose curved part and bottom part are not excessively heated, and which has a shape excellent in formability and contains few internal air bubbles. <P>SOLUTION: In the method for producing the quartz glass crucible, comprising arc-melting a quartz powder molding filled in a rotating mold while evacuating it, an electrode is moved to the side relatively to the mold center line at the start of arc-melting or during arc-melting, and arc-melting is performed at the eccentric position. Preferably, the time for heating the whole body is ≤60% of the total time for arc-melting. The quartz glass crucible produced by this method is also provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a quartz glass crucible used for pulling up a silicon single crystal, and more particularly to a quartz glass crucible having excellent moldability and few internal bubbles, and a method and apparatus for producing the same.

  Single crystal silicon is mainly manufactured by the CZ method. In this method, a seed crystal is immersed in a silicon melt in a quartz crucible at a high temperature, and this is gradually pulled up to produce single crystal silicon. A high-purity quartz glass crucible for storing the silicon melt is used. ing.

  Quartz glass crucibles used for pulling single crystal silicon are mainly manufactured by the arc melting method. In this method, quartz powder is deposited on the inner surface of a rotating mold made of carbon to a certain thickness to form a quartz powder compact, and the quartz powder is heated and melted by arc discharge of an electrode placed inside the mold. This is a method (rotating mold method) for producing a vitreous silica glass crucible.

  In the above manufacturing method, in order to remove bubbles inside the glass layer, a method is known in which quartz powder is melted while being sucked from the mold side and degassing the quartz powder molded body under reduced pressure (Patent Document 1, Patent Document 2). ). In this melting step, the quartz powder molded body is degassed under reduced pressure (this is called evacuation) by melting the inner surface of the quartz powder molded body uniformly and thinly to form a thin glass layer on the surface. It is necessary to seal and increase the degree of vacuum in the quartz powder molded body.

In the above production method for producing a glass crucible by melting a quartz powder molded body, conventionally, an arc electrode is set on the center line of the rotary mold, and the quartz powder molded body around the mold is generally heated uniformly. is there. However, the rim end at the top of the quartz powder molded body formed on the inner surface of the mold has a lower heat retention than the curved and bottom portions of the molded body, so the melting speed of the rim end is slow, and a thin glass layer is sufficient on the rim end surface. Thus, the degree of vacuum of the quartz powder molded body does not increase, and a crucible with few internal bubbles in the glass layer cannot be obtained. On the other hand, when the rim end is melted by increasing the amount of heat generated by arc melting in order to compensate for the insufficient melting of the rim end, the curved part and the bottom part are excessively heated and melted, and the shape of the quartz powder compact tends to collapse. There is a problem.
Japanese Patent Laid-Open No. 06-191986 Japanese Patent Laid-Open No. 10-025184

  The present invention solves the above problems in the conventional manufacturing method, the rim end of the crucible is sufficiently sealed inside and the curved portion and the bottom portion are not excessively heated, and the degree of vacuum of the quartz powder compact is high, A method for producing a quartz glass crucible having excellent shape moldability and few internal bubbles, a quartz glass crucible produced by the method, and a production apparatus therefor are provided.

The present invention relates to a method for producing a quartz glass crucible that solves the above problems by the following configuration.
(1) In a method of producing a quartz glass crucible by arc melting while evacuating a quartz powder compact filled in a rotary mold, the electrode is positioned relatively to the mold center line during or after arc melting. The method for producing a quartz glass crucible is characterized by moving in the direction and arc melting at an eccentric position.
(2) The quartz glass crucible described in the above (1), in which the entire heating in which the electrode is arc-melted on the mold center line and the local heating in which the electrode is arc-melted at an eccentric position removed from the mold center line are performed. Production method.
(3) The method for producing a quartz glass crucible as described in (1) or (2) above, wherein the total heating time is 60% or less of the total arc melting time.
(4) In local heating, the distance L2 between the center of the electrode tip and the heated portion of the quartz powder molded body is maintained at 5 to 80% of the distance L1 from the mold center line to the heated portion, and the above (1) The method for producing a quartz glass crucible according to any one of (3) to (3).
(5) The quartz glass crucible according to any one of (1) to (4) above, wherein an area of a circumscribed circle in contact with a plurality of electrode tips is 710 cm ² or less, and the entire inside of the circumscribed circle is arc-heated. Production method.
(6) A method for producing a quartz glass crucible, wherein the distance between the electrode centers is 15 cm or less in the method (5).
(7) The crucible manufactured by any one of the above methods (1) to (6), wherein the curvature W2 of the curved portion inner surface is 0.8 to 1.2 times the curvature W1 of the curved portion outer surface. Quartz glass crucible.
(8) A crucible manufactured by any one of the above methods (1) to (6), wherein internal bubbles of 0.5 mm or more are curved in a thickness range of 1.0 mm from the inner surface of the entire crucible. Quartz glass crucible with 5 or fewer parts as a whole.
(9) An apparatus for producing a quartz glass crucible having a means for moving to the side of at least one of an arc electrode and a rotary mold so that the relative position of the arc electrode with respect to the rotary mold can be eccentric.

  In the manufacturing method of the present invention, the electrode is moved laterally with respect to the mold center line during arc melting start or during arc melting, and arc melting is performed at the eccentric position. The rim end can be sufficiently heated and melted by suppressing excessive heating of the lower portion of the side wall, the curved portion and the bottom portion, and an inner surface seal with a thin glass layer can be uniformly formed on the entire inner surface of the crucible. Therefore, a quartz glass crucible with few internal bubbles can be obtained.

  The manufacturing method of the present invention performs the whole heating in which the electrode is arc-melted on the mold center line and the local heating in which the electrode is melted at an eccentric position where the electrode is removed from the mold center line. By controlling the arc melting so that it is 60% or less of the total melting time, the rim end is sufficiently heated and melted, and overheating from the lower part of the crucible side wall to the curved part / bottom part is suppressed. A glass crucible with excellent moldability can be prevented without drastically lowering the glass viscosity, preventing the glass from sagging from the lower part of the side wall, or shifting the glass from the bottom. Obtainable.

Specifically, in the manufacturing method of the present invention, for example, in local heating, the distance L2 between the center of the electrode tip and the heating part of the quartz powder molded body is set to 5 to 80 of the distance L1 from the mold center line to the heating part. In the arc melting with a three-phase alternating current electrode, the area of the circumscribed circle in contact with the tip of each electrode is set to 710 cm ² or less, and the entire inner circle of the circumscribed circle is arc-heated, Is set to 15 cm or less, for example, the curvature W2 of the inner surface of the curved portion is 0.8 to 1.2 times the curvature W1 of the outer surface of the curved portion, and 1 from the entire inner surface of the crucible. In the thickness range of 0.0 mm, it is possible to obtain a quartz glass crucible in which internal bubbles of 0.5 mm or more are 5 or less in the entire curved portion.

Hereinafter, the present invention will be specifically described with reference to embodiments.
The production method of the present invention is a method for producing a silica glass crucible by evacuating a quartz powder molded body filled in a rotating mold to produce a quartz glass crucible. It is a method for producing a quartz glass crucible, which moves relatively to the side and arc melts at an eccentric position.

  FIG. 1 shows an outline of a method for producing a quartz glass crucible by arc-melting a quartz powder compact filled in a rotary mold. As shown in the drawing, the quartz powder compact 11 is formed by filling the inner surface of the rotating mold 10 with a predetermined thickness of quartz powder. The mold 10 is provided with a vent hole 12 for evacuation, and the vent hole 12 opens on the inner surface of the mold. An arc heating electrode 13 is provided on the center line L of the mold 10. The quartz powder molded body 11 is arc-melted by the electrode 13 while evacuating it, and the quartz powder is melted to produce a glass crucible. To do.

  As an apparatus for carrying out the manufacturing method of the present invention, vertical movement means (not shown) is provided in either the mold 10 or the electrode 13, and lateral movement means is provided in either the mold 10 or the electrode 13. What is provided (illustration omitted) is preferable. As shown in FIG. 2, the manufacturing method of the present invention moves the electrode 13 sideways relative to the mold center line L by moving either the rotary mold 10 or the arc electrode 13 sideways. The arc melts at the eccentric position.

  Since the mold 10 is rotating at the time of arc melting, even if the electrode 13 is brought close to one rim end 15b and arc melting is performed, the entire rim end 15 is intermittently melted at a position close to the electrode 13 continuously. Then, the entire rim end is heated and melted uniformly.

  The manufacturing method of the present invention performs the entire heating for performing the arc melting of the electrode 13 on the mold center line and the local heating for performing the arc melting at an eccentric position where the electrode 13 is removed from the mold center line. Is preferably controlled to 60% or less of the total arc melting time.

  In general, the rim end 15 of the quartz powder molded body 11 has lower heat retention than the side wall portion 16, the curved portion 17, and the bottom portion 18 because the side surface and the upper surface are in contact with the atmosphere. For this reason, when the entire heating based on the rim end 15 is performed throughout the total arc melting time, the portion from the lower portion of the side wall portion 16 to the curved portion 17 and the bottom portion 18 is heated exceeding an appropriate temperature. Excessive heating greatly reduces the glass viscosity of the above part. As a result, the molten glass sags from the lower portion of the side wall due to gravity and the glass shifts from the bottom due to the centrifugal force of mold rotation, which may cause variations in the thickness of the curved portion.

  On the other hand, in the manufacturing method of the present invention, if the total heating time is controlled to 60% or less of the total arc melting time, the rim end 15 is heated sufficiently while the portion from the lower portion of the side wall to the curved portion / bottom portion is overheated. Since the glass viscosity at this portion is not significantly reduced, an extreme increase in the thickness of the corner portion of the curved portion 17 is prevented, and a crucible with excellent moldability can be obtained. In addition, in order to suppress the variation in the thickness at each part, it is preferable that the entire heating is performed about 50% of the total arc melting time. Therefore, the local heating is 40 to 50% with respect to the total arc melting time. It is preferable to perform the entire heating by 50 to 60%.

  Specifically, for example, when producing a quartz crucible having a diameter of 28 to 32 inches and an average wall thickness of 11 to 16 mm, when the temperature of the inner surface of the crucible is 1600 to 2500 ° C. and the total time of arc melting is 20 to 40 minutes, the electrode 13 To the rim end 15, and local heating is performed for 10 to 20 minutes from the start of arc melting, and then the entire heating is preferably performed for 10 to 20 minutes.

  As shown in FIG. 2, the manufacturing method of the present invention is such that the distance L2 between the center of the electrode tip and the heating part of the quartz powder molded body 11 is 5 to 5 of the distance L1 from the mold center line L to the heating part. It is preferable to hold at 80% and perform arc melting. If the distance L2 is greater than 80% of L1, the tip of the electrode is too far away from the heating part, and the effect of local heating becomes insufficient. On the other hand, if the distance L2 is smaller than 5% of L1, the tip of the electrode is too close to the heated portion, so that quartz powder or molten glass is blown by the air flow generated by arc discharge.

When using a plurality of electrodes, as shown in FIG. 3, the manufacturing method of the present invention sets the area of the circumscribed circle S in contact with the outer periphery of each tip of these electrodes 21, 22, 23 to 710 cm ² or less, It is preferable to arc-heat the entire circle of the circumscribed circle S. The center-to-center distance L3 of each electrode is preferably 15 cm or less. Specifically, for example, in the arc melting condition (paragraph 0018) exemplified in the local heating, when the area of the circumscribed circle S is larger than the above range and the center-to-center distance L3 between the electrodes is more than 15 cm, The heating area is too wide and local heating does not occur.

  According to the manufacturing method of the present invention, the curvature W2 of the curved portion inner surface is 0.8 to 1.2 times the curvature W1 of the curved portion outer surface (W2 / W1 = 0.8 to 1.2) in the arc melting condition. In addition, a quartz glass crucible can be obtained in which the internal bubbles of 0.5 mm or more are 5 or less in the entire curved portion in the thickness range of 1.0 mm from the inner surface of the entire crucible. Note that the inner surface curvature W2 and the outer surface curvature W1 of the curved portion are the curvatures measured for the inner surface and the outer surface, respectively, in the constant measurement range R of the curved portion, as shown in FIG. What is necessary is just to measure about the whole and to judge by the average value.

  If the curvature W2 of the inner surface of the curved portion deviates from 0.8 to 1.2 times the curvature W1 of the outer surface of the curved portion, the thickness nonuniformity of the curved portion becomes large, and the moldability deteriorates. Also, if the number of internal bubbles of 0.5 mm or more exceeds 5 in the entire curved portion within a thickness range of 1.0 mm from the inner surface of the entire crucible, the internal bubbles expand at a high temperature when the crucible is used, and the inside of the crucible This is not preferable because it may cause problems such as peeling the surface and reducing the yield of the silicon single crystal.

Examples of the present invention are shown below together with comparative examples.
A quartz glass crucible having a diameter of 28 inches, a height of 500 mm, and an average wall thickness of 11 mm is made of synthetic quartz powder or natural quartz powder and arc-heated so that the temperature on the inner surface of the crucible is 1600 to 2500 ° C. A quartz glass crucible was produced according to the conditions. Table 1 shows the number of internal bubbles of the curved portion, the ratio of the internal curvature and the external curvature of this crucible together with the manufacturing conditions.

  In Table 1, the ratio of the total heating is the ratio (%) of the total heating to the total arc time, and the distance between the electrode tips is the ratio of the distance L2 between the heating site and the electrode tip to the distance L1 between the heating site and the mold center line (L2). / L1:%), the ultimate vacuum is the maximum vacuum at the time of arc melting of the quartz powder compact, and the number of bubbles is a bubble of 0.5 mm or more in size within the thickness of 1.0 mm from the inner surface of the entire crucible The number and the curvature ratio are values based on an average value obtained by measuring the ratio (W2 / W1) of the curved portion inner surface curvature W2 and the curved portion outer surface curvature W1 for each predetermined range with respect to the entire curved portion.

  As shown in Table 1, each of Examples 1 to 6 of the present invention has a high ultimate vacuum and therefore has a small number of bubbles. Further, the curvature ratio is in the range of 0.8 to 1.2, and the moldability is good. On the other hand, Comparative Examples 1 to 5 outside the scope of the present invention all have a low ultimate vacuum and a large number of bubbles in each stage. Moreover, a curvature ratio is larger than 1.2, and a moldability is inferior.

Conceptual diagram of quartz glass crucible production by rotary mold method Conceptual diagram showing the curvature of the crucible curve Conceptual diagram showing electrodes and circumscribed circle Explanatory drawing showing the curvature of the crucible curved part

Explanation of symbols

10-mold, 11-quartz powder compact, 12-air vent, 13-electrode, 15-rim top, 16-side wall, 17-curved, 18-bottom, L-mold center line, L1-heating site Measurement of distance from mold center line, L2-distance between heated part and electrode tip, distance between L3-electrode centers, W1-curved portion outer surface curvature, W2-curved portion inner surface curvature, S- circumscribed circle, R-curvature range.

Claims (9)

In the method of producing a quartz glass crucible by arc melting while vacuuming the quartz powder compact filled in the rotary mold, the electrode is moved to the side relative to the mold center line during or after arc melting. And a method for producing a quartz glass crucible, wherein arc melting is performed at an eccentric position.
The method for producing a quartz glass crucible according to claim 1, wherein the whole heating is performed in which the electrode is arc-melted on the mold center line, and the local heating is performed in which the electrode is melted at an eccentric position removed from the mold center line.
The method for producing a quartz glass crucible according to claim 1 or 2, wherein the total heating time is 60% or less of the total arc melting time.
In the local heating, the distance L2 between the center of the electrode tip and the heating part of the quartz powder molded body is maintained at 5 to 80% of the distance L1 from the mold center line to the heating part, and heat melting is performed. 4. A method for producing a quartz glass crucible according to any one of 3).
The method for producing a quartz glass crucible according to any one of claims 1 to 4, wherein an area of a circumscribed circle in contact with a plurality of electrode tips is set to 710 cm ² or less, and the entire inside of the circumscribed circle is arc-heated.
6. The method of manufacturing a quartz glass crucible according to claim 5, wherein the distance between the electrode centers is 15 cm or less.
A crucible manufactured by the method according to any one of claims 1 to 6, wherein the curvature W2 of the curved portion inner surface is 0.8 to 1.2 times the curvature W1 of the curved portion outer surface.
A crucible manufactured by the method according to any one of claims 1 to 6, wherein five internal bubbles of 0.5 mm or more are present in the entire curved portion in a thickness range of 1.0 mm from the inner surface of the entire crucible. A quartz glass crucible that is:
An apparatus for producing a quartz glass crucible having a means for moving to the side of at least one of an arc electrode and a rotary mold, wherein the relative position of the arc electrode with respect to the rotary mold can be eccentric.

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