Glass substrate and method for manufacturing glass substrate
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2026-01-29
- Publication Date
- 2026-08-13
Smart Images
Figure JP2026003058_13082026_PF_FP_ABST
Abstract
Description
Glass substrate and method for manufacturing a glass substrate
[0001] This disclosure relates to a glass substrate and a method for manufacturing a glass substrate.
[0002] In recent years, development has progressed on semiconductor stacking devices known as 2.5D devices and 3D devices, which use substrates with through-electrodes called interposers to mount and interconnect multiple semiconductor chips. Silicon, glass, organic materials, and ceramics are being considered as substrate materials. Among these, glass excels in flatness, thermal stability, and electrical insulation.
[0003] Patent Document 1 discloses a technique for forming through holes in a glass substrate. This technique includes the steps of forming a modified area in the glass substrate by irradiating it with a laser beam at the location where the through holes are to be formed, and then immersing the glass substrate in an etching solution after the first step to form the through holes. The through holes are formed by selectively etching the modified area.
[0004] Patent Document 2 discloses a technique for forming a concave cavity on the surface of a substrate. A laser beam is irradiated onto the substrate to form multiple filament-like damaged areas, and then the substrate is exposed to an etching medium to expand and combine the multiple filament-like damaged areas, thereby forming a single cavity.
[0005] Japanese Patent Publication No. 2023-082984 Japanese Patent Publication No. 2019-214507
[0006] A technique is being investigated for forming a concave cavity on the first main surface of a glass substrate. The cavity has a bottom surface and side surfaces. For example, a semiconductor chip is provided on the bottom surface. The side surfaces have tapered surfaces at their boundary with the bottom surface. The tapered surfaces incline inward from the opening edge of the cavity when viewed from a direction perpendicular to the first main surface, as the depth from the first main surface increases.
[0007] As a technique for forming a concave cavity on the first main surface of a glass substrate, it is conceivable to perform wet etching of the glass substrate after applying a mask to the first main surface of the glass substrate. In this case, the slope of the side surface becomes gentle, and the bottom area of the cavity becomes smaller than the opening area.
[0008] One embodiment of the present disclosure provides a technique capable of improving the ratio of the bottom area to the opening area of the cavity.
[0009] The glass substrate according to one embodiment of the present disclosure has a first main surface and a second main surface opposite to the first main surface, and has a concave cavity on the first main surface. The cavity has a bottom surface and side surfaces. When the depth from the first main surface to the center of the bottom surface is b, the side surfaces are portions where the depth from the first main surface is 0.9b or less. The side surfaces have tapered surfaces at the boundaries with the bottom surface. The tapered surfaces are inclined inward of the opening edge of the cavity when viewed from a direction perpendicular to the first main surface as the depth from the first main surface increases. The ratio (a / b) of the width (a) of the side surfaces to the depth (b) has an average value greater than 0 and not more than 1.0, and 3σ (σ is the standard deviation) / average value is greater than 0 and not more than 1.0. The width (a) of the side surfaces is the distance between the opening edge of the cavity and the peripheral edge of the bottom surface when viewed from a direction perpendicular to the first main surface.
[0010] A method for manufacturing a glass substrate according to an embodiment of the present disclosure has a first main surface and a second main surface opposite to the first main surface, and has a concave cavity on the first main surface. The cavity has a bottom surface and a side surface. When the depth from the first main surface to the center of the bottom surface is b, the side surface is a portion where the depth from the first main surface is 0.9b or less. The side surface has a tapered surface at the boundary with the bottom surface. The tapered surface is inclined inward of the opening edge of the cavity as viewed from a direction perpendicular to the first main surface as the depth from the first main surface increases. The method for manufacturing a glass substrate includes forming a plurality of modified portions by irradiating a laser beam at a position where the cavity of the glass substrate is to be formed, selectively etching the modified portions to form a plurality of bottomed holes, and expanding and connecting the plurality of bottomed holes to obtain the cavity. By changing the length of the modified portion in a first region, which is a frame-shaped region along the opening edge of the cavity, from the length of the modified portion in a second region, which is a region inside the first region, the ratio (a / b) of the width (a) of the side surface to the depth (b) is such that the average value is greater than 0 and not more than 1.0, and 3σ (σ is the standard deviation) / average value is greater than 0 and not more than 1.0. The width (a) of the side surface is the distance between the opening edge of the cavity and the peripheral edge of the bottom surface as viewed from a direction perpendicular to the first main surface.
[0011] According to an embodiment of the present disclosure, the ratio of the bottom area to the opening area of the cavity can be improved.
[0012] FIG. 1A is a cross-sectional view showing an example of a glass substrate. FIG. 1B is a cross-sectional view showing another example of a glass substrate. FIG. 2 is a plan view showing an example of a measurement location of the shape of the cavity. FIG. 3A is a diagram showing an example of the depth distribution. FIG. 3B is a diagram showing an example of the inclination distribution calculated based on FIG. 3A. FIG. 3C is a diagram showing the moving average distribution of the inclination in FIG. 3B. FIG. 4 is a micrograph showing an example of the inclination (θ) of the side surface at the boundary between the side surface and the bottom surface. FIG. 5 is a flowchart showing an example of the method for manufacturing a glass substrate. FIG. 6 is a cross-sectional view showing an example of step S101. FIG. 7A is a micrograph of the glass substrate according to Example 1. FIG. 7B is a micrograph of the glass substrate according to Example 2.
[0013] The embodiments for implementing this disclosure will be described below with reference to the drawings. In each drawing, identical or similar components will be denoted by the same reference numeral, and their descriptions may be omitted. In the specification, the "~" indicating a numerical range means that the numbers written before and after it are included as the lower and upper limits. The numerical range includes the rounded range.
[0014] An example of a glass substrate will be described with reference to Figures 1A and 1B. The glass substrate may be used, for example, as glass for semiconductor components. However, the glass substrate is not limited to glass for semiconductor components, and may be used for other applications such as glass for electronic components or glass for optical components. The glass substrate 10 has a first main surface 11 and a second main surface 12 facing the opposite direction from the first main surface 11, and has a concave cavity 13 on the first main surface 11. Although not shown, multiple cavities 13 may be formed on the first main surface 11. Also, although not shown, cavities 13 may be formed not only on the first main surface 11 but also on the second main surface 12.
[0015] The cavity 13 has a bottom surface 13a and a side surface 13b. A semiconductor chip (not shown) may be provided on the bottom surface 13a. Since semiconductor chips are generally rectangular in shape, the bottom surface 13a may also be rectangular. A through hole (not shown) may also be formed in the bottom surface 13a. The through hole penetrates from the bottom surface 13a to the second main surface 12. A through electrode is formed in the through hole. The through electrode electrically connects the semiconductor chip provided on the bottom surface 13a to the wiring formed on the second main surface 12.
[0016] Furthermore, the through-holes and thus the through-electrodes do not necessarily have to be formed on the bottom surface 13a. It is also possible to electrically connect a semiconductor chip provided on the bottom surface 13a to wiring formed on the first main surface 11. In addition, the through-holes may be formed outside the cavity 13 and may penetrate from the first main surface 11 to the second main surface 12. A glass substrate 10 having through-holes can be used, for example, as a glass core substrate.
[0017] If the depth from the first main surface 11 to the center of the bottom surface 13a is b, then the side surface 13b is the portion whose depth from the first main surface 11 is 0.9b or less. The side surface 13b has a tapered surface 13b1 at its boundary with the bottom surface 13a. The tapered surface 13b1 rounds the corner between the side surface 13b and the bottom surface 13a, suppressing stress concentration at that corner.
[0018] The tapered surface 13b1 inclines inward from the opening edge 13c of the cavity 13 as its depth from the first main surface 11 increases, when viewed from a direction perpendicular to the first main surface 11. The tapered surface 13b1 may be straight in cross-sectional view as shown in Figure 1A, or curved in cross-sectional view as shown in Figure 1B. The opening edge 13c is the boundary line between the first main surface 11 and the side surface 13b.
[0019] As shown in Figures 1A and 1B, the width of the side surface 13b is denoted as a. The width of the side surface 13b is the distance between the opening edge 13c of the cavity 13 and the periphery of the bottom surface 13a when viewed from a direction perpendicular to the first main surface 11.
[0020] An example of measuring the shape of the cavity 13 will be described with reference to Figures 2 and 3A to 3C. As shown in Figure 2, the opening edge 13c of the cavity 13 may be rectangular when viewed from a direction perpendicular to the first main surface 11. The opening edge 13c has a pair of first sides 13c1 and a pair of second sides 13c2 perpendicular to the pair of first sides 13c1. The length of the first sides 13c1 is longer than the length of the second sides 13c2, but may be equal to the length of the second sides 13c2. The length of the first sides 13c1 should be greater than or equal to the length of the second sides 13c2.
[0021] In this specification, a rectangle includes a shape with chamfered corners. When the corners of a rectangle are chamfered, the length of the first side 13c1 is the length of the first side 13c1 when the first side 13c1 and the second side 13c2 are extended so that the first side 13c1 and the second side 13c2 intersect perpendicularly. Also, when the corners of a rectangle are chamfered, the length of the second side 13c2 is the length of the second side 13c2 when the first side 13c1 and the second side 13c2 are extended so that the first side 13c1 and the second side 13c2 intersect perpendicularly.
[0022] The ratio (a / b) is measured on the straight line L1 shown in Figure 2. Straight line L1 is set on the first main surface 11, and five lines are set perpendicular to the first side 13c1 in the remaining 80% range R1, excluding the range where the distance from both ends of the first side 13c1 is less than 10% of the length of the first side. The ratio (a / b) is measured at two points on each straight line L1 where the straight line L1 intersects with a pair of first sides 13c1, for a total of 10 points of measurement. The specific measurement method will be explained below.
[0023] First, cut pieces are prepared by cutting along a straight line L1. The cut pieces are obtained by cutting the glass substrate perpendicular to the first main surface 11. The obtained cut pieces are observed with an optical microscope, and the depth from the first main surface 11 is measured at each point along the straight line L1, as shown in Figure 3A. The depth from the first main surface 11 is the depth from a plane that approximates the first main surface 11 using the least squares method. The inclination of the plane is corrected in advance so that the plane is horizontal.
[0024] Next, as shown in Figure 3B, the slope between two adjacent points is calculated. The distance between two adjacent points along the straight line L1 is 0.5 μm. Subsequently, the slope shown in Figure 3B is smoothed using the moving average method to obtain the moving average of the slopes shown in Figure 3C. The moving average of the slopes is a simple, unweighted average of the four most recent slopes. When there are six consecutive points where the absolute value of the moving average of the slopes is 1 or greater, the point P1 furthest from the center of the base surface 13a is defined as the boundary between the first main surface 11 and the side surface 13b. Point P1 is shown in Figure 3A.
[0025] Next, the average depth from the first main surface 11 in the remaining 50% of the range R2, excluding the range where the distance from both ends of the second side 13c2 shown in Figure 2 is less than 25% of the length of the second side 13c2, is defined as the depth (b) from the first main surface 11 to the center of the bottom surface 13a. Among the points where the depth from the first main surface 11 is 0.9b, the point P2 furthest from the center of the bottom surface 13a is defined as the boundary between the bottom surface 13a and the side surface 13b. Point P2 is shown in Figure 3A.
[0026] The ratio (a / b) is such that the mean value is greater than 0 and less than or equal to 1.0, and 3σ (σ is the standard deviation) / mean value is greater than 0 and less than or equal to 1.0. If the mean value of the ratio (a / b) is 1.0 or less, the ratio of the base area to the aperture area is large. The aperture area is the area enclosed by the aperture edge 13c. The base area is the area of the base surface 13a. The base area is set to be larger than the contact area of the semiconductor chip.
[0027] Table 1 shows the relationship between the average ratio (a / b), the opening area, and the base area when the length of the first side 13c1 is 6 mm and the length of the second side 13c2 is 3 mm. Table 2 shows the relationship between the average ratio (a / b), the opening area, and the base area when the length of the first side 13c1 is 0.5 mm and the length of the second side 13c2 is 0.3 mm. In Tables 1 and 2, b is 100 μm.
[0028]
[0029]
[0030] From Tables 1 and 2, it can be seen that the larger the average value of the ratio (a / b), the smaller the ratio of the base area to the opening area. Also, as shown in Table 2, when the opening area is small, if the average value of the ratio (a / b) exceeds 1.0, the ratio of the base area to the opening area becomes zero, or in other words, the base area becomes zero.
[0031] The average value of the ratio (a / b) is preferably 1.0 or less. From the viewpoint of improving the ratio of the bottom area to the opening area, the smaller the average value of the ratio (a / b), the more preferable it is to be 0.8 or less, even more preferably 0.6 or less, and particularly preferably 0.5 or less.
[0032] However, from the viewpoint of improving durability against impact, a larger average value of the ratio (a / b) is preferable. The larger the average value of the ratio (a / b), the more effectively stress concentration at the boundary between the side surface 13b and the bottom surface 13a can be suppressed. The average value of the ratio (a / b) is preferably 0.01 or higher, more preferably 0.05 or higher, and even more preferably 0.1 or higher.
[0033] The 3σ / mean value of the ratio (a / b) is preferably greater than 0 and 1.0 or less. If the 3σ / mean value of the ratio (a / b) is 1.0 or less, the variation in the ratio (a / b) is small, the semiconductor chip fits easily into the cavity 13, and the margin can be kept small. The 3σ / mean value of the ratio (a / b) is more preferably 0.8 or less, more preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.3 or less.
[0034] As shown in Figure 4, it is preferable that the inclination (θ) of the side surface 13b with respect to the first main surface 11 at the boundary between the side surface 13b and the bottom surface 13a is 25° or more and less than 90°. If the inclination (θ) is 25° or more, the rise of the side surface 13b is steep, so the ratio of the bottom area to the opening area is large.
[0035] From the viewpoint of improving the ratio of the base area to the opening area, a larger inclination (θ) is preferable, preferably 25° or more, more preferably 30° or more, and even more preferably 35° or more.
[0036] However, from the viewpoint of improving durability against impact, a smaller inclination (θ) is preferable. The smaller the inclination (θ), the more effectively stress concentration at the boundary between the side surface 13b and the bottom surface 13a can be suppressed. The inclination (θ) is preferably 85° or less, more preferably 80° or less, more preferably 75° or less, and even more preferably 70° or less.
[0037] The arithmetic mean roughness Ra of the base surface 13a is preferably between 1 nm and 8 μm, with a mean value of 3σ (σ is the standard deviation) / mean value greater than 0 and less than 1.5. The maximum height roughness Rz of the base surface 13a is preferably between 1 μm and 30 μm, with a mean value of 3σ (σ is the standard deviation) / mean value greater than 0 and less than 1.5. Ra and Rz were measured using a Keyence VK-X1000 with a reference length of 100 μm. Ra and Rz are measured on each straight line L1 shown in Figure 2. If Ra and Rz are within the above range, the surface roughness of the base surface 13a is small, and the tilt of the semiconductor chip can be suppressed.
[0038] From the viewpoint of suppressing the tilt of the semiconductor chip, the average value of Ra is preferably small, preferably 8 μm or less, more preferably 5 μm or less, more preferably 3 μm or less, more preferably 1 μm or less, and even more preferably 0.5 μm or less. Furthermore, from the viewpoint of improving adhesion with the adhesive when placing the semiconductor chip, a larger Ra is preferable, preferably 1 nm or more, more preferably 0.05 μm or more, and even more preferably 0.1 μm or more. Furthermore, the 3σ / average value of Ra is preferably small, preferably less than 1.5, preferably 1.0 or less, even more preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.5 or less.
[0039] From the viewpoint of suppressing the tilt of the semiconductor chip, the average value of Rz is preferably as small as possible, preferably 30 μm or less, more preferably 25 μm or less, more preferably 20 μm or less, more preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. Also, from the viewpoint of improving adhesion with the adhesive when placing the semiconductor chip, a larger Rz is preferable, preferably 1 μm or more, more preferably 2 μm or more, and even more preferably 3 μm or more. Furthermore, the 3σ / average value of Rz is preferably as small as possible, preferably less than 1.5, preferably 1.0 or less, more preferably 0.8 or less, more preferably 0.7 or less, and even more preferably 0.5 or less.
[0040] An example of a method for manufacturing the glass substrate 10 will be described with reference to Figures 5 and 6. The method for manufacturing the glass substrate 10 includes steps S101 to S103, as shown in Figure 5, for example. In addition to steps S101 to S103, the method for manufacturing the glass substrate 10 may also include other steps.
[0041] Step S101 involves preparing the glass substrate 10. The material of the glass used for the glass substrate 10 is not particularly limited, and for example, soda lime glass, aluminosilicate glass, borosilicate glass, alkali-free glass, low-alkali glass, quartz, sapphire glass, crystallized glass, etc. are used. Also, the glass may or may not contain coloring components such as Ti, Cu, etc., but preferably does not contain coloring components.
[0042] The alkali-free glass may have the following composition, for example, expressed in mol% based on oxides. <Alkali-free [1]> SiO ２ : 60 - 75, Al ２ O ３ : 0 - 10, B ２ O ３ : 0 - 10, MgO + CaO + SrO + BaO: 10 - 22, Li ２ O + Na ２ O + K ２ O: 0 - 0.1 <Alkali-free [1']> SiO ２ : 60 - 70, Al ２ O ３ : 10 - 15, B ２ O ３ : 1 - 10, MgO: 3 - 10, CaO: 3 - 10, SrO: 1 - 8, BaO: 0 - 1, MgO + CaO + SrO + BaO: 15 - 20, Li ２ O + Na ２ O + K ２ O: 0 - 0.1, or, <Alkali-free [2]> SiO ２ : 50 - 75, Al ２ O ３ : 0 - 10, B ２ O ３ : 0 - 10, MgO + CaO: 0 - 10, SrO + BaO: 10 - 35, Li ２ O + Na ２ O + K ２ O: 0 - 0.1, particularly, <Alkali-free [2']> SiO ２ : 65 - 75, Al ２ O ３ : 5 - 10, B ２ O ３ : 0 - 3, MgO + CaO: 0 - 5, SrO + BaO: 15 - 25, Li ２ O + Na２ O+K ２ O: 0 to 0.1, or <alkali-free [3]> SiO ２ : 50-75, Al ２ O ３ : 0-10, B ２ O ３ :10~25, MgO+CaO+SrO+BaO:5~15, Li ２ O + Na ２ O+K ２ O: 0-0.1
[0043] As an alkali-containing glass, for example, it may have the following composition expressed in mol% based on oxide: <Alkali-containing [1]> SiO ２ : 70-85, Al ２ O ３ : 0-5, B ２ O ３ :5~20, MgO+CaO+SrO+BaO:0~5, Li ２ O + Na ２ O+K ２ O: 1-5, or <alkali-containing [2]> SiO ２ : 55-75, Al ２ O ３ : 5-20, B ２ O ３ : 0-5, P ２ O ５ :0~5, MgO+CaO+SrO+BaO:0~10, Li ２ O + Na ２ O+K ２ O: 10-20, or <alkali-containing [3]> SiO ２ : 60-75, Al ２ O ３ : 0-5, B ２ O ３ :0~1, MgO+CaO+SrO+BaO:5~15, Li ２ O + Na ２ O+K ２ O: 10-20, or <alkali-containing [4]> SiO ２ : 60-75, Al ２ O ３ : 1-5, B ２ O ３ :5~10, MgO+CaO+SrO+BaO+ZnO:1~10, Li２ O + Na ２ O+K ２ O: 10-20
[0044] The thickness of the glass substrate 10 is not particularly limited, but is, for example, 0.2 mm to 2.0 mm before laser processing (step S102). In order to maintain the strength or dielectric properties of the semiconductor package, the thickness of the glass substrate 10 before step S102 is preferably 0.5 mm or more, more preferably 0.8 mm or more. Considering the difficulty of laser processing, the thickness of the glass substrate 10 before step S102 is preferably 1.8 mm or less.
[0045] The thickness of the glass substrate 10 after the wet etching process (step S103) is not particularly limited, but may be, for example, 0.2 mm to 2.0 mm. After step S103, the thickness of the glass substrate 10 is preferably 0.5 mm or more, more preferably 0.8 mm or more. Also, after step S103, the thickness of the glass substrate 10 is preferably 1.8 mm or less.
[0046] Step S102 involves laser processing of the glass substrate 10. Specifically, as shown in Figure 6, for example, step S102 involves forming a plurality of modified portions 15 at the location where the cavity 13 is to be formed. The modified portions 15 are parts where the structure of the glass has been altered by irradiation with a laser beam. The modified portions 15 have, for example, voids. The portion of the glass substrate 10 excluding the modified portions 15 is called the unmodified portion 16.
[0047] The modified portion 15 is formed linearly from the first main surface 11 of the glass substrate 10 to a desired depth. The length of each modified portion 15 is shorter than the thickness of the glass substrate 10. Each modified portion 15 is selectively etched in step S103, described later, to become a blind hole. By expanding and connecting multiple blind holes, a cavity 13 is obtained.
[0048] The above ratio (a / b) can be adjusted by changing the length of the modified portion 15 in the first region A1 compared to the length of the modified portion 15 in the second region A2, as shown in Figure 6. The first region A1 is a frame-shaped region along the opening edge 13c of the cavity 13. The second region A2 is a region inside the first region A1. In this embodiment, the length of the modified portion 15 in the first region A1 is shorter than the length of the modified portion 15 in the second region A2, but it may be longer.
[0049] Although not shown in the diagram, the modified portion 15 is also formed at the location where the through hole is to be formed. When forming a through hole that penetrates from the first main surface 11 to the second main surface 12 of the glass substrate 10, the modified portion 15 can be formed linearly from the first main surface 11 to the second main surface 12 of the glass substrate 10. The length of the modified portion 15 is approximately the same as the thickness of the glass substrate 10.
[0050] The laser beam is preferably highly transparent to the glass substrate 10. The laser beam may be transmitted from the first main surface 11 to the second main surface 12, or from the second main surface 12 to the first main surface 11. The wavelength of the laser beam is preferably 300 nm to 1100 nm.
[0051] The modified portion 15 is more easily formed when the pulse width of the laser beam is preferably 1 nsec or less, more preferably 500 psec or less, and even more preferably 100 psec or less. On the other hand, the pulse width of the laser beam is preferably 1 psec or more.
[0052] Preferably, the laser beam is focused by a focusing lens and has a linearly focused region (focused line) extending from the first main surface 11 of the glass substrate 10 to a desired depth. The optical system that produces such a focused line preferably includes a lens with spherical aberration or an axicon lens.
[0053] Step S103 involves performing wet etching of the glass substrate 10. Specifically, step S103 involves supplying an etching solution to the glass substrate 10. For example, step S103 includes immersing the glass substrate 10 in the etching solution or spraying the etching solution onto the glass substrate 10.
[0054] The surface to which the etching solution is supplied includes at least the first main surface 11, and may also include the second main surface 12. When forming through holes as well as cavities 13, it is preferable that the surface to which the etching solution is supplied includes both the first main surface 11 and the second main surface 12.
[0055] The etching solution selectively etches the modified portion 15 of the glass substrate 10, forming a blind hole. Subsequently, the etching solution uniformly etches the unmodified portion 16 of the glass substrate 10, expanding and connecting the multiple blind holes. By expanding and connecting the multiple blind holes, a cavity 13 is obtained.
[0056] The etching solution is not particularly limited, but for example, an aqueous solution containing hydrofluoric acid is selected. The etching solution may contain only hydrofluoric acid as the acid, or it may contain hydrofluoric acid in addition to at least one of hydrochloric acid and nitric acid. The etching solution may contain hydrochloric acid in addition to at least one of nitric acid, from the viewpoint of dissolving the salt generated during etching and suppressing the phenomenon of sludge (residue) accumulating inside the bottomed holes.
[0057] From the viewpoint of ensuring sufficient etching, the concentration of hydrogen fluoride in the etching solution is preferably 0.1 wt% or more relative to the total amount of the etching solution. On the other hand, the concentration of hydrogen fluoride is preferably 5.0 wt% or less, and more preferably 10 wt% or less, relative to the total amount of the etching solution.
[0058] When the etching solution contains hydrochloric acid in addition to hydrofluoric acid, the concentration of hydrogen chloride is preferably 0.5 wt% or more, more preferably 1 wt% or more, relative to the total etching solution, from the viewpoint of significantly exhibiting the salt-dissolving effect. On the other hand, from the viewpoint of maintaining the removal speed of the modified portion 15 by hydrofluoric acid, the concentration of hydrogen chloride is preferably 30 wt% or less, more preferably 15 wt% or less, relative to the total etching solution.
[0059] When the etching solution contains nitric acid in addition to hydrofluoric acid, the concentration of nitric acid is preferably 0.5 wt% or more, more preferably 1 wt% or more, relative to the total etching solution, from the viewpoint of significantly exhibiting the effect of dissolving salts. On the other hand, from the viewpoint of maintaining the removal speed of the modified parts by hydrofluoric acid, the concentration of nitric acid is preferably 35 wt% or less, more preferably 15 wt% or less, relative to the total etching solution.
[0060] The etching solution may be an aqueous solution containing an alkali. The etching solution may contain, for example, NaOH, KOH, LiOH, or TMAH (tetramethylammonium hydroxide) as the alkali. The etching solution may also contain, but is not limited to, EDTA (ethylenediaminetetraacetic acid), HEDP (1-hydroxyethane-1,1-diphosphonic acid), NTA (nitrilotriacetic acid), or DTPA (diethylenetriaminepentaacetic acid) as chelating agents.
[0061] The experimental data is described below. Example 1-1 below is an example, and Example 1-2 below is a comparative example.
[0062] In Example 1-1, steps S101 to S103 shown in Figure 5 were performed. In step S101, a glass substrate made of alkali-free glass was prepared. In step S102, a laser beam with a wavelength of 532 nm, a pulse width of 10 ps, and an output of 30 W was irradiated to form a modified area. In step S103, an aqueous solution containing 10% by mass of NaOH and 7% by mass of EDTA (V1: 0.07 μm / min, temperature: 90°C) was used as the etching solution. In step S103, the entire glass substrate was immersed in the above aqueous solution. Figure 7A shows an optical microscope image of the cross-section of the glass substrate obtained in Example 1. The ratio (a / b) of the glass substrates obtained in Example 1 was 0.59 on average, and 3σ / average was 0.38.
[0063] In Example 1-2, instead of step S102, an etching mask was applied to the first main surface of the glass substrate, and wet etching with hydrofluoric acid was performed. All of steps S101 to S103 shown in Figure 5 were performed. Figure 7B shows an optical microscope image of the cross-section of the glass substrate obtained in Example 2. The ratio (a / b) of the glass substrates obtained in Example 2 was greater than 1.0 on average, and 3σ / average was 0.177. Thus, with the conventional processing method, although the variation is small, the ratio (a / b) is large.
[0064] Furthermore, the following experimental data will also be explained. Examples 2-1 to 2-4 below are examples. Table 3 shows the laser processing pitch, laser output, cavity depth, average value of arithmetic mean roughness Ra, standard deviation σ and 3σ / average value, and average value of maximum height roughness Rz for Examples 2-1 to 2-4.
[0065] In Example 2-1, steps S101 to S103 shown in Figure 5 were performed. In step S102, a laser beam with a wavelength of 532 nm, a pulse width of 30 ps, and an output of 0.45 W was irradiated to form a modified area. The processing pitch was 10 μm. In step S103, an aqueous solution containing 10% by mass of NaOH and 7% by mass of EDTA (V1: 0.07 μm / min, temperature: 90°C) was used as the etching solution. The etching amount was 65 μm. In step S103, the entire glass substrate was immersed in the above aqueous solution. The cross-section of the glass substrate obtained in Example 2-1 was measured by optical microscope photography, and the bottom surface of the recess was measured by laser microscope. The measurement conditions were as follows: for the optical microscope, transmitted illumination was used with an Evident MX63, and observation was performed at a magnification of 5x. Using a laser microscope, the arithmetic mean roughness Ra and maximum height roughness Rz were measured with a reference length of 100 μm using a Keyence VK-X1000. The optical microscope image was 1024 × 768 pixels, the measurement area was 285 μm × 214 μm, ΔX was 278 nm / pixel, and line roughness was measured at 10 locations within the measurement area. The depth of the bottom surface obtained in Example 2-1 was 99.1 μm. The average value of Ra was 0.70 μm, the σ of Ra was 0.18 μm, and the 3σ / average value of Ra was 0.75. The average value of Rz was 3.54 μm, the σ of Rz was 0.90 μm, and the 3σ / average value of Rz was 0.76.
[0066] In Example 2-2, the process was the same as in Example 2-1, except that the machining pitch in step S102 was 15 μm. The depth of the bottom surface obtained in Example 2-2 was 84.2 μm. The average value of Ra was 0.82 μm, the σ of Ra was 0.21 μm, and the 3σ / average value of Ra was 0.77. The average value of Rz was 4.05 μm, the σ of Rz was 0.71 μm, and the 3σ / average value of Rz was 0.52.
[0067] In Example 2-3, the process was the same as in Example 2-1, except that the machining pitch in step S102 was 20 μm. The depth of the bottom surface obtained in Example 2-3 was 84.4 μm. The average value of Ra was 1.00 μm, the σ of Ra was 0.35 μm, and the 3σ / average value of Ra was 1.05. The average value of Rz was 4.91 μm, the σ of Rz was 1.50 μm, and the 3σ / average value of Rz was 0.92.
[0068] In Example 2-4, the process was the same as in Example 2-1, except that the processing pitch in step S102 was 20 μm and the laser output was 0.75 W. The depth of the bottom surface obtained in Example 2-4 was 64.7 μm. The average value of Ra was 0.75 μm, the σ of Ra was 0.30 μm, and the 3σ / average value of Ra was 1.23. The average value of Rz was 3.75 μm, the σ of Rz was 1.35 μm, and the 3σ / average value of Rz was 1.08.
[0069]
[0070] When comparing lasers with the same output power, the average Ra value increases as the laser processing pitch increases. A processing pitch of 55 μm or less is preferable.
[0071] The glass substrate relating to this disclosure has been described above, but this disclosure is not limited to the embodiments described above. Various changes, modifications, substitutions, additions, deletions, and combinations are possible within the scope of the claims. These also naturally fall within the technical scope of this disclosure.
[0072] This application claims priority based on Japanese Patent Application No. 2025-019982, filed on 10 February 2025, and Japanese Patent Application No. 2025-185308, filed on 4 November 2025, and incorporates all of their disclosures herein.
[0073] 10 Glass substrate 11 First main surface 12 Second main surface 13 Cavity 13a Bottom surface 13b Side surface 13b1 Tapered surface
Claims
1. A glass substrate having a first main surface and a second main surface facing the opposite direction to the first main surface, and having a concave cavity in the first main surface, wherein the cavity has a bottom surface and a side surface, and if the depth from the first main surface to the center of the bottom surface is b, the side surface is a portion with a depth of 0.9b or less from the first main surface, the side surface has a tapered surface at its boundary with the bottom surface, the tapered surface inclined inward from the opening edge of the cavity when viewed from a direction perpendicular to the first main surface as the depth from the first main surface increases, the ratio (a / b) of the width (a) of the side surface to the depth (b) is greater than 0 and 1.0 or less on average, and 3σ (σ is the standard deviation) / average is greater than 0 and 1.0 or less, and the width (a) of the side surface is the distance between the opening edge of the cavity and the periphery of the bottom surface when viewed from a direction perpendicular to the first main surface.
2. The glass substrate according to claim 1, wherein at the boundary between the side surface and the bottom surface, the inclination (θ) of the side surface with respect to the first main surface is 25° or more and less than 90°.
3. The glass substrate according to claim 1 or 2, wherein the arithmetic mean roughness Ra of the bottom surface has an average value of 1 nm or more and 8 μm or less, and 3σ (σ is the standard deviation) / average value is greater than 0 and less than 1.5, and the maximum height roughness Rz of the bottom surface has an average value of 1 μm or more and 30 μm or less, and 3σ (σ is the standard deviation) / average value is greater than 0 and less than 1.
5.
4. The glass substrate according to claim 1 or 2, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is 0.01 or more and 0.8 or less on average.
5. The glass substrate according to claim 1 or 2, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is 0.05 or more and 0.6 or less on average.
6. The glass substrate according to claim 1 or 2, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is greater than 0 and less than or equal to 0.8 in terms of 3σ (where σ is the standard deviation) / mean value.
7. A method for manufacturing a glass substrate having a first main surface and a second main surface facing the opposite direction to the first main surface, the first main surface having a concave cavity, the cavity having a bottom surface and a side surface, where the depth from the first main surface to the center of the bottom surface is b, the side surface is a portion with a depth of 0.9b or less from the first main surface, the side surface has a tapered surface at the boundary with the bottom surface, and the tapered surface is inclined inward from the opening edge of the cavity when viewed from a direction perpendicular to the first main surface as the depth from the first main surface increases, comprising: forming a plurality of modified portions by irradiating the glass substrate at a position where the cavity is to be formed with a laser beam; selectively etching the modified portions to form a plurality of bottomed holes, and expanding and connecting the plurality of bottomed holes to obtain the cavity, A method for manufacturing a glass substrate, wherein the length of the modified portion in the first region, which is a frame-shaped region along the opening edge of the cavity, is different from the length of the modified portion in the second region, which is a region inside the first region, so that the ratio (a / b) of the width (a) of the side surface to the depth (b) is greater than 0 and 1.0 or less on average, and 3σ (σ is the standard deviation) / average value is greater than 0 and 1.0 or less, and the width (a) of the side surface is the distance between the opening edge of the cavity and the periphery of the bottom surface when viewed from a direction perpendicular to the first main surface.
8. The method for manufacturing a glass substrate according to claim 7, wherein the inclination (θ) of the side surface with respect to the first main surface at the boundary between the side surface and the bottom surface is 25° or more and less than 90°.
9. The method for manufacturing a glass substrate according to claim 7 or 8, wherein the arithmetic mean roughness Ra of the bottom surface is such that the average value is 1 nm or more and 8 μm or less, and 3σ (σ is the standard deviation) / average value is greater than 0 and less than 1.5, and the maximum height roughness Rz of the bottom surface is such that the average value is 1 μm or more and 30 μm or less, and 3σ (σ is the standard deviation) / average value is greater than 0 and less than 1.
5.
10. The method for manufacturing a glass substrate according to claim 7 or 8, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is 0.01 or more and 0.8 or less on average.
11. The method for manufacturing a glass substrate according to claim 7 or 8, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is 0.05 or more and 0.6 or less on average.
12. The method for manufacturing a glass substrate according to claim 7 or 8, wherein the ratio (a / b) of the width of the side surface (a) to the depth (b) is such that 3σ (σ is the standard deviation) / mean value is greater than 0 and 0.8 or less.