JP4683665B2 - Method for producing silica plate - Google Patents

Description

  The present invention relates to a method for manufacturing a silica plate, and more particularly to a method for manufacturing a silica plate used for a large mask required for LCD manufacturing or the like.

  In general, synthetic silica is synthesized by a gas phase reaction method. A synthetic silica crude ingot synthesized by a gas phase reaction method has a substantially cylindrical shape, and layered striae remain along the growth surface. This crude ingot is placed in a molding die and pressed into a predetermined shape, for example, a prismatic shape, by being pressed with a push rod while being heated to a high temperature. The molded product (block) obtained in this way is sliced thinly to obtain final products such as a photomask material, a CVD device window material, and optical synthetic silica.

A conventional mold is made of graphite as described in Japanese Utility Model Laid-Open No. 61-73629 (see Patent Document 1). When a synthetic silica ingot is placed in a graphite or a graphite mold described in this publication and heated, SiO ₂ and C react to generate SiO gas and CO gas. In particular, when the temperature is 1700 ° C. or higher, a large amount of SiO gas and CO gas is generated, and these gases enter the synthetic silica or roughen the surface of the synthetic silica, adversely affecting the quality of the synthetic silica product. . Since the viscosity of synthetic silica decreases as the temperature increases, it is easier to perform molding at a high temperature. However, since a large amount of SiO gas and CO gas is generated at a temperature of 1700 ° C. or higher, the molding must be completed particularly in a short time. Therefore, molding has been performed at a high temperature of 1600 to 1700 ° C. where the viscosity is relatively small, using a pressurizing device such as a push rod. On the other hand, at a temperature of 1600 ° C. or lower, since the viscosity is relatively large, there is a drawback that molding takes time even if pressurization is performed, and thus devitrification easily occurs. Moreover, in a high temperature furnace, the mechanism of the pressurizing device using a push rod or the like is difficult to be realized.

  Furthermore, a method for discharging SiO gas and CO gas generated by performing molding at a high temperature of 1700 ° C. or more for a short time to reduce the viscosity to the outside by a porous body used in a mold is disclosed in Japanese Patent Laid-Open No. 5-17174 (Patent Document 2). Reference). However, the method described in this publication not only has a large material loss due to the reaction between the synthetic silica ingot and the mold, but also the shape change due to the burning of the mold affects the block shape. It becomes bulky. Furthermore, a vacuum furnace is required to discharge the generated SiO gas and CO gas from the surface of the synthetic silica, increasing the cost of the apparatus. In addition, since the synthetic silica mask requires a large plate material such as LCD in recent years, the above-described problems become more prominent.

Further, in the conventional method for producing a synthetic silica plate, when producing a product having a length or width exceeding 1 m, a large ingot or a carbon member which is a consumable is required to be a large one. Compared with the case of manufacturing, the unit price is higher, which is a big problem in terms of manufacturing cost. In particular, it is indispensable to purify the carbon member with a halogen gas in order to prevent the devitrification of the silica plate due to impurities, and the higher the temperature, the more it is consumed because it reacts with SiO ₂ to silicify, and the manufacturing cost increases . Furthermore, from the viewpoint of facilities, there is a heavy burden on capital investment such as large ingot manufacturing facilities and large surface grinders.

  For this reason, in the case of a large glass plate, optical properties and the like are inferior to synthetic silica in terms of quality, but soda glass and crystallized glass that can be manufactured at low temperatures without worrying about furnace materials are often substituted. It is a problem due to its characteristics. On the other hand, when using a mold made of ceramic or the like, similarly, a large case for melting is required, which is a big problem in terms of cost.

  Furthermore, a synthetic silica ingot is melted at a high temperature of 1800 ° C or higher in a carbon mold and pulled out from a die by forced or dead weight, and formed into a pipe shape, or the ingot is processed into a hollow state and formed into a pipe shape by rotational heating. However, this manufacturing method cannot directly manufacture a silica plate. Silica crucibles and silica bell jars can be manufactured by an arc rotation heating molding method using silica powder, but this method cannot directly manufacture a silica plate.

  Therefore, in order to produce a large silica plate material, it is necessary to expand the silica pipe produced as described above and make it into a plate shape by pressing. However, in such a method of forming a plate by pressing, stress is applied to the silica plate material, distortion occurs, and heat treatment for removing the residual stress is required, resulting in reduced productivity and high cost.

  Further, if a multi-layer plate having a transparent layer and an opaque layer is to be manufactured, a method of welding the transparent silica plate and the opaque silica plate after manufacturing must be employed, but there is a problem in terms of cost. Further, paragraph No. 0010 and FIG. 11 of Japanese Patent Laid-Open No. 11-116265 (see Patent Document 3) include a description of two-layer silica in which the surface of an opaque silica layer is covered with a transparent silica layer. Layered silica is produced by cutting a silica ingot into a plate shape to produce a two-layered silica plate. Like the conventional manufacturing method, a large ingot or a carbon member that is a consumable needs to be large. As a result, the unit price is high and there is a major problem in terms of manufacturing cost.

Japanese Utility Model Publication No. 61-73629 Japanese Patent Laid-Open No. 5-17174 JP-A-11-116265 Japanese Patent No. 2794475

  Accordingly, there has been a demand for a method for producing a silica plate that has a good material yield, is inexpensive in production cost, and is suitable for producing a high-quality large plate. There has also been a demand for inexpensive, high-quality, large-sized single-layer or multilayer silica plates.

  The present invention has been made in consideration of the above-described circumstances, and provides a manufacturing method that can easily obtain silica suitable for the manufacture of high-quality large-sized plate materials with good material yield, low manufacturing cost. For the purpose. It is another object of the present invention to provide an inexpensive, high-quality and large-sized single layer or multilayer silica plate.

  In view of the above problems, the present inventors have intensively studied and obtained the following results.

  That is, first, the silica body is heated and shaped from an ingot into a tubular shape, or directly shaped into a tubular shape without going through an ingot. Next, if the silica tube is left on a flat plate horizontally along the axis and heated to a sufficiently high temperature, it can be expected that the silica tube will be crushed and a convolution will occur. When a slit-like opening is provided along the entire length in the axial direction, conventionally, it has been thought that convolution occurs toward the inside of the tube unless it is forcibly opened as in Patent Document 4 described above. However, I thought that it should not be judged in general about what the deformation process would be, and I thought there were still two possibilities. One of them is the same as the deformation of a synthetic silica tube without opening that everyone imagines, the upper tube wall on both sides of the slit hangs down and folds into both sides, and the other is the fold-down deformation Instead, if the molding time is long enough, it will be a single plate. Under the above conditions, the process of forming a slit-shaped silica tube was simulated by a computer, and the experiment succeeded in reproducing the same result, confirming that the process of opening a single plate was correct. . During the experiment, it was found that if deformation of symmetry can be guaranteed, the deformation process can be reproduced, and further, it has been confirmed that the characteristics of this deformation process are not related to the viscosity coefficient of the deformed body, and the above problem can be solved. . The present invention is based on such knowledge.

  In order to achieve the above object, according to one aspect of the present invention, a slit is formed in an axial direction in a tubular silica body, and the silica body is placed in a furnace so that the slit becomes an upper surface. There is provided a method for producing a silica plate, wherein the tubular silica body is heated only by viscous deformation due to its own weight until the tubular silica body becomes plate-like. Thereby, the material yield is good, the manufacturing cost is low, and a high-quality large plate can be manufactured.

  In a preferred example, the temperature of the lower end and the upper end of the silica body is heated and controlled so that the lower end temperature ≧ the upper end temperature.

  In a preferred example, the maximum temperature of the tubular silica body is controlled at 1600 ° C. or lower. As a result, the reaction between the silica and the mold can be prevented, the quality of the silica plate can be improved, and the selection range of the peripheral materials used in the molding apparatus is widened due to the decrease in the molding temperature. In some cases, the vacuum condition of the molding furnace is not required, and molding can be performed under atmospheric conditions.

  Moreover, in another suitable example, it is supported in the said furnace by inserting the movement suppression member which suppresses the movement of this silica body in the slit of the said silica body. Thereby, a movement of a silica body is suppressed and a pipe | tube is opened more reliably.

  According to the method for producing a silica plate according to the present invention, regardless of whether synthetic or natural (silica) raw materials are used, the production rate of silica is good, the production cost is low, and the production cost is low. A method can be provided. In addition, an inexpensive, high-quality and large single-layer or multilayer silica plate can be provided.

  Hereinafter, a first embodiment of a method for producing a silica plate according to the present invention will be described with reference to the accompanying drawings.

  As shown in FIG. 1, the manufacturing method of the silica plate of 1st Embodiment of this invention forms the slit 2 in the axial direction in the tubular silica body (henceforth only a tubular body) 1, and the slit 2 is an upper surface. The tubular body 1 is horizontally placed on a base 3 as a flat mold provided in the heating furnace, and an elongated plate-like movement restraining member 4 is loosely inserted into the slit 2 and fixed. For example, the temperature of the lower end and the upper end of No. 1 is controlled to be 1600 ° C. or higher but not lower than the softening temperature of silica so that the lower end temperature ≧ the upper end temperature. At this time, the difference between the upper end temperature and the lower end temperature may be 100 ° C. or less, preferably 5 to 40 ° C.

  According to this manufacturing method, as shown in the molding process shown in FIG. 2 by performing simulation, the molding time and the molding temperature are interdependent, and the tube walls on both sides of the slit are deformed symmetrically to be flattened. . Further, this manufacturing method is a simple manufacturing method that can be stably molded without using a jig if the slit of the silica body is positioned at the center in the initial stage.

  The molding temperature can be set to 1600 ° C. or lower. By reducing the molding temperature in this way, the reaction between the silica and the mold can be prevented, and the quality of the silica plate can be improved. In addition, since the molding temperature is lowered, the selection range of peripheral materials used in the molding apparatus is widened. In some cases, vacuum conditions in the molding furnace are not required, and molding can be performed under atmospheric conditions. However, when it is carried out in a continuous furnace or the like, it may be moved to the next stage when the tube is opened to some extent and heated at a high temperature. Further, although the cost is high, the silica plate can be obtained even if the temperature is 1600 ° C. or higher from the beginning. When devitrification does not become a problem or when natural silica is used, it may be 1800 ° C. or lower.

  In order to prevent the synthetic silica and the mold from reacting and devitrifying, and in order to leave a large amount of hydrogen molecules for use as a mask material, it is preferably carried out at 1360 ° C. or higher and 1480 ° C. or lower. Even within this temperature range, it is possible to open the tube in tubular silica having a wall thickness of at least 2 mm to 30 mm. Further, it can be applied to silica having various viscosities.

  The tubular body 1 is produced by forming a silica ingot produced by ordinary oxyhydrogen flame melting into a tubular shape, and its uneven thickness is preferably within 20%. If the wall thickness differs by 20% or more, the tube may not open properly.

  As shown in FIG. 1, the tubular body 1 is horizontally fixed by inserting an elongated plate-like movement restraining member 4 into the slit 2 of the tubular body 1 placed on a base 3 as a mold and moving the tubular body 1. This is performed by supporting the restraining member 4 with support bases (not shown) provided on both sides of the movement restraining member 4.

  The slit 2 is preferably straight and needs to be consistent from the end face of the tubular silica to the other end face.

  As the furnace, a normal furnace capable of temperature control is used, and it may be a batch furnace or a continuous furnace.

  According to the production method as described above, the molding speed from the tubular body to the flat plate is about 10 to 100 times faster under the same temperature condition as compared with the conventional method of molding from an ingot. Can be made sufficiently low. In addition, since a molding die is not used, the slicing step is unnecessary, there is no material loss, the material yield is good, no special equipment is required, the processing time can be shortened, and the manufacturing cost is reduced. Suitable for manufacturing high-quality large plates.

In addition, the silica plate of the first embodiment formed by the present manufacturing method (tube opening method) is subjected to a heat treatment step compared to the conventional method, so that the hydrogen molecule concentration in silica is reduced, and the hydrogen molecule concentration is low on the surface. When tube opening is performed at a low temperature of, for example, 1600 ° C. or less, the hydrogen molecule concentration is 1 × 10 ¹⁸ molecules / cm ³ or less from the surface layer to about 2 mm, but the inside is a mask material. As a result, the silica plate sufficiently satisfies the functions of The distortion caused by the tube opening method does not cause a problem by performing cooling for 10 hours or more. As for the striae, as shown in FIG. 23 (a), it is normally present in the ingot, but the mandrel enters the pipe making process, and the silica glass is pulled to deform the pipe into a concentric shape ( When FIG. 23 (b)) and the pipe are pipe-opened, they are arranged side by side vertically and in a very good state (FIG. 23 (c)). As a result, the striae with a large inclination which are problematic by visual observation are not observed. On the other hand, in the conventional vacuum melt molding, even when the ingot has the same diameter (FIG. 23 (a)), when the melt mold (mold) is enlarged (FIG. 23 (d)), that is, when z is increased, Since the movement of the existing striae increases, a striae with an angle of 45 ° or more with the flat surface is observed at the tip of the melting mold (FIG. 23 (e)). In a large silica product such as a large mask for LCD, when it is molded by a conventional method, a manufacturing defect tends to occur, and the tube opening molding method is advantageous in terms of cost. As described above, the silica plate of the first embodiment has no striae that adversely affect, and a silica plate suitable for a photomask material and optical silica can be obtained.

  As described above, since synthetic silica is generally accumulated to produce an ingot, striae exist perpendicular to the axis of the ingot. In order to make a mask material, it had to be molded into a plate shape with care not to be affected by striae. However, once the tube is made as in the present invention, the striae can be concentric. it can. Combining the tubular synthetic silica thus obtained with any of the methods of claims 1 to 7 can easily solve the problem of striae.

  Next, a modified example of the slit used in the method for producing a silica plate according to the present invention will be described.

  The slits in the first embodiment of the method for producing the silica plate are formed in parallel, whereas the slits in this modification are formed so as to become narrower from the outer periphery toward the inner periphery.

  For example, as shown in FIG. 11, the slit 2A of the present modification is formed in a wedge shape so as to become narrower from the outer periphery 1Aa of the tubular body 1A toward the inner periphery 1Ab. When the silica tubular body 1A into which the slit 2A of this modification is cut is flattened by the above-described method for producing a silica plate according to the present invention, as shown by a solid line in FIG. 12, the end face 1Ac of the silica plate 10A is obtained. Are formed perpendicular to the plane. Therefore, the amount of machining after softening can be eliminated or reduced as much as possible, the manufacturing efficiency is improved, the residual stress associated with machining is reduced, and the heat treatment for eliminating the residual stress is eliminated. Or it can be shortened.

  On the other hand, in the above-described embodiment, under the heating and softening conditions that do not apply a compulsory force to the material and do not affect the thickness accuracy of the material, the difference between the inner and outer diameters of the material tubular body is reduced after molding. When using a material with a large wall thickness, the side of the inner side of the tubular body is short and the side of the outer peripheral side is long. When the plate is observed from the cross-sectional direction of the tubular body, it becomes a trapezoid 1Ad as shown by a dotted line in FIG.

  Moreover, 2nd Embodiment of the silica plate concerning this invention is described.

  The silica plate of the second embodiment is a multilayer of a transparent layer and an opaque layer, whereas the silica plate of the first embodiment is a single layer of a transparent layer.

  As shown in FIG. 13, the silica plate 10B of the second embodiment has two or more high-purity transparent silica layers 10Bb and multi-bubble silica layers 10Ba having an OH group content of 100 ppm or more, and a thickness of 3 A silica plate of ˜100 mm.

  The silica plate 10B is manufactured using the above-described method for manufacturing a silica plate according to the present invention, and the tubular body 1B used therefor is manufactured as follows.

  For example, it is performed using a silica crucible manufacturing apparatus 41B as shown in FIG. 14, and the crucible molding die 43B is rotated at a predetermined speed by operating the rotation drive source and rotating the rotating shaft 42B in the direction of the arrow. High-purity silica powder is supplied from the top into the crucible molding die 43B by the raw material supply nozzle 44B. The supplied silica powder is pressed to the inner surface member 45B side of the crucible molding die 43B by centrifugal force to form a crucible-shaped molded body R1. The inside of the inner member 15B is depressurized by the operation of the depressurization mechanism 46B, and further, helium gas or argon gas, for example, helium gas is supplied from the inert gas supply pipe 47B to the hollow portion R1i of the molded body R1 at a constant rate. After the elapse of a predetermined time after the supply of helium gas, the arc electrode 48B is energized and continued, heated from the inside of the molded body R1, and a molten layer is formed on the inner surface R1S of the molded body R1.

  After a predetermined time has elapsed, in order to appropriately form an opaque layer containing a large number of bubbles outside the silica crucible, the pressure reducing mechanism 46B is adjusted or stopped to adjust or stop the pressure reduction in the crucible molding die 2. Continue the arc for a predetermined time with the reduced pressure reduced or stopped, stop the helium gas supply after a certain time from the start of arc melting, stop the helium gas supply, and then supply the hydrogen gas simultaneously with the stop Hydrogen gas is supplied from the pipe 48B to the hollow portion R1i of the molded body R1 at a constant rate. The supply of hydrogen gas is started at the latest several minutes before the end of arc melting and after a certain period of time with respect to the total arc melting time. After a predetermined time has elapsed from the start of arc melting, the arc energization is stopped, the supply of hydrogen gas is stopped, and the melting crucible manufacturing process ends.

  By the above melting crucible manufacturing process, the amount of bubbles contained in the seed layer (inner surface) and the outer opaque layer formed in the silica crucible R in the initial stage of melting can be appropriately reduced. By supplying hydrogen gas, the amount of bubbles in the transparent layer can be significantly reduced, and by performing melting under reduced pressure, the amount of bubbles remaining in the transparent layer can be reduced. A silica crucible whose inner layer is a transparent layer can be produced. In addition, a tubular body can also be directly formed by changing the bottom structure of the crucible molding die. A tubular body having such a layer structure is easier to produce using natural silica (quartz) rather than synthetic silica.

The tubular body manufactured in this way is cut into a tube shape by cutting off the top and bottom, and further, as shown in FIG. 15, a slit 2B is cut into a multilayer tubular body 1B composed of an opaque layer 1Ba and a transparent layer 1Bb. After processing or as shown in FIG. 16 or FIG. 17, the tubular body is divided and cut into a plurality of arcs 1B1, and then the tubular body 1B or arc 1B1 is depressurized or processed as shown in FIGS. In an inert atmosphere such as Ar or N ₂ , normal pressure is preferably 1350 ° C to 1800 ° C, more preferably 1350 ° C to 1500 ° C, and particularly preferably 1360 ° C to 1480 ° C. Molded into a silica plate.

  This silica plate has a multilayer composed of a transparent layer having a high purity and a smooth surface and an opaque layer having a heat shielding effect.

  Moreover, 3rd Embodiment of the silica plate concerning this invention is described.

  The silica plate of the third embodiment is manufactured from a crucible or tubular body manufactured by arc rotation melting, while the silica plate of the second embodiment is manufactured by center resistance heating rotation melting or Manufactured from a tubular body.

  For example, as shown in FIG. 21, the crucible or tubular body used for the silica plate of the third embodiment is formed by rotating the tubular mold 52C of the central resistance heating rotary melting device 51C around the longitudinal axis. Fill with silica powder. The silica powder is uniformly pressed to the inner surface of the tubular mold 52C by the centrifugal force, and the silica powder tubular body 53C is formed on the inner surface of the tubular mold 52C. Next, the heating element 54C inserted into the tubular mold 52C is energized and heated from the inner side 53Cb of the silica powder tubular body 53C to melt. At the same time, hydrogen gas and / or helium gas is supplied from the gas blowing hole 56C of the housing 55C for a predetermined time. The gas supply here is, for example, a predetermined ratio of helium gas. As a result, from the start of melting, the tubular body 53C is blown with hydrogen or helium gas through the silica powder layer from the outside to the inside. Further, the thickness of the substantially silica-free transparent silica layer can be adjusted by setting the supply time.

  Since the hydrogen or helium gas has a small atomic radius and passes through the silica formed on the inner surface of the silica tube and is exhausted, the inner layer can be made transparent with few bubbles. Thereafter, the supply of hydrogen or helium gas is stopped, the inside of the housing is decompressed and heated and melted, and after cooling, the tubular body is removed from the mold, and the unmelted portion of the outer layer is polished and removed, so that the outer layer becomes an opaque layer and an inner layer. A transparent tubular silica body can be produced. The silica crucible can be formed by changing the structure of the tubular body forming die, the heating element, and the housing.

  The silica tubular body manufactured in this way is formed into a flat plate material in the same manner as the silica plate of the second embodiment. Manufacturing costs are reduced, and high quality and large size are possible.

  The fourth embodiment is a method of manufacturing a plate-like body from a bullet-like ingot such as Bernoulli method. An ingot obtained by melting and depositing silica is generally used, but since it is deposited and manufactured, striae exist in a substantially horizontal direction as shown in FIG. In order to manufacture a tubular body from this ingot, first, a mandrel is inserted into the ingot to form a through hole in the center. When the ingot is placed in the heating furnace corresponding to the diameter of the ingot, the mandrel is placed above or below, and the ingot is heated and softened, the mandrel and the ingot are moved relatively on the same axis, and the mandrel penetrates the ingot. To do. At this time, the ingot is deformed so as to be pulled by the mandrel to form a tubular body, and at the same time, the striae are concentric as shown in FIG.

  If a slit is made in this tubular body and it is molded as in the first embodiment, a plate-like body having no striae and optimal for a large mask or the like can be manufactured. That is, the size can be increased and the manufacturing method can be facilitated, and the problem of striae can be solved. The striae can be visually observed from the side surface of the plate material as shown in FIGS. 23 (c) and (e). The striae parallel to the plane of the plate has no problem in use, but as shown in FIG. 23 (f), the angle 痾 between the plane of the plate and the striae, for example, exceeds 40 °. If it has striae, it is considered inappropriate as a mask material. In the present invention, it can be easily controlled to 40 ° or less, preferably 30 ° or less, more preferably 20 ° or less.

Example 1
Using the method for producing a silica plate according to the present invention, the interdependence between the molding temperature and the molding time of the tubular silica body is examined. FIG. 3 shows the relationship between the molding temperature and molding time of a silica tube (outer diameter D / thickness t = 16.4) of silica ceramic T-4040 (registered trademark) made by Toshiba Ceramics. In this molding process, since the time until the end of the silica plate (one side of the slit) completely contacts the base is theoretically infinite, in practice the length of the developed plate (silica 90% and 95% of the circumference of the tube shows the time for contacting the base. As shown, at 1600 ° C., the molding times are 1.87 hours and 2.83 hours, respectively.

(Example 2)
4 and 5 show a top view and a side view of a forming apparatus used in the method for producing a silica plate of the present invention. The silica tube 11 with slits is supported by a pair of elongated cylindrical supports 12. The support 12 is supported by a recess 15 formed on the side wall 14 of the base 13. In order to direct the slit of the silica tube directly above, the movement restraining member 16 is inserted into the recess 15 of the side wall 14 of the base 13 and the slit is passed through. FIG. 6 shows a process for forming a silica tube using the forming apparatus shown in FIGS.

  In order to deform and flatten the tube walls on both sides of the slit using this manufacturing apparatus, the pair of supports may be arranged symmetrically so that the diameter of the circle circumscribed by the pair of supports is smaller than the inner diameter of the silica tube. . It has been found that it is more preferable that the central angle between the contact point and the horizontal diameter of the silica tube is 0 to 60 °, preferably 0 to 30 °.

(Example 3)
7 and 8 show a top view and a side view of another molding apparatus used in the method for producing a silica plate of the present invention (note that only half are shown in the drawings for symmetry). The silica tube 21 with slits is supported by two columnar supports 22. This support 22 is supported by the side wall 24 of the base 23, and can slide on it. In order to prevent the support body 22 from moving toward the center, a stop projection 27 is provided. In order to direct the slit of the silica tube directly above, the movement restraining member 26 is inserted into the recess 25 of the side wall 24 of the base 23 and is loosely inserted into the slit. In the opening deformation of the silica tube, the support 22 slides downward along the slope of the side wall 24 of the base 23 while contacting the inner surface of the silica tube as the silica tube is deformed. In this way, deformation symmetry is realized by the two supports 22 even during the molding process. When the opening deformation of the silica tube proceeds to another stop projection 28 on the side wall 24 of the base 23, the silica comes into contact with the mold in a large area, and the symmetry condition can be stably secured. At this time, the support 22 is stopped by the stop protrusions 27 and 28. Under the conditions shown, in the initial stage of molding, the silica tube is separated from the lower mold by a certain distance. In the initial state, the distance between the lower part of the silica tube and the mold is set to be equal to or smaller than the distance between the upper part of the silica tube and the center line of the support 22. This distance may be eliminated. By providing a slight distance, the molding efficiency can be increased. That is, the molding time can be shortened under the same molding conditions. However, the reduction amount is only about 1.2%.

Example 4
9 and 10 show a top view and a side view of another molding apparatus used in the method for producing a silica plate of the present invention. The molding apparatus has a single balancing member 31. The balance member 31 should have a width smaller than the inner diameter of the silica tube 32 and as large as possible. The balance member 31 is attached to a guide column 34 provided on the base 33 so as to be movable up and down. When the balance member 31 moves along the guide column 34, the horizontal plane does not change. In flattening the silica tube 32, the balancing member 31 moves downward. Thereby, the symmetry of the opening deformation of the silica tube 32 is guaranteed. The movement restraining member 36 is erected in a recess 35 provided in the upper part of the base 33 and is loosely inserted into the slit 37 of the silica tube 32. Thereby, the symmetry of the initial state of molding is also guaranteed.

(Example 5)
Comparative Example: Using a manufacturing method as shown in FIG. 2, slitting a silica pipe having an outer diameter of 200 mm, an inner diameter of 170 mm, and a length of 200 mm, performing flattening (opening) molding, and measuring the outer and inner peripheral plate dimensions did. As a result, the dimensional change before and after opening is an average of 5 points measurement, the outer peripheral side 612 mm → 572 mm, the inner peripheral side 516 mm → 564 mm, the difference between the inner and outer peripheral dimensions of the post-molded plate is 8 mm, and the end face of the flat plate in FIG. It was trapezoidal as shown by the dotted line.

  Example: In the above comparative example, since the inner and outer peripheral dimension difference of the silica plate after molding was 8 mm, the outer peripheral length was 608 mm (612 mm-4 mm), the inner peripheral length, as shown in FIG. After performing wedge-shaped slit processing so that the thickness becomes 520 mm (516 mm + 4 mm), flattening (opening) molding was performed. As a result, as shown in FIGS. 22 (a) and 22 (b), the outer peripheral side length and the inner peripheral side length of the flat plate were both 568 mm, and the both surfaces and end surfaces could be formed into vertical plates.

(Example 6)
As shown in FIG. 14, a crucible of φ400 (outer diameter) × 400 (length) × 20 (thickness) mm was formed from high-purity silica powder by arc rotation discharge melting. The obtained crucible-shaped bottom was removed to form a tubular body having a diameter of 400 × 300 × 20 mm, and a slit was further formed. After the processing, the processing impurities were removed by washing with 10 wt% HF for 1 hour. This silica tubular body with slits was placed on a carbon mold purified with halogen gas so as to be symmetrical from the slits, and the atmosphere was replaced with high-purity Ar gas, followed by heat treatment at 1450 ° C. for 3 hours. As a result, a high-purity silica plate having a width of 1200 × length of 300 × thickness of 20 mm, a transparent layer of 10 mm, and an opaque layer of 10 mm having many bubbles could be produced. As a result of measuring the OH concentration of the obtained plate material by a laser Raman method, a uniform distribution having an average of about 200 ppm in the transparent layer and an average of about 90 ppm in the opaque layer was obtained.

(Example 7)
As shown in FIG. 21, a tubular body of φ300 (outer diameter) × 1000 (length) × 10 (thickness) mm was formed from high-purity silica powder by center resistance heating and melting. A slit was made in the obtained pipe shape. After the processing, the processing impurities were removed by washing with 10 wt% HF for 1 hour. This silica tubular body with slits was placed on a carbon mold purified with halogen gas so as to be symmetrical from the slits, and the atmosphere was replaced with high-purity Ar gas, followed by heat treatment at 1450 ° C. for 2.2 hours. As a result, a silica plate having a width of 940 × length of 1000 × thickness of 10 mm and having many bubbles was obtained.

(Example 8)
A synthetic silica ingot produced by the Bernoulli method was prepared. This ingot was placed in a heating furnace having a furnace inner diameter substantially the same as that of the ingot so that the axis was vertical. Below the ingot is a mandrel (core) for forming into a tube. In this state, the ingot was softened by heating and forced to pass between the mandrel and the furnace wall. When cooled, the ingot was formed into a tubular shape (inner diameter 150 mm, wall thickness 20 mm, length 500 mm), and the striae were concentric. The same processing as in Example 7 was performed using this ingot. A plate material of width 500 × length 500 × thickness 20 mm was obtained. When the state of striae was confirmed, it entered as shown in FIG. 23 (d) and was suitable for use as a mask material.

The conceptual diagram explaining the manufacturing method of the silica board concerning this invention. The simulation figure of flattening by the manufacturing method of the silica board concerning this invention. The relationship figure of the shaping | molding temperature and shaping | molding time of the Example of the manufacturing method of the silica plate concerning this invention. The top view of the shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The side view of the shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The simulation figure of flattening by the manufacturing method of the silica plate of this invention using the shaping | molding apparatus shown in FIG.4 and FIG.5. The top view of the other shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The side view of the other shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The top view of the other shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The side view of the other shaping | molding apparatus used for the manufacturing method of the silica board concerning this invention. The conceptual diagram which shows the modification of the slit in embodiment of the manufacturing method of the silica board concerning this invention. The state figure of the silica board manufactured using the modification of a slit in embodiment of the manufacturing method of the silica board concerning this invention. The sectional view of one embodiment of the silica board concerning the present invention. The conceptual diagram of the silica crucible manufacturing apparatus used for manufacture of one Embodiment of the silica plate concerning this invention. The perspective view of the silica tubular body used for one embodiment of the silica board concerning the present invention. The perspective view of the silica circular arc body used for one Embodiment of the silica plate concerning this invention. The perspective view of the silica circular arc body used for one Embodiment of the silica plate concerning this invention. The conceptual diagram of the manufacturing method of one Embodiment of the silica plate concerning this invention. The conceptual diagram of the manufacturing method of one Embodiment of the silica plate concerning this invention. The conceptual diagram of the manufacturing method of one Embodiment of the silica plate concerning this invention. The conceptual diagram of the silica tubular body manufacturing apparatus used for manufacture of one Embodiment of the silica plate concerning this invention. (A) And (b) is a test result figure which shows the change of the length of the silica plate manufactured using the modification of the slit shown in FIG. The conceptual diagram which shows the generation | occurrence | production state of striae when a silica plate is manufactured from an ingot by this invention ((a)-(c)) and the conventional method ((d)-(f)).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Tubular silica body 2 Slit 3 Base 4 Movement suppression member

Claims (5)

  A slit is formed in the tubular silica body in the axial direction, and the silica body is placed in the furnace so that the slit is on the upper surface. The tubular silica body is formed into a plate shape only by viscous deformation due to its own weight. The manufacturing method of the silica board characterized by heating until it becomes.   2. The method for producing a silica plate according to claim 1, wherein the temperature of the lower end and the upper end of the silica body is controlled by heating so that the lower end temperature ≧ the upper end temperature.   The method for producing a silica plate according to claim 1 or 2, wherein the maximum temperature of the tubular silica body is controlled at 1600 ° C or lower.   The method for producing a silica plate according to claim 1 or 2, wherein the maximum temperature of the tubular silica body is controlled at 1360 ° C or higher and 1480 ° C or lower.   The manufacture of a silica plate according to any one of claims 1 to 4, wherein the silica plate is supported in the furnace by inserting a movement restraining member that suppresses the movement of the silica body into the slit of the silica body. Method.

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