Radiation detection element, radiation detector, and radiation detection device

Abstract

Provided are a radiation detection element, a radiation detector, and a radiation detection device for suppressing an increase in the rise time of a signal that is output when detecting radiation.　The radiation detection element comprises: a semiconductor part that is plate-shaped and has a radiation incident surface; a signal output electrode that is provided on a rear surface and into which flows a charge generated in the semiconductor part by the incidence of radiation, and that outputs a signal corresponding to the charge; an incident-side electrode that is positioned on the rear side of the signal output electrode and to which a voltage is applied; a plurality of first drift electrodes that surround the signal output electrode; and a plurality of second drift electrodes that surround the incident-side electrode. A voltage is applied to the plurality of first drift electrodes and the plurality of second drift electrodes so as to generate, in the semiconductor, an electric field for guiding the charge to the signal output electrode. The average of the intensity of electric fields generated by first drift electrodes for which the distance from the signal output electrode is less than a prescribed distance is higher than the average of the intensity of the electric fields generated by the first drift electrodes for which the distance from the signal output electrode exceeds the prescribed distance.

Description

Radiation detection element, radiation detector, and radiation detection device

[0001] The present invention relates to a radiation detection element, a radiation detector, and a radiation detection apparatus.

[0002] Some radiation detectors that detect radiation such as X-rays include a radiation detection element that uses a semiconductor. A radiation detection element that uses a semiconductor includes a flat semiconductor portion. A signal output electrode for outputting a signal is provided on one surface of the semiconductor portion. When radiation is incident on the semiconductor portion, charge is generated inside the semiconductor portion. Electrodes that generate an electric field to collect the charge to the signal output electrode are arranged around the signal output electrode. The charge generated by the incident radiation moves according to the electric field and collects at the signal output electrode, and a signal corresponding to the amount of collected charge is output from the signal output electrode. Radiation is counted according to the signal output, and radiation is detected. Patent Document 1 discloses an example of a radiation detection element.

[0003] International Publication No. 2024 / 070737

[0004] Increasing the area of ​​the radiation detection element improves the radiation detection sensitivity of the radiation detector. However, a radiation detection element with an increased area increases the rise time of the output signal. When radiation is incident, a charge cluster containing a large number of charges is generated in the semiconductor portion. The charge cluster generated by radiation incident at a position far from the signal output electrode spreads before reaching the signal output electrode, increasing the time it takes for the charge cluster to flow into the signal output electrode and increasing the rise time of the signal. If the rise time of the output signal is long, the time during which radiation is not detected increases, and the radiation detection efficiency deteriorates. For this reason, it is desirable to suppress the increase in the rise time of the signal output when radiation is detected.

[0005] An object of the present invention is to provide a radiation detection element, a radiation detector, and a radiation detection apparatus that can suppress an increase in the rise time of a signal output during radiation detection.

[0006] A radiation detection element according to one aspect of the present invention includes a plate-shaped semiconductor portion having an incident surface onto which radiation is incident, a signal output electrode provided on a back surface behind the incident surface, into which charges generated by the incidence of radiation on the semiconductor portion flow and which outputs a signal corresponding to the charges, an incident side electrode provided on the incident surface, located behind the signal output electrode, and to which a voltage necessary for the charges to flow into the signal output electrode is applied, a plurality of first drift electrodes provided on the back surface, surrounding the signal output electrode, and located at different distances from the signal output electrode, and a plurality of second drift electrodes provided on the incident surface, surrounding the incident side electrode, and located at different distances from the incident side electrode. a voltage is applied to the plurality of first drift electrodes and the plurality of second drift electrodes so as to generate an electric field in the semiconductor for guiding the charges to the signal output electrode, the plurality of first drift electrodes include a plurality of electrodes that are located less than a predetermined distance from the signal output electrode and a plurality of electrodes that are located more than the predetermined distance from the signal output electrode, and the average strength of the electric field generated by the plurality of first drift electrodes that are located less than the predetermined distance from the signal output electrode is higher than the average strength of the electric field generated by the plurality of first drift electrodes that are located more than the predetermined distance from the signal output electrode.

[0007] In one aspect of the present invention, a radiation detection element includes a semiconductor portion, a signal output electrode located on the back side of the incident surface, an incident-side electrode located on the incident surface, a plurality of first drift electrodes surrounding the signal output electrode, and a plurality of second drift electrodes surrounding the incident-side electrode. A voltage is applied to the first drift electrode and the second drift electrode, generating an electric field for guiding charges generated by radiation incident on the semiconductor portion to the signal output electrode. The average strength of the electric field generated by the first drift electrode located less than a predetermined distance from the signal output electrode is higher than the average strength of the electric field generated by the first drift electrode located more than the predetermined distance from the signal output electrode. The electric field generated by the second drift electrode prevents a decrease in the electric field strength even in a region close to the incident surface. At a position far from the signal output electrode, the electric field generated by the second drift electrode supplements the electric field generated by the first drift electrode. Therefore, changes in the electric field strength within the semiconductor portion are small. Since the change in the electric field strength is small, the group of electrons generated by the radiation is less likely to spread on the path of movement to the signal output electrode, and the rise time of the signal output when radiation is detected is prevented from becoming long.

[0008] In a radiation detection element according to one embodiment of the present invention, the area of ​​the incident-side electrode on the incident surface is larger than the area of ​​the signal output electrode on the back surface, and when a voltage is applied to the plurality of second drift electrodes, the potential of the plurality of second drift electrodes changes monotonically from the outermost second drift electrode among the plurality of second drift electrodes toward the incident-side electrode.

[0009] In one aspect of the present invention, the area of ​​the incident-side electrode is larger than the area of ​​the signal output electrode. The potential of the second drift electrode changes monotonically from the outermost second drift electrode toward the incident-side electrode. The electric field generated by the second drift electrode acts to move generated charges toward the back surface side rather than the incident surface. When the second drift electrode is located close to the signal output electrode, the electric field acts on electrons near the signal output electrode. Near the signal output electrode, the electron movement path is close to the back surface, and the electric field acts to move charges toward the back surface side, increasing the probability that charges will reach the back surface and stop flowing into the signal output electrode. In one aspect of the present invention, since the area of ​​the incident-side electrode is larger than the area of ​​the signal output electrode, the distance from the signal output electrode to the second drift electrode is longer, making it difficult for the electric field generated by the second drift electrode to act on charges near the signal output electrode. This reduces the probability that charges will stop flowing into the signal output electrode, preventing a decrease in the accuracy of radiation detection.

[0010] In a radiation detection element according to one embodiment of the present invention, among the plurality of first drift electrodes, the plurality of electrodes that are located at a distance from the signal output electrode that is less than the predetermined distance are located on the back side of the incident side electrode.

[0011] In one aspect of the present invention, the first drift electrode that is located at a distance less than a predetermined distance from the signal output electrode is located behind the entrance-side electrode, and therefore the average strength of the electric field generated by the first drift electrode located behind the entrance-side electrode is higher than the average strength of the electric field generated by the first drift electrode located outside the range behind the entrance-side electrode.

[0012] In a radiation detection element according to one embodiment of the present invention, among the plurality of first drift electrodes, those electrodes whose distance from the signal output electrode exceeds the predetermined distance are located outside the range on the back side of the incident side electrode.

[0013] In one aspect of the present invention, the first drift electrode located more than a predetermined distance from the signal output electrode is located outside the range behind the entrance-side electrode, and therefore the average strength of the electric field generated by the first drift electrode located behind the entrance-side electrode is higher than the average strength of the electric field generated by the first drift electrode located outside the range behind the entrance-side electrode.

[0014] In a radiation detection element according to one embodiment of the present invention, when a voltage is applied to the plurality of first drift electrodes, the potential of the plurality of first drift electrodes changes monotonically from the outermost first drift electrode to the innermost first drift electrode, and when a voltage is applied to the plurality of first drift electrodes that are located less than the predetermined distance from the signal output electrode, the potential of the plurality of first drift electrodes changes in proportion to the square of the distance from the signal output electrode.

[0015] In one embodiment of the present invention, the potentials of the first drift electrodes vary monotonically from the outermost first drift electrode to the innermost first drift electrode, and the potentials of the first drift electrodes that are less than a predetermined distance from the signal output electrode vary in proportion to the square of the distance from the signal output electrode, thereby increasing the average strength of the electric field generated by the first drift electrodes that are less than the predetermined distance from the signal output electrode.

[0016] In a radiation detection element according to one embodiment of the present invention, when a voltage is applied to the plurality of first drift electrodes, the potential of the plurality of electrodes whose distance from the signal output electrode exceeds the predetermined distance changes in proportion to the distance from the signal output electrode.

[0017] In one embodiment of the present invention, the potential of the first drift electrode that is more than a predetermined distance from the signal output electrode varies in proportion to the distance from the signal output electrode, so that the average strength of the electric field generated by the first drift electrode that is less than the predetermined distance from the signal output electrode is higher than the average strength of the electric field generated by the first drift electrode that is more than the predetermined distance from the signal output electrode.

[0018] A radiation detection element according to one aspect of the present invention is characterized in that an insulating layer is provided on the incident surface in a linear shape spanning the plurality of second drift electrodes, and a linear conductive layer connected to the incident-side electrode is provided on the insulating layer.

[0019] In one aspect of the present invention, a linear insulating layer is provided on the incident surface so as to straddle the plurality of second drift electrodes, and a linear conductive layer connected to the incident-side electrode is provided on the insulating layer. By connecting a wire to the conductive layer, connection to the incident-side electrode using a wire is possible without being obstructed by a collimator arranged above the radiation detection element.

[0020] A radiation detector according to one aspect of the present invention includes the radiation detection element according to the present invention, and is characterized in that at least a portion of a plurality of second drift electrodes included in the radiation detection element is not covered by a collimator.

[0021] In one aspect of the present invention, in a radiation detector including a radiation detection element, at least a portion of the plurality of second drift electrodes is not covered by a collimator, and when radiation is incident on the semiconductor portion near the position where the second drift electrode is disposed, charges generated by the radiation are moved by an electric field generated by the second drift electrode.

[0022] A radiation detection device according to one aspect of the present invention is characterized by comprising: an irradiation unit that irradiates a sample with radiation; a radiation detector according to the present invention; a voltage application unit that applies a voltage to a radiation detection element included in the radiation detector; a spectrum generation unit that generates a spectrum of radiation detected by the radiation detector; and a display unit that displays the spectrum generated by the spectrum generation unit.

[0023] In one aspect of the present invention, the radiation detection device irradiates a sample with radiation, generates a spectrum of the radiation emitted from the sample, and displays the generated spectrum on a display unit, allowing a user to check the spectrum of the radiation emitted from the sample.

[0024] The present invention has excellent effects, such as suppressing the rise time of a signal output upon detection of radiation from becoming long.

[0025] 4 is a schematic cross-sectional view showing an example of a radiation detection element. FIG. 5 is a schematic plan view showing an example of a radiation detection element viewed from the incident surface side. FIG. 6 is a schematic plan view showing an example of a radiation detection element viewed from the electrode surface side. FIG. 7 is a schematic cross-sectional view showing an example of a radiation detection element obtained by cutting the radiation detection element along line IV-IV in FIG. 2. FIG. 8 is a block diagram showing an example of the functional configuration of a radiation detection device using a radiation detection element. FIG. 9 is a schematic view showing an example of a connection mode between a radiation detection element and a voltage application unit. FIG. 10 is a schematic cross-sectional view showing an example of the configuration of a radiation detector. FIG. 11 is a schematic cross-sectional view showing an example of a radiation detection element and a collimator. FIG. 12 is a schematic graph showing an example of a signal output from a radiation detector. FIG. 13 is a schematic graph showing an example of the relationship between the position and potential of a first drift electrode.

[0026] The present invention will be described in detail below with reference to the drawings illustrating embodiments thereof. FIG. 1 is a schematic cross-sectional view showing an example of a radiation detection element 1. The radiation detection element 1 is a silicon drift type radiation detection element. The radiation detection element 1 is generally flat. The radiation detection element 1 includes a disk-shaped semiconductor portion 11 made of Si (silicon). The semiconductor portion 11 is composed of n-type Si. The radiation detection element 1 has an incident surface 111 located on the incident side where radiation to be detected is incident, and an electrode surface 112 located on the back side of the incident surface 111. The electrode surface 112 corresponds to the back surface.

[0027] Fig. 2 is a schematic plan view showing an example of the radiation detection element 1 as viewed from the incident surface 111 side. Fig. 3 is a schematic plan view showing an example of the radiation detection element 1 as viewed from the electrode surface 112 side. Fig. 1 shows a cross-sectional view of the radiation detection element 1 taken along line II in Figs. 2 and 3. Fig. 4 is a schematic cross-sectional view showing an example of the radiation detection element 1 taken along line IV-IV in Fig. 2.

[0028] A signal output electrode 13, which is an electrode that outputs a signal when radiation is detected, is provided on the electrode surface 112. The component of the signal output electrode 13 is the same type of Si as the semiconductor portion 11. For example, the component of the signal output electrode 13 is n+Si, which is Si doped with a specific dopant such as phosphorus.

[0029] A plurality of first drift electrodes 14 arranged in a multiple annular configuration are provided on the electrode surface 112 at positions surrounding the signal output electrode 13. The first drift electrode 14 is made of a semiconductor of a different type from that of the semiconductor portion 11, i.e., p-type Si doped with a specific dopant such as boron. For example, the first drift electrode 14 is made of p+Si. The signal output electrode 13 is located approximately at the center of the multiple annular first drift electrodes 14. The distances between the signal output electrode 13 and each of the first drift electrodes 14 surrounding the signal output electrode 13 are different. While FIGS. 1 , 3 , and 4 show an example in which six first drift electrodes 14 are provided, the number of the first drift electrodes 14 may be more than six or less than six.

[0030] An annular guard electrode 141 and an annular ground electrode 142 are provided on the electrode surface 112. The guard electrode 141 is disposed in a position surrounding the plurality of first drift electrodes 14, and the ground electrode 142 is disposed in a position surrounding the guard electrode 141. The ground electrode 142 is connected to a ground potential. The potential of the guard electrode 141 is a floating potential. The guard electrode 141 prevents dielectric breakdown between the first drift electrode 14 and the ground electrode 142. Although FIGS. 1, 3, and 4 show a single guard electrode 141, in reality, a plurality of multiple annular guard electrodes 141 are provided. The signal output electrode 13, the first drift electrode 14, the guard electrode 141, and the ground electrode 142 are formed by doping a dopant into a portion of the semiconductor portion 11.

[0031] An incident-side electrode 12, which is an electrode to which a voltage is applied, is provided on the incident surface 111. The incident-side electrode 12 is doped with a dopant that makes Si a semiconductor of a different type from the component of the semiconductor portion 11. For example, the component of the incident-side electrode 12 is p+Si. The incident-side electrode 12 is disposed at a position behind the signal output electrode 13. The area of ​​the incident-side electrode 12 along the incident surface 111 is larger than the area of ​​the signal output electrode 13 along the electrode surface 112.

[0032] A plurality of second drift electrodes 15 arranged in multiple rings are provided on the incidence surface 111 at positions surrounding the incidence electrode 12. The second drift electrodes 15 are made of the same type of semiconductor as the incidence electrode 12. The distances between the incidence electrode 12 and each of the second drift electrodes 15 surrounding the incidence electrode 12 are different. Although an example in which three second drift electrodes 15 are provided is shown in FIGS. 1, 2, and 4, the number of the plurality of second drift electrodes 15 may be more than three or less than three.

[0033] An annular guard electrode 151 is provided on the incident surface 111. The guard electrode 151 is disposed in a position surrounding the plurality of second drift electrodes 15. The potential of the guard electrode 151 is a floating potential. Although a single guard electrode 151 is shown in FIGS. 1, 2, and 4, in reality, a plurality of multiple annular guard electrodes 151 are provided. The guard electrode 151 prevents dielectric breakdown between the edge of the semiconductor portion 11 and the second drift electrode 15. The entrance-side electrode 12, the second drift electrode 15, and the guard electrode 151 are formed by doping a part of the semiconductor portion 11 with a dopant.

[0034] The radiation detection element 1 may have a configuration in which the ground electrode 142 is not provided on the electrode surface 112 side, but is provided on the incident surface 111 side. That is, the ground electrode 142 may not be provided, and the ground electrode may be provided outside the guard electrode 151. In this configuration, the guard electrode 151 prevents dielectric breakdown between the second drift electrode 15 and the ground electrode. The radiation detection element 1 may have a configuration in which the ground electrodes are provided on both the incident surface 111 and the electrode surface 112.

[0035] As shown in FIGS. 2 and 4 , an insulating layer 161 is provided on the incident surface 111 in a linear shape spanning the plurality of second drift electrodes 15 and the protection electrodes 151. The insulating layer 161 may be made of any insulating material, and may be inorganic or organic. As shown in FIG. 2 , the insulating layer 161 covers a portion of the incident surface 111. A linear conductive layer 162 is provided on the insulating layer 161. One end of the conductive layer 162 is located near the edge of the semiconductor portion 11, and the other end of the conductive layer 162 is connected to the incident-side electrode 12. The insulating layer 161 insulates the second drift electrode 15 and the protection electrode 151 from the conductive layer 162. By electrically connecting one end of the conductive layer 162, electrical connection to the incident-side electrode 12 can be achieved via the conductive layer 162.

[0036] Radiation such as X-rays, photons in general (including UV and visible light), electron beams, or other charged particle beams is incident on the radiation detection element 1. The radiation is absorbed in the semiconductor portion 11, and an amount of charge corresponding to the energy of the absorbed radiation is generated in the semiconductor portion 11. The generated charges are electrons and holes. As will be described later, the generated charges move due to an electric field inside the semiconductor portion 11, and one type of charge flows into the signal output electrode 13. In this embodiment, electrons generated by the incidence of radiation move and flow into the signal output electrode 13. The signal output electrode 13 outputs a current signal corresponding to the flowed-in charge, i.e., a current signal corresponding to the energy of the radiation.

[0037] 5 is a block diagram showing an example of the functional configuration of a radiation detection device 100 that uses the radiation detection element 1. The radiation detection device 100 is, for example, an X-ray fluorescence analysis device. The radiation detection device 100 includes an irradiation unit 36 ​​that irradiates a sample 42 with radiation such as an electron beam or X-rays, a sample stage 41 on which the sample 42 is placed, and a radiation detector 2. Radiation is irradiated from the irradiation unit 36 ​​to the sample 42, causing radiation such as fluorescent X-rays to be generated in the sample 42, and the radiation detector 2 detects the radiation generated from the sample 42. In the figure, the radiation is indicated by arrows. The radiation detection device 100 may also be configured to hold the sample 42 by a method other than placing it on the sample stage 41.

[0038] The radiation detector 2 includes a radiation detection element 1 and a preamplifier 21. A part of the preamplifier 21 may be included inside the radiation detector 2, and the other part may be located outside the radiation detector 2. The signal output electrode 13 of the radiation detection element 1 is connected to the preamplifier 21. The preamplifier 21 outputs a signal with an intensity corresponding to the energy of the radiation.

[0039] Radiation from the sample 42 enters the radiation detector 2 and then enters the radiation detection element 1. The signal output electrode 13 outputs a current signal corresponding to the energy of the radiation. The signal output by the signal output electrode 13 is input to the preamplifier 21. The preamplifier 21 converts the current signal into a voltage signal and outputs a voltage signal proportional to the energy of the radiation. In this way, the radiation detector 2 outputs a signal with an intensity corresponding to the energy of the detected radiation.

[0040] A voltage application unit 31 is connected to the radiation detector 2. The voltage application unit 31 is connected to the radiation detection element 1. Fig. 6 is a schematic diagram showing an example of the connection between the radiation detection element 1 and the voltage application unit 31. More specifically, the voltage application unit 31 is connected to the entrance-side electrode 12 and the outermost second drift electrode 15 of the multiple second drift electrodes 15. The voltage application unit 31 is also connected to the innermost first drift electrode 14 of the multiple first drift electrodes 14 (i.e., the first drift electrode 14 that is the shortest distance from the signal output electrode 13) and the outermost first drift electrode 14.

[0041] The voltage application unit 31 applies a voltage between the innermost first drift electrode 14 and the outermost first drift electrode 14 so that the innermost first drift electrode 14 has a high potential and the outermost first drift electrode 14 has a low potential. In the radiation detection element 1, a path having electrical resistance is formed between adjacent first drift electrodes 14 that are at different distances from the signal output electrode 13. For example, by adjusting the components of the portion located between adjacent first drift electrodes 14, an electrical resistance channel connecting the two first drift electrodes 14 is formed. That is, the multiple first drift electrodes 14 are electrically connected via electrical resistance. The resistance value between adjacent first drift electrodes 14 is adjusted by adjusting the length of the path having electrical resistance between the adjacent first drift electrodes 14.

[0042] When a voltage is applied, the potential of each first drift electrode 14 monotonically increases from the outermost first drift electrode 14 to the innermost first drift electrode 14. That is, the potential of the first drift electrodes 14 increases from the outermost first drift electrode 14 to the innermost first drift electrode 14. The potential of each first drift electrode 14 is determined by adjusting the resistance value between the plurality of first drift electrodes 14. Note that the plurality of first drift electrodes 14 may include a pair of adjacent first drift electrodes 14 having the same potential. The potential of the plurality of first drift electrodes 14 generates an electric field (potential gradient) in the semiconductor portion 11 such that the potential is higher closer to the signal output electrode 13 and lower farther from the signal output electrode 13.

[0043] Furthermore, the voltage application unit 31 applies a voltage between the incident-side electrode 12 and the outermost second drift electrode 15 so that the potential of the incident-side electrode 12 is high and the potential of the outermost second drift electrode 15 is low. In the radiation detection element 1, paths having electrical resistance are formed between the incident-side electrode 12 and the innermost second drift electrode 15, and between adjacent second drift electrodes 15. In other words, the multiple second drift electrodes 15 and the incident-side electrode 12 are electrically connected via electrical resistance.

[0044] When a voltage is applied, a potential is generated that monotonically increases in sequence from the outermost second drift electrode 15 toward the entrance-side electrode 12. That is, the potential increases in sequence from the outermost second drift electrode 15 toward the entrance-side electrode 12. Note that the plurality of second drift electrodes 15 may include a pair of adjacent second drift electrodes 15 that have the same potential. The potentials of the entrance-side electrode 12 and the plurality of second drift electrodes 15 generate an electric field near the entrance surface 111 in the semiconductor portion 11, in which the potential is gradually higher the closer to the entrance-side electrode 12 and the potential is gradually lower the farther from the entrance-side electrode 12.

[0045] The voltage application unit 31 applies a voltage so that the potential of the incident-side electrode 12 becomes equal to the potential between the innermost first drift electrode 14 and the outermost first drift electrode 14. As a result, an electric field is generated inside the semiconductor portion 11, the potential of which increases the closer it is to the signal output electrode 13. Electrons generated in response to the incidence of radiation are likely to move inside the semiconductor portion 11 toward the signal output electrode 13 due to the electric field.

[0046] As shown in Fig. 5, the radiation detector 2 is connected to a signal processing unit 32 that processes the output signal. The signal processing unit 32 is connected to the preamplifier 21. The signal processing unit 32 is connected to an analysis unit 34. The analysis unit 34 is configured to include a calculation unit that performs calculations and a memory that stores data. The analysis unit 34 is connected to a display unit 35. The display unit 35 displays an image. The display unit 35 is, for example, a liquid crystal display or an EL display (Electroluminescent Display).

[0047] The radiation detection device 100 includes a control unit 33. The control unit 33 is connected to an irradiation unit 36, a voltage application unit 31, a signal processing unit 32, an analysis unit 34, and a display unit 35. The control unit 33 controls the operations of the voltage application unit 31, the signal processing unit 32, the analysis unit 34, and the display unit 35. For example, the control unit 33 is configured using a computer having an arithmetic unit and a memory. The control unit 33 may be configured to include an operation unit to accept operations from a user and to control each unit of the radiation detection device 100 in accordance with the accepted operation. The control unit 33 and the analysis unit 34 may be integrated into one device. Some of the functions of the control unit 33 or the analysis unit 34 may be executed using a device external to the radiation detection device 100.

[0048] The radiation detector 2 outputs a signal having an intensity corresponding to the energy of the radiation to the signal processing unit 32. The signal processing unit 32 receives the signal output by the radiation detector 2 and determines the intensity of the signal, thereby detecting the signal intensity corresponding to the energy of the radiation detected by the radiation detector 2. The signal processing unit 32 counts the signals by signal intensity, and outputs data indicating the relationship between the signal intensity and the count number to the analysis unit 34.

[0049] The analysis unit 34 receives data indicating the relationship between the signal intensity and the count number output by the signal processing unit 32. The analysis unit 34 generates a spectrum of the radiation incident on the radiation detector 2 based on the data from the signal processing unit 32. Since the signal intensity corresponds to the energy of the radiation and the count number corresponds to the number of times the radiation is detected, i.e., the intensity of the radiation, the spectrum of the radiation can be obtained from the relationship between the signal intensity and the count number. The spectrum represents the relationship between the energy of the radiation and the intensity of the radiation. The signal processing unit 32 and the analysis unit 34 correspond to a spectrum generation unit. The process of counting the signals output by the radiation detector 2 by signal intensity may be performed by the analysis unit 34 instead of the signal processing unit 32. The generation of the spectrum of the radiation may be performed by the signal processing unit 32.

[0050] The analysis unit 34 stores spectral data representing the spectrum of the radiation. The display unit 35 displays the spectrum of the radiation. A user can check the spectrum of the radiation generated from the sample 42. The analysis unit 34 may perform information processing based on the spectrum of the radiation. For example, the analysis unit 34 performs qualitative or quantitative analysis of elements contained in the sample 42 based on the spectrum of the radiation.

[0051] 5 shows a configuration in which radiation is irradiated onto the sample 42 and radiation generated from the sample 42 is detected, but the radiation detection device 100 may be configured to detect radiation that has passed through the sample 42 or radiation that has been reflected by the sample 42. The radiation detection device 100 may be configured to scan the sample 42 with radiation by changing the direction of the radiation. The radiation detection device 100 may be configured not to include the irradiation unit 36, the analysis unit 34, or the display unit 35.

[0052] FIG. 7 is a schematic cross-sectional view showing an example of the configuration of a radiation detector 2. The radiation detector 2 is an SDD (Silicon Drift Detector). The radiation detector 2 includes a housing 25 shaped like a cylinder with a truncated cone connected to one end. The housing 25 is configured with a plate-shaped bottom plate covered with a cap-shaped cover. A window 26 made of a window material that transmits radiation is provided at the tip of the housing 25. The radiation detection element 1, a collimator 22, a circuit board 23, a cooling unit 24, and a cold finger 27 are arranged inside the housing 25. The housing 25 accommodates the radiation detection element 1, the collimator 22, the circuit board 23, and the cooling unit 24. The cooling unit 24 is, for example, a Peltier element. The shape of the housing 25 is not limited to the shape shown in FIG. 7 and may be other shapes.

[0053] The radiation detection element 1 is mounted on the surface of the circuit board 23 and is arranged at a position facing the window 26. The radiation detection element 1 is arranged so that its electrode surface 112 faces the circuit board 23 and its incident surface 111 faces the window 26. The collimator 22 is cylindrical with both ends open and made of a radiation-shielding material. The collimator 22 is arranged between the radiation detection element 1 and the window 26. One end of the collimator 22 faces the window 26 and the other end faces the surface of the radiation detection element 1. Radiation mainly passes through the window 26 and enters the inside of the housing 25, and the collimator 22 blocks part of the radiation. The radiation detection element 1 detects incident radiation that is not shielded by the collimator 22.

[0054] A circuit is formed on the circuit board 23, and the preamplifier 21 is mounted on it. The back surface of the circuit board 23 is in thermal contact with the heat absorption portion of the cooling unit 24, either directly or via an intervening object. The heat dissipation portion of the cooling unit 24 is in thermal contact with the cold finger 27. The cold finger 27 has a flat portion with which the heat dissipation portion of the cooling unit 24 is in thermal contact, and a portion that penetrates the bottom plate of the housing 25. Heat from the radiation detection element 1 is absorbed by the cooling unit 24 through the circuit board 23. The heat is conducted from the cooling unit 24 to the cold finger 27, and is dissipated to the outside of the radiation detector 2 through the cold finger 27.

[0055] The radiation detector 2 has a plurality of lead pins 28 that penetrate the bottom plate portion of the housing 25. The lead pins 28 are connected to the circuit board 23 by a method such as wire bonding. The radiation detection element 1 is connected to the circuit board 23 by a method such as wire bonding. In particular, the incident side electrode 12 is connected to the circuit board 23 via a conductive layer 162 and a wire connected to the conductive layer 162. The incident side electrode 12 and the circuit board 23 are connected using a wire without being obstructed by the collimator 22. By using the conductive layer 162, the wire can be made short. The application of a voltage to the radiation detection element 1 by the voltage application unit 31 and the output of a signal from the preamplifier 21 are performed via the lead pins 28.

[0056] The radiation detection element 1 may not include the insulating layer 161 and the conductive layer 162, and the incident side electrode 12 and the circuit board 23 may be connected using a wire connected to the incident side electrode 12. The radiation detector 2 may not include the cold finger 27, and the heat dissipation portion of the cooling unit 24 may be in thermal contact with the bottom plate portion of the housing 25. The radiation detector 2 may not include the cooling unit 24. The radiation detector 2 may not include the window 26 made of a window material, and a portion of the housing 25 corresponding to the window 26 may be open. Alternatively, the radiation detector 2 may not include the housing 25. The radiation detector 2 may further include other components.

[0057] 8 is a schematic cross-sectional view showing an example of the radiation detection element 1 and the collimator 22. The collimator 22 is configured to cover the region of the incident surface 111 where the protective electrode 151 is provided and the region outside the protective electrode 151, but not to cover the regions where the incident-side electrode 12 and the second drift electrode 15 are provided. In other words, the second drift electrode 15 is not covered by the collimator 22. Therefore, when radiation is incident on the semiconductor portion 11 near the region where the second drift electrode 15 is provided, generated electrons are accelerated by an electric field generated by applying a voltage to the second drift electrode 15 and can quickly move to the signal output electrode 13. Note that some of the second drift electrodes 15 included in the plurality of second drift electrodes 15 may not be covered by the collimator 22, and the other second drift electrodes 15 may be covered by the collimator 22. For example, among the multiple second drift electrodes 15, the second drift electrode 15 located closer to the entrance electrode 12 may not be covered with the collimator 22, and the second drift electrode 15 located further out may be covered with the collimator 22.

[0058] FIG. 9 is a schematic graph showing an example of a signal output from the radiation detector 2. In the graph, the horizontal axis represents time, and the vertical axis represents signal value. Each time radiation is incident on the semiconductor portion 11 of the radiation detection element 1 and the radiation detection element 1 detects radiation, the radiation detector 2 outputs a staircase wave in which the signal value rises in a single step. In response to one event, one staircase wave in which the signal value rises in a single step is generated. If radiation is detected multiple times, a signal including multiple staircase waves is output. The signal value rises each time radiation is detected. The height of the step in the rising signal value is the signal intensity corresponding to the energy of the radiation. When radiation is detected, the time from when the signal value starts to rise in a single step until the signal value stops rising is the signal rise time.

[0059] When radiation is incident on the semiconductor portion 11, a group of electrons and holes is generated, and the group of electrons moves within the semiconductor portion 11 and flows into the signal output electrode 13. The time from when the first electron in the group flows into the signal output electrode 13 to when the last electron flows into the signal output electrode 13 corresponds to the signal rise time. If the group of electrons spreads while moving, the signal rise time becomes longer. During the signal rise time, it is not possible to output a signal in response to further incidence of radiation, so radiation is not detected. If the signal rise time is long, the time during which radiation is not detected becomes longer, and the radiation detection efficiency deteriorates.

[0060] The diffusion of electron populations is suppressed by the electric field, and they tend to diffuse when the electric field strength is low. If the electric field strength changes significantly along the path of electron populations from their generation to their flow into the signal output electrode 13, it becomes difficult to converge the electrons that have once diffused at positions of low electric field strength, causing the electron population to spread and lengthening the signal rise time. In conventional radiation detection elements that have the first drift electrode 14 but no second drift electrode 15, the electric field strength decreases in regions close to the incident surface 111, causing large changes in the electric field strength within the semiconductor portion 11 and lengthening the signal rise time. In the radiation detection element 1 according to this embodiment, the second drift electrode 15 is provided on the incident surface 111, preventing a decrease in electric field strength even in regions close to the incident surface 111. This reduces changes in the electric field strength within the semiconductor portion 11.

[0061] The electric field generated by the second drift electrode 15 acts to move generated electrons toward the electrode surface 112 rather than the incident surface 111. In a radiation detection element in which the area of ​​the incident-side electrode 12 is approximately the same as that of the signal output electrode 13, the second drift electrode 15 is closer to the signal output electrode 13, and the electric field generated by the second drift electrode 15 acts on electrons near the signal output electrode 13. In the vicinity of the signal output electrode 13, the electron movement path is closer to the electrode surface 112. The electric field generated by the second drift electrode 15 acts to move electrons moving near the electrode surface 112 closer to the electrode surface 112. This increases the probability that electrons will reach the electrode surface 112, flow through the electrode surface 112, and not flow into the signal output electrode 13, thereby reducing the accuracy of radiation detection. In the radiation detection element 1 according to this embodiment, the area of ​​the incident-side electrode 12 on the incident surface 111 is larger than the area of ​​the signal output electrode 13 on the electrode surface 112. The distance between the signal output electrode 13 and the second drift electrode 15 becomes longer, making it difficult for the electric field from the second drift electrode 15 to act on electrons in the vicinity of the signal output electrode 13, reducing the probability that electrons will not flow into the signal output electrode 13. Therefore, in this embodiment, a decrease in the accuracy of radiation detection is prevented.

[0062] Since the area of ​​the entrance electrode 12 is larger than that of the signal output electrode 13, the electric field inside the semiconductor portion 11 is generated mainly by the first drift electrode 14 at a position close to the signal output electrode 13, and is generated by the first drift electrode 14 and the second drift electrode 15 at a position far from the signal output electrode 13. At a position far from the signal output electrode 13, the electric field generated by the second drift electrode 15 complements the electric field generated by the first drift electrode 14, so the strength of the electric field generated by the first drift electrode 14 can be reduced compared to a position close to the signal output electrode 13.

[0063] The first drift electrode 14 is configured so that the potential difference is large at positions closer to the signal output electrode 13 and small at positions farther from the signal output electrode 13. Fig. 10 is a schematic graph showing an example of the relationship between the position of the first drift electrode 14 and the potential. The horizontal axis in the figure indicates the distance from the signal output electrode 13 of each first drift electrode 14 and corresponds to the position of the first drift electrode 14. The position where the distance is zero is the position of the signal output electrode 13. The vertical axis in the figure indicates the potential of each first drift electrode 14. The longer the distance from the signal output electrode 13 to the first drift electrode 14, the lower the potential of the first drift electrode 14.

[0064] As shown in Fig. 10 , in the range where the distance from the signal output electrode 13 to the first drift electrode 14 is less than a predetermined distance, the potential of the first drift electrode 14 decreases in proportion to the square of the distance from the signal output electrode 13. In the range where the distance from the signal output electrode 13 to the first drift electrode 14 exceeds a predetermined distance, the potential of the first drift electrode 14 decreases in proportion to the distance from the signal output electrode 13. The potential of the first drift electrode 14 when a voltage is applied is adjusted in advance by adjusting the length of the electrically resistive path between adjacent first drift electrodes 14. The larger the potential difference between the multiple first drift electrodes 14, the higher the electric field strength, and the smaller the potential difference, the lower the electric field strength. In the range where the distance from the signal output electrode 13 to the first drift electrode 14 exceeds a predetermined distance, the average potential difference between the first drift electrodes 14 is smaller than in the range where the distance from the signal output electrode 13 to the first drift electrode 14 is less than the predetermined distance. That is, the average strength of the electric field generated on the electrode surface 112 by the first drift electrode 14 that is less than a predetermined distance from the signal output electrode 13 is higher than the average strength of the electric field generated on the electrode surface 112 by the first drift electrode 14 that is more than a predetermined distance from the signal output electrode 13.

[0065] In this embodiment, the predetermined distance is equal to the radius of the incidence-side electrode 12. A plurality of first drift electrodes 14 that are located less than the predetermined distance from the signal output electrode 13 are located in a range behind the incidence-side electrode 12. The range behind the incidence-side electrode 12 is the range of the incidence-side electrode 12 projected onto the electrode surface 112 perpendicular to the incidence surface 111. Furthermore, a plurality of first drift electrodes 14 that are located more than the predetermined distance from the signal output electrode 13 are located outside the range behind the incidence-side electrode 12. Therefore, the potential of the first drift electrode 14 in the range behind the incidence-side electrode 12 decreases in proportion to the square of the distance from the signal output electrode 13, whereas the potential of the first drift electrode 14 in the range outside the range behind the incidence-side electrode 12 decreases in proportion to the distance from the signal output electrode 13. This makes it easy to realize a state in which the average strength of the electric field generated by the first drift electrode 14 in the area behind the entrance side electrode 12 is higher than the average strength of the electric field generated by the first drift electrode 14 in the area outside the area behind the entrance side electrode 12.

[0066] 10 shows the relationship between the position and potential of the first drift electrode 14 in a conventional radiation detection element not provided with the second drift electrode 15, using dotted lines. In the past, the potential difference of the first drift electrode 14 increased as the distance from the signal output electrode 13 increased, resulting in a higher electric field strength. For example, the potential of the conventional first drift electrode 14 decreased in proportion to the square of the distance from the signal output electrode 13, from the first drift electrode 14 closest to the signal output electrode 13 to the first drift electrode 14 furthest from the signal output electrode 13. In a conventional radiation detection element not provided with the second drift electrode 15, in order to move charges generated at a position far from the signal output electrode 13 to the signal output electrode 13, it was necessary to increase the electric field strength the farther from the signal output electrode 13.

[0067] In this embodiment, the average strength of the electric field generated by the first drift electrode 14 in the area behind the incidence-side electrode 12 is higher than the average strength of the electric field generated by the first drift electrode 14 in the area outside the area behind the incidence-side electrode 12. That is, the average strength of the electric field generated by the first drift electrode 14 is high in the area close to the signal output electrode 13, and the average strength of the electric field generated by the first drift electrode 14 is low in the area far from the signal output electrode 13. Because the second drift electrode 15 is disposed outside the incidence-side electrode 12, the electric field generated by the second drift electrode 15 complements the electric field generated by the first drift electrode 14. This increases the electric field strength throughout the entire interior of the semiconductor portion 11. Furthermore, the electric field generated by the second drift electrode 15 provided on the incidence surface 111 prevents a decrease in the electric field strength even in the area close to the incidence surface 111. In the range outside the range on the back side of the incidence-side electrode 12, the average strength of the electric field generated by the first drift electrode 14 is low, and therefore the influence of the electric field generated by the second drift electrode 15 is large, effectively preventing a decrease in the electric field strength in the region close to the incidence surface 111. Therefore, the change in the electric field strength inside the semiconductor part 11 is small.

[0068] As described above in detail, in this embodiment, the strength of the electric field generated inside the semiconductor portion 11 is increased, and changes in the electric field strength are reduced. The electric field strength is increased over the entire path along which electrons generated by radiation move, making it easier for the electrons to move. Because the change in the electric field strength is small, the group of electrons generated by radiation is less likely to spread along the path along which they move, and the time from when the first electron in the group of electrons flows into the signal output electrode 13 to when the last electron flows into the signal output electrode 13 is less likely to increase. This prevents the rise time of the signal output from the radiation detector 2 when radiation is detected from increasing. By preventing the rise time of the signal from increasing, the time during which radiation is not detected can be prevented from increasing, and a deterioration in radiation detection efficiency can be prevented.

[0069] In the present embodiment, an example has been shown in which the predetermined distance from the signal output electrode 13, which forms the boundary between the range in which the potential of the first drift electrode 14 is proportional to the square of the distance from the signal output electrode 13 and the range in which the potential is proportional to the distance from the signal output electrode 13, is a distance equal to the radius of the entrance-side electrode 12. Alternatively, the predetermined distance may be another distance. The radiation detection element 1 may be configured to make the average electric field strength different between the range close to the signal output electrode 13 and the range far from the signal output electrode 13 by a method other than providing a range in which the potential is proportional to the square of the distance and a range in which the potential is proportional to the distance. For example, the potential of the first drift electrode 14 may be proportional to the distance from the signal output electrode 13 in both the range in which the distance from the signal output electrode 13 is less than the predetermined distance and the range in which the distance exceeds the predetermined distance, with the proportionality coefficient being different for each range.

[0070] In this embodiment, the semiconductor constituting the radiation detection element 1 is Si, but the radiation detection element 1 may be configured to be configured to be made of a semiconductor other than Si. In this embodiment, the semiconductor portion 11 is configured to be an n-type semiconductor, and the incident-side electrode 12 and the first drift electrode 14 are configured to be p-type semiconductors, but the radiation detection element 1 may be configured to have the semiconductor portion 11 be a p-type semiconductor, and the incident-side electrode 12 and the first drift electrode 14 be an n-type semiconductor. In this configuration, the level of potential is reversed from that in the example shown in this embodiment, and holes generated by the incidence of radiation flow into the signal output electrode 13, thereby detecting radiation.

[0071] In this embodiment, the semiconductor portion 11 is disk-shaped and the radiation detection element 1 has a circular shape in a plan view, but the shape of the radiation detection element 1 may be a shape other than circular, such as a rectangular shape in a plan view, and the semiconductor portion 11 may have a plate shape other than a disk. The radiation detection element 1 may have a plurality of sets of the signal output electrode 13, the incident-side electrode 12, the first drift electrode 14, and the second drift electrode 15. In this embodiment, the radiation detection element 1 is a silicon drift type radiation detection element, but the radiation detection element 1 may be an element made of a semiconductor other than a silicon drift type radiation detection element. Therefore, the radiation detector 2 may be a radiation detector other than an SDD.

[0072] The present invention is not limited to the contents of the above-described embodiment, and various modifications are possible within the scope of the claims. In other words, embodiments obtained by combining technical means modified appropriately within the scope of the claims are also included in the technical scope of the present invention.

[0073] The matters described in each embodiment can be combined with each other. Furthermore, the independent claims and dependent claims described in the claims can be combined with each other in any and all combinations, regardless of the reference format. Furthermore, the claims use a format in which a claim references two or more other claims (multiple claim format), but this is not limited to this. A multiple claim (multi-multi claim) that references at least one other multiple claim may also be used.

[0074] REFERENCE SIGNS LIST 100 Radiation detection device 1 Radiation detection element 11 Semiconductor section 111 Incident surface 112 Electrode surface (rear surface) 12 Incident side electrode 13 Signal output electrode 14 First drift electrode 15 Second drift electrode 161 Insulating layer 162 Conductive layer 2 Radiation detector 22 Collimator 31 Voltage application section 32 Signal processing section (spectrum generation section) 34 Analysis section (spectrum generation section) 35 Display section 36 Irradiation section 42 Sample

Claims

1. A semiconductor device comprising: a plate-shaped semiconductor portion having an incident surface onto which radiation is incident; a signal output electrode provided on a back surface located on the back side of the incident surface, into which charges generated by the incidence of radiation onto the semiconductor portion flow and which outputs a signal corresponding to the charges; an incident side electrode provided on the incident surface, located on the back side of the signal output electrode, and to which a voltage necessary for the charges to flow into the signal output electrode is applied; a plurality of first drift electrodes provided on the back surface, surrounding the signal output electrode, and at different distances from the signal output electrode; and a plurality of second drift electrodes provided on the incident surface, surrounding the incident side electrode, and at different distances from the incident side electrode, wherein a voltage is applied to the plurality of first drift electrodes and the plurality of second drift electrodes so as to generate an electric field within the semiconductor for guiding the charges to the signal output electrode; and the plurality of first drift electrodes include a plurality of electrodes whose distance from the signal output electrode is less than a predetermined distance and a plurality of electrodes whose distance from the signal output electrode is greater than the predetermined distance, a radiation detection element characterized in that the average strength of the electric field generated by a plurality of the first drift electrodes that are located at a distance from the signal output electrode that is less than the predetermined distance is higher than the average strength of the electric field generated by a plurality of the first drift electrodes that are located at a distance from the signal output electrode that is greater than the predetermined distance.

2. The radiation detection element described in claim 1, characterized in that the area of ​​the incident side electrode on the incident surface is larger than the area of ​​the signal output electrode on the back surface, and when a voltage is applied to the multiple second drift electrodes, the potential of the multiple second drift electrodes changes monotonically from the second drift electrode located outermost among the multiple second drift electrodes toward the incident side electrode.

3. The radiation detection element according to claim 2, wherein among the plurality of first drift electrodes, the plurality of electrodes that are located at a distance from the signal output electrode that is less than the predetermined distance are located on the rear side of the incident side electrode.

4. The radiation detection element described in claim 3, characterized in that among the plurality of first drift electrodes, those whose distance from the signal output electrode exceeds the predetermined distance are located outside the range on the back side of the incident side electrode.

5. A radiation detection element as described in any one of claims 1 to 4, characterized in that when a voltage is applied to the plurality of first drift electrodes, the potential changes monotonically from the outermost first drift electrode to the innermost first drift electrode, and when a voltage is applied to the plurality of first drift electrodes that are located less than the predetermined distance from the signal output electrode, the potential changes in proportion to the square of the distance from the signal output electrode.

6. The radiation detection element of claim 5, wherein when a voltage is applied to the plurality of first drift electrodes whose distance from the signal output electrode exceeds the predetermined distance, the potential of the plurality of electrodes changes in proportion to the distance from the signal output electrode.

7. A radiation detection element as described in any one of claims 1 to 6, characterized in that an insulating layer is provided on the incident surface in a linear shape spanning the plurality of second drift electrodes, and a linear conductive layer connected to the incident-side electrode is provided on the insulating layer.

8. A radiation detector comprising the radiation detection element according to any one of claims 1 to 7, wherein at least a portion of the plurality of second drift electrodes of said radiation detection element is not covered by a collimator.

9. A radiation detection device comprising: an irradiation unit that irradiates a sample with radiation; a radiation detector according to claim 8; a voltage application unit that applies a voltage to a radiation detection element of said radiation detector; a spectrum generation unit that generates a spectrum of radiation detected by said radiation detector; and a display unit that displays the spectrum generated by said spectrum generation unit.

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