JP7729427B2 - Optical elements - Google Patents

Description

The present invention relates to an optical element equipped with a mark.

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

The light sources used for these sensors have wavelength distributions, brightness, spread, etc. that are appropriate for the application. Wavelengths of light that are often used range from visible light to infrared. Infrared light, in particular, is widely used because it is less susceptible to external light, is invisible, and allows for observation of the interior of an object. LED light sources, laser light sources, etc. are commonly used as light sources. For example, laser light sources, which have a small spread of light, are ideal for detecting distant objects, while LED light sources are ideal for detecting relatively close objects or illuminating an area with a certain degree of spread.

However, the size, shape, etc. of the target irradiation area do not necessarily match the spread (profile) of light from the light source, and it is necessary to shape the light using a diffuser, lens, shielding plate, etc. One example of a means for shaping light is a diffractive optical element (DOE). This utilizes the diffraction phenomenon that occurs when light passes through a location where materials with different refractive indices are periodically arranged. Although diffractive optical elements are basically designed for light of a single wavelength, theoretically, they can shape light into almost any shape. Furthermore, diffractive optical elements can control the uniformity of the light distribution within the irradiation area. These characteristics of diffractive optical elements are advantageous in terms of increasing efficiency by suppressing irradiation of unnecessary areas and miniaturizing devices by reducing the number of light sources, etc.
Furthermore, the diffractive optical element can be used with both parallel light sources such as lasers and diffuse light sources such as LEDs, and can be applied to a wide range of wavelengths from ultraviolet light to visible light and infrared light.

When such diffractive optical elements are used in high-precision sensors, extremely high precision is required. To achieve this high precision, traceability is important, allowing 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, it is also necessary to inspect for dust and other particles that may adhere during the manufacturing process. To ensure traceability, positioning, inspection, etc., 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.

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 minute 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.

Japanese Patent Application Laid-Open No. 2018-189939 JP 2015-43400 A

The objective of the present invention is to provide an optical element with a mark that is easy to see regardless of lighting conditions.

The present invention solves the above-mentioned problems by the following solutions. For ease of understanding, the following explanation uses reference numerals corresponding to the embodiments of the present invention, but the present invention is not limited to these.

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

The second invention is the optical element (1) described in the first invention, characterized in that the uneven shape includes at least one of a curve and a broken line connecting multiple line segments, at the boundary between the convex portion and the concave portion when viewed from the normal direction.

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.

The fourth invention is the optical element (1) described in 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.

The fifth invention is the optical element (1) described in 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.

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) that are regions of a diffraction grating that can emit the pattern, and that a plurality of the unit areas are arranged within the mark (20, 30, 40, 50).

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).

The eighth invention is the optical element (1) described in the seventh invention, characterized in that the optical function region (10) is provided with a diffraction grating.

The ninth invention is the optical element (1) described in 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 region.

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 in the optical function region (10).

The present invention makes it possible to provide an optical element with a mark that is easy to see regardless of lighting conditions.

1A and 1B are diagrams showing an embodiment of a diffractive optical element 1 according to the present invention. 2 is a cross-sectional view taken along the line GG in FIG. 1. 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. 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. FIG. 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. 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 . 7 is a cross-sectional view of the diffractive optical element taken along the line G-G' in FIG. 6. FIG. 1 is a diagram illustrating a diffractive optical element. FIG. 1 is a diagram showing a polygonal body 500 on which diffractive optical elements 1 are attached on multiple surfaces. FIG. 10 is an enlarged view of a portion of the multi-faceted body 500. FIG. 10 is a diagram illustrating a foreign substance inspection. FIG. 2 is an enlarged view of the area where the mold identification code 20 is formed. FIG. 2 is an enlarged view of a region where a defect mark 40 is formed. 10A and 10B are diagrams illustrating the concave and convex shapes formed on the mold identification code 20 and the like. 10A and 10B are diagrams showing other examples of diffraction gratings that are preferably formed in a unit region. FIG. 10 is a diagram showing the results of evaluating visibility for a comparative example and the present embodiment. 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.

The best mode for implementing the present invention will be described below with reference to the drawings.

(Embodiment)
FIG. 1 is a diagram showing an embodiment of a diffractive optical element 1 according to the present invention.
FIG. 2 is a cross-sectional view taken along the line 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 appropriately exaggerated 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.

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 may be made of a transparent resin such as polycarbonate (PC) resin, polyethylene terephthalate (PET) resin, methyl methacrylate butadiene styrene (MBS) resin, methyl methacrylate styrene (MS) resin, acrylic styrene (AS) resin, or 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.

Resin layer 1b is formed on substrate 1a and has a shaped shape (10, 20, 30, 40, 50, etc.) that corresponds to the shape formed in the mold. Resin layer 1b can be formed, for example, by using a mold on which concave-convex patterns corresponding to each of the above-mentioned shaped shapes are formed to transfer the concave-convex pattern by molding ultraviolet-curing resin applied to substrate 1a, and then curing it by irradiating it with ultraviolet light.

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

The resin layer 1b has the following shaped features: a diffraction grating 10, a mold identification code 20, a position identification code 30, a defect mark 40, and a cutting position mark 50.

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 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.
In this embodiment, as an example, the present invention can be applied to a diffractive optical element having a seemingly irregular pattern of concave-convex shapes, 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 irregular. 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 consisting of straight lines or broken lines connecting curved line segments. Therefore, in an irregular diffraction grating pattern, when viewed from the normal direction of the surface on which the concave-convex shapes of the high refractive index portion (described below) are formed, the boundary between the convex portions and the concave portions includes at least one of a curve and a broken line connecting multiple line segments. 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.

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, as shown in FIG. 4 , in which a plurality of unit cells, each having the same concave-convex shape, are tiled. In the following description, this type of diffractive optical element 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.

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.

In the present invention, "shaping light" refers to controlling the direction of light travel 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.

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 examples of partial periodic structures.

As shown in Figure 7, the diffraction grating 10 has a high refractive index portion 11 in which multiple convex portions 11a are arranged side by side in the 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 as the cross-sectional position changes, resulting in an arrangement of many diffraction gratings with various cross-sectional shapes.

In addition, the upper part of Figure 3, including 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 sections 14 with a lower refractive index than the high-refractive-index sections 11. The periodic structure in which these high-refractive-index sections 11 and low-refractive-index sections 14 are alternately arranged forms a diffractive layer 15 with the ability to shape light.

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 portion 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.

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 x 3 mm. Therefore, during the manufacturing process, a polygonal assembly 500 is fabricated, in which a large number of diffractive optical elements 1 are arranged in a grid pattern, as shown in FIG. 9 , 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.

Returning to Figures 1 and 2, the mold identification code 20 is a mark that identifies the mold, and in the example shown in Figure 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 diffractive optical elements 1 within the polygonal body 500 (see Figure 10).

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 Figure 9, one molding die has 100 locations where 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 in Figure 1 shows an example of "X49, Y53," which indicates the 49th column in the X direction (the horizontal direction in Figures 9 and 10) and the 53rd row in the Y direction (the vertical direction in Figures 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. In the above example, for example, the code may be "900A-X49Y53."

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, the first code region is located in the left half rectangular region, and the second code region is located in the right half rectangular region, and the first code region and the second code region each contain one of the mold identification code 20 and the position identification code 30, which are different codes. 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 gap between them, which allows them to be recognized as different codes.
Furthermore, specific identification codes may be provided for 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 added to the initial letter of each of the mold identification code 20 and the position identification code 30. Specifically, for example, "M (Master)" is added to the mold identification code 20, "X (X-Coordinate)" is added to the X coordinate of the position identification code 30, and "Y (Y-Coordinate)" is added 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 at which position the diffractive optical element 1 was manufactured, even if it is an individualized diffractive optical element 1.

The defect mark 40 is a mark formed to a specified dimension and is provided for the inspector to refer to during visual inspection. Alternatively, it may be used as a judgment standard for automatic inspection using inspection equipment. 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 through inspector training alone. It is also difficult to standardize judgment criteria 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 inspection takt time, and also to make it easier to develop inspector skills.

When one defect mark 40 is provided, its dimensions should preferably be the threshold for determining a defect, or slightly smaller than the threshold. For example, if defects larger than 40 μm are to be considered defective as described above, the defect mark 40 should be a 40 μm x 40 μm square, a 40 μm diameter circle, a 30 μm x 30 μm square, or a 30 μm diameter circle. Shapes such as rectangles and ellipses are also acceptable, rather than being limited to squares and circles. Furthermore, if the tendency for defects to occur is known, the defect mark 40 may be configured in 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 x 2000 μm rectangle.

In addition, 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, if defects larger than 40 μm are considered to be defective products, defect mark 40a is a 40 μm x 40 μm square, defect mark 40b is a 30 μm x 30 μm square, and defect mark 40c is a 20 μm x 20 μm square. By arranging defect marks 40 whose dimensions gradually change at a constant rate in this manner, it is expected that inspectors will be able to quickly and accurately grasp the size of the object (area 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 also be arranged near each defect mark.

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 Figure 1, or they may be removed during cutting so that they do not remain on the diffractive optical element 1.

FIG. 11 is a diagram for explaining foreign matter inspection.
11, when a foreign particle P is observed in the diffractive optical element 1 of this embodiment 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 the inspectors, making it possible to achieve 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.

When inspecting for foreign particles or the like as shown in Figure 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 illumination devices equipped with 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 of the marks, namely, the mold identification code 20, the position identification code 30, the defect mark 40, and the cutting position mark 50. In the following description, the mold identification code 20, the position identification code 30, the defect mark 40, and the cutting position mark 50 will be collectively referred to simply as "marks."

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.

FIG. 14 is a diagram illustrating the concave and convex shapes 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 closely arranged 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. Note that in FIG. 14( a), the black areas represent the convex shapes.
Here, the unit area may be, for example, 500 μm, which is a size larger than the mark and 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 while the other edge may be poorly visible, and the light emitted from the mark may be biased. Therefore, it is desirable that the size of the unit area be smaller than the mark.

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 design of a diffraction grating pattern (FIG. 14(a)) that diffracts light into such a desired irradiation pattern (FIG. 14(b)) can be performed using, for example, IFTA (Iterative Fourier Transform Algorithm). IFTA is a commonly used design method that repeats Fourier transforms while moving a pattern. Using IFTA, it is possible to design a diffraction grating with high accuracy relative to a target (design objective) at high speed.
The pattern emitted from the unit region 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 region 1001 be a diffraction grating that emits light over a wide range in order to improve visibility from various directions.

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 x 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 of 11 x 11 irradiation spots SP arranged at equal intervals in wavenumber space, as shown in Fig. 15(b).

In both the diffraction gratings of Figures 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, this uneven shape is arranged so that the boundaries between the convex and concave portions face in 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, and even when the direction of illumination is changed to see light-scattering transparent foreign matter, opaque foreign matter, scratches, etc., the mark's light-bending structure makes it possible to clearly differentiate the scattering and transmission behavior of the base substrate and the mark when exposed to light sources from various directions, resulting in a mark with excellent visibility.

Here, the light of the corresponding wavelength may be appropriately selected to design the diffraction grating of the unit region 1001 (or unit region 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 region 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.

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 the light 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 fact that the results of Comparative Example 2 are improved compared to Comparative Example 1, which uses a bright field.

The diffraction angle of a diffraction grating can be set arbitrarily depending on its design. Therefore, mark substrates with different line widths were fabricated using a simple line-and-space pattern (shown as L/S in FIG. 16 ) to confirm mark visibility, and inspection visibility evaluation was performed. Note that the line-and-space pattern also has the function of diffracting light as a diffraction grating. Two line widths, 4 μm and 2 μm, were evaluated.
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 the diffraction angle of Comparative Example 3 with a line width of 2 μm is 8 degrees, indicating that a larger diffraction angle improves 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.

However, it was confirmed that the visibility of the marks in the line and space pattern decreased when the substrate setting position (mark line arrangement direction) was rotated 90 degrees with respect to the irradiation direction of the dark field illumination (Comparative Example 4).
In order to solve this problem, 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.

Furthermore, in this embodiment, the method of forming the diffraction grating on the mark can be performed by utilizing the process of manufacturing the diffraction grating 10, and the mark can be easily manufactured at the same time. Therefore, the inclusion of the mark of this embodiment does not increase the manufacturing cost of the diffractive optical element 1.

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 using 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, an image of the pattern from above can be obtained using a microscope or SEM, and the contour can be extracted to serve as the input value for the plan view of the simulation. If the unevenness height can be obtained using an AFM or SEM, it can be used as the input value for the height direction of the simulation. This simulation can be either a thin model using a Fourier transform or a rigorous model using RCWA or FDTD. When using the thin model, the unevenness height can be converted into a phase difference and input as the input value for the height direction. When using the rigorous model, the unevenness height can be used as the input value for the simulation height as is, and the unevenness height obtained using an AFM or SEM can be used as the average value of the measurement results.

The light source can be a wavelength of 550 nm, which is a representative value for visible light. The characteristics of orthogonal linearly polarized light, such as at angles of 0 and 90 degrees, can 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 can 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 for 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, if the individual optical element pieces are large, the refractive index can be obtained using a measuring device such as an ellipsometer, and this value can be input.

FIG. 17 is a diagram showing the results of comparing the diffractive optical element having the defect mark of 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.

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 are lit under different conditions: Example 1 is bright field, Example 2 is dark field, and Example 3 is special dark field.

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 lighting 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 lighting conditions change. Note that Figure 17 shows a black and white photograph, 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.

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 illumination conditions.
(Modified form)
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.

(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, when 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 a limitation, and the diffraction grating formed in the mark may be, for example, a grating cell array as shown in Figure 4. However, when forming a grating cell array in the mark, it is desirable to arrange multiple types of diffraction gratings even in the narrow part of the mark.

(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 exhibits the optical function originally intended. 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 exhibits the optical function originally intended. This can simplify the manufacturing process. Furthermore, the height 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 exhibits 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.

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 may 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 in 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.

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

(4) In the embodiment, an example has been described in which the diffraction grating formed in the mark has a two-level uneven shape. This is not limiting, and for example, the diffraction grating formed in the mark may have four levels, eight levels, etc., and the number of steps in the uneven shape of the diffraction grating can be changed as appropriate.

(5) In the embodiment, the diffractive optical element 1 has been described as having 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 on which the shaping shape is to be formed. 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 shaping processing date and time of the polygonal body 500, or may be various codes such as a barcode or two-dimensional code associated therewith.

(Position where substrate ID is provided)
The substrate ID must not affect the optical properties of the element, and is usually preferably provided 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 back surface. However, if the coating is applied before molding, it is preferable to form it on the surface opposite to the molding surface, taking into consideration the effect on the molding process. If the coating is applied after molding, it may be applied to either the resin surface or the back surface, and if the coating is applied after singulation, it may be applied to the side surface of the element. The method of applying the coating to the side surface is effective when the effective area of the element is wide and the area to apply it is too narrow, and the coating is applied while the element is picked up.

(Timing of providing 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, in consideration of convenience when the process is carried out in the substrate state, it may be combined with an operation in which a substrate ID of a visible size is attached to the shaping substrate.

(Method of providing substrate ID)
Methods such as laser marking, inkjet printing, stamping, etc. 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 part 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 for resin materials. When marking on glass substrates, there is a concern that the marking may be easily damaged, so it is best to keep the 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, a stamp should be used that allows for different numbers to be used for each substrate. The ink to be used can be selected from inks 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 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.

By providing the above-mentioned substrate ID on each individual diffractive optical element, the lot of the molded substrate itself can be identified from the individualized diffractive optical element itself. The 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, along with the mold identification code and position identification code, on each diffractive optical element, it is possible to trace from the diffractive optical element itself mounted on the assembled product to the DOE lot and master.

Note that the embodiments and variations can be used in combination as appropriate, but detailed explanations will be omitted. Furthermore, the present invention is not limited to the embodiments described above.

REFERENCE SIGNS LIST 1 Diffractive optical element 1a Base material 1b Resin layer 10 Diffraction grating 11 High refractive index portion 11a Convex portion 11b Side wall portion 12 Concave portion 13 Space 14 Low refractive index portion 15 Diffraction layer 20 Mold identification code 30 Position identification code 40, 40a, 40b, 40c Defect mark 50 Cutting position mark 200 Screen 201 Light 202 Irradiation area 204 Irradiation area 210 Light source unit 500 Polyhedron body 1001, 1002 Unit area

Claims (7)

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