WO2024004712A1 - Optical element manufacturing method and optical element - Google Patents

Abstract

Provided are an optical element manufacturing method and an optical element that has high moldability and that can easily suppress the influence of scattering loss. This method is for manufacturing an optical element 10 formed of a glass substrate 3 having a diffraction pattern 31, and involves forming the diffraction pattern 31 on the glass substrate 3 by using at least two resist layers.

Description

Optical element manufacturing method and optical element

The present invention relates to a method for manufacturing an optical element and an optical element.

AR/MR glasses are glasses-type wearable devices that allow you to see a digital virtual image superimposed on top of a real image. For this reason, applications are progressing in a variety of fields, including traffic guidance, work support, educational settings, and medical settings.

One known method of projecting a digital image onto a device is to guide the image using an optical element such as a light guide plate. The light guide plate includes, for example, a substrate made of glass or resin, and a diffraction grating (diffraction pattern) formed on the substrate. The diffraction pattern can be formed, for example, by applying a resin onto a substrate and pressing a mold having a periodic structure onto the resin (Patent Document 1).

Japanese Patent Application Publication No. 2001-235746 Special table 2019-533040 publication

In order to widen the viewing angle of digital images, the refractive index of substrates has been increasing in recent years, and the difference in refractive index between the substrate and the diffraction pattern is becoming larger. Such a refractive index difference causes scattering loss at the interface, which may lead to a decrease in image brightness and image quality.

To solve the above problem, for example, a diffraction grating in which metal nanoparticles are contained in a resin has been studied (Patent Document 2). However, in order to improve the refractive index of the resin, it is necessary to contain a large amount of metal nanoparticles, and there is a concern that the moldability and transmittance will decrease accordingly.

In view of the above, an object of the present invention is to provide a method for manufacturing an optical element and an optical element that have high moldability and can easily suppress the influence of scattering loss.

A method for manufacturing an optical element and various aspects of the optical element that solve the above problems will be described.

The method for manufacturing an optical element according to aspect 1 is a method for manufacturing an optical element comprising a glass substrate having a diffraction pattern, and is characterized in that the diffraction pattern is formed on the glass substrate using at least two or more resist layers. .

The method for manufacturing an optical element according to Aspect 2 includes the steps of forming a lower resist layer on the glass substrate, forming an upper resist layer on the lower resist layer, and forming a first resist pattern on the upper resist layer in Aspect 1. a first etching step of forming a second resist pattern on the lower resist layer using the first resist pattern; and a second etching step of forming a diffraction pattern on the glass substrate using the second resist pattern. is preferred.

In the method for manufacturing an optical element according to Aspect 3, in Aspect 2, when the etching rate of the lower resist layer in the second etching step is Rr2b, and the etching rate of the glass substrate in the second etching step is Gr, Gr>Rr2b. It is preferable that there be.

In the method for manufacturing an optical element according to Aspect 4, in Aspect 2 or Aspect 3, the ratio Rt2/Rr2b of the etching rate Rr2b of the lower resist layer in the second etching step and the thickness Rt2 of the lower resist layer is 1 to 40 min. is preferred.

The method for manufacturing an optical element according to Aspect 5 includes the steps of forming a lower resist layer on the glass substrate, forming an upper resist layer on the lower resist layer, and forming a first resist pattern on the upper resist layer in Aspect 1. The method preferably includes a first etching step of forming a second resist pattern in the lower resist layer using the first resist pattern.

In the method for manufacturing an optical element according to aspect 6, in any one of aspects 2 to 5, the etching rate of the upper resist layer in the first etching step is set to Rr1, and the etching rate of the lower resist layer in the first etching step is set to Rr1. When the etching rate is Rr2a, it is preferable that Rr1>Rr2a.

In the method for manufacturing an optical element according to Aspect 7, in any one of Aspects 2 to 6, the lower resist layer may be made of a metal-based resist or a metal oxide-based resist, and the upper resist layer may be made of a resin-based resist. preferable.

In the method for manufacturing an optical element according to Aspect 8, in any one of Aspects 1 to 7, it is preferable that the optical element is a light guide plate.

The optical element of aspect 9 is an optical element made of a glass substrate having a diffraction pattern, the glass substrate has a refractive index of 2 or more, and the diffraction pattern is formed directly on the glass substrate. .

The optical element of aspect 10 is an optical element comprising a glass substrate and a diffraction pattern disposed on the glass substrate, wherein the glass substrate has a refractive index of 2 or more, and the refractive index difference Δnd between the glass substrate and the diffraction pattern is is 0.2 or less.

In the optical element of aspect 11, in aspect 10, it is preferable that the Abbe number difference Δνd between the glass substrate and the diffraction pattern is 21 or less.

In the optical element of aspect 12, in any one of aspects 9 to 11, when the width at the bottom of the convex part of the diffraction pattern is a, and the width at 2/3 height from the bottom of the convex part is b. , a/b is preferably larger than 1.

In the optical element of Aspect 13, in any one of Aspects 9 to 12, Ra1/Ra2 is greater than 1, where Ra1 is the surface roughness of the concave portion of the diffraction pattern, and Ra2 is the surface roughness of the convex portion of the diffraction pattern. It is preferable.

In the optical element of Aspect 14, in any one of Aspects 9 to 13, where r is the radius of curvature of the convex portion of the diffraction pattern, it is preferable that r is 3 nm to 200 nm.

In the optical element of aspect 15, in any one of aspects 9 to 14, the glass substrate contains 0% to 12% of SiO ₂ , 0% to 10% of B ₂ O ₃ , and 0% to BaO in mass %. 13%, ZnO 0% to 5%, ZrO ₂ 2% to 10%, La ₂ O ₃ 15% to 45%, Gd ₂ O ₃ 0% to 15%, Nb ₂ O ₅ 0% to 15%, WO ₃ It is preferable to contain 0% to 10%, TiO ₂ 13% to 50%, and Y ₂ O ₃ 0.1% to 10%.

In the optical element of Aspect 16, in any one of Aspects 10 to 15, the diffraction pattern is preferably made of a metal oxide material.

The optical element of Aspect 17 is preferably used as a light guide plate in any one of Aspects 9 to 16.

According to the present invention, it is possible to provide a method for manufacturing an optical element and an optical element that have high moldability and can easily suppress the influence of scattering loss.

FIG. 1 is a schematic cross-sectional view of an optical member according to a first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view enlarging a part of the diffraction pattern. FIG. 3 is a schematic cross-sectional view of an optical member according to a second embodiment of the invention. FIG. 4 is a schematic cross-sectional view of an optical member according to a third embodiment of the present invention. FIGS. 5(a) to 5(d) are cross-sectional views for explaining each step of a method for manufacturing an optical element according to an embodiment of the present invention. FIGS. 6(e) to 6(g) are cross-sectional views for explaining each step of a method for manufacturing an optical element according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail using the drawings. However, the present invention is not limited to the following embodiments. Furthermore, in the following explanation regarding the content of each component, "%" means "% by mass" unless otherwise specified.

The method for manufacturing an optical element of the present invention is a method for manufacturing an optical element comprising a glass substrate having a diffraction pattern, and is characterized in that the diffraction pattern is formed on the glass substrate using at least two or more resist layers. . Further, the optical element of the present invention is an optical element comprising a glass substrate having a diffraction pattern, the glass substrate has a refractive index of 2 or more, and the diffraction pattern is formed directly on the glass substrate. shall be. Furthermore, the optical element of the present invention is an optical element comprising a glass substrate and a diffraction pattern arranged on the glass substrate, wherein the glass substrate has a refractive index of 2 or more, and the refractive index of the glass substrate and the diffraction pattern is 2 or more. It is characterized in that the difference Δnd is 0.2 or less.

<Optical element first embodiment>
FIG. 1 is a schematic cross-sectional view of an optical member according to a first embodiment of the present invention. As shown in FIG. 1, the optical element 10 consists of a glass substrate 3 having a diffraction pattern 31. As shown in FIG. The diffraction pattern 31 is directly formed on the glass substrate 3. In other words, the glass substrate 3 and the diffraction pattern 31 are made of the same glass having a refractive index of 2 or more. Further, no interface is formed between the glass substrate 3 and the diffraction pattern 31. That is, since there is no difference in refractive index between the glass substrate 3 and the diffraction pattern 31, no scattering loss occurs.

In this embodiment, the diffraction pattern 31 is a concavo-convex pattern that repeats a predetermined concavo-convex structure. The diffraction pattern 31 may be formed over the entire main surface of the glass substrate 3, or may be formed on a part of the main surface of the glass substrate 3, depending on the purpose. Further, a plurality of diffraction patterns 31 may be formed on the main surface of the glass substrate 3 like an optical element according to a second embodiment described later.

FIG. 2 is a schematic cross-sectional view enlarging a part of the diffraction pattern. In this embodiment, the uneven structure of the diffraction pattern 31 preferably has a trapezoidal cross-sectional shape. At this time, when the width at the bottom of the convex part of the diffraction pattern 31 is a, and the width at 2/3 height from the bottom of the convex part is b, a/b is 1 from the viewpoint of suppressing damage to the diffraction pattern. Preferably larger. Further, from the viewpoint of facilitating formation, a/b is preferably smaller than 2. More specifically, a/b is preferably 1.90 or less, 1.50 or less, 1.30 or less, particularly 1.20 or less. Note that the cross-sectional shape of the uneven structure is not limited to a trapezoidal shape, and any uneven structure that functions as a diffraction grating can be selected, such as a rectangular shape, a sawtooth shape, and a sine wave shape. For example, when the cross-sectional shape of the uneven structure is rectangular, a/b may be 1 or more.

The width a at the bottom of the convex portion of the diffraction pattern 31 (ie, the line width of the diffraction pattern 31) is preferably 100 nm to 1000 nm. More specifically, the lower limit of the width a is preferably 100 nm or more, 150 nm or more, 200 nm or more, especially 210 nm or more, and the upper limit of the width a is preferably 1000 nm or less, 800 nm or less, especially 700 nm or less. Furthermore, the width b at 2/3 height from the bottom of the convex portion is preferably 100 nm to 1000 nm. More specifically, the lower limit of the width b is preferably 100 nm or more, 140 nm or more, 190 nm or more, especially 200 nm or more, and the upper limit of the width b is preferably 1000 nm or less, 990 nm or less, 790 nm or less, particularly preferably 690 nm or less. .

The height H of the convex portions of the diffraction pattern 31 (that is, the depth of the concave portions of the diffraction pattern 31) is preferably 100 nm to 1000 nm. More specifically, the lower limit of the height H is preferably 100 nm or more, 150 nm or more, 200 nm or more, especially 250 nm or more, and the upper limit of the height H is 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, especially 600 nm or less. It is preferable that When the diffraction pattern 31 has the above height H, it becomes easier to obtain desired optical characteristics.

The pitch P of the diffraction pattern 31 (ie, the period of the uneven structure) is preferably 200 nm to 2000 nm. More specifically, the lower limit of pitch P is preferably 200 nm or more, 250 nm or more, especially 300 nm or more, and the upper limit of pitch P is 2000 nm or less, 1500 nm or less, 1000 nm or less, 900 nm or less, 800 nm or less, 700 nm or less, 600 nm or less In particular, it is preferably 500 nm or less. When the diffraction pattern 31 has the pitch P, it becomes easier to obtain desired optical characteristics.

The ratio P/H between the pitch P of the diffraction pattern 31 and the height H of the convex portion is preferably 0.2 to 20. More specifically, the lower limit of P/H is preferably 0.2 or more, 0.5 or more, especially 0.7 or more, and the upper limit of P/H is 20 or less, 10 or less, 5 or less, especially 2 or less. It is preferable that When the diffraction pattern 31 satisfies the ratio, it becomes easier to obtain desired optical characteristics.

In the uneven structure of the diffraction pattern 31, it is preferable that the ratio Ra1/Ra2 of the two is larger than 1, where the surface roughness in the concave portion is Ra1 and the surface roughness in the convex portion is Ra2. More specifically, the lower limit of Ra1/Ra2 is preferably greater than 1, 1.01 or more, 1.05 or more, particularly 1.08 or more. A concavo-convex structure having this shape is likely to be easily formed. In addition, in order to obtain desired optical characteristics, the upper limit of Ra1/Ra2 is preferably 3 or less, 2.5 or less, particularly 2.4 or less.

It is preferable that Ra1 is 0.05 nm to 1 nm. More specifically, the lower limit of Ra1 is preferably 0.05 nm or more, especially 0.1 nm or more, and the upper limit of Ra1 is 1 nm or less, 0.5 nm or less, 0.3 nm or less, 0.2 nm or less, especially 0. It is preferably 15 nm or less. Further, Ra2 is preferably 0.05 nm to 1 nm. More specifically, the lower limit of Ra2 is preferably 0.05 nm or more, particularly 0.06 nm or more, and the upper limit of Ra2 is 1 nm or less, 0.5 nm or less, 0.3 nm or less, 0.2 nm or less, 0.15 nm. In particular, it is preferably 0.12 nm or less.

The uneven structure of the diffraction pattern 31 preferably has a radius of curvature of 3 nm to 200 nm, where r is the radius of curvature at the convex portion. More specifically, the lower limit of r is preferably 3 nm or more, 4 nm or more, especially 5 nm or more, and the upper limit of r is preferably 200 nm or less, 150 nm or less, especially 130 nm or less. The concavo-convex structure having this shape tends to improve optical properties.

The refractive index (nd) of the glass used for the glass substrate 3 is 2 or more, 2.01 or more, 2.02 or more, 2.04 or more, 2.05 or more, 2.06 or more, 2.07 or more, 2.09. Above, it is preferably 2.10 or more, particularly 2.12 or more. If the refractive index is too low, the light guide plate of wearable image display devices such as projector glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR), mixed reality (MR) display devices, virtual image display devices, etc. When used as a camera, the viewing angle tends to become narrower. On the other hand, if the refractive index is too high, defects such as devitrification and striae are likely to occur, so the upper limit of the refractive index nd is preferably 2.5 or less, particularly 2.4 or less.

The density of the glass used for the glass substrate 3 is preferably 7.0 g/cm ³ or less, particularly 6.5 g/cm ³ or less. If the density is too high, the weight of the wearable device using the glass substrate 3 will increase, which will increase discomfort when the device is worn. On the other hand, if the density is too low, other properties such as optical properties tend to deteriorate, so the lower limit of density is 4 g/cm ³ or more, 4.5 g/cm ³ or more, 5.0 g/cm ^{3 or} more, especially 5 It is preferable that it is .1 g/cm ³ or more.

The internal transmittance of the glass used for the glass substrate 3 at a wavelength of 450 nm is preferably 70% or more, 75% or more, 80% or more, particularly 85% or more. In this way, when a light guide plate using the glass is used in a wearable image display device, the brightness of the image seen by the user can be easily increased. The upper limit of the internal transmittance is not particularly limited, but may be, for example, 99% or less, or 98% or less. Note that the above internal transmittance is a value measured using a 10 mm thick sample.

The thickness of the glass substrate 3 is preferably 1 mm or less, 0.8 mm or less, 0.6 mm or less, particularly 0.5 mm or less. If the thickness of the glass substrate 3 is too large, the weight of the wearable image display device will increase, which will increase discomfort when the device is worn. On the other hand, if the thickness of the glass substrate 3 is too small, the mechanical strength tends to decrease, so the lower limits of the thickness are 0.01 mm or more, 0.02 mm or more, 0.03 mm or more, 0.04 mm or more, and 0.02 mm or more. It is preferably 0.05 mm or more, 0.1 mm or more, 0.2 mm or more, particularly 0.3 mm or more.

The difference between the maximum and minimum distances between the first main surface and the second main surface of the glass substrate 3 (TTV=Total Thickness Variation) is 5 μm or less, 3 μm or less, 2 μm or less, especially 1.5 μm or less. It is preferable. By setting TTV to the above value, it becomes easier to reduce blurring and deviation of the obtained image. The lower limit of TTV is preferably 0.01 μm or more, and preferably 0.1 μm or more.

The surface roughness Ra of the glass substrate 3 is preferably 0.05 nm to 1 nm in order to obtain desired optical characteristics. More specifically, the lower limit of the surface roughness is preferably 0.05 nm or more, and the upper limit of the surface roughness is 1 nm or less, 0.5 nm or less, 0.3 nm or less, 0.2 nm or less, particularly 0.15 nm or less. It is preferable that

The shape of the glass substrate 3 is preferably a plate shape, for example, a polygon such as a circle, an ellipse, or a rectangle in plan view. In this case, the major axis of the glass substrate 3 (diameter if circular) is preferably 100 mm or more, 120 mm or more, 150 mm or more, 160 mm or more, 170 mm or more, 180 mm or more, 190 mm or more, particularly 200 mm or more. If the long axis of the glass substrate 3 is too small, it will be difficult to use it for applications such as wearable image display devices. Additionally, mass production tends to be poor. Although the upper limit of the major axis of the glass substrate 3 is not particularly limited, it is realistically 1000 mm or less.

The melting temperature of the glass used for the glass substrate 3 is preferably 1400°C or lower, 1350°C or lower, 1300°C or lower, particularly 1280°C or lower. If the melting temperature is too high, components of the melting container (Pt, Rh, etc.) tend to dissolve into the glass melt, and the light transmittance of the resulting glass substrate 3 tends to decrease. On the other hand, when the melting temperature becomes low, bubbles and foreign substances (for example, foreign substances derived from undissolved substances) tend to be generated more easily. Therefore, in order to reduce bubbles and foreign matter in the glass, the melting temperature is preferably 1200°C or higher, particularly 1250°C or higher.

The optical element 10 and the optical element 30 are wearables selected from projector-equipped glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR), mixed reality (MR) display devices, and virtual image display devices. It can be suitably used for image display devices. It is particularly preferable that the optical element 10 and the optical element 30 be used as a light guide plate. In other words, it is preferable that the optical element 10 and the optical element 30 are light guide plates. The light guide plate is used in a glasses lens portion of a wearable image display device, and plays the role of guiding light emitted from an image display element included in the wearable image display device and emitting it toward the user's eyes.

A plurality of optical elements 10 and 30 may be stacked and used as a laminate. In this way, when the optical element 10 is used as a light guide plate of a wearable image display device, it is possible to guide an image for each wavelength, and a clear image can be obtained. From the viewpoint of weight reduction, the number of laminated sheets is preferably 6 or less, 5 or less, 4 or less, 3 or less, particularly 2 or less.

The glass used for the glass substrate 3 preferably contains at least one component selected from SiO ₂ , B ₂ O ₃ , La ₂ O ₃ and Nb ₂ O ₅ . For example, a glass containing 0% to 20% of SiO ₂ , 0% to 25% of B ₂ O ₃ , 10% to 60% of La ₂ O ₃ , and 0% to 30% of Nb ₂ O ₅ in mass % may be used. is preferred. For example, in mass %, SiO ₂ 0% to 12%, B ₂ O ₃ 0% to 10%, BaO 0% to 13%, ZnO 0% to 5%, ZrO ₂ 2% to 10%, La ₂ O ₃ 15% to 45%, Gd ₂ O ₃ 0% to 15%, Nb ₂ O ₅ 0% to 15%, WO ₃ 0% to 10%, TiO ₂ 13% to 50%, Y ₂ O ₃ 0.1% It is preferable to contain up to 10%.

Here, the preferred content of each component will be explained below. In addition, in the following description regarding the content of each component, "%" means "mass %" unless otherwise specified.

SiO ₂ is a glass skeleton component and is a component that improves vitrification stability and chemical durability. However, if the content is too large, the melting temperature will become extremely high. When the melting temperature becomes high, transition metal components such as Nb and Ti are reduced, absorption occurs in the visible region, and the internal transmittance tends to decrease. Furthermore, the refractive index tends to decrease. The lower limit of the content of _SiO2 is preferably 0% or more, 1% or more, 3% or more, 5% or more, 5.5% or more, especially 6% or more, and the upper limit is 20% or less, 15% or less, It is preferably 12% or less, 11% or less, 10% or less, 9.5% or less, particularly 9% or less.

B ₂ O ₃ is a component that contributes to the stability of vitrification. In particular, when the refractive index nd is as high as 2.00 or more, vitrification tends to become unstable, but the stability of vitrification can be improved by containing an appropriate amount of B ₂ O ₃ . The lower limit of the content of B ₂ O ₃ is preferably 0% or more, 0.1% or more, 0.2% or more, 0.5% or more, 1% or more, 2% or more, particularly 3% or more, The upper limit is preferably 25% or less, 20% or less, 19% or less, 15% or less, 10% or less, 8% or less, 7% or less, 6% or less, and particularly preferably 5% or less. If the content of B ₂ O ₃ is too small, it will be difficult to obtain the above effects. On the other hand, if the content of B ₂ O ₃ is too large, the refractive index tends to decrease.

Note that in order to increase the stability of vitrification and improve mass productivity, it is preferable to appropriately adjust the ratio of SiO ₂ and B ₂ O ₃ . Specifically, in terms of mass ratio, B ₂ O ₃ /SiO ₂ is 0 or more, 0.02 or more, 0.04 or more, 0.05 or more, 0.1 or more, 0.3 or more, especially 0.4 or more. It is preferably 3 or less, 2 or less, 1.5 or less, 1.2 or less, 1 or less, 0.8 or less, 0.6 or less, particularly preferably 0.5 or less. Note that "x/y" means the value obtained by dividing the content of x by the content of y.

In addition, from the viewpoint of increasing the stability of vitrification, the content of Si ⁴⁺ +B ³⁺ in terms of cation% is 5% or more, 6% or more, 7% or more, 8% or more, 9% or more, 10% or more, especially 11 % or more. The upper limit of the content of Si ⁴⁺ +B ³⁺ is not particularly limited, but if it is too large, the refractive index tends to decrease and the melting temperature increases. It is preferably 20% or less, 19% or less, 15% or less, particularly 14% or less.

BaO is a component that stabilizes vitrification. However, when the BaO content increases, the density of the glass increases, and the weight of the glass substrate 3 tends to increase. Therefore, it is particularly unfavorable for applications such as wearable image display devices. Therefore, the lower limit of the BaO content is preferably 0% or more, 0.1% or more, 0.3% or more, especially 1% or more, and the upper limit is 13% or less, 9% or less, 8% or less, 5% or more. % or less, particularly preferably 3% or less. In addition, when prioritizing weight reduction of the glass substrate 3, the content of BaO is preferably 1% or less, particularly 0.5% or less, and most preferably not contained.

ZnO is a component that promotes solubility (solubility of raw materials). However, if the content is too large, it is difficult to obtain high refractive index characteristics, and devitrification resistance and acid resistance tend to decrease. Therefore, the lower limit of the ZnO content is preferably 0% or more, 0.1% or more, 0.3% or more, 0.5% or more, especially 1% or more, and the upper limit is 5% or less, 4% or less. , 3% or less, 2.8% or less, 2.5% or less, particularly preferably 2% or less.

ZrO ₂ is a component that increases refractive index and chemical durability. However, if the content is too large, the melting temperature tends to become extremely high. Therefore, the lower limit of the ZrO ₂ content is preferably 2% or more, 3% or more, 4% or more, especially 5% or more, and the upper limit is 10% or less, 9.5% or less, 9% or less, especially 8 % or less.

La ₂ O ₃ is a component that significantly increases the refractive index and also improves the stability of vitrification. The lower limit of the content of La ₂ O ₃ is preferably 10% or more, 15% or more, 25% or more, 30% or more, 31% or more, especially 35% or more, and the upper limit is 60% or less, 45% or less, In particular, it is preferably 43% or less. If the content of La ₂ O ₃ is too small, it will be difficult to obtain the above effects. On the other hand, if the content of La ₂ O ₃ is too large, the devitrification resistance tends to decrease, resulting in poor mass productivity.

Gd ₂ O ₃ is a component that increases the refractive index and also improves the stability of vitrification. The lower limit of the content of Gd ₂ O ₃ is preferably 0% or more, 1% or more, especially 2% or more, and the upper limit is 15% or less, 13% or less, 10% or less, 9% or less, 8% or less, It is preferably 7% or less, particularly 6% or less. If the content of Gd ₂ O ₃ is too small, it will be difficult to obtain the above effects. On the other hand, if the content of Gd ₂ O ₃ is too large, the devitrification resistance tends to decrease, resulting in poor mass productivity.

Nb ₂ O ₅ is a component that significantly increases the refractive index of glass. However, if the content is too large, the light transmittance in the visible range tends to decrease. Therefore, the lower limit of the content of Nb ₂ O ₅ is preferably 0% or more, 1% or more, 3% or more, especially 5% or more, and the upper limit is 30% or less, 15% or less, 12% or less, especially 10% or more. % or less.

Although WO ₃ is a component that increases the refractive index, it tends to absorb light in the visible range and reduce light transmittance. Therefore, the lower limit of the content of _WO3 is preferably 0% or more, 0.1% or more, especially 1% or more, and the upper limit is 10% or less, 9% or less, 8% or less, 6% or less, 5%. Below, it is preferably 3% or less, less than 3%, 2% or less, particularly less than 2%. In addition, from the viewpoint of increasing the transmittance in the visible region, the content of WO ₃ is preferably 1% or less, particularly 0.5% or less, and most preferably not contained.

TiO ₂ is a component that significantly increases the refractive index of glass. However, if the content is too large, vitrification tends to be difficult. Furthermore, the light transmittance in the visible range tends to decrease. Therefore, the lower limit of the TiO ₂ content is preferably 13% or more, 15% or more, 16% or more, 18% or more, 20% or more, 21% or more, 22% or more, especially 23% or more, and the upper limit is It is preferably 50% or less, 40% or less, 35% or less, 30% or less, 29% or less, particularly 28% or less.

The upper limit of the content of TiO ₂ + WO ₃ (total amount of TiO ₂ and WO ₃ ) is 60% or less, 50% or less, 40% or less, 35% or less, 30% or less, 29% or less, 28% or less, especially 25% or less % or less, and the lower limit is preferably 15% or more, 18% or more, particularly 20% or more. In this way, it becomes easier to increase the light transmittance in the visible range.

Y ₂ O ₃ is a component that increases the refractive index and chemical durability, but if its content is too large, the melting temperature tends to become extremely high. Additionally, vitrification tends to become unstable. Therefore, the lower limit of the content of Y ₂ O ₃ is preferably 0.1% or more, 1% or more, 2% or more, 2.5% or more, especially 3% or more, and the upper limit is 10% or less, 7% Below, it is preferably 6% or less, 5% or less, particularly 4% or less.

Ga ₂ O ₃ is a component that forms a glass skeleton as an intermediate oxide and expands the range of vitrification. It also has the effect of increasing the refractive index. However, if the content of Ga ₂ O ₃ is too large, it becomes difficult to vitrify. Furthermore, raw material costs tend to be high. Therefore, the lower limit of the content of Ga ₂ O ₃ is preferably 0% or more, 1% or more, especially 2% or more, and the upper limit is 10% or less, 7% or less, 6% or less, 5% or less, especially 4 % or less.

MgO, CaO, and SrO are components that stabilize vitrification. If the content is too large, the refractive index tends to decrease. Additionally, the liquidus temperature tends to increase. The content of these components is preferably 5% or less, 2% or less, 1% or less, particularly 0.5% or less.

Ta ₂ O ₅ is a component that increases the refractive index. However, if the content is too large, phase separation and devitrification are likely to occur. Moreover, since Ta ₂ O ₅ is a rare and expensive component, the raw material batch cost increases as its content increases. In view of the above, the content of Ta ₂ O ₅ is preferably 5% or less, 3% or less, or 1% or less, and is particularly preferably not contained.

Yb ₂ O ₃ is also a component that increases the refractive index. However, if the content is too large, devitrification and striae are likely to occur. Therefore, the content of Yb ₂ O ₃ is preferably 10% or less, 8% or less, 5% or less, 3% or less, particularly 1% or less.

In order to increase the refractive index and light transmittance of the glass in the visible range and improve the stability of vitrification, it is preferable to appropriately adjust the ratio (cation ratio) of Y ³⁺ and Gd ³⁺ +Y ³⁺ +Yb ³⁺ . Specifically, Y ³⁺ /(Gd ³⁺ +Y ³⁺ +Yb ³⁺ ) is 0.2 or more, 0.25 or more, 0.3 or more, 0.4 or more, 0.5 or more, 0.52 or more, 0.55. As mentioned above, it is preferably 0.6 or more, particularly 0.61 or more. Further, the upper limit is preferably 1.5 or less, 1 or less, 0.9 or less, particularly 0.8 or less. Note that “Y ³⁺ /(Gd ³⁺ +Y ³⁺ +Yb ³⁺ )” means the value obtained by dividing the content of Y ³⁺ by the total amount of Gd ³⁺ , Y ³⁺ and Yb ³⁺ .

Al ₂ O ₃ is a component that improves water resistance. However, if the content is too large, devitrification tends to occur. Therefore, the content of Al ₂ O ₃ is preferably 5% or less, 3% or less, 1% or less, or 0.5% or less, and it is particularly preferably not contained.

Li ₂ O, Na ₂ O, and K ₂ O are components that lower the softening point, but if their content is too large, devitrification tends to occur. Therefore, the content of each of these components is preferably 10% or less, each 5% or less, and each 1% or less, and it is particularly preferable that they are not contained. Furthermore, when two or more types of Li ₂ O, Na ₂ O, and K ₂ O are contained, the total amount thereof is preferably 10% or less, 5% or less, or 1% or less, and it is particularly preferable that they are not contained.

Note that it is preferable that As components (such as As ₂ O ₃ ), Pb components (such as PbO), and fluorine components (such as F ₂ ) are substantially not included because they have a large environmental load. Moreover, Bi ₂ O ₃ and TeO ₂ are coloring components, and since the transmittance in the visible range tends to decrease, it is preferable that they are not substantially contained. In this specification, "substantially not containing" means intentionally not containing it as a raw material, and does not exclude the inclusion of unavoidable impurities. Objectively, this means that the content of each of the above components is less than 0.1%.

Pt, Rh, and Fe ₂ O ₃ are coloring components, and since the transmittance in the visible range tends to decrease, it is preferable that their content is small. Specifically, Pt is preferably 10 ppm or less, 9 ppm or less, especially 5 ppm or less, Rh is preferably 0.1 ppm or less, particularly 0.01 ppm or less, and Fe ₂ O ₃ is 1 ppm or less. In particular, it is preferably 0.5 ppm or less. Note that from the viewpoint of suppressing coloration, the lower the Pt content, the better; however, for this purpose, it is necessary to lower the melting temperature, and as a result, the solubility tends to decrease. Therefore, in consideration of solubility, the lower limit of the Pt content is preferably 0.1 ppm or more, particularly 0.5 ppm or more.

The glass may contain each of the clarifying agent components Cl, CeO ₂ , SO ₂ , Sb ₂ O ₃ or SnO ₂ in a proportion of 0.1% or less.

<Optical element second embodiment>
FIG. 3 is a schematic cross-sectional view of an optical member according to a second embodiment of the invention. As shown in FIG. 3, the optical element 20 has diffraction patterns 31 and 32 formed on a portion of the glass substrate 3, respectively. In this embodiment, the diffraction patterns 31 and 32 are formed on the same main surface (first main surface). In this embodiment, for example, light can be made incident through the diffraction pattern 31, guided between two main surfaces by total reflection, and emitted from the other diffraction pattern 32. Therefore, the optical element 20 is a wearable image display selected from projector-equipped glasses, glasses or goggle displays, virtual reality (VR) or augmented reality (AR), mixed reality (MR) display devices, and virtual image display devices. It is particularly suitable as a light guide plate used in equipment. Note that the diffraction patterns 31 and 32 do not necessarily need to be provided on the same main surface; for example, the diffraction pattern 31 is provided on the first main surface, and the diffraction pattern 2 is provided on the other main surface opposite to the first main surface. (the second main surface).

In the optical element 20, the surface roughness Ra of the main surface of the glass substrate 3 on which the diffraction patterns 31 and 32 are not formed is preferably 10 nm or less, 5 nm or less, 3 nm or less, particularly 2 nm or less. If the surface roughness Ra of the first main surface and the second main surface of the glass substrate 3 is too large, scattering loss is likely to occur when the light incident on the inside of the glass substrate 3 undergoes repeated total reflection and is guided. It becomes difficult to obtain bright and clear images. Although the lower limit of the surface roughness Ra of the first main surface and the second main surface of the glass substrate 3 is not particularly limited, it is realistically 0.1 nm or more.

As shown in FIG. 3, the optical element 20 consists of a glass substrate 3 having diffraction patterns 31 and 32. The diffraction patterns 31 and 32 are directly formed on the glass substrate 3. In other words, the glass substrate 3 and the diffraction patterns 31 and 32 are made of the same glass having a refractive index of 2 or more. Further, there is no interface between the glass substrate 3 and the diffraction patterns 31 and 32. Therefore, since there is no difference in refractive index between the glass substrate 3 and the diffraction patterns 31 and 32, scattering loss can be reduced.

Although the glass substrate 3 of this embodiment has two diffraction patterns 31 and 32 on its main surface, the number of diffraction patterns is not limited to two. For example, the glass substrate 3 may include three or more diffraction patterns.

As for the preferred configuration of the optical element 20, the preferred configuration of the optical element 10 can be applied as appropriate.

<Optical element third embodiment>
FIG. 4 is a schematic cross-sectional view of an optical member according to a third embodiment of the present invention. As shown in FIG. 4, the optical element 30 includes a glass substrate 3 and a diffraction pattern 33 arranged on the glass substrate 3. In this embodiment, the refractive index difference Δnd between the glass substrate 3 and the diffraction pattern 33 is 0.2 or less.

In this embodiment, an interface exists between the glass substrate 3 and the diffraction pattern 33, but by limiting the refractive index difference Δnd between the two to 0.2 or less, the influence of scattering loss can be suppressed. More specifically, the upper limit of the refractive index difference Δnd is 0.2 or less, 0.15 or less, 0.1 or less, 0.09 or less, 0.08 or less, 0.06 or less, 0.05 or less, especially 0. It is preferable that it is .03 or less. The lower limit of the refractive index difference Δnd is not particularly limited, but may be, for example, 0.0001 or more, particularly 0.001 or more.

In this embodiment, an interface exists between the glass substrate 3 and the diffraction pattern 33, but by limiting the Abbe difference Δνd between the two to 21 or less, the influence of scattering loss can be suppressed. More specifically, the upper limit of the Abbe number difference Δνd is preferably 21 or less, 20 or less, 18 or less, 16 or less, 14 or less, 12 or less, 11 or less, 10 or less, 8 or less, particularly 6 or less. The lower limit of the Abbe difference Δνd is not particularly limited, but may be, for example, 0.1 or more, particularly 0.5 or more.

The diffraction pattern 33 is preferably formed from a lower resist layer in optical element manufacturing method II described below. From the viewpoint of use as a light guide plate, the diffraction pattern 33 is preferably made of a material that exhibits light transparency, and is particularly preferably made of a metal oxide material.

Regarding the metal oxide material, the refractive index nd is preferably 1.9 or more, 1.95 or more, especially 2 or more, and preferably 2.6 or less, especially 2.5 or less. Further, the Abbe number νd is preferably 5 or more, 6 or more, particularly 8 or more, and preferably 40 or less, 39 or less, especially 35 or less. For example, the refractive index nd of HfO ₂ is 1.92 and the Abbe number νd is 23, the refractive index nd of TiO ₂ is 2.43 and the Abbe number νd is 9, and the refractive index nd of ZrO ₂ is 2.16. , the Abbe number νd is 34, the refractive index nd of Nb ₂ O ₅ is 2.34, and the Abbe number νd is 14, the refractive index nd of Ta ₂ O ₅ is 2.13, and the Abbe number νd is 26. , the refractive index nd of the ITO film is 1.90, the Abbe number νd is 8, the refractive index nd of BaTiO ₃ is 2.43, the Abbe number νd is 12, the refractive index nd of KTaO ₃ is 2.24, The Abbe number νd is 17, the refractive index nd of KNbO ₃ is 2.18, the Abbe number νd is 18, the refractive index nd of WO ₃ is 1.99, the Abbe number νd is 20, and the refractive index of ZnO nd is 2.00, and Abbe's number νd is 12.

As for the preferred configuration of the optical element 30, the preferred configurations of the optical element 10 and the optical element 20 can be applied as appropriate.

<Method for manufacturing optical elements>
5(a) to 5(d) and FIGS. 6(e) to 6(g) are cross-sectional views for explaining each step of a method for manufacturing an optical element according to an embodiment of the present invention. Hereinafter, a method for manufacturing an optical element according to the present invention will be explained in detail using the drawings.

The method for manufacturing an optical element of the present invention is a method for manufacturing an optical element comprising a glass substrate having a diffraction pattern, and is characterized in that the diffraction pattern is formed on the glass substrate using at least two or more resist layers. . Specifically, as shown in FIGS. 5A to 5D and FIGS. 6E to 6G, at least two or more resist layers include an upper resist layer 1 and a lower resist layer 2. The method is characterized in that a diffraction pattern 31 is formed on the glass substrate 3 by etching the glass substrate 3 using the upper resist layer 1 and the lower resist layer 2. More specifically, the steps of forming the lower resist layer 2 on the glass substrate 3, forming the upper resist layer 1 on the lower resist layer 2, forming the first resist pattern 11 on the upper resist layer 1, and a first etching step of forming a second resist pattern 21 on the lower resist layer 2 using the first resist pattern 11; a second etching step of forming a diffraction pattern 31 on the glass substrate 3 using the second resist pattern 21; (Optical element manufacturing method I). Alternatively, a step of forming the lower resist layer 2 on the glass substrate 3, a step of forming the upper resist layer 1 on the lower resist layer 2, a step of forming the first resist pattern 11 on the upper resist layer 1, a step of forming the first resist pattern. It is preferable to include a first etching step of forming a second resist pattern 21 on the lower resist layer 2 using a resist film 11 (optical element manufacturing method II).

The etching rate of glass substrates tends to be lower than that of silicon substrates commonly used in semiconductor processes. In particular, in the case of a glass substrate having a refractive index of 2 or more, the etching rate tends to become even smaller. Therefore, for example, in etching using only one layer of resin resist, the resin resist with a large etching rate disappears before the uneven structure is formed on the glass substrate, making it difficult to form a desired diffraction pattern on the glass substrate. This can easily become difficult. Therefore, in the present invention, the glass substrate 3 is etched using two or more resist layers. That is, in the optical element manufacturing method I, the glass substrate 3 is etched using the upper resist layer 1 and the lower resist layer 2. Thereby, a diffraction pattern 31 having a desired depth can be formed on the glass substrate 3. Further, in the optical element manufacturing method II, a second resist pattern 21 is formed on the lower resist layer 2 using the upper resist layer 1. In this case, the second resist pattern corresponds to the diffraction pattern. Even with this method, the diffraction pattern 31 having a desired depth can be formed on the glass substrate 3.

Hereinafter, the method for manufacturing an optical element according to the present invention will be explained in detail for each step.

<Step of forming a lower resist layer on the glass substrate>
First, a lower resist layer 2 is formed on a glass substrate 3 (FIG. 5(a)). Preferably, the lower resist layer 2 is made of a metal resist. In this way, it becomes easier to make the etching rate Gr of the glass substrate 3 larger than the etching rate Rr2b of the lower resist layer 2 in the second etching step described later. As the metal resist, any material having a desired etching rate can be used as appropriate, but it is preferable to use, for example, Ni, Cr, Al, Pt, Si, or the like.

The material of the lower resist layer 2 is not limited to a metal resist, but may be a resin resist, an inorganic resist, an organic-inorganic hybrid resist, or the like. For example, it is preferable to use a metal oxide resist as the inorganic resist. As the metal oxide, for example, at least one selected from HfO ₂ , TiO ₂ , ZrO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , ITO, BaTiO ₃ , KTaO ₃ , KNbO ₃ , WO ₃ or ZnO is used. It is preferable to use ZrO ₂ or TiO ₂ , and it is particularly preferable to use TiO ₂ . Further, the lower resist layer 2 may be a combination of multiple types of metal oxides.

The thickness of the lower resist layer 2 can be appropriately set depending on the desired depth of the diffraction pattern 31 and the etching rate of the lower resist layer 2. For example, the thickness of the lower resist layer 2 is preferably 1 nm or more, particularly 10 nm or more. The upper limit is not particularly limited, but may be, for example, 500 nm or less.

<Step of forming an upper resist layer on the lower resist layer>
Next, the upper resist layer 1 is formed on the lower resist layer 2 (FIG. 5(b)). In this embodiment, the upper resist layer 1 is preferably made of a resin resist. This makes it easier to make the etching rate Rr2b of the lower resist layer 2 smaller than the etching rate Rr1 of the upper resist layer 1 in the first etching step described later. As the resin resist, any material having a desired etching rate can be used as appropriate, and for example, commercially available photoresists and electron beam resists can be used as appropriate.

The thickness of the upper resist layer 1 can be appropriately set depending on the desired depth of the first resist pattern 11 and the etching rate of the upper resist layer 1. For example, the thickness of the upper resist layer 1 is preferably 1 nm or more, particularly 10 nm or more. The upper limit is not particularly limited, but may be, for example, 1000 nm or less.

The thickness of the upper resist layer 1 is preferably greater than the thickness of the lower resist layer 2. In this way, it becomes easier to stably form the second resist pattern 21 having a desired depth in the lower resist layer 2.

It is preferable that the lower resist layer 2 is made of a metal resist, and the upper resist layer 1 is made of a resin resist. In this way, it becomes easier to form the first resist pattern 11 and the second resist pattern 21 with good shape quality, and it becomes easier to stably form the diffraction pattern 31 having a desired depth on the glass substrate 3.

<Step of forming a first resist pattern on the upper resist layer>
Next, a first resist pattern 11 is formed on the upper resist layer 1 (FIG. 5(c)). For example, when the upper resist layer 1 is made of a resin-based resist, the first resist pattern 11 can be formed by exposing it to light or an electron beam so as to obtain a desired diffraction pattern, and then performing a development process.

<First etching step>
Next, a second resist pattern 21 is formed on the lower resist layer 2 using the first resist pattern 11 (first etching step, FIG. 5(d)). Specifically, a first etching process is performed using the first resist pattern 11 as a mask to form a second resist pattern 21 on the lower resist layer 2 . The second resist pattern 21 has a pattern shape corresponding to the first resist pattern 11.

In the first etching step, wet etching or dry etching is preferably used, and dry etching is particularly preferably used. This makes it easier to obtain a precise second resist pattern 21. As the etching gas, a gas suitable for the resist material used can be used as appropriate. For example, it is preferable to use a Cl ₂ -based gas, an Ar-based gas, a C ₄ F ₈ -based gas, or the like.

When the etching rate of the upper resist layer 1 in the first etching step is Rr1 and the etching rate of the lower resist layer 2 is Rr2a, it is preferable that Rr1>Rr2a. That is, it is preferable that Rr1 is larger than Rr2a. This makes it easier to form the second resist pattern 21. More specifically, the etching rate Rr1 of the upper resist layer 1 is 5 nm/min or more, 10 nm/min or more, 20 nm/min or more, 30 nm/min or more, 40 nm/min or more, 50 nm/min or more, 60 nm/min or more, It is preferably 70 nm/min or more, especially 80 nm/min or more, and preferably 200 nm or less, 150 nm/min or less, 140 nm/min or less, especially 120 nm/min or less. Further, the etching rate Rr2a of the lower resist layer 2 is preferably 5 nm/min or more, 10 nm/min or more, especially 20 nm/min or more, and preferably 100 nm or less, 50 nm/min or less, especially 40 nm/min or less. preferable.

In the first etching process, the ratio Rr1/Rr2a of the etching rate Rr1 of the upper resist layer 1 to the etching rate Rr2b of the lower resist layer 2 is 1.1 or more, 1.2 or more, 1.5 or more, 1.8 or more , 2 or more, 2.1 or more, particularly 2.3 or more. By setting the ratio to the above value, it becomes easier to form the second resist pattern 21. The upper limit of Rr1/Rr2a is not particularly limited, but is preferably, for example, 5 or less, 4 or less, 3.5 or less, particularly 3.3 or less.

After this step, the optical member 30 according to the third embodiment of the present invention can be obtained by removing only the upper resist layer 1. That is, in the optical member 30, the lower resist layer 2 having the second resist pattern 21 functions as a diffraction pattern. The upper resist layer 1 can be removed using a suitable solvent. For example, when using a resin resist as the upper resist layer 1, it can be removed using an organic solvent such as acetone.

<Second etching process>
Next, a diffraction pattern 31 is formed using the second resist pattern 21 (second etching step, FIGS. 6(e) to 6(g)). Specifically, a second etching process is performed using the second resist pattern 21 as a mask to form the diffraction pattern 31 on the glass substrate 3. The diffraction pattern 31 has a pattern shape corresponding to the second resist pattern 21.

The second etching process can use wet etching or dry etching. In particular, it is preferable to use dry etching. This makes it easier to obtain a precise diffraction pattern 31. As the etching gas, a gas suitable for the resist material used can be used as appropriate, and for example, it is preferable to use a Cl2 _- based gas, an Ar-based gas, a _{C4F8 -} based gas, or the like.

When the etching rate of the lower resist layer in the second etching step is Rr2b and the etching rate of the glass substrate is Gr, it is preferable that Gr>Rr2b. That is, it is preferable that Gr is larger than Rr2b. Thereby, it is possible to prevent the lower resist layer 2 from disappearing before a sufficient uneven structure is formed on the glass substrate 3, and it is possible to stably form a diffraction pattern 31 having a desired depth on the glass substrate 3. It becomes easier. More specifically, in the second etching process, the etching rate Rr2b of the lower resist layer 2 is preferably 5 nm/min or more, 10 nm/min or more, particularly preferably 20 nm/min or more, and 100 nm/min or less, 50 nm/min. Hereinafter, it is preferably 40 nm/min or less, particularly 35 nm/min or less. Further, the etching rate Gr of the glass substrate 3 is preferably, for example, 30 nm/min or more, 40 nm/min or more, especially 41 nm/min or more, and 100 nm/min or less, 60 nm/min or less, 55 nm/min or less, especially It is preferable that it is 50 nm/min or less.

In the second etching process, the ratio Rr2b/Gr of the etching rate Rr2b of the lower resist layer 2 to the etching rate Gr of the glass substrate 3 is 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more , particularly preferably 0.45 or more, less than 1, preferably 0.9 or less, particularly preferably 0.8 or less. By setting the ratio to the above value, it becomes easier to stably form the diffraction pattern 31 having a desired depth on the glass substrate 3.

In the second etching process, it is preferable that no lower resist layer 2 remains when the desired diffraction pattern 31 is formed (FIG. 6(g)). In this way, it becomes easier to obtain the diffraction pattern 31 with excellent shape quality. Further, there is no need to wash and remove the residue on the lower resist layer 2, and the diffraction pattern 31 is less likely to be contaminated. Note that the diffraction pattern 31 may be cleaned even if the lower resist layer 2 does not remain. Furthermore, if residues of the lower resist layer 2 are present, they can be removed using an appropriate solvent. For example, when using a metal resist as the lower resist layer 2, it can be removed using an etching solution or a chemical polishing solution.

In the second etching process, the ratio Rt2/Rr2b of the etching rate Rr2b (nm/min) of the lower resist layer 2 to the thickness Rt2 (nm) of the lower resist layer 2 is preferably 1 to 40 min.

As described above, according to the method for manufacturing an optical element of the present invention, it is possible to manufacture an optical element 10 that has high moldability and can easily suppress the influence of scattering loss. The optical element 10 and the optical element 30 are wearables selected from projector-equipped glasses, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR), mixed reality (MR) display devices, and virtual image display devices. It is suitable as an optical element such as a light guide plate or a diffraction grating used in image display equipment.

Hereinafter, the present invention will be explained in detail based on Examples, but the present invention is not limited to these Examples.

Tables 1 and 2 show Examples 1 to 5, 8, and 9 of the present invention and Comparative Example 7. Moreover, Table 3 shows the composition of the glass substrate.

Examples were produced as follows. First, glass having the refractive index shown in Tables 1 and 2 was processed to a predetermined thickness, and the surface was mirror-polished to produce a glass substrate.

Next, the refractive index nd, density, and internal transmittance of the glass at a sample thickness of 10 mm and a wavelength of 450 nm were measured. In addition, the TTV and surface roughness of the glass substrate were measured. The refractive index nd was measured using KPR-2000 (manufactured by Kalnew). Density was measured by Archimedes method. The internal transmittance was measured using a visible and ultraviolet spectrophotometer V670 (manufactured by JASCO Corporation) at a sample thickness of 10 mm and a wavelength of 450 nm. TTV was measured using a Bow/Warp measuring device SBW-331ML/d manufactured by Kobelco Scientific Research. The surface roughness was measured using AFM Dimension Icon manufactured by Bruker at a scan size of 3 μm square and a scan speed of 1 Hz.

Next, a diffraction pattern was formed on the glass substrate. First, a lower resist layer was formed on a glass substrate using an electron beam evaporator (EB1200). As the lower resist material, Cr was selected for Examples 1 to 6, and ZrO ₂ was selected for Examples 8 and 9. The refractive index of the resist layers of Examples 8 and 9 was measured using an ellipsometer. Next, an upper resist layer was formed on the lower resist layer by spin coating. ZEP520A (1:1 copolymer of α-chloromethacrylate and α-methylstyrene (manufactured by Zeon Corporation)) was used as the upper resist material. Note that in Comparative Example 7, only the upper resist layer (ZEP520A) was applied without applying the lower resist layer (Cr).

Next, the upper resist layer was irradiated with an electron beam using an electron beam drawing device (F7000S-KYT01). Next, the electron beam drawn portion was dissolved and developed using ZED-N50 (n-Amylacetate C ₇ H ₁₄ O ₂ ) to form a first resist pattern in the upper resist layer.

Next, a second resist pattern was formed in the lower resist layer by dry etching using the first resist pattern as a mask (first etching process). A Cl2 _- based etching gas was used for the etching process. A magnetic neutral discharge dry etching apparatus (NLD-570) was used as the dry etching apparatus. After the dry etching process, the residue of the upper resist layer was removed with acetone. In Comparative Example 7, since there was no lower resist layer, the shape of the diffraction pattern on the glass substrate was measured after dry etching using the first resist pattern as a mask. Further, in Examples 8 and 9, the second etching process was not performed, and only the first etching process was performed.

Next, in Examples 1 to 6, a diffraction pattern was formed on the glass substrate by dry etching using the second resist pattern as a mask (second etching). C ₄ F ₈ etching gas was used for the etching process. After the dry etching process, the residue of the lower resist layer was removed using S-clean (S-24) to obtain an optical element with a diffraction pattern formed on the glass substrate.

The shape of the obtained diffraction pattern was measured using AFM. From the cross-sectional line profile image of the optical element, the bottom width of the diffraction pattern (line width a), the width at the 2/3 height position (line width b), the ratio a/b of line width a to line width b, and the height The pitch width P, the pitch-to-height ratio P/H, the surface roughness Ra2 and Ra1 of the convex portion and the concave portion, the surface roughness ratio Ra1/Ra2, and the radius of curvature r of the convex edge were confirmed. In Examples 8 and 9, the refractive index nd of the diffraction pattern and the refractive index difference Δnd between the glass substrate and the diffraction pattern were also confirmed. Further, the etching rates of the upper resist layer, the lower resist layer, and the glass substrate (Rr1, Rr2a, Rr2b, and Gr, respectively) were determined from the step difference in AFM line profile images before and after etching.

Regarding the obtained optical element, screen image evaluation, viewing angle, and ratio of output light amount when the incident light amount was set to 100% were determined.

Screen image evaluation was performed by visually evaluating the blurring and distortion of the screen image transmitted through the optical element. Specifically, using an optical element with diffraction patterns formed on the entrance and exit sides, an image of a character was made incident through the diffraction pattern on the entrance side, and an image was taken out from the diffraction pattern on the exit side and projected onto a screen. If blurring or distortion occurred at the edges of the projected characters, it was marked as ×, if it was slightly blurred, it was marked as △, and if it could not be visually confirmed, it was marked as ○.

The viewing angle was calculated from the refractive index of the glass and the pitch (nm) of the diffraction pattern using the following formula. Here, θ ⁺ means the angle of light entering the light guide plate from the side in which the light travels, and θ ⁻ means the angle of light entering the light guide plate from the opposite direction to the direction in which the light travels. Furthermore, n _Glass and n _air are the refractive indexes of glass and air, respectively, λ is the wavelength of incident light, and P is the pitch of the diffraction pattern. n _air =1 and λ = 530 nm.

Viewing angle = θ ⁺ -θ ^- = arcsin ((n _Glass - λ/P)/n _air ) - arcsin ((n _air - λ/P)/n _air )

The amount of light before entering the diffraction pattern and the amount of light after exiting were measured using a power meter, and the ratio of the amount of output light when the amount of incident light was taken as 100% was determined.

As shown in Table 1, the optical elements of Examples 1 to 6, 8, and 9 had high screen image evaluations and large viewing angles. In addition, the efficiency of incident light has increased. On the other hand, in Comparative Example 7, since only one resist layer was used, it was not possible to form a sufficient uneven shape on the glass substrate, and it was not possible to form a desired diffraction pattern. For this reason, it was not possible to confirm the waveguide of the image.

Optical elements manufactured by the optical element manufacturing method of the present invention can be used in glasses with a projector, eyeglass-type or goggle-type displays, virtual reality (VR) or augmented reality (AR), mixed reality (MR) display devices, and virtual image displays. It is suitable for optical elements such as light guide plates and diffraction gratings used in wearable image display devices selected from devices.

1 Upper resist layer 2 Lower resist layer 3 Glass substrate 10, 20, 30 Optical element 11 First resist pattern 21 Second resist pattern 31, 32, 33 Diffraction pattern

Claims (17)

1. A method for manufacturing an optical element comprising a glass substrate having a diffraction pattern, the method comprising:
   A method for manufacturing an optical element, comprising forming a diffraction pattern on the glass substrate using at least two or more resist layers.
2. forming a lower resist layer on the glass substrate;
   forming an upper resist layer on the lower resist layer;
   forming a first resist pattern on the upper resist layer;
   a first etching step of forming a second resist pattern on the lower resist layer using the first resist pattern;
   The method for manufacturing an optical element according to claim 1, comprising a second etching step of forming a diffraction pattern on the glass substrate using the second resist pattern.
3. The optical element according to claim 2, wherein Gr>Rr2b, where Rr2b is the etching rate of the lower resist layer in the second etching step, and Gr is the etching rate of the glass substrate in the second etching step. manufacturing method.
4. The method for manufacturing an optical element according to claim 2 or 3, wherein the ratio Rt2/Rr2b of the etching rate Rr2b of the lower resist layer and the thickness Rt2 of the lower resist layer in the second etching step is 1 to 40 min.
5. forming a lower resist layer on the glass substrate;
   forming an upper resist layer on the lower resist layer;
   forming a first resist pattern on the upper resist layer;
   The method for manufacturing an optical element according to claim 1, comprising a first etching step of forming a second resist pattern on the lower resist layer using the first resist pattern.
6. According to claim 2 or 5, when the etching rate of the upper resist layer in the first etching step is Rr1 and the etching rate of the lower resist layer in the first etching step is Rr2a, Rr1>Rr2a. A method for manufacturing an optical element.
7. 6. The method for manufacturing an optical element according to claim 2, wherein the lower resist layer is made of a metal resist or a metal oxide resist, and the upper resist layer is made of a resin resist.
8. The method for manufacturing an optical element according to claim 1, 2 or 5, wherein the optical element is a light guide plate.
9. An optical element comprising a glass substrate having a diffraction pattern,
   The glass substrate has a refractive index of 2 or more,
   The optical element, wherein the diffraction pattern is directly formed on the glass substrate.
10. An optical element comprising a glass substrate and a diffraction pattern disposed on the glass substrate,
    The glass substrate has a refractive index of 2 or more,
    An optical element, wherein a refractive index difference Δnd between the glass substrate and the diffraction pattern is 0.2 or less.
11. The optical element according to claim 10, wherein an Abbe number difference Δνd between the glass substrate and the diffraction pattern is 21 or less.
12. The optical system according to claim 9 or 10, wherein a/b is greater than 1, where a is the width at the bottom of the convex part of the diffraction pattern, and b is the width at 2/3 height from the bottom of the convex part. element.
13. The optical element according to claim 9 or 10, wherein Ra1/Ra2 is larger than 1, where Ra1 is the surface roughness at the concave portions of the diffraction pattern, and Ra2 is the surface roughness at the convex portions of the diffraction pattern.
14. The optical element according to claim 9 or 10, wherein r is 3 nm to 200 nm, where r is the radius of curvature of the convex portion of the diffraction pattern.
15. The glass substrate contains, in mass %, SiO ₂ 0% to 12%, B ₂ O ₃ 0% to 10%, BaO 0% to 13%, ZnO 0% to 5%, ZrO ₂ 2% to 10%, La ₂ O ₃ 15% to 45%, Gd ₂ O ₃ 0% to 15%, Nb ₂ O ₅ 0% to 15%, WO ₃ 0% to 10%, TiO ₂ 13% to 50%, Y ₂ O ₃ 0 The optical element according to claim 9 or 10, containing .1% to 10%.
16. The optical element according to claim 9 or 10, wherein the diffraction pattern is made of a metal oxide material.
17. The optical element according to claim 9 or 10, which is used as a light guide plate.
    

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