Silica glass disk with dimples formed

Abstract

To provide a silica glass disc that can have a minimized amount of deformation of the silica glass disc in heat treatment and have an increased surface area of the silica glass surface.SOLUTION: A silica glass disc has a dimple-formed area in which a large number of dimples are formed on at least the front surface or at least the back surface of a silica glass body. The dimples in the dimple-formed area are formed regularly. It is preferable that the dimples are formed by laser.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a silica glass disk having regularly formed dimples on the surface of the silica glass.

Background Art

[0002] Generally, in the semiconductor manufacturing process, an Si wafer is heated using a heat treatment apparatus made of quartz glass, and a thin film treatment is performed on the surface of the Si wafer. Recently, the method of thin film treatment is being switched from the CVD (Chemical Vapor Deposition) method to the ALD (Atomic Layer Deposition) method. This is because the film thickness of the thin film formed on the Si wafer becomes as thin as several hundred angstroms, and it is necessary to control the variation in the film thickness between the central part and the peripheral part on the Si wafer to 10 Å or less, and in severe cases, several Å or less. For this reason, the dummy wafers arranged on the upper and lower sides of the Si wafer used as a product are also required to have the same surface area as the product.

[0003] As semiconductor miniaturization progresses, Si wafers and silica glass disks with uneven surfaces formed on their surfaces have been used as dummy wafers. However, Si wafers have problems such as the need to be removed during cleaning, and recently, silica glass disks have begun to be actively used instead of dummy wafers.

[0004] In Patent Document 1, a gas distribution adjustment member made of quartz is proposed. It is proposed that the surface of the quartz member should have a surface area substantially equal to that of the product wafer or that the surface area should be 0.8 times or more.

[0005] However, in reality, due to the differences in Young's modulus and Poisson's ratio of the mechanical properties between the Si wafer and silica glass, when they are set in a holder that holds the Si wafer and silica glass disc in a shelf-like manner, it has been found that a difference in the amount of deformation occurs at the tip portion of the disc. Considering such a deformation amount, if unevenness is not formed on the silica glass disc, there is a possibility of accelerating the deformation amount. When the deformation amount becomes large, a difference occurs between the center and the tip in the gap between the Si wafer and the silica glass disc, resulting in a slight difference in the amount of gas flow. Such a slight difference in the gap also causes a subtle difference in the film thickness on the actual Si wafer, leading to a large variation in the film thickness of the thin film within the Si wafer surface, which is a problem.

[0006] Also, in the cross-sectional view showing the gas distribution adjusting member made of the quartz, unevenness formed vertically is shown. However, in the case of vertical unevenness, there are problems such as the film being easily peeled off when the film adheres, and when right-angled corners are formed, damage is likely to occur from this part.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] An object of the present invention is to provide a silica glass disc capable of minimizing the deformation amount of the silica glass disc in heat treatment and increasing the surface area of the silica glass surface.

Means for Solving the Problems

[0009] As a result of intensive research on the variation of thin films in order to solve the above problems, the inventors of the present invention have found that by forming regular dimples on a silica glass disk, it is possible to minimize the amount of deformation of the silica glass disk during heat treatment, and further, by forming an uneven surface of the dimple shape, it is possible to increase the surface area of the silica glass surface.

[0010] That is, the silica glass disk of the present invention is a silica glass disk having a dimple formation area in which a large number of dimples are formed on at least the front surface or at least the back surface of the silica glass body, and the dimples in the dimple formation area are regularly formed.

[0011] It is preferable that the dimples are formed by a laser. It is preferable that the laser is at least one selected from a CO2 laser, a picosecond laser, and a femtosecond laser. Also, it is preferable that the dimples are formed by scanning laser light to an arbitrary point on the XY axis with a galvanometer scanner.

[0012] It is preferable that the dimples are formed on the front surface and the back surface of the silica glass body.

[0013] The density of the dimples may be different between the central portion and the peripheral portion of the dimple formation area.

[0014] It is preferable that the shape of the dimples is an inverted conical shape or an inverted frustum of a cone shape, or a bent shape in which the edge of the dimple bottom and the dimple side wall are not perpendicular.

[0015] It is preferable that the silica glass body is transparent silica glass, white silica glass, or black silica glass.

[0016] When dimples are formed on the back surface of the silica glass body, it is preferable that the dimple formation area on the back surface of the silica glass body is formed at a distance of 10 mm or more from the end of the silica glass disk.

[0017] When the silica glass disk is used in the heat treatment process in a vertical heat treatment apparatus, the amount of deformation occurring at the tip of the peripheral edge of the silica glass disk can be made 1 mm or less. It is preferable that the heat treatment process is a heat treatment process when film formation treatment is performed by the ALD method.

[0018] The silica glass disk is suitably used as an alternative to an Si-made dummy wafer.

Advantages of the Invention

[0019] According to the present invention, it is possible to provide a silica glass disk capable of minimizing the amount of deformation of the silica glass disk in heat treatment and increasing the surface area of the silica glass surface. Further, according to the present invention, by regularly forming non-directional dimples on the silica glass disk, when this silica glass disk is used as an alternative to a dummy wafer for a vertical heat treatment furnace, the amount of deformation at the tip of the silica glass disk can be suppressed. Furthermore, by regularly forming dimples on the silica glass surface, it is also possible to obtain a predetermined surface area by using this silica glass disk as a gas distribution adjusting member, and to achieve more uniform film thickness distribution of the thin film formed on the Si wafer surface.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

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Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0021] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings. However, it goes without saying that the illustrated examples are shown exemplarily and various modifications are possible without departing from the technical idea of the present invention.

[0022] The silica glass disk of the present invention is a silica glass disk having a dimple formation area in which a large number of dimples are formed on at least the front surface or at least the back surface of the silica glass body, and the dimples in the dimple formation area are regularly formed. In the present invention, a dimple means a dimple-shaped recess formed on the front surface and / or the back surface of the silica glass disk. And, in the present invention, the dimple shape means an independent recess formed on the plane of the silica glass disk, the portion in contact with the plane is approximately circular, and the adjacent recesses do not contact each other. By forming regular dimples in the silica glass disk, it becomes possible to minimize the amount of deformation of the silica glass disk. Furthermore, by forming the concave and convex surfaces of the dimple shape, it becomes possible to increase the surface area of the silica glass surface.

[0023] The silica glass disk of the present invention is preferably used as an alternative to the Si dummy wafer. In particular, it is preferably used as an alternative to the dummy wafer in the heat treatment process in a vertical heat treatment apparatus, and more preferably used as an alternative to the dummy wafer in the heat treatment process when film formation treatment is performed by the ALD method. When the silica glass disk is set in a vertical heat treatment apparatus, for example, a shelf-shaped holder and used in a heat treatment process (300°C to 700°C), the amount of deformation at the tip of the peripheral edge of the silica glass disk can be made 1 mm or less. The amount of deformation at the tip of the peripheral edge of the silica glass disk is more preferably 1 mm or less, and even more preferably 0.5 mm or less. When the amount of deformation exceeds 1 mm, the variation in the thin film on the Si wafer surface is large, and the influence becomes a problem.

[0024] It should be noted that it has been found that when the silica glass disk and the Si wafer are set in a shelf-shaped holder even if no dimples are formed on the surface of the quartz glass disk, a difference in the amount of deformation occurs. Since the Si wafer has a larger Young's modulus and Poisson's ratio than the silica glass disk, it is known that the Si wafer is less likely to deform. In order to suppress the amount of deformation, it is important to make the dimples regular and non-directional. For example, when a linear shape with directionality such as the groove described in Patent Document 1 is formed on the surface of the silica glass disk, it is important to make the direction of deformation and the direction in which the groove is formed orthogonal so that the deformation at the tip of the silica glass disk is not accelerated. However, if the direction of the groove and the direction of deformation overlap, the deformation may be accelerated and the amount of deformation may exceed 2 mm. In order to suppress such risks, it is necessary to form a non-directional shape such as a dimple on the silica glass surface.

[0025] The method of forming dimples is not particularly limited, but it is preferably formed by a laser. In particular, in order to increase the surface area, it is necessary to form many dimples on the silica glass surface, and it is also necessary to stabilize the shape of the dimples. Therefore, it is preferable to use laser light for forming hundreds of thousands to millions of dimples.

[0026] There is no particular limitation on the type of laser light, but picosecond lasers or femtosecond lasers using the second harmonic or third harmonic of CO2 lasers or YAG lasers may also be used. When irradiating with laser light, it is preferable to control the irradiation position of the laser light using a control device such as a galvanometer scanner capable of multi-axis (for example, two-dimensional of the XY axis or three-dimensional of the XYZ) control. The two-axis galvanometer scanner is an XY deflection unit that deflects and condenses laser light two-dimensionally in the X and Y directions and scans the laser in an arbitrary position in the two-dimensional area. By scanning the laser light to an arbitrary point on the XY axis using a galvanometer scanner, it becomes possible to perform dimple processing on the entire surface of the silica glass.

[0027] The material of the silica glass body to be used is not particularly limited as long as it is silica glass, and both natural silica glass and synthetic silica glass can be used, but high-purity synthetic silica glass is more preferably used. In particular, silica glass with a SiO2 composition amount of 99.99 mass% to 100 mass% is more preferable. The color and transparency of the silica glass body are also not particularly limited. For example, transparent silica glass, white silica glass, or black silica glass, etc. are preferably used, and they can be appropriately selected considering the usage. For any of these silica glasses, the workability of forming dimples does not change, so dimples can be formed by the same means. For example, a white silica glass disk can be prepared by adding a solvent to silica fine particles to make a slurry, and then pouring this into a mold and using the slip casting method. Also, in the case of black silica glass, a black additive such as powder of C, SiC, Si, SiO, etc. can be added to the slurry to color the slurry.

[0028] The silica glass disc of the present invention is a silica glass body with a circular shape on both the front and back surfaces. When the silica glass disc is used as a substitute for a dummy wafer, it is preferably the same shape as the Si wafer, but the thickness is slightly thicker to match the weight. Also, since the weight of the silica glass body changes depending on the density of the dimples on the surface, it is also possible to make the thickness thicker than that of the Si wafer to match the weight.

[0029] FIG. 1 shows one embodiment of the silica glass disc 10 of the present invention, and is a schematic diagram of a main part of an aspect in which dimples 12 are arranged at the vertices of a virtual quadrilateral 14. FIG. 2 shows another embodiment of the silica glass disc 10 of the present invention, and is a schematic diagram of a main part of an aspect in which dimples 12 are arranged at the vertices of a virtual triangle 16.

[0030] In the present invention, the formation of regular dimples means that the dimples are formed in a regular arrangement according to a predetermined rule. The arrangement of the dimples is not particularly defined as long as they are formed regularly. However, as shown in FIG. 1, it is preferable that the dimple formation area is composed of repetitions of dimple structure units in which dimples are regularly formed, and the dimple structure unit is composed of dimples arranged at the vertices of the virtual quadrilateral 14. Also, it is preferable to avoid a design with directivity such as the conventional groove shape as much as possible (see Comparative Example 1).

[0031] In a simple comparison, when the dimples 12 are arranged in the state of a virtual quadrilateral (□) [FIG. 1] and when the dimples 12 are arranged in the state of a virtual triangle (△) [FIG. 2], it is a subtle difference that does not matter under conditions where the gas adhesion characteristics are not strictly required. However, under conditions where strict gas adhesion characteristics are required, when the dimples are arranged in the state of a virtual triangle (△) as shown in FIG. 2, there are directions in which the distance between the dimples becomes partially long depending on the orientation of the silica glass disc, and there may be inconveniences such as having to fix the orientation of the silica glass disc constantly.

[0032] As shown in FIG. 1(b), when the dimples 12 are arranged in the state of a virtual square (□), the ratio of the distance between adjacent dimples to the shortest distance is maximized at √2. However, as shown in FIG. 2(b), when the dimples 12 are arranged in the state of a virtual equilateral triangle (△), the ratio of the distance between adjacent dimples to the shortest distance is maximized at √3. Therefore, depending on the orientation of the silica glass disk, there is a direction in which the distance between the dimples becomes partially longer, so some directivity appears. Therefore, under conditions where strict requirements are placed on the gas adhesion characteristics, it is necessary to fix the orientation of the silica glass disk. Even so, when the dimples 12 are arranged in the state of a virtual triangle (△), it is not a design with obvious directivity like the conventional groove shape, so it is not a serious problem under conditions where strict requirements are not placed on the gas adhesion characteristics.

[0033] Even when the dimples are arranged in the state of a square (□), the distance between the dimples becomes partially longer depending on the direction, but it does not become as long as in the case of a triangle (△), and there is a large degree of freedom in the direction with respect to the orientation of the silica glass disk. Therefore, as shown in FIG. 1, it is preferable to arrange the dimples at the vertices of a virtual quadrilateral, and more preferably at the vertices of a virtual square.

[0034] In the silica glass disk, the dimple formation area may be formed on either the front surface or the back surface of the silica glass body, or may be formed on both the front and back surfaces. The formation of dimples is basically a method of increasing the surface area. However, if unevenness is mechanically formed on both surfaces, there is a risk of cracking during the processing for forming the unevenness. However, when forming using a laser as in the case of the present dimples, since mechanical processing is unnecessary, it is convenient for forming uneven surfaces on both surfaces.

[0035] FIG. 7 shows a partial cross-sectional view of one embodiment of the silica glass disk of the present invention in FIG. 1. In FIG. 7, as the dimple 12, an example is shown in which the edge of the dimple bottom and the dimple side wall have a bent shape, and the dimple 12 is regularly formed only on the surface of the silica glass body 18 in the silica glass disk 10. In FIG. 7(b), the dimple 12 is regularly formed on both the front and back surfaces of the silica glass body 18 in the silica glass disk 10.

[0036] In addition, the arrangement in which the dimple forming area is formed in the silica glass disk is not particularly limited. However, when it is used instead of the dummy wafer, it is preferable to provide the dimple forming area at least in the central portion of the silica glass disk. The central portion of the silica glass disk is a region including the central portion or the vicinity of the central portion of the silica glass disk. As the central portion, a range of 80% or more of the silica glass disk is preferable, and a range of 90% or more is more preferable.

[0037] In addition, when it is used instead of the dummy wafer, it is preferable not to provide the dimple forming area at the peripheral edge of the back surface of the silica glass disk or to reduce the density of the dimples compared to the central portion of the silica glass disk. The peripheral edge of the silica glass disk is a region including the end or the end of the disk. For example, in the case of a disk with a diameter of 300 mm, as the peripheral edge of the back surface of the silica glass disk, a range of at least 15 mm from the end of the disk is preferable, and a range of at least 10 mm from the end of the disk is more preferable.

[0038] When a silica glass disk is used as a substitute for a dummy wafer in the heat treatment process in a vertical heat treatment apparatus, deformation occurs at the tip of the shelf-shaped silica glass disk. In order to suppress this amount of deformation, it is important not to form dimples in the 10 mm width of the peripheral portion on the back surface of the silica glass disk. If dimples are formed in this portion, the deformation at the tip will be accelerated. The reason for the acceleration of the deformation is not clear, but it is thought that by forming dimples, the thickness of the silica glass disk becomes partially thinner, and the deformation mode may be accelerated. Since the dimple shapes are arranged from the center to the tip, the deformation mode of each individual dimple affects up to the tip. However, when forming a region where dimples are not formed in at least the 10 mm width of the peripheral portion, it becomes possible to block the influence of the deformation mode of the dimples once and suppress the amount of deformation.

[0039] There is no particular limitation on the density of the dimples in the dimple formation area, and the dimples may be uniformly present, or the density of the dimples may be varied depending on the part of the silica glass disk. Even when the density of the dimples is varied depending on the part of the silica glass disk, there is no particular regulation on the shape of the dimples.

[0040] The number of dimples in the silica glass disk is not particularly limited, but the number of dimples in the central part of the silica glass disk is preferably 100,000 to 2,000,000, and more preferably 500,000 to 1,000,000. Also, regarding the number of dimples in the peripheral part, it is the same as the above range, but depending on the conditions, the number of dimples in the central part may be more or less than that in the peripheral part. However, the number (density) of dimples in the peripheral part on the back surface of the silica glass disk is preferably 0.

[0041] There is no particular limitation on the size of the dimples, but a hole diameter of 50 to 500 μm is preferable, and 200 to 400 μm is more preferable. Also, the depth of the dimples is preferably 10 to 1000 μm, and 200 to 600 μm is more preferable. As a specific example of the dimples, for example, dimples adjusted to a hole diameter of several 100 μm and a depth of several 100 μm are suitable.

[0042] The shape of the dimple is not particularly limited, but it is preferably an inverted conical shape or a frustum of an inverted cone shape, or a bent shape in which the edge of the dimple bottom and the dimple side wall are not perpendicular.

[0043] Figures 8 and 9 show partial cross-sectional views of another embodiment of the silica glass disk of the present invention. In the example of Figure 8, the silica glass disk 20 shows an example of an inverted conical shape as the dimple 22 formed in the silica glass body 26. Further, in Figure 9, an example in which the shape of the dimple 22 is a frustum of an inverted cone shape is shown. In Figures 8(a) and 9(a), the dimple 22 is regularly formed only on the surface of the silica glass body 26 in the silica glass disk 20. In Figures 8(b) and 9(b), the dimple 22 is regularly formed on both the front and back surfaces of the silica glass body 26 in the silica glass disk 20. In this specification, the description of the silica glass surface refers to the silica glass surface itself and is a concept that can include both the front and back surfaces of the silica glass body. The silica glass disk of the present invention is preferably used by placing it on a shelf-shaped holder or the like. In this specification, the front and back surfaces of the silica glass disk refer to the side that becomes the upper surface side and the side that becomes the lower surface side when placed on a shelf-shaped holder or the like.

[0044] As a result of the inventors' intensive examination of the laser irradiation conditions and the like, fortunately, since the dimple formed by the laser has a power distribution in the depth direction, the power is large on the opening side and tends to gradually decrease on the bottom side. For this reason, the dimple formed by the laser naturally becomes conical, and the corners of the bottom surface can be rounded. Therefore, while maintaining the effect of adsorbing gas with this dimple, unlike the groove shape or the uneven shape by sandblasting as before, even if gas adheres to the silica glass surface, it is difficult to peel off, and since sharp corners are not formed, the risk of crack generation and breakage can be reduced. Furthermore, when cleaning the film deposited with gas, gas can be uniformly supplied into the dimple, and the deposited film can be removed cleanly.

Example

[0045] The present invention will be described in more detail with reference to the following examples. It goes without saying that these examples are illustrative and should not be construed in a limiting sense.

[0046] (Example 1) Using a CO2 gas laser, 800,000 dimples with a hole diameter of 200 - 250 μm and a depth of 200 μm were uniformly created on the entire surface of the silica glass body of a transparent synthetic silica glass disk (diameter 300 mm, thickness 1.5 mm) so as to be regularly arranged at the vertices of a virtual square. When irradiating the laser light, a two-axis galvanometer scanner (manufactured by Raylase), which is an XY deflection unit for deflecting and condensing the laser beam two-dimensionally, was used as a control device. Since the CO2 gas laser scanned the surface of the silica glass body using the galvanometer scanner, it took about one and a half hours to form dimples on the surface. Regarding the back surface of the silica glass body, within a range of 10 mm from the end of the synthetic silica glass disk (peripheral part), dimples were created under the same conditions as the surface without forming dimples, and 700,000 dimples with a hole diameter of 200 - 250 μm and a depth of 200 μm were uniformly formed in the central part (other than the peripheral part) of the back surface of the synthetic silica glass disk.

[0047] A micrograph of the surface of the silica glass body of the silica glass disk with dimples formed on both sides obtained above is shown in Fig. 3. As shown in Fig. 3, a large number of dimples regularly arranged at the vertices of a virtual square were formed on the front and back surfaces of the silica glass body of the silica glass disk. Also, the shape of the formed dimples was an inverted conical shape. The silica glass disk with dimples formed on both sides obtained above was placed on a shelf-shaped holder, heat-treated (550 °C), and then the amount of deformation at the tip was measured. A height gauge was used for the measurement. The actual measurement results are shown in Table 1, and the simulation results of the deformation amount distribution are shown in Fig. 4.

[0048] (Example 2) On the entire surface of the silica glass body of a natural silica glass disk (diameter 300 mm, thickness 1.5 mm), 500,000 dimples with a hole diameter of 200 to 250 μm and a depth of 400 μm were uniformly created using a CO2 gas laser. Note that since the CO2 gas laser was scanned on the surface of the silica glass body using a galvanometer scanner, it took about 1 hour to form dimples on the surface. Regarding the back surface of the silica glass body, in the range of 20 mm from the end of the natural silica glass disk (peripheral part), dimples were created under the same conditions as the front surface without forming dimples, and 350,000 dimples with a hole diameter of 200 to 250 μm and a depth of 400 μm were uniformly formed in the central part (other than the peripheral part) of the back surface of the natural silica glass disk.

[0049] A micrograph of the surface of the silica glass body of the silica glass disk with dimples formed on both surfaces obtained above is shown in FIG. 5. As shown in FIG. 5, a large number of dimples were regularly arranged at the vertices of the virtual quadrilateral on the front and back surfaces of the silica glass body of the silica glass disk. Also, the shape of the formed dimples was a truncated inverted cone shape. Also, with respect to the silica glass disk with dimples formed on both surfaces obtained above, the deformation amount of the tip after heat treatment was measured in the same manner as in Example 1. The results are shown in Table 1.

[0050] (Example 3) On the entire surface of the silica glass body of a white silica glass disk (diameter 300 mm, thickness 1.5 mm), 1,000,000 dimples with a hole diameter of 50 to 60 μm and a depth of 100 μm were uniformly created using a picosecond laser of the second harmonic of a YAG laser. Note that since the second harmonic of the YAG laser was scanned on the surface of the silica glass body using a galvanometer scanner, it took about 3 hours to form dimples on the surface. Regarding the back surface of the silica glass body, within a range of 15 mm from the edge of the white silica glass disc (peripheral part), under the condition of not forming dimples, dimples were created under the same conditions as the front surface. In the central part (excluding the peripheral part) of the back surface of the white silica glass disc, 800,000 dimples with a hole diameter of 50 - 60 μm and a depth of 100 μm were uniformly formed.

[0051] On the front and back surfaces of the silica glass body of the obtained white silica glass disc, a large number of dimples were regularly arranged at the vertices of a virtual quadrilateral. Also, the shape of the formed dimples was a frustum of an inverted cone. Regarding the silica glass disc with dimples formed on both surfaces obtained above, the deformation amount of the tip part after heat treatment was measured in the same manner as in Example 1. The results are shown in Table 1.

[0052] (Example 4) On the front surface of the silica glass body of a transparent synthetic silica glass disc (diameter 300 mm, thickness 1.5 mm), 1,000,000 dimples with a hole diameter of 200 - 250 μm and a depth of 500 μm were created using a CO2 gas laser. However, 300,000 dimples were uniformly formed in the central part (central portion) with a diameter of φ200 mm, and 700,000 dimples were uniformly formed in the part other than the φ200 mm part (peripheral part), resulting in a design with different dimple densities in the central and peripheral parts of the disc. Note that since the CO2 gas laser was scanned on the front surface of the silica glass body using a galvanometer scanner, it took about one and a half hours to form dimples on the front surface. Regarding the back surface of the silica glass body, within a range of 10 mm from the edge of the synthetic silica glass disc (peripheral part), under the condition of not forming dimples, dimples were created under the same conditions as the front surface. In the central part (excluding the peripheral part) of the back surface of the synthetic silica glass disc, 600,000 dimples with a hole diameter of 200 - 250 μm and a depth of 500 μm were uniformly formed.

[0053] On the front and back surfaces of the silica glass body of the obtained synthetic silica glass disc, a large number of dimples were regularly arranged at the vertices of a virtual quadrilateral. Also, the shape of the formed dimples was an inverted cone. With respect to the silica glass disk with dimples formed on both of the remembered surfaces, the amount of deformation of the tip portion after heat treatment was measured in the same manner as in Example 1. The results are shown in Table 1.

[0054] (Example 5) On the surface of the silica glass body of a transparent synthetic silica glass disk (diameter 300 mm, thickness 1.5 mm), 700,000 dimples with a hole diameter of 200 to 250 μm and a depth of 500 μm were created using a CO2 gas laser. However, 300,000 dimples were uniformly formed in the central part (central portion) with a diameter of φ200 mm, and 400,000 dimples were uniformly formed in the portion other than the φ200 mm part (peripheral portion), creating a design with different dimple densities in the central and peripheral parts of the disk. Incidentally, since the CO2 gas laser was scanned on the silica glass surface using a galvanometer scanner, it took about one and a half hours to form dimples on the surface. Regarding the back surface of the silica glass body, in the range of 10 mm from the end of the synthetic silica glass disk (peripheral portion), dimples were created under the same conditions as the surface without forming dimples, and 400,000 dimples with a hole diameter of 200 to 250 μm and a depth of 500 μm were uniformly formed in the central part (other than the peripheral portion) of the back surface of the synthetic silica glass disk.

[0055] On the peripheral part of the surface and the back surface of the silica glass body of the obtained synthetic silica glass disk, a large number of dimples regularly arranged at the vertices of virtual triangles were formed, and on the central part of the surface, a large number of dimples regularly arranged at the vertices of virtual quadrilaterals were formed. Also, the shape of the formed dimples was an inverted conical shape. With respect to the silica glass disk with dimples formed on both of the obtained surfaces, the amount of deformation of the tip portion after heat treatment was measured in the same manner as in Example 1. The results are shown in Table 1.

[0056] (Comparative Example 1) On a natural silica glass disk (diameter: 300 mm, thickness: 1.5 mm), 400 grooves with a width of 200 - 250 μm and a depth of 400 μm were formed. Since the grooves were formed using a grooving machine, it took 10 hours. The grooves were formed on the entire front and back surfaces of the silica glass body, including the peripheral part. Grooving is a problem because it is very time-consuming and reduces productivity. A micrograph of the surface of the silica glass body of the silica glass disk with grooves formed on both surfaces obtained above is shown in FIG. 6. With respect to the silica glass disk with grooves formed on both surfaces obtained above, the amount of deformation at the tip after heat treatment was measured in the same manner as in Example 1. However, in Comparative Example 1, since the amount of deformation varied depending on the positional relationship between the direction in which the grooves were formed and the holder, the measurement results in the directions of the grooves (horizontal and vertical) were also measured. The results are shown in Table 1.

[0057] (Comparative Example 2) On a synthetic silica glass disk (diameter: 300 mm, thickness: 1.5 mm), 600 grooves with a width of 200 - 250 μm and a depth of 400 μm were formed using a grooving machine, and 300 grooves with the same groove width and groove depth were formed in the same manner so as to be orthogonal to these grooves. The grooves were formed only on the surface of the silica glass body, and grooves were also formed on the peripheral part in the same manner. With respect to the silica glass disk with grooves formed on the surface of the silica glass body obtained above, the amount of deformation at the tip after heat treatment was measured in the same manner as in Comparative Example 1. However, when grooving was performed, many of the grooves fell off, making it difficult to measure the amount of deformation.

[0058] [Table 1]

[0059] As shown in Table 1, the silica glass disks with regularly formed dimples in Examples 1 - 4 were able to significantly reduce the amount of deformation at the tip of the silica glass disk. [Explanation of Symbols]

[0060] 10, 20: Silica glass disk, 12, 22: Dimple, 14: Virtual quadrilateral, 16: Virtual triangle, 18, 26: Silica glass body.

Claims

1. A silica glass disc having a dimple formation area with a large number of dimples formed on the front and back surfaces of the silica glass body, wherein the dimples in the dimple formation area are regularly formed, wherein the shape of the dimples is an inverted conical shape or an inverted frustum of a cone shape, or a bent shape in which the edge of the dimple bottom and the dimple side wall are not perpendicular, a silica glass disc.

2. The silica glass disc according to claim 1, wherein the dimples are formed by a laser.

3. The silica glass disc according to claim 1 or 2, wherein the density of the dimples is different between the central portion and the peripheral portion of the silica glass disc.

4. The silica glass disc according to any one of claims 1 to 3, wherein the silica glass body is transparent silica glass, white silica glass, or black silica glass.

5. The silica glass disc according to any one of claims 1 to 4, wherein the dimple formation area on the back surface of the silica glass body is formed at a distance of 10 mm or more from the end of the silica glass disc.

6. When the silica glass disc is used in a heat treatment step at 300°C to 700°C in a vertical heat treatment apparatus, which is a heat treatment step when film formation treatment is performed by the ALD method, the amount of deformation generated at the tip of the peripheral portion of the silica glass disc is 1 mm or less. The silica glass disc according to any one of claims 1 to 5.

7. The silica glass disc according to any one of claims 1 to 6, wherein the silica glass disc is used as a substitute for a Si-made dummy wafer.

8. The manufacturing method of the silica glass disc according to claim 2, The laser is CO ２ A method for manufacturing a silica glass disk, wherein the laser is at least one selected from a CO laser, a picosecond laser, and a femtosecond laser.

9. The manufacturing method of the silica glass disc according to claim 2, wherein the dimples are formed by scanning a laser beam to an arbitrary point on the XY axis by a galvanometer scanner. A manufacturing method of a silica glass disc.

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