Light detection device

Abstract

The present disclosure relates to a light detection device capable of improving light collection efficiency and improving photoelectric conversion efficiency. This light detection device comprises: a lens layer formed by lamination of at least two layers of a first lens layer and a second lens layer using different materials; a photoelectric conversion part formed by sandwiching a photoelectric conversion layer between an upper electrode and a lower electrode; and an insulation film between the lens layer and the photoelectric conversion part. The second lens layer below the first lens layer has a concave inner lens. A refractive index n1 of the first lens layer, a refractive index n2 of the second lens layer, and a refractive index n3 of the insulation film have a relationship of n1 > n2 > n3. The configuration of the present disclosure can be applied to, for example, a light detection device that detects light in a non-visible light region and performs photoelectric conversion.

Description

Photodetector

[0001] The present disclosure relates to a photodetector, and more particularly to a photodetector that is capable of improving light collection efficiency and photoelectric conversion efficiency.

[0002] In some image sensors, an uneven structure is formed on the surface of an on-chip lens to reduce the reflectance at the on-chip lens surface, or a multiple lens structure in which an inner lens is disposed between the on-chip lens and the light receiving unit is used to reduce the reflectance and increase the light collection efficiency (see, for example, Patent Document 1).

[0003] JP 2012-174885 A

[0004] It is expected that light with wavelengths longer than visible light is difficult to collect optically, and further improvement in light collection efficiency is desired.

[0005] The present disclosure has been made in view of such circumstances, and aims to improve light collection efficiency and photoelectric conversion efficiency.

[0006] A photodetector according to one aspect of the present disclosure comprises: a lens layer formed by laminating at least two layers, a first lens layer and a second lens layer, each of which is made of a different material; a photoelectric conversion unit formed by sandwiching a photoelectric conversion layer between an upper electrode and a lower electrode; and an insulating film between the lens layer and the photoelectric conversion unit, wherein the second lens layer below the first lens layer has a concave inner lens, and the refractive index n1 of the first lens layer, the refractive index n2 of the second lens layer, and the refractive index n3 of the insulating film satisfy the relationship n1>n2>n3.

[0007] In one aspect of the present disclosure, a lens layer is provided which is composed of a laminate of at least two layers, a first lens layer and a second lens layer made of different materials, a photoelectric conversion unit which is composed of a photoelectric conversion layer sandwiched between an upper electrode and a lower electrode, and an insulating film between the lens layer and the photoelectric conversion unit, and the second lens layer which is below the first lens layer is provided with a concave inner lens, and is configured so that the refractive index n1 of the first lens layer, the refractive index n2 of the second lens layer, and the refractive index n3 of the insulating film have the relationship n1>n2>n3.

[0008] The photodetector device may be a stand-alone device or a module that is incorporated into another device.

[0009] 1 is a diagram showing a schematic configuration of a photodetector to which the technology of the present disclosure is applied; FIG. 2 is a diagram showing an example of a circuit configuration of each pixel of the photodetector; FIG. 3 is a cross-sectional view showing an example of a pixel structure; FIG. 4 is a diagram explaining the effect of the pixel structure of FIG. 3; FIG. 5 is a diagram explaining a method for manufacturing the pixel of FIG. 3; FIG. 6 is a diagram explaining a method for manufacturing the pixel of FIG. 3; FIG. 7 is a cross-sectional view showing a first modified example of a pixel; FIG. 8 is a cross-sectional view showing a second modified example of a pixel; FIG. 9 is a cross-sectional view showing a third modified example of a pixel; FIG. 10 is a block diagram showing an example of the configuration of an imaging device as an electronic device to which the technology of the present disclosure is applied; and FIG. 11 is a diagram explaining an example of use of an image sensor.

[0010] Hereinafter, modes for carrying out the technology of the present disclosure (hereinafter referred to as embodiments) will be described with reference to the accompanying drawings. The description will be given in the following order: 1. Example of overall configuration of a photodetector 2. Pixel circuit 3. Pixel structure 4. Pixel manufacturing method 5. Modified pixel structure 6. Summary of pixel structure of the present disclosure 7. Application example to electronic device 8. Example of use of image sensor

[0011] In this specification and drawings, identical or similar parts are denoted by identical or similar reference numerals, and redundant explanations are omitted as appropriate. The drawings are schematic, and the relationship between thickness and planar dimensions, the thickness ratio of each layer, etc. may differ from the actual ones. Furthermore, there may be parts in which the dimensional relationships and ratios differ between the drawings.

[0012] Furthermore, the definitions of directions such as up and down in the following description are merely for the convenience of explanation and do not limit the technical idea of ​​the present disclosure. For example, if an object is rotated 90 degrees and observed, up and down are converted to left and right and read, and if it is rotated 180 degrees and observed, up and down are read inverted.

[0013] The technology disclosed herein can be applied to photodetection devices in general, including a pixel array in which pixels are arranged two-dimensionally in a matrix, that photoelectrically convert incident light and output pixel signals corresponding to the amount of light. The light to be detected may be light in the visible light range, including wavelengths such as R (Red), G (Green), and B (Blue), or light in the non-visible light range, such as infrared light. Alternatively, light in both the visible and non-visible light ranges may be used. The photodetection device can be used as a solid-state imaging device that generates and outputs an image signal corresponding to the amount of incident light, or as a light receiving device (ranging sensor) in a ranging system that receives infrared light irradiated as active light and measures the distance to a subject using a direct or indirect ToF method. Below, an example is described in which the technology disclosed herein is applied to a photodetection device that receives light in the infrared range and generates and outputs an image signal corresponding to the amount of incident light.

[0014] 1. Example of Overall Configuration of Photodetector FIG. 1 shows a schematic configuration of a photodetector to which the technology of the present disclosure is applied.

[0015] 1 includes a pixel array section 3 in which pixels 2 are arranged two-dimensionally in a matrix on a semiconductor substrate 12 made of, for example, single-crystal silicon (Si) as a semiconductor, and a peripheral circuit area around the pixel array section 3. The peripheral circuit area includes a vertical drive circuit 4, a column signal processing circuit 5, a horizontal drive circuit 6, an output circuit 7, a control circuit 8, etc.

[0016] The pixel 2 includes a photoelectric conversion portion made of a semiconductor thin film and a plurality of pixel transistors, each of which includes, for example, three MOS transistors: a reset transistor, an amplification transistor, and a selection transistor.

[0017] The control circuit 8 receives an input clock and data instructing the operation mode and the like, and outputs data such as internal information of the photodetector 1. That is, the control circuit 8 generates clock signals and control signals that serve as references for the operations of the vertical drive circuit 4, column signal processing circuit 5, horizontal drive circuit 6, etc., based on a vertical synchronization signal, a horizontal synchronization signal, and a master clock. The control circuit 8 then outputs the generated clock signals and control signals to the vertical drive circuit 4, column signal processing circuit 5, horizontal drive circuit 6, etc.

[0018] The vertical drive circuit 4 is configured by, for example, a shift register, selects a predetermined pixel drive wiring 10, supplies a pulse for driving the pixels 2 to the selected pixel drive wiring 10, and drives the pixels 2 row by row. That is, the vertical drive circuit 4 selects and scans each pixel 2 in the pixel array section 3 row by row in the vertical direction, and supplies a pixel signal based on a signal charge generated in the photoelectric conversion section of each pixel 2 according to the amount of received light to the column signal processing circuit 5 through the vertical signal line 9.

[0019] The column signal processing circuits 5 are arranged for each column of pixels 2, and perform signal processing such as noise removal for each column of signals output from one row of pixels 2. For example, the column signal processing circuits 5 perform signal processing such as CDS (Correlated Double Sampling) for removing fixed pattern noise specific to each pixel and AD conversion.

[0020] The horizontal drive circuit 6 is configured, for example, by a shift register, and sequentially outputs horizontal scanning pulses to select each of the column signal processing circuits 5 in turn, causing each of the column signal processing circuits 5 to output a pixel signal to the horizontal signal line 11.

[0021] The output circuit 7 processes and outputs signals sequentially supplied from each of the column signal processing circuits 5 through the horizontal signal line 11. The output circuit 7 may perform only buffering, or may perform black level adjustment, column variation correction, various digital signal processing, etc. The input / output terminal 13 exchanges signals with the outside.

[0022] The photodetector 1 configured as above has a structure called a column AD system in which the column signal processing circuits 5 for performing CDS processing and AD conversion processing are arranged for each column.

[0023] 2. Pixel Circuit FIG. 2 shows an example of the circuit configuration of each pixel 2 of the photodetector device 1. As shown in FIG.

[0024] Each pixel 2 includes a photoelectric conversion unit 21 , a capacitance element 22 , a reset transistor 23 , an amplification transistor 24 , and a selection transistor 25 .

[0025] The photoelectric conversion unit 21 has a photoelectric conversion layer using, for example, a compound semiconductor such as InGaAs, an amorphous silicon (non-crystalline silicon) film, a germanium (Ge) film, an organic semiconductor film, or a quantum dot film, and absorbs light of a predetermined wavelength to generate electric charges (signal charges) corresponding to the amount of light. The signal charges can be either holes or electrons, but in this embodiment, they are described as electrons. One electrode of the photoelectric conversion unit 21, specifically the other electrode different from the one connected to the capacitive element 22, is connected to ground (GND).

[0026] The capacitance element 22 is connected to one electrode of the photoelectric conversion unit 21 and stores the charge generated by the photoelectric conversion unit 21. The capacitance element 22 may include, for example, at least one of a PN junction capacitance, a MOS capacitance, and a wiring capacitance. The capacitance element 22 is also connected to the source of the reset transistor 23 and the gate of the amplification transistor 24.

[0027] When the reset transistor 23 is turned on by a reset signal RST, the charge stored in the capacitance element 22 is discharged to the drain (constant voltage source Vdd), thereby resetting the potential of the capacitance element 22 .

[0028] The amplification transistor 24 outputs a pixel signal corresponding to the accumulated potential of the capacitance element 22. That is, the amplification transistor 24 forms a source follower circuit together with a load MOS (not shown) serving as a constant current source connected via the vertical signal line 9, and a pixel signal indicating a level corresponding to the charge accumulated in the capacitance element 22 is output from the amplification transistor 24 to the column signal processing circuit 5 via the selection transistor 25.

[0029] The selection transistor 25 is turned on when the pixel 2 is selected by the selection signal SEL, and outputs a pixel signal of the pixel 2 to the column signal processing circuit 5 via the vertical signal line 9. The signal lines through which the selection signal SEL and the reset signal RST are transmitted correspond to the pixel drive wiring 10 in FIG.

[0030] 3. Pixel Structure FIG. 3 is a cross-sectional view showing an example of the structure of the pixel 2 of the photodetector 1. As shown in FIG.

[0031] 3 shows a cross-sectional view including a portion where three pixels 2 are arranged horizontally or vertically in the pixel array section 3 of the photodetector device 1. In FIG. 3, the region to the right of the region where the three pixels 2 are arranged corresponds to the peripheral circuit region around the pixel array section 3.

[0032] The photodetector 1 has a multilayer wiring layer 31 on one surface of a semiconductor substrate 12, and a photoelectric conversion unit 21 formed above the multilayer wiring layer 31. Furthermore, an insulating film 32, a lens layer 33, and an anti-reflection film 34 are formed above the photoelectric conversion unit 21. The surface of the semiconductor substrate 12 on which the photoelectric conversion unit 21, the lens layer 33, etc. are formed is the front surface of the semiconductor substrate 12, and is the light incident surface onto which light to be photoelectrically converted is incident. Although not shown, pixel transistors such as a reset transistor 23, an amplification transistor 24, and a selection transistor 25 are formed on the semiconductor substrate 12 for each pixel.

[0033] The photoelectric conversion unit 21 is formed between the semiconductor substrate 12 and the insulating film 32 and has a stacked structure in which a photoelectric conversion layer 41 and a buffer film 42 are sandwiched between an upper electrode 43 and a lower electrode 44. In this embodiment, the photoelectric conversion unit 21 photoelectrically converts incident long-wavelength light having a wavelength of approximately 850 nm or more, for example, light in the infrared region having a wavelength of 1000 nm or more. The upper electrode 43 is formed over the entire pixel array unit 3, while the lower electrode 44 is formed in the multilayer wiring layer 31, separated for each pixel. The upper electrode 43 is connected to metal wiring 56 formed in the peripheral circuit region and is connected to, for example, ground (GND) via the metal wiring 56. The voltage applied to the upper electrode 43 is not limited to ground, but may be any voltage that provides a predetermined potential difference between the upper electrode 43 and the lower electrode 44.

[0034] The photoelectric conversion layer 41 is made of a quantum dot film, which is a conductive film containing an aggregate of nanoparticles with a particle size of, for example, 10 nm or less. Examples of materials that can be used for the nanoparticles include lead sulfur compounds (PbS), lead selenium compounds (PbSe), lead tellurium compounds (PbTe), indium phosphide compounds (InP), indium arsenic compounds (InAs), indium antimony compounds (InSb), cadmium sulfur compounds (CdS), cadmium selenium compounds (CdSe), and cadmium tellurium compounds (CdTe).

[0035] The photoelectric conversion layer 41 may be made of a film using an organic material or an inorganic material in addition to the quantum dot film described above.

[0036] In the case where the photoelectric conversion layer 41 is a film using an organic material, examples of the organic material include a p-type organic semiconductor, an n-type semiconductor, or a stack or mixed layer (bulk heterostructure) of a p-type organic semiconductor and an n-type semiconductor. Examples of p-type organic semiconductors include naphthalene derivatives, anthracene derivatives, phenanthrene derivatives, pyrene derivatives, perylene derivatives, tetracene derivatives, pentacene derivatives, quinacridone derivatives, thiophene derivatives, thienothiophene derivatives, benzothiophene derivatives, benzothienobenzothiophene derivatives, triallylamine derivatives, carbazole derivatives, perylene derivatives, picene derivatives, chrysene derivatives, fluoranthene derivatives, phthalocyanine derivatives, subphthalocyanine derivatives, subporphyrazine derivatives, metal complexes having a heterocyclic compound as a ligand, polythiophene derivatives, polybenzothiadiazole derivatives, and polyfluorene derivatives. Examples of n-type organic semiconductors include fullerenes and fullerene derivatives (for example, fullerenes (higher fullerenes) such as C60, C70, and C74, endohedral fullerenes, etc.) or fullerene derivatives (for example, fullerene fluorides, PCBM fullerene compounds, fullerene polymers, etc.)), organic semiconductors having larger (deeper) HOMO and LUMO than p-type organic semiconductors, and transparent inorganic metal oxides. Examples of n-type organic semiconductors include heterocyclic compounds containing nitrogen atoms, oxygen atoms, or sulfur atoms, pyridine derivatives, pyrazine derivatives, pyrimidine derivatives, triazine derivatives, quinoline derivatives, quinoxaline derivatives, isoquinoline derivatives, acridine derivatives, phenazine derivatives, phenanthroline derivatives, tetrazole derivatives, pyrazole derivatives, imidazole derivatives, thiazole derivatives, oxazole derivatives, imidazole derivatives, benzimidazole derivatives, benzotriazole derivatives, benzoxazole derivatives, carbazole derivatives, benzofuran derivatives, dibenzofuran derivatives, subporphyrazine derivatives, polyphenylenevinylene derivatives, polybenzothiadiazole derivatives, and polyfluorene derivatives, and organic molecules having such derivatives as part of their molecular skeletons, as well as organometallic complexes and subphthalocyanine derivatives.

[0037] In the case where the photoelectric conversion layer 41 is a film using an inorganic material, examples of the inorganic material include crystalline silicon, amorphous silicon, amorphous selenium, CIGS (a Cu, In, Ga, Se compound), CIS (a Cu, In, Se compound), chalcopyrite structure semiconductors, and compound semiconductors such as GaAs.

[0038] The buffer film 42 is intended to facilitate the supply of electrons, which are signal charges generated in the photoelectric conversion layer 41, to the lower electrode 44, and is made of, for example, zinc oxide (ZnO), titanium oxide (TiO2), or the like.

[0039] The upper electrode 43 (first electrode) is made of a conductive film that is transparent to light to be photoelectrically converted, and is formed of a transparent electrode such as indium tin oxide (ITO), indium zinc oxide, or zinc oxide. The lower electrode 44 (second electrode) is also formed of a transparent electrode such as indium tin oxide, indium zinc oxide, or zinc oxide. Note that the lower electrode 44 does not need to be a film that is transparent to light, and may be formed of a metal material such as tungsten, titanium, titanium nitride, or aluminum. In this embodiment, the upper electrode 43 and the lower electrode 44 are formed of ITO using, for example, a sputtering method.

[0040] The insulating film 32 is formed using a material with a smaller refractive index than the first lens layer 45 and the second lens layer 46 that constitute the upper lens layer 33. The insulating film 32 is formed of, for example, silicon nitride (SiN), silicon oxide (SiO2), or the like. For example, the refractive index n3 of silicon nitride (SiN) at a wavelength of 1450 nm is about 1.8, and the refractive index n3 of silicon oxide (SiO2) at a wavelength of 1450 nm is about 1.5.

[0041] The lens layer 33 is composed of at least two layers: a first lens layer 45 and a second lens layer 46. The first lens layer 45 has an on-chip lens 61 with a convex lens surface for each pixel, and the second lens layer 46 has an inner lens 62 with a concave lens surface for each pixel. The first lens layer 45 and the second lens layer 46 are made of a material having a refractive index n greater than that of the underlying insulating film 32. Furthermore, when comparing the refractive indices n of the first lens layer 45 and the second lens layer 46, the refractive index n1 of the first lens layer 45 is greater than the refractive index n2 of the second lens layer 46. That is, the first lens layer 45 is made of a material such that the refractive index n1 of the first lens layer 45, the refractive index n2 of the second lens layer 46, and the refractive index n3 of the insulating film 32 satisfy the relationship n1 > n2 > n3 at the wavelength of light to be photoelectrically converted (hereinafter also referred to as the target wavelength). The first lens layer 45 can be made of, for example, amorphous silicon or polycrystalline silicon. The material for the second lens layer 46 can be, for example, aluminum nitride, titanium oxide, zirconium oxide, or aluminum oxide. When the material for the first lens layer 45 is, for example, amorphous silicon, the refractive index n1 of amorphous silicon at a wavelength of 1450 nm is approximately 3.4, and the refractive index n2 of each material for the second lens layer 46 at a wavelength of 1450 nm has a value between the refractive index n1=3.4 of the first lens layer 45 and the refractive index n3=1.5 to 1.8 of the insulating film 32.

[0042] The anti-reflection film 34 can be formed of, for example, a single layer or a laminated layer of silicon oxide film. When the anti-reflection film 34 is formed of a laminated layer, for example, a laminated layer in which a silicon oxide film or the like is formed on a silicon nitride film or a silicon oxynitride film can be used.

[0043] The multilayer wiring layer 31 includes multiple layers of metal wiring 51 and insulating films (interlayer insulating films) 52. While FIG. 3 shows an example in which the metal wiring 51 has five layers, the number of layers of the metal wiring 51 is not limited. The metal wiring 51 can be formed of, for example, copper (Cu), tungsten (W), titanium (Ti), tantalum (Ta), a titanium-tungsten alloy (TiW), polysilicon, or the like. The insulating film 52 can be formed of, for example, an SiO2 film, a low-k film (a low-dielectric-constant insulating film), an SiOC film, or the like. The insulating film 52 may also be composed of multiple insulating films made of different materials. Among the multiple layers of metal wiring 51 in the multilayer wiring layer 31, the metal wiring 51A connected to the lower electrode 44 via the plug 55 is formed of the same metal material as the bonding pad formed in the peripheral circuit region, for example, AlCu. The signal charge generated by the photoelectric conversion unit 21 is accumulated in a capacitance element 22 (not shown) formed in the multilayer wiring layer 31 or the semiconductor substrate 12 via a lower electrode 44, a plug 55, a metal wiring 51A, a plug 53, multiple layers of metal wiring 51, etc., which are formed separately for each pixel. The plug 53 and the plug 55 are made of, for example, tungsten.

[0044] The pixel 2 of the photodetector 1 is configured as described above.

[0045] It is expected that long-wavelength light in the infrared region, which is the target wavelength of the photoelectric conversion unit 21 of the pixel 2, will be difficult to optically focus. Therefore, the pixel 2 has the lens layer 33 configured as a stack of at least two layers, a first lens layer 45 and a second lens layer 46. The upper first lens layer 45 is made of a high-refractive-index material, such as amorphous silicon, and the lower second lens layer 46 is made of a material whose refractive index n2 satisfies the relationship n1 > n2 > n3, as shown in FIG. 4 , i.e., a refractive index between the refractive index n3 of the lower insulating film 32 and the refractive index n1 of the upper first lens layer 45, such as aluminum nitride, titanium oxide, zirconium oxide, or aluminum oxide. By configuring the lens layer 33 as a plurality of lens layers rather than a single lens layer, incident light can be efficiently focused on the photoelectric conversion unit 21, as indicated by the arrows in FIG. 4 , thereby improving the light-focusing efficiency. Furthermore, the refractive index of the lower second lens layer 46 and the insulating film 32 thereunder is gradually reduced so that n1>n2>n3, relative to the upper first lens layer 45 made of a high refractive index material, and the refractive index difference between the interfaces is suppressed, thereby reducing the interface reflectance and improving the light collection efficiency.

[0046] When a quantum dot film is used as the photoelectric conversion layer 41 of the photoelectric conversion unit 21, the quantum dot film offers a high degree of freedom in wavelength selectivity, allowing a desired wavelength to be set as the target wavelength. This makes it suitable for sensing applications where the target wavelength is light in the infrared region, for example, long-wavelength light of 1000 nm or longer. However, because quantum dot films have poor weather resistance to oxygen and moisture, high passivation properties must be ensured. In the pixel 2, the upper layer of the upper electrode 43, which constitutes part of the photoelectric conversion unit 21, is protected by multiple layers, including the insulating film 32, the second lens layer 46, and the first lens layer 45, thereby improving passivation and increasing reliability. By configuring the lens layer 33 as multiple lens layers rather than a single lens layer, sealing properties can be improved without increasing the thickness of the insulating film 32.

[0047] 4. Pixel Manufacturing Method> Next, a method for manufacturing the pixel 2 will be described with reference to Fig. 5 to Fig. 7. Fig. 5 to Fig. 7 describe a method for manufacturing the stacked structure above the photoelectric conversion unit 21 in the structure of the pixel 2 shown in Fig. 3.

[0048] 5A, an insulating film 32 is formed on the upper surface of the upper electrode 43 on the photoelectric conversion layer 41 by, for example, chemical vapor deposition (hereinafter referred to as CVD) or atomic layer deposition (hereinafter referred to as ALD). As described above, the insulating film 32 is made of a film having a refractive index smaller than those of the first lens layer 45 and the second lens layer 46, and can be made of, for example, silicon nitride (SiN), silicon oxide (SiO2), or the like.

[0049] The photoelectric conversion layer 41 can be formed by a coating device or the like, and the upper electrode 43 can be formed of indium tin oxide (ITO) by using, for example, a sputtering method.

[0050] 5B, a lens material 46A is formed as the second lens layer 46, which is the lower layer of the two-layered lens layer 33. The material of the lens material 46A has a refractive index n2 greater than the refractive index n3 of the insulating film 32 (n2>n3), and may be, for example, aluminum nitride, titanium oxide, zirconium oxide, or aluminum oxide.

[0051] Next, as shown in Figure 5C, photoresist 101 is formed on the entire upper surface of the lens material 46A using a coating device or the like, and then the photoresist 101 is patterned using a lithography method according to the formation position of the concave inner lens 62, as shown in Figure 5D.

[0052] Next, as shown in FIG. 6A, the lens material 46A is formed into a concave lens shape by wet etching based on the patterned photoresist 101, and then the photoresist 101 is removed by ashing.

[0053] Next, as shown in Fig. 6B, photoresist 102 is patterned using lithography so as to cover the concave surface of the inner lens 62, and the lens material 46A is removed using dry etching or the like based on the patterned photoresist 102 until a predetermined film thickness is reached, thereby forming the second lens layer 46 shown in Fig. 3. Fig. 6C shows the state in which the photoresist 102 has been removed by ashing after dry etching. The inner lens 62 is formed in the area where the photoresist 102 was patterned.

[0054] 6D, a lens material 45A of the first lens layer 45 is formed on the entire upper surface of the second lens layer 46 on which the inner lens 62 is formed. A material having a refractive index n1 greater than the refractive index n2 of the second lens layer 46 (n1>n2) is selected for the material of the first lens layer 45, such as amorphous silicon.

[0055] Next, as shown in FIG. 7A, a photoresist 103 is formed on the upper surface of the lens material 45A by a coating device or the like, and then patterned using lithography so as to leave a position where the on-chip lens 61 is to be formed.

[0056] Next, as shown in FIG. 7B, the patterned photoresist 103 is formed into a convex lens shape by thermal reflow or the like.

[0057] Next, as shown in FIG. 7C, dry etching is performed based on the photoresist 103 formed in a convex lens shape, whereby the convex lens shape of the photoresist 103 is transferred to the lens material 45A, and the first lens layer 45 on which the convex on-chip lenses 61 are formed is completed.

[0058] 7D, an anti-reflection coating 34 is formed on the entire upper surface of the first lens layer 45 by atomic layer deposition, plasma CVD, or the like. The anti-reflection coating 34 can be formed, for example, by a single layer of silicon oxide film or a multilayer film using silicon oxide film.

[0059] The portion of pixel 2 above photoelectric conversion unit 21 shown in Fig. 3 can be manufactured as described above. Multilayer wiring layer 31 of pixel 2 and the pixel transistor portion formed on semiconductor substrate 12 can be formed using a known manufacturing method for forming a logic substrate.

[0060] 5. Modified Examples of Pixel Structure Next, modified examples of the pixel 2 will be described with reference to Fig. 8 to Fig. 10. Fig. 8 to Fig. 10 show cross-sectional views of the pixel 2 above the multilayer wiring layer 31.

[0061] FIG. 8 is a cross-sectional view showing a first modified example of the pixel 2. As shown in FIG.

[0062] In a first modified example of the pixel 2 shown in FIG. 8 , the second lens layer 46 forming the concave inner lens 62 in the basic structure of the pixel 2 shown in FIG. 3 is replaced with a second lens layer 46X. In the basic structure of the pixel 2 shown in FIG. 3 , the second lens layer 46 has an inner lens 62 formed for each pixel. However, the second lens layer 46X of the first modified example has an inner lens 120 formed across multiple pixels (e.g., three pixels). In relation to the first lens layer 45 having the convex on-chip lenses 61, the second lens layer 46X has one inner lens 120 corresponding to the multiple on-chip lenses 61 (e.g., three on-chip lenses 61). In this way, by having one inner lens 120 for multiple pixels in the second lens layer 46X, it is possible to accommodate even miniaturized pixel sizes. 3, the second lens layer 46 is thin at the pixel boundary between the inner lenses 62. However, in the second lens layer 46X of the first modified example, the thin region between the inner lenses 62 can be reduced or eliminated. This allows the average thickness of the second lens layer 46X to be increased, further improving passivation and increasing reliability. The combined thickness of the upper electrode 43 and the insulating film 32 is, for example, approximately 0.85 μm, and the thickness of the lens layer 33 consisting of the first lens layer 45 and the second lens layer 46X is, for example, approximately 0.4 μm.

[0063] FIG. 9 is a cross-sectional view showing a second modified example of the pixel 2. As shown in FIG.

[0064] In the second modified example of the pixel 2 shown in FIG. 9 , the second lens layer 46 forming the concavely curved inner lens 62 in the basic structure of the pixel 2 shown in FIG. 3 is replaced with a second lens layer 46Y. In the basic structure of the pixel 2 shown in FIG. 3 , the second lens layer 46 is formed so that the height of the inner lens 62 of each pixel 2 is the same. In contrast, the second lens layer 46Y of the second modified example is formed so that the height H of the inner lens 121 differs between adjacent pixels. Specifically, among the multiple pixels 2 in the pixel array section 3, the first pixel 2A has an inner lens 121A with a height Ha, the second pixel 2B has an inner lens 121B with a height Hb, and the third pixel 2C has an inner lens 121C with a height Hc. The heights Ha, Hb, and Hc are different from one another. In the example of FIG. 9 , the heights Ha, Hb, and Hc satisfy the relationship Ha<Hc<Hb. In the pixel array section 3, three types of pixels 2 with different heights H of the inner lens 121 are arranged in a mixed manner according to a predetermined rule. The target wavelength can be changed by changing the height H of the inner lens 121. By arranging a plurality of inner lenses 121 having different heights H in the pixel array section 3 in this way, simultaneous detection of light of a plurality of wavelengths can be achieved for the entire pixel array section 3. In this example, an example has been described in which there are three types of pixels 2 with different heights H, but the number of types of pixels 2 with different heights H is not limited to three, and any type (number) of pixels can be formed depending on the wavelength to be detected.

[0065] FIG. 10 is a cross-sectional view showing a third modified example of the pixel 2. As shown in FIG.

[0066] In the third modified example of pixel 2 shown in FIG. 10 , the second lens layer 46 forming the concave inner lens 62 in the basic structure of pixel 2 shown in FIG. 3 is replaced with a second lens layer 46Z. While the second lens layer 46 in the basic structure of pixel 2 shown in FIG. 3 is formed of the same lens material for all pixels, the second lens layer 46Z in the third modified example is formed of lens materials with different target wavelengths for adjacent pixels. Specifically, among the multiple pixels 2 in the pixel array section 3, the inner lens 122A of the first pixel 2A is formed using a first lens material, the inner lens 122B of the second pixel 2B is formed using a second lens material, and the inner lens 122C of the third pixel 2C is formed using a third lens material, with the first, second, and third lens materials being different from one another. The first, second, and third lens materials are selected from the aforementioned aluminum nitride, titanium oxide, zirconium oxide, and aluminum oxide, for example, to maximize the light collection efficiency for the target wavelength. In this way, by arranging a plurality of inner lenses 122 using lens materials with different target wavelengths within the pixel array unit 3, it is possible to simultaneously detect light of a plurality of wavelengths throughout the pixel array unit 3. In this example, an example has been described in which there are three types of pixels 2 with different lens materials, but the number of types (number) of pixels 2 with different lens materials is not limited to three, and any type (number) can be formed depending on the wavelength to be detected.

[0067] 6. Summary of Pixel Structure of the Present Disclosure The pixel 2 of the photodetector 1 includes a lens layer 33 configured by stacking at least two layers, a first lens layer 45 and a second lens layer 46, each made of a different material, a photoelectric conversion unit 21 configured by sandwiching a photoelectric conversion layer 41 between an upper electrode 43 and a lower electrode 44, and an insulating film 32 between the lens layer 33 and the photoelectric conversion unit 21. The second lens layer 46, which is located below the first lens layer 45, has a concave inner lens 62, and the refractive index n1 of the first lens layer 45, the refractive index n2 of the second lens layer 46, and the refractive index n3 of the insulating film 32 satisfy the relationship n1 > n2 > n3. By configuring the lens layer 33 as a stack of at least two layers and disposing the insulating film 32 between the lens layer 33 and the photoelectric conversion unit 21 in this manner, it is possible to improve sealing performance without increasing the thickness of the insulating film 32.

[0068] In the above example, the lens layer 33 is configured as a laminate of two layers, the first lens layer 45 and the second lens layer 46, but it may be configured as a laminate of three or more layers using different materials. In this case, the sealing performance can be further improved. When the lens layer 33 is configured as a laminate of three or more layers, the concave inner lens 62 may be disposed in any lens layer as long as it is a lens layer below the lens layer (first lens layer 45) in which the on-chip lens 61 is formed.

[0069] Furthermore, by forming pixel 2 using materials in which the refractive index n1 of first lens layer 45, the refractive index n2 of second lens layer 46, and the refractive index n3 of insulating film 32 satisfy the relationship n1>n2>n3, the difference in refractive index between interfaces is suppressed, thereby reducing interface reflectance and improving light collection efficiency. Therefore, pixel 2 can improve photoelectric conversion efficiency (external quantum efficiency).

[0070] 7. Application Examples to Electronic Devices The technology of the present disclosure can be applied to general electronic devices that use a photodetector in an image capture unit (photoelectric conversion unit), such as imaging devices such as digital still cameras and video cameras, portable terminal devices with imaging functions, copiers that use a photodetector in an image reading unit, etc. The photodetector may be formed as a single chip, or may be a module having an imaging function in which the imaging unit and a signal processing unit or an optical system are packaged together.

[0071] FIG. 11 is a block diagram showing an example of the configuration of an imaging device as an electronic device to which the technology of the present disclosure is applied.

[0072] The imaging device 200 in Fig. 11 includes an optical unit 201 including a group of lenses and the like, a solid-state imaging device (imaging device) 202 that employs the configuration of the photodetector 1 in Fig. 1 , and a DSP (Digital Signal Processor) circuit 203 that is a camera signal processing circuit. The imaging device 200 also includes a frame memory 204, a display unit 205, a recording unit 206, an operation unit 207, and a power supply unit 208. The DSP circuit 203, frame memory 204, display unit 205, recording unit 206, operation unit 207, and power supply unit 208 are connected to each other via a bus line 209.

[0073] The optical unit 201 captures incident light (image light) from a subject and forms an image on the imaging surface of the solid-state imaging device 202. The solid-state imaging device 202 converts the amount of incident light imaged on the imaging surface by the optical unit 201 into an electrical signal for each pixel and outputs the signal as a pixel signal. The solid-state imaging device 202 is a solid-state imaging device having the configuration of the photodetector 1 in FIG. 1 , specifically, a solid-state imaging device that includes a lens layer 33 formed by stacking at least two layers, a first lens layer 45 and a second lens layer 46, the lower second lens layer 46 having a concave inner lens 62, and where the refractive index n1 of the first lens layer 45, the refractive index n2 of the second lens layer 46, and the refractive index n3 of the insulating film 32 satisfy the relationship n1>n2>n3, thereby improving light collection efficiency and photoelectric conversion efficiency.

[0074] The display unit 205 is configured with a thin display such as an LCD (Liquid Crystal Display) or an organic EL (Electro Luminescence) display, and displays moving images or still images captured by the solid-state imaging device 202. The recording unit 206 records the moving images or still images captured by the solid-state imaging device 202 on a recording medium such as a hard disk or semiconductor memory.

[0075] An operation unit 207, under the operation of a user, issues operation commands for various functions of the imaging device 200. A power supply unit 208 appropriately supplies various types of power to the DSP circuit 203, frame memory 204, display unit 205, recording unit 206, and operation unit 207 as operating power sources.

[0076] As described above, a high-quality captured image can be generated by using the photodetector 1 with improved light collection efficiency and improved photoelectric conversion efficiency as the solid-state imaging device 202. Therefore, a high-quality captured image can be obtained even in the imaging device 200 such as a video camera, a digital still camera, or even a camera module for a mobile device such as a mobile phone.

[0077] 8. Example of Use of Image Sensor FIG. 12 is a diagram showing an example of use of an image sensor using the above-described photodetector device 1. In FIG.

[0078] The above-described photodetector 1 can be used as an image sensor in various cases for sensing light such as visible light, infrared light, ultraviolet light, and X-rays, for example, as described below.

[0079] ・Devices for taking images for viewing purposes, such as digital cameras and mobile devices with camera functions. ・Devices for traffic purposes, such as in-vehicle sensors that take images of the front, rear, surroundings, and interior of a car for safe driving such as automatic stopping, and for recognizing the driver's state, surveillance cameras that monitor moving vehicles and roads, and distance measuring sensors that measure distances between vehicles. ・Devices for home appliances such as TVs, refrigerators, and air conditioners that take images of user gestures and operate the device according to those gestures. ・Devices for medical and healthcare purposes, such as endoscopes and devices that take images of blood vessels by receiving infrared light. ・Devices for security purposes, such as surveillance cameras for crime prevention and cameras for person authentication. ・Devices for beauty purposes, such as skin measuring devices that take images of the skin and microscopes that take images of the scalp. ・Devices for sports purposes, such as action cameras and wearable cameras for sports, etc. ・Devices for agricultural purposes, such as cameras to monitor the condition of fields and crops.

[0080] In the above example, a photodetector using electrons as signal charges has been described, but the present disclosure can also be applied to a photodetector using holes as signal charges.

[0081] Furthermore, in the above example, an example has been described in which the technology of the present disclosure is applied to a photodetector that outputs an image signal. However, the technology of the present disclosure is not limited to application to photodetectors that detect the distribution of incident light amount of visible light and capture an image, but can be applied to photodetectors that capture an image of the distribution of incident amounts of infrared rays, X-rays, particles, etc., and in a broad sense, to photodetectors in general (physical quantity distribution detection devices) such as fingerprint detection sensors that detect the distribution of other physical quantities such as pressure or capacitance and capture an image.

[0082] The embodiments of the present disclosure are not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the technology of the present disclosure. For example, a configuration in which all or part of the above-described configuration examples are combined may be adopted.

[0083] The effects described in this specification are merely examples and are not limiting, and there may be effects other than those described in this specification.

[0084] The technology disclosed herein may have the following configurations: (1) A photodetector including a lens layer formed by laminating at least two layers, a first lens layer and a second lens layer, each of which is made of a different material; a photoelectric conversion unit formed by sandwiching a photoelectric conversion layer between an upper electrode and a lower electrode; and an insulating film between the lens layer and the photoelectric conversion unit, wherein the second lens layer below the first lens layer has a concave inner lens, and a refractive index n1 of the first lens layer, a refractive index n2 of the second lens layer, and a refractive index n3 of the insulating film satisfy the relationship n1 > n2 > n3. (2) The photodetector according to (1), wherein the photoelectric conversion layer is formed by a quantum dot film including an aggregate of nanoparticles, and the nanoparticles are any one of a lead sulfur compound, a lead selenium compound, a lead tellurium compound, an indium phosphide compound, an indium arsenic compound, an indium antimony compound, a cadmium sulfur compound, a cadmium selenium compound, and a cadmium tellurium compound. (3) The photodetector according to (1), wherein the photoelectric conversion layer is formed of a film using any one of an organic semiconductor, amorphous silicon, or compound semiconductor. (4) The photodetector according to any one of (1) to (3), wherein the first lens layer has an on-chip lens, and wherein the first lens layer is formed of amorphous silicon. (5) The photodetector according to any one of (1) to (4), wherein the second lens layer is formed of any one of aluminum nitride, titanium oxide, zirconium oxide, or aluminum oxide. (6) The photodetector according to any one of (1) to (5), wherein the insulating film is formed of silicon nitride or silicon oxide. (7) The photodetector according to any one of (1) to (6), wherein the photoelectric conversion unit is formed between a semiconductor substrate and the insulating film. (8) The photodetector according to any one of (1) to (7), wherein the photoelectric conversion unit further includes a buffer film between the photoelectric conversion layer and the lower electrode. (9) The photodetector according to any one of (1) to (8), wherein the first lens layer has an on-chip lens for each pixel, and the second lens layer has the inner lens for each pixel.(10) The photodetector according to (9), wherein the second lens layer has the inner lenses of different heights. (11) The photodetector according to (9) or (10), wherein the second lens layer has the inner lenses made of different materials. (12) The photodetector according to any of (1) to (8), wherein the first lens layer has an on-chip lens for each pixel, and the second lens layer has the inner lens spanning multiple pixels. (13) The photodetector according to any of (1) to (8), wherein the first lens layer has an on-chip lens for each pixel, and the inner lenses of the second lens layer are formed corresponding to multiple on-chip lenses.

[0085] REFERENCE SIGNS LIST 1 Photodetector, 2 Pixel, 3 Pixel array section, 21 Photoelectric conversion section, 22 Capacitor element, 23 Reset transistor, 24 Amplification transistor, 25 Selection transistor, 31 Multilayer wiring layer, 32 Insulating film, 33 Lens layer, 34 Anti-reflection film, 41 Photoelectric conversion layer, 42 Buffer film, 43 Upper electrode, 44 Lower electrode, 45 First lens layer, 46, 46X, 46Y, 46Z Second lens layer, 61 On-chip lens, 62 Inner lens, 120 Inner lens, 121, 121A, 121B, 121C Inner lens, 122, 122A, 122B, 122C Inner lens, 200 Imaging device, 202 Solid-state imaging device

Claims

1. A photodetector comprising: a lens layer formed of at least two layers, a first lens layer and a second lens layer made of different materials; a photoelectric conversion section formed by sandwiching a photoelectric conversion layer between an upper electrode and a lower electrode; and an insulating film between the lens layer and the photoelectric conversion section, wherein the second lens layer below the first lens layer has a concave inner lens, and the refractive index n1 of the first lens layer, the refractive index n2 of the second lens layer, and the refractive index n3 of the insulating film satisfy the relationship n1>n2>n3.

2. The optical detection device according to claim 1, wherein the photoelectric conversion layer is composed of a quantum dot film containing an aggregate of nanoparticles, and the nanoparticles are any one of a lead sulfur compound, a lead selenium compound, a lead tellurium compound, an indium phosphide compound, an indium arsenide compound, an indium antimony compound, a cadmium sulfur compound, a cadmium selenium compound, and a cadmium tellurium compound.

3. The photodetector according to claim 1, wherein the photoelectric conversion layer is made of a film using either an organic semiconductor, amorphous silicon, or a compound semiconductor.

4. The photodetector according to claim 1, wherein the first lens layer has an on-chip lens, and the first lens layer is made of amorphous silicon.

5. The light detection device according to claim 1, wherein the second lens layer is formed of any one of aluminum nitride, titanium oxide, zirconium oxide, and aluminum oxide.

6. The photodetector according to claim 1, wherein the insulating film is made of silicon nitride or silicon oxide.

7. The photodetector according to claim 1, wherein the photoelectric conversion section is formed between a semiconductor substrate and the insulating film.

8. The photodetector according to claim 1, wherein the photoelectric conversion section further comprises a buffer film between the photoelectric conversion layer and the lower electrode.

9. The photodetector according to claim 1, wherein the first lens layer has an on-chip lens for each pixel, and the second lens layer has an inner lens for each pixel.

10. The optical detection device according to claim 9, wherein the second lens layer has inner lenses of different heights.

11. The optical detection device of claim 9, wherein the second lens layer has an inner lens made of a different material.

12. The photodetector according to claim 1, wherein the first lens layer has an on-chip lens for each pixel, and the second lens layer has an inner lens that spans a plurality of pixels.

13. The photodetector according to claim 1, wherein the first lens layer has an on-chip lens for each pixel, and the inner lenses of the second lens layer are formed corresponding to a plurality of the on-chip lenses.

Images