Glass plate and method for manufacturing glass plate

Abstract

A glass plate G comprises a first principal surface G1, a second principal surface G2, and a plurality of modified regions Gm. The modified regions Gm comprise a plurality of maximum points at which the phase difference of retardation takes a maximum value when the phase difference distribution of retardation on the first principal surface G1 is viewed in the thickness direction of the glass plate. The maximum points comprise a first maximum point P1 at which the phase difference of retardation is the largest, and a second maximum point P2 at which the phase difference of retardation is the second largest. The phase difference of retardation at the first maximum point P1 and the phase difference of retardation at the second maximum point P2 are each 10 nm or more. The differences between the fast axis directions of retardation at a first measurement point Q1 and a second measurement point Q2, and the fast axis directions of retardation at the first maximum point P1 and the second maximum point P2, are each −30° to 30°. This configuration makes it possible to increase the etching rate in the modified regions.

Description

Glass plate and method for manufacturing the same

[0001] The present invention relates to a glass plate and a method for manufacturing the same.

[0002] In glass substrates used in displays such as tiling displays and bezel-less displays, and electronic devices such as glass interposers, fine through-holes (TGV: Through Glass Via) and / or blind vias are formed for wiring such as through electrodes. In recent years, it has been studied to use a glass plate having such fine through-holes and / or blind vias as a core substrate or an interposer for semiconductor packaging.

[0003] As a method for manufacturing a glass plate having this type of through-hole and / or blind via, for example, there are provided a reforming step of reforming a portion where a through-hole and / or blind via is to be formed in a glass plate by irradiation with a laser beam, and an etching step of forming a through-hole and / or blind via in the portion where formation is planned by etching after the reforming step (see, for example, Patent Document 1).

[0004] The reformed portion reformed in the reforming step has a higher etching rate than the non-reformed portion that was not reformed in the reforming step. Therefore, in the etching step, the reformed portion is preferentially removed. Therefore, if a reformed portion is formed in the portion where a through-hole and / or blind via is to be formed, a through-hole and / or blind via can be formed in the portion where formation is planned by etching.

[0005] Specifically, when a glass plate is irradiated with a laser beam, the irradiated portion is heated and partially melted. The melted portion solidifies again as heat diffuses to the periphery. By undergoing such local melting and solidification of the glass, stress is applied to the reformed portion. In the glass plate to which such stress is applied, fine cracks may be formed. When the glass plate having fine cracks is immersed in an etching solution, the etching solution penetrates into the fine cracks, and the glass around the fine cracks is removed by etching. In this way, the reformed portion formed by laser irradiation has a higher etching rate than the non-reformed portion and can be selectively removed by etching.

[0006] Japanese Patent Application Laid-Open No. 2020-196665

[0007] However, when the distribution of the stress applied to the modified portion by laser irradiation or the magnitude of the stress is inappropriate, an appropriate modified region may not be formed on the glass plate, and the etching rate in the modified portion may not be increased. When the etching rate in the modified portion is low, for example, various defects may occur, such as an unacceptable shape in which the hole diameter at the center in the plate thickness direction is significantly smaller than the hole diameter on the main surface of the glass plate, or the hole may not penetrate within a predetermined processing time. And defects in the holes in the glass plate can be a cause of defects in the final product such as an electronic device on which it is mounted.

[0008] In view of such problems, an object of the present invention is to provide a glass plate capable of increasing the etching rate in a modified portion and a method for manufacturing the glass plate.

[0009] (1) The present invention devised to solve the above problems is a glass plate including a first main surface, a second main surface that is the opposite surface of the first main surface, and a modified portion extending between the first main surface and the second main surface. The modified portion includes a plurality of maximum points at which the retardation phase difference takes a maximum value when the retardation phase difference distribution on the first main surface is viewed in the plate thickness direction of the glass plate. The maximum points include a first maximum point having the largest retardation phase difference and a second maximum point having the second largest retardation phase difference. The retardation phase difference at the first maximum point and the retardation phase difference at the second maximum point are each 10 nm or more, and are on a circumference having a line segment connecting the first maximum point and the second maximum point as a diameter. When two points equidistant from the first maximum point and the second maximum point are defined as a first measurement point and a second measurement point, the difference between the fast axis directions of the retardation at the first measurement point and the second measurement point and the fast axis directions of the retardation at the first maximum point and the second maximum point is each -30° or more and 30° or less.

[0010] If the fast axis direction of the retardation has such a distribution, anisotropic stress acts on the modified portion. Further, if the phase difference of the retardation is 10 nm or more, sufficient stress acts to generate minute cracks in the modified portion or to cause the minute cracks to grow due to stress corrosion when the glass plate is etched. According to the present invention, minute cracks can be formed in the modified portion, and the etching rate in the modified portion can be increased. Note that the modified portion in the present invention means a region where stress is applied by laser irradiation.

[0011] (2) In the configuration of (1) above, the angles formed by the fast axis directions of the first measurement point and the second measurement point and the direction from the first maximum point to the second maximum point are preferably 60° or more and 120° or less, respectively.

[0012] If the fast axis direction of the retardation on the first main surface has such a distribution, the fast axis direction of the retardation is symmetrically distributed with respect to the line segment connecting the first maximum point and the second maximum point. Therefore, stress acts symmetrically on the first maximum point and the second maximum point. Thereby, the difference in the etching rates at the first maximum point and the second maximum point can be reduced.

[0013] (3) In the configuration of (1) or (2) above, the distance between the first maximum point and the second maximum point is preferably 5 μm or less.

[0014] The greater the phase difference of the retardation in the modified portion, the greater the stress acting on the modified portion. For this reason, large stress acts on the first maximum point and the second maximum point where the magnitude of the retardation takes the maximum value, and it is easy to form minute cracks or to cause the minute cracks to grow due to stress corrosion when the glass plate is etched. Therefore, when etching a glass plate having a modified portion, the etching rates of the first maximum point and the second maximum point increase. For this reason, when etching a glass plate having a large distance between the first maximum point and the second maximum point to form a through hole and / or a non-through hole, the hole shape is likely to be an elliptical shape or an oval shape in plan view. By setting the distance between the first maximum point and the second maximum point to 5 μm or less, the roundness of the through hole and / or the non-through hole in plan view can be improved.

[0015] (4) In any of the configurations (1) to (3) above, the magnitude of the stress acting on the first maximum point and the second maximum point is preferably 7 MPa or more.

[0016] If the magnitude of the stress is 7 MPa or more, minute cracks can be formed in the modified portion, or minute cracks can be propagated due to stress corrosion when the glass plate is etched.

[0017] (5) In any of the configurations (1) to (4) above, when the modified portion is viewed in the plate thickness direction of the glass plate with respect to the retardation phase difference distribution on the second main surface, the modified portion includes a plurality of maximum points at which the retardation phase difference takes a maximum value. The maximum points include a third maximum point having the largest retardation phase difference and a fourth maximum point having the second largest retardation phase difference. The retardation phase difference at the third maximum point and the retardation phase difference at the fourth maximum point are each 10 nm or more. When two points equidistant from the third maximum point and the fourth maximum point are defined as the third measurement point and the fourth measurement point, the difference between the fast axis directions of the retardation at the third measurement point and the fourth measurement point and the fast axis directions of the retardation at the third maximum point and the fourth maximum point is preferably -30° or more and 30° or less.

[0018] If the fast axis direction of the retardation on the second main surface has such a distribution, anisotropic stress acts on the modified portion also on the second main surface. Also, if the retardation phase difference is 10 nm or more, sufficient stress acts to generate minute cracks in the modified portion or to propagate minute cracks due to stress corrosion when the glass plate is etched. According to the present invention, minute cracks can be formed in the modified portion from both the first main surface and the second main surface, and the etching rate in the modified portion can be increased.

[0019] (6) In any of the configurations of (1) to (5) above, when viewing the retardation phase difference distribution on a virtual intermediate plane located between the first major surface and the second major surface in the thickness direction of the glass plate, the reformed portion includes a plurality of maximum points where the retardation phase difference takes a maximum value. The maximum points include a fifth maximum point where the retardation phase difference is the largest and a sixth maximum point where the retardation phase difference is the second largest. The retardation phase difference at the fifth maximum point and the retardation phase difference at the sixth maximum point are each 10 nm or more. When two points that are equidistant from the fifth maximum point and the sixth maximum point are defined as the fifth measurement point and the sixth measurement point on the circumference having a line segment connecting the fifth maximum point and the sixth maximum point as the diameter, the difference between the fast axis directions of the retardation at the fifth measurement point and the sixth measurement point and the fast axis directions of the retardation at the fifth maximum point and the sixth maximum point is preferably each -30° or more and 30° or less.

[0020] If the fast axis direction of the retardation has such a distribution, anisotropic stress acts on the reformed portion even on the intermediate plane. Also, if the retardation phase difference is 10 nm or more, sufficient stress acts to generate minute cracks in the reformed portion or to cause the minute cracks to progress due to stress corrosion when etching the glass plate. According to the present invention, minute cracks can be formed in the reformed portion, and further, the minute cracks can be easily advanced inside the glass plate, and the etching rate in the reformed portion can be increased.

[0021] (7) The present invention devised to solve the above problems is a method for manufacturing a glass plate, comprising a laser irradiation step of forming a modified portion on the glass plate by irradiating the glass plate with a laser. The laser is a pulsed laser. In the laser irradiation step, the laser is shaped into a Bessel beam shape. The pulse energy of the laser is 35 μJ or more and 80 μJ or less. When the retardation phase difference distribution on the first major surface is viewed in the plate thickness direction of the glass plate, the modified portion includes a plurality of maximum points where the retardation phase difference takes a maximum value, and the maximum points include a first maximum point where the retardation phase difference is the largest and a second maximum point where the retardation phase difference is the second largest. The glass plate is irradiated with the laser as described above.

[0022] By irradiating the glass plate with laser light having such pulse energy, a glass plate having the retardation distribution of the configuration of (1) above can be manufactured.

[0023] (8) The present invention devised to solve the above problems is a glass plate including a first major surface, a second major surface opposite to the first major surface, and a modified portion extending from the first major surface to the second major surface and having its birefringence characteristics modified based on stress. The maximum diameter of the modified portion is 10 μm or less. When observing the retardation phase difference distribution or the fast axis direction distribution on the first major surface, the modified portion has optical anisotropy.

[0024] For a glass plate having optical anisotropy in the modified portion, an anisotropic stress can be applied to the modified portion. Thereby, minute cracks can be formed in the modified portion, or when the glass plate is etched, the minute cracks can be advanced due to the stress corrosion phenomenon, and the etching rate in the modified portion can be increased.

[0025] According to the present invention, it is possible to provide a glass plate capable of increasing the etching rate in the modified portion and a method for manufacturing the glass plate.

[0026] FIG. 1 is a plan view of a glass plate according to the present invention. FIG. 2 is a cross-sectional view taken along line A-A of FIG. 1. FIG. 3 is an example of an image showing the measurement result of the retardation of the glass plate according to the present invention. FIG. 4 is a schematic view showing a method for evaluating the anisotropy of the retardation of the first main surface of the glass plate according to the present invention. FIG. 5 is a schematic view showing a method for evaluating the anisotropy of the retardation of the second main surface and the intermediate surface of the glass plate according to the present invention. FIG. 6 is a perspective view schematically showing an example of a method for manufacturing the glass plate according to the present invention. FIG. 7 is a graph showing the diameter of the non-through hole of the glass plate according to an embodiment of the present invention. FIG. 8 is an example of an image showing the measurement result of the retardation of the glass plate according to Sample 8. FIG. 9 is an example of an image showing the measurement result of the retardation at a position where the distance from the upper surface of the glass plate according to Sample 9 is 50 μm. FIG. 10 is an example of an image showing the measurement result of the retardation at a position where the distance from the upper surface of the glass plate according to Sample 9 is 250 μm. FIG. 11 is an example of an image showing the measurement result of the retardation at a position where the distance from the upper surface of the glass plate according to Sample 9 is 450 μm.

[0027] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIGS. 1 and 2 show an embodiment of a glass plate according to the present invention.

[0028] (Glass Plate) The material of the glass plate G can be soda glass, quartz glass, alkali-free glass, borosilicate glass, aluminosilicate glass, crystallized glass, etc. When the glass plate G is used as a substrate for electronic devices, it is preferably quartz glass, alkali-free glass, borosilicate glass, or alkali aluminosilicate glass. Here, alkali-free glass means glass that substantially does not contain an alkali component (alkali metal oxide), specifically, glass in which the weight ratio of the alkali component in the glass composition is 3000 ppm or less. The weight ratio of the alkali component in the glass composition of the glass plate G of the present invention is preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less.

[0029] When the glass plate G is made of non-alkali glass, as the glass composition, for example, in mol%, SiO ２ 60 to 75%, Al ２ O ３ 5 to 20%, B ２ O ３ 0 to 15%, Li ２ O + Na ２ O + K ２ O (total amount of Li ２ O, Na ２ O and K ２ O) less than 0 to 1%, MgO 0 to 10%, CaO 0 to 15%, SrO 0 to 10%, BaO 0 to 10% are preferably contained.

[0030] When the glass plate G is made of borosilicate glass, as the glass composition, for example, in mol%, SiO ２ 70 to 85%, Al ２ O ３ 0 to 10%, B ２ O ３ 5 to 20%, Li ２ O 0 to 5%, Na ２ O 0 to 10%, K ２ O 0 to 5%, MgO 0 to 5%, CaO 0 to 5%, SrO 0 to 5%, BaO 0 to 5% are preferably contained.

[0031] When the glass plate G is made of alkali aluminosilicate glass, as the glass composition, for example, in mol%, SiO ２ 50 to 80%, Al ２ O ３ 8 to 25%, B ２ O ３ 0 to 10%, Li ２ O 1 to 15%, Na ２ O 3 to 21%, K ２ O 0 to 10%, MgO 0 to 10%, CaO 0 to 5%, SrO 0 to 5%, BaO 0 to 5%, P ２ O ５ 0 to 15%, ZnO 0 to 5% are preferably contained.

[0032] Fig. 1 is a plan view of a glass plate G having a plurality of modified portions Gm, and Fig. 2 is a cross-sectional view taken along line A-A of the glass plate G shown in Fig. 1. As shown in Fig. 2, the glass plate G has a first main surface G1, a second main surface G2 opposite to the first main surface G1, and a modified portion Gm formed from the first main surface G1 to the second main surface G2. In the present embodiment, the glass plate G has a plurality of modified portions Gm. Further, at a virtual intermediate surface G3 located between the first main surface G1 and the second main surface G2, the modified portion Gm is formed in the same manner as the first main surface G1 and the second main surface G2. The distance between the first main surface G1 and the second main surface G2, that is, the plate thickness of the glass plate G, is preferably 0.03 mm or more and 10 mm or less. The lower limit value of the plate thickness of the glass plate is preferably 0.05 mm or more, 0.1 mm or more, 0.2 mm or more, 0.3 mm or more. The upper limit value of the plate thickness of the glass plate is preferably 5 mm or less, 3 mm or less, 2 mm or less, 1.5 mm or less. Further, the glass plate G is preferably rectangular, and its dimensions in plan view may be, for example, 10 mm × 10 mm or more and 700 mm × 700 mm or less.

[0033] FIG. 3 is an image showing the distribution of the retardation phase difference and the fast axis direction on the first main surface G1 of the glass plate G according to the present embodiment. The image in FIG. 3 can be obtained by imaging the target glass in the plate thickness direction using various birefringence measuring devices such as PA-micro manufactured by Photonic Lattice Co., Ltd. In FIG. 3, the darker the black, the larger the retardation phase difference, and the lighter the color (closer to white), the smaller the retardation phase difference. As shown in FIG. 3, the glass plate G according to the present embodiment has a plurality of extreme points where the retardation phase difference reaches a maximum value on the first main surface G1. In the present embodiment, among these extreme points, the point with the largest retardation phase difference is called the first extreme point P1, and the point with the second largest retardation phase difference is called the second extreme point P2. Note that the modified portion Gm in the present embodiment is a columnar region having a bottom surface on the first main surface G1 and the second main surface G2 and having side surfaces parallel to the plate thickness direction. The bottom surface of the modified portion Gm is a region surrounded by a circular shape, an elliptical shape, an oval shape, or an arbitrary closed curve, and the shape and size of the bottom surface may be different between the first main surface G1 and the second main surface G2. Inside the modified portion Gm, at least one of the stress, density, and optical properties changes at any position in the plate thickness direction due to laser irradiation, or minute cracks or pores are formed. In glass, the region where stress is applied has a large retardation phase difference. That is, the birefringence characteristics are modified. The modified portion Gm can be easily distinguished from the non-modified portion other than the modified portion Gm by observing with an optical microscope. The maximum diameter of the modified portion may be defined, for example, as the maximum dimension of the region that is observed separately from the non-modified portion when the modified portion Gm is observed with an optical microscope from the first main surface G1 side. In this case, the size of the modified portion Gm is preferably 10 μm or less, 9 μm or less, 8 μm or less, 7 μm or less, 6 μm or less, 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, 1 μm or less. In FIG. 3, the modified portion Gm when viewed from the first main surface G1 side with a line of sight perpendicular to the plate thickness direction is shown by an elliptical broken line. In other words, the elliptical broken line shown in FIG. 3 represents the bottom surface of the modified portion Gm, which is a columnar body, on the first main surface G1. As shown in FIG. 3, the region of the non-modified portion other than the modified portion Gm is shown in white, and the retardation phase difference is almost zero.That is, no stress acts on the non-modified portion of the glass sheet G, or only a small stress that can be substantially ignored acts on the non-modified portion.

[0034] The greater the retardation phase difference in the modified region Gm, the greater the stress acting on the modified region Gm. Therefore, large stress acts on the first maximum point P1 and the second maximum point P2, where the retardation magnitude is maximized, which easily forms microcracks or propagates the microcracks due to stress corrosion when the glass sheet G is etched. Therefore, when a glass sheet G having a modified region Gm is etched, the etching rate of the first maximum point P1 and the second maximum point P2 increases. Therefore, when a glass sheet G having a large distance between the first maximum point P1 and the second maximum point P2 is etched to form through holes and / or non-through holes, the hole shape tends to become elliptical or oblong in plan view. From the viewpoint of improving the roundness of the through holes and / or non-through holes in plan view, the upper limit of the distance between the first maximum point P1 and the second maximum point P2 is preferably 5 μm or less, 4 μm or less, 3 μm or less, 2 μm or less, or 1 μm or less. Furthermore, the magnitude of the stress acting on the first maximum point P1 and the second maximum point P2 is preferably 7 MPa or more, 10 MPa or more, 15 MPa or more, 20 MPa or more, 25 MPa or more, 30 MPa or more, 35 MPa or more, or 40 MPa or more.

[0035] The magnitude of the stress acting on the modified portion can be calculated, for example, from the magnitude of the retardation phase difference using the following formula (1): Stress (σ) = Retardation Phase Difference R / (Glass Plate Thickness t × Photoelastic Constant C) (1) The photoelastic constant C can be measured, for example, using a photoelastic constant measuring device (manufactured by Orihara Manufacturing Co., Ltd.).

[0036] Each of the multiple arrows B in FIG. 3 indicates the fast axis direction of retardation at the position corresponding to the center of the arrow B. The fast axis direction of retardation coincides with the direction perpendicular to the direction in which compressive stress acts or the direction in which tensile stress acts. In this embodiment, the fast axis direction of retardation is substantially constant in the modified region Gm. In other words, the fast axis direction of retardation at any point in the modified region Gm is anisotropic. Furthermore, the direction from the first maximum point P1 to the second maximum point P2 intersects with the fast axis direction of retardation at a substantially right angle.

[0037] When the retardation phase difference and fast axis direction show an anisotropic distribution as described above (i.e., when the glass plate has optical anisotropy in the modified region), compressive stress acts along the line segment connecting the first maximum point P1 and the second maximum point P2, or tensile stress acts in a direction perpendicular to the line segment connecting the first maximum point P1 and the second maximum point P2. When such tensile or compressive stress acts, microcracks are likely to occur in the modified region Gm. When a glass plate G having microcracks in the regions near the first maximum point P1 and the second maximum point P2 in the modified region Gm is immersed in an etching solution, the etching solution penetrates into the microcracks, making it easier to remove the glass around the microcracks. In other words, the etching rate of the modified region Gm can be increased. In this embodiment, the length of the microcracks may be, for example, 1 μm or less. When the length of the microcracks is large, the occurrence of the microcracks can be confirmed using an optical microscope, an electron microscope, an X-ray CT scan, or the like. However, when the length of the microcracks is small, it is not possible to directly confirm the occurrence of the microcracks. Even in such cases, it is possible to indirectly infer the occurrence of the microcracks based on the magnitude of the stress in the modified region Gm and the anisotropy of the stress.

[0038] Specifically, even if the length of the microcracks is short, if an appropriate amount of tensile stress is present at the tip of the microcracks, the tip of the cracks will propagate in the thickness direction due to stress corrosion. By repeating the process of removing glass by etching and propagating the cracks, etching of the modified region Gm progresses, and the modified region Gm can be efficiently removed. Note that even if the length of the microcracks is long, crack propagation due to stress corrosion may occur at the tip of the cracks.

[0039] As described above, evaluating the degree of retardation anisotropy in the modified region Gm is important in increasing the etching rate of the modified region Gm. Hereinafter, a method for evaluating the retardation phase difference and anisotropy in the fast axis direction on the first main surface G1 of the glass sheet G will be described with reference to FIG. 4 . First, a virtual circle (hereinafter referred to as virtual circle C) is set, the diameter of which is the line segment connecting the first maximum point P1 and the second maximum point P2. Next, two points on the virtual circle C that are equidistant from the first maximum point P1 and the second maximum point P2 are set as the first measurement point Q1 and the second measurement point Q2, respectively. In this embodiment, the point on the virtual circle C that is shifted 90° counterclockwise from the first maximum point P1 is set as the first measurement point Q1, and the point that is shifted 90° clockwise from the first maximum point P1 is set as the second measurement point Q2. Then, the retardation fast axis directions θ1, θ2, φ1, and φ2 at the first maximum point P1, the second maximum point P2, the first measurement point Q1, and the second measurement point Q2 are obtained, respectively.

[0040] When the difference between the fast axis directions θ1 and θ2 of the retardation at the first maximum point P1 and the second maximum point P2 and the fast axis directions φ1 and φ2 of the retardation at the first measurement point Q1 and the second measurement point Q2 is −30° or more and 30° or less, anisotropic tensile stress or compressive stress acts on the modified region Gm, which tends to form fine cracks in the vicinity of the first maximum point P1 and the second maximum point P2 or to propagate the fine cracks due to the stress corrosion phenomenon when the glass plate G is etched. Specifically, the following are calculated: the difference θ1-φ1 between the fast axis direction θ1 at the first maximum point P1 and the fast axis direction φ1 at the first measurement point Q1; the difference φ1-θ2 between the fast axis direction φ1 at the first measurement point Q1 and the fast axis direction θ2 at the second maximum point P2; the difference θ2-φ2 between the fast axis direction θ2 at the second maximum point P2 and the fast axis direction φ2 at the second measurement point Q2; and the difference φ2-θ1 between the fast axis direction φ2 at the second measurement point Q2 and the fast axis direction θ1 at the first maximum point P1.

[0041] On the other hand, when the difference between the fast axis directions θ1 and θ2 of the retardation at the first maximum point P1 and the second maximum point P2 and the fast axis directions φ1 and φ2 of the retardation at the first measurement point Q1 and the second measurement point Q2 is less than −30° or greater than 30°, isotropic tensile stress or compressive stress acts on the modified region Gm, and fine cracks are less likely to form near the first maximum point P1 and the second maximum point P2.

[0042] That is, when the glass plate G of the present invention is observed in the sheet thickness direction, it is preferable that the fast axis direction of retardation at any point in the region of the modified region Gm exhibits anisotropy in a direction intersecting a line segment connecting the first maximum point P1 and the second maximum point P2. In other words, when the glass plate G of the present invention is observed in the sheet thickness direction, it is preferable that the glass plate G does not have a site in the region of the modified region Gm where the fast axis direction of retardation exhibits isotropy.

[0043] As shown in Figure 5, the retardation on the second principal surface G2 of the glass plate G can be evaluated in the same manner as the retardation on the first principal surface G1. On the second principal surface G2, the position where the retardation phase difference has the largest maximum value is designated as the third maximum point P3, and the position where the retardation phase difference has the second largest maximum value is designated as the fourth maximum point P4. Next, a third measurement point Q3 and a fourth measurement point Q4 are set in the same manner as on the first principal surface G1. Then, the retardation fast axis directions θ3, θ4, φ3, and φ4 at the third maximum point P3, the fourth maximum point P4, the third measurement point Q3, and the fourth measurement point Q4 are obtained, respectively. When the difference between the fast axis directions θ3 and θ4 of the retardation at the third maximum point P3 and the fourth maximum point P4 and the fast axis directions φ3 and φ4 of the retardation at the third measurement point Q3 and the fourth measurement point Q4 is −30° or more and 30° or less, anisotropic tensile stress or compressive stress acts on the modified region Gm, which tends to form fine cracks in the vicinity of the third maximum point P3 and the fourth maximum point P4 or to propagate the fine cracks due to the stress corrosion phenomenon when the glass plate G is etched. On the other hand, when the difference between the fast axis directions θ3 and θ4 of the retardation at the third maximum point P3 and the fourth maximum point P4 and the fast axis directions φ3 and φ4 of the retardation at the third measurement point Q3 and the fourth measurement point Q4 is less than −30° or greater than 30°, an isotropic tensile stress or compressive stress acts on the modified region Gm, and fine cracks are unlikely to form in the vicinity of the third maximum point P3 and the fourth maximum point P4, or to propagate due to stress corrosion when the glass plate G is etched.

[0044] In this way, it is preferable that, within the region of the modified region Gm, the fast axis direction of retardation at any point on the first main surface G1 of the glass plate G exhibits anisotropy in a direction intersecting a line segment connecting the first maximum point P1 and the second maximum point P2, and that, within the region of the modified region Gm, the fast axis direction of retardation at any point on the second main surface G2 of the glass plate G exhibits anisotropy in a direction intersecting a line segment connecting the third maximum point P3 and the fourth maximum point P4. With such retardation distributions in the first main surface G1 and the second main surface G2, fine cracks can be generated from both the first main surface G1 and the second main surface G2, and through holes and / or non-through holes can be efficiently formed.

[0045] The retardation at a virtual intermediate surface G3 (illustrated in FIG. 2 ) located midway between the first principal surface G1 and the second principal surface G2 of the glass plate G can also be evaluated in the same manner as the retardation at the first principal surface G1 and the second principal surface G2. At the intermediate surface G3, the position where the retardation phase difference has the largest maximum value is designated as the fifth maximum point P5, and the position where the retardation phase difference has the second largest maximum value is designated as the sixth maximum point P6. Next, a fifth measurement point Q5 and a sixth measurement point Q6 are set in the same manner as for the first principal surface G1. Then, the retardation fast axis directions θ5, θ6, φ5, and φ6 at the fifth maximum point P5, the sixth maximum point P6, the fifth measurement point Q5, and the sixth measurement point Q6 are obtained, respectively. When the difference between the fast axis directions θ5 and θ6 of the retardation at the fifth maximum point P5 and the sixth maximum point P6 and the fast axis directions φ5 and φ6 of the retardation at the fifth measurement point Q5 and the sixth measurement point Q6 is −30° or more and 30° or less, anisotropic tensile stress or compressive stress acts on the modified region Gm, which tends to form fine cracks in the vicinity of the fifth maximum point P5 and the sixth maximum point P6 or to propagate the fine cracks due to the stress corrosion phenomenon when the glass plate G is etched. On the other hand, when the difference between the fast axis directions θ5 and θ6 of the retardation at the fifth maximum point P5 and the sixth maximum point P6 and the fast axis directions φ5 and φ6 of the retardation at the fifth measurement point Q5 and the sixth measurement point Q6 is less than −30° or greater than 30°, an isotropic tensile stress or compressive stress acts on the modified region Gm, and fine cracks are unlikely to form in the vicinity of the fifth maximum point P5 and the sixth maximum point P6, or to propagate due to stress corrosion when the glass plate G is etched.

[0046] In this way, it is preferable that, within the region of the modified region Gm, the fast axis direction of retardation at an arbitrary point on the first main surface G1 of the glass plate G exhibits anisotropy in a direction intersecting with a line segment connecting the first maximum point P1 and the second maximum point P2, and that, within the region of the modified region Gm, the fast axis direction of retardation at an arbitrary point on the second main surface G2 of the glass plate G exhibits anisotropy in a direction intersecting with a line segment connecting the third maximum point P3 and the fourth maximum point P4, and further, within the region of the modified region Gm, the fast axis direction of retardation at an arbitrary point on the intermediate surface G3 exhibits anisotropy in a direction intersecting with a line segment connecting the fifth maximum point P5 and the sixth maximum point P6. If the first main surface G1, the second main surface G2, and the intermediate surface G3 have such retardation distributions, fine cracks are generated from both the first main surface G1 and the second main surface G2, and the fine cracks are likely to propagate further into the interior of the glass plate G, making it possible to efficiently form through holes and / or non-through holes.

[0047] Furthermore, the retardation fast axis directions φ1 and φ2 at the first measurement point Q1 and the second measurement point Q2 preferably intersect at approximately right angles with the direction from the first maximum point P1 to the second maximum point P2. Here, "approximately right angles" means that the angles between the fast axis directions at the first measurement point Q1 and the second measurement point Q2 and the direction from the first maximum point P1 to the second maximum point P2 are 60° or more and 120° or less. When the retardation fast axis directions on the first main surface G1 are distributed in this manner, the retardation fast axis directions are distributed symmetrically with respect to the line segment connecting the first maximum point P1 and the second maximum point P2. Therefore, stress acts symmetrically on the first maximum point P1 and the second maximum point P2. This reduces the difference in etching rate between the first maximum point P1 and the second maximum point P2.

[0048] Also on the second principal surface G2, similarly to the first principal surface G1, it is preferable that the fast axis directions φ3 and φ4 of the retardation at the third measurement point Q3 and the fourth measurement point Q4 intersect at approximately right angles with the direction from the third maximum point P3 to the fourth maximum point P4, thereby making it possible to reduce the difference in etching rate between the third maximum point P3 and the fourth maximum point P4.

[0049] Also in the intermediate surface G3, similarly to the first principal surface G1 and the second principal surface G2, it is preferable that the fast axis directions φ5 and φ6 of the retardation at the fifth measurement point Q5 and the sixth measurement point Q6 intersect at approximately right angles with the direction from the fifth maximum point P5 to the sixth maximum point P6, thereby making it possible to reduce the difference in etching rate between the fifth maximum point P5 and the sixth maximum point P6.

[0050] (Method for Producing Glass Plate) The method for producing a glass plate of the present invention includes a laser irradiation step of forming a modified portion in the glass plate G by irradiating the glass plate G with a laser.

[0051] First, as shown in Fig. 6, the glass sheet G is placed flat with the second main surface G2 facing downward. The glass sheet G may be placed on, for example, a surface plate (not shown). The irradiation unit of the laser irradiation device 1 is disposed at a position away from the first main surface G1 of the glass sheet G so as to face the first main surface G1. The irradiation unit of the laser irradiation device 1 is configured to be movable three-dimensionally by a driving device (not shown).

[0052] Next, the laser irradiation device 1 irradiates the first main surface G1 of the glass sheet G with laser light 2 in a direction perpendicular to the first main surface G1 (laser irradiation step). The laser irradiation device 1 is, for example, a pulsed laser irradiation device, and it is preferable that the laser irradiation device 1 irradiates a pulsed laser. With a pulsed laser, the glass sheet G can be efficiently heated by increasing the energy per pulse, and the pulse duration can be shortened to prevent the glass sheet G from being damaged by thermal diffusion. The laser light 2 is preferably a picosecond laser or a femtosecond laser, and the pulse width is preferably, for example, 50 fs or more and 100 ps or less. Furthermore, the energy per pulse of the laser light 2 is preferably 35 μJ or more and 80 μJ or less. The lower limit of the energy per pulse of the laser light 2 is preferably 40 μJ or more, 45 μJ or more, 50 μJ or more, or 55 μJ or more. The upper limit of the energy per pulse of the laser light 2 is preferably 75 μJ or less, 70 μJ or less, 65 μJ or less, or 60 μJ or less.

[0053] The wavelength of the laser beam 2 is preferably 400 nm or more and 1050 nm or less. Furthermore, in this wavelength range, the linear transmittance of the glass sheet G is preferably 80% or more. If the wavelength of the laser beam 2 is within this range, the region in which the modified region Gm is formed by multiphoton absorption can be reduced, for example, the distance between the first maximum point P1 and the second maximum point P2 can be shortened. Therefore, the modified region Gm can be removed by etching, and the circularity of the through-holes and / or non-through-holes formed can be improved. On the other hand, if the wavelength of the laser beam 2 is not within this range, the absorption coefficient of the laser beam 2 for the glass sheet G increases, and the proportion of the laser beam 2 absorbed near the first main surface G1 increases, making it difficult to sufficiently heat the interior of the glass sheet G and the second main surface G2. Therefore, when forming through-holes by etching the glass sheet G, the hole diameters on the first main surface G1 side and the second main surface G2 side may differ significantly. Furthermore, if the temperature of the laser irradiated portion becomes too high, the stress generated in the glass becomes too high, which makes it more likely that cracks will occur when through holes and / or blind holes are formed.

[0054] The laser irradiation device 1 preferably shapes the laser light 2 into a Bessel beam using an optical system (not shown) including an axicon lens, etc. This allows a modified region Gm to be formed throughout the entire thickness direction of the glass plate with a single pulse of laser irradiation, thereby shortening the time required to form the modified region Gm. In this embodiment, the length of the focal point of the laser light 2 in the irradiation direction of the laser light 2 is, for example, 0.1 mm or more and 10 mm or less. The spot diameter of the laser light 2 is, for example, 0.1 μm or more and 10 μm or less.

[0055] The laser irradiation device 1 irradiates the first main surface G1 of the glass sheet G with the laser light 2, thereby forming a modified region Gm in the glass sheet G. By repeatedly moving the irradiation position of the laser light 2 on the glass sheet G and irradiating the glass sheet G with the laser light 2 multiple times, multiple modified regions Gm are formed in the glass sheet G. In this embodiment, the laser irradiation device 1 moves the irradiation position of the laser light 2 on the glass sheet G each time it irradiates one pulse of the laser light 2. That is, each of the multiple modified regions Gm is formed by a single pulse of the laser light 2. Note that the modified region Gm in this embodiment is a columnar region having a bottom surface on the first main surface G1 and the second main surface G2 and having side surfaces parallel to the plate thickness direction. The bottom surface is a region surrounded by a circular, elliptical, oval, or any closed curve. Inside the modified region Gm, at least one of stress, density, and optical properties is changed or minute cracks or voids are formed at a position in the plate thickness direction due to the laser irradiation.

[0056] By etching the glass sheet G on which the modified regions Gm have been formed by the above-described method with an etching solution, through holes and / or non-through holes can be formed. Here, for example, an HF aqueous solution, a NaOH aqueous solution, or a KOH aqueous solution can be used as the etching solution, but it is preferable to use an HF aqueous solution because it can shorten the time required to form holes. In addition, it is also possible to add HCl or H ２ SO ４ , HNO ３ Furthermore, a surfactant may be added.

[0057] The present invention will be described in detail below based on examples.

[0058] In Table 1, Samples 1 to 4 are examples of the present invention, and Samples 5 to 8 are comparative examples of the present invention.

[0059] First, the glass composition is, in mol%, SiO ２ 66.2%, Al ２ O ３ 12.8%, B ２ O ３A glass plate sample was prepared with a composition of 6.4% of SiO2, 4.2% of MgO, 7.6% of CaO, 0.3% of SrO, and 2.5% of BaO. The glass plate sample was rectangular, measuring 35 mm x 20 mm, and had a thickness of 0.5 mm. The photoelastic constant of the glass plate sample was 29.6 (nm / cm) / MPa.

[0060] This glass plate sample was irradiated with laser light 2 from the first principal surface G1 side, forming 800 modified regions arranged in an 8 × 100 array. The center-to-center distance between adjacent modified regions was 150 μm. The laser light was pulsed laser light with a wavelength of 1030 nm and a pulse width of 900 fs. Laser irradiation (laser irradiation process) was performed in single-pulse mode without burst pulses, resulting in a glass plate sample with modified regions. The laser pulse energy was varied from 30 μJ to 150 μJ as shown in Table 1, and 1 × 100 modified regions were formed for each pulse energy. The laser beam was shaped into a Bessel beam using an optical system using an axicon lens or the like. The focal length of the Bessel beam was approximately 1 mm, which was greater than the thickness of the glass plate sample. By irradiating the glass plate with the center of the Bessel beam focal point approximately aligned with the center of the glass plate in the thickness direction, modified regions could be formed throughout the entire thickness direction of the glass plate sample with a single pulse of laser irradiation.

[0061] The retardation of the first main surface of the glass plate sample having the modified portion formed thereon was measured. Photonic Lattice's PA-micro was used to measure the retardation. The retardation phase difference and fast axis direction were obtained by measuring the retardation. The fast axis direction of the retardation is based on the X direction shown in FIG. 4, with the counterclockwise direction being positive.

[0062] From the measurement results of the retardation phase difference, the positions of the first maximum point P1, where the retardation phase difference on the first principal surface has the largest maximum value, and the second maximum point P2, where the retardation phase difference has the second largest maximum value, were calculated. Next, the positions of a point (first measurement point Q1) and a point (second measurement point Q2) shifted 90° counterclockwise from the first maximum point P1 on a circumference whose diameter is the line segment connecting the first maximum point P1 and the second maximum point P2 were calculated. Furthermore, the retardation fast axis directions θ1, θ2, φ1, and φ2 at the first maximum point P1, the second maximum point P2, the first measurement point Q1, and the second measurement point Q2 were obtained, respectively.

[0063] To evaluate the anisotropy of retardation, the differences between the fast-axis direction θ1 at the first maximum point P1 and the fast-axis direction θ2 at the second maximum point P2, and the fast-axis direction φ1 at the first measurement point Q1 and the fast-axis direction φ2 at the second measurement point Q2 were evaluated. Specifically, θ1-φ1, φ1-θ2, θ2-φ2, and φ2-θ1 were calculated, respectively.

[0064] The glass plate sample with the modified portion formed thereon was then immersed in an etching solution to perform an etching treatment. The etching solution used was a mixed acid solution consisting of 2.5 mol / L HF and 1.0 mol / L HCl. The temperature of the etching solution was maintained at 30°C using a chiller. When etching was performed for 20 minutes under the above conditions, non-through holes extending from the first main surface and the second main surface toward the plate thickness direction of the glass plate sample were formed.

[0065] The glass plate sample having the non-through pores formed therein was cut, and the cross section was observed to measure the depth of the non-through pores.

[0066]

[0067] As shown in Table 1, in Samples 1 to 4, which are examples of the present invention, the phase differences of the retardation at the first maximum point P1 and the second maximum point P2 are both 10 nm or more. Furthermore, the differences between the fast axis directions θ1 and θ2 at the first maximum point P1 and the second maximum point P2 and the fast axis directions φ1 and φ2 at the first measurement point Q1 and the second measurement point Q2 are all in the range of -30° to 30°. As a result, in Samples 1 to 4, the depth of the non-through pores in the first and second main surfaces is 75 μm or more, and the modified regions Gm can be efficiently removed by etching.

[0068] Furthermore, of the 100 non-through holes formed in each of Samples 1 to 8, 50 randomly selected holes formed in the first main surface were measured for diameter in the first main surface. A Mitutoyo Hyper QV 606 was used for the measurement. The average values ​​and standard deviations of the hole diameters are shown in Table 2.

[0069] As shown in Table 2, the standard deviation of hole diameters for Samples 1 to 4 was small, at 1.03 μm or less. On the other hand, the standard deviation of hole diameters for Samples 7 and 8 was large, at 1.14 μm or more. Figure 7 also shows the hole diameters in a box-and-whisker plot. The "○" symbols for pulse energies of 90 μJ and 150 μJ (i.e., Samples 6 and 8) represent outliers in the box-and-whisker plot. Thus, for pulse energies of 40 to 70 μJ (i.e., Samples 1 to 4), either no outliers were present in the box-and-whisker plot or the standard deviation of hole diameters was small. Therefore, it was revealed that pulse energies of 40 to 70 μJ are suitable for glass substrates used in semiconductor packaging core substrates and interposers, where uniform hole shape is required.

[0070] As an example, the retardation phase difference and fast axis direction of the glass plate sample of Sample 2 are shown in Figure 3. In the glass plate sample of Sample 2, the fast axis direction of retardation is oriented in approximately the same direction at all observation points, and it is considered that anisotropy is exhibited throughout the entire modified region. In other words, in the glass plate sample of Sample 2, anisotropic stress acts on the modified region Gm. When the stress is anisotropic, even a small stress value can easily cause fine cracks to occur in the modified region, or the fine cracks can easily propagate due to stress corrosion when the glass plate is etched. In other words, a glass plate having anisotropic retardation (a glass plate having optical anisotropy) is likely to increase the etching rate of the modified region and has deeper non-through holes than a glass plate having isotropic retardation.

[0071] As an example, the retardation phase difference and fast axis direction of the glass plate of Sample 8 are shown in Figure 8. In the glass plate of Sample 8, the retardation fast axis direction is distributed in an arc shape in the modified region Gm. In other words, isotropic stress acts on the modified region Gm of the glass plate of Sample 8. When the stress is isotropic, even if the stress value is large, it is difficult for fine cracks to occur in the glass plate, and the fine cracks are unlikely to progress due to stress corrosion when the glass plate is etched. In other words, a glass plate with isotropic retardation is difficult to increase the etching rate of the modified region, and the depth of the non-through holes is shallower than a glass plate with anisotropic retardation.

[0072] Next, a glass plate sample having the same composition and shape as Samples 1 to 8 described above was irradiated with laser light under the same laser irradiation conditions as Sample 2 (i.e., pulse energy of 50 μJ) to form a modified portion, thereby producing a glass plate sample according to Sample 9. For this glass plate sample, retardation was measured at positions 50 μm, 250 μm, and 450 μm from the top surface (laser irradiated surface) in the plate thickness direction. Retardation measurements were performed using a PA-micro manufactured by Photonic Lattice, and the position in the plate thickness direction was set by setting the focal position at 50 μm, 250 μm, and 450 μm from the top surface of the glass plate sample. The position 50 μm away from the top surface corresponds to the first main surface in the present invention. The position 450 μm away from the top surface corresponds to the second main surface in the present invention. The position 250 μm away from the top surface corresponds to a virtual intermediate surface located midway between the first and second main surfaces in the present invention. These measurement results are shown in Table 3.

[0073]

[0074] As shown in Table 3, in Sample 9, an example of the present invention, at a position 50 μm away from the top surface, the retardation phase difference at the first maximum point P1 and the second maximum point P2 is 10 nm or more, and the differences between the fast-axis directions θ1 and θ2 at the first maximum point P1 and the second maximum point P2 and the fast-axis directions φ1 and φ2 at the first measurement point Q1 and the second measurement point Q2 are both in the range of −30° to 30°. Furthermore, at a position 250 μm away from the top surface, the retardation phase difference at the fifth maximum point P5 and the sixth maximum point P6 is 10 nm or more, and the differences between the fast-axis directions θ5 and θ6 at the fifth maximum point P5 and the sixth maximum point P6 and the fast-axis directions φ5 and φ6 at the fifth measurement point Q5 and the sixth measurement point Q6 are both in the range of −30° to 30°. Furthermore, at a position 450 μm away from the top surface, the phase difference of the retardation at the third maximum point P3 and the fourth maximum point P4 is 10 nm or more, and the differences between the fast axis directions θ3 and θ4 at the third maximum point P3 and the fourth maximum point P4 and the fast axis directions φ3 and φ4 at the third measurement point Q3 and the fourth measurement point Q4 are all in the range of −30° or more and 30° or less. That is, in Sample 9, at positions 50 μm, 250 μm, and 450 μm away from the top surface, the differences between the fast axis directions at the maximum points and the fast axis directions at the measurement points are −30° or more and 30° or less, and it is found that the retardation distribution is anisotropic at multiple positions in the sheet thickness direction.

[0075] The retardation phase difference and fast axis direction of the glass plate sample of Sample 9 at a position 50 μm from the top surface are shown in Figure 9, the retardation phase difference and fast axis direction of the glass plate sample of Sample 9 at a position 250 μm from the top surface are shown in Figure 10, and the retardation phase difference and fast axis direction of the glass plate sample of Sample 9 at a position 450 μm from the top surface are shown in Figure 11. It can be seen that the retardation fast axis direction of the glass plate sample of Sample 9 faces in approximately the same direction at all observation points, and anisotropy is exhibited throughout the entire modified region.

[0076] 1 Laser irradiation device 2 Laser light G Glass plate G1 First principal surface G2 Second principal surface G3 Intermediate surface Gm Modified portion P1 First maximum point P2 Second maximum point P3 Third maximum point P4 Fourth maximum point P5 Fifth maximum point P6 Sixth maximum point Q1 First measurement point Q2 Second measurement point Q3 Third measurement point Q4 Fourth measurement point Q5 Fifth measurement point Q6 Sixth measurement point C Virtual circle θ1 Fast axis direction of retardation at first maximum point θ2 Fast axis direction of retardation at second maximum point θ3 Fast axis direction of retardation at third maximum point θ4 Fast axis direction of retardation at fourth maximum point θ5 Fast axis direction of retardation at fifth maximum point θ6 Fast axis direction of retardation at sixth maximum point φ1 Fast axis direction of retardation at the first measurement point φ2 Fast axis direction of retardation at the second measurement point φ3 Fast axis direction of retardation at the third measurement point φ4 Fast axis direction of retardation at the fourth measurement point φ5 Fast axis direction of retardation at the fifth measurement point φ6 Fast axis direction of retardation at the sixth measurement point

Claims

1. A glass plate comprising a first main surface, a second main surface opposite to the first main surface, and a modified portion extending between the first main surface and the second main surface, wherein the modified portion comprises a plurality of maximum points at which the retardation phase difference assumes a maximum value when a retardation phase difference distribution on the first main surface is viewed in the thickness direction of the glass plate, the maximum points comprising a first maximum point at which the retardation phase difference is the largest and a second maximum point at which the retardation phase difference is the second largest, and the retardation phase difference at the first maximum point and the second maximum point are each 10 nm or more, a first measurement point and a second measurement point, the first measurement point and the second measurement point being on a circumference whose diameter is a line segment connecting the first maximum point and the second maximum point and equidistant from the first maximum point and the second maximum point; and a difference between the fast axis direction of retardation at the first measurement point and the second measurement point and the fast axis direction of retardation at the first maximum point and the second maximum point being in the range of −30° to 30°.

2. The glass plate according to claim 1, wherein the angles formed by the fast axis directions of the first measurement point and the second measurement point and the direction from the first maximum point to the second maximum point are 60° or more and 120° or less.

3. The glass plate according to claim 1 or 2, wherein the distance between the first maximum point and the second maximum point is 5 μm or less.

4. The glass plate according to claim 1 or 2, wherein the magnitude of the stress acting on the first maximum point and the second maximum point is 7 MPa or more.

5. The glass plate according to claim 1 or 2, wherein the modified portion comprises a plurality of maximum points at which the retardation phase difference assumes a maximum value when the retardation phase difference distribution on the second principal surface is viewed in the thickness direction of the glass plate, the maximum points comprising a third maximum point at which the retardation phase difference is the largest and a fourth maximum point at which the retardation phase difference is the second largest, the retardation phase difference at the third maximum point and the retardation phase difference at the fourth maximum point are each 10 nm or more, and when a third measurement point and a fourth measurement point are two points which are on a circumference having a diameter equal to a line segment connecting the third maximum point and the fourth maximum point and are equidistant from the third maximum point and the fourth maximum point, the differences between the fast axis direction of retardation at the third measurement point and the fast axis direction of retardation at the third maximum point and the fourth maximum point are -30° or more and 30° or less, respectively.

6. The modified portion has a plurality of maximum points at which the retardation phase difference assumes a maximum value when the retardation phase difference distribution at a virtual intermediate surface located midway between the first principal surface and the second principal surface is viewed in the thickness direction of the glass plate, the maximum points including a fifth maximum point at which the retardation phase difference is the largest and a sixth maximum point at which the retardation phase difference is the second largest, and the retardation phase difference at the fifth maximum point and the sixth maximum point are each 10 nm or more, 3. The glass plate according to claim 1, wherein a fifth measurement point and a sixth measurement point are two points that are on a circumference having a diameter defined by a line segment connecting the fifth maximum point and the sixth maximum point and are equidistant from the fifth maximum point and the sixth maximum point, and wherein differences between the fast axis directions of retardation at the fifth measurement point and the sixth measurement point and the fast axis directions of retardation at the fifth maximum point and the sixth maximum point are each −30° or more and 30° or less.

7. A method for manufacturing a glass plate, comprising a laser irradiation step of irradiating a glass plate with a laser to form a modified portion in the glass plate, wherein the laser is a pulsed laser, and in the laser irradiation step, the pulse energy of the laser is 35 μJ or more and 80 μJ or less, the laser is shaped into a Bessel beam shape, and the modified portion has a plurality of maximum points at which the phase difference of retardation takes a maximum value when the phase difference distribution of retardation on the first main surface is viewed in the plate thickness direction of the glass plate, and the maximum points include a first maximum point at which the phase difference of retardation is largest and a second maximum point at which the phase difference of retardation is second largest.

8. A glass plate comprising a first main surface, a second main surface opposite to the first main surface, and a modified portion extending from the first main surface to the second main surface and having modified birefringence characteristics based on stress, wherein the modified portion has a maximum diameter of 10 μm or less, and when the phase difference distribution or fast axis direction distribution of retardation on the first main surface is observed, the modified portion has optical anisotropy.

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