JP3357222B2 - Glass substrate with minute recess and flat microlens array using this glass substrate - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a glass substrate having minute concave portions suitable for manufacturing a flat microlens in which a concave portion of a flat glass substrate is filled with a transparent resin or the like, and a method of manufacturing the same.

[0002]

2. Description of the Related Art A projector television (PTV) using a transmission type liquid crystal display device has been put to practical use. Currently, in the development of this PTV, the focus is on how to achieve high brightness on the screen, and the development of high-output light valves and optical devices and the application of flat microlenses are being vigorously studied. Have been.

If a flat microlens is used for the PTV, light that has entered the black matrix or pixel electrode portion of the liquid crystal display element and has not contributed to the illumination of the pixel opening can be greatly reduced. It is possible to improve the luminance on the screen without increasing the luminance, and as a result, it is possible to solve the problem of deterioration of characteristics of the display element due to light and heat.

In this case, the flat microlens is disposed on the light incident side of the liquid crystal display element, and condenses the light incident on the black matrix and the pixel electrode portion to the pixel opening to effectively use the light. It has the function of improving the aperture efficiency.

Conventionally, as a flat plate microlens, a soda lime glass has a corrosion-resistant protective film (mask film) of Ti or the like.
By using a well-known photolithography technique, a circular or linear slit-shaped opening is provided, and the cross-section is substantially formed by a so-called ion exchange method in which this is immersed in a molten salt and ion-exchanged from the opening. Flat microlens array having a semicircular refractive index distribution (Japanese Patent Laid-Open No. 57-537)
No. 02), and a flat microlens in which a hemispherical concave portion is formed on the surface of a glass substrate by chemical etching and filled with a transparent resin or the like and used as a lens is known (Japanese Patent Application Laid-Open No. 5-45624). Furthermore, a method of forming a concave portion on the surface of a semiconductor substrate by dry etching is disclosed (JP-A-1-219702).

[0006]

In particular, a planar glass substrate provided with a mask film having a large number of fine openings formed on its surface is subjected to chemical etching, and etching is performed from the fine openings to obtain a contour in plan view. In the production of a flat microlens in which a substantially circular concave portion is filled with a transparent resin or the like to form a lens, a defect sometimes occurs during chemical etching. Specifically, a part that should originally have a circular contour shape may have a distorted elliptical (rugby ball) contour shape, or the mask film may peel off from the glass substrate during chemical etching. Was.

Therefore, when a lens is formed by filling the concave portion with a resin or the like having a different refractive index from that of the glass substrate, the light-collecting characteristic is determined by the difference between the refractive index of the glass substrate and the refractive index of the resin or the like. Only be decided. Further, the refractive index of the glass substrate and the refractive index of the resin and the like,
It is difficult to freely change the light-collecting characteristics of the lens, since the selection cannot be made freely.

An object of the present invention is to provide a glass substrate for a flat plate type microlens in which minute concave portions formed by etching and arranged one-dimensionally or two-dimensionally have a circular contour. Further, a flat microlens using the same is provided.

[0009]

According to the present invention, an elliptical defect and peeling of a corrosion-resistant film which occur when a glass substrate provided with a corrosion-resistant film is immersed in an etchant to form a minute concave portion of a microlens are formed on the surface of the glass substrate. This is based on the finding that it is governed by the degree of polishing, especially the surface roughness.

In general, a glass substrate is subjected to lapping and polishing after cutting to create a smooth surface. However, the scratch once generated in the lapping or polishing process remains in the vicinity of the surface of the glass substrate in the form of a latent scratch even if the polish progresses and it cannot be apparently determined.

When the latent scratch remaining near the surface of the glass substrate comes in contact with the glass etchant, the etchant penetrates into the deep scratch and the latent scratch is etched. by this,
Latent scratches that could not be determined before etching become apparent.

When a corrosion-resistant protective film is formed on a glass substrate having a latent scratch, for example, a minute opening corresponding to the arrangement of the lens array is formed in the corrosion-resistant film, and a concave portion is to be formed by etching from the minute opening. When the latent scratches become apparent, the etching proceeds in an elliptical shape, or the etching proceeds rapidly in a specific direction, so that the corrosion-resistant film may peel off from the glass substrate.

FIG. 2 shows the surface roughness (Ra) of the glass substrate.
An example of a contour of a concave portion when a concave portion formed when a corrosion-resistant protective film is formed on the substrate, a minute opening is formed in the corrosion-resistant film, and isotropically etched from the minute hole, and a concave portion is formed in a plan view. Is shown. Note that a was defined and measured as a being the shortest length of the contour of the concave portion and b being the longest length. Arrows in the figure indicate the directions of latent scratches on the glass substrate surface. The surface roughness (Ra) was measured with an atomic force microscope (Digital Instruments Co., Ltd .: NanoScope). In other words, it was confirmed that if there is a latent flaw on the surface of the glass substrate, the direction of the latent flaw is particularly preferentially etched, and the recess formed has a rugby ball shape as described above.

FIG. 3 is a graph showing this relationship. In this example, when Ra of the glass substrate is 0.55 nm or more, the contour b / a of the concave portion formed by etching becomes 1.5 / nm.
As described above, it can be seen that the contour is disturbed and it can no longer be said that it is no longer circular. On the other hand, when Ra of the substrate is less than 0.4 nm, the b
/ A is 1.1 or less, and it can be said that the contour keeps a substantially circular shape.

Further, when the Ra is 0.24 nm or less, the b / a is almost 1, and it can be said that the outline is a perfect circle.

This is caused by the presence of the latent scratches in the minute recesses formed by etching, and not all the recesses have the above-mentioned rugby ball shape. When the Ra of the glass substrate is large (for example, Ra
> 0.7 nm), most of the recesses have the above-mentioned rugby ball shape. For example, 0.4 <Ra <0.5n
In the range of m, there is a problem of establishing the existence of latent scratches on the surface of the glass substrate. Therefore, even if one concave portion has a good circular contour shape, another concave portion may have a rugby ball shape. .

The etching mechanism of glass containing silica as a main component by HF is simply represented by the following equation. SiO ₂ + 6HF → H ₂ SiF ₆ + 2H ₂ O In general, it is known that HF ₂ ^- ions govern the etching rate (Nikkei Micro Devices, 19
HF ₂ ^- ion concentration is determined by the following equilibrium of the dissociation reaction. _{HF + H 2 O → H 3} O + + F - HF + F - → HF 2 -

Here, the relationship between the opening diameter of the mask film in the etching and the shape of the concave portion will be considered. The etching reaction proceeds isotropically from the opening of the mask film. At this time, the ratio between the opening diameter and the etching length is 1
In the case of / 4 or less, the progress of the etching reaction can be treated as point diffusion. The shape of the recess at this time can be regarded as substantially hemispherical.

However, when the ratio between the opening diameter and the etching length exceeds 1/4, it can no longer be treated as point diffusion. The shape of the recess at this time is a shape like a bowl having a bottom corresponding to the opening diameter, that is, a shape obtained by rotating a semi-ellipse obtained by bisecting an ellipse in the major axis direction (strictly speaking. And this shape
Although different from the shape of a bowl as is commercially available, this shape will be referred to herein as a bowl shape.

In the present invention, the minute concave portions are 1 to 1
It means a size of about 00 μm, especially about 20 to 40 μm. This is because if the size of the concave portion is large, even if uneven etching occurs due to the appearance of the latent scratches and polishing scratches described above, the influence thereof is small.

In the present invention, a corrosion-resistant film is formed in order to suppress the occurrence of non-uniform etching and the peeling of the corrosion-resistant film due to the appearance of the latent scratch, and to make the contour of the minute concave portion circular when viewed in plan. It is characterized in that the surface roughness of the glass substrate is strictly controlled to a center line average roughness Ra of 0.4 nm or less.

When the center line average roughness Ra of the surface of the glass substrate exceeds 0.4 nm, uneven etching due to the appearance of latent scratches and polishing scratches and peeling of the corrosion-resistant film are liable to occur.

Basically, the surface roughness of a glass substrate on which a corrosion resistant film is formed is preferably as small as possible, but in practice, it is technically very difficult to make the center line average roughness Ra less than 0.05 nm. It is difficult and it is difficult to secure its productivity.

Further, considering the technical and economical points after achieving the above-mentioned problems, Ra of the glass substrate is set to 0.1.
About 1 to 0.24 nm is particularly preferable.

The surface of the glass substrate whose center line average roughness Ra is controlled to 0.4 nm or less can be created by the following method or the like. (1) In a final polishing step using abrasive grains such as cerium oxide in a conventional polishing method, polishing is performed gently under low load and low speed conditions. (2) Cerium oxide having a small particle size in the final polishing step Polishing is performed using abrasive grains. (3) Polishing is performed using abrasive grains having a relatively low hardness such as colloidal silica having a spherical shape.

For a substrate having a center line average roughness Ra of more than 0.4 nm, a film having the same composition as the glass substrate is formed on the surface of the glass substrate by a coating film thermal decomposition method, a sol-gel method, or the like. By sintering and filling the latent wound,
The surface roughness of the glass substrate can be improved, and the center line average roughness can be reduced to 0.4 nm or less. In addition, the surface roughness of the glass substrate can be improved by using high-energy charged particles to collide with the glass substrate by ion implantation to achieve local high temperature and use viscous flow and sintering of the glass. The average roughness can be 0.4 nm or less.

By smoothing the surface of the glass substrate by the above-mentioned various methods, it is possible to eliminate the occurrence of uneven etching due to latent scratches on the glass substrate. further,
When a corrosion-resistant protective film having a desired pattern is formed on a glass substrate, etching can proceed isotropically from the minute opening of the desired pattern. When a transparent resin or the like is filled in the concave portion of the substrate to produce a flat microlens, a favorable microlens can be formed.

Examples of the glass substrate used in the present invention include quartz glass, soda lime glass, alkali aluminosilicate glass, alkali borosilicate glass, multi-component alkali-free glass, and low expansion crystallized glass.

The smoothness of the glass substrate referred to in the present invention is a polishing level conventionally called photomask polishing. The smoothness of the glass substrate at this level has a high resolution such as that of an atomic force microscope. It can be evaluated by an analysis method.

As the corrosion-resistant protective film material used in the present invention, an appropriate material can be selected depending on the resistance to the etchant used, the workability of photolithographic patterning, and the film forming cost. The film thickness to be formed can be arbitrarily selected according to the purpose, and film materials having different compositions can be laminated in multiple layers.

For example, examples of the corrosion-resistant protective film material include metals such as chromium, nickel, tantalum, silicon, and gold, and oxides or nitrides thereof. These corrosion-resistant protective films can be formed by a sputtering method, an evaporation method, or the like.

When etching the above-mentioned glass substrate with a corrosion-resistant film, the etchant composition is selected according to the composition of the glass substrate to be etched. For example, when etching a quartz glass substrate, an aqueous solution containing hydrogen fluoride and a surfactant such as sodium dodecylbenzenesulfonate can be used as an etchant. In addition, when etching a soda lime glass substrate, a mineral acid such as sulfuric acid and an organic acid such as acetic acid are often added in addition to hydrogen fluoride, and a surfactant such as sodium dodecylbenzenesulfonate is used as necessary. Should be added.

In the present invention, the boundary with the surface of the glass substrate formed by the above-mentioned minute concave portion is a substantially perfect circle when viewed in plan. Therefore, a flat microlens having good optical performance can be obtained by filling the minute concave portion with a resin or the like having a different refractive index from the substrate.

Further, in the manufacturing method of the present invention, the surface roughness of the glass substrate on which the corrosion-resistant film is formed is controlled in order to suppress the occurrence of minute uneven etching and the peeling of the corrosion-resistant film having openings. Strictly, the center line average roughness Ra is 0.4 nm or less by the method, more preferably 0.1 to 0.
It is controlled to 24 nm. For this reason, it is possible to eliminate the occurrence of uneven etching due to latent scratches on the glass substrate surface.

Further, by further etching the above-mentioned glass substrate, a glass substrate in which minute concave portions are densely filled can be obtained.

[0036]

BEST MODE FOR CARRYING OUT THE INVENTION

(Example 1) Cerium oxide abrasive grains having a small particle diameter (average particle diameter of primary particles: 0.05 μm, average particle diameter of secondary particles: about 0.5 μm)
m), the final polishing of the quartz glass substrate was performed at low load (30 gf / cm ² ) and low speed (50 rpm).
Atomic force microscope (Digital Instruments Co., Ltd.):
As a result of examining the surface roughness of the polished glass substrate by NanoScope (hereinafter referred to as “AFM”), the center line average roughness R
a was found to be 0.15 nm.

As a corrosion-resistant protective film against an etchant on the surface of the present quartz glass substrate by a sputtering method,
A three-layer film of CrOx / Cr / CrOx was formed. As a result of ESCA analysis of the Cr film, 40
Cr ・ 60CrOx / 75Cr ・ 25CrOx / 45Cr
-It had a three-layer structure of 55CrOx (atomic%). Next, small openings were formed in the three-layer Cr film in a predetermined micro-recess arrangement pattern by photolithography of applying, exposing, and developing a photoresist. The formed small aperture array has a hexagonal array (pitch in the x direction 50 μm, pitch 4 in the y direction).
0 μm), whereby a six-row array of minute concave portions is obtained. In the first embodiment, in order to obtain a minute concave portion,
The small opening diameter is 10 μm, and the etching length is 15 μm.
(Etching length / etching length = ２).

The substrate with the Cr film having the small opening is
Chemical etching was performed by immersion in an aqueous solution containing F and sodium dodecylbenzenesulfonate as a surfactant. Here, the concentrations of HF and sodium dodecylbenzenesulfonate were 10% by weight and 0.1% by weight, respectively. Thus, the surface of the quartz glass substrate was etched starting from the small opening. The corrosion-resistant protective film was etched with an aqueous solution containing cerium ammonium nitrate and perchloric acid, and was completely removed.

As a result of observing the substrate with an electron microscope (SEM), it was found that a side wall of an isotropic recess having a radius of curvature of about 15 μm and a bowl-shaped recess having a bottom having a diameter of 10 μm (the cross-sectional shape was 40 μm long axis, single It was found that a half-ellipse obtained by dividing an ellipse having an axis of 30 μm into two in the major axis direction) was obtained corresponding to the position where the mask opening was formed (FIG. 1). As a result of observing the minute concave portions all over, defects such as elliptical defects were not observed at all. FIG. 4A shows a trace of a row of contours having minute recesses formed, and FIG. 4B shows a partially enlarged cross-sectional view thereof.

By the above-described procedure, a substrate having minute concave portions each independently having a circular outline can be obtained.

Further, a case where the minute concave portions are densely arranged on the entire surface of the substrate will be described below. The substrate was immersed again in the previous etchant to etch the entire substrate surface. The two-stage etching resulted in a completely densely packed arrangement in which adjacent hexagonal concave portions formed the same hexagon in plan view and were in close contact with each other.

After the two-step etching process, the fine concave portions were filled with an epoxy-based transparent resin material having a higher refractive index than that of the quartz glass substrate, and a quartz substrate was separately bonded thereon, and the resin was light-cured. As a result, a defect-free quartz flat plate microlens could be obtained.

(Example 2) The final polishing of the quartz glass substrate was performed under the same conditions as in Example 1 by using colloidal silica (average particle size: 0.05 µm) as abrasive grains. According to the AFM observation, the center line average roughness Ra of the polished glass substrate is:
It turned out to be 0.12 nm.

On the surface of the quartz glass substrate, a Cr film was formed as a corrosion-resistant protective film against an etchant by a sputtering method. As a result of ESCA analysis of the Cr film, it was found to be 80Cr.20CrOx (atomic%) with a total film thickness of 120 nm. Next, in the same manner as in Example 1, a small opening pattern was formed in the corrosion-resistant protective film, an etching process was performed, and then the corrosion-resistant protective film was removed.

As a result of observing the substrate with an electron microscope (SEM), it was found that a side wall of an isotropic recess having a radius of curvature of about 15 μm and a bowl-shaped recess having a bottom with a diameter of 10 μm (the cross-sectional shape was 40 μm long axis, single It has been found that a half-ellipse obtained by dividing an ellipse whose axis is 30 μm into two in the major axis direction) was obtained corresponding to the mask opening forming position. As a result of observing the minute concave portions all over, defects such as elliptical defects were not observed at all.

Next, the substrate was immersed again in the above etchant to etch the entire surface of the substrate. The two-stage etching resulted in a completely densely packed arrangement in which adjacent hexagonal concave portions formed the same hexagon in plan view and were in close contact with each other.

After the two-step etching, the fine concave portions were filled with an epoxy-based transparent resin material having a higher refractive index than that of the quartz glass substrate, and a quartz substrate was separately bonded thereon, and the resin was cured by light. As a result, a defect-free quartz flat plate microlens could be obtained.

Example 3 Tetraethoxysilane (Si
Dilute hydrochloric acid (1% by weight) was added to an ethanol solution of (OC ₂ H ₅ ) ₄ ), and the mixture was stirred at room temperature for 1 hour to carry out hydrolysis and condensation polymerization of tetraethoxysilane. Here, the molar ratio of ethanol and water to tetraethoxysilane was set to 5 and 6, respectively. This solution was further diluted with ethanol to control the thickness of the coating,
A sol-gel coating solution was used.

Using this coating solution, a quartz glass substrate (Ra = 0.6 nm) having a normal final polishing level
Was subjected to dip coating. After drying at room temperature for 1 hour, heat treatment is performed at 850 ° C. for 5 hours,
The sol-gel SiO ₂ film was sintered. After sintering, the thickness of the sol-gel SiO ₂ film was 200 nm. As a result of observation by AFM, Ra of the fired glass substrate was about 0.2 n.
m.

On the surface of the quartz glass substrate, a Cr film was formed as a corrosion-resistant protective film against an etchant by a sputtering method. This Cr film was the same as in Example 2. Next, in the same manner as in Example 1, a small opening pattern was formed in the corrosion-resistant protective film, an etching process was performed, and then the corrosion-resistant protective film was removed.

As a result of observing the substrate with an electron microscope (SEM), it was found that an isotropic concave side wall surface having a radius of curvature of about 15 μm and a bowl-shaped concave section having a bottom with a diameter of 10 μm (the cross-sectional shape was 40 μm long axis, single It has been found that a half-ellipse obtained by dividing an ellipse whose axis is 30 μm into two in the major axis direction) was obtained corresponding to the mask opening forming position. As a result of observing the minute concave portions all over, defects such as elliptical defects were not observed at all.

Next, the substrate was immersed again in the above etchant to etch the entire surface of the substrate. The two-stage etching resulted in a completely densely packed arrangement in which adjacent hexagonal concave portions formed the same hexagon in plan view and were in close contact with each other.

After the two-step etching, the fine concave portions were filled with an epoxy-based transparent resin material having a higher refractive index than that of the quartz glass substrate, and a quartz substrate was separately bonded thereon, and the resin was cured by light. As a result, a defect-free quartz flat plate microlens could be obtained.

(Example 4) Using a cerium oxide abrasive having a small particle diameter (average particle diameter of primary particles: 0.05 μm, average particle diameter of secondary particles: about 0.5 μm), low load (30 gf / c)
m ² ), the final polishing of the soda lime glass substrate was performed at a low speed (50 rpm). As a result of examining the surface roughness of the polished glass substrate by an atomic force microscope (AFM), it was found that the center line average roughness Ra was 0.20 nm.

Under the same conditions as in Example 1 of the present soda lime glass substrate, a three-layer film of CrOx / Cr / CrOx was formed. Next, in the same manner as in Example 3, a small opening pattern was formed in the corrosion-resistant protective film, and an etching process was performed.
Subsequently, the corrosion-resistant protective film was removed.

As a result of observing the substrate with an electron microscope (SEM), it was found that an isotropic concave side wall having a radius of curvature of about 15 μm and a bowl-shaped concave having a bottom having a diameter of 10 μm (the cross-sectional shape was 40 μm long axis, single It has been found that a half-ellipse obtained by dividing an ellipse whose axis is 30 μm into two in the major axis direction) was obtained corresponding to the mask opening forming position. As a result of observing the minute concave portions all over, defects such as elliptical defects were not observed at all.

Next, the substrate was immersed again in the above etchant to etch the entire surface of the substrate. The two-stage etching resulted in a completely densely packed arrangement in which adjacent hexagonal concave portions formed the same hexagon in plan view and were in close contact with each other.

After the two-step etching process, the fine concave portions were filled with an epoxy-based transparent resin material having a higher refractive index than the soda-lime glass substrate, and a quartz substrate was separately bonded thereon, and the resin was light-cured. . As a result, a defect-free soda-lime glass flat microlens could be obtained.

Example 5 A soda-lime glass substrate was finally polished under the same conditions as in Example 4 using colloidal silica (average particle size: 0.05 μm) as abrasive grains. AF
Observation of the center line average roughness Ra of the polished glass substrate by observation
Was found to be 0.14 nm.

A Cr film was formed on the surface of the present soda lime glass substrate under the same conditions as in Example 2. Next, a small opening pattern was formed on the corrosion-resistant protective film in the same manner as in Example 2.
Further, an etching treatment was performed, and then the corrosion-resistant protective film was removed.

As a result of observing the substrate with an electron microscope (SEM), it was found that a side wall of an isotropic recess having a radius of curvature of about 15 μm and a bowl-shaped recess having a bottom with a diameter of 10 μm (the cross-sectional shape was 40 μm long axis, single It has been found that a half-ellipse obtained by dividing an ellipse whose axis is 30 μm into two in the major axis direction) was obtained corresponding to the mask opening forming position. As a result of observing the minute concave portions all over, defects such as elliptical defects were not observed at all.

Next, the substrate was immersed again in the above etchant to etch the entire surface of the substrate. The two-stage etching resulted in a completely densely packed arrangement in which adjacent hexagonal concave portions formed the same hexagon in plan view and were in close contact with each other.

After the two-stage etching process, the fine concave portions were filled with an epoxy resin material having a higher refractive index than that of the soda lime glass substrate, and a quartz substrate was separately bonded thereon, and the resin was cured by light. As a result, a defect-free soda-lime glass flat microlens could be obtained.

In each of the first to fifth embodiments described above, the minute concave portions are arranged hexagonally.
If the fine recesses are arranged in four directions according to the purpose and the above-described two-stage etching process is performed, the outline thereof is square or rectangular in a plan view, and the glass substrate with the fine recesses is arranged on the substrate surface in a completely dense manner. Needless to say, this is obtained.

Further, in the above-described first to fifth embodiments, the glass substrate with minute recesses arranged on the substrate surface in a completely dense manner was obtained by the above-described two-stage etching process. Depending on the processing time,
Needless to say, a glass substrate with minute concave portions with a part of the initial substrate surface left can be obtained.

Comparative Example 1 The same three-layer CrOx / Cr / CrOx film as in Example 1 and photolithographic patterning were performed on a quartz glass substrate (R = 0.45 nm) of a conventional polished level. Further, the conventional polishing of the quartz substrate with the Cr film having the small opening was etched under the same conditions as in Example 1. Thus, the surface of the quartz glass substrate was etched starting from the small opening.

After removing the corrosion-resistant protective film, observation was made with an optical microscope and an electron microscope (SEM). Latent scratches are left on the surface of a quartz glass substrate having a conventional polishing level of Ra of about 0.45 nm, and these should become evident in the etching process and minute recesses should be formed. Corresponding to the direction, the shape in plan view became an elliptical distorted opening. When it was attempted to form a lens by filling the concave portion with a transparent resin or the like, it was determined that the concave portion would cause a lens defect.
FIG. 5 shows a trace of the outline of one row having the concave portion.

Comparative Example 2 The same three-layer film of CrOx / Cr / CrOx and photolithographic patterning as in Example 4 were performed on a soda-lime glass substrate (R = 0.75 nm) of the conventional polishing level. . Further, etching of the conventional polished soda lime glass substrate with the Cr film having the small opening was performed under the same conditions as in Example 4. Thereby, the surface of the soda lime glass substrate was etched starting from the small opening.

After removing the corrosion-resistant protective film, observation was performed with an optical microscope and an electron microscope (SEM). Latent scratches remain on the surface of a soda lime glass substrate having a conventional polishing level of Ra of about 0.75 nm, and these should become evident in the etching process, and minute recesses should be formed. The shape in plan view became an elliptical distorted opening corresponding to the direction of the scratch. Also, C
The r film was peeled off during the etching process, and the recess was not formed. It was determined that the concave portion and the portion where the Cr film was peeled off were defects such as lens defects.

In the present embodiment, the results for the quartz glass substrate and the soda lime glass substrate are shown. However, the relationship between the glass surface roughness and the etching characteristics is the same for multi-component alkali-free glass and low expansion crystallized glass. showed that.

[0071]

According to the various methods described above, when a fine concave portion is formed on a glass substrate whose surface is smoothed to have a center line average roughness Ra of 0.4 nm or less by an etching method, latent scratches on the glass substrate can be obtained. It is possible to eliminate uneven etching caused by polishing scratches.

[Brief description of the drawings]

FIG. 1 is a plan view of a glass substrate having minute concave portions formed by etching according to the present invention.

FIG. 2 is a schematic diagram illustrating a relationship between Ra of a glass substrate and a contour of a minute concave portion.

FIG. 3 is a graph showing the relationship between Ra of a glass substrate and the contour of a minute concave portion.

FIG. 4 is a schematic diagram showing a contour of a minute concave portion and a partially enlarged cross section when Ra = 0.15 nm of a glass substrate.

FIG. 5 shows a case where a conventional polishing state is poor (Ra = 0.45n)
The schematic diagram showing the outline of the elliptical (rugby ball-shaped) outline concave part obtained from the glass substrate of m).

[Explanation of symbols]

Reference numeral 1 denotes a glass substrate, 2 denotes an etched portion, 3 denotes a contour of a minute concave portion, 4 denotes a transparent resin.

Continuation of the front page (72) Inventor Kenjiro Hamanaka 3-5-1-11 Doshomachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd. (56) References JP-A-8-220306 (JP, A) JP-A-9 −43588 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02B 3/00

Claims (5)

(57) [Claims] 1. A large number of minute recesses formed by an etching method are regularly arranged one-dimensionally or two-dimensionally on a glass substrate surface having a center line average roughness Ra of 0.4 nm or less by a polishing method. A glass substrate for a flat microlens, wherein the minute concave portion has a substantially bowl shape, a radius of curvature of a bottom portion is larger than a radius of curvature of a side portion, and an outline of the minute concave portion when viewed in plan is substantially circular. And a ratio of the major axis to the minor axis of 1.1 or less. However, the longest diameter of the contour is the long diameter, and the shortest diameter is the short diameter. 2. The glass substrate with minute recesses according to claim 1, wherein the outline is circular. 3. A large number of minute concave portions formed by an etching method are regularly arranged in a one-dimensional or two-dimensional manner on the surface of a glass substrate having a center line average roughness Ra of 0.4 nm or less by a polishing method. A glass substrate for a flat microlens, wherein the minute concave portion has a substantially bowl shape, a radius of curvature of a bottom portion is larger than a radius of curvature of a side portion, and is formed on substantially the entire surface of the substrate on which a lens is formed. A glass substrate with minute recesses. 4. The glass substrate with minute recesses according to claim 3, wherein the minute recesses are arranged in a completely dense manner, and the outline shape is a square, a rectangle, a regular hexagon or a hexagon in plan view. With glass substrate. 5. A flat plate type wherein the minute concave portions of the glass substrate with minute concave portions according to claim 1 are filled with a resin having a refractive index different from that of the glass substrate to have a lens function. Micro lens array.