Photoelectric conversion element, imaging element, and imaging system

Abstract

This photoelectric conversion element receives reflected light due to reflection by a subject of emitted light emitted from a light source and having a predetermined wavelength profile. In a cross-sectional view of the photoelectric conversion element, a phase adjustment layer has an upper surface and a lower surface, wherein a plane in contact with the upper surface and parallel to a substrate provides a first surface and the lower surface provides a second surface. The phase adjustment layer is configured such that, when the reflected light is incident on the photoelectric conversion element vertically, the optical path length as the reflected light passes the first surface and reaches the second surface varies depending on the incident position of the reflected light on the first surface.

Description

[Technical field]

[0001] The present invention relates to a photoelectric conversion element, an imaging element, and an imaging system. This application claims priority based on Japanese Patent Application No. 2019-157644 filed in Japan on August 30, 2019, and Japanese Patent Application No. 2019-157645 filed in Japan on August 30, 2019, the contents of which are incorporated herein by reference. [Background technology]

[0002] Photoelectric conversion elements are used in a variety of fields, including imaging systems capable of measuring distances. Such an imaging system generally includes a light source that generates light to be irradiated onto a subject, and a photoelectric conversion element that functions as an imaging sensor that captures an image of the light reflected from the subject.

[0003] The photoelectric conversion element has a silicon substrate in which a charge generating region is formed. One or more dielectric layers are formed on the front surface side of the silicon substrate, and signal wiring is disposed within the dielectric layers. That is, the photoelectric conversion element usually has a dielectric multilayer film configuration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-41590 Summary of the Invention [Problem to be solved by the invention]

[0005] In the photoelectric conversion element having the above-mentioned configuration, the multilayer film acts on the incident light, causing the reflectance to oscillate within the wavelength region. The amplitude and phase of the reflectance oscillation change in a complex manner depending on the film thickness and refractive index of each layer constituting the multilayer film, as well as on the variations in thickness and composition of the dielectric layers within the element plane, and the variations in the central wavelength of the light emitted from the light source.

[0006] A large amplitude of the reflectance vibration causes a large variation in the sensitivity of each of the multiple pixels that make up the photoelectric conversion element. Since this variation ultimately affects the distance measurement accuracy of the imaging system, it is preferable that the amplitude of the reflectance vibration is as small as possible. However, as described above, there are many factors that affect the amplitude and phase of the reflectance vibration, and it is not easy to control them.

[0007] In view of the above circumstances, an object of the present invention is to provide a photoelectric conversion element in which the fluctuation in reflectance of incident light is reduced. Another object of the present invention is to provide an image sensor and an image capturing system in which the variation in distance measurement accuracy among each of a plurality of pixels is small. [Means for solving the problem]

[0008] A photoelectric conversion element according to one embodiment of the present invention is a photoelectric conversion element that receives reflected light that is emitted from a light source and has a predetermined wavelength band and is reflected by a subject, and includes a substrate having a charge generation region, a dielectric layer formed on the substrate, and a phase adjustment layer disposed on the dielectric layer and having an upper surface and a lower surface. the phase adjustment layer has a plurality of scattering particles having a particle size of 3 μm or less, When viewed in cross-section of the photoelectric conversion element, a plane that is in contact with the upper surface of the phase adjustment layer and parallel to the substrate is defined as a first surface, and the lower surface of the phase adjustment layer is defined as a second surface.The phase adjustment layer is configured so that when the reflected light is incident perpendicularly to the photoelectric conversion element, the optical path length of the reflected light from passing through the first surface to the second surface differs depending on the incident position of the reflected light on the first surface.

[0009] In the photoelectric conversion element according to the aspect of the present invention, a maximum value of an optical path length difference of the reflected light transmitted through the phase adjustment layer may be equal to or greater than ¼ of an average wavelength of the emitted light.

[0010] In the photoelectric conversion element according to the aspect of the present invention, the phase adjustment layer may be a phase adjustment lens having an aspect ratio h / d, which is a ratio of a bottom diameter d to a height h, of 0.35 to 1.2.

[0011] In the photoelectric conversion element according to the aspect of the present invention, the phase adjusting lens may cover 75% or more of the substrate in a plan view of the photoelectric conversion element.

[0012] In the photoelectric conversion element according to the aspect of the present invention, the phase adjustment layer may have fine irregularities.

[0014] An image sensor according to one aspect of the present invention includes a plurality of photoelectric conversion elements according to the above aspect, the photoelectric conversion elements being arranged two-dimensionally.

[0015] An imaging element according to one aspect of the present invention comprises a plurality of photoelectric conversion elements according to the above-described aspect, the photoelectric conversion elements being arranged two-dimensionally, and in a planar view of the photoelectric conversion elements, the diameter of the phase adjustment lens is larger than the length of a side of the substrate, and the phase adjustment lens has a shape in which a portion of the phase adjustment lens that protrudes outside the side of the substrate has been removed.

[0016] An imaging system according to one aspect of the present invention includes a light source that emits light having a predetermined wavelength band, and the imaging element according to the aspect described above.

[0017] An imaging system according to one aspect of the present invention includes a light source that emits light having a predetermined wavelength band, and the photoelectric conversion element according to the above aspect. Effect of the Invention

[0018] In a photoelectric conversion element according to one embodiment of the present invention, fluctuations in the reflectance of incident light are reduced. An image sensor and an image capturing system according to an aspect of the present invention have little variation in distance measurement accuracy among a plurality of pixels. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic cross-sectional view showing a photoelectric conversion element according to a first embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view showing a photoelectric conversion element according to a second embodiment of the present invention. [Diagram 3] 5 is a schematic cross-sectional view showing another example of the phase adjustment layer in the photoelectric conversion element according to the first embodiment and the second embodiment. FIG. [Figure 4] 5 is a schematic cross-sectional view showing another example of the phase adjustment layer in the photoelectric conversion element according to the first embodiment and the second embodiment. FIG. [Diagram 5] 5 is a schematic cross-sectional view showing another example of the phase adjustment layer in the photoelectric conversion element according to the first embodiment and the second embodiment. FIG. [Figure 6] 5 is a schematic cross-sectional view showing another example of the phase adjustment layer in the photoelectric conversion element according to the first embodiment and the second embodiment. FIG. [Figure 7] 5 is a schematic cross-sectional view showing another example of the phase adjustment layer in the photoelectric conversion element according to the first embodiment and the second embodiment. FIG. [Figure 8] 10 is a graph showing the effect of a change in thickness of a phase adjustment layer on the amount of light absorption in the photoelectric conversion elements according to the first and second embodiments. [Figure 9] 1 is a graph showing the effect of changing the angle at which light is incident on a dielectric layer on the amount of light absorption. [Figure 10] FIG. 1 is a diagram illustrating an example of an imaging element to which a photoelectric conversion element according to a first embodiment and a second embodiment is applied. [Figure 11] FIG. 1 is a diagram illustrating an example of an imaging system to which a photoelectric conversion element according to a first embodiment and a second embodiment is applied. [Figure 12] 10A to 10C are diagrams illustrating phase adjustment layers according to modified examples of the first and second embodiments of the present invention. [Figure 13]10A to 10C are diagrams illustrating phase adjustment layers according to modified examples of the first and second embodiments of the present invention. [Figure 14] 10A to 10C are diagrams illustrating phase adjustment layers according to modified examples of the first and second embodiments of the present invention. [Figure 15] FIG. 4 is a schematic cross-sectional view showing a photoelectric conversion element according to a third embodiment of the present invention. [Figure 16] FIG. 13 is a diagram showing simulation conditions for a phase adjustment lens of a photoelectric conversion element according to a third embodiment of the present invention. [Figure 17] 13 is a graph showing a simulation result regarding the phase adjusting lens according to the third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] First embodiment A first embodiment of the present invention will be described with reference to FIG. 1 is a schematic cross-sectional view showing a photoelectric conversion element 1 according to this embodiment. The photoelectric conversion element 1 includes a substrate 10 made of a semiconductor, a dielectric layer 20 formed on the substrate 10, and a phase adjustment layer 30 formed on the dielectric layer 20.

[0021] The substrate 10 is made of, for example, silicon, and includes a charge generation region 11 and a floating diffusion FD. Charge generation region 11 has a three-dimensional shape that spreads from first surface 10a of substrate 10 in the planar direction of first surface 10a and in the thickness direction of substrate 10. Charge generation region 11 is provided with a first conductivity type (P+ type) semiconductor region and a second conductivity type (N type) semiconductor region as shown in FIG. 1. In this structure, a photodiode is formed that has a configuration that generates and accumulates electrons as signal charges according to the amount (light quantity) of light incident on charge generation region 11. The structure of charge generation region 11 is known and can be formed, for example, by injecting an impurity (dopant) into substrate 10.

[0022] The dielectric layer 20 has a low refractive index layer 21 in contact with the first surface 10a, and a high refractive index layer 22 located on the low refractive index layer 21. A wiring layer W for connecting the photoelectric conversion element 1 to an external circuit or the like is disposed within the dielectric layer 20, and a gate electrode G is formed on a part of the wiring layer W. When a potential is applied to the gate electrode G, electrons generated in the charge generation region 11 are transferred to the floating diffusion FD. The basic structures of the gate electrode G and the floating diffusion FD are publicly known.

[0023] The phase adjustment layer 30 has an upper surface 30T (surface) and a lower surface 30B, and is formed on the high refractive index layer 22. The upper surface 30T is an incident surface onto which light is incident. The lower surface 30B is a contact surface where the phase adjustment layer 30 and the high refractive index layer 22 come into contact with each other. The phase adjustment layer 30 has a structure in which scattering particles 32 are dispersedly arranged in a transparent base resin 31. The phase adjustment layer 30 has a fine uneven shape on an upper surface 30T. Either transparent or opaque particles can be used as the scattering particles 32, but when opaque particles are used, it should be noted that if the ratio of scattering particles 32 in the phase adjustment layer 30 is too high, the incident light will be excessively reduced. When transparent particles are used, it is necessary that the refractive index is different from that of the base resin 31. An example of the transparent scattering particles is silica particles, and an example of the opaque scattering particles is titania particles.

[0024] In a cross-sectional view of the photoelectric conversion element 1, a plane that is in contact with the upper surface 30T of the phase adjustment layer 30 and parallel to the substrate 10 is defined as a first surface PL1, and a lower surface 30B of the phase adjustment layer 30 is defined as a second surface PL2. In this case, the phase adjustment layer 30 is configured such that, when reflected light RL is perpendicularly incident on the photoelectric conversion element 1, the optical path length from when the reflected light RL passes through the first surface PL1 to when it reaches the second surface PL2 differs depending on the incident position of the reflected light RL on the first surface PL1 (the position indicated by the symbol RL in FIG. 1).

[0025] The behavior of incident light in the photoelectric conversion element 1 of this embodiment configured as above will be described. Light incident on the photoelectric conversion element 1 enters the phase adjustment layer 30 before reaching the dielectric layer. A portion of the light incident on the phase adjustment layer 30 hits the scattering particles 32 and changes its optical path in various directions, resulting in light with various optical path lengths. As a result, a phase difference occurs between the light that hits the scattering particles 32 and the light that does not hit the scattering particles 32 due to the change in optical path length. Furthermore, a phase difference also occurs between the light that hits the scattering particles 32. The light emitted from the phase adjustment layer 30 is incident on the high refractive index layer 22 at various angles of incidence, and the optical path length changes depending on the angle of incidence, causing a phase difference.

[0026] In the dielectric layer 20, interference occurs due to the multilayer structure of the low refractive index layer 21 and the high refractive index layer 22, causing the reflectance to oscillate. However, the light that passes through the phase adjustment layer 30 and enters the high refractive index layer 22 contains a plurality of types of light with different optical path lengths as described above. Therefore, a portion of the oscillation is offset by the phase difference, and the amplitude is reduced.

[0027] As a result, the amplitude of the interference vibration in the dielectric layer 20 is reduced compared to when the phase adjustment layer 30 is not provided. Therefore, the amplitude of the interference vibration can be reduced very simply without considering the film thickness or material of the low refractive index layer 21 and the high refractive index layer 22. As a result, in the case of an imaging system having a single pixel, the sensitivity variation between products can be suppressed, and in the case of an imaging system having multiple pixels, the sensitivity variation between pixels can be suppressed. In either case, the configuration of this embodiment including the phase adjustment layer 30 contributes to stabilizing the distance measurement accuracy.

[0028] Whether the phase adjustment layer 30 can reduce the amplitude of the interference vibration depends on the wavelength of the incident light. In other words, the interference vibrations of light with a phase shift of 1 / 2 period cancel each other out. In order to increase the optical path length by 1 / 2 wavelength on a round trip, the phase adjustment layer 30 should be designed so that the light that passes through the phase adjustment layer 30 includes light whose optical path length has increased by 1 / 4 wavelength or more. For example, when the photoelectric conversion element 1 of this embodiment is applied to an imaging system that uses light with a wavelength in the near-infrared region, the phase adjustment layer 30 can be designed so that the light that passes through the phase adjustment layer 30 includes light whose optical path length has increased by approximately 190 nm to 350 nm or more, depending on the specific wavelength of the light emitted from the light source. As an example of the design of the phase adjustment layer 30, it is desirable that the scattering by the scattering particles 32 be forward scattering in order to increase the transmittance. The forward scattering may be geometric scattering or Mie scattering, but in either case, the light scattered outside the pixel region increases as the phase adjustment layer 30 becomes thicker. Therefore, from the viewpoint of designing the phase adjustment layer 30 to be thin, it is desirable that the particle size of the scattering particles 32 is small, for example, preferably 3 μm or less, and more preferably 1.5 μm or less. On the other hand, if the particle size of the scattering particles 32 is sufficiently small relative to the wavelength, Rayleigh scattering occurs, and the backscattering component increases, which is not preferable. Therefore, in the near-infrared light region, the particle size of the scattering particles 32 is preferably 10 nm or more, and more preferably 0.1 μm or more.

[0029] Second Embodiment A second embodiment of the present invention will be described with reference to Figures 2 to 5. In the following description, configurations common to those already described will be given the same reference numerals and duplicated description will be omitted.

[0030] 2 is a schematic cross-sectional view showing a photoelectric conversion element 201 according to this embodiment. The phase adjustment layer 230 formed on the dielectric layer 20 does not contain scattering particles and has fine irregularities on the surface 230a. That is, the material of the phase adjustment layer 230 is uniform, but the thickness varies from part to part due to the fine irregularities, and the layer has a plurality of thickness dimensions. Therefore, by making the difference between the thickness dimension Th1 of the thinnest part and the thickness dimension Th2 of the thickest part in the phase adjustment layer 230 greater than or equal to 1 / 4 of the wavelength of the light emitted from the light source, the amplitude of the interference vibration can be reduced extremely simply, as in the first embodiment.

[0031] In this embodiment, the structure of the fine projections and recesses can be set appropriately. For example, as in the phase adjustment layer 230, a structure having a step with a plurality of parts with a constant thickness may be used, or as in the phase adjustment layer 230A shown in FIG. 3, the thickness may change continuously and smoothly in a predetermined cross section, and there may be no step. In the case of a structure without a step, as in the phase adjustment layer 230B shown in FIG. 4, the thickness may change continuously and linearly in a predetermined cross section. There is also no particular limitation on the structure in which the thickness increases or decreases. Therefore, the structure may be one in which the thickness increases or decreases in a predetermined cycle, as in the phase adjustment layer 230C shown in Fig. 5, or the structure may be one in which the thickness increases or decreases so as to be symmetrical about a line in a predetermined cross section of the photoelectric conversion element 1, as in the phase adjustment layer 230D shown in Fig. 6 and the phase adjustment layer 230E shown in Fig. 7.

[0032] The inventors found that the above-mentioned amplitude reduction effect (hereinafter referred to as the amplitude reduction effect) can be achieved by disposing the phase adjustment layer 230 on the dielectric layer 20, and conducted a study to enhance the effect through simulation. The details are shown below.

[0033] FIG. 8 is a graph showing the change in the amount of light absorption in the photoelectric conversion element 201 when the thickness of the phase adjustment layer 230 is arranged on the dielectric layer 20 with an increment of 0.2 μm. The photoelectric conversion element 201 was a square with a side length of 16.8 μm (diagonal 23.8 μm). Fig. 8 shows the amount of light absorbed within a range from the first surface 10a side of the substrate 10 to a depth of 13 μm.

[0034] As shown in Figure 8, for the phase adjustment layer with the reference thickness, a drop in the amount of light absorption is observed near wavelengths of 750 nm and 800 nm. In contrast, for "+Δz1", which is 0.2 μm thicker than the reference, there is no drop near the wavelength of 800 nm. For "+Δz1", which is 0.4 μm thicker than the reference, there is no drop near the wavelength of 750 nm. That is, it can be seen from FIG. 8 that by providing regions having a plurality of thicknesses in the phase adjustment layer, the drops in optical absorption are complemented by each other, and the interference amplitude of optical absorption according to wavelength can be suppressed.

[0035] 8 also shows that the peak value of the interference amplitude of the amount of light absorption does not change much even if only the thickness of the phase adjustment layer 230 changes. This is because the optical path length in the dielectric layer 20 does not change even if only the thickness of the phase adjustment layer 230 changes. In order to suppress the peak portion of the interference amplitude, it is effective to change the optical path length in the dielectric layer 20. In order to change the optical path length in the dielectric layer 20, a plurality of types of incident angles of light to the dielectric layer may be generated. Specifically, it is preferable to continuously change the thickness of the phase adjustment layer, as in the above-mentioned phase adjustment layers 230A and 230B. A continuous change in thickness of the phase adjustment layer creates a slope on part of the surface of the phase adjustment layer. Light incident on the slope is refracted and travels obliquely through the dielectric layer 20, changing the optical path length. In the simulation results shown in FIG. 9, it can be seen that when the incident angle changes by about 17 degrees in the low refractive index layer 21 (Angle 1), the amplitude is roughly inverted.

[0036] Therefore, by providing the phase adjustment layer with multiple locations of different thicknesses and continuously changing the thickness between those locations, it is possible to achieve both the interference suppression effect due to the change in thickness and the interference suppression effect due to the change in optical path length in the dielectric layer 20.

[0037] As another example, the angle of light incident on the dielectric layer 20 can be deflected by diffracting the incident light using the uneven structure of the phase adjustment layer. In this case, the period of the uneven structure is 5 μm or less, and preferably 3 μm or less.

[0038] The photoelectric conversion element according to each embodiment of this embodiment can be used alone, but a plurality of the photoelectric conversion elements may be arranged in a two-dimensional matrix to form an imaging element. An example of an image sensor is shown in a block diagram in Fig. 10. The image sensor 40 has a light receiving area 41 in which a plurality of photoelectric conversion elements 1 are arranged two-dimensionally. The image sensor 40 includes a control circuit 50, a vertical drive circuit 60, a horizontal drive circuit 70, an AD conversion circuit 80, and an output circuit 90, but this structure is only an example of an image sensor, and various known configurations may be appropriately combined in consideration of specifications, etc. It is natural that a photoelectric conversion element 201 may be used instead of the photoelectric conversion element 1.

[0039] In the image sensor 40, the number and arrangement of photoelectric conversion elements arranged in the light receiving area 41 can be set as appropriate. The multiple photoelectric conversion elements may be two-dimensionally arranged without any gaps. In this case, the multiple photoelectric conversion elements arranged two-dimensionally may be formed on a single semiconductor wafer.

[0040] Fig. 11 shows a schematic diagram of an example of an imaging system to which the photoelectric conversion element of this embodiment is applied. The imaging system 100 shown in Fig. 11 includes a light emitting unit 110 having a light source 101, and a light receiving unit 120 having an imaging sensor 121. The light source 101 emits outgoing light L1 having a predetermined wavelength and wavelength band (wavelength profile) toward an object O. Reflected light L2 generated when the outgoing light L1 is reflected by the object O is incident on the imaging sensor 121 of the light receiving unit 120. As the imaging sensor 121, either a single photoelectric conversion element or an imaging element 40 having a plurality of photoelectric conversion elements can be used. By designing the phase adjustment layer in the image sensor 121 based on the wavelength band of the emitted light L1, it is possible to provide an image pickup system with little variation in distance measurement accuracy.

[0041] (Modification) The phase adjustment layer in the present invention is not limited to the above-mentioned embodiment. The phase adjustment layer 330 of the modified example shown in FIG. 12 has a first region 331, a second region 332, a third region 333, and a fourth region 334 with different refractive indices. Since the light transmitted through the regions with different refractive indices has a different effective optical path length, even if the thickness of all the regions in the phase adjustment layer 330 is the same, the amplitude reduction effect is achieved by appropriately setting the refractive index of each region based on the light source wavelength, etc. The number and arrangement of each region can be appropriately set. For example, the regions may be arranged so that the refractive index gradually increases or decreases, or may be arranged randomly as shown in FIG. 12.

[0042] As in the phase adjustment layer 330A shown in FIG. 13, by making the thicknesses of the regions 331 to 334 different and further by varying the thickness continuously, it is possible to enhance the amplitude reduction effect. As in the phase adjustment layer 330B shown in FIG. 14, the regions 331 to 334 may be arranged side by side in the thickness direction of the phase adjustment layer.

[0043] Scattering particles 32 may also be included in phase adjustment layer 230 or phase adjustment layer 330 .

[0044] Third embodiment A third embodiment of the present invention will be described with reference to FIGS. 15 is a schematic cross-sectional view showing a photoelectric conversion element 301 according to this embodiment. The photoelectric conversion element 301 includes a substrate 10 made of a semiconductor, a dielectric layer 20 formed on the substrate 10, and a phase adjustment lens 30L formed on the dielectric layer 20. The phase adjustment lens 30L corresponds to the phase adjustment layer of the present invention.

[0045] The phase adjusting lens 30L is formed on the high refractive index layer 22. In this embodiment, the aspect ratio (h / d) of the phase adjusting lens 30L, which is the ratio of the bottom diameter d to the thickness h, is 0.6 to 1.0. Although a microlens having such an aspect ratio is not publicly known, it can be manufactured by publicly known microlens technology by appropriately setting appropriate manufacturing conditions. When the shape of the phase adjustment lens 30L in a plan view is rectangular due to the arrangement of the phase adjustment lens 30L, it is possible that the diagonal length of the rectangle is shorter than the diameter of the phase adjustment lens 30L having a circular shape. In this case, the upper curved surface of the phase adjustment lens 30L is extended to the bottom surface of the phase adjustment lens 30L, and the diameter of the shape of the phase adjustment lens 30L is defined as the bottom diameter d.

[0046] The behavior of incident light in the photoelectric conversion element 301 of this embodiment configured as above will be described. The light incident on the photoelectric conversion element 301 is incident on the lens surface 30a of the phase adjustment lens 30L at various angles of incidence, and the optical path length changes, before reaching the dielectric layer 20. As a result, the light is incident on the high refractive index layer 22 in a state in which a phase difference occurs between the lights incident on the phase adjustment lens 30L.

[0047] In the dielectric layer 20, interference occurs due to the multi-layer structure of the low refractive index layer 21 and the high refractive index layer 22, causing the reflectance to vibrate. However, the light incident on the high refractive index layer 22 from the phase adjustment lens 30L contains light of various phases. Therefore, part of the vibration is offset, and the amplitude is reduced.

[0048] As a result, the amplitude of the interference vibration in the dielectric layer 20 is reduced compared to when the phase adjustment lens 30L is not provided. Therefore, the amplitude of the interference vibration can be reduced very simply without considering the film thickness or material of the low refractive index layer 21 and the high refractive index layer 22. As a result, in the case of an imaging system having a single pixel, the sensitivity variation between products can be suppressed, and in the case of an imaging system having multiple pixels, the sensitivity variation between pixels can be suppressed. In either case, the configuration of this embodiment equipped with the phase adjustment lens 30L contributes to stabilizing the distance measurement accuracy.

[0049] Whether or not the phase adjustment lens 30L can reduce the amplitude of the interference vibration depends on the wavelength of the incident light. In other words, the interference vibrations of light with a phase shift of 1 / 2 period cancel each other out. In order to increase the optical path length by 1 / 2 wavelength on the round trip, the phase adjustment lens 30L should be designed so that the light that passes through the phase adjustment lens 30L includes light whose optical path length has increased by 1 / 4 wavelength or more. For example, when the photoelectric conversion element 301 of this embodiment is applied to an imaging system that uses light with a wavelength in the near-infrared region, the lens shape of the phase adjustment lens 30L can be designed so that the light that passes through the phase adjustment lens 30L includes light whose optical path length has increased by approximately 190 nm to 350 nm or more, depending on the specific wavelength of the light emitted from the light source.

[0050] The inventors discovered that the above-mentioned amplitude reduction effect can be achieved by disposing the phase adjusting lens 30L on the dielectric layer 20, and carried out studies to enhance this effect through simulations. The details of these studies are given below.

[0051] 16 shows the dimensions of the photoelectric conversion element 301 in a plan view under the simulation conditions. The shape and dimensions of the photoelectric conversion element 301 in a plan view were a square with a side length of 16.8 μm (diagonal length 23.8 μm). The bottom diameter d of the phase adjustment lens 30L was 20.0 μm. The phase adjustment lens 30L was positioned so that the optical axis of the phase adjustment lens 30L coincided with the center of the photoelectric conversion element 301 in a plan view. In this state, approximately 95% of the substrate 10 was covered by the phase adjustment lens 30L. The wavelength of light incident on photoelectric conversion element 301 was set to 800 to 900 nm, and the height h of phase adjustment lens 30L was changed to study the change in the amplitude reduction effect. As an index, the amount of light absorbed within a range from the first surface 10a side of substrate 10 to a depth of 13 μm (light absorption amount) was used.

[0052] The results are shown in Figure 17. In Figure 17, the horizontal axis indicates the aspect ratio of the phase adjustment lens 30L, and the vertical axis indicates the ratio of the amplitude to the average wavelength of the incident light. When the phase adjustment lens 30L was not provided, the light absorption amount of the substrate fluctuated within a range of about 50% of the average wavelength of the incident light, 850 nm. The amplitude was reduced by providing the phase adjustment lens 30L. The effect of reducing the amplitude increased as the aspect ratio of the phase adjustment lens 30L increased, and at an aspect ratio of 0.35, the amplitude was reduced to about half of the amplitude when the phase adjustment lens 30L was not provided.

[0053] As the aspect ratio becomes larger, the amplitude reduction effect increases further. However, it can be seen that the increase in the amplitude reduction effect slows down once the aspect ratio exceeds 0.6, at which the amplitude reduction effect becomes approximately 1 / 3. When the aspect ratio of the phase adjusting lens 30L increases, the thickness of the phase adjusting lens 30L and the tangent angle range of the lens surface that increases the optical path length of the incident light by optical refraction increase, so that the interference is cancelled out and the amplitude reduction effect due to the interference increases. However, when the aspect ratio exceeds 0.5, the thickness of the phase adjusting lens 30L increases, but the tangent angle range of the lens surface does not increase any further.

[0054] The proportion of high-angle components in the tangent angle range of the lens surface of the phase adjustment lens 30L with an aspect ratio of 0.5 is small. In the aspect ratio range of 0.5 to 0.6, the high-angle components of the tangent to the lens surface increase, so the effect of reducing the amplitude of interference increases. However, once the aspect ratio exceeds 0.6, the high-angle components of the tangent to the lens surface start to become excessive, and the effect of reducing the amplitude of interference starts to weaken.

[0055] When the aspect ratio exceeds 0.7, the effect becomes weaker and is saturated at an aspect ratio of 1.0. It is practically difficult to manufacture a phase adjusting lens having an aspect ratio exceeding 1.2. From the above, when considering both the ease of manufacturing the phase adjusting lens and the effect of reducing the amplitude, it was considered that the aspect ratio of the phase adjusting lens 30L is preferably 0.35 or more and 1.2 or less, and more preferably 0.6 or more and 1.0 or less.

[0056] 16, the coverage of the phase adjusting lens 30L (the proportion of the substrate covered by the phase adjusting lens in a plan view of the photoelectric conversion element) is set to about 95%. If the coverage of the phase adjusting lens 30L is at least 75% or more, the effects of the present invention can be obtained. It is more preferable that the charge generation region 11 is completely covered when the photoelectric conversion element 301 is viewed in a plan view.

[0057] The area of ​​substrate 10 that charge generation region 11 occupies varies depending on the layout design of the pixels that constitute photoelectric conversion element 301, but is generally about 30% to 50% of photoelectric conversion element 301 in a plan view. On the other hand, the planar shape of the charge generation region 11 can be various shapes such as a square, a rectangle, a trapezoid, etc., depending on the layout design of the pixels. Therefore, it is desirable that the coverage of the phase adjusting lens 30L is 75% or more.

[0058] For example, when phase adjusting lens 30L having a circular bottom surface is arranged to cover photoelectric conversion element 301, which is square in plan view, at a coverage rate of about 75%, phase adjusting lens 30L is positioned so as to be substantially inscribed in square photoelectric conversion element 301. Therefore, phase adjusting lens 30L can cover the entire charge generation region 11, regardless of the area and shape of charge generation region 11. Moreover, in a plan view of the photoelectric conversion element 301, it is more desirable that the center of the charge generation region 11 and the center of the optical axis of the phase adjustment lens 30L coincide with each other.

[0059] The photoelectric conversion element 301 according to this embodiment can be used alone, but a plurality of the photoelectric conversion elements 301 may be arranged in a two-dimensional matrix to form an imaging element. For example, as shown in a block diagram in FIG. 10, an image sensor 40 may have a light receiving area 41 in which a plurality of photoelectric conversion elements 301 are arranged two-dimensionally.

[0060] In the image sensor 40, the number and arrangement of the photoelectric conversion elements 301 arranged in the light receiving area 41 can be set appropriately. Also, the shape of the phase adjustment lens 30L of each of the photoelectric conversion elements 301 can be set appropriately. For example, in the photoelectric conversion element 301, as shown in FIG. 16, the diameter d of the phase adjustment lens 30L may be larger than the length of one side of the substrate 10 in a plan view. In this case, the phase adjustment lens 30L is formed so as to remove a part of the periphery of the phase adjustment lens 30L in accordance with the shape of the substrate 10, that is, so as to remove a part of the phase adjustment lens 30L that protrudes outside the side of the substrate 10 in a plan view. This allows a plurality of photoelectric conversion elements 301 to be two-dimensionally arranged without gaps, without adjacent phase adjustment lenses 30L interfering with each other. Also, a plurality of photoelectric conversion elements arranged two-dimensionally may be formed on a single semiconductor wafer.

[0061] 11, the imaging element 40 may be an imaging sensor 121 including a plurality of photoelectric conversion elements 301 applied to the imaging system. As the imaging sensor 121, either a single photoelectric conversion element 301 or an imaging element 40 including a plurality of photoelectric conversion elements 301 can be used. By designing the phase adjustment lens 30L in the imaging sensor 121 based on the wavelength band of the emitted light L1, it is possible to provide an imaging system with little variation in distance measurement accuracy.

[0062] Although each embodiment and modified example of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and configuration changes and combinations that do not deviate from the gist of the present invention are also included.

[0063] For example, the structure of the phase adjustment layer 230 described in the second embodiment may be applied to the phase adjustment lens 30L according to the third embodiment. In this case, a structure in which minute projections and recesses are formed on the surface (lens surface) of the phase adjustment lens 30L is obtained.

[0064] For example, in the above-described embodiment and modified examples, examples of so-called front-illuminated photoelectric conversion elements have been described, but the present invention is also applicable to so-called back-illuminated photoelectric conversion elements. [Explanation of symbols]

[0065] 1, 201, 301 Photoelectric conversion element 10 Substrate 11 Charge generation region 20 Dielectric layer 30, 230, 230A, 230B, 230C, 230D, 230E, 330, 330A, 330B Phase adjustment layer 30L Phase Adjustment Lens (Phase Adjustment Layer) 30T top 30B Bottom 32 scattering particles 40 Image sensor 100 Imaging System 101 Light source L1 output light RL, L2 reflected light PL1 front page PL2 second side

Claims

1. A photoelectric conversion element that receives light reflected by an object from an emission light having a predetermined wavelength band emitted from a light source, a substrate having a charge generating region; a dielectric layer formed on the substrate; a phase adjustment layer disposed on the dielectric layer and having an upper surface and a lower surface; Equipped with the phase adjustment layer has a plurality of scattering particles having a particle size of 3 μm or less; In a cross-sectional view of the photoelectric conversion element, a plane that is in contact with the upper surface of the phase adjustment layer and is parallel to the substrate is defined as a first surface, and the lower surface of the phase adjustment layer is defined as a second surface. The phase adjustment layer is configured such that, when the reflected light is perpendicularly incident on the photoelectric conversion element, an optical path length from when the reflected light passes through the first surface to when it reaches the second surface varies depending on an incident position of the reflected light on the first surface. Photoelectric conversion element.

2. a maximum value of an optical path length difference of the reflected light transmitted through the phase adjustment layer is equal to or greater than ¼ of an average wavelength of the emitted light; The photoelectric conversion element according to claim 1 .

3. The phase adjustment layer is a phase adjustment lens having an aspect ratio h / d, which is a ratio of a bottom diameter d to a height h, of 0.35 to 1.

2. The photoelectric conversion element according to claim 1 or 2.

4. The phase adjustment lens covers 75% or more of the substrate in a plan view of the photoelectric conversion element. The photoelectric conversion element according to claim 3 .

5. The phase adjustment layer has fine irregularities. The photoelectric conversion element according to claim 1 or 2.

6. A photoelectric conversion element according to any one of claims 1 to 5, The photoelectric conversion elements are arranged two-dimensionally. Image sensor.

7. A photoelectric conversion device according to claim 3 or 4, The photoelectric conversion elements are arranged two-dimensionally, In a plan view of the photoelectric conversion element, a diameter of the phase adjustment lens is larger than a length of a side of the substrate, The phase adjustment lens has a shape in which a part of the phase adjustment lens protruding outside the side of the substrate is removed. Image sensor.

8. A light source that emits light having a predetermined wavelength band; The imaging element according to claim 6 or 7, Equipped with Imaging system.

9. A light source that emits light having a predetermined wavelength band; The photoelectric conversion element according to any one of claims 1 to 5, Equipped with Imaging system.

Images