Light detection element

Abstract

There is provided a light detection element including: an avalanche photodiode having a light incident surface on which light is incident; and a plasma structure part that diffracts light by surface plasmon resonance. The avalanche photodiode includes: a p-type first semiconductor region; and an n-type second semiconductor region that is formed on the opposite side of the first semiconductor region from the light incident surface and forms a pn junction with the first semiconductor region. The plasma structure section has a plurality of unit structures arranged on the first semiconductor region. Each of the plurality of unit structures has: a top surface on the opposite side of the light incident surface; a bottom surface opposite to the light incident surface; and a side surface connected to the top surface and the bottom surface. The height of each of the plurality of unit structures is 100 nm or more and 250 nm or less.

Description

Technical Field

[0001] One aspect of the present invention relates to a light detection element. Background Art

[0002] A solid-state imaging device using avalanche multiplication is described in International Publication No. 2017 / 038542. This document describes the generation of surface plasmon resonance by disposing metal nanoparticles on the surface of a silicon substrate constituting a solid-state imaging device (Fig. 23). Summary of the Invention

[0003] Technical Problem to be Solved by the Invention

[0004] The inventors of the present invention have found that there is room for improvement in the above-described configuration from the viewpoint of improving the quantum efficiency. An object of one invention of the present invention is to provide a light detection element capable of improving the quantum efficiency.

[0005] Technical Means for Solving the Technical Problem

[0006] A light detection element according to one aspect of the present invention is [1] "a light detection element including: an avalanche photodiode having a light incident surface for light to enter; and a plasma structure portion formed on the light incident surface for diffracting the light by surface plasmon resonance, the avalanche photodiode having: a p-type first semiconductor region; and an n-type second semiconductor region formed on the side of the first semiconductor region opposite to the light incident surface to form a pn junction with the first semiconductor region, the plasma structure portion having a plurality of unit structures arranged on the first semiconductor region, each of the plurality of unit structures having: a top surface on the side opposite to the light incident surface; a bottom surface facing the light incident surface; and a side surface connecting the top surface and the bottom surface, and the height of each of the plurality of unit structures being 100 nm or more and 250 nm or less".

[0007] In this optical detection element, an avalanche photodiode has a p-type first semiconductor region and an n-type second semiconductor region. The n-type second semiconductor region is formed on the side of the first semiconductor region opposite to the light incident surface, and a pn junction is formed with the first semiconductor region. In a so-called PonN structure where a p-type semiconductor region is formed on an n-type semiconductor region, the light absorption amount of the p-type semiconductor region tends to be small. Regarding this point, in this optical detection element, by using a plasma structure portion to diffract incident light, the optical path length of the p-type first semiconductor region can be increased. As a result, the light absorption amount can be increased and the quantum efficiency can be improved. In addition, in this optical detection element, each unit structure constituting the plasma structure portion has a top surface, a bottom surface, and side surfaces, and the height of each unit structure is 100 nm or more and 250 nm or less. Thereby, localized surface plasmon resonance can be generated in the plasma structure portion, and incident light can be appropriately diffracted. As a result, the above-described effects, that is, the effects of increasing the light absorption amount and improving the quantum efficiency, can be obtained. Therefore, by using this optical detection element, the quantum efficiency can be improved.

[0008] The optical detection element according to one aspect of the present invention may also be [2] "the optical detection element according to [1], wherein the side surfaces of the plurality of unit structures are formed perpendicular to the light incident surface, and the height of each of the plurality of unit structures is 100 nm or more and 150 nm or less". In this case, localized surface plasmon resonance can be generated when the side surfaces are formed perpendicularly, and incident light can be appropriately diffracted.

[0009] The optical detection element according to one aspect of the present invention may also be [3] "the optical detection element according to [1], wherein the side surfaces of the plurality of unit structures are inclined so as to widen as they approach the bottom surface". In this case, the wavelength range in which surface plasmon resonance is generated can be broadened. In addition, for example, in the case where a shape defect occurs at the boundary portion between the top surface and the side surface during the manufacturing process or the like (for example, when a notch is formed at a corner or the corner becomes rounded), it may lead to the inability to obtain the required function. However, when the side surfaces are inclined, for example, compared with the case where the side surfaces are formed perpendicularly, the influence of such shape defects can be suppressed.

[0010] The optical detection element according to one aspect of the present invention may also be [4] "the optical detection element according to [3], wherein the height of each of the plurality of unit structures is 125 nm or more and 250 nm or less". In this case, when the side surfaces are inclined, localized surface plasmon resonance can be generated, and incident light can be appropriately diffracted.

[0011] The light detection element according to one aspect of the present invention may also be "[5] the light detection element according to any one of [1] to [4], wherein in each of the plurality of unit structures, the top surface and the side surface are connected to each other via a curved surface". In this case, even when an external force is applied, the plasma structure portion is not easily damaged, and the stability of the light detection element can be improved.

[0012] The light detection element according to one aspect of the present invention may also be "[6] the light detection element according to any one of [1] to [5], wherein a silicon dioxide layer is formed between the plasma structure portion and the first semiconductor region". In this case, by adjusting the thickness of the silicon dioxide layer, surface plasmon resonance can be generated within the required wavelength range.

[0013] The light detection element according to one aspect of the present invention may also be "[7] the light detection element according to [6], wherein an adhesion layer made of a metal material is formed between the plasma structure portion and the silicon dioxide layer". In this case, the bonding strength between the plasma structure portion and the silicon dioxide layer can be improved.

[0014] The light detection element according to one aspect of the present invention may also be "[8] the light detection element according to any one of [1] to [7], wherein a groove for reflecting the light diffracted by the plasma structure portion is formed in the avalanche photodiode, and the groove surrounds the first semiconductor region when viewed from a direction perpendicular to the light incident surface". In this case, by reflecting the light using the groove, the optical path length of the first semiconductor region can be further increased.

[0015] The light detection element according to one aspect of the present invention may also be "[9] the light detection element according to any one of [1] to [8], wherein when viewed from a direction perpendicular to the light incident surface, the plurality of unit structures are arranged in a first direction, and each of the plurality of unit structures has a shape that is longer in a second direction perpendicular to the first direction". In this case, for example, one of the P-polarized light and the S-polarized light can be diffracted by the plasma structure portion, and the other of the P-polarized light and the S-polarized light can be reflected by the plasma structure portion.

[0016] The light detection element according to one aspect of the present invention may also be "

[10] the light detection element according to [1] or [2], wherein the plasma structure portion is configured such that the second diffracted light travels at an angle of 70° or more and less than 90° with respect to the direction perpendicular to the light incident surface". In this case, the size of the plasma structure portion can be ensured, and the manufacturing accuracy can be ensured.

[0017] The light detection element according to one aspect of the present invention may also be "

[11] the light detection element as described in [1] or [2], wherein the plasma structure portion is covered by a protective layer, and the protective layer enters between adjacent unit structures". In this case, the physical durability and chemical durability of the plasma structure portion can be improved, and a predetermined optical element can be further provided on the protective layer.

[0018] The light detection element according to one aspect of the present invention may also be "

[12] the light detection element as described in [6], wherein the thickness of the silicon dioxide layer is 1 nm or more and 5 nm or less". In this case, the following effect can be significantly obtained, that is, by adjusting the thickness of the silicon dioxide layer, the effect of generating surface plasmon resonance in the required wavelength range can be achieved.

[0019] The light detection element according to one aspect of the present invention may also be "

[13] the light detection element as described in [7], wherein the adhesion layer is a titanium layer". In this case, the light absorption rate can be improved.

[0020] According to one aspect of the present invention, a light detection element capable of improving the quantum efficiency can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1A is a top view of the light detection element, Figure 1B is along Figure 1A sectional view taken along line B-B of.

[0022] Figure 2A is a perspective view of the unit structure, Figure 2B is a photograph showing the unit structure.

[0023] Figure 3 is a sectional view of the unit structure of the first example.

[0024] Figure 4 is a sectional view of the unit structure of the second example.

[0025] Figure 5A is a sectional view of the PonN-type structure, Figure 5B is a sectional view of the NonP-type structure.

[0026] Figure 6A is a sectional view of the structure in which the plasma structure portion is arranged in the PonN type, Figure 6B is showing Figure 6A diagram of the electric field pattern in the structure of.

[0027] Figs. 7 to 11 are graphs showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the case where the period P is 520 nm in the first example.Figure 7A It is a graph when the height H is 50 nm. Figure 7B It is a graph when the height H is 60 nm.

[0028] Figure 8A It is a graph when the height H is 70 nm. Figure 8B It is a graph when the height H is 80 nm.

[0029] Figure 9A It is a graph when the height H is 90 nm. Figure 9B It is a graph when the height H is 100 nm.

[0030] Figure 10A It is a graph when the height H is 125 nm. Figure 10B It is a graph when the height H is 150 nm.

[0031] Figure 11A It is a graph when the height H is 175 nm. Figure 11B It is a graph when the height H is 200 nm.

[0032] Figure 12 to Figure 14 It is a graph showing the relationship between wavelength, absorptivity, transmittance, and reflectance when the period P is 250 nm in the first example. Figure 12A It is a graph when the height H is 100 nm. Figure 12B It is a graph when the height H is 125 nm.

[0033] Figure 13A It is a graph when the height H is 150 nm. Figure 13B It is a graph when the height H is 175 nm.

[0034] Figure 14 It is a graph when the height H is 200 nm.

[0035] Figure 15 to Figure 17 It is a graph showing the relationship between wavelength, absorptivity, transmittance, and reflectance when the period P is 260 nm in the first example. Figure 15A It is a graph when the height H is 100 nm. Figure 15B It is a graph when the height H is 125 nm.

[0036] Figure 16A It is a graph when the height H is 150 nm. Figure 16B It is a graph when the height H is 175 nm.

[0037] Figure 17It is a graph when the height H is 200 nm.

[0038] Figure 18 to Figure 25 It is a graph showing the relationship between wavelength and absorptance, transmittance, and reflectance when the angle θ is 80.5° and the period P is 520 nm in the second example. Figures 18 to 22 are graphs when the gap is 20 nm to 60 nm, and Figures 23 to Figure 25 It is a graph when the gap is 70 nm to 130 nm. Figure 18A It is a graph when the height H is 100 nm, Figure 18B It is a graph when the height H is 125 nm.

[0039] Figure 19A It is a graph when the height H is 150 nm, Figure 19B It is a graph when the height H is 175 nm.

[0040] Figure 20A It is a graph when the height H is 200 nm, Figure 20B It is a graph when the height H is 210 nm.

[0041] Figure 21A It is a graph when the height H is 220 nm, Figure 21B It is a graph when the height H is 230 nm.

[0042] Figure 22A It is a graph when the height H is 240 nm, Figure 22B It is a graph when the height H is 250 nm.

[0043] Figure 23A It is a graph when the height H is 100 nm, Figure 23B It is a graph when the height H is 125 nm.

[0044] Figure 24A It is a graph when the height H is 150 nm, Figure 24B It is a graph when the height H is 175 nm.

[0045] Figure 25 It is a graph when the height H is 200 nm.

[0046] Figure 26 to Figure 32 It is a graph showing the relationship between wavelength and absorptance, transmittance, and reflectance when the angle θ is 77.5° and the period P is 520 nm in the second example. Figures 26 to Figure 29 It is a graph when the gap is 20 nm to 60 nm, and Figures 30 toFigure 32 It is a graph when the gap is from 70 nm to 130 nm. Figure 26A It is a graph when the height H is 100 nm. Figure 26B It is a graph when the height H is 125 nm.

[0047] Figure 27A It is a graph when the height H is 150 nm. Figure 27B It is a graph when the height H is 175 nm.

[0048] Figure 28A It is a graph when the height H is 200 nm. Figure 28B It is a graph when the height H is 225 nm.

[0049] Figure 29 It is a graph when the height H is 250 nm.

[0050] Figure 30A It is a graph when the height H is 100 nm. Figure 30B It is a graph when the height H is 125 nm.

[0051] Figure 31A It is a graph when the height H is 150 nm. Figure 31B It is a graph when the height H is 175 nm.

[0052] Figure 32 It is a graph when the height H is 200 nm.

[0053] Figure 33 to Figure 35 It is a graph showing the relationship between wavelength, absorptance, transmittance, and reflectance when the angle θ is 77.5° and the period P is 250 nm in the second example. Figure 33A It is a graph when the height H is 100 nm. Figure 33B It is a graph when the height H is 125 nm.

[0054] Figure 34A It is a graph when the height H is 150 nm. Figure 34B It is a graph when the height H is 175 nm.

[0055] Figure 35 It is a graph when the height H is 200 nm.

[0056] Figure 36 to Figure 38 It is a graph showing the relationship between wavelength, absorptance, transmittance, and reflectance when the angle θ is 77.5° and the period P is 260 nm in the second example. Figure 36AIt is a graph when the height H is 100 nm. Figure 36B It is a graph when the height H is 125 nm.

[0057] Figure 37A It is a graph when the height H is 150 nm. Figure 37B It is a graph when the height H is 175 nm.

[0058] Figure 38 It is a graph when the height H is 200 nm.

[0059] Figure 39 and Figure 40 is a graph showing the relationship between the wavelength and the reflectivity when the angle θ is 77.5° and the period P is 520 nm in the second example. Figure 39A The upper graph of shows the calculation result when the height H is 150 nm. Figure 39A The lower graph of shows the measurement result when the height H is 150 nm. Figure 39B The upper graph of shows the calculation result when the height H is 175 nm. Figure 39B The lower graph of shows the measurement result when the height H is 175 nm.

[0060] Figure 40 The upper graph shows the calculation result when the height H is 200 nm, and the lower graph shows the measurement result when the height H is 200 nm.

[0061] Figures 41A to 41C It is a graph showing Figure 40 the relationship between the wavelength and the light absorption rate calculated based on the measurement results of Figure 39 and Figure 41A , Figure 41B and Figure 41C are graphs when the height H is 150 nm, 175 nm, and 200 nm respectively.

[0062] Figures 42 to 44 are graphs showing the relationship between the wavelength and the absorption rate, transmittance, and reflectivity when the presence or absence and the thickness of the silica layer are changed when the angle θ is 77.5° and the period P is 520 nm in the second example. Figure 42A It is a graph when there is no silica layer. Figure 42B It is a graph when the thickness of the silica layer is 1 nm.

[0063] Figure 43A It is a graph when the thickness of the silica layer is 2 nm. Figure 43B It is a graph when the thickness of the silica layer is 3 nm.

[0064] Figure 44A It is a graph when the thickness of the silicon dioxide layer is 4 nm. Figure 44B It is a graph when the thickness of the silicon dioxide layer is 5 nm.

[0065] Figures 45 and 46 are graphs showing the relationship between wavelength and absorptance, transmittance, and reflectance in the second example where the angle θ is 80.5°, the period P is 520 nm, and an adhesion layer made of titanium is provided. Figure 45A It is a graph when the height H is 125 nm. Figure 45B It is a graph when the height H is 150 nm.

[0066] Figure 46A It is a graph when the height H is 175 nm. Figure 46B It is a graph when the height H is 200 nm.

[0067] Figure 47A It is a perspective view of the unit structure of the first modified example. Figure 47B It is a photograph showing the unit structure of the first modified example.

[0068] Figure 48A and Figure 48B They are graphs showing the case where the angle θ is 77.5°, the period P is 520 nm, and the height H is 200 nm in the second example. Figure 48A It is a graph showing the relationship between the wavelength of S-polarized light and reflectance and light absorptance. Figure 48B It is a graph showing the relationship between the wavelength of P-polarized light and reflectance and light absorptance.

[0069] Figure 49A and Figure 49B They are graphs showing the case where the angle θ is 77.5°, the period P is 520 nm, and the height H is 200 nm in the first modified example. Figure 49A It is a graph showing the relationship between the wavelength of S-polarized light and reflectance and light absorptance. Figure 49B It is a graph showing the relationship between the wavelength of P-polarized light and reflectance and light absorptance.

[0070] Figure 50A It is a diagram showing an example of the electric field pattern in the first example. Figure 50B It is a diagram showing an example of the electric field pattern in the second example.

[0071] Figure 51A The upper graph shows the relationship between wavelength and reflectance when the height H is 50 nm in the first example, and the lower diagram shows the electric field pattern when the wavelength is 905 nm in this case. Figure 51BThe upper graph shows the relationship between wavelength and reflectivity when the height H is 150 nm in the first example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. The results for the first-order diffracted light output from the plasma structure are shown in Fig. 51.

[0072] Figure 52A The upper graph shows the relationship between wavelength and reflectivity when the height H is 100 nm in the second example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. Figure 52B The upper graph shows the relationship between wavelength and reflectivity when the height H is 200 nm in the second example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. The results for the first-order diffracted light output from the plasma structure are shown in the example of Fig. 52.

[0073] Figure 53A The upper graph shows the relationship between wavelength and reflectivity when the height H is 50 nm in the first example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. Figure 53B The upper graph shows the relationship between wavelength and reflectivity when the height H is 125 nm in the first example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. In the example of Fig. 53, the results for the second-order diffracted light output from the plasma structure are shown.

[0074] Figure 54A The upper graph shows the relationship between wavelength and reflectivity when the height H is 100 nm in the second example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. Figure 54B The upper graph shows the relationship between wavelength and reflectivity when the height H is 200 nm in the second example, and the lower graph shows the electric field pattern when the wavelength is 905 nm in this case. In the example of Fig. 54, the results for the second-order diffracted light output from the plasma structure are shown.

[0075] Figure 55A is a diagram for explaining local-type surface plasmon resonance, Figure 55B is a diagram for explaining propagating surface plasmon resonance, Figure 55C is a diagram for explaining grating surface plasmon resonance.

[0076] Figure 56A and Figure 56B and Figure 52A and Figure 52B corresponds, and is a diagram for explaining the difference between dipole SLR and quadrupole SLR.

[0077] Figure 57 It is a diagram for explaining the electric field pattern in the case of dipole SLR.

[0078] Figure 58 It is a diagram for explaining the electric field pattern in the case of quadrupole SLR.

[0079] Figure 59 A diagram for explaining the electric field pattern in the case of quadrupole SLR.

[0080] Figure 60 It is a cross-sectional view of the unit structure of the second modification example.

[0081] Figure 61 and Figure 62 It is a graph showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the case where the angle θ is 71.6° and the period P is 520 nm in the second example. Figure 61A It is a graph in the case where the height H is 230 nm, Figure 61B It is a graph in the case where the height H is 240 nm.

[0082] Figure 62 It is a graph in the case where the height H is 250 nm. Detailed implementation mode

[0083] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, the same or corresponding elements are denoted by the same reference numerals, and repeated descriptions are omitted.

[0084] As shown in FIG. 1, the light detection element 1 includes an avalanche photodiode (hereinafter also referred to as "APD") 10. The APD 10 has a light incident surface 10a for light L to enter and a surface 10b on the opposite side of the light incident surface 10a. The light incident surface 10a and the surface 10b are, for example, flat surfaces parallel to each other. The APD 10 is a photodiode that utilizes avalanche multiplication, absorbs the light L, and converts it into a photocurrent. In the APD 10, the photocurrent is multiplied by the application of a reverse voltage. The light detection element 1 has sensitivity to light in the near-infrared region (for example, 750 nm to 2.5 μm), for example.

[0085] The APD 10 has a plurality of pixel portions 11. In the example of FIG. 1, three pixel portions 11 are arranged along the X direction (the first direction). The plurality of pixel portions 11 can be arranged in a grid pattern (matrix pattern), for example, or can be arranged along the X direction and the Y direction (the direction perpendicular to the X direction) (the second direction), respectively. The number of pixel portions 11 is not limited. For example, only one pixel portion 11 can be provided, or four or more pixel portions 11 can be provided.

[0086] Each pixel portion 11 is formed in a rectangular shape, for example, when viewed from above (when viewed in the Z direction). The Z direction is perpendicular to the X direction and the Y direction, and is perpendicular to the light incident surface 10a. Each pixel portion 11 is formed, for example, on a semiconductor substrate 12 made of silicon (Si). Each pixel portion 11 has an n-type semiconductor region 13, an n-type semiconductor region 14, a p-type semiconductor region 15 (first semiconductor region), and an n-type semiconductor region 16 (second semiconductor region). The semiconductor regions 15 and 16 function as avalanche multiplication regions for generating avalanche multiplication.

[0087] The n-type semiconductor region 13 is, for example, a substrate region. The semiconductor region 13 constitutes the surface 10b of the APD 10. The n-type semiconductor region 14 is, for example, an epitaxial region (epitaxial layer) and has an impurity concentration lower than that of the semiconductor region 13. The semiconductor region 14 functions as a sensitivity region (light absorption region) having sensitivity to light L together with the semiconductor regions 15 and 16. A part of the semiconductor region 14 is exposed on the light incident surface 10a.

[0088] The p-type semiconductor region 15 and the n-type semiconductor region 16 are, for example, regions (layers) in which the impurity concentration is increased by ion implantation. The n-type semiconductor region 16 has an impurity concentration higher than that of the semiconductor region 14 and lower than that of the semiconductor region 13. The impurity concentrations of the semiconductor regions 15 and 16 are set to concentrations at which avalanche multiplication can occur. The semiconductor region 15 is disposed on the light incident surface 10a side so as to be exposed on the light incident surface 10a. The semiconductor region 16 is formed on the side of the semiconductor region 15 opposite to the light incident surface 10a and forms a pn junction with the semiconductor region 15. A part of the semiconductor region 14 is located on the side of the semiconductor regions 15 and 16 opposite to the light incident surface 10a. When viewed from above, the semiconductor regions 15 and 16 are surrounded by the semiconductor region 14.

[0089] At the outer edge of each pixel portion 11, a trench 17 is formed over the entire circumference. The trench 17 surrounds the semiconductor region 15 when viewed in the Z direction. The trench 17 is formed so as to extend in the Z direction from the light incident surface 10a. The trench 17 functions as a low-sensitivity region having no sensitivity (or having low sensitivity) to light L. The trench 17 is formed, for example, by embedding a metal material in a groove formed in the light incident surface 10a.

[0090] As shown in FIGS. 1 to Figure 4 As shown, the light detection element 1 further includes a plasma structure portion 20 formed on the light incident surface 10a. As Figure 3 and Figure 4As shown, the plasma structure portion 20 diffracts the light L through surface plasmon resonance and causes the diffracted light to travel in a direction intersecting the Z direction. The angle of the traveling direction of the diffracted light with respect to the Z direction is, for example, 80°. Details of the surface plasmon resonance will be described later.

[0091] The plasma structure portion 20 has a plurality of unit structures 21 arranged on the light incident surface 10a (semiconductor region 15) of the APD 10. The unit structures 21 are arranged, for example, in a grid pattern (matrix pattern) and are arranged along the X direction and the Y direction, respectively. In this example, the unit structures 21 are formed in a square shape when viewed from above. The unit structures 21 are formed of, for example, a metal material, a dielectric material, or a semiconductor material (such as silicon). As an example of the dielectric material constituting the unit structure 21, TiO 2 , SiO 2 , HfO 2 , SiN, a-Si can be cited. In this example, the unit structure 21 is formed of gold (Au) as a metal material. As other examples of the metal material constituting the unit structure 21, silver (Ag) and aluminum (Al) can be cited. In addition, Figure 1B The unit structure 21 is schematically illustrated, and in fact, more small unit structures 21 than those illustrated are arranged and configured.

[0092] The unit structure 21 has, for example, Figure 3 the shape of the first example shown in Figure 4 or the second example shown in Figure 2A . The unit structure 21 of the first example has: a top surface 21a on the opposite side of the light incident surface 10a; a bottom surface 21b opposite to the light incident surface 10a; and side surfaces 21c connecting the top surface 21a and the bottom surface 21b. The top surface 21a and the bottom surface 21b are, for example, flat surfaces parallel to the light incident surface 10a. The side surfaces 21c are flat surfaces perpendicular to the light incident surface 10a. That is, the unit structure 21 of the first example is formed in a substantially rectangular shape in a cross section perpendicular to the X direction and a cross section perpendicular to the Y direction. The boundary portion (the edge of the top surface 21a) between the top surface 21a and the side surface 21c is formed in an arc shape over the entire circumference without having sharp corners ( )). That is, the top surface 21a and the side surface 21c are connected to each other via a curved surface 21d. The curved surface 21d is curved in an arc shape, for example, in a cross section perpendicular to the X direction and a cross section perpendicular to the Y direction.

[0093] Figure 4The difference between the unit structure 21 of the second example shown and the unit structure 21 of the first example is that the side surface 21c is inclined (formed in a conical shape). In the second example, the side surface 21c is inclined in a manner that widens as it approaches the bottom surface 21b. That is, the unit structure 21 of the second example is formed in a frustum shape in a cross-section perpendicular to the X direction and a cross-section perpendicular to the Y direction. The angle θ of the side surface 21c with respect to the bottom surface 21b is, for example, 50° or more and less than 90°.

[0094] Hereinafter, as Figure 2A shown, let the arrangement period of the unit structure 21 in the X direction be Px, let the arrangement period of the unit structure 21 in the Y direction be Py, let the distance between adjacent unit structures 21 in the X direction be Gx, let the distance between adjacent unit structures 21 in the Y direction be Gy, and let the height of the unit structure 21 be H. The period Px is the length obtained by adding the width of the unit structure 21 in the X direction and 2×Gx, and the period Py is the length obtained by adding the width of the unit structure 21 in the Y direction and 2×Gy. The height H is 100 nm or more and 250 nm or less. Figure 2B is a photograph of the unit structure 21 when Px and Py are 250 nm and Gx and Gy are 40 nm.

[0095] As Figure 3 and Figure 4 shown, the light detection element 1 further includes: a silicon dioxide (SiO 2 ) layer 31 formed between the plasma structure portion 20 and the light incident surface 10a (semiconductor region 15); and an adhesion layer 32 formed between the plasma structure portion 20 and the silicon dioxide layer 31. That is, in this example, the plasma structure portion 20 is formed on the light incident surface 10a with the silicon dioxide layer 31 and the adhesion layer 32 interposed therebetween. The silicon dioxide layer 31 has a thickness of, for example, 1 nm to 5 nm. The adhesion layer 32 is formed of a metal material. In this example, the adhesion layer 32 is made of titanium (Ti). As other examples of the metal material constituting the adhesion layer 32, chromium (Cr) can be cited. The adhesion layer 32 has a thickness of about 3 nm, for example.

[0096] The light detection element 1 is provided with a pair of electrodes for applying a voltage to the APD 10 on the light incident surface 10a side and the surface 10b side, for example, but the illustration is omitted. A reverse voltage can be applied to the light detection element 1 through this pair of electrodes. The APD 10 operates in, for example, Geiger mode, and in this case, a reverse voltage higher than the breakdown voltage is applied. The APD 10 can also operate in linear mode, and in this case, a reverse voltage smaller than the breakdown voltage is applied. In addition, the light detection element 1 can also be provided with a lens for condensing the light L in the sensitivity region within the APD 10.

[0097] Referring to FIGS. 5 and 6, the optical detection element 1 will be described. As an avalanche photodiode, a PonN-type structure as shown in Figure 5A and a NonP-type structure as shown in Figure 5B can be considered. As shown in Figure 5A , in the PonN-type structure, a p-type semiconductor layer 41 is formed on an n-type semiconductor layer 42 on the light incident surface side. As shown in Figure 5B , in the NonP-type structure, an n-type semiconductor layer 43 is formed on an n-type semiconductor layer 44 on the light incident surface side. The above-described optical detection element 1 is of the PonN type.

[0098] In an avalanche photodiode, the p layer is used as a light absorption layer. For example, when an avalanche photodiode is configured to be sensitive to visible light and light in the near ultraviolet region, the PonN type can be adopted. This is because, since the light absorption layer formed of the p layer easily absorbs light in these wavelength regions, the p-type semiconductor layer 41 can be formed thin as shown in Figure 5A . On the other hand, when an avalanche photodiode is configured to be sensitive to light in the near infrared region, the NonP type can be adopted. This is because, since the light absorption layer formed of the p layer does not easily absorb light in the near infrared region, when the p-type semiconductor layer 41 is thin as in the PonN type, the incident light cannot be sufficiently absorbed, so it is necessary to also use the p-type semiconductor layer on the substrate side to absorb light as shown in Figure 5B .

[0099] In this regard, the optical detection element 1 of the embodiment is sensitive to light in the near infrared region and is configured as the PonN type. This is because, by providing the plasma structure portion 20 as shown in Figure 6A , light can be diffracted by surface plasmon resonance and the diffracted light can travel in a direction intersecting the Z direction, and the optical path length of the p-type semiconductor layer 41 (semiconductor region 15) can be increased to increase the light absorption amount. By adopting the PonN type in the case of being sensitive to light in the near infrared region in this way, the time resolution and sensitivity can be improved. The reason why the time resolution can be improved is that the effect of concentrating the diffracted light of the plasma structure near the surface can be used to limit the excitation site to a thin layer (p layer) near the surface, and the variation in the time until the excited electrons reach avalanche multiplication can be suppressed. In addition, in the optical detection element 1, since the trench 17 is formed so as to surround the sensitivity region, the optical path length in the p-type semiconductor layer 41 can be further increased by reflecting the diffracted light from the plasma structure portion 20 using the trench 17.

[0100] As shown in Figure 6BAs shown, in the optical detection element 1, local surface plasmon resonance is generated in the plasma structure portion 20. In local surface plasmon resonance, an electric field pattern is formed such that a dipole 45 composed of a pair of a positive electrode and a negative electrode extends in the Z direction. Thereby, diffraction is performed in such a manner that the light L travels in a direction intersecting the Z direction. On the other hand, the inventors of the present invention found that in order to cause the plasma structure portion 20 to generate local surface plasmon resonance, it is necessary to design the structure of the plasma structure portion 20. Hereinafter, this point will be described.

[0101] FIGS. 7 to 11 are graphs showing the relationship between the wavelength (Wavelength), absorption rate (Absorption), transmittance (Transmittance), and reflectivity (Reflectivity) when the period P (the above-mentioned Px and Py) is 520 nm in the first example (the side surface 21c is perpendicular) shown in Figure 3 The absorption rate, transmittance, and reflectivity of each graph are the absorption rate, transmittance, and reflectivity in the APD 10. The simulation results using the FDTD method (Finite Difference Time Domain Method) are shown in each graph. Figure 7A , Figure 7B , Figure 8A , Figure 8B , Figure 9A , Figure 9B , Figure 10A , Figure 10B , Figure 11A , Figure 11B They are graphs in the cases where the height H is 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm, respectively. The results in the cases where the gap (the above-mentioned Gx and Gy) is 20 nm, 30 nm, 40 nm, 50 nm, and 60 nm are shown in each graph. In addition, as "W / o Au grating (grating)", the results in the case where the plasma structure portion 20 is not provided are shown. In this simulation, the thickness of the silica layer 31 is 3 nm. The bonding layer 32 is not provided. The plasma structure portion 20 is configured such that the second diffracted light travels at an angle of 70° or more and less than 90° with respect to the Z direction (the direction perpendicular to the light incident surface 10a). The results regarding the second diffracted light output from the plasma structure portion 20 are shown in each figure.

[0102] As can be understood from the various figures, for example, when the reflectance at the target wavelength (in this example, not less than 750 nm) is lower than that in the case where the plasma structure portion 20 is not provided, by providing the plasma structure portion 20, reflection can be suppressed, and localized surface plasmon resonance can be generated in the plasma structure portion 20.

[0103] As can be seen from FIGS. 7 to 11, in the range where the height H is 100 nm to 150 nm, the reflectance at the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and localized surface plasmon resonance can be generated in the plasma structure portion 20. In particular, it can be seen that in the range where the height H is 100 nm to 125 nm, the wavelength range in which the reflectance decreases is narrow, and localized surface plasmon resonance can be generated in a specific wavelength region.

[0104] FIGS. 12 to Figure 14 is a graph showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the case where the period P is 250 nm in the first example. Figure 12A 、 Figure 12B 、 Figure 13A 、 Figure 13B 、 Figure 14 are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm, respectively. Other points are the same as those in FIGS. 7 to 11. In addition, in Figure 13A , the reference numerals "20" and "30" represent the results in the cases where the gaps are 20 nm and 30 nm, respectively, and in Figure 13B , the reference numeral "w / o" represents the result in the case where the plasma structure portion 20 is not provided. This is the same in the subsequent figures.

[0105] According to FIGS. 12 to Figure 14 it can be seen that in the range where the height H is 100 nm to 150 nm, the reflectance at the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and localized surface plasmon resonance can be generated in the plasma structure portion 20.

[0106] FIGS. 15 to Figure 17 is a graph showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the case where the period P is 260 nm in the first example. Figure 15A 、 Figure 15B 、 Figure 16A 、 Figure 16B 、 Figure 17 are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm, respectively. Other points are the same as those in FIGS. 7 to 11.

[0107] According to FIGS. 15 toFigure 17 It can be seen that in the range where the height H is 100 nm to 150 nm, the reflectance of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local surface plasmon resonance can be generated in the plasma structure portion 20.

[0108] According to the results of FIGS. 7 to 11, the results of FIGS. 12 to Figure 14 and the results of FIGS. 15 to Figure 17 It can be seen from the results that in the first example where the side surface 21c is perpendicular, local surface plasmon resonance can be generated in the range where the height H is 100 nm to 150 nm, and the incident light can be diffracted appropriately low. In addition, the same calculation was performed in the case where the period P is 500 nm in the first example, and it was confirmed that the same result could be obtained. The illustration is omitted here.

[0109] FIGS. 18 to Figure 25 is a graph showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the second example (the side surface 21c is inclined) shown in Figure 4 when the angle θ is 80.5° (Atan(6.0)) and the period P is 520 nm. FIGS. 18 to 22 are graphs in the case where the gap is 20 nm to 60 nm, and FIGS. 23 to Figure 25 are graphs in the case where the gap is 70 nm to 130 nm. Figure 18A , Figure 18B , Figure 19A , Figure 19B , Figure 20A , Figure 20B , Figure 21A , Figure 21B , Figure 22A , Figure 22B are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 210 nm, 220 nm, 230 nm, 240 nm, and 250 nm, respectively. Figure 23A , Figure 23B , Figure 24A , Figure 24B , Figure 25 are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm, respectively. Other points are the same as those in FIGS. 7 to 11.

[0110] According to FIGS. 18 to Figure 25It can be seen that in the range where the height H is from 125 nm to 210 nm, the reflectivity of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local surface plasmon resonance can be generated in the plasma structure portion 20. In particular, in the range where the height H is from 200 to 210 nm, the wavelength range where the reflectivity decreases is narrow, and local surface plasmon resonance can be generated in a specific wavelength region. In addition, in the case of the second example where the side surface 21c is inclined, the wavelength range in which local surface plasmon resonance can be generated can be increased compared to the case of the first example where the side surface 21c is perpendicular.

[0111] FIG. 26 to Figure 32 shows the relationship between wavelength and absorption rate, transmittance, and reflectivity in the second example (where the side surface 21c is inclined) shown in Figure 4 where the angle θ is 77.5 (Atan(4.5)) and the period P is 520 nm. FIG. 26 to Figure 29 is a graph in the case where the gap is from 20 nm to 60 nm, and FIGS. 30 to Figure 32 is a graph in the case where the gap is from 70 nm to 130 nm. Figure 26A , Figure 26B , Figure 27A , Figure 27B , Figure 28A , Figure 28B , Figure 29 are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, 200 nm, 225 nm, and 250 nm, respectively. Figure 30A , Figure 30B , Figure 31A , Figure 31B , Figure 32 are graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm, respectively. Other points are the same as those in FIGS. 7 to 11.

[0112] From FIGS. 26 to Figure 32 it can be seen that in the range where the height H is from 150 nm to 230 nm (225 nm), the reflectivity of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local surface plasmon resonance can be generated in the plasma structure portion 20.

[0113] FIG. 33 to Figure 35 shows the relationship between wavelength and absorption rate, transmittance, and reflectivity in the second example (where the side surface 21c is inclined) shown in Figure 4 where the angle θ is 77.5° (Atan(4.5)) and the period P is 250 nm. Figure 33A , Figure 33B ,Figure 34A , Figure 34B , Figure 35 They are the curve graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm respectively. Other points are the same as those in FIGS. 7 to 11.

[0114] According to FIGS. 33 to Figure 35 it can be seen that in the range where the height H is from 125 nm to 200 nm, the reflectance of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local type surface plasmon resonance can be generated in the plasma structure portion 20.

[0115] FIGS. 36 to Figure 38 is a curve graph showing the relationship between the wavelength and the absorption rate, transmittance, and reflectance in the case where the angle θ is 77.5° and the period P is 260 nm in the second example. Figure 36A , Figure 36B , Figure 37A , Figure 37B , Figure 38 They are the curve graphs in the cases where the height H is 100 nm, 125 nm, 150 nm, 175 nm, and 200 nm respectively. Other points are the same as those in FIGS. 7 to 11.

[0116] According to FIGS. 36 to Figure 38 it can be seen that in the range where the height H is from 125 nm to 200 nm, the reflectance of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local type surface plasmon resonance can be generated in the plasma structure portion 20.

[0117] According to the results of FIGS. 18 to Figure 25 , the results of FIGS. 26 to Figure 32 , the results of FIGS. 33 to Figure 35 , and the results of FIGS. 36 to Figure 38 it can be seen that in the second example where the side surface 21c is inclined, local type surface plasmon resonance can be generated in the range where the height H is from 125 nm to 230 nm, and the incident light can be appropriately diffracted. In addition, in the third example, the same calculation was also performed in the cases where the angle θ is 77.5° and the periods P are 270 nm, 280 mm, and 500 nm, and it was confirmed that the same results can be obtained. The illustrations are omitted here.

[0118] FIGS. 39 and Figure 40 is a curve graph showing the relationship between the wavelength and the reflectance in the second example (side surface 21c is inclined) shown in Figure 4 where the angle θ is 77.5° and the period P is 520 nm. Figure 39A The upper curve graph shows the calculation results in the case where the height H is 150 nm, Figure 39AThe graph on the lower side shows the measurement results when the height H is 150 nm. Figure 39B The graph on the upper side shows the calculation results when the height H is 175 nm, Figure 39B The graph on the lower side shows the measurement results when the height H is 175 nm. Figure 40 The graph on the upper side shows the calculation results when the height H is 200 nm, Figure 40 The graph on the lower side shows the measurement results when the height H is 200 nm. The calculation results are the above-mentioned simulation results.

[0119] According to FIG. 39 and Figure 40 it can be seen that in any case where the height H is 150 nm, 175 nm, or 200 nm, the calculation results and the measurement results show the same tendency. Based on this, it can be known that the actual characteristics can be grasped based on the simulation.

[0120] FIG. 41 is a graph showing the relationship between the wavelength and the light absorption rate calculated based on the measurement results of FIG. 39 and Figure 40 . Figure 41A 、 Figure 41B and Figure 41C are graphs in the cases where the height H is 150 nm, 175 nm, and 200 nm, respectively. In each graph, the light absorption rate (enhancement) is the ratio of the light absorption amount calculated with the light absorption amount without the plasma structure portion 20 being 1 (reference). As shown in FIG. 41, in any case where the height H is 150 nm, 175 nm, or 200 nm, the light absorption rate at the target wavelength is increased by about 20%. Based on this, it can be known that the light absorption rate can be increased by providing the plasma structure portion 20.

[0121] FIGS. 42 to 44 are graphs showing the relationship between the wavelength and the absorption rate, the transmittance, and the reflectance when the angle θ is 77.5° and the period P is 520 nm in the second example (the side surface 21c is inclined) shown in Figure 4 , and the presence or absence and the thickness of the silica layer 31 are changed. Figure 42A is a graph in the case where there is no silica layer, Figure 42B 、 Figure 43A 、 Figure 43B 、 Figure 44A 、 Figure 44B are graphs in the cases where the thickness (T) of the silica layer 31 is 1 nm, 2 nm, 3 nm, 4 nm, and 5 nm, respectively. The height H of the unit structure 21 is 200 nm. Other points are the same as those in FIGS. 7 to 11.

[0122] As can be seen from FIGS. 42 to 44, when the thickness of the silicon dioxide layer 31 is different, the reflectance decreases in different wavelength regions. Accordingly, it can be seen that by adjusting the thickness of the silicon dioxide layer 31, local type surface plasmon resonance can be generated within the required wavelength range.

[0123] FIGS. 45 and 46 are graphs showing the relationship between wavelength and absorbance, transmittance, and reflectance in the case of the second example (where the side surface 21c is inclined) shown in Figure 4 where the angle θ is 80.5°, the period P is 520 nm, and an adhesion layer 32 made of titanium is provided. Figure 45A , Figure 45B , Figure 46A , Figure 46B They are graphs in the cases where the height H is 125 nm, 150 nm, 175 nm, and 200 nm respectively. Other points are the same as those in FIGS. 7 to 11.

[0124] Comparing the graphs of the corresponding height H between FIGS. 45 and 46 (where the adhesion layer 32 is provided) and FIGS. 18 to 22 (where the adhesion layer 32 is not provided), it can be seen that in the graphs of FIGS. 45 and 46, the light absorbance is increased compared to the corresponding graphs in FIGS. 18 to 22. For example, comparing the part indicated by an arrow in the upper side absorption (Absorption) graph of Figure 46B with the corresponding part in the upper side absorption (Absorption) graph of Figure 20A , it can be seen that the absorbance becomes about twice as large. Accordingly, it can be seen that by providing the adhesion layer 32 made of titanium, the light absorbance can be increased. In addition, by providing the adhesion layer 32, the bonding strength (adhesion) between the plasma structure portion 20 and the silicon dioxide layer 31 can also be increased.

[0125] The plasma structure portion 20 may also be configured as in the first modification example shown in FIG. 47. In the first modification example, the unit structure 21 has a shape that is longer in the Y direction. That is, the length of the unit structure 21 in the Y direction is longer than the length of the unit structure 21 in the X direction. In this example, the unit structure 21 is formed in a rectangular shape when viewed from above. Figure 47B is a photograph of the unit structure 21 in the case where Px is 500 nm, Py is 3000 nm, Gx is 70 nm, and Gy is 100 nm. In the first modification example, the side surface 21c may be formed vertically as in the Figure 3 first example shown, or may be inclined as in the Figure 4 second example shown. Gy may be 0. That is, the unit structure 21 may be formed continuously along the Y direction without having a gap.

[0126] FIG. 48 is in Figure 4Graph of the case of the second example (side 21c inclined) shown, where the angle θ is 77.5°, the period P is 520 nm, and the height H is 200 nm. Figure 48A It is a graph showing the relationship between the wavelength of S-polarized light and the reflectance and light absorption rate. Figure 48 It is a graph showing the relationship between the wavelength of P-polarized light and the reflectance and light absorption rate. Assume that the vibration direction of S-polarized light is parallel to the Y direction and the vibration direction of P-polarized light is parallel to the X direction.

[0127] Figure 49 is a graph of the case where in the first modified example, the side 21c is inclined at an angle θ of 77.5°, the period P is 520 nm, and the height H is 200 nm. ​ It is a graph showing the relationship between the wavelength of S-polarized light and the reflectance and light absorption rate. ​ It is a graph showing the relationship between the wavelength of P-polarized light and the reflectance and light absorption rate. Assume that the vibration direction of S-polarized light is parallel to the Y direction and the vibration direction of P-polarized light is parallel to the X direction ( ​ ).

[0128] As shown in Figure 48, when the unit structure 21 is square-shaped, both S-polarized light and P-polarized light are diffracted by the plasma structure portion 20. On the other hand, as shown in Figure 49, when the unit structure 21 is rectangular-shaped, P-polarized light is diffracted by the plasma structure portion 20, while S-polarized light is reflected without being diffracted by the plasma structure portion 20. Thus, in the first modified example, it is possible to diffract one of P-polarized light and S-polarized light using the plasma structure portion 20 and reflect the other of P-polarized light and S-polarized light using the plasma structure portion 20. Such a function can be used, for example, in fields such as LiDAR (Light Detection And Ranging) to separate signal light and noise.

[0129] ​ It is a diagram showing an example of the electric field mode (electric field vector) in the first example. ​ It is a diagram showing an example of the electric field mode in the second example. As ​ shown, in the first example, an electric field mode is formed in the plasma structure portion 20 such that the dipole 45 extends along the Z direction. As ​ shown, in the second example, an electric field mode is formed in the plasma structure portion 20 such that the dipole 45 extends obliquely with respect to the Z direction. In either case, the light L is diffracted in a direction crossing the Z direction.

[0130] Figs. 51 to 54 are diagrams for explaining the relationship between the electric field mode in which the dipole 45 extends along the Z direction or obliquely with respect to the Z direction (not perpendicular to the Z direction) in the plasma structure portion 20 and the height H of the unit structure 21. Figs. 51 and 52 show the results regarding the first-order diffracted light output from the plasma structure portion 20. Fig. 51 shows the results in the first example where the height H is 50 nm and 150 nm, and Fig. 52 shows the results in the second example where the height H is 100 nm and 200 nm.

[0131] As ​ shown, in the case of the first example, when the height H is 50 nm, the dipole 45 extends perpendicular to the Z direction (parallel to the light incident surface). On the other hand, as ​ shown, when the height H is 150 nm, the dipole 45 extends obliquely with respect to the Z direction. As ​ shown, in the case of the second example, when the height H is 100 nm, the dipole 45 extends perpendicular to the Z direction (parallel to the light incident surface). On the other hand, as Figure 52B shown, when the height H is 200 nm, the dipole 45 extends obliquely with respect to the Z direction.

[0132] Figs. 53 and 54 show the results regarding the second-order diffracted light output from the plasma structure portion 20. Fig. 53 shows the results in the first example where the height H is 50 nm and 125 nm, and Fig. 54 shows the results in the second example where the height H is 100 nm and 200 nm.

[0133] As Figure 53A shown, in the case of the first example, when the height H is 50 nm, the dipole 45 extends perpendicular to the Z direction (parallel to the light incident surface). On the other hand, as Figure 53B shown, when the height H is 125 nm, there is a dipole 45 that extends obliquely with respect to the Z direction. As Figure 54A shown, in the case of the second example, when the height H is 100 nm, the dipole 45 extends perpendicular to the Z direction (parallel to the light incident surface). On the other hand, as Figure 54B shown, when the height H is 200 nm, there is a dipole 45 that extends obliquely with respect to the Z direction.

[0134] Referring to Figs. 55 to Figure 59 , the localized surface plasmon resonance is described. The surface plasmon resonance includes the localized surface plasmon resonance, the propagating surface plasmon resonance, and the grating surface plasmon resonance. In Figure 55AIn the shown Localized Surface Plasmon Resonance (LSPR), in a structure sufficiently smaller than the wavelength (λ), depending on the structure shape and size (W), the collective vibration of free electrons is excited in a specific wavelength band. As a result, the scattered light (emitted light) is enhanced in the specific wavelength band. Figure 55B The shown Surface Plasmon Resonance (SPR) is based on a principle different from that of the localized surface plasmon resonance. When an evanescent wave is coupled with an interface as a boundary, a wave propagating on the interface is generated. For this coupling, a prism and a grating are required.

[0135] Figure 55C The shown Surface Lattice Resonance (SLR) is generated by a combination of the localized surface plasmon resonance and the propagating surface plasmon resonance. Specifically, the surface lattice resonance is generated by the interference between the diffracted light at the grating interface and the local surface plasmon. By exciting the propagating surface plasmon via the local surface plasmon, a high Q value can be achieved. The optical detection element 1 of the embodiment utilizes this surface lattice resonance. The localized surface plasmon resonance depends on the structure shape, and the propagating surface plasmon resonance depends on the structure period. The surface lattice resonance depends on both the structure shape and the structure period. That is, in the optical detection element 1 of the embodiment, by exciting the propagating surface plasmon depending on the period P and exciting the localized surface plasmon depending on the shape of the plasma structure portion 20, the surface lattice resonance is generated.

[0136] Figure 56 corresponds to Figure 52. Figure 56A The electric field mode in which the dipole 45 in [reference] extends perpendicular to the Z direction (parallel to the light incident surface) is the Dipolar SLR (DSLR) generated by the combination of the dipole (dipole) and the SPR. Since light is emitted perpendicular to the extension direction of the dipole in the plasma structure portion, in this case, the diffracted light travels parallel to the light incident surface, and light cannot be diffracted appropriately. Figure 56B The electric field mode in which the dipole 45 in [reference] extends along the Z direction or obliquely with respect to the Z direction is the Quadrupole SLR (QSLR) generated by the combination of the quadrupole and the SPR. Since light is emitted perpendicular to the extension direction of the dipole in the plasma structure portion, in this case, as shown by the arrow in the figure, light can be diffracted appropriately.

[0137] Figure 57 It is a diagram for explaining the electric field pattern in the case of dipole SLR. Figure 58 and Figure 59 It is a diagram for explaining the electric field pattern in the case of quadrupole SLR. Figure 57 corresponds to Figure 51A . As Figure 57 shown, in the first example where the height H is 50 nm, at any wavelength, the dipole 45 extends perpendicular to the Z direction (parallel to the light incident surface), generating dipole SLR. Figure 58 corresponds to Figure 51B . As Figure 58 shown, in the second example where the height H is 150 nm, at any wavelength, the dipole 45 extends along the Z direction or obliquely with respect to the Z direction, generating quadrupole SLR. Figure 59 corresponds to Figure 54B . As Figure 59 shown, in the first example where the height H is 200 nm, at any wavelength, there are dipoles 57 that extend along the Z direction or obliquely with respect to the Z direction, generating quadrupole SLR. In addition, Figure 57 RA in Figures 57 - 59 refers to the anomalous transmission phenomenon that occurs with the same period as the wavelength, namely Rayleigh anomaly. As Figure 57 shown, the resonance dips are excited in the order of SPR (propagating surface plasmon resonance), SLR (grating surface plasmon resonance), and LSPR (localized surface plasmon) from the long wavelength side. In

[0138] As Figure 60 shown in the second modified example, the light detection element 1 may also include a protective layer 50 that covers the plasma structure portion 20. The protective layer 50 covers the entire plasma structure portion 20 and is provided in such a way as to enter between adjacent unit structures 21. The protective layer 50 is, for example, a silicon dioxide or aluminum oxide (Al 2 O 3 ) film and is an ALD film formed by atomic layer deposition (Atomic Layer Deposition). By providing the protective layer 50, the physical durability and chemical durability can be improved, and a prescribed optical element can also be provided on the protective layer 50. In addition, the protective layer 50 may be provided only between adjacent unit structures 21.

[0139] [Function and Effect]

[0140] In the optical detection element 1, the APD 10 has: a p-type semiconductor region 15 (first semiconductor region); an n-type semiconductor region 16 (second semiconductor region) formed on the side of the semiconductor region 15 opposite to the light incident surface 10a and forming a pn junction with the semiconductor region 15. In the so-called PonN type structure in which the p-type semiconductor region is formed on the n-type semiconductor region, the light absorption amount of the p-type semiconductor region tends to be small. Regarding this point, in the optical detection element 1, by diffracting the incident light using the plasma structure portion 20, the optical path length of the p-type semiconductor region 15 can be increased. As a result, the light absorption amount can be increased and the quantum efficiency can be improved. In addition, in the optical detection element 1, each unit structure body 21 constituting the plasma structure portion 20 has a top surface 21a, a bottom surface 21b, and a side surface 21c, and the height H of each unit structure body 21 is 100 nm or more and 250 nm or less. Thereby, a localized surface plasmon resonance can be generated in the plasma structure portion 20, and the incident light can be appropriately diffracted. As a result, the above-described effect, that is, the effect of increasing the light absorption amount and improving the quantum efficiency, can be significantly obtained. Therefore, according to the optical detection element 1, the quantum efficiency can be improved. In addition, as described above, in the first example, a localized surface plasmon resonance can be generated in the range where the height H is 100 nm to 150 nm. In the second example, in the case where the angle θ is 80.5°, a localized surface plasmon resonance can be generated in the range where the height H is 125 nm to 210 nm. In the second example, in the case where the angle θ is 77.5°, a localized surface plasmon resonance can be generated in the range where the height H is 150 nm to 230 nm. Therefore, it can be considered that when the angle θ is further reduced, the range of the height H for generating the localized surface plasmon resonance becomes higher. In addition, for example, when the unit structure body 21 is formed by lift off, about 250 nm can be the manufacturing limit as the height H. In addition, since there is a possibility that the light absorption of the plasma structure portion 20 becomes large when the height H is too large, the height H can be set to 250 nm or less.

[0141] FIG. 61 and Figure 62 is a graph showing the relationship between the wavelength and the absorption rate, the transmittance, and the reflectance in the second example when the angle θ is 71.6° (Atan(3.0)) and the period P is 520 nm. Figure 61A , Figure 61B , Figure 62 are graphs in the cases where the height H is 230 nm, 240 nm, and 250 nm, respectively. According to FIG. 61 and Figure 62It can be seen that when the angle θ is 71.6°, in the range where the height H is from 230 nm to 250 nm, the reflectivity of the target wavelength is lower than that in the case where the plasma structure portion 20 is not provided, and local surface plasmon resonance can be generated in the plasma structure portion 20. In addition, according to this result and the above results, it can be known that in the second example where the side surface 21c is inclined, local surface plasmon resonance can be generated in the range where the height H is from 125 nm to 250 nm, and the incident light can be appropriately diffracted.

[0142] In Figure 3 In the first example shown, the side surface 21c of each unit structure 21 is formed perpendicular to the light incident surface 10a, and the height H of each unit structure 21 can be 100 nm or more and 150 nm or less. In this case, local surface plasmon resonance can be generated, and the incident light can be appropriately diffracted.

[0143] In Figure 4 In the second example shown, the side surface 21c of each unit structure 21 is inclined so as to become wider as it approaches the bottom surface 21b. Thereby, the wavelength range in which surface plasmon resonance is generated can be increased. In addition, for example, in the case where a shape defect or the like occurs at the boundary portion between the top surface 21a and the side surface 21c during the manufacturing process or the like (for example, when a notch is formed or the corner becomes rounded at the corner portion), there is a possibility that the required function cannot be obtained. However, in the case where the side surface 21c is inclined, for example, compared with the case where it is formed perpendicular to the side surface 21c, the influence of such a shape defect can be suppressed.

[0144] In the second example, the height H of each unit structure 21 can also be 125 nm or more and 250 nm or less. In this case, local surface plasmon resonance can be generated, and the incident light can be appropriately diffracted.

[0145] In the light detection element 1, in each unit structure 21, the top surface 21a and the side surface 21c are connected to each other via a curved surface 21d. Thereby, even when an external force is applied, the plasma structure portion 20 is not easily damaged, and the stability of the light detection element 1 can be improved.

[0146] A silica layer 31 is formed between the plasma structure portion 20 and the semiconductor region 15. Thereby, by adjusting the thickness of the silica layer 31, surface plasmon resonance can be generated in the required wavelength range.

[0147] An adhesion layer 32 made of a metal material is formed between the plasma structure portion 20 and the silica layer 31. Thereby, the bonding strength between the plasma structure portion 20 and the silica layer 31 can be improved.

[0148] In the APD 10, a groove 17 is formed to reflect the light diffracted by the plasma structure portion 20, and the groove 17 surrounds the semiconductor region 15 in a plan view. Thus, by reflecting the light using the groove 17, the optical path length in the semiconductor region 15 can be further increased.

[0149] In the above-described first modification, in a plan view, a plurality of unit structures 21 are arranged in the X direction (first direction), and each unit structure 21 has a shape that is longer in the Y direction (second direction) perpendicular to the X direction. In this case, for example, one of the P-polarized light and the S-polarized light can be diffracted by the plasma structure portion 20, and the other of the P-polarized light and the S-polarized light can be reflected by the plasma structure portion 20.

[0150] The plasma structure portion 20 (unit structure 21) is formed of a metal material. Thus, the plasma structure portion 20 can function as a wavelength filter that transmits only a specific wavelength.

[0151] In the above example, the plasma structure portion 20 is configured such that the second diffracted light travels at an angle of 70° or more and less than 90° with respect to the Z direction (direction perpendicular to the light incident surface 10a). Thus, compared with the case of using the first diffracted light, for example, the size of the plasma structure portion 20 can be ensured, and the manufacturing accuracy can be ensured.

[0152] In the second modification, the plasma structure portion 20 is covered with a protective layer 50, and the protective layer 50 enters between adjacent unit structures 21. Thus, the physical durability and chemical durability of the plasma structure portion 20 can be improved, and a predetermined optical element can also be provided on the protective layer 50.

[0153] The thickness of the silicon dioxide layer 31 is 1 nm or more and 5 nm or less. Thus, the above-described effect, that is, the effect of generating surface plasmon resonance within a required wavelength range by adjusting the thickness of the silicon dioxide layer 31, can be significantly obtained.

[0154] The adhesion layer 32 is a titanium layer. Thus, the light absorption rate can be increased.

[0155] The present invention is not limited to the above-described embodiments and modifications. For example, the materials and shapes of the respective structures are not limited to the above materials and shapes, and various materials and shapes can be adopted. The silicon dioxide layer 31 can be omitted, and the plasma structure portion 20 can be directly formed on the light incident surface 10a. The groove 17 can be omitted. The curved surface 21d can be omitted, or a sharp corner portion can be formed at the boundary portion between the top surface 21a and the side surface 21c.

[0156] In the above example, the plasma structure portion 20 is configured such that the second diffracted light (positive and negative second diffracted lights) travels at an angle of 70° or more and less than 90° with respect to the Z direction. However, it may also be configured such that the first diffracted light (positive and negative first diffracted lights) travels at an angle of 70° or more and less than 90° with respect to the Z direction. That is, the first diffracted light may be used instead of the second diffracted light. However, when using the first diffracted light, it is necessary to reduce the size of the plasma structure portion 20, and there is a possibility that the manufacturing accuracy will decrease. In other words, when using the second diffracted light, the size of the plasma structure portion 20 can be ensured, and the manufacturing accuracy can be improved.

[0157] In the above-described embodiment and each modification, the APD 10 may also be configured as NonP type. That is, similar to the structure shown in Figure 5B , in the APD 10, the semiconductor region 13 is p-type, the semiconductor region 14 is p-type, the semiconductor region 15 (first semiconductor region) is n-type, and the semiconductor region 16 (second semiconductor region) is p-type. That is, the APD 10 may be PonN type or NonP type. As described above, when adopting the PonN type, the time resolution and sensitivity can be improved. On the other hand, when the plasma structure portion 20 is provided in the NonP type, compared with the case where the plasma structure portion 20 is not provided in the NonP type, the optical path length in the light absorption region can be increased, and the light absorption amount can be increased. Specifically, it can be expressed in the form of L = Leff * sin(90° - θ). L is the optical path length in the film thickness direction of Si, Leff is the effective optical path length, and θ is the diffraction angle. In addition, the NonP type structure can be appropriately used for the case where the light diffracted by the plasma structure portion 20 travels at an angle of, for example, 70° to 80° with respect to the Z direction. The reason for this will be described below. The diffraction angle of the plasma structure portion 20 (the angle at which the light diffracted by the plasma structure portion 20 travels) is determined according to the period P and the wavelength of the light L. For example, when the period P is 260 nm and the wavelength is 905 nm (the effective wavelength is 905 nm / 3.6 (refractive index of Si) = 251 nm), the diffraction angle is 75°. In the case of such a small diffraction angle, when it is PonN type, in the light absorption layer formed of the p layer ( Figure 5A of the semiconductor layer 41) is several hundred nm and very thin, so there is a possibility that light cannot be sufficiently absorbed. On the other hand, when it is NonP type, the light absorption layer formed of the p layer ( Figure 5BThe semiconductor layer 44 and the p-type semiconductor layer on the substrate side) have a thickness of 1 μm or more and can sufficiently absorb light. Thus, when the diffraction angle is relatively large, for example, 70° to 80°, the NonP type structure can be appropriately used. In the light detection element 1 of the embodiment, by adjusting the structure of the plasma structure portion 20 according to the structure of the APD 10 and the wavelength of the detection target, the detection sensitivity can be effectively improved.

Claims

1. A light detection element, characterized in that: include: an avalanche photodiode having a light incident surface for incident light; and a plasmon structure formed on the light incident surface and causing the light to diffract by surface plasmon resonance, The avalanche photodiode comprises: a p-type first semiconductor region; and an n-type second semiconductor region, which is formed on the side of the first semiconductor region opposite to the light incident surface and forms a pn junction with the first semiconductor region. The plasma structure portion includes a plurality of unit structures arranged on the first semiconductor region. Each of the plurality of unit structures has: a top surface on the side opposite to the light incident surface; a bottom surface opposite to the light incident surface; and a side surface connected to the top surface and the bottom surface, The height of each of the plurality of unit structures is greater than or equal to 100 nm and less than or equal to 250 nm.

2. The light detecting element according to claim 1, wherein: The side surfaces of each of the plurality of unit structures are formed perpendicular to the light incident surface, The height of each of the plurality of unit structures is greater than or equal to 100 nm and less than or equal to 150 nm.

3. The light detecting element according to claim 1, wherein: The side surfaces of each of the plurality of unit structures are inclined so as to become wider as approaching the bottom surface.

4. The light detecting element according to claim 3, wherein: The height of each of the plurality of unit structures is greater than or equal to 125 nm and less than or equal to 250 nm.

5. The light detection element according to any one of claims 1 to 4, characterized in that: In each of the plurality of unit structures, the top surface and the side surface are connected to each other via a curved surface.

6. The light detection element according to any one of claims 1 to 5, characterized in that: A silicon dioxide layer is formed between the plasma structure portion and the first semiconductor region.

7. The light detecting element according to claim 6, wherein: An adhesion layer made of a metal material is formed between the plasma structure portion and the silicon dioxide layer.

8. The light detection element according to any one of claims 1 to 7, wherein: A groove for reflecting the light diffracted by the plasmon structure is formed in the avalanche photodiode, and the groove surrounds the first semiconductor region when viewed in a direction perpendicular to the light incident surface.

9. The light detection element according to any one of claims 1 to 8, wherein: The plurality of unit structures are arranged along a first direction when viewed from a direction perpendicular to the light incident surface, and each of the plurality of unit structures has a shape that is long in a second direction perpendicular to the first direction.

10. The light detecting element according to claim 1 or 2, wherein: The plasmon structure is configured such that the second-order diffracted light travels at an angle of 70° or more and less than 90° with respect to a direction perpendicular to the light incident surface.

11. The light detecting element according to claim 1 or 2, wherein: The plasma structure is covered with a protective layer, and the protective layer enters between adjacent unit structures.

12. The light detecting element according to claim 6, wherein: The silicon dioxide layer has a thickness of not less than 1 nm and not more than 5 nm.

13. The light detecting element according to claim 7, wherein: The adhesion layer is a titanium layer.

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