Silica heat reflector and its manufacturing method

Abstract

The present disclosure aims to provide a silica heat reflector and a manufacturing method thereof that can withstand use up to 1000°C, maintains better adhesion between the silica plate and the reflector than conventional ones, suppresses deterioration of the metal components of the reflector, has good heat reflection properties, has good bonding between the silica plates, and has a long life. The silica heat reflector according to the present disclosure is a silica heat reflector in which the reflector 3 reflects infrared rays L1 incident from the first silica plate side or infrared rays L2 incident from the second silica plate side, the first silica plate 1 and the second silica plate 2 have an OH group content of 1000 ppm or less, the reflector 3 is a thin film, and the surface layer including at least the reflection surface of the reflector is made of one selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo, or is made of an alloy containing at least one selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo and having a melting point of 1200°C or higher.

Description

[Technical field]

[0001] The present disclosure relates to a silica heat reflector that can be used as a heat reflector in various heat treatment devices that heat treat wafers, substrates, etc. at high temperatures, for example in the fields of semiconductors and electronic components, and that has high reflectivity, thereby enabling energy saving in the heat treatment device and suppressing contamination, and a method for manufacturing the same. [Background technology]

[0002] In the manufacturing or processing of semiconductor wafers, heat treatment is performed to impart various properties to the semiconductor wafers. For example, the semiconductor wafers are stored in a furnace core tube made of high purity quartz, and the heat treatment is performed by controlling the atmosphere inside the furnace core tube. In the heat treatment device used in this heat treatment process, a heat retainer (lid) is provided between the furnace interior and the hearth to cover the furnace opening in order to maintain a high temperature inside the furnace and prevent heat dissipation to the hearth.

[0003] One such heat retaining body is one that blocks the opening of the heat treatment chamber, has quartz plates that are stacked apart from each other and exposed to the heat treatment chamber, and has a smooth surface without bubbles and a thin gold film formed inside the quartz plate by gold vapor deposition (see, for example, Patent Document 1).

[0004] There is a disclosure of a technology in which a heat insulating structure of a vertical heat treatment furnace is composed of a plurality of support columns and a plurality of heat shield plates having reflectivity provided on the support columns at a predetermined interval in the vertical direction (for example, see Patent Document 2). According to Patent Document 2, the heat shield plate is formed of a reflective film and a transparent quartz layer covering the surface of the reflective film. One method of forming the heat shield plate is to use a pair of circular transparent quartz plates forming a transparent quartz layer, provide a reflective film on one surface of one of the transparent quartz plates, sandwich the reflective film between the other transparent quartz plate, and weld the peripheries of both transparent quartz plates to seal and integrate them. Another method of forming a heat shield plate is to provide a reflective film on the upper surface of a circular transparent quartz plate forming one of the transparent quartz layers, pour transparent quartz onto the reflective film, and seal the reflective film to form the other transparent quartz layer.

[0005] Also, a silica heat reflector has a silica plate and a reflector that is disposed inside the silica plate and completely covers the outer periphery with the silica plate, and reflects infrared rays incident on one surface of the silica plate, the reflector being a thin film, plate or foil, and the surface layer including at least the reflecting surface of the reflector is made of Ir, Pt, Rh, Ru, Re, Hf or Mo, or is made of an alloy containing at least one selected from Ir, Pt, Rh, Ru, Re, Hf and Mo (see, for example, Patent Document 3). Patent Document 3 discloses a form in which the bonding method of the silica plate is surface activated bonding. According to Patent Document 3, a silica heat reflector having a high reflectivity by securing a higher reflection area ratio than the conventional method, a small heat capacity allows energy saving, and contamination inside the furnace is suppressed, and a long-life silica heat reflector can be provided. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2001-102319 A [Patent Document 2] Japanese Patent Application Publication No. 11-97360 [Patent Document 3] Patent Publication No. 2022-105255 Summary of the Invention [Problem to be solved by the invention]

[0007] In Patent Document 1, a gold thin film with high reflectance in the infrared region is used as the metal reflective film that contributes to infrared reflection. However, the melting point of gold is 1064°C, and the temperature of heat treatment in the manufacturing or processing process of semiconductor wafers rises to nearly 90% of the melting point of gold, so there are problems with the gold thin film melting, peeling off, and shrinking, and there are problems with heat resistance in practical use. In addition, bonding of silica plates is required to encapsulate the gold thin film that contributes to infrared reflection in the silica plate. However, when attempting to melt and bond silica plates, silica has a very high softening point of 1720°C and an annealing point of 1180°C, so a temperature of at least 1200°C is required, and materials with low melting points such as gold cannot be used.

[0008] In Patent Document 2, a reflective film is sandwiched between quartz plates and the periphery of the quartz plates is welded. However, the reflective film is subject to the effects of heat, which can lead to the problem of the reflective film peeling off. Furthermore, it is difficult to maintain a vacuum inside, and there is an unavoidable risk of the thin film being damaged by an increase in internal pressure during high-temperature use. In addition, other methods for forming heat shields involve pouring transparent quartz, which means that thermal and physical damage to the metal thin film cannot be avoided.

[0009] In Patent Document 3, a reflector made of a metal material with a high melting point is subjected to surface activation bonding in order to suppress thermal and physical damage to the metal material. However, since metal silicon used in surface activation bonding and OH groups due to plasma treatment remain on the metal reflector during surface activation bonding, when the silica heat reflector of Patent Document 3 is used to perform heat treatment in the manufacturing or processing process of semiconductor wafers, if the heat treatment temperature exceeds 800°C, the bonding rate between the silica plates may decrease and the metal reflector may deteriorate, which may result in a decrease in the life of the silica heat reflector and a decrease in the yield of the silica heat reflector.

[0010] The present disclosure aims to provide a silica heat reflector and a method for manufacturing the same that can withstand use up to 1000°C, maintain better adhesion between the silica plate and the reflector than conventional methods, suppress deterioration of the metal components of the reflector, have good heat reflection properties, good bonding between the silica plates, and have a long life. [Means for solving the problem]

[0011] As a result of intensive research, the inventors have found that the above problem can be solved by adjusting the content of OH groups in the silica plate to a predetermined range, and have completed the present invention. That is, the silica heat reflecting plate according to the present invention includes a first silica plate, a second silica plate whose surface faces the first silica plate, a reflector provided on at least one of the surface of the second silica plate facing the first silica plate and the surface of the first silica plate facing the second silica plate, and a joint portion in which at least the peripheral portion of the joint surface between the first silica plate and the second silica plate is continuously joined in a ring shape along the peripheral portion, and has a structure of a joint plate of the first silica plate and the second silica plate. The reflector is a silica heat reflecting plate that reflects infrared rays incident from the first silica plate side or the second silica plate side, the first silica plate and the second silica plate have an OH group content of 1000 ppm or less, the reflector is a thin film, and a surface layer including at least the reflective surface of the reflector is made of one type selected from the group consisting of Ir, Pt, Rh, Ru, Re and Mo, or is made of an alloy containing at least one type selected from the group consisting of Ir, Pt, Rh, Ru, Re and Mo and having a melting point of 1200°C or higher.

[0012] In the silica heat reflector according to the present invention, the first silica plate and the second silica plate preferably have a content of each of Li, Na, K, Ca, Mg, B, Fe, and Cu of 1 ppm or less, and an Al content of 10 ppm or less, which can suppress contamination in a heat treatment furnace.

[0013] In the silica heat reflection plate according to the present invention, it is preferable that the surface roughness of at least one of the outer peripheral flat surfaces of the first silica plate and the second silica plate is 5 μm or less in arithmetic mean roughness Ra of at least a part of the outer peripheral flat surface. It is possible to appropriately adjust the increase in reflectivity and the dispersion of reflected heat.

[0014] In the silica heat reflector according to the present invention, the reflectance of the reflector in the infrared region of 1500 to 2400 nm incident from the first silica plate side or the second silica plate side is preferably 75% or more. From the behavior of the maximum wavelength of thermal radiation when the furnace body temperature is 950°C and the reflectance of the metal reflector, it is important to ensure high reflectance in the infrared region of 1500 to 2400 nm.

[0015] In the silica heat reflecting plate according to the present invention, the first silica plate and the second silica plate preferably have a thickness of 0.5 to 2.0 mm, which can suppress energy loss due to heat absorption by the silica heat reflecting plate itself and improve thermal response during heating and cooling of the furnace body.

[0016] In the silica heat reflector according to the present invention, the reflector preferably has a thickness of 50 to 500 nm, which allows the reflector to maintain close contact with the silica plate and efficiently reflect heat.

[0017] In the silica heat reflector according to the present invention, at least one of the first silica plate and the reflector and the second silica plate and the reflector has an oxide layer containing one selected from the group of oxides consisting of silicon oxide, aluminum oxide, sapphire, lithium tantalate, lithium niobate, magnesium oxide, titanium oxide, yttrium oxide, strontium titanate, germanium oxide, zinc oxide, indium oxide, indium tin oxide, tin oxide, tungsten-added tin oxide, and tantalum oxide, or an oxide layer containing two or more selected from the group of oxides, and the thickness of the oxide layer is preferably 50 nm or less. The oxide layer promotes adhesion between the reflector and the silica plate, suppresses heat absorption by the oxide layer, and efficiently reflects heat.

[0018] The manufacturing method of the silica thermal reflector of the present invention is characterized by including a first step of preparing a first silica plate and a second silica plate, a second step of forming a reflector on at least one of the surfaces of the first silica plate and the second silica plate, a third step of joining the first silica plate and the second silica plate with the surfaces of the reflector formed on at least one of the first silica plate and the second silica plate as opposing surfaces, and a fourth step of joining at least the peripheral portions of the opposing surfaces of the first silica plate and the second silica plate.

[0019] In the method for manufacturing a silica heat reflector according to the present invention, it is preferable to carry out a fifth step of polishing the outer peripheral planes of the first silica plate and the second silica plate to adjust the final plate thickness after the fourth step, so that the final plate thickness can be adjusted more accurately.

[0020] In the manufacturing method of the silica heat reflector according to the present invention, in the fourth step, it is preferable to bond the first silica plate and the second silica plate at a pressure of 3500 kPa or less and a temperature of 400 to 1000° C. after creating a vacuum atmosphere of 100 Pa or less, an argon atmosphere, or a nitrogen atmosphere. This can suppress deterioration of the reflector due to oxygen or hydrogen and deterioration of the reflector due to heat, and maintain the heat reflectance.

[0021] In the method for manufacturing a silica heat reflector according to the present invention, it is preferable to further include a step A between the third step and the fourth step, in which a pressing material made of carbon, oxide, nitride or boride, or a pressing material containing at least one selected from the group consisting of carbon, oxide, nitride and boride, is placed at a location in contact with at least the outer circumferential flat surface of the first silica plate and the second silica plate. The first silica plate and the second silica plate can be bonded while suppressing contamination of the reflector by impurities.

[0022] In the method for producing a silica heat reflecting plate according to the present invention, between the third step and the fourth step, a step B is further included in which a plurality of stacks of the first and second silica plates obtained in the third step are prepared, and 2 to 30 pairs of the stacks are stacked in the stacking direction with spacers interposed therebetween, and the spacers are preferably made of carbon, oxide, nitride, or boride, or contain at least one selected from the group consisting of carbon, oxide, nitride, and boride, and the fourth step is preferably a step in which 2 to 30 stacked pairs of the stacks are simultaneously bonded. A plurality of pairs of the first silica plate and the second silica plate can be simultaneously bonded while suppressing bonding of different silica plates, such as a first silica plate and another second silica plate, or another first silica plate and a second silica plate.

[0023] In the method for manufacturing a silica heat reflector according to the present invention, in the second step, the reflector is preferably formed by any one of a sputtering method, a chemical vapor deposition method, and a deposition method. The thickness of the reflector can be made uniform, and the heat reflectance can be made uniform. In addition, the density of the film can be improved, and therefore the heat reflectance can be improved.

[0024] In the method for manufacturing a silica heat reflector according to the present invention, it is preferable to further include a step C between the first step and the second step, in which the surfaces to be opposed to the first silica plate and the second silica plate in the third step are reverse sputtered. By cleaning the opposing surfaces of the first silica plate and the second silica plate to remove impurities, the adhesion between the first silica plate and the reflector, the first silica plate and the oxide layer, the second silica plate and the reflector, and the second silica plate and the oxide layer is improved, and the adhesion of the joint between the first silica plate and the second silica plate in the peripheral part can be improved. By removing the impurities, the impurities on the surfaces of the first silica plate 1 and the second silica plate 2 come into contact with the surface of the reflector 3 and react with each other, and deterioration of the reflector 3 can be suppressed.

[0025] In the method for producing a silica heat reflector according to the present invention, it is preferable to further include at least one step selected from the group consisting of step D, in which heat treatment is performed at 1000° C. or less after the second step, and step E, in which heat treatment is performed at 1000° C. or less after the fourth step, which can improve the density of the reflector and improve the heat reflectance. Effect of the Invention

[0026] According to the present disclosure, it is possible to provide a silica heat reflector and a manufacturing method thereof that can withstand use up to 1000°C, maintain better adhesion between the silica plate and the reflector than conventional methods, suppress deterioration of the metal components of the reflector, have good heat reflection properties, have good bonding between the silica plates, and have a long life. [Brief description of the drawings]

[0027] [Figure 1] 1 is a schematic plan view showing a silica heat reflector according to an embodiment of the present invention. [Diagram 2] 2 is a schematic diagram showing a first example of the AA cross section of the silica heat reflector shown in FIG. 1. FIG. [Diagram 3] 2 is a schematic diagram showing a second example of the AA cross section of the silica heat reflector shown in FIG. 1. FIG. [Figure 4] FIG. 2 is a schematic diagram showing a third example of the AA cross section of the silica heat reflector shown in FIG. 1, which is a schematic diagram of a silica heat reflector having an oxide layer between the silica plate and the reflector. [Diagram 5] FIG. 2 is a schematic diagram showing a fourth example of the AA cross section of the silica heat reflector shown in FIG. 1, which is a schematic diagram of a silica heat reflector having an oxide layer between the first reflector and the first silica plate, and between the second reflector and the second silica plate. [Figure 6]FIG. 3 is a schematic diagram showing a manufacturing method of the first example silica heat reflector shown in FIG. 2, in which (a) shows a first step of preparing a first silica plate and a second silica plate, (b) shows a second step of forming a reflector on the surface of the first silica plate, (c) shows a third step of joining the first silica plate and the second silica plate with the surface of the reflector formed on the first silica plate as the opposing surface, and (d) shows a fourth step of joining at least the peripheral portions of the opposing surfaces of the first silica plate and the second silica plate. [Figure 7] FIG. 4 is a schematic diagram showing a manufacturing method of the second example silica heat reflector shown in FIG. 3, in which (e) shows a first step of preparing a first silica plate and a second silica plate, (f) shows a second step of forming a reflector on both the surface of the first silica plate and the surface of the second silica plate, (g) shows a third step of joining the first silica plate and the second silica plate by opposing the surface of the reflector formed on the first silica plate to the surface of the reflector formed on the second silica plate, and (h) shows a fourth step of joining at least the peripheral portions of the opposing surfaces of the first silica plate and the second silica plate. [Figure 8] FIG. 7 is a schematic diagram showing another example of steps performed following the first step (a), the second step (b), and the third step (c) shown in FIG. 6, in which (c-1) shows step B in which a plurality of stacks of the first silica plate and the second silica plate obtained in the third step are prepared, and 2 to 30 pairs of the stacks are stacked in the stacking direction with spacers in between, and (d-1) shows the fourth step in which each of the 2 to 30 stacked pairs is simultaneously bonded. [Figure 9] FIG. 8 is a schematic diagram showing another example of steps performed following the first step (e), the second step (f), and the third step (g) shown in FIG. 7, in which (g-1) shows step B in which a plurality of stacks of the first silica plate and the second silica plate obtained in the third step are prepared, and 2 to 30 pairs of the stacks are stacked in the stacking direction with spacers in between, and (h-1) shows the fourth step in which each of the 2 to 30 stacked pairs is simultaneously bonded. [Figure 10] 4 is a graph showing the results of measuring the reflectance of the silica heat reflector plate according to Example 1 using a spectrophotometer. [Figure 11]11 is a graph showing the results of measuring the reflectance of the silica heat reflector plate according to Example 2 using a spectrophotometer. [Figure 12] 4 is a graph showing the results of measuring the reflectance of the silica heat reflector plate according to Comparative Example 1 using a spectrophotometer. [Figure 13] 13 is a graph showing the relationship between the arithmetic mean roughness Ra and the reflectance in Example E. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0028] Hereinafter, the present invention will be described in detail with reference to the embodiments, but the present invention is not limited to these descriptions. Various modifications of the embodiments may be made as long as the effects of the present invention are achieved.

[0029] (Reflector formed on the first silica plate) The silica heat reflector according to this embodiment will be described with reference to Figures 1 and 2. The silica heat reflector 100 according to this embodiment includes a first silica plate 1, a second silica plate 2 whose surface faces the first silica plate 1, a reflector 3 provided on the surface of the first silica plate 1 facing the second silica plate 2, and a joint 4 in which at least the peripheral portion of the joint surface between the first silica plate 1 and the second silica plate 2 is continuously joined in an annular shape along the peripheral portion, and has a structure of a joint plate of the first silica plate 1 and the second silica plate 2, and the reflector 3 is formed by joining the first silica plate 1 and the second silica plate 2 together. a first silica plate (1) and a second silica plate (2) each have an OH group content of 1000 ppm or less; a reflector (3) is a thin film; and a surface layer of the reflector (3) including at least the reflective surface is made of one type selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo, or is made of an alloy containing at least one type selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo and having a melting point of 1200°C or higher.

[0030] (An embodiment in which a reflector is formed on the first silica plate and the second silica plate) As shown in FIG. 1 and FIG. 3, the reflector 3 is preferably provided on both the first silica plate 1 and the second silica plate 2. When a silica plate provided with a reflective film and a silica plate without a reflective film are combined, gaps are likely to occur, so it is preferable to provide a reflective film on both silica plates and join them together. In the silica heat reflector 200, the first silica plate 1 is provided with a first reflector 3a (hereinafter, sometimes simply referred to as "reflector 3"), the second silica plate 2 is provided with a second reflector 3b (hereinafter, sometimes simply referred to as "reflector 3"), and the first reflector 3a and the second reflector 3b are combined. The reflectance can be further increased. In addition, peeling due to film stress is unlikely to occur. Furthermore, it is more preferable that the first reflector 3a and the second reflector 3b are joined together. Hereinafter, the first reflector 3a and the second reflector 3b are sometimes referred to as "reflector 3" without being distinguished from the reflector 3.

[0031] (Reflector composition) The surface layer including at least the reflecting surface of the reflector 3 is made of one selected from the group consisting of Ir, Pt, Rh, Ru, Re and Mo, or is made of an alloy containing at least one selected from the group consisting of Ir, Pt, Rh, Ru, Re and Mo and having a melting point of 1200°C or higher. When a Si substrate on which a circuit or the like is formed is heat-treated in a semiconductor heat treatment furnace, a silica heat reflector is used at about 1000°C. If the reflector 3 is made of the above metal or alloy, the reflector 3 can be prevented from melting or softening. If the reflector 3 melts or softens, stains will occur due to the reaction between the first silica plate 1 and the second silica plate 2 and the reflector 3, or the reflectance will decrease. The total content of Ir, Pt, Rh, Ru, Re and Mo in the alloy is preferably 50% by mass or more, more preferably 60% by mass or more.

[0032] (Reflector thickness) The reflector 3 is a thin film. The thickness of the reflector 3 is preferably 50 to 500 nm, and more preferably 100 to 400 nm. If the thickness of the reflector 3 is less than 50 nm, heat is not reflected by the reflector 3 but is transmitted through it, resulting in a decrease in heat reflectance, and if the thickness of the reflector 3 is greater than 500 nm, peeling may occur due to film stress. When the first reflector 3a and the second reflector 3b are provided, the total thickness is preferably 50 to 500 nm, and more preferably 100 to 400 nm.

[0033] (Composition of the first and second silica plates) The first silica plate 1 and the second silica plate 2 include a form in which they are crystalline silica plates or amorphous silica plates. They also include a form in which they are synthetic quartz glass plates or fused quartz glass plates. They are preferably synthetic quartz glass plates. The first silica plate 1 and the second silica plate 2 preferably have an elemental content of Li, Na, K, Ca, Mg, B, Fe, and Cu of 1 ppm or less, and an Al content of 10 ppm or less. Contamination inside a heat treatment furnace can be suppressed. If the elemental content of Li, Na, K, Ca, Mg, B, Fe, and Cu in the first silica plate 1 and the second silica plate 2 exceeds 1 ppm, or if the Al content in the first silica plate 1 and the second silica plate 2 exceeds 10 ppm, when a heat reflector is used in a heat treatment furnace for semiconductors to heat-treat a Si substrate on which a circuit or the like is formed, the inside of the heat treatment furnace may be contaminated, making it impossible to use the Si substrate on which a circuit or the like is formed.

[0034] (Size and thickness of the first and second silica plates) The shape of the first silica plate 1 and the second silica plate 2 when the reflector 3 is viewed from the front is, for example, a circle, an ellipse, a rectangle, or a square, and a circle is preferable. The diameter of the circle is, for example, 5 to 50 cm. The width of the annular shape of the joint 4 between the peripheral parts is, for example, 0.5 to 20 mm. The plate thickness of the first silica plate 1 and the second silica plate 2 is preferably 0.5 to 2.0 mm, and more preferably 1.0 to 1.5 mm. The energy loss due to the heat absorption of the silica heat reflector itself can be suppressed, and the thermal response during heating and cooling of the furnace body can be improved. The plate thickness difference between the first silica plate 1 and the second silica plate 2 is preferably 0.1 mm or less, and more preferably the same thickness. If the plate thickness of the first silica plate 1 and the second silica plate 2 is thinner than 0.5 mm, when the heat reflector is used in a semiconductor heat treatment furnace to heat-treat a Si substrate on which a circuit or the like is formed, the heat reflector may be damaged or deformed due to a decrease in strength. On the other hand, if the thickness of the first silica plate 1 and the second silica plate 2 exceeds 2.0 mm, when a heat reflector is used in a semiconductor heat treatment furnace to heat treat a Si substrate on which circuits or the like are formed, the heat reflector, particularly the silica plate, may absorb heat (thermal radiation, infrared rays), which may reduce the thermal efficiency in the semiconductor heat treatment furnace.

[0035] (Surface roughness of the outer peripheral planes of the first and second silica plates) In at least one of the outer peripheral planes of the first silica plate 1 and the second silica plate 2, the surface roughness of at least a part of the outer peripheral plane is preferably 5 μm or less in arithmetic mean roughness Ra. More preferably, it is 2 μm or less, even more preferably, it is 1 μm or less, and even more preferably, it is 0.5 μm or less. It is possible to appropriately adjust the increase in reflectance and the dispersion of reflected heat. The lower limit of the arithmetic mean roughness Ra is, for example, preferably 0.01 μm or more, and more preferably 0.1 μm or more. Examples of surfaces with such surface roughness include blasted surfaces and etched surfaces. When the outer peripheral plane is a blasted surface, the arithmetic mean roughness Ra is preferably 2 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. The blasting process includes wet blasting and dry blasting. The etching process includes wet etching and dry etching. In addition, the degree of arithmetic mean roughness may be equal or different on the outer peripheral plane. For example, the arithmetic mean roughness Ra of the entire peripheral flat surface may be 5 μm or less, or the central part of the peripheral flat surface may be a smooth surface, and the arithmetic mean roughness Ra of the outer annular part surrounding the central part may be 5 μm or less. The term "smooth surface" refers to a surface that is not roughened by blasting or etching when manufacturing the silica heat reflector of this embodiment. Furthermore, the arithmetic mean roughness Ra of the central part of the peripheral flat surface may be 2 μm or less, and the arithmetic mean roughness Ra of the outer annular part surrounding the central part may be 5 μm or less, or the entire peripheral flat surface may be a smooth surface. Furthermore, the surface of the silica plate at the peripheral part other than the part where the metal film is formed may be rougher than the surface of the silica plate at the part where the metal film is formed and surrounded by the peripheral part. In this case, it is possible to suppress the transmission of heat incident on the peripheral part. In this embodiment, the term "peripheral flat surface" is synonymous with "outer flat surface".

[0036] (OH group content of the first and second silica plates) The OH group content of the first silica plate 1 and the second silica plate 2 is 1000 ppm or less, preferably 900 ppm or less, and more preferably 800 ppm or less. Silica is a material with high infrared transmittance, but on the other hand, OH groups absorb infrared rays near 1400 nm, 2200 nm, and 2700 nm. As the wavelength increases, the infrared transmittance of the silica plate decreases, so wavelengths from 1500 nm to 2400 nm are particularly important, and by suppressing the absorption near 2200 nm by OH groups to improve the reflectance, a high reflectance can be achieved. In addition, the absorption of infrared rays by OH groups near 2700 nm can be suppressed. If the OH group content of the first silica plate 1 and the second silica plate 2 exceeds 1000 ppm, deterioration due to the reaction between the reflector 3 and the OH groups is promoted, causing partial disappearance or alteration of the metal film, resulting in the occurrence of spots. In addition, infrared rays passing through the silica plate are absorbed by the OH groups, decreasing the reflectance of the silica heat reflector. The lower limit of the OH group content of the first silica plate 1 and the second silica plate 2 is preferably 1 ppm or more, and preferably 20 ppm or more. If the OH group content is too small, the bonding strength between the silica plates may decrease. The OH group present in the silica plate is not unevenly distributed depending on the location.

[0037] The OH group content of the first silica plate 1 and the second silica plate 2 was calculated as follows: First, the absorbance was measured using a Fourier transform infrared spectrophotometer (FT-IR), and then the absorbance value near 2720 nm was applied to the Beer-Lambert equation to calculate the absorbance, and the calculated value was divided by the density to obtain the OH group concentration.

[0038] (Reflectance of silica heat reflector) In the silica heat reflecting plate 100, 200, 300, 400 according to this embodiment, the reflectance by the reflector 3 in the infrared region of 1500 to 2400 nm incident from the first silica plate side or the second silica plate side is preferably 75% or more. In FIG. 2, the incident direction L1 from the first silica plate side and the incident direction L2 from the second silica plate side are illustrated as an example. The temperature of the furnace body for semiconductors to which the heat reflecting plate is provided is 1000°C or less, but there is an optimal wavelength for efficient heating. From Planck's law, the radiation intensity radiated in all directions is expressed by the following formula 1.

number

number

[0039] (Oxide layer) As shown in FIG. 4, the silica heat reflector 300 has an oxide layer 5 containing one selected from the group of oxides consisting of silicon oxide, aluminum oxide, sapphire, lithium tantalate, lithium niobate, magnesium oxide, titanium oxide, yttrium oxide, strontium titanate, germanium oxide, zinc oxide, indium oxide, indium tin oxide, tin oxide, tungsten-added tin oxide, and tantalum oxide between the first silica plate 1 and the reflector 3, or an oxide layer 5 containing two or more selected from the group of oxides, and the thickness of the oxide layer 5 is preferably 50 nm or less. It is more preferable that the thickness of the oxide layer 5 is 40 nm or less. The silica heat reflector may have an oxide layer 5 between the second silica plate and the reflector (not shown). Also, as shown in FIG. 5, the silica heat reflector 400 may have an oxide layer 5a between the first silica plate 1 and the first reflector 3a, and an oxide layer 5b between the second silica plate 2 and the second reflector 3b. The oxide layer 5 (5a, 5b) improves the adhesion between the reflector 3 (3a, 3b) and the silica plates 1, 2, and also suppresses the absorption of heat by the oxide layer 5 (5a, 5b), thereby allowing efficient reflection of heat. The material of the oxide layer 5 (5a, 5b) is preferably a material that can further improve the adhesion between the first silica plate 1 or the second silica plate 2 and the reflector 3, and can reflect heat by the reflector 3 without absorbing heat itself. In addition, if the thickness of the oxide layer 5 (5a, 5b) exceeds 50 nm, the oxide layer 5 (5a, 5b) may absorb heat (thermal radiation, infrared rays), and the heat reflectance of the silica heat reflector may decrease. In the case where the reflector 3 and the oxide layer 5 are provided, the incident infrared rays may be applied to the oxide layer 5 before the reflector 3, as shown in, for example, L1 in FIG. 4.

[0040] (Manufacturing method in which the reflector is formed on the first silica plate) A method for manufacturing a silica heat reflector 100 will be described with reference to FIG. 6. The method for manufacturing a silica heat reflector 100 includes a first step of preparing a first silica plate 1 and a second silica plate 2 as shown in FIG. 6(a), a second step of forming a reflector 3 on the surface of the first silica plate 1 as shown in FIG. 6(b), a third step of joining the first silica plate 1 and the second silica plate 2 with the surface of the reflector 3 formed on the first silica plate 1 as the opposing surface as shown in FIG. 6(c), and a fourth step of joining at least the peripheral parts of the opposing surfaces of the first silica plate 1 and the second silica plate 2 as shown in FIG. 6(d). The peripheral parts are joined to form a joint 4. In FIG. 6(b), the reflector 3 is formed on the surface of the first silica plate 1, but the reflector 3 may be formed on the surface of the second silica plate 2. Since the first silica plate 1 and the second silica plate 2 are not substantially distinguished from each other, a form in which the reflector 3 is formed on the surface of the first silica plate 1 is illustrated here.

[0041] (Manufacturing method in which reflectors are formed on the first silica plate and the second silica plate) A method for manufacturing the silica heat reflector 200 will be described with reference to FIG. 7. The method for manufacturing the silica heat reflector 200 includes a first step of preparing the first silica plate 1 and the second silica plate 2 as shown in FIG. 7(e), a second step of forming a reflector 3a on the surface of the first silica plate 1 and a reflector 3b on the surface of the second silica plate 2 as shown in FIG. 7(f), a third step of joining the first silica plate 1 and the second silica plate 2 with the surface of the reflector 3a formed on the first silica plate 1 and the surface of the reflector 3b formed on the second silica plate 2 as opposing surfaces as shown in FIG. 7(g), and a fourth step of bonding at least the peripheral portions of the opposing surfaces of the first silica plate 1 and the second silica plate 2 as shown in FIG. 7(h). The peripheral portions are bonded to form a bonding portion 4.

[0042] In the manufacturing method of the silica heat reflecting plates 100, 200, it is preferable to carry out a fifth step after the fourth step in which the outer peripheral planes of the first silica plate 1 and the second silica plate 2 are polished to adjust the final plate thickness. This allows the final plate thickness to be adjusted more accurately. The silica heat reflecting plates 100, 200 are adjusted to have a plate thickness of, for example, 1.0 to 4.0 mm. Also, the plate thicknesses of the first silica plate 1 and the second silica plate 2 are each adjusted to be 0.5 to 2.0 mm.

[0043] In the manufacturing method of the silica heat reflector 100, 200, in the fourth step, it is preferable to perform bonding at a temperature of 400 to 1000°C under a pressure of 3500 kPa or less after creating a vacuum atmosphere of 100 Pa or less, an argon atmosphere, or a nitrogen atmosphere. This can suppress deterioration of the reflector due to oxygen or hydrogen, and deterioration of the reflector due to heat, and maintain the heat reflectance. Welding can also be performed using an oxyhydrogen burner, but it is difficult to control the temperature, and furthermore, a high temperature of 1000°C or more is required for bonding, which deteriorates the metal film due to this temperature, resulting in a decrease in reflectance. The argon atmosphere or nitrogen atmosphere may be an argon atmosphere under reduced pressure lower than atmospheric pressure or a nitrogen atmosphere under reduced pressure, but may also be atmospheric pressure. In addition, if the vacuum atmosphere is more than 100 Pa, impurities remaining in the atmosphere remain attached to the surfaces of the first silica plate 1, the second silica plate 2, and the reflector 3 in the subsequent bonding process, and the impurities come into contact with the surface of the reflector 3 during the manufacturing of the silica heat reflector 100, 200, causing a reaction, which may cause deterioration of the reflector 3 and make it easier for heat to pass through. In addition, when the manufactured silica heat reflector 100, 200 is used in a semiconductor heat treatment furnace, the impurities may scatter inside the semiconductor heat treatment furnace, etc. When the vacuum atmosphere is 100 Pa or less, it is preferably a vacuum atmosphere of 80 Pa or less. If the pressure for pressing the first silica plate 1 and the second silica plate 2 against each other exceeds 3500 kPa, the pressure may be too high, which may cause defects such as cracking of the first silica plate 1 and the second silica plate 2. It is more preferable that the pressure for pressing the first silica plate 1 and the second silica plate 2 against each other is 3000 kPa or less. The lower limit of this pressure is preferably 800 kPa, more preferably 1000 kPa, in order to ensure reliable bonding. If the temperature during bonding is lower than 400°C, the bonding strength between the first silica plate 1 and the second silica plate 2 will be insufficient, and there is a risk that the first silica plate 1 and the second silica plate 2 will peel off when the manufactured heat reflector 100, 200 is used in a semiconductor heat treatment furnace or the like. If the temperature during bonding is higher than 1000°C, there is a risk that the reflective surface of the reflector 3 will become cloudy, and the reflectance of the reflector 3 will decrease.The temperature during bonding is preferably 500 to 900°C, and more preferably 600 to 850°C.

[0044] (Method of manufacturing a form including an oxide layer) The manufacturing method of the silica heat reflecting plate 300 will be described while showing the difference from the manufacturing method of the silica heat reflecting plate 100. The manufacturing method of the heat reflecting plate 300 further includes a step F (not shown) of forming an oxide layer on the surface of the first silica plate 1 after the first step of preparing the first silica plate 1 and the second silica plate 2 shown in FIG. 6(a). The oxide layer is preferably formed by any of the sputtering method, the chemical vapor deposition method, and the deposition method. Then, the manufacturing method further includes a step G (not shown) of forming a reflector on the oxide layer. After that, the manufacturing method proceeds in the same manner as the third and fourth steps in the manufacturing method of the heat reflecting plate 100.

[0045] The manufacturing method of the silica heat reflecting plate 400 will be described while showing the difference from the manufacturing method of the heat reflecting plate 200. The manufacturing method of the silica heat reflecting plate 400 further includes a step H (not shown) of forming an oxide layer on the surface of the first silica plate 1 and an oxide layer on the surface of the second silica plate 2 after the first step of preparing the first silica plate 1 and the second silica plate 2 shown in FIG. 7(e). The oxide layer is preferably formed by any of the sputtering method, the chemical vapor deposition method, and the deposition method. Then, the manufacturing method further includes a step I (not shown) of forming a reflector on the oxide layer formed on the first silica plate 1 and forming a reflector on the oxide layer formed on the second silica plate 2. After that, the manufacturing method proceeds in the same manner as the third and fourth steps in the manufacturing method of the heat reflecting plate 200.

[0046] (Pressing material) In the manufacturing method of the silica heat reflecting plate 100, 200, 300, 400, as shown in FIG. 6(d) or FIG. 7(h), it is preferable to further include a step A between the third step and the fourth step, in which a pressing material made of carbon, oxide, nitride or boride, or a pressing material 6 containing at least one selected from the group consisting of carbon, oxide, nitride and boride, is placed at a location in contact with at least the outer peripheral flat surface of the first silica plate 1 and the second silica plate 2. The first silica plate and the second silica plate can be joined while suppressing contamination of the reflector by impurities. The pressing material 6 is, for example, a plate material such as a flat plate or a curved plate. The shape and size of the pressing material 6 are preferably similar or congruent to those of the first silica plate and the second silica plate, and when they are similar, they may be increased by up to +10%. The thickness of the pressing material 6 is preferably 1 to 70 mm, more preferably 30 to 50 mm. When bonding, it is necessary for the components of the pressurizer to come into contact with the first silica plate 1 and the second silica plate 2. If a pressing material made of a material other than "a pressing material made of carbon, oxide, nitride or boride, or a pressing material containing at least one selected from the group consisting of carbon, oxide, nitride and boride" is used, there is a risk that it will react with the first silica plate and the second silica plate and be altered. Furthermore, there is a risk that the manufactured silica heat reflecting plates 100, 200, 300, 400 will have an adverse effect on the semiconductor substrate when used in a semiconductor heat treatment furnace, etc.

[0047] (Multiple presses) As shown in FIG. 8, the manufacturing method of the silica heat reflector 100 according to this embodiment further includes a step B (FIG. 8(c-1)) between the third and fourth steps, in which a plurality of stacks of the first and second silica plates obtained in the third step are prepared, and 2 to 30 pairs of the stacks are stacked in the stacking direction with spacers 7 interposed therebetween, the spacers 7 being made of carbon, oxide, nitride or boride, or containing at least one type selected from the group consisting of carbon, oxide, nitride and boride, and the fourth step is preferably a step of simultaneously joining the stacks of 2 to 30 pairs (FIG. 8(d-1)). As shown in FIG. 9, the method for manufacturing the silica heat reflecting plate 200 according to this embodiment further includes a step B (FIG. 9(g-1)) between the third step and the fourth step, in which a plurality of stacks of the first and second silica plates obtained in the third step are prepared, and 2 to 30 stacks of the stacks are stacked in the stacking direction with spacers 7 interposed therebetween, and the spacers 7 are preferably made of carbon, oxide, nitride, or boride, or contain at least one selected from the group consisting of carbon, oxide, nitride, and boride, and the fourth step is preferably a step (FIG. 9(h-1)) in which the stacks of 2 to 30 stacks are simultaneously bonded. It is possible to simultaneously bond a plurality of first and second silica plates while suppressing the bonding of different silica plates, such as a first silica plate and another second silica plate, or another first silica plate and a second silica plate, by the spacer 7. If the number of stacks of stacks exceeds 30, the handling properties may be deteriorated. Similarly, for the silica heat reflecting plates 300 and 400, step B is carried out, and the laminate is simultaneously bonded in step 4, so that multiple sets can be bonded at the same time. The shape and size of the spacer 7 are preferably similar or congruent to those of the first and second silica plates, and when similar, may be increased by up to +10%. The thickness of the spacer 7 is preferably 1 to 70 mm, and more preferably 30 to 50 mm.

[0048] In the method for manufacturing the silica heat reflectors 100, 200, 300, and 400 according to the present embodiment, In the second step, it is preferable to form the reflector 3 (3a, 3b) by any one of the sputtering method, the chemical vapor deposition method, and the deposition method. The thickness of the reflector can be made uniform, and the heat reflectance can be made uniform. In addition, the density of the film can be improved, and therefore the heat reflectance can be improved.

[0049] In the method for manufacturing the silica heat reflectors 100, 200, 300, and 400 according to the present embodiment, It is preferable to further include a step C between the first and second steps, in which the surfaces to be opposed to the first and second silica plates 1 and 2 in the third step are reverse sputtered. By cleaning the opposing surfaces of the first and second silica plates to remove impurities, the adhesion between the first silica plate and the reflector, the first silica plate and the oxide layer, the second silica plate and the reflector, and the second silica plate and the oxide layer can be improved, and the adhesion of the joint between the first and second silica plates in the peripheral portion can be improved. By removing the impurities, the impurities on the surfaces of the first and second silica plates 1 and 2 and the surface of the reflector 3 come into contact with each other and react with each other, which can suppress deterioration of the reflector 3. In addition, the adhesion of the film is improved due to the anchor effect.

[0050] In the manufacturing method of the silica heat reflector 100, 200, 300, 400 according to the present embodiment, it is more preferable to include a step D of performing heat treatment at 1000°C or less after the second step, preferably after the second step and before the third step. It is also more preferable to include a step E of performing heat treatment at 1000°C or less after the fourth step. The lower limit temperature of the heat treatment is, for example, 100°C or more, preferably 200°C or more. Both steps D and E may be included. Furthermore, in the fourth step, when heating is performed at 400 to 1000°C during bonding, bonding and heat treatment are performed simultaneously. The density of the reflector 3 can be improved, and the heat reflectance can be improved. The heat treatment improves the reflectance by about 4%. When the density of the film during the formation of the reflective film is insufficient, sufficient reflectance cannot be obtained, but by performing the heat treatment, the reflective film becomes dense and the desired reflectance can be exhibited. If the heat treatment is performed at a temperature higher than 1000° C., there is a risk that reactions will occur between the first silica plate 1, the second silica plate 2 and the reflector 3 (3a, 3b). EXAMPLES

[0051] Example 1 As the first silica plate 1 and the second silica plate 2, silica plates (synthetic quartz plates) were used, with a plate size of Φ300 mm, a thickness of 1.0 mm, Li, Na, K, Ca, Mg, B, Fe, and Cu at 1 ppm or less, Al at 10 ppm or less, and an OH group concentration of 1000 ppm. Impurities were measured using an ICP mass analyzer, and OH groups were quantified using a Fourier transform infrared spectrophotometer (manufactured by JASCO, PS-4000). After cleaning the surfaces of these silica plates, a Mo film with a thickness of 100 nm was formed as reflectors 3a and 3b on each of the first silica plate 1 and the second silica plate 2 by a sputtering method. The plates were bonded together so that the reflective film was on the inside, and a carbon plate material was placed as a pressing material in contact with the outer peripheral planes of the first silica plate 1 and the second silica plate 2, and set in an atmosphere control pressurizer. The specimens were then evacuated and held for 1 hour under conditions of a vacuum atmosphere of 10 Pa, a temperature of 800°C, and a pressure of 1400 kPa to perform bonding. After bonding, the reflectance was measured using a spectrophotometer (Shimadzu Corporation, UV-3100PC). The measurement results are shown in Figure 10. As a result, the average reflectance from 1500 to 2400 nm was 82.98%, with reflectances of 77.71% at 1500 nm, 77.60% at 2220 nm, and 86.94% at 2400 nm.

[0052] Example 2 The silica heat reflector prepared in Example 1 was placed in a vacuum annealing furnace (manufactured by ULVAC Riko Co., Ltd.) at a pressure of 1.0 × 10 ‐4 A heat treatment was performed in a vacuum atmosphere of 1 Pa at a temperature of 800°C, and the temperature was raised to 800°C and held for 20 minutes, and the reflectance of the silica heat reflector after the heat treatment was measured with a spectrophotometer in the same manner as in Example 1. The measurement results are shown in Figure 11. As a result, the average reflectance from 1500 to 2400 nm was 87.97%, with reflectances of 82.22% at 1500 nm, 82.39% at 2220 nm, and 91.72% at 2400 nm, showing an overall improvement in reflectance of about 4 to 5% compared to the reflectance of Example 1.

[0053] Comparative Example 1 As the first silica plate 1 and the second silica plate 2, silica plates (synthetic quartz plates) were used, with a plate size of Φ300 mm, a thickness of 1.0 mm, Li, Na, K, Ca, Mg, B, Fe, and Cu at 1 ppm or less, Al at 10 ppm or less, and an OH group concentration of 1200 ppm. Impurities were measured using an ICP mass analyzer, and the OH group was quantified using a Fourier transform infrared spectrophotometer. After cleaning the surfaces of these silica plates, a Mo film with a thickness of 100 nm was formed as reflectors 3a and 3b on each of the first silica plate 1 and the second silica plate 2 by a sputtering method. The plates were bonded together with the reflective film facing inward, and a carbon plate material was placed in contact with the outer peripheral plane of the first silica plate 1 and the second silica plate 2 as a pressing material, and set in an atmosphere control pressurizer. The plates were evacuated, and the plates were held for 1 hour under conditions of a vacuum atmosphere of 10 Pa, a temperature of 800° C., and a pressure of 1400 kPa, for bonding. After bonding, the reflectance was measured using a spectrophotometer. The measurement results are shown in Figure 12. As a result, the average reflectance from 1500 to 2400 nm was 72.20%, with the reflectance at 1500 nm being 65.46%, at 2220 nm being 71.97%, and at 2400 nm being 76.85%.

[0054] Example A As the first silica plate 1, a silica plate (synthetic quartz plate) was used, with a plate size of Φ300 mm, a thickness of 1.03 mm, an OH group concentration of 912.39 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm. As the second silica plate 2, a silica plate (synthetic quartz plate) was used, with a plate size of Φ300 mm, a thickness of 1.04 mm, an OH group concentration of 926.50 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm. Other than that, a silica heat reflector was produced in the same manner as in Example 1.

[0055] (Example A-1) Heat treatment temperature: 850°C The same heat treatment as in Example 2 was carried out except that the silica heat reflector of Example A was kept at 850°C for 1 hour, and the reflectance of the silica heat reflector after the heat treatment was measured with a spectrophotometer in the same manner as in Example 1. The measurement results are shown in Table A. As a result, the average reflectance from 1500 to 2400 nm was 86.41%, with reflectances of 80.46% at 1500 nm, 83.29% at 2220 nm, and 89.42% at 2400 nm.

[0056] (Example A-2) Heat treatment temperature: 900°C The silica heat reflector of Example A was subjected to heat treatment in the same manner as in Example A-1, except that the heat treatment temperature was 900° C., and the reflectance was measured. The measurement results are shown in Table A. As a result, the average reflectance from 1500 to 2400 nm was 86.58%, with reflectances of 80.64% at 1500 nm, 83.76% at 2220 nm, and 89.99% at 2400 nm.

[0057] (Example A-3) Heat treatment temperature: 950°C The silica heat reflector of Example A was subjected to heat treatment in the same manner as in Example A-1, except that the heat treatment temperature was 950°C, and the reflectance was measured. The measurement results are shown in Table A. As a result, the average reflectance from 1500 to 2400 nm was 82.26%, with reflectances of 74.73% at 1500 nm, 79.77% at 2220 nm, and 86.81% at 2400 nm.

[0058] (Example A-4) Heat treatment temperature: 1000°C The silica heat reflector of Example A was subjected to heat treatment in the same manner as in Example A-1, except that the heat treatment temperature was 1000°C, and the reflectance was measured. The measurement results are shown in Table A. As a result, the average reflectance from 1500 to 2400 nm was 79.04%, with reflectances of 73.81% at 1500 nm, 78.12% at 2220 nm, and 84.50% at 2400 nm.

[0059] (Reference Example A) Heat treatment temperature 1050℃ The silica heat reflector of Example A was subjected to heat treatment in the same manner as in Example A-1, except that the heat treatment temperature was 1050°C, and the reflectance was measured. The measurement results are shown in Table A. As a result, the average reflectance from 1500 to 2400 nm was 70.00%, with reflectances of 64.74% at 1500 nm, 67.49% at 2220 nm, and 75.57% at 2400 nm.

[0060] [Table A]

[0061] In Examples A-1 and A-2, the reflectance at each wavelength of 1500 nm, 2200 nm, and 2400 nm is 75% or more, and the average reflectance is also 75% or more, so that it can efficiently reflect heat when used as a silica heat reflector. In Examples A-3 and A-4, the reflectance at a wavelength of 1500 nm is less than 75%, but the average reflectance is 75% or more, so that it can reflect heat without any problems when used as a silica heat reflector.

[0062] On the other hand, in Reference Example A, the reflectance at a wavelength of 2400 nm was barely 75% or more, but the reflectance at each wavelength of 1500 nm and 2200 nm was less than 75%, and the average reflectance was also less than 75%. It is considered that the first silica plate 1, the second silica plate 2, and the reflector 3 (3a, 3b) reacted with each other because the silica heat reflector was heat-treated at a temperature higher than 1000°C. Therefore, it is preferable that the first silica plate 1, the second silica plate 2, and the reflector 3 (3a, 3b) do not react with each other.

[0063] Example B As the first silica plate 1, a silica plate (fused quartz plate) was used, with a plate size of Φ324 mm, a thickness of 1.04 mm, an OH group concentration of 256.59 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm. As the second silica plate 2, a silica plate (fused quartz plate) was used, with a plate size of Φ324 mm, a thickness of 1.04 mm, an OH group concentration of 245.77 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm. Other than that, a silica heat reflector was produced in the same manner as in Example 1.

[0064] (Example B-1) Heat treatment temperature: 850°C The same heat treatment as in Example 2 was carried out except that the silica heat reflector of Example B was kept at 850°C for 1 hour, and the reflectance of the silica heat reflector after the heat treatment was measured with a spectrophotometer as in Example 1. The measurement results are shown in Table B. As a result, the average reflectance from 1500 to 2400 nm was 87.25%, with reflectances of 80.30% at 1500 nm, 89.27% ​​at 2220 nm, and 90.95% at 2400 nm.

[0065] (Example B-2) Heat treatment temperature: 900°C The silica heat reflector of Example B was subjected to heat treatment in the same manner as in Example B-1, except that the heat treatment temperature was 900° C., and the reflectance was measured. The measurement results are shown in Table B. As a result, the average reflectance from 1500 to 2400 nm was 86.97%, with reflectances of 76.98% at 1500 nm, 85.81% at 2220 nm, and 87.26% at 2400 nm.

[0066] (Example B-3) Heat treatment temperature: 950°C The silica heat reflector of Example B was subjected to heat treatment in the same manner as in Example B-1, except that the heat treatment temperature was 950° C., and the reflectance was measured. The measurement results are shown in Table B. As a result, the average reflectance from 1500 to 2400 nm was 88.78%, with reflectances of 82.14% at 1500 nm, 89.51% at 2220 nm, and 92.11% at 2400 nm.

[0067] (Example B-4) Heat treatment temperature 1000°C The silica heat reflector of Example B was subjected to heat treatment in the same manner as in Example B-1, except that the heat treatment temperature was 1000° C., and the reflectance was measured. The measurement results are shown in Table B. As a result, the average reflectance from 1500 to 2400 nm was 87.28%, with reflectances of 80.81% at 1500 nm, 88.98% at 2220 nm, and 89.59% at 2400 nm.

[0068] [Table B]

[0069] In Examples B-1 to B-4, the reflectance at each wavelength of 1500 nm, 2200 nm, and 2400 nm is all 75% or more, and the average reflectance is also 75% or more, so that when used as a silica heat reflector, heat can be reflected efficiently.

[0070] Example C As the first silica plate 1, a silica plate (synthetic quartz plate) was used, with a plate size of Φ300 mm, a thickness of 1.22 mm, an OH group concentration of 71.60 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu of 1 ppm or less, and Al of 10 ppm or less. As the second silica plate 2, a silica plate (synthetic quartz plate) was used, with a plate size of Φ300 mm, a thickness of 1.23 mm, an OH group concentration of 71.60 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu of 1 ppm or less, and Al of 10 ppm or less. Other than that, a silica heat reflector was produced in the same manner as in Example 1.

[0071] (Example C-1) Heat treatment temperature: 850°C The same heat treatment as in Example 2 was carried out except that the silica heat reflector of Example C was kept at 850°C for 1 hour, and the reflectance of the silica heat reflector after the heat treatment was measured with a spectrophotometer as in Example 1. The measurement results are shown in Table C. As a result, the average reflectance from 1500 to 2400 nm was 88.83%, with reflectances of 82.01% at 1500 nm, 91.15% at 2220 nm, and 91.42% at 2400 nm.

[0072] (Example C-2) Heat treatment temperature: 900°C The silica heat reflector of Example C was subjected to heat treatment in the same manner as in Example C-1, except that the heat treatment temperature was 900° C., and the reflectance was measured. The measurement results are shown in Table C. As a result, the average reflectance from 1500 to 2400 nm was 88.94%, with reflectances of 81.95% at 1500 nm, 91.25% at 2220 nm, and 92.66% at 2400 nm.

[0073] (Example C-3) Heat treatment temperature: 950°C The silica heat reflector of Example C was subjected to heat treatment in the same manner as in Example C-1, except that the heat treatment temperature was 950° C., and the reflectance was measured. The measurement results are shown in Table C. As a result, the average reflectance from 1500 to 2400 nm was 88.55%, with reflectances of 81.36% at 1500 nm, 91.11% at 2220 nm, and 92.03% at 2400 nm.

[0074] (Example C-4) Heat treatment temperature 1000°C The silica heat reflector of Example C was subjected to heat treatment in the same manner as in Example C-1, except that the heat treatment temperature was 1000°C, and the reflectance was measured. The measurement results are shown in Table C. As a result, the average reflectance from 1500 to 2400 nm was 88.13%, with reflectances of 81.42% at 1500 nm, 90.44% at 2220 nm, and 91.80% at 2400 nm.

[0075] (Reference Example C) Heat treatment temperature 1050℃ The silica heat reflector of Example C was subjected to heat treatment in the same manner as in Example C-1, except that the heat treatment temperature was 1050° C., and the reflectance was measured. The measurement results are shown in Table C. As a result, the average reflectance from 1500 to 2400 nm was 73.01%, with reflectances of 65.70% at 1500 nm, 75.56% at 2220 nm, and 77.09% at 2400 nm.

[0076] [Table C]

[0077] In Examples C-1 to C-4, the reflectance at each wavelength of 1500 nm, 2200 nm, and 2400 nm is all 75% or more, and the average reflectance is also 75% or more, so that when used as a silica heat reflector, heat can be reflected efficiently.

[0078] On the other hand, in Reference Example C, the reflectance at each wavelength of 2200 nm and 2400 nm was barely 75% or more, but the reflectance at the wavelength of 1500 nm was less than 75%, and the average reflectance was also less than 75%. It is considered that the first silica plate 1, the second silica plate 2, and the reflector 3 (3a, 3b) react with each other because the silica heat reflector was heat-treated at a temperature higher than 1000°C. Therefore, it is preferable that the first silica plate 1, the second silica plate 2, and the reflector 3 (3a, 3b) do not react with each other.

[0079] Examples A-1 to A-4, Reference Example A, Examples B-1 to B-4, Examples C-1 to C-4, and Reference Example C are compared. It was confirmed that the reflectance was higher when the OH group concentration was lower.

[0080] (Example D-1) 100 nm Rh film As the first silica plate 1, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.02 mm, an OH group concentration of 888.48 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the second silica plate 2, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.03 mm, an OH group concentration of 956.99 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the reflectors 3a and 3b, Rh films were formed to a film thickness of 100 nm, and as conditions in the atmosphere control pressurizer, evacuation was performed, and the conditions were held for 3 hours under the conditions of a vacuum atmosphere of 10 Pa or less, a temperature of 900 ° C, and a pressure of 2000 kPa, except that the silica heat reflector was produced in the same manner as in Example 1. After preparation, the reflectance of the silica heat reflector was measured in the same manner as in Example 1. The measurement results are shown in Table D. As a result, the average reflectance from 1500 to 2400 nm was 87.91%, with the reflectances being 84.14% at 1500 nm, 85.78% at 2220 nm, and 90.99% at 2400 nm.

[0081] (Example D-2) Laminated film of 10 nm TiO2 layer / 50 nm Ir layer In the silica heat reflector of Example D-1, a TiO2 layer was formed on each of the first silica plate 1 and the second silica plate 2 to a thickness of 10 nm, and then an Ir layer was formed on the TiO2 layer as a reflector 3a, 3b to a thickness of 50 nm by sputtering, except that a silica heat reflector was produced in the same manner as in Example D-1, and the reflectance was measured. The measurement results are shown in Table D. As a result, the average reflectance from 1500 to 2400 nm was 87.45%, with reflectances of 81.23% at 1500 nm, 87.60% at 2220 nm, and 92.26% at 2400 nm.

[0082] (Example D-3) Laminated film of 10 nm TiO2 layer / 50 nm Ru layer In the silica heat reflector of Example D-1, a TiO2 layer was formed on each of the first silica plate 1 and the second silica plate 2 to a thickness of 10 nm, and then a Ru layer was formed on the TiO2 layer as a reflector 3a, 3b to a thickness of 50 nm by sputtering, except that a silica heat reflector was produced in the same manner as in Example D-1, and the reflectance was measured. The measurement results are shown in Table D. As a result, the average reflectance from 1500 to 2400 nm was 84.13%, with reflectances of 74.40% at 1500 nm, 85.10% at 2220 nm, and 89.47% at 2400 nm.

[0083] [Table D]

[0084] In Examples D-1 and D-2, the reflectance at each wavelength of 1500 nm, 2200 nm, and 2400 nm is all 75% or more, and the average reflectance is also 75% or more, so that when used as a silica heat reflector, it can reflect heat efficiently.

[0085] In Example D-3, the reflectance at each wavelength at 1500 nm is less than 75%, but the average reflectance is 75% or more, so that heat can be reflected without any problems when used as a silica heat reflector.

[0086] (Example E) Effect of arithmetic mean roughness Ra As the first silica plate 1, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.03 mm, an OH group concentration of 941.06 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the second silica plate 2, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.03 mm, an OH group concentration of 981.08 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the reflectors 3a and 3b, Mo films were formed to a film thickness of 50 nm, and as conditions in the atmosphere control pressurizer, evacuation was performed, and the conditions were held for 3 hours under the conditions of a vacuum atmosphere of 10 Pa or less, a temperature of 850 ° C, and a pressure of 3000 kPa, except that a silica heat reflector was produced in the same manner as in Example 1. After preparation, the arithmetic mean roughness Ra of the silica heat reflector was measured using a surface roughness measuring instrument (Mitutoyo Corporation, model number 178-560-11). In addition, the reflectance of the silica heat reflector was measured from the first silica plate side using a spectrophotometer (Shimadzu Corporation, UV-3100PC). After that, the silica heat reflector was subjected to blasting treatment, and the operation of measuring the arithmetic mean roughness Ra and reflectance of the silica heat reflector whose surface was roughened by blasting treatment was repeated, and a graph of the arithmetic mean roughness Ra and reflectance was created. The graph is shown in FIG. 13. From the graph in FIG. 13, the average reflectance exceeded 75% when the arithmetic mean roughness Ra was 2 μm or less. When the OH group concentration was measured before and after blasting, no change in concentration occurred. Therefore, the reflectivity of a portion where a reflector is present improves as the arithmetic mean roughness Ra decreases, and exceeds 75% when the arithmetic mean roughness Ra of the surface of the silica plate is 2 μm or less, and by setting the arithmetic mean roughness Ra of the surface of the silica plate where there is no reflector to 5 μm or less, the transmission of infrared rays can be suppressed even in portions where there is no reflector.

[0087] (Example F-1) The thickness of each Mo film is 25 nm As the first silica plate 1, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.04 mm, an OH group concentration of 962.35 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the second silica plate 2, a silica plate (synthetic quartz plate) having a plate size of 20 mm x 40 mm and a thickness of 1.02 mm, an OH group concentration of 904.67 ppm, Li, Na, K, Ca, Mg, B, Fe, Cu less than 1 ppm, and Al less than 10 ppm was used. As the reflectors 3a and 3b, Mo films were formed to a film thickness of 25 nm, and as conditions in the atmosphere control pressurizer, evacuation was performed, and the conditions were held for 3 hours under the conditions of a vacuum atmosphere of 10 Pa or less, a temperature of 850 ° C, and a pressure of 3000 kPa, except that a silica heat reflector was produced in the same manner as in Example 1. After preparation, the reflectance of the silica heat reflector was measured in the same manner as in Example 1. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 84.41%, with the reflectances being 77.16% at 1500 nm, 81.57% at 2220 nm, and 88.78% at 2400 nm.

[0088] (Example F-2) The thickness of each Mo film is 35 nm. For the silica heat reflector of Example F-1, a silica heat reflector was prepared in the same manner as in Example F-1, except that a Mo film was formed on each of the reflectors 3a and 3b to a thickness of 35 nm, and the reflectance was measured. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 86.26%, with reflectances of 79.98% at 1500 nm, 82.89% at 2220 nm, and 90.45% at 2400 nm.

[0089] (Example F-3) The thickness of each Mo film is 40 nm For the silica heat reflector of Example F-1, a silica heat reflector was prepared in the same manner as in Example F-1, except that a Mo film was formed on each of the reflectors 3a and 3b to a thickness of 40 nm, and the reflectance was measured. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 87.02%, with reflectances of 81.02% at 1500 nm, 83.45% at 2220 nm, and 90.60% at 2400 nm.

[0090] (Example F-4) The thickness of each Mo film is 45 nm For the silica heat reflector of Example F-1, a silica heat reflector was prepared in the same manner as in Example F-1, except that a Mo film was formed on each of the reflectors 3a and 3b to a thickness of 45 nm, and the reflectance was measured. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 87.65%, with reflectances of 81.67% at 1500 nm, 84.03% at 2220 nm, and 91.64% at 2400 nm.

[0091] (Example F-5) The thickness of each Mo film is 50 nm. For the silica heat reflector of Example F-1, a silica heat reflector was prepared in the same manner as in Example F-1, except that a Mo film was formed on each of the reflectors 3a and 3b to a thickness of 50 nm, and the reflectance was measured. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 88.09%, with reflectances of 82.32% at 1500 nm, 84.58% at 2220 nm, and 92.09% at 2400 nm.

[0092] (Example F-6) The thickness of each Mo film is 60 nm For the silica heat reflector of Example F-1, a silica heat reflector was prepared in the same manner as in Example F-1, except that a Mo film was formed on each of the reflectors 3a and 3b to a thickness of 60 nm, and the reflectance was measured. The measurement results are shown in Table F. As a result, the average reflectance from 1500 to 2400 nm was 88.55%, with reflectances of 82.14% at 1500 nm, 87.96% at 2220 nm, and 92.42% at 2400 nm.

[0093] [Table F]

[0094] In Examples F-1 to F-6, the reflectance at each wavelength of 1500 nm, 2200 nm, and 2400 nm is all 75% or more, and the average reflectance is also 75% or more, so that when used as a silica heat reflector, heat can be reflected efficiently. [Explanation of symbols]

[0095] 1. First Silica Plate 2. Second Silica Plate 3 reflector 3a 1st reflector 3b Second reflector 4 Joint 5,5a,5b oxide layer 6 Pressing material 7 Spacer L1 Incident direction from the first silica plate side L2 Incident direction from the second silica plate side

Claims

1. A first silica plate; a second silica plate facing the first silica plate; a reflector provided on at least one of a surface of the second silica plate facing the first silica plate and a surface of the first silica plate facing the second silica plate; At least a peripheral portion of the mating surface between the first silica plate and the second silica plate includes a joint portion that is continuously joined in an annular shape along the peripheral portion, and The first silica plate and the second silica plate are laminated together, The reflector is a silica heat reflecting plate that reflects infrared rays incident from the first silica plate side or the second silica plate side, The first silica plate and the second silica plate have an OH group content of 1000 ppm or less, The reflector is a thin film, A silica heat reflector, characterized in that a surface layer including at least the reflective surface of the reflector is made of one type selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo, or is made of an alloy containing at least one type selected from the group consisting of Ir, Pt, Rh, Ru, Re, and Mo and having a melting point of 1200°C or higher.

2. The silica heat reflector according to claim 1, characterized in that the first silica plate and the second silica plate have a content of each of the elements Li, Na, K, Ca, Mg, B, Fe, and Cu of 1 ppm or less, and an Al content of 10 ppm or less.

3. The silica heat reflector according to claim 1, characterized in that, in at least one of the outer peripheral planes of the first silica plate and the second silica plate, the surface roughness of at least a portion of the outer peripheral plane is an arithmetic mean roughness Ra of 5 μm or less.

4. The silica heat reflector according to claim 1, characterized in that the reflectance of the reflector in the infrared region of 1500 to 2400 nm incident from the first silica plate side or the second silica plate side is 75% or more.

5. 2. The silica heat reflector according to claim 1, wherein the first silica plate and the second silica plate have a thickness of 0.5 to 2.0 mm.

6. 2. The silica heat reflector according to claim 1, wherein the reflector has a thickness of 50 to 500 nm.

7. At least one of between the first silica plate and the reflector and between the second silica plate and the reflector has an oxide layer containing one selected from the group of oxides consisting of silicon oxide, aluminum oxide, sapphire, lithium tantalate, lithium niobate, magnesium oxide, titanium oxide, yttrium oxide, strontium titanate, germanium oxide, zinc oxide, indium oxide, indium tin oxide, tin oxide, tungsten-doped tin oxide, and tantalum oxide, or an oxide layer containing two or more selected from the group of oxides; and 2. The silica heat reflector according to claim 1, wherein the oxide layer has a thickness of 50 nm or less.

8. A method for producing the silica heat reflector of claim 1, comprising the steps of: A first step of preparing a first silica plate and a second silica plate; a second step of forming a reflector on at least one of a surface of the first silica plate and a surface of the second silica plate; a third step of joining the first silica plate and the second silica plate together with a surface of the reflector formed on at least one of the first silica plate and the second silica plate facing each other; a fourth step of bonding at least peripheral portions of the opposing surfaces of the first silica plate and the second silica plate; A method for producing a silica heat reflector, comprising the steps of:

9. The method for manufacturing a silica heat reflector according to claim 8, characterized in that a fifth step is carried out after the fourth step, in which the outer peripheral flat surfaces of the first silica plate and the second silica plate are polished to adjust the final plate thickness.

10. In the fourth step, The method for manufacturing a silica heat reflector according to claim 8, characterized in that after creating a vacuum atmosphere of 100 Pa or less, an argon atmosphere, or a nitrogen atmosphere, the first silica plate and the second silica plate are bonded at a pressure of 3500 kPa or less and a temperature of 400 to 1000°C.

11. The method for manufacturing a silica heat reflector according to claim 8, further comprising a step A between the third step and the fourth step, in which a pressing material made of carbon, oxide, nitride or boride, or a pressing material containing at least one selected from the group consisting of carbon, oxide, nitride and boride, is placed at a location in contact with at least the outer peripheral flat surface of the first silica plate and the second silica plate.

12. The method further includes a step B between the third step and the fourth step, in which a plurality of stacks of the first silica plate and the second silica plate obtained in the third step are prepared, and 2 to 30 pairs of the stacks are stacked in the stacking direction with spacers interposed therebetween; the spacer is made of carbon, an oxide, a nitride, or a boride, or contains at least one selected from the group consisting of carbon, an oxide, a nitride, and a boride; 9. The method for producing a silica heat reflector according to claim 8, wherein the fourth step is a step of simultaneously bonding 2 to 30 stacked sets of the laminate.

13. 9. The method for producing a silica heat reflector according to claim 8, wherein in the second step, the reflector is formed by any one of a sputtering method, a chemical vapor deposition method, and a deposition method.

14. The method for manufacturing a silica heat reflector as described in claim 8, further comprising a step C between the first step and the second step of reverse sputtering the surfaces that are to face each other in the third step, the first silica plate and the second silica plate.

15. The method for producing a silica heat reflector according to claim 8, further comprising at least one step selected from the group consisting of step D, in which heat treatment is performed at 1000°C or less after the second step, and step E, in which heat treatment is performed at 1000°C or less after the fourth step.

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