The light detector includes: a substrate including at least one light receiving area and a light incident surface on which light is incident; and a meta-lens formed on the light incident surface of the substrate to focus the light incident on the light incident surface. When viewed from the thickness direction (Z-axis direction) of the substrate, the meta-lens is formed so as to overlap both an adjacent region adjacent to the light receiving area and a peripheral region that is continuous with the adjacent region and is a region inside the light receiving area along the outer edge of the light receiving area. When viewed from the Z-axis direction, a non-forming region in which the meta-lens is not formed is provided in a region overlapping a central region of the light receiving area in the light incident surface.

TECHNICAL FIELD

The present disclosure relates to a light detector.

BACKGROUND ART

A configuration in which a grating structure that is a refractive-index modulation structure is provided on a light incident surface of a light sensor substrate including a light receiving area is known (for example, see Patent Document 1). The grating structure described in Patent Document 1 is provided in a surrounding region that does not overlap the light receiving area when viewed from a thickness direction of the light sensor substrate in the light incident surface, and is not provided in a region that overlaps the light receiving area when viewed from the thickness direction.

CITATION LIST

Patent Document

Patent Document 1: US Patent Application Publication No. 2018/0130914

SUMMARY OF INVENTION

Technical Problem

In the above-described configuration described in Patent Document 1, light incident on the surrounding region is focused on the light receiving area by the grating structure, thereby improving the light focusing efficiency. On the other hand, in the above-described configuration, the grating structure is not formed in the entire region overlapping the light receiving area when viewed from the thickness direction of the light sensor substrate. That is, when viewed from the thickness direction of the light sensor substrate, an opening region in which the grating structure is not formed includes the entire light receiving area. When the light to be analyzed includes a component (oblique incident light) obliquely incident on the light incident surface, there is a possibility that many components of the oblique incident light passing through the opening region escape to the outside of the light receiving area as they are. Therefore, in the configuration described in Patent Document 1, there is room for improvement in improving the light focusing efficiency to the light receiving area at least with respect to such oblique incident light.

Therefore, an object of the present disclosure is to provide a light detector capable of further improving light focusing efficiency to a light receiving area.

Solution to Problem

A light detector according to an aspect of the present disclosure includes: a substrate including at least one light receiving area and a light incident surface on which light is incident; and a meta-lens formed on the light incident surface of the substrate so as to focus the light incident on the light incident surface. When viewed from a thickness direction of the substrate, the meta-lens is formed to overlap both an adjacent region adjacent to the light receiving area and a peripheral region that is continuous with the adjacent region and is a region inside the light receiving area along an outer edge of the light receiving area. When viewed from the thickness direction, a non-forming region in which the meta-lens is not formed is provided in a region overlapping a central region of the light receiving area in the light incident surface.

According to the light detector, since the meta-lens is formed in the adjacent region, it is possible to suitably guide light incident on the adjacent region to the light receiving area. In addition, since the non-forming region is formed, incident light traveling straight from a front side of the light receiving area toward the light receiving area may be incident on the light receiving area without passing through the meta-lens. Therefore, it is possible to suppress the optical loss caused by the light passing through the meta-lens. In addition, the meta-lens is also formed in the peripheral region overlapping with the edge of the light receiving area. Thus, even when the light to be analyzed includes oblique incident light that is obliquely incident on the light incident surface, a component of the oblique incident light that is incident on the meta-lens provided in the peripheral region can be suitably guided to the light receiving area. As described above, the light focusing efficiency to the light receiving area can be further improved.

The meta-lens may be configured by a plurality of convex portions periodically arranged. According to the above configuration, the meta-lens can have a physically robust structure.

The meta-lens may be configured by a plurality of concave portions periodically arranged. According to the above configuration, the meta-lens can be made to have a more physically robust structure. Further, each of the plurality of concave portions may be filled with a dielectric. According to the above configuration, the meta-lens can be made to have a physically robust structure more effectively, and the surface reflectance of the meta-lens can be reduced. Accordingly, it is possible to further improve light focusing efficiency to the light receiving area.

The meta-lens may be formed to overlap at least a first peripheral region and a second peripheral region facing each other in one direction perpendicular to the thickness direction among the peripheral region. According to the above configuration, the light focusing efficiency can be improved one-dimensionally at least in the one direction.

The meta-lens may be formed to overlap an entire annular peripheral region formed over an entire circumference of the light receiving area. According to the above configuration, it is possible to improve two-dimensionally the light focusing efficiency.

A width of the non-forming region may be set in a range in which a main lobe of light incident on the non-forming region is included in the light receiving area, based on a spread width due to diffraction of the light incident on the non-forming region. As the width of the non-forming region is reduced, the spread width of light incident on the non-forming region due to diffraction increases. According to the above configuration, since the width of the non-forming region is set in a range in which the main lobe of the light in which the diffraction spread occurs is included in the light receiving area, it is possible to make most of the light (main lobe) incident on the non-forming region incident on the light receiving area. As a result, the light focusing efficiency can be effectively improved.

An antireflection film may be provided in the non-forming region. According to the above configuration, it is possible to suppress reflection loss of incident light at the interface between the light incident surface and the external environment (for example, air).

The substrate may include: a first substrate having a first surface provided with the light receiving area and a second surface opposite to the first surface; and a second substrate bonded to the second surface of the first substrate via an adhesive resin layer and supporting the first substrate. The light incident surface may be constituted by a surface located on an opposite side of the first substrate in the second substrate. Further, the first substrate may be a silicon substrate, and the second substrate may be a glass substrate. According to the above configuration, the substrate is configured by the first substrate in which the light receiving unit is provided and the second substrate that supports the first substrate, and thus it is possible to appropriately secure the strength of the substrate.

An antireflection film may be provided between the first substrate and the second substrate. According to the above configuration, it is possible to suppress reflection loss of incident light at the interface between the first substrate and the second substrate.

A meta-lens layer may be provided between the first substrate and the second substrate. According to the above configuration, the incident light directed toward the light receiving area is further focused at the interface between the first substrate and the second substrate, so that the light focusing efficiency can be further improved.

The substrate may be formed of a single substrate member having a first surface provided with the light receiving area and a second surface opposite to the first surface, and the light incident surface may be constituted by the second surface. According to the above configuration, it is possible to obtain the above-described effect of improving the light focusing efficiency while simplifying the structure of the light detector.

Advantageous Effects of Invention

According to an aspect of the present disclosure, it is possible to provide a light detector capable of further improving light focusing efficiency to a light receiving area.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals, and redundant description is omitted.

[Configuration of Light Detector According to Embodiment]

As shown inFIGS.1and2, the light detector1includes a substrate2and a meta-lens3. In the present embodiment, as an example, the light detector1is an elongated light receiving sensor including a light receiving area10corresponding to one pixel. However, the light detector1may include a plurality of light receiving areas10corresponding to a plurality of pixels. For example, the light detector1may have a structure in which a plurality of unit structures (substrate2) corresponding to one pixel illustrated inFIG.1are one-dimensionally arranged in the X-axis direction or the Y-axis direction, or may have a structure in which a plurality of the unit structures are two-dimensionally (grid-like) arranged in each of the X-axis direction and the Y-axis direction. InFIGS.1and2and other drawings to be described later, three dimensional orthogonal coordinates including an X axis, a Y axis, and a Z axis are illustrated for convenience of description. The X-axis direction, the Y-axis direction, and the Z-axis direction correspond to a lateral direction, a longitudinal direction, and a thickness direction of the light detector1(substrate).

The substrate2includes at least one light receiving area10and has a light incident surface2aon which the light to be analyzed is incident. As an example, the substrate2is formed in a rectangular plate shape. The substrate2is, for example, about 20 μm long in the lateral direction (X-axis direction). The substrate2is, for example, about 201.5 μm long in the longitudinal direction (Y-axis direction). The substrate2includes a silicon substrate21(first substrate) which is a semiconductor substrate provided with the light receiving area10and a glass substrate22(second substrate) provided with the meta-lens3.

The silicon substrate21has a main surface21a(first surface) provided with the light receiving area10and a back surface21b(second surface) opposite to the main surface21a. The silicon substrate21is about 10 μm thick (in the Z-axis direction). The glass substrate22is bonded to the back surface21bof the silicon substrate21via an adhesive resin layer23and supports the silicon substrate21. The glass substrate22has a surface22afacing the main surface21aof the silicon substrate21and a surface22bopposite to the surface22a. The light incident surface2aof the substrate2is constituted by the surface22bof the glass substrate22. The glass substrate22is, for example, about 300 μm thick (in the Z-axis direction).

As shown inFIG.1, the light receiving area10is provided along the main surface21ain a substantially central portion of the main surface21aof the silicon substrate21. As an example, the light receiving area is formed in a rectangular shape. The lateral direction and the longitudinal direction of the light receiving area10coincide with the lateral direction and the longitudinal direction of the substrate2, respectively. The length of the light receiving area10in the lateral direction (X-axis direction) is, for example, about 6.2 μm. The length of the light receiving area10in the longitudinal direction (Y-axis direction) is, for example, about 50 μm. The thickness (length in the Z-axis direction) of the light receiving area10is, for example, about 3 μm. The meta-lens3is formed on the light incident surface2aof the substrate2(in the present embodiment, a surface22bof the glass substrate22). The meta-lens3is a meta-surface structure that functions as a lens that focuses light incident on the light incident surface2a. More specifically, the meta-lens3is a nanostructure (fine concave-convex structure) in which unit cells C1, which are a basic configuration (unit lattice) illustrated inFIG.3, are periodically arranged in a lattice shape along the X-axis direction and the Y-axis direction. As an example, the unit cell C1is a square region when viewed from the Z-axis direction. One pillar31(convex portion) having a columnar shape (cylindrical shape as an example in the present embodiment) is formed for each unit cell C1. The pillar31is erected on the surface22bof the glass substrate22in the central portion of the unit cell C1. That is, the meta-lens3is configured by a plurality of pillars31periodically arranged in a lattice pattern. The material of the pillar31is silicon, titanium dioxide (TiO2), or the like, for example.

The pitch a of the pillars31(i.e., the center-to-center distance between adjacent pillars31, the length of one side of the unit cell C1) is set to be shorter than a wave length of the light to be analyzed. That is, the meta-lens3has a sub-wavelength structure of the light to be analyzed. As an example, when the wave length λ, of the light to be analyzed is 940 nm, the pitch a of the pillar31can be set to 400 nm, for example. The height h of the pillar31can be selected from the range of 450 nm to 550 nm, for example. The width d (diameter) of the pillar31can be selected from the range of 100 nm to 300 nm, for example. As an example, in the entire meta-lens3(that is, all the unit cells C1), the heights h of the pillars31are set to a constant value (for example, 500 nm). On the other hand, the width d of the pillar31of each unit cell C1is selected from the above-described range according to the arrangement location of each unit cell C1. In this way, by setting the width d of the pillar31of each unit cell C1in accordance with the location of each unit cell C1, the amount of phase modulation is controlled for each location of each unit cell C1, and the meta-lens3that functions as a condenser lens is obtained. For example, when viewed from the Z-axis direction, the meta-lens3has a structure in which a plurality of regions for one cycle (regions including a plurality of unit cells C1), which are formed such that the phase changes continuously by 2π along a direction from the outside of the meta-lens3toward the center (center of a non-forming region R3described later), are repeatedly arranged along the direction.

The structure of the meta-lens3described above will be supplemented. As types of meta-lens structure (metasurface structure), so-called refractive index modulation type and resonance type are known. The meta-lens3may have any of the metasurface structures described above. The metasurface structure of the refractive index modulation type is a structure of controlling an effective refractive index determined by a filling rate (occupancy) of a meta-lens material in each of the unit cell C1. The metasurface structure of the resonance type is a structure of controlling phase and transmissivity by adjusting electric resonance and magnetic resonance according to the structure of each unit cell C1(that is, the shape and size of a nanostructure composed of a plurality of regularly arranged concave-convex structures). More specifically, the resonance type metasurface structure is a structure of realizing the above-described lens function by adjusting a transmittance coefficient t represented by the following Equation (1). In the following Equation (1), ωe,krepresents a resonance frequency related to electric resonance in the k-th order mode, and ωm,krepresents a resonance frequency related to magnetic resonance in the k-th order mode. In addition, ω represents a resonance angular frequency in the Lorentz oscillator model that describes electron polarization. In addition, γe,krepresents an attenuation coefficient related to electric resonance of the k-th order mode in the Lorentz oscillator model, and γm,krepresents an attenuation coefficient related to magnetic resonance of the k-th order mode in the Lorentz oscillator model. In addition, akis a parameter representing the degree of contribution of electric resonance in the k-th order mode in the Lorentz oscillator model, and bkis a parameter representing the degree of contribution of magnetic resonance in the k-th order mode in the Lorentz oscillator model. The resonance type metasurface structure includes a Huygens type (Nanodisk type) corresponding to a case of “m=n=1” in the following Equation (1) (that is, a case of using resonance of electric dipoles and magnetic dipoles in a single mode) and an HCG type (Micropost type) corresponding to a case other than “m=n=1” in the following Equation (1) (that is, a case of using resonance in a higher order mode). When the meta-lens30is configured by the resonance type metasurface structure, any type of the Huygens type and the HCG type described above may be used.

In a case where the refractive index modulation type is adopted as the structure of the meta-lens3, it is possible to secure robustness with respect to a change in the wavelength of the light to be analyzed, compared to a case where the resonance type is adopted. On the other hand, when the resonance type is adopted, the phase change can be made sharp and high transmittance can be secured as compared with the refractive index modulation type. In addition, when the Huygens type is adopted, the aspect ratio of the pillar31can be reduced (that is, the height of the pillar31can be lowered) as compared with the refractive index modulation type and the HCG type, and thus the structure of the meta-lens3can be made more robust. On the other hand, when the HCG type is adopted, since it is possible to use resonance of a plurality of higher-order modes, it is possible to increase the degree of freedom of the structural design of the meta-lens3.

As shown inFIGS.1and2, when viewed from the Z-axis direction (thickness direction of the substrate2), the meta-lens3is formed so as to overlap both an adjacent region R1adjacent to the light receiving area10and a peripheral region R2that is continuous with the adjacent region R1and is a region inside of the light receiving area10along an outer edge of the light receiving area10. When viewed from the Z-axis direction, a non-forming region R3is provided in a region overlapping the central region of the light receiving area10in the light incident surface2a(in the present embodiment, the surface22bof the glass substrate22). The non-forming region R3is a region where the meta-lens3is not formed.

In the present embodiment, the meta-lens3is formed so as to overlap the entire annular peripheral region R2formed over the entire circumference of the light receiving area10. That is, when viewed from the Z-axis direction, the meta-lens3has a rectangular annular shape in which a rectangular opening3acorresponding to the non-forming region R3is formed in the central portion. That is, the non-forming region R3is formed to be slightly smaller than the light receiving area10by the peripheral region R2. In other words, when viewed from the Z-axis direction, the non-forming region R3is completely contained inside the light receiving area10. In other words, when viewed from the Z-axis direction, the outer edge of the non-forming region R3is located inside the outer edge of the light receiving area10over the entire circumference of the non-forming region R3.

An example of a process of manufacturing the meta-lens3will be described with reference toFIG.4. First, a silicon layer30(amorphous silicon) including a portion to be the meta-lens3(that is, the plurality of pillars31) is formed on the surface22bof the glass substrate22(quartz substrate) by a sputtering method (step S1). The thickness of the silicon layer30is determined based on a design value (for example, a value selected from the range of 450 nm to 550 nm) of the height h of the pillar31. Subsequently, an electron-beam (EB) resist100having a thickness of about 300 nm is applied onto the front side of the silicon layer30(the side opposite to the glass substrate22side) (step S2). Subsequently, a pattern designed in advance is EB drawn on the EB resist100by the EB lithography method (step S3). In detail, openings100acorresponding to a non-forming region R3and a portion in which the pillar31is not formed in each unit cell C1included in the adjacent region R1and the peripheral region R2are formed in the EB resist100. In the present embodiment (example ofFIG.1), the EB drawing region is a rectangular region having a short side of 20 μm and a long side of 201.5 μm. Subsequently, etching (for example, dry etching such as inductively coupled plasma (ICP-RIE) etching) using the EB resist100as a mask is performed to remove a portion (that is, an exposed portion) of the silicon layer30corresponding to the opening100aof the EB resist100. Thereafter, the EB resist100is stripped (step S4). As described above, the meta-lens3(that is, a structure in which the plurality of pillars31are periodically arranged) is formed on the surface22bof the glass substrate22.

[Effects of Light Detector According to Embodiment]

The effect of the light detector1described above will be described with reference toFIG.5. As shown inFIG.5, since the meta-lens3is formed in the adjacent region R1, the light L1incident on the adjacent region R1can be suitably guided to the light receiving area10. For example, in the adjacent region R1, the meta-lens3changes the traveling direction of the light L1traveling straight in the direction orthogonal to the light incident surface2a(that is, the light proceeding to the outside of the light receiving area10) to the light receiving area10side, so that the light L1can be incident on the light receiving area10. In addition, since the non-forming region R3is formed, incident light (light L3) traveling straight from the front side of the light receiving area toward the light receiving area10may be incident on the light receiving area10without passing through the meta-lens3. Therefore, it is possible to suppress the optical loss caused by the light L3passing through the meta-lens3.

Furthermore, in the light detector1, the meta-lens3is also formed on the peripheral region R2overlapping with the edge of the light receiving area10. That is, when viewed from the Z-axis direction, the outer edge of the non-forming region R3is located inside the outer edge of the light receiving area10. Thus, even when the light L to be analyzed includes components (obliquely incident light) obliquely incident on the light incident surface2a, the components incident on the meta-lens3provided in the peripheral region R2among the obliquely incident light can be suitably guided to the light receiving area10.

With reference toFIG.6, the effect about the oblique incident light will be described in detail. A light detector200illustrated in (A) ofFIG.6is a simulation model having a simple configuration created to verify an effect achieved by forming the meta-lens3in the peripheral region R2. In the light detector200, the light receiving area10is formed on the entire surface22aof the glass substrate22, and the meta-lens3described above is formed on the surface22b. An opening3a(opening corresponding to the above-described non-forming region R3) is provided in the center of the meta-lens3. A region in which the meta-lens3is provided in the surface22bcorresponds to the peripheral region R2described above. Here, the refraction index of the glass substrate22is “1.51”, and the thickness d1of the glass substrate22is 40 μm. Further, the pitch a (seeFIG.3) of the meta-lens3is 400 nm, and the height d2of the meta-lens3(i.e., the height of the pillar31) is 500 nm. In addition, the light detector200is formed in a square plate shape having a side w1of 40 μm. The width w2(length of the side) of the opening3ais 10 μm. The upper drawing of (A) ofFIG.6shows one cross section along the thickness direction of the light detector200passing through the center of the light receiving area10(the center of the opening3a). Here, the light L to be analyzed is light which is inclined with respect to the light incident surface (surface22b) and is incident on the entire light incident surface in the one cross section. The wave length λ, of the light L is 940 nm. The inclination angle θ of the light L with respect to the light incident surface is set to 20 degrees. On the other hand, a light detector300illustrated in (B) ofFIG.6is a simulation model corresponding to the comparative example. The light detector300is different from the light detector200in that the meta-lens3is not formed, and other configurations of the light detector300are the same as those of the light detector200.

The horizontal axis of the graph shown on the lower side of (A) ofFIG.6represents the distance from the center position of the light detector200in the one cross section when the center position is “0” (the distance is represented with the right direction in the drawing as the positive direction and the left direction in the drawing as the negative direction). The vertical axis of the graph represents the intensity of light incident on each position of the light detector200. The graph shown on the lower side of (B) ofFIG.6is a graph of the light detector300corresponding to the graph of the light detector200described above. The following can be seen from these graphs. That is, as shown in the graph shown on the lower side of (B) ofFIG.6, in the light detector300in which the meta-lens3is not formed, it can be confirmed that the light L escapes to the outside of the light receiving area10toward the traveling direction side of the light L (right side in this example). On the other hand, as shown in the graph on the lower side of (A) ofFIG.6, in the light detector200, it can be confirmed that the peak position of the light amount is located within the light receiving area10although the peak position is slightly shifted to the traveling direction side of the light L from the center position of the light receiving area10. That is, it may be confirmed that most of the components of the light L are efficiently focused in the light receiving area10by the meta-lens3(i.e., the meta-lens3formed on the peripheral region R2). From the above, by forming the meta-lens3in the peripheral region R2overlapping with the edge portion of the light receiving area10, it is possible to suitably focus the obliquely incident light to the light receiving area10.

As described above, according to the light detector1, it is possible to further improve the light focusing efficiency to the light receiving area10. In addition, for example, in a case where the light detector1has a structure in which a plurality of unit structures (substrate2) for one pixel shown inFIG.1are arranged along the X-axis direction, it is possible to suppress occurrence of oblique incident light incident on one pixel (that is, light incident surface2acorresponding to one light receiving area10) being incident on a pixel adjacent to the one pixel (so-called crosstalk).

The meta-lens3is configured by a plurality of pillars31arranged periodically. According to this configuration, the meta-lens3can have a physically robust structure.

In addition, as shown inFIG.5, the light passing through the non-forming region R3(i.e., the opening3aof the meta-lens3) is directed toward the light receiving area10while being diffused by the diffraction of the light in the opening3a. Therefore, if the non-forming region R3and the light receiving area10have the same size and completely overlap each other when viewed from the Z-axis direction, a part of the diffracted light L2leaks to the outside of the light receiving area10. On the other hand, in the present embodiment, since the meta-lens3is provided in the peripheral region R2, the non-forming region R3is formed to have a size smaller than the light receiving area10. Thus, as shown inFIG.5, the diffracted light L2that passes through the non-forming region R3and spreads toward the light receiving area10can be appropriately accommodated in the light receiving area10. In addition, although the light incident on the meta-lens3disposed in the peripheral region R2is somewhat attenuated by the meta-lens3, the light is guided to the light receiving area10by the condensing effect of the meta-lens3. Therefore, the sensitivity can be improved as compared with the case where the light passes out of the light receiving area10due to the spread caused by the opening diffraction described above.

More preferably, the width of the non-forming region R3(that is, the width (length of one side) of the opening3a) may be set as follows based on the spread width of the light L incident on the non-forming region R3due to diffraction. That is, the width of the non-forming region R3may be set to a range in which the main lobe of the light L incident on the non-forming region R3is included in the light receiving area10. This will be described in detail with reference toFIG.7. As shown inFIG.7, the spread caused by diffraction in the opening3aof the meta-lens3(the spread of the main lobe of the light L at the position where the light receiving area10is provided) is expressed by the following Equation (2). Here, λ represents the wave length of the light L, Z represents the propagation length (i.e., the distance from the light incident surface2ato the light receiving area10), n represents a refractive index of the propagation medium, and W represents the opening width (diameter) of the opening3a. In this embodiment, there are three types of media of a glass substrate22, an adhesive resin layer23, and a silicon substrate21, as propagation media from the light incident surface2ato the light receiving area10. In this case, the refractive index n is an average refractive index calculated based on the refractive index and the thickness of each medium.

Spread width of the main lobe=2λZ/nW(Equation 2)

Therefore, when the width of the light receiving area10is represented by D, by setting the width W of the opening3aso as to satisfy the following Equation (3), the entire main lobe of the light L incident on the non-forming region R3can be made incident on the light receiving area10. As a result, the light focusing efficiency can be effectively improved.FIG.7shows a case where an equality sign (=) is satisfied in the following Equation (3) (that is, a case where the width W is set to a lower limit value for focusing the entire main lobe on the light receiving area10).

In a case where the non-forming region R3(opening3a) is formed in a circular shape instead of a rectangular shape (for example, see (C) ofFIG.14), the above Equations (2) and (3) are replaced by the following Equations (4) and (5). In this case, the width W of the opening3ameans the diameters of the opening3a. When the non-forming region R3(opening3a) has a shape that is neither rectangular nor circular (for example, when the corners of the rectangular shape are rounded), a value (for example, an intermediate value) between the value of the left side of the above Equation (3) and the value of the left side of the following Equation (5) may be used as the lower limit of the opening3a.

Spread width of the main lobe=2.44λZ/nW(Equation 4)

In addition, the meta-lens3is formed to overlap the entire annular peripheral region R2formed over the entire circumference of the light receiving area10. According to the above configuration, it is possible to improve the light focusing efficiency two-dimensionally. That is, in the present embodiment, the above-described effect of improving the light focusing efficiency is obtained in both the plane along the X-axis direction and the plane along the Y-axis direction.

Further, the substrate2includes the silicon substrate21having the main surface21a(first surface) provided with the light receiving area and the back surface21bopposite to the main surface21a, and the glass substrate22bonded to the back surface21bof the silicon substrate21via the adhesive resin layer23and supporting the silicon substrate21. The light incident surface2ais constituted by a surface22bof the glass substrate22. According to the above-described configuration, the substrate2is configured by the first substrate (the silicon substrate21in the present embodiment) provided with the light receiving area10and the second substrate (the glass substrate22in the present embodiment) supporting the first substrate. Thus, the strength of the substrate2can be appropriately secured.

[First Modification Example of Substrate]

With reference toFIG.8, a first modification example of substrate (substrate2A) included in the light detector1will be described. As shown inFIG.8, the substrate2A is different from the substrate2in that an antireflection film4and an antireflection film5are further provided, and is the same as the substrate2in other respects.

The antireflection film4is provided in the non-forming region R3(a region corresponding to the opening3a) of the light incident surface2a(here, a surface22bof the glass substrate22). The antireflection film4plays a role of suppressing reflection loss of incident light at the interface between the light incident surface2aand the external environment (air). The antireflection film4can be formed by, for example, single-layer AR coating on the surface22bof the glass substrate22. According to the antireflection film4, transmissivity of light passing through the non-forming region R3can be suitably improved. Accordingly, it is possible to effectively improve light focusing efficiency to the light receiving area10.

The refractive index n and the film thickness dARof the antireflection film4can be set based on the refractive index of each medium disposed on both sides of the antireflection film4. In particular, the refraction index nARof the antireflection film4has a value between the refraction index nAirof air and the refraction index nSiO2of the glass substrate22(SiO2). That is, the following Equation (6) is established. More preferably, from the viewpoint of widening the wavelength band in which reflection can be suppressed, the refractive index nARof the antireflection film4may be set based on the following Equation (7). The film thickness dARof the antireflection film4is set based on the following Equation (8). Here, λ represents the wavelength of light to be analyzed, and in represents an arbitrary integer of 1 or more.

The antireflection film5is provided between the silicon substrate21and the glass substrate22(in the present embodiment, between the silicon substrate21and the adhesive resin layer23). The antireflection film5plays a role of suppressing reflection loss of incident light at the interface between the silicon substrate21and the glass substrate22. The antireflection film5can be formed by, for example, single-layer AR coating on the back surface21bof the silicon substrate21. According to the antireflection film5, the transmissivity of light passing through the interface between the silicon substrate21and the glass substrate22can be suitably improved. Accordingly, it is possible to effectively improve light focusing efficiency to the light receiving area10. The refractive index and the film thickness of the antireflection film5can also be set based on the refractive index of each medium disposed on both sides of the antireflection film5, similarly to the antireflection film4.

Although a configuration including both the antireflection film4and the antireflection film5has been described here as an example, only one of the antireflection film4and the antireflection film5may be provided. In addition, the antireflection film5may be provided between the adhesive resin layer23and the glass substrate22. In addition, an antireflection film may be provided each of between the silicon substrate21and the adhesive resin layer23and between the adhesive resin layer23and the glass substrate22.

[Second Modification Example of Substrate]

With reference toFIG.9, a second modification example of substrate (substrate2B) included in the light detector1will be described. As shown inFIG.9, the substrate2B is different from the substrate2in that it further includes a meta-lens layer6, and is the same as the substrate2in other respects.

The meta-lens layer6is provided between the silicon substrate21and the glass substrate22(in the present embodiment, between the silicon substrate21and the adhesive resin layer23). The meta-lens layer6has a fine concave-convex structure (for example, a structure in which a plurality of pillars31are periodically arranged) similar to that of the above-described meta-lens3, and serves to further focus light traveling from the glass substrate22side to the silicon substrate21side into the light receiving area10. Accordingly, it is possible to effectively improve light focusing efficiency to the light receiving area10. In the substrate2B, an antireflection film4similar to that in the substrate2A may be further provided.

[Third Modification Example of Substrate]

With reference toFIG.10, a third modified example of substrate (substrate2C) included in the light detector1will be described. As shown inFIG.10, the substrate2C is different from the substrate2in that the substrate2C is formed of a single substrate member (silicon substrate21) and the light incident surface substrate2ais formed by a back surface21bof the silicon substrate21, and is the same as the substrate2in other respects. That is, the light detector1including the substrate2C is a back-illuminated type light receiving sensor, and has a configuration in which the meta-lens3is formed on an incident surface (back surface21b) of the light receiving sensor. According to the above configuration, by omitting the second substrate (glass substrate22) included in the substrate2, it is possible to obtain the same effect of improving the light focusing efficiency as that of the substrate2described above while simplifying the structure of the light detector1. In the substrate2C, an antireflection film4similar to that in the substrate2A may be further provided.

The substrate2has a structure in which the first substrate (silicon substrate21) and the second substrate (glass substrate22) are joined, but the combination of the first substrate and the second substrate is not limited to the example described above. For example, as the second substrate, a silicon substrate similar to the first substrate may be used instead of the glass substrate22. Further, in this case, the first substrate and the second substrate (that is, the silicon substrate) may be directly bonded to each other without using the adhesive resin layer23.

[First Modification Example of Basic Configuration of Meta-Lens]

With reference toFIG.11, a first modification example (unit cell C2) of the basic configuration (unit lattice) of the meta-lens3will be described. The unit cell C2is formed by an inorganic material layer32formed on the surface22bof the glass substrate22. In the inorganic material layer32, one columnar hole32a(concave portion) is formed for each unit cell C2(in the embodiment, as an example, a cylindrical shape). The hole32apenetrates from the upper surface32bof the inorganic material layer32(the surface opposite to the surface in contact with the surface22b) to the surface22bof the glass substrate22in the central portion of the unit cell C2. The inorganic material layer32is formed of, for example, a material similar to that of the pillar31. The meta-lens3may have a hole structure in which unit cells C2are periodically arranged in a lattice shape, instead of the pillar structure in which the unit cells C1are periodically arranged in a lattice shape.

When the unit cell C2is adopted as the basic configuration of the meta-lens3, the pitch a of the hole32a(i.e., the center-to-center distance between adjacent holes32a, the length of one side of the unit cell C2) is set to be shorter than the wave length of the light to be analyzed, as in the case where the unit cell C1is adopted. As an example, when the wave length λ, of the light to be analyzed is 940 nm, the pitch a of the hole32ais set to 400 nm, for example. The height h of the hole32a(the depth of the concave portion) can be selected from the range of 300 nm to 400 nm, for example. The width d (diameter) of the hole32acan be selected from the range of 100 nm to 300 nm, for example. As an example, in the entire meta-lens3(that is, all the unit cells C2), the heights h of the holes32aare set to a constant value (for example, 500 nm). On the other hand, the width d of the hole32aof each unit cell C2is selected from the above-described range according to the arrangement location of each unit cell C2. In this way, by setting the width d of the hole32aof each unit cell32aaccording to the location of each unit cell C2, the amount of phase modulation is controlled for each location of each unit cell C2, and the meta-lens3that functions as a condenser lens is obtained. For example, when viewed from the Z-axis direction, the meta-lens3has a structure in which a plurality of regions for one cycle (regions including a plurality of unit cells C2), which are formed such that the phase continuously changes by 2π along a direction from the outside of the meta-lens3toward the center (center of the non-forming region R3), are repeatedly arranged along the direction.

When the unit cell C2is adopted as the basic configuration of the meta-lens3, that is, when the meta-lens3is configured by a plurality of holes32a(concave portions) periodically arranged, the meta-lens3may have a physically stronger structure than when the meta-lens3is configured by the pillar structure (a plurality of unit cells C1).

[Second Modification Example of Basic Configuration of Meta-Lens]

With reference toFIG.12, a second modification example (unit cell C3) of the basic configuration (unit lattice) of the meta-lens3will be described. The unit cell C3is different from the unit cell C2in that the hole32ais filled with dielectric33, and is the same as the unit cell C2in other respects. The dielectric33is, for example, Al2O3, SiO2, SiN, HfO2, or the like. As shown inFIG.12, the dielectric33may be filled in the hole32aof each unit cell C3and may also be deposited on the upper surface32bof the inorganic material layer32. The distance from the upper surface32bof the inorganic material layer32to the upper surface33aof the dielectric33(i.e., the height of the dielectric33deposited on the inorganic material layer32) is, for example, about the 150 nm.

When the unit cell C3is adopted as the basic configuration of the meta-lens3, the meta-lens can be made to have a physically robust structure more effectively. That is, since the dielectric33is provided, the structure can be made physically stronger than the unit cell C2. Further, by embedding the dielectric33in the hole32a, the reflectivity of the meta-lens3can be reduced. Accordingly, it is possible to further improve light focusing efficiency to the light receiving area.

An example of a process of manufacturing the meta-lens3including the unit cells C2and C3of the first modification example and the second modification example will be described with reference toFIG.13. First, a silicon layer30(amorphous silicon) including a portion to be the inorganic material layer32is formed on the surface22bof the glass substrate22(quartz substrate) by a sputtering method (step S11). The thickness of the silicon layer30may be selected from the range of 300 nm to 400 nm, for example. Subsequently, an electron-beam (EB) resist100having a thickness of about 300 nm is applied onto the front side of the silicon layer30(the side opposite to the glass substrate22side) (step S12). Subsequently, a pattern designed in advance is EB drawn on the EB resist100by the EB lithography method (step S13). In detail, openings100acorresponding to the non-forming region R3and the hole32aamong unit cells C2and C3included in the adjacent region R1and the peripheral region R2are formed in the EB resist100. In the present embodiment (example ofFIG.1), the EB drawing region is a rectangular region having a short side of 20 μm and a long side of 201.5 μm. Subsequently, etching (for example, dry etching such as inductively coupled plasma (ICP-RIE) etching) using the EB resist100as a mask is performed to remove a portion (that is, an exposed portion) of the silicon layer30corresponding to the opening100aof the EB resist100. Thereafter, the EB resist100is stripped (step S14). By the processing up to this point, the meta-lens3having the unit cell C2as a basic configuration is formed on the surface22bof the glass substrate22. When the meta-lens3having the unit cell C3as a basic configuration is formed, the following processing is further executed. That is, the dielectric33is formed (deposited) in the hole32aand on the inorganic material layer32by the atom layer deposition method (ALD) (step S15). When the ALD is performed, the non-forming region R3is masked so that the dielectric33is not formed on the non-forming region R3. By the above processing, the meta-lens3having the unit cell C3as a basic configuration is formed on the surface22bof the glass substrate22.

Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment. The material and shape of each component are not limited to those described above, and various materials and shapes may be employed. For example, as illustrated in (A) to (D) ofFIG.14, the shape of the substrate, the shape of the light receiving area, and the shape of the region in which the meta-lens is formed are not limited to those in the above embodiment.

In the light detector1A of the first modification example shown in (A) ofFIG.14, a meta-lens3A (a pair of meta-lenses3A1and3A2) is formed in regions on both sides of the light receiving area10in the longitudinal direction (Y-axis direction) of the substrate2. In other words, the meta-lens is not formed in regions on both sides of the central portion (region corresponding to the non-forming region R3) of the light receiving area10in the lateral direction (X-axis direction) of the substrate2. The meta-lens3A is formed to overlap a first peripheral region R21and a second peripheral region R22facing each other in the Y-axis direction among the peripheral region R2. Even with such a configuration, it is possible to improve the light focusing efficiency one-dimensionally at least in the longitudinal direction (Y-axis direction) of the substrate2. In addition, in the light detector1A, the meta-lens3A may be formed in only one region of both regions interposing the light receiving area10in the longitudinal direction of the substrate2. In other words, one of the meta-lenses3A1and3A2may be omitted. According to this configuration as well, the above-described effects are exhibited with respect to the peripheral region R2on the side on which the meta-lens3A is formed.

In the light detector1B of the second modification example illustrated in (B) ofFIG.14, a meta-lens3B (a pair of meta-lenses3B1and3B2) is formed in regions on both sides of the light receiving area10in the lateral direction (X-axis direction) of the substrate2. In other words, the meta-lens is not formed on both sides of the central portion of the light receiving area10(corresponding to the non-forming region R3) in the longitudinal direction (Y-axis direction) of the substrate2. The meta-lens3B is formed to overlap a first peripheral region R21and a second peripheral region R22facing each other in the X-axis direction among the peripheral region R2. Even with such a configuration, it is possible to improve the light focusing efficiency one-dimensionally at least in the lateral direction (X-axis direction) of the substrate2. In addition, in the light detector1B, the meta-lens3B may be formed in only one region of both regions interposing the light receiving area10in the lateral direction of the substrate2. In other words, one of the meta-lenses3B1and3B2may be omitted. According to this configuration as well, the above-described effects are exhibited with respect to the peripheral region R2on the side on which the meta-lens3B is formed.

The light detector1C of the third modification example shown in (C) ofFIG.14has a square plate-shaped substrate2C. The light detector1D of the fourth modification example shown in (D) ofFIG.14is shorter than the substrate2and longer than the substrate2C. As described above, the substrate included in the light detector may be formed in various shapes.

Further, the light detector1C has a circular light receiving area10C and a meta-lens3C having a shape corresponding to the shape of the light receiving area10C. That is, the meta-lens3C has a circular opening3athat is slightly smaller than the light receiving area10C so as not to overlap with the central portion of the circular light receiving area10C. The light detector1D has an elliptical light receiving area10D having a minor axis in the X-axis direction and a major axis in the Y-axis direction, and also has a meta-lens3D having a shape corresponding to the shape of the light receiving area10D. That is, the meta-lens3D has an elliptical opening3athat is slightly smaller than the light receiving area10D so as not to overlap with the central portion of the elliptical light receiving area10D. As described above, the light receiving area included in the light detector may be formed in various shapes. In addition, the shape of the area where the meta-lens is formed may be formed in various shapes according to the shape of the light receiving area.

REFERENCE SIGNS LIST