Light-receiving element

Abstract

To provide a light-receiving element capable of further improving efficiency of light condensation into a light-receiving region.SOLUTION: A light-receiving element 1 includes at least one light-receiving region 10 and comprises: a substrate 2 including a light incident plane 2a to which light is incident; and a meta lens 3 configured to condense light, that is incident to the light incident plane 2a, on the light incident plane 2a of the substrate 2. In a view in a thickness direction (Z-axis direction) of the substrate 2, the meta lens 3 is formed so as to overlap both an adjacent region R1, which is adjacent to the light-receiving region 10, and a peripheral region R2 that is a region continued with the adjacent region R1 and inside of the light-receiving region 10 along an outer edge of the light-receiving region 10. In the view in the Z-axis direction, a non-formation region R3 in which the meta lens 3 is not formed is provided in a region which overlaps a central region of the light-receiving region 10 on the light incident plane 2a.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present disclosure relates to a light receiving element. [Background technology]

[0002] A configuration is known in which a grating structure, which is a refractive index modulation structure, is provided on the light incident surface of an optical sensor substrate including a light receiving region (see, for example, Patent Document 1). The grating structure described in Patent Document 1 is provided in a peripheral region on the light incident surface that does not overlap with the light receiving region when viewed in the thickness direction of the optical sensor substrate, and is not provided in a region that overlaps with the light receiving region when viewed in the thickness direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0130914 Summary of the Invention [Problem to be solved by the invention]

[0004] The configuration described in Patent Document 1 improves light collection efficiency by collecting light incident on the peripheral region onto the light-receiving region using a grating structure. However, in the configuration described in Patent Document 1, the grating structure is not formed over the entire area that overlaps with the light-receiving region when viewed from the thickness direction of the optical sensor substrate. That is, when viewed from the thickness direction of the optical sensor substrate, the opening region without the grating structure encompasses the entire light-receiving region. When the light to be analyzed includes a component that is incident at an angle with respect to the light incident surface (oblique incident light), many components of the oblique incident light that pass through the opening region may escape directly to the outside of the light-receiving region. Therefore, the configuration described in Patent Document 1 leaves room for improvement in terms of improving the light-collection efficiency onto the light-receiving region, at least for such oblique incident light.

[0005] Therefore, an object of one aspect of the present disclosure is to provide a light-receiving element that can further improve the efficiency of collecting light onto a light-receiving region. [Means for solving the problem]

[0006] A light-receiving element according to one aspect of the present disclosure includes a substrate including at least one light-receiving region and having a light incident surface through which light is incident, and a metalens formed on the light incident surface of the substrate so as to focus light that is incident on the light incident surface, wherein, when viewed in the thickness direction of the substrate, the metalens is formed to overlap both an adjacent region adjacent to the light-receiving region and a peripheral region that is a region inside the light-receiving region that is continuous with the adjacent region and follows the outer edge of the light-receiving region, and when viewed in the thickness direction, a non-forming region in which no metalens is formed is provided in the region of the light incident surface that overlaps with the central region of the light-receiving region.

[0007] In the light-receiving element, the metalens is formed in the adjacent region, thereby enabling light incident on the adjacent region to be suitably guided to the light-receiving region. Furthermore, the non-formed region allows incident light traveling directly from the front of the light-receiving region toward the light-receiving region to be incident on the light-receiving region without passing through the metalens. This reduces light loss caused by light passing through the metalens. Furthermore, the metalens is also formed in the peripheral region that overlaps with the edge of the light-receiving region. This allows the component of the obliquely incident light that is incident on the metalens provided in the peripheral region to be suitably guided to the light-receiving region, even when the light to be analyzed includes obliquely incident light that is incident at an angle with respect to the light incident surface. As a result, the light-collection efficiency on the light-receiving region can be further improved.

[0008] The metalens may be formed by a plurality of periodically arranged convex portions. This configuration allows the metalens to have a physically robust structure.

[0009] The metalens may be composed of a plurality of periodically arranged recesses. This configuration can provide the metalens with an even more physically robust structure. Furthermore, the interior of each of the plurality of recesses may be filled with a dielectric. This configuration can provide the metalens with an even more effectively physically robust structure and can reduce the surface reflectance of the metalens 3. This can further improve the light collection efficiency on the light receiving area.

[0010] The metalens may be formed to overlap at least the first peripheral region and the second peripheral region that face each other in one direction of the peripheral region that is perpendicular to the thickness direction. This configuration can improve the light collection efficiency one-dimensionally in at least the one direction.

[0011] The metalens may be formed so as to overlap the entire annular peripheral region formed around the entire periphery of the light receiving region. With this configuration, it is possible to improve the light collection efficiency two-dimensionally.

[0012] The width of the non-forming region may be set to a range in which the main lobe of light incident on the non-forming region is contained within the light-receiving region, based on the spread width of light incident on the non-forming region due to diffraction. The smaller the width of the non-forming region, the greater the spread width of light incident on the non-forming region due to diffraction. According to the above configuration, the width of the non-forming region is set to a range in which the main lobe of light that has undergone diffraction spread is contained within the light-receiving region, thereby allowing most of the light incident on the non-forming region (main lobe) to enter the light-receiving region. This effectively improves the light-collection efficiency.

[0013] An anti-reflection 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 outside world (for example, air).

[0014] The substrate may include a first substrate having a first surface on which the light receiving region is provided and a second surface opposite 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, and the light incident surface may be formed by a surface of the second substrate located opposite the first substrate. 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 formed by the first substrate on which the light receiving region is provided and the second substrate supporting the first substrate, thereby ensuring appropriate strength of the substrate.

[0015] An anti-reflection 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.

[0016] A metalens layer may be provided between the first substrate and the second substrate. According to the above configuration, incident light proceeding toward the light receiving region is further collected at the interface between the first substrate and the second substrate, thereby further improving the light collection efficiency.

[0017] The substrate may be a single substrate member having a first surface on which the light receiving region is provided and a second surface opposite to the first surface, and the second surface may serve as the light incident surface. With this configuration, the structure of the light receiving element can be simplified while achieving the above-mentioned effect of improving the light collection efficiency. [Effects of the Invention]

[0018] According to one aspect of the present disclosure, it is possible to provide a light-receiving element capable of further improving the efficiency of light collection onto a light-receiving region. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a plan view of a light receiving element according to an embodiment of the present disclosure. [Figure 2] 1. (A) is a cross-sectional view taken along line IIa-IIa in FIG. 1, and (B) is a cross-sectional view taken along line IIb-IIb in FIG. [Figure 3] FIG. 1 is a diagram showing the basic structure (unit cell) of a metalens. [Figure 4] 1A-1C are diagrams illustrating a manufacturing process for a metalens. [Figure 5] 10A and 10B are diagrams for explaining the effect of a light receiving element. [Figure 6] 10A and 10B are diagrams for explaining the light collection efficiency of obliquely incident light in the examples and the comparative examples. [Figure 7] FIG. 10 is a diagram illustrating diffraction broadening at the aperture of a metalens. [Figure 8] FIG. 10 is a diagram showing a first modified example of a substrate provided on a light receiving element. [Figure 9] FIG. 10 is a diagram showing a second modified example of a substrate provided on a light receiving element. [Figure 10] FIG. 10 is a diagram showing a third modified example of a substrate provided on a light receiving element. [Figure 11] FIG. 1 shows a first modified example of the basic configuration of a metalens. [Figure 12] FIG. 10 is a diagram showing a second modified example of the basic configuration of a metalens. [Figure 13] FIG. 10 is a diagram showing the manufacturing process of a metalens having the basic configuration of the first and second modified examples. [Figure 14] 10A to 10D are diagrams showing first to fourth modified examples of the light receiving element. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be designated by the same reference numerals, and redundant description will be omitted.

[0021] [Configuration of the light receiving element according to the embodiment] As shown in FIGS. 1 and 2, the light-receiving element 1 includes a substrate 2 and a metalens 3. In this embodiment, as an example, the light-receiving element 1 is an elongated light-receiving sensor including a light-receiving region 10 for one pixel. However, the light-receiving element 1 may include multiple light-receiving regions 10 corresponding to multiple pixels. For example, the light-receiving element 1 may have a structure in which multiple unit structures (substrate 2) for one pixel shown in FIG. 1 are arranged one-dimensionally in the X-axis or Y-axis direction, or may have a structure in which multiple unit structures are arranged two-dimensionally (in a lattice pattern) in each of the X-axis and Y-axis directions. For convenience of explanation, FIGS. 1 and 2 and other drawings described below illustrate a three-dimensional Cartesian coordinate system consisting of the X-axis, Y-axis, and Z-axis. The X-axis, Y-axis, and Z-axis directions correspond to the short-side direction, long-side direction, and thickness direction of the light-receiving element 1 (substrate).

[0022] The substrate 2 includes at least one light-receiving region 10 and has a light incident surface 2a onto which light to be analyzed is incident. As an example, the substrate 2 is formed in the shape of a rectangular plate. The length of the substrate 2 in the short direction (X-axis direction) is, for example, about 20 μm. The length of the substrate 2 in the long direction (Y-axis direction) is, for example, about 201.5 μm. The substrate 2 has a silicon substrate 21 (first substrate) which is a semiconductor substrate on which the light-receiving region 10 is provided, and a glass substrate 22 (second substrate) on which the metalens 3 is provided.

[0023] The silicon substrate 21 has a main surface 21a (first surface) on which the light receiving region 10 is provided and a back surface 21b (second surface) opposite to the main surface 21a. The thickness (length in the Z-axis direction) of the silicon substrate 21 is, for example, about 10 μm. The glass substrate 22 is bonded to the back surface 21b of the silicon substrate 21 via an adhesive resin layer 23 and supports the silicon substrate 21. The glass substrate 22 has a surface 22a facing the main surface 21a of the silicon substrate 21 and a surface 22b opposite to the surface 22a. The light incident surface 2a of the substrate 2 is formed by the surface 22b of the glass substrate 22. The thickness (length in the Z-axis direction) of the glass substrate 22 is, for example, about 300 μm.

[0024] As shown in FIG. 1, the light-receiving region 10 is provided along the main surface 21a at approximately the center of the main surface 21a of the silicon substrate 21. As an example, the light-receiving region 10 is formed in a rectangular shape. The short-side direction and long-side direction of the light-receiving region 10 respectively coincide with the short-side direction and long-side direction of the substrate 2. The length of the light-receiving region 10 in the short-side direction (X-axis direction) is, for example, approximately 6.2 μm. The length of the light-receiving region 10 in the long-side direction (Y-axis direction) is, for example, approximately 50 μm. The thickness of the light-receiving region 10 (length in the Z-axis direction) is, for example, approximately 3 μm.

[0025] The metalens 3 is formed on the light incident surface 2a of the substrate 2 (in this embodiment, the surface 22b of the glass substrate 22). The metalens 3 is a metasurface structure that functions as a lens that focuses light incident on the light incident surface 2a. More specifically, the metalens 3 is a nanostructure (fine concave-convex structure) in which unit cells C1, which are the basic structure (unit lattice) shown in FIG. 3, are periodically arranged in a lattice pattern along the X-axis and Y-axis directions. As an example, the unit cell C1 is a square region when viewed from the Z-axis direction. One columnar (cylindrical in this embodiment, as an example) pillar 31 (convex portion) is formed in each unit cell C1. The pillar 31 is erected on the surface 22b of the glass substrate 22 at the center of the unit cell C1. That is, the metalens 3 is composed of multiple pillars 31 periodically arranged in a lattice pattern. The pillars 31 are made of, for example, silicon (Si), titanium oxide (TiO2), or the like.

[0026] The period a of the pillars 31 (i.e., the distance between the centers of adjacent pillars 31, i.e., the length of one side of a unit cell C1) is set to be shorter than the wavelength of the light to be analyzed. That is, the metalens 3 has a subwavelength structure for the light to be analyzed. As an example, when the wavelength λ of the light to be analyzed is 940 nm, the period a of the pillars 31 may be set to, for example, 400 nm. Furthermore, the height h of the pillars 31 may be selected from the range of, for example, 450 nm to 550 nm. The width d (diameter) of the pillars 31 may be selected from the range of, for example, 100 nm to 300 nm. As an example, the height h of the pillars 31 throughout the entire metalens 3 (i.e., all unit cells C1) is set to a constant value (e.g., 500 nm). Meanwhile, the width d of the pillars 31 of each unit cell C1 is selected from the above range depending on the location of each unit cell C1. In this way, by setting the width d of the pillar 31 of each unit cell C1 according to the location of each unit cell C1, the amount of phase modulation can be controlled for each location of each unit cell C1, resulting in a metalens 3 that functions as a focusing lens. For example, when viewed in the Z-axis direction, the metalens 3 has a structure in which one period of regions (regions including multiple unit cells C1) formed so that the phase continuously changes by 2π along the direction from the outside of the metalens 3 toward the center (the center of the non-forming region R3 described below) are repeatedly arranged along the above direction.

[0027] Here is some additional information about the structure of the metalens 3 described above. Known types of metalens structures (metasurface structures) are the so-called refractive index modulation type and resonant type. The metalens 3 may have either of the above metasurface structures. The refractive index modulation type metasurface structure is a system that controls the effective refractive index, which is determined by the filling rate (occupancy rate) of the metalens material in each unit cell C1. The resonant type metasurface structure is a system that controls the phase and transmittance by adjusting the electric resonance and magnetic resonance through the structure of each unit cell C1 (i.e., the shape and size of the nanostructure consisting of a plurality of regularly arranged uneven structures). More specifically, the resonant type metasurface structure is a system that realizes the above-mentioned lens function by adjusting the transmittance coefficient t shown in the following formula (1). In the following formula (1), ω e,krepresents the resonant frequency for the kth mode electric resonance, and ω m,k represents the resonance frequency of the kth mode magnetic resonance. ω represents the resonance angular frequency in the Lorentz oscillator model that describes the electron polarization. γ e,k represents the damping coefficient for the electric resonance of the kth mode in the above Lorentz oscillator model, and γ m,k represents the damping coefficient for the magnetic resonance of the kth mode in the above Lorentz oscillator model. k is a parameter that represents the contribution of the electric resonance of the kth mode in the above Lorentz oscillator model, and b k is a parameter that represents the contribution of magnetic resonance of the kth mode in the above Lorentz oscillator model. Note that resonant metasurface structures include the Huygens type (nanodisk type) corresponding to the case where "m = n = 1" in the following formula (1) (i.e., when using resonance of a single mode of electric dipoles and magnetic dipoles), and the HCG type (micropost type) corresponding to the case where "m = n = 1" in the following formula (1) (i.e., when using resonance of a higher mode). When the metalens 3 is configured with a resonant metasurface structure, either the Huygens type or the HCG type described above may be used.

number

[0028] When a refractive index modulation type is employed as the structure of the metalens 3, robustness to changes in the wavelength of the light to be analyzed can be ensured compared to when a resonance type is employed. On the other hand, when a resonance type is employed, the phase change can be made sharper and high transmittance can be ensured compared to when a refractive index modulation type is employed. Furthermore, when a Huygens type is employed, the aspect ratio of the pillars 31 can be made lower (i.e., the height of the pillars 31 can be reduced) compared to when a refractive index modulation type or an HCG type is employed, thereby making the structure of the metalens 3 even more robust. On the other hand, when an HCG type is employed, resonances of multiple higher-order modes can be utilized, thereby increasing the degree of freedom in the structural design of the metalens 3.

[0029] 1 and 2, when viewed in the Z-axis direction (thickness direction of the substrate 2), the metalens 3 is formed so as to overlap both an adjacent region R1 adjacent to the light-receiving region 10 and a peripheral region R2 that is continuous with the adjacent region R1 and is a region inside the light-receiving region 10 along the outer edge of the light-receiving region 10. Furthermore, when viewed in the Z-axis direction, a non-formation region R3 is provided in a region of the light incident surface 2a (in this embodiment, the surface 22b of the glass substrate 22) that overlaps with the central region of the light-receiving region 10. The non-formation region R3 is a region where the metalens 3 is not formed.

[0030] In this embodiment, the metalens 3 is formed so as to overlap the entire annular peripheral region R2 formed around the entire periphery of the light-receiving region 10. That is, when viewed from the Z-axis direction, the metalens 3 has a rectangular annular shape with a rectangular opening 3a corresponding to the non-formation region R3 formed in the center. That is, the non-formation region R3 is formed to be slightly smaller than the light-receiving region 10 by the size of the peripheral region R2. In other words, when viewed from the Z-axis direction, the non-formation region R3 is completely contained inside the light-receiving region 10. In further words, when viewed from the Z-axis direction, the outer edge of the non-formation region R3 is located inside the outer edge of the light-receiving region 10 around the entire periphery of the non-formation region R3.

[0031] An example of a manufacturing process for the metalens 3 will be described with reference to FIG. 4. First, a silicon layer 30 (amorphous silicon) including a portion intended to become the metalens 3 (i.e., a plurality of pillars 31) is formed on the surface 22b of the glass substrate 22 (quartz substrate) by sputtering (step S1). The thickness of the silicon layer 30 is determined based on the design value of the height h of the pillars 31 (e.g., a value selected from the range of 450 nm to 550 nm). Next, an electron beam (EB) resist 100 having a thickness of approximately 300 nm is applied to the surface of the silicon layer 30 (the surface opposite the glass substrate 22) (step S2). Next, a pre-designed pattern is written onto the EB resist 100 by EB lithography (step S3). Specifically, openings 100a corresponding to the portions of each unit cell C1 included in the adjacent region R1 and peripheral region R2 where the pillars 31 are not formed and the non-pillar formation region R3 are formed in the EB resist 100. In this embodiment (the example of FIG. 1 ), the EB writing region is a rectangular region with short sides of 20 μm and long sides of 201.5 μm. Next, etching (e.g., dry etching such as inductively coupled plasma (ICP-RIE) etching) is performed using the EB resist 100 as a mask, thereby removing portions of the silicon layer 30 that correspond to the openings 100a in the EB resist 100 (i.e., exposed portions). Thereafter, the EB resist 100 is peeled off (step S4). As a result, a metalens 3 (i.e., a structure in which a plurality of pillars 31 are periodically arranged) is formed on the surface 22b of the glass substrate 22.

[0032] [Functions and Effects of the Light-Receiving Element According to the Embodiment] The effects of the light-receiving element 1 described above will be described with reference to FIG. 5. As shown in FIG. 5, by forming the metalens 3 in the adjacent region R1, light L1 incident on the adjacent region R1 can be suitably guided to the light-receiving region 10. For example, in the adjacent region R1, the metalens 3 changes the direction of light L1 traveling straight in a direction perpendicular to the light incident surface 2a (i.e., light that would otherwise deviate from the light-receiving region 10) toward the light-receiving region 10, allowing the light L1 to be incident on the light-receiving region 10. Furthermore, by forming the non-forming region R3, incident light (light L3) traveling straight from the front of the light-receiving region 10 toward the light-receiving region 10 can be incident on the light-receiving region 10 without passing through the metalens 3. This reduces optical loss caused by light L3 passing through the metalens 3.

[0033] Furthermore, in the light receiving element 1, a metalens 3 is also formed in a peripheral region R2 that overlaps with the edge of the light receiving region 10. In other words, when viewed from the Z-axis direction, the outer edge of the non-forming region R3 is located more inward than the outer edge of the light receiving region 10. This allows the component of the obliquely incident light that is incident on the metalens 3 provided in the peripheral region R2 to be suitably guided to the light receiving region 10, even if the light L to be analyzed includes a component that is incident at an angle with respect to the light incident surface 2a (obliquely incident light).

[0034] The effect on obliquely incident light will be described in detail with reference to FIG. 6. The light-receiving element 200 shown in FIG. 6(A) is a simulation model with a simple configuration created to verify the effect achieved by forming the metalens 3 in the peripheral region R2. In the light-receiving element 200, the light-receiving region 10 is formed over the entire surface 22a of the glass substrate 22, and the metalens 3 described above is formed on the surface 22b. An opening 3a (an opening corresponding to the non-forming region R3 described above) is provided in the center of the metalens 3. The region on the surface 22b where the metalens 3 is provided corresponds to the peripheral region R2 described above. The refractive index of the glass substrate 22 is 1.51, and the thickness d1 of the glass substrate 22 is 40 μm. The period a of the metalens 3 (see FIG. 3) is 400 nm, and the height d2 of the metalens 3 (i.e., the height of the pillars 31) is 500 nm. The light-receiving element 200 is formed in the shape of a square plate with a side length w1 of 40 μm. The width w2 (length of one side) of the opening 3a is 10 μm. The upper diagram in FIG. 6A shows a cross section of the light receiving element 200 along the thickness direction, passing through the center of the light receiving region 10 (the center of the opening 3a). Here, the light L to be analyzed is light that is incident on the entire light incident surface (surface 22b) at an angle with respect to the light incident surface in the cross section. The wavelength λ of the light L is 940 nm. The angle of inclination θ of the light L with respect to the light incident surface is set to 20 degrees. Meanwhile, the light receiving element 300 shown in FIG. 6B is a simulation model corresponding to a comparative example. The light receiving element 300 differs from the light receiving element 200 in that the metalens 3 is not formed, but is otherwise similar in configuration to the light receiving element 200.

[0035] The horizontal axis of the graph shown at the bottom of FIG. 6A represents the distance from the center position of the light receiving element 200 in the cross section (the distance is represented as a positive direction toward the right and a negative direction toward the left). The vertical axis of the graph represents the intensity of light incident at each position on the light receiving element 200. The graph shown at the bottom of FIG. 6B is a graph for the light receiving element 300 corresponding to the graph for the light receiving element 200 described above. These graphs reveal the following. That is, as shown in the graph shown at the bottom of FIG. 6B, in the light receiving element 300 in which the metalens 3 is not formed, it can be seen that the light L escapes outside the light receiving region 10 in the traveling direction of the light L (to the right in this example). In contrast, as shown in the graph shown at the bottom of FIG. 6A, it can be seen that in the light receiving element 200, the peak position of the light amount is slightly shifted toward the traveling direction of the light L from the center position of the light receiving region 10, but is still located within the light receiving region 10. That is, it can be seen that the metalens 3 (i.e., the metalens 3 formed in the peripheral region R2) efficiently focuses most of the components of the light L into the light-receiving region 10. From the above, it can be seen that by forming the metalens 3 in the peripheral region R2 that overlaps with the edge of the light-receiving region 10, obliquely incident light can be suitably focused onto the light-receiving region 10.

[0036] As a result, the light receiving element 1 can further improve the efficiency of light collection onto the light receiving region 10. In addition, for example, when the light receiving element 1 has a structure in which a plurality of unit structures (substrates 2) each corresponding to one pixel shown in Fig. 1 are arranged along the X-axis direction, it is possible to prevent obliquely incident light incident on one pixel (i.e., the light incident surface 2a corresponding to one light receiving region 10) from being incident on a pixel adjacent to the one pixel (so-called crosstalk).

[0037] Furthermore, the metalens 3 is composed of a plurality of periodically arranged pillars 31. With such a configuration, the metalens 3 can have a physically robust structure.

[0038] Furthermore, as shown in FIG. 5 , light passing through the non-formation region R3 (i.e., the opening 3 a of the metalens 3) is diffracted at the opening 3 a and spreads as it heads toward the light-receiving region 10. For this reason, if the non-formation region R3 and the light-receiving region 10 were the same size and completely overlapped when viewed from the Z-axis direction, some of the diffracted light L2 would leak outside the light-receiving region 10. On the other hand, in this embodiment, the metalens 3 is provided in the peripheral region R2, so the non-formation region R3 is formed to be slightly smaller than the light-receiving region 10. This makes it possible to appropriately contain, within the light-receiving region 10, the diffracted light L2 that passes through the non-formation region R3 and spreads as it heads toward the light-receiving region 10, as shown in FIG. 5 . Note that although light incident on the metalens 3 disposed in the peripheral region R2 is somewhat attenuated by the metalens 3, it is still guided to the light-receiving region 10 due to the light-collecting effect of the metalens 3. Therefore, the sensitivity can be improved compared to the case where light escapes outside the light receiving region 10 due to the spreading caused by the aperture diffraction described above.

[0039] More preferably, the width of the non-formation region R3 (i.e., the width (length of one side) of the opening 3a) can be set as follows based on the spread width due to diffraction of the light L incident on the non-formation region R3. That is, the width of the non-formation region R3 can be set within a range such that the main lobe of the light L incident on the non-formation region R3 is encompassed by the light-receiving region 10. This will be explained in more detail with reference to FIG. 7. As shown in FIG. 7, the spread width caused by diffraction at the opening 3a of the metalens 3 (the spread width of the main lobe of the light L at the position where the light-receiving region 10 is provided) is expressed by the following formula (2): where λ represents the wavelength of the light L, Z represents the propagation distance (i.e., the distance from the light incident surface 2a to the light-receiving region 10), n represents the refractive index of the propagation medium, and W represents the opening width (diameter) of the opening 3a. In this embodiment, there are three types of propagation media from the light incident surface 2a to the light receiving region 10: the glass substrate 22, the adhesive resin layer 23, and the silicon substrate 21. In this case, the refractive index n is an average refractive index calculated based on the refractive index and thickness of each medium. Main lobe spread = 2λZ / nW …(2)

[0040] Therefore, if the width of the light-receiving region 10 is represented as D, then by setting the width W of the opening 3a so as to satisfy the following formula (3), it is possible to make the entire main lobe of the light L incident on the non-forming region R3 incident on the light-receiving region 10. This makes it possible to effectively improve the light-collection efficiency. Note that FIG. 7 shows the case where the equal sign (=) holds in the following formula (3) (i.e., the case where the width W is set to the lower limit value for collecting the entire main lobe on the light-receiving region 10). 2λZ / nD≦W …(3)

[0041] When the non-forming region R3 (opening 3a) is formed in a circular shape rather than a rectangular shape (for example, see (C) of FIG. 14), the above formulas (2) and (3) are replaced with the following formulas (4) and (5). In this case, the width W of the opening 3a means the diameter of the opening 3a. Note that when the non-forming region R3 (opening 3a) has a shape that is neither rectangular nor circular (for example, when the rectangular shape has chamfered corners), a value between the value on the left side of the above formula (3) and the value on the left side of the above formula (5) (for example, an intermediate value) may be used as the lower limit value of the width W of the opening 3a. Main lobe spread = 2.44λZ / nW … (4) 2.44λZ / nD≦W …(5)

[0042] Furthermore, the metalens 3 is formed so as to overlap the entire annular peripheral region R2 that is formed around the entire periphery of the light-receiving region 10. With the above configuration, it is possible to improve the light-collection efficiency two-dimensionally. That is, in this embodiment, the above-described improvement in light-collection efficiency is achieved in both the plane along the X-axis direction and the plane along the Y-axis direction.

[0043] The substrate 2 also includes a silicon substrate 21 having a main surface 21a (first surface) on which the light-receiving region 10 is provided and a back surface 21b opposite to the main surface 21a, and a glass substrate 22 that is bonded to the back surface 21b of the silicon substrate 21 via an adhesive resin layer 23 and supports the silicon substrate 21, and the light incident surface 2a is formed by the surface 22b of the glass substrate 22. According to the above configuration, by forming the substrate 2 with the first substrate (the silicon substrate 21 in this embodiment) on which the light-receiving region 10 is provided and the second substrate (the glass substrate 22 in this embodiment) that supports the first substrate, the strength of the substrate 2 can be appropriately ensured.

[0044] [First Modified Example of Substrate] 8, a first modified example (substrate 2A) of the substrate included in the light receiving element 1 will be described. As shown in FIG. 8, the substrate 2A differs from the substrate 2 in that it further includes an antireflection film 4 and an antireflection film 5, but is otherwise similar to the substrate 2.

[0045] The anti-reflection film 4 is provided in a non-formation region R3 (a region corresponding to the opening 3a) of the light incident surface 2a (here, the surface 22b of the glass substrate 22). The anti-reflection film 4 serves to suppress reflection loss of incident light at the interface between the light incident surface 2a and the outside world (air). The anti-reflection film 4 can be formed, for example, by a single-layer AR coating on the surface 22b of the glass substrate 22. The anti-reflection film 4 can suitably improve the transmittance of light passing through the non-formation region R3. This can effectively improve the light collection efficiency to the light receiving region 10.

[0046] Refractive index n of anti-reflection coating 4 AR and film thickness d AR can be set based on the refractive index of each medium disposed on both sides of the anti-reflection coating 4. Specifically, the refractive index n AR is the refractive index of air n Air and the refractive index n of the glass substrate 22 (SiO2) SiO2 That is, the following formula (6) is established. More preferably, from the viewpoint of widening the wavelength band in which reflection can be suppressed, the refractive index n ARmay be set based on the following formula (7): AR is set based on the following formula (8): where λ represents the wavelength of the light to be analyzed, and m represents an arbitrary integer of 1 or more. n Air <n AR <n SiO2 …(6) n AR =(n Air n SiO2 ) 1 / 2 …(7) d AR =(2m+1)λ / 4n AR …(8)

[0047] The antireflection film 5 is provided between the silicon substrate 21 and the glass substrate 22 (between the silicon substrate 21 and the adhesive resin layer 23 in this embodiment). The antireflection film 5 serves to suppress reflection loss of incident light at the interface between the silicon substrate 21 and the glass substrate 22. The antireflection film 5 can be formed, for example, by a single-layer AR coating on the back surface 21b of the silicon substrate 21. The antireflection film 5 can suitably improve the transmittance of light passing through the interface between the silicon substrate 21 and the glass substrate 22. This can effectively improve the light collection efficiency to the light-receiving region 10. As with the antireflection film 4, the refractive index and film thickness of the antireflection film 5 can be set based on the refractive index of each medium arranged on both sides of the antireflection film 5.

[0048] Although the configuration including both the anti-reflection film 4 and the anti-reflection film 5 has been described as an example here, only one of the anti-reflection film 4 and the anti-reflection film 5 may be provided. The anti-reflection film 5 may be provided between the adhesive resin layer 23 and the glass substrate 22. An anti-reflection film may be provided between the silicon substrate 21 and the adhesive resin layer 23, and between the adhesive resin layer 23 and the glass substrate 22.

[0049] [Second modified example of substrate] 9, a second modified example (substrate 2B) of the substrate included in light receiving element 1 will be described. As shown in FIG. 9, substrate 2B differs from substrate 2 in that it further includes a metalens layer 6, but is otherwise similar to substrate 2.

[0050] The metalens layer 6 is provided between the silicon substrate 21 and the glass substrate 22 (in this embodiment, between the silicon substrate 21 and the adhesive resin layer 23). The metalens layer 6 has a fine uneven structure (for example, a structure in which a plurality of pillars 31 are periodically arranged) similar to that of the metalens 3 described above, and serves to further focus light traveling from the glass substrate 22 side toward the silicon substrate 21 side onto the light-receiving region 10. This effectively improves the light-focusing efficiency onto the light-receiving region 10. An anti-reflection film 4 similar to that on the substrate 2A may also be provided on the substrate 2B.

[0051] [Third modified example of the substrate] A third modified example of the substrate (substrate 2C) of the light-receiving element 1 will be described with reference to FIG. 10. As shown in FIG. 10, the substrate 2C is made of a single substrate member (silicon substrate 21), and differs from the substrate 2 in that the light incident surface 2a is formed by the back surface 21b of the silicon substrate 21. The substrate 2C is otherwise similar to the substrate 2. That is, the light-receiving element 1 including the substrate 2C is a back-illuminated light-receiving sensor, and has a configuration in which a metalens 3 is formed on the incident surface (back surface 21b) of the light-receiving sensor. By omitting the second substrate (glass substrate 22) included in the substrate 2, the structure of the light-receiving element 1 can be simplified while achieving the same effect of improving the light collection efficiency as the substrate 2 described above. The substrate 2C may further be provided with an anti-reflection film 4 similar to that of the substrate 2A.

[0052] [Other variations of the substrate] Although the substrate 2 has a structure in which a first substrate (silicon substrate 21) and a second substrate (glass substrate 22) are bonded together, the combination of the first and second substrates is not limited to the above example. For example, a silicon substrate similar to the first substrate may be used as the second substrate instead of the glass substrate 22. In this case, the first and second substrates (i.e., the silicon substrates) may be bonded directly without using an adhesive (adhesive resin layer 23).

[0053] [First modified example of the basic configuration of the metalens] Referring to FIG. 11 , a first modified example (unit cell C2) of the basic structure (unit lattice) of the metalens 3 will be described. The unit cell C2 is formed by an inorganic material layer 32 deposited on the surface 22b of the glass substrate 22. The inorganic material layer 32 has one columnar (cylindrical in this embodiment, as an example) hole 32a (recess) formed for each unit cell C2. The hole 32a penetrates from the upper surface 32b of the inorganic material layer 32 (the surface opposite to the surface in contact with the surface 22b) to the surface 22b of the glass substrate 22 at the center of the unit cell C2. The inorganic material layer 32 is formed, for example, from the same material as the pillar 31. The metalens 3 may have a hole structure in which unit cells C2 are periodically arranged in a lattice pattern, instead of the pillar structure in which the above-described unit cells C1 are periodically arranged in a lattice pattern.

[0054] When the unit cell C2 is used as the basic configuration of the metalens 3, the period a of the holes 32a (i.e., the center-to-center distance between adjacent holes 32a, i.e., the length of one side of the unit cell C2) is set to be shorter than the wavelength of the light to be analyzed, as in the case when the unit cell C1 is used. As an example, when the wavelength λ of the light to be analyzed is 940 nm, the period a of the holes 32a is set to, for example, 400 nm. Furthermore, the height h of the holes 32a (depth of the recess) may be selected, for example, from a range of 300 nm to 400 nm. The width d (diameter) of the holes 32a may be selected, for example, from a range of 100 nm to 300 nm. As an example, the height h of the holes 32a is set to a constant value (e.g., 500 nm) throughout the entire metalens 3 (i.e., all unit cells C2). Meanwhile, the width d of the holes 32a of each unit cell C2 is selected from the above range depending on the location of each unit cell C2. In this way, by setting the width d of the hole 32a in each unit cell C2 according to the location of each unit cell C2, the amount of phase modulation can be controlled for each location of each unit cell C2, resulting in a metalens 3 that functions as a focusing lens. For example, when viewed in the Z-axis direction, the metalens 3 has a structure in which one period of regions (regions including multiple unit cells C2) formed so that the phase continuously changes by 2π along the direction from the outside of the metalens 3 toward the center (the center of the non-forming region R3 described below) are repeatedly arranged along the above direction.

[0055] When the unit cell C2 is employed as the basic structure of the metalens 3, that is, when the metalens 3 is formed from a plurality of periodically arranged holes 32a (recesses), the metalens 3 can have a structure that is even more physically robust than when the metalens 3 is formed from a pillar structure (a plurality of unit cells C1).

[0056] [Second modified example of the basic configuration of the metalens] Referring to FIG. 12, a second modified example (unit cell C3) of the basic structure (unit lattice) of the metalens 3 will be described. Unit cell C3 differs from unit cell C2 in that the holes 32a are filled with a dielectric 33, but is otherwise similar to unit cell C2. The dielectric 33 may be, for example, Al2O3, SiO2, SiN, or HfO2. As shown in FIG. 12, the dielectric 33 fills the holes 32a of each unit cell C3 and may also be deposited on the upper surface 32b of the inorganic material layer 32. The distance from the upper surface 32b of the inorganic material layer 32 to the upper surface 33a of the dielectric 33 (i.e., the height of the dielectric 33 deposited on the inorganic material layer 32) is, for example, approximately 150 nm.

[0057] When unit cell C3 is used as the basic configuration of metalens 3, the metalens can be made even more effectively physically robust. That is, the provision of dielectric 33 makes the metalens structure more physically robust than unit cell C2. Furthermore, by embedding dielectric 33 in hole 32a, it is possible to reduce the surface reflectance of metalens 3. This can further improve the efficiency of light collection onto the light-receiving region.

[0058] Referring to FIG. 13 , an example of a manufacturing process for a metalens 3 having unit cells C2 and C3 according to the first and second modifications described above will be described. First, a silicon layer 30 (amorphous silicon) including a portion intended to become the inorganic material layer 32 is formed on the surface 22b of a glass substrate 22 (quartz substrate) by sputtering (step S11). The film thickness of the silicon layer 30 may be selected, for example, from a range of 300 nm to 400 nm. Next, an electron beam (EB) resist 100 having a film thickness of approximately 300 nm is applied to the surface of the silicon layer 30 (the surface opposite the glass substrate 22) (step S12). Next, a pre-designed pattern is written on the EB resist 100 by EB lithography (step S13). Specifically, openings 100a corresponding to the portions of each unit cell C2 and C3 included in the adjacent region R1 and peripheral region R2 described above that correspond to the holes 32a and the non-forming region R3 are formed in the EB resist 100. In this embodiment (the example of FIG. 1 ), the EB writing region is a rectangular region with short sides of 20 μm and long sides of 201.5 μm. Next, etching (e.g., dry etching such as inductively coupled plasma (ICP-RIE) etching) is performed using the EB resist 100 as a mask, thereby removing portions of the silicon layer 30 corresponding to the openings 100a of the EB resist 100 (i.e., exposed portions). Then, the EB resist 100 is peeled off (step S14). Through the processes up to this point, a metalens 3 having a unit cell C2 as its basic structure is formed on the surface 22b of the glass substrate 22. To form a metalens 3 having a unit cell C3 as its basic structure, the following process is further performed. Specifically, a dielectric 33 is formed (deposited) in the holes 32a and on the inorganic material layer 32 by atomic layer deposition (ALD) (step S15). Note that when performing ALD, the non-formation region R3 is masked to prevent the dielectric 33 from being formed in the non-formation region R3. Through the above processing, a metalens 3 having a basic structure of unit cells C3 is formed on surface 22b of glass substrate 22.

[0059] [Other variations] Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment. The materials and shapes of each component are not limited to those described above, and various materials and shapes can be used. For example, as shown in (A) to (D) of FIG. 14, the shape of the substrate, the shape of the light receiving region, and the shape of the region where the metalens is formed are not limited to those of the above embodiment.

[0060] In a light-receiving element 1A of a first modified example shown in FIG. 14A, a metalens 3A (a pair of metalenses 3A1 and 3A2) is formed in regions on both sides of the light-receiving region 10 in the longitudinal direction (Y-axis direction) of the substrate 2. In other words, no metalens is formed in regions on both sides of the center of the light-receiving region 10 (regions corresponding to the non-forming region R3) in the lateral direction (X-axis direction) of the substrate 2. The metalens 3A is formed so as to overlap with the first peripheral region R21 and the second peripheral region R22 that face each other in the Y-axis direction of the peripheral region R2. This configuration also makes it possible to improve the light-collection efficiency one-dimensionally, at least in the longitudinal direction (Y-axis direction) of the substrate 2. Furthermore, in the light-receiving element 1A, the metalens 3A may be formed in only one of the regions on both sides of the light-receiving region 10 in the longitudinal direction of the substrate 2. That is, one of the metalenses 3A1 and 3A2 may be omitted. Even with this configuration, the effects described above are achieved with respect to the peripheral region R2 on the side where the metalens 3A is formed.

[0061] In a light-receiving element 1B of a second modified example shown in FIG. 14(B), a metalens 3B (a pair of metalenses 3B1 and 3B2) is formed in regions on both sides of the light-receiving region 10 in the short-side direction (X-axis direction) of the substrate 2. In other words, no metalenses are formed in regions on both sides of the center of the light-receiving region 10 (regions corresponding to the non-forming region R3) in the long-side direction (Y-axis direction) of the substrate 2. The metalens 3B is formed so as to overlap with the first peripheral region R21 and the second peripheral region R22 that face each other in the X-axis direction in the peripheral region R2. This configuration also makes it possible to improve the light-collection efficiency one-dimensionally, at least in the short-side direction (X-axis direction) of the substrate 2. Furthermore, in the light-receiving element 1B, the metalens 3B may be formed in only one of the regions on both sides of the light-receiving region 10 in the short-side direction of the substrate 2. In other words, one of the metalenses 3B1 and 3B2 may be omitted. Even with this configuration, the effects described above are achieved with respect to the peripheral region R2 on the side where the metalens 3B is formed.

[0062] A light receiving element 1C of a third modified example shown in Fig. 14(C) has a square plate-shaped substrate 2C. A light receiving element 1D of a fourth modified example shown in Fig. 14(D) has a shape that is shorter than the substrate 2 and longer than the substrate 2C. In this way, the substrate provided in the light receiving element can be formed in various shapes.

[0063] Furthermore, the light-receiving element 1C has a circular light-receiving region 10C and a metalens 3C shaped according to the shape of the light-receiving region 10C. That is, the metalens 3C has a circular opening 3a that is slightly smaller than the light-receiving region 10C so as not to overlap with the center of the circular light-receiving region 10C. The light-receiving element 1D has an elliptical light-receiving region 10D with its minor axis in the X-axis direction and its major axis in the Y-axis direction, and a metalens 3D shaped according to the shape of the light-receiving region 10D. That is, the metalens 3D has an elliptical opening 3a that is slightly smaller than the light-receiving region 10D so as not to overlap with the center of the elliptical light-receiving region 10D. In this way, the light-receiving region of a light-receiving element can be formed in various shapes. Furthermore, the shape of the region where the metalens is formed can be formed in various shapes according to the shape of the light-receiving region. [Explanation of symbols]

[0064] 1, 1A, 1B, 1C, 1D...photodetector, 2, 2A, 2B, 2C...substrate, 2a...light incident surface, 3, 3A, 3A1, 3A2, 3B, 3B1, 3B2, 3C, 3D...metalens, 4, 5...antireflection coating, 6...metalens layer, 10, 10C, 10D...light receiving region, 21...silicon substrate (first substrate), 21a...main surface (first surface), 21b...rear surface (second surface), 22...glass substrate (second substrate), 22b...surface, 23...adhesive resin layer, 31...pillar (convex portion), 32a...hole (concave portion), 33...dielectric, R1...adjacent region, R2...peripheral region, R3...non-forming region, R21...first peripheral region, R22...second peripheral region.

Claims

1. a substrate including at least one light receiving region and having a light incident surface onto which light of a specific wavelength to be analyzed is incident; a metasurface structure that functions as a lens for condensing the light incident on the light incident surface of the substrate, the metasurface structure having a subwavelength structure of the light; when viewed in the thickness direction of the substrate, the metalens is formed so as to overlap both an adjacent region adjacent to the light receiving region and a peripheral region that is a region inside the light receiving region that is continuous with the adjacent region and follows an outer edge of the light receiving region, a non-formation region in which the metalens is not formed is provided in a region of the light incident surface that overlaps with a central region of the light receiving region when viewed from the thickness direction.

2. The light-receiving element according to claim 1 , wherein the metalens is formed of a plurality of periodically arranged convex portions.

3. The light-receiving element according to claim 1 , wherein the metalens is formed by a plurality of periodically arranged recesses.

4. The light-receiving element according to claim 3 , wherein the interior of each of the plurality of recesses is filled with a dielectric material.

5. 5. The light-receiving element according to claim 1, wherein the metalens is formed so as to overlap at least a first peripheral region and a second peripheral region that face each other in one direction of the peripheral region that is perpendicular to the thickness direction.

6. 5. The light-receiving element according to claim 1, wherein the metalens is formed so as to overlap the entire annular peripheral region formed around the entire periphery of the light-receiving region.

7. The light-receiving element according to any one of claims 1 to 6, wherein the width of the non-forming region is set to a range in which a main lobe of the light incident on the non-forming region is included in the light-receiving region.

8. 8. The light-receiving element according to claim 1, wherein an anti-reflection film is provided in the non-forming region.

9. The substrate is a first substrate having a first surface on which the light receiving region is provided and a second surface opposite to the first surface; a second substrate bonded to the second surface of the first substrate and supporting the first substrate; 9. The light-receiving element according to claim 1, wherein the light incident surface is formed by a surface of the second substrate located on the opposite side to the first substrate.

10. the first substrate is a silicon substrate, The light-receiving element according to claim 9 , wherein the second substrate is a glass substrate.

11. 11. The light-receiving element according to claim 9, further comprising an anti-reflection film provided between the first substrate and the second substrate.

12. The light-receiving element according to claim 9 or 10, further comprising a metalens layer provided between the first substrate and the second substrate.

13. the substrate is made of a single substrate member having a first surface on which the light receiving region is provided and a second surface opposite to the first surface, 9. The light-receiving element according to claim 1, wherein the light incident surface is formed by the second surface.

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