WO2025173365A1 - Infrared sensor cover and infrared sensor - Google Patents

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

The present invention relates to an infrared sensor cover and an infrared sensor.
This application claims the benefit of priority based on Japanese Patent Application No. 2024-019704, filed on February 13, 2024, the contents of which are incorporated herein by reference.

In recent years, in the automotive sector and elsewhere, technology has become widespread that detects the distance and relative speed between a vehicle and an obstacle (object being measured) by emitting infrared light (especially near-infrared light) from an infrared sensor toward the area around the vehicle and detecting the infrared light reflected off the obstacle (object being measured), such as a preceding vehicle or pedestrian. For example, optical ranging devices that utilize infrared remote sensing technology such as LiDAR (Light Detection and Ranging) are used.

Infrared sensors generally have a cover around the sensor body to protect it. Glass or resin is often used as the material for infrared sensor covers. However, simply using glass or resin can result in infrared rays being reflected from the cover surface, resulting in insufficient infrared transmittance through the cover and potentially degrading the performance of the infrared sensor. For this reason, Patent Document 1, for example, proposes an infrared sensor cover with an anti-reflection layer on the cover surface to prevent infrared rays from being reflected.

JP 2018-124279 A

However, even the conventional infrared sensor cover described in Patent Document 1 above was unable to sufficiently suppress the reflection of obliquely incident infrared rays when they were incident on the cover surface at an angle (hereinafter referred to as "oblique incidence"), resulting in a problem of reduced infrared transmittance. Particularly in systems that use infrared sensors to scan and detect infrared rays at a wide angle (e.g., 60°), the deterioration in transmittance of infrared rays that were obliquely incident on the cover surface was significant, causing a decrease in the detection accuracy of the infrared sensor. For this reason, there has been a demand for a cover that provides excellent anti-reflection performance for infrared rays (particularly near-infrared rays) that are obliquely incident over a wide range of angles, including wide-angle incidence (e.g., -60° to +60°), and that improves the detection accuracy of infrared sensors.

The present invention was made in consideration of the above problems, and its object 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.

In order to solve the above problem, according to one aspect of the present invention,
An infrared sensor cover for covering an infrared sensor that measures the distance to a measurement object using infrared rays,
A substrate;
a fine concave-convex structure provided on at least one surface of the base material and having a plurality of convex portions arranged at a pitch P equal to or less than the wavelength λ of the infrared ray;
Equipped with
the infrared sensor cover is disposed on the infrared sensor so that the infrared ray can be incident on the infrared sensor cover from a direction inclined with respect to the surface of the infrared sensor cover,
The infrared sensor cover has a ratio (H/λ) of the height H of the convex portion to the wavelength λ of 0.5 or more.

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

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

The infrared rays may be near-infrared rays with a wavelength λ of 800 nm or more and 2500 nm or less.

The shape of the convex portion may be substantially an elliptical cone shape, an elliptical truncated cone shape, or a bell or dome shape with an elliptical planar shape.

The reflectance of the infrared rays may be 3% or less when the infrared rays are incident on the surface of the infrared sensor cover at an angle of incidence greater than 0° and less than 60°.

In order to solve the above problems, according to another aspect of the present invention,
The infrared sensor cover;
a light irradiation device that irradiates an infrared laser beam toward a measurement object through the infrared sensor cover;
a light detection device that detects the infrared light reflected by the object to be measured through the infrared sensor cover;
An infrared sensor is provided, comprising:

The present invention can improve anti-reflection performance against infrared light that is obliquely incident over a wide range of angles of incidence, including wide angles of incidence.

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 the infrared sensor cover according to the embodiment. FIG. 3 is a cross-sectional view showing an infrared sensor cover according to a modified example of the embodiment. FIG. 4 is a plan view showing the arrangement of a plurality of convex portions of the fine concave-convex structure according to the embodiment. FIG. 5 is a plan view showing the arrangement of a plurality of convex portions of a fine concave-convex structure according to a modified example of the embodiment. FIG. 6 is a perspective view showing an example of a convex portion of the fine concave-convex structure according to the embodiment. FIG. 7 is a perspective view showing an example of a convex portion of the fine concave-convex structure according to the embodiment. FIG. 8 is a perspective view showing an example of a convex portion of the fine concave-convex structure according to the embodiment. FIG. 9 is a partially enlarged cross-sectional view showing the fine concave-convex structure according to the embodiment. FIG. 10 is a graph showing the results of a simulation of the relationship between the height of the convex portions of the fine concave-convex structure according to the embodiment, the angle of incidence, and the reflectance. FIG. 11 is a perspective view schematically showing the master according to the same embodiment. FIG. 12 is a schematic diagram showing the configuration of a transfer device that produces a transfer product using the master according to the same embodiment. FIG. 13 is an explanatory diagram showing the schematic configuration of an exposure apparatus according to the same embodiment. FIG. 14 is a schematic diagram showing a method for measuring reflectance and diffracted light according to an example.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in these embodiments are merely examples to facilitate understanding of the invention and do not limit the present invention unless otherwise specified. Furthermore, in this specification and drawings, elements having substantially the same function and configuration are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[1. Overall configuration of optical distance measuring 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.

As shown in FIG. 1, the optical ranging device 1 equipped with an infrared sensor according to this embodiment is a device that irradiates light toward a ranging area 5 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 ranging device 1 is equipped with a ranging sensor (infrared sensor) that uses remote sensing technology such as LiDAR. The ranging method used by the optical ranging 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 ranging methods, such as triangulation, may also be used. The time of flight (TOF) of light is the round-trip time between when the optical ranging device 1 emits irradiated light and when it receives reflected light.

The optical ranging device 1 according to this embodiment can be applied to various technical fields that utilize remote sensing. For example, the optical ranging device 1 can be used in autonomous driving technology in the automotive field, radar equipment for ADAS (Advanced Driver-Assistance Systems) or traffic enforcement, surveying in the construction field, surveying using aircraft or satellites, vacuum cleaner robots, 3D mapping measurements on various terminal devices (smartphones, smart glasses, smartwatches, 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.

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 or ADAS. In this case, the optical distance measuring device 1 can measure the distance and direction to a measurement object 6 present in the space around the vehicle, particularly in front of the vehicle, and can create 3D mapping. However, the 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.

As shown in FIG. 1, the 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.

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 emitted from the light irradiation device 2 is laser light having an infrared wavelength band (wavelength: approximately 700 nm to 1000 μm). Examples of infrared laser light that can be used include laser light having wavelength bands such as near-infrared (wavelength: approximately 700 nm to 2500 nm), mid-infrared (wavelength: approximately 2.5 μm to 4 μm), and far-infrared (wavelength: approximately 4 μm to 1000 μm). 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.

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, and a housing (all not 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 change the irradiation direction of the pulsed laser light emitted from the light source, thereby irradiating the laser light so as to scan the distance measurement target area 5 at a wide angle.

The light detection device 3 is a device (receiver) for detecting infrared light (reflected light) emitted from the light irradiation device 2 and reflected by the object to be measured 6. The light detection device 3 includes, for example, an optical filter and a light receiving unit equipped with a light receiving element (neither of which are shown). The optical filter cuts out light other than the reflected light reflected by the object to be measured 6 (for example, 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 measurement object 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.

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

The processor may be, 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 executed, and various functions defined by the programs to be realized.

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 the 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 performed by the processor. Programs stored in ROM are read into RAM and executed by a processor such as a CPU.

The controller 4 controls the light irradiation device 2 and 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 scanning the distance measurement target area 5 three-dimensionally 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 of laser light by the light irradiation device 2 and the detection of reflected light by the light detection device 3 (i.e., the time of flight of light: TOF).

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 located within the distance measurement target area 5. To achieve this, the optical distance measuring device 1 is required to emit 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 as a distance measuring sensor will be narrow if left as is. For this reason, it is preferable to diffuse the laser light using a diffuser or the like, and then emit the diffused light toward the distance measurement target area 5 over a wide field of view, thereby expanding the irradiation area.

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

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

[2. Overview of the infrared sensor cover]
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.

The cover 7 is arranged to cover both or either the light-emitting surface and the light-receiving surface of the sensor body of the infrared sensor. For example, the cover 7 shown in Figure 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.

Note that the shape and arrangement of the cover 7 are not limited to the example shown in Figure 1. For example, the cover 7 may be configured as a curved plate-like cover rather than a flat plate-like cover. Furthermore, multiple covers 7 may be provided for one infrared sensor, and the light-emitting surface of the light irradiation device 2 and the light-receiving surface of the light detection device 3 may each be individually covered by these multiple covers 7.

The cover 7 is made of a material that is transmissive to the infrared rays used in the infrared sensor, and is particularly suitable for transmitting near-infrared rays. This allows the infrared laser light emitted from the infrared sensor's light irradiation device 2 to pass through the cover 7 from the inside to the outside. 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.

As such, in the optical distance measuring device 1 (infrared sensor) of this embodiment, the sensor body, that is, the light irradiation device 2 and light detection device 3, are covered by the cover 7. The light irradiation device 2 then 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 object to be measured 6. Meanwhile, when the emitted infrared laser light is reflected by the object to be measured 6 and returns from the front and oblique directions of the optical distance measuring device 1, the light detection device 3 receives and detects the reflected light through the cover 7.

As described above, infrared laser light and its reflected light are incident on the cover 7 of the infrared sensor of this embodiment from both the inside and outside. Furthermore, in the optical distance measuring device 1 (infrared sensor) of 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 incident obliquely 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 (negative X-axis direction) relative to the normal direction (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 obliquely incident light is incident from a direction tilted to the other side (positive X-axis direction) with respect to the normal direction (Z direction) of the surface of the cover 7.

As such, when infrared laser light, which has a wavelength longer than visible light, is obliquely incident on an infrared sensor cover at a wide incident angle θ (for example, approximately 60°), conventional covers are unable 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 falls to, for example, less than 97%, resulting in a problem of reduced detection accuracy of the infrared sensor.

The infrared sensor and cover 7 of this embodiment therefore 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 angles of incidence, including normal incidence and wide-angle incidence (for example, -60° or more and +60° or less), and to improve the detection accuracy of the infrared sensor through the cover 7. To this end, the surface of the cover 7 of 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 of this embodiment are described in detail below.

[3. Configuration of the infrared sensor cover]
Next, the configuration of the infrared sensor cover 7 according to this embodiment will be described with reference to Figures 2 and 3. Figure 2 is a cross-sectional view showing the infrared sensor cover 7 according to this embodiment. Figure 3 is a cross-sectional view showing the infrared sensor cover 7 according to a modified example of this embodiment.

As shown in Figure 2, the infrared sensor cover 7 includes a substrate 10 and a micro-relief structure 11.

The substrate 10 is the base material that constitutes the main body of the cover 7. The substrate 10 is a plate- or sheet-shaped substrate. The substrate 10 is, for example, flat, but it may also be curved, as long as it is a plate-shaped substrate that is 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.

The substrate 10 is formed, for example, from an inorganic material such as glass, or an organic material such as resin. The material of the substrate 10 is preferably a resin with excellent infrared transmittance (e.g., thermoplastic resin, photocurable resin, etc.) 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 from 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.

The micro-relief structure 11 is a micro-relief structure (moth-eye structure) formed on the surface of the substrate 10. The micro-relief structure 11 has the function of preventing infrared light from being reflected on the surface of the cover 7 (anti-reflection function).

As shown in Figures 2 and 3, the micro-relief structure 11 is provided on at least one surface of the substrate 10. In the example of Figure 2, the micro-relief 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 micro-relief structure 11 is provided on only one surface of the substrate 10 (i.e., the front surface 10A).

The micro-relief structure 11 has multiple convex portions 12 and multiple concave portions 13. The convex portions 12 are protruding structures that protrude vertically 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, on the order of several tens of nanometers to several tens of micrometers, preferably on the order of several hundred nanometers to several micrometers (nanometer order), and are therefore very fine.

In order for the fine uneven structure 11 to exhibit its infrared anti-reflection function, 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 light 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 light used in the infrared sensor. For example, if the infrared light used in the infrared sensor is near-infrared light and the wavelength λ of this near-infrared light is in the range of 800 nm or more and 2500 nm or less, the pitch P of the convex portions 12 is preferably equal to or less than the wavelength λ of the near-infrared light. 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 Figure 4).

In this embodiment, by providing the surface of the cover 7 with a fine uneven structure 11 consisting of multiple protrusions 12 arranged at such a fine pitch P, a moth-eye structure with excellent infrared anti-reflection performance can be formed on the surface of the cover 7. This creates 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.

As shown in Figure 2, by forming a micro-relief structure 11 on both surfaces (surface 10A and back surface 10B) of the substrate 10, it is possible to suppress reflection of infrared rays on surface 10A and back surface 10B of the substrate 10. Therefore, as shown in Figure 1, in an infrared sensor where infrared rays (irradiated light, reflected light) are incident on cover 7 from both the front and back sides of the cover 7, it is preferable to suppress reflection of infrared rays incident on both surfaces of the cover 7 by providing a micro-relief structure 11 on both surfaces (surface 10A and back surface 10B) of the substrate 10 of the cover 7, as shown in Figure 2.

Also, as shown in Figure 3, the micro-relief structure 11 may be formed on only one surface (surface 10A) of the substrate 10, and not on the other surface (back surface 10B). This also makes it possible to suppress reflection of infrared rays on surface 10A of the substrate 10, and to suppress reflection of infrared rays on one surface of the cover 7. Although not shown, the micro-relief structure 11 may be formed on one surface of the substrate 10, and a multi-layer anti-reflection film may be formed on the other surface.

[4. Configuration of the fine uneven 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.

The multiple convex portions 12 of the micro-relief structure 11 may be arranged regularly or irregularly on the surface of the substrate 10. Figure 4 shows an example in which multiple convex portions 12 having an elliptical planar shape are arranged regularly. Figure 5 shows an example in which multiple convex portions 12 having a circular planar shape are arranged regularly.

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 plurality of convex portions 12 are arranged at a predetermined interval (dot pitch P _D ) along a plurality of tracks T extending in the X direction. The tracks T are imaginary lines representing the arrangement direction of the convex portions 12. The plurality of tracks T are parallel to each other and arranged at a predetermined interval (track pitch P _T ) in the Y direction.

Here, the dot pitch _PD 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 _PD is the distance between the vertices of two convex portions 12 adjacent to each other in the track direction (X direction). The dot pitch _PD is equal to the pitch P ( _PD = P). On the other hand, the track pitch _PT is the pitch of the convex portions 12 along the track perpendicular direction (Y direction) _, which is perpendicular to the track direction (X direction). The track pitch PT is equal to the distance between two tracks T adjacent to each other in the track perpendicular direction (Y direction). As shown in FIG. 4, when the convex portions 12 are arranged in a hexagonal lattice pattern, the track pitch _PT is smaller than the pitch P ( _PT < P). Although not shown, when the convex portions 12 are arranged in a square lattice pattern, the dot pitch _PD and the track pitch _PT are equal to the pitch P ( _PD = _PT = P).

As shown in Figures 4 and 5, the multiple convex portions 12 are regularly arranged in a hexagonal lattice pattern along the multiple tracks T. Therefore, between any two arbitrarily selected convex portions 12, the dot pitch P _D is approximately constant, and the track pitch P _T is also approximately constant. Furthermore, when comparing two rows of convex portions 12 arranged along two tracks T adjacent to each other in the Y direction, the X-direction arrangement of the convex portions 12 in one row is shifted in the X direction by half the dot pitch P _D (P _D /2) relative to the convex portions 12 in the other row. By shifting the convex portions 12 in the X direction by P _D /2 for each track T in this way, the multiple convex portions 12 are regularly arranged in a hexagonal lattice pattern throughout the entire fine concave-convex structure 11. This allows the convex portions 12 to be closely packed on the surface of the substrate 10, thereby increasing the packing rate of the convex portions 12. Therefore, the anti-reflection performance of the fine concave-convex structure 11 per unit area of the surface of the substrate 10 can be improved.

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 Figure 4, when the multiple convex portions 12 are arranged on the surface (flat surface) of the substrate 10 with some gaps between them and there are flat surfaces in the recesses 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 Figure 4, it is preferable to minimize the gaps and increase the filling rate to, for example, 80% or more, and preferably 90% or more. This improves the anti-reflection performance of the micro-relief structure 11.

Furthermore, as shown in Figures 4 and 5, the micro-relief structure 11 preferably has a hexagonal lattice arrangement on the surface of the substrate 10, in which multiple protrusions 12 are arranged at the vertices and centers of hexagons. This allows the multiple protrusions 12 to be arranged so as to be closely packed on the surface of the substrate 10 (on the XY plane), improving the anti-reflection performance of the moth-eye structure. However, the multiple protrusions 12 of the micro-relief structure 11 are not limited to the above-mentioned hexagonal lattice example, and may be arranged regularly in other manners, such as a square lattice, rectangular lattice, or triangular lattice. Alternatively, the multiple protrusions 12 may be arranged irregularly 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 arranged irregularly at positions randomly deviated from the reference position within a predetermined range of variation.

[4.1. Preferred range of pitch P of convex portions]
The pitch P of the convex portions 12 may be, for example, the arithmetic mean value of the pitches (dot pitch P _D or track pitch P _T ) of multiple pairs of adjacent convex portions 12, 12. For example, multiple pairs of two convex portions 12, 12 adjacent to each other in the track direction (X direction) are picked up, and the dot pitch P _D of these multiple pairs of convex portions 12, 12 is calculated or measured. Then, the arithmetic mean value of the multiple calculated or measured dot pitches P _D may be found, and this arithmetic mean value may be used as the pitch P.

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

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, although the lower limit of the pitch P is not particularly limited, it is preferably 100 nm or more from the viewpoint of stably forming the fine uneven structure 11. 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 sizes of the dot pitch _PD and the track pitch _PT may be the same or different, as long as they are within the preferred range of the pitch P described above.

[4.2. Preferred shape of the protrusion 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).

From the standpoint of ease of molding the convex portions 12, it is preferable that the three-dimensional shape of the convex portions 12 be a three-dimensional shape whose planar shape is substantially elliptical (see Figure 4). Specifically, it is preferable that the three-dimensional shape of the convex portions 12 be a substantially elliptical cone shape (see Figure 6), an elliptical truncated cone shape with a flat top (see Figure 7), or a bell or dome shape whose planar shape is elliptical (see Figure 8).

As such, the three-dimensional shape of the convex portions 12 is preferably a shape such as an elliptical cone, which is a cone shape stretched or shrunk in the track direction (X direction). If the convex portions 12 have a three-dimensional shape with an elliptical planar shape (see FIG. 4), it becomes easier to efficiently manufacture a fine uneven structure 11 having a large number of such convex portions 12. For example, in a manufacturing method of a master 100 using a laser exposure method (described later) (see FIG. 13), the planar shape of the recesses 122 (see FIG. 11) of the fine uneven 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 fine uneven structure 120 of this master 100 have an inverted shape of the convex portions 12 of the fine uneven structure 11 of the cover 7. Therefore, it is preferable to allow the shape of the convex portions 12 of the fine uneven structure 11 formed using the roll-shaped master 100 to have a three-dimensional shape with an elliptical planar shape. This makes it possible to easily and highly accurately manufacture the fine concave-convex structure 11 with the elliptical convex portions 12 using a master manufacturing method that uses this laser exposure method.

In this specification, "substantially elliptical" is not limited to a geometrically strict elliptical shape, but includes shapes that can be roughly regarded as ellipses, such as ovals and ovals. 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 includes 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 truncated cone shape in the track direction (X direction)).

[4.3. Materials of the Micro-Relief Structure]
As will be described in detail later, the fine uneven structure 11 is formed, for example, by roll-to-roll imprinting using a roll master. The uneven shape formed on the outer peripheral surface of the roll master has an inverted shape of the fine uneven structure 11. The uneven shape on 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 fine uneven structure 11. In this way, by using the roll master to transfer the fine uneven 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 fine uneven 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 fine uneven structure 11 is formed is made of, for example, a cured product of a curable resin.

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 cures in the presence of a curing initiator. Examples of polymerizable compounds include epoxy polymerizable compounds and acrylic polymerizable compounds. Epoxy polymerizable compounds are monomers, oligomers, or prepolymers that have one or more epoxy groups in their molecules. Examples of epoxy polymerizable compounds 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.

Acrylic polymerizable compounds are monomers, oligomers, or prepolymers that have one or more acrylic groups in their molecules. Here, monomers are further classified into monofunctional monomers that have one acrylic group in their molecules, bifunctional monomers that have two acrylic groups in their molecules, and polyfunctional monomers that have three or more acrylic groups in their molecules.

"Monofunctional monomers" include, for example, carboxylic acids (acrylic acid), hydroxyl groups (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.

Examples of "bifunctional monomers" include tri(propylene glycol) diacrylate, trimethylolpropane diallyl ether, and urethane acrylate.

Examples of "polyfunctional monomers" include trimethylolpropane triacrylate, dipentaerythritol penta- and hexaacrylate, and ditrimethylolpropane tetraacrylate.

Other examples of acrylic polymerizable compounds besides 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, acrylic polymerizable compounds are preferred as the polymerizable compound.

A curing initiator is a material that hardens a curable resin. Examples of curing initiators include heat-curing initiators and photo-curing initiators. The curing initiator may also be one that hardens due to heat, some kind of energy beam other than light (e.g., electron beam), etc. 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.

Here, from the perspective of the transparency of the cover 7, it is preferable that the curing initiator be an ultraviolet curing initiator. Therefore, it is preferable that the curable resin be an ultraviolet curing acrylic resin. An 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.

Furthermore, the resin forming the micro-relief structure 11 may be a resin that has been given functionality such as hydrophilicity, water repellency, and anti-fogging properties.

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 fine metal oxide particles such _{as SiO2} , _TiO2 , _ZrO2 , _SnO2 , and _Al2O3 .

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

[5. Characteristics of height H and pitch P of convex portions of fine concave-convex structure]
Next, features relating to 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.

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") that is incident from an oblique direction relative to the surface (XY plane) of the substrate 10. The fine uneven structure 11 has a plurality of convex portions 12 regularly arranged at a predetermined pitch P on the surface of the substrate 10. Each convex portion 12 protrudes so as to extend perpendicularly (Z direction: normal direction) to the surface of the substrate 10. The height H of a convex portion 12 is the length in the normal direction (Z direction) from the base to the apex of the convex portion 12. The pitch P of the convex portions 12 is the distance between the apexes of adjacent convex portions 12, 12 on the XY plane.

From the viewpoint of uniform infrared transmittance and light distribution in the cover 7, it is preferable that the heights H of the multiple protrusions 12 are the same and that the pitch P of the protrusions 12 is uniform, as in the example shown in Figure 9. However, this is not limited to this example, and the heights H of the multiple protrusions 12 may be uneven within a predetermined error range. The pitch P of the protrusions 12 may also be uneven within a predetermined error range.

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 causes the micro-relief structure 11 to function as a moth-eye structure that suppresses the reflection of infrared light of that wavelength λ, thereby suppressing the reflection of infrared light of that wavelength λ on the surface of the cover 7.

[5.1. Ratio of height H of convex portion to wavelength λ (first condition)]
Here, as a first condition for the fine concave-convex structure 11 according to this embodiment, the condition for the height H of the convex portions 12 will be described.

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)

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 micro-relief structure 11 against obliquely incident light 31 over a wide range of incident angles θ (e.g., θ = -60° to +60°), including wide angles of incidence (e.g., 45° or greater). The reasons for this are explained below.

In this embodiment, a fine uneven structure 11 (moth-eye structure) in which multiple minute protrusions 12 are arranged at a pitch P that is equal to or less than the wavelength λ of the incident infrared light 31 is formed on the surface of the base material 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 increase the anti-reflection effect of the fine uneven structure 11 on 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 a predetermined other height.

The inventors therefore conducted simulations using RCWA (Rigorous Coupled-Wave Analysis) and conducted extensive research into the relationship between the anti-reflection effect for obliquely incident light, particularly wide-angle obliquely incident light 31, and the height H of the convex portions 12. As a result, they 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 for obliquely incident light 31 can be improved, and that the improvement in the anti-reflection effect becomes particularly significant as the incident angle θ of the obliquely incident light 31 increases. Based on this finding, the 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 micro-relief structure 11 that satisfies this first condition.

By having the micro-relief 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 from the surface of the cover 7 can be reduced and the transmitted light 33 transmitted through the cover 7 can be increased. This reduces the reflectance of obliquely incident light 31 on the surface of the cover 7 to, for example, 3% or less, preferably 2.5% or less, and increases the transmittance of obliquely incident light 31 transmitted through the cover 7 to, for example, 97% or more, preferably 97.5% or more. Therefore, compared to conventional technology, the cover 7 having the micro-relief structure 11 according to this embodiment significantly improves anti-reflection performance against infrared light (particularly near-infrared light) that is obliquely incident at a wide range of incident angles θ (e.g., -60° to +60°), including wide-angle incidence, and reduces the reflectance of wide-angle obliquely incident light 31 to 3% or less. This significantly improves the detection accuracy of an infrared sensor covered with the cover 7 according to this embodiment.

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

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)

By satisfying formula (2), the amount of infrared incident light 31 that passes through the cover 7 can be increased. Therefore, the amount of light received by the infrared sensor covered by the cover 7 and the amount of light emitted from the infrared sensor can be increased, improving the detection accuracy of the infrared sensor. The reasons for this are explained below.

Generally, when a periodic micro-relief structure is provided on the surface of an optical element, higher-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 Figure 14). However, if 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.

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.

In contrast, with the micro-relief structure 11 according to 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, 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.

Furthermore, by satisfying both the first condition (H/λ≧0.5) and the second condition (P/λ≦0.5), it is possible to achieve a fine uneven structure 11 that has excellent anti-reflection effects against wide-angle oblique incident light 31 and excellent effects in suppressing diffracted light.

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

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)

By satisfying formula (3), when the fine relief structure 11 is formed on the surface of the cover 7 by imprinting using a master, the releasability can be improved when peeling the master from the cover 7 to which the fine relief structure 11 has been transferred. Therefore, the fine relief structure 11 can be formed easily and with high precision by imprinting using a master.

In other words, if the pitch P of the convex portions 12 that make up 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) will be too large. This reduces the releasability during the imprinting process, making it difficult to manufacture the fine concave-convex structure 11.

In contrast, with the fine concave-convex structure 11 according to 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 demolding during the imprinting process, and makes it possible to easily and accurately mold the fine concave-convex structure 11 into the desired shape without generating defects in the fine concave-convex structure 11.

5.4. Simulation Results
Next, referring to Fig. 10, in order to verify the anti-reflection effect under the first condition (H/λ≧0.5) regarding 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 incident angle θ [°] will be described. Fig. 10 is a graph showing the simulation results.

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 the convex portion 12: 200 nm, 300 nm, 500 nm, 650 nm
Vertical cross-sectional shape of the protrusions 12: Approximate parabola Planar shape of the protrusions 12: Circular Planar arrangement of the protrusions 12: Hexagonal lattice (see FIG. 5 ).
Pitch P of the convex portions 12: 300 nm
Refractive index of the material of the convex portion 12: 1.5
Refractive index of air: 1.0

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, obtained through this simulation. This relationship is also shown in the graph in Figure 10.

As shown in Table 1 and Figure 10, regardless of the height H of the convex portion 12, the reflectance R increases as the angle of incidence θ of obliquely incident light increases. However, when H = 500 nm and 650 nm, the absolute value and rate of increase of reflectance R are suppressed to lower values compared to when H = 200 nm and 300 nm. For example, when θ = 60°, the reflectance R is 6.14% and 3.52%, respectively, when H = 200 nm and 300 nm, which significantly exceeds 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, the reflectance R is 1.14% and 1.41%, respectively, when H = 500 nm and 650 nm, which is significantly 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 approximately 60° is excellent. The reference reflectance is the upper limit of the reference reflectance required for covers for infrared sensors used in vehicle-mounted LiDAR, etc. (e.g., 3%, preferably 2.5%).

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) and H/λ is equal to or greater than 0.5, then the reflectance R of obliquely incident light over a wide range (10° to 60°), including wide-angle incidence of approximately 60°, can be suppressed to 3% or less, preferably 1.5% or less, and therefore the anti-reflection effect for such obliquely incident light can be said to be significantly superior.

[6. Master Configuration]
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.

The master 100 is a mold for transferring the 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 perspective of efficiently producing the transfer object, the master 100 is preferably a roll-shaped master having a cylindrical or columnar shape, but it 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 for the production of transfer objects onto which the fine relief structure 120 of the master 100 has been transferred with high production efficiency.

As shown in Figure 11, the master 100 comprises a roll-shaped substrate 110 and a micro-relief structure 120 formed on the outer peripheral surface of the substrate 110.

The substrate 110 is, for example, a roll-shaped member that serves as the substrate for a roll master. The shape of the substrate 110 may be a hollow cylinder as shown in FIG. 11 , or a solid columnar shape without an internal cavity. The material of the substrate 110 is not particularly limited, and quartz glass (SiO ₂ ) such as fused silica glass or synthetic quartz glass, 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. The radial thickness of the cylindrical substrate 110 may be 2 mm or more and 50 mm or less.

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 comprises a plurality of minute recesses 122 arranged at a predetermined pitch P, and a plurality of minute 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 described above). For example, the shape of the recesses 122 of the fine uneven structure 120 of the master 100 is the inverted shape of the protrusions 12 of the fine uneven structure 11 of the cover 7 described above (see Figures 2 to 9). Similarly, the shape of the protrusions 123 of the fine uneven structure 120 of the master 100 is the inverted shape of the recesses 13 of the fine uneven structure 11 of the cover 7 described above (see Figures 2 to 9). Furthermore, the pitch (circumferential dot pitch) of the recesses 122 in the microrelief structure 120 of the master 100 is the same as the pitch P of the protrusions 12 in the microrelief structure 11 of the cover 7.

The master 100 having such a configuration is mounted in a roll-to-roll imprint transfer device, such as the transfer device 300 shown in FIG. 12. The master 100 can be used to produce a transferred product (such as the infrared sensor cover 7 according to this embodiment) in which the fine relief structure 120 formed on the outer peripheral surface of the master 100 has been 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.

[7. Method for producing transcripts]
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.

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

As shown in FIG. 12, the transfer device 300 includes a 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, an application device 307, and a light source 309.

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 the film-like substrate 331 having the 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 having the resin layer 312 laminated thereon against the master 100. The peeling roll 306 is a roll for peeling the film-like substrate 311, to which the microrelief structure 120 has been transferred to the resin layer 312, from the master 100.

The film-like substrate 311 may be the same substrate as the substrate 10 of the infrared sensor cover 7 according to this embodiment described above (see FIG. 2, etc.), or it 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 this embodiment, the cover 7 having the fine uneven structure 11 is constructed 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.).

The coating device 307 is equipped with a coating means such as a coater, and applies the photocurable resin composition to 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.

A photocurable resin composition is a resin that hardens when irradiated with light of a specific wavelength. Specifically, the photocurable resin composition may be, for example, an ultraviolet-curable resin such as an acrylic resin acrylate or an epoxy acrylate. Furthermore, the photocurable resin composition may contain initiators, fillers, functional additives, solvents, inorganic materials, pigments, antistatic agents, sensitizing dyes, or the like, as needed.

The resin layer 312 may be formed from 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 microrelief structure 120. The thermosetting resin composition may be, for example, a phenolic resin, an epoxy resin, a melamine resin, or a urea resin.

Next, we will explain how to produce a transfer product using the transfer device 300 described above.

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

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 roll 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.

Next, the substrate 311 with the cured resin layer 312 laminated thereon is peeled off from the outer peripheral surface of the master 100 by the peeling roll 306. As a result, a micro-relief structure 11 having an inverted shape of the micro-relief structure 120 of the master 100 is formed in the resin layer 312. Thereafter, the substrate 311 peeled off from the master 100 is transported via the guide roll 304 and taken up by the take-up roll 302.

In this way, using the roll-to-roll transfer device 300, it is possible to continuously produce transferred products (e.g., the infrared sensor cover 7 according to this embodiment) onto which the fine uneven 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 uneven structure 120 has been transferred with high precision.

[8. Manufacturing method of master disc]
[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 the manufacturing apparatus for the master 100 according to this embodiment. The manufacturing apparatus for 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.

(S10: Resist film forming process)
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.

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.

The resist layer is formed from an inorganic or organic material that can form a latent image using laser light. As an 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 using, for example, a sputtering method. On the other hand, as an organic material, for example, a novolac resist or a chemically amplified resist can be used. Such organic materials can be formed into a resist layer using, for example, a spin coating method.

(S20: Exposure control signal generation 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 an exposure control device.

(S30: Exposure step)
Furthermore, the exposure device irradiates the resist layer with laser light based on the exposure control signal generated in S20, thereby exposing the resist layer with a predetermined exposure pattern to form a latent image corresponding to the fine concave-convex structure 120.

More specifically, the exposure device irradiates the resist layer with laser light, modifying the areas of the resist layer irradiated with the laser light. This exposes the resist layer, forming multiple latent images in the resist layer. During this exposure, the laser light serving as exposure light may be irradiated onto the resist layer continuously or intermittently.

(S40: Development process)
Next, the resist layer on which the latent image has been formed is developed by a developing device, whereby a resist pattern corresponding to the fine concave-convex structure 120 is formed in the resist layer.

More specifically, the developing device drops a developer onto the resist layer on which the latent image was formed in S30 above, and develops the resist layer. As a result, a resist pattern with a three-dimensional uneven structure is formed on the resist layer. This resist pattern is composed of multiple recesses with three-dimensional shapes. The three-dimensional shapes of the multiple recesses each correspond to the three-dimensional shapes of each recess 122 in the micro-relief structure 120.

If the resist layer is a positive resist, the exposed portions exposed to laser light dissolve faster in developer compared to the unexposed portions, and are 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, if the resist layer is a negative resist, the exposed portions exposed to laser light dissolve slower in developer compared to the unexposed portions, and the unexposed portions are removed by the development process. As a result, a resist pattern is formed in the resist layer, with the latent image portion remaining.

(S50: Etching step)
Thereafter, the resist layer on which the resist pattern is formed is used as a mask by an etching device 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.

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 above. 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 above, and is equivalent to the inverted shape of the three-dimensional shape of the fine concave-convex structure 11 of the transferred object.

Either dry etching or wet etching can be used to etch the substrate 110. For example, if the material of the substrate 110 is quartz glass (SiO ₂ ), the substrate 110 can be etched by dry etching using a fluorocarbon gas (e.g., CHF ₃ ) or by wet etching using hydrofluoric acid or the like.

[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.

As shown in FIG. 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 can rotate around the central axis 110a.

Laser light source 201 is a light source that emits laser light 200A, and is, for example, a solid-state laser or semiconductor laser. The wavelength of laser light 200A emitted by 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. Furthermore, the spot diameter of laser light 200A (the diameter of the spot irradiated onto the resist layer) only needs to be smaller than the diameter of the opening surface of recess 122 in micro-relief structure 120, and may be, for example, approximately 200 nm. Laser light 200A emitted from laser light source 201 is controlled by control mechanism 230.

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

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

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

In the deflection optical system, laser beam 200A is focused onto electro-optical deflection element 209 by focusing lens 207. Electro-optical deflection element 209 is an element capable of controlling the irradiation position of laser beam 200A. The exposure device 200 can also change the irradiation position of laser beam 200A guided onto the movable optical table 220 using the electro-optical deflection element 209 (a so-called wobble mechanism). After the irradiation position of laser beam 200A is adjusted by the electro-optical deflection element 209, it is re-collimated by collimator lens 211. Laser beam 200A emitted from the deflection optical system is reflected by second mirror 213 and guided horizontally and parallel onto the movable optical table 220.

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 the desired beam shape by the beam expander 221, and then irradiated via the objective lens 223 onto the resist layer formed on the substrate 110 of the master 100.

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 every time the substrate 110 makes one rotation. 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 in the resist layer along the spiral irradiation trajectory of the laser beam 200A.

The control mechanism 230 also includes a formatter 231 and a driver 233, and controls the emission of the laser light 200A.

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. The greater the output intensity of the laser light 200A, the larger the size and depth of the latent image formed in the resist layer can be, and therefore the larger the size and depth of the opening of the recess 122 ultimately formed in the substrate 110 can be.

By controlling the exposure using this 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 any 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 allows a fine concave-convex structure 120 having a concave-convex pattern corresponding to the drawing pattern of the input image to be formed on the outer peripheral surface of the substrate 110 of the master 100. Therefore, by preparing a concave-convex pattern that depicts the inverse shape of the fine concave-convex structure 11 of the infrared sensor cover 7, which is the transfer product, as the drawing pattern, a fine concave-convex structure 120 having the inverse shape of the fine concave-convex structure 11 of the cover 7 can be suitably formed on the outer peripheral surface of the master 100.

[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.

According to this embodiment, an infrared sensor cover 7 is provided 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 enter the cover 7 from a direction oblique to the surface of the cover 7. The cover 7 comprises 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 the 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).

As such, the surface of the cover 7 according to this embodiment is provided with a micro-relief structure 11 as an anti-reflection layer. The height H of the multiple convex portions 12 of this micro-relief 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 of, for example, approximately 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. This can significantly improve the detection accuracy of infrared sensors that emit and receive obliquely incident infrared light.

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 be 0.5 or less (second condition: P/λ≦0.5).

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. Therefore, the amount of light received and emitted by the infrared sensor can be increased, further improving the detection accuracy of the infrared sensor.

Furthermore, it is preferable that the ratio (H/P) of the height H to the pitch P of the convex portions 12 is 3 or less (third condition: H/P≦3). In other words, it is preferable that the aspect ratio of the convex portions 12 is 3 or less.

This allows the ratio (aspect ratio) of the pitch P to the height H of the convex portions 12 of the micro-relief structure 11 to be adjusted to a size suitable for imprinting using the roll-shaped master 100. Therefore, during the imprinting, the micro-relief structure 11 of the cover 7 can be favorably peeled from the micro-relief structure 120 on the outer peripheral surface of the master 100, improving releasability. Therefore, the micro-relief structure 11 of the desired shape can be easily and accurately molded without causing defects in the micro-relief structure 11.

Furthermore, it is preferable that the infrared light used in the infrared sensor be near-infrared light with a wavelength λ of 800 nm or more and 2500 nm or less.

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

Furthermore, it is preferable that the shape of the convex portions 12 of the micro-relief structure 11 is substantially an elliptical cone shape, an elliptical truncated cone shape, or a bell or dome shape whose planar shape is an ellipse.

As such, if the shape of the convex portions 12 is a three-dimensional shape (see Figures 6 to 8) having an elliptical planar shape (see Figure 4), it becomes easier to efficiently manufacture a fine concave-convex structure 11 having a large number of such convex portions 12. For example, according to the master manufacturing method using the above-mentioned laser exposure method (see Figure 13), the planar shape of the recesses 122 (see Figure 11) of the fine concave-convex 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 fine concave-convex 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 accurately manufacture a fine concave-convex structure 11 having such elliptical convex portions 12 using the master manufacturing method using the laser exposure method.

It is preferable that the reflectance of infrared rays used in the infrared sensor be 3% or less when the infrared rays are incident on the surface of the infrared sensor cover 7 at an incident angle θ greater than 0° and less than 60°.

As a result, even when 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, further improving the detection accuracy of the infrared sensor.

Below, specific examples of the infrared sensor cover 7 according to the present embodiment will be described. Note that the following examples are merely examples intended to demonstrate 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.

In the following examples, several 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. The test conditions, evaluation method, and evaluation results are described below.

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

First, the substrate 110 of the cylindrical master 100 shown in Figure 11 (see Figure 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. In detail, 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 Figure 13). Next, the substrate 110 was etched using the developed resist layer as a mask to form the microrelief structure 120 having a plurality of recesses 122. In this way, a roll-shaped master 100 having the microrelief structure 120 formed on its outer peripheral surface was manufactured.

Next, the master 100 was used to mold the microrelief structure 11 of the cover 7 by a roll-to-roll process. Specifically, using a transfer device 300 such as that shown in FIG. 12 , an uncured resin layer 312 made of a UV-curable resin was laminated on the surface of a film-like substrate 311, and the microrelief structure 120 on the outer peripheral surface of the master 100 was transferred to the uncured resin layer 312. A 60 μm-thick polyethylene terephthalate (PET) film was used as the film-like substrate 311. Next, the resin layer 312 made of UV-curable resin was cured by irradiating it with UV light at 1000 mJ/cm ² using a metal halide lamp for 1 minute. The cured resin layer 312 was then peeled off from the master 100. In this manner, a transfer product was produced in which the microrelief structure 120 of the master 100 was transferred to the resin layer 312.

Next, the transfer 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 with a thickness of 2 mm was used as the substrate 10 of the cover 7.

In this manner, a micro-relief structure 11 having multiple protrusions 12 arranged in a hexagonal lattice pattern as shown in Figure 4 was molded using the imprinting method, and a cover 7 was produced in which the micro-relief structure 11 was provided on the surface of the substrate 10.

In each of the examples detailed below, the height H and pitch P of the convex portions 12 of the fine uneven structure 11 molded as described above were changed. In addition, in the comparative example, a cover 7 having a fine uneven structure 11 similar to the above examples was produced, but the height H and pitch P of the convex portions 12 of the fine uneven structure 11 were changed to values different from those in the examples.

(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.

Table 2 shows Examples 1 to 8 and Comparative Example 1 when near-infrared light with a wavelength λ of 905 nm is used as the incident light on cover 7 (infrared light used in the infrared sensor). Table 3 shows Examples 10 to 13 and Comparative Examples 10 to 13 when near-infrared light with a wavelength λ of 1550 nm is used as the incident light on cover 7 (infrared light used in the infrared sensor).

2. Evaluation Method
Tables 2 and 3 also show the results of evaluating the covers 7 of 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.

(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.

The procedure for measuring reflectance was to first measure the amount of incident light Qi without the cover 7 on the micro-relief structure 11 of each example and comparative example. Next, incident light was irradiated onto the micro-relief structure 11 of 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 using a laser power meter installed at a reflection angle θr that was the same as the incident angle θi (θ = θi = θr).

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

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).
A rating: Reflectance R is 1.0% or less (particularly excellent anti-reflection effect for obliquely incident light)
B rating: Reflectance R is greater than 1.0% and less than 2.5% (excellent anti-reflection effect for obliquely incident light)
C rating: Reflectance R exceeds 2.5% (poor anti-reflection effect for obliquely incident light)

(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).

The following criteria were used to evaluate the effect of suppressing diffracted light (increase in the amount of transmitted light).
A rating: No diffracted light was generated (excellent effect in suppressing diffracted light)
C rating: Diffracted light occurred (poor effect of suppressing diffracted light)

(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.

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 release properties.
A rating: No defects were observed and demolding was stable (especially excellent demolding properties)
B: No defects were observed, but the release was unstable and the film tension was unstable (excellent release properties)
C rating: Defects occurred, demolding was unstable, and film tension was unstable (poor demolding properties)

[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).

As a result, in Comparative Example 1, the reflectance R increases as the angle of incidence θi of obliquely incident light increases, resulting in a lower anti-reflection performance rating. 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 of 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.

In contrast, in Examples 1 to 8, even when the angle of incidence θi of obliquely incident light increases, the reflectance R barely increases, and the anti-reflection performance rating remains generally at 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 of 1.68% (rating B) is significantly lower than the reflectance R of 4.89% (rating C) of Comparative Example 1. Therefore, it can be seen that Example 8 also significantly improves the anti-reflection performance for obliquely incident light at a wide angle (θ = +60°). As described above, in Examples 1 to 8, the reflectance R for obliquely incident light at such a wide angle is suppressed to a value sufficiently lower than the reference reflectance (e.g., 3%, preferably 2.5%) described above.

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 must 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 less than 0.5 times the wavelength λ, and therefore does not satisfy the first condition (H/λ≧0.5).

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

In contrast, in Examples 10 to 13, although the reflectance R increases slightly as the incident angle θi of obliquely incident light increases, the anti-reflection performance is rated A or B. For example, even when θ = +60°, the reflectance R of Examples 10 to 13 is 2.11% or less (rated B), which is 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 above-mentioned wide-angle obliquely incident light is suppressed to a value sufficiently lower than the above-mentioned reference reflectance (e.g., 3%, preferably 2.5%).

The above comparison results demonstrate that by ensuring that 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, of approximately 60°, can be significantly improved. Therefore, by satisfying the first condition (H/λ≧0.5), the transmittance of obliquely incident near-infrared light passing through the cover 7 can be increased, improving the detection accuracy of the infrared sensor.

(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 needs to 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).

As a result, in Example 8, reflected diffracted light (m = ±1, ±2) was generated on the surface of the convex portions 12 of the micro-relief structure 11, as shown in Figure 14. Therefore, in Example 8, the obliquely incident light entering the micro-relief structure 11 was bent, reducing the linearity of the obliquely incident light and reducing the transmittance of the obliquely incident light passing through the cover 7. As a result, the diffracted light suppression effect in Example 8 was rated C.

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 micro-relief structure 11. In Examples 1 to 7, the linearity of obliquely incident light entering the micro-relief structure 11 did not decrease, and there was no decrease in the transmittance of obliquely incident light passing through the cover 7. As a result, Examples 1 to 7 were excellent in suppressing diffracted light, and were rated A.

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

(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).

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, demolding was unstable, and the film tension was unstable, so the demolding performance was rated C.

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 mold release performance was rated A. In addition, 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 film tension were somewhat unstable, so the mold release performance was rated B.

The above comparison results demonstrate 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 demolding properties during imprinting and prevent defects from occurring in the convex portions 12 of the microrelief structure 11. Furthermore, it can be said that when the aspect ratio satisfies the condition of 2.8 or less (H/P≦2.8), as in Examples 1 to 3, 5, 6, 8 and 11 and 12, it is possible to prevent defects from occurring in the convex portions 12 during imprinting, and it is also possible to stabilize demolding and film tension during imprinting, thereby further improving demolding properties.

Although 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 a person skilled in the art could conceive of various modifications or alterations within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

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 (7)

An infrared sensor cover for covering an infrared sensor that measures the distance to a measurement object using infrared rays,
A substrate;
a fine concave-convex structure provided on at least one surface of the base material and having a plurality of convex portions arranged at a pitch P equal to or less than the wavelength λ of the infrared ray;
Equipped with
the infrared sensor cover is disposed on the infrared sensor so that the infrared ray can be incident on the infrared sensor cover from a direction inclined with respect to the surface of the infrared sensor cover,
The cover for an infrared sensor, wherein the ratio (H/λ) of the height H of the convex portion to the wavelength λ is 0.5 or more. The infrared sensor cover of claim 1, wherein the ratio (P/λ) of the pitch P of the convex portions to the wavelength λ is 0.5 or less. The infrared sensor cover of claim 1, wherein the ratio (H/P) of the height H of the convex portions to the pitch P is 3 or less. 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. The infrared sensor cover of claim 1, wherein the shape of the convex portion is substantially an elliptical cone shape, an elliptical truncated cone shape, or a bell or dome shape with an elliptical planar shape. The infrared sensor cover of claim 1, wherein the reflectance of the infrared rays is 3% or less when the infrared rays are incident on the surface of the infrared sensor cover at an incident angle greater than 0° and less than 60°. The infrared sensor cover according to any one of claims 1 to 6,
a light irradiation device that irradiates an infrared laser beam toward a measurement object through the infrared sensor cover;
a light detection device that detects the infrared light reflected by the object to be measured through the infrared sensor cover;
An infrared sensor comprising: