Radiation detection device

Abstract

To provide a radiation detection device with high reliability.SOLUTION: A radiation detection device includes a transistor using an oxide semiconductor layer for a channel, a photoelectric conversion layer connected to the transistor, a wavelength conversion layer facing the photoelectric conversion layer and emitting visible light on the basis of the absorbed radiation, and an oxide layer in contact with the oxide semiconductor layer between the transistor and the photoelectric conversion layer and being 50 nm or less. The transistor may include a gate electrode layer facing the oxide semiconductor layer and a gate insulating layer between the oxide semiconductor layer and the gate electrode layer. The oxide semiconductor layer may be closer to the photoelectric conversion layer than the gate electrode layer.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] One embodiment of the present invention relates to a radiation detection device, and in particular to a radiation detection device including a semiconductor device in which an oxide semiconductor is used as a channel. [Background technology]

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

[0003] In order to stably operate a semiconductor device using an oxide semiconductor for a channel, it is important to supply oxygen to the oxide semiconductor layer in the manufacturing process and reduce oxygen vacancies formed in the oxide semiconductor layer. As one method for supplying oxygen to the oxide semiconductor layer, for example, a technique has been disclosed in which an insulating layer covering the oxide semiconductor layer is formed under conditions in which the insulating layer contains more oxygen. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2021-141338 A [Patent Document 2] JP 2014-099601 A [Patent Document 3] Patent Publication No. 2021-153196 [Patent Document 4] JP 2018-006730 A [Patent Document 5] JP 2016-184771 A [Patent Document 6] Patent Publication No. 2021-108405 Summary of the Invention [Problem to be solved by the invention]

[0005] However, an insulating layer formed under conditions containing a larger amount of oxygen contains many defects. As a result, the characteristics of the semiconductor device fluctuate during reliability testing, which is believed to be caused by holes being trapped in the defects. When a semiconductor device having hole traps is used in a radiation detection device, the characteristics of the semiconductor device fluctuate due to holes generated by the radiation being trapped. There is a demand for suppressing such characteristic fluctuations.

[0006] An object of one embodiment of the present invention is to realize a highly reliable radiation detection device. [Means for solving the problem]

[0007] A radiation detection device according to one embodiment of the present invention includes a transistor having an oxide semiconductor layer used for a channel, a photoelectric conversion layer connected to the transistor, a wavelength conversion layer facing the photoelectric conversion layer and emitting visible light based on absorbed radiation, and an oxide layer having a thickness of 50 nm or less between the transistor and the photoelectric conversion layer and in contact with the oxide semiconductor layer. [Brief description of the drawings]

[0008] [Figure 1] 1 is a cross-sectional view showing an overview of a radiation detection device according to an embodiment of the present invention. [Diagram 2] 1 is a circuit diagram showing an overview of a radiation detection device according to an embodiment of the present invention. [Diagram 3] 6 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. FIG. [Figure 4]5 is a diagram showing the results of a reliability test against radiation of a transistor used in a radiation detection device according to an embodiment of the present invention. FIG. [Diagram 5] 5 is a diagram showing the results of a reliability test against radiation of a transistor used in a radiation detection device according to an embodiment of the present invention. FIG. [Figure 6] 6 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. FIG. [Figure 7] 6 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Each embodiment 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 come up with by appropriately modifying the configuration of the embodiment while maintaining the gist of the invention is naturally included in the scope of the present invention. In order to make the explanation clearer, the drawings may be schematic in terms of the width, thickness, shape, etc. of each part compared to the actual form. However, the illustrated shapes are merely examples and do not limit the interpretation of the present invention. In this specification and each figure, the same symbols are used for configurations similar to those described above with respect to the previous figures, and detailed explanations may be omitted as appropriate.

[0010] In each embodiment of the present invention, the direction from the substrate toward the oxide semiconductor layer is referred to as "up" or "upper". Conversely, the direction from the oxide semiconductor layer toward the substrate is referred to as "down" or "down". Thus, for convenience of explanation, the terms "up" or "down" are used in the explanation, but, for example, the vertical relationship between the substrate and the oxide semiconductor layer may be arranged in a direction different from that illustrated. In the following explanation, for example, the expression "oxide semiconductor layer on a substrate" merely describes the vertical relationship between the substrate and the oxide semiconductor layer as described above, and another member may be arranged between the substrate and the oxide semiconductor layer. "Up" or "down" means the stacking order in a structure in which multiple layers are stacked, and when the first member is expressed as being above the transistor, the transistor and the first member may not overlap in a planar view. On the other hand, when the first member is expressed as being vertically above the transistor, the transistor and the first member may overlap in a planar view.

[0011] In this specification, unless otherwise specified, expressions such as "α includes A, B, or C," "α includes any one of A, B, and C," and "α includes one selected from the group consisting of A, B, and C" do not exclude cases where α includes multiple combinations of A to C. Furthermore, these expressions do not exclude cases where α includes other elements.

[0012] The following embodiments can be combined with each other as long as no technical contradiction occurs.

[0013] [1. First embodiment] A radiation detection device 10 according to one embodiment of the present invention will be described with reference to FIGS.

[0014] [1-1. Configuration of radiation detection device 10] The configuration of a radiation detection device 10 according to one embodiment of the present invention will be described with reference to Figures 1 and 2. Figure 1 is a cross-sectional view showing an overview of a radiation detection device according to one embodiment of the present invention. Figure 2 is a circuit diagram showing an overview of a radiation detection device according to one embodiment of the present invention.

[0015] 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. In addition to the above-mentioned components, the radiation detection device 10 also includes an insulating layer 160, a light-shielding layer 210, a connection wiring 220, an insulating layer 230, a lower electrode 310, an upper electrode 320, insulating layers 330, 340, and wiring 350, 360.

[0016] 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, the circuit configuration, and the potential of each node, the source electrode and the drain electrode of the transistor may be interchanged. When the source electrode 201 and the drain electrode 203 are not particularly distinguished from each other, they may be collectively referred to as the source-drain electrode 200. In this embodiment, a bottom-gate type transistor in which the gate electrode 105 is provided below the oxide semiconductor layer 140 will be described as the radiation detection device 10.

[0017] In this embodiment, 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 illustrated as an example of the radiation detection device 10, but the radiation detection device 10 is not limited to a bottom-gate transistor. For example, the radiation detection device 10 may be a dual-gate transistor in which gate electrodes are provided both above and below the oxide semiconductor layer 140.

[0018] 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.

[0019] The oxide layer 150 and the insulating layer 160 are provided over 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 over 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. It can be said that the oxide layer 150 is provided between the transistor 20 and the photoelectric conversion layer 300.

[0020] The oxide semiconductor layer 140 has a polycrystalline structure that transmits light and includes a plurality of crystal grains. Although details will be described later, the oxide semiconductor layer 140 having a polycrystalline structure can be formed by using a polycrystalline oxide semiconductor (Poly-OS) technique. The configuration of the oxide semiconductor layer 140 will be described below, and an oxide semiconductor having a polycrystalline structure may be referred to as Poly-OS.

[0021] The crystal grains contained in the Poly-OS have a crystal grain size of, for example, 0.1 μm or more, 0.3 μm or more, or 0.5 μm or more. The crystal grain size can be obtained by, for example, cross-sectional SEM observation, cross-sectional TEM observation, or an electron backscattered diffraction (EBSD) method.

[0022] As described above, the crystal grains contained in the Poly-OS have a grain size of 0.1 μm or more, and therefore, in the oxide semiconductor layer 140 having a thickness of 10 nm or more and 30 nm or less, there is a region that contains only one crystal grain along the film thickness direction.

[0023] The thickness of the gate insulating layer 110 is, for example, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, 50 nm to 150 nm, or 50 nm to 100 nm. The thickness of the gate insulating layer 120 is, for example, 10 nm to 200 nm, or 10 nm to 100 nm. The total thickness of the gate insulating layers 110 and 120 is, for example, 100 nm to 700 nm, 100 nm to 500 nm, 100 nm to 400 nm, 100 nm to 250 nm, 100 nm to 200 nm, or 100 nm to 150 nm.

[0024] The thickness of the metal oxide layer 130 is, for example, 1 nm to 20 nm or 1 nm to 10 nm. In this embodiment, aluminum oxide is used as the metal oxide layer 130. Aluminum oxide has high barrier properties against gases such as oxygen and hydrogen. The barrier properties refer to a function of suppressing the permeation of gases such as oxygen and hydrogen through aluminum oxide. In other words, even if gases such as oxygen or hydrogen are released from a layer provided under the aluminum oxide film, the gases do not move to a layer provided above the aluminum oxide film. Or, even if gases such as oxygen or hydrogen are released from a layer provided on the aluminum oxide film, the gases do not move to a layer provided below the aluminum oxide film.

[0025] The oxide semiconductor layer 140 has a thickness of 10 to 50 nm, 10 to 40 nm, or 10 to 30 nm. The oxide layer 150 has a thickness of 50 to 300 nm, 60 to 200 nm, or 70 to 150 nm.

[0026] The oxide layer 150 has a thickness of, for example, 100 nm or less, 50 nm or less, 30 nm or less, 20 nm or less, or 10 nm or less. When the oxide layer 150 has a thickness in the above range, the reliability of the transistor 20 against visible light and radiation is improved, as described later.

[0027] The thickness of the insulating layer 160 is, for example, 50 nm to 500 nm, 50 nm to 400 nm, 50 nm to 300 nm, or 50 nm to 200 nm.

[0028] The light-shielding layer 210 is provided on the insulating layer 160. The light-shielding layer 210 is provided in a region overlapping with the oxide semiconductor layer 140 in a plan view. In a top view, the light-shielding layer 210 is provided so as to cover at least the oxide semiconductor layer 140 exposed from the source-drain electrodes 200. When the light-shielding layer 210 is made of a conductive material, the same voltage as that of the gate electrode 105 may be supplied to the light-shielding layer 210. In this case, the transistor 20 functions as a dual-gate transistor.

[0029] An opening 161 is provided in the oxide layer 150 and the insulating layer 160. The opening 161 reaches the source electrode 201. The connection wiring 220 is provided on the insulating layer 160 and inside the opening 161. The connection wiring 220 contacts the source electrode 201 at the bottom of the opening 161.

[0030] An insulating layer 230 is provided on the insulating layer 160, the light-shielding layer 210, and the connection wiring 220. The insulating layer 230 covers the pattern end of the light-shielding layer 210 and the pattern end of the connection wiring 220. The insulating layer 230 reduces the step formed by the light-shielding layer 210 and the connection wiring 220. The insulating layer 230 can be called a planarizing layer. An organic insulating layer is used as the insulating layer 230. An opening 231 is provided in the insulating layer 230. The opening 231 reaches the connection wiring 220.

[0031] A lower electrode 310 is provided on the insulating layer 230 and inside the opening 231. The lower electrode 310 contacts the connection wiring 220 at the bottom of the opening 231. A photoelectric conversion layer 300 and an upper electrode 320 are provided 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 connection 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 and the P-type semiconductor layer contacts the lower electrode 310, and the other contacts the upper electrode 320.

[0032] The photoelectric conversion layer 300 has a function of converting light energy into electrical energy. When light energy is absorbed by the intrinsic semiconductor layer of the photoelectric conversion layer 300, the semiconductor is photoexcited to generate pairs of electrons and holes. The generated electrons and holes flow to the lower electrode 310 and the upper electrode 320 via the N-type semiconductor layer and the P-type semiconductor layer. By detecting the current generated by the electrons and holes generated by photoexcitation, the intensity of light irradiated on the photoelectric conversion layer 300 can be detected.

[0033] An insulating layer 330 is provided on the upper electrode 320. An opening 331 is provided in the insulating layer 330. The opening 331 reaches the upper electrode 320. An insulating layer 340 is provided on the insulating layer 330. An opening 341 is provided in the insulating layer 340. In a plan view, the opening 341 is larger than the opening 331. The opening 341 reaches a part 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 the step formed by the lower electrode 310, the photoelectric conversion layer 300, and the upper electrode 320. On the other hand, the insulating layer 340 relieves the step. In other words, the insulating layer 340 is a planarizing layer.

[0034] A wiring 360 is provided on the insulating layer 340 in a region that does not overlap with the photoelectric conversion layer 300 in a plan view. A wiring 350 is provided on the insulating layer 340, on the wiring 360, and inside the opening 341. The wiring 350 contacts the upper electrode 320 at the bottom of the opening 341.

[0035] Although details will be described later, in order for visible light emitted from the wavelength conversion layer 400 to efficiently reach the photoelectric conversion layer 300, a transparent conductive layer is used as the upper electrode 320 and the wiring 350. On the other hand, the wiring 360 is an opaque metal layer. The electrical resistance of the metal layer used as the wiring 360 is lower than the electrical resistance of the transparent conductive layer used as the wiring 350. However, a transparent conductive layer may be used as the wiring 360.

[0036] 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 wavelength conversion layer 400 and the wiring 350 and the insulating layer 340 may be fixed by another fixing member. The wavelength conversion layer 400 has a function of converting radiation into visible light. For example, the wavelength conversion layer 400 includes a phosphor that absorbs X-rays, α-rays, or γ-rays and emits visible light. The wavelength conversion layer 400 can be called a scintillator.

[0037] When radiation is incident on 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 is incident on the photoelectric conversion layer 300, the light energy is converted into electrical energy and 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 intensity of the radiation can be evaluated from the magnitude of the current.

[0038] As shown in Fig. 2, the radiation detection device 10 has pixels 30 arranged in a matrix. The pixels 30 include a transistor 20 and a photoelectric conversion layer 300. A gate electrode of the transistor 20 is connected to a gate control line 109. A source electrode 201 of the transistor 20 is connected to a cathode of the photoelectric conversion layer 300. An anode of the photoelectric conversion layer 300 is connected to a wiring 309. A drain electrode 203 of the transistor 20 is connected to the wiring 209. The wiring 209 is connected to a charge amplifier circuit 500.

[0039] As described above, 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, a bias voltage is supplied to the wiring 309 connected to the pixel 30 that detects radiation, and the gate control line 109 connected to the pixel 30 is controlled to be in an on state, whereby 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 signal is converted into a voltage signal by the charge amplifier circuit 500, and the voltage signal is output to the outside. Through the above operations, the intensity of the radiation irradiated to the pixel 30 can be evaluated.

[0040] As shown in FIG. 1, ideally, all radiation incident from above is absorbed by the wavelength conversion layer 400, but in reality, some of the radiation passes through the wavelength conversion layer 400. Furthermore, ideally, the radiation that passes through the wavelength conversion layer 400 is blocked by the light-shielding layer 210, but in reality, the radiation goes around the light-shielding layer 210 due to reflection by other members, etc., and reaches the oxide semiconductor layer 140. When the radiation is incident on the oxide semiconductor layer 140, electron-hole pairs are 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 holes are trapped in the oxide layer 150. As a result, a problem may occur in which the electrical characteristics of the transistor 20 are shifted in the negative direction.

[0041] [1-2. Materials of each component of the radiation detection device 10] As the substrate 100, a rigid substrate having optical transparency, such as a glass substrate, a quartz substrate, or a sapphire substrate, is used. When the substrate 100 needs to be flexible, a substrate containing a resin, such as a polyimide substrate, an acrylic substrate, a siloxane substrate, or a fluororesin substrate, is used as the substrate 100. When a substrate containing a resin is used as the substrate 100, impurities may be introduced into the resin in order to improve the heat resistance of the substrate 100. As the substrate 100, a substrate not having optical transparency, such as a semiconductor substrate, such as a silicon substrate, a silicon carbide substrate, or a compound semiconductor substrate, or a conductive substrate, such as a stainless steel substrate, may be used.

[0042] General metal materials are used for the gate electrode 105, the source-drain electrodes 200, the light-shielding layer 210, the connection wiring 220, the lower electrode 310, and the wiring 360. For example, 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 are used for these members. The above materials may be used as a single layer or a laminated layer for these electrodes and wiring. When the light-shielding layer 210 does not need to have electrical conductivity, a black resin may be used as the light-shielding layer 210.

[0043] A transparent conductive layer is used as the upper electrode 320 and the wiring 350. The transparent conductive layer may be made of a mixture of indium oxide and tin oxide (ITO) and a mixture of indium oxide and zinc oxide (IZO). Materials other than those mentioned above may also be used as the transparent conductive layer.

[0044] A general insulating material is used for the gate insulating layers 110 and 120, the oxide layer 150, and the insulating layers 160 and 330. For example, silicon oxide (SiO x ), silicon oxynitride (SiO x N y), aluminum oxide (AlO x ), aluminum oxide nitride (AlO x N y The gate insulating layer 110 and the insulating layer 160 are made of an inorganic insulating layer containing oxygen, such as silicon nitride (SiN x ), silicon oxynitride (SiN x O y ), Aluminum Nitride (AlN x ), aluminum oxide nitride (AlN x O y However, the gate insulating layer 110 and the insulating layer 160 may be formed of an inorganic insulating layer containing oxygen as described above. The gate insulating layer 120 and the oxide layer 150 may be formed of an inorganic insulating layer containing nitrogen as described above.

[0045] An insulating layer having a function of releasing oxygen by heat treatment is used as the oxide layer 150. That is, an oxide insulating layer containing excess oxygen is used as the oxide layer 150. The temperature of the heat treatment 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. That is, the oxide layer 150 releases oxygen at a heat treatment temperature performed in the manufacturing process of the transistor 20 when a glass substrate is used as the substrate 100.

[0046] Although the details will be described later, the oxide layer 150 has different film properties depending on the thickness direction. Specifically, the oxide layer 150 near the oxide semiconductor layer 140 has a smaller amount of hole traps than the other oxide layer 150. For convenience of explanation, the region of the oxide layer 150 near the oxide semiconductor layer 140 may be referred to as a first region, and the other region may be referred to as a second region. In this case, it can be said that the hole traps formed in the oxide layer 150 in the first region are fewer than the 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. Since the first region is only the region near the oxide semiconductor layer 140, the first region is thinner than the second region.

[0047] An insulating layer with few defects is used as the gate insulating layer 120. For example, when the oxygen composition ratio in the gate insulating layer 120 is compared 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 the stoichiometric ratio for the insulating layer than the oxygen composition ratio in the other insulating layer. Specifically, silicon oxide (SiO x ), the composition ratio of oxygen in the silicon oxide used as the gate insulating layer 120 is closer to the stoichiometric ratio of silicon oxide than the composition ratio of oxygen in the silicon oxide used as the oxide layer 150. For example, the gate insulating layer 120 may be a layer in which no defects are observed when evaluated by electron spin resonance (ESR).

[0048] The above SiO x N y and AlO x N y is a silicon and aluminum compound that contains a smaller ratio (x>y) of nitrogen (N) than oxygen (O). SiN x O y and AlN x O y are silicon and aluminum compounds that contain a smaller proportion of oxygen than nitrogen (x>y).

[0049] An organic insulating layer is used as the insulating layers 230 and 340. For example, polyimide resin, acrylic resin, epoxy resin, silicone resin, fluorine resin, and siloxane resin are used as the organic insulating layer.

[0050] A metal oxide containing aluminum as a main component is used as the metal oxide layer 130. For example, aluminum oxide (AlO x ), aluminum oxide nitride (AlO x N y) is used. "Metal oxide layer 130 containing aluminum as a main component" means that the ratio of aluminum contained in metal oxide layer 130 is 1% or more of the entire metal oxide layer. The ratio of aluminum contained in 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 above ratio may be a mass ratio or a weight ratio.

[0051] A metal oxide having semiconductor properties can be used as the oxide semiconductor layer 140. The oxide semiconductor layer 140 has a polycrystalline structure. The oxide semiconductor layer 140 having a polycrystalline structure can be manufactured by using a Poly-OS technique.

[0052] For example, an oxide semiconductor containing indium (In), gallium (Ga), zinc (Zn), and oxygen (O) may be used as the oxide semiconductor layer 140. For example, an oxide semiconductor having a composition ratio of In:Ga:Zn:O=1:1:1:4 may be used as the oxide semiconductor layer 140. However, the oxide semiconductor containing In, Ga, Zn, and O used in this embodiment is not limited to the above composition. An oxide semiconductor having a composition different from the above may be used as the oxide semiconductor. For example, an oxide semiconductor layer having a ratio of In larger than the above may be used to improve mobility. On the other hand, an oxide semiconductor layer having a ratio of Ga larger than the above may be used to increase the band gap and reduce the influence of light irradiation.

[0053] For example, an oxide semiconductor containing two or more metals including indium (In) may be used as the oxide semiconductor layer 140 having a ratio of In larger than the above. In this case, the ratio of indium elements to all metal elements in the oxide semiconductor layer 140 may be 50% or more in atomic ratio. In addition to indium, gallium (Ga), zinc (Zn), aluminum (Al), hafnium (Hf), yttrium (Y), zirconia (Zr), and lanthanoids may be used as the oxide semiconductor layer 140. Elements other than the above may be used as the oxide semiconductor layer 140.

[0054] As the oxide semiconductor layer 140, other elements may be added to an oxide semiconductor containing In, Ga, Zn, and O, and for example, a metal element such as Al or Sn may be added. In addition to the above oxide semiconductors, 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), an oxide semiconductor containing In and Ga (IGO), or the like may be used as the oxide semiconductor layer 140.

[0055] When the ratio of the indium element is high, the oxide semiconductor layer 140 is likely to crystallize. As described above, by using a material in which the ratio of the indium element to all metal elements in the oxide semiconductor layer 140 is 50% or more, the oxide semiconductor layer 140 having a polycrystalline structure can be easily obtained. As a metal element other than indium, the oxide semiconductor layer 140 preferably contains gallium. Gallium belongs to the same Group 13 element as indium. Therefore, the crystallinity of the oxide semiconductor layer 140 is not inhibited by gallium, and the oxide semiconductor layer 140 has a polycrystalline structure.

[0056] The oxide semiconductor layer 140 can be formed by 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 if 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 composition of the metal elements of the oxide semiconductor layer 140 can be specified based on the composition of the metal elements of the sputtering target.

[0057] When the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the oxide semiconductor layer may be identified by X-ray diffraction (XRD). Specifically, the composition of the metal elements in the oxide semiconductor layer can be identified based on the crystal structure and lattice constant of the oxide semiconductor layer obtained by XRD. Furthermore, the composition of the metal elements in the oxide semiconductor layer 140 can also be identified by fluorescent X-ray analysis or Electron Probe Micro Analyzer (EPMA) analysis. However, the oxygen element contained in the oxide semiconductor layer 140 may not be identified by these methods because it varies depending on the process conditions of sputtering.

[0058] [1-3. Method for forming oxide layer 150] As described above, the oxide layer 150 included in the radiation detection device 10 according to this embodiment includes a first region in the vicinity of the oxide semiconductor layer 140, in which the number of hole traps is relatively small, and a second region located above the first region, in which the number of hole traps is relatively large. The difference between the oxide layer 150 in the first region and the second region is due to the film formation method.

[0059] The film formation steps in forming a silicon oxide layer as the oxide layer 150 include the following steps (1) and (2). The oxide layer 150 in the first region is formed in step (1), and the oxide layer 150 in the second region is formed in step (2). (1) Interface formation treatment (2) Bulk formation process

[0060] (1) The conditions for the interface formation treatment are as follows: ·SiH4 / N2O flow rate=3 / 1000sccm Chamber pressure = 200Pa ·RF power=20W ·F ratio (RF / SiH4)=6.7 ·Deposition film thickness=10nm

[0061] (2) The processing conditions for the bulk formation process are as follows: ·SiH4 / N2O flow rate=10 / 1000sccm Chamber pressure = 333Pa ·RF power=200W ·F ratio (RF / SiH4)=10.0 · Film thickness = arbitrary

[0062] In this embodiment, the electrode size of the CVD apparatus in which the oxide layer 150 was formed was a circle with a radius of 9 cm, and the area of ​​the electrode was 254 cm. 2 Therefore, the power density of the RF power (20 W) under the interface formation treatment condition (1) is 0.079 W / cm 2 (2) The power density of the RF power (200 W) under the bulk formation processing conditions is 0.79 W / cm 2 It is.

[0063] As described above, regarding the deposition power (RF power) in the sputtering method, the RF power (20 W) in the deposition of the oxide layer 150 in the first region is lower than the RF power (200 W) in the deposition of the oxide layer 150 in the second region. Similarly, the ratio of SiH4 gas to N2O gas (3 / 1000) in the deposition of the oxide layer 150 in the first region is lower than the ratio of SiH4 gas to N2O gas (10 / 1000) in the deposition of the oxide layer 150 in the second region. Similarly, the ratio of RF power to SiH4 gas (6.7) in the deposition of the oxide layer 150 in the first region is lower than the ratio of RF power to SiH4 gas (10) in the deposition of the oxide layer 150 in the second region.

[0064] As described above, by forming the oxide layer 150 in the first region in contact with the oxide semiconductor layer 140 with low power, an oxide layer with fewer hole traps can be formed as the oxide layer 150 near the oxide semiconductor layer 140. In addition, as will be described in detail later, by making the thickness of the oxide layer 150 100 nm or less or 50 nm or less, the amount of hole traps contained in the oxide layer 150 can be reduced. As a result, it is possible to suppress the characteristic fluctuation of the transistor 20 caused by holes generated in the oxide semiconductor layer 140 by the incidence of radiation being trapped in the oxide layer 150.

[0065] [1-4. Reliability test results of transistor 20] Fig. 3 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. The reliability test shown in Fig. 3 is the result of a reliability test for Negative Bias Temperature Illumination Stress (NBTIS). In Fig. 3, the electrical characteristics of the transistor 20 before NBTIS in each of Example 1 and Comparative Example 1 are shown by dotted lines, and the electrical characteristics after NBTIS are shown by solid lines.

[0066] The conditions of the NBTIS reliability test are as follows: Channel area size: W / L=3.0μm / 3.0μm Light irradiation conditions: With irradiation (7000lx) Gate voltage: -30V Source and drain voltage: 0V Stage temperature when stress is applied: 85℃ Stress application time: 1000 sec

[0067] The structures of the transistors according to Example 1 and Comparative Example 1 for which the reliability test of FIG. 3 was performed are as follows. Gate insulation layer 110\120: SiN\SiO=300\10nm Oxide semiconductor layer 140: 30 nm (polycrystalline) Oxide layer 150\insulation layer 160: SiO\SiN=300\100nm

[0068] The deposition conditions for the oxide layer 150 in the transistor 20 according to Example 1 are as shown in the above steps (1) and (2). On the other hand, the deposition conditions for the oxide layer in the transistor according to Comparative Example 1 are different from those in Example 1 in step (1).

[0069] (1') The conditions for the interface formation treatment in Comparative Example 1 were as follows. ·SiH4 / N2O flow rate=10 / 1000sccm Chamber pressure = 200Pa ·RF power=100W ·F ratio (RF / SiH4)=10.0 ·Deposition film thickness=10nm

[0070] As described above, the processing conditions of the interface film formation process in Comparative Example 1 have a higher RF power in film formation, a higher ratio of SiH4 gas to N2O gas, and a higher ratio of RF power to SiH4 gas, compared to the processing conditions of the interface film formation process in Example 1. The amount of hole traps in the oxide layer formed under these conditions is greater than the amount of hole traps in the oxide layer 150 in Example 1. In the following description, the above processing conditions (1) may be referred to as low-power film formation, and the processing conditions (1') may be referred to as conventional condition film formation.

[0071] 3, the threshold change before and after NBTIS of the transistor 20 in accordance with Example 1 is smaller than the threshold change before and after NBTIS of the transistor in accordance with Comparative Example 1. This result is due to the fact that the amount of hole traps contained in the oxide layer 150 in accordance with Example 1 is smaller than the amount of hole traps contained in the oxide layer in accordance with Comparative Example 1.

[0072] 4 and 5 are diagrams showing reliability test results against radiation of a transistor used in a radiation detection device according to an embodiment of the present invention. The reliability test shown in FIG. 4 is the result of an X-ray irradiation test. In FIG. 4, the electrical characteristics of the transistor 20 before X-ray irradiation are shown by a dotted line, and the electrical characteristics after X-ray irradiation are shown by a solid line. Three results (#1 to #3) of the X-ray irradiation test of Example 1 and Comparative Example 1 are shown. The structures of the transistors according to Example 1 and Comparative Example 1 that were subjected to the X-ray irradiation test of FIG. 4 are the same as those of FIG. 3. The bar graph shown in FIG. 5 shows the amount of change before and after the reliability test for the threshold voltage Vth obtained from the electrical characteristics of FIG. 4.

[0073] The conditions for the X-ray irradiation test are as follows: Channel area size: W / L=3.0μm / 3.0μm X-ray irradiation equipment: MBR-1520R-3 (Hitachi Power Solutions) X-ray irradiation conditions: 30Gy, 60Gy, 90Gy (20mA continuous irradiation) X-ray irradiation conditions: Filter Al=1mm

[0074] As shown in FIG. 4 and FIG. 5, the threshold fluctuation before and after the X-ray irradiation test of the transistor 20 according to Example 1 is smaller than the threshold fluctuation before and after the X-ray irradiation test of the transistor according to Comparative Example 1. This result is similar to that of 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, a similar tendency is confirmed in NBTIS and the X-ray irradiation test. The reason why the same tendency is confirmed is thought to be that the threshold fluctuation in NBTIS and the threshold fluctuation in the X-ray irradiation test are both due to holes generated by light irradiation or X-ray irradiation being trapped in the oxide layer 150.

[0075] As described above, a correlation between the threshold shift in the NBTIS and the threshold shift in the X-ray irradiation test was confirmed, so hereafter, only the results of the NBTIS are shown.

[0076] Fig. 6 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. The reliability test results shown in Fig. 6 are the results of evaluating the variation in threshold voltage Vth due to NBTIS for samples with different structures. Fig. 6 shows Example 2, in which reliability is improved by thinning the oxide layer 150, and Comparative Examples 2 to 5.

[0077] The samples of Example 2 and Comparative Examples 2 to 5 shown in FIG. 6 have the following common structure. Oxide semiconductor layer 140: 30 nm (polycrystalline) Conditions for forming the oxide layer 150: steps (1') and (2)

[0078] Regarding the samples shown in FIG. 6, the structures that differ for each sample are as follows. [Gate insulation layer 110\120] ·Comparative example 2: SiN\SiO=300\100nm ·Comparative example 3: SiN\SiO=300\50nm ·Comparative example 4: SiN\SiO=300\30nm ·Comparative example 5: SiN\SiO=300\10nm Example 2: SiN\SiO=300\30nm [Oxide layer 150 \ Insulation layer 160] ·Comparative example 2: SiO\SiN=300\100nm ·Comparative example 3: SiO\SiN=300\100nm ·Comparative example 4: SiO\SiN=300\100nm ·Comparative example 5: SiO\SiN=300\100nm Example 2: SiO\SiN=50\100nm

[0079] As shown in FIG. 6, the variation in threshold voltage Vth in Example 2 is smaller than that in Comparative Examples 2 to 5. In other words, it is found that the thickness of the oxide layer 150 has a large effect on the variation in threshold voltage Vth. On the other hand, it is found that the thickness of the gate insulating layers 110 and 120 has a small effect on the variation in threshold voltage Vth. As shown in FIG. 6, when the thickness of the oxide layer 150 is 50 nm or less, the effect of improving reliability by NBTIS can be obtained. Similar to this result, when the thickness of the oxide layer 150 is 50 nm or less, the effect of improving reliability by X-ray irradiation test can be obtained.

[0080] Fig. 7 is a diagram showing the results of a reliability test for visible light of a transistor used in a radiation detection device according to one embodiment of the present invention. The reliability test results shown in Fig. 7 are the results of evaluating the variation in threshold voltage Vth due to NBTIS for samples with different structures. Fig. 7 shows Examples 3 to 6 in which reliability was improved by low-power deposition and thinning of the oxide layer 150.

[0081] The samples of Examples 3 to 6 shown in FIG. 7 have the following common structure. Oxide semiconductor layer 140: 30 nm (polycrystalline) Conditions for forming the oxide layer 150: steps (1) and (2)

[0082] Regarding the samples shown in FIG. 7, the structures that differ for each sample are as follows. [Gate insulation layer 110\120] Example 3: SiN\SiO=300\50nm Example 4: SiN\SiO=300\50nm Example 5: SiN\SiO=300\30nm Example 6: SiN\SiO=300\10nm [Oxide layer 150 \ Insulation layer 160] Example 3: SiO\SiN=300\100nm Example 4: SiO\SiN=100\100nm Example 5: SiO\SiN=50\100nm Example 6: SiO\SiN=50\100nm

[0083] As shown in FIG. 7, in all of Examples 3 to 6, the oxide layer 150 is formed under low power deposition conditions. Therefore, under all conditions, the variation in threshold voltage Vth is smaller than that in the results of FIG. 6. Among them, when Example 3 is compared with Examples 4 to 6, it is found that the variation in threshold voltage Vth is smaller when the thickness of the oxide layer 150 is reduced from 300 nm to 100 nm. In other words, when the oxide layer 150 is formed under low power deposition conditions, 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, and the effect of improving reliability by NBTIS can be obtained. Similar to this result, when the thickness of the oxide layer 150 is 100 nm or less, the effect of improving reliability by X-ray irradiation test can be obtained.

[0084] The above-described embodiments of the present invention may be combined as appropriate as long as they are not mutually inconsistent. Furthermore, those in which a person skilled in the art appropriately adds or removes components or modifies designs, or adds or omits steps or modifies conditions, based on the transistor and radiation detection device of each embodiment are included in the scope of the present invention as long as they include the gist of the present invention.

[0085] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those which are clear from the description in this specification or which can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0086] 10: radiation detection device, 20: transistor, 30: pixel, 100: substrate, 105: gate electrode, 109: gate control line, 110: gate insulating layer, 120: gate insulating layer, 130: metal oxide layer, 140: oxide semiconductor layer, 150: oxide layer, 160: insulating layer, 161: opening, 200: source-drain electrode, 201: source electrode, 203: drain electrode, 209: wiring, 210: light shielding layer, 220: connection wiring, 230: insulating layer, 231: opening, 300: photoelectric conversion layer, 309: wiring, 310: lower electrode, 320: upper electrode, 330: insulating layer, 331: opening, 340: insulating layer, 341: opening, 350: wiring, 360: wiring, 400: wavelength conversion layer, 500: charge amplifier circuit

Claims

1. a transistor including an oxide semiconductor layer as a channel; A photoelectric conversion layer connected to the transistor; a wavelength conversion layer facing the photoelectric conversion layer and emitting visible light based on absorbed radiation; an oxide layer having a thickness of 50 nm or less, the oxide layer being between the transistor and the photoelectric conversion layer and in contact with the oxide semiconductor layer.

2. the transistor includes a gate electrode layer facing the oxide semiconductor layer and a gate insulating layer between the oxide semiconductor layer and the gate electrode layer; The radiation detection device according to claim 1 , wherein the oxide semiconductor layer is closer to the photoelectric conversion layer than the gate electrode layer.

3. The radiation detection device of claim 1 , wherein the oxide layer is a silicon oxide layer.

4. The radiation detection device of claim 1 , wherein the oxide layer is 30 nm or less.

5. the oxide layer includes a first region and a second region; the first region is in contact with the oxide semiconductor layer, 5. The radiation detection device of claim 1, wherein the oxide layer in the first region is thinner than the oxide layer in the second region.

6. The radiation detection device of claim 5 , wherein the oxide layer in the first region has fewer hole traps than the oxide layer in the second region.

7. 6. The radiation detection device according to claim 5, wherein the oxide layer in the first region is a layer formed under conditions of a lower deposition power in a sputtering method than the oxide layer in the second region.

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