Manufacturing method of composite silica glass plate

Abstract

To provide a manufacturing method of a composite silica glass plate by laminating and heating different kinds or same kinds of silica glass plates while suppressing air bubble formation on heating.SOLUTION: A manufacturing method of a composite silica glass plate includes steps of: preparing a first silica glass plate having at least on one surface a first tool mark formed to a stable direction and a second silica glass plate having at least on one surface a second tool mark formed to a stable direction; laminating the first silica glass plate and the second silica glass plate in a manner that the formation direction of the first tool mark and the formation direction of the second tool mark are in the same direction and in a state that surfaces having the tool mark are faced to each other; and heating in order from an edge of the laminated silica glass plate in the same direction of the formation direction of the tool mark.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing a composite silica glass plate used in semiconductor manufacturing equipment and the like. [Background technology]

[0002] There is a known method for manufacturing composite silica glass, which is a silica glass laminate, by stacking different or the same type of silica glass plates and heating them. Conventional methods for manufacturing composite silica glass include, for example, Patent Documents 1 to 4. However, the known methods have a problem that large bubbles are likely to be generated at the interface between the silica glass plates when the stacked silica glass plates are heated to form a laminate. If bubbles are generated during the manufacturing process, the product becomes defective and the yield is reduced. Demands for the performance of such composite silica glass are increasing year by year, and a manufacturing method for composite silica glass that does not generate bubbles during the manufacturing process has been awaited. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication 51-061522 [Patent Document 2] Patent Publication No. 63-201026 [Patent Document 3] Patent Publication No. 2004-067456 [Patent Document 4] Patent Publication No. 2004-091314 Summary of the Invention [Problem to be solved by the invention]

[0004] As a result of extensive research, the inventors have discovered that by overlapping and fixing silica glass plates of different or the same type together with the tool marks created on the surfaces of the silica glass plates during processing oriented in the same direction, and then sequentially heating them from the edges, the generation of air bubbles during heating is suppressed, and a good composite silica glass plate can be obtained, thus arriving at the present invention.

[0005] In other words, the present invention aims to provide a method for producing a composite silica glass plate by stacking and heating different or the same type of silica glass plates, in which the generation of air bubbles during heating is suppressed. [Means for solving the problem]

[0006] In order to solve the above problems, the manufacturing method of the composite silica glass plate of the present invention includes the steps of: preparing a first silica glass plate having a first tool mark formed in a certain direction on at least one surface thereof, and a second silica glass plate having a second tool mark formed in a certain direction on at least one surface thereof; overlapping the first silica glass plate and the second silica glass plate with the surfaces having the tool marks facing each other, with the forming directions of the first tool mark and the second tool mark being the same; and a heating step of sequentially heating the overlapped silica glass plates from the ends in the same direction as the forming direction of the tool marks.

[0007] It is preferable that the tool marks are a plurality of linear tool marks formed over the entire surface of at least one surface of the first silica glass plate and the second silica glass plate.

[0008] The PV (peak-to-valley) value of the linear tool mark is preferably 0.1 μm to 10 μm.

[0009] It is preferable that the PV (peak-to-valley) interval of the linear tool marks is 30 μm to 120 μm.

[0010] Preferably, the linear tool marks are substantially parallel.

[0011] It is preferable that the surfaces having the tool marks are opposed to each other with the linear tool marks being substantially parallel to each other.

[0012] The silica glass plate is preferably made of opaque silica glass and / or transparent silica glass.

[0013] The heating is preferably performed by a burner flame.

[0014] It is preferable that the burner flame is a burner flame using propane gas as a combustion gas.

[0015] It is preferable that the silica glass plate is stretched during the heating. Effect of the Invention

[0016] According to the present invention, the remarkable effect of providing a method for producing a composite silica glass plate by stacking and heating different or the same type of silica glass plates, in which the generation of air bubbles during heating is suppressed, can be achieved. In addition, the generation of bubbles during heating is suppressed, which has the effect of improving yield. [Brief description of the drawings]

[0017] [Figure 1] 1A and 1B are diagrams showing the state of opposing silica glass plates before heating in one embodiment of a method for producing a composite silica glass plate of the present invention, where (a) is a schematic right side view and (b) is a schematic front view. [Diagram 2] FIG. 2A is a cross-sectional view showing an example of a tool mark, and FIG. 2B is a plan view of the tool mark of FIG. [Diagram 3] FIG. 13A is a plan view showing another example of the tool mark, and FIG. 13B is a plan view showing another example of the tool mark. [Figure 4] (a) is a schematic right side view showing the scaffold rod attached to the upper clamp being attached to the opposing silica glass plates in Figure 1 before heating, and (b) is a schematic right side view showing the scaffold rod attached to the upper clamp after being attached to the opposing silica glass plates in Figure 1 before heating. [Diagram 5] (a) is a view similar to Figure 4(b), (b) is a schematic right side view showing the scaffolding rod attached to the lower clamp being attached to the opposing silica glass plates in Figure 5(a) before heating, and (c) is a schematic right side view showing the scaffolding rod attached to the lower clamp after being attached to the opposing silica glass plates in Figure 5(a) before heating. [Figure 6] 5(a) is a schematic right side view showing the opposing silica glass plates in FIG. 5(c) being heated with a burner, and FIG. 5(b) is a schematic right side view showing the opposing silica glass plates in FIG. 5(c) being heated with a burner. [Figure 7] FIG. 11 is a plan view showing still another example of a tool mark. [Figure 8] FIG. 1A is a schematic diagram showing an example of a case where surfaces having tool marks are placed opposite each other, showing a state in which angular misalignment occurs between the tool marks, and FIG. 1B is an enlarged view of a main portion of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The following describes the embodiments of the present invention, but these embodiments are shown by way of example only, and it goes without saying that various modifications are possible without departing from the technical spirit of the present invention. In the drawings, the same members are represented by the same reference numerals.

[0019] 1 to 6 show one embodiment of the method for producing a composite silica glass plate of the present invention. Fig. 1 shows the state of opposing silica glass plates 10 before heating. Fig. 1(a) is a schematic right side view of the silica glass plate 10, and Fig. 1(b) is a schematic front view of the silica glass plate 10.

[0020] In the present invention, a silica glass plate is used that has a tool mark formed on at least one surface. A tool mark is a mark left on the surface of a workpiece in the direction of the blade when a machine process such as cutting or milling is performed. Such a blade path is generally called a tool mark, and is sometimes called a machining tool mark.

[0021] An example of a tool mark is shown in Fig. 2. In Fig. 2, a tool mark 30 is formed on one surface of the first silica glass plate 12a. In Fig. 2, (a) is a cross-sectional view showing the tool mark 30, and (b) is a plan view of the tool mark 30.

[0022] The tool mark 30 is a linear tool mark in which linear protrusions 32 and recesses 34 are formed in a substantially regular pattern. In the example shown, the tool mark 30 is formed over the entire surface of at least one surface of the first silica glass plate 12a. It is preferable that the linear tool marks are substantially parallel.

[0023] In the present invention, it is sufficient that the tool mark is formed in a certain direction, so that the tool mark formed partially on at least one surface of the silica glass plate is also included in the present invention, but it is preferable that the tool mark is formed over the entire surface of at least one surface of the silica glass plate.

[0024] In the case of the tool mark 30 shown in Fig. 2, the difference L1 between the height of the peak portion of the protrusion 32 and the depth of the deepest portion of the recess 34 is defined as the PV (peak-to-valley) value of the tool mark in the present invention. An example of the difference L1, which is the PV value, is shown in Fig. 2(a). Also, in the present invention, the distance from the peak portion of the protrusion 32 to the deepest portion of the recess 34 is defined as the PV (peak-to-valley) interval (pitch) of the tool mark, and an example of the PV interval D1 is shown in Fig. 2(b).

[0025] The PV (peak-to-valley) value of the linear tool mark is preferably 0.1 μm to 10 μm, and more preferably 2 μm to 5 μm. Moreover, the PV (peak-to-valley) interval of the linear tool mark is preferably 30 μm to 120 μm, and more preferably 60 μm to 80 μm. The PV values ​​and PV intervals were measured using the three-dimensional measurement function of a Keyence digital microscope (VHX-8000).

[0026] Another example of the tool mark is shown in Fig. 3(a), and yet another example of the tool mark is shown in Fig. 3(b). Fig. 3(a) shows a meandering linear tool mark 36. The tool mark 36 is a linear tool mark in which meandering linear protrusions 40 and recesses 38 are formed in a generally regular pattern.

[0027] 3(b) shows a diagonal tool mark 42. The tool mark 42 is a linear tool mark in which diagonal protrusions 46 and recesses 44 are formed in a generally regular pattern.

[0028] Fig. 7 shows another example of the shape of the tool mark. Fig. 7 shows a tool mark 50 having an arched curved shape. The tool mark 50 is a linear tool mark in which convex portions 52 and concave portions 54 having an arched curved shape are formed in a generally regular pattern.

[0029] In this way, the tool mark may be a linear tool mark formed substantially parallel to the end of a polygonal silica glass plate, particularly a rectangular silica glass plate, as well as a meandering linear tool mark, a diagonal tool mark, a bow-shaped curved tool mark, etc., as long as the tool mark is formed in a substantially fixed direction. For example, when the silica glass plate is rectangular, it is preferable that the tool mark is formed in the vertical direction of the silica glass plate, or in the horizontal direction of the silica glass plate. That is, it is preferable that the tool mark is formed in either the vertical or horizontal direction in a rectangular silica glass plate.

[0030] As the tool mark, a tool mark made when cutting a block-shaped silica glass lump into a plate-shaped silica glass using a wire saw is suitable.

[0031] The manufacturing method of the composite silica glass plate of the present invention includes the steps of preparing a first silica glass plate 12a having a first tool mark 30 formed on at least one surface in a certain direction as shown by the arrow A in Figures 1 and 4, and a second silica glass plate 12b having a second tool mark (similar to the tool mark 30) formed on at least one surface in a certain direction; overlapping the first silica glass plate 12a and the second silica glass plate 12b with the surfaces having the tool marks facing each other, with the formation direction of the first tool mark 30 and the formation direction of the second tool mark being the same; and a heating step of sequentially heating the overlapped silica glass plates 10 from the end in the same direction as the formation direction of the tool mark (the direction of the arrow A).

[0032] For example, when the first silica glass plate 12a and the second silica glass plate 12b are superimposed with the surfaces having the tool marks facing each other, with the direction in which the first tool mark 30 and the direction in which the second tool mark similar to the tool mark 30 are formed being the same as each other as shown in Fig. 2, it is preferable that the first tool mark and the second tool mark are superimposed so as to be parallel to each other. This is because the flow of heated air during the heating process flows in a fixed direction.

[0033] When the first silica glass plate 12a and the second silica glass plate 12b are superimposed, it is ideal that the first tool mark and the second tool mark are superimposed so that there is no angular misalignment between them and the tool mark on one side is perfectly aligned so that the tool mark on the other side is parallel to the tool mark on the other side, but some angular misalignment is acceptable. The angular misalignment between the tool marks is preferably 30 degrees or less. Figures 8(a) and 8(b) show a case where a surface having a first tool mark 30 similar to that shown in Figure 2 and a second tool mark 60 similar to the tool mark 30 are faced to each other with an angular misalignment. An angular misalignment occurs at an angle θ1 between the boundary line 56 between the convex portion 32 and the concave portion 34 of the first tool mark 30 and the boundary line 64 between the convex portion 58 and the concave portion 62 of the second tool mark 60. And, it is preferable that the angular misalignment θ1 between the tool marks shown in Figure 8(b) is 30 degrees or less.

[0034] The heating step is preferably carried out using, for example, the multilayer quartz glass plate manufacturing apparatus described in Patent Document 3. In the explanation of the embodiment of the present invention, an example in which the heating step is carried out using the multilayer quartz glass plate manufacturing apparatus described in Patent Document 3 will be shown.

[0035] The opposed overlapped silica glass plates 10 are at least two silica glass plates 12a, 12b, 14 (three rectangular plates in the illustrated example) overlapped so that the tool mark facing portions 13a, 13b are formed, with the tool marks facing each other with the tool mark forming directions in the same direction (vertical direction in the illustrated example), and are fixed with tapes 18a, 18b, 18c, 18d. In the illustrated example, one opaque silica glass plate, the opaque silica glass plate 14, is sandwiched between two transparent silica glass plates, the transparent silica glass plates 12a and 12b (a first silica glass plate and a second silica glass plate 12b). However, as long as at least two silica glass plates face each other, combinations other than those shown in the illustration are also possible.

[0036] In the illustrated example, an example is described in which tool marks are formed on both sides of the transparent silica glass plates 12a, 12b and the opaque silica glass plate 14, but as long as tool mark facing portions 13a, 13b are formed, the tool marks may be formed on only one side of each of the transparent silica glass plates 12a, 12b and the opaque silica glass plate 14.

[0037] 4 to 6, the scaffolding bars 22a, 22b attached to the upper clamps 20a, 20b are attached to the opposing silica glass plates 12a, 12b, 14. After attachment, the scaffolding bars 22a, 22b are further attached to the opposing silica glass plates 12a, 12b, 14 by welding. Note that the upper clamps 20a, 20b and the scaffolding bars 22a, 22b in the illustrated example correspond to the upper support arms and the quartz glass support plates, respectively, of the multilayer quartz glass plate manufacturing apparatus described in Patent Document 3.

[0038] 5, the scaffolding bars 26a, 26b attached to the lower clamps 24a, 24b are attached to the opposing silica glass plates 12a, 12b, 14. After attachment, the scaffolding bars 26a, 26b are further attached to the opposing silica glass plates 12a, 12b, 14 by welding. Note that the lower clamps 24a, 24b and the scaffolding bars 26a, 26b in the illustrated example correspond to the lower support arms and the quartz glass support plates, respectively, of the multilayer quartz glass plate manufacturing apparatus described in Patent Document 3.

[0039] Next, as shown in FIG. 6, the outermost layers of the opposing silica glass plates 12a, 12b, and 14 (in the illustrated example, the outer layers of the silica glass plates 12a and 12b) are heated, but the tapes 18a, 18b, 18c, and 18d are left as they are and burned when heated with a burner 28, thereby eliminating the peeling step and saving labor.

[0040] Then, as shown in Fig. 6, the outermost layers of the opposing silica glass plates 12a, 12b, 14 (in the illustrated example, the outer layers of the silica glass plates 12a, 12b) are heated in sequence. Heating is performed by a burner 28 from the lower end portions of the opposing silica glass plates 12a, 12b, 14 in an upward direction as shown in Fig. 6. That is, heating is performed in the same direction as the direction in which the tool marks 30 are formed. The burners 28 are opposing burners, and while simultaneously heating the lower end portions of the outermost layers of the opposing silica glass plates 12a, 12b, 14 (in the illustrated example, the outer layers of the silica glass plates 12a, 12b) from both sides as shown in Fig. 6(a), the upper clamps 20a, 20b are lowered and the overlapped opposing silica glass plates 10 are pulled down by the lower clamps 24a, 24b.

[0041] The burner flame of the burner 28 is preferably propane gas as the combustion gas. In this heating process, the feed-down speed of the upper clamps 20a, 20b is set to 3 mm / min, and the pull-down speed of the lower clamps 24a, 24b is set to 9 mm / min. By setting and heating in this way, the opposing silica glass plates 12a, 12b, 14 are heated and melted by the burner flame and are lowered, and at the same time, the lower clamps 24a, 24b are lowered at three times the speed of the upper clamps 20a, 20b, so that the transparent silica glass plates 12a, 12b and the opaque silica glass plate 14, which are melted and fused to each other, act as a downward stretching force and are lowered while being stretched. As a method for heating the opposing silica glass plates 12a, 12b, 14 in this way, the heating method described in Patent Document 3 can be applied.

[0042] When welding is performed by heating in this manner, the opposing silica glass plates 12a, 12b, and 14 are elongated to form a composite silica glass plate 48, as shown in FIG. 6(b).

[0043] Although the tool marks have projections and recesses, in the present invention, the forming direction of the first tool mark and the forming direction of the second tool mark are aligned in the same direction, and heating is performed with the surfaces having the tool marks facing each other, i.e., with the tool mark facing parts 13a and 13b in Figure 1 formed. Therefore, in the tool mark facing parts 13a and 13b, there is an escape route for the trapped air in the opposite direction to the stretching direction caused by heating, so that when the composite silica glass plate 48 (see Figure 6(b)) is formed, the air does not remain as air bubbles, and therefore the generation of air bubbles is suppressed.

[0044] All of the above examples show the use of three silica glass plates, but at least two plates will suffice, so any combination of two silica glass plates facing each other, or four or more plates facing each other, are within the scope of the present invention. EXAMPLES

[0045] The present invention will be described in more detail below with reference to examples. However, it goes without saying that these examples are given for illustrative purposes and should not be construed as limiting.

[0046] Example 1 As shown in Fig. 1, on both sides of a 400 mm × 400 mm × 6 mm rectangular opaque silica glass plate 14 on which linear tool marks as shown in Fig. 2 are formed vertically, and on both sides of 400 mm × 400 mm × 3 mm rectangular transparent silica glass plates 12a, 12b on which linear tool marks as shown in Fig. 2 are formed vertically. The tool marks are those made when cutting a block-shaped silica glass lump into a plate-shaped silica glass using a wire saw, and the direction of the tool marks is the same as the arrow A in Fig. 1. The PV (peak-to-valley) value of the linear tool mark was in the range of 0.1 μm to 10 μm. The PV (peak-to-valley) interval of the linear tool mark was in the range of 30 μm to 120 μm. The 3D dimension measurement function of a Keyence digital microscope (VHX-8000) was used to measure the PV value and the PV interval.

[0047] The plates were laminated in the order of transparent silica glass plate-opaque silica glass plate-transparent silica glass plate, with the tool marks facing each other so that they were approximately parallel to each other and the tool marks were formed in the same direction, and fixed with tape to obtain laminated silica glass plates 10 facing each other before heating (composite silica glass plates before heating).

[0048] A scaffolding rod made of silica glass was attached to the upper clamping part of a composite silica glass plate manufacturing device having a clamping part that moves up and down, and the scaffolding rod and the unheated composite silica glass plate were welded with an oxyhydrogen flame.

[0049] A scaffolding rod made of silica glass was attached to the lower clamp part of the composite silica glass plate manufacturing device, and the scaffolding rod and the pre-heated composite silica glass plate were welded with an oxyhydrogen flame.

[0050] The unheated composite silica glass plate was heated from below with a propane-oxygen burner so that the direction of tool mark formation and the direction of heating were the same, while the feed descent speed of the upper clamp was set to 3 mm / min and the pull descent speed of the lower clamp was set to 9 mm / min. The upper clamp part and the lower clamp part were moved downward to stretch the unheated composite silica glass plate, thereby obtaining a composite silica glass plate which is the composite silica glass plate of the present invention.

[0051] <Method for evaluating bubble generation> The bubbles in the composite silica glass plate produced by the above method were observed with a graduated magnifying glass (Stand Microscope, manufactured by Tokai Sangyo Co., Ltd.), and the bubbles with a longitudinal length of 5 mm or more were counted. The count was performed within a 300 x 300 mm area of ​​the composite silica glass plate, and the number of bubbles counted by the above method was rated as best when it was 0, good when it was more than 0 but less than 10, and poor when it was 10 or more. As a result of the evaluation of bubble generation, the number of bubbles counted was 1.

[0052] Example 2 As in Example 1, two rectangular transparent silica glass plates measuring 400 mm × 400 mm × 3 mm each having linear tool marks formed vertically on both sides thereof were prepared, one on each side of a rectangular opaque silica glass plate measuring 400 mm × 400 mm × 6 mm each having linear tool marks formed vertically on both sides thereof as shown in FIG. 2 . The peak-to-valley (PV) values ​​of the linear tool marks were in the range of 2 μm to 5 μm, and the peak-to-valley (PV) intervals were in the range of 60 μm to 80 μm. The 3D dimension measurement function of a Keyence digital microscope (VHX-8000) was used to measure the PV values ​​and the PV intervals.

[0053] In addition, in Example 2, when cutting a block-shaped silica glass lump into plate-shaped silica glass using a wire saw, the cutting speed was slower than the cutting speed using the wire saw in Example 1, and the PV (peak-to-valley) value and PV (peak-to-valley) spacing of the linear tool marks formed on the opaque silica glass plate and the transparent silica glass plate were changed.

[0054] The plates were overlapped in the order of transparent silica glass plate-opaque silica glass plate-transparent silica glass plate, with the tool marks facing each other and approximately parallel to each other with the tool marks being formed in the same direction, and then secured together with tape to obtain overlapping silica glass plates 10 facing each other before heating (composite silica glass plates before heating).

[0055] A scaffolding rod made of silica glass was attached to the upper clamping part of a composite silica glass plate manufacturing device having a clamping part that moves up and down, and the scaffolding rod and the unheated composite silica glass plate were welded with an oxyhydrogen flame.

[0056] A scaffolding rod made of silica glass was attached to the lower clamp part of the composite silica glass plate manufacturing device, and the scaffolding rod and the pre-heated composite silica glass plate were welded with an oxyhydrogen flame.

[0057] The unheated composite silica glass plate was heated from below with a propane-oxygen burner so that the direction of tool mark formation and the direction of heating were the same, while the feed descent speed of the upper clamp was set to 3 mm / min and the pull descent speed of the lower clamp was set to 9 mm / min. The upper clamp part and the lower clamp part were moved downward to stretch the unheated composite silica glass plate, thereby obtaining a composite silica glass plate which is the composite silica glass plate of the present invention.

[0058] The composite silica glass plate thus obtained was evaluated for bubble generation in the same manner as in Example 1. As a result, the number of bubbles counted was zero.

[0059] Comparative Example 1 Two 400 mm × 400 mm × 3 mm rectangular transparent silica glass plates having linear tool marks formed vertically on both sides were prepared on either side of a 400 mm × 400 mm × 6 mm rectangular opaque silica glass plate having linear tool marks formed vertically on both sides similar to those in Example 1. The transparent silica glass plate-opaque silica glass plate-transparent silica glass plate were placed face to face with the tool marks formed in the same direction and fixed with tape to obtain opposing laminated silica glass plates 10 before heating.

[0060] This laminated silica glass plate 10 was rotated 90° to the right to obtain a laminated silica glass plate before heating (pre-heated composite silica glass plate) on which a linear tool mark was formed in the lateral direction.

[0061] A scaffolding rod made of silica glass was attached to the upper clamping part of a composite silica glass plate manufacturing device having a clamping part that moves up and down, and the scaffolding rod and the unheated composite silica glass plate were welded with an oxyhydrogen flame.

[0062] A scaffolding rod made of silica glass was attached to the lower clamp part of the composite silica glass plate manufacturing device, and the scaffolding rod and the pre-heated composite silica glass plate were welded with an oxyhydrogen flame.

[0063] The unheated composite silica glass plate was heated from below with a propane-oxygen burner so that the direction of tool mark formation and the direction of heating were perpendicular, while the feed descent speed of the upper clamp was set to 3 mm / min and the pull descent speed of the lower clamp was set to 9 mm / min. The upper clamp part and the lower clamp part moved downward to stretch the unheated composite silica glass plate, thereby obtaining a composite silica glass plate that is a composite silica glass plate. The composite silica glass plate thus obtained was evaluated for bubble generation in the same manner as in Example 1. The number of bubbles counted was 10. [Explanation of symbols]

[0064] 10: overlapping silica glass plates, 12a: transparent silica glass plate (first silica glass plate), 12b: transparent silica glass plate (second silica glass plate), 13a, 13b: tool mark facing portion, 14: opaque silica glass plate, 18a, 18b, 18c, 18d: tape, 20a, 20b: upper clamp, 22a, 22b: scaffolding rod, 24a, 24b: lower clamp, 26a, 26b: scaffolding rod, 28: burner, 30, 36, 42, 50, 60: tool mark, 32, 40, 46, 52, 58: convex portion, 34, 38, 44, 54, 62: concave portion, 48: composite silica glass plate, boundary line: 56, 64, A: tool mark formation direction, L1: PV value, D1: PV interval, θ1: angle of angular deviation.

Claims

1. A step of preparing a first silica glass plate having a first tool mark formed in a certain direction on at least one surface thereof and a second silica glass plate having a second tool mark formed in a certain direction on at least one surface thereof; a step of overlapping the first silica glass plate and the second silica glass plate with the surfaces having the tool marks facing each other, with the first tool mark and the second tool mark being formed in the same direction; a heating step of sequentially heating the overlapped silica glass plates from an end portion in the same direction as the tool mark formation direction; Including, A method for manufacturing a composite silica glass plate.

2. 2. The method for manufacturing a composite silica glass plate according to claim 1, wherein the tool marks are a plurality of linear tool marks formed over the entire surface of at least one surface of the first silica glass plate and the second silica glass plate.

3. The method for manufacturing a composite silica glass plate according to claim 2, wherein the PV (peak-to-valley) value of the linear tool mark is 0.1 μm to 10 μm.

4. The method for manufacturing a composite silica glass plate according to claim 2, wherein the PV (peak-to-valley) interval of the linear tool marks is 30 μm to 120 μm.

5. The method for manufacturing a composite silica glass plate according to any one of claims 2 to 4, wherein the linear tool marks are approximately parallel.

6. The method for producing a composite silica glass plate according to claim 5 , wherein the surfaces having the tool marks are opposed to each other with the linear tool marks being approximately parallel to each other.

7. The method for producing a composite silica glass plate according to claim 1 , wherein the silica glass plate is opaque silica glass and / or transparent silica glass.

8. The method for producing a composite silica glass plate according to claim 1 , wherein the heating is performed by a burner flame.

9. 9. The method for producing a composite silica glass plate according to claim 8, wherein the burner flame uses propane gas as a combustion gas.

10. The method for producing a composite silica glass plate according to claim 1 , wherein the silica glass plate is stretched during the heating.

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