JP6163936B2 - Manufacturing method of two-dimensional radiation detector - Google Patents

Description

  The present invention relates to a method for manufacturing a two-dimensional radiation detector, which includes a semiconductor that generates electric charge upon incidence of radiation or light incident upon the incidence of radiation, and is used in the medical field, industrial field, nuclear power field, and the like.

  Conventionally, in a medical field, an industrial field, and the like, a two-dimensional radiographic image capturing apparatus is used as an image capturing apparatus for acquiring a radiographic image. The two-dimensional radiographic imaging apparatus includes a radiation source that emits radiation and a two-dimensional radiation detector that has a wide light receiving surface in a two-dimensional direction and detects incident radiation.

  Two-dimensional radiation detectors that detect radiation using X-rays as an example are mainly classified into two types. One is an “indirect conversion type” detector that detects light by indirectly converting charge from radiation by generating light based on the incidence of radiation and generating charge based on the generated light. is there. The other is a “direct conversion type” detector that detects radiation by converting radiation directly into electric charge when a radiation-sensitive semiconductor generates electric charge upon incidence of radiation. In recent years, a direct conversion type two-dimensional radiation detector is mainly used, and a flat panel X-ray detector (FPD) is known as an example.

  A direct conversion type two-dimensional radiation detector according to a conventional example will be described with reference to FIG. The two-dimensional radiation detector 101 includes a common electrode 103, a conversion layer 105, and an active matrix substrate 107. The common electrode 103, the conversion layer 105, and the active matrix substrate 107 are stacked in the order described above. A plurality of pixel electrodes 109 are provided between the conversion layer 105 and the active matrix substrate 107. A bias voltage is applied to the common electrode 103. The conversion layer 105 is made of a crystal such as cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe). The substrate composed of the common electrode 103 and the conversion layer 105 is also referred to as a “counter substrate” with respect to the active matrix substrate 107.

  The active matrix substrate 107 is provided with a plurality of capacitors 111, switching elements 113, and output electrodes 115. The pixel electrode 109 is in contact with the conversion layer 105 and is electrically connected to the capacitor 111. The capacitor 111 is electrically connected to the output electrode 115 via the switching element 113 and accumulates the charge converted by the conversion layer 105. For example, a thin film transistor (TFT) is used as the switching element 113, and the charge accumulated in the capacitor 111 is output from the output electrode 115. The pixel electrode 109, the capacitor 111, the switching element 113, and the output electrode 115 are each arranged in a two-dimensional matrix.

  Crystals such as CdZnTe constituting the conversion layer are useful as a material for a highly sensitive two-dimensional radiation detector. However, in order to apply for medical diagnosis and industrial purposes, it is necessary to form a conversion layer having a large area of, for example, several tens of centimeters by several tens of centimeters. For CdZnTe and the like, it is unrealistic in terms of technology and cost to form such a large-area crystal, and therefore, a technique for forming a polycrystalline film using a proximity sublimation method or the like is used. (For example, refer to Patent Document 1).

  However, regardless of which method is used, it is necessary to deposit the material constituting the conversion layer at a high temperature. Therefore, it is difficult to form CdZnTe directly on the active matrix substrate. Therefore, the material CdZnTe is once deposited on the common electrode, and then the surface of the CdZnTe film is flattened to form a counter substrate. Then, a counter substrate and an active matrix substrate having pixel electrodes and the like are bonded together to manufacture a two-dimensional radiation detector.

  Next, the operation of the two-dimensional radiation detector 101 will be described. When the subject is irradiated with radiation from the direction indicated by the symbol x in the figure, the radiation image transmitted through the subject is projected onto the conversion layer 105, and charges are generated in proportion to the density of the radiation image. That is, in the conversion layer 105, the radiation is converted into electric charges that are electrical signals. Since a bias voltage is applied to the common electrode 103, the charges converted in the conversion layer 105 are induced by the generated electric field and collected by the pixel electrode 109. The collected charge is accumulated in the capacitor 111. The electric charge accumulated in the capacitor 111 is output as a radiation detection signal when the switching element 113 is turned on. Image processing or the like is performed based on the output radiation detection signal, and a fluoroscopic image of the subject corresponding to the two-dimensional intensity distribution of radiation is created.

  In the two-dimensional radiation detector 101 having the above-described configuration, leakage charges (electron-holes) that do not contribute to sensitivity may be injected into the conversion layer 105. When leakage charge is injected, the leakage current increases, so that the detection characteristics of the two-dimensional radiation detector 101 are deteriorated. The leakage charge is injected into the conversion layer 105 through the adjacent common electrode 103 or the active matrix substrate 107. Therefore, a carrier-selective blocking layer is provided between at least one of the common electrode 103 and the conversion layer 105 or between the pixel electrode 109 and the conversion layer 105.

  Carrier selectivity refers to the property that the contribution rate to the charge transfer action differs significantly between electrons and holes, which are charge transfer media (carriers) in a semiconductor. For example, when a negative bias voltage is applied to the common electrode 103, the blocking layer provided between the common electrode 103 and the conversion layer 105 functions as an electron blocking layer that blocks injection of electrons from the common electrode 103 to the conversion layer 105. . The blocking layer provided between the pixel electrode 109 and the conversion layer 105 functions as a hole blocking layer that blocks injection of holes from the pixel electrode 109 to the conversion layer 105.

  For the conversion layer 105 made of CdZnTe or CdTe, ZnS, ZnO, ZnSe, CdS, or the like is used as the hole blocking layer. As the electron blocking layer, ZnTe or the like is used as a material. By forming these blocking layers on the conversion layer 105, the two-dimensional radiation detector 51 can obtain effects such as reduction of the leak current generated and improvement of responsiveness.

  For the blocking layer described above, a technique that can be formed for a large area is desired. As a method for forming such a blocking layer, a solution growth method, an electrodeposition method, a proximity sublimation method, or the like is used (for example, see Patent Documents 2 and 3). Among them, the solution growth method is a useful technique in that a blocking layer having a large area can be easily formed and the blocking layer can be formed at low cost.

JP 2001-242255 A JP 2007-235039 A JP 2008-71961 A

  However, the conventional two-dimensional radiation detector having such a configuration has the following problems. That is, when the hole blocking layer is formed on the polished surface of the conversion layer made of a polycrystalline film of CdZnTe by using the solution growth method, the formed hole blocking layer does not have a uniform thickness. That is, since the film thickness unevenness occurs in the hole blocking layer, the semiconductor junction characteristics between the conversion layer and the hole blocking layer deteriorate. Further, since fine holes having a diameter of 1 mm or less are formed in the hole-blocking layer to be formed, injection of holes into the conversion layer cannot be suitably prevented. As a result, the leakage current generated in the radiation detector is not suitably reduced by the hole blocking layer formed.

  The present invention has been made in view of such circumstances, and includes a two-dimensional radiation detector that includes a uniformly formed blocking layer and can suitably suppress the occurrence of leakage current. It aims to provide a method.

  As a result of intensive studies on the cause of the above problems, the following findings have been obtained. That is, when the surface of the conversion layer is polished, the surface of the conversion layer is flat and clean immediately after polishing. However, since CdZnTe constituting the conversion layer reacts quickly with oxygen in the atmosphere, the polished surface of the conversion layer is quickly covered with Te oxide.

  When the hole blocking layer is formed without removing the Te oxide layer covering the conversion layer, the hole blocking layer is formed so as to be stacked on the Te oxide covering the conversion layer. Te oxide is not uniformly formed on the polished surface of the conversion layer. Therefore, the hole blocking layer formed on the nonuniformly formed Te oxide also becomes nonuniform, and fine holes are formed in the hole blocking layer. Since holes leak to the conversion layer through the fine holes, the conventional two-dimensional radiation detector cannot reduce the leakage current suitably despite the formation of the hole blocking layer.

In order to solve such a problem, the present invention has the following configuration.
That is, the method for manufacturing a two-dimensional radiation detector according to the present invention includes a conversion layer forming step in which a common electrode for applying a bias voltage and a conversion layer that converts incident electromagnetic waves into electric charges are stacked to form a laminate. After the conversion layer formation step, an oxide removal step of planarizing the surface of the conversion layer by removing oxide formed on the surface of the conversion layer; and after the oxide removal step, to the conversion layer A blocking layer forming step of forming a counter substrate by laminating a hole blocking layer that blocks injection of holes on the surface of the conversion layer that has been flattened by removing the oxide, and the blocking layer After the forming step, a bonding step of bonding the counter substrate and the active matrix substrate is provided.

  [Operation / Effect] According to the method of manufacturing a two-dimensional radiation detector according to the present invention, the oxide removing step is performed before the blocking layer forming step. Therefore, it is possible to manufacture a two-dimensional radiation detector that includes a hole blocking layer that is uniformly formed and suitably suppresses the generation of leakage current.

  In the two-dimensional radiation detector according to the conventional manufacturing method, when the hole blocking layer is formed on the conversion layer made of a polycrystalline film such as CdZnTe, the thickness of the formed hole blocking layer is not uniform. That is, the semiconductor junction characteristics at the interface between the hole blocking layer and the conversion layer deteriorate due to the film thickness unevenness of the hole blocking layer. Furthermore, since a fine hole (pinhole) having a diameter of 1 mm or less is formed in the hole-blocking layer to be formed, the hole-blocking layer cannot block the injection of holes into the conversion layer. Therefore, in the two-dimensional radiation detector according to the conventional example, even if the hole blocking layer is formed, it is difficult to suitably reduce the generation of leakage current.

  On the other hand, in the two-dimensional radiation detector according to the present invention, the oxide formed on the surface of the conversion layer is removed in the oxide removal step. Therefore, since the hole blocking layer is formed on the flat and clean surface of the conversion layer, the hole blocking layer formed in the blocking layer forming step is uniform. Further, no pinhole is formed in the hole blocking layer to be formed. That is, the holes toward the conversion layer are preferably blocked by the hole blocking layer. Therefore, in the two-dimensional radiation detector according to the manufacturing method of the present invention, generation of leakage current is preferably suppressed.

  Then, in the bonding process, the conversion layer and the active matrix substrate are bonded while being pressed. Pin holes are not formed in the hole blocking layer formed on the surface of the conversion layer, and the hole blocking layer is uniformly formed. Therefore, the conversion layer and the active matrix substrate are stably coupled through the uniformly formed hole blocking layer. That is, ideal hetero-coupling is performed between the conversion layer and the active matrix substrate. Therefore, in the two-dimensional radiation detector according to the manufacturing method of the present invention, it is possible to realize high stability and reliability.

In the above-described invention, the oxide removal step is performed by treating the laminate with a bromine methanol solution, and further includes a washing step of washing Te bromide remaining in the laminate with methanol after the oxide removal step. It is preferable to provide.

  [Operation / Effect] According to the above configuration, the oxide removal step is performed by treating the laminate with a bromine methanol solution. The bromine methanol solution can suitably decompose and remove oxides such as Te oxide. For this reason, the oxide formed on the surface of the conversion layer can be more suitably removed by the oxide removing step. And after performing an oxide removal process, the bromide produced | generated by a bromine methanol solution process is suitably removed from the surface of a laminated body by wash | cleaning a laminated body with methanol. Therefore, in the manufactured two-dimensional radiation detector, it is possible to avoid the problem of an increase in leakage current due to residual bromide.

Further, in the invention described above, the material constituting the conversion layer state, and are either CdTe or CdZnTe, wherein the oxide comprises a Te oxide, wherein the oxide removal process, the laminate with bromine methanol solution It is preferable to remove Te oxide by treatment to flatten the surface of the conversion layer .

  [Operation / Effect] According to the above-described configuration, the conversion layer for converting radiation into electric charge is configured using CdTe or CdZnTe. Therefore, the sensitivity and detection efficiency of the conversion layer with respect to radiation can be increased. Therefore, higher stability and reliability can be realized in the manufactured two-dimensional radiation detector.

In the above-described invention, the blocking layer forming step is preferably performed using a solution growth method .

[Operation and Effect] According to the above-described configuration, the hole blocking layer is formed using the solution growth method . These techniques are techniques that can easily form a hole blocking layer having a large area at low cost. Therefore, it is possible to manufacture a two-dimensional radiation detector having a large area of several tens of centimeters and several tens of centimeters that can be used in practical applications with simple processes.

  In the above-described invention, the material constituting the hole blocking layer formed in the blocking layer forming step is preferably either ZnS or CdS.

  [Operation and Effect] According to the above-described configuration, the hole blocking layer is configured using ZnS or CdS. Since ZnS and CdS are materials having a high contribution ratio to electrons, the hole blocking layer formed using them can more preferably block the injection of holes. Therefore, in the manufactured two-dimensional radiation detector, it is possible to more efficiently suppress the generation of leakage current.

  In the above-described invention, the conversion layer forming step includes stacking a common electrode for applying a bias voltage, an electron blocking layer for blocking injection of electrons, and a conversion layer for converting incident electromagnetic waves into charges. It is preferable to form a laminate.

  [Operation and Effect] According to the above-described configuration, in the conversion layer forming step, the electron blocking layer is stacked on the common electrode, and the conversion layer is further stacked on the stacked electron blocking layer. That is, the electron blocking layer is formed between the common electrode and the conversion layer. Therefore, the electron blocking layer can preferably block the injection of electrons from the common electrode to the conversion layer. That is, injection of holes into the conversion layer is blocked by the hole blocking layer, and injection of electrons into the conversion layer is blocked by the electron blocking layer. Therefore, it is possible to more suitably reduce the generation of leakage current in the conversion layer for the two-dimensional radiation detector.

  In the above-described invention, the bromine methanol solution used in the oxide removal step preferably has a bromine content ratio of 0.1% to 10% by weight with respect to methanol.

  [Operation / Effect] According to the above-described configuration, the bromine-methanol solution can more suitably decompose and remove the oxide when the bromine content relative to the methanol is 0.1% or more and 10% or less. Can do. For this reason, the oxide formed on the surface of the conversion layer can be more efficiently removed by the oxide removal step.

  According to the method for manufacturing a two-dimensional radiation detector according to the present invention, since the oxide removal step is performed before the blocking layer formation step, the oxide formed on the surface of the conversion layer is removed in the oxide removal step. The As a result, the hole blocking layer is formed on the flat and clean surface of the conversion layer, so that the hole blocking layer is uniformly formed in the blocking layer forming step. Therefore, the conversion layer and the hole blocking layer can form a more ideal heterojunction, and the effect of reducing the leakage current approaches the ideal state and the effect increases. Further, no pinhole is formed in the hole blocking layer to be formed. That is, the holes toward the conversion layer are preferably blocked by the hole blocking layer. Furthermore, the manufacturing method according to the present invention can be applied when forming a hole blocking layer using a solution growth method or the like. Therefore, it is possible to realize a two-dimensional radiation detector that has a large-area hole blocking layer formed uniformly and can efficiently suppress the generation of leakage current at low cost.

It is a top view explaining the schematic structure of the two-dimensional radiation detector which concerns on an Example. It is a longitudinal cross-sectional view explaining schematic structure of the two-dimensional radiation detector which concerns on an Example. It is a flowchart explaining the process of the manufacturing method of the two-dimensional radiation detector which concerns on an Example. In the conversion layer forming step according to the example, (a) is a schematic configuration of the two-dimensional radiation detector after the formation of the electron blocking layer, (b) after the formation of the conversion layer, and (c) after the polishing of the conversion layer. FIG. In the oxide removal process which concerns on an Example, (a) is an initial state, (b) is a schematic diagram which shows a two-dimensional radiation detector in the time of a bromine methanol immersion after coat | covering with a reaction prevention film. It is the schematic which shows the two-dimensional radiation detector which concerns on the Example in (a) a washing | cleaning process and (b) in a blocking layer formation process. It is a longitudinal cross-sectional view which shows the two-dimensional radiation detector in the bonding process based on an Example. About the manufacturing method of the two-dimensional radiation detector which concerns on an Example, (a) is an initial state, (b) is after an oxide removal process, (c) is after a blocking layer formation process, (d) is after a bonding process, It is a longitudinal cross-sectional view explaining the two-dimensional radiation detector in FIG. It is a graph figure of a X-ray photoelectron spectroscopy spectrum explaining the effect of a bromine methanol solution process. It is the photograph of the blocking layer surface observed with the microscope explaining the effect of a bromine methanol solution process, (a) is a prior art example, (b) is an Example. It is a graph which shows the reduction rate of the leakage current explaining the effect of a bromine methanol solution process. It is a longitudinal cross-sectional view explaining an example of schematic structure which concerns on the two-dimensional radiation detector which concerns on a prior art example. It is a flowchart which shows the process of the manufacturing method of the two-dimensional radiation detector which concerns on a prior art example. About the manufacturing method of the two-dimensional radiation detector which concerns on a prior art example, (a) is an initial state, (b) is after Te oxide layer formation, (c) is after a blocking layer formation process, (d) is after a bonding process It is a longitudinal cross-sectional view explaining the two-dimensional radiation detector in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, a direct conversion type flat panel X-ray detector (hereinafter abbreviated as FPD) will be described as an example of the two-dimensional radiation detector. In the following description, X-rays are used as an example of radiation.

<Description of overall configuration>
As shown in FIG. 1, the FPD 1 according to the embodiment includes an X-ray detection matrix 3, a gate driver 5, an amplifier 7, and an AD converter 9. The image processing device 11 and the image display device 13 are connected to the subsequent stage of the FPD 1. The X-ray detection matrix 3 is connected to the gate driver 5 through the gate wiring 15 and is connected to the amplifier 7 through the signal line 17.

  In the X-ray detection matrix 3, a plurality of X-ray detection pixels 19 are arranged in a two-dimensional matrix. In the first embodiment, X-ray detection pixels 19 are arranged in a two-dimensional matrix of about 4,096 × 4,096. However, in FIG. 1, a simplified X-ray detection pixel 19 is arranged in a two-dimensional matrix of 4 × 4.

  The gate driver 5 controls on / off of a switching element, which will be described later, via the gate wiring 15. The amplifier 7 is connected to the AD converter 9 through a signal line 17. The amplifier 7 amplifies the input electric signal and outputs it to the AD converter 9. The AD converter 9 converts the input electrical signal from an analog signal to a digital signal and outputs the converted signal to the image processing device 11. The image processing apparatus 11 performs image processing based on the signal input from the AD converter 9. The image display device 13 displays the image information input from the image processing device 11 as an image.

  Next, the configuration of the FPD 1 will be described more specifically with reference to FIG. The FPD 1 has a structure in which the common electrode 21, the conversion layer 23, the pixel electrode 25, and the active matrix substrate 27 are stacked in the order described above. A high bias voltage is applied to the common electrode 21 and is composed of, for example, a conductive graphite substrate. The conversion layer 23 converts X-rays that are electromagnetic information into electric charges that are electrical information, and is made of, for example, a polycrystalline film of CdZnTe. The pixel electrode 25 collects the charges converted in the conversion layer 23.

  The active matrix substrate 27 is provided with a capacitor 29, a switching element 31, and an output electrode 33. The pixel electrode 25 is electrically connected to the capacitor 29. The capacitor 29 is electrically connected to the output electrode 33 via the switching element 31 and accumulates the charge converted by the conversion layer 23. For example, a thin film transistor (TFT) is used as the switching element 31, and charges accumulated in the capacitor 29 are output from the output electrode 33. The output electrode 33 is electrically connected to the amplifier 7 via the signal line 17, and charges output from the switching element 31 are input to the amplifier 7.

  The conversion layer 23 and the capacitor 29 are connected in series via the pixel electrode 25. Therefore, for example, when a negative bias voltage is applied to the common electrode 21, among the charges generated in the conversion layer 23, electrons move to the pixel electrode 25 side and holes move to the common electrode 21 side. As a result, charges are accumulated in the capacitor 29. On the other hand, leakage charges that do not contribute to sensitivity are easily injected into the conversion layer 23. That is, when a negative bias voltage is applied to the common electrode 21, electrons are easily injected from the common electrode 21 into the conversion layer 23. Then, holes are easily injected from the active matrix substrate 27 into the conversion layer 23 via the collecting electrode 25. As a result, the leakage current generated in the FPD 1 increases.

  Therefore, in order to reduce the leakage current resulting from the injection of leakage charges, in this embodiment, as shown in FIG. 2, an electron blocking layer 35 is provided between the common electrode 21 and the conversion layer 23, and the conversion layer 23 is also provided. A hole blocking layer 37 is provided between the pixel electrode 25 and the pixel electrode 25. The electron blocking layer 35 blocks injection of electrons from the common electrode 21 to the conversion layer 23. The hole blocking layer 37 blocks hole injection from the pixel electrode 25 to the conversion layer 23.

  As described above, the leakage current can be reduced by providing the electron blocking layer 35 and the hole blocking layer 37. A suitable material for the electron blocking layer 35 includes a polycrystalline semiconductor such as ZnTe, and a suitable material for the hole blocking layer 37 includes ZnS or CdS. In the embodiment of the present invention, ZnTe is used as a material for forming the electron blocking layer 35, and ZnS is used as a material for forming the hole blocking layer 37.

<Description of operation>
Next, the operation of the FPD 1 will be described with reference to FIG. First, X-rays that have passed through the subject are emitted from the direction indicated by the symbol x to the X-ray detection pixels 19 constituting the FPD 1. In the conversion layer 23, X-rays that are electromagnetic wave information are converted into electric charges that are electrical information. Since a bias voltage is applied to the common electrode layer 21, the charges converted in the conversion layer 23 are induced by the generated electric field, collected by each pixel electrode 25, and accumulated in each capacitor 29.

  Next, a read signal is output from the gate driver 5 to the switching element 31 via the gate line 15. The switching element 31 shifts from an off state to an on state based on the output read signal. The switching element 31 in the on state outputs the electric charge accumulated in each capacitor 29 from the output electrode 33 as an X-ray detection signal. The output X-ray detection signal is input to the amplifier 7 via the signal line 17.

  The amplifier 7 amplifies the input X-ray detection signal, and the amplified radiation detection signal is input to the AD converter 9. The AD converter 9 converts the input X-ray detection signal from an analog signal to a digital signal. The digital signal obtained for each X-ray detection pixel 19 is input to the image processing apparatus 11. The image processing device 11 performs imaging based on the input digital signal, and inputs the obtained image information to the image display device 13. The image display device 13 acquires an X-ray fluoroscopic image corresponding to the two-dimensional intensity distribution of the X-ray transmitted through the subject based on the image information input from the image processing device 11, and the series of operations ends. That is, the FPD 1 according to the present embodiment is a two-dimensional array type X-ray detector capable of detecting a two-dimensional intensity distribution of X-rays.

  Here, the manufacturing method of the two-dimensional radiation detector according to the present embodiment will be described with reference to the drawings. FIG. 3 is a flowchart illustrating the steps of the method for manufacturing a two-dimensional radiation detector according to the embodiment.

Step S1 (conversion layer forming step)
First, as shown in FIG. 4A, an electron blocking layer 35 made of ZnTe is formed on the common electrode 21 formed of a conductive graphite substrate. For example, proximity sublimation is used to form the electron blocking layer 35. Then, as shown in FIG. 4B, a conversion layer 23 made of a polycrystalline film of CdZnTe is formed on the common electrode 21 on which the electron blocking layer 35 is formed. For example, proximity sublimation is used to form the conversion layer 23. After the conversion layer 23 is formed, the surface of the conversion layer 23 is planarized as shown in FIG. For the planarization treatment, chemical mechanical polishing (CMP) or the like is used. When the flattening process is performed, the conversion layer forming process ends. In addition, a structure including the common electrode 21, the electron blocking layer 35, and the conversion layer 23 formed by the conversion layer forming step is referred to as a stacked body 39.

  When the surface of the conversion layer 23 is polished in the conversion layer forming step, the surface of the conversion layer 23 is flat and clean immediately after polishing. However, when CdZnTe constituting the conversion layer 23 is exposed on the surface, it reacts with oxygen in the atmosphere to generate Te oxide. Therefore, as shown in FIG. 5A, in the stacked body 39 formed in the conversion layer forming step, the polished surface of the polished conversion layer 23 is quickly covered with the Te oxide layer 41.

Step S2 (oxide removal process)
Therefore, after the conversion layer forming step is finished, an oxide removal step is performed on the polished surface of the conversion layer 23 on which the planarization process has been performed. First, as shown in FIG. 5 (b), the surface of the laminate 39 excluding the polishing surface of the conversion layer 23 is covered with a reaction preventing film 43. As the reaction preventing film 43, for example, a fluorine-based resin or the like is used. By covering with a reaction preventing film, only the Te oxide layer 41 covering the polished surface of the conversion layer 23 can be reacted in the oxide removal step. Next, as shown in FIG. 5C, the laminate 39 is immersed in the bromine methanol solution 47 in the first treatment tank 45. The bromine content in the bromine methanol solution 47 is 0.1% or more and 10% or less by weight. The specified time for dipping is, for example, 2 minutes. In addition, it is preferable that the temperature of bromine methanol is 15 degreeC or more and 18 degrees C or less. By immersing in the bromine methanol solution 47, the Te oxide layer 41 present on the polished surface of the conversion layer 23 is removed. By immersing the laminate 39 in the bromine methanol solution 47 for a specified time, the oxide removal step is completed.

Step S3 (cleaning process)
After completion of the oxide removal step, Te bromide produced by reaction with bromine methanol remains. When impurities such as Te bromide are present at the interface between the CdZnTe film and the hole blocking layer, the problem of increased leakage current occurs.

  Therefore, a cleaning process is performed after the oxide removal process. That is, the laminate 39 is pulled up from the first treatment tank 45, and the laminate 39 is immersed in the methanol 51 in the second treatment tank 49 for a specified time, as shown in FIG. The specified time for dipping is, for example, 30 seconds. The immersion in methanol 45 is performed twice. By immersing in methanol 45, bromine remaining on the surface of the composite 39 is washed and removed. The oxide removal step is completed by immersing the laminate A in the methanol 45 for a specified time.

Step S4 (blocking layer forming step)
The blocking layer forming step is performed simultaneously with the end of the cleaning step. That is, the hole blocking layer 37 is formed on the polished surface of the conversion layer 23 from which the Te oxide layer 41 has been removed using a solution growth method. In the solution growth method, the hole blocking layer 37 is formed using a circulation tank in which the temperature of the solution can be controlled. As shown in FIG. 6 (b), the solution 55 in the circulation tank 53 is circulated to control the temperature of the solution 55 so as to maintain a specified temperature. Then, the laminate 39 washed with methanol is immersed in the solution 55 in the circulation tank 53. By immersing the laminate 39 in the solution 55 for a specified time, crystallization of ZnS from the solution 55 is started. The crystallized ZnS grows on the polished surface of the conversion layer 23 and is formed on the polished surface of the conversion layer 23 as the hole blocking layer 37. The specified time is, for example, 60 minutes. By immersing the laminate 39 in the solution 55 for a specified time, the hole blocking layer 37 is formed to a thickness of, for example, 200 nm. And the laminated body 39 in which the hole-blocking layer 37 was formed is pulled up from the circulation tank 53, the reaction prevention film 43 is removed, and water washing and drying are performed. By drying the laminated body 39, the blocking layer forming step is completed. Note that the stacked body 39 on which the hole blocking layer 37 is formed by the blocking layer forming step is referred to as a counter substrate 57.

  Details of the solution 55 used in the blocking layer forming step will be described. Solution 55 was prepared by mixing 1.5 mol / liter of aqueous ammonia, 4.5 mol / liter of hydrazine monohydrate, 0.05 mol / liter of zinc sulfate heptahydrate, and 0.14 mol / liter of thiourea. It is a thing. In order to prepare the solution 55, first, aqueous ammonia and hydrazine monohydrate are mixed, and then zinc sulfate heptahydrate is dissolved. These are mixed with water and heated to 70 ° C. while circulating in the circulation tank 53. After raising the temperature, thiourea dissolved in a small amount of water is introduced into the circulation tank 53 and mixed, whereby the solution 55 is produced.

Step S5 (bonding process)
A bonding process is performed after completion of the blocking layer forming process. That is, the counter substrate 57 is bonded to the active matrix substrate 27. As shown in FIG. 7, the active matrix substrate 27 is configured by patterning gate lines 15, data lines 17, pixel electrodes 25, capacitors 29, switching elements 31, output electrodes 33, and the like on a glass substrate 59. . As a method for forming a pattern, for example, screen printing or the like is used. Then, the counter substrate 57 formed by the blocking layer forming step is disposed on the incident side of the patterned active matrix substrate 27, and is pressed and held from the directions indicated by the arrows. The counter substrate 57 and the active matrix substrate 27 are bonded to each other through the pixel electrode 25 by pressurization and the FPD 1 is manufactured.

  Here, the present embodiment and the conventional example will be compared for the method of manufacturing the two-dimensional radiation detector. FIG. 13 is a flowchart showing the steps of the manufacturing method according to the conventional example.

  As shown in FIG. 13, the two-dimensional radiation detector according to the conventional example is manufactured by three processes including a conversion layer forming process, a blocking layer forming process, and a bonding process. That is, in the manufacturing method according to this example, as shown in FIG. 3, the oxide removal step and the cleaning step are performed between the conversion layer formation step and the blocking layer formation step, whereas in the conventional example, the oxide removal step is performed. The blocking layer forming step is performed without performing the step and the cleaning step.

  As shown in FIG. 14A, when the surface of the conversion layer 23 is polished in the conversion layer forming step, the surface of the conversion layer 23 is flat and clean immediately after polishing. However, when CdZnTe constituting the conversion layer 23 is exposed on the surface, it reacts with oxygen in the atmosphere to generate Te oxide, so that as shown in FIG. The surface is quickly covered with the Te oxide layer 41. The bromine methanol solution has an effect of removing Te oxide. Therefore, the Te oxide layer 41 covering the surface of the conversion layer 23 can be removed by treating the surface of the conversion layer 23 with a bromine methanol solution in the oxide removal step.

  In the blocking layer forming process according to the conventional example, the blocking layer forming process is performed without performing the oxide removing process. Therefore, the hole blocking layer 37 is formed without removing the Te oxide layer 41 covering the conversion layer 23. That is, as shown in FIG. 14C, the hole blocking layer 37 is formed so as to be laminated on the Te oxide layer 41 covering the conversion layer 23. Since the Te oxide is not uniformly formed on the surface of the conversion layer 23, the Te oxide layer 41 covers the polished surface of the conversion layer 23 non-uniformly. Therefore, the hole blocking layer 37 formed on the non-uniform Te oxide layer 41 is also non-uniform. Therefore, as shown in FIG. 14D, a gap is formed between the hole blocking layer 37 and the pixel electrode 25 in the bonding step. Therefore, the coupling between the counter substrate 57 and the active matrix substrate 27 becomes very unstable.

  Further, in the two-dimensional radiation detector according to the conventional example, as shown in FIG. 14C, many pinholes 59 are generated in the hole blocking layer 37 to be formed. That is, since holes are injected into the conversion layer 23 through the generated pinholes 59, the hole blocking layer 37 according to the conventional manufacturing method cannot appropriately suppress the leakage current. Therefore, in the two-dimensional radiation detector according to the conventional example, the generation of leakage current cannot be suppressed.

  On the other hand, in this embodiment, the Te oxide layer 41 shown in FIG. 8A is removed by the oxide removing step. Therefore, the polishing surface of the conversion layer 23 becomes flat and clean by the oxide removal step, as shown in FIG. Therefore, in the blocking layer forming step, as shown in FIG. 8C, the hole blocking layer 37 is formed by the solution growth method on the polished surface of the conversion layer 23 that has become flat and clean again. Since the blocking layer forming step is performed by immersing the conversion layer 23 in the solution, the hole blocking layer 37 is formed without oxidizing the surface of the conversion layer 23. Since the hole blocking layer 37 is formed on the polished surface of the flat and clean conversion layer 23, the hole blocking layer 37 can be formed uniformly without unevenness, and a more ideal heterojunction can be formed between CdZnTe and the hole blocking layer 37 (ZnS). As a result, the hole blocking property is prominent.

  Furthermore, in the two-dimensional radiation detector according to the present embodiment, no pinhole is formed in the hole blocking layer that is formed. That is, the holes going to the conversion layer via the pixel electrode are more reliably blocked by the hole blocking layer. Therefore, in the two-dimensional radiation detector according to the present embodiment, the generation of leakage current is more preferably suppressed.

  Finally, the effect obtained in the present embodiment will be specifically described. First, FIG. 9 is a graph in which Te oxide on the polished surface of the conversion layer is verified using an X-ray photoelectron spectrum. The peaks indicated by reference signs A and C are peaks indicating tellurium dioxide (TeO2), which is a Te oxide, and the peaks indicated by reference signs B and D respectively indicate tellurium element (Te) that is not oxidized. It is a peak. A peak indicating tellurium dioxide appears in the spectrum of the polished surface of the conversion layer that is not treated with the bromine-methanol solution, as indicated by symbol E (dark solid line). On the other hand, no peak indicating tellurium dioxide appears in the spectrum of the polished surface of the conversion layer treated with the bromine-methanol solution, indicated by the symbol F (thin solid line). Therefore, it has been shown that Te oxide is suitably removed by treatment with a bromine-methanol solution.

  FIG. 10 shows the surface of the hole blocking layer observed with a microscope after forming a hole blocking layer by a solution growth method on the polished surface of CdZnTe. FIG. 10A shows a hole blocking layer formed on CdZnTe not treated with bromine methanol solution, and FIG. 10B shows a film formed on CdZnTe treated with bromine methanol solution. In FIG. 10A, the surface of the hole blocking layer is rough and fine holes are observed. On the other hand, in FIG. 10B, the surface of the hole blocking layer is smooth and no fine holes are observed. Thus, it has been shown that the oxide removal step, i.e., the treatment of the bromine-methanol solution, forms a smoother and pore-free hole blocking layer.

  Further, FIG. 11 is a graph showing the leakage current reduction rate for the two-dimensional radiation detectors according to the conventional example and the example. The reduction rate of each leakage current is calculated by comparing with the leakage current generated in the two-dimensional radiation detector having no hole blocking layer. The left bar graph shows the reduction rate of leakage current in the two-dimensional radiation detector having the hole blocking layer according to the conventional example, and the right bar graph shows the leakage current reduction rate in the two-dimensional radiation detector having the hole blocking layer according to the example. Yes.

  As shown in the left bar graph, in the two-dimensional radiation detector having the hole blocking layer according to the conventional example, the leakage current is reduced by less than 20%. On the other hand, as shown by the bar graph on the right, in the two-dimensional radiation detector having the hole blocking layer according to the present embodiment, the generation of leakage current can be reduced by 50% or more. Therefore, it has been shown that the generation of leakage current is more preferably reduced by the oxide removal step, that is, the treatment with a bromine-methanol solution.

  The present invention is not limited to the above-described embodiment, and can be modified as follows.

  (1) In the above-described embodiments, the X-ray detector has been described as an example of the radiation detector. However, the present invention can also be applied to a radiation detector that detects radiation other than X-rays, for example, γ-rays.

  (2) In the embodiment described above, the hole blocking layer 37 is formed using the solution growth method in the blocking layer forming step, but the present invention is not limited to this. That is, if an oxide removing step and a cleaning step are performed between the conversion layer forming step and the blocking layer forming step, the technique used in the blocking layer forming step may be a vapor deposition method or a sputtering method.

  (3) In the above-described embodiment, the electron blocking layer 35 is formed by the vapor deposition method between the common electrode 21 and the conversion layer 23, but is not limited thereto. The method for forming the electron blocking layer 35 may be a solution growth method or a sputtering method. Further, the electron blocking layer 35 need not be formed.

  (4) In the above-described embodiment, conductive graphite is used as a material for forming the common electrode 21. However, an alumina substrate having an ITO (Indium Tin Oxide) film formed on the surface may be used, or an MgAg alloy. A metal such as

  (5) In the above-described embodiment, the first treatment tank 45 is used in the oxide removal process and the second treatment tank 49 is used in the cleaning process. However, these treatment tanks may be used as a circulation tank. In this case, since the bromine methanol solution or methanol continuously circulates in the circulation tank, more uniform treatment can be performed on the laminate 39.

  (6) In the above-described embodiment, ZnS is used as a material for forming the hole blocking layer 37, but CdS may be used.

  (7) In the above-described embodiment, CdZnTe is used as a material for forming the conversion layer 23, but CdTe may be used.

1 ... FPD
DESCRIPTION OF SYMBOLS 21 ... Common electrode 23 ... Conversion layer 25 ... Pixel electrode 27 ... Active matrix substrate 35 ... Electron blocking layer 37 ... Hole blocking layer 39 ... Laminate 41 ... Te oxide layer 57 ... Opposite substrate 59 ... Glass substrate

Claims (7)

A conversion layer forming step of forming a laminate by laminating a common electrode for applying a bias voltage and a conversion layer that converts incident electromagnetic waves into charges; and
After the conversion layer formation step, an oxide removal step of planarizing the surface of the conversion layer by removing oxide formed on the surface of the conversion layer ;
After the oxide removal step, a hole blocking layer that blocks injection of holes into the conversion layer is laminated on the surface of the conversion layer that has been flattened by removing the oxide, and the counter substrate is formed. A blocking layer forming step to be formed;
The manufacturing method of a two-dimensional radiation detector provided with the bonding process which bonds a counter substrate and an active matrix substrate after the said blocking layer formation process. In the manufacturing method of the two-dimensional radiation detector of Claim 1,
In the two-dimensional radiation detector, the oxide removal step is performed by treating the laminate with a bromine methanol solution, and further includes a washing step of washing Te bromide remaining in the laminate with methanol after the oxide removal step. Production method. In the manufacturing method of the two-dimensional radiation detector of Claim 2,
The bromine methanol solution used in the oxide removal step is a method for producing a two-dimensional radiation detector, wherein the bromine content relative to methanol is 0.1% or more and 10% or less by weight. In the manufacturing method of the two-dimensional radiation detector in any one of Claims 1 thru | or 3,
The material constituting the conversion layer state, and are either CdTe or CdZnTe,
The oxide includes Te oxide, and in the oxide removing step, the stacked body is treated with a bromine-methanol solution to remove Te oxide and planarize the surface of the conversion layer. A method for manufacturing a three-dimensional radiation detector. In the manufacturing method of the two-dimensional radiation detector in any one of Claims 1 thru | or 4,
The blocking layer forming step is a method for manufacturing a two-dimensional radiation detector, which is performed using a solution growth method. In the manufacturing method of the two-dimensional radiation detector in any one of Claims 1 thru | or 5,
The material constituting the hole blocking layer formed in the blocking layer forming step is either a ZnS or CdS manufacturing method of a two-dimensional radiation detector. In the manufacturing method of the two-dimensional radiation detector in any one of Claims 1 thru | or 6,
The conversion layer forming step is a two-dimensional structure in which a common electrode for applying a bias voltage, an electron blocking layer for blocking electron injection, and a conversion layer for converting incident electromagnetic waves into charges are stacked to form a stacked body. A method for manufacturing a radiation detector.