Neutron detection element

Abstract

This neutron detection element (100) is provided with: a neutron detection part which detects a neutron and converts the neutron into an electrical signal; and an amplifier part which amplifies the output of the neutron detection part. The neutron detection part comprises: a semiconductor layer of a first conductivity type; a detection part diffusion layer of a second conductivity type, said detection part diffusion layer being formed in the semiconductor layer; and a neutron conversion layer which is formed on the detection part diffusion layer and convers a neutron into an α-ray. The amplifier part comprises a plurality of transistors that are formed in the semiconductor layer. The neutron conversion layer is a metal film that has a layer containing boron 10 or a layer containing lithium 6.

Description

[Technical Field]

[0001] This disclosure relates to a neutron detection element and a neutron two-dimensional sensor. [Background technology]

[0002] Neutrons are particles with no electric charge and have the property of passing through various materials. For this reason, they are used in neutron radiography to observe the inside of materials. When using neutrons for internal observation or treatment, it is important to detect the neutrons that have passed through.

[0003] Furthermore, research is being conducted on using neutrons in cancer treatment, such as in Boron Neutron Capture Therapy (BNCT). In such cases, it is also important to detect how the irradiated neutrons are absorbed.

[0004] Methods for detecting neutrons include gas discharge, scintillation, and imaging plate methods. In recent years, semiconductor-based neutron detection elements have also been investigated (see, for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2012-181065 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Conventional semiconductor neutron detectors generate charged particles from neutrons and detect the generated charged particles. When generating charged particles from neutrons, the neutrons are converted into boron-10( 10B) etc. are incident to generate helium nuclei (alpha rays) and lithium nuclei (Li particle beams). When alpha rays and Li particle beams are incident on the depletion layer, electron-hole pairs are generated, and neutrons can be detected by measuring the current caused by the generated electron-hole pairs. However, neutrons 10 When B is incident, alpha particles and Li particles are emitted in opposite directions, so the depletion layer will be affected by either alpha particles or Li particles. Since the amount of charge generated in the depletion layer differs depending on whether alpha particles or Li particles are incident, the output of the detector will fluctuate depending on the incident charged particle beam.

[0007] The objective of this disclosure is to realize a neutron detection element made of semiconductors that is less susceptible to output fluctuations. [Means for solving the problem]

[0008] One embodiment of the neutron detection element of the present disclosure comprises a neutron detection unit that detects neutrons and converts them into electrical signals, and an amplification unit that amplifies the output of the neutron detection unit, wherein the neutron detection unit has a semiconductor layer of a first conductivity type, a detection unit diffusion layer of a second conductivity type formed on the semiconductor layer, and a neutron conversion layer formed on the detection unit diffusion layer that converts neutrons into alpha rays, and the amplification unit has a plurality of transistors formed on the semiconductor layer, and the neutron conversion layer is a metal film having a layer containing boron 10 or a layer containing lithium 6. [Effects of the Invention]

[0009] According to the neutron detection element of this disclosure, only alpha rays can be incident on the semiconductor layer, making it possible to reduce output fluctuations. [Brief explanation of the drawing]

[0010] [Figure 1] This is a circuit diagram showing a neutron detection element according to one embodiment. [Figure 2] This is a cross-sectional view showing a neutron detection element according to one embodiment. [Figure 3A]It is a cross-sectional view showing a manufacturing process of a neutron detection element according to an embodiment. [Figure 3B] It is a cross-sectional view showing a manufacturing process of a neutron detection element according to an embodiment. [Figure 3C] It is a cross-sectional view showing a manufacturing process of a neutron detection element according to an embodiment. [Figure 3D] It is a cross-sectional view showing a manufacturing process of a neutron detection element according to an embodiment. [Figure 3E] It is a cross-sectional view showing a manufacturing process of a neutron detection element according to an embodiment. [Figure 4] It is a plan view showing a neutron two-dimensional sensor according to an embodiment. [Figure 5] It is a cross-sectional view showing a neutron detection element according to a modified example.

Mode for Carrying Out the Invention

[0011] As shown in FIG. 1, a neutron detection element 100 according to an embodiment includes a neutron detection unit 101 that detects neutrons and converts them into an electric signal, and an amplification unit 102 that amplifies the output of the neutron detection unit. The amplification unit 102 includes a reset transistor (RST), a source follower transistor (SF), and a row selection transistor (RS). By applying a reset signal to φR and a row selection signal to φX, it can be driven as a neutron detection element.

[0012] As shown in FIG. 2, the neutron detection unit 101 and the amplification unit 102 are formed in a p - -type semiconductor layer 112 formed on an n-type semiconductor substrate 111. In this embodiment, the semiconductor substrate 111 and the semiconductor layer 112 are made of silicon carbide (SiC).

[0013] In the semiconductor layer 112, an n + -type detection unit diffusion layer 113 and a source-drain diffusion layer 121 and a p + -type potential stabilization region 114 are formed. On the semiconductor layer 112, a gate insulating An insulating film 123 is formed, and a gate electrode 124 is formed in a predetermined region above the gate insulating film 123. Also, an ohmic electrode 117 that makes an ohmic contact with the potential stabilization region 114 and a source-drain electrode 122 that makes an ohmic contact with the source-drain diffusion layer 121 are formed. The ohmic electrode 117 and the source-drain electrode 122 are formed by a silicide layer 141 that makes an ohmic contact with the diffusion layer and a metal electrode layer 142 that covers the silicide layer 141.

[0014] An interlayer insulating film 133 is formed on the semiconductor layer 112 so as to cover each electrode, and a neutron conversion layer 115, wirings 135 and 136 are formed on the interlayer insulating film 133. Thereby, the neutron detection unit 101 and the amplification unit 102 have an amplification unit 102 having a reset transistor (RST), a source follower transistor (SF), and a row selection transistor (RS). In the present embodiment, one of the source-drain diffusion layers of the reset transistor (RST) is formed integrally with the detection unit diffusion layer 113.

[0015] A back surface electrode 126 is provided on the back surface of the semiconductor substrate 111. The back surface electrode 126 is an ohmic electrode that makes an ohmic contact with the back surface of the semiconductor substrate 111 and can be formed of niobium-nickel silicide or the like. The back surface electrode 126 quickly discharges electron-hole carriers generated in the semiconductor substrate 111 and has an effect of stabilizing device operation.

[0016] The neutron conversion layer 115 is a metal film having a B-containing layer 115A that is an isotope of boron which is a conversion functional layer. 10 Boron-10 ( 10 B) 10 The B-containing layer 115A can be formed, for example, 10 by ion-implanting B or by depositing B by a sputtering method, a vapor deposition method, or the like. The conversion functional layer can be 10 a layer containing lithium-6 ( 10 Li), which is an isotope of lithium, instead of the B-containing layer. 6

[0017] In this embodiment, 10 A lower metal layer 115B exists below the B-containing layer 115A, and an upper metal layer 115C exists above it, although the upper metal layer 115C is optional. From the viewpoint of reducing the likelihood of alpha and lithium rays passing through, the lower metal layer 115B and the upper metal layer 115C are preferably made of metals with relatively large atomic numbers. For example, aluminum (Al), tungsten (W), and molybdenum (Mo) can be used. Among these, Al is preferred because it can be formed in the same way as Al wiring.

[0018] Neutrons incident on neutron conversion layer 115, 10 It reacts with B to generate alpha rays and Li particle beams. In the lower metal layer 115B made of Al, etc., the Li particle beams are attenuated more easily than the alpha rays, and only the alpha rays pass through the lower metal layer 115B and are incident on the detection unit diffusion layer 113, n + Type check An electron-hole pair is generated in the depletion layer near the PN junction between the outflow diffusion layer 113 and the p-type semiconductor layer 112. The negative charge (electron) of the generated electron-hole pair is n + Transfer to the type detection unit diffusion layer 113 This charge is transferred through wirings 135 and 136 to the gate electrode of the SF transistor, changing the potential of this gate electrode.

[0019] Furthermore, in this embodiment, since an n-type semiconductor substrate 111 exists beneath the p-type semiconductor layer 112, a parasitic bipolar junction transistor (BJT) is formed. Positive charges (holes) from electron-hole pairs generated in the depletion layer are injected into the base portion of the parasitic BJT, temporarily turning the parasitic BJT ON, and electrons move from the semiconductor substrate 111 through the base portion to the detection diffusion layer 113. These electrons, like the electrons from the electron-hole pairs generated in the depletion layer, are accumulated at the gate electrode of the SF transistor through the wiring 135 and 135, further changing the potential of this gate electrode. At this time, if a negative voltage is applied to the back electrode 126 of the semiconductor substrate 111, the amplification effect by the parasitic BJT is further increased, that is, the number of electrons injected from the semiconductor substrate 111 to the detection diffusion layer 113 can be increased. The presence of the parasitic BJT makes the sensor more sensitive. However, parasitic BJTs are not necessarily required, and the sensor will operate with only the detection diffusion layer 113.

[0020] The charge accumulated on the gate electrode of the SF transistor changes the potential of this gate electrode. As a result, after the RS transistor is turned on, the output voltage changes according to the potential of the gate electrode of the SF transistor. By measuring this potential, it becomes possible to measure the number of neutrons incident on the sensor.

[0021] In this embodiment, the detection unit diffusion layer 113 is integrated with the source-drain diffusion layer of the reset transistor (RST). The negative charge that has moved to the detection unit diffusion layer 113 is read out by the amplification unit 102, and a signal corresponding to the energy of the neutron incident on the neutron conversion layer 115 is obtained. On the other hand, positive charges (holes) are discharged through the potential stabilization region 114. The formation of parasitic BJTs improves the detection sensitivity of neutrons, but it is also possible to configure the system so that parasitic BJTs do not form.

[0022] In this embodiment, the neutron detection element 100 detects neutrons using only the alpha rays from the alpha rays and Li particle beams generated by neutrons incident on the neutron conversion layer 115. Therefore, the quantitative accuracy of neutron detection can be improved.

[0023] In this embodiment, the neutron conversion layer 115 is formed only directly above the detection unit diffusion layer 113 and not on the transistors or other components that constitute the amplification unit 102. By forming the neutron conversion layer 115 only directly above the detection unit diffusion layer 113, alpha rays emitted from the neutron conversion layer 115 are less likely to be incident on parts of the semiconductor layer 112 other than the detection unit diffusion layer 113, thereby reducing the likelihood of malfunctions. Directly above the detection unit diffusion layer 113 is the part that overlaps with the detection unit diffusion layer 113 in a plan view, but the detection unit diffusion layer 113 and the neutron conversion layer 115 do not need to completely overlap. It is also possible to configure the neutron conversion layer 115 to be formed in a part other than directly above the detection unit diffusion layer 113.

[0024] The silicon carbide photodetector of this embodiment can be formed, for example, as follows. First, as shown in Figure 3A, a p-type semiconductor layer 112 is epitaxially grown on an n-type semiconductor substrate 111. Subsequently, n-type impurities are selectively implanted into the semiconductor layer 112 using a first ion implantation mask. + A detection unit diffusion layer 113 and a source-drain diffusion layer 121 are formed. Furthermore, using a second ion implantation mask, p + Forms a type of potential stabilization region 114 Next, activation annealing will be performed.

[0025] The semiconductor substrate 111 is not particularly limited, but can be 4H-SiC. The thickness of the semiconductor layer 112 can be, for example, about 1 μm to 5 μm. The first ion implantation mask and the second ion implantation mask can be formed, for example, from a silicon oxide (SiO2) film. This can be done. For SiC semiconductors, activation annealing can be performed by covering the ion-implanted semiconductor layer 112 with a carbon cap film and then performing a heat treatment at around 1700°C.

[0026] Next, as shown in Figure 3B, thermal oxidation is performed to form a gate insulating film 123 with a thickness of approximately 20 nm, after which the ohmic electrode 117, source / drain electrode 122, gate electrode 124, and back electrode 126 are formed. The ohmic electrode 117 and source / drain electrode 122 can be formed, for example, by a silicide layer 141 and a metal electrode layer 142. The silicide layer 141 can be formed by selectively forming a metal film that will become the silicide layer 141 using, for example, a lift-off method using a resist mask, and then silicideizing it by heat treatment. In this case, the metal film can be, for example, a niobium-nickel film, but it can also be formed from other metals that form silicides, such as a nickel-molybdenum alloy film. The metal electrode layer 142 can be formed by forming a metal film made of Al or the like so as to cover the silicide layer 141 and selectively etching it away. The metal electrode layer 142 and the gate electrode 124 can be formed by the same process. The metal electrode layer 142 and the gate electrode 124 can also be formed from titanium nitride or polysilicon or the like. The back electrode 126 can be formed by forming a metal film, such as a niobium-nickel film, on the back surface of the semiconductor substrate 111 and then silicideizing it.

[0027] Next, as shown in Figure 3C, an interlayer insulating film 133 made of silicon oxide or the like is formed over the entire surface of the semiconductor substrate 111, and a lower metal layer 115B is formed on top of the interlayer insulating film 133. The thickness of the interlayer insulating film 133 affects the incidence of alpha rays emitted from the neutron conversion layer 115 to the detection part diffusion layer 113, but it can be, for example, about 1 μm. After this, the lower metal layer 115B 10 B is ion-implanted, and the impurity diffusion layer is 10 A B-containing layer 115A is formed. The lower metal layer 115B can be any metal layer that attenuates Li particle beams, and can be formed from aluminum, tungsten, molybdenum, etc. 10 The B-containing layer 115A is not limited to ion implantation, but can also be produced by sputtering or vapor deposition, etc. 10It can be formed by depositing B. The thickness of the lower metal layer 115B is such that Li particle beams do not penetrate but alpha particles do. The thickness can be appropriately determined depending on the type of metal used, but for example, it can be about 2 μm to 4 μm for aluminum and about 0.4 μm for tungsten. 10 When forming the B-containing layer 115A by ion implantation, the implantation amount is 1 × 10⁻⁶. 15 cm -2 Degree ~4x10 15 cm -2 It can be set to a certain extent. The thickness of the upper metal layer 115C is not particularly limited, but for example, in the case of aluminum, it can be approximately 10 nm to 1000 nm. 6 Li-containing layers can be formed in a similar manner.

[0028] Next, as shown in Figure 3D, 10 The lower metal layer 115B on which the B-containing layer 115A is formed is selectively removed, except for the area directly above the detection unit diffusion layer 113. Next, as shown in Figure 3E, the upper metal layer 115C and the wiring 135 and wiring 136 are formed. If the upper metal layer 115C and the wiring 135 and wiring 136 are made of the same metal, they can be formed by the same process.

[0029] As shown in Figure 4, the neutron detection elements 100 of this embodiment can be arranged in a matrix to form a two-dimensional neutron sensor 200, with each neutron detection element 100 acting as a single pixel. By using the two-dimensional neutron sensor 200, the distribution of neutrons on a plane can be easily measured, and neutron transmission and absorption can be evaluated in real time in neutron radiography and BNCT. Furthermore, because the neutron detection elements 100 of this embodiment have excellent quantitative properties, it is possible to visualize the neutron intensity distribution with high accuracy.

[0030] As shown in Figure 5, a high-density layer 151 can also be formed between the neutron conversion layer 115 and the detection unit diffusion layer 113. By forming the high-density layer 151, the amount of alpha rays that penetrate the detection unit diffusion layer 113 can be reduced. This further improves the detection sensitivity. The high-density layer 151 can be any layer with a higher density than the semiconductor layer 112, and a layer containing metal is preferred. For example, it can be a simple metal layer, an alloy layer containing multiple metals, or a silicide layer, which is a layer containing both metal and nonmetal. In particular, it is preferable to include a metal with an atomic number greater than 14, and from the viewpoint of ease of handling, it is even more preferable to include nickel, niobium, titanium, and cobalt. These metals are also preferable from the viewpoint of being easy to form silicides on. If the high-density layer is formed using the same silicide layer as the source-drain electrode 122, the high-density layer can be formed without increasing the number of processes. In this case, the silicide layer 141 of the source-drain electrode 122 and the high-density layer 151 can be formed integrally.

[0031] The high-density layer 151 is preferably in contact with the detection unit diffusion layer 113, but it is also possible to have another layer, such as an insulating film, between the high-density layer 151 and the detection unit diffusion layer 113. The high-density layer 151 is preferably formed directly below at least the neutron conversion layer 115 of the detection unit diffusion layer 113. It can be formed to cover the entire detection unit diffusion layer 113, or to cover a wider area than the detection unit diffusion layer 113. The thickness of the high-density layer 115 is not particularly limited, but from the viewpoint of allowing alpha rays to reach the detection unit diffusion layer and preventing penetration, it is preferably about 0.01 μm to 0.3 μm thick. When the high-density layer 151 is formed by the same process as the silicide layer 141 of the source-drain electrode 122, its thickness can be matched to that of the silicide layer 141 of the source-drain electrode 122.

[0032] In this embodiment, the semiconductor layer 112 is p-type, and an n-type transistor is formed. + By providing a potential stabilization region 114 of the type, alpha rays Since the generated holes can be quickly discharged, the output potential of the detection element can be stabilized. However, it is also possible to make the semiconductor layer 112 n-type and form a p-type detection diffuser layer and transistor. In this case, the potential stabilization region is n + It can be made into a type. The stabilization region may be provided as needed, or it may not be provided. In this embodiment, the potential stabilization region 114 is arranged adjacent to the detection unit diffusion layer 113, but spaced apart. This configuration makes it possible to further enhance the effect of stabilizing the potential. However, the potential stabilization region 114 can be formed in any of the semiconductor layers 112, the same as the detection unit diffusion layer 113. Note that the + sign attached to the p or n symbol indicating the conductivity type indicates a higher impurity concentration compared to the case without a sign, and the - sign indicates a lower impurity concentration compared to the case without a sign.

[0033] As in this embodiment, by using SiC semiconductors, radiation resistance can be improved, thereby significantly extending the lifespan of the device. However, devices can also be formed using silicon semiconductors. [Industrial applicability]

[0034] The neutron detection element disclosed herein is less prone to output fluctuations, facilitates quantitative detection of neutrons, and is particularly useful in fields such as medicine that utilize neutrons. [Explanation of Symbols]

[0035] 100 Neutron detection elements 101 Neutron detection unit 102 Amplifier 111 Semiconductor substrates 112 Semiconductor layer 113 Detection unit diffusion layer 114 Potential stabilization region 115 Neutron Conversion Layer 115A 10 B-containing layer 115B Lower metal layer 115C Upper metal layer 117 Ohmic electrodes 121 Source-Drain Diffusion Layer 122 Source and Drain Electrodes 123 Gate insulating film 124 Grid gate 126 Backside electrode 133 Interlayer insulating film 135 Wiring 136 Wiring 141 Silicide layer 142 Metal electrode layer 151 High density layer 200 Neutron 2D Sensor

Claims

1. A neutron detection unit that detects neutrons and converts them into electrical signals, The system includes an amplification unit that amplifies the output of the neutron detection unit, The neutron detection unit comprises a semiconductor layer of a first conductivity type, a detection unit diffusion layer of a second conductivity type formed on the semiconductor layer, a neutron conversion layer formed on the detection unit diffusion layer to convert neutrons into alpha rays, and a high-density layer formed between the neutron conversion layer and the detection unit diffusion layer, which is made of a material with a higher density than the semiconductor layer. The amplification unit has a plurality of transistors formed in the semiconductor layer, The neutron conversion layer is a metal film having a layer containing boron 10 or a layer containing lithium 6. The aforementioned high-density layer is a metal silicide layer, which is used in the neutron detection element.

2. The neutron detection element according to claim 1, wherein the neutron detection unit is formed in the semiconductor layer and has a potential stabilization region of a first conductivity type having a higher impurity concentration than the semiconductor layer.

3. A neutron detection unit that detects neutrons and converts them into electrical signals, The system includes an amplification unit that amplifies the output of the neutron detection unit, The neutron detection unit comprises a semiconductor layer of a first conductivity type, a detection unit diffusion layer of a second conductivity type formed on the semiconductor layer, a neutron conversion layer formed on the detection unit diffusion layer that converts neutrons into alpha rays, and a potential stabilization region of the first conductivity type formed on the semiconductor layer, having a higher impurity concentration than the semiconductor layer. The amplification unit has a plurality of transistors formed in the semiconductor layer, The neutron conversion layer is a metal film having a layer containing boron 10 or a layer containing lithium 6, in a neutron detection element.

4. The neutron detection element according to any one of claims 1 to 3, wherein the layer containing boron 10 or the layer containing lithium 6 is an impurity diffusion layer.

5. The neutron detection element according to any one of claims 1 to 4, wherein the semiconductor layer is a silicon carbide semiconductor layer.

6. The neutron detection element according to any one of claims 1 to 5, wherein the neutron conversion layer is formed directly above the detection unit diffusion layer via an insulating film.

7. A two-dimensional neutron sensor comprising neutron detection elements according to any one of claims 1 to 6 arranged in a matrix.

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