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. In particular, one embodiment of the present invention relates to a radiation detection device including a semiconductor device in which an oxide semiconductor is used as a channel.

Background Art

[0002] In recent years, development of semiconductor devices in which an oxide semiconductor is used as a channel has been promoted in place of amorphous silicon, low-temperature polysilicon, and single-crystalline silicon (for example, Patent Documents 1 to 6). A semiconductor device in which an oxide semiconductor is used as a channel can be formed with a simple structure and a low-temperature process, similarly to a semiconductor device in which amorphous silicon is used as a channel. A semiconductor device in which an oxide semiconductor is used as a channel is known to have higher mobility than a semiconductor device in which amorphous silicon is used as a channel.

[0003] In order for a semiconductor device in which an oxide semiconductor is used as a channel to operate stably, it is important to supply oxygen to the oxide semiconductor layer in its manufacturing process to reduce oxygen deficiencies formed in the oxide semiconductor layer. As one method of supplying oxygen to the oxide semiconductor layer, for example, a technique of forming an insulating layer covering the oxide semiconductor layer under conditions where the insulating layer contains more oxygen has been disclosed.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

[0005] However, an insulating layer formed under conditions containing more oxygen contains many defects. Due to this influence, characteristic variations of semiconductor devices in reliability tests are caused, presumably because holes are trapped in the defects. When a semiconductor device with hole trapping is used as a detection device for radiation, characteristic variations of the semiconductor device occur due to holes generated by the radiation being trapped. Suppression of such characteristic variations has been required.

[0006] One of the embodiments of the present invention aims to realize a highly reliable radiation detection device. [Means for Solving the Problems]

[0007] A radiation detection device according to an embodiment of the present invention includes a transistor in which an oxide semiconductor layer is 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 the absorbed radiation, and an oxide layer having a thickness of 50 nm or less and in contact with the oxide semiconductor layer between the transistor and the photoelectric conversion layer. [Brief Description of the Drawings]

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0009] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. The following disclosure is merely an example. Configurations that can be easily conceived by those skilled in the art by appropriately changing the configuration of the embodiment while maintaining the gist of the invention are naturally included in the scope of the present invention. For the sake of clarity in the explanation, the drawings may be schematically represented in terms of the width, thickness, shape, etc. of each part compared to the actual aspect. However, the illustrated shape is merely an example and does not limit the interpretation of the present invention. In this specification and each figure, components having the same configuration as those described above with respect to the previously shown figures may be denoted by the same reference numerals, and detailed descriptions 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 upward. Conversely, the direction from the oxide semiconductor layer toward the substrate is referred to as down or downward. Thus, for the sake of convenience in explanation, the terms upward or downward are used, but for example, the vertical relationship between the substrate and the oxide semiconductor layer may be arranged in a direction different from that shown in the drawing. In the following description, for example, the expression an oxide semiconductor layer on a substrate merely explains the vertical relationship between the substrate and the oxide semiconductor layer as described above, and other members may be arranged between the substrate and the oxide semiconductor layer. Upward or downward means the stacking order in a structure in which a plurality of layers are stacked. When expressing the first member above the transistor, in a plan view, the positional relationship may be such that the transistor and the first member do not overlap. On the other hand, when expressing the first member directly above the transistor in the vertical direction, in a plan view, it means the positional relationship in which the transistor and the first member overlap.

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

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

[0013] [1. First Embodiment] With reference to FIGS. 1 and 2, a radiation detection device 10 according to an embodiment of the present invention will be described.

[0014] [1-1. Configuration of Radiation Detection Device 10] With reference to FIGS. 1 and 2, the configuration of a radiation detection device 10 according to an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing an outline of a radiation detection device according to an embodiment of the present invention. FIG. 2 is a circuit diagram showing an outline of a radiation detection device according to an embodiment of the present invention.

[0015] As shown in FIG. 1, the radiation detection device 10 is provided on the 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 members, the radiation detection device 10 includes an insulating layer 160, a light-shielding layer 210, connection wiring 220, an insulating layer 230, a lower electrode 310, an upper electrode 320, insulating layers 330, 340, and wirings 350, 360.

[0016] The transistor 20 includes a gate electrode 105, gate insulating layers 110, 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 above-described transistor may be interchanged. When the source electrode 201 and the drain electrode 203 are not particularly distinguished, they may be collectively referred to as a source-drain electrode 200. In the present 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 the present embodiment, a bottom-gate type transistor in which the oxide semiconductor layer 140 is closer to the photoelectric conversion layer 300 than the gate electrode 105 is exemplified as the radiation detection device 10, but the radiation detection device 10 is not limited to a bottom-gate type transistor. For example, the radiation detection device 10 may be a dual-gate type 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. On the oxide semiconductor layer 140, a source electrode 201 and a drain electrode 203 are provided. 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 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. It can be said that the oxide layer 150 is provided between the transistor 20 and the photoelectric conversion layer 300.

[0020] The film 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. The film 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. The total film 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.

[0021] The film 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, aluminum oxide is used as the metal oxide layer 130. Aluminum oxide has a high barrier property against gases such as oxygen or hydrogen. The barrier property means a function of suppressing the permeation of gases such as oxygen or hydrogen through aluminum oxide. That is, even if a gas such as oxygen or hydrogen is released from the layer provided under the aluminum oxide film, the gas does not move to the layer provided above the aluminum oxide film. Or, even if a gas such as oxygen or hydrogen is released from the layer provided above the aluminum oxide film, the gas does not move to the layer provided under the aluminum oxide film.

[0022] The film 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. The film thickness of the oxide layer 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.

[0023] The film 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. By the thickness of the oxide layer 150 being in the above range, as will be described later, the reliability of the transistor 20 with respect to visible light and radiation is improved.

[0024] The film 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.

[0025] 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 plan view. In 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 formed 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.

[0026] 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 is in contact with the source electrode 201 at the bottom of the opening 161.

[0027] 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 ends of the light-shielding layer 210 and the connection wiring 220. The insulating layer 230 relaxes the step formed by the light-shielding layer 210 and the connection wiring 220. The insulating layer 230 can be referred to as a planarization 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.

[0028] A lower electrode 310 is provided on the insulating layer 230 and inside the opening 231. The lower electrode 310 is in contact with 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 is in contact with the lower electrode 310, and the other is in contact with the upper electrode 320.

[0029] 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 through the N-type semiconductor layer and the P-type semiconductor layer to the lower electrode 310 and the upper electrode 320. By detecting the current generated by the electrons and holes generated by photoexcitation, the intensity of the light irradiated on the photoelectric conversion layer 300 can be detected.

[0030] 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 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 relaxes the step. That is, the insulating layer 340 is a planarization layer.

[0031] A wiring 360 is provided on the insulating layer 340 and in a region that does not overlap with the photoelectric conversion layer 300 in plan view. A wiring 350 is provided on the insulating layer 340, on the wiring 360, and inside the opening 341. The wiring 350 is in contact with the upper electrode 320 at the bottom of the opening 341.

[0032] Although details will be described later, a transparent conductive layer is used as the upper electrode 320 and the wiring 350 so that the visible light emitted from the wavelength conversion layer 400 can reach the photoelectric conversion layer 300 efficiently. 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.

[0033] 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 adhered to the wiring 350 and the insulating layer 340 by an adhesive layer, or the positional relationship with the wiring 350 and the insulating layer 340 may be fixed by other fixing members. The wavelength conversion layer 400 has a function of converting 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 can be called a scintillator.

[0034] 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, 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.

[0035] As shown in FIG. 2, pixels 30 are arranged in a matrix in the radiation detection device 10. The pixel 30 includes a transistor 20 and a photoelectric conversion layer 300. The gate electrode of the transistor 20 is connected to the gate control line 109. The source electrode 201 of the transistor 20 is connected to the cathode of the photoelectric conversion layer 300. The anode of the photoelectric conversion layer 300 is connected to the wiring 309. The drain electrode 203 of the transistor 20 is connected to the wiring 209. The wiring 209 is connected to the charge amplifier circuit 500.

[0036] 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 supplying a bias voltage to the wiring 309 connected to the pixel 30 that detects the radiation and controlling the gate control line 109 connected to the pixel 30 to be in 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 the charge signal into a voltage signal, and the voltage signal is output to the outside. By the above operation, the intensity of the radiation irradiated on the pixel 30 can be evaluated.

[0037] As shown in FIG. 1, ideally, all the radiation incident from above is absorbed by the wavelength conversion layer 400. However, in reality, a part of the radiation passes through the wavelength conversion layer 400. Further, ideally, the radiation that has passed through the wavelength conversion layer 400 is blocked by the light shielding layer 210. However, in reality, the radiation bypasses the light shielding layer 210 due to reflection by other members and reaches the oxide semiconductor layer 140. When the radiation enters the oxide semiconductor layer 140, electron-hole pairs are generated in the oxide semiconductor layer 140. Since hole traps are 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, there may occur a problem that the electrical characteristics of the transistor 20 shift in the negative direction.

[0038] [1-2. Materials of Each Member of the Radiation Detection Device 10] As the substrate 100, a rigid substrate having translucency, such as a glass substrate, a quartz substrate, and a sapphire substrate, is used. When the substrate 100 needs to have flexibility, a substrate containing a resin, such as a polyimide substrate, an acrylic substrate, a siloxane substrate, and 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 above resin in order to improve the heat resistance of the substrate 100. A substrate that does not have translucency, such as a semiconductor substrate such as a silicon substrate, a silicon carbide substrate, and a compound semiconductor substrate, or a conductive substrate such as a stainless steel substrate, may be used as the substrate 100.

[0039] As the gate electrode 105, source / drain electrodes 200, light-shielding layer 210, connection wiring 220, lower electrode 310, and wiring 360, common metal materials are used. For example, as these members, 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 their alloys or compounds are used. As these electrodes and wirings, the above materials may be used in a single layer or in a laminated structure. When the light-shielding layer 210 does not need to have conductivity, a black resin may be used as the light-shielding layer 210.

[0040] As the upper electrode 320 and wiring 350, a transparent conductive layer is used. As the transparent conductive layer, 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, materials other than the above may be used.

[0041] As the gate insulating layers 110, 120, oxide layer 150, insulating layers 160, 330, common insulating materials are used. For example, as the gate insulating layer 120 and oxide layer 150, inorganic insulating layers containing oxygen such as silicon oxide (SiO x ), silicon oxynitride (SiO x N y ), aluminum oxide (AlO x ), aluminum oxynitride (AlO x N y ) are used. As the gate insulating layer 110 and insulating layer 160, silicon nitride (SiN x ), silicon oxynitride (SiN x O y ), aluminum nitride (AlN x ), aluminum oxynitride (AlN x O yAn inorganic insulating layer containing nitrogen such as etc. is used. However, as the gate insulating layer 110 and the insulating layer 160, an inorganic insulating layer containing oxygen as described above may be used. As the gate insulating layer 120 and the oxide layer 150, an inorganic insulating layer containing nitrogen as described above may be used.

[0042] As the oxide layer 150, an insulating layer having a function of releasing oxygen by heat treatment is used. That is, as the oxide layer 150, an oxide insulating layer containing an excessive amount of oxygen is used. The temperature of the heat treatment in which the oxide layer 150 releases oxygen is, for example, 600 °C or lower, 500 °C or lower, 450 °C or lower, or 400 °C or lower. That is, the oxide layer 150 releases oxygen at the heat treatment temperature performed in the manufacturing process of the transistor 20 when a glass substrate is used as the substrate 100, for example.

[0043] Details will be described later, but the film quality of the oxide layer 150 varies depending on the film thickness direction. Specifically, the oxide layer 150 near the oxide semiconductor layer 140 has a smaller amount of hole traps than the other oxide layers 150. For the sake of convenience of explanation, among the oxide layers 150, the region near the oxide semiconductor layer 140 may be referred to as the first region, and the other regions may be referred to as the 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.

[0044] As the gate insulating layer 120, an insulating layer with few defects is used. 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 "other insulating layer"), the oxygen composition ratio in the gate insulating layer 120 is closer to the stoichiometric ratio with respect to the insulating layer than the oxygen composition ratio in the other insulating layer. Specifically, silicon oxide (SiO x) When used, the oxygen composition ratio in the silicon oxide used as the gate insulating layer 120 is closer to the stoichiometric ratio of silicon oxide than the oxygen composition ratio in the silicon oxide used as the oxide layer 150. For example, as the gate insulating layer 120, a layer in which no defects are observed when evaluated by the electron spin resonance method (ESR) may be used.

[0045] The above SiO x N y and AlO x N y are silicon compounds and aluminum compounds containing nitrogen (N) in a ratio less than that of oxygen (x>y). SiN x O y and AlN x O y are silicon compounds and aluminum compounds containing oxygen in a ratio less than that of nitrogen (x>y).

[0046] As the insulating layers 230 and 340, an organic insulating layer is used. For example, as the organic insulating layer, a polyimide resin, an acrylic resin, an epoxy resin, a silicone resin, a fluororesin, and a siloxane resin are used.

[0047] As the metal oxide layer 130, a metal oxide mainly composed of aluminum is used. For example, as the metal oxide layer 130, an inorganic insulating layer such as aluminum oxide (AlO x ), aluminum oxynitride (AlO x N y ) is used. "The metal oxide layer 130 mainly composed of aluminum" means that the ratio of aluminum contained in the metal oxide layer 130 is 1% or more of the entire metal oxide layer. The ratio 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 above ratio may be a mass ratio or a weight ratio.

[0048] As the oxide semiconductor layer 140, a metal oxide having semiconductor characteristics can be used. The oxide semiconductor layer 140 has a polycrystalline structure. 。

[0049] 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 the sputtering target. 。This In this case, the composition of the metal elements in the oxide semiconductor layer 140 can be specified based on the composition of the metal elements in the sputtering target.

[0050] When the oxide semiconductor layer 140 has a polycrystalline structure, the composition of the oxide semiconductor layer may be specified using an X-ray Diffraction (XRD) method. Specifically, based on the crystal structure and lattice constant of the oxide semiconductor layer obtained by the XRD method, the composition of the metal elements in the oxide semiconductor layer can be specified. Furthermore, the composition of the metal elements in the oxide semiconductor layer 140 can also be specified using fluorescence X-ray analysis or Electron Probe Micro Analyzer (EPMA) analysis, etc. However, since the oxygen element contained in the oxide semiconductor layer 140 changes depending on the sputtering process conditions, etc., there may be cases where it cannot be specified by these methods.

[0051] [1-3. Film formation method of oxide layer 150] 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 a first region with relatively few hole traps and a second region located above the first region and having relatively many hole traps. The difference in the oxide layer 150 between the first region and the second region is due to its film formation method.

[0052] When forming a silicon oxide layer as the oxide layer 150, the film formation steps include the following steps (1) to (2). The oxide layer 150 in the first region is formed by the step (1), and the oxide layer 150 in the second region is formed by the step (2). (1) Interface formation process (2) Bulk formation process

[0053] (1) The processing conditions for the 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 of film formation = 10 nm

[0054] (2) The processing conditions for the bulk 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 of film formation = arbitrary

[0055] In addition, in this embodiment, the electrode size of the CVD apparatus for forming the oxide layer 150 is a circle with a radius of 9 cm, and the area of the electrode is 254 cm 2 is. Therefore, the power density of the RF power (20 W) under the conditions of the (1) interface formation process is 0.079 W / cm 2 is. The power density of the RF power (200 W) under the conditions of the (2) bulk formation process is 0.79 W / cm 2 is.

[0056] As described above, regarding the film formation power (RF power) in the sputtering method, the RF power (20 W) in the film formation of the oxide layer 150 in the first region is lower than the RF power (200 W) in the film formation of the oxide layer 150 in the second region. Similarly, the ratio of SiH4 gas to N2O gas (3 / 1000) in the film formation of the oxide layer 150 in the first region is smaller than the ratio of SiH4 gas to N2O gas (10 / 1000) in the film formation of the oxide layer 150 in the second region. Similarly, the ratio of RF power to SiH4 gas (6.7) in the film formation of the oxide layer 150 in the first region is smaller than the ratio of RF power to SiH4 gas (10) in the film formation of the oxide layer 150 in the second region.

[0057] As described above, by forming the oxide layer 150 in the first region in contact with the oxide semiconductor layer 140 at a low power, an oxide layer with few hole traps can be formed as the oxide layer 150 near the oxide semiconductor layer 140. Further, although details will be described later, by setting the film thickness of the oxide layer 150 to 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 characteristic variations of the transistor 20 caused by holes generated in the oxide semiconductor layer 140 being trapped in the oxide layer 150 due to the incidence of radiation.

[0058] [1-4. Reliability test results of transistor 20] FIG. 3 is a diagram showing the results of a reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention with respect to visible light. 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 for each of Example 1 and Comparative Example 1 are indicated by dotted lines, and the electrical characteristics after NBTIS are indicated by solid lines.

[0059] The conditions of the NBTIS reliability test are as follows. · Size of channel region: W / L = 3.0 μm / 3.0 μm · Light irradiation condition: With irradiation (7000 lx) · Gate voltage: -30 V · Source and drain voltages: 0 V · Stage temperature during stress application: 85 °C · Stress application time: 1000 sec

[0060] The structures of the transistors according to Example 1 and Comparative Example 1, in which the reliability test of FIG. 3 was performed, are all as follows. · Gate insulating layers 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

[0061] The film formation conditions of the oxide layer 150 in the transistor 20 according to Example 1 are as shown in the steps (1) to (2) above. On the other hand, the film formation conditions of the oxide layer in the transistor according to Comparative Example 1 are different from those of Example 1 in the step (1).

[0062] (1’) The processing conditions of the interface formation treatment 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 formation thickness = 10 nm

[0063] As described above, the processing conditions of the interface film formation treatment of Comparative Example 1 have a higher RF power in film formation, a larger ratio of SiH4 gas to N2O gas, and a larger ratio of RF power to SiH4 gas compared to the processing conditions of the interface film formation treatment of Example 1. The amount of hole traps in the oxide layer formed under this condition is larger than the amount of hole traps in the oxide layer 150 of Example 1. In the following description, the processing conditions of (1) above may be referred to as low-power film formation, and the processing conditions of (1’) may be referred to as conventional-condition film formation.

[0064] As shown in FIG. 3, the threshold voltage variation before and after NBTIS of the transistor 20 according to Example 1 is smaller than the threshold voltage variation before and after 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.

[0065] FIGS. 4 and 5 are diagrams 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. 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 indicated by a dotted line, and the electrical characteristics after X-ray irradiation are indicated by a solid line. The results of the X-ray irradiation tests of Example 1 and Comparative Example 1 are shown in three each (#1 to #3). The structures of the transistors according to Example 1 and Comparative Example 1 that underwent the X-ray irradiation test in FIG. 4 are the same as those in FIG. 3. The bar graph shown in FIG. 5 shows the amount of variation in the threshold voltage Vth obtained from the electrical characteristics in FIG. 4 before and after the reliability test.

[0066] The conditions of the X-ray irradiation test are as follows. · Size of channel region: W / L = 3.0 μm / 3.0 μm · X-ray irradiation device: MBR-1520R-3 (manufactured by Hitachi Power Solutions) · X-ray irradiation conditions: 30 Gy, 60 Gy, 90 Gy (continuous irradiation at 20 mA) · X-ray irradiation conditions: Filter Al = 1 mm

[0067] As shown in FIGS. 4 and 5, the threshold voltage variation of the transistor 20 according to Example 1 before and after the X-ray irradiation test is smaller than that of the transistor according to Comparative Example 1 before and after the X-ray irradiation test. This result is the same as the result 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, the same tendency is confirmed in NBTIS and the X-ray irradiation test. The reason why the same tendency is confirmed is considered to be that the threshold voltage variation in NBTIS and the threshold voltage variation in the X-ray irradiation test are both caused by holes generated by light irradiation or X-ray irradiation being trapped in the oxide layer 150.

[0068] As described above, since the correlation between the threshold voltage variation in NBTIS and the threshold voltage variation in the X-ray irradiation test is confirmed, hereinafter, only the results of NBTIS are shown.

[0069] FIG. 6 is a diagram showing the results of a reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention with respect to visible light. The reliability test results shown in FIG. 6 are the results of evaluating the variation of the threshold voltage Vth by NBTIS for samples with different structures. FIG. 6 shows Example 2 in which the reliability is improved by thinning the oxide layer 150 and Comparative Examples 2 to 5 thereof.

[0070] Regarding the samples of Example 2 and Comparative Examples 2 to 5 shown in FIG. 6, the common structure is as follows. · Oxide semiconductor layer 140: 30 nm (polycrystalline) · Film formation conditions of the oxide layer 150: steps (1’) and (2)

[0071] Regarding the samples shown in FIG. 6, the different structures for each sample are as follows. [Gate insulating layers 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

[0072] As shown in FIG. 6, the variation in the threshold voltage Vth of Example 2 is smaller than that of Comparative Examples 2 to 5. That is, it can be seen that the film thickness of the oxide layer 150 greatly affects the variation in the threshold voltage Vth. On the other hand, it can be seen that the film thicknesses of the gate insulating layers 110 and 120 have little effect on the variation in the threshold voltage Vth. As shown in FIG. 6, when the film thickness of the oxide layer 150 is 50 nm or less, the effect of improving the reliability by NBTIS can be obtained. Similarly to this result, when the film thickness of the oxide layer 150 is 50 nm or less, the effect of improving the reliability by the X-ray irradiation test can be obtained.

[0073] FIG. 7 is a diagram showing the results of a reliability test of a transistor used in a radiation detection device according to an embodiment of the present invention with respect to visible light. The reliability test results shown in FIG. 7 are the results of evaluating the variation in the threshold voltage Vth by NBTIS for samples with different structures. FIG. 7 shows Examples 3 to 6 in which the reliability is improved by low-power film formation and thinning of the oxide layer 150.

[0074] Regarding the samples of Examples 3 to 6 shown in FIG. 7, the common structure is as follows. · Oxide semiconductor layer 140: 30 nm (polycrystalline) · Film formation conditions of the oxide layer 150: Steps (1) and (2)

[0075] Regarding the samples shown in FIG. 7, the different structures for each sample are as follows. [Gate insulating layers 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

[0076] As shown in FIG. 7, in Examples 3 to 6, the film formation conditions of the oxide layer 150 are all low-power film formation. Therefore, under all conditions, the variation in the threshold voltage Vth is smaller than that in the result of FIG. 6. Among them, when comparing Example 3 with Examples 4 to 6, it can be seen that as the film thickness of the oxide layer 150 decreases from 300 nm to 100 nm, the variation in the threshold voltage Vth becomes smaller. That is, when the film formation conditions of the oxide layer 150 are low-power film formation, by making the film thickness of the oxide layer 150 100 nm or less, the amount of hole traps contained in the oxide layer 150 can be reduced, and the effect of improving the reliability due to NBTIS can be obtained. Similarly to this result, when the film thickness of the oxide layer 150 is 100 nm or less, the effect of improving the reliability by the X-ray irradiation test can be obtained.

[0077] Each of the embodiments described above as embodiments of the present invention can be implemented in appropriate combination as long as they do not contradict each other. Further, based on the transistors and radiation detection devices of each embodiment, those in which a person skilled in the art appropriately adds, deletes, or changes the design of components, or adds, omits, or changes the conditions of the process, are also included in the scope of the present invention as long as they have the gist of the present invention.

[0078] Even if there are other operational effects different from those brought about by the aspects of the above-described embodiments, those that are obvious from the description in this specification or can be easily predicted by those skilled in the art are naturally construed as being brought about by the present invention.

Description of Reference Numerals

[0079] 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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