Radiation detection device

Abstract

[Problem] Realization of an extremely reliable radiation detection device. [Means of solving the problem] A radiation detection device according to an embodiment of the present invention comprises: a transistor in which an oxide semiconductor layer is used in a channel of the transistor; a photoelectric conversion layer connected to the transistor; a wavelength conversion layer facing the photoelectric conversion layer and capable of emitting visible light on the basis of radioactive rays absorbed by the wavelength conversion layer; and an oxide layer in contact with the oxide semiconductor layer between the transistor and the photoelectric conversion layer, wherein the thickness of the oxide layer is 50 nm or less.

Description

[Technical area]

[0001] One embodiment of the present invention relates to a radiation detection device. In particular, one embodiment of the present invention relates to a radiation detection device comprising a semiconductor device in which an oxide semiconductor is used as a channel. [State of the art]

[0002] In recent years, instead of amorphous silicon, low-temperature polysilicon, and single-crystal silicon, the development of a semiconductor device using an oxide semiconductor as a channel has been promoted (for example, Patent Literature 1 to 6). The semiconductor device using the oxide semiconductor as a channel can be formed by a simple structure and a low-temperature process similar to a semiconductor device using amorphous silicon as a channel. It is known that the semiconductor device using the oxide semiconductor as a channel has higher mobility than the semiconductor device using amorphous silicon as a channel.

[0003] For the stably functioning of a semiconductor device using an oxide semiconductor as a channel, it is important to reduce oxygen vacancies formed in an oxide semiconductor layer by supplying oxygen to the oxide semiconductor layer during the manufacturing process of the semiconductor device. As a method for supplying oxygen to the oxide semiconductor layer, for example, a technique for forming an insulating layer covering the oxide semiconductor layer under the condition that the insulating layer contains more oxygen is disclosed. [Citation list][Patent literature] [Patent Literature 1] Japanese Patent Laid-Open No. 2021-141338 [Patent Literature 2] Japanese Patent Laid-Open No. 2014-099601 [Patent Literature 3] Japanese Patent Laid-Open No. 2021-153196 [Patent Literature 4] Japanese Patent Laid-Open No. 2018-006730 [Patent Literature 5] Japanese Patent Laid-Open No. 2016-184771 [Patent Literature 6] Japanese Patent Laid-Open No. 2021-108405 [Summary of the Invention][Technical Problem]

[0004] However, an insulating layer formed under conditions containing more oxygen will have many defects. Due to this effect, a characteristic deviation of the semiconductor device occurs during a reliability test. The characteristic fluctuations in the reliability test are attributed to the trapping of holes in the defects in the insulating layer. When a semiconductor device in which a hole trap is formed is used in a radiation detection device, a characteristic change in the semiconductor device occurs due to the trapping of a hole created by the radiation. It is necessary to suppress such characteristic deviations.

[0005] An object of an embodiment of the present invention is to realize a highly reliable radiation detection device. [Solution for problems]

[0006] A radiation detection device according to an embodiment of the present invention comprises: a transistor in which an oxide semiconductor layer is used in a channel of the transistor; a photoelectric conversion layer connected to the transistor; a wavelength conversion layer facing the photoelectric conversion layer and capable of emitting visible light based on radioactive rays absorbed by the wavelength conversion layer; and an oxide layer in contact with the oxide semiconductor layer between the transistor and the photoelectric conversion layer, wherein a thickness of the oxide layer is 50 nm or less. [Brief description of the drawings] Fig. 1 is a cross-sectional view showing the outline of a radiation detection device according to an embodiment of the present invention. Fig. 2 is a circuit diagram showing the outline of a radiation detection device according to an embodiment of the present invention. Fig. 3 is a diagram showing the results of a visible light reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. 4 is a diagram showing the results of a radiation reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. 5 is a diagram showing the results of a radiation reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. 6 is a diagram showing results of a visible light reliability test of a transistor used in a radiation detection apparatus according to an embodiment of the present invention. Fig. 7 is a diagram showing results of a visible light reliability test of a transistor used in a radiation detection apparatus according to an embodiment of the present invention. [Description of the embodiments]

[0007] Embodiments of the present invention will be described below with reference to the drawings. The following disclosure is merely an example. A configuration that a person skilled in the art can easily devise by appropriately changing the configuration of the embodiment while maintaining the gist of the invention is, of course, included within the scope of the present invention. For clarity, the drawings may be schematically illustrated with respect to widths, thicknesses, shapes, etc. of the respective portions in comparison with actual embodiments. However, the shapes shown are merely examples and do not limit the interpretation of the present invention.In this specification and the drawings, the same components as those described above with reference to the drawings already described are assigned the same reference numerals, and a detailed description thereof may be omitted where appropriate.

[0008] In each embodiment of the present invention, a direction from a substrate to an oxide semiconductor layer is referred to as "up" or "over." Conversely, a direction from the oxide semiconductor layer to the substrate is referred to as "down" or "down." For example, although the terms "up" or "down" are used for explanation for convenience, the vertical relationship between the substrate and the oxide semiconductor layer may be arranged in a different direction than shown in the diagrams. For example, in the following description, the term "oxide semiconductor layer on the substrate" only describes the vertical relationship between the substrate and the oxide semiconductor layer as described above, and other elements may be arranged between the substrate and the oxide semiconductor layer.An upper portion or a lower portion means a stacking order in a structure in which a plurality of layers are stacked. In the case where a first element is expressed as the first element above the transistor, the transistor and the first element may have a positional relationship in which the transistor and the first element do not overlap in a plan view. On the other hand, the term "first element vertically above the transistor" means a positional relationship in which the transistor and the first element overlap in a plan view.

[0009] As used herein, the expression "α includes A, B, or C," "α includes any one of A, B, or C," "α includes a value selected from a group consisting of A, B, and C," and the like do not exclude cases where α includes a plurality of combinations of A through C, unless otherwise specified. Furthermore, these expressions do not exclude the case where α includes other elements.

[0010] Furthermore, the following embodiments can be combined with each other, provided there are no technical contradictions. [1. First embodiment]

[0011] With reference to Fig. 1 and Fig. 2, a radiation detection device 10 according to an embodiment of the present invention is described. [1-1. Structure of the radiation detection device 10]

[0012] With reference to Fig. 1 and Fig. 2, a configuration of the radiation detection apparatus 10 according to an embodiment of the present invention will be described. Fig. 1 is a cross-sectional view showing the outline of a radiation detection device according to an embodiment of the present invention. Fig. 2 is a circuit diagram showing the outline of a radiation detection device according to an embodiment of the present invention.

[0013] As in Fig. As shown in Figure 1, the radiation detection device 10 is provided on a substrate 100. The radiation detection device 10 includes a transistor 20, a photoelectric conversion layer 300, a wavelength conversion layer 400, and an oxide layer 150. The radiation detection device 10 includes, in addition to the elements described above, an insulating layer 160, a light-shielding layer 210, a connecting wiring 220, an insulating layer 230, a lower electrode 310, an upper electrode 320, insulating layers 330 and 340, and wirings 350 and 360.

[0014] The transistor 20 includes a gate electrode 105, gate insulating layers 110 and 120, a metal oxide layer 130, an oxide semiconductor layer 140, a source electrode 201, and a drain electrode 203. The transistor 20 is a transistor in which the oxide semiconductor layer 140 is used as a channel. Depending on the polarity of the transistor, a circuit configuration, and the potential of each node, the source electrode and drain electrode of the transistor may be interchanged with each other. If the source electrode 201 and the drain electrode 203 are not particularly different from each other, they may be collectively referred to as the source-drain electrode 200. In the present embodiment, a bottom-gate transistor in which the gate electrode 105 is provided below the oxide semiconductor layer 140 is described as the radiation detection device 10.

[0015] Although a bottom-gate transistor in which the oxide semiconductor layer 140 is closer to the photoelectric conversion layer 300 than the gate electrode 105 is used as an example of the radiation detection device 10 in the present embodiment, the radiation detection device 10 is not limited to the bottom-gate transistor. For example, the radiation detection device 10 may be a double-gate transistor in which a gate electrode is provided both above and below the oxide semiconductor layer 140.

[0016] The gate electrode 105 is provided on the substrate 100. The gate electrode 105 faces the oxide semiconductor layer 140. The gate insulating layers 110 and 120 are provided between the gate electrode 105 and the oxide semiconductor layer 140. The gate insulating layers 110 and 120 have a stacked structure. The metal oxide layer 130 is provided on the gate insulating layer 120. The oxide semiconductor layer 140 is provided on the metal oxide layer 130. A source electrode 201 and a drain electrode 203 are provided on the oxide semiconductor layer 140. The source electrode 201 and the drain electrode 203 are in contact with the oxide semiconductor layer 140 from above the oxide semiconductor layer 140.

[0017] The oxide layer 150 and the insulating layer 160 are provided on the oxide semiconductor layer 140, the source electrode 201, and the drain electrode 203. The oxide layer 150 and the insulating layer 160 have a stacked structure. The insulating layer 160 is provided on the oxide layer 150. The oxide layer 150 and the insulating layer 160 cover the source electrode 201 and the drain electrode 203. The oxide layer 150 is in contact with the oxide semiconductor layer 140. The oxide layer 150 can be said to be provided between the transistor 20 and the photoelectric conversion layer 300.

[0018] The oxide semiconductor layer 140 is light-transmitting and has a polycrystalline structure with a plurality of crystal grains. As described later, the oxide semiconductor layer 140 with the polycrystalline structure can be formed using a poly-OS (polycrystalline oxide semiconductor) technique. Although the structure of the oxide semiconductor layer 140 is described below, an oxide semiconductor with a polycrystalline structure may be referred to as a poly-OS.

[0019] The grain size of the crystal grains contained in the poly-OS is, for example, 0.1 µm or more, 0.3 µm or more, or 0.5 µm or more. The grain size of the crystal grains can be determined, for example, by cross-sectional SEM observation, cross-sectional TEM observation, or electron backscatter diffraction (EBSD) method.

[0020] As described above, since the grain size of the crystal grains contained in the poly-OS is 0.1 μm or more, in the oxide semiconductor layer 140 having a film thickness of 10 nm or more and 30 nm or less, there are regions comprising only one crystal grain along the film thickness.

[0021] A thickness of the gate insulating layer 110 is, for example, 50 nm or more and 500 nm or less, 50 nm or more and 400 nm or less, 50 nm or more and 300 nm or less, 50 nm or more and 150 nm or less, or 50 nm or more and 100 nm or less. A thickness of the gate insulating layer 120 is, for example, 10 nm or more and 200 nm or less, or 10 nm or more and 100 nm or less. A total thickness of the gate insulating layers 110 and 120 is, for example, 100 nm or more and 700 nm or less, 100 nm or more and 500 nm or less, 100 nm or more and 400 nm or less, 100 nm or more and 250 nm or less, 100 nm or more and 200 nm or less, or 100 nm or more and 150 nm or less.

[0022] A thickness of the metal oxide layer 130 is, for example, 1 nm or more and 20 nm or less, or 1 nm or more and 10 nm or less. In the present embodiment, alumina is used as the metal oxide layer 130. Alumina has a high barrier property against gases such as oxygen or hydrogen. Barrier property refers to the function of suppressing the permeation of a gas such as oxygen or hydrogen through the alumina. That is, even if a gas such as oxygen or hydrogen is released from a layer located below an alumina film, the gas does not enter a layer located above the alumina film. Alternatively, even if the gas is released from the layer located above the alumina film, for example, oxygen or hydrogen, it does not move into the layer located below the alumina film.

[0023] A thickness of the oxide semiconductor layer 140 is 10 nm or more and 50 nm or less, 10 nm or more and 40 nm or less, or 10 nm or more and 30 nm or less. A thickness of the oxide layers 150 is 50 nm or more and 300 nm or less, 60 nm or more and 200 nm or less, or 70 nm or more and 150 nm or less.

[0024] The thickness of the oxide layer 150 is, for example, 100 nm or less, 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. Since the thickness of the oxide layer 150 is within the above-mentioned range, the reliability of the transistor 20 with respect to visible light and radiation is improved, as described later.

[0025] A thickness of the insulating layer 160 is, for example, 50 nm or more and 500 nm or less, 50 nm or more and 400 nm or less, 50 nm or more and 300 nm or less, or 50 nm or more and 200 nm or less.

[0026] The light-shielding layer 210 is provided on the insulating layer 160. The light-shielding layer 210 is provided in a region that overlaps the oxide semiconductor layer 140 in a plan view. In a plan view, the light-shielding layer 210 is provided to cover at least the oxide semiconductor layer 140 exposed from the source-drain electrode 200. If the light-shielding layer 210 is formed of a conductive material, the same voltage can be applied to the light-shielding layer 210 as to the gate electrode 105. In this case, the transistor 20 functions as a dual-gate transistor.

[0027] Openings 161 are provided on the oxide layer 150 and the insulating layer 160. The openings 161 extend to the source electrode 201. The connecting wiring 220 is provided on the insulating layer 160 and within the opening 161. The connecting wiring 220 is in contact with the source electrode 201 at a lower portion of the opening 161.

[0028] The insulating layer 230 is provided on the insulating layer 160, the light-shielding layer 210, and the connecting wiring 220. The insulating layer 230 covers a pattern end portion of the light-shielding layer 210 and a pattern end portion of the connecting wiring 220. The insulating layer 230 softens a step formed by the light-shielding layer 210 and the connecting wiring 220. The insulating layer 230 may be referred to as a planarization layer. An organic insulating layer is used as the insulating layer 230. An opening 231 is provided on the insulating layer 230. The opening 231 extends to the connecting wiring 220.

[0029] The lower electrode 310 is provided on the insulating layer 230 and within the opening 231. The lower electrode 310 is in contact with the connecting wiring 220 at a lower portion of the opening 231. The photoelectric conversion layer 300 and the upper electrode 320 are disposed on the lower electrode 310. That is, the photoelectric conversion layer 300 is connected to the transistor 20 via the lower electrode 310 and the connecting wiring 220. The photoelectric conversion layer 300 includes an N-type semiconductor layer, a P-type semiconductor layer, and an intrinsic semiconductor layer. The intrinsic semiconductor layer is provided between the N-type semiconductor layer and the P-type semiconductor layer. One of the N-type semiconductor layer or the P-type semiconductor layer is in contact with the lower electrode 310, and the other is in contact with the upper electrode 320.

[0030] The photoelectric conversion layer 300 functions to convert light energy into electrical energy. When the light energy is absorbed by the intrinsic semiconductor layer of the photoelectric conversion layer 300, the semiconductor is photoexcited to generate a pair of electrons and holes. The generated electrons and holes flow through the N-type semiconductor layer and the P-type semiconductor layer to the lower electrode 310 and the upper electrode 320. The intensity of the light irradiated onto the photoelectric conversion layer 300 can be measured by detecting a current generated by the electrons and holes generated by the photoexcitation.

[0031] The insulating layer 330 is provided on the upper electrode 320. An opening 331 is provided on the insulating layer 330. The opening 331 reaches the upper electrode 320. The insulating layer 340 is provided on the insulating layer 330. An opening 341 is provided on the insulating layer 340. In plan view, the opening 341 is larger than the opening 331. The opening 341 reaches parts of the upper electrode 320 and the insulating layer 330. An inorganic insulating layer is used as the insulating layer 330. An organic insulating layer is used as the insulating layer 340. The insulating layer 330 has a shape that reflects steps formed by the lower electrode 310, the photoelectric conversion layer 300, and the upper electrode 320. On the other hand, the insulating layer 340 alleviates the steps. That is, the insulating layer 340 is a planarization layer.

[0032] Wiring 360 is provided on insulating layer 340 and in an area that does not overlap photoelectric conversion layer 300 in a plan view. Wiring 350 is provided on insulating layer 340, on wiring 360, and within opening 341. Wiring 350 is in contact with upper electrode 320 at a lower portion of opening 341.

[0033] In order for the visible light emitted from the wavelength conversion layer 400 to efficiently reach the photoelectric conversion layer 300, as described in detail later, a transparent conductive layer is used as the upper electrode 320 and wiring 350. Wiring 360, on the other hand, is an opaque metal layer. The electrical resistance of the metal layer used as wiring 360 is lower than the electrical resistance of the transparent conductive layer used as wiring 350. However, a transparent conductive layer may also be used as wiring 360.

[0034] The wavelength conversion layer 400 is provided above the wiring 350 so as to face the photoelectric conversion layer 300. The wavelength conversion layer 400 may be bonded to the wiring 350 and the insulating layer 340 by an adhesive layer, or the positional relationship between the wiring 350 and the insulating layer 340 may be fixed by another fixing member. The wavelength conversion layer 400 functions to convert radiation into visible light. For example, the wavelength conversion layer 400 contains a phosphor that absorbs X-rays, α-rays, or γ-rays and emits visible light. The wavelength conversion layer 400 may be referred to as a scintillator.

[0035] When radiation enters the wavelength-conversion layer 400 from above, the radiation is converted into visible light by the wavelength-conversion layer 400. When the converted visible light enters the photoelectric conversion layer 300, light energy is converted into electrical energy, and the converted electrical energy is detected as a current. Since there is a correlation between the intensity of the radiation incident on the wavelength-conversion layer 400 and the detected current, the radiation intensity can be evaluated from the current strength.

[0036] As in Fig. As shown in Figure 2, pixels 30 in the radiation detection device 10 are arranged in a matrix. The pixel 30 includes the transistor 20 and the photoelectric converter layer 300. The gate electrode of the transistor 20 is connected to a gate control line 109. The source electrode 201 of the transistor 20 is connected to a cathode of the photoelectric converter layer 300. An anode of the photoelectric converter layer 300 is connected to a wiring 309. The drain electrode 203 of the transistor 20 is connected to a wiring 209. The wiring 209 is connected to a charge amplifier circuit 500.

[0037] As described above, the radiation incident on the wavelength conversion layer 400 is converted into visible light, and the visible light is converted into electrical energy by the photoelectric conversion layer 300. Here, by applying a bias voltage to the radiation detection wiring 309 connected to the pixel 30 and controlling the gate control line 109 connected to the pixel 30 to an on state, the electrical energy is detected as a current flowing through the transistor 20. The current flowing through the transistor 20 is supplied to the charge amplifier circuit 500 via the wiring 209. Then, the charge amplifier circuit 500 converts a charge signal into a voltage signal and outputs the voltage signal to the outside. Through the above operation, it is possible to evaluate the intensity of the radiation irradiated to the pixel 30.

[0038] As in Fig. As shown in Figure 1, ideally, all the radiation incident from above is absorbed by the wavelength-converting layer 400, but in practice, some of the radiation is transmitted through the wavelength-converting layer 400. Furthermore, the radiation passing through the wavelength-converting layer 400 is ideally blocked by the light-shielding layer 210, but in practice, the radiation bypasses the light-shielding layer 210 due to reflection by another element or the like and reaches the oxide semiconductor layer 140. When radiation penetrates the oxide semiconductor layer 140, a pair of electrons and holes is generated in the oxide semiconductor layer 140. Since a hole trap is formed in the oxide layer 150 in contact with the oxide semiconductor layer 140, the generated hole is trapped in the oxide layer 150.This can cause a problem in that the electrical properties of transistor 20 shift in a negative direction. [1-2. Material of each element of the radiation detection device 10]

[0039] A rigid substrate with light transmission, such as a glass substrate, a quartz substrate, or a sapphire substrate, is used as the substrate 100. In cases where the substrate 100 needs to be flexible, a resinous substrate such as a polyimide substrate, an acrylic substrate, a siloxane substrate, or a fluororesin substrate is used as the substrate 100. When a resinous substrate is used as the substrate 100, impurities may be incorporated into the resin to improve the heat resistance of the substrate 100. A non-light-transmitting substrate, such as a silicon substrate, a silicon carbide substrate, a semiconductor substrate, such as a compound semiconductor substrate, or a conductive substrate, such as a stainless steel substrate, may be used as the substrate 100.

[0040] General metal materials are used for the gate electrode 105, source-drain electrode 200, light-shielding layer 210, connecting wiring 220, lower electrode 310, and wiring 360. Examples of these elements include aluminum (Al), titanium (Ti), chromium (Cr), cobalt (Co), nickel (Ni), molybdenum (Mo), hafnium (Hf), tantalum (Ta), tungsten (W), bismuth (Bi), silver (Ag), copper (Cu), and alloys or compounds thereof. The materials described above can be used as these electrodes and wirings in a single layer or in a stacked layer. In the case where the light-shielding layer 210 does not need to be electrically conductive, a black resin can be used as the light-shielding layer 210.

[0041] A transparent conductive layer is used as the upper electrode 320 and wiring 350. A mixture of indium oxide and tin oxide (ITO) and a mixture of indium oxide and zinc oxide (IZO) can be used as the transparent conductive layer. A material other than the one mentioned above can also be used as the transparent conductive layer.

[0042] A general insulating material is used for gate insulating layers 110 and 120, oxide layer 150, and insulating layers 160 and 330. For example, an oxygen-containing inorganic insulating layer such as silicon oxide (SiOx), silicon oxynitride (SiOxNy), aluminum oxide (AlOx), or aluminum oxynitride (AlOxNy) is used for gate insulating layer 120 and oxide layer 150. A nitrogen-containing inorganic insulating layer such as silicon nitride (SiNx), silicon nitride oxide (SiNxOy), aluminum nitride (AlNx), or aluminum nitride oxide (AlNxOy) is used for gate insulating layer 110 and insulating layer 160. However, the oxygen-containing inorganic insulating layer described above can also be used for gate insulating layer 110 and insulating layer 160. The above-described inorganic insulating layer containing nitrogen can also be used as the gate insulating layer 120 and the oxide layer 150.

[0043] An insulating layer with the function of releasing oxygen through heat treatment is used as the oxide layer 150. This means that an oxide insulating layer with an excess of oxygen is used as the oxide layer 150. The heat treatment temperature at which the oxide layer 150 releases oxygen is, for example, 600°C or less, 500°C or less, 450°C or less, or 400°C or less. This means that the oxide layer 150 releases oxygen at a heat treatment temperature performed in a manufacturing process of the transistor 20 when, for example, a glass substrate is used as the substrate 100.

[0044] As will be described in detail later, the oxide layer 150 is a layer that has different film quality depending on the film thickness direction. In particular, the oxide layer 150 near the oxide semiconductor layer 140 has a smaller number of hole traps than the other oxide layers 150. For convenience, in the oxide layer 150, a region near the oxide semiconductor layer 140 may be referred to as a first region, and other regions may be referred to as a second region. In this case, it can be said that the amount of hole traps formed in the oxide layer 150 in the first region is smaller than the amount of hole traps formed in the oxide layer 150 in the second region. Similarly, it can be said that the first region of the oxide layer 150 is in contact with the oxide semiconductor layer 140. The first region is merely a region near the oxide semiconductor layer 140.This means that the first area is thinner than the second area.

[0045] An insulating layer with few defects is used as the gate insulating layer 120. For example, when comparing the oxygen composition ratio in the gate insulating layer 120 with the oxygen composition ratio in an insulating layer having the same composition as the gate insulating layer 120 (hereinafter referred to as "another insulating layer"), the oxygen composition ratio in the gate insulating layer 120 is closer to a stoichiometric ratio with respect to the insulating layer than the oxygen composition ratio in the other insulating layer.Specifically, in the case where silicon oxide (SiOx) is used for the gate insulating layer 120 and the oxide layer 150, the composition ratio of oxygen in the silicon oxide used as the gate insulating layer 120 is closer to a stoichiometric ratio of silicon oxide than the composition ratio of oxygen in the silicon oxide used as the oxide layer 150. For example, a layer in which no defects are observed during electron spin resonance (ESR) analysis may be used as the gate insulating layer 120.

[0046] SiOxNy and AlOxNy are silicon- and aluminum-containing compounds that contain a lower proportion of nitrogen (N) than oxygen (O) (x > y). SiNxOy and AlNxOy are silicon- and aluminum-containing compounds that contain a lower proportion of oxygen than nitrogen (x > y).

[0047] An organic insulating layer is used as insulating layers 230 and 340. Examples of organic insulating layers used include polyimide resin, acrylic resin, epoxy resin, silicone resin, fluororesin, and siloxane resin.

[0048] A metal oxide containing aluminum as a main component is used as the metal oxide layer 130. For example, an inorganic insulating layer such as aluminum oxide (AlOx) or aluminum oxynitride (AlOxNy) is used as the metal oxide layer 130. The "metal oxide layer 130 containing aluminum as a main component" means that the proportion of aluminum contained in the metal oxide layer 130 is 1% or more of the entire metal oxide layer. The proportion of aluminum contained in the metal oxide layer 130 may be 5% or more and 70% or less, 10% or more and 60% or less, or 30% or more and 50% or less of the entire metal oxide layer. The ratio described above may be a mass ratio or a weight ratio.

[0049] A metal oxide with semiconductor properties is used as the oxide semiconductor layer 140. The oxide semiconductor layer 140 has a polycrystalline structure. The polycrystalline oxide semiconductor layer 140 can be manufactured using the poly-OS technique.

[0050] For example, an oxide semiconductor containing indium (In), gallium (Ga), zinc (Zn), and oxygen (O) can be used as the oxide semiconductor layer 140. For example, an oxide semiconductor with a composition ratio of In:Ga:Zn:O = 1:1:1:4 can be used as the oxide semiconductor layer 140. However, the oxide semiconductors used in the present embodiment, including In, Ga, Zn, and O, are not limited to the components described above. An oxide semiconductor with a composition other than that described above can be used as the oxide semiconductor. For example, to improve mobility, an oxide semiconductor layer with a higher In content than those described above can be used. On the other hand, an oxide semiconductor layer with a higher Ga content than those described above can be used to widen a band gap and reduce the effects of light irradiation.

[0051] For example, as the oxide semiconductor layer 140 in which the In content is greater than those described above, an oxide semiconductor containing two or more metals, including indium (In), can be used. In this case, in the oxide semiconductor layer 140, the ratio of indium elements to the total amount of metal elements in atomic ratio can be 50% or more. In addition to indium, gallium (Ga), zinc (Zn), aluminum (Al), hafnium (Hf), yttrium (Y), zirconia (Zr), and lanthanides can be used as the oxide semiconductor layer 140. An element other than the elements described above can be used as the oxide semiconductor layer 140.

[0052] As the oxide semiconductor layers 140, other elements may be added to an oxide semiconductor containing In, Ga, Zn, and O, and a metallic element such as Al or Sn may be added. In addition to the oxide semiconductor described above, an oxide semiconductor containing In and Zn (IZO), an oxide semiconductor containing In, Sn, and Zn (ITZO), an oxide semiconductor containing In, Sn, Ga, and Zn (ITGZO), and an oxide semiconductor containing In and Ga (IGO), or the like, may be used as the oxide semiconductor layer 140.

[0053] In the case where the content of the indium element is large, the oxide semiconductor layer 140 is easily crystallized. As described above, in the oxide semiconductor layer 140, the oxide semiconductor layer 140 having the polycrystalline structure can be easily obtained by using a material in which the ratio of the indium element to the total metal element is 50% or more. The oxide semiconductor layer 140 preferably contains gallium as a metal element other than indium. Gallium belongs to the same Group 13 element as indium. Therefore, the crystallinity of the oxide semiconductor layer 140 is not affected by gallium, and the oxide semiconductor layer 140 has a polycrystalline structure.

[0054] The oxide semiconductor layer 140 can be formed using a sputtering method. The composition of the oxide semiconductor layer 140 formed by the sputtering method depends on the composition of a sputtering target. Even in the case where the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the sputtering target and the composition of the oxide semiconductor layer 140 are substantially the same. In this case, the metal element composition of the oxide semiconductor layer 140 can be determined based on the metal element composition of the sputtering target.

[0055] In the case where the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the oxide semiconductor layer can be determined using an X-ray diffraction (XRD) method. Specifically, the composition of the metallic element of the oxide semiconductor layer can be specified based on the crystal structure and a lattice constant of the oxide semiconductor layer obtained by the XRD method. Furthermore, the composition of the metallic element of the oxide semiconductor layer 140 can also be determined using fluorescence X-ray analysis, electron probe microanalyzer (EPMA) analysis, or the like. However, the oxygen element contained in the oxide semiconductor layer 140 varies depending on the process conditions of sputtering and the like, and therefore, in some cases, cannot be specified by these methods. [1-3. Film formation process for the oxide layer 150]

[0056] As described above, the oxide layer 150 included in the radiation detection device 10 according to the present embodiment is a region near the oxide semiconductor layer 140 and includes the first region with relatively few hole traps and the second region located above the first region and having relatively many hole traps. The difference between the oxide layers 150 in the first region and the second region is caused by a film formation process of the oxide layer 150.

[0057] A film formation step in the case of forming the silicon oxide layer as the oxide layer 150 includes the following steps (1) to (2). The oxide layer 150 in the first region is formed by step (1), and the oxide layer 150 in the second region is formed by step (2). (1)Interface formation process (2) Mass formation process (1) The processing conditions of an interface formation process are as follows. • SiH4 / N2O flow rate = 3 / 1000 sccm • Chamber pressure = 200 Pa • RF power = 20 W • F ratio (RF / SiH4) = 6.7 • Film thickness = 10 nm (2) The processing conditions of a mass formation process are as follows. • SiH4 / N2O flow rate = 10 / 1000 sccm • Chamber pressure = 333 Pa • RF power = 200 W • F ratio (RF / SiH4) = 10.0 • Film thickness = any

[0058] In the present embodiment, the electrode size of a CVD device used to deposit the oxide layer 150 is circular with a radius of 9 cm, and the area of ​​the electrode of the CVD device is 254 cm². Therefore, the power density of the RF power (20 W) in the (1) interface formation process is 0.079 W / cm² 2. The power density of the RF power (200 W) in the (2) bulk formation process is 0.79 W / cm2.

[0059] As described above, regarding the film-forming power (RF power) in the sputtering process, the RF power (20 W) during the film formation of the oxide layer 150 in the first region is lower than the RF power (200 W) during the film formation of the oxide layer 150 in the second region. Similarly, the ratio of SiH4 gas to N2O gas (3 / 1000) during the formation of the oxide layer 150 in the first region is smaller than the ratio of SiH4 gas to N2O gas (10 / 1000) during the formation of the oxide layer 150 in the second region. Similarly, the ratio of RF power to SiH4 gas (6.7) during the film formation of the oxide layer 150 in the first region is smaller than the ratio of RF power to SiH4 gas (10) during the film formation of the oxide layer 150 in the second region.

[0060] As described above, it is possible to form an oxide layer with a small amount of hole traps as the oxide layer 150 near the oxide semiconductor layer 140 by forming the oxide layer 150 in the first region in contact with the oxide semiconductor layer 140 with low power. As described later, the amount of hole traps contained in the oxide layer 150 can be reduced by making the thickness of the oxide layer 150 100 nm or less or 50 nm or less. This makes it possible to suppress characteristic fluctuations of the transistor 20 caused by holes generated in the oxide semiconductor layer 140 being trapped in the oxide layer 150 by the radiation incident. [1-4. Results of the reliability test of transistor 20]

[0061] Fig. 3 is a diagram showing the results of a visible light reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. The reliability test presented is a reliability test for Negative Bias Temperature Illumination Stress (NBTIS). In Fig. 3, the electrical characteristics of the transistor 20 before the NBTIS of Example 1 and Comparative Example 1 are indicated by dotted lines, respectively, and the electrical characteristics after the NBTIS are indicated by solid lines.

[0062] The conditions for the NBTIS reliability test are as follows. • Channel area size: W / L = 3.0 µm / 3.0 µm • Irradiation condition: Irradiation available (7000 lx) • Gate voltage: -30 V • Source / Drain voltage: 0 V • Stage temperature under load: 85°C • Duration of stress application: 1000 sec.

[0063] The structures of the transistors of Example 1 and Comparative Example 1 subjected to the reliability test of Fig. 3 are as follows. • Gate electrode 110\120: SiN\SiO = 300\10 nm • Oxide semiconductor layer 140: 30 nm (polycrystalline) • Oxide layer 150 \ Insulating layer 160: SiO\SiN = 300\100 nm

[0064] The film formation conditions of the oxide layer 150 in the transistor 20 according to Example 1 are as shown in the above-described steps (1) to (2). On the other hand, in a film formation condition of an oxide layer in the transistor according to Comparative Example 1, a film formation condition in a step (1') of Comparative Example 1 differs from the film formation condition in step (1) of Example 1.

[0065] (1') The processing conditions of an interface forming process of Comparative Example 1 are as follows. • SiH4 / N2O flow rate = 10 / 1000 sccm • Chamber pressure = 200 Pa • RF power = 100 W • F ratio (RF / SiH4) = 10.0 • Film thickness = 10 nm

[0066] As described above, under the processing conditions of the interfacial film formation process of Comparative Example 1, the power RF in film formation is higher, the ratio of N2O gas to SiH4 gas is larger, and the ratio of power RF to SiH4 gas is larger than under the processing conditions of the interfacial film formation process of Example 1. The number of hole traps formed in the oxide layer under these conditions is larger than the number of hole traps in the oxide layer 150 of Example 1. In the following description, the processing condition (1) described above may be referred to as low-power film formation, and the processing condition (1') may be referred to as film formation under conventional conditions.

[0067] As in Fig. 3, the threshold variation before and after the NBTIS of the transistor 20 according to Example 1 is smaller than the threshold variation before and after the NBTIS of the transistor according to Comparative Example 1. This result is due to the fact that the amount of hole traps contained in the oxide layer 150 according to Example 1 is smaller than the amount of hole traps contained in the oxide layer according to Comparative Example 1.

[0068] Fig. 4 and Fig. 5 are diagrams showing reliability test results of a transistor used in a radiation detection device according to an embodiment of the present invention with respect to radiation. Fig. The reliability test shown represents the result of an X-ray irradiation test. In Fig. 4, the electrical characteristics of the transistor 20 before X-ray irradiation are indicated by dotted lines, and the electrical characteristics after X-ray irradiation are indicated by solid lines. The results of the X-ray irradiation test of Example 1 and Comparative Example 1 are represented by three figures (No. 1 to No. 3), respectively. The structures of the transistors of Example 1 and Comparative Example 1 subjected to the X-ray irradiation test of Fig. 4 are the same as those of Fig. 3. A Fig. The bar chart shown in Figure 5 shows a variation of a threshold voltage Vth resulting from the electrical properties of Fig. 4 was determined before and after the reliability test.

[0069] The conditions of the X-ray irradiation test are as follows. -Channel area size: W / L = 3.0 µm / 3.0 µm • X-ray source: MBR-1520R-3 (Hitachi Power Solutions) • X-ray irradiation conditions: 30 Gy, 60 Gy, 90 Gy (20 mA continuous irradiation) • Irradiation condition: Filter Al = 1 mm

[0070] As in Fig. 4 and Fig. 5, the threshold variation before and after the X-ray irradiation test of the transistor 20 according to Example 1 is smaller than the threshold variation before and after the X-ray irradiation test of the transistor according to Comparative Example 1. This result is the same as in Fig. 3 and is due to the fact that the amount of hole traps contained in the oxide layer 150 according to Example 1 is smaller than the amount of hole traps contained in the oxide layer according to Comparative Example 1. As described above, similar tendencies are observed in the NBTIS and the X-ray irradiation test. The reason why the same tendencies are confirmed in this way is believed to be that the threshold variation in the NBTIS and the threshold variation in the X-ray irradiation test are caused by the hole created by the light irradiation and the X-ray irradiation, respectively, which is enclosed in the oxide layer 150.

[0071] As described above, a correlation between the threshold variation in the NBTIS and the threshold variation in the X-ray irradiation test was confirmed, so only the NBTIS is shown below.

[0072] Fig. 6 is a diagram showing results of a visible light reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. The reliability test results shown in Figure 6 are the results of evaluating the variation of the threshold voltage Vth by the NBTIS for samples with different configurations. Fig. 6 shows Example 2 and Comparative Examples 2 to 5 in which reliability is improved by thinning the oxide layer 150.

[0073] Common structures of the samples of Example 2 and Comparative Examples 2 to 5, which are shown in Fig. 6 are as follows. -Oxide semiconductor layer 140: 30 nm (polycrystalline) • Film formation conditions of the oxide layer 150: steps (1') and (2)

[0074] For those in Fig. samples shown, the different structures for each sample are as follows. [Gate insulating layer 110 \ 120] • Comparative example 2: SiN\SiO = 300\100 nm • Comparative example 3: SiN\SiO = 300\50 nm • Comparative example 4: SiN\SiO = 300\30 nm • Comparative example 5: SiN\SiO = 300\10 nm • Example 2: SiN\SiO = 300\30 nm [Oxide layer 150 \ Insulating layer 160] • Comparative example 2: SiO\SiN = 300\100 nm • Comparative example 3: SiO\SiN = 300\100 nm • Comparative example 4: SiO\SiN = 300\100 nm • Comparative example 5: SiO\SiN = 300\100 nm • Example 2: SiO\SiN = 50\100 nm

[0075] As in Fig. As shown in Figure 6, the variation of the threshold voltage Vth of Example 2 is smaller than that of Comparative Examples 2 to 5. In other words, it can be seen that the thickness of the oxide layer 150 greatly influences the variation of the threshold voltage Vth. On the other hand, it can be seen that the thicknesses of the gate insulating layers 110 and 120 have little influence on the variation of the threshold voltage Vth. As shown in Fig. As shown in Figure 6, reliability can be improved by NBTIS when the thickness of the oxide layers is 150 nm or less. Similarly, when the thickness of the oxide layers is 150 nm or less, reliability in X-ray testing can be improved.

[0076] Fig. Fig. 7 is a diagram showing results of a visible light reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention. Fig. The reliability test results shown in Figure 7 are the results of the evaluation of the variation of the threshold voltage Vth for samples with different configurations by the NBTIS. In Fig. 7 shows examples 3 to 6 in which reliability is improved by power-saving film formation and thinning of the oxide layer 150.

[0077] For the samples of the Fig. In examples 3 to 6 shown, the common structure is as follows. • Oxide semiconductor layer 140:30nm (polycrystalline) • Film formation conditions of the oxide layer 150: steps (1) and (2).

[0078] For those in Fig. sample shown, the different structures for each sample are as follows. [Gate insulating layer 110 \ 120] • Example 3: SiN\SiO = 300\50 nm • Example 4: SiN\SiO = 300\50 nm • Example 5: SiN\SiO = 300\30 nm • Example 6: SiN\SiO = 300\10 nm [Oxide layer 150 \ Insulating layer 160] • Example 3: SiO\SiN = 300\100 nm • Example 4: SiO\SiN = 100\100 nm • Example 5: SiO\SiN = 50\100 nm • Example 6: SiO\SiN = 50\100 nm

[0079] As in Fig. 7, in each of Examples 3 to 6, the film formation conditions of the oxide layer 150 are low-power film formation. Therefore, the threshold voltage Vth is lower than that in Fig.6. Among them, comparing Example 3 with Examples 4 to 6, it can be seen that the thickness of the oxide layers 150 is reduced from 300 nm to 100 nm, so the fluctuation of the threshold voltage Vth is reduced. In other words, in the case where the film formation condition of the oxide layer 150 is low-power film formation, the thickness of the oxide layer 150 is 100 nm or less, so the amount of hole traps contained in the oxide layer 150 can be reduced and the reliability by the NBTIS can be improved. Similarly, in the case where the thickness of the oxide layers 150 is 100 nm or less, the reliability in the X-ray test can be improved.

[0080] Each of the embodiments described above as an embodiment of the present invention can be combined accordingly, as long as they do not contradict each other. Furthermore, based on the transistor and radiation detection device of each embodiment, additions, deletions, or design changes of the components, or those additions, deletions, or state changes of the steps made by a person skilled in the art as appropriate, are also included within the scope of the present invention, as long as they encompass the gist of the present invention.

[0081] It is to be understood that the present invention provides other operating effects that are different from the operating effects provided by aspects of the embodiments described above and those that are obvious from the descriptions of the present specification or that can be readily predicted by one skilled in the art. [List of reference symbols] 10 radiation detection device, 20 transistors, 30 pixels, 100 substrate, 105 Gate electrode, 109 Gate control line, 110 Gate insulating layer, 110 Gate insulating layer, 120 gate insulation layer, 130 metal oxide layer, 140 oxide semiconductor layer, 150 oxide layer, 160 insulation layer, 161 opening, 200 source-drain electrode, 201 source electrode, 203 drain electrode, 209 wiring, 210 light-shielding layer, 220 connecting wiring, 230 insulation layer, 231 opening, 300 photoelectric conversion layer, 309 wiring, 310 lower electrode, 320 upper electrode, 330 insulation layer, 331 opening, 340 insulation layer, 341 opening, 350 wiring, 360 wiring, 400 wavelength conversion layer, 500 charge amplifier circuit QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2021-141338

[0003] JP 2014-099601

[0003] JP 2021-153196

[0003] JP 2018-006730

[0003] JP 2016-184771

[0003] JP 2021-108405

[0003]

Claims

[1] A radiation detection device comprising: a transistor in which an oxide semiconductor layer is used in a channel of the transistor; a photoelectric conversion layer connected to the transistor; a wavelength conversion layer facing the photoelectric conversion layer and capable of emitting visible light based on radioactive rays absorbed by the wavelength conversion layer; and an oxide layer in contact with the oxide semiconductor layer between the transistor and the photoelectric conversion layer, wherein a thickness of the oxide layer is 50 nm or less. [2] A radiation detection device according to claim 1, wherein the transistor comprises a gate electrode layer facing the oxide semiconductor layer and a gate insulating layer between the oxide semiconductor layer and the gate electrode layer, and wherein the oxide semiconductor layer is closer to the photoelectric converter layer than the gate electrode layer. [3] The radiation detection device according to claim 1, wherein the oxide layer is a silicon oxide layer. [4] The radiation detection device according to claim 1, wherein the thickness of the oxide layer is 30 nm or less. [5] Radiation detection device according to one of claims 1 to 4, wherein the oxide layer comprises a first region and a second region, the first region is in contact with the oxide semiconductor layer and a thickness of the oxide layer in the first region is smaller than a thickness of the oxide layer in the second region. [6] The radiation detection device according to claim 5, wherein a hole trapping property of the oxide layer in the first region is lower than a hole trapping property of the oxide layer in the second region. [7] A radiation detection device according to claim 5, wherein the oxide layer in the first region is a layer deposited in a sputtering process under a condition of lower deposition power than the oxide layer in the second region.

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