Photodetector element and photoelectric conversion device

Abstract

To provide a photodetection element having high efficiency for light utilization.SOLUTION: The photodetection element has a first electrode 10, a second electrode 30, and a photoelectric conversion film 20 arranged between the first electrode 10 and the second electrode 30. The first electrode 10 has a first metal layer 12 and a second metal layer 14 arranged between the first metal layer 12 and the photoelectric conversion film 20. The reflectance of the first electrode 10 for light of a certain wavelength transmitted through the photoelectric conversion film 20 is higher than the reflectance inherent of a material constituting the second metal layer 14 for light of the certain wavelength.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a photodetector and a photoelectric conversion device. [Background technology]

[0002] Stacked photoelectric conversion devices have been proposed as photoelectric conversion devices used in camera image sensors and the like. In stacked photoelectric conversion devices, a photodetector element including a photoelectric conversion film is stacked on a semiconductor substrate. A transparent electrode is disposed on the photoelectric conversion film, and a pixel electrode is disposed below the photoelectric conversion film. Patent Document 1 describes a photodetector element in which a metal electrode layer having an aluminum layer on its surface, an electron extraction layer which is a zinc oxide layer, a photoelectric conversion layer, and a transparent electrode layer are stacked in this order. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-124264 Summary of the Invention [Problem to be solved by the invention]

[0004] One known method for improving the light utilization efficiency of a photodetector using a photoelectric conversion film is to construct pixel electrodes using a metal material with high reflectivity and efficiently utilize the light reflected by the pixel electrodes. However, in the structure described in Patent Document 1, a zinc oxide layer is provided between the metal electrode layer and the photoelectric conversion layer, making it impossible to efficiently utilize the light reflected by the pixel electrodes.

[0005] An object of the present invention is to provide a photodetector element with high light utilization efficiency and a highly sensitive photoelectric conversion device using the same. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a light-detecting element having a first electrode, a second electrode, and a photoelectric conversion film disposed between the first electrode and the second electrode, wherein the first electrode has a first metal layer and a second metal layer disposed between the first metal layer and the photoelectric conversion film, a layer of an oxide of the metal of the second metal layer is disposed between the second metal layer and the photoelectric conversion film, and the second metal layer is made of a material in which an oxide of a metal or alloy constituting the second metal layer can have electrical properties that allow the movement of carriers of a first conductivity type and restrict the movement of carriers of a second conductivity type different from the first conductivity type; A photodetector element is provided in which the reflectance of the first electrode for light of a certain wavelength that has passed through the photoelectric conversion film is higher than the reflectance of the material that constitutes the second metal layer for the light of the certain wavelength.

[0007] According to another aspect of the present invention, there is provided a light-detecting element having a first electrode, a second electrode, and a photoelectric conversion film disposed between the first electrode and the second electrode, wherein the first electrode has a first metal layer and a second metal layer disposed between the first metal layer and the photoelectric conversion film, a layer of an oxide of the metal of the second metal layer is disposed between the second metal layer and the photoelectric conversion film, and the second metal layer is made of a material in which an oxide of a metal or alloy constituting the second metal layer can have electrical properties that allow the movement of carriers of a first conductivity type and restrict the movement of carriers of a second conductivity type different from the first conductivity type; the first metal layer is made of a metal or alloy containing aluminum or silver as a main material, The main material of the second metal layer is different from the main material of the first metal layer, The photodetector element may have a thickness of the second metal layer of 5 nm or more and 50 nm or less. [Effects of the Invention]

[0009] According to the present invention, it is possible to realize a photodetector element with high light utilization efficiency and a highly sensitive photoelectric conversion device using the same. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic cross-sectional view showing a photodetector according to a first embodiment of the present invention. [Figure 2] FIG. 4 is a schematic cross-sectional view showing a photodetector according to a modified example of the first embodiment of the present invention. [Figure 3] 1 is a graph showing the dependency of reflectance on titanium film thickness in a titanium / aluminum stacked structure. [Figure 4] 1 is a graph showing the current-voltage characteristics of a photodetector element. [Figure 5] 10 is a graph showing the results of measuring the external quantum efficiency of a photodetector element. [Figure 6]FIG. 4 is a schematic cross-sectional view showing an example of the configuration of a photoelectric conversion device according to a second embodiment of the present invention. [Figure 7] FIG. 4 is a schematic cross-sectional view showing a photodetector in a photoelectric conversion device according to a second embodiment of the present invention. [Figure 8] 10A to 10C are cross-sectional views (part 1) illustrating steps in a method for manufacturing a photoelectric conversion device according to a second embodiment of the present invention. [Figure 9] 10A to 10C are cross-sectional views (part 2) illustrating the steps of the method for manufacturing the photoelectric conversion device according to the second embodiment of the present invention. [Figure 10] 10A to 10C are cross-sectional views (part 3) illustrating the steps of the method for manufacturing the photoelectric conversion device according to the second embodiment of the present invention. [Figure 11] 10A and 10B are a plan view and a schematic cross-sectional view showing a photodetector in a photoelectric conversion device according to a third embodiment of the present invention. [Figure 12] 10A and 10B are a plan view and a schematic cross-sectional view showing a photodetector in a photoelectric conversion device according to a fourth embodiment of the present invention. [Figure 13] FIG. 10 is a block diagram showing a schematic configuration of an imaging system according to a fifth embodiment of the present invention. [Figure 14] FIG. 13 is a diagram showing an example of the configuration of an imaging system and transportation equipment according to a sixth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] [First embodiment] A photodetector according to a first embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a schematic cross-sectional view showing the structure of the photodetector according to this embodiment. Figure 2 is a schematic cross-sectional view showing the structure of a photodetector according to a modified example of this embodiment.

[0012] 1, the photodetector according to this embodiment has a first electrode 10, a second electrode 30, and a photoelectric conversion film 20 disposed between the first electrode 10 and the second electrode 30. The first electrode 10 has a first metal layer 12 and a second metal layer 14 disposed between the first metal layer 12 and the photoelectric conversion film 20. The second metal layer 14 is provided so as to be in direct contact with the first metal layer 12.

[0013] The photodetector element of this embodiment is configured so that light to be detected passes through the second electrode 30 and enters the photoelectric conversion film 20. The photoelectric conversion film 20 is made of a photoelectric conversion material and generates charges according to the amount of incident light. By applying a predetermined bias voltage between the first electrode 10 and the second electrode 30 and collecting the charges generated in the photoelectric conversion film 20 via the first electrode 10 and the second electrode 30, a signal according to the amount of charges generated in the photoelectric conversion film 20 can be output to the outside.

[0014] The first electrode 10 is an electrode for collecting charges (electrons) generated in the photoelectric conversion film 20 and is conductive. In this embodiment, the first electrode 10 is an anode, and the metal material constituting the first metal layer 12 and the second metal layer 14 is preferably a material suitable for collecting electrons, i.e., a metal material with a small work function, for example, a work function of 4.5 eV or less. The first electrode 10 also functions as a reflective film for reflecting light that has reached the first electrode 10 without being absorbed by the photoelectric conversion film 20, allowing it to enter the photoelectric conversion film 20 again. This configuration can improve the utilization efficiency of incident light.

[0015] Of the first metal layer 12 and the second metal layer 14 that constitute the first electrode 10, the first metal layer 12 may mainly function as a reflective film. From this perspective, the first metal layer 12 may be selected from metals or alloys that have a high reflectivity for light corresponding to the absorption wavelength band of the photoelectric conversion film 20. For example, when visible light is detected by a photodetector, the main material of the first metal layer 12 may be: aluminum Metals such as aluminum (Al) and silver (Ag) and alloys thereof can be used. The thickness of the first metal layer 12 is not particularly limited and can be determined appropriately taking into consideration the constituent materials, required conductivity, etc., but is generally about 10 nm to 10 μm.

[0016] The second metal layer 14 is thinner than the first metal layer 12 and can protect the first metal layer 12, for example, by acting as an anti-oxidation layer to prevent oxidation of the first metal layer 12 during the manufacturing process of the photodetector element. The provision of the second metal layer 14 can suppress an increase in contact resistance between the photoelectric conversion film 20 and the first electrode 10 due to oxidation of the first metal layer 12, thereby improving the efficiency of collecting charges generated in the photoelectric conversion film 20. Examples of the main material of the second metal layer 14 include metals such as titanium (Ti), zinc (Zn), zirconium (Zr), and tantalum (Ta), as well as alloys thereof. Oxides of these metal materials constituting the second metal layer 14 can have n-type semiconductor properties and function as a layer that blocks holes and conducts only electrons (hole blocking layer). Therefore, even if the second metal layer 14 is oxidized during the manufacturing process of the photodetector element, the resulting metal oxide layer does not impede electron collection.

[0017] The second metal layer 14 is preferably made of a metal material to reduce the contact resistance between the first electrode 10 and the photoelectric conversion film 20. However, if the second metal layer 14 is too thick, the light absorption rate increases, preventing the first metal layer 12 from achieving a sufficient reflective effect. From this perspective, the thickness of the second metal layer 14 is preferably set to 50 nm or less. Furthermore, when forming a metal thin film by vapor phase epitaxy, the initial growth transitions from nucleation to film formation. A thickness of less than approximately 5 nm is still in the nucleation stage and is insufficient as a protective layer. Therefore, the thickness of the second metal layer 14 is preferably at least 5 nm or more. When the second metal layer 14 is formed by a deposition method with high film quality controllability, such as atomic layer deposition (ALD), the thickness of the second metal layer 14 may be less than 5 nm. However, to realize the practical function of the second metal layer 14 itself, the thickness of the second metal layer 14 is preferably at least 1 nm or more.

[0018] By setting the film thickness of the second metal layer 14 to 50 nm or less, the reflectance of the photoelectric conversion film 20 side of the first electrode 10 in the absorption wavelength band of the photoelectric conversion film 20 can be made higher than the reflectance of the material constituting the second metal layer 14. Alternatively, the reflectance of the first electrode 10 for light of a certain wavelength (e.g., 940 nm) transmitted through the photoelectric conversion film 20 can be made higher than the reflectance inherent to the material constituting the second metal layer 14 for light of the certain wavelength. Note that the reflectance of the photoelectric conversion film 20 side of the first electrode 10 refers to the reflectance when light is incident from the photoelectric conversion film 20 side relative to the stacked structure of the first metal layer 12 and the second metal layer 14. Furthermore, the reflectance inherent to the material constituting the second metal layer 14 refers to the reflectance (reflectance of the bulk material) when the material constituting the second metal layer 14 has a thickness sufficient to block incident light.

[0019] As described above, the photoelectric conversion film 20 is made of a photoelectric conversion material. The photoelectric conversion material that makes up the photoelectric conversion film 20 is not particularly limited, and for example, amorphous silicon, organic semiconductors, quantum dots that are aggregates of nanoparticles such as compound semiconductors, etc. can be applied. As the organic semiconductor, for example, fullerene (C 60 ), coumarin 6 (C6), rhodamine 6G (R6G), quinacridone, phthalocyanine-based, naphthalocyanine-based, etc. In this embodiment, an example is shown in which the photoelectric conversion film 20 is formed using colloidal quantum dots, which are nanoparticles of a compound semiconductor material.

[0020] Colloidal quantum dots are composed of nanoparticles (typically with an average particle diameter of 0.5 nm or more and less than 100 nm). Nanoparticles can be made from common semiconductor materials, such as group IV semiconductors, group III-V compound semiconductors, group II-VI compound semiconductors, and compound semiconductors consisting of a combination of three or more of group II, group III, group IV, group V, and group VI elements. Specific examples of such semiconductor materials include PbS, PbSe, PbTe, InN, InAs, InP, InSb, InGaAs, CdS, CdSe, CdTe, Ge, CuInS, CuInSe, CuInGaSe, and Si. Quantum dots made from these semiconductor materials are also called semiconductor quantum dots.

[0021] The photoelectric conversion film 20 may contain at least one type of semiconductor quantum dot, or may contain two or more types of semiconductor quantum dots. The nanoparticles may have a core-shell structure including a semiconductor quantum dot core and a coating material that covers the core. Semiconductor quantum dots with a size equal to or smaller than the exciton Bohr radius specific to each semiconductor material exhibit a quantum size effect and have an energy band gap corresponding to their size. Therefore, by appropriately selecting the size of the semiconductor quantum dots, it is possible to control the energy band gap, i.e., the light absorption wavelength.

[0022] Among these semiconductor quantum dot materials, PbS and PbSe are particularly preferred from the viewpoint of ease of synthesis. Since the exciton Bohr radius of PbS is approximately 18 nm, the average particle size of the nanoparticles is preferably in the range of 2 nm to 15 nm from the viewpoint of controlling crystal growth and realizing the quantum size effect. By setting the average particle size of the nanoparticles to 2 nm or more, it becomes easier to control crystal growth during nanoparticle synthesis. A transmission electron microscope can be used to measure the particle size of the nanoparticles.

[0023] The method for manufacturing the photoelectric conversion film 20 containing an aggregate of nanoparticles is not particularly limited. The film thickness of the photoelectric conversion film 20 is not particularly limited, but from the viewpoint of obtaining high light absorption characteristics, it is preferably 10 nm or more, and more preferably 50 nm or more. Furthermore, from the viewpoint of ease of manufacturing, the film thickness of the photoelectric conversion film 20 is preferably 800 nm or less.

[0024] The second electrode 30 is preferably transparent in the absorption wavelength band of the photoelectric conversion film 20 so that at least a portion of the light to be detected can be transmitted and incident on the photoelectric conversion film 20. The material of the second electrode 30 is not particularly limited, but examples include transparent electrode materials such as a metal oxide layer containing indium oxide, tin oxide, or the like, or a metal oxide layer containing a composite oxide of these (e.g., ITO or IZO). Alternatively, the second electrode 30 may be formed from a metal material such as platinum, gold, silver, aluminum, chromium, nickel, copper, titanium, or magnesium thinned to a thin film that is translucent. Alternatively, the second electrode 30 may be formed using a conductive composite material in which a conductive material such as carbon black, fullerene, carbon nanotubes, or graphene is dispersed in a matrix material such as a polymer binder. The material of the second electrode 30 may be one of the materials listed above, or two or more of the materials may be combined and combined in a predetermined ratio.

[0025] Between the first electrode 10 and the photoelectric conversion film 20, or between the photoelectric conversion film 20 and the second electrode 30, one or more layers having other functions may be further provided.

[0026] For example, a metal compound layer 16, an intermediate layer 18, and the like may be further provided between the first electrode 10 and the photoelectric conversion film 20, as shown in FIG.

[0027] The metal compound layer 16 may be a carrier injection blocking layer that restricts the movement of one of the holes and electrons (ensuring electrical insulation) and allows the movement of the other (ensuring conductivity) between the first electrode 10 and the photoelectric conversion film 20. When the first electrode 10 is an electrode (anode) that collects electrons as in this embodiment, the metal compound layer 16 disposed between the first electrode 10 and the photoelectric conversion film 20 may be a layer that blocks holes and conducts electrons (hole blocking layer). Note that one of the holes and electrons may be a carrier of a first conductivity type, and the other may be a carrier of a second conductivity type different from the first conductivity type.

[0028] The function required of the hole blocking layer is to block the holes and transport the electrons to the first electrode 10 out of the electrons and holes generated in the photoelectric conversion film 20. Therefore, a material that can efficiently transport the electrons generated in the photoelectric conversion film 20 to the first electrode 10 is preferred as the constituent material of the hole blocking layer. That is, the constituent material of the hole blocking layer preferably has electrical properties such as high electron mobility, high electrical conductivity, a small electron injection barrier between the hole blocking layer and the first electrode 10, and a small electron injection barrier from the photoelectric conversion film 20 to the hole blocking layer. Furthermore, from the viewpoint of effectively utilizing light that passes through the photoelectric conversion film 20 and enters the first electrode 10, it is desirable for the hole blocking layer to have high transmittance for the light to be detected.

[0029] From this viewpoint, the main material of the hole blocking layer is wide band gap oxides such as titanium oxide, zinc oxide, zirconium oxynitride, and tantalum oxide, nitrides, and oxynitrides, as well as fullerene C 60 N-type semiconductor materials such as these are preferred. Among these, oxide-based materials are particularly preferred because their electrical conductivity can be easily changed by controlling the film formation conditions and the degree of oxidation through post-film formation processes. At least a portion of the hole-blocking layer may be a metal oxide layer formed by oxidizing the second metal layer 14.

[0030] The intermediate layer 18 is an adhesion layer for suppressing peeling of the photoelectric conversion film 20, which occurs due to poor wettability between the first electrode 10 or the metal compound layer 16 and the photoelectric conversion film 20. The intermediate layer 18 is formed between the first electrode 10 or the metal compound layer 16 and the photoelectric conversion film 20, with a film thickness of approximately 1 nm to 100 nm. Because the intermediate layer 18 is provided between the first electrode 10 and the photoelectric conversion film 20, it is preferable to select a material that has little effect on the contact resistance between the first electrode 10 and the photoelectric conversion film 20. In one example, the intermediate layer 18 and the metal compound layer 16 can be made of the same material. Instead of the metal compound layer 16 and the intermediate layer 18, a layer having the functions of both the metal compound layer 16 and the intermediate layer 18 may be provided between the first electrode 10 and the photoelectric conversion film 20.

[0031] Furthermore, a metal compound layer 32 can be further provided between the photoelectric conversion film 20 and the second electrode 30, as shown in FIG.

[0032] The metal compound layer 32 may be a carrier injection blocking layer that restricts the movement of one of the carriers, holes and electrons, between the photoelectric conversion film 20 and the second electrode 30 (ensuring electrical insulation) and allows the movement of the other carrier (ensuring conductivity). When the second electrode 30 is an electrode (cathode) that collects holes as in this embodiment, the metal compound layer 32 disposed between the photoelectric conversion film 20 and the second electrode 30 may be a layer that blocks electrons and conducts holes (electron blocking layer). As the carrier injection blocking layer, an organic material layer may be used instead of an inorganic material layer such as the metal compound layer 32.

[0033] The function required of the electron blocking layer is to block the electrons and holes generated in the photoelectric conversion film 20 and transport the holes to the second electrode 30. Therefore, a material that can efficiently transport the holes generated in the photoelectric conversion film 20 to the second electrode 30 is preferred for the electron blocking layer. That is, the material that forms the electron blocking layer preferably has electrical properties such as high hole mobility, high electrical conductivity, a small hole injection barrier between the electron blocking layer and the second electrode 30, and a small hole injection barrier from the photoelectric conversion film 20 to the electron blocking layer. Furthermore, the electron blocking layer preferably has high transmittance to the light to be detected so as not to inhibit light incidence on the photoelectric conversion film 20.

[0034] From this perspective, the main material of the electron blocking layer is preferably a P-type semiconductor material, such as inorganic materials like molybdenum oxide (MoO3) or nickel oxide (NiO), or organic materials like PEDOT:PSS, which is a composite of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrene sulfonate (PSS).

[0035] 2 shows an example in which the metal compound layers 16, 32 and the intermediate layer 18 are provided, it is also possible to provide only some of these layers. Also, it is also possible to provide a layer having a function different from that of the metal compound layers 16, 32 and the intermediate layer 18.

[0036] Next, optical properties suitable for the first metal layer 12 and second metal layer 14 constituting the first electrode 10 will be described in more detail with reference to FIGS. 3 to 5. FIG. 3 is a graph showing the dependency of reflectance on titanium film thickness in a titanium / aluminum laminate structure. FIG. 4 is a graph showing the current-voltage characteristics of a photodetector. FIG. 5 is a graph showing the results of measuring the external quantum efficiency of the photodetector.

[0037] In general, when light L is incident perpendicularly on the surface of an object O made of material M and is reflected at the surface of the object O, the light reflectance R specific to material M at the surface of the object O is expressed as shown in equation (1), where n is the refractive index of material M and k is the extinction coefficient of the object O. R={(n-1) 2 +k 2} / {(n+1) 2 +k 2} …(1)

[0038] If light L is incident perpendicularly to the surface of the second metal layer 14 from the photoelectric conversion film 20 side, the light reflectance Ra at the surface of the first metal layer 12 and the light reflectance Rb at the surface of the second metal layer 14 are expressed by equations (2) and (3), respectively. Here, Na is the refractive index of the first metal layer 12, Ka is the extinction coefficient of the first metal layer 12, Nb is the refractive index of the second metal layer 14, and Kb is the extinction coefficient of the second metal layer 14. Ra = {(Na-1) 2 +Ka 2} / {(Na+1) 2 +Ka 2} …(2) Rb={(Nb-1) 2 +Kb 2} / {(Nb+1) 2 +Kb 2} …(3)

[0039] The amount of light L reflected by the first electrode 10 can be increased by increasing the light reflectance Ra of the first metal layer 12. In this case, the light reflectance Rb of the second metal layer 14 may be lower than the light reflectance Ra of the first metal layer 12. In other words, it is sufficient that the relationship Ra>Rb is satisfied. Satisfying the relationship Ra>Rb means satisfying the relationship of formula (4). {(Na-1) 2 +Ka 2} / {(Na+1) 2 +Ka 2} >{(Nb-1) 2 +Kb 2} / {(Nb+1) 2 +Kb 2} …(4)

[0040] Although equation (1) is a relational expression when light L is perpendicularly incident, the incidence angle dependency of the reflectance of the metal layer can be ignored. This is because the incidence angle dependency of the reflectance of light incident on a metal layer is smaller than that of light incident on an insulator (dielectric).

[0041] Here, the intensity of light L incident on object O is Is, the intensity of light reflected by the surface of object O is Ir, and the intensity of light L that enters object O is Ie. Of the light that enters object O, the intensity of light absorbed by object O is Ia, and the intensity of light that transmits through object O is It. Also, the light reflectance at the surface of object O is R, the light transmittance of object O is τ, and the light absorptance of object O is A. In this case, intensities Is, Ir, Ie, Ia, It, light reflectance R, light transmittance τ, and light absorptance A are expressed as in equations (5) to (11). Is = Ir + Ie …(5) Ie = Ia + It …(6) Ir = Is × R …(7) Ie = Is × (1-R) ​​… (8) Ia = Ie × A …(9) It = Ie × (1-A) … (10) It = Is × τ …(11)

[0042] From equations (5) to (11), the light transmittance τ of the object O is expressed as in equation (12). τ = It / Is = (1-R) ​​× (1-A) … (12)

[0043] The intensity It of transmitted light and the light absorptance A can be expressed as equations (13) and (14) using the distance d from the light incident point to the light exit point in the object O and the light absorption coefficient α of the material M that makes up the object O. It = Ie × exp[-α × d] …(13) A=(Ie-It) / Ie=1-exp[-α×d] …(14)

[0044] Here, the relationship between the light absorption coefficient α and the extinction coefficient k is expressed as in equation (15), and equation (14) can be transformed into equation (16). α=4π×k / λ …(15) A=1-exp[-4π×k×d / λ] …(16)

[0045] When material M is uniform, the light absorption rate A depends on the distance d. When the front and back surfaces of object O are parallel and light L is incident perpendicularly to the surface of object O, the distance d corresponds to the distance between the front and back surfaces, i.e., the thickness T of object O.

[0046] Here, if the thickness of the second metal layer 14 is Tb, the extinction coefficient of the second metal layer 14 is Kb, and the wavelength of light L in the second metal layer 14 is λb, the light absorptance Ab of the second metal layer 14 can be expressed as in equation (17). Ab=1-exp[-4π×Kb×Tb / λb] …(17)

[0047] It is effective to reduce the light absorptance Ab of the second metal layer 14. Specifically, it is desirable to set the light absorptance Ab of the second metal layer 14 to 90% or less (Ab≦0.9).

[0048] When light enters the photoelectric conversion element through the blue filter CFB, the light that enters the second metal layer 14 is mainly blue light. Therefore, the wavelength λa for evaluating the refractive index Na and extinction coefficient Ka of the first metal layer 12 is preferably blue light (for example, a wavelength of 450±10 nm). The light that enters the second metal layer 14 may include light that has passed through the photoelectric conversion film 20, and is therefore light that is not easily absorbed by the photoelectric conversion film 20. For example, if the photoelectric conversion film 20 is a silicon layer, the light that enters the first metal layer 12 is mainly red light. Therefore, the wavelength λb for evaluating the refractive index Nb and extinction coefficient Kb of the second metal layer 14 is preferably red light (for example, a wavelength of 630±10 nm).

[0049] However, it is not necessarily the case that only blue light is incident on the first metal layer 12, and it is not necessarily the case that only red light is incident on the second metal layer 14. Therefore, the refractive index Na and extinction coefficient Ka of the first metal layer 12 and the refractive index Nb and extinction coefficient Kb of the second metal layer 14 may be evaluated using the wavelength λc of green light (for example, a wavelength of 550±10 nm), which is a wavelength between blue light and red light.

[0050] In order to make the optical absorptance Ab of the second metal layer 14 0.9 or less, it is necessary to satisfy the following formula (18). By modifying this formula (18), formula (18') is obtained. Furthermore, by substituting specific values ​​of Napier's constant e and the circular constant π into formula (18'), formula (18") is obtained. Ab=1-exp[-4π×Kb×Tb / λb]≦0.9 …(18) exp[4π×Kb×Tb / λb]≦10 …(18') Kb×Tb≦0.183×λb …(18”)

[0051] Table 1 summarizes the refractive index n, extinction coefficient k, optical reflectance R, and distance d (d≦0.183×λ / k) that satisfies equation (18") for blue light, green light, and red light for aluminum (Al), silver (Ag), titanium (Ti), and tantalum (Ta). If the thickness Tb of second metal layer 14 is within the range of distance d shown in Table 1, the optical absorptance Ab of second metal layer 14 will be 0.9 or less.

[0052] [Table 1] As shown in Table 1, aluminum and silver have a higher optical reflectance R than other materials, making them suitable materials for the first metal layer 12. Although not shown in Table 1, the extinction coefficient k of titanium for infrared light with a wavelength of 940 nm is 3.3. When the second metal layer 14 is made of titanium, the optical absorptance Ab of the second metal layer 14 will be 0.9 or less if the distance d is 52 nm or less.

[0053] Figure 3 shows aluminum1 is a graph showing the dependence of reflectance on titanium film thickness when infrared light with a wavelength of 940 nm is incident on a titanium / aluminum stacked structure having a titanium film formed on a titanium film. The aluminum film is assumed to be the first metal layer 12, and the titanium film is assumed to be the second metal layer 14.

[0054] As shown in Figure 3, the reflectance of the titanium / aluminum laminated structure is almost constant when the titanium film thickness is 100 nm or more. When the titanium film thickness is 100 nm or more, the reflectance is slightly lower than 0.55 (shown by the dashed line in Figure 3). This value is the reflectance inherent to titanium.

[0055] When the thickness of the titanium film is thinner than 100 nm, the reflectance of the titanium / aluminum laminated structure begins to change. This is because some light passes through the titanium film. If the titanium film is underlain by a low-reflection film, the reflectance will be lower than that shown in Figure 3. Therefore, when forming a titanium film with a thickness of less than 100 nm, it is preferable to form the titanium film underlain by a highly reflective film such as aluminum. The reason why the reflectance is less than 0.55 when the titanium film is between 100 nm and 40 nm thick is due to interference.

[0056] The reflectance of a titanium / aluminum laminate structure reaches its lowest value when the titanium film thickness is 55 nm. When the titanium film thickness is 50 nm or less, the reflectance of the titanium / aluminum laminate structure becomes higher than the reflectance when the titanium film thickness is 55 nm. Therefore, it is preferable to set the titanium film thickness to 50 nm or less. Setting the titanium film thickness to 40 nm or less is more preferable, as the reflectance becomes 0.55 or higher, which is higher than the inherent reflectance of titanium. Furthermore, setting the titanium film thickness to 30 nm or less is even more preferable, as the reflectance becomes 0.6 or higher. Setting the titanium film thickness to 5 nm to 20 nm can further increase the reflectance.

[0057] In this way, aluminumIn order to utilize the high reflectance of titanium and increase the light absorption efficiency of the photoelectric conversion film 20, it is desirable to set the thickness of the titanium film (second metal layer 14) to 50 nm or less. Furthermore, when forming a metal thin film by vapor phase growth, there is a transition from nucleation in the early stages of growth to film formation, and a thickness of less than about 5 nm is still in the nucleation stage and is insufficient as a protective layer. Therefore, it is desirable that the thickness of the second metal layer 14 be at least 5 nm or more. Note that, although the example here shows the case where a titanium film is used as the second metal layer 14, similar thickness dependence was also obtained when a zinc film or a zirconium film was used as the second metal layer 14.

[0058] Furthermore, when a metal compound layer 16, an intermediate layer 18, or the like is formed on the first electrode 10, as in the modified example of this embodiment shown in FIG. 2, the first electrode 10 (second metal layer 14) may be oxidized during the formation of these layers. The thickness of the oxide film thus formed varies depending on the conditions for forming the metal compound layer 16 or the intermediate layer 18, but is generally on the order of several nanometers to several tens of nanometers. Therefore, particularly when the metal compound layer 16 or the intermediate layer 18 is provided, it is preferable to set the film thickness of the second metal layer 14 to about 10 nm to 20 nm so that the entire second metal layer 14 is not replaced with a metal oxide layer.

[0059] In summary, the film thickness of the second metal layer 14 is preferably set in the range of 5 nm to 50 nm, and more preferably in the range of 10 nm to 20 nm.

[0060] By configuring the second metal layer 14 in this manner, it is possible to effectively utilize the reflected light from the first metal layer 12, while suppressing an increase in contact resistance between the first electrode 10 and the photoelectric conversion film 20.

[0061] 4 is a graph showing the results of measuring the current-voltage characteristics of a photodetector element when the second metal layer 14 is provided and when it is not provided. The horizontal axis represents the voltage between the first electrode 10 and the second electrode 30 (first electrode voltage - second electrode voltage), and the vertical axis represents the value of the current flowing between the first electrode 10 and the second electrode 30 on a logarithmic scale (log|I|). In FIG. 4, the solid line represents the measurement results for the structure of this embodiment in which the second metal layer 14 is provided, and the dashed line represents the measurement results for the structure of the comparative example in which the second metal layer 14 is not provided.

[0062] 4, in the structure (dashed line) without the second metal layer 14, almost no current flows in the voltage range shown. This is thought to be because the movement of carriers is inhibited by oxidation of the first metal layer 12. In contrast, in the structure of this embodiment in which the second metal layer 14 is provided (solid line), ideal Schottky barrier diode characteristics can be obtained.

[0063] 5 is a graph showing the results of measuring the external quantum efficiency when the first electrode 10 is formed of a laminated film of a first metal layer 12 made of aluminum and a second metal layer 14 made of titanium, and when the first electrode 10 is formed of only the first metal layer 12 made of titanium. The horizontal axis represents the wavelength of incident light, and the vertical axis represents the external quantum efficiency. In FIG. 4, the solid line represents the measurement result for the structure of this embodiment in which the first electrode 10 is formed of a laminated film of aluminum and titanium, and the dashed line represents the measurement result for the structure of the comparative example in which the first electrode 10 is formed only of titanium.

[0064] As shown in FIG. 5, by applying the electrode structure of this embodiment (solid line), the external quantum efficiency could be improved by approximately 30% compared to the electrode structure of the comparative example (dashed line).

[0065] Thus, according to this embodiment, it is possible to effectively utilize the reflected light from the first metal layer 12 while suppressing an increase in contact resistance between the first electrode 10 and the photoelectric conversion film 20, thereby realizing a photodetector element with high light utilization efficiency.

[0066] [Second embodiment] A photoelectric conversion device and a method for manufacturing the same according to a second embodiment of the present invention will be described with reference to FIGS.

[0067] In this embodiment, a photoelectric conversion device will be described as an example of a semiconductor device to which the photodetector element according to Embodiment 1 is applied. Photoelectric conversion devices may include devices intended to acquire images, such as imaging devices, as well as devices intended for focus detection and other purposes that do not primarily aim to acquire images.

[0068] First, the structure of the photoelectric conversion device according to this embodiment will be described with reference to Fig. 6 and Fig. 7. Fig. 6 is a schematic cross-sectional view showing an example of the configuration of the photoelectric conversion device according to this embodiment. Fig. 7 is a schematic cross-sectional view showing a specific structure of a photodetector in the photoelectric conversion device according to this embodiment.

[0069] The photoelectric conversion device according to this embodiment has a substrate 100. The substrate 100 has a main surface P1. In this embodiment, the substrate 100 is assumed to be a semiconductor substrate such as a silicon single crystal substrate. However, the substrate 100 does not necessarily have to be a semiconductor substrate, and may be an insulating substrate such as glass or ceramic having a semiconductor layer provided on its surface portion. The substrate 100 may also function as a support substrate for supporting a photodetector element or the like.

[0070] A transistor 101 and an element isolation portion 113 are provided near a main surface P1 of the substrate 100. The transistor 101 is, for example, an N-type MOS transistor, and includes N-type semiconductor regions 102 and 105 that form source / drain regions, a gate insulating film 103, and a gate electrode 104. The N-type semiconductor regions 102 and 105 are provided in the substrate 100. The gate electrode 104 is provided on the main surface P1 between the N-type semiconductor region 102 and the N-type semiconductor region 105, with the gate insulating film 103 interposed therebetween. The element isolation portion 113 is an insulating structure provided inside the substrate 100, and may be formed, for example, by an STI (Shallow Trench Isolation) structure.

[0071] A wiring structure 106 is provided on a main surface P1 of the substrate 100. The wiring structure 106 has multiple wiring layers disposed in an insulating layer 112. FIG. 6 shows a two-layer multilayer wiring structure including a first wiring layer including wiring 108 and a second wiring layer including wiring 110. However, the multilayer wiring structure constituting the wiring structure 106 does not necessarily have to be two-layered, and may be one-layered or three or more layers. The wiring structure 106 also includes a contact plug 107 connecting the transistor 101 and the wiring 108, a via plug 109 connecting the wiring 108 and the wiring 110, and a via plug 111 connected to the wiring 110. Note that in this specification, the substrate 100 and the wiring structure 106 may be collectively referred to as the "substrate."

[0072] These components constituting the wiring structure 106 can be formed using materials and manufacturing processes commonly used in semiconductor devices. For example, the contact plug 107 and the via plugs 109, 111 can be made of one or more conductive materials selected from aluminum, copper, tungsten, titanium, and titanium nitride. Typically, the contact plug 107 and the via plugs 109, 111 can have a layered structure of titanium, titanium nitride, and tungsten. The wirings 108, 110 can be made of one or more conductive materials selected from aluminum, copper, tungsten, titanium, titanium nitride, tantalum, etc. Typically, the wirings 108, 110 can have a layered structure of tantalum and copper. The insulating layer 112 can be made of an insulating material selected from silicon oxide, silicon nitride, aluminum oxide, etc. Although not shown in detail in FIGS. 2 and 3, the insulating layer 112 is generally made of a multilayer film composed of multiple types of insulating materials.

[0073] A plurality of lower electrode structures 121 are provided on the wiring structure 106. Each of the lower electrode structures 121 includes a lower electrode 122 and a metal compound layer 125 provided on the lower electrode 122. Each of the lower electrodes 122 is connected to a via plug 111. An intermediate layer 128 is provided on the wiring structure 106, including the upper and side surfaces of the lower electrode structures 121. A photoelectric conversion film 130 is provided on the intermediate layer 128. An upper electrode 132 is provided on the photoelectric conversion film 130.

[0074] An insulating layer 134 is provided on the upper electrode 132. The insulating layer 134 can function as a protective layer or a sealing layer. A color filter layer 136 is provided on the insulating layer 134. The color filter layer 136 has color filters of multiple colors. A planarization layer 138 having a flat upper surface is provided on the color filter layer 136. A microlens layer 140 including a plurality of microlenses 142 is provided on the planarization layer 138.

[0075] Each unit cell 120 may include one microlens 142, one color filter, at least one photodetector element, and a readout circuit provided on the substrate 100 and the wiring structure 106. Each photodetector element includes a lower electrode 122, a photoelectric conversion film 130, and an upper electrode 132. The lower electrode 122 is an individual electrode provided for each photodetector element and corresponds to the first electrode 10 in the photodetector element according to the first embodiment. The upper electrode 132 is a common electrode shared by multiple photodetectors and corresponds to the second electrode 30 in the photodetector element according to the first embodiment. The transistor 101 disposed on the substrate 100, together with the wiring structure 106, constitutes a readout circuit for reading out signals output from the photodetector element. While FIG. 6 shows an example of a configuration in which one unit cell 120 includes one photodetector element, the number of photodetectors included in one unit cell 120 is not particularly limited. The unit cell 120 is sometimes called a pixel or a subpixel.

[0076] Next, the photodetector element in the photoelectric conversion device according to this embodiment will be described in more detail with reference to FIG.

[0077] 7, the photodetector element of the photoelectric conversion device according to this embodiment includes a lower electrode 122, a metal compound layer 125, an intermediate layer 128, a photoelectric conversion film 130, a metal compound layer 131, and an upper electrode 132. The lower electrode 122 and the metal compound layer 125 form an independent lower electrode structure 121 for each photodetector element. The intermediate layer 128 is provided on the insulating layer 112 (wiring structure 106) including the upper and side surfaces of the lower electrode structure 121. The photoelectric conversion film 130 is provided on the intermediate layer 128. The metal compound layer 131 is provided on the photoelectric conversion film 130. The upper electrode 132 is provided on the metal compound layer 131.

[0078] The lower electrode 122 corresponds to the first electrode 10 in the photodetector according to the first embodiment and includes a first metal layer 123 and a second metal layer 124 disposed on the first metal layer 123. The first metal layer 123 corresponds to the first metal layer 12 in the photodetector according to the first embodiment and has the functions of reflecting light incident from above the upper electrode 132 and collecting electrons generated in the photoelectric conversion film 130. The first metal layer 123 preferably has a structure that does not diffuse light so that reflected light does not affect adjacent photodetector elements. For example, the first metal layer 123 preferably has a flat or concave surface. The second metal layer 124 corresponds to the second metal layer 14 in the photodetector according to the first embodiment and may have the function of protecting the first metal layer 123. The metal materials constituting the first metal layer 123 and the second metal layer 124 are also similar to those of the first metal layer 12 and the second metal layer 14 in the light-detecting element according to the first embodiment.

[0079] The metal compound layer 125 corresponds to the metal compound layer 16 in the photodetector element according to the first embodiment. The metal compound layer 125 can be composed of a metal oxide layer 126 and a carrier injection blocking layer 127 provided on the metal oxide layer 126. The metal oxide layer 126 is composed of an oxide of the metal material that constitutes the second metal layer 124. The metal oxide layer 126 and the carrier injection blocking layer 127 can function as layers that block holes and conduct electrons (hole blocking layers). The materials that constitute the metal oxide layer 126 and the carrier injection blocking layer 127 are the same as those of the metal compound layer 16 in the photodetector element according to the first embodiment.

[0080] The intermediate layer 128 corresponds to the intermediate layer 18 in the photodetector element according to the first embodiment and serves to suppress peeling of the photoelectric conversion film 130, which occurs due to poor wettability between the metal compound layer 125 and the photoelectric conversion film 130 and between the insulating layer 112 and the photoelectric conversion film 130. For this purpose, the intermediate layer 128 is preferably provided over the entire surface to increase the contact area with the photoelectric conversion film 130. The material constituting the intermediate layer 128 is the same as that of the intermediate layer 18 in the photodetector element according to the first embodiment. Because the intermediate layer 128 is inserted between the metal compound layer 125 and the photoelectric conversion film 130, it is preferably made of a material that has little effect on the contact resistance between the metal compound layer 125 and the photoelectric conversion film 130. From this perspective, it is preferable that the intermediate layer 128 be made of the same material as that of the metal compound layer 125, so that it reduces contact resistance with the metal compound layer 125 and also serves as a hole-blocking layer.

[0081] The intermediate layer 128 can control the movement of charges in the direction in which the electric field is applied (thickness direction of the intermediate layer 128), but cannot control the movement of charges in the direction intersecting the direction in which the electric field is applied (plane direction of the intermediate layer 128). Therefore, if the conductivity of the material constituting the intermediate layer 128 is high, leakage current or crosstalk may occur between the unit cells 120 via the intermediate layer 128. In such a case, the intermediate layer 128 is not a film, but a thin film of, for example, several nm thick. 2 It may be composed of an aggregate of island structures of about the same size.

[0082] The photoelectric conversion film 130 corresponds to the photoelectric conversion film 20 in the photodetector according to the first embodiment. The photoelectric conversion film 130 is made of a photoelectric conversion material, and generates charges according to the amount of light incident through the microlens 142, color filter, and upper electrode 132, and light that passes through the photoelectric conversion film 130, is reflected by the lower electrode 122, and then re-incident. The material constituting the photoelectric conversion film 130 is the same as that of the photoelectric conversion film 20 in the photodetector according to the first embodiment.

[0083] The metal compound layer 131 corresponds to the metal compound layer 32 in the photodetector element according to the first embodiment. The metal compound layer 131 can function as a layer that blocks electrons and conducts holes (electron blocking layer). The material that constitutes the metal compound layer 131 is the same as that of the metal compound layer 32 in the photodetector element according to the first embodiment.

[0084] The upper electrode 132 corresponds to the second electrode 30 in the light-detecting element according to the first embodiment. The material forming the upper electrode 132 is the same as that of the second electrode 30 in the light-detecting element according to the first embodiment.

[0085] In order to effectively utilize incident light in the photodetector element, the first metal layer 123 of the lower electrode 122 needs to have high reflectivity in the wavelength band of light to which the photoelectric conversion film 130 is photosensitive. Examples of materials with high reflectivity for visible light include aluminum and silver. However, aluminum Materials with high reflectivity, such as SiO2, are easily oxidized during the manufacturing process, forming an oxide layer with high electrical resistivity on the surface. For example, in this embodiment, the carrier injection blocking layer 127 is disposed between the lower electrode 122 and the photoelectric conversion film 130, and the material constituting the carrier injection blocking layer 127 is typically an oxide material. Therefore, if the carrier injection blocking layer 127 is formed directly on the first metal layer 123, an oxide layer with high electrical resistivity will be formed between the lower electrode 122 and the photoelectric conversion film 130, preventing the lower electrode 122 from collecting electrons.

[0086] From this viewpoint, in this embodiment, the lower electrode 122 is composed of a first metal layer 123 and a second metal layer 124. Of the first metal layer 123 and the second metal layer 124 that compose the lower electrode 122, the first metal layer 123 mainly functions as a reflective film. Therefore, the first metal layer 123 can be selected from among metal materials that have a high reflectivity for light corresponding to the absorption wavelength band of the photoelectric conversion film 130. For example, when visible light is detected by a photodetector, the first metal layer 123 can be made of a material such as aluminum (Al), silver (Ag), and alloys thereof can be used.

[0087] The second metal layer 124 has a function of protecting the first metal layer 123, specifically, serves as an anti-oxidation layer for preventing the first metal layer 123 from being oxidized during the formation of the carrier injection blocking layer 127. By disposing the second metal layer 124 between the first metal layer 123 and the carrier injection blocking layer 127, it is possible to prevent the first metal layer 123 from being oxidized and a layer with high electrical resistivity from being formed between the first metal layer 123 and the carrier injection blocking layer 127.

[0088] Forming the carrier injection blocking layer 127 on the second metal layer 124 may oxidize the second metal layer 124. Therefore, the material constituting the second metal layer 124 is selected from among materials whose oxides have electrical properties equivalent to those of the carrier injection blocking layer 127, that is, metal materials whose oxides can function as a hole blocking layer that blocks holes and conducts only electrons. Examples of metal materials whose oxides can function as a hole blocking layer include titanium, tantalum, and zirconium. The metal oxide layer 126 constituting part of the metal compound layer 125 is formed by oxidizing the second metal layer 124.

[0089] The second metal layer 124 needs to have a thickness sufficient to suppress oxidation of the first metal layer 123, but if it is too thick, the amount of light that reaches the first metal layer 123 will decrease, making it impossible to effectively utilize the light reflected from the first metal layer 123. From this perspective, it is preferable to make the thickness of the second metal layer 124 as thin as possible within a range that still suppresses oxidation of the first metal layer 123. That is, as explained in the first embodiment, the thickness of the second metal layer 124 is preferably set in the range of 5 nm to 50 nm, and more preferably in the range of 10 nm to 20 nm.

[0090] By configuring the second metal layer 124 in this manner, it is possible to effectively utilize the reflected light from the first metal layer 123, while suppressing an increase in contact resistance between the lower electrode 122 and the photoelectric conversion film 130.

[0091] Next, a method for manufacturing the photoelectric conversion device according to this embodiment will be described with reference to Figures 8 to 10. Figures 8 to 10 are cross-sectional views showing the steps in the method for manufacturing the photoelectric conversion device according to this embodiment.

[0092] First, using a general semiconductor process, predetermined elements such as a transistor 101 and an element isolation portion 113 are formed on a main surface P1 of a substrate 100, which is, for example, a silicon substrate. The transistor 101 is, for example, an N-type MOS transistor, and includes N-type semiconductor regions 102 and 105, a gate insulating film 103, and a gate electrode 104. The element isolation portion 113 has, for example, an STI (Shallow Trench Isolation) structure.

[0093] Next, a wiring structure 106 having multiple wiring layers in an insulating layer 112 is formed on the main surface P1 of the substrate 100 on which the transistor 101, the element isolation portion 113, etc. are provided, using a typical semiconductor process (FIG. 8(a)). FIG. 8(a) shows the wiring structure 106 including a first wiring layer including a wiring 108 and a second wiring layer including a wiring 110. The wiring structure 106 further includes a contact plug 107 connecting the transistor 101 and the wiring 108, a via plug 109 connecting the wiring 108 and the wiring 110, and a via plug 111 connected to the wiring 110.

[0094] These components constituting the wiring structure 106 can be formed using materials and manufacturing processes commonly used in semiconductor devices. For example, the contact plug 107 and the via plugs 109, 111 can be made of one or more conductive materials selected from aluminum, copper, tungsten, titanium, and titanium nitride. Typically, the contact plug 107 and the via plugs 109, 111 can have a layered structure of titanium, titanium nitride, and tungsten. The wirings 108, 110 can be made of one or more conductive materials selected from aluminum, copper, tungsten, titanium, titanium nitride, tantalum, etc. Typically, the wirings 108, 110 can have a layered structure of tantalum and copper. The insulating layer 112 can be made of an insulating material such as silicon oxide or silicon nitride. Although not shown in detail in FIG. 8( a ), the insulating layer 112 is generally made of a multilayer film made of multiple types of insulating materials.

[0095] Next, for example, by sputtering, an aluminum film 123a having a thickness of 200 nm and a titanium film 124a having a thickness of 10 nm are sequentially deposited on the wiring structure 106. The aluminum film 123a is a film that will become the first metal layer 123 of the lower electrode 122, and the titanium film 124a is a film that will become the second metal layer 124 of the lower electrode 122.

[0096] Next, a titanium oxide film 127a having a thickness of, for example, 50 nm is deposited on the titanium film 124a by, for example, sputtering. The titanium oxide film 127a is a film that will become the carrier injection blocking layer 127. Generally, when forming a titanium oxide film by sputtering, a reactive sputtering method is used, using a TiO2 target or a Ti target as the target and argon and oxygen as the sputtering gas. For example, the film can be formed using a TiO2 target as the target and argon gas mixed with 5% oxygen as the sputtering gas under conditions of an RF power of 500 W and a chamber pressure of 0.5 Pa.

[0097] When forming a titanium oxide film, if oxygen is not mixed into the sputtering gas, the deposited titanium oxide film will have many oxygen defects and will have a low degree of oxidation. Here, when titanium oxide is expressed as TiOx, the larger the oxygen composition x, the higher the degree of oxidation of the titanium oxide. The stoichiometric composition of titanium oxide is TiO2, and titanium oxide with a low degree of oxidation will contain low-valence TiO components.

[0098] The Fermi level of titanium oxide can be controlled by the degree of oxidation. For example, when no oxygen is mixed into the sputtering gas, the Fermi level is about -4.5 eV, whereas when a sputtering gas containing 20% ​​oxygen mixed into argon is used, the Fermi level is about -4.8 eV. As the Fermi level changes, the conductivity also changes from low to high resistance. For example, when no oxygen is mixed into the sputtering gas, the resistivity is 8 x 10 2 The resistivity is about Ω-cm, whereas when a sputtering gas containing 5% oxygen in argon is used, the resistivity is 1×10 13 When a sputtering gas containing 10% oxygen in argon is used, the resistivity of titanium oxide is 3×10 13 It is about Ω-cm.

[0099] When the titanium oxide film 127a is formed on the titanium film 124a under these conditions, the surface of the titanium film 124a is oxidized to a thickness of several nanometers. The titanium oxide film 126a thus formed is the film that becomes the metal oxide layer 126 (FIG. 8(b)).

[0100] Next, the aluminum film 123a, titanium film 124a, and titanium oxide films 126a and 127a are patterned using photolithography and dry etching to form a plurality of lower electrode structures 121. Each lower electrode structure 121 has a lower electrode 122 and a metal compound layer 125 provided on the lower electrode 122. The lower electrode 122 includes a first metal layer 123 made of an aluminum film 123a and a second metal layer 124 made of a titanium film 124a. The metal compound layer 125 includes a metal oxide layer 126 made of a titanium oxide film 126a and a carrier injection blocking layer 127 made of a titanium oxide film 127a (FIG. 9(a)).

[0101] Next, titanium oxide is deposited by vapor deposition or sputtering, for example, to a thickness of about 1 nm to 100 nm over the entire surface of the wiring structure 106, including the upper and side surfaces of the lower electrode structure 121, to form an intermediate layer 128 made of titanium oxide (FIG. 9(b)). When the intermediate layer 128 is made of titanium oxide, the same film formation conditions as for the titanium oxide film 127a can be applied.

[0102] When forming the intermediate layer 128, by setting the film thickness thin (for example, about 1 nm in terms of film formation rate), it is possible to form a thin film, for example, a thin film of several nm. 2 It is also possible to form the intermediate layer 128 consisting of an aggregate of island structures each having a size of about 1 / 2. By configuring the intermediate layer 128 in this way, it is possible to suppress leakage current and crosstalk between the unit cells 120 via the intermediate layer 128.

[0103] Next, the photoelectric conversion film 130 is formed on the intermediate layer 128. The photoelectric conversion film 130 is not particularly limited, but in this example, the photoelectric conversion film 130 is formed to include quantum dots made of nanoparticles of lead sulfide (PbS), which is a compound semiconductor.

[0104] First, a quantum dot coating solution containing PbS nanoparticles is applied onto the intermediate layer 128 by spin coating. The resulting coating film is referred to as a provisional quantum dot film. The spin-coated provisional quantum dot film is an aggregate of quantum dots protected by long-molecular ligands (e.g., oleic acid), resulting in large inter-quantum dot spacing. This results in poor conductivity of photocarriers generated by light irradiation, resulting in extremely low photoelectric conversion performance. Therefore, ligand exchange is performed on the provisional quantum dot film, replacing the long-molecular ligands with short-molecular ligands (e.g., benzenedithiol or methylbenzoic acid). The ligand exchange is performed by applying a solution containing short-molecular ligands (ligand solution) onto the provisional quantum dot film. Specifically, the ligand solution is applied to the provisional quantum dot film, and the ligand exchange reaction is carried out for a predetermined time. After the predetermined reaction time has elapsed, the substrate is rotated to shake off the liquid and dried. After the ligand exchange, the film is rinsed to remove excess ligands remaining on the film and ligands that have desorbed from the provisional quantum dot film. The film thickness of the quantum dot film after the ligand exchange is 40 nm to 60 nm.

[0105] The above-described formation of the temporary quantum dot film, the ligand exchange, and the rinsing are repeated to form a quantum dot film of a desired thickness. For example, by repeating the series of processes seven times, a photoelectric conversion film 130 having a thickness of about 280 nm to 420 nm and including seven quantum dot film layers can be formed.

[0106] Next, molybdenum oxide is deposited on the photoelectric conversion film 130 by, for example, vacuum deposition to form a metal compound layer 131 made of molybdenum oxide.

[0107] Next, indium tin oxide (ITO) is deposited on the metal compound layer 131 by, for example, sputtering to form an upper electrode 132 made of ITO (FIG. 10(a)).

[0108] Next, an insulating layer 134, a color filter layer 136, a planarizing layer 138, a microlens layer 140, and the like are sequentially formed on the upper electrode 132 in the same manner as in a general semiconductor device manufacturing method (FIG. 10(b)). In this way, the photoelectric conversion device according to this embodiment is completed.

[0109] As described above, according to this embodiment, a highly sensitive photoelectric conversion device having a photodetector with high light utilization efficiency can be realized.

[0110] [Third embodiment] A photoelectric conversion device according to a third embodiment of the present invention will be described with reference to Fig. 11. Fig. 11 is a plan view and a schematic cross-sectional view showing the structure of a photodetector element of a photoelectric conversion device according to this embodiment. Components similar to those in the second embodiment are given the same reference numerals, and their description will be omitted or simplified.

[0111] The photoelectric conversion device according to this embodiment is similar to the photoelectric conversion device according to the second embodiment, except for the structure of the photodetector. That is, in the photodetector element of the photoelectric conversion device according to this embodiment, as shown in FIG. 11 , the second metal layer 124 includes a first region 150 and a second region 152 that is thicker than the first region 150. The thickness of the first region 150 is 5 nm or more and 50 nm or less, preferably 10 nm or more and 20 nm or less. The thickness of the second region 152 is thicker than 50 nm, for example, approximately 60 nm. The second region 152 is disposed around the first region 150, for example, surrounding the first region 150 in a plan view. Note that in this specification, a plan view refers to the state in which each component of the photoelectric conversion device is projected onto a plane parallel to the surface of the substrate 100, and corresponds to the planar layout diagram in FIG. 11( a).

[0112] From the viewpoint of effective use of incident light, it is preferable that the reflectivity of the lower electrode 122 is high. However, when a plurality of photodetector elements are arranged adjacent to each other as shown in FIG. 6, for example, there is a risk that light reflected by the lower electrode 122 may enter an adjacent unit cell 120. This light generates electron-hole pairs in the photoelectric conversion film 130, and if these are collected by the lower electrode 122 and the upper electrode 132 of the adjacent unit cell 120, this may cause crosstalk between the unit cells 120. In particular, light incident on the periphery of the lower electrode 122 has a large angle of incidence with respect to the lower electrode 122, increasing the possibility that light reflected by the lower electrode 122 may leak into an adjacent unit cell 120.

[0113] Therefore, in this embodiment, the second metal layer 124 is configured to include a first region 150 and a second region 152 that is thicker than the first region 150. If the thickness of the first region 150 is 10 nm and the thickness of the second region 152 is 60 nm, the reflectance in the first region 150 is approximately 80%, and the reflectance in the second region 152 is approximately 50%, as shown in FIG.

[0114] By reducing the reflectance at the periphery of the lower electrode 122 in this way, the reflectance of light that is obliquely incident on the second region 152 decreases, making it possible to reduce light leakage into adjacent unit cells 120. This makes it possible to reduce crosstalk between unit cells 120. Since light that is incident near the center of the lower electrode 122 has a small angle of incidence with respect to the lower electrode 122 and has little effect on adjacent unit cells 120, it is preferable to arrange the first region 150, which provides high reflectance, in the center of the lower electrode 122.

[0115] The second metal layer 124 of the light detecting element of this embodiment is not particularly limited, but can be formed by, for example, the following method.

[0116] The first method is to deposit a titanium film 124a with a thickness of, for example, 60 nm on an aluminum film 123a that will become the first metal layer 123, and then thin the titanium film 124a in the first region 150 to 10 nm to 20 nm using photolithography and dry etching.

[0117] The second method is to deposit the titanium film 124a in two steps. First, a titanium film with a thickness of, for example, 40 nm to 50 nm is formed on the aluminum film 123a that will become the first metal layer 123. Next, the titanium film in the second region 152 is removed using photolithography and dry etching. Next, a titanium film with a thickness of, for example, 10 nm to 20 nm is deposited on the entire surface.

[0118] Thereafter, by patterning the titanium film 124a in the step of FIG. 9(a), the second metal layer 124 can be formed, which has a first region 150 with a thickness of about 10 to 20 nm and a second region 152 with a thickness of about 60 nm.

[0119] As described above, according to this embodiment, a highly sensitive photoelectric conversion device having a photodetector element with high light utilization efficiency can be realized. Furthermore, by devising the electrode structure of the photodetector element, crosstalk between adjacent unit cells can be suppressed.

[0120] [Fourth embodiment] A photoelectric conversion device according to a fourth embodiment of the present invention will be described with reference to Fig. 12. Fig. 12 is a plan view and a schematic cross-sectional view showing the structure of a photodetector element of a photoelectric conversion device according to this embodiment. Components similar to those in the second and third embodiments are given the same reference numerals, and descriptions thereof will be omitted or simplified.

[0121] The photoelectric conversion device according to this embodiment is similar to the photoelectric conversion device according to the second embodiment, except for the structure of the photodetector. That is, the photodetector of the photoelectric conversion device according to this embodiment has a plurality of lower electrode structures 121, as shown in FIG. 12 . These plurality of lower electrode structures 121 include a lower electrode structure 121a in which the second metal layer 124 has a first film thickness, and a lower electrode structure 121b in which the second metal layer 124 has a second film thickness that is thicker than the first film thickness. The first film thickness corresponds to the film thickness of a first region 150 of the second metal layer 124 in the third embodiment. The second film thickness corresponds to the film thickness of a second region 152 of the second metal layer 124 in the third embodiment.

[0122] The lower electrode structure 121b is disposed between the lower electrode structure 121a and the adjacent unit cell 120. In the example of Fig. 12, two lower electrode structures 121b are provided to sandwich the lower electrode structure 121a, but the number of lower electrode structures 121b disposed around the lower electrode structure 121a is not particularly limited. The arrangement of the lower electrode structures 121b can be determined appropriately depending on the relationship with the adjacent unit cells 120 (for example, the arrangement interval).

[0123] Furthermore, the lower electrode structure 121a and the lower electrode structure 121b may or may not be electrically connected. The manner in which the lower electrode structure 121a and the lower electrode structure 121b are electrically connected is not particularly limited. For example, the lower electrode structure 121a and the lower electrode structure 121b may be electrically connected to each other via a via plug 111 and a wiring 110.

[0124] The method for reading out a signal from the lower electrode 122 can be selected as appropriate depending on the electrical connection state of the lower electrode structures 121a and 121b, etc. For example, signals may be read out from both the lower electrode structure 121a and the lower electrode structure 121b. Alternatively, if a signal is read out from one of the lower electrode structure 121a and the lower electrode structure 121b, it is not necessary to read out a signal from the other of the lower electrode structure 121a and the lower electrode structure 121b.

[0125] By disposing the lower electrode structure 121b between the lower electrode structure 121a and the adjacent unit cell 120, it is possible to reduce the reflectance between the lower electrode structure 121a and the adjacent unit cell 120, as in the third embodiment. This makes it possible to reduce light leakage into the adjacent unit cell 120, and to reduce crosstalk between the unit cells 120.

[0126] The photoelectric conversion device according to this embodiment can be formed using the same manufacturing method as that for the photoelectric conversion device according to the third embodiment.

[0127] As described above, according to this embodiment, a highly sensitive photoelectric conversion device having a photodetector element with high light utilization efficiency can be realized. Furthermore, by devising the electrode structure of the photodetector element, crosstalk between adjacent unit cells can be suppressed.

[0128] [Fifth embodiment] An imaging system according to a fifth embodiment of the present invention will be described with reference to Fig. 13. Fig. 13 is a block diagram showing a schematic configuration of the imaging system according to this embodiment.

[0129] The photoelectric conversion devices described in the second to fourth embodiments are applicable to various imaging systems. Photoelectric conversion device Examples of devices to which the present invention can be applied include digital still cameras, digital camcorders, surveillance cameras, copiers, fax machines, mobile phones, smartphones, in-vehicle cameras, and observation satellites. Camera modules equipped with an optical system such as a lens and an imaging device are also applicable. Photoelectric conversion device These devices may include a photoelectric conversion device and an information processing device that processes information based on a signal output from the photoelectric conversion device. Figure 13 shows a block diagram of a digital still camera as an example of such devices.

[0130] The imaging system 200 illustrated in FIG. Photoelectric conversion device 204 , the optical image of the subject Photoelectric conversion device 204a lens 202 for forming an image on the object; and an aperture for varying the amount of light passing through the lens 202. 203 , a barrier for protecting the lens 202 201 The lens 202 and the aperture 203 teeth, Photoelectric conversion device 204 It is an optical system that focuses light onto a target. Photoelectric conversion device 204 is a photoelectric conversion device described in any one of the second to fourth embodiments, and light Converts academic images into image data.

[0131] The imaging system 200 also includes: Photoelectric conversion device 204 The signal processing unit 208 processes the output signal output from the Photoelectric conversion device 204 The signal processing unit 208 performs various corrections and compressions as necessary and outputs the image data. Photoelectric conversion device 204 may include an AD conversion unit that generates a digital signal to be processed by the signal processing unit 208. Photoelectric conversion device 204 Alternatively, the photoelectric conversion portion may be formed on a semiconductor layer (semiconductor substrate) on which the photoelectric conversion portion is formed. Photoelectric conversion device 204 The signal processing unit 208 may be formed on a semiconductor substrate different from the semiconductor layer on which the photoelectric conversion unit is formed. Photoelectric conversion device 204 The semiconductor device may be formed on the same semiconductor substrate as the semiconductor device.

[0132] The imaging system 200 further includes a memory unit for temporarily storing image data. 209 , an external interface section (external I / F section) for communicating with external computers, etc. 210 The imaging system 200 further includes a recording medium 214 such as a semiconductor memory for recording or reading out imaging data, and a recording medium control interface unit (recording medium control I / F unit) for recording or reading out imaging data on the recording medium 214. 213 The recording medium 214 may be built into the imaging system 200 or may be removable.

[0133] Furthermore, the imaging system 200 includes an overall control and calculation unit that performs various calculations and controls the entire digital still camera. 212 , Photoelectric conversion device 204 and a timing generator that outputs various timing signals to the signal processor 208. 211 Here, a timing signal or the like may be input from an external source, and the imaging system 200 has at least Photoelectric conversion device 204 and, Photoelectric conversion device 204 and a signal processing unit 208 that processes the output signal output from the

[0134] Photoelectric conversion device 204 outputs the imaging signal to the signal processing unit 208. The signal processing unit 208 Photoelectric conversion device 204 The signal processing unit 208 performs predetermined signal processing on the imaging signal output from the imaging unit 204 and outputs image data. The signal processing unit 208 generates an image using the imaging signal.

[0135] As described above, according to this embodiment, it is possible to realize an imaging system to which the photoelectric conversion device according to the second to fourth embodiments is applied.

[0136] [Sixth embodiment] An imaging system and transportation equipment (moving object) according to a sixth embodiment of the present invention will be described with reference to Fig. 14. Fig. 14 is a diagram showing the configuration of the imaging system and transportation equipment according to this embodiment.

[0137] FIG. 14(a) shows an example of an imaging system related to an in-vehicle camera. The imaging system 300 includes an imaging device 310. The imaging device 310 is the photoelectric conversion device described in any one of the second to fourth embodiments. The imaging system 300 includes an image processing unit 312 that performs image processing on multiple pieces of image data acquired by the imaging device 310, and a parallax acquisition unit 314 that calculates parallax (phase difference between parallax images) from the multiple pieces of image data acquired by the imaging system 300. The imaging system 300 also includes a distance acquisition unit 316 that calculates the distance to an object based on the calculated parallax, and a collision determination unit 318 that determines whether or not there is a possibility of a collision based on the calculated distance. Here, the parallax acquisition unit 314 and the distance acquisition unit 316 are examples of distance information acquisition means that acquire information about the distance to the object. That is, the distance information is information about the parallax, the defocus amount, the distance to the object, etc. The collision determination unit 318 may determine the possibility of a collision using any of this distance information. The distance information acquisition means may be realized by dedicated hardware, a software module, a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), or a combination thereof.

[0138] The imaging system 300 is connected to a vehicle information acquisition device 320 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. The imaging system 300 is also connected to a control ECU 330, which is a control device that outputs a control signal to generate a braking force on the vehicle based on the determination result of a collision determination unit 318. The imaging system 300 is also connected to an alarm device 340 that issues an alarm to the driver based on the determination result of the collision determination unit 318. For example, if the determination result of the collision determination unit 318 indicates a high possibility of a collision, the control ECU 330 performs vehicle control to avoid the collision and mitigate damage by applying the brakes, releasing the accelerator, suppressing engine output, etc. The alarm device 340 warns the user by sounding an alarm, displaying alarm information on a screen of a car navigation system, etc., or vibrating the seat belt or steering wheel.

[0139] In this embodiment, the surroundings of the vehicle, for example, the front or rear, are imaged by the imaging system 300. Fig. 14(b) shows an imaging system for imaging the area in front of the vehicle (imaging range 350). The vehicle information acquisition device 320 sends instructions to the imaging system 300 or the imaging device 310. This configuration can further improve the accuracy of distance measurement.

[0140] While the above describes an example of control to prevent collisions with other vehicles, the present invention can also be applied to autonomous driving control to follow other vehicles and autonomous driving control to prevent vehicles from drifting out of their lanes. Furthermore, transportation equipment equipped with an imaging system is not limited to vehicles such as the vehicle itself, but can also be applied to ships and aircraft, for example. The above-described embodiments are not limited to electronic devices such as cameras and smartphones, and transportation equipment, but can also be widely applied to equipment that uses object recognition, such as industrial equipment such as industrial robots and machine vision systems, medical equipment such as endoscopes and radiological diagnostics, and office equipment such as multifunction printers. These devices may be configured to include a light source that emits light in the absorption wavelength band of the photoelectric conversion film of the photoelectric conversion device that constitutes the imaging device 310. In this case, the light in the absorption wavelength band of the photoelectric conversion film of the photoelectric conversion device may be infrared light.

[0141] [Modified embodiment] The present invention is not limited to the above-described embodiment, and various modifications are possible. For example, each of the embodiments shows one aspect of the present invention, and the present invention is not limited to numerical values, shapes, materials, components, arrangement and connection of components, etc. Furthermore, an example in which part of the configuration of one embodiment is added to another embodiment, or an example in which part of the configuration of another embodiment is substituted for another embodiment, is also an embodiment of the present invention.

[0142] In addition, although the above embodiment shows an example in which the present invention is applied to a photodetector element, the present invention can also be applied to elements other than photodetectors. The present invention is widely applicable to optical elements in which a functional layer is sandwiched between a reflective electrode and a transparent electrode, and can be applied not only to photodetectors but also to light-emitting elements.

[0143] Furthermore, the imaging systems shown in the fifth and sixth embodiments above are examples of imaging systems to which the photoelectric conversion device of the present invention can be applied, and imaging systems to which the photoelectric conversion device of the present invention can be applied are not limited to the configurations shown in Figures 13 and 14.

[0144] The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program.The present invention can also be realized by a circuit (e.g., ASIC) that realizes one or more functions.

[0145] It should be noted that the above-described embodiments are merely examples of specific embodiments for carrying out the present invention, and the technical scope of the present invention should not be construed as being limited by these embodiments. In other words, the present invention can be carried out in various forms without departing from its technical concept or main features. [Explanation of symbols]

[0146] 10...1st electrode 12...First metal layer 14…Second metal layer 16...Metal compound layer 18,32...middle class 20...Photoelectric conversion film 30…Second electrode 100...Substrate 101...Transistor 106...Wiring structure 120...unit cell 122...Lower electrode 123...first metal layer 124…Second metal layer 125...Metal compound layer 126...metal oxide layer 127, 131...Carrier injection blocking layer 128...Middle class 130...Photoelectric conversion film 132...Top electrode 150…First area 152…Second area

Claims

1. A light-detecting element having a first electrode, a second electrode, and a photoelectric conversion film disposed between the first electrode and the second electrode, the first electrode has a first metal layer and a second metal layer disposed between the first metal layer and the photoelectric conversion film; a layer of an oxide of a metal of the second metal layer is disposed between the second metal layer and the photoelectric conversion film; the second metal layer is made of a material in which an oxide of a metal or alloy constituting the second metal layer can have electrical properties that allow the movement of carriers of a first conductivity type and restrict the movement of carriers of a second conductivity type different from the first conductivity type; The reflectance of the first electrode for light of a certain wavelength that has passed through the photoelectric conversion film is higher than the reflectance inherent to a material that constitutes the second metal layer for the light of the certain wavelength. A photodetector element characterized by:

2. A light-detecting element having a first electrode, a second electrode, and a photoelectric conversion film disposed between the first electrode and the second electrode, the first electrode has a first metal layer and a second metal layer disposed between the first metal layer and the photoelectric conversion film; a layer of an oxide of a metal of the second metal layer is disposed between the second metal layer and the photoelectric conversion film; the second metal layer is made of a material in which an oxide of a metal or alloy constituting the second metal layer can have electrical properties that allow the movement of carriers of a first conductivity type and restrict the movement of carriers of a second conductivity type different from the first conductivity type; the first metal layer is made of a metal or alloy containing aluminum or silver as a main material, a main material of the second metal layer is different from a main material of the first metal layer; The thickness of the second metal layer is 5 nm or more and 50 nm or less. A photodetector element characterized by:

3. The reflectance of the first electrode with respect to light of a certain wavelength that has passed through the photoelectric conversion film is 0.6 or more.

3. The photodetector element according to claim 1 or 2.

4. The second metal layer is thinner than the first metal layer.

4. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

5. The thickness of the second metal layer is 10 nm or more and 30 nm or less.

5. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

6. The refractive index of the first metal layer is Na, the extinction coefficient of the first metal layer is Ka, the refractive index of the second metal layer is Nb, and the extinction coefficient of the second metal layer is Kb, {(--1) ２ +KK ２ } / {(N++1) ２ +KK ２ } >{(Nb-1) ２ +Kb ２ } / {(Nb+1) ２ +Kb ２ } Meet the relationship 6. The photodetector element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

7. where Kb is the extinction coefficient of the second metal layer, Tb is the thickness of the second metal layer, and λb is the wavelength of light incident on the second metal layer, Kb × Tb ≦ 0.183 × λb Meet the relationship 7. The photodetector element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

8. The first metal layer is made of a metal or alloy containing aluminum or silver as a main material.

2. The photodetector element according to claim 1.

9. The second metal layer is made of a metal or alloy containing at least one of titanium, zinc, and zirconium as a main material.

9. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

10. The metal oxide layer of the second metal layer includes an oxide mainly composed of at least one of titanium, zinc, zirconium, and tantalum.

10. The photodetector element according to claim 1, wherein the first and second electrodes are electrically connected to each other.

11. The photoelectric conversion film further includes an intermediate layer disposed between the first electrode and the photoelectric conversion film.

11. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

12. The intermediate layer contains an oxide, nitride, or oxynitride containing at least one of titanium, zinc, zirconium, and tantalum as a main material.

12. The photodetector element according to claim 11.

13. the second metal layer has a first region with a first thickness and a second region with a second thickness that is thicker than the first thickness; the first film thickness is 5 nm or more and 50 nm or less; The second film thickness is greater than 50 nm.

2. The photodetector element according to claim 1.

14. The second region is disposed around the first region.

14. The photodetector element according to claim 13.

15. The second metal layer separates the first region and the second region.

15. The photodetector element according to claim 13 or 14.

16. The second electrode includes a metal oxide layer.

16. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

17. the first metal layer is made of a metal or alloy containing aluminum as a main material, the second metal layer is made of a metal or alloy containing titanium as a main material, The thickness of the second metal layer is 40 nm or less.

13. The photodetector element according to claim 1, wherein the light-detecting element is a light-detecting element.

18. 18. A photodetector comprising a plurality of unit cells, each of which includes a photodetector element according to claim 1 and a readout circuit for reading out a signal output from the photodetector element. A photoelectric conversion device characterized by:

19. a photoelectric conversion device comprising the photodetector element according to any one of claims 1 to 17 and a substrate supporting the photodetector element; an information processing device that processes information based on the signal output from the photoelectric conversion device; An apparatus characterized by having:

20. a light source that emits light in the absorption wavelength range of the photoelectric conversion film.

20. The device of claim 19.

21. The light in the absorption wavelength range of the photoelectric conversion film is infrared light.

21. The device of claim 20.

Images