Optical elements

Abstract

To provide an optical element equipped with an easy-to-see mark regardless of lighting conditions.SOLUTION: Disclosed is an optical element which is equipped with a mark constituted of uneven shapes. When viewed from a normal direction of the surface on which the uneven shapes are provided, the boundary between a convex part and a concave part is oriented in a plurality of directions. Accordingly, achievement of the mark with good visibility is possible regardless of the lighting conditions. Moreover, a diffraction grating configured into the mark has a plurality of unit regions, which are regions of the diffraction grating capable of emitting a specific pattern, arranged in the mark.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to an optical element provided with a mark. [Background technology]

[0002] In recent years, the applications of sensor systems have expanded. There are many different types of sensors, and they detect a variety of information. One method involves irradiating an object with light from a light source and obtaining information from the reflected light. Examples of this include pattern recognition sensors and infrared radar.

[0003] The light sources used for these sensors have wavelength distribution, brightness, spread, etc. according to the application. The wavelength of light that is often used ranges from visible light to infrared light. Infrared light, in particular, is widely used because it is less affected by external light, is invisible, and allows for observation of the interior of an object. LED light sources, laser light sources, etc. are often used as light sources. For example, laser light sources, which have little spread of light, are preferably used when detecting distant objects, while LED light sources are preferably used when detecting relatively close objects or when illuminating an area with a certain degree of spread.

[0004] However, the size and shape of the target illumination area do not necessarily match the light profile from the light source, making it necessary to shape the light using diffusers, lenses, shielding plates, etc. Diffractive optical elements (DOEs) are one example of a light shaping method. They utilize the diffraction phenomenon that occurs when light passes through a periodic arrangement of materials with different refractive indices. While DOEs are primarily designed for light of a single wavelength, they are theoretically capable of shaping light into almost any shape. Furthermore, DOEs can control the uniformity of the light distribution within the illumination area. These characteristics of DOEs are advantageous in terms of increasing efficiency by suppressing illumination of unnecessary areas and miniaturizing devices by reducing the number of light sources. Furthermore, diffractive optical elements can be used with both parallel light sources such as lasers and diffuse light sources such as LEDs, and are applicable to a wide range of wavelengths from ultraviolet light to visible light and infrared light.

[0005] When such diffractive optical elements are applied to high-precision sensors, extremely high precision is required. To achieve high precision, traceability is important, enabling the manufacturing history of any defective diffractive optical elements to be tracked. It is also necessary to accurately position the element during the manufacturing process. Furthermore, inspection of dust and other particles that adhere during the manufacturing process is also necessary. To ensure traceability, positioning, inspection, and the like, marks are sometimes provided on the outer edge of the element. Furthermore, such marks are not limited to diffractive optical elements, and may also be used in optical elements equipped with microlens arrays, for example.

[0006] Conventionally, it has been known to use a regularly arranged pattern called a line and space pattern in order to improve the visibility of such marks (Patent Document 1). However, even with a line and space pattern, the marks can be difficult to see depending on the lighting conditions during inspection. Alternatively, a technique is known in which fine irregularities are created by processing such as shot peening or sandblasting to improve visibility (Patent Document 2). However, there were issues such as precision deviations due to alignment processing, the difficulty of making the scattered light anisotropic, and increased costs due to additional processes. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2018-189939 [Patent Document 2] JP 2015-43400 A Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present invention is to provide an optical element having a mark that is easy to see regardless of lighting conditions. [Means for solving the problem]

[0009] The present invention solves the above-mentioned problems by the following means: For ease of understanding, the following description will be given with reference to the corresponding embodiments of the present invention, but the present invention is not limited to these.

[0010] The first invention is an optical element (1) having a mark (20, 30, 40, 50) formed by a concave-convex shape, in which the boundaries between the convex portions and the concave portions are arranged facing in multiple directions when viewed from the normal direction of the surface on which the concave-convex shape is provided.

[0011] A second invention is the optical element (1) according to the first invention, characterized in that the concave-convex shape includes at least one of a curve and a broken line connecting a plurality of line segments at the boundary between the convex portion and the concave portion when viewed from the normal direction.

[0012] The third invention is the optical element (1) according to the first or second invention, characterized in that the uneven shape is a diffraction grating, and first-order diffracted light is emitted in a pattern of at least four or more axial directions.

[0013] The fourth invention is the optical element (1) according to the third invention, characterized in that the uneven shape is a diffraction grating, and when light with a wavelength of 550 nm is incident from the front, the diffraction angle of at least four or more patterns of first-order diffracted light is 8 degrees or more.

[0014] The fifth invention is the optical element (1) according to the third invention, characterized in that the uneven shape is a diffraction grating, and when light with a wavelength of 550 nm is incident from the front, the diffraction angle of at least four or more patterns of first-order diffracted light is 10 degrees or more.

[0015] The sixth invention is an optical element (1) according to any one of the third to fifth inventions, characterized in that the uneven shape has unit areas (1001, 1002) which are areas of a diffraction grating that can emit the pattern, and the unit areas are arranged in multiple locations within the mark (20, 30, 40, 50).

[0016] The seventh invention is an optical element (1) according to any one of the first to sixth inventions, characterized in that it comprises an optical function region (10) that exhibits the optical function of the optical element (1), and the marks (20, 30, 40, 50) are arranged around the optical function region (10).

[0017] An eighth invention is the optical element (1) according to the seventh invention, characterized in that the optical function region (10) comprises a diffraction grating.

[0018] The ninth invention is the optical element (1) according to the eighth invention, characterized in that the uneven shape is a diffraction grating and has the same uneven height as the diffraction grating in the optical function area.

[0019] The tenth invention is the optical element (1) according to the eighth or ninth invention, characterized in that the uneven shape is a diffraction grating and is configured by a diffraction grating of the same design as the diffraction grating of the optical function region (10). [Effects of the Invention]

[0020] According to the present invention, an optical element having a mark that is easy to see regardless of the lighting conditions can be provided. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a diagram showing an embodiment of a diffractive optical element 1 according to the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along the arrow GG in FIG. [Figure 3] 10 is a plan view showing an example of a diffractive optical element in which the uneven shape of the diffraction grating, as viewed from the normal direction of the sheet surface, is formed in a regular or irregular pattern in which the boundaries between the convex portions and the concave portions include curved lines. FIG. [Figure 4] FIG. 10 is a plan view showing an example of a diffractive optical element in which the uneven shape of the diffraction grating, as viewed from the normal direction of the sheet surface, is formed into a grid-like pattern in which multiple unit cells, each having the same uneven shape arranged side by side, are tiled. [Figure 5] 4 is a perspective view showing an example of a partially periodic structure in the example of the irregular diffractive optical element shown in FIG. 3. FIG. [Figure 6] 5 is a perspective view showing an example of a partial periodic structure in the example of the GCA type diffractive optical element shown in FIG. 4. FIG. [Figure 7] 7 is a cross-sectional view of the diffractive optical element taken along the line GG' in FIG. 6. [Figure 8] FIG. 1 is a diagram illustrating a diffractive optical element. [Figure 9] FIG. 1 is a diagram showing a polygonal body 500 on which diffractive optical elements 1 are attached in multiple faces. [Figure 10] FIG. 2 is an enlarged view of a portion of the multi-faceted body 500. [Figure 11] FIG. 10 is a diagram illustrating foreign matter inspection. [Figure 12] FIG. 2 is an enlarged view of the area where the mold identification code 20 is formed. [Figure 13] FIG. 2 is an enlarged view of a region where a defect mark 40 is formed. [Figure 14] 10 is a diagram illustrating the uneven shape formed on the mold identification code 20 and the like. FIG. [Figure 15] 10A and 10B are diagrams showing other examples of diffraction gratings that are preferably formed in a unit region. [Figure 16] FIG. 10 is a diagram showing the results of evaluating visibility for a comparative example and the present embodiment. [Figure 17] 10A and 10B are diagrams showing the results of comparing a diffractive optical element having a defect mark according to the present embodiment with a comparative example having a conventional defect mark. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

[0023] (Embodiment) FIG. 1 shows an embodiment of a diffractive optical element 1 according to the present invention. FIG. 2 is a cross-sectional view taken along the arrow GG in FIG. Note that the drawings shown below, including FIGS. 1 and 2, are schematic diagrams, and the size and shape of each part are exaggerated as appropriate to facilitate understanding. In the following description, specific numerical values, shapes, materials, etc. are given, but these can be changed as appropriate. Furthermore, the terms used in the present invention that specify the shape and geometric conditions, as well as the degree thereof, such as "parallel," "orthogonal," "identical," and the values ​​of length and angle, are not limited to their strict meanings, but are interpreted to include the range within which similar functions can be expected. In the present invention, "transparent" refers to a material that transmits at least light of the wavelength to be used. For example, even if a material does not transmit visible light, if it transmits infrared light, it will be treated as transparent when used in infrared applications.

[0024] The diffractive optical element 1 of this embodiment includes a substrate 1a and a resin layer 1b. The substrate 1a is a layer that serves as the base of the diffractive optical element 1, and various transparent resin films, resin sheets, etc. can be used. The substrate 1a can be made of transparent resins such as polycarbonate (PC) resin, polyethylene terephthalate (PET) resin, methyl methacrylate butadiene styrene (MBS) resin, methyl methacrylate styrene (MS) resin, acrylic styrene (AS) resin, and acrylonitrile butadiene styrene (ABS) resin. Alternatively, the substrate 1a may be made of a glass substrate. Although not shown, an adhesive layer may be provided on the substrate 1a to enhance adhesion with a coated ultraviolet-curable resin or the like.

[0025] The resin layer 1b is formed on the substrate 1a and has a shaped shape (10, 20, 30, 40, 50, etc.) corresponding to the shape formed in the mold. The resin layer 1b can be formed, for example, by using a mold on which a concave-convex pattern corresponding to each pattern of the shaped shape is formed, by molding an ultraviolet curable resin applied to the substrate 1a to transfer the concave-convex pattern, and then curing it by irradiating it with ultraviolet light.

[0026] Examples of the UV-curable resin that can be used include urethane acrylate, polyester acrylate, epoxy acrylate, polyether acrylate, polythiol, and butadiene acrylate. The material for forming the resin layer 1b is not limited to UV-curable resin. The resin layer 1b may be formed of, for example, an electron beam curable resin. The resin layer 1b may also be formed using a heat-curable or UV-curable SOG (Spin on Glass). The above patterns are not limited to being transferred from an original by molding, but may also be molded using an intermediate resin plate made from an original having the concave and convex shapes of the above patterns.

[0027] The resin layer 1b has a diffraction grating 10, a mold identification code 20, a position identification code 30, a defect mark 40, and a cutting position mark 50 as shaped shapes.

[0028] The diffraction grating 10 is arranged in the center of the diffractive optical element 1 and is composed of a large number of minute concave and convex shapes. This diffraction grating 10 is an optical function area that exhibits the optical function originally intended by the diffractive optical element 1, and is different from the diffraction grating provided in the defect mark described below. FIG. 3 is a plan view showing an example of a diffractive optical element in which the concave and convex shape of the diffraction grating, as viewed from the normal direction of the sheet surface, is formed in a regular or irregular pattern in which the boundaries between the convex and concave portions include curved lines. As an example, this embodiment can be applied to a diffractive optical element having a seemingly irregular concave-convex pattern as shown in FIG. 3 . In the following description, this type of diffractive optical element shown in FIG. 3 will also be referred to as an irregular type. However, since this irregular pattern may become a regular pattern depending on the target emission pattern of the diffractive optical element, the term "irregular type" is a convenient name and is not limited to irregularity. Furthermore, although the irregular pattern in FIG. 3 is composed of curves, depending on the target emission pattern of the diffractive optical element, it may also include a pattern of straight lines or broken lines connecting curved line segments. Therefore, the irregular diffraction grating pattern includes at least one of curved lines and broken lines connecting multiple line segments at the boundary between the convex and concave portions when viewed from the normal direction of the surface on which the concave-convex shape of the high refractive index portion (described below) is formed. Furthermore, a specific irregular type pattern may be used as a unit cell, and a large number of these unit cells may be arranged in a lattice pattern.

[0029] Figure 4 is a plan view showing an example of a diffractive optical element in which the uneven shape of the diffraction grating, as viewed from the normal direction of the sheet surface, is formed into a grid-like pattern in which multiple unit cells, each having the same uneven shape arranged side by side, are tiled. As another example, the present embodiment can be applied to a diffractive optical element formed in a grid-like pattern by tiling a plurality of unit cells, each of which has the same concave-convex shape, as shown in FIG. 4. In the following description, the diffractive optical element of the type shown in FIG. 4 will also be referred to as a grating cell array type or GCA type. In a grating cell array type diffractive optical element, the direction and angle of light diffracted by the diffraction grating differs for each unit cell, and a diffractive optical element that can obtain desired optical characteristics is configured by tiling a large number of unit cells. That is, in a grating cell array type diffractive optical element, the high refractive index portion is partitioned into a grid-like pattern when viewed from the normal direction of the surface on which the concave-convex shape is formed. Within each partition, convex portions of the same shape extending in a specific direction are arranged side by side in a direction perpendicular to the specific extension direction, and the width and extension direction of the convex portions differ from partition to partition.

[0030] FIG. 5 is a perspective view showing an example of a partially periodic structure in the example of the irregular diffractive optical element shown in FIG. FIG. 6 is a perspective view showing an example of a partial periodic structure in the example of the GCA type diffractive optical element shown in FIG. FIG. 7 is a cross-sectional view of the diffractive optical element taken along the line GG' in FIG. FIG. 8 is a diagram illustrating a diffractive optical element.

[0031] In the present invention, "shaping light" refers to controlling the traveling direction of light so that the shape of light (illumination area) projected onto an object or target area has any shape. For example, as shown in the example of FIG. 8, a light source unit 210 is prepared that emits light 201 (FIG. 8(b)) that, when directly projected onto a flat screen 200, results in a circular illumination area 202. By transmitting this light 201 through the diffractive optical element 1 of the present invention, the illumination area 204 can be shaped into a desired shape, such as a square (FIG. 8(a)), rectangle, or circle (not shown). This is referred to as "shaping light." Furthermore, by combining the light source unit 210 with at least one diffractive optical element 1 of this embodiment, which is arranged at a position where the light emitted by the light source unit 210 passes through, it is possible to create a light irradiation device that can irradiate light in a shaped state.

[0032] The diffractive optical element 1 of this embodiment is a diffractive optical element (DOE) that shapes light. The diffraction grating 10 of the diffractive optical element 1 is designed to spread light from a light source unit 210 that emits light with a wavelength of 500 nm, for example, in a cross shape, specifically, in a shape where two bands of light that spread at an angle of ±50 degrees and a width of ±3.3 degrees intersect with each other. The diffraction grating 10 of this embodiment has different depths at positions A, B, C, and D shown in FIG. 3. That is, the diffraction grating 10 is configured with a multi-step shape with four different heights. The diffraction grating 10 typically has multiple regions with different periodic structures (partial periodic structures: for example, regions E and F in FIG. 3). FIGS. 5 and 6 show an example of a partial periodic structure.

[0033] 7, the diffraction grating 10 has a high refractive index portion 11 in which a plurality of convex portions 11a are arranged side by side in a cross-sectional shape. In a GCA-type diffractive optical element, this high refractive index portion 11 extends in the depth direction of the cross section while maintaining the same cross-sectional shape. On the other hand, in an irregular-type diffractive optical element, the cross-sectional shape changes depending on the cross-sectional position, resulting in an arrangement of many diffraction gratings with various cross-sectional shapes.

[0034] 3, which includes the recesses 12 formed between the protrusions 11a and the spaces 13 near the tops of the protrusions 11a, is filled with air and forms low-refractive-index portions 14 that have a lower refractive index than the high-refractive-index portions 11. A diffractive layer 15 having a light-shaping effect is formed by a periodic structure in which the high-refractive-index portions 11 and the low-refractive-index portions 14 are alternately arranged.

[0035] The protrusion 11a has a multi-step shape with four steps of different heights on one side of its side shape (the left side in FIG. 7). Specifically, the protrusion 11a has, on one side, the most protruding level 3 step 11a-3, a level 2 step 11a-2 that is one step lower than the level 3 step 11a-3, a level 1 step 11a-1 that is one step lower than the level 2 step 11a-2, and a level 0 step 11a-0 that is one step lower than the level 1 step 11a-1. The other side of the side shape of the protrusion 11a (the right side in FIG. 7) is a side wall 11b that connects the level 3 step 11a-3 to the level 0 step 11a-0 in a straight line. The convex portion 11a in this embodiment has a shape that imitates a sawtooth shape using a multi-step contour shape, and since a four-level shape has been described, the shape is a relatively rough imitation, but if the number of levels is increased to 8 levels, 16 levels, or even more, a more accurate imitation shape can be obtained.

[0036] FIG. 9 is a diagram showing a polygonal body 500 on which the diffractive optical element 1 is attached to multiple surfaces. FIG. 10 is an enlarged view of a portion of the multi-faceted body 500. As shown in FIG. The diffractive optical element 1 of this embodiment is a very small component, for example, with an outer shape of approximately 3 mm × 3 mm. Therefore, during the manufacturing process, as shown in FIG. 9 , a polygonal assembly 500 is fabricated in which a large number of diffractive optical elements 1 are arranged in a grid pattern, thereby improving the efficiency of the manufacturing process. The diffractive optical elements 1 are fabricated by cutting this polygonal assembly 500 into individual pieces. Note that in FIG. 9 , for ease of understanding, the boundaries between adjacent diffractive optical elements 1 are shown with solid lines. However, since these boundaries are not formed before cutting, they are shown with two-dot chain lines in FIG. 10 . Note that in FIG. 9 , for ease of illustration and understanding, a total of 100 diffractive optical elements 1 are illustrated as being arranged in 10 rows and 10 columns. However, in reality, many more diffractive optical elements 1 are arranged. For example, several thousand to several tens of thousands of diffractive optical elements 1 may be arranged on a single polygonal assembly 500. The following description will be given on the assumption that the diffractive optical element 1 is produced by cutting the polygonal body 500 in this manner.

[0037] 1 and 2, the mold identification code 20 is a mark for identifying the mold, and in the example shown in Fig. 1, it is written as "900A." The mold identification code 20 is a code unique to the mold, and it is possible to determine which mold was used to mold the diffractive optical element 1 using this mold identification code 20. Because this mold identification code 20 is a code unique to the mold, it is the same code for all of the diffractive optical elements 1 in the polygonal body 500 (see Fig. 10).

[0038] The position identification code 30 is a mark that identifies the position of the diffractive optical element 1 in the molding die. In the example of FIG. 9, one molding die has 100 locations where the diffractive optical elements 1 are molded, and the position identification code 30 is provided as a code that can identify which of these 100 locations the diffractive optical element 1 was molded at. The example of FIG. 1 shows an example of "X49, Y53," which indicates the position of the 49th column in the X direction (the horizontal direction in FIGS. 9 and 10) and the 53rd row in the Y direction (the vertical direction in FIGS. 9 and 10). Note that the indication is not limited to column and row numbers as in this example, and numbers starting from 1 may also be used. Furthermore, the molding die identification code 20 and the position identification code 30 may be combined into a single code that has both functions. Taking the above case as an example, for example, "900A-X49Y53" may be used.

[0039] In this embodiment, when viewing the diffractive optical element 1 from the normal direction of the surface on which the concave-convex shape is formed, a first code region is located in the left half rectangular region, and a second code region is located in the right half rectangular region, with the first code region and the second code region each containing a different code from the mold identification code 20 and the position identification code 30. Specifically, when the first code region contains the mold identification code 20, the second code region contains the position identification code 30, and the reverse combination is also possible. In other words, the mold identification code 20 and the position identification code 30 are located with a sufficient distance between them, which allows them to be recognized as different codes. Furthermore, specific identification codes may be assigned to the mold identification code 20 and the position identification code 30 so that they can be distinguished from each other. For example, a unique symbol may be assigned to the initial letter of each of the mold identification code 20 and the position identification code 30. Specifically, for example, "M (Master)" is assigned to the mold identification code 20, "X (X-Coordinate)" is assigned to the X coordinate of the position identification code 30, and "Y (Y-Coordinate)" is assigned to the Y coordinate. By providing the mold identification code 20 and the position identification code 30, it is possible to easily identify which mold and which position the diffractive optical element 1 was manufactured in, even if it is an individualized diffractive optical element 1.

[0040] The defect mark 40 is a mark formed to a predetermined dimension and is provided for the inspector's reference during visual inspection. Alternatively, it may be used as a judgment standard for automatic inspection using an inspection device. For example, even if an inspection standard is set that defects larger than 40 μm are deemed defective, it is difficult to determine the size of the defect through inspector training alone. It is also difficult to standardize judgment standards for each inspector. Therefore, by making it possible to observe areas that may be defective by comparing them with the defect mark 40, it is possible to improve the accuracy of inspection pass / fail judgments and improve the inspection takt time, and to facilitate the development of inspector skills.

[0041] When one defect mark 40 is provided, its dimensions are preferably set to a threshold value for determining a defect, or to a dimension slightly smaller than the threshold value. For example, if defects larger than 40 μm are to be considered defective as described above, the defect mark 40 may be a 40 μm × 40 μm square, a 40 μm diameter circle, a 30 μm × 30 μm square, or a 30 μm diameter circle. Shapes such as rectangles and ellipses are also acceptable. Furthermore, if the tendency of defects to occur is known, the defect mark 40 may be configured to have a shape similar to that defect to facilitate comparison during inspection. For example, if hair adhesion is a common defect, the defect mark 40 may be configured as a 10 μm × 2000 μm rectangle.

[0042] In this embodiment, three defect marks 40a, 40b, and 40c with different dimensions are arranged in order of size. As described above, in this embodiment, assuming that defects larger than 40 μm are considered defective, defect mark 40a is a 40 μm × 40 μm square, defect mark 40b is a 30 μm × 30 μm square, and defect mark 40c is a 20 μm × 20 μm square. By arranging defect marks 40 whose dimensions gradually change at a constant rate in this manner, an inspector can quickly and accurately grasp the size of an object (a portion that may be defective) when observing it. Note that numbers or other symbols indicating the size of each defect mark 40a, 40b, and 40c may be further arranged near each defect mark.

[0043] The cutting position marks 50 are marks that serve as guides for the cutting positions when cutting the polygonal body 500 into individual diffractive optical elements 1. The cutting position marks 50 may remain on the diffractive optical element 1 after cutting as shown in FIG. 1 , or may be configured to be removed during cutting so that they do not remain on the diffractive optical element 1.

[0044] FIG. 11 is a diagram for explaining foreign substance inspection. 11, when a foreign particle P is observed during foreign particle inspection, the defect mark 40 and the foreign particle P can be observed in the same field of view of the microscope, allowing for accurate, quick, and easy visual inspection. Furthermore, when this inspection is performed by multiple inspectors, the provision of the defect mark 40 reduces variations in inspection accuracy among inspectors, enabling stable, high-precision inspection. Alternatively, when automatic inspection is performed using image analysis, the defect mark 40 can be used as a calibration value in the image analysis, and high-precision inspection can be achieved by suppressing variations in inspection sensitivity of the polygonal body.

[0045] When inspecting for foreign particles or the like as shown in FIG. 11, the illumination state during microscope observation is often switched to make defects such as foreign particles easier to see. That is, observation is performed by turning on all or only some of the light-emitting elements of an illumination device having multiple light-emitting elements. The angle and position of the illumination device may also be adjusted. Conventionally, when providing marks on optical elements, the marks have simply been formed in a convex or concave shape, or a regularly arranged pattern known as a line-and-space pattern has been formed on the marks. However, depending on the lighting conditions, conventional marks may have poor visibility. Therefore, in this embodiment, a special pattern is configured to improve visibility for all marks, including the mold identification code 20, position identification code 30, defect mark 40, and cutting position mark 50. In the following description, the mold identification code 20, position identification code 30, defect mark 40, and cutting position mark 50 will be collectively referred to simply as "marks."

[0046] FIG. 12 is an enlarged view of the area where the mold identification code 20 is formed. FIG. 13 is an enlarged view of the area where the defect mark 40 is formed. In this embodiment, the mold identification code 20 and the defect mark 40 have a concave-convex shape that forms a diffraction grating. Although not shown, the position identification code 30 and the cutting position mark 50 also have a concave-convex shape that forms a similar diffraction grating.

[0047] FIG. 14 is a diagram illustrating the uneven shape formed on the mold identification code 20 and the like. The uneven shape provided in the mark of this embodiment is such that an area in which diffraction gratings of 3 μm × 3 μm size are arranged as one unit (hereinafter referred to as unit area 1001) as shown in FIG. 14(a). A plurality of unit areas 1001 are arranged closely together within the mark. The diffraction grating formed in the unit area 1001 in this embodiment is a two-level diffraction grating, and the uneven shape includes both curved lines and broken lines connecting multiple line segments at the boundaries between the convex and concave portions when viewed from the normal direction of the surface on which the diffraction grating is formed. In FIG. 14(a), the black parts are convex shapes. Here, the unit area may be a size larger than the mark, such as 500 μm, cut to the size of the mark, and this configuration also allows light to be emitted over a wide area. However, in this configuration, although most of the light is emitted at the same position as the irradiation spot intended at the time of design, the intensity balance may deviate significantly from the intensity balance intended at the time of design. For example, one edge of a rectangular mark may be highly visible, but the other edge may be less visible, resulting in a bias toward the light emitted from the mark. For this reason, it is desirable for the size of the unit area to be smaller than the mark.

[0048] When light of the corresponding wavelength is irradiated onto the unit area 1001 of this embodiment, the unit area 1001 emits light that forms a pattern in which 5 × 5 irradiation spots SP are arranged at equal intervals in wave number space as shown in Fig. 14(b). Since the unit areas 1001 are arranged closely together in the mark, when light of the corresponding wavelength is irradiated onto the mark, light that forms a pattern in which 5 × 5 irradiation spots SP are arranged at equal intervals in wave number space as shown in Fig. 14(b) is emitted. The diffraction grating pattern (Fig. 14(a)) that diffracts light into such a desired irradiation pattern (Fig. 14(b)) can be designed using, for example, IFTA (Iterative Fourier Transform Algorithm). IFTA is a commonly used design method that repeats Fourier transforms while moving the pattern. Using IFTA, it is possible to design a diffraction grating with high accuracy for the target (design objective) at high speed. The pattern emitted from the unit area 1001 is not limited to the form shown in Fig. 14(b) and may be other patterns. However, it is preferable that the pattern emitted from the unit area 1001 be a diffraction grating that emits light over a wide range in order to improve visibility from various directions.

[0049] FIG. 15 is a diagram showing another example of a diffraction grating that is preferably formed in a unit area. As shown in Fig. 15(a), an area in which diffraction gratings each measuring 8 μm × 8 μm are arranged is defined as a unit area 1002. This diffraction grating is also a two-level diffraction grating, and its uneven shape includes both curved lines and broken lines connecting multiple line segments at the boundaries between the convex and concave portions when viewed from the normal direction of the surface on which the diffraction grating is formed. When this unit area 1002 is irradiated with light of the corresponding wavelength, it emits light that forms a pattern in which 11 × 11 irradiation spots SP are arranged at equal intervals in wavenumber space, as shown in Fig. 15(b).

[0050] 14(a) and 15(a), the uneven shape includes both curved lines and broken lines connecting multiple line segments at the boundaries between the convex and concave portions when viewed from the normal direction. Furthermore, the uneven shape is arranged so that the boundaries between the convex and concave portions face multiple directions when viewed from the normal direction of the surface on which the uneven shape is provided. This allows light irradiated from various directions to be emitted in various directions. Even when the direction of illumination is changed to see light-scattering transparent foreign matter, opaque foreign matter, scratches, etc., the mark has a light-bending structure, which allows for a clear difference in the scattering and transmission behavior of the base substrate and the mark when viewed from various directions by light sources, resulting in a mark with excellent visibility.

[0051] Here, the light of the corresponding wavelength may be appropriately selected to design the diffraction grating of the unit area 1001 (or unit area 1002), but it is desirable that the wavelength be close to that of the light used during observation in order to improve visibility. In this embodiment, since observation is performed with visible light, a diffraction grating that emits the above pattern with light of a wavelength of 550 nm is configured in the unit area 1001. The illumination device used during observation is often a so-called dark field illumination, which illuminates from an oblique angle. Assuming that this illumination light is bent by a marker and introduced into an objective lens, it is desirable that one of the illumination spots SP shown in this embodiment has a diffraction angle of 8 degrees or more, more preferably 10 degrees or more.

[0052] FIG. 16 is a diagram showing the results of evaluating visibility for the comparative example and this embodiment. In the method using dark-field illumination, light is irradiated from an angle so that it does not directly enter the objective lens, and therefore only the light scattered or diffracted by the mark can be observed, which improves mark visibility compared to the method using bright-field illumination. This can also be seen from the improvement in the results of Comparative Example 2 compared to Comparative Example 1, which uses bright-field illumination.

[0053] The diffraction angle of a diffraction grating can be set arbitrarily depending on its design. Therefore, using a simple line and space pattern (shown as L / S in Figure 16), mark substrates with different line widths were created to check mark visibility, and an inspection visibility evaluation was carried out. Note that the line and space pattern also has the function of diffracting light as a diffraction grating. Two line widths were evaluated: 4 μm and 2 μm. As a result, it was confirmed that the mark visibility was improved in Comparative Example 3 with a width of 2 μm compared to Comparative Example 2 with a width of 4 μm. Furthermore, when the diffraction angle is calculated using the theoretical formula sinθ=λ / pitch, the diffraction angle of Comparative Example 2 with a line width of 4 μm is 4 degrees, while that of Comparative Example 3 with a line width of 2 μm is 8 degrees, indicating that the larger the diffraction angle, the better the visibility. For the above reasons, the diffraction angle of the first-order light is preferably 8 degrees or more, and more preferably 10 degrees or more.

[0054] However, it was confirmed that the visibility of the marks in the line and space pattern decreased when the substrate set position (mark line arrangement direction) was rotated 90 degrees with respect to the irradiation direction of the dark field illumination (Comparative Example 4). To address this issue, a mark substrate was fabricated on which a DOE pattern having two or more first-order diffraction angles on each of two orthogonal axes was developed, and an inspection visibility evaluation was carried out. As a result, the mark visibility did not change even when the substrate setting position (mark line arrangement direction) was rotated from 0 degrees to 90 degrees, and furthermore, the visibility was significantly improved (this embodiment). From the above, it can be said that a configuration in which first-order diffracted light is emitted in a pattern of at least four or more axial directions is desirable.

[0055] Furthermore, in this embodiment, the method of forming the diffraction grating on the mark can be performed by utilizing the process of fabricating the diffraction grating 10, and the mark can be fabricated simultaneously with the fabrication of the diffraction grating 10, making fabrication easy. Therefore, providing the mark of this embodiment does not increase the manufacturing cost of the diffractive optical element 1.

[0056] To verify the scattering and transmission characteristics of a mark made up of a diffraction grating, one method is to shine a spot beam that is smaller than the mark or the same size as the mark and project the scattered light and transmitted light onto a screen for observation, or to directly observe the scattered light and transmitted light with a detector such as a CMOS or CCD. Alternatively, the shape of the mark can be identified, and the scattering and transmission characteristics can be verified by simulation. Specifically, a top view of the pattern can be acquired using a microscope or SEM, and the contours can be extracted to serve as input values ​​for the plan view of the simulation. If the irregularity height can be acquired using an AFM or SEM, it can be used as the input value for the height direction of the simulation. This simulation can be performed using either a thin model based on a Fourier transform or a rigorous model based on RCWA or FDTD. When using the thin model, the irregularity height can be converted into a phase difference and input as the input value for the height direction. When using the rigorous model, the irregularity height can be used as the input value for the simulation height directly, and the irregularity height measured by AFM or SEM can be used as the average value of the measurement results.

[0057] The light source may be a wavelength of 550 nm, a representative wavelength for visible light. The characteristics of orthogonal linearly polarized light, such as polarized light at angles of 0 and 90 degrees, may be calculated and then averaged. When calculating the phase difference or using the simulated height, the refractive index of the substrate and optical element portion is required. This refractive index may be input as a representative value estimated from the composition of the optical element material. For example, borosilicate glass has a refractive index in the range of 1.45 to 1.5 at a wavelength of 550 nm, while typical photocurable resins often have a refractive index in the range of 1.45 to 1.6. On the other hand, when the size of the optical element pieces is large, the refractive index may be obtained using a measuring instrument such as an ellipsometer, and this value may be input.

[0058] FIG. 17 is a diagram showing the results of comparing a diffractive optical element having a defect mark according to this embodiment with a comparative example having a conventional defect mark. The samples prepared for comparison shown in Fig. 17 are Comparative Examples 1 to 3, which are conventional configurations in which lines and spaces are configured in the defect mark, and Examples 1 to 3, which are samples of this embodiment in which a diffraction grating is configured in the defect mark. Note that Fig. 17 shows an enlarged view of the position corresponding to defect mark 40. Also, Fig. 17 shows a configuration in which four defect marks are provided.

[0059] Comparative Examples 1 to 3 have the same line-and-space mark configuration, but different illumination conditions. Comparative Example 1 is an illumination state in which all lights arranged around the objective lens of the microscope are turned on (hereinafter referred to as bright field). Comparative Example 2 is an illumination state in which some of the lights arranged around the objective lens are turned off (hereinafter referred to as dark field). Comparative Example 3 is an illumination state in which some of the lights arranged around the objective lens are turned off and fine-tuned (hereinafter referred to as special dark field). Similarly, Examples 1 to 3 have the same mark configuration, that is, a diffraction grating, but the illumination conditions are different: Example 1 is a bright field, Example 2 is a dark field, and Example 3 is a special dark field.

[0060] As shown in Figures 17(a) to 17(c), in Comparative Examples 1 to 3, some of the defect marks are difficult to see due to changes in illumination conditions. In contrast, as shown in Figures 17(d) to 17(f), in Examples 1 to 3, the entire surface and outline of the defect mark are clearly visible even when the illumination conditions change. Note that Figure 17 shows black and white photographs, so the differences between the Comparative Examples and Examples may be difficult to see, but in the actual observation field, there were more significant differences between the Comparative Examples and Examples than those shown in Figure 17.

[0061] As described above, in the diffractive optical element 1 of this embodiment, diffraction gratings are configured for all of the marks, namely, the mold identification code 20, the position identification code 30, the defect mark 40, and the cutting position mark 50. Therefore, the marks can be made highly visible regardless of the lighting conditions. (Variations) The present invention is not limited to the above-described embodiment, and various modifications and variations are possible, and these are also within the scope of the present invention.

[0062] (1) In the embodiment, the diffraction grating formed in the mark has been described as having a complex uneven shape in which the boundaries between the convex and concave portions, as viewed from the normal direction of the surface on which the diffraction grating is formed, include both curved lines and broken lines connecting multiple line segments. This is not limiting, and the diffraction grating formed in the mark may be, for example, a grating cell array as shown in Fig. 4. However, when a grating cell array is formed in the mark, it is desirable to arrange multiple types of diffraction gratings even in the narrow part of the mark.

[0063] (2) In the embodiment, an example has been described in which the diffraction grating provided in the mark is different from the diffraction grating 10, which is the optical function region of the diffractive optical element 1 that fulfills the intended optical function. This is not limiting, and for example, the diffraction grating provided in the mark may be a diffraction grating with the same configuration as the diffraction grating 10, which is the optical function region of the diffractive optical element 1 that fulfills the intended optical function. This simplifies the manufacturing process. Furthermore, the heights of the recesses and protrusions of the diffraction grating provided in the mark and the diffraction grating 10, which is the optical function region that fulfills the optical function, may be different or the same. If the heights are the same, the manufacturing process can be simplified, for example, when manufacturing a mold in a lithography process.

[0064] The height of the irregularities mentioned here is preferably defined as the average height difference between the convex and concave portions of the pattern shape, or between the convex and convex portions, by extracting an observation area of ​​several tens of micrometers that can be observed using an AFM, SEM, or the like. Specifically, in the case of a multi-step structure as shown in Figure 7, there are multiple convex portions, but any step can be used to define the average height difference, such as between 11a-3 and 11a-0, 11a-3 and 11a-2, or 11a-3 and 11a-1. This is because, regardless of which step is being created in the manufacturing process of a mold with a multi-step structure, a mark can be created at the same time. Furthermore, when comparing the average height difference between the diffraction grating provided in the mark and the diffraction grating that is the optical function region that exhibits the optical function, even if there is a difference of about 30%, they can be considered to be the same height. This is because, as shown in Figure 14, the pattern width of a diffractive optical element is often submicron or smaller, and when processing such fine patterns, large manufacturing errors often occur, such as changes in the etching depth in the lithography process depending on the pattern width.

[0065] (3) In the embodiment, the diffractive optical element 1 has been described as an example in which the optical function region that exhibits the optical function originally intended by the optical element is a diffraction grating 10. However, the present invention is not limited to this, and for example, the optical function region that exhibits the optical function originally intended by the optical element may be, for example, a microlens array, and the present invention may be applied to optical elements of other configurations, not limited to diffractive optical elements.

[0066] (4) In the embodiment, the diffraction grating formed in the mark has been described as having a two-level concave-convex shape. However, the present invention is not limited to this, and the diffraction grating formed in the mark may have four or eight levels, for example, and the number of steps in the concave-convex shape of the diffraction grating can be changed as appropriate.

[0067] (5) In the embodiment, an example has been described in which the diffractive optical element 1 includes a mold identification code 20, a position identification code 30, a defect mark 40, and a cutting position mark 50. However, this is not limiting, and for example, each diffractive optical element 1 may be provided with a unique variable code (hereinafter referred to as a substrate ID) that can individually identify the polygonal body 500 that will be molded into the molded shape. The substrate ID may be, for example, a unique code for each substrate 1a prepared for producing the polygonal body 500. This code may simply be a sequential number, or may be a code related to the date and time of molding of the polygonal body 500, or may be any of various codes associated therewith, such as a barcode or two-dimensional code.

[0068] (Position for substrate ID) The substrate ID must not affect the optical properties of the element, and it is usually preferable to provide it outside the effective area where light hits the element, but this does not apply if a method that does not affect the light used is used. For example, if ink that is substantially transparent at the target wavelength is used, the substrate ID may be provided within the effective area where light hits the element. The coating may be applied to either the optical element surface (the side with the fine irregularities) or the backside. However, if the coating is applied before molding, it is preferable to form it on the side opposite the molding surface, taking into consideration the impact on the molding process. If the coating is applied after molding, it may be applied to either the resin surface or the backside, and if the coating is applied after singulation, it may be applied to the side of the element. The method of applying the coating to the side is effective when the effective area of ​​the element is large and the area to apply it is too narrow, and the coating is applied while the element is picked up.

[0069] (Timing for setting substrate ID) Possible processes include attaching the ID to the shaping substrate before shaping, attaching after shaping, attaching after inspection, and attaching to each chip after dicing. Since the substrate ID attached to the chip is difficult to see with the naked eye when the chip size is small, considering the convenience of carrying out the process in the substrate state, it may be possible to use the same operation in which a visible substrate ID is attached to the shaping substrate.

[0070] (Method of setting substrate ID) Methods such as laser marking, inkjet printing, and stamping can be used to assign a substrate ID. It does not necessarily have to be visually identifiable, as long as the drawn pattern can be identified by comparing it with the base using a microscope or depth sensing device. There are various methods for laser marking, but the appropriate method should be selected depending on the material of the surface to be marked and the size of the marking. Methods that involve evaporation of the material are likely to result in the generation of foreign matter, so excimer lasers are preferred when marking resin materials. When marking glass substrates, there is a concern that the marking may be prone to breakage, so it is best to keep the marking depth as shallow as possible (a few μm or less). Methods that cause the resin material to develop color, such as foaming or carbonization, can also be applied. In this case, it is sufficient to create contrast with the non-marked areas, and a method can be used in which a pre-formed background uneven pattern is irradiated with a laser to change the shape, and the change in shape creates contrast. There are no particular restrictions on the uneven pattern, but making it the same shape as the defect mark will make it easier to see later. Ink application methods such as inkjet printing or stamping can also be used to assign substrate IDs. When using stamps, use ink that allows different numbers to be used for each substrate. The ink to be used can be selected from those commonly used in industrial applications, taking into account the material and wettability of the surface to be printed, but it is also important to select ink that will not fade during environmental testing. Furthermore, if the ink is substantially transparent at the target wavelength, restrictions on the printing location are relaxed. For example, in the case of infrared optical elements, ink that transmits infrared light can be used to print within the effective area. In this case, the substrate ID display size can be made relatively large, making it easier to detect. Furthermore, while laser, inkjet, and stamping methods require precise control of the printing position because they must avoid the effective area of ​​the element, using substantially transparent ink relaxes the alignment precision requirements and increases the process flexibility.

[0071] By providing the above-mentioned substrate ID on each diffractive optical element, it is possible to identify the lot of the molded substrate itself from the individualized diffractive optical element itself. Information linked to the substrate ID is information necessary to ensure traceability, such as the "lot of substrate used," "lot of material used," and "date molded." By providing the substrate ID on each diffractive optical element together with the mold identification code and position identification code, it is possible to trace from the diffractive optical element itself mounted on the assembled product to the DOE lot and master.

[0072] The embodiments and modifications may be used in combination as appropriate, but detailed description thereof will be omitted. The present invention is not limited to the above-described embodiments. [Explanation of symbols]

[0073] 1 Diffractive optical element 1a Base material 1b Resin layer 10 Diffraction Grating 11 High refractive index section 11a Convex part 11b Side wall part 12 recess 13 Space 14 Low refractive index section 15 Diffraction layer 20 Molding mold identification code 30 Location identification code 40, 40a, 40b, 40c Defective marks 50 Cutting position mark 200 screens 201 light 202 Irradiation area 204 Irradiation area 210 Light source section 500 Polyhedral Body 1001,1002 unit area

Claims

1. An optical element having a plurality of marks formed by concave and convex shapes, the plurality of marks have different dimensions and the same shape; the mark has a unit area in which a diffraction grating is arranged, An optical element in which the boundary between a convex portion and a concave portion of the unit area includes both a curved line and a broken line connecting a plurality of line segments when viewed from the normal direction of the surface on which the diffraction grating is formed.

2. The optical element according to claim 1, a plurality of the unit areas are arranged closely together within the mark; An optical element characterized by:

3. The optical element according to claim 1 or claim 2, the plurality of marks are arranged so that their dimensions gradually change at a constant rate; An optical element characterized by:

4. The optical element according to any one of claims 1 to 3, The size of the unit area is smaller than that of the mark; An optical element characterized by:

5. The optical element according to claim 2, the convex portions of the unit areas are connected to the convex portions of the unit areas that are closely arranged side by side; An optical element characterized by:

6. The optical element according to any one of claims 1 to 5, When light having a wavelength of 550 nm is incident from the front, diffracted light emits a pattern in wave number space in which 5 × 5 or more irradiation spots are arranged at equal intervals when viewed from the normal direction of the surface of the mark on which the concave-convex shape is provided. An optical element characterized by:

7. The optical element according to any one of claims 1 to 5, When light having a wavelength of 550 nm is incident from the front, diffracted light emits a pattern in wave number space in which 11 × 11 or more irradiation spots are arranged at equal intervals when viewed from the normal direction of the surface of the mark on which the concave-convex shape is provided. An optical element characterized by:

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