Infrared sensor cover and infrared sensor

Abstract

The present invention provides an infrared sensor cover 7 for covering an infrared sensor that uses infrared rays to measure the distance to an object of measurement, said cover comprising a base material 10 and a microasperity structure 11 which is provided on at least one surface of a base material 19 and which has a plurality of raised parts 12 arranged at a pitch P no greater than the wavelength λ of the infrared rays, wherein the infrared sensor cover 7 is disposed on the infrared sensor so as to allow the infrared rays to be incident on the infrared sensor cover 7 from a direction inclined relative to the surface of the infrared sensor cover 7, and the ratio (H / λ) of the height H of the raised parts 12 to the wavelength λ is 0.5 or greater.

Description

Infrared sensor cover and infrared sensor

[0001] This application claims the benefit of priority from Japanese Patent Application No. 2024-019704, filed February 13, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, in the automotive field and the like, a technology has become widespread in which an infrared sensor emits infrared rays (particularly near-infrared rays) toward the periphery of a vehicle and detects the infrared rays reflected off an obstacle (measurement target) such as a preceding vehicle or a pedestrian, thereby detecting the distance and relative speed between the vehicle and the obstacle. For example, an optical ranging device that uses infrared remote sensing technology such as LiDAR (Light Detection and Ranging) is used.

[0003] In general, an infrared sensor is provided with a cover around the sensor body to protect the sensor body. Glass or resin is often used as the material for an infrared sensor cover. However, simply using glass or resin can result in insufficient infrared transmittance through the cover, as infrared rays are reflected from the cover surface, which can lead to poor performance of the infrared sensor. For this reason, for example, Patent Document 1 proposes an infrared sensor cover provided with an anti-reflection layer on the cover surface to prevent infrared rays from being reflected.

[0004] JP 2018-124279 A

[0005] However, even with the conventional infrared sensor cover described in Patent Document 1, when infrared rays are incident on the surface of the cover from an oblique direction (hereinafter referred to as "oblique incidence"), the reflection of the obliquely incident infrared rays cannot be sufficiently suppressed, resulting in a problem of reduced infrared transmittance. In particular, in systems that use an infrared sensor to scan and detect infrared rays at a wide angle (e.g., 60°), the transmittance of infrared rays that are obliquely incident on the surface of the cover is significantly degraded, which is a factor in reducing the detection accuracy of the infrared sensor. For this reason, there has been a need for a cover that has excellent anti-reflection performance for infrared rays (e.g., near-infrared rays) that are obliquely incident over a wide range of incident angles, including wide-angle incidence (e.g., -60° to +60°), and that improves the detection accuracy of the infrared sensor.

[0006] Therefore, the present invention has been made in consideration of the above problems, and an object of the present invention is to provide an infrared sensor cover and an infrared sensor that can improve the anti-reflection performance against infrared rays that are obliquely incident over a wide range of incident angles, including wide-angle incidence.

[0007] In order to solve the above problem, according to one aspect of the present invention, there is provided an infrared sensor cover that covers an infrared sensor that measures the distance to a measurement object using infrared rays, comprising: a base material; and a fine uneven structure provided on at least one surface of the base material, the fine uneven structure having a plurality of convex portions arranged at a pitch P that is equal to or less than the wavelength λ of the infrared rays, wherein the infrared sensor cover is positioned on the infrared sensor so that the infrared rays can be incident on the infrared sensor cover from a direction inclined with respect to the surface of the infrared sensor cover, and the ratio (H / λ) of the height H of the convex portions to the wavelength λ is 0.5 or more.

[0008] The ratio (P / λ) of the pitch P of the convex portions to the wavelength λ may be 0.5 or less.

[0009] The ratio (H / P) of the height H of the convex portions to the pitch P may be 3 or less.

[0010] The infrared rays may be near-infrared rays having a wavelength λ of 800 nm or more and 2500 nm or less.

[0011] The shape of the convex portion may be substantially an elliptical cone shape, an elliptical truncated cone shape, or a bell shape or a dome shape whose planar shape is an ellipse.

[0012] The reflectance of the infrared ray when the infrared ray is incident on the surface of the infrared sensor cover at an incident angle of more than 0° and not more than 60° may be 3% or less.

[0013] In addition, in order to solve the above problem, according to another aspect of the present invention, there is provided an infrared sensor comprising: the above-mentioned infrared sensor cover; a light irradiation device that irradiates infrared laser light toward an object to be measured through the infrared sensor cover; and a light detection device that detects the infrared light reflected by the object to be measured through the infrared sensor cover.

[0014] According to the present invention, it is possible to improve the anti-reflection performance against infrared rays that are obliquely incident at a wide range of incident angles, including wide angles of incidence.

[0015] FIG. 1 is a schematic diagram showing the overall configuration of an optical distance measuring device according to a first embodiment of the present invention. FIG. 2 is a cross-sectional view showing an infrared sensor cover according to the same embodiment. FIG. 3 is a cross-sectional view showing an infrared sensor cover according to a modified example of the same embodiment. FIG. 4 is a plan view showing the arrangement of multiple convex portions of a fine concave-convex structure according to the same embodiment. FIG. 5 is a plan view showing the arrangement of multiple convex portions of a fine concave-convex structure according to a modified example of the same embodiment. FIG. 6 is a perspective view showing an example of convex portions of a fine concave-convex structure according to the same embodiment. FIG. 7 is a perspective view showing an example of convex portions of a fine concave-convex structure according to the same embodiment. FIG. 8 is a perspective view showing an example of convex portions of a fine concave-convex structure according to the same embodiment. FIG. 9 is a partially enlarged cross-sectional view showing a fine concave-convex structure according to the same embodiment. FIG. 10 is a graph showing the results of a simulation of the relationship between the height of convex portions of the fine concave-convex structure according to the same embodiment, the angle of incidence, and the reflectance. FIG. 11 is a perspective view showing a master according to the same embodiment. FIG. 12 is a schematic view showing the configuration of a transfer device for manufacturing a transferred object using the master according to the same embodiment. FIG. 13 is an explanatory diagram showing the general configuration of an exposure device according to the same embodiment. FIG. 14 is a schematic diagram showing a method for measuring reflectance and diffracted light according to an example.

[0016] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in the embodiments are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0017] [1. Overall Configuration of Optical Distance Metering Device] First, the overall configuration of an optical distance measuring device 1 using an infrared sensor according to a first embodiment of the present invention will be described with reference to Fig. 1. Fig. 1 is a schematic diagram showing the overall configuration of the optical distance measuring device 1 according to this embodiment.

[0018] As shown in FIG. 1 , an optical distance measuring device 1 equipped with an infrared sensor according to this embodiment irradiates a distance measurement area 5 with light and detects the light reflected by the object 6 to measure the distance and direction to the object 6, as well as the size, shape, and relative speed of the object 6. The optical distance measuring device 1 includes a distance measuring sensor (infrared sensor) that utilizes remote sensing technology such as LiDAR. The distance measuring method used by the optical distance measuring device 1 is preferably a TOF method that calculates the distance to the object 6 by measuring the time of flight (TOF) of light, but various other distance measuring methods, such as triangulation, may also be used. The time of flight (TOF) of light is the round-trip time from when the optical distance measuring device 1 emits irradiated light to when it receives reflected light.

[0019] The optical ranging device 1 according to this embodiment can be applied to various technical fields that use remote sensing. For example, the optical ranging device 1 can be used in autonomous driving technology in the automotive field, radar devices for ADAS (Advanced Driver-Assistance Systems) or traffic enforcement, surveying in the construction field, surveying using aircraft or artificial satellites, vacuum cleaner robots, 3D mapping measurements in various terminal devices (smartphones, smart glasses, smart watches, personal computers, tablet PCs, etc.) that use technologies such as AR (Augmented Reality), MR (Mixed Reality), and VR (Virtual Reality), various measurements in geology, seismology, atmospheric physics, oceanography, etc., and military applications.

[0020] The optical distance measuring device 1 according to this embodiment is mounted on vehicles such as automobiles, buses, trucks, and motorcycles, and is suitable for use in autonomous driving technology, ADAS, etc. In this case, the optical distance measuring device 1 can measure the distance and direction to a measurement target 6 present in the space around the vehicle, particularly in front of the vehicle, and can create 3D mapping. However, the present invention is not limited to this example, and the optical distance measuring device 1 can be mounted on various products in the various technical fields mentioned above.

[0021] 1, an optical distance measuring device 1 according to this embodiment includes a light irradiation device 2 (emitter), a light detection device 3 (receiver), and a controller 4. The optical distance measuring device 1 is an example of an infrared sensor that uses infrared rays to measure the distance to a measurement object, and functions as a distance measuring sensor such as LiDAR.

[0022] The light irradiation device 2 is a device (emitter) for irradiating the distance measurement target area 5 with light (infrared light). The light irradiation device 2 irradiates the distance measurement target area 5 with infrared light emitted from a light source. The infrared light irradiated from the light irradiation device 2 is laser light having an infrared wavelength band (wavelength: approximately 700 nm to 1000 μm). As the infrared laser light, for example, laser light having a wavelength band such as near-infrared (wavelength: approximately 700 nm to 2500 nm), mid-infrared (wavelength: approximately 2.5 μm to 4 μm), or far-infrared (wavelength: approximately 4 μm to 1000 μm) can be used. The infrared laser light is preferably laser light having a near-infrared wavelength band (e.g., 800 nm to 2500 nm, preferably 850 nm to 1550 nm) that is invisible to the human eye. The light source provided in the light irradiation device 2 is preferably a laser light source such as a semiconductor laser that emits infrared laser light in the above wavelength band.

[0023] The light irradiation device 2 includes, for example, a light source having a light-emitting element that emits infrared laser light, an optical element that diffuses the laser light, a housing, etc. (none of which are shown). The light irradiation device 2 emits pulsed laser light from the light source, diffuses the laser light using the optical element, and irradiates the diffused light (irradiated light) toward the distance measurement target area 5. Alternatively, the light irradiation device 2 may irradiate the laser light so as to scan the distance measurement target area 5 at a wide angle by changing the irradiation direction of the pulsed laser light emitted from the light source.

[0024] The light detection device 3 is a device (receiver) for detecting infrared light (reflected light) irradiated from the light irradiation device 2 and reflected by the measurement object 6. The light detection device 3 includes, for example, an optical filter and a light receiving unit including a light receiving element (neither of which is shown). The optical filter filters out light other than the reflected light reflected by the measurement object 6 (e.g., sunlight or illumination light) as noise, and transmits only light corresponding to the wavelength of the infrared laser light emitted from the light irradiation device 2. This improves the detection sensitivity of the reflected light by the light receiving element. The light receiving element is composed of a photoelectric conversion element that receives the incident reflected light and generates a voltage. The light receiving element is composed of, for example, an image sensor such as a CMOS (Complementary Metal Oxide Semiconductor) sensor or a CCD (Charge Coupled Device) sensor. The light receiving unit receives reflected light from the object to be measured 6, for example, using multiple light receiving elements arranged two-dimensionally on the light receiving surface, converts the received light intensity at each pixel position on the light receiving surface into an electrical signal, and outputs it to the controller 4.

[0025] The controller 4 is an example of a control unit that controls the operations of the light irradiation device 2, the light detection device 3, and various other devices included in the optical distance measuring device 1. The controller 4 includes, for example, a processor, a memory, an input device, an output device, a communication device, and the like (none of which are shown).

[0026] The processor is, for example, a CPU (Central Processing Unit) or other microprocessor. The processor executes programs stored in memory or other storage media. This allows various processes in the optical distance measuring device 1 to be performed, and various functions defined by the programs to be realized.

[0027] A memory is a storage medium that stores programs and various other data. Examples of memory include RAM (Random Access Memory) and ROM (Read Only Memory). ROM is a non-volatile memory that stores programs used by a processor and data for running the programs. RAM is a volatile memory that temporarily stores data such as variables, calculation parameters, and calculation results used in processing executed by a processor. Programs stored in ROM are read into RAM and executed by a processor such as a CPU.

[0028] The controller 4 controls the light irradiation device 2 and the light detection device 3 to perform distance measurement operations using the optical distance measuring device 1. For example, the controller 4 creates a three-dimensional mapping while three-dimensionally scanning the distance measurement target area 5 by repeatedly emitting laser light using the light irradiation device 2 and detecting reflected light using the light detection device 3. In this case, the controller 4 calculates the distance, direction, relative speed, etc. from the optical distance measuring device 1 to the measurement target 6 based on the time difference between the emission timing of the laser light from the light irradiation device 2 and the detection timing of the reflected light by the light detection device 3 (i.e., the time of flight of light: TOF).

[0029] In this way, the optical distance measuring device 1 scans the distance measurement target area 5 with laser light to create a three-dimensional mapping that indicates the distance and direction to the measurement target object 6 that exists within the distance measurement target area 5. To achieve this, the optical distance measuring device 1 is required to irradiate the laser light over as wide an angular range as possible (i.e., field of view (FOV)). Because the laser light emitted from the light source of the light irradiation device 2 has a narrow spread, the field of view angle as a distance measuring sensor becomes narrow if left as is. For this reason, it is preferable to diffuse the laser light using a diffuser plate or the like and irradiate the diffused light toward the distance measurement target area 5 over a wide field of view angle to expand the irradiation area.

[0030] The diffuser plate is equipped with a microlens array to diffuse the laser light, and the desired diffusion angle (i.e., field of view angle) can be obtained by changing the shape of the microlenses. However, as described above, in a distance measurement sensor such as a TOF sensor, there is a trade-off between the size of the irradiation area of ​​the laser light (the horizontal and vertical range of the measurement target area 5) and the irradiation distance of the laser light (the measurable distance). Therefore, it is preferable to determine the size of the irradiation area by striking a balance between the two.

[0031] In this way, the optical ranging device 1 of this embodiment uses infrared laser light to scan a wide range of the ranging target area 5, irradiating infrared laser light not only in the front direction of the optical ranging device 1 but also in the inclined direction, and receiving reflected light of the laser light reflected by the measuring object 6 from the inclined direction as well.

[0032] 1 , the optical distance measuring device 1 (infrared sensor) according to this embodiment includes an infrared sensor cover 7. The infrared sensor cover 7 (hereinafter sometimes simply referred to as the "cover 7") is a cover for protecting the sensor body of the infrared sensor, and is provided to cover the sensor body. Here, the sensor body of the infrared sensor is a device group including, for example, the light irradiation device 2 (emitter), the light detection device 3 (receiver), and the controller 4.

[0033] The cover 7 is arranged to cover both or either of the light-emitting surface and the light-receiving surface of the sensor body of the infrared sensor. For example, the cover 7 shown in Fig. 1 is a flat member that is provided in an opening formed on one side of the housing of the optical distance measuring device 1 (infrared sensor) and is arranged to cover both the light-emitting surface of the light irradiation device 2 and the light-receiving surface of the light detection device 3.

[0034] The shape and arrangement of the cover 7 are not limited to the example shown in Fig. 1. For example, the cover 7 may be a curved plate-like cover instead of a flat plate-like cover. Furthermore, one infrared sensor may be provided with multiple covers 7, and the multiple covers 7 may cover the light-emitting surface of the light irradiation device 2 and the light-receiving surface of the light detection device 3, respectively.

[0035] The cover 7 is made of a material that is transmissive to infrared rays used in the infrared sensor, particularly a material that is suitably transmissive to near-infrared rays, so that the infrared laser light irradiated from the light irradiating device 2 of the infrared sensor can pass through the cover 7 from the inside to the outside of the cover 7. In addition, the reflected light of the laser light reflected by the measurement object 6 can also pass through the cover 7 from the outside to the inside of the cover 7.

[0036] As described above, in the optical distance measuring device 1 (infrared sensor) according to this embodiment, the light emitting device 2 and light detecting device 3, which are the sensor main body, are covered with the cover 7. The light emitting device 2 emits infrared laser light through the cover 7 in the front and oblique directions of the optical distance measuring device 1 so as to scan the entire distance measuring area 5 including the measurement object 6. Meanwhile, when the emitted infrared laser light is reflected by the measurement object 6 and returns from the front and oblique directions of the optical distance measuring device 1, the light detecting device 3 receives and detects the reflected light through the cover 7.

[0037] As described above, infrared laser light and its reflected light are incident on the cover 7 of the infrared sensor according to this embodiment from both the inside and outside. Furthermore, in the optical distance measuring device 1 (infrared sensor) according to this embodiment, the cover 7 is positioned so that the infrared laser light and its reflected light can be incident at a wide angle of incidence θ, not only from a direction perpendicular to the surface of the cover 7 (normal direction) but also from a direction inclined relative to the surface (inclination direction). The range of the incidence angle θ of the infrared laser light and its reflected light that is obliquely incident on the cover 7 varies depending on the specifications and application of the optical distance measuring device 1 (infrared sensor), but can be, for example, −45° to +45°, −60° to +60°, or −75° to +75°, and can be a very wide range. In this specification, a positive incidence angle θ (e.g., +45°) means that the obliquely incident light is incident from a direction inclined to one side (the negative X-axis direction) relative to the normal direction (the Z direction) of the surface of the cover 7. On the other hand, if the incident angle θ is a negative value (for example, −45°), this means that the oblique incident light is incident from a direction inclined to the other side (positive X-axis direction) relative to the normal direction (Z direction) of the surface of the cover 7.

[0038] In this way, when infrared laser light, which has a wavelength longer than that of visible light, is obliquely incident on the cover of an infrared sensor at a wide angle of incidence θ (for example, about 60°), conventional covers have not been able to sufficiently suppress the reflection of the obliquely incident infrared light. As a result, with conventional covers, the reflectance of the obliquely incident infrared light becomes, for example, 3% or more, and the transmittance of the obliquely incident infrared light decreases to, for example, less than 97%, resulting in a problem of reduced detection accuracy of the infrared sensor.

[0039] Therefore, the infrared sensor and cover 7 according to this embodiment aim to significantly improve the anti-reflection performance of the cover 7 against infrared rays (particularly near-infrared rays) that are obliquely incident at a wide range of incident angles (for example, -60° or more and +60° or less), including normal incidence and wide-angle incidence, thereby improving the detection accuracy of the infrared sensor through the cover 7. To this end, the surface of the cover 7 according to this embodiment is provided with a fine uneven structure as an anti-reflection layer that is compatible with infrared rays that are obliquely incident at a wide angle. The features of the fine uneven structure provided on the cover 7 according to this embodiment will be described in detail below.

[0040] 2 and 3, the configuration of the infrared sensor cover 7 according to this embodiment will be described. Fig. 2 is a cross-sectional view showing the infrared sensor cover 7 according to this embodiment. Fig. 3 is a cross-sectional view showing the infrared sensor cover 7 according to a modified example of this embodiment.

[0041] As shown in FIG. 2 , the infrared sensor cover 7 includes a substrate 10 and a fine concave-convex structure 11 .

[0042] The substrate 10 is a substrate that constitutes the main body of the cover 7. The substrate 10 is a plate-shaped or sheet-shaped substrate. The substrate 10 is, for example, flat, but may also be curved, and may have any plate shape suitable for installing the cover 7 in the infrared sensor. The thickness of the substrate 10 is not particularly limited, and may be adjusted as appropriate depending on the wavelength λ of the infrared rays used in the infrared sensor, the application of the cover 7, etc.

[0043] The substrate 10 is formed of, for example, an inorganic material such as glass, or an organic material such as resin. The material of the substrate 10 is preferably a resin (e.g., a thermoplastic resin, a photocurable resin, etc.) with excellent infrared transmittance used in infrared sensors, and is particularly preferably a resin with excellent near-infrared transmittance. Examples of such resins include polymethyl methacrylate, polycarbonate, A-PET, cycloolefin copolymer, and cycloolefin polymer. The substrate 10 may also be formed of an inorganic material with excellent infrared transmittance. Examples of such inorganic materials include silicon-based materials, more specifically glass. The infrared transmittance of the substrate 10 is preferably 97% or higher.

[0044] The fine uneven structure 11 is a fine uneven structure (moth-eye structure) formed on the surface of the substrate 10. The fine uneven structure 11 has a function of preventing reflection of infrared rays on the surface of the cover 7 (anti-reflection function).

[0045] As shown in Figures 2 and 3, the microrelief structure 11 is provided on at least one surface of the substrate 10. In the example of Figure 2, the microrelief structure 11 is provided on both surfaces of the substrate 10 (i.e., the front surface 10A and the back surface 10B). On the other hand, in the example of Figure 3, the microrelief structure 11 is provided on only one surface of the substrate 10 (i.e., the front surface 10A).

[0046] The fine uneven structure 11 has a plurality of convex portions 12 and a plurality of concave portions 13. The convex portions 12 are protruding structures that protrude perpendicularly from the surface of the substrate 10. The concave portions 13 are recessed portions between adjacent convex portions 12. The size and arrangement pitch P of the convex portions 12 are, for example, about several tens of nanometers to several tens of micrometers, preferably about several hundred nanometers to several micrometers (nano-order), and are therefore very fine.

[0047] In order for the fine uneven structure 11 to exhibit its anti-reflection function for infrared rays, the convex portions 12 of the fine uneven structure 11 are arranged on the surface of the substrate 10 at a pitch P that is equal to or less than the wavelength λ of the infrared rays used in the infrared sensor. In other words, the pitch P of the convex portions 12 of the fine uneven structure 11 is equal to or less than the wavelength λ of the infrared rays used in the infrared sensor. For example, if the infrared rays used in the infrared sensor are near-infrared rays and the wavelength λ of this near-infrared rays is in the range of 800 nm or more and 2500 nm or less, it is preferable that the pitch P of the convex portions 12 is equal to or less than the wavelength λ of the near-infrared rays. The pitch P is the distance between the vertices of two adjacent convex portions 12 (i.e., the distance between the center points of the planar shapes of the two convex portions 12) (see FIG. 4).

[0048] In this embodiment, by providing the surface of the cover 7 with the fine uneven structure 11 made up of a plurality of convex portions 12 arranged at such a fine pitch P, it is possible to form a moth-eye structure with excellent infrared anti-reflection performance on the surface of the cover 7. This forms an effective refractive index gradient between the air and the material of the cover 7, so that light (infrared light) that enters the surface of the cover 7 and passes through the fine uneven structure 11 is gently refracted, suppressing surface reflection.

[0049] As shown in Fig. 2, forming a fine concave-convex structure 11 on both surfaces (surface 10A and back surface 10B) of the substrate 10 can suppress reflection of infrared rays on the surface 10A and back surface 10B of the substrate 10. Therefore, as shown in Fig. 1, in the case where infrared rays (irradiated light, reflected light) are incident on the cover 7 from both the front and back surfaces of the cover 7 in the infrared sensor, it is preferable to suppress reflection of infrared rays incident on both surfaces of the cover 7 by providing a fine concave-convex structure 11 on both surfaces (surface 10A and back surface 10B) of the substrate 10 of the cover 7, as shown in Fig. 2.

[0050] 3, the microrelief structure 11 may be formed only on one surface (surface 10A) of the substrate 10, and the microrelief structure 11 may not be formed on the other surface (back surface 10B). This also makes it possible to suppress reflection of infrared rays on the surface 10A of the substrate 10, and to suppress reflection of infrared rays on one surface of the cover 7. Although not shown, the microrelief structure 11 may be provided on one surface of the substrate 10, and a multilayer anti-reflection film may be provided on the other surface.

[0051] [4. Configuration of the Microrelief Structure] Next, the configuration of the microrelief structure 11 according to this embodiment will be described in more detail with reference to Fig. 4 to Fig. 8. Fig. 4 is a plan view showing the arrangement of multiple convex portions 12 of the microrelief structure 11 according to this embodiment. Fig. 5 is a plan view showing the arrangement of multiple convex portions 12 of the microrelief structure 11 according to a modified example of this embodiment. Figs. 6 to 8 are perspective views showing examples of the convex portions 12 of the microrelief structure 11 according to this embodiment.

[0052] The plurality of convex portions 12 of the microrelief structure 11 may be arranged regularly or irregularly on the surface of the substrate 10. Fig. 4 shows an example in which a plurality of convex portions 12 having an elliptical planar shape are arranged regularly. Fig. 5 shows an example in which a plurality of convex portions 12 having a circular planar shape are arranged regularly.

[0053] 4 and 5, in the microrelief structure 11 according to this embodiment, a plurality of convex portions 12 are regularly arranged in a hexagonal lattice pattern on the surface (on the XY plane) of the substrate 10. The convex portions 12 are arranged at predetermined intervals (dot pitch P) along a plurality of tracks T extending in the X direction. Ｄ The tracks T are imaginary lines that represent the arrangement direction of the convex portions 12. The tracks T are parallel to each other and are arranged at a predetermined interval (track pitch P) in the Y direction. Ｔ ) are arranged.

[0054] Here, the dot pitch P Ｄ is the pitch of the convex portions 12 along the track direction (X direction), which is the length direction of the track T. In other words, the dot pitch P Ｄis the distance between the vertices of two adjacent convex portions 12 in the track direction (X direction). Ｄ is equal to the pitch P (P Ｄ On the other hand, the track pitch P Ｔ is the pitch of the convex portions 12 along the track perpendicular direction (Y direction), which is a direction perpendicular to the track direction (X direction). Ｔ is equal to the distance between two adjacent tracks T, T in the direction perpendicular to the track (Y direction). When the convex portions 12 are arranged in a hexagonal lattice pattern as shown in FIG. 4, the track pitch P Ｔ is a value smaller than the pitch P (P Ｔ <P). Although not shown, when the convex portions 12 are arranged in a square lattice pattern, the dot pitch P Ｄ and track pitch P Ｔ is equal to the pitch P (P Ｄ =P Ｔ =P).

[0055] 4 and 5, the plurality of convex portions 12 are regularly arranged in a hexagonal lattice pattern along the plurality of tracks T. Therefore, between any two arbitrarily extracted convex portions 12, the dot pitch P Ｄ is a nearly constant value, and the track pitch P Ｔ Also, when comparing two rows of convex portions 12 arranged along two tracks T, T adjacent to each other in the Y direction, the arrangement of the convex portions 12 in one row in the X direction is different from the arrangement of the convex portions 12 in the other row by the dot pitch P Ｄ Half of (P Ｄ In this way, the convex portion 12 is shifted in the X direction by P Ｄ By arranging the protrusions 12 with a shift of 1 / 2 in the X direction, the plurality of protrusions 12 are regularly arranged in a hexagonal lattice pattern throughout the fine uneven structure 11. This allows the protrusions 12 to be closest packed on the surface of the substrate 10, thereby increasing the packing rate of the protrusions 12. Therefore, the anti-reflection performance of the fine uneven structure 11 per unit area of ​​the surface of the substrate 10 can be improved.

[0056] The filling rate is the percentage of the area occupied by the multiple convex portions 12 on the surface (XY plane) of the substrate 10. When the surface (flat surface) of the substrate 10 is completely filled with the multiple convex portions 12 and there are no flat surfaces between the convex portions 12, the filling rate is 100%. On the other hand, as shown in FIG. 4, when the multiple convex portions 12 are arranged on the surface (flat surface) of the substrate 10 with a certain amount of gap between them and there is a flat surface in the recess 13 between the multiple convex portions 12, the filling rate is less than 100%. Even when the multiple convex portions 12 are arranged with gaps between them as shown in FIG. 4, it is preferable to make the gaps as small as possible and increase the filling rate to, for example, 80% or more, preferably 90% or more. This can improve the anti-reflection performance of the fine concave-convex structure 11.

[0057] Furthermore, as shown in Figures 4 and 5, the microrelief structure 11 is preferably a hexagonal lattice arrangement in which multiple protrusions 12 are arranged at the vertices and centers of hexagons on the surface of the substrate 10. This allows the multiple protrusions 12 to be arranged in a close-packed manner on the surface of the substrate 10 (on the XY plane), thereby improving the anti-reflection performance of the moth-eye structure. However, the multiple protrusions 12 of the microrelief structure 11 are not limited to the above-mentioned hexagonal lattice example and may be regularly arranged in other manners, such as a square lattice, a rectangular lattice, or a triangular lattice. Alternatively, the multiple protrusions 12 may be irregularly arranged on the surface of the substrate 10. For example, the multiple protrusions 12 may be arranged based on the various lattice arrangements described above, but may also be irregularly arranged at positions randomly shifted from the reference position within a predetermined range of variation.

[0058] [4.1. Preferred Range of Pitch P of Convex Portions] The pitch P of the convex portions 12 is, for example, the pitch of a plurality of pairs of adjacent convex portions 12, 12 (dot pitch P Ｄ or track pitch P Ｔ For example, a plurality of pairs of two adjacent convex portions 12, 12 in the track direction (X direction) are picked up, and the dot pitch P Ｄ Then, the calculated or measured dot pitches P ＤThe arithmetic mean value of the pitch P may be calculated.

[0059] The size of the pitch P is equal to or less than the wavelength λ of the infrared light used in the infrared sensor, and is preferably less than the minimum value of the wavelength band of the infrared light. For example, the pitch P may be less than 1000 nm, and preferably 100 nm to 900 nm. This allows the fine uneven structure 11 to function favorably as a moth-eye structure that suppresses reflection of incident infrared light over a wide wavelength band.

[0060] However, if the pitch P is less than 100 nm, it is difficult to form the fine uneven structure 11 by nanoimprinting or the like, which is not preferable. Therefore, the lower limit of the pitch P is not particularly limited, but from the viewpoint of stably forming the fine uneven structure 11, it is preferable that it is 100 nm or more. Furthermore, if the pitch P exceeds the wavelength λ of the infrared light used in the infrared sensor, diffraction of the infrared light occurs, which is not preferable, as it reduces the anti-reflection performance of the moth-eye structure. Note that the dot pitch P Ｄ and track pitch P Ｔ The sizes of the pitches P may be the same or different as long as they are within the preferred range of the pitch P described above.

[0061] [4.2. Preferred Shape of the Convex Portions 12] As shown in Figures 6 to 8, the three-dimensional shape of the convex portions 12 of the microrelief structure 11 may be any shape, such as a cone shape (circular cone shape, elliptical cone shape, or pyramidal shape), a truncated cone shape (circular cone shape, elliptical cone shape, or pyramidal shape), a bell shape, a dome shape, or a protrusion or needle shape, as long as it protrudes in a direction perpendicular to the surface of the substrate 10 (Z direction). The planar shape of the convex portions 12 is preferably, for example, a circle (see Figure 5) or an ellipse (see Figure 4), but may also be any shape, such as a polygon. The planar shape of the convex portions 12 is a planar shape that shows the outer shape of the convex portions 12 when the convex portions 12 are projected onto the surface of the substrate 10 (XY plane).

[0062] From the viewpoint of ease of molding the protrusions 12, the three-dimensional shape of the protrusions 12 is preferably a three-dimensional shape whose planar shape is substantially elliptical (see FIG. 4). Specifically, the three-dimensional shape of the protrusions 12 is preferably a substantially elliptical cone shape (see FIG. 6), an elliptical truncated cone shape with a flat top (see FIG. 7), or a bell or dome shape whose planar shape is elliptical (see FIG. 8).

[0063] As such, the three-dimensional shape of the convex portions 12 is preferably a shape such as an elliptical cone obtained by stretching or shrinking a cone shape in the track direction (X direction). Thus, if the convex portions 12 have a three-dimensional shape having an elliptical planar shape (see FIG. 4 ), it becomes easier to efficiently manufacture a microrelief structure 11 having a large number of such convex portions 12. For example, according to a manufacturing method of the master 100 using a laser exposure method (see FIG. 13 ) described below, the planar shape of the recesses 122 (see FIG. 11 ) of the microrelief structure 120 formed on the outer peripheral surface of the roll-shaped master 100 tends to be elliptical, and it is difficult to make them perfectly circular. The recesses 122 of the microrelief structure 120 of this master 100 have an inverted shape of the convex portions 12 of the microrelief structure 11 of the cover 7. Therefore, it is preferable to allow the shape of the convex portions 12 of the microrelief structure 11 formed using the roll-shaped master 100 to have a three-dimensional shape having an elliptical planar shape. This makes it possible to easily and highly accurately manufacture the fine concave-convex structure 11 having the elliptical convex portions 12 by utilizing the master manufacturing method using the laser exposure method.

[0064] In this specification, "substantially elliptical" is not limited to a geometrically strict elliptical shape, but means including shapes that can be roughly regarded as ellipses, such as ovals, ovals, etc. Similarly, "substantially elliptical cone shape" or "elliptical truncated cone shape" is not limited to a geometrically strict elliptical cone shape or elliptical truncated cone shape, but means including shapes that can be roughly regarded as elliptical cones or elliptical truncated cones (for example, shapes distorted by stretching or shrinking a cone shape or a truncated cone shape in the track direction (X direction)).

[0065] [4.3. Material of the Microrelief Structure] As will be described in detail later, the microrelief structure 11 is formed, for example, by roll-to-roll imprinting using a roll master. The concave-convex shape formed on the outer peripheral surface of the roll master has an inverted shape of the microrelief structure 11. The concave-convex shape of the outer peripheral surface of the roll master is transferred to an uncured resin layer laminated on the surface of the substrate 10, and then the uncured resin layer is cured to form the microrelief structure 11. In this way, by using the roll master to transfer the microrelief structure 11 to the surface of the substrate 10 of the cover 7, a cover 7 having an anti-reflection function can be easily manufactured. To manufacture the cover 7 using such an imprinting technique, the microrelief structure 11 may be formed, for example, in a resin layer laminated on the surface of the substrate 10, or may be formed in a resin layer constituting the substrate 10 itself. The resin layer on which the microrelief structure 11 is formed is made of, for example, a cured product of a curable resin.

[0066] The cured product of the curable resin preferably has transparency. The curable resin contains a polymerizable compound and a curing initiator. The polymerizable compound is a resin that is cured by the curing initiator. Examples of the polymerizable compound include epoxy polymerizable compounds and acrylic polymerizable compounds. The epoxy polymerizable compound is a monomer, oligomer, or prepolymer having one or more epoxy groups in the molecule. Examples of the epoxy polymerizable compound include various bisphenol-type epoxy resins (bisphenol A type, F type, etc.), novolac-type epoxy resins, various modified epoxy resins such as rubber and urethane, naphthalene-type epoxy resins, biphenyl-type epoxy resins, phenol novolac-type epoxy resins, stilbene-type epoxy resins, triphenolmethane-type epoxy resins, dicyclopentadiene-type epoxy resins, triphenylmethane-type epoxy resins, and prepolymers thereof.

[0067] The acrylic polymerizable compound is a monomer, oligomer, or prepolymer having one or more acrylic groups in the molecule. Here, the monomer is further classified into a monofunctional monomer having one acrylic group in the molecule, a bifunctional monomer having two acrylic groups in the molecule, and a polyfunctional monomer having three or more acrylic groups in the molecule.

[0068] Examples of "monofunctional monomers" include carboxylic acids (acrylic acid), hydroxyls (2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate), alkyl or alicyclic monomers (isobutyl acrylate, t-butyl acrylate, isooctyl acrylate, lauryl acrylate, stearyl acrylate, isobornyl acrylate, cyclohexyl acrylate), and other functional monomers (2-methoxyethyl acrylate, methoxyethylene glycol acrylate, 2-ethoxyethyl acrylate, tetrahydrofurfuryl acrylate, benzyl acrylate, ethyl carbitol acrylate, phenoxyethyl acrylate, N,N-dimethylaminoethyl acrylate). , N,N-dimethylaminopropylacrylamide, N,N-dimethylacrylamide, acryloylmorpholine, N-isopropylacrylamide, N,N-diethylacrylamide, N-vinylpyrrolidone, 2-(perfluorooctyl)ethyl acrylate, 3-perfluorohexyl-2-hydroxypropyl acrylate, 3-perfluorooctyl-2-hydroxypropyl acrylate, 2-(perfluorodecyl)ethyl acrylate, 2-(perfluoro-3-methylbutyl)ethyl acrylate), 2,4,6-tribromophenol acrylate, 2,4,6-tribromophenol methacrylate, 2-(2,4,6-tribromophenoxy)ethyl acrylate), 2-ethylhexyl acrylate, and the like.

[0069] Examples of the "bifunctional monomer" include tri(propylene glycol) diacrylate, trimethylolpropane diallyl ether, and urethane acrylate.

[0070] Examples of the "polyfunctional monomer" include trimethylolpropane triacrylate, dipentaerythritol penta- and hexaacrylate, and ditrimethylolpropane tetraacrylate.

[0071] Examples of the acrylic polymerizable compound other than those listed above include acrylic morpholine, glycerol acrylate, polyether acrylate, N-vinylformamide, N-vinylcaprolactone, ethoxydiethylene glycol acrylate, methoxytriethylene glycol acrylate, polyethylene glycol acrylate, EO-modified trimethylolpropane triacrylate, EO-modified bisphenol A diacrylate, aliphatic urethane oligomer, polyester oligomer, etc. From the viewpoint of the transparency of the cover 7, the polymerizable compound is preferably an acrylic polymerizable compound.

[0072] A curing initiator is a material that hardens a curable resin. Examples of the curing initiator include a heat-curing initiator and a photo-curing initiator. The curing initiator may be one that hardens by heat, some kind of energy ray other than light (e.g., electron beam), or the like. When the curing initiator is a heat-curing initiator, the curable resin becomes a thermosetting resin, and when the curing initiator is a photo-curing initiator, the curable resin becomes a photo-curable resin.

[0073] Here, from the viewpoint of transparency of the cover 7, it is preferable that the curing initiator is an ultraviolet curing initiator. Therefore, it is preferable that the curable resin is an ultraviolet curing acrylic resin. The ultraviolet curing initiator is a type of photocuring initiator. Examples of ultraviolet curing initiators include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxy-cyclohexyl phenyl ketone, and 2-hydroxy-2-methyl-1-phenylpropan-1-one.

[0074] The resin forming the fine uneven structure 11 may be a resin that has been given functionality such as hydrophilicity, water repellency, and anti-fogging properties.

[0075] The resin forming the microrelief structure 11 may contain additives depending on the application of the cover 7. Examples of such additives include inorganic fillers, organic fillers, leveling agents, surface conditioners, and antifoaming agents. Examples of inorganic fillers include SiO ２ , TiO ２ , ZrO ２ , SnO ２ , Al ２ O ３ and other metal oxide fine particles.

[0076] The fine uneven structure 11 may be formed directly on the resin layer on the surface of the substrate 10 by imprinting using a roll master as described above. However, the present invention is not limited to this example, and for example, a resin film (e.g., a thermoplastic resin film) on which the fine uneven structure 11 is formed may be adhered to the surface of the substrate 10.

[0077] 5. Characteristics of height H and pitch P of convex portions of fine concave-convex structure Next, characteristics of the height H and pitch P of the convex portions 12 of the fine concave-convex structure 11 according to this embodiment will be described with reference to Fig. 9. Fig. 9 is a partially enlarged cross-sectional view showing the fine concave-convex structure 11 according to this embodiment.

[0078] As shown in FIG. 9 , the infrared sensor cover 7 according to this embodiment has a fine uneven structure 11 to suppress reflection of incident light 31 (hereinafter sometimes referred to as "oblique incident light 31") incident from an oblique direction relative to the surface (XY plane) of the substrate 10. The fine uneven structure 11 has a plurality of protrusions 12 regularly arranged at a predetermined pitch P on the surface of the substrate 10. Each protrusion 12 protrudes so as to extend perpendicularly (in the Z direction: normal direction) to the surface of the substrate 10. The height H of the protrusion 12 is the length in the normal direction (Z direction) from the base to the apex of the protrusion 12. The pitch P of the protrusions 12 is the distance between the apexes of adjacent protrusions 12, 12 on the XY plane.

[0079] From the viewpoint of uniform infrared transmittance and light distribution in the cover 7, it is preferable that the heights H of the plurality of protrusions 12 are the same and that the pitches P of the protrusions 12 are uniform, as in the example shown in Fig. 9. However, without being limited to such an example, the heights H of the plurality of protrusions 12 may be unequal within a predetermined error range. The pitches P of the protrusions 12 may also be unequal within a predetermined error range.

[0080] The pitch P of the convex portions 12 is preferably equal to or less than the wavelength λ of the infrared incident light 31 incident on the cover 7 (P≦λ). This allows the fine uneven structure 11 to function as a moth-eye structure that suppresses reflection of infrared light with the wavelength λ, thereby suppressing reflection of infrared light with the wavelength λ on the surface of the cover 7.

[0081] [5.1. Ratio of Height H of Convex Portions to Wavelength λ (First Condition)] Here, the condition for the height H of the convex portions 12 will be described as the first condition for the fine concave-convex structure 11 according to this embodiment.

[0082] The ratio (=H / λ) of the height H of the convex portion 12 to the wavelength λ of the incident infrared light 31 is preferably 0.5 or more. That is, it is preferable that the height H of the convex portion 12 is 0.5 times or more the wavelength λ and satisfies the following formula (1): H / λ≧0.5 (1)

[0083] By satisfying formula (1), it is possible to improve the anti-reflection performance against obliquely incident light 31. Therefore, it is possible to improve the anti-reflection properties of the fine uneven structure 11 against obliquely incident light 31 in a wide range of incident angles θ (for example, θ=−60° to +60°), including wide-angle incidence (for example, 45° or more). The reason for this will be explained below.

[0084] In this embodiment, a fine uneven structure 11 (moth-eye structure) in which a plurality of fine protrusions 12 are arranged at a pitch P that is equal to or less than the wavelength λ of incident infrared light 31 is formed on the surface of the substrate 10 of the cover 7. This allows the refractive index n at the interface between air and the cover 7 to change continuously, thereby suppressing reflection of the incident light 31 on the surface of the cover 7. Here, in order to enhance the anti-reflection effect of the fine uneven structure 11 against reflection of obliquely incident light, it is preferable to make the change in the refractive index n as gradual as possible, and for this purpose, it is preferable to make the height H of the protrusions 12 of the fine uneven structure 11 greater than or equal to a predetermined other height.

[0085] Therefore, the present inventors conducted simulations using RCWA (Rigorous Coupled-Wave Analysis) and intensively studied the relationship between the anti-reflection effect against obliquely incident light, particularly wide-angle obliquely incident light 31, and the height H of the convex portions 12. As a result, it was found that if the height H of the convex portions 12 is 0.5 times or more the wavelength λ of the obliquely incident infrared light (i.e., if the above formula (1) is satisfied), the anti-reflection effect against the obliquely incident light 31 can be improved, and in particular, the improvement in the anti-reflection effect becomes more significant as the incident angle θ of the obliquely incident light 31 increases. Based on this finding, the present inventors found that the condition (first condition) that the ratio (H / λ) of the height H of the convex portions 12 to the wavelength λ of the obliquely incident light 31 is 0.5 or more is important, and came up with a fine uneven structure 11 that satisfies the first condition.

[0086] By having the microrelief structure 11 satisfy the first condition (H / λ≧0.5), as shown in FIG. 9 , even when obliquely incident infrared light 31 is incident on the surface of the cover 7 at a wide angle, the reflected light 32 reflected on the surface of the cover 7 can be reduced, and the transmitted light 33 transmitted through the cover 7 can be increased. This allows the reflectance of the obliquely incident light 31 on the surface of the cover 7 to be suppressed to, for example, 3% or less, preferably 2.5% or less, and the transmittance of the obliquely incident light 31 transmitted through the cover 7 to be increased to, for example, 97% or more, preferably 97.5% or more. Therefore, the cover 7 having the microrelief structure 11 according to this embodiment can significantly improve the anti-reflection performance against infrared light (particularly near-infrared light) obliquely incident at a wide range of incident angles θ (e.g., −60° to +60°), including wide-angle incidence, compared to conventional techniques, and the reflectance of wide-angle obliquely incident light 31 can be reduced to 3% or less. This significantly improves the detection accuracy of an infrared sensor covered with the cover 7 according to this embodiment.

[0087] [5.2. Ratio of Pitch P to Wavelength λ (Second Condition)] Next, the condition of the pitch P of the convex portions 12 will be described as the second condition of the fine concave-convex structure 11 according to this embodiment.

[0088] The ratio (=P / λ) of the pitch P of the convex portions 12 to the wavelength λ of the incident infrared light 31 is preferably 0.5 or less. That is, it is preferable that the pitch P of the convex portions 12 is 0.5 times or less the wavelength λ and satisfies the following formula (2): P / λ≦0.5 (2)

[0089] By satisfying formula (2), it is possible to increase the amount of infrared incident light 31 transmitted through the cover 7. Therefore, it is possible to increase the amount of light received by the infrared sensor covered by the cover 7 and the amount of light emitted from the infrared sensor, thereby improving the detection accuracy of the infrared sensor. The reason for this is explained below.

[0090] Generally, when a periodic micro-relief structure is provided on the surface of an optical element, high-order diffracted light is generated when light passes through the micro-relief structure, and the linear component of the transmitted light is significantly reduced (see FIG. 14). However, when the pitch P of the convex portions of the micro-relief structure is shorter than the wavelength λ of the transmitted light, the diffracted light is reduced.

[0091] In this regard, if the pitch P is too wide compared to the wavelength λ of the obliquely incident light 31, the obliquely incident light 31 will be bent due to diffraction of the obliquely incident light 31 on the surface of the cover 7. This reduces the amount of light received and emitted by the infrared sensor, thereby reducing the detection accuracy of the infrared sensor.

[0092] In contrast, according to the microrelief structure 11 of this embodiment, the ratio of the pitch P to the wavelength λ is 0.5 or less (second condition), and the pitch P is set to an appropriate size according to the wavelength λ. This suppresses the generation of higher-order diffracted light on the surface of the cover 7, thereby improving the linearity of the obliquely incident light 31 and increasing the amount of transmitted light 33 that passes through the cover 7. This therefore increases the amount of transmitted light 33 that passes through the cover 7 and heads toward the infrared sensor, as well as the amount of irradiated light that is emitted from the infrared sensor and passes through the cover 7. This therefore increases the amount of light received and emitted by the infrared sensor, further improving the detection accuracy of the infrared sensor.

[0093] Furthermore, by satisfying both the first condition (H / λ≧0.5) and the second condition (P / λ≦0.5), a fine uneven structure 11 can be realized that has an excellent anti-reflection effect against wide-angle oblique incident light 31 and an excellent effect of suppressing diffracted light.

[0094] [5.3. Aspect Ratio (H / P) of Convex Portions (Third Condition)] Next, the condition for the aspect ratio of the convex portions 12 will be described as the third condition for the fine concave-convex structure 11 according to this embodiment.

[0095] The aspect ratio is the ratio (=H / P) of the height H of the convex portions 12 to the pitch P. This aspect ratio (H / P) is preferably 3 or less. That is, it is preferable that the height H of the convex portions 12 is 3 times or less the pitch P, and satisfies the following formula (3): H / P≦3 (3)

[0096] By satisfying formula (3), when the fine concave-convex structure 11 is formed on the surface of the cover 7 by imprinting using a master, it is possible to improve the releasability when peeling the master from the cover 7 to which the fine concave-convex structure 11 has been transferred. Therefore, the fine concave-convex structure 11 can be formed easily and with high precision by imprinting using a master.

[0097] That is, if the pitch P of the convex portions 12 constituting the fine concave-convex structure 11 is too narrow or if the height H of the convex portions 12 is too high, the aspect ratio (H / P) becomes too large, which reduces the mold releasability during the imprinting process, making it difficult to manufacture the fine concave-convex structure 11.

[0098] In contrast, according to the fine concave-convex structure 11 of this embodiment, the aspect ratio (H / P) is 3 or less (third condition), and the height H is set to an appropriate size according to the pitch P. This improves the demolding properties during the imprinting, and therefore, the fine concave-convex structure 11 can be easily and highly accurately molded into a desired shape without generating defects in the fine concave-convex structure 11.

[0099] 10 , in order to verify the anti-reflection effect under the first condition (H / λ≧0.5) related to the height H of the convex portions 12, the relationship between the height H of the convex portions 12 of the fine concave-convex structure 11 and the reflectance R [%] of incident light on the surface of the fine concave-convex structure 11 for each angle of incidence θ [°] will be described. Fig. 10 is a graph showing the simulation results.

[0100] The conditions for this simulation are as follows: Wavelength λ of incident light: 900 nm Incident angle θ of incident light: 10°, 40°, 60°, 70° Height H of convex portions 12: 200 nm, 300 nm, 500 nm, 650 nm Vertical cross-sectional shape of convex portions 12: approximated as a parabola Planar shape of convex portions 12: circular Planar arrangement of convex portions 12: hexagonal lattice (see FIG. 5 ) Pitch P of convex portions 12: 300 nm Refractive index of material of convex portions 12: 1.5 Refractive index of air: 1.0

[0101] Table 1 shows the relationship between the height H [nm] of the convex portion 12, the angle of incidence θ [°], and the reflectance R [%] of incident light, which was obtained by this simulation. This relationship is also shown in the graph of FIG.

[0102]

[0103] As shown in Table 1 and FIG. 10 , regardless of the height H of the convex portion 12, the reflectance R increases as the incident angle θ of obliquely incident light increases. However, when H = 500 nm or 650 nm, the absolute value and rate of increase of the reflectance R can be suppressed to lower values ​​compared to when H = 200 nm or 300 nm. For example, when the incident angle is wide, θ = 60°, the reflectances R for H = 200 nm and 300 nm are 6.14% and 3.52%, respectively, which significantly exceed the reference reflectance (e.g., 3%, preferably 2.5%). Therefore, when the height H is low, the anti-reflection effect of the micro-relief structure 11 is reduced. In contrast, when H = 500 nm and 650 nm, the reflectances R are 1.14% and 1.41%, respectively, which are sufficiently lower than the reference reflectance (e.g., 3%, preferably 2.5%). Therefore, when the height H is high, it can be said that the anti-reflection effect against obliquely incident light at a wide angle of about 60° is excellent. The reference reflectance is the reference upper limit value (e.g., 3%, preferably 2.5%) of reflectance required for a cover for an infrared sensor used in an in-vehicle LiDAR or the like.

[0104] Therefore, according to the above simulation results, if the height H of the convex portions 12 is equal to or greater than a certain height (for example, 500 nm) with respect to the wavelength λ of the obliquely incident light, and H / λ is equal to or greater than 0.5, the reflectance R of the obliquely incident light over a wide range (10° to 60°) including a wide angle of incidence of about 60° can be suppressed to 3% or less, preferably 1.5% or less, and therefore it can be said that the anti-reflection effect against the obliquely incident light is remarkably excellent.

[0105] 6. Configuration of Master Next, a master 100 used to mold the fine concave-convex structure 11 of the infrared sensor cover 7 according to this embodiment will be described with reference to Fig. 11. Fig. 11 is a perspective view schematically showing the master 100 according to this embodiment.

[0106] The master 100 is a mold for transferring a fine relief structure 120 to the surface of a transfer object (for example, the infrared sensor cover 7 according to this embodiment) by roll-to-roll imprinting. From the viewpoint of efficiently producing the transfer object, the master 100 is preferably a roll-shaped master having a cylindrical or columnar shape, but may also be a flat plate-shaped master. If the master 100 is a roll-shaped master, the fine relief structure 120 of the master 100 can be seamlessly transferred to the substrate of the transfer object by the roll-to-roll method. This allows the transfer object to which the fine relief structure 120 of the master 100 has been transferred to be manufactured with high production efficiency.

[0107] As shown in FIG. 11, the master 100 includes a roll-shaped substrate 110 and a fine concave-convex structure 120 formed on the outer peripheral surface of the substrate 110 .

[0108] The substrate 110 is, for example, a roll-shaped member that serves as the substrate of a roll master. The shape of the substrate 110 may be a hollow cylindrical shape as shown in FIG. 11, or may be a solid cylindrical shape without an internal cavity. The material of the substrate 110 is not particularly limited, and may be fused silica glass or synthetic silica glass (SiO ２ ), or a metal such as stainless steel can be used. The size of the substrate 110 is not particularly limited, but for example, the length of the substrate 110 in the direction of the central axis 110a (hereinafter sometimes referred to as the axial direction) may be 100 mm or more, and the outer diameter of the substrate 110 may be 50 mm or more and 300 mm or less. Furthermore, the radial thickness of the cylindrical substrate 110 may be 2 mm or more and 50 mm or less.

[0109] The fine uneven structure 120 is a fine uneven pattern formed on the outer peripheral surface of the master 100. The fine uneven structure 120 includes a plurality of fine recesses 122 arranged at a predetermined pitch P and a plurality of fine protrusions 123 provided between two adjacent recesses 122. The fine uneven structure 120 of the master 100 has an inverted shape of the fine uneven structure of the transferred object (e.g., the fine uneven structure 11 of the cover 7). For example, the shape of the recesses 122 of the fine uneven structure 120 of the master 100 is an inverted shape of the protrusions 12 of the fine uneven structure 11 of the cover 7 (see FIGS. 2 to 9). Similarly, the shape of the protrusions 123 of the fine uneven structure 120 of the master 100 is an inverted shape of the recesses 13 of the fine uneven structure 11 of the cover 7 (see FIGS. 2 to 9). Furthermore, the pitch (circumferential dot pitch) of the recesses 122 of the fine concave-convex structure 120 of the master 100 is the same as the pitch P of the protrusions 12 of the fine concave-convex structure 11 of the cover 7 .

[0110] The master 100 having such a configuration is provided in a roll-to-roll imprint transfer device, for example, a transfer device 300 shown in Fig. 12. The master 100 can be used to produce a transferred product (for example, the infrared sensor cover 7 according to this embodiment) in which a fine relief structure 120 formed on the outer peripheral surface of the master 100 is transferred. For example, the fine relief structure 120 on the outer peripheral surface of the master 100 can be continuously transferred to a resin layer on the surface of the cover 7, thereby molding the fine relief structure 11 on the surface of the cover 7 with high precision and efficiency.

[0111] 7. Method for Manufacturing Transferred Product Next, a method for efficiently manufacturing a transferred product such as the infrared sensor cover 7 according to this embodiment using a transfer device 300 including the master 100 will be described with reference to Fig. 12. Fig. 12 is a schematic diagram showing the configuration of the transfer device 300 that manufactures a transferred product using the master 100 according to this embodiment.

[0112] 12, the transfer device 300 is a roll-to-roll imprint transfer device. The transfer device 300 transfers the fine relief structure 120 of the master 100 to a resin layer of a transfer target using the roll-to-roll method. This makes it possible to continuously manufacture transferred products to which the fine relief structure 120 formed on the outer peripheral surface of the master 100 has been transferred.

[0113] As shown in FIG. 12, the transfer device 300 includes the master 100 , a substrate supply roll 301 , a take-up roll 302 , guide rolls 303 and 304 , a nip roll 305 , a peeling roll 306 , a coating device 307 , and a light source 309 .

[0114] The substrate supply roll 301 is, for example, a roll on which a film-like substrate 311 is wound. The take-up roll 302 is a roll for winding up a film-like substrate 331 having a resin layer 312 to which the microrelief structure 120 has been transferred. The guide rolls 303 and 304 are rolls for transporting the film-like substrate 311 before and after transfer. The nip roll 305 is a roll for pressing the film-like substrate 311 on which the resin layer 312 has been laminated against the master 100. The peeling roll 306 is a roll for peeling the film-like substrate 311, on which the microrelief structure 120 has been transferred to the resin layer 312, from the master 100.

[0115] The film-like substrate 311 may be the same substrate as the substrate 10 of the infrared sensor cover 7 according to the present embodiment described above (see FIG. 2, etc.), or may be a substrate different from the substrate 10. In the latter case, the cover 7 may be manufactured by attaching the substrate 311 having the resin layer 312 to which the fine uneven structure 120 has been transferred by the transfer device 300 of FIG. 12 to the surface of the substrate 10 of the cover 7 (see FIGS. 2, 3, etc.). For example, in the present embodiment, the cover 7 having the fine uneven structure 11 is configured by attaching the film-like substrate 311 (see FIG. 12) having the resin layer 312 to which the fine uneven structure 120 has been transferred to the surface of the substrate 10 of the cover 7 (see FIGS. 2, 3, etc.).

[0116] The coating device 307 includes a coating means such as a coater, and coats the photocurable resin composition on the film-like substrate 311 to form a resin layer 312. The coating device 307 may be, for example, a gravure coater, a wire bar coater, or a die coater. The light source 309 is a light source that emits light of a wavelength capable of curing the photocurable resin composition, and may be, for example, an ultraviolet lamp.

[0117] The photocurable resin composition is a resin that cures when irradiated with light of a predetermined wavelength. Specifically, the photocurable resin composition may be, for example, an ultraviolet-curable resin such as an acrylic resin acrylate or an epoxy acrylate. The photocurable resin composition may also contain an initiator, a filler, a functional additive, a solvent, an inorganic material, a pigment, a static inhibitor, or a sensitizing dye, as needed.

[0118] The resin layer 312 may be formed of a thermosetting resin composition. In this case, the transfer device 300 is provided with a heater instead of the light source 309, and the resin layer 312 is heated by the heater to harden the resin layer 312 and transfer the fine unevenness structure 120. The thermosetting resin composition may be, for example, a phenolic resin, an epoxy resin, a melamine resin, or a urea resin.

[0119] Next, a method for producing a transfer product using the transfer device 300 will be described.

[0120] First, a film-like substrate 311 is continuously fed from a substrate supply roll 301 and transported by a guide roll 303. Next, a photocurable resin composition is applied to the surface of the fed substrate 311 by an application device 307, and an uncured resin layer 312 is laminated on the surface of the substrate 311.

[0121] Furthermore, the uncured resin layer 312 laminated on the surface of the substrate 311 is pressed against the outer peripheral surface of the master 100 by the nip rolls 305. As a result, the fine uneven structure 120 formed on the outer peripheral surface of the master 100 is transferred to the uncured resin layer 312. Thereafter, light such as ultraviolet light is irradiated from the light source 309 onto the resin layer 312 onto which the fine uneven structure 120 has been transferred. As a result, the uncured resin layer 312 is cured, and the shape of the uneven pattern transferred to the cured resin layer 312 is stabilized.

[0122] Next, the substrate 311 on which the cured resin layer 312 is laminated is peeled off from the outer peripheral surface of the master 100 by a peeling roll 306. As a result, a fine concave-convex structure 11 having an inverted shape of the fine concave-convex structure 120 of the master 100 is formed on the resin layer 312. Thereafter, the substrate 311 peeled off from the master 100 is transported via a guide roll 304 and taken up by a take-up roll 302.

[0123] In this way, the roll-to-roll transfer device 300 can be used to continuously produce transferred products (for example, the infrared sensor cover 7 according to this embodiment) onto which the fine relief structure 120 formed on the master 100 has been transferred. This makes it possible to efficiently and inexpensively mass-produce transferred products onto which the fine relief structure 120 has been transferred with high precision.

[0124] [8. Master Manufacturing Method] [8.1. Overview of Master Manufacturing Method] Next, a description will be given of a method (steps S10 to S50) for manufacturing the master 100 using an apparatus for manufacturing the master 100 according to this embodiment. The apparatus for manufacturing the master 100 according to this embodiment includes, for example, a film forming apparatus, an exposure control apparatus, an exposure apparatus, a developing apparatus, an etching apparatus, an exposure control apparatus, and various other control apparatuses.

[0125] (S10: Resist Film Forming Step) According to the method for manufacturing the master 100 according to this embodiment, first, a resist layer is formed on the outer peripheral surface of the substrate 110 of the master 100 by a film forming device.

[0126] More specifically, it is preferable to use a substrate made of, for example, quartz glass as the substrate 110 of the master 100. The substrate 110 is a roll-shaped substrate having a cylindrical or columnar shape. A resist layer is formed on the outer peripheral surface of this substrate 110 using a resist material.

[0127] The resist layer is formed from an inorganic or organic material capable of forming a latent image by laser light. As the inorganic material, a metal compound containing a transition metal can be used, and preferably, a metal oxide containing one or more transition metals such as tungsten (W) or molybdenum (Mo) can be used. Such inorganic materials can be formed into a resist layer by, for example, a sputtering method. On the other hand, as the organic material, novolac resists or chemically amplified resists can be used. Such organic materials can be formed into a resist layer by, for example, a spin coating method.

[0128] (S20: Exposure Control Signal Generating Step) Next, an exposure control signal corresponding to the concave-convex pattern (exposure pattern) of the fine concave-convex structure 120 of the master 100 is generated by the exposure control device.

[0129] (S30: Exposure step) Furthermore, the exposure device irradiates the resist layer with laser light based on the exposure control signal generated in S20 above. This exposes the resist layer with a predetermined exposure pattern, and forms a latent image corresponding to the fine concave-convex structure 120.

[0130] More specifically, the exposure device irradiates the resist layer with laser light, and the portions of the resist layer irradiated with the laser light are modified. This exposes the resist layer, forming multiple latent images in the resist layer. During this exposure, the laser light as exposure light may be irradiated onto the resist layer continuously or intermittently.

[0131] (S40: Development Step) Next, the resist layer on which the latent image has been formed is developed by a developing device, thereby forming a resist pattern corresponding to the fine concave-convex structure 120 on the resist layer.

[0132] More specifically, the developing device drops a developer onto the resist layer on which the latent image was formed in S30, thereby developing the resist layer. As a result, a resist pattern having a three-dimensional uneven structure is formed on the resist layer. The resist pattern is composed of a plurality of recesses each having a three-dimensional shape. The three-dimensional shapes of the plurality of recesses each correspond to the three-dimensional shapes of each recess 122 in the fine uneven structure 120.

[0133] When the resist layer is a positive resist, the exposed portion exposed to the laser light dissolves faster in a developer compared to the non-exposed portion, and is therefore removed by the development process. As a result, a resist pattern is formed in the resist layer, with the latent image portion of the resist layer removed. On the other hand, when the resist layer is a negative resist, the exposed portion exposed to the laser light dissolves slower in a developer compared to the non-exposed portion, and is therefore removed by the development process. As a result, a resist pattern is formed in the resist layer, with the latent image portion remaining.

[0134] (S50: Etching step) Then, using an etching device, the resist layer on which the resist pattern is formed is used as a mask to etch the outer peripheral surface of the substrate 110 of the master 100. As a result, a concavo-convex pattern corresponding to the fine concavo-convex structure 120 is formed on the outer peripheral surface of the substrate 110.

[0135] More specifically, the outer peripheral surface of the substrate 110 is etched using as a mask the resist layer on which the resist pattern corresponding to the fine concave-convex structure 120 has been formed in S40. As a result, a fine concave-convex structure 120 (convex-convex pattern) consisting of a plurality of recesses 122 is formed on the outer peripheral surface of the substrate 110. The concave-convex shape of the fine concave-convex structure 120 of the master 100 corresponds to the concave-convex shape of the resist pattern, and corresponds to the inverted shape of the three-dimensional shape of the fine concave-convex structure 11 of the transferred object.

[0136] The substrate 110 can be etched by either dry etching or wet etching. For example, when the substrate 110 is made of silica glass (SiO ２ ), a fluorocarbon gas (e.g., CHF ３The substrate 110 can be etched by dry etching using a solvent such as fluorine, or by wet etching using hydrofluoric acid or the like.

[0137] [8.2. Exposure Apparatus and Exposure Method] Next, the exposure apparatus 200 and exposure method used in the manufacturing method of the master 100 according to this embodiment will be described in more detail with reference to Fig. 13. Fig. 13 is an explanatory diagram showing the schematic configuration of the exposure apparatus 200 according to this embodiment.

[0138] 13, the exposure device 200 includes a laser light source 201, a first mirror 203, a photodiode 205, a deflection optical system, a control mechanism 230, a second mirror 213, a movable optical table 220, a spindle motor 225, and a turntable 227. The substrate 110 is placed on the turntable 227 and is rotatable about a central axis 110a.

[0139] The laser light source 201 is a light source that emits laser light 200A, and is, for example, a solid-state laser or a semiconductor laser. The wavelength of the laser light 200A emitted by the laser light source 201 is not particularly limited, but may be, for example, a wavelength in the blue light band of 400 nm to 500 nm. The spot diameter of the laser light 200A (the diameter of the spot irradiated on the resist layer) only needs to be smaller than the diameter of the opening surface of the recess 122 of the microrelief structure 120, and may be, for example, approximately 200 nm. The laser light 200A emitted from the laser light source 201 is controlled by a control mechanism 230.

[0140] A laser beam 200A emitted from a laser light source 201 travels straight as a parallel beam, is reflected by a first mirror 203, and is guided to a deflection optical system.

[0141] The first mirror 203 is configured as a polarizing beam splitter and has the function of reflecting one polarized component and transmitting the other polarized component. The polarized component that has transmitted through the first mirror 203 is received by a photodiode 205 and photoelectrically converted. The photoelectrically converted light reception signal is input to the laser light source 201, and the laser light source 201 performs phase modulation of the laser light 200A based on the input light reception signal.

[0142] The deflection optical system includes a condenser lens 207 , an electro-optic deflector (EOD) 209 , and a collimator lens 211 .

[0143] In the deflection optical system, the laser beam 200A is focused onto an electro-optical deflector 209 by a condenser lens 207. The electro-optical deflector 209 is an element capable of controlling the irradiation position of the laser beam 200A. The exposure apparatus 200 is also capable of changing the irradiation position of the laser beam 200A guided onto the movable optical table 220 by the electro-optical deflector 209 (a so-called wobble mechanism). After the irradiation position of the laser beam 200A is adjusted by the electro-optical deflector 209, the laser beam 200A is collimated again by a collimator lens 211. The laser beam 200A emitted from the deflection optical system is reflected by a second mirror 213 and guided horizontally and parallel onto the movable optical table 220.

[0144] The movable optical table 220 includes a beam expander 221 and an objective lens 223. The laser light 200A guided to the movable optical table 220 is shaped into a desired beam shape by the beam expander 221, and then irradiated onto the resist layer formed on the substrate 110 of the master 100 via the objective lens 223.

[0145] Furthermore, the movable optical table 220 moves by one feed pitch (track pitch) in the direction of arrow 224 (feed pitch direction) along the axial direction of the substrate 110 for each rotation of the substrate 110. The substrate 110 is placed on a turntable 227. A spindle motor 225 rotates the turntable 227, thereby rotating the substrate 110 around the central axis 110a of the cylindrical master 100. By moving the movable optical table 220 in the R direction while rotating the substrate 110 in this manner, the laser beam 200A is irradiated along a spiral trajectory onto the resist layer on the outer peripheral surface of the substrate 110. As a result, a latent image is formed on the resist layer along the spiral irradiation trajectory of the laser beam 200A.

[0146] The control mechanism 230 includes a formatter 231 and a driver 233, and controls the irradiation of the laser light 200A.

[0147] The driver 233 controls the emission of the laser light source 201 based on the exposure signal generated by the formatter 231. Specifically, the driver 233 may control the laser light source 201 so that the output intensity of the laser light 200A increases as the waveform amplitude of the exposure signal increases. The driver 233 may also control the irradiation position of the laser light 200A by controlling the emission timing of the laser light 200A based on the waveform shape of the exposure signal. As the output intensity of the laser light 200A increases, the size and depth of the latent image formed in the resist layer can be increased, and therefore the size and depth of the opening of the recess 122 finally formed in the substrate 110 can be increased.

[0148] Through exposure control by the control mechanism 230, the resist layer on the outer peripheral surface of the substrate 110 of the master 100 is exposed, and a latent image of an arbitrary pattern is formed on the resist layer. The resist layer is then developed, and the outer peripheral surface of the substrate 110 is etched using the developed resist layer as a mask. This makes it possible to form a fine concavo-convex structure 120 having a concavo-convex pattern corresponding to the drawing pattern of the input image on the outer peripheral surface of the substrate 110 of the master 100. Therefore, by preparing a concavo-convex pattern in which the inverted shape of the fine concavo-convex structure 11 of the infrared sensor cover 7, which is the transfer product, is drawn, it is possible to suitably form a fine concavo-convex structure 120 having the inverted shape of the fine concavo-convex structure 11 of the cover 7 on the outer peripheral surface of the master 100.

[0149] 9. Summary The infrared sensor cover 7 according to this embodiment and the optical distance measuring device 1 including the infrared sensor covered by the infrared sensor cover 7 have been described in detail above.

[0150] According to this embodiment, there is provided an infrared sensor cover 7 that covers an infrared sensor that uses infrared rays to measure the distance to a measurement object. The cover 7 according to this embodiment is arranged on the infrared sensor so that infrared rays can be incident on the cover 7 from a direction oblique to the surface of the cover 7. The cover 7 includes a substrate 10 and a fine uneven structure 11 provided on at least one surface of the substrate 10. The fine uneven structure 11 has a plurality of convex portions 12 arranged at a pitch P that is equal to or less than the wavelength λ of infrared rays used in the infrared sensor. In the fine uneven structure 11, the ratio (H / λ) of the height H of the convex portions 12 to the wavelength λ of the infrared rays is 0.5 or greater (first condition: H / λ≧0.5).

[0151] As described above, the surface of the cover 7 according to this embodiment is provided with a microrelief structure 11 as an anti-reflection layer. The height H of the multiple convex portions 12 of this microrelief structure 11 is at least 0.5 times the wavelength λ of the infrared light (H / λ≧0.5), and is adjusted to a height that provides excellent anti-reflection performance against infrared light incident obliquely at a wide angle, for example, about 60°. This significantly improves the anti-reflection performance of the cover 7 against infrared light (particularly near-infrared light) incident obliquely at a wide range of incident angles, including normal incidence (θ=0°) and wide-angle incidence (for example, θ=-60° or more, +60° or less). Therefore, the reflectance of obliquely incident infrared light on the surface of the cover 7 can be significantly reduced to, for example, 3% or less, and the transmittance of infrared light passing through the cover 7 can be significantly increased to, for example, 97% or more. Therefore, infrared light irradiated from the infrared sensor through the cover 7 at a wide angle and reflected infrared light incident on the infrared sensor through the cover 7 at a wide angle can pass through the cover 7 with sufficient transmittance. Therefore, This makes it possible to significantly improve the detection accuracy of an infrared sensor that emits and receives obliquely incident infrared light.

[0152] Furthermore, it is preferable that the ratio (P / λ) of the pitch P of the convex portions 12 to the wavelength λ of the infrared light is 0.5 or less (second condition: P / λ≦0.5).

[0153] This allows the pitch P of the convex portions 12 to be adjusted to an appropriate size according to the wavelength λ of the obliquely incident infrared light. Therefore, the generation of higher-order diffracted light on the surface of the cover 7 can be suppressed, improving the linearity of the obliquely incident infrared light that enters the cover 7. This increases the amount of transmitted light that passes through the cover 7 and heads toward the infrared sensor, as well as the amount of irradiated light that is emitted from the infrared sensor and passes through the cover 7. This increases the amount of light received and emitted by the infrared sensor, further improving the detection accuracy of the infrared sensor.

[0154] Furthermore, the ratio (H / P) of the height H to the pitch P of the convex portions 12 is preferably 3 or less (third condition: H / P≦3). That is, it is preferable that the aspect ratio of the convex portions 12 is 3 or less.

[0155] This allows the ratio (aspect ratio) of the pitch P to the height H of the convex portions 12 of the fine concave-convex structure 11 to be adjusted to a size suitable for imprinting using the roll-shaped master 100. Therefore, during the imprinting, the fine concave-convex structure 11 of the cover 7 can be suitably peeled from the fine concave-convex structure 120 on the outer peripheral surface of the master 100, improving releasability. Therefore, the fine concave-convex structure 11 of a desired shape can be easily formed with high precision without generating defects in the fine concave-convex structure 11.

[0156] Moreover, the infrared rays used in the infrared sensor are preferably near-infrared rays having a wavelength λ of 800 nm or more and 2500 nm or less.

[0157] This makes it possible to suitably apply the cover 7 according to this embodiment to an optical distance measuring device 1 such as LiDAR equipped with a near-infrared sensor that uses near-infrared rays.

[0158] Furthermore, the shape of the convex portions 12 of the fine uneven structure 11 is preferably a substantially elliptical cone shape, an elliptical truncated cone shape, or a bell or dome shape whose planar shape is an ellipse.

[0159] Thus, if the shape of the convex portions 12 is a three-dimensional shape (see FIGS. 6 to 8 ) having an elliptical planar shape (see FIG. 4 ), it becomes easier to efficiently manufacture a microrelief structure 11 having a large number of such convex portions 12. For example, according to the master manufacturing method using the above-described laser exposure method (see FIG. 13 ), the planar shape of the recesses 122 (see FIG. 11 ) of the microrelief structure 120 formed on the outer peripheral surface of the roll-shaped master 100 tends to be elliptical, and it is difficult to make them perfectly circular. Therefore, it is preferable to allow the shape of the convex portions 12 of the microrelief structure 11 of the cover 7 formed using the roll-shaped master 100 to be a three-dimensional shape having an elliptical planar shape. This makes it possible to easily and highly accurately manufacture a microrelief structure 11 having such elliptical convex portions 12 using the master manufacturing method using the laser exposure method.

[0160] When infrared rays used in the infrared sensor are incident on the surface of the infrared sensor cover 7 at an incident angle θ of more than 0° and not more than 60°, the reflectance of the infrared rays is preferably 3% or less.

[0161] As a result, even if the infrared rays are obliquely incident on the cover 7 at a wide range of incident angles θ as described above, the infrared rays can pass through the cover 7 with a high transmittance of 97% or more, thereby further improving the detection accuracy of the infrared sensor.

[0162] Examples of the infrared sensor cover 7 according to the present embodiment will be described below in detail. Note that the following examples are merely examples for illustrating the feasibility and effects of the infrared sensor cover 7 according to the present embodiment, and the present invention is not limited to the following examples.

[0163] In the following examples, a plurality of samples of the infrared sensor cover 7 described in the above embodiment were prepared, and tests were conducted to evaluate the anti-reflection performance of these samples, etc. The test conditions, evaluation methods, and evaluation results are described below.

[0164] [1. Test Conditions] (1) Method for Producing Infrared Sensor Cover In the example, an infrared sensor cover 7 having a fine concave-convex structure 11 formed on the surface was produced by the following steps.

[0165] First, a substrate 110 of a cylindrical master 100 shown in FIG. 11 (see FIG. 11 ) was prepared. Next, a microrelief structure 120 having an inverted shape of the microrelief pattern of the microrelief structure 11 of the cover 7 according to the example was formed on the outer peripheral surface of the substrate 110 of the master 100. Specifically, the resist layer on the outer peripheral surface of the substrate 110 of the master 100 was exposed using the laser exposure method described above (see FIG. 13 ). Next, the substrate 110 was etched using the developed resist layer as a mask to form a microrelief structure 120 having a plurality of recesses 122. In this way, a roll-shaped master 100 having a microrelief structure 120 formed on its outer peripheral surface was produced.

[0166] Next, the master 100 was used to mold the fine relief structure 11 of the cover 7 by a roll-to-roll method. Specifically, using a transfer device 300 such as that shown in FIG. 12 , an uncured resin layer 312 made of an ultraviolet curable resin was laminated on the surface of a film-like substrate 311, and the fine relief structure 120 on the outer peripheral surface of the master 100 was transferred to the uncured resin layer 312. Note that a polyethylene terephthalate (PET) film with a thickness of 60 μm was used as the film-like substrate 311. Next, a metal halide lamp was used to apply 1000 mJ / cm ２ The resin layer 312 made of the ultraviolet curable resin was cured by irradiating it with ultraviolet light of 10 ...

[0167] Next, the transfer product consisting of the resin layer 312 and the film-like substrate 311 was attached to the surface of the substrate 10 of the cover 7 with an adhesive film, thereby producing the cover 7 according to the example. A polycarbonate substrate having a thickness of 2 mm was used as the substrate 10 of the cover 7.

[0168] In this manner, a fine uneven structure 11 having a plurality of convex portions 12 arranged in a hexagonal lattice pattern as shown in Figure 4 was molded by the imprinting method, and a cover 7 was produced in which the fine uneven structure 11 was provided on the surface of the substrate 10.

[0169] In each example described in detail below, the height H and pitch P of the convex portions 12 of the fine concave-convex structure 11 molded as described above were changed. Also, in a comparative example, a cover 7 having a fine concave-convex structure 11 was produced in the same manner as in the above examples, but the height H and pitch P of the convex portions 12 of the fine concave-convex structure 11 were changed to values ​​different from those in the examples.

[0170] (2) Conditions for the height H and pitch P of the convex portions 12 of the fine concave-convex structure 11 Tables 2 and 3 show the conditions for the height H and pitch P of the convex portions 12 of the fine concave-convex structure 11 of the cover 7 according to each example and each comparative example. As shown in Tables 2 and 3, in each example and each comparative example, the height H and pitch P of the convex portions 12 were changed to different values ​​to form the fine concave-convex structure 11. In all cases, the convex portions 12 were arranged in a hexagonal lattice pattern as shown in FIG. 4, the planar shape of the convex portions was elliptical, and the fine concave-convex structure 11 was formed on only one surface of the cover 7.

[0171] Table 2 shows Examples 1 to 8 and Comparative Example 1 in which near-infrared light with a wavelength λ of 905 nm was used as the incident light on the cover 7 (infrared light used in the infrared sensor). On the other hand, Table 3 shows Examples 10 to 13 and Comparative Examples 10 to 13 in which near-infrared light with a wavelength λ of 1550 nm was used as the incident light on the cover 7 (infrared light used in the infrared sensor).

[0172]

[0173]

[0174] [2. Evaluation Method] Tables 2 and 3 also show the results of evaluating the covers 7 according to each example and each comparative example in terms of (1) the anti-reflection effect (reflectance R), (2) the effect of suppressing diffracted light (the effect of increasing the amount of transmitted light), and (3) the releasability during transfer of the fine uneven structure 11. The evaluation methods are as follows.

[0175] (1) Method for Measuring Reflectance R and Evaluation Criteria for Anti-Reflection Effect Figure 14 is a schematic diagram showing a method for measuring reflectance R and diffracted light according to the example. As shown in Figure 14, near-infrared light was incident on the surface of the cover 7 from a direction inclined with respect to the normal direction (Z direction) at an incident angle θi, and the light quantity Qr of specularly reflected light (m = 0) was measured. A semiconductor laser with a wavelength λ = 905 nm or 1550 nm was used as the incident light source. A laser power meter (S122C manufactured by Tholabs) was used as the light quantity measuring device.

[0176] As a procedure for measuring the reflectance, first, the amount of incident light Qi was measured without the cover 7 of the microrelief structure 11 according to each example and comparative example. Next, incident light was made incident on the microrelief structure 11 according to each example and comparative example at an incident angle θi (+10°, +40°, +60° relative to the normal direction), and the amount of reflected light Qr was measured with a laser power meter installed at a reflection angle θr that was the same as the incident angle θi (θ=θi=θr).

[0177] Then, the reflectance R (%) was calculated from the measured amount of incident light Qi and the amount of reflected light Qr using the following formula: R (%) = (Qr / Qi) x 100

[0178] The reflectance R is an index representing the anti-reflection performance of the fine uneven structure 11 on the surface of the cover 7. The lower the reflectance R of obliquely incident light, the higher the anti-reflection performance of the fine uneven structure 11 for obliquely incident light. The following criteria were used to evaluate the reflectance R (anti-reflection performance): Grade A: Reflectance R is 1.0% or less (particularly excellent anti-reflection effect for obliquely incident light) Grade B: Reflectance R is more than 1.0% and 2.5% or less (excellent anti-reflection effect for obliquely incident light) Grade C: Reflectance R is more than 2.5% (poor anti-reflection effect for obliquely incident light)

[0179] (2) Diffracted light measurement method and evaluation criteria for the diffracted light suppression effect Also, as shown in Figure 14, near-infrared light (wavelength λ = 905 nm or 1550 nm) was incident on the surface of the cover 7 from a direction inclined with respect to the normal direction (Z direction) to measure the presence or absence of diffracted light. Specifically, as a procedure for measuring diffracted light, incident light was obliquely incident on the fine uneven structure 11 according to each example and each comparative example at an incident angle θi (+60 °, +70 °, +80 ° with respect to the normal direction), and the power meter was scanned in an angle range of -89 ° to +89 ° with respect to the normal direction to measure the presence or absence of higher-order reflected diffracted light (m = ±1, ±2, ...) other than regular reflected light (m = 0).

[0180] The following criteria were used to evaluate the diffracted light suppression effect (increase in the amount of transmitted light): A rating: No diffracted light was generated (excellent diffracted light suppression effect); C rating: diffracted light was generated (poor diffracted light suppression effect).

[0181] (3) Test and evaluation criteria for demolding properties As described above, a roll-to-roll method using a cylindrical master 100 was used to transfer the fine uneven structure 11 of each example and each comparative example to a resin layer 312 (ultraviolet curable resin) on a substrate 311 (PET film), harden the resin layer 312, and then a test (transfer / mold release test) was conducted in which the hardened resin layer 312 was peeled off from the outer peripheral surface of the master 100.

[0182] As a result, the appearance of the fine concave-convex structure 11 transferred to the resin layer 312 was visually observed, and (a) the presence or absence of defects in the fine concave-convex structure 11, (b) the stability of release of the resin layer 312 from the master 100, and (c) the stability of film tension in the roll-to-roll method were evaluated. The following criteria were used to evaluate the releasability: Rating A: No defects occurred, and release was stable (particularly excellent releasability) Rating B: No defects occurred, but release was unstable, and film tension was unstable (excellent releasability) Rating C: Defects occurred, release was unstable, and film tension was unstable (poor releasability)

[0183] [3. Evaluation Results] (1) Evaluation 1 of the First Condition (H / λ≧0.5) As shown in Table 2, when the wavelength λ of obliquely incident light is 905 nm, in order to satisfy the first condition (H / λ≧0.5), the height H of the convex portions 12 of the fine uneven structure 11 needs to be 452.5 nm or more, which is half the wavelength λ. In this regard, in Examples 1 to 8, the height H of the convex portions 12 is 487 nm or more, which is 0.5 times the wavelength λ or more, and therefore satisfies the first condition (H / λ≧0.5). In contrast, in Comparative Example 1, the height H of the convex portions 12 is 250 nm, which is less than 0.5 times the wavelength λ, and therefore does not satisfy the first condition (H / λ≧0.5).

[0184] As a result, in Comparative Example 1, the reflectance R increases as the incident angle θi of obliquely incident light increases, resulting in a lower evaluation of anti-reflection performance. For example, when θ=+40°, the reflectance R of Comparative Example 1 is 1.89%, and the anti-reflection performance is rated B. Furthermore, when the wide-angle incidence is θ=+60°, the reflectance R of Comparative Example 1 is an extremely high 4.89%, and the anti-reflection performance is rated C.

[0185] In contrast, in Examples 1 to 8, even when the incident angle θi of obliquely incident light increases, the reflectance R hardly increases, and the anti-reflection performance rating remains roughly an A rating. For example, in Examples 1 to 7, the reflectance R is 1.0% or less at all of θ = +10°, +40°, and +60°, ensuring an A rating. Furthermore, in Example 8, the reflectance R = 1.68% (rating B) is significantly lower than the reflectance R = 4.89% (rating C) of Comparative Example 1. Therefore, it can be seen that Example 8 also exhibits significantly improved anti-reflection performance against obliquely incident light at a wide angle (θ = +60°). As described above, in Examples 1 to 8, the reflectance R for the wide-angle obliquely incident light is suppressed to a value sufficiently lower than the reference reflectance (e.g., 3%, preferably 2.5%) described above.

[0186] Furthermore, as shown in Table 3, when the wavelength λ of obliquely incident light is 1550 nm, in order to satisfy the first condition (H / λ≧0.5), the height H of the convex portions 12 needs to be equal to or greater than 775 nm, which is half the wavelength λ. In this regard, in Examples 10 to 13, the height H of the convex portions 12 is equal to or greater than 810 nm, which is equal to or greater than 0.5 times the wavelength λ, and therefore satisfies the first condition (H / λ≧0.5). In contrast, in Comparative Examples 10 to 13, the height H of the convex portions 12 is equal to or less than 520 nm, which is equal to or less than 0.5 times the wavelength λ, and therefore does not satisfy the first condition (H / λ≧0.5).

[0187] As a result, in Comparative Examples 10 to 13, the reflectance R increased as the angle of incidence θi of obliquely incident light increased, resulting in a lower anti-reflection performance rating. For example, in the case of a wide-angle incidence of θ=+60°, the reflectance R of Comparative Examples 10 to 13 was 2.51% to 6.8%, resulting in an anti-reflection performance rating of C. In particular, in Comparative Example 13, because H / λ was very small at 0.16, the reflectance R was high at 3.2% (rating C) even in the case of θ=+40°. Furthermore, in the case of a wide-angle incidence of θ=+60°, the reflectance R was significantly higher at 6.8% (rating C), resulting in a significantly lower anti-reflection performance.

[0188] In contrast, in Examples 10 to 13, although the reflectance R increased somewhat as the incident angle θi of obliquely incident light increased, the anti-reflection performance was rated A or B. For example, even when θ = +60°, the reflectance R of Examples 10 to 13 was 2.11% or less (rated B), which was significantly lower than the reflectance R of Comparative Examples 10 to 14, which was 2.51 to 6.8% (rated C). As described above, even in Examples 10 to 13, the reflectance R for the wide-angle obliquely incident light was suppressed to a value sufficiently lower than the above-mentioned reference reflectance (e.g., 3%, preferably 2.5%).

[0189] The above comparison results demonstrate that when the height H and wavelength λ of the convex portions 12 satisfy the first condition (H / λ≧0.5), the anti-reflection effect against obliquely incident near-infrared light can be improved over a wide range of incident angles θ. In particular, it can be demonstrated that the anti-reflection effect against obliquely incident light at a wide angle, for example, about 60°, can be significantly improved. Therefore, when the first condition (H / λ≧0.5) is satisfied, the transmittance of obliquely incident near-infrared light passing through the cover 7 can be increased, thereby improving the detection accuracy of the infrared sensor.

[0190] (2) Evaluation 2 of the second condition (P / λ≦0.5) As shown in Table 2, when the wavelength λ of obliquely incident light is 905 nm, in order to satisfy the second condition (P / λ≦0.5), the pitch P of the convex portions 12 of the fine uneven structure 11 must be 452.5 nm or less, which is half the wavelength λ. In this regard, in Examples 1 to 7, the pitch P of the convex portions 12 is 450 nm or less, which is 0.5 times the wavelength λ or less, and therefore satisfies the second condition (P / λ≦0.5). In contrast, in Example 8, the pitch P of the convex portions 12 is 500 nm, which is 0.5 times the wavelength λ or more, and therefore does not satisfy the second condition (P / λ≦0.5).

[0191] As a result, in Example 8, reflected diffracted light (m = ±1, ±2) was generated on the surface of the convex portions 12 of the fine concave-convex structure 11, as shown in Figure 14. Therefore, in Example 8, the obliquely incident light incident on the fine concave-convex structure 11 was bent, the straightness of the obliquely incident light was reduced, and the transmittance of the obliquely incident light passing through the cover 7 was reduced. As a result, in Example 8, the effect of suppressing diffracted light was rated C.

[0192] In contrast, in Examples 1 to 7, no reflected diffracted light (m = ±1, ±2) was generated on the surface of the convex portions 12 of the fine concave-convex structure 11. In Examples 1 to 7, the linearity of the obliquely incident light incident on the fine concave-convex structure 11 did not decrease, and there was no decrease in the transmittance of the obliquely incident light passing through the cover 7. As a result, Examples 1 to 7 were excellent in the suppression effect of diffracted light, and were rated A.

[0193] The above comparison results demonstrate that the effect of suppressing diffracted light from obliquely incident near-infrared light can be improved over a wide range of incident angles θ when the pitch P of the convex portions 12 and the wavelength λ satisfy the second condition (P / λ≦0.5). Therefore, if the second condition (P / λ≦0.5) is satisfied, the transmittance of obliquely incident near-infrared light that passes through the cover 7 can be further increased, and the detection accuracy of the infrared sensor can be further improved.

[0194] (3) Evaluation 3 of the third condition (H / P≦3) As shown in Tables 2 and 3, in Examples 1 to 6, 8 and 10 to 12, the ratio of the height H to the pitch P of the convex portions 12 (i.e., aspect ratio = H / P) was 2.8 or less, satisfying the third condition (H / P≦3). In contrast, in Examples 7 and 13, the aspect ratio was 3.52, which did not satisfy the third condition (H / P≦3).

[0195] As a result, in Examples 7 and 13, when imprinting was performed to transfer the fine uneven structure 11 using a roll-to-roll method using a roll-shaped master 100, defects occurred in the convex portions 12 of the fine uneven structure 11, the mold release was unstable, and the film tension was unstable, so the mold release performance was rated C.

[0196] In contrast, in Examples 1 to 3, 5, 6, 8 and 11 and 12, when the above imprinting was performed, no defects occurred in the convex portions 12 of the fine concave-convex structure 11, and both the mold release and the film tension were stable, so the releasability was evaluated as an A. Furthermore, in Examples 4 and 10, when the above imprinting was performed, no defects occurred in the convex portions 12 of the fine concave-convex structure 11, but the mold release and the film tension were somewhat unstable, so the releasability was evaluated as a B.

[0197] From the above comparison results, it can be said that it has been demonstrated that when the ratio of the height H to the pitch P of the convex portions 12 (i.e., aspect ratio = H / P) satisfies the third condition (H / P≦3), it is possible to improve the mold releasability during imprinting and prevent the occurrence of defects in the convex portions 12 of the microrelief structure 11. Furthermore, it can be said that it has been demonstrated that when the condition that the aspect ratio is 2.8 or less (H / P≦2.8) is met, as in Examples 1 to 3, 5, 6, 8 and 11 and 12, in addition to the effect of preventing the occurrence of defects in the convex portions 12 during imprinting, it is possible to stabilize the mold release and film tension during imprinting, thereby further improving the mold releasability.

[0198] While the present invention has been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present invention.

[0199] REFERENCE SIGNS LIST 1 Optical distance measuring device (infrared sensor) 2 Light irradiation device 3 Light detection device 4 Controller 5 Distance measurement target area 6 Measurement target object 7 Infrared sensor cover 10 Substrate 11 Fine concave-convex structure 12 Convex portion 13 Convex portion 100 Master 110 Substrate 120 Fine concave-convex structure 122 Convex portion 123 Convex portion 300 Transfer device 311 Substrate 312 Resin layer

Claims

1. An infrared sensor cover that covers an infrared sensor that uses infrared rays to measure the distance to a measurement object, comprising: a base material; and a fine uneven structure provided on at least one surface of the base material, the fine uneven structure having a plurality of convex portions arranged at a pitch P that is equal to or less than the wavelength λ of the infrared rays, wherein the infrared sensor cover is positioned on the infrared sensor so that the infrared rays can enter the infrared sensor cover from a direction inclined with respect to the surface of the infrared sensor cover, and the ratio (H / λ) of the height H of the convex portions to the wavelength λ is 0.5 or greater.

2. The infrared sensor cover according to claim 1, wherein the ratio (P / λ) of the pitch P of the convex portions to the wavelength λ is 0.5 or less.

3. The infrared sensor cover according to claim 1, wherein the ratio (H / P) of the height H of the convex portions to the pitch P is 3 or less.

4. The cover for an infrared sensor according to claim 1, wherein the infrared rays are near-infrared rays having a wavelength λ of 800 nm or more and 2500 nm or less.

5. The infrared sensor cover according to claim 1, wherein the shape of the convex portion is substantially an elliptical cone shape, an elliptical truncated cone shape, or a bell shape or dome shape whose planar shape is an ellipse.

6. An infrared sensor cover as described in claim 1, wherein the reflectance of the infrared rays when the infrared rays are incident on the surface of the infrared sensor cover at an incident angle of more than 0° and not more than 60° is 3% or less.

7. An infrared sensor comprising: an infrared sensor cover according to any one of claims 1 to 6; a light irradiation device that irradiates an infrared laser beam through said infrared sensor cover towards an object to be measured; and a light detection device that detects the infrared light reflected by said object to be measured through said infrared sensor cover.

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