Radiation detection element manufacturing method, radiation detection element, and radiation detector

Abstract

Provided are a radiation detection element manufacturing method, a radiation detection element, and a radiation detector that make it possible to accurately detect radiation having low energy.　This radiation detection element manufacturing method comprises: forming an oxide layer composed of an oxide of a semiconductor on a first semiconductor layer; forming a second semiconductor layer on the oxide layer; and implanting, into the first semiconductor layer via the second semiconductor layer and the oxide layer, ions of a dopant that alters a semiconductor forming the first semiconductor layer to a semiconductor of a different type, thereby forming a doping layer composed of a semiconductor doped with the dopant between the first semiconductor layer and the oxide layer.

Description

Method for manufacturing radiation detection element, radiation detection element, and radiation detector

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

[0002] Some radiation detectors for detecting radiation such as X-rays include a radiation detection element using a semiconductor. A radiation detection element using a semiconductor includes a semiconductor layer, and a doping layer doped with a dopant and made of a different type of semiconductor from the semiconductor layer is provided on the incident side where radiation is incident. A voltage is applied to the semiconductor layer via the doping layer, generating an electric field inside the semiconductor layer. Charges are generated inside the semiconductor layer in response to the incidence of radiation, and the charges are collected according to the electric field, and a signal corresponding to the amount of charge is output, thereby detecting radiation. Patent Document 1 discloses an example of a radiation detection element.

[0003] Patent No. 6905825

[0004] The doping layer of a radiation detection element is overlaid with an oxide layer, and a conductive layer such as a metal layer is overlaid on the oxide layer. Radiation passes through the conductive layer and oxide layer and enters the semiconductor layer. When the radiation energy is low, the transmittance of the radiation through the oxide layer decreases, resulting in a decrease in radiation detection sensitivity. In addition, charges generated in the oxide layer by the radiation are accelerated by the electric field within the oxide layer, causing defects to form at the interface between the doping layer and the oxide layer. Some of the charges generated by the radiation are lost through the defects, reducing the amount of charge corresponding to the radiation. Since the radiation energy is detected according to the amount of charge, a decrease in the amount of charge results in a lower radiation energy being detected. These problems can be thought to be addressed by making the oxide layer thinner.

[0005] The doping layer of a radiation detection element is formed by implanting dopant ions into a semiconductor layer through an oxide layer. If the oxide layer is made thinner, the ions will be implanted deeper under the same acceleration voltage, resulting in a thicker doping layer. If the doping layer is thicker, the probability that charges generated by radiation incident on the semiconductor layer will be absorbed by the doping layer increases, resulting in the problem of low radiation energy being detected.

[0006] It is also possible to implant dopant ions into the semiconductor layer while the oxide layer is still thick, and then thin the oxide layer by etching. However, the ion implantation weakens the oxide bonds, making it difficult to adjust the etching rate. This makes it difficult to adjust the thickness of the oxide layer. As a result, it is difficult to realize a radiation detection element that can accurately detect low-energy radiation.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for manufacturing a radiation detection element, a radiation detection element, and a radiation detector that enable accurate detection of low-energy radiation.

[0008] A method for manufacturing a radiation detection element according to one aspect of the present invention includes forming an oxide layer made of an oxide of a semiconductor on a first semiconductor layer, forming a second semiconductor layer on the oxide layer, and injecting ions of a dopant that turns the semiconductor constituting the first semiconductor layer into a different type of semiconductor into the first semiconductor layer via the second semiconductor layer and the oxide layer, thereby forming a doped layer made of a semiconductor doped with the dopant between the first semiconductor layer and the oxide layer.

[0009] In one embodiment of the present invention, an oxide layer is formed on a first semiconductor layer, a second semiconductor layer is formed on the oxide layer, and dopant ions are implanted into the first semiconductor layer through the second semiconductor layer and the oxide layer to form a doped layer. Because the dopant ions penetrate the second semiconductor layer in addition to the oxide layer, the thickness of the doped layer can be made equivalent to that of a conventional doped layer even if the thickness of the oxide layer is made thinner than conventional. By making the thickness of the doped layer equivalent to that of conventional doped layers, problems such as reduced radiation detection sensitivity and low-energy radiation detection due to the thickness of the doped layer are prevented. Furthermore, by making the thickness of the oxide layer thinner than conventional doped layers, the detection sensitivity of low-energy radiation is improved. Therefore, low-energy radiation can be detected with high sensitivity and accuracy.

[0010] In a method for manufacturing a radiation detection element according to one aspect of the present invention, the thickness of the second semiconductor layer is reduced after the doping layer is formed.

[0011] In one embodiment of the present invention, the thickness of the second semiconductor layer is reduced after the doping layer is formed, which reduces the probability that radiation is absorbed by the second semiconductor layer when it passes through the second semiconductor layer, thereby improving the detection sensitivity for low-energy radiation.

[0012] A method for manufacturing a radiation detection element according to one aspect of the present invention is characterized in that a conductive layer is formed on the second semiconductor layer.

[0013] In one embodiment of the present invention, a conductive layer is formed on the second semiconductor layer. By forming a conductive layer with high light-shielding properties on the second semiconductor layer, the amount of light transmitted through the second semiconductor layer and the oxide layer is reduced, thereby reducing the generation of noise caused by light.

[0014] A method for manufacturing a radiation detection element according to one aspect of the present invention is characterized in that, after forming the doping layer, the second semiconductor layer is removed and a conductive layer is formed on the oxide layer.

[0015] In one embodiment of the present invention, the second semiconductor layer is removed and a conductive layer is formed on the oxide layer. Since the second semiconductor layer is no longer included in the radiation detection element, radiation is more easily incident on the first semiconductor layer of the radiation detection element, improving the detection sensitivity of low-energy radiation.

[0016] A method for manufacturing a radiation detection element according to one aspect of the present invention includes thermally oxidizing the first semiconductor layer to form the oxide layer, removing a portion of the oxide layer, and thermally oxidizing the first semiconductor layer after the portion of the oxide layer has been removed, thereby forming the oxide layer again in the portion from which the oxide layer was removed.

[0017] In one embodiment of the present invention, an oxide layer is formed by thermal oxidation of a first semiconductor layer, a portion of the oxide layer is removed, and an oxide layer is formed again by thermal oxidation of the first semiconductor layer. By adjusting the time of thermal oxidation, an oxide layer having a desired thickness can be easily formed.

[0018] A radiation detection element according to one aspect of the present invention is characterized by comprising: a first semiconductor layer into which radiation to be detected enters; a doping layer provided on the surface of the first semiconductor layer on which the radiation is incident and made of a semiconductor doped with a dopant that turns the semiconductor constituting the first semiconductor layer into a semiconductor of a different type; an oxide layer provided on the doping layer and made of an oxide of the semiconductor; and a second semiconductor layer provided on the oxide layer.

[0019] In one aspect of the present invention, a radiation detection element includes a first semiconductor layer, a doping layer provided on one surface of the first semiconductor layer, an oxide layer provided on the doping layer, and a second semiconductor layer provided on the oxide layer. When forming the doping layer, dopant ions can be implanted through the oxide layer and the second semiconductor layer. By allowing the dopant ions to penetrate the second semiconductor layer in addition to the oxide layer, the thickness of the doping layer can be made equivalent to that of a conventional element even if the thickness of the oxide layer is made thinner than conventional elements. By making the thickness of the doping layer equivalent to that of conventional elements, problems such as a decrease in radiation detection sensitivity and detection of low-energy radiation caused by the thickness of the doping layer are prevented. Furthermore, by making the thickness of the oxide layer thinner than conventional elements, the detection sensitivity of low-energy radiation is improved. Therefore, low-energy radiation can be detected with high sensitivity and accuracy.

[0020] A radiation detection element according to one aspect of the present invention is characterized in that the semiconductor constituting the first semiconductor layer is n-type, the dopant is boron, and the semiconductor constituting the second semiconductor layer is p-type.

[0021] In one embodiment of the present invention, the first semiconductor layer is an n-type semiconductor and is doped with boron to form a doped layer. The second semiconductor layer is a p-type semiconductor. The doped layer and the second semiconductor layer are made of the same type of semiconductor, and the second semiconductor layer can be used as an electrode for the doped layer. Since no electric field is generated between the second semiconductor layer and the doped layer, no electric field is generated in the oxide layer. Charges in the oxide layer are not accelerated by the electric field, and defects are not formed at the interface between the oxide layer and the doped layer due to the accelerated charges. Charges generated by radiation incident on the first semiconductor layer are not lost through defects, and low radiation energy is not detected due to defects.

[0022] In the radiation detection element according to one aspect of the present invention, the second semiconductor layer is made of polysilicon.

[0023] In one embodiment of the present invention, the second semiconductor layer is made of polysilicon, which allows the second semiconductor layer to be easily formed without adversely affecting the manufacturing process of the radiation detection element, such as by contaminating it.

[0024] The radiation detection element according to one aspect of the present invention further includes a conductive layer provided on the second semiconductor layer.

[0025] In one embodiment of the present invention, the radiation detection element includes a conductive layer on the second semiconductor layer. The conductive layer has a high light-shielding property, so that the amount of light transmitted through the second semiconductor layer and the oxide layer and incident on the doping layer or the first semiconductor layer is reduced. This reduces noise caused by light.

[0026] A radiation detection element according to one aspect of the present invention includes: a first semiconductor layer into which radiation to be detected is incident; a doping layer provided on a surface of the first semiconductor layer on which the radiation is incident and made of a semiconductor doped with a dopant that causes the semiconductor constituting the first semiconductor layer to become a semiconductor of a different type; an oxide layer provided on the doping layer and made of an oxide of the semiconductor; and a conductive layer provided on the oxide layer, wherein the oxide layer has a thickness of less than 50 nm, and the concentration of the dopant contained in the doping layer is 1×10 at a position 60 nm deep from the interface between the oxide layer and the doping layer. 18 atoms / cm 3 The present invention is characterized by the following:

[0027] In one embodiment of the present invention, the radiation detection element does not include a second semiconductor layer, but includes a conductive layer provided on an oxide layer, wherein the oxide layer has a thickness of less than 50 nm and a dopant concentration of 1×10 at a position 60 nm deep from the interface between the oxide layer and the doping layer. 18 atoms / cm 3 The thickness of the doping layer is the same as that of the conventional one, and the problems of reduced radiation detection sensitivity and low radiation energy detection caused by the thickness of the doping layer are prevented. Because there is no second semiconductor layer and the oxide layer is thinner than that of the conventional one, radiation can more easily enter the first semiconductor layer, improving radiation detection sensitivity.

[0028] A radiation detection element according to one embodiment of the present invention is characterized in that it further comprises a signal output electrode provided on the surface of the first semiconductor layer opposite to the surface on which the doped layer is provided, the signal output electrode outputting a signal in response to incident radiation, and a plurality of curved electrodes arranged in positions surrounding the signal output electrode, at different distances from the signal output electrode, and to which a voltage is applied so that the potential changes depending on the distance from the signal output electrode.

[0029] In one aspect of the present invention, the radiation detection element includes a signal output electrode provided on the back side of the doping layer and a plurality of curved electrodes arranged at positions surrounding the signal output electrode. A voltage is applied to the curved electrodes so that the potential varies depending on the distance from the signal output electrode. This allows the radiation detection element to function as a silicon drift type radiation detection element.

[0030] A radiation detector according to one aspect of the present invention includes a radiation detection element according to one aspect of the present invention, a circuit board on which the radiation detection element is mounted, a collimator that blocks a portion of the radiation before it enters the radiation detection element, and a housing that accommodates the radiation detection element, the circuit board, and the collimator, wherein the housing has an unobstructed opening, the radiation detection element is arranged with its incident surface, on which radiation is incident, facing the opening, and the collimator is arranged between the radiation detection element and the opening.

[0031] In one aspect of the present invention, a radiation detector includes a housing that houses a radiation detection element, and the housing has an opening that is not blocked by a window material. Because the opening is not blocked by a window material, low-energy radiation is easily incident on the radiation detection element. In other words, low-energy radiation is easily incident on the radiation detection element and is detected by the radiation detection element with high sensitivity.

[0032] The present invention has excellent effects such as making it possible to detect low-energy radiation with high sensitivity and precision.

[0033] 1 is a schematic cross-sectional view showing an example of a radiation detection element according to embodiment 1. FIG. 2 is a block diagram showing an example of the functional configuration of a radiation detection apparatus using the radiation detection element. FIG. 3 is a schematic cross-sectional view showing an example of the configuration of a radiation detector including the radiation detection element. FIG. 4 is a schematic cross-sectional view showing an example of a conventional radiation detection element. FIG. 5 is a schematic cross-sectional view showing a part of a process for manufacturing a conventional radiation detection element. FIG. 6 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 1. FIG. 7 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 1. FIG. 8 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 1. FIG. 9 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 1. FIG. 10 is a graph showing the transmittance of X-rays incident on a doping layer in the radiation detection element according to embodiment 1. FIG. 11 is a schematic cross-sectional view showing an example of a radiation detection element according to embodiment 2. FIG. 12 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 2. FIG. 13 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 2. FIG. 14 is a schematic cross-sectional view showing an example of a radiation detection element including a conductive layer formed on a second semiconductor layer whose thickness has been reduced. 1 is a graph showing the transmittance of X-rays incident on a doping layer in the radiation detection element according to embodiment 2. FIG. 2 is a schematic cross-sectional view showing an example of a radiation detection element according to embodiment 3. FIG. 3 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 3. FIG. 4 is a schematic cross-sectional view for explaining a method for manufacturing the radiation detection element according to embodiment 3. FIG. 5 is a graph showing the transmittance of X-rays incident on a doping layer in the radiation detection element according to embodiment 3.

[0034] The present invention will be described in detail below with reference to the drawings illustrating embodiments thereof. <Embodiment 1> Fig. 1 is a schematic cross-sectional view showing an example of a radiation detection element 1 according to embodiment 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 first semiconductor layer 11 made of Si (silicon). The first semiconductor layer 11 is composed of n-type Si. The first semiconductor layer 11 has a first surface 111 and a second surface 112 located on the back side of the first surface 111. The second surface 112 is a surface located on the incident side onto which radiation to be detected is incident.

[0035] A signal output electrode 15, which is an electrode that outputs a signal when radiation is detected, is provided at the center of the first surface 111. The signal output electrode 15 is made of the same type of Si as the first semiconductor layer 11. For example, the signal output electrode 15 is made of n+Si, which is Si doped with a specific dopant such as phosphorus. Furthermore, multiple ring-shaped curved electrodes 151 are provided on the first surface 111. The curved electrode 151 is made of a semiconductor of a different type from the first semiconductor layer 11, and is made of p-type Si, which is Si doped with a specific dopant such as boron. For example, the curved electrode 151 is made of p+Si. The ring-shaped curved electrodes 151 are approximately concentric, and the signal output electrode 15 is located approximately at the center of the multiple curved electrodes 151. In other words, the multiple curved electrodes 151 surround the signal output electrode 15, and the distances between the signal output electrode 15 and each curved electrode 151 are different.

[0036] 1 shows four curved electrodes 151, but in reality, more curved electrodes 151 are provided. Note that the shape of the curved electrodes 151 may be a modified ring shape, and the multiple curved electrodes 151 do not have to be concentric. Furthermore, the signal output electrode 15 may be disposed at a position other than the center of the multiple curved electrodes 151, or at a position other than the center of the first surface 111.

[0037] An annular guard electrode 152 is provided outside the multiple curved electrodes 151, and an annular ground electrode 153 is provided outside the guard electrode 152. The ground electrode 153 is connected to a ground potential. The potential of the guard electrode 152 is a floating potential. The guard electrode 152 prevents dielectric breakdown between the curved electrode 151 and the ground electrode 153. Although a single guard electrode 152 is shown in FIG. 1, multiple annular guard electrodes 152 are actually provided.

[0038] The first surface 111 is covered with an oxide layer 16 made of an oxide of Si. The signal output electrode 15, the curved electrode 151, the protective electrode 152, and the ground electrode 153 are connected by electrodes that penetrate the oxide layer 16. The oxide layer 16 and the electrodes may be covered with an insulating film (not shown) made of an oxide or nitride of Si.

[0039] A doping layer 12 made of a semiconductor doped with a dopant that turns Si into a semiconductor of a different type from the components of the first semiconductor layer 11 is formed on the second surface 112. The component of the doping layer 12 is p-type Si in which a specific dopant such as boron is doped into Si, for example, p+Si. The doping layer 12 is formed by doping a dopant into a portion of the first semiconductor layer 11. The doping layer 12 functions as an electrode to which a voltage is applied. The doping layer 12 includes a portion of the second surface 112 including the center of the second surface 112. The second surface 112 is an incident surface at a position where radiation to be detected by the radiation detection element 1 is incident, and the portion where the doping layer 12 is provided is an incident region where the radiation is incident. The incident region includes most of the area of ​​the second surface 112, including the center of the second surface 112.

[0040] The second surface 112 has a portion where the doping layer 12 is not formed, and an annular guard electrode 121 is provided outside the doping layer 12. The potential of the guard electrode 121 is floating. Although FIG. 1 shows a single guard electrode 121, in reality, multiple annular guard electrodes 121 are provided. The guard electrode 121 prevents dielectric breakdown between the edge of the first semiconductor layer 11 and the doping layer 12. The radiation detection element 1 may not include the ground electrode 153 on the first surface 111 side, but may include a ground electrode on the second surface 112 side. That is, the ground electrode 153 may not be provided, and a ground electrode may be provided outside the guard electrode 121. In this configuration, the guard electrode 121 prevents dielectric breakdown between the doping layer 12 and the ground electrode. The radiation detection element 1 may also include ground electrodes on both the first surface 111 side and the second surface 112 side.

[0041] The second surface 112 is covered with an oxide layer 13 made of an oxide of Si. That is, the oxide layer 13 is provided on the doped layer 12. In this embodiment, the radiation incident side is defined as the upper side. The protective electrode 121 is connected to an electrode that penetrates the oxide layer 13. A second semiconductor layer 14 is provided on the portion of the oxide layer 13 that covers the doped layer 12. Therefore, the portion of the oxide layer 13 that covers the doped layer 12 is covered with the second semiconductor layer 14. The second semiconductor layer 14 is made of the same semiconductor type as the doped layer 12, and is polysilicon. That is, the second semiconductor layer 14 is made of p-type polysilicon. The second semiconductor layer 14 is connected to the doped layer 12 through a portion of the oxide layer 13. The second semiconductor layer 14 is conductive and therefore functions as an electrode for the doped layer 12. In embodiment 1, no metallic conductive layer is provided on the second semiconductor layer 14.

[0042] A voltage is applied to the multiple curved electrodes 151 so that the innermost curved electrode 151 has the highest potential and the outermost curved electrode 151 has the lowest potential. The radiation detection element 1 is also configured so that a predetermined electrical resistance is generated between adjacent curved electrodes 151 that are at different distances from the signal output electrode 15. For example, an electrical resistance channel connecting the two curved electrodes 151 is formed by adjusting the components of the portion between adjacent curved electrodes 151. That is, the multiple curved electrodes 151 are connected in a daisy chain through electrical resistance. When a voltage is applied, each curved electrode 151 has a potential that monotonically increases in order from the outer curved electrode 151 to the inner curved electrode 151. That is, the potential of the curved electrodes 151 increases in order from the curved electrode 151 farthest from the signal output electrode 15 to the curved electrode 151 closest to the signal output electrode 15. The plurality of curved electrodes 151 may include a pair of adjacent curved electrodes 151 having the same potential.

[0043] The potentials of the multiple curved electrodes 151 generate an electric field (potential gradient) within the first semiconductor layer 11 such that the potential is higher the closer to the signal output electrode 15 and lower the farther from the signal output electrode 15. Furthermore, a voltage is applied to the doping layer 12 so that the potential of the doping layer 12 becomes the potential between the innermost curved electrode 151 and the outermost curved electrode 151. In this way, an electric field is generated within the first semiconductor layer 11 such that the potential is higher the closer to the signal output electrode 15.

[0044] Radiation such as X-rays, photons in general (including visible light, ultraviolet light, and infrared light), electron beams, or other charged particle beams is incident on the radiation detection element 1. The radiation mainly passes through the second surface 112 and enters the first semiconductor layer 11. An amount of charge corresponding to the energy of the radiation absorbed in the first semiconductor layer 11 is generated in the first semiconductor layer 11. The generated charges are electrons and holes. The generated charges move due to the electric field inside the first semiconductor layer 11, and one type of charge flows into the signal output electrode 15 in a concentrated manner. In this embodiment, electrons generated by the incidence of radiation move and flow into the signal output electrode 15. The signal output electrode 15 outputs a current signal corresponding to the amount of charge that has flowed in. The action of the electric field enables high-sensitivity radiation detection.

[0045] FIG. 2 is a block diagram showing an example of the functional configuration of a radiation detection apparatus 100 that uses a radiation detection element 1. The radiation detection apparatus 100 is, for example, an X-ray fluorescence analyzer. The radiation detection apparatus 100 includes an irradiation unit 4 that irradiates a sample 6 with radiation such as an electron beam or X-rays, a sample stage 5 on which the sample 6 is placed, and a radiation detector 2. The radiation detector 2 includes the radiation detection element 1 and a preamplifier 21. The preamplifier 21 is connected to a signal output electrode 15 of the radiation detection element 1. A signal output by the signal output electrode 15 is input to the preamplifier 21. The preamplifier 21 converts a current signal into a voltage signal. The value of the current signal corresponds to the amount of charge flowing into the signal output electrode 15, and the amount of charge corresponds to the energy of the radiation. Therefore, the preamplifier 21 outputs a signal with an intensity corresponding to the energy of the radiation. Note that a portion of the preamplifier 21 may be included inside the radiation detector 2, with the other portion being located outside the radiation detector 2.

[0046] Radiation is irradiated from the irradiation unit 4 to the sample 6, causing radiation such as fluorescent X-rays to be generated in the sample 6, and the radiation detector 2 detects the radiation generated from the sample 6. The radiation is indicated by arrows in FIG. 2 . The radiation detector 2 outputs a signal proportional to the energy of the detected radiation. Note that the radiation detection device 100 may be configured to hold the sample 6 by a method other than placing it on the sample stage 5.

[0047] The radiation detector 2 is connected to a voltage application unit 31 and a signal processing unit 32 that processes the output signal. The voltage application unit 31 is connected to the radiation detection element 1. The voltage application unit 31 applies a voltage to the curved electrode 151 and the doping layer 12. The signal processing unit 32 is connected to the preamplifier 21. When the preamplifier 21 outputs a signal, the radiation detector 2 outputs a signal with an intensity corresponding to the energy of the radiation. The signal processing unit 32 is connected to the analysis unit 34. The analysis unit 34 is configured to include a calculation unit that performs calculations and a memory that stores data. The voltage application unit 31, the signal processing unit 32, the analysis unit 34, and the irradiation unit 4 are connected to a control unit 33. The control unit 33 controls the operations of the voltage application unit 31, the signal processing unit 32, the analysis unit 34, and the irradiation unit 4.

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

[0049] The analysis unit 34 receives data indicating the relationship between the signal value output by the signal processing unit 32 and the count number. 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 value corresponds to the radiation energy and the count number corresponds to the number of times the radiation is detected, the radiation spectrum can be obtained from the relationship between the signal value and the count number. The spectrum indicates the relationship between the radiation energy and intensity. The process of counting the signals output by the radiation detector 2 for each signal value may be performed by the analysis unit 34 instead of the signal processing unit 32. The generation of the radiation spectrum may be performed by the signal processing unit 32. The analysis unit 34 may further perform information processing based on the radiation spectrum. For example, the analysis unit 34 performs qualitative or quantitative analysis of elements contained in the sample 6 based on the spectrum of characteristic X-rays from the sample 6.

[0050] A display unit 35 such as a liquid crystal display is connected to the analysis unit 34. The display unit 35 displays the spectrum generated by the analysis unit 34 and the analysis results by the analysis unit 34. The control unit 33 may be configured to receive operations from a user and control each unit of the radiation detection apparatus 100 in accordance with the received operations. The control unit 33 and the analysis unit 34 may also be configured as a single computer.

[0051] 2 shows a configuration in which radiation is irradiated onto the sample 6 and radiation generated from the sample 6 is detected, but the radiation detection device 100 may be configured to detect radiation that has passed through or been reflected by the sample 6. The radiation detection device 100 may be configured to scan the sample with radiation by changing the direction of the radiation. The radiation detection device 100 may be configured not to include the irradiation unit 4, the sample stage 5, the analysis unit 34, or the display unit 35.

[0052] FIG. 3 is a schematic cross-sectional view showing an example of the configuration of a radiation detector 2 including a radiation detection element 1. 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 includes a plate-like bottom plate covered with a cap-like cover. An opening 251 is formed at the tip of the housing 25. The opening 251 does not include a window having a window material, and is not blocked. The radiation detection element 1, a collimator 22, a circuit board 23, a cooling unit 26, and a cold finger 24 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 26. The cooling unit 26 is, for example, a Peltier element.

[0053] The radiation detection element 1 is mounted on the surface of the circuit board 23 and is disposed at a position facing the opening 251. The radiation detection element 1 is disposed so that its first surface 111 faces the circuit board 23 and its second surface 112 faces the opening 251. The collimator 22 is cylindrical with both ends open and made of a radiation-shielding material. The collimator 22 is disposed between the radiation detection element 1 and the opening 251. One end of the collimator 22 faces the opening 251, and the other end faces the surface of the radiation detection element 1. Radiation mainly passes through the opening 251 and enters the inside of the housing 25, and the collimator 22 blocks a portion of the radiation before it enters the radiation detection element 1. The portion of the second surface 112 other than the incident region where the doping layer 12 is present is covered with the radiation-shielding collimator 22, and radiation is not incident thereon. The incident region is not covered with the collimator 22, and radiation is incident thereon. The radiation detection element 1 detects incident radiation that is not blocked by the collimator 22 .

[0054] A circuit is formed on the circuit board 23, and the preamplifier 21 is mounted on its surface. The preamplifier 21 is omitted from Fig. 3 . The back surface of the circuit board 23 is in thermal contact with the heat absorption portion of the cooling unit 26, either directly or via an intervening object. The heat dissipation portion of the cooling unit 26 is in thermal contact with the cold finger 24. The cold finger 24 has a flat portion with which the heat dissipation portion of the cooling unit 26 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 26 through the circuit board 23, conducted from the cooling unit 26 to the cold finger 24, and dissipated to the outside of the radiation detector 2 through the cold finger 24.

[0055] The radiation detector 2 has a plurality of lead pins 27 penetrating the bottom plate portion of the housing 25. The lead pins 27 are connected to the circuit board 23 by a method such as wire bonding. The application of 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 through the lead pins 27. The radiation detector 2 may further include other components. Alternatively, the radiation detector 2 may have a configuration that does not include the cooling unit 26 and the cold finger 24.

[0056] In this embodiment, radiation that has passed through the opening 251 is mainly incident on and detected by the radiation detection element 1. Because the opening 251 is not blocked by a window material, radiation that is too low in energy to pass through the window material can also be incident on the radiation detection element 1. This allows the radiation detection device 100 to detect radiation that is too low in energy to pass through the window material. For example, by detecting low-energy fluorescent X-rays, it becomes possible to detect elements that emit fluorescent X-rays with low energy.

[0057] 4 is a schematic cross-sectional view showing an example of a conventional radiation detection element. In the conventional radiation detection element, the portion of the oxide layer 13 that covers the doping layer 12 is covered with a conductive layer 17 made of a conductive material. For example, the conductive layer 17 is a metal layer, and the component of the conductive layer 17 is Al (aluminum). The conductive layer 17 penetrates a part of the oxide layer 13 and is connected to the doping layer 12. The conductive layer 17 functions as an electrode for the doping layer 12.

[0058] In conventional radiation detection elements, radiation passes through the conductive layer 17 and the oxide layer 13 and enters the doping layer 12 and the first semiconductor layer 11. When the radiation energy is low, the radiation cannot pass through the oxide layer 13 and is absorbed, preventing the radiation from entering the first semiconductor layer 11, resulting in a decrease in radiation detection sensitivity. When radiation is absorbed by the oxide layer 13, charges are generated in the oxide layer 13. There is a difference between the work function of the metal that constitutes the conductive layer 17 and the work function of the semiconductor that constitutes the doping layer 12, and due to this difference, an electric field is generated between the conductive layer 17 and the doping layer 12, i.e., in the oxide layer 13. For example, the work function of Al is 4 eV, and the work function of p+Si is 5 eV.

[0059] Some of the charges generated in the oxide layer 13 are accelerated by the electric field in the oxide layer 13, causing defects to form at the interface between the oxide layer 13 and the doped layer 12. For example, the generated holes are accelerated toward the doped layer 12 and penetrate into the doped layer 12, breaking the lattice bonds near the interface and generating defects. For example, negatively charged defects (recombination centers) are generated on the doped layer 12 side of the interface, and positively charged defects are generated on the oxide layer 13 side.

[0060] A portion of the charge generated by the radiation incident on the first semiconductor layer 11 is lost through defects at the interface between the oxide layer 13 and the doping layer 12. For example, the generated electrons combine with holes through recombination centers and are lost. This reduces the amount of charge flowing into the signal output electrode 15 in response to the incident radiation. Since the energy of the radiation is determined by the amount of charge, a decrease in the amount of charge results in the radiation being detected as having a lower energy. In the radiation spectrum, a tailing characteristic defect occurs in which the intensity of the peak decreases and the intensity of the tail portion on the lower energy side of the peak increases.

[0061] It is thought that the reduction in radiation detection sensitivity and poor tailing characteristics can be improved by thinning the oxide layer 13. However, simply thinning the oxide layer 13 does not solve the problem. FIG. 5 is a schematic cross-sectional view showing a part of the process for manufacturing a conventional radiation detection element. After the oxide layer 13 is formed, ions are implanted into the first semiconductor layer 11 through the oxide layer 13 before the conductive layer 17 is formed. The ion trajectories are indicated by arrows. The implanted ions are dopant ions that make Si p-type, such as boron ions. The dopant ions penetrate the oxide layer 13 and are implanted into the first semiconductor layer 11. As a result of the ion implantation, a portion of the first semiconductor layer 11 is doped with the dopant, forming a doped layer 12.

[0062] If the oxide layer 13 is thin, dopant ions reach deeper positions in the first semiconductor layer 11 during ion implantation, resulting in a thicker doped layer 12. As the doped layer 12 becomes thicker, the probability that charges generated by radiation incident on the first semiconductor layer 11 will disappear increases. More specifically, the thicker the doped layer 12, the higher the probability that electrons generated by radiation will enter the doped layer 12 without moving to the signal output electrode 15, and the electrons that enter the doped layer 12 combine with holes in the doped layer 12 and disappear. Therefore, the amount of charges that flow into the signal output electrode 15 in response to incident radiation decreases. Consequently, a decrease in radiation detection sensitivity and poor tailing characteristics still occur.

[0063] It is also conceivable to perform ion implantation with the oxide layer 13 thickened, and then thin the oxide layer 13 by etching. However, the ion implantation weakens the bonds of the oxide, making it difficult to adjust the etching rate. This makes it difficult to adjust the thickness of the oxide layer 13. For example, the thickness of the oxide layer 13 may become non-uniform or unclear. This requires work to confirm whether the thickness of the oxide layer 13 is appropriate, which increases costs.

[0064] In the first embodiment, the thickness of the oxide layer 13 is thinner than that of a conventional oxide layer 13. Furthermore, as shown in Fig. 1, in the first embodiment, the radiation detection element 1 includes a second semiconductor layer 14 on a portion of the oxide layer 13 that covers the doped layer 12. The total thickness of the oxide layer 13 and the second semiconductor layer 14 in the first embodiment is equivalent to the thickness of the oxide layer 13 in the conventional radiation detection element.

[0065] 6A, 6B, 6C, 7A, and 7B are schematic cross-sectional views illustrating a manufacturing method of the radiation detection element 1 according to the first embodiment. As shown in FIG. 6A, the radiation detection element 1 is manufactured from a plate-shaped semiconductor substrate. The semiconductor substrate is a first semiconductor layer 11. As shown in FIG. 6B, an oxide layer 16 covering the first surface 111 and an oxide layer 13 covering the second surface 112 are formed. The oxide layers 13 and 16 are formed by thermally oxidizing the first semiconductor layer 11. The first semiconductor layer 11 is gradually oxidized from the surface, and a portion of the first semiconductor layer 11 becomes an oxide, thereby forming the oxide layers 13 and 16. By adjusting the time for thermal oxidation, the oxide layer 13 having a desired thickness can be easily formed.

[0066] 6C , at least a portion of the oxide layer 13 along the second surface 112 is partially etched in the thickness direction to reduce the thickness of a portion of the oxide layer 13. The reduced thickness of the oxide layer 13 is located above the doped layer 12 to be formed. The thickness of the portion of the oxide layer 13 above the doped layer 12 is thinner than the thickness of the portion of the oxide layer 13 above the doped layer 12 in a conventional radiation detection element. Note that the entire thickness of the oxide layer 13 may be reduced.

[0067] Alternatively, a portion of the oxide layer 13 along the second surface 112 may be removed by etching, and the first semiconductor layer 11 after the oxide layer 13 has been removed may be thermally oxidized to form the oxide layer 13 again in the portion from which the oxide layer 13 was once removed. In this case, the thickness of the portion of the oxide layer 13 to be formed again is made thinner than that of the other portions of the oxide layer 13. By adjusting the length of time for which the thermal oxidation of the first semiconductor layer 11 is continued, the thickness of the portion of the oxide layer 13 to be formed again can be adjusted to a predetermined thickness. In this way, the thickness of a portion of the oxide layer 13, i.e., the thickness of the portion of the oxide layer 13 where the second semiconductor layer 14 will be formed, can be made thinner. This method makes it easy to obtain an oxide layer 13 having a desired thickness.

[0068] Appropriately positioned portions of the oxide layer 13 are removed by etching, and dopant ions are implanted into the first semiconductor layer 11, thereby forming the protective electrode 121. Also, appropriate positions of the oxide layer 16 are removed by etching, and dopant ions are implanted into the first semiconductor layer 11, thereby forming the signal output electrode 15, the curved electrode 151, the protective electrode 152, and the ground electrode 153.

[0069] 7A , the second semiconductor layer 14 is formed on the thinner portion of the oxide layer 13. For example, the second semiconductor layer 14 is formed by vapor phase growth. By using polysilicon as the component of the second semiconductor layer 14, the second semiconductor layer 14 can be easily formed without adversely affecting the manufacturing process of the radiation detection element 1, such as by contamination. The total thickness of the oxide layer 13 and the second semiconductor layer 14 is adjusted to be the same as the thickness of the oxide layer 13 in a conventional radiation detection element. For example, the thickness of the oxide layer 13 is 20 nm, and the thickness of the second semiconductor layer 14 is 60 nm.

[0070] 7B , ions are implanted into the first semiconductor layer 11 through the oxide layer 13 and the second semiconductor layer 14. For example, ion implantation is performed by colliding dopant ions accelerated by a voltage with the second semiconductor layer 14. The ion trajectories are indicated by arrows. The dopant ions pass through the second semiconductor layer 14 and the oxide layer 13 and are implanted into the first semiconductor layer 11. By implanting the dopant ions, the dopant is doped into Si, producing p-type Si. The portion of the first semiconductor layer 11 doped with the dopant becomes the doped layer 12. In this way, the doped layer 12 is formed. The concentration of the dopant contained in the doped layer 12 is 1×10 at a position 60 nm deep from the interface between the oxide layer 13 and the doped layer 12. 18 atoms / cm 3 Here, atoms indicates the number of dopant atoms, and atoms / cm 3 is a unit of concentration, indicating the number of dopant atoms per cubic centimeter.

[0071] The total thickness of the oxide layer 13 and the second semiconductor layer 14 is equivalent to the thickness of the oxide layer 13 in a conventional radiation detection element. Furthermore, polysilicon and silicon oxide have equivalent dopant ion permeability. Therefore, the depth to which the dopant ions reach into the first semiconductor layer 11 during ion implantation is substantially the same as that in a conventional radiation detection element. Therefore, the thickness of the doped layer 12 is substantially the same as that of the doped layer 12 in a conventional radiation detection element. After the doped layer 12 is formed, electrodes connected to the protection electrode 121, the signal output electrode 15, the curved electrode 151, the protection electrode 152, and the ground electrode 153 are formed, completing the radiation detection element 1 as shown in FIG. 1 .

[0072] In the radiation detection element 1 according to the first embodiment, radiation to be detected passes through the oxide layer 13 and the second semiconductor layer 14 and enters the first semiconductor layer 11. The thickness of the oxide layer 13 is thinner than the thickness of the oxide layer 13 in conventional radiation detection elements. The total thickness of the oxide layer 13 and the second semiconductor layer 14 is equivalent to the thickness of the oxide layer 13 in conventional radiation detection elements. The radiation detection element 1 according to the first embodiment does not have a conductive layer, so the thickness of the material through which the radiation to be detected passes before entering the first semiconductor layer 11 is thinner than in conventional elements. The proportion of the radiation to be detected that is absorbed before entering the first semiconductor layer 11 is lower than in conventional elements, improving the detection sensitivity for low-energy radiation.

[0073] In the radiation detection element 1 according to embodiment 1, the thickness of the doped layer 12 is substantially the same as the thickness of the doped layer 12 in conventional radiation detection elements, and the probability that electrons generated by radiation will penetrate the doped layer 12 is approximately the same as in conventional radiation detection elements. Therefore, the amount of charge flowing into the signal output electrode 15 in response to incident radiation is not reduced compared to conventional cases due to the thickness of the doped layer 12. Therefore, a decrease in radiation detection sensitivity and poor tailing characteristics due to the thickness of the doped layer 12 do not occur.

[0074] In the radiation detection element 1 according to the first embodiment, the second semiconductor layer 14 also functions as an electrode for the doped layer 12. The second semiconductor layer 14 and the doped layer 12 are made of the same type of semiconductor, and there is no difference in the work function of the semiconductor constituting the second semiconductor layer 14 and the semiconductor constituting the doped layer 12. Therefore, no electric field is generated between the second semiconductor layer 14 and the doped layer 12. That is, no electric field is generated within the oxide layer 13. Even if radiation is absorbed within the oxide layer 13 and charges are generated, the charges are not accelerated by the electric field. Therefore, defects are not formed at the interface between the oxide layer 13 and the doped layer 12 due to the accelerated charges. Because no defects are formed at the interface, charges generated by radiation incident on the first semiconductor layer 11 are not lost through the defects. The amount of charges flowing into the signal output electrode 15 in response to the incidence of radiation is not reduced due to defects formed at the interface. Defects formed at the interface do not cause tailing characteristic defects.

[0075] Even if some voltage is generated within the oxide layer 13, the oxide layer 13 is thin, so the probability that radiation will be absorbed within the oxide layer 13 and electric charges will be generated is low. Furthermore, because the oxide layer 13 is thin, the distance over which electric charges are accelerated is short, and the electric charges are not accelerated very much. Therefore, few defects are formed at the interface between the oxide layer 13 and the doping layer 12, and the amount of electric charges flowing into the signal output electrode 15 is unlikely to decrease due to defects. Therefore, poor tailing characteristics due to defects formed at the interface are unlikely to occur. Similar effects can be achieved if the thickness of the oxide layer 13 is 50 nm or less.

[0076] FIG. 8 is a graph showing the transmittance of X-rays incident on the doping layer 12 in the radiation detection element 1 according to embodiment 1. The horizontal axis in the graph represents X-ray energy, and the vertical axis represents X-ray transmittance. The dashed line represents the transmittance in the conventional radiation detection element, and the solid line represents the transmittance in the radiation detection element 1 according to embodiment 1. In the conventional radiation detection element whose transmittance is shown in FIG. 8, the oxide layer has a thickness of 80 nm, and the conductive layer has a thickness of 30 nm. In the radiation detection element 1 according to embodiment 1 whose transmittance is shown in FIG. 8, the oxide layer 13 has a thickness of 20 nm, and the second semiconductor layer 14 has a thickness of 60 nm. For the conventional radiation detection element, the transmittance of X-rays transmitted through the oxide layer and the conductive layer is shown. For the radiation detection element 1 according to embodiment 1, the transmittance of X-rays transmitted through the oxide layer 13 and the second semiconductor layer 14 is shown.

[0077] The radiation detection element 1 according to the first embodiment has a higher X-ray transmittance than conventional elements in the low-energy region below 250 eV. In particular, the X-ray transmittance is significantly higher in the low-energy region below 100 eV. In this way, the first embodiment improves the sensitivity for detecting low-energy radiation. For example, the sensitivity for detecting characteristic X-rays of Be (beryllium) with an energy of 109 eV or characteristic X-rays of B (boron) with an energy of 183 eV is improved.

[0078] As described above in detail, the radiation detection element 1 according to embodiment 1 has improved radiation detection sensitivity, particularly improved detection sensitivity for low-energy radiation. Furthermore, even when low-energy radiation is incident on the radiation detection element 1, poor tailing characteristics are unlikely to occur. This makes it possible to accurately identify the energy of radiation, even if the energy is low. Therefore, the radiation detection element 1 according to embodiment 1 can detect low-energy radiation with high sensitivity and precision. In embodiment 1, the opening 251 is not covered with a window material, so low-energy radiation is more likely to be incident on the radiation detection element 1. That is, low-energy radiation is more likely to be incident on the radiation detection element 1, and is detected by the radiation detection element 1 with high sensitivity and precision. Therefore, by using the radiation detector 2 according to embodiment 1, it is possible to reliably detect low-energy radiation with high sensitivity and precision.

[0079] 9 is a schematic cross-sectional view showing an example of a radiation detection element 1 according to embodiment 2. The configuration of the radiation detection device 100 other than the radiation detection element 1 is the same as that of embodiment 1. The thickness of the second semiconductor layer 14 in embodiment 2 is thinner than that of the second semiconductor layer 14 in embodiment 1. The configuration of the other parts of the radiation detection element 1 is the same as that of embodiment 1.

[0080] 10A and 10B are schematic cross-sectional views for explaining a manufacturing method of a radiation detection element 1 according to embodiment 2. As in embodiment 1, an oxide layer 13 is formed, and then a signal output electrode 15, a curved electrode 151, a protective electrode 152, and a ground electrode 153 are formed. As in embodiment 1, the thickness of the portion of the oxide layer 13 above the doping layer 12 is thinner than the thickness of the portion of the oxide layer 13 above the doping layer 12 in a conventional radiation detection element. As in embodiment 1, a second semiconductor layer 14 is formed on the oxide layer 13. The total thickness of the oxide layer 13 and the second semiconductor layer 14 at this point is the same as in embodiment 1.

[0081] 10A, ions are implanted into the first semiconductor layer 11 through the oxide layer 13 and the second semiconductor layer 14, as in the first embodiment. The trajectories of the dopant ions are indicated by arrows. A doped layer 12 is formed by the ion implantation. Since the total thickness of the oxide layer 13 and the second semiconductor layer 14 at the time of ion implantation is the same as in the first embodiment, the thickness of the doped layer 12 is also the same as in the first embodiment. In the second embodiment, the concentration of the dopant contained in the doped layer 12 is 1×10 at a position 60 nm deep from the interface between the oxide layer 13 and the doped layer 12. 18 atoms / cm 3 The following is the result.

[0082] As shown in Fig. 10B , after the ion implantation, the thickness of the second semiconductor layer 14 is reduced. In Fig. 10B , the surface of the second semiconductor layer 14 before the thickness reduction is indicated by a dashed line. The thickness of the second semiconductor layer 14 is reduced, for example, by etching. After the thickness of the second semiconductor layer 14 is reduced, electrodes connected to the protection electrode 121, the signal output electrode 15, the curved electrode 151, the protection electrode 152, and the ground electrode 153 are formed, thereby completing the radiation detection element 1 as shown in Fig. 9 . The second semiconductor layer 14 also functions as an electrode for the doping layer 12.

[0083] In the second embodiment, the thickness of the second semiconductor layer 14 is reduced after ion implantation, and therefore the thickness of the second semiconductor layer 14 is thinner than the second semiconductor layer 14 in the first embodiment. This reduces the probability that radiation will be absorbed by the second semiconductor layer 14 when passing through the second semiconductor layer 14. This improves the detection sensitivity for low-energy radiation. The thickness of the second semiconductor layer 14 in the second embodiment is less than 60 nm and equal to or greater than 20 nm. For example, the thickness of the second semiconductor layer 14 is 20 nm. If the thickness of the second semiconductor layer 14 is less than 20 nm, the performance as an electrode will be reduced.

[0084] The manufacturing method of the radiation detection element 1 may be in a form in which a conductive layer is formed on the second semiconductor layer 14 whose thickness has been reduced. FIG. 11 is a schematic cross-sectional view showing an example of a radiation detection element 1 including a conductive layer 17 formed on the second semiconductor layer 14 whose thickness has been reduced. The radiation detection element 1 includes the conductive layer 17 provided on the second semiconductor layer 14. The conductive layer 17 covers the second semiconductor layer 14. For example, the conductive layer 17 is made of Au (gold). The conductive layer 17 may also be made of Al, Be, or C (carbon). For example, the thickness of the conductive layer 17 is 10 nm. The conductive layer 17 also functions as an electrode for the doping layer 12.

[0085] In this method of manufacturing the radiation detection element 1, after the process of reducing the thickness of the second semiconductor layer 14 shown in Fig. 10B, the conductive layer 17 is formed on the second semiconductor layer 14. For example, the conductive layer 17 is formed by sputtering. After the conductive layer 17 is formed, electrodes connected to the protection electrode 121, the signal output electrode 15, the curved electrode 151, the protection electrode 152, and the ground electrode 153 are formed, thereby completing the radiation detection element 1 as shown in Fig. 11.

[0086] 12 is a graph showing the transmittance of X-rays incident on the doping layer 12 in the radiation detection element 1 according to embodiment 2. The horizontal axis in the graph represents X-ray energy, and the vertical axis represents X-ray transmittance. The transmittance in the conventional radiation detection element is shown by a dashed line, the transmittance in the radiation detection element 1 according to embodiment 2 that does not have the conductive layer 17 is shown by a broken line, and the transmittance in the radiation detection element 1 according to embodiment 2 that has the conductive layer 17 is shown by a solid line. For the radiation detection element 1 according to embodiment 2 that does not have the conductive layer 17, the transmittance of X-rays that have passed through the oxide layer 13 and the second semiconductor layer 14 is shown. For the radiation detection element 1 according to embodiment 2 that has the conductive layer 17, the transmittance of X-rays that have passed through the oxide layer 13, the second semiconductor layer 14, and the conductive layer 17 is shown.

[0087] In the conventional radiation detection element whose transmittance is shown in Figure 12, the oxide layer has a thickness of 80 nm and the conductive layer has a thickness of 30 nm. In the radiation detection element 1 according to embodiment 2 whose transmittance is shown in Figure 12, ion implantation is performed with the oxide layer 13 having a thickness of 20 nm and the second semiconductor layer 14 having a thickness of 60 nm, and then the thickness of the second semiconductor layer 14 is reduced to 20 nm. In other words, ion implantation is performed with the total thickness of the oxide layer 13 and the second semiconductor layer 14 set to the same thickness as the oxide layer in the conventional radiation detection element, and then the thickness of the second semiconductor layer 14 is reduced. In addition, the conductive layer 17 is made of Au, and its thickness is 10 nm.

[0088] In the radiation detection element 1 according to embodiment 2 that does not have the conductive layer 17, the thickness of the second semiconductor layer 14 is thinner than in embodiment 1, and therefore the transmittance of X-rays is higher than in embodiment 1. In the radiation detection element 1 according to embodiment 2 that has the conductive layer 17, the number of layers through which X-rays pass before entering the doped layer 12 increases, and therefore the transmittance of X-rays is lower than in the radiation detection element 1 that does not have the conductive layer 17.

[0089] In both radiation detection elements 1 according to embodiment 2, the transmittance of X-rays in the low-energy region of less than 250 eV is higher than that of conventional elements. For example, in the radiation detection element 1 without the conductive layer 17, the transmittance of Be characteristic X-rays with an energy of 109 eV is about 3.7 times that of conventional radiation detection elements, and the transmittance of B characteristic X-rays with an energy of 183 eV is about twice that of conventional radiation detection elements. In this way, embodiment 2 also improves the sensitivity for detecting low-energy radiation.

[0090] In the second embodiment, the thickness of the doping layer 12 is the same as in the first embodiment, so a decrease in radiation detection sensitivity and poor tailing characteristics due to the thickness of the doping layer 12 do not occur. As in the first embodiment, there is no difference between the work function of the semiconductor constituting the second semiconductor layer 14 and the work function of the semiconductor constituting the doping layer 12, so no electric field is generated in the oxide layer 13. As in the first embodiment, defects are not formed at the interface between the oxide layer 13 and the doping layer 12 due to the influence of the electric field, so poor tailing characteristics due to defects do not occur. Therefore, the radiation detection element 1 can detect low-energy radiation with high sensitivity and accuracy. Furthermore, by using the radiation detector 2, it is possible to reliably detect low-energy radiation with high sensitivity and accuracy.

[0091] The conductive layer 17 has a higher light-shielding property than the second semiconductor layer 14. In the radiation detection element 1 having the conductive layer 17, the conductive layer 17 covers the second semiconductor layer 14, and therefore, compared to embodiment 1, less light is transmitted through the second semiconductor layer 14 and the oxide layer 13 and enters the doped layer 12 or the first semiconductor layer 11. This reduces the generation of noise caused by light entering the doped layer 12 or the first semiconductor layer 11. Therefore, the radiation detection element 1 having the conductive layer 17 can detect radiation with higher accuracy.

[0092] 13 is a schematic cross-sectional view showing an example of a radiation detection element 1 according to embodiment 3. The configuration of the radiation detection device 100 other than the radiation detection element 1 is the same as that of embodiment 1. The radiation detection element 1 according to embodiment 3 does not have a second semiconductor layer 14. The radiation detection element 1 includes an oxide layer 13 and a conductive layer 17 provided on the oxide layer 13. The conductive layer 17 covers the oxide layer 13.

[0093] The thickness of the oxide layer 13 is less than 50 nm and equal to or greater than 10 nm. For example, the thickness of the oxide layer 13 is 20 nm. The component of the conductive layer 17 is Au, Al, Be, or C. For example, the conductive layer 17 is made of Au, and the thickness of the conductive layer 17 at the portion overlapping the oxide layer 13 is 10 nm. If the component of the conductive layer 17 is Al or Be, Al and Be oxidize, so the thickness of the conductive layer 17 must be greater than the thickness of Au to maintain conductivity. For example, the conductive layer 17 is made of Al, and the thickness of the conductive layer 17 at the portion overlapping the oxide layer 13 is 30 nm. The concentration of the dopant contained in the doping layer 12 is 1×10 at a position 60 nm deep from the interface between the oxide layer 13 and the doping layer 12. 18 atoms / cm 3 The following is the result.

[0094] 14A, 14B, and 14C are schematic cross-sectional views for explaining a manufacturing method of a radiation detection element 1 according to embodiment 3. As in embodiments 1 and 2, an oxide layer 13 is formed, a signal output electrode 15, a curved electrode 151, a protective electrode 152, and a ground electrode 153 are formed, and a second semiconductor layer 14 is formed. At this time, the second semiconductor layer 14 is formed so as not to contact the first semiconductor layer 11. As shown in FIG. 14A, as in embodiments 1 and 2, ions are implanted into the first semiconductor layer 11 through the oxide layer 13 and the second semiconductor layer 14. The trajectories of the dopant ions are indicated by arrows. A doped layer 12 is formed by the ion implantation. The thickness of the oxide layer 13 and the second semiconductor layer 14 is such that the dopant concentration is 1×10 at a position 60 nm deep from the interface between the oxide layer 13 and the doped layer 12. 18 atoms / cm 3 It has been adjusted as follows:

[0095] After the doping layer 12 is formed by ion implantation, the second semiconductor layer 14 is removed as shown in FIG. 14B. For example, the second semiconductor layer 14 is removed by dry etching or wet etching. Also, as shown in FIG. 14B, a portion of the oxide layer 13 is opened. Next, as shown in FIG. 14C, a conductive layer 17 is formed on the oxide layer 13. For example, the conductive layer 17 is formed by sputtering. After the conductive layer 17 is formed, electrodes connected to the guard electrode 121, the signal output electrode 15, the curved electrode 151, the guard electrode 152, and the ground electrode 153 are formed.

[0096] The conductive layer 17 stabilizes the surface potential of the oxide layer 13. The conductive layer 17 functions as an electrode for the doping layer 12 and also has a light-shielding property. Because the conductive layer 17 has a light-shielding property, the amount of light that passes through the oxide layer 13 and enters the doping layer 12 or the first semiconductor layer 11 is reduced. This reduces the generation of noise caused by light that enters the doping layer 12 or the first semiconductor layer 11, improving the accuracy of radiation detection.

[0097] In a conventional radiation detection element that does not utilize a second semiconductor layer during manufacturing, poor tailing characteristics occur when the oxide layer thickness is less than 50 nm. The concentration of the dopant contained in the conventional radiation detection element was measured by SIMS (Secondary Ion Mass Spectrometry). In a conventional radiation detection element with an oxide layer thickness of 50 nm, the dopant concentration was 1×10 at a position 60 nm deep from the interface between the oxide layer and the doping layer. 18 atoms / cm 3 The measurement result was that, in the conventional radiation detection device, when the oxide layer becomes thinner, the dopant concentration becomes higher. That is, in the conventional radiation detection device, when the oxide layer thickness is less than 50 nm, the dopant concentration becomes 1×10 at a position 60 nm deep from the interface between the oxide layer and the doping layer. 18 atoms / cm 3In conventional radiation detection elements, when the thickness of the oxide layer is less than 50 nm, poor tailing characteristics occur. Therefore, the dopant concentration at a position 60 nm deep from the interface exceeds 1×10 18 atoms / cm 3 On the other hand, if the dopant concentration exceeds 1×10 at a position 60 nm deep from the interface, poor tailing characteristics will occur. 18 atoms / cm 3 If it is below this value, no tailing characteristic defects will occur.

[0098] In the third embodiment, the thickness of the oxide layer 13 is set to less than 50 nm by the manufacturing method using the second semiconductor layer 14, and the dopant concentration at a position 60 nm deep from the interface between the oxide layer 13 and the doped layer 12 is set to 1×10 18 atoms / cm 3 The dopant concentration was 1×10 18 atoms / cm 3 The portion exceeding this is located at a depth of less than 60 nm from the interface. Therefore, the thickness of the doping layer 12 is the same as that of the conventional doping layer. Because the thickness of the doping layer 12 is the same as that of the conventional doping layer, a decrease in radiation detection sensitivity and poor tailing characteristics caused by the thickness of the doping layer 12 do not occur. While preventing the occurrence of poor tailing characteristics, the thickness of the oxide layer 13 is thinner than that of the oxide layer in the conventional radiation detection element. Because the second semiconductor layer 14 is absent and the oxide layer 13 is thinner than that of the conventional doping layer 12, radiation is more easily incident on the first semiconductor layer 11, improving radiation detection sensitivity. In particular, low-energy radiation is more easily incident on the first semiconductor layer 11, making it possible to detect low-energy radiation with higher sensitivity and accuracy.

[0099] If the thickness of the oxide layer 13 is less than 10 nm, it is difficult to form the oxide layer 13 so that the thickness is stable. For example, holes may be formed in the oxide layer 13. For this reason, the thickness of the oxide layer 13 is 10 nm or more. Preferably, the thickness of the oxide layer 13 is 10 nm or more and 20 nm or less.

[0100] 15 is a graph showing the transmittance of X-rays incident on the doping layer 12 in the radiation detection element 1 according to embodiment 3. In the graph, the horizontal axis represents X-ray energy, and the vertical axis represents X-ray transmittance. The transmittance is the transmittance of X-rays that have passed through the conductive layer 17 and the oxide layer 13. The transmittance in the conventional radiation detection element is shown by a dashed-dotted line. In the conventional radiation detection element, the oxide layer is 80 nm thick, the conductive layer is made of Al, and the conductive layer is 30 nm thick. The solid line shows the transmittance in the radiation detection element 1 according to embodiment 3, in which the conductive layer 17 is made of Al. In this radiation detection element 1, the oxide layer 13 is 20 nm thick, and the conductive layer 17 made of Al is 30 nm thick. The dashed line shows the transmittance in the radiation detection element 1 according to embodiment 3, in which the conductive layer 17 is made of Au. In this radiation detection element 1, the oxide layer 13 has a thickness of 20 nm, and the conductive layer 17 made of Au has a thickness of 10 nm.

[0101] In all of the radiation detection elements 1 according to embodiment 3, the transmittance of X-rays is higher than conventional ones in the low-energy region below 250 eV. For example, in a radiation detection element 1 in which the conductive layer 17 is made of Au and has a thickness of 10 nm, the transmittance of Be characteristic X-rays is about 3.9 times that of conventional radiation detection elements, and the transmittance of B characteristic X-rays is about 2.4 times that of conventional radiation detection elements. Thus, embodiment 3 also improves the sensitivity for detecting low-energy radiation.

[0102] The radiation detection element 1 according to Embodiments 1 to 3 may have a configuration in which another layer is present between the first semiconductor layer 11 and the doping layer 12. The radiation detection element 1 may have a configuration in which another layer is present between the doping layer 12 and the oxide layer 13, or may have a configuration in which another layer is present between the oxide layer 13 and the second semiconductor layer 14. The radiation detection element 1 according to Embodiment 1 may have a configuration in which another layer is present on the second semiconductor layer 14. The radiation detection element 1 according to Embodiment 2 may have a configuration in which another layer is present between the second semiconductor layer 14 and the conductive layer 17, or may have a configuration in which another layer is present on the conductive layer 17. The radiation detection element 1 according to Embodiment 3 may have a configuration in which another layer is present between the oxide layer 13 and the conductive layer 17.

[0103] In the first to third embodiments, the radiation detection element 1 has one set of the signal output electrode 15 and the plurality of curved electrodes 151. However, the radiation detection element 1 may have a plurality of sets of the signal output electrode 15 and the plurality of curved electrodes 151. In the first to third embodiments, the radiation detection element 1 is configured using a semiconductor made of Si. However, the radiation detection element 1 may be configured using a semiconductor other than Si. In the first to third embodiments, the first semiconductor layer 11 is configured using an n-type semiconductor, and the doping layer 12 and the second semiconductor layer 14 are configured using a p-type semiconductor. However, the radiation detection element 1 may be configured using a first semiconductor layer 11 made using a p-type semiconductor, and the doping layer 12 and the second semiconductor layer 14 are configured using an n-type semiconductor. In the first to third embodiments, the radiation detection element 1 is configured using a silicon drift radiation detection element. However, the radiation detection element 1 may be a semiconductor element other than a silicon drift radiation detection element. Therefore, the radiation detector 2 may be a radiation detector other than an SDD.

[0104] In the first to third embodiments, the radiation detector 2 does not have a window having a window material, but the radiation detector 2 may have a window having a window material. In the first to third embodiments, the radiation detector 2 has a collimator 22, but the radiation detector 2 may not have the collimator 22. In the first to third embodiments, the radiation detection element 1 is housed in the housing 25, but the radiation detector 2 may not have the housing 25.

[0105] 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.

[0106] 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.

[0107] REFERENCE SIGNS LIST 100 Radiation detection device 1 Radiation detection element 11 First semiconductor layer 12 Doping layer 13 Oxide layer 14 Second semiconductor layer 15 Signal output electrode 151 Curved electrode 17 Conductive layer 2 Radiation detector 21 Preamplifier 22 Collimator 23 Circuit board 25 Housing 251 Opening 4 Irradiation unit 6 Sample

Claims

1. A method for manufacturing a radiation detection element comprising the steps of: forming an oxide layer made of an oxide of a semiconductor on a first semiconductor layer; forming a second semiconductor layer on said oxide layer; and injecting ions of a dopant that turns the semiconductor constituting said first semiconductor layer into a different type of semiconductor into said first semiconductor layer through said second semiconductor layer and said oxide layer, thereby forming a doped layer made of a semiconductor doped with said dopant between said first semiconductor layer and said oxide layer.

2. The method for manufacturing a radiation detection element according to claim 1, characterized in that after forming the doping layer, the thickness of the second semiconductor layer is reduced.

3. The method for manufacturing a radiation detection element according to claim 1 or 2, further comprising forming a conductive layer on the second semiconductor layer.

4. The method for manufacturing a radiation detection element according to claim 1, characterized in that after forming the doping layer, the second semiconductor layer is removed and a conductive layer is formed on the oxide layer.

5. A method for manufacturing a radiation detection element as claimed in any one of claims 1 to 4, characterized in that the oxide layer is formed by thermally oxidizing the first semiconductor layer, a portion of the oxide layer is removed, and the first semiconductor layer after the portion of the oxide layer has been removed is thermally oxidized to re-form the oxide layer in the portion from which the oxide layer was removed.

6. A radiation detection element comprising: a first semiconductor layer into which radiation to be detected enters; a doping layer provided on the surface of the first semiconductor layer on which the radiation is incident and made of a semiconductor doped with a dopant that makes the semiconductor constituting the first semiconductor layer a different type of semiconductor; an oxide layer provided on the doping layer and made of an oxide of a semiconductor; and a second semiconductor layer provided on the oxide layer.

7. The radiation detection element according to claim 6, wherein the semiconductor constituting the first semiconductor layer is n-type, the dopant is boron, and the semiconductor constituting the second semiconductor layer is p-type.

8. The radiation detection element according to claim 6 or 7, characterized in that the second semiconductor layer is made of polysilicon.

9. A radiation detection element according to any one of claims 6 to 8, further comprising a conductive layer provided on said second semiconductor layer.

10. A semiconductor device comprising: a first semiconductor layer into which radiation to be detected is incident; a doping layer provided on the surface of the first semiconductor layer on which the radiation is incident and made of a semiconductor doped with a dopant that changes the semiconductor constituting the first semiconductor layer to a semiconductor of a different type; an oxide layer provided on the doping layer and made of an oxide of a semiconductor; and a conductive layer provided on the oxide layer, wherein the thickness of the oxide layer is less than 50 nm, and the concentration of the dopant contained in the doping layer is 1×10 or less at a position 60 nm deep from the interface between the oxide layer and the doping layer. 18 atoms / cm 3 A radiation detection element comprising:

11. A radiation detection element as described in any one of claims 6 to 10, further comprising: a signal output electrode provided on a surface opposite to the surface on which the doped layer of the first semiconductor layer is provided, for outputting a signal in response to incidence of radiation; and a plurality of curved electrodes arranged in positions surrounding the signal output electrode, at different distances from the signal output electrode, and to which a voltage is applied so that the potential changes in response to the distance from the signal output electrode.

12. A radiation detector comprising: a radiation detection element according to any one of claims 6 to 11; a circuit board on which the radiation detection element is mounted; a collimator that blocks a portion of the radiation before it enters the radiation detection element; and a housing that contains the radiation detection element, the circuit board and the collimator, wherein the housing has an opening that is not blocked, the radiation detection element is disposed with an incident surface through which radiation is incident facing the opening, and the collimator is disposed between the radiation detection element and the opening.