WO2017073251A1

WO2017073251A1 - Diffuser, method for designing diffuser, method for manufacturing diffuser, display device, projection device, and illumination device

Info

Publication number: WO2017073251A1
Application number: PCT/JP2016/079345
Authority: WO
Inventors: 直樹花島; 昭夫高田; 和幸渋谷; 雄介松野
Original assignee: デクセリアルズ株式会社
Priority date: 2015-10-29
Filing date: 2016-10-03
Publication date: 2017-05-04
Also published as: CN114325900A; CN108351437B; CN108351437A

Abstract

[Problem] To manufacture, at high productivity, a diffuser which exhibits excellent diffusion characteristics while having excellent durability against highly coherent light. [Solution] The diffuser according to the present invention is a microlens array diffuser comprising a microlens group positioned on the surface of a transparent substrate, and is configured from two or more unit cells continuously provided in an array. The unit cells are provided with a plurality of microlenses positioned on the surface of the transparent substrate. The ridges between the mutually adjoining microlenses are not parallel to each other, and are not parallel to the transparent substrate.

Description

Diffusion plate, diffusion plate design method, diffusion plate manufacturing method, display device, projection device, and illumination device

The present invention relates to a diffusion plate, a diffusion plate design method, a diffusion plate manufacturing method, a display device, a projection device, and an illumination device.

Diffusers that scatter incident light in various directions are widely used in various devices such as display devices such as displays, projection devices such as projectors, and various illumination devices. The diffusion mechanism of incident light in such a diffuser plate uses light refraction caused by the surface shape of the diffuser plate, and uses scattering caused by a substance present in the bulk body and having a refractive index different from that of the surroundings. It is roughly divided into One of the diffusion plates using light refraction caused by the surface shape is a so-called microlens array type diffusion plate in which a plurality of microlenses having a size of several tens of μm are arranged on the surface of a bulk body.

In the micro lens array type diffusion plate, various proposals have been made for methods of suppressing the generation of diffracted light by making the lens shape and lens arrangement irregular, for example, as in Patent Document 1 and Patent Document 2 below. Has been. The following Patent Document 1 discloses a diffusing plate for a focusing screen, and the diffusing plate is designed with variations in the pitch and height of the microlenses. Specifically, in Patent Document 1 below, the pitch P of the microlens is 8 μm ≦ P ≦ 30 μm, and the height H of the microlens is 0.01 × P ≦ H ≦ 0.1 × P. The effect is disclosed. Further, Patent Document 2 below discloses a microlens array in which a plurality of microlenses are irregularly arranged, and a boundary region of the plurality of microlenses has a curvature with a sign different from the surface curvature of the microlens. It is disclosed that it consists of aspects.

When an irregularly arranged structure as described above is actually manufactured, it is common to perform drawing with a laser or an electron beam in the production of a transfer mold or a photomask. At this time, there is a problem that the amount of data becomes enormous if the entire drawing area is a pattern that does not repeat. Further, when evaluating the drawn product, there is a problem that the manufacturing cost increases, for example, because the evaluation portion cannot be narrowed down because there is no repetition in the pattern, so that the entire surface evaluation takes a lot of time.

In order to solve the above-described productivity problem, for example, in Patent Document 3 below, a focusing screen that performs exposure of a second area by a step-and-repeat method using a reticle pattern configured by a random pattern is manufactured. A method is disclosed. In Patent Document 3, it is mentioned that the pattern at the periphery of the reticle is not discontinuous at the joint. Further, in Patent Document 3, the suppression of the diffracted light component is also mentioned while paying attention to the functional characteristics as a focusing screen such as blur and brightness.

Japanese Patent Laid-Open No. 3-192232 JP 2007-108400 A JP 59-208536 A

Here, the focusing screen (that is, the focusing screen) manufactured by the manufacturing method disclosed in Patent Document 3 described above realizes desired characteristics when light is incident over a wide area of the focusing screen. Is possible. However, if such a manufacturing method is applied to a microlens array type diffusion plate, it is difficult to obtain desired diffused light for light incident on a spot-like narrow region such as laser light. There was a problem.

When the spot-like incident light as described above is incident, especially when laser light is incident, the coherence of the incident light is increased. For this reason, in order to suppress the diffracted light component, the influence of not only the lens arrangement but also the boundary portion between the lenses cannot be ignored, and only the lens portion existing in the irradiated spot affects the emitted light. Become. From these viewpoints, it is important to optimize a microlens array structure different from the focusing screen. Furthermore, in order to maintain durability against a high light intensity density in the spot, it is important to form the entire diffuser plate including the lens portion using an appropriate material. However, the above-mentioned Patent Document 3 does not disclose the influence of the restrictions on the manufacturing process caused by the material of the diffusion plate on the microlens structure.

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to exhibit excellent diffusion characteristics and excellent durability against coherent light. An object of the present invention is to provide a diffusion plate, a diffusion plate design method and a diffusion plate manufacturing method that can be manufactured with higher productivity, and a display device, a projection device, and an illumination device using the diffusion plate.

In order to solve the above-described problem, according to an aspect of the present invention, there is provided a microlens array type diffusing plate composed of a group of microlenses located on the surface of a transparent substrate, which is continuous with respect to the array arrangement The unit cell is composed of a plurality of microlenses positioned on the surface of the transparent substrate, and ridge lines between the adjacent microlenses are not parallel to each other, and the transparent substrate A diffusion plate is provided that is not parallel to.

The distance between the apexes of the adjacent microlenses constituting the unit cell is included within a range of ± 60% of the average value, and the radius of curvature of each of the microlenses constituting the unit cell is The average value is preferably within a range of ± 20%.

The degree of variation from the average value of the distance between the apexes of the adjacent microlenses constituting the unit cell is σ _p, and the degree of variation from the average value of the radius of curvature of the adjacent microlenses constituting the unit cell It is preferable that the following (Equation 1) is satisfied when σ _R is set.

The length of the diagonal of the unit cell is preferably 3 mm or less.

It is preferable that the length of at least one side of the unit cell is an integer multiple of the average pitch of the microlenses included in the unit cell.

It is preferable that the number of microlenses included in the unit cell is at least nine.

In the unit cell, it is preferable that a boundary portion between the microlenses adjacent to each other is not flat.

It is preferable that a half lens is disposed on at least a part of the boundary portion.

The shape of the micro lens may be a polygon.

The microlens is preferably a concave lens.

The transparent substrate may be made of an inorganic material.

The inorganic material may be a glass mainly composed of silicon having an alkali component content of 20% or less.

An antireflection layer may be provided on the surface of the microlens and the surface of the transparent substrate on which the microlens group is not disposed.

The antireflection layer may be a multilayer structure composed of Nb ₂ O ₅ and SiO ₂ .

The antireflection layer provided on the surface of the microlens may be an antireflection structure including irregularities having a size equal to or smaller than the wavelength of light, which is formed on the surface of the microlens group.

The antireflection structure may be a structure that is provided anisotropically on the surface of the microlens and has a pitch of unevenness of 300 nm or less.

In order to solve the above-mentioned problem, according to another aspect of the present invention, there is provided a method for designing a microlens array type diffusing plate composed of a microlens group located on the surface of a transparent substrate, which comprises the microlens group. There is provided a diffusion plate design method for determining the curvature radius of each microlens based on the product of the reciprocal of the etching selectivity between the transparent substrate and the resist and the curvature radius developed on the resist.

In order to solve the above problems, according to still another aspect of the present invention, there is provided a method of manufacturing the diffusion plate, comprising: a step of laminating a resist on a transparent substrate; and a grayscale mask having a transmittance distribution. There is provided a method of manufacturing a diffusion plate, which includes a step of exposing the resist and a step of dry etching the developed transparent substrate using a fluorine-based gas so as to obtain a desired lens shape.

In the dry etching step, the radius of curvature of each microlens constituting the microlens group is determined by the product of the reciprocal of the etching selectivity of the transparent substrate and the resist and the radius of curvature developed on the resist. Also good.

In order to solve the above problems, according to another aspect of the present invention, there is provided a display device including the above diffusion plate.

In order to solve the above problems, according to another aspect of the present invention, there is provided a projection apparatus including the above diffusion plate.

Moreover, in order to solve the above-described problems, according to another aspect of the present invention, an illumination device including the above diffusion plate is provided.

As described above, according to the present invention, it is possible to produce a diffuser plate that exhibits excellent diffusion characteristics and has excellent durability against coherent light with higher productivity. Thus, it is possible to provide a display device, a projection device, and an illumination device using such a diffusion plate.

It is explanatory drawing which showed typically the diffusion plate which concerns on the 1st Embodiment of this invention. It is explanatory drawing which showed typically a part of unit cell which comprises the diffuser plate which concerns on the embodiment. It is explanatory drawing which showed typically an example of the state of the boundary between the adjacent microlenses in the unit cell which concerns on the embodiment. It is explanatory drawing which showed an example of the state of the boundary between the adjacent microlenses in the unit cell which concerns on the same embodiment. It is explanatory drawing which showed an example of the state of the boundary between the adjacent microlenses in the unit cell which concerns on the same embodiment. It is explanatory drawing which showed an example of the state of the boundary between the adjacent microlenses in the unit cell which concerns on the same embodiment. It is explanatory drawing which showed typically the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating arrangement | positioning of the unit cell in the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating arrangement | positioning of the unit cell in the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating arrangement | positioning of the unit cell in the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating arrangement | positioning of the unit cell in the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating arrangement | positioning of the unit cell in the diffusion plate which concerns on the same embodiment. It is the flowchart which showed an example of the flow of the manufacturing method of the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating the manufacturing method of the diffusion plate which concerns on the same embodiment. It is explanatory drawing for demonstrating the manufacturing method of the diffusion plate which concerns on the same embodiment. It is the flowchart which showed an example of the flow of the design method of the diffusion plate which concerns on the same embodiment. It is explanatory drawing which showed typically a part of unit cell which comprises the diffuser plate which concerns on the 2nd Embodiment of this invention. It is explanatory drawing for demonstrating the dispersion | variation in the distance between vertices in the microlens group which concerns on the embodiment. It is explanatory drawing for demonstrating the dispersion | variation in the curvature radius in the microlens group which concerns on the same embodiment. It is explanatory drawing for demonstrating the attenuation width in the diffusion plate which concerns on the same embodiment. It is the graph which showed the relationship between the dispersion | variation in the distance between vertices and a curvature radius, and an attenuation factor. It is the graph which showed the relationship between the dispersion | variation in the distance between vertices and a curvature radius, and an attenuation factor. It is explanatory drawing for demonstrating the relationship between the diffusion full angle and attenuation factor in a diffusion plate. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 1st Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 1st Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 1st Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 1st Embodiment of this invention. It is the table | surface which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is the table | surface which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is the graph which showed the result of the Example regarding the diffusion plate which concerns on the 2nd Embodiment of this invention. It is explanatory drawing which showed an example of arrangement | positioning of the micro lens in the diffusion plate which concerns on the 2nd Embodiment of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[First Embodiment]
(About diffusion plate)
Hereinafter, the diffusion plate 1 according to the first embodiment of the present invention will be described in detail with reference to FIGS. 1 to 7B.
FIG. 1 is an explanatory view schematically showing a diffusion plate according to this embodiment. FIG. 2 is an explanatory view schematically showing a part of the unit cell constituting the diffusion plate according to the present embodiment. 3A to 4B are explanatory diagrams showing an example of a boundary state between adjacent microlenses in the unit cell according to the present embodiment. FIG. 5 is an explanatory view schematically showing the diffusion plate according to the present embodiment. 6A to 7B are explanatory views for explaining the arrangement of unit cells in the diffusion plate according to the present embodiment.

The diffusing plate 1 according to the present embodiment is a microlens array type diffusing plate in which a microlens group including a plurality of microlenses is arranged on a substrate. The diffusion plate 1 is composed of a plurality of unit cells 3 as schematically shown in FIG. In addition, between the unit cells 3, as schematically shown in the diagram on the right side of FIG. 1, the layout pattern (arrangement pattern) of the plurality of microlenses provided in the unit cell 3 is the unit cell arrangement direction (in other words, In this case, it is continuous in the array arrangement direction).

Here, FIG. 1 shows an example in which the shape of the unit cell 3 constituting the diffusion plate 1 is a rectangle, but the shape of the unit cell 3 is limited to that shown in FIG. For example, any shape that can fill the plane without gaps, such as a regular triangle shape or a regular hexagonal shape, may be used.

The number of unit cells 3 constituting the diffusion plate 1 according to the present embodiment is not particularly limited, but the diffusion plate 1 is preferably composed of at least two unit cells 3.

FIG. 2 is an explanatory view schematically showing a part of the structure of the unit cell 3 according to the present embodiment. As schematically shown in FIG. 2, the unit cell 3 according to the present embodiment includes a transparent substrate 10 and a microlens group 20 formed on the surface of the transparent substrate 10.

<About the transparent substrate 10>
The transparent substrate 10 is a substrate made of a material that can be regarded as transparent in the wavelength band of light incident on the diffusion plate 1 according to the present embodiment. Such a substrate is preferably formed using an inorganic material having high light resistance. Examples of inorganic materials having high light resistance include, for example, known optical glasses such as quartz glass, borosilicate glass, white plate glass, etc., and the main component is silicon having an alkali component content of 20% by mass or less. It is preferable to use glass. By using such an inorganic material, it is possible to eliminate the deterioration of the diffusion characteristics of the diffusion plate due to the alteration of the material even when a high-power laser beam is used as the incident light. In FIG. 2, the case where the transparent substrate 10 is rectangular is illustrated as an example. However, the shape of the transparent substrate 10 is not limited to a rectangle, for example, a display device on which the diffusion plate 1 is mounted, It may have an arbitrary shape depending on the shape of the projection device, lighting device, or the like.

<About the micro lens group 20>
A microlens group 20 including a plurality of microlenses 21 is formed on the surface of the transparent substrate 10. In the diffusing plate, since the original use method is to diffuse light, as shown in the lower part of FIG. 2, the exit surface of the microlens 21 constituting the unit cell 3 is a concave lens. Is preferred. This is because when the exit surface of the diffuser plate is a convex lens, a condensing part is generated at the focal position, which may cause problems in installation restrictions and safety. Further, in the microlens group 20 according to the present embodiment, each microlens 21 is not the same in radius of curvature or pitch between vertices, and has a variation in a certain range, so that the focal length is also a certain distribution. have. In the case of a concave lens, the focal position is a virtual point, but the light intensity density is large at the focal position. Therefore, the focal position of each microlens 21 may be in a region adjacent to the transparent substrate 10 constituting the diffusion plate 1. preferable. This is because when the focal position of each microlens 21 is located away from the transparent substrate 10, there may be restrictions on the optical system such as various components cannot be arranged at the focal position.

Also, in the microlens group 20 according to the present embodiment, each microlens 21 constituting the unit cell 3 is arranged so as to satisfy the following three conditions.

(1) The boundary of the four sides of the unit cell 3 should not be discontinuous in the pattern in the array arrangement.
(2) The planar position and height position of the apex of each microlens 21 (in other words, the position where the depth of the concave lens is the lowest) and the ridge line between the microlenses 21 are not so large that diffraction is sufficiently suppressed. Be regular.
(3) There is no non-lens region between adjacent microlenses 21 in order to suppress non-diffuse transmitted light.

Here, the “irregularity” referred to in the above (2) means that there is substantially no regularity regarding the arrangement of the microlenses 21 in an arbitrary region of the microlens group 20 in the diffusion plate 1. To do. Therefore, even if there is a certain regularity in the arrangement of the microlenses 21 in a micro area in an arbitrary area, the irregularity in which the arrangement of the microlenses 21 does not exist in the entire arbitrary area is “irregular”. Shall be included.

In the microlens group 20 according to the present embodiment arranged so as to satisfy the above three conditions, the ridge lines between the adjacent microlenses 21 are not all parallel to each other and are parallel to the transparent substrate 10. It is not like that. This is because the diffracted light component increases when there are ridge lines parallel to each other between the microlenses 21.

Here, the “ridge line” refers to a linear region in which the curvature radius of the microlens 21 is abruptly changed at an adjacent lens boundary where the plurality of microlenses 21 are adjacent to each other. The width of such a ridge line is about the wavelength of normal light or less, but the width of the ridge line is controlled so that the diffracted light has an appropriate size under process conditions such as etching. Further, “not parallel” includes a case where at least one of two lines for determining whether or not parallel is a curve.

Specifically, as shown in FIGS. 3A and 3B, the region of the microlens surrounded by the adjacent microlens 21 is a polygon when viewed from the optical axis direction of the microlens. The sides are curved when viewed from the cross section of the microlens.

In addition, the length of at least one side of the unit cell 3 composed of the microlenses 21 satisfying the above three conditions is the average pitch of the microlenses 21 included in the unit cell 3 (for example, between the vertex positions of the microlenses 21). It is preferable that it is an integral multiple of the average distance). In other words, the period of the unit cell 3 in the diffusing plate 1 according to the present embodiment is preferably a period in which the length of at least one side of the unit cell 3 is an integral multiple of the average pitch of the microlenses 21.

Thus, the adjacent microlenses 21 in the microlens group 20 are determined so as to satisfy the above-described conditions, and are not completely random.

It should be noted that the ridgeline between adjacent microlenses 21 can be further devised to reduce the diffracted light component. For example, as schematically shown in FIG. 3A, a part of the ridge line is not a simple straight line or curve, but a convex or concave shape, or as shown in FIGS. 4A and 4B, a half lens part is formed on a part of the ridge line. It is also possible to arrange different shapes such as. Here, in the present embodiment, the half-lens portion refers to a region where the change in the radius of curvature of the microlens 21 is relatively gradual such that the width of the ridge line is 10 μm or more. In addition, such a half-lens part includes one having a different sign of curvature in an orthogonal direction, such as a saddle type. By forming the ridgeline between the microlenses 21 as described above, the boundary portion between the adjacent microlenses 21 is not flat, and the phase of the diffracted wavefront generated at the ridgeline portion is disturbed. It is possible to prevent a diffracted light component in the direction from being generated.

The number of microlenses 21 constituting the unit cell 3 is preferably 3 × 3 = 9 or more. This is because, when incident light having a diameter equal to that of the unit cell 3 is incident, if the average pitch of the microlenses 21 is about 1/3 or less of the incident light diameter, the diffusion characteristic is less than the deviation of the incident light position. It is derived from not changing. The relationship between the average pitch of the microlenses 21 and the incident light diameter will be described in detail later.

<About the antireflection layer>
The diffusion plate 1 according to the present embodiment has a front surface and a back surface (in other words, the surface of the microlens 21 and the surface on the side where the microlens group 20 of the transparent substrate 10 is not disposed). As schematically shown in FIG. 5, the antireflection layer 30 may be formed for the purpose of increasing transmittance and preventing reflection stray light.

The antireflection layer 30 is made of, for example, SiO ₂ , Al ₂ O ₃ , MgF ₂ , CeO ₂ , TiO ₂ , Ta ₂ O ₅ , Nb ₂ O ₅ , Y ₂ O ₃ , Tb ₂ O ₃ , ZnS, ZrO _2. It can be formed by a known method such as vapor deposition or sputtering using a general dielectric such as. Here, by forming the antireflection layer 30 using a material having high light resistance such as Ta ₂ O ₅ , Nb ₂ O ₅ , and SiO ₂ , the incident light has a high light density such as a high output laser. Even so, it is possible to obtain a sufficient effect without being deteriorated by the light. At this time, the antireflection layer 30 is formed into a multilayer structure in which materials having high light resistance such as Ta ₂ O ₅ , Nb ₂ O ₅ , and SiO ₂ are laminated with each other, thereby further improving light resistance. It can be realized. The film thickness of the antireflection layer 30 is not particularly limited, and may be set as appropriate according to the use of the diffusion plate 1, the light density of incident light, and the like.

When the antireflection layer 30 is formed on the diffusion plate 1, since the unevenness of the microlens 21 exists on the surface of the diffusion plate 1, the thickness of the antireflection layer 30 is different from that of the central portion of the microlens 21. In view of this point, it is preferable to form the antireflection layer 30 because there is a possibility that it differs depending on the peripheral portion. In addition, since the incident angle of incident light is different between the central portion and the peripheral portion of the microlens 21, it is more preferable to devise such as taking a wider angle range than usual.

Further, the antireflection layer 30 provided on the surface of the microlens 21 is formed on the surface of the microlens group 20 (also the surface of the microlens 21) and has fine irregularities having a size equal to or smaller than the wavelength of light (so-called so-called). An antireflection structure made of a moth-eye structure may be used. In particular, when realizing diffusion characteristics exceeding a diffusion angle of 10 degrees, the inclination of the surface of the microlens 21 increases, so that the moth-eye structure having a small dependency on the incident angle of the reflectance is advantageous over the multilayer structure as described above. There is. From the standpoint of reducing stray light and reflection, the antireflection structure is preferably a structure that is provided anisotropically in the surface of the microlens 21 and has a pitch of fine irregularities of 300 nm or less.

<About arrangement of unit cell 3>
As conventionally known, when light is incident on a periodic repeating structure, diffracted light is generated. The diffraction angle θ is given by Equation 101 below, where p is the pitch (repetition period) of the repetitive structure, m is the diffraction order (integer), and λ is the wavelength of incident light.

In the case of a microlens array type diffusing plate as noted in the present embodiment, the emitted light is a superimposition of the diffusion effect by the lens element (microlens 21) and the diffracted light component by the periodic arrangement of the microlenses 21. It becomes. The diffracted light component has a discrete distribution with respect to the angle, and the peak intensity of the diffracted light component decreases in inverse proportion to the diffraction order m. If these discrete diffraction components become smaller than the intensity level of the diffused light spread by the lens array, they will be buried in the diffused light and cannot be distinguished from them. By reducing the peak, adverse effects due to diffraction are suppressed.

Also, the peak intensity of the diffracted light component depends on the incident conditions such as the incident light diameter. For example, when light having an incident light diameter having the same size as that of the microlens 21 is incident on the microlens 21, even if the microlens group 20 is regularly arranged, the microlens 21 to which the light has entered is arranged. Since only a small amount of light is incident on the microlens 21 adjacent to, diffracted light is hardly generated. On the other hand, when incident light having an incident light diameter approximately equal to the size of the microlens 21 is incident on the microlens 21, a phenomenon in which emission characteristics change depending on the relationship between the incident optical axis and the optical axis of the microlens 21. Is likely to occur.

6A to 6C show examples in which the emission light distribution of the irregularly arranged microlens array is simulated by a commercially available electromagnetic field simulator. In this simulation, the pitch p (also the diameter of the microlens) of the microlens 21 in the microlens array is 82 μm, and the size of the rectangular microlens array is 738 μm × 710 μm (diagonal length: about 1024 μm). It was. In addition, when the incident light diameter of the light incident on the microlens array is changed to 200 μm, 300 μm, and 650 μm, how the emitted light distribution including the diffracted light is projected onto the detector screen. I verified. In FIG. 6A to FIG. 6C, the bright spot in the figure indicates the diffracted light by the microlens array.

As shown in FIG. 6A, when the size difference between the diameter (82 μm) of the microlens 21 and the incident light diameter is relatively small, the diffracted bright spot in the diffused light becomes large. As is apparent from 6C, it can be seen that it is preferable to reduce the diameter of the microlens 21 (or increase the incident light diameter). Specifically, by setting the pitch of the microlens array to be approximately 1/3 or less of the incident light diameter, it is possible to reduce the influence of the bright spots as described above to a level that does not cause a problem in practice.

On the other hand, when actually manufacturing a microlens array, consider creating a photomask or mold for transfer. In this case, in general, the shape of the microlens 21 is often formed by direct drawing with a laser or an electron beam. However, in order to reduce the amount of data to be produced, the unit cell 3 having a relatively small area is used. In many cases, a so-called step-and-repeat technique is employed in which the array is repeatedly arranged in the vertical and horizontal directions and expanded to a desired size. When light is incident on an element having such an array structure, two types of diffracted light components having a double repeated structure in the unit cell 3 and between the unit cells 3 are generated. For each diffraction angle, the diffraction angle in the unit cell 3 is determined by the pitch of the lens arrangement, and the diffraction angle between the unit cells 3 is determined by the size (size) of the unit cell 3.

Consider the diffraction angle by the unit cell array (diffraction angle between unit cells 3). For example, when the unit cell pitch is 700 μm and the wavelength of incident light is 450 nm, the angle (half angle) of the first-order diffracted light (diffracted light when m = 1) is 0. It will be 03 degrees. Therefore, even when the diffusion angle (half angle) of the diffusion plate is about 3 degrees, (3 / 0.03) ² = 10 ⁴ diffracted lights are generated in the diffused light. The intensity of the diffracted light rapidly decreases as the diffraction order m becomes higher (for example, the peak intensity becomes (2 / π) ^{m at} the diffraction order m). A certain degree of diffraction peak will appear in the diffused light. Hereinafter, the diffracted light resulting from such a unit cell array will be referred to as sub-diffracted light.

On the other hand, each bright spot of the diffracted light by the lens array as described above (in other words, each bright spot of the diffracted light in the unit cell 3) is sub-diffraction by the unit cell array as described above. The peaks are further discretely separated. Therefore, the clarity of the bright spot in the diffused light is reduced by the sub-diffracted light peak. As the conditions change from FIG. 6A to FIG. 6C, the diffracted bright spot in the diffused light becomes smaller because the diffracted light by the diffraction in the unit cell 3 as described above (hereinafter also referred to as main diffracted light). Is due to the phenomenon of being separated by the sub-diffraction light.

Here, since the diffraction angle by the unit cell is very small, the bright spot of the sub-diffraction component does not become a problem in actual use of the diffusion plate 1 according to the present embodiment. Therefore, by appropriately generating the sub-diffracted light by the unit cell 3, as described with reference to FIGS. 6A to 6C, the peak intensity of the main diffracted light can be reduced.

The intensity of the sub-diffracted light is determined by the relationship between the unit cell 3 and the magnitude of the incident light. In general, when the unit cell 3 is larger than the incident light, sub-diffracted light due to the periodic structure of the unit cell 3 is not generated. Here, considering the full width at half maximum of the incident light intensity as shown in FIG. 7A, the diameter in the direction in which the full width at half maximum is minimized is defined as the “incident light diameter” as shown in FIG. 7B. Further, the unit cell 3 is a rectangle such as a rectangle or a square, and the length of the diagonal line of the unit cell 3 is defined as “unit cell size”. At this time, as shown in FIG. 7B, if the unit cell size is smaller than the incident light diameter, sub-diffracted light caused by diffraction between the unit cells 3 is generated and caused by the lens array (in other words, It becomes possible to reduce the peak intensity of the main diffracted light (due to diffraction in the unit cell 3).

Here, even if the light incident on the diffusion plate 1 is a laser beam, the incident light diameter as shown in FIG. 7B is considered to be about 3 mm at the maximum. Therefore, if the unit cell size as shown in FIG. 7B is 3 mm or less, the diffusion plate 1 according to this embodiment can be used for any laser light source.

As described above, the microlens array type diffusing plate 1 according to this embodiment includes two or more unit cells 3, and each unit cell 3 is a microlens group including a plurality of microlenses 21. 20 The microlenses 21 included in each unit cell 3 are continuous with respect to the array arrangement, and the ridgelines of the microlenses 21 are not parallel to each other and are not parallel to the transparent substrate 10. And Thereby, the diffusing plate 1 according to the present embodiment can suppress the diffracted light component in the diffused light, and exhibits excellent diffusion characteristics.

The diffusion plate 1 according to this embodiment has been described in detail above with reference to FIGS. 1 to 7B.

(Diffusion plate manufacturing method)
Hereinafter, an example of a method for manufacturing the diffusion plate 1 according to the present embodiment will be briefly described with reference to FIGS. FIG. 8 is a flowchart showing an example of the flow of the manufacturing method of the diffusion plate according to the embodiment. 9 and 10 are explanatory diagrams for explaining the manufacturing method of the diffusion plate according to the present embodiment.

The diffusion plate 1 according to the present embodiment can be manufactured by transferring a pattern made of an organic material such as a photoresist onto a substrate by dry etching, as will be described below.

In such a manufacturing method, first, a resist is applied to a predetermined transparent substrate 10 (step S101). Here, in the manufacturing method described below, since the fluorine-based etching gas such as CF ₄ , SF ₆ , CHF ₃ or the like is generally used as the etching gas, the transparent substrate 10 is as described above. Does not contain alkali components such as Al ₂ O ₃ and alkali metals that react with various fluorine-based etching gases to become nonvolatile substances (or the content of alkali components is 20% by mass or less, more preferably 10% by mass or less). It is preferable to use quartz glass or Tempax glass. For example, when a glass substrate containing 27% Al ₂ O ₃ and containing no alkali metal (for example, Corning product name: Eagle XG) is dry-etched using the fluorine-based etching gas as described above, the surface A problem arises in that microscopic protrusions of Al ₂ O ₃ that are not etched are generated and the transmittance is reduced.

Subsequently, stepper exposure is performed on the transparent substrate 10 coated with resist using a gray scale mask (step S103).

At this time, as schematically shown in FIG. 9, a unit cell 3 of about 1 mm or less and further vertically and horizontally repeated is used as a basic cell of about 1 to 20 mm, and this basic cell is used in step-and-repeat exposure. It can also be a repeating unit. In this case, depending on the positional accuracy in the stepping, a pattern joint having a width of about several μm at maximum is generated between the basic cells. However, as schematically shown in FIG. 9, the exposure shot is moved at the unit cell interval. By performing the exposure while overlapping the patterns, it is possible to eliminate the connection between the patterns. At this time, if the exposure amount by one exposure is half of the desired exposure amount, the desired exposure amount can be realized by four exposures. It is also possible to eliminate joints by performing step-and-repeat exposure so that the edges of adjacent basic cells are slightly overlapped (for example, a width of 500 nm or less). In this case, multiple exposures are not necessary.

Subsequently, the resist pattern after the stepper exposure is developed (step S105). As a result, a desired microlens pattern is formed on the resist applied on the transparent substrate 10.

Subsequently, dry etching is performed on the transparent substrate 10 that has been developed using the fluorine-based etching gas as described above (step S107). As a result, the microlens pattern formed on the resist is transferred to the transparent substrate 10.

Thereafter, the antireflection layer 30 is formed by performing AR coating on the front and back surfaces of the transparent substrate 10 on which the microlens pattern is formed by vapor deposition or sputtering using the dielectric as described above (step S109). Moreover, you may form the antireflection structure which consists of an unevenness | corrugation below the wavelength of light with the well-known moth-eye structure manufacturing method as the antireflection layer 30 with respect to the surface of a microlens.

As described above, the diffusion plate 1 according to this embodiment forms a resist pattern having a lens curved surface on a transparent substrate 10 such as a glass substrate by gray scale exposure, and then dry-etches the resist pattern on the transparent substrate 10. It is produced by transferring the lens shape to the lens. Here, the lens-like resist pattern shape transferred to the transparent substrate 10 is determined in consideration of not only the gray scale exposure conditions but also the dry etching conditions.

Here, the ratio of the etching rate of the resist in dry etching and the etching rate of the transparent substrate 10 (for example, glass) (= the etching rate of the transparent substrate / the etching rate of the resist) is referred to as “etching selectivity”. . At this time, the etching selectivity as described above can be changed by adjusting the flow rate ratio of each etching gas in the dry etching process. Thereby, it is possible to finely adjust the shape of the lens to be transferred (for example, the radius of curvature of the microlens 21).

Specifically, when CF ₄ , Ar, or O ₂ is used as the etching gas, the flow rate ratio (= “flow rate of CF ₄ gas / flow rate of Ar gas”) is changed in the range of 0.25 to 4, Etching selectivity varies from 1.0 to 1.7. Further, when O ₂ gas is added in an amount of 3% to 10% in this state, the etching selectivity as described above can be reduced to 0.7 to 1.0. Thus, the etching selectivity as described above can be changed from 0.7 to 1.7 depending on the conditions of the etching gas. This phenomenon means that the radius of curvature of a microlens made of a photoresist obtained by gray scale exposure can be adjusted in a range of 70 to 170% by etching.

The shape of the resist pattern created by the gray scale exposure is determined in consideration of the lens pattern of the transparent substrate 10 which is a final finished diffuser and the shape deformation caused by the etching. Specifically, if the etching selectivity is represented by η and the depth (also sag amount) of each microlens 21 is represented by S, the depth of the microlens 21 actually formed on the transparent substrate 10 is Approximately η × S. When the curvature radius of the resist pattern is R, the curvature radius after etching is R ÷ η.

FIG. 10 shows the result of actually measuring the shape of the formed resist pattern when the etching selectivity is 0.6 and 1.7. In this measurement, the shape of the substantially central portion of the microlens array (the shape in the vicinity of the AA cutting line in the upper part of FIG. 10) was actually measured with a laser confocal microscope. As is clear from FIG. 10, the resist design value and the transferred finished product shape do not always match.

Therefore, when manufacturing the diffusion plate according to the present embodiment, a design method as shown in FIG. 11 is adopted.

(Diffusion plate design method)
Below, an example of the design method of the diffusion plate 1 which concerns on this embodiment is demonstrated easily, referring FIG. FIG. 11 is a flowchart showing an example of the flow of the diffusion plate design method according to the present embodiment.

In the diffusing plate designing method according to the present embodiment, first, basic design conditions such as the refractive index n of the transparent substrate 10, the diffusion angle size θ desired to be realized, the pitch p of the microlenses 21, and the like are set (step S <b> 201). ). Thereafter, a curvature radius R (n, θ, p) is calculated based on the following equation 103 (step S203).

Subsequently, in the diffusing plate design method according to the present embodiment, change allowable widths such as a curvature radius change width ΔR, a pitch change width Δp, and a lens apex height change width Δh are set (step S205). Then, a unit cell layout is implemented using a known lens arrangement calculation algorithm (step S207).

When the layout of the unit cell is completed, it is determined whether or not the unit cell that has been laid out meets the layout standard (step S209). Such a layout standard is the conditions (1) to (3) as described above.

If the unit cell that has been laid out does not satisfy all of the above (1) to (3), the process returns to step S207, and the unit cell is changed again while changing the basic setting condition within the allowable change range. Layout is implemented. On the other hand, if the unit cell thus laid out satisfies all of the above (1) to (3), the temporary layout of the unit cell is completed (step S211).

Subsequently, in the diffusion plate designing method according to the present embodiment, the etching selectivity η as described above is set (step S211). Thereafter, the sag data (that is, the height S) of the temporary layout is corrected to a value represented by η × S based on the set etching selection ratio η (step S215). Thereby, the final layout of the unit cell is completed (step S213).

In the above, an example of the design method of the diffusion plate 1 according to the present embodiment has been briefly described with reference to FIG.

By using the manufacturing method as described above, the diffusion plate 1 according to the present embodiment can be manufactured with higher productivity by using a simpler manufacturing process called a dry etching process.

(Specific example of diffusion plate manufacturing method)
The specific example of the manufacturing method of the diffusion plate which concerns on this embodiment as demonstrated above is described easily below. In addition, the specific example shown below is only one specific example of the manufacturing method of the diffusion plate which concerns on this invention, and the manufacturing method of the diffusion plate which concerns on this invention is not limited to the following specific example.

First, for example, a Tempax glass substrate is used as the transparent substrate 10, and a positive resist is applied on the glass substrate. At this time, the film thickness of the resist is 11 μm so as to be larger than the sag depth of the microlens 21 to be manufactured.

Next, step-and-repeat exposure is performed using a gray scale mask and an exposure apparatus (stepper). At this time, the layout of the gray scale mask to be used is composed of a rectangular unit cell 3 having a horizontal dimension of 737.6 μm and a vertical length of 709.6 μm (that is, a basic cell) arranged vertically and horizontally. To do. The unit cell 3 is designed so that, for example, the arrangement of microlenses in the horizontal direction has an average pitch of 82 μm and nine lenses (100 or more in total in the cell) are arranged so as not to form a discontinuous pattern when repeated vertically and horizontally.

Here, regarding the arrangement conditions of each microlens in the unit cell 3, the in-plane position of the vertex is within a radius of 42 μm from the hexagonal vertex, the change width of the height position is 2 μm or less, and between adjacent lenses. It is assumed that the boundary is not parallel and is not parallel to the substrate. With respect to the radius of curvature, if the diffusion angle θ = 3 degrees, R = 752 μm after etching according to the above equation 103. At this time, considering the change due to the etching selection ratio 0.90, the curvature of the resist pattern can be R ′ = 752 × 0.90 = 677 μm and the change width can be 67 μm.

A unit cell 3 is a unit cell 3 in which an arrangement that satisfies the above conditions is determined by a known lens arrangement calculation algorithm.

Further, the above-described unit cells 3 arranged in an array of 16 in the horizontal direction and 17 in the vertical direction are used as basic cells, and step-and-repeat exposure is performed using the basic cells as exposure unit positions.

Next, dry etching is performed using a resist shape obtained after development as a mask and a mixed gas of CF ₄ and Ar as an etching gas. The etching rate is, for example, glass: 0.5 μm / min, resist: 0.45 μm / min. By performing etching deeper than the sag of the resist pattern, the microlens shape of the resist is transferred to the glass substrate. The Rukoto.

After forming the lens by etching, the antireflection layer 30 made of, for example, a Nb ₂ O ₅ / SiO ₂ multilayer film is formed on both surfaces of the glass substrate by vapor deposition or sputtering.

It is possible to actually manufacture the diffusion plate according to this embodiment by performing such a manufacturing method.

(Application example of diffusion plate)
Next, an application example of the diffusion plate 1 according to the present embodiment will be briefly described.

The diffusion plate 1 according to the present embodiment as described above can be appropriately mounted on a device that needs to diffuse light in order to realize its function. Examples of the device that needs to diffuse light in order to realize the function include a display device such as various displays and a projection device such as a projector.

Further, the diffusion plate 1 according to the present embodiment can be applied to the backlight of the liquid crystal display device, and can also be used for light shaping. Furthermore, the diffusion plate 1 according to the present embodiment can be applied to various illumination devices.

Note that the device that needs to diffuse light in order to realize the function is not limited to the above example, and the device that uses light diffusion is not limited to this well-known device. It is possible to apply the diffusion plate 1 according to the embodiment.

[Second Embodiment]
As a diffusion plate used for light having high coherence such as laser light, diffusion plates having various diffusion full angles such as a diffusion full angle of about 1 to 30 degrees are used. For example, in an application in which the incident laser light is spread uniformly on the phosphor surface, a diffusion plate having a total diffusion angle of less than 10 degrees is used, and an application for obtaining the same diffusion characteristics as a phosphor film using blue light In applications for reducing speckles, a diffusion plate having a total diffusion angle of about 10 to 30 degrees is used. When a diffusion plate having a relatively large diffusion full angle such that the total diffusion angle is 10 degrees to 30 degrees is to be realized with a microlens-type diffusion plate, the diffusion light is diffused in an angular region where the diffused light intensity is attenuated. There was a problem that the attenuation was not steep.

Therefore, in the case where the diffusion plate applicable to the above uses is realized by a microlens type diffusion plate, in addition to the suppression of the diffraction component as described in the first embodiment, the diffused light intensity It is important to realize more excellent diffusion characteristics such that the attenuation of diffused light becomes steep even in the angle region where the light is attenuated.

Therefore, in the diffusion plate according to the second embodiment described in detail below, the conditions (1) to (3) regarding each microlens constituting the unit cell focused on the diffusion plate according to the first embodiment. In addition to the suppression of the diffraction component, in addition to the suppression of the diffraction component, a more excellent diffusion characteristic is realized such that the attenuation of the diffused light becomes steep in the angular region where the intensity of the diffused light attenuates.

(About diffusion plate)
Similar to the diffusion plate 1 according to the first embodiment, the diffusion plate 1 according to the second embodiment of the present invention is a microlens array type in which a microlens group including a plurality of microlenses is arranged on a substrate. This is a diffusion plate. The diffusing plate 1 is composed of a plurality of unit cells 3 like the diffusing plate 1 according to the first embodiment shown in FIG. In addition, between the unit cells 3, the layout pattern (arrangement pattern) of the plurality of microlenses provided in the unit cell 3 is continuous in the unit cell arrangement direction (in other words, the array arrangement direction).

In the following, the difference from the diffusion plate 1 according to the first embodiment will be mainly described with reference to FIGS. 12 to 16, and the same configuration as the diffusion plate 1 according to the first embodiment will be described. The detailed description of those having is omitted.
FIG. 12 is an explanatory view schematically showing a part of the unit cell constituting the diffusion plate according to the present embodiment. FIG. 13A is an explanatory diagram for explaining the variation in the inter-vertex distance in the microlens group according to the present embodiment, and FIG. 13B is for explaining the variation in the radius of curvature in the microlens group according to the present embodiment. It is explanatory drawing. FIG. 14 is an explanatory diagram for explaining the attenuation width in the diffusion plate according to the present embodiment, and FIGS. 15A and 15B are graphs showing the relationship between the inter-vertex distance and the variation in the radius of curvature and the attenuation rate. It is. FIG. 16 is an explanatory diagram for explaining the relationship between the full diffusion angle and the attenuation factor in the diffusion plate.

Similar to the unit cell 3 according to the first embodiment shown in FIG. 2, the unit cell 3 included in the diffusion plate 1 according to the present embodiment is a transparent substrate 10 and a microlens formed on the surface of the transparent substrate 10. And a group 20.

<About the transparent substrate 10>
Here, the transparent substrate 10 of the unit cell 3 according to the present embodiment has the same configuration as the transparent substrate 10 of the unit cell 3 according to the first embodiment, and has the same effects. Then, detailed explanation is omitted.

<About the micro lens group 20>
Similar to the first embodiment, a microlens group 20 including a plurality of microlenses 21 is formed on the surface of the transparent substrate 10. Since the diffusion plate is originally intended to diffuse light, it is preferable that the exit surface of the microlens 21 constituting the unit cell 3 is a concave lens. Also in the microlens group 20 according to the present embodiment, each microlens 21 is not the same in radius of curvature or pitch between vertices, and has variations in a certain range, so that the focal length is also constant. Have a distribution. In the case of a concave lens, the focal position is a virtual point, but the light intensity density is large at the focal position. Therefore, the focal position of each microlens 21 may be in a region adjacent to the transparent substrate 10 constituting the diffusion plate 1. preferable.

In the microlens group 20 according to the present embodiment, each microlens 21 constituting the unit cell 3 satisfies the following three conditions (1) to (3), as in the first embodiment. It is arranged to do.

Also in the microlens group 20 according to the present embodiment arranged so as to satisfy the above three conditions, the ridge lines between the adjacent microlenses 21 are not all parallel to each other and are parallel to the transparent substrate 10. It is not like that.

In the following, the average value (average pitch) of the pitches of the repeating structure of the microlenses 21 (that is, the distance between the apexes between adjacent microlenses 21 in FIG. The average value of the radius of curvature of the curve corresponding to the cross-sectional profile in FIG. In this case, the diffusion full angle (full width at half maximum) θ of the microlens type diffusion plate is obtained by using the refractive index n, the average pitch (average inter-vertex distance) p, and the average curvature radius R of the microlens 21. The following equation 201 can be expressed. At this time, the average inter-vertex distance p and the average radius of curvature R are determined based on the following formula 201 so that the desired diffusion full angle θ is obtained.

When the microlens group 20 has a uniform and regular arrangement, the diffused light from all the microlenses 21 constituting the array coincides, and a diffusion characteristic having a flat central portion and a steep attenuation characteristic is obtained. However, in this state, a large number of diffracted lights are generated due to the periodicity of the array structure, which is not preferable as a diffusion plate. Therefore, as in the first embodiment, the diffraction component is suppressed by introducing appropriate irregularities in the lens shape and lens arrangement. As a result, as schematically shown in FIGS. 13A and 13B, the values of the distance between the vertices and the radius of curvature will vary.

Now, as shown in FIG. 13A, when the maximum value of the distance between vertices resulting from the introduction of irregularity is p _max and the minimum value of the distance between vertices is p _min , in this embodiment, Σ _p given by Equation 203 is used as the degree of variation from the average value of the distance between vertices. Similarly, as shown in FIG. 13B, when the maximum value of the radius of curvature resulting from the introduction of irregularity is R _max and the minimum value of the radius of curvature is R _min , in the present embodiment, Σ _R given by 205 is used as the degree of variation from the average value of the radius of curvature.

In this embodiment, the steepness in the diffusion characteristic (particularly the attenuation characteristic) is represented by an attenuation rate α expressed by the following expression 207. Here, θ in the following expression 207 is the full width of diffusion, and corresponds to the full width at half maximum of the diffusion angle distribution curve as schematically shown in FIG. Further, as schematically shown in FIG. 14, in the diffusion angle distribution curve, an angle region from an angle at which the intensity is 90% of the maximum value to an angle at which the intensity is 10% of the maximum value is referred to as an attenuation region. The average value in the circumferential direction of the width of the attenuation region (that is, the angular width) is defined as an attenuation width δ in the following expression 207. For example, in the example shown in FIG. 14, there are two attenuation ranges, a region where the angle value is positive and a region where the angle value is negative, but the attenuation width used in the following Expression 207 δ is an average value of the width (angular width) of these two attenuation regions.

Further, regarding the irregularity of the arrangement of the microlenses to be introduced, the variation width dp between the vertices and the variation radius of the curvature radius are obtained by using the variation degrees σ _p and σ _R given by the equations 203 and 205. Let dR be expressed as in Equation 209 and Equation 211 below.

In this case, the attenuation width δ can be expressed as the following expression 213 using the above expression 201, expression 209, and expression 211. Here, when an approximation that the value of (p / R) is sufficiently small is performed, the following expression 213 can be expressed as expression 215. Therefore, the attenuation rate α defined by the above equation 207 can be expressed as the following equation 217 using the following equation 215.

The variation degree σ _{p of the} distance between vertices is fixed to 0.4 (40%), 0.6 (60%), and 0.8 (80%), respectively, and the variation degree σ _R of the curvature radius is set to 0. FIG. 15A shows how the attenuation factor α given by the above equation 217 changes when the value is changed from 02 (2%) to 0.3 (30%). It was. Further, assuming a diffusion plate having an average inter-vertex distance p = 90 μm, an average curvature radius R = 300 μm, and a refractive index n = 1.47 (that is, a total diffusion angle θ≈8 degrees), the variation degree σ _p of the inter-vertex distance is When changing from 0.4 (40%) to 0.8 (80%) and changing the curvature radius variation degree σ _R from 0.02 (2%) to 0.3 (30%), A diffusion angle distribution curve was calculated using a commercially available ray tracing simulator. Then, the result of calculating the attenuation rate α from the obtained diffusion angle distribution curve is shown in FIG. 15B. As is clear from a comparison between FIGS. 15A and 15B, the calculation result of the attenuation rate α using the approximate expression shown in the above expression 217 almost coincides with the ray tracing simulation result, and the approximation shown in the above expression 217. It can be said that the formula is valid.

The diffusion plate 1 according to the present embodiment can be suitably used for applications such as spreading a coherent light beam such as a laser beam uniformly on the phosphor surface. In such applications, the attenuation rate α as described above is required to be usually 1 or less, more preferably 0.9 or less, because it affects the light conversion efficiency in the phosphor.

Here, looking at the result of FIG. 15A calculated using the above equation 217, the variation degree σ _p = 0.6 (60%) of the distance between the vertices and the variation degree σ _R = 0. It can be seen that the attenuation rate α = 0.83 when 2 (20%). As a result, the distance between the vertices of the adjacent microlenses 21 constituting the unit cell 3 has a variation within a range of ± 60% of the average value (in other words, the variation degree σ _{p of the} distance between the vertices is , 0 <σ _p ≦ 0.6), and the radius of curvature of each microlens 21 constituting the unit cell 3 varies within a range of ± 20% of the average value (in other words, For example, the variation degree σ _{R of the} radius of curvature satisfies the relationship 0 <σ _R ≦ 0.2), which suggests that the attenuation rate α of the diffusion characteristic can be made 0.9 or less.

Therefore, in the microlens group 20 according to the present embodiment, it is preferable that the following conditions (4) and (5) are further satisfied, and that the following conditions (4) to (6) are further satisfied. preferable.

(4) The distance between the apexes of the adjacent microlenses 21 constituting the unit cell 3 is included within a range of ± 60% of the average value.
(5) The radius of curvature of the microlens 21 is included within a range of ± 20% of the average value.
(6) When the degree of variation from the average value of the distance between vertices is σ _p and the degree of variation from the average value of the radius of curvature is σ _R , the relationship of the above equation 217 is established.

Here, even if the attenuation rate α is constant, when the diffusion full angle θ increases, the width δ of the attenuation region increases in proportion to the diffusion full angle θ. The conversion efficiency of the phosphor depends on the width δ of the attenuation region rather than the attenuation factor α, and as shown schematically in FIG. 16, the light energy that is wasted increases as the width δ of the attenuation region increases. . Accordingly, when a diffusion plate having a larger diffusion full angle θ is realized, the required attenuation rate α is smaller. Therefore, the effect of improving the conversion efficiency by the diffusion plate 1 according to the present embodiment is greater when the diffusion total angle θ is 10 degrees or more (in other words, the F value is 5.5 or less).

Note that the average vertex distance and the average radius of curvature of the microlens 21 are determined by the above equation 201 according to the required diffusion full angle θ (for example, θ = 1 to 30 degrees), as mentioned above. When the ratio between the average vertex distance and the average radius of curvature is the same, the total diffusion angle θ is the same value, but the average vertex distance is limited by the incident light diameter, production sag, etc. Is limited by the resolution in the depth direction determined by the production method, in addition to the production sag. Therefore, considering these practical restrictions, the average apex distance p is preferably in the range of 13 to 90 μm, and the average radius of curvature R is preferably in the range of 20 to 2000 μm.

As described above, in the diffusing plate 1 according to the present embodiment, the attenuation characteristic is related to two parameters, that is, the distribution of the microlens arrangement and the distribution of the curvature radius with respect to the new viewpoint of optimization of the attenuation characteristic. Focusing on this, the range of these two parameters is defined. Thereby, in the diffusion plate according to the present embodiment, it is possible to optimize the attenuation characteristics while reducing the diffraction component.

<About the antireflection layer>
The diffusion plate 1 according to the present embodiment has a front surface and a back surface (in other words, the surface of the microlens 21 and the surface on the side where the microlens group 20 of the transparent substrate 10 is not disposed). The antireflection layer 30 may be formed for the purpose of increasing transmittance and preventing reflection stray light. Since such an antireflection layer 30 can be provided in the same manner as the antireflection layer 30 in the diffusing plate 1 according to the first embodiment, detailed description thereof will be omitted below.

The diffusion plate according to this embodiment has been described in detail above with reference to FIGS.

(Diffusion plate design method)
In the diffusion plate according to the present embodiment, the procedure for arranging the microlenses 21 is not particularly limited. For example, the apexes of the microlenses 21 are initially arranged at positions corresponding to the apexes of the hexagon. Thereafter, the vertex position may be shifted within a range satisfying the above conditions (1) to (5), more preferably the above conditions (1) to (6). Similarly to the method described in the first embodiment, a position that satisfies the above conditions (1) to (5), more preferably the above conditions (1) to (6), without providing an initial position. The relationship may be obtained sequentially using various computers.

Here, when designing the diffusing plate according to the present embodiment, it is important to consider restrictions on the manufacturing process. For example, when performing gray mask exposure, the resist depth that can be exposed is defined by the depth of focus of the stepper (= λ / NA ² ). For example, when i-line (λ = 365 nm) is used, the NA of the stepper is 0.4 to 0.6, and the resist depth that can be exposed is about 15 μm. For this reason, the sag depth is preferably 15 μm or less.

When determining the arrangement of the microlenses by the method of providing the initial arrangement, it is possible to easily control the statistic (for example, the average value or range) of the distance between the apexes of the microlenses. On the other hand, when the arrangement of the microlenses is sequentially determined without providing the initial arrangement, the diffraction component can be more efficiently reduced.

(Diffusion plate manufacturing method)
The diffusion plate 1 according to the present embodiment can be manufactured in the same manner as the manufacturing method of the diffusion plate 1 according to the first embodiment.

In the case of manufacturing a diffusion plate having a large diffusion angle (in other words, a large F value), it is possible to obtain a greater effect according to the present embodiment. When the F value is adjusted according to the intended use, the F value can be precisely controlled by changing the sag depth even if the planar shape is the same by the array arrangement according to the present embodiment. That is, a desired F value can be realized by changing the process time by a manufacturing method described later, and the productivity is high. For the purpose of enlarging the incident light, it is desirable that the F value is 5.5 or less. However, even if the F value is higher than that (for example, for the purpose of uniforming the light intensity of the laser array light source, 8 Even with an F value of about ˜60), it is possible to manufacture by shortening the process time with the same pattern.

Subsequently, the diffusion plate according to the present invention will be specifically described with reference to Examples and Comparative Examples. In addition, the Example shown below is only an example of the diffusion plate which concerns on this invention to the last, and the diffusion plate which concerns on this invention is not limited to the following example.

In the following, in order to verify the validity of the diffusion plate according to the first embodiment of the present invention, the intensity distribution of the emitted light when the incident light diameter is changed while the unit cell size and the pitch of the lens array are fixed. Calculated. In the following verification, the unit cell 3 is 738 μm wide × 710 μm long, unit cell size = 1024 μm, and the unit cell 3 arranged in a 3 × 3 array is used as a verification model.

In the case where four types of circular incident light having full width at half maximum of (a) 650 μm, (b) 1000 μm, (c) 1500 μm, and (d) 2000 μm are incident on the verification model as described above, commercially available ray tracing is performed. Calculations were performed using a simulator. In the calculation, a spatial filter that restricts the spatial resolution of the detector was arranged so as to approach the actual evaluation conditions. For this reason, the bright spots by diffraction seen in the results of FIGS. 6A to 6C are averaged to some extent in the calculation results shown below, and the results shown in FIGS. 6A to 6C and the results shown below are as follows. Is a little different.

The obtained results are shown in FIGS. 17A to 17D.
As shown in FIG. 17A, only when the incident light diameter is 650 μm, the diffusion angle (center angle ±) that cannot be seen in the case of other incident light diameters (FIGS. 17B, 17C, and 17D). It can be seen that there is a sudden intensity change in the range of 1 degree. This is because when the incident light diameter is 650 μm, most of the incident light components exist within the unit cell size, so that the sub-diffraction by the unit cell 3 does not occur sufficiently, and the main diffracted light is not separated by the sub-diffracted light. This is probably because the light is emitted. On the other hand, in FIG. 17A and FIG. 17D, when the unit cell size is equal to or smaller than the incident light diameter, the sub-diffracted light as described above is generated, and the sudden intensity change remarkably observed in FIG. You can see that

From these results, it has been clarified that it is possible to provide a diffusion plate in which sub-diffracted light is generated by setting the unit cell size to be equal to or smaller than the incident light diameter and a sudden intensity change does not occur in the diffused outgoing light.

Hereinafter, in order to verify the validity of the diffusion plate according to the second embodiment of the present invention, verification was performed using a commercially available ray tracing simulator.

The model of the microlens array type diffuser plate used for the calculation is one in which a large number of concave lenses having a certain variation in shape and arrangement are arranged on the surface of a glass substrate (refractive index n = 1.47). In this simulation, incident light having a wavelength λ = 450 nm and an incident light diameter φ = 0.6 mm is incident on the diffusion plate as described above, and the light diffusion pattern projected on the screen 200 mm ahead is converted into an angular distribution. did.

FIG. 18 shows the conditions of the diffusing plate model on which the simulation was performed as a table, and the obtained diffused light distribution is shown in FIGS. 19A and 19B. FIG. 19A shows a simulation result when the variation degree σ _{R of the} radius of curvature is ± 10%, and FIG. 19B shows a simulation result when the variation degree σ _{R of the} curvature radius is ± 20%. The table shown in FIG. 18 also shows the attenuation rate α calculated from the results shown in FIGS. 19A and 19B.

As is clear from the comparison in FIG. 19A and the comparison in FIG. 19B, it can be seen that the attenuation rate α increases as the variation range of the inter-vertex distance increases. Further, from the comparison between the condition A and the condition D, the comparison between the condition B and the condition E, and the comparison between the condition C and the condition F, when the variation range of the distance between the vertices is almost the same, the variation range of the curvature radius It can be seen that the larger the is, the larger the attenuation rate α is.

Here, when the relationship between the variation amount and the attenuation rate shown in FIG. 18 obtained by the ray tracing simulation is plotted in the graph shown in FIG. 15A, it becomes clear that the curve almost coincides with the curve in the graph. It was. From these results, it can be seen that the relationship between the degree of variation in the distance between the vertices, the degree of variation in the radius of curvature, and the attenuation rate based on the above equation 217 is reasonable.

In the above examples, the results in the vicinity of the curvature of 300 μm (generally in the range of the diffusion angle of 2 ° to 4 °) are described. However, even in the case of a wider diffusion angle, it conforms to the second embodiment of the present invention. By setting the design or process conditions, it is possible to widen the diffusion angle while keeping the attenuation characteristic constant. For example, the distance between the vertices is 82 μm ± 42 μm (variation range: ± 50%), and the radius of curvature is 370 μm to 760 μm on average, the variation range is ± 10%, and the selection ratio at the time of etching is An appropriate change was made in the range of 0.8 to 1.4. The diffusion characteristics of the diffusion plate obtained by such design and process conditions are shown in FIG. As can be seen from FIG. 20, the above diffusion plate exhibits diffusion characteristics with a diffusion angle of 2 to 9 degrees.

Furthermore, the microlens array configuration when the diffusion angle is larger was verified. In this verification, three types of conditions as shown in FIG. 21 were examined. The values of the obtained diffusion full angle, attenuation width, and attenuation rate are shown in FIG. Further, the diffusion characteristics of the obtained diffusion plate are shown in FIG. As is clear from FIGS. 21 and 22, as a design that satisfies the sag restrictions in the process, the distance between the vertices is 15 μm ± 10 μm (variation range: ± 0.67), and the curvature radius is 22 μm ± 2.2 μm ( By setting the variation width to ± 0.10, the attenuation rate can be set to 0.65. The arrangement state of the microlens in such a case is shown in FIG.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

1 Diffusion plate 3 Unit cell 10 Transparent substrate 20 Micro lens group 21 Micro lens

Claims

A microlens array type diffusion plate composed of a group of microlenses located on the surface of a transparent substrate,
It consists of two or more unit cells that are contiguous to the array arrangement,
The unit cell is composed of a plurality of microlenses located on the surface of the transparent substrate,
The ridge plate between the microlenses adjacent to each other is not parallel to each other and is not parallel to the transparent substrate.
The distance between the apexes of the adjacent microlenses constituting the unit cell is included within a range of ± 60% of the average value, and
The diffusing plate according to claim 1, wherein the radius of curvature of each of the microlenses constituting the unit cell is included in a range of ± 20% of an average value.
The degree of variation from the average value of the distance between the apexes of the adjacent microlenses constituting the unit cell is σ p, and the degree of variation from the average value of the radius of curvature of the adjacent microlenses constituting the unit cell The diffusion plate according to claim 1, wherein the following (Equation 1) is established when σ R is:
The diffusion plate according to any one of claims 1 to 3, wherein a length of a diagonal line of the unit cell is 3 mm or less.
The diffusion plate according to any one of claims 1 to 4, wherein the length of at least one side of the unit cell is an integer multiple of an average pitch of the microlenses included in the unit cell.
The diffusion plate according to any one of claims 1 to 5, wherein the number of microlenses contained in the unit cell is at least nine.
The diffusion plate according to any one of claims 1 to 6, wherein a boundary portion between the microlenses adjacent to each other in the unit cell is not flat.
The diffusing plate according to claim 7, wherein a half lens is disposed on at least a part of the boundary portion.
The diffusion plate according to any one of claims 1 to 8, wherein the microlens has a polygonal shape.
10. The diffusion plate according to claim 1, wherein the micro lens is a concave lens.
The diffusion plate according to any one of claims 1 to 10, wherein the transparent substrate is made of an inorganic material.
The diffusion plate according to claim 11, wherein the inorganic material is a glass mainly composed of silicon having an alkali component content of 20% or less.
The diffusing plate according to any one of claims 1 to 12, further comprising an antireflection layer on a surface of the microlens and a surface of the transparent substrate on which the microlens group is not disposed.
The diffusion plate according to claim 13, wherein the antireflection layer is a multilayer structure composed of Nb 2 O 5 and SiO 2 .
The diffusing plate according to claim 13, wherein the antireflection layer provided on the surface of the microlens is an antireflection structure formed on the surface of the microlens group and having irregularities having a size equal to or smaller than the wavelength of light. .
The diffusing plate according to claim 15, wherein the antireflection structure is a structure provided anisotropically in the surface of the microlens and having an uneven pitch of 300 nm or less.
A method of designing a microlens array type diffusion plate composed of a group of microlenses located on the surface of a transparent substrate,
A method of designing a diffusion plate, wherein the radius of curvature of each microlens constituting the microlens group is determined based on the product of the reciprocal of the etching selectivity of the transparent substrate and the resist and the radius of curvature developed on the resist. .
A method of manufacturing a diffusion plate according to any one of claims 1 to 16,
Laminating a resist on a transparent substrate;
Exposing the resist with a grayscale mask having a transmittance distribution;
A step of dry etching the developed transparent substrate using a fluorine-based gas so as to obtain a desired lens shape;
A method for manufacturing a diffuser plate.
In the dry etching step, the radius of curvature of each microlens constituting the microlens group is determined by the product of the reciprocal of the etching selectivity of the transparent substrate and the resist and the radius of curvature developed on the resist. Item 19. A method for producing a diffuser plate according to Item 18.
A display device comprising the diffusion plate according to any one of claims 1 to 16.
A projection apparatus comprising the diffusion plate according to any one of claims 1 to 16.
An illumination device comprising the diffusion plate according to any one of claims 1 to 16.