US20180340262A1 - Method for producing glass with fine structure

Info

Abstract

Description

Claims

US20180340262A1

Publication number: US20180340262A1
Application number: US15/755,855
Authority: US
Inventors: Yuji Hiranuma
Original assignee: Nippon Sheet Glass Co Ltd
Current assignee: Nippon Sheet Glass Co Ltd
Priority date: 2015-08-31
Filing date: 2016-08-29
Publication date: 2018-11-29
Also published as: WO2017038075A1; JPWO2017038075A1; TW201722881A; CN107922254A; TWI712568B; KR20180048891A

The present invention provides a method for producing a glass with a fine structure, the method being capable of avoiding forming a hole with a shallow wall angle and capable of producing a glass with a fine structure such as a deep hole or groove extending with high straightness in the thickness direction of a substrate. The present invention relates to a method for producing a glass with a fine structure, the method including an etching step of etching a glass by irradiating the glass with an ultrasonic wave, wherein: an etchant used in the etching step includes hydrofluoric acid, at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid, and a surfactant; and in the etchant, a concentration of the hydrofluoric acid is 0.05 mass % to 8.0 mass %, a concentration of the inorganic acid is 2.0 mass % to 16.0 mass %, and a content of the surfactant is 5 ppm to 1000 ppm.

TECHNICAL FIELD

The present invention relates to a method for producing a glass with a fine structure such as a through hole, blind hole, or groove by using a laser pulse. The present invention more particularly relates to a method for producing a glass with the fine structure by irradiating a glass substrate or the like with a laser to form a modified portion or a processing hole in the glass substrate and subjecting the modified portion or the processing hole to a removal process using ultrasonically-assisted etching.

BACKGROUND ART

A method for forming desired holes or grooves in a glass substrate by forming modified portions or minute processing holes in the glass substrate and etching the glass substrate is disclosed, for example, in Patent Literature 1. In this method, a glass substrate is irradiated with laser pulses to form modified portions, and holes or grooves are formed in the glass substrate by etching with an etchant that etches the modified portions at an etching rate (also referred to as “etching speed” hereinafter) higher than an etching rate at which the etchant etches the glass substrate. Patent Literature 2 discloses a method for processing a substrate by modifying some portions of the substrate, irradiating the portions with a laser to form minute processing holes, and then performing etching. That is, as shown in FIG. 1, a glass substrate 11 having modified portions or minute processing holes formed therein is etched to form desired holes.
When, for example, a glass substrate or the like having through holes formed therein is used as an electronic substrate such as an interposer, it is desirable, for example, that the through holes should have high straightness, in view of the subsequent step such as an electrode formation step and in order to obtain a stable current.
However, with conventional techniques as disclosed in Patent Literatures 1 and 2, holes formed by etching may have a shallow wall angle and fail to have a sufficient depth. The etching rate of the base glass material used is not zero, since the fine modified portions or processing holes need to be widen by etching to obtain a desired shape. Additionally, the etchant has difficulty entering the interior of the fine modified portions or processing holes. Thus, the etching proceeds more readily at a smaller depth from the substrate surface and becomes slower at a greater depth in the substrate, even if a rod-, plate-, or propeller-shaped stirrer is rotated in the etchant-containing bath or the etchant is stirred by bubbling. When the etching rate of the modified portions is higher than that of the rest of the substrate, the entry of the etchant or the replacement of the etchant is not a very important factor in forming holes having a steep wall angle and high straightness. However, when the glass substrate used has such properties that the difference in etching rate between modified portions and the rest of the substrate is small, etching of the rest of the substrate significantly proceeds around the modified portions in the vicinity of the substrate surface before the modified portions are etched deep into the substrate. Thus, a smaller difference in etching rate may cause the modified portions to have a shallower wall angle in the vicinity of the substrate surface as shown in FIG. 2.

CITATION LIST

Patent Literature

Patent Literature 1: JP 2011-37707 A
Patent Literature 2: JP 2001-105398 A

SUMMARY OF INVENTION

Technical Problem

The present invention has been made in view of the above problem, and an object of the present invention is to provide a method for producing a glass with a fine structure with the aid of a laser pulse, the method being capable of avoiding forming a hole with a shallow wall angle as the fine structure and capable of producing a glass having a fine structure such as a deep hole or groove extending with high straightness in the thickness direction of a glass substrate. More particularly, an object of the present invention is to provide a method for producing a glass with a fine structure with the aid of a laser pulse, the method being capable of avoiding forming a hole with a shallow wall angle as the fine structure and capable of producing a glass having as the fine structure a through hole extending with high straightness in the thickness direction of a substrate. The present invention also aims to provide an industrially advantageous method for producing a glass with a fine structure with the aid of a laser pulse.

Solution to Problem

The present invention provides a method for producing a glass with a fine structure, the method including an etching step of etching a glass by irradiating the glass with an ultrasonic wave, wherein
an etchant used in the etching step includes:
hydrofluoric acid;
at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid; and
a surfactant, and
in the etchant, a concentration of the hydrofluoric acid is 0.05 mass % to 8.0 mass %, a concentration of the inorganic acid is 2.0 mass % to 16.0 mass %, and a content of the surfactant is 5 ppm to 1000 ppm.

Advantageous Effects of Invention

With the use of the method for producing a glass with a fine structure according to the present invention, it is possible to avoid forming a hole with a shallow wall angle and produce a glass having a fine structure such as a deep hole or groove extending with high straightness in the thickness direction of a substrate. More particularly, the present invention provides a method for producing a glass with a fine structure with the aid of a laser pulse, the method being capable of avoiding forming a hole with a shallow wall angle as the fine structure and capable of producing a glass having as the fine structure a through hole extending with high straightness in the thickness direction of a substrate. The present invention also aims to provide an industrially advantageous method for producing a glass with a fine structure with the aid of a laser pulse.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating a conventional method for etching a glass substrate.

FIG. 2 is a schematic cross-sectional view illustrating a conventional method for etching a glass substrate, particularly for the case where the difference in etching rate between modified portions and the glass substrate is small.

FIG. 3 is a schematic cross-sectional view illustrating a step of forming modified portions according to Example 1.

FIG. 4 is a schematic cross-sectional view showing a glass substrate according to Example 1 to illustrate how to evaluate holes after etching.

FIG. 5 is a cross-sectional image of a glass substrate according to Example 1 as observed after etching.

FIG. 6 is a cross-sectional image of a glass substrate according to Comparative Example 1 as observed after etching.

FIG. 7 is a cross-sectional image of a glass substrate according to Example 12 as observed after etching.

FIG. 8 is an image of a glass substrate according to Example 14 as observed after formation of modified portions or processing holes and before etching.

FIG. 9 is a cross-sectional image of a glass substrate according to Example 14 as observed after etching.

DESCRIPTION OF EMBODIMENTS

The method for producing a glass with a fine structure according to the present invention includes an etching step of etching a glass by irradiating the glass with an ultrasonic wave, the method being characterized in that: an etchant used in the etching step includes hydrofluoric acid, at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid, and a surfactant; and in the etchant, the concentration of the hydrofluoric acid is 0.05 mass % to 8.0 mass %, the concentration of the inorganic acid is 2.0 mass % to 16.0 mass %, and the content (mass concentration) of the surfactant is 5 ppm to 1000 ppm.
The method for producing a glass with a fine structure according to the present invention preferably includes, prior to the etching step, a step of irradiating a glass with a laser pulse to form a modified portion or a processing hole. That is, the glass to be subjected to the etching step preferably has a modified portion or processing hole formed before the etching step.
The step of forming a modified portion or processing hole in a glass (this step may hereinafter be referred to as “modified portion formation step”) will be described prior to the detailed explanation of the etching process. In forming a fine structure such as a through hole in a glass, a method described in JP 2008-156200 A can be employed as a step (method) of forming a modified portion to be removed by the subsequent etching. Specifically, a laser pulse having a wavelength λ is focused by a lens, and an area of a glass is irradiated with the focused laser pulse to form a modified portion or processing hole in the area irradiated with the laser pulse.
The glass used in the present invention (this glass may hereinafter be referred to as “glass for laser processing”) is suitably a quartz glass, borosilicate glass, aluminosilicate glass, soda-lime glass, or titanium-containing silicate glass. An alkali-free glass classified as any one of the above glasses and substantially free of alkali components (alkali metal oxides), or a low-alkali glass classified as any one of the above glasses and containing only a slight amount of alkali components, is also suitable as the glass for laser processing.
To effectively increase the absorption coefficient of the glass, the glass may contain, as a coloring component, at least one oxide of a metal selected from Bi, W, Mo, Ce, Co, Fe, Mn, Cr, V, and Cu.
Examples of the borosilicate glass include #7059 glass (composition in mass %: 49% SiO₂, 10% Al₂O₃, 15% B₂O₃, 25% RD (alkaline-earth metal oxides)) and Pyrex (registered trademark) (glass code 7740) which are available from Corning Incorporated.
A preferred embodiment (Embodiment 1) of the aluminosilicate glass is a glass composition having the following composition in mass %:
50 to 70% SiO₂;
14 to 28% Al₂O₃;
1 to 5% Na₂O;
1 to 13% MgO; and
0 to 14% ZnO.
Another preferred embodiment (Embodiment 2) of the aluminosilicate glass is a glass composition having the following composition in mass %:
56 to 70% SiO₂;
7 to 17% Al₂O₃;
0 to 9% B₂O₃;
4 to 8% Li₂O;
1 to 11% MgO;
4 to 12% ZnO;
0 to 2% TiO₂;
14 to 23% Li₂O+MgO+ZnO; and
0 to 3% CaO+BaO.
Another preferred embodiment (Embodiment 3) of the aluminosilicate glass is a glass composition having the following composition in mass %:
58 to 66% SiO₂;
13 to 19% Al₂O₃;
3 to 4.5% Li₂O;
6 to 13% Na₂O;
0 to 5% K₂O;
10 to 18% R₂O (R₂O=Li₂O+Na₂O+K₂O);
0 to 3.5% MgO;
1 to 7% CaO;
0 to 2% SrO;
0 to 2% BaO;
2 to 10% RO (RO=MgO+CaO+SrO+BaO);
0 to 2% TiO₂;
0 to 2% CeO₂;
0 to 2% Fe₂O₃;
0 to 1% MnO; and
0.05 to 0.5% SO₃,
wherein TiO₂+CeO₂+Fe₂O₃+MnO=0.01 to 3%.
Another preferred embodiment (Embodiment 4) of the aluminosilicate glass is a glass composition having the following composition in mass %:
60 to 70% SiO₂;
5 to 20% Al₂O₃;
5 to 25% Li₂O+Na₂O+K₂O;
0 to 1% Li₂O;
3 to 18% Na₂O;
0 to 9% K₂O;
5 to 20% MgO+CaO+SrO+BaO;
0 to 10% MgO;
1 to 15% CaO;
0 to 4.5% SrO;
0 to 1% BaO;
0 to 1% TiO₂; and
0 to 1% ZrO₂.
Another preferred embodiment (Embodiment 5) of the aluminosilicate glass is a glass composition having the following composition in mass %:
59 to 68% SiO₂;
9.5 to 15% Al₂O₃;
0 to 1% Li₂O;
3 to 18% Na₂O;
0 to 3.5% K₂O;
0 to 15% MgO;
1 to 15% CaO;
0 to 4.5% SrO;
0 to 1% BaO;
0 to 2% TiO₂; and
1 to 10% ZrO₂.
The soda-lime glass is a glass composition widely used, for example, in glass sheets.
A preferred embodiment (Embodiment 1) of the titanium-containing silicate glass is a glass composition having the following composition in mol %:
5 to 25% TiO₂;
50 to 79% SiO₂+B₂O₃;
5 to 25% Al₂O₃+TiO₂; and
5 to 20% Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+CaO+SrO+BaO.
In Embodiment 1 of the titanium-containing silicate glass, the glass composition preferably contains in mol %:
60 to 65% SiO₂;
12.5 to 15% TiO₂;
12.5 to 15% Na₂O; and
70 to 75% SiO₂+B₂O₃.
Further, in Embodiment 1 of the titanium-containing silicate glass, the following expression is more preferably satisfied: (Al₂O₃+TiO₂)/(Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+CaO+SrO+BaO)≤0.9, wherein the amounts of the components are expressed in mol %.
Another preferred embodiment (Embodiment 2) of the titanium-containing silicate glass is a glass composition having the following composition in mol %:
10 to 50% B₂O₃;
25 to 40% TiO₂;
20 to 50% SiO₂+B₂O₃; and
10 to 40% Li₂O+Na₂O+K₂O+Rb₂O+Cs₂O+MgO+CaO+SrO+BaO.
A preferred embodiment (Embodiment 1) of the low-alkali glass is a glass composition having the following composition in mol %:
45 to 68% SiO₂;
2 to 20% B₂O₃;
3 to 20% Al₂O₃;
0.1 to 5.0% (exclusive of 5.0%) TiO₂;
0 to 9% ZnO; and
0 to 2.0% (exclusive of 2.0%) Li₂O+Na₂O+K₂O.
In Embodiment 1 of the low-alkali glass, the glass composition preferably contains the following coloring components in mol %:
0 to 3.0% CeO₂; and
0 to 1.0% Fe₂O₃.
Further, in Embodiment 1 of the low-alkali glass, the glass composition is more preferably an alkali-free glass substantially free of alkali metal oxides (Li₂O+Na₂O+K₂O).
The low-alkali glass or alkali-free glass according to Embodiment 1 contains TiO₂as an essential component. The content of TiO₂in the low-alkali glass or alkali-free glass is 0.1 mol % or more and less than 5.0 mol %. To achieve high smoothness of the inner walls of holes obtained through laser irradiation, the content of TiO₂is preferably 0.2 to 4.0 mol %, more preferably 0.5 to 3.5 mol %, and even more preferably 1.0 to 3.5 mol %. Incorporation of an appropriate amount of TiO₂in a low-alkali glass or alkali-free glass having a particular composition makes it possible to form modified portions by relatively low-energy laser irradiation and produces the effect of allowing the modified portions to be easily removed by ultrasonically-assisted etching in the subsequent step. TiO₂is known to have a binding energy approximately equal to the energy of ultraviolet light and absorb ultraviolet light. When an appropriate amount of TiO₂is incorporated in a glass, the coloring of the glass can be controlled by exploiting interaction of TiO₂with other colorants; this interaction is generally known as charge-transfer absorption. Thus, adjusting the content of TiO₂can control absorption of certain light to a desired level. The incorporation of an appropriate amount of TiO₂in a glass is preferred also in view of the fact that modified portions in which holes are to be formed by etching can easily be formed in the glass when the glass has an appropriate absorption coefficient.
The low-alkali glass or alkali-free glass according to Embodiment 1 may contain ZnO as an optional component. The content of ZnO in the low-alkali glass or alkali-free glass is preferably 0 to 9.0 mol %, more preferably 1.0 to 8.0 mol %, even more preferably 1.5 to 5.0 mol %, and particularly preferably 1.5 to 3.5 mol %. ZnO, like TiO₂, is a component that shows absorption in the ultraviolet region. ZnO thus produces a beneficial effect when contained in the glass used in the present invention.
The low-alkali glass or alkali-free glass according to Embodiment 1 may contain CeO₂as a coloring component. In particular, the use of CeO₂in combination with TiO₂makes easier the formation of modified portions. The content of CeO₂in the low-alkali glass or alkali-free glass is preferably 0 to 3.0 mol %, more preferably 0.05 to 2.5 mol %, even more preferably 0.1 to 2.0 mol %, and particularly preferably 0.2 to 0.9 mol %.
Fe₂O₃is also effective as a coloring component in the glass used in the present invention and may be contained in the glass. In particular, the use of Fe₂O₃in combination with TiO₂or in combination with TiO₂and CeO₂makes easier the formation of modified portions. The content of Fe₂O₃in the low-alkali glass or alkali-free glass is preferably 0 to 1.0 mol %, more preferably 0.008 to 0.7 mol %, even more preferably 0.01 to 0.4 mol %, and particularly preferably 0.02 to 0.3 mol %.
Components of the low-alkali glass or alkali-free glass according to Embodiment 1 are not limited to those described above. The low-alkali glass or alkali-free glass may contain an appropriate coloring component so that the absorption coefficient of the glass at a predetermined wavelength (a wavelength of 535 nm or less) is adjusted to 1 to 50/cm, preferably to 3 to 40/cm.
Another preferred embodiment (Embodiment 2) of the low-alkali glass is a glass composition having the following composition in mol %:
45 to 70% SiO₂;
2 to 20% B₂O₃;
3 to 20% Al₂O₃;
0.1 to 2.0% CuO;
0 to 15.0% TiO₂;
0 to 9.0% ZnO; and
0 to 2.0% (exclusive of 2.0%) Li₂O+Na₂O+K₂O.
Further, in Embodiment 2 of the low-alkali glass, the glass composition is more preferably an alkali-free glass substantially free of alkali metal oxides (Li₂O+Na₂O+K₂O).
The low-alkali glass or alkali-free glass according to Embodiment 2 may, like the low-alkali glass or alkali-free glass according to Embodiment 1, contain TiO₂. The content of TiO₂in the low-alkali glass or alkali-free glass according to Embodiment 2 is 0 to 15.0 mol %. To achieve high smoothness of the inner walls of holes obtained through laser irradiation, the content of TiO₂is preferably 0 to 10.0 mol %, more preferably 1 to 10.0 mol %, even more preferably 1.0 to 9.0 mol %, and particularly preferably 1.0 to 5.0 mol %.
The low-alkali glass or alkali-free glass according to Embodiment 2 may contain ZnO. The content of ZnO in the low-alkali glass or alkali-free glass according to Embodiment 2 is 0 to 9.0 mol %, preferably 1.0 to 9.0 mol %, and more preferably 1.0 to 7.0 mol %. ZnO, like TiO₂, is a component that shows absorption in the ultraviolet region. ZnO thus produces a beneficial effect when contained in the glass used in the present invention.
Further, the low-alkali glass or alkali-free glass according to Embodiment 2 contains CuO. The content of CuO in the low-alkali glass or alkali-free glass is preferably 0.1 to 2.0 mol %, more preferably 0.15 to 1.9 mol %, even more preferably 0.18 to 1.8 mol %, and particularly preferably 0.2 to 1.6 mol %. Incorporation of CuO in the glass colors the glass and adjusts the absorption coefficient of the glass at a predetermined laser wavelength to an appropriate range, thus enabling the glass to appropriately absorb the energy of the applied laser and making it possible to easily form modified portions based on which holes are to be formed.
Components of the low-alkali glass or alkali-free glass according to Embodiment 2 are not limited to those described above. The low-alkali glass or alkali-free glass may contain an appropriate coloring component so that the absorption coefficient of the glass at a predetermined wavelength (a wavelength of 535 nm or less) is adjusted to 1 to 50/cm, preferably to 3 to 40/cm.
The low-alkali glass or alkali-free glass according to Embodiment 1 or 2 may contain MgO as an optional component. MgO is an alkaline-earth metal oxide characterized by suppressing an increase in coefficient of thermal expansion without causing a significant decrease in strain point, and also provides an improvement in meltability. MgO may therefore be contained. The content of MgO in the low-alkali glass or alkali-free glass is preferably 15.0 mol % or less, more preferably 12.0 mol % or less, even more preferably 10.0 mol % or less, and particularly preferably 9.5 mol % or less. The content of MgO is preferably 2.0 mol % or more, more preferably 3.0 mol % or more, even more preferably 4.0 mol % or more, and particularly preferably 4.5 mol % or more.
The low-alkali glass or alkali-free glass according to Embodiment 1 or 2 may contain CaO as an optional component. Like MgO, CaO is characterized by suppressing an increase in coefficient of thermal expansion without causing a significant decrease in strain point, and also provides an improvement in meltability. CaO may therefore be contained. The content of CaO in the low-alkali glass or alkali-free glass is preferably 15.0 mol % or less, more preferably 12.0 mol % or less, even more preferably 10.0 mol % or less, and particularly preferably 9.3 mol % or less. The content of CaO is preferably 1.0 mol % or more, more preferably 2.0 mol % or more, even more preferably 3.0 mol % or more, and particularly preferably 3.5 mol % or more.
The low-alkali glass or alkali-free glass according to Embodiment 1 or 2 may contain SrO as an optional component. Like MgO and CaO, SrO is characterized by suppressing an increase in coefficient of thermal expansion without causing a significant decrease in strain point, and also provides an improvement in meltability. Thus, SrO may be contained to achieve improved devitrification resistance and acid resistance. The content of SrO in the low-alkali glass or alkali-free glass is preferably 15.0 mol % or less, more preferably 12.0 mol % or less, even more preferably 10.0 mol % or less, and particularly preferably 9.3 mol % or less. The content of SrO is preferably 1.0 mol % or more, more preferably 2.0 mol % or more, even more preferably 3.0 mol % or more, and particularly preferably 3.5 mol % or more.
Saying that a glass is “substantially free” of a component means that the content of the component in the glass is less than 0.1 mol %, preferably less than 0.05 mol %, and more preferably 0.01 mol % or less. The upper and lower limits of value ranges (such as the ranges of the contents of the components, the ranges of values calculated for the components, and the ranges of values of various properties) described herein can be combined as appropriate.
The coefficient of thermal expansion of the glass used in the present invention is preferably 100×10⁻⁷/° C. or less, more preferably 70×10⁻⁷/° C. or less, even more preferably 60×10⁻⁷/° C. or less, and particularly preferably 50×10⁻⁷/° C. or less. The lower limit of the coefficient of thermal expansion is not particularly defined. For example, the coefficient of thermal expansion may be 10×10⁻⁷/° C. or more or may be 20×10⁻⁷/° C. or more.
The coefficient of thermal expansion is measured as follows. First, a cylindrical glass sample having a diameter of 5 mm and a height of 18 mm is prepared. This glass sample is heated from 25° C. up to the yield point of the glass sample, the elongation of the glass sample is measured at various temperatures, and the coefficient of thermal expansion is calculated on the basis of the elongation. The average of values of the coefficient of thermal expansion in the temperature range of 50 to 350° C. is calculated, and thus the average coefficient of thermal expansion can be determined. The measurement of the average coefficient of thermal expansion can be conducted using a thermomechanical analyzer (TMA). The actual measurement of the coefficient of thermal expansion was carried out at a temperature rise rate of 5° C./min using TMA 4000 SA, a thermomechanical analyzer manufactured by NETZSCH Japan K.K.
The glass is not limited to a particular shape. For example, a glass sheet is used. The modified portion formation step does not require the use of a so-called photosensitive glass, and is capable of processing a wide variety of glasses. Specifically, a glass substantially free of gold or silver can be processed by the modified portion formation step according to the present invention.
In particular, a glass with high rigidity can be suitably processed by the modified portion formation step according to the present invention, since both of the upper and lower surfaces of such a glass resist being cracked when the glass is exposed to laser irradiation. For example, a glass with a Young's modulus of 80 GPa or more is preferred.
The absorption coefficient α can be calculated by measuring the transmittance and reflectance of a glass substrate having a thickness t (cm). For the glass substrate having a thickness t (cm), the transmittance T (%) and the reflectance R (%) at an incident angle of 12° are measured at a predetermined wavelength (wavelength of 535 nm or less) using a spectrophotometer (such as V-670, an ultraviolet/visible/near-infrared spectrophotometer manufactured by JASCO Corporation). The absorption coefficient α is calculated from the measured values using the following equation.
α=(1/t)*ln {(100−R)/T}
The absorption coefficient α of the glass used in the present invention is preferably 1 to 50/cm and more preferably 3 to 40/cm.
Some of the glasses described above are commercially-available and can be acquired by purchase. Even if a desired glass is not commercially-available, the desired glass can be produced by a known glass forming method (such as an overflow process, float process, slit draw process, or casting process), and the glass produced can be subjected to a post-process such as cutting or polishing to obtain a glass composition of a desired shape.
In the modified portion formation step, a modified portion can be formed by a single irradiation with a laser pulse. Thus, in this step, modified portions can be formed by applying laser pulses in such a manner that irradiated sites do not overlap each other. It should be understood, however, that the laser pulses may be applied in such a manner that the applied pulses overlap each other.
In the modified portion formation step, laser pulses are typically focused in the glass by a lens. For example, when through holes are to be formed in a glass sheet, laser pulses are typically focused on the vicinity of the thickness center of the glass sheet. When only the upper portion (portion in the vicinity of the laser pulse incident surface) of a glass sheet is to be processed, laser pulses are typically focused on the upper portion of the glass sheet. When only the lower portion (portion remote from the laser pulse incident surface) of the glass sheet is to be processed, laser pulses are typically focused on the lower portion of the glass sheet. It should be understood, however, that laser pulses may be focused on points outside the glass as long as modified portions can be formed in the glass. For example, laser pulses may be focused on points located outside the glass sheet at a predetermined distance (for example, 1.0 mm) from the upper surface or lower surface of the glass sheet. That is, as long as modified portions can be formed in the glass, laser pulses may be focused on points within a distance of 1.0 mm from the upper surface of the glass (the points including those on the upper surface of the glass) in an upward direction (the direction opposite to the traveling direction of the laser pulses), may be focused on points within a distance of 1.0 mm from the lower surface of the glass (the points including those on the lower surface of the glass) in a downward direction (the direction in which the laser pulses having passed through the glass travel), or may be focused on points within the glass.
When using nanosecond laser pulses or a nanosecond laser apparatus, the pulse width of the laser pulses is preferably 1 to 200 ns (nanoseconds), more preferably 1 to 100 ns, and even more preferably 5 to 50 ns. If the pulse width is greater than 200 ns, the peak value of the laser pulses may be decreased so that the process may not be completed successfully. Laser beams having an energy of 5 to 100 μJ/pulse are applied to the above-described glass for laser processing. Increasing the energy of the laser pulses leads to a corresponding increase in the length of the modified portions. The beam quality parameter M₂of the laser pulses may be, for example, 2 or less. The use of laser pulses having a parameter M₂of 2 or less makes it easy to form minute holes or minute grooves. Any explanation about laser in the following description is directed to nanosecond laser pulses or a nanosecond laser apparatus, unless otherwise explicitly stated.
In the modified portion formation step, the laser pulses may be harmonic beams from a Nd:YAG laser, harmonic beams from a Nd:YVO₄laser, or harmonic beams from a Nd:YLF laser. The harmonic beams are, for example, second harmonic beams, third harmonic beams, or fourth harmonic beams. The wavelength of the second harmonic beams from the above lasers is around 532 nm to 535 nm. The wavelength of the third harmonic beams is around 355 nm to 357 nm. The wavelength of the fourth harmonic beams is around 266 nm to 268 nm. The adoption of such laser beams allows for inexpensive processing of the glass.
An exemplary laser processing apparatus used in the modified portion formation step is AVIA 355-4500, a high-repetition-rate, solid-state pulsed UV laser manufactured by Coherent Japan, Inc. This apparatus is a Nd:YVO₄laser that emits third harmonic beams, and outputs a maximum laser power of around 6 W at a repetition frequency of 25 kHz. The wavelength of the third harmonic beams is 350 nm to 360 nm.
The wavelength of the laser pulses is preferably 535 nm or less and may be, for example, in the range of 350 to 360 nm. If the wavelength of the laser pulses is more than 535 nm, the spot size is increased so that formation of fine structures is difficult and, in addition, cracks are likely to occur due to heat around the irradiated spots.
An optical system typically used is one in which an oscillated laser beam is expanded by a factor of 2 to 4 by a beam expander (the spot diameter in processing area is 7.0 to 14.0 mm at this moment), the central portion of the laser beam is cut by a variable iris, then the optical axis of the beam is adjusted by a galvanometer mirror, and finally the beam is focused on/in the glass with the focal point being adjusted by an fθ lens with a focal length of around 100 mm.
The focal length L (mm) of the lens is, for example, in the range of 50 to 500 mm and may be selected from the range of 100 to 200 mm.
The beam diameter D (mm) of the laser pulses is, for example, in the range of 1 to 40 mm and may be selected from the range of 3 to 20 mm. The beam diameter D as defined herein refers to the beam diameter of the laser pulse incident on the lens, and refers to the diameter at which the beam intensity drops to [1/e²] times the beam intensity at the center of the beam.
In the modified portion formation step, a value obtained by dividing the focal length L by the beam diameter D, namely, the value of [L/D], is 7 or more. The value of [L/D] is preferably 7 or more and 40 or less, and may be 10 or more and 20 or less. This value is associated with the degree of focusing of the laser applied to the glass. The smaller the value is, the more localized the laser focusing is, so the more difficult it is to form long, uniform modified portions. If this value is less than 7, the laser power may be so excessively high in the vicinity of the beam waist that cracks are likely to occur within the glass.
In the modified portion formation step, it is unnecessary, before laser pulse irradiation, to subject the glass to a pretreatment (such as formation of a film thereon for promoting the absorption of the laser pulses). However, such a treatment may be carried out as long as the effect of the present invention is obtained.
The numerical aperture (NA) may be varied in the range of 0.020 to 0.075 by changing the size of the iris and thus adjusting the laser beam diameter. If the NA is excessively large, the laser energy is concentrated only at and around the focal points, which leads to a failure to effectively form modified portions in the thickness direction of the glass.
The use of pulsed laser beams having a small NA allows a single irradiation to form modified portions that are relatively long in the thickness direction of the glass, and is therefore effective in shortening the tact time.
In the laser irradiation of a sample, the repetition frequency is preferably 10 to 25 kHz. The positions of modified portions to be formed in the glass can be optimally adjusted (toward the upper surface or lower surface) by shifting the focal points in the thickness direction of the glass.
Further, the output power of the laser, the operation of the galvanometer mirror, etc., can be controlled by a controlling PC. The laser can be applied to a glass substrate at a predetermined speed on the basis of two-dimensional graphic data created, for example, by CAD software.
In a laser-irradiated area of the glass there is formed a modified portion distinct from the rest of the glass. This modified portion can easily be identified, for example, with the aid of an optical microscope. The modified portion formed is generally cylindrical, although the shape of the modified portion may vary depending on the composition of the glass. The modified portion extends from the vicinity of the upper surface of the glass to the vicinity of the lower surface.
This modified portion is thought to be a portion with a defect such as E′ center or non-bridging oxygen which has resulted from photochemical reaction induced by laser irradiation or a portion with a sparse glass structure generated at a high temperature due to rapid heating during laser irradiation and maintained due to rapid cooling after laser irradiation.
With the hole formation technique employing laser irradiation according to the modified portion formation step of the present invention in combination with wet etching, modified portions can be formed by a single irradiation with laser pulses.
The conditions employed in the modified portion formation step are, for example, as follows: The absorption coefficient of the glass is 1 to 50/cm, the pulse width of the laser pulses is 1 to 100 ns, the energy of the laser pulses is 5 to 100 μJ/pulse, the wavelength of the laser pulses is 350 to 360 nm, and the beam diameter D of the laser pulses is 3 to 20 mm, and the focal length L of the lens is 100 to 200 mm.
The glass sheet may, if desired, be polished in advance of etching to reduce the variation in diameter of the modified portions. However, excessive polishing may reduce the effect of etching on the modified portions. The depth of polishing is thus preferably 1 to 20 μm from the upper surface of the glass sheet.
The size of the modified portions formed by the modified portion formation step varies depending on, for example, the beam diameter D of the laser pulses incident on the lens, the focal length L of the lens, the absorption coefficient of the glass, and the power of the laser pulses. The diameter of the resulting modified portions is, for example, around 5 to 200 μm and may be around 10 to 150 μm. The depth of the modified portions may be, for example, around 50 to 300 μm, although the depth may vary depending on the laser irradiation conditions, the absorption coefficient of the glass, and the thickness of the glass.
Holes can be formed to connect with each other so that a groove is formed. In this case, laser pulses are applied in an aligned manner to form modified portions arranged in a line. After that, the modified portions are etched to form the groove. The sites to which the laser pulses are applied need not overlap each other, and holes formed as a result of the etching may connect neighboring holes to each other.
The method for forming modified portions is not limited to that described above. For example, modified portions or processing holes may be formed by irradiation using a femtosecond laser apparatus as mentioned above. The conditions employed when using femtosecond laser pulses or a femtosecond laser apparatus are not particularly limited, as long as the effect of the present invention is obtained. For example, the pulse width of the laser pulses is preferably 100 to 2000 fs (femtoseconds) and more preferably 200 to 1000 fs. In the laser irradiation of a sample, the repetition frequency is preferably 0.5 to 10 kHz. The energy of the laser pulses is preferably 1 to 20 μJ/pulse. The optical system is preferably adjusted so that a spot with a diameter of 1 to 30 μm is formed in the processing area on the target glass by a laser pulse with an energy of 1 to 20 μJ/pulse. These suitable conditions can be employed in appropriate combination when using femtosecond laser pulses or a femtosecond laser apparatus.
It is also conceivable to form processing holes, instead of modified portions, in a glass substrate and then form intended structures such as through holes by the etching process in the subsequent step. In this step of forming processing holes, for example, an appropriate glass substrate (such as a Ti-containing silicate glass which has the advantage of offering a low processing threshold for laser processing) is irradiated with a laser having certain properties to cause ablation or evaporation leading to formation of processing holes. The laser apparatus used is, for example, a YAG laser with a central wavelength of 266 nm or 355 nm (pulse width: from 5 to 8 nm). It is preferable to irradiate the glass with the laser for 0.5 to 10 seconds, with the focal length L (mm) of the lens being, for example, in the range of 50 to 500 mm and the repetition frequency being, for example, in the range of 10 to 25 kHz.
The laser ablation can, by itself, result in formation of holes or grooves with a diameter of 10 to 100 μm or more. Thus, the laser ablation, combined with the etching process in the subsequent step, allows an increase in hole diameter and an improvement in straightness and also provides the effect of diminishing the appearance of glass deformities such as debris around the processed area or eliminating fine cracks.
The method for forming modified portions is not limited to those described above, as long as fine structures can be formed in a glass substrate by combination of the modified portion formation and the etching process in the subsequent step.
The production method according to the present invention includes an etching step including irradiating a glass with an ultrasonic wave. Ultrasonically-induced cavitation, vibrational acceleration, and water flow promote the diffusion of an etchant and an etching product deep in fine holes or grooves. The ultrasonic irradiation during etching can eliminate the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves, thereby leading to formation of fine, deep holes or grooves with a steep wall angle (high straightness).
Propagation of an ultrasonic wave through a liquid causes a phenomenon called cavitation, which is the formation of cavities in the liquid. The cavitation induces alternate increase and decrease in pressure in a very short time and causes the water molecules to be extended or compressed under vibration, thus helping the etchant or etching product to move deep in fine holes or grooves. However, the higher the oscillation frequency is, the higher is the threshold at which cavitation occurs; in particular, it is difficult to generate cavitation when the oscillation frequency is more than 100 kHz because the threshold sharply increases in an exponential fashion as the oscillation frequency exceeds 100 kHz. To eliminate the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves and thereby form fine, deep holes or grooves with a steep wall angle, the oscillation frequency in the ultrasonically-assisted etching is preferably 120 kHz or less and more preferably 10 to 120 kHz. The oscillation frequency is even more preferably 20 to 100 kHz to generate sufficient cavitation in the etchant. Two or more different oscillation frequencies may be employed in combination.
The intensity of the ultrasonic wave is preferably, but not limited to, 0.10 to 5.0 W/cm², more preferably 0.15 to 4.0 W/cm², and even more preferably 0.20 to 3.0 W/cm². The intensity of the ultrasonic wave applied to the glass to be processed can be increased within the above range as long as the glass is not damaged. The selection of the intensity of the ultrasonic wave within the above range is preferred to enhance the effect of facilitating replacement of the etchant at the vicinity of the boundary between the inside and outside of fine structures. The intensity of the ultrasonic wave refers to a value calculated by dividing the output power (in units of W) by the area (in units of cm²) of the bottom surface of an etching bath.
The apparatus used for the ultrasonication is not particularly limited and can be a known apparatus. For example, an apparatus sold under the product code W-113 (manufactured by Honda Electronics Co., Ltd.; output power: 100 W, oscillation frequency: 28 kHz/45 kHz/100 kHz, bath size: W240×D140×H100 (in units of mm)) or an apparatus sold under the product code US-3R (manufactured by AS ONE Corporation; output power: 120 W, oscillation frequency: 40 kHz, bath size: W303×D152×H150 (in units of mm)) can be used.
In the etching step, a surface protective coating agent may be applied to one of the upper and lower surfaces of the glass sheet to protect the one surface and thus allow etching to proceed only from the other surface. A commercially-available product can be used as the surface protective coating agent, and an example of the commercially-available product is SILITECT-II (manufactured by Trylaner International).
The etchant used for the ultrasonically-assisted etching in the present invention includes: hydrofluoric acid; at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid; and a surfactant. The etchant may include an additional component as long as the effect of the present invention is not disturbed. Examples of the additional component include: inorganic acids other than hydrofluoric acid, nitric acid, hydrochloric acid, and sulfuric acid; organic acids such as oxalic acid, tartaric acid, iodoacetic acid, fumaric acid, and maleic acid; and chelate agents. Chelate agents are useful since they can form complexes with metal ions and thus prevent the metal ions from reattaching to the substrate surface. Examples of the chelate agents include dimethylglyoxime, dithizone, oxine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, hydroxyethylidene diphosphonic acid (HEDP), and nitrilotris(methylene phosphonic acid) (NTMP). HEDP and NTMP are highly soluble in an acidic system based on hydrofluoric acid and are thus useful. The etchant may be substantially free of these additional components. Saying that the etchant is “substantially free” of a component means that the content of the component in the etchant is less than 1.0 mass %, preferably less than 0.5 mass %, and more preferably less than 0.1 mass %. Examples of surfactants that can be used in the present invention include amphoteric surfactants, cationic surfactants, anionic surfactants, and non-ionic surfactants. One of these may be used alone, or two or more thereof may be used in combination to the extent that the effect of the present invention is not impaired. Examples of the amp hoteric surfactants include 2-alkyl-N-carboxymethyl-N-hydroxyethyl imidazolinium betaine, cocamidopropyl betaine, sodium cocoyl alkylaminopropionate, and sodium lauryl aminodipropionate.
Examples of the cationic surfactants include quaternary ammonium salts (such as lauryl trimethyl ammonium chloride), higher amine salts of halogen acids (such as hardened tallow amine), and halogenated alkylpyridinium compounds (such as dodecylpyridinium chloride). Examples of the anionic surfactants include alkyl sulfate salts, alkyl aryl sulfonic acid salts, alkyl ether sulfate salts, α-olefin sulfonic acid salts, alkyl sulfonic acid salts, alkylbenzene sulfonic acid salts, alkylnaphthalene sulfonic acid salts, taurine surfactants, sarcosinate surfactants, isethionate surfactants, N-acyl acidic amino acid surfactants, monoalkyl phosphate salts, higher fatty acid salts, and acylated polypeptide. Examples of the non-ionic surfactants include: polyoxyalkylene alkyl ethers such as polyoxyethylene alkyl ethers; polyoxyethylene alkyl phenyl ethers; polyoxyalkylene glycol derivatives; polyoxyethylene derivatives such as polyoxyethylene alkylamines, polyoxyethylene fatty acid amides, polyoxyethylene fatty acid bisphenyl ethers, polyoxyethylene fatty acid esters, and polyoxyethylene sorbitan fatty acid esters; monoglycerin fatty acid esters; polyglycerin fatty acid esters; sorbitan fatty acid esters; sucrose fatty acid esters; polyoxyethylene castor oil; and polyoxyethylene hardened castor oil. The number of carbon atoms in the alkyl group of any of the surfactants mentioned above may be, for example, 6 to 20 or 8 to 18.
A glass dissolution reaction induced by hydrofluoric acid is expressed as follows.
SiO₂+6HF→2H₂O+H₂SiF₆
Raising the hydrofluoric acid concentration increases the etching speed. However, if the etching speed is excessively increased, the ultrasonic irradiation fails to sufficiently promote the flow of the etchant and etching product in fine holes or grooves.
The concentration of hydrofluoric acid contained in the etchant is 0.05 mass % to 8.0 mass %. For the ultrasonically-assisted etching, the hydrofluoric acid concentration is preferably 0.10 mass % to 7.0 mass % and more preferably 0.20 mass % to 5.0 mass % to eliminate the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves and thereby form fine, deep holes or grooves with a steep wall angle. Lowering the hydrofluoric acid concentration can increase the wall angle of the resulting holes. However, excessively lowering the hydrofluoric acid concentration leads to a decrease in etching rate and therefore an undesired reduction in process efficiency.
Fluoride and silicofluoride resulting from etching of a glass with hydrofluoric acid have low solubility and thus tend to lodge within fine holes or grooves and hinder the progress of etching.
When the etchant includes a mixed acid of hydrofluoric acid and at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid, plenty of H⁺ is present in the etchant due to ionization of nitric acid, hydrochloric acid, and/or sulfuric acid, and thus the equilibrium of the reaction expressed as HF⇔H⁺+F⁻ shifts to the left. The decrease in the amount of free F⁻ reduces the formation of fluoride and silicofluoride, and thus makes it possible to stably maintain the ultrasonically-enhanced flow of the etchant and etching product in fine holes or grooves. Merely lowering the hydrofluoric acid concentration can decrease the amount of free F⁻, but slows the progress of etching instead. Thus, it is better to use a strong acid to reduce the formation of free F⁻. Raising the concentrations of nitric acid, hydrochloric acid, and sulfuric acid increases the etching rate. If the etching rate is excessively increased, the ultrasonic irradiation fails to sufficiently promote the flow of the etchant and etching product in fine holes or grooves.
The addition of a surfactant improves the ability of the etchant to wet the glass and thus makes it easier for the etchant to enter the interior of fine holes or grooves. Further, the surfactant provides the effect of removing dirt and preventing particles or the etching product from reattaching to the glass, thus allowing the ultrasonically-assisted etching to successfully proceed in the fine holes or grooves. The amount of the surfactant may be increased to enhance the dirt removal effect. However, excessively increasing the amount of the surfactant leads to bubbling-induced defects or necessitates cumbersome rinsing. The addition of at least 5 ppm of the surfactant provides the desired effect.
The concentration of the at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid (suitably nitric acid) in the etchant is 2.0 mass % to 16.0 mass %. For the ultrasonically-assisted etching, the concentration of the at least one inorganic acid is preferably 2.5 mass % to 15.0 mass % and more preferably 3.0 mass % to 14.0 mass % to eliminate the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves and thereby form fine, deep holes or grooves with a steep wall angle.
The content (mass concentration) of the surfactant in the etchant is 5 ppm to 1000 ppm. For the ultrasonically-assisted etching, the content of the surfactant is preferably 10 ppm to 800 ppm and more preferably 15 ppm to 600 ppm to eliminate the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves and thereby form fine, deep holes or grooves with a steep wall angle. The content of the surfactant can be measured, for example, by high-performance liquid chromatography (HPLC).
The etching time and the etchant temperature are selected according to the shape of the modified portions or the desired shape to be obtained by the etching process. Raising the etchant temperature in the etching can increase the etching speed. The etching speed can be adjusted also by the composition of the etchant. In the production method according to the present invention, the etching speed in those portions of the glass substrate which are other than the modified portions is preferably, but not limited to, 0.1 to 9.0 μm/min, more preferably 0.2 to 7.0 μm/min, and even more preferably 0.5 to 6.0 μm/min. The diameter of the resulting holes can be controlled by the etching conditions.
The etching time is preferably, but not limited to, around 30 to 180 minutes, although the etching time may vary depending on the thickness of the glass. The etchant temperature can be varied to adjust the etching rate, and is preferably around 5 to 45° C. and more preferably around 15 to 40° C. The etching process can be accomplished even when the etchant temperature is 45° C. or higher. However, such a high etchant temperature is not practical since the etchant quickly evaporates. The etching process can be accomplished even when the etchant temperature is 5° C. or lower. However, a low etchant temperature leading to an extremely low etching rate is not practical.
The etchant used in the present invention can be obtained by mixing the above-described components in a solvent. The solvent is preferably, but not limited to, water.
In the glass with a fine structure that is obtained by the production method according to the present invention, the wall angle is preferably 80° or more and more preferably 85° or more at both the laser pulse-incident surface (first surface) and the opposite surface (second surface) so that high straightness is ensured. The method for measuring the wall angle is as described later in EXAMPLES. In the glass with a fine structure that is obtained by the production method according to the present invention, the opening diameter is preferably 20 to 110 μm, more preferably 25 to 100 μm, and even more preferably 30 to 95 μm. The opening diameter can be calculated on the basis of an image used for examination of the wall angle.

EXAMPLES

Hereinafter, the present invention will be described in more detail with examples. The present invention is by no means limited by these examples, and various modifications can be made by ordinarily skilled persons in the art within the technical concept of the present invention.

Example 1

A glass substrate having a size of 30 mm×30 mm×t0.52 mm and containing components as shown for glass sample 1 in Table 1 below was used as a sample.

TABLE 1

	Glass	Glass	Glass
	sample 1	sample 2	sample 3	Glass sample 4
Com-	(Alkali-free	(Alkali-free	(Alkali-free	(Ti-containing
ponents*	glass)	glass)	glass)	silicate glass)

SiO₂	59.47	63.1	65.9	60.0
B₂O₃	7.5	9.5	7.4	10.0
Al₂O₃	11.0	9.0	10.9	0
TiO₂	3.0	3.0	0	15.0
Na₂O	0	0	0	15.0
ZnO	3.0	3.0	0	0
MgO	4.0	4.0	5.0	0
CaO	8.0	4.0	5.0	0
SrO	4.0	4.0	5.0	0
Fe₂O₃	0.03	0	0	0
CeO₂	0	0.4	0	0
CuO	0	0	0.8	0
Absorption	6.4	28.2	11.2	5.4
coefficient
(/cm)
Coefficient	45	43	38	75
of
thermal
expansion
(×10⁻⁷/° C.)

*The unit of the values is mol %.

<Modified Portion Formation Step>
Laser-assisted formation of modified portions was carried out using AVIA 355-4500, a high-repetition-rate, solid-state pulsed UV laser manufactured by Coherent Japan, Inc. This laser is a Nd:YVO₄laser that emits third harmonic beams, and outputs a maximum laser power of around 6 W at a repetition frequency of 25 kHz. The dominant wavelength of the third harmonic beams is 355 nm.
Laser pulses (having a pulse width of 9 ns, a power of 1.2 W, and a beam diameter of 3.5 mm) emitted from the laser apparatus were expanded by a factor of 4 by a beam expander, and the expanded beams were cut by a variable iris whose diameter can be varied in the range of 5 to 15 mm. The optical axes of the beams were adjusted by a galvanometer mirror, and the beams were focused on points within the glass sheet by an fθ lens with a focal length of 100 mm. The NA was varied in the range of 0.020 to 0.075 by changing the size of the iris and thus adjusting the laser beam diameter. The points on which the laser beams were focused were at a physical distance of 0.15 mm from the upper surface of the glass sheet. The laser beams were scanned at a speed of 400 mm/s in such a manner that the applied pulses did not overlap each other.
After the laser irradiation, the glass as a sample was observed with an optical microscope, and it was confirmed that modified portions distinct from the rest of the glass were formed in the laser-irradiated areas. The modified portions formed were generally cylindrical, although the shape of the modified portions could vary depending on the type of the glass. As shown in FIG. 3, the modified portions extended from the vicinity of the upper surface of the glass to the vicinity of the lower surface of the glass.
In the laser irradiation of the sample, the repetition frequency was 10 to 25 kHz. The focal points were shifted in the thickness direction of the glass so that the positions of the modified portions to be formed in the glass were optimally adjusted (toward the upper surface or lower surface).
<Ultrasonically-Assisted Etching Step>
A 1 L polyethylene container was used as an etching bath, and an etchant was prepared by mixing the following components in the proportions shown in Table 2 using pure water as a solvent.

- Hydrofluoric acid 46%, Morita Chemical Industries Co., Ltd.
- Nitric acid (1.38) 60%, Kanto Chemical Co., Inc.
- High-performance non-ionic surfactant, NCW-1001 (30% aqueous solution of polyoxyalkylene alkyl ether), Wako Pure Chemical Industries, Ltd.

	TABLE 2

	Components	Example 1

	Hydrofluoric acid (mass %)	2.0
	Nitric acid (mass %)	6.0
	Surfactant* (ppm)	15

	*Amount exclusive of solvent

An ultrasonic bath was filled with water to a predetermined level, and the etching bath filled with the etchant containing the components shown in Table 2 was placed in the ultrasonic bath. The etchant was heated to a temperature of 30° C. The sample (glass substrate) was set in a cassette made of vinyl chloride, this cassette with the sample was placed in the etching bath, and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². The temperature of the etchant was maintained at 30° C.±2° C. by replacing some of water in the ultrasonic bath and thus controlling the ultrasonically-induced temperature rise of the etchant. In the course of the process, the sample was withdrawn from the etching bath once, and the etching rate was determined from the change in thickness of the substrate. The etching time was set on the basis of the determined etching rate so that the substrate would have a thickness of 440 μm at the end of the etching. The etching was performed in this manner to obtain a glass with fine structures. The sample thus obtained was withdrawn from the etching bath, thoroughly rinsed with pure water, and dried with hot air. The intensity of the ultrasonic wave was defined as a value calculated by dividing the output power (in units of W) by the area (in units of cm²) of the bottom surface of the etching bath. The ultrasonic bath used was an ultrasonic bath sold under the product code US-3R (manufactured by AS ONE Corporation; output power: 120 W, oscillation frequency: 40 kHz, bath size: W303×D152×H150 (in units of mm)).
The sample was cut with a glass cutter, and the cross-section was polished with an abrasive sheet #1000 and then with an abrasive sheet #4000. The amount of polishing was controlled so that the modified portions having been etched were not exposed at the cross-section, since exposure of the modified portions at the cross-section would make it impossible to observe the actual contour. A CNC video measuring system sold under the product code Nexiv VMR-6555 (manufactured by Nikon Corporation; magnification: 8, field of view: 0.58×0.44 (in units of mm)) was used as an image measuring instrument. The sample was observed with this measuring instrument in the cross-sectional direction (along the thickness) of the sample, and the focus of the instrument was adjusted to a hole resulting from the etching. Two angles formed between the substrate surface and the circumferential surface of the hole on each side of the sample and indicated by the reference characters 51 a and 51 b in FIG. 4 were measured with the measuring instrument, and the wall angle of the hole was determined as the average of the measured angles. The wall angle was 86° at the laser pulse-incident surface (hereinafter referred to as “first surface”) and 86° at the opposite surface (hereinafter referred to as “second surface”). The opening diameter was calculated on the basis of the image used for examination of the wall angle. An actually captured image is shown in FIG. 5.
As demonstrated by Example 1, when fine modified portions or processing holes formed in a glass were subjected to the ultrasonically-assisted etching using an etchant according to the present invention, desired holes, namely, fine, deep holes with a steep wall angle (straight holes) were successfully formed.
The ultrasonic irradiation induces cavitation, vibrational acceleration, and water flow, which promote the diffusion of the etchant and etching product deep in fine holes.
The concentration of hydrofluoric acid and the concentration of nitric acid in the etchant are adjusted to control the etching speed to a level that allows the ultrasonic irradiation to sufficiently promote the flow of the etchant and etching product in fine holes. Nitric acid reduces the formation of fluoride and silicofluoride which have low solubility in the fine holes, and thus makes it possible to stably maintain the ultrasonically-enhanced flow of the etchant and etching product in the fine holes.
The surfactant increases the ability of the etchant to wet the glass and thus makes it easier for the etchant to enter the interior of fine holes or grooves. Further, the surfactant prevents the etching product from attaching to the inner walls of the holes, thus allowing the ultrasonically-assisted etching to successfully proceed in the fine holes or grooves.
For these reasons, with the ultrasonically-assisted etching, the difference in the degree of etching of fine holes or grooves between the vicinity of the substrate surface and the interior of the fine holes or grooves is eliminated, and thus fine, deep holes with a steep wall angle (straight holes) can be formed.
In a variant of Example 1, structures of the glass to be subjected to the ultrasonically-assisted etching may be through structures or closed-bottom structures and may be holes or grooves, as long as a desired shape can be obtained by etching modified portions or structures formed in the glass.
As for the oscillation frequency of the ultrasonic wave in Example 1, different frequencies may be sequentially applied or different frequencies may be simultaneously applied. Modulated frequencies may also be employed.
Enhancing the intensity of the ultrasonic wave increases the wall angle. When the temperature of the etchant is raised or when the concentration of hydrofluoric acid or the at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid is increased, the wall angle is decreased while the etching speed is increased. The ultrasonic wave intensity, the etching temperature, and the compounding ratio of the etchant can be appropriately selected according to the desired wall angle and processing speed.
In a variant of Example 1, hydrochloric acid or sulfuric acid may be used instead of nitric acid in the etchant.
In a variant of Example 1, the etching bath may be made of a commodity plastic other than polyethylene or an engineering plastic, as long as the etching bath is resistant to the etchant. An etching bath made of a metal or coated metal may be used to increase the efficiency of ultrasonic propagation.
In a variant of Example 1, the sample may be positioned parallel or perpendicular to the direction of the applied ultrasonic wave during the ultrasonically-assisted etching. The sample may be shaken or rotated to reduce the influence of uneven irradiation of the ultrasonic wave.

Examples 2 to 6

Glasses with fine structures were produced by performing ultrasonically-assisted etching in the same manner as in Example 1, except for changing the etching conditions (the composition of the etchant and the etching speed) to those shown in Table 3. The etching conditions and the evaluation results are shown in Table 3.
In Examples 2 to 6, the type of the sample (glass substrate), the thickness of the sample before etching, and the thickness of the sample after etching were the same as those in Example 1, and the composition of the etchant differed from that in Example 1. The etchant used in Example 2 differed from the etchant used in Example 1 in that the concentration of hydrofluoric acid was decreased to 0.2 mass %, the concentration of nitric acid was increased to 14.0 mass %, and the content of the surfactant was increased to 150 ppm. The etchant used in Example 3 differed from the etchant used in Example 1 in that the concentration of hydrofluoric acid was increased to 5.0 mass % and the concentration of nitric acid was increased to 14.0 mass %. In both of Examples 2 and 3, favorable through holes with a wall angle of 85° or more were obtained.
The etchant used in Example 4 differed from the etchant used in Example 1 in that the concentration of nitric acid was decreased to 3.0 mass %, and the etchant used in Example 5 differed from the etchant used in Example 1 in that the concentration of nitric acid was increased to 14.0 mass % and the content of the surfactant was increased to 150 ppm. In both of Examples 4 and 5, favorable through holes with a wall angle of 85° or more were obtained.
In Example 6, where the etchant used differed from the etchant used in Example 5 in that the content of the surfactant was increased to 500 ppm, favorable through holes with a wall angle of 85° or more were obtained.

TABLE 3

Example 1	Example 2	Example 3	Example 4	Example 5	Example 6

Glass sample

1

Etchant	Hydrofluoric acid	2.0	0.2	5.0	2.0	2.0	2.0
	(mass %)
	Nitric acid (mass %)	6.0	14.0	14.0	3.0	14.0	14.0
	Surfactant* (ppm)	15	150	15	15	150	500

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	40	40	40	40	40	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.26	0.26	0.26	0.26	0.26	0.26
Substrate thickness	Before etching (μm)	520	520	520	520	520	520
	After etching (μm)	440	440	440	440	440	440

Etching speed (μm/min)

2.2

0.4

5.2

2.0

3.1

3.8

Opening diameter	First surface (μm)	64	36	50	60	69	70
	Second surface (μm)	84	72	96	80	88	88
Wall angle	First surface (°)	86	85	87	85	85	85
	Second surface (°)	86	85	85	85	85	85

*Amount exclusive of solvent

Examples 7 to 9

Glasses with fine structures were produced by performing ultrasonically-assisted etching in the same manner as in Example 1, except for changing the etching conditions (the composition of the etchant, the ultrasonic irradiation conditions, and the etching speed) to those shown in Table 4. The etching conditions and the evaluation results are shown in Table 4.
In Examples 7 to 9, the type of the sample (glass substrate), the thickness of the sample before etching, and the thickness of the sample after etching were the same as those in Example 1. The composition of the etchant was the same among Examples 7 to 9, and the conditions of the ultrasonic irradiation were different among Examples 7 to 9. In Example 7, an ultrasonic wave was applied at an oscillation frequency of 28 kHz during the etching process, while in Example 8, an ultrasonic wave was applied at an oscillation frequency of 45 kHz. In both of Examples 7 and 8, cavitation actively occurred, and favorable through holes with a wall angle of 85° or more (straight holes) were obtained. The ultrasonic bath used was an ultrasonic bath capable of varying the oscillation frequency and sold under the product code W-113 (manufactured by Honda Electronics Co., Ltd.; output power: 100 W, oscillation frequency: 28 kHz/45 kHz/100 kHz, bath size: W240×D140×H100 (in units of mm)).
In Example 9, an ultrasonic wave was applied at an oscillation frequency of 100 kHz. Cavitation hardly occurred, and the wall angle was 81° at the first surface and 82° at the second surface. Namely, the wall angle was smaller than those achieved at a lower oscillation frequency. Enhancing the ultrasonic wave intensity can increase the wall angle and may thus be advantageous in the case of a sample susceptible to damage. However, an oscillation frequency higher than 100 kHz is not preferred because the threshold for the occurrence of cavitation sharply increases when such a high oscillation frequency is employed.

Comparative Example 1

A sample (glass sample 1) identical to that used in Example 1 was etched so that a substrate thickness equal to that in Example 1 was obtained. In this etching, an etchant free of any surfactant and containing 0.5 mass % of hydrofluoric acid and 3.0 mass % of nitric acid was used, the temperature of the etchant was controlled to 30° C., and the etchant was stirred with a stirrer rather than with an ultrasonic wave. The wall angle was measured for the resulting glass in the same manner as in Example 1. In the resulting glass, the wall angle was 76° at the first surface and 77° at the second surface, and through holes formed were obviously constricted in the middle. An actually captured image is shown in FIG. 6.

Comparative Example 2

A sample (glass sample 1) identical to that used in Example 1 was etched until through holes were formed. In this etching, an etchant free of any surfactant and containing 2.0 mass % of hydrofluoric acid and 3.0 mass % of nitric acid was used, the temperature of the etchant was controlled to 30° C., and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². The wall angle was measured for the resulting glass in the same manner as in Example 1. In the resulting glass, the wall angle was 72° at the first surface and 73° at the second surface, and the through holes formed were obviously constricted in the middle.

Glass sample

1

Etchant	Hydrofluoric acid	0.5	0.5	0.5	0.5	2.0
	(mass %)
	Nitric acid (mass %)	13.0	13.0	13.0	3.0	3.0
	Surfactant* (ppm)	150	150	150	0	0

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	28	45	100	—	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.30	0.30	0.30	—	0.26
Substrate	Before etching (μm)	520	520	520	520	520
thickness	After etching (μm)	440	440	440	430	350

Etching speed (μm/min)

0.9

1.0

0.5

2.9

As described above, it was confirmed that the production method according to the present invention is capable of avoiding forming a hole with a shallow wall angle and capable of producing a glass with a fine structure such as a deep hole or groove extending with high straightness in the thickness direction of a substrate.

Examples 10 to 12

Glass substrates having a size of 30 mm×30 mm×t0.52 mm and containing components as shown for glass samples 2 to 4 in Table 1 were used as samples. Glasses with fine structures were produced by performing ultrasonically-assisted etching in the same manner as in Example 1, except for changing the etching conditions to those shown in Table 5. The etching conditions and the evaluation results are shown in Table 5. In all the examples, favorable through holes with a wall angle of 85° or more were obtained. An image captured for Example 12 is shown as an example in FIG. 7.

TABLE 5

Example	Example	Example
10	11	12

Glass sample

2

3

4

Etchant	Hydrofluoric acid	2.0	2.0	2.0
	(mass %)
	Nitric acid (mass %)	3.0	3.0	3.0
	Surfactant* (ppm)	15	15	15

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	40	40	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.26	0.26	0.26
Substrate	Before etching (μm)	520	520	520
thickness	After etching (μm)	440	440	440

Etching speed (μm/min)

1.9

1.8

2.8

Opening	First surface (μm)	61	64	50
diameter	Second surface (μm)	79	82	55
Wall angle	First surface (°)	85	86	87
	Second surface (°)	85	87	88

*Amount exclusive of solvent

Example 13

A sample identical to that used in Example 1 was etched until through holes were formed. In this etching, hydrochloric acid (35.0 to 37.0% aqueous solution, manufactured by Kanto Chemical Co., Inc.) was used instead of nitric acid as the inorganic acid. Specifically, an etchant containing 2.0 mass % of hydrofluoric acid, 6.0 mass % of hydrochloric acid, and 150 ppm of the surfactant was used, the temperature of the etchant was controlled to 30° C., and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². That is, a glass with fine structures was obtained in the same manner as in Example 1, except for changing the conditions to those shown in Table 6. In the resulting glass, the wall angle was 85° at the first surface and 88° at the second surface; namely, favorable through holes with a wall angle of 85° or more were obtained. The etching conditions and evaluation results are shown in Table 6.

	TABLE 6

	Example 13

Glass sample

1

Etchant	Hydrofluoric acid	2.0
	(mass %)
	Hydrochloric acid	6.0
	(mass %)
	Surfactant* (ppm)	150

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.26
Substrate	Before etching (μm)	520
thickness	After etching (μm)	460

Etching speed (μm/min)

3.2

Opening	First surface (μm)	62
diameter	Second surface (μm)	59
Wall angle	First surface (°)	85
	Second surface (°)	88

*Amount exclusive of solvent

Example 14

A substrate of synthesized quartz (manufactured by Shin-Etsu Chemical Co., Ltd.) having a size of 30 mm×30 mm×t0.50 mm was used as a glass sample. The laser-assisted formation of modified portions was carried out using a femtosecond laser under the following conditions: output power=6 μJ, spot diameter in processing area=9 μm, pulse width=800 fs, repetition frequency=2 kHz, and processing speed=0.2 mm/sec. It was confirmed with an optical microscope that modified portions or fine cavities having a diameter of about 10 μm and distinct from the rest of the glass sample were formed in the laser-irradiated areas. A captured image is shown in FIG. 8.
A glass with fine structures was produced by performing ultrasonically-assisted etching in the same manner as in Example 1, except for changing the etching conditions (the composition of the etchant, the ultrasonic irradiation conditions, and the etching speed) to those shown in Table 7. In the resulting glass, the wall angle was 90° at the first surface and 89° at the second surface; namely, substantially perpendicular through holes were formed in the synthesized quartz. The etching conditions and evaluation results are shown in Table 7. A captured image is shown in FIG. 9.

	TABLE 7

	Example 14

	Glass sample	Synthesized
		quartz

Etchant	Hydrofluoric acid	8.0
	(mass %)
	Nitric acid (mass %)	16.0
	Surfactant* (ppm)	150

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.26
Substrate	Before etching (μm)	500
thickness	After etching (μm)	455

Etching speed (μm/min)

0.26

Opening	First surface (μm)	64
diameter	Second surface (μm)	61
Wall angle	First surface (°)	90
	Second surface (°)	89

*Amount exclusive of solvent

Comparative Example 3

A sample identical to that used in Example 1 was etched. In this etching, an etchant free of hydrofluoric acid and containing 14.0 mass % of nitric acid and 150 ppm of the surfactant was used, the temperature of the etchant was controlled to 30° C., and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². Despite continuing the etching for 3 hours, the thickness of the glass substrate remained unchanged, and no through holes were obtained. This demonstrates that without the addition of hydrofluoric acid, etching fails to proceed sufficiently to form fine structures such as holes or grooves in the glass.

Comparative Example 4

A sample identical to that used in Example 1 was etched until through holes were formed. In this etching, an etchant free of nitric acid and containing 2.0 mass % of hydrofluoric acid and 150 ppm of the surfactant was used, the temperature of the etchant was controlled to 30° C., and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². In the resulting glass, the wall angle was 78° at the first surface and 81° at the second surface; namely, through holes with a wall angle of 80° or more were not obtained, unlike the case where nitric acid was added.

Comparative Example 5

A sample identical to that used in Example 1 was etched until through holes were formed. In this etching, the concentration of nitric acid was increased. Specifically, an etchant containing 2.0 mass % of hydrofluoric acid, 20.0 mass % of nitric acid, and 150 ppm of the surfactant was used, the temperature of the etchant was controlled to 30° C., and an ultrasonic wave was applied at 40 kHz and 0.26 W/cm². In the resulting glass, the wall angle was 78° at the first surface and 79° at the second surface; namely, through holes with a wall angle of 80° or more were not obtained.

TABLE 8

Compar-	Compar-	Compar-
ative	ative	ative
Example 3	Example 4	Example 5

Glass sample

1

Etchant	Hydrofluoric acid	0.0	2.0	2.0
	(mass %)
	Nitric acid (mass %)	14.0	0.0	20.0
	Surfactant* (ppm)	150	150	150

Temperature (° C.)

30

Ultrasonic	Oscillation frequency	40	40	40
irradiation	(kHz)
conditions	Intensity (W/cm²)	0.26	0.26	0.26
Substrate	Before etching (μm)	520	520	520
thickness	After etching (μm)	460	460	430

Etching speed (μm/min)

0.0

1.6

3.7

Opening	First surface (μm)	—	67	54
diameter	Second surface (μm)	—	57	83
Wall angle	First surface (°)	—	78	78
	Second surface (°)	—	81	79

*Amount exclusive of solvent

INDUSTRIAL APPLICABILITY

With the method for producing a glass with a fine structure according to the present invention, it is possible to avoid forming a hole with a shallow wall angle and obtain a glass having a fine structure such as a deep hole or groove extending with high straightness in the thickness direction of a substrate.

Comparative

Comparative

1. A method for producing a glass with a fine structure, the method comprising an etching step of etching a glass by irradiating the glass with an ultrasonic wave, wherein

an etchant used in the etching step comprises:

hydrofluoric acid;

at least one inorganic acid selected from the group consisting of nitric acid, hydrochloric acid, and sulfuric acid; and

a surfactant, and

in the etchant, a concentration of the hydrofluoric acid is 0.05 mass % to 8.0 mass %, a concentration of the inorganic acid is 2.0 mass % to 16.0 mass %, and a content of the surfactant is 5 ppm to 1000 ppm.

2. The method for producing a glass with a fine structure according to claim 1, further comprising, prior to the etching step, a step of forming a modified portion or a processing hole by irradiating the glass with a laser pulse.

3. The method for producing a glass with a fine structure according to claim 1, wherein an oscillation frequency in the irradiation with the ultrasonic wave is 100 kHz or less.

4. The method for producing a glass with a fine structure according to claim 1, wherein an intensity of the ultrasonic wave is 0.10 W/cm²to 5.0 W/cm².

5. The method for producing a glass with a fine structure according to claim 1, wherein the inorganic acid is nitric acid.

6. The method for producing a glass with a fine structure according to claim 1, wherein the content of the surfactant is 10 ppm to 800 ppm.

7. The method for producing a glass with a fine structure according to claim 1, wherein the surfactant is a non-ionic surfactant.

8. The method for producing a glass with a fine structure according to claim 1, wherein the glass is a low-alkali glass or alkali-free glass containing TiO₂in an amount of 0.1 mol % or more and less than 5.0 mol %.

9. The method for producing a glass with a fine structure according to claim 1, wherein the glass is a low-alkali glass or alkali-free glass containing CuO in an amount of 0.1 mol % or more and 2.0 mol % or less.

10. The method for producing a glass with a fine structure according to claim 1, wherein the fine structure in the glass subjected to the etching step is a through hole, and a wall angle of the through hole is 80° or more.