Manufacturing method of optical element, and optical element

Abstract

To provide a manufacturing method of a pupil expansion optical element for wide-viewing-angle head-mounted displays, and an optical element.SOLUTION: The optical element includes a pattern portion 104 including a microstructure 104a and a flat surface 105, which is less likely to cause pattern defects by using a high refractive index resin containing particles 207. The optical element is less likely to cause pattern defects even in pupil dilation optical elements made of high-viscosity, brittle, high-refractive-index resins by using an imprint master 101 in which the pattern portion is formed at a position lower than the flat surface, the boundary between the flat surface and the pattern portion is an inclined surface 106, and the inclination angle θ between the flat surface and the inclined surface is 0.17° or more and 0.5° or less.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing an optical element having a microstructure for use in an optical diffraction grating used in, for example, a head-up display (HUD) or a head-mounted display (HMD), and to an optical element using the same. [Background technology]

[0002] Head-up displays (HUDs) and head-mounted displays (HMDs) use diffraction grating units to generate visible images. The diffraction grating unit consists of an in-coupling grating that connects the image from the image source to the waveguide, and an out-coupling grating that generates the image that the user can finally see. These diffraction grating units are designed to be recognized over a wide field of view and are used as pupil-widening optical elements.

[0003] As a method for forming the fine unevenness used in these diffraction gratings in a pattern portion surrounded by convex portions as a frame portion, a method for forming a pattern on a silicon wafer by dry etching can be mentioned. Furthermore, when producing a large number of diffraction gratings, this is used as a master to prepare an intermediate mold by imprinting, and this intermediate mold is further used to form imprint elements which are diffraction gratings by imprinting.

[0004] The fine unevenness is formed with a pitch of 1 micrometer or less and an aspect ratio (depth of unevenness / width of unevenness) of 1.5 or more, and is easily damaged by application of external force to the unevenness. For this reason, as in Patent Document 1, a prior art example, a method has been used in which the fine unevenness of a pattern portion surrounded by convex portions as a frame portion is formed at a position lower than the plane of the convex portions (i.e., the reference plane) to prevent application of external force to the fine unevenness.

[0005] Meanwhile, head-mounted displays require a wider viewing angle to project images over a wider area in front of the eyes. To achieve this, it is essential to increase the refractive index of the optical materials used in the elements to transmit images with a wider viewing angle. Specifically, a resin with a refractive index of nd 1.7 or higher is required to achieve a viewing angle of 50° or more (Patent Document 2). When a higher refractive index is desired for the UV-curable resin used in nanoimprinting to form elements, a refractive index of nd 1.8 or higher can be achieved by incorporating high-refractive-index particles of TiO2 or ZrO2 into the resin. However, there are two points to note: First, the viscosity of the liquid state before polymerization is very high, and second, the solid state after polymerization is brittle. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2023-148806 [Patent Document 2] US2022 / 0128817A1 publication Summary of the Invention [Problem to be solved by the invention]

[0007] Of these, the viscosity of the liquid state before polymerization is very high. Although the viscosity can be reduced by mixing an organic solvent, which solves the problem during application such as spin coating, this can cause air bubbles to be expelled when the intermediate mold described above is pressed against the material to perform imprinting, or can affect the overall flatness of the pattern in the final product. In addition, even when the master used in Patent Document 1 is used, the pattern portion is formed at a position higher than the reference plane in the imprint element after molding, which poses the problem of external forces being easily applied to the fine uneven shape.

[0008] From the above, it can be said that solving the above problems is necessary to realize a pupil expansion optical element that realizes a head-mounted display with a wide viewing angle.

[0009] The object of the present invention is to provide a method for manufacturing an optical element such as a pupil expansion optical element for a wide viewing angle head-mounted display, and an optical element, which prevents the pattern portion from being formed at a position higher than the reference plane, which is the plane of the convex portion that acts as a frame portion surrounding the pattern portion, even when a brittle high refractive index resin containing high refractive index particles is used, and which prevents external forces from being applied to the fine uneven shape. [Means for solving the problem]

[0010] In order to achieve the above object, according to one aspect of the present invention, there is provided a method for manufacturing an optical element, comprising: the pattern portion is formed at a position lower than the flat surface, and a boundary portion between the flat surface and the pattern portion is connected by an inclined surface, an imprint master in which the inclination angle θ of the inclined surface relative to the bottom surface of the pattern portion is 0.17° or more and 0.5° or less; The shape of the pattern portion of the imprint master is transferred using an ultraviolet curable resin containing particles with a refractive index of 1.7 or more.

[0011] An optical element manufactured by the manufacturing method according to any one of the above aspects of the present invention. [Effects of the Invention]

[0012] According to the present invention, even when a brittle high refractive index resin containing high refractive index particles such as TiO2 or ZrO2 particles is used, the pattern portion is not formed at a position higher than the reference plane, which is the plane of the convex portion that serves as a frame portion surrounding the pattern portion, and external forces are prevented from being applied to the fine uneven shape of the pattern portion, making it possible to provide a manufacturing method for optical elements such as pupil widening optical elements for head-mounted displays with wide viewing angles that are resistant to surface abrasion, and optical elements.

[0013] Therefore, for example, by using an imprint master with a tilt angle θ of 0.17° or more and 0.5° or less and applying a steep pressure change, it is possible to push out the highly viscous UV-curable resin and form the pattern portion at a position lower than the reference plane, thereby providing sufficient protection for the pattern portion from external forces. [Brief explanation of the drawings]

[0014] [Figure 1A] 1 is a schematic plan view of an imprint master according to the present embodiment; [Figure 1B] 1 is a schematic cross-sectional view of an imprint master according to the present embodiment; [Figure 2] Schematic diagram of a manufacturing method of an optical element according to the present embodiment. [Figure 3] Strength characteristics of high refractive index UV curable resin used in this invention DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0016] (Embodiment) FIG. 1A is a top view of an imprint master 101 according to an embodiment of the present invention, FIG. 1B is a schematic cross-sectional view, and FIG. 2 is a schematic diagram of a method for manufacturing an optical element according to an embodiment of the present invention.

[0017] The method for manufacturing an optical element in this embodiment uses an imprint master 101 that has a pattern portion 104 including a microstructure 104a and a flat surface 105, where the pattern portion 104 is formed at a position lower than the flat surface 105, and the boundary between the flat surface 105 and the pattern portion 104 is connected by an inclined surface 106, and the inclination angle θ of the inclined surface 106 relative to the bottom surface of the pattern portion 104, i.e., 103a, is 0.17° or more and 0.5° or less, and transfers the shape of the pattern portion 104 of the imprint master 101 using an ultraviolet-curable resin 204 that contains particles 207 with a refractive index of 1.7 or more.

[0018] This will be explained in detail below.

[0019] 1A and 1B show schematic diagrams of an imprint master 101 according to this embodiment. The imprint master 101 includes a grating layer 102 and a substrate 103 underlying the grating layer 102.

[0020] The grating layer 102 includes a pattern portion 104 and a ring-shaped flat surface 105 that is the flat surface of the convex portion serving as a frame surrounding the pattern portion 104 .

[0021] The pattern portion 104 is composed of, for example, a number of rectangular columnar microstructures 104a arranged as a micropattern with a comb-like cross-sectional shape. In the X-axis direction of Fig. 1B, the microstructures 104a may have different heights, for example, so that their heights gradually increase along the +X direction of Fig. 1B and change continuously. Note that, although Fig. 1A shows the pattern portion 104 as a simple circle, it is not limited to this.

[0022] Specifically, the microstructures 104a are formed in plurality on the main surface 103a (in other words, the bottom surface of the pattern portion 104), which is the upper surface of the substrate 103, which is the XY plane in FIG. 1B, and are columnar cross-sectional structures extending away from the main surface 103a of the substrate 103. Each microstructure 104a extends in the +Z direction. Each microstructure 104a is a columnar structure having a height H, for example, in the micrometer or nanometer dimension. Here, in the case of a microstructure 104a whose height changes continuously, the height of the part with the greatest structural height (for example, the end in the +X direction in FIG. 1B) is set to be H.

[0023] The microstructures 104a may be regularly arranged with intervals between them. For example, the microstructures 104a are arranged side by side at equal intervals in the X and Y directions. The microstructures 104a collectively constitute the pattern portion 104 of the grating layer 102.

[0024] On the other hand, the flat surface 105 is arranged as the upper surface of a protrusion 115 that is wider than one of the microstructures 104a, has a trapezoidal cross section, and functions as a frame, at both ends of the pattern portion 104 in the X-axis direction in a side view of the cross section. As an example, the microstructures 104a at both ends of the pattern portion 104 in the X-axis direction are formed integrally with the protrusions 115 adjacent to them.

[0025] In addition, in the vertical cross-sectional shape of the imprint master 101 as viewed from the side, the upper surfaces 104b of all of the microstructures 104a of the pattern portion 104 are formed at a position lower than the flat surface 105. In addition, in the side view, the boundary between the flat surface 105 of the convex portion 115 and the microstructures 104a at the ends of the pattern portion 104 formed integrally with the convex portions 115 is formed as an inclined surface 106. The inclination of the inclined surface 106 is such that, in the vertical cross-section of Figure 1B, the thickness of the convex portions 115 in the Z-axis direction gradually increases from the outer edge of the microstructures 104a at the ends of the pattern portion 104 toward the inner edge of the flat surface 105 as it moves away from the outer edge of the microstructures 104a at the ends.

[0026] Examples of materials for the grating layer 102 of the imprint master 101 include SiO2, SiN, SiO, Si3N4, and Al2O3, and the material can be selected appropriately depending on the etching selectivity with respect to the substrate 103. The shape of the pattern portion 104 of the grating layer 102 can be an L / S pattern (i.e., a line / space pattern) such as a binary, slant, sawtooth, or sinusoidal shape, and the material can be selected appropriately depending on the optical characteristics required for the product. The pitch of the L / S pattern can be, for example, 200 to 600 nm, and the pitch can be selected appropriately depending on the optical characteristics required for the product. For example, the thickness (i.e., the dimension in the Z-axis direction) of the convex portion 115 having the flat surface 105 of the grating layer 102 is between 500 and 750 nm, and the thickness (i.e., the dimension in the Z-axis direction) of the pattern portion 104 including multiple microstructures 104a with different heights is varied between 50 and 250 nm, and the thickness can be selected appropriately depending on the optical characteristics required for the product.

[0027] The material of the substrate 103 of the imprint master 101 may be Si, Si3N4, TiO2, Al2O3, or SiC, and may be selected appropriately depending on the selectivity with respect to the grating layer 102 during etching.

[0028] As such, the shape of the imprint master 101 includes at least, as an example, a pattern portion 104 including a microstructure 104a, and a flat surface 105, and in the vertical cross-sectional shape when viewed from the side, the upper surface 104b of each microstructure 104a of the pattern portion 104 is formed at a position lower than the flat surface 105.

[0029] Furthermore, the imprint master 101 having the above-described configuration can be used to fabricate an intermediate mold 202 by imprinting, and this intermediate mold 202 can be used to fabricate an imprint element 201, which is a diffraction grating, by imprinting.

[0030] Here, a schematic diagram of the process for producing the imprint element 201 in this embodiment is shown in FIG.

[0031] First, the ultraviolet curable resin 204 is applied to the base material 203 by spin coating or spray coating.

[0032] Thereafter, the intermediate mold 202 is pressed against the substrate 203 from one end by a roller 205 , thereby filling the ultraviolet curable resin 204 formed on the substrate 203 into the fine structure formed in the intermediate mold 202 .

[0033] Then, by irradiating the ultraviolet curing resin 204 with an ultraviolet light source 206 (for example, an ultraviolet LED light source or a metal halide lamp), a pattern portion of the desired microstructure similar to the pattern portion 104 of the microstructure 104a of the imprint master 101 in Figure 1B is formed on the substrate 203.

[0034] Here, the material of the substrate 203 of the imprint element 201 may be a transparent substance such as SiO2, but it may be selected appropriately depending on the optical properties required for the product.

[0035] Furthermore, the UV-curable resin 204 used in the imprint element 201 contains high-refractive-index particles 207 with a refractive index of 1.7 or higher, at a concentration of 30 wt% or more and 80 wt% or less after solvent removal, to achieve a viewing angle of 50° or more and a high refractive index. If the added high-refractive-index particles 207 are less than 30 wt%, the resin's refractive index cannot be increased to 1.7 or higher, narrowing the viewing angle of the HUD or HMD. Furthermore, if the added high-refractive-index particles exceed 80 wt%, the particle-resin interface increases, making the resin more brittle after UV curing and making resin molding by imprinting difficult. Examples of high-refractive-index particles 207 include TiO2 and ZrO2, and particle sizes of less than the wavelength of light are acceptable.

[0036] On the other hand, if a high refractive index is desired for the UV-curable resin 204, a refractive index of 1.7 or higher can be achieved by incorporating high refractive index particles 207 of TiO2 or ZrO2 into the resin. However, this results in problems such as an extremely high viscosity in the liquid state before polymerization and brittleness in the solid state after polymerization.

[0037] Regarding the extremely high viscosity of the liquid state before polymerization, although the problem of spin coating or other coating processes can be solved by lowering the viscosity by mixing an organic solvent, this can cause air bubbles to be expelled when the intermediate mold described above is pressed against the material to perform imprinting, or can affect the overall flatness of the pattern portion in the final product. In conventional technologies, there has been a problem in that the pattern portion in the imprint element is formed at a position higher than the reference plane, which is the flat surface of the convex portion that acts as a frame surrounding the pattern portion.

[0038] 3 shows the shear fracture strength of the cured UV-curable resin when the refractive index nd of the cured UV-curable resin is changed by changing the concentration of solids contained in the UV-curable resin 204. As a result, the higher the concentration of solids contained in the UV-curable resin before curing in order to increase the refractive index of the UV-curable resin, the lower the shear fracture strength of the cured UV-curable resin, making it more susceptible to fracture due to external forces.

[0039] From the above, in the prior art, the completed element is weak against external forces, and the pattern portion is formed at a position higher than the reference plane, resulting in insufficient protection of the pattern portion against external forces.

[0040] 1B is used, the imprint master 101 having an inclination angle θ of 0.17° or more and 0.5° or less for the inclined surface 106 at the boundary between the flat surface 105 and the pattern portion 104. As a result, when the imprint element 201 is produced via the intermediate mold 202, when the ultraviolet curable resin 204 is filled into the microstructure portion 202g formed in the intermediate mold 202, a steep pressure change is applied to the ultraviolet curable resin 204 by the inclined surface of the intermediate mold 202 corresponding to the inclined surface 106, thereby pushing aside the applied highly viscous ultraviolet curable resin 204, and ensuring that a portion equivalent to the microstructure 104a of the pattern portion 104 is formed at a position lower than the reference plane. This ensures sufficient protection against external forces for the portion equivalent to the pattern portion 104 (in the following explanation, it is the UV-curable resin 204, not the imprint master 101, that actually functions; however, to clarify the correspondence with the imprint master 101, the explanation will be given as the imprint master 101, and the phrase "portion equivalent to" will be omitted). Here, if the tilt angle θ is less than 0.17°, the resolution will deteriorate due to a decrease in brightness caused by an expansion of the invalid area or light scattering at the boundary between the pattern portion area and the flat surface area. On the other hand, if the tilt angle θ exceeds 0.5°, air bubbles will be mixed in the resin around the periphery of the pattern portion area during filling, and the resin will not harden sufficiently after UV curing, resulting in poor mold release.

[0041] Furthermore, when the maximum height of the microstructure 104a of the pattern portion 104 is H, it is even better if the maximum height h of the inclined surface 106 is equal to or greater than H. It is even better to use an imprint master 101 in which the inclined width 116 (horizontal direction in the figure) is equal to or greater than H×117 and equal to or less than H×333. If the inclined width 116 is less than H×117, air bubbles may be trapped in the resin around the periphery of the pattern portion area during filling, resulting in insufficient curing of the resin after UV curing, leading to problems such as poor mold release. On the other hand, if the inclined width 116 exceeds H×333, there are problems such as a decrease in brightness due to an expansion of the invalid area, or a deterioration in resolution due to light scattering at the boundary between the pattern portion area and the flat surface area.

[0042] Furthermore, it is more preferable that the maximum height h of the inclined surface 106 is equal to or greater than H and equal to or less than 2H. If the maximum height h of the inclined surface 106 is less than H, the pattern portion 104 will be higher than the flat surface 105, increasing the likelihood of breakage upon contact. If the maximum height h of the inclined surface 106 exceeds 2H, the resin film thickness of the imprint element 201, which is an optical element after transfer, will become thick, and the brightness of the HUD or HMD will decrease due to light absorption.

[0043] According to this embodiment, even when a brittle high-refractive index resin containing high-refractive index particles such as TiO2 or ZrO2 particles is used, the pattern portion 104 is not formed at a position higher than the reference plane, which is the plane of the convex portion 115 that serves as a frame portion surrounding the pattern portion 104, and external forces are prevented from being applied to the fine uneven shape of the pattern portion 104, making it possible to provide a manufacturing method for optical elements such as pupil widening optical elements for head-mounted displays with wide viewing angles that are resistant to surface abrasion, and optical elements.

[0044] Therefore, for example, by using an imprint master 101 with an inclination angle θ of 0.17° or more and 0.5° or less and applying a sudden change in pressure, it is possible to push aside the applied high-viscosity UV-curable resin 204, and form the pattern portion 104 at a position lower than the reference plane. This ensures that the pattern portion 104 is adequately protected from external forces.

[0045] It should be noted that any of the various embodiments or modifications described above can be appropriately combined to achieve the effects of each. In addition, combinations of embodiments, combinations of examples, or combinations of embodiments and examples are possible, and combinations of features from different embodiments or examples are also possible.

[0046] (Addendum) The above description of the embodiments discloses the following techniques.

[0047] (Technology 1) A patterned portion including a fine structure and a flat surface are provided. the pattern portion is formed at a position lower than the flat surface, and a boundary portion between the flat surface and the pattern portion is connected by an inclined surface, an imprint master in which the inclination angle θ of the inclined surface relative to the bottom surface of the pattern portion is 0.17° or more and 0.5° or less; A method for manufacturing an optical element, comprising transferring the shape of the pattern portion of the imprint master using an ultraviolet curable resin containing particles with a refractive index of 1.7 or more.

[0048] (Technology 2) A method for manufacturing an optical element according to Technology 1, in which the imprint master is an imprint master in which the maximum height h of the inclined surface is equal to or greater than H and equal to or less than 2H, where H is the height of the part of the pattern portion with the greatest structural height.

[0049] (Technology 3) The method for manufacturing an optical element according to any one of Techniques 1 and 2, wherein the imprint master has a width of the inclined surface of H×117 or more and H×333 or less.

[0050] (Technique 4) The method for manufacturing an optical element according to any one of Techniques 1 to 3, wherein the ultraviolet curable resin is a high refractive index resin containing 30 wt % to 80 wt % of the particles after solvent removal.

[0051] (Technology 5) An intermediate mold is produced by imprinting using the imprint master; When an imprint element that is a diffraction grating is produced by imprinting using the intermediate mold for the transfer, Applying the ultraviolet curable resin to a substrate; pressing the intermediate mold against the ultraviolet curing resin from an end of the substrate with a roller, thereby filling the ultraviolet curing resin into a microstructure portion formed in the intermediate mold by the microstructure of the pattern portion of the imprint master; the ultraviolet curable resin is irradiated with ultraviolet light from an ultraviolet light source to be cured, and then the intermediate mold is released from the ultraviolet curable resin, thereby transferring the shape of the pattern portion of the imprint master to the ultraviolet curable resin on the base material. The method for producing an optical element according to any one of techniques 1 to 4.

[0052] (Technology 6) An optical element manufactured by any one of the manufacturing methods of Technologies 1 to 4.

[0053] (Technology 7) An optical element manufactured by the manufacturing method of Technology 5.

[0054] According to each of these configurations, even when a brittle high-refractive index resin containing high-refractive index particles such as TiO2 or ZrO2 particles is used, the pattern portion is not formed at a position higher than the reference plane, which is the plane of the convex portion that acts as a frame portion surrounding the pattern portion, and external forces are prevented from being applied to the fine uneven shape of the pattern portion, making it possible to provide a manufacturing method for optical elements such as pupil expansion optical elements for head-mounted displays with wide viewing angles that are resistant to surface abrasion, and optical elements. [Industrial Applicability]

[0055] The optical element manufacturing method and the optical element according to the above aspect of the present disclosure can suppress protrusion of the pattern portion onto the surface and suppress damage to the pattern portion, which is effective for imprint elements having fine patterns, and is useful for, for example, surface relief head-up displays (HUDs) or head-mounted displays (HMDs) using fine patterns. [Explanation of symbols]

[0056] 101 Imprint Master 102 lattice layer 103 Substrate 103a Main surface 104 Pattern section 104a Microstructure 104b Top surface of the microstructure 105 Flat surface 106 Slope 115 Convex part 116 Slope width 201 Imprint element 202 Intermediate mold 202g Microstructure part 203 Base material 204 UV curing resin 205 Laura 206 Ultraviolet light source 207 High refractive index particles

Claims

1. A pattern portion including a microstructure and a flat surface, the pattern portion is formed at a position lower than the flat surface, and a boundary portion between the flat surface and the pattern portion is connected by an inclined surface, an imprint master in which the inclination angle θ of the inclined surface with respect to the bottom surface of the pattern portion is 0.17° or more and 0.5° or less; A method for manufacturing an optical element, comprising: transferring the shape of the pattern portion of the imprint master using an ultraviolet curable resin containing particles having a refractive index of 1.7 or more.

2. 2. The method for manufacturing an optical element according to claim 1, wherein the imprint master is an imprint master in which the maximum height h of the inclined surface is greater than or equal to H and less than 2H, where H is the height of the part of the pattern portion with the greatest structural height.

3. 3. The method for manufacturing an optical element according to claim 1, wherein the imprint master has a width of the inclined surface of H×117 or more and H×333 or less.

4. 3. The method for manufacturing an optical element according to claim 1, wherein a high refractive index resin containing 30 wt % to 80 wt % of the particles after solvent removal is used as the ultraviolet curable resin.

5. producing an intermediate mold by imprinting using the imprint master; When an imprint element that is a diffraction grating is produced by imprinting using the intermediate mold for the transfer, Applying the ultraviolet curable resin to a substrate; pressing the intermediate mold against the ultraviolet curing resin from an end of the substrate with a roller, thereby filling the ultraviolet curing resin into a microstructure portion formed in the intermediate mold by the microstructure of the pattern portion of the imprint master; the ultraviolet curable resin is irradiated with ultraviolet light from an ultraviolet light source to be cured, and then the intermediate mold is released from the ultraviolet curable resin, thereby transferring the shape of the pattern portion of the imprint master to the ultraviolet curable resin on the base material. The method for manufacturing an optical element according to any one of claims 1 to 2.

6. An optical element manufactured by the manufacturing method according to any one of claims 1 and 2.

7. An optical element manufactured by the manufacturing method of claim 5.

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