JP5170263B2 - Manufacturing method of radiation detector - Google Patents

Description

  The present invention relates to a radiation detector used in a computed tomography (CT) apparatus that handles radiation such as X-rays, α-rays, β-rays, and γ-rays, and in particular, a high-resolution X-ray CT apparatus using a scintillator element. The present invention relates to a radiation detector.

  A radiation CT apparatus includes a radiation source (for example, an X-ray tube) and a radiation detector arranged symmetrically with respect to an object to be imaged, and measures the radiation intensity at each detection position to measure the inside of the object to be imaged. It is configured to observe the structure.

The basic structure of the radiation detector is one in which a scintillator element is arranged on a plurality of arranged semiconductor photodetecting elements, and the scintillator element opens to the radiation source side to receive radiation such as X-rays. A scintillator element is generally made of a material such as CdWO ₄ , Bi ₄ Ge ₃ O ₁₂ , or Gd ₂ O ₂ S processed into a columnar shape, and a plurality of scintillator elements are two-dimensionally arranged with an interval between adjacent elements. ing. When radiation is incident on the opening surface of the scintillator element, the scintillator element itself emits light to emit visible light, and the semiconductor light detecting element disposed on the opposite surface of the opening surface receives the light and outputs an electrical signal. In the radiation CT apparatus, a plurality of scintillator elements arranged adjacent to each other correspond to each pixel of the CT image. Therefore, the scintillator element of the radiation detector is designed so as to be as small as possible and the distance between adjacent elements is narrowed to improve the resolution and resolution.

  The outer peripheral surface of the scintillator element processed into a columnar shape is covered with a light reflecting material except for the surface facing the semiconductor photodetector element. Patent Document 1 discloses an example in which a scintillator element is coated with a white paint (light reflecting material) in which a powder such as titanium oxide is kneaded with an epoxy resin or the like. Thus, by covering the outer peripheral surface of the scintillator element with the light reflecting material, the visible light emitted by the scintillator element is confined inside the scintillator element and efficiently guided to the semiconductor photodetector element.

  As another example of the light reflecting material for covering the scintillator element, Patent Document 2 discloses a metal reflection such as Au, Ag, Al, Ni, etc. on the surface of the scintillator element by a method such as sputtering or CVD (chemical vapor deposition). An example of covering the material is disclosed.

  In addition, as a metal reflector, Patent Document 3 discloses an example in which a sintered body of metal particles is used as a reflector. In this document, a metal reflector is obtained by sintering a coating material in which metal fine particles having a particle size of 1 μm or less, preferably 0.1 μm or less are dispersed in a solvent.

JP-A-5-19060 JP 2005-189234 A Japanese Patent Laid-Open No. 2004-333381

  Along with the demand for higher resolution of the radiation CT apparatus, radiation detectors using scintillator elements have been improved so that the opening area of the scintillator elements is small and the distance between adjacent elements is narrow. In recent years, an interval between adjacent scintillator elements is required to be 100 μm or less. The production of a radiation detector in which scintillator elements are arranged at such a narrow interval has the following problems in the prior art.

  In the prior art, as in Patent Document 1, a white paint in which a powder of titanium oxide or the like is kneaded with an epoxy resin or the like is filled in a gap between adjacent scintillator elements to make a reflective material. In this method, the visible light emitted from the scintillator element is reflected by the titanium oxide powder in the white paint and guided to the semiconductor photodetector element.

  However, when the interval between adjacent scintillator elements becomes narrow, the white paint to be filled becomes thin, and part of the visible light emitted by the scintillator elements is not reflected by the titanium oxide powder, but passes through the white paint and adjoins. It will enter the scintillator element. This phenomenon is called crosstalk, and causes a reduction in the resolution and resolution of the radiation detector.

  FIG. 8 shows the relationship between the thickness of the reflective material and the light transmittance of light having a wavelength of 500 nm in a white paint kneaded with titanium oxide powder and an epoxy resin. When the white paint, which is a reflective material, becomes thinner, the light transmittance tends to increase. In particular, when the thickness is 100 μm or less, the increase in light transmittance is remarkable. With such light transmittance, the occurrence of crosstalk is inevitable in the radiation detector.

  As a method of solving this problem, a method of increasing the density of the titanium oxide powder to be kneaded with the epoxy resin and increasing the density of the titanium oxide powder so as not to transmit light can be considered. However, as the amount of the titanium oxide powder increases, the viscosity of the white paint increases, and it becomes difficult to fill the gaps between adjacent scintillator elements.

  Therefore, it is difficult to fill a white detector in which powders such as titanium oxide are kneaded with an epoxy-based resin into a radiation detector in which the interval between adjacent scintillator elements is narrow from the viewpoint of both filling properties and optical characteristics. I know.

  On the other hand, when the reflective material is a metal, if the thickness is generally a metal having a thickness of 0.1 μm or more, total reflection is possible without transmitting visible light. Therefore, if metal is used for the reflective material that covers the scintillator elements, crosstalk can be avoided even if the interval between adjacent scintillator elements is narrow.

  However, it is very difficult to form a metal reflector in the gap between adjacent scintillator elements because the scintillator element is thick with respect to the gap. For example, if the gap between adjacent scintillator elements is 100 μm and the thickness of the scintillator element is 1.7 mm, a metal reflector must be formed on the side surface of the groove having a width of 100 μm and a depth of 1.7 mm. As described above, even when an attempt is made to form a metal reflective film on the side surface of a groove having a high aspect ratio by using a vapor deposition method, a sputtering method, a CVD method, or the like as disclosed in Patent Document 2, the closer the surface is to the bottom surface of the groove. Since the film thickness becomes thin, it is very difficult to form a metal having a thickness that functions as a reflector on the entire side surface of the scintillator element.

  FIG. 9 shows an Ag film thickness distribution in the groove depth direction when an Ag film is formed in a groove having a width of 100 μm and a depth of 1.7 mm by sputtering. In FIG. 9, the film is formed so that the Ag film thickness at the top of the groove is 1 μm. However, the film thickness of Ag formed on the side surface of the groove is reduced in proportion to the groove depth, and the depth from the surface is reduced. When the thickness is 0.2 mm or more, the Ag film is not formed on the side surface of the groove. Therefore, with the method as shown in FIG. 9, it is not possible to form a reflector in the gap between adjacent scintillator elements.

  In addition, as a method of forming a metal reflector on the side surface of a groove having a high aspect ratio, a method of forming a metal film by applying and sintering a solution containing metal fine particles as disclosed in Patent Document 3 is considered. It is done. However, in this method, since the film structure becomes rough reflecting the particle size of the metal fine particles, light cannot be scattered and high light reflectance cannot be obtained.

  FIG. 10 shows the reflection characteristics of an Ag film obtained by applying a solution in which Ag fine particles having an average particle diameter of 25 nm are dispersed to the surface of the scintillator element and sintering it. In the Ag film of FIG. 10, only a light reflectance of 50% or less can be obtained in the entire visible light region with a wavelength of 400 nm to 900 nm.

  Furthermore, the solution containing the metal fine particles becomes a very expensive solution because a step of preparing the metal fine particles and dispersing them in the solvent is required. Therefore, when a solution containing fine metal particles is used, there is a problem that the manufacturing cost of the radiation detector is increased.

  The present invention solves the above-described problems, and provides a radiation detector and a method for manufacturing the same, in which crosstalk is small even when the interval between adjacent scintillator elements is narrow.

  In the radiation detector of the present invention, a plurality of scintillator elements are arrayed on a semiconductor photodetector element array in which a plurality of semiconductor photodetector elements are arranged in a matrix so that the bottom faces the semiconductor photodetector elements. A radiation detector provided with a light reflecting material on a surface other than the bottom surface of the scintillator element,

  The scintillator elements are arranged adjacent to each other with an interval of 100 μm or less, and the light reflecting material is formed by sequentially forming a base material and a metal reflecting material.

  Here, the base material may be a base material containing an inorganic oxide. The inorganic oxide may include silicon oxide. Furthermore, the inorganic oxide film may contain titanium oxide.

  According to one aspect of the radiation detector of the present invention, the inorganic oxide containing silicon oxide may be a fired product of SOG (Spin On Glass). The inorganic oxide containing titanium oxide may be a fired product of a titanium oxide precursor. The metal reflector may be a fired product of an organometallic compound containing at least one of Ag, Au, Al, and Ni.

  In the manufacturing method of the radiation detector of the present invention, a step of forming a processing groove having a grid shape of 100 μm or less on one side of a scintillator substrate, and an inorganic oxide base material and a metal reflecting material are sequentially formed on the side of the processing groove. Forming a scintillator array composed of a plurality of scintillator elements by processing a surface opposite to the groove processing surface of the scintillator substrate, a semiconductor photodetector element array composed of a plurality of semiconductor photodetector elements, and the scintillator array, The semiconductor photodetecting element and the scintillator element are provided with a step of bonding so as to face each other.

  In addition, the inorganic oxide precursor solution is filled in the processed groove by one of a dip coating method, a screen printing method, a spin coating method, and a dispensing method and baked to form the base material. Also good. Further, the viscosity of the inorganic oxide precursor solution may be 20 cP (0.020 Pa · s) or less.

  Further, in one aspect of the method for producing a radiation detector of the present invention, the processing in which the base material is formed from an organometallic compound solution by any one of a dip coating method, a screen printing method, a spin coating method, and a dispensing method. The metal reflector may be formed by filling the groove and firing. The viscosity of the organometallic compound solution may be 20 cP (0.020 Pa · s) or less.

  According to the present invention, even if the interval between adjacent scintillator elements is narrow, a radiation detector with small crosstalk can be obtained. The radiation detector of the present invention can be used as a radiation detector for a high-resolution X-ray CT apparatus with high resolution and resolution.

It is a perspective view of a radiation detector concerning an embodiment of the invention. It is a cross-sectional enlarged view of the radiation detector which concerns on embodiment of this invention. It is explanatory drawing which shows the manufacturing method of the radiation detector which concerns on embodiment of this invention. It is explanatory drawing showing the SEM image of the metal reflecting material which concerns on embodiment of this invention. It is explanatory drawing showing the SEM image of the metal reflecting material which concerns on an example of the Example of this invention. It is a figure which shows the relationship between the calcination temperature of the organometallic compound liquid used in one Example of this invention, and the light reflectivity of a metal reflector. It is a figure which shows the relationship between the scintillator element space | interval and crosstalk in the other Example of this invention. It is a figure which shows the relationship between the thickness of the conventional white coating material reflective material, and light transmittance. It is a figure which shows film thickness distribution when a metal reflecting material is formed in a processing groove with the conventional film-forming method. It is a figure which shows the light reflectivity of Ag reflecting material using the conventional metal microparticle. It is explanatory drawing showing the SEM image of the metal reflecting material which concerns on embodiment of this invention. It is explanatory drawing showing the SEM image of the metal reflecting material which concerns on an example of the Example of this invention.

  Embodiments of the radiation detector and manufacturing method of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a perspective view showing the radiation detector of the present embodiment. In the radiation detector 1 of the present invention, a scintillator array 3 is attached to a semiconductor photodetector element array 2 via an adhesive layer 4. The semiconductor photodetecting element array 2 has a plurality of semiconductor photodetecting elements 21 arranged on a flat plate. In the example of FIG. 1, it is assumed that N pieces are arranged in a row direction and M pieces are arranged in a column direction. The arrangement method is not limited to this. The scintillator array 3 includes scintillator elements 31 processed into a columnar shape. In this scintillator array 3, each scintillator element 31 is aligned so that its bottom surface coincides with the surface of the corresponding semiconductor photodetecting element 21, and is attached via an adhesive layer 4.

The scintillator element 31 can be made of a ceramic scintillator material such as CdWO ₄ , Bi ₄ Ge ₃ O ₁₂ , Gd ₂ O ₂ S, and the adhesive layer 4 is an optical adhesive having a high light transmittance, such as Epoxy Technologies. Epo-Tek301 (trademark) manufactured by KK is used. Although not shown in FIG. 1, a reflecting material that reflects visible light emitted from the scintillator element 31 is formed on the side surface and the upper surface of the scintillator element 31 (opposite surface opposite to the surface facing the semiconductor light detection element 31). Has been.

  FIG. 2 is an enlarged schematic view of the cross section of the radiation detector 1 shown in FIG. A base material 32 and a metal reflector 33 are sequentially formed on the side surface of the scintillator element 31, and the scintillator element 31 is attached to the corresponding semiconductor photodetecting element 21 through the adhesive layer 4.

  Here, the base material 32 is formed to a thickness of 10 nm to 10 μm using an inorganic oxide material having high light transmittance at the emission wavelength of the scintillator element 31 such as silicon oxide or titanium oxide. The metal reflector 33 is formed to a thickness of 0.1 μm to 10 μm using a material containing at least one of Ag, Au, Al, and Ni and having high light reflectance at the emission wavelength of the scintillator element 31. In order to prevent oxidation of the metal reflector 33, a protective material such as silicon oxide may be further coated on the metal reflector 33.

  In the case where a gap is generated between the plurality of scintillator elements 31 in which the base material 32 and the metal reflector 33 are formed on the side surfaces, the filler 34 may be filled in the gap between the adjacent scintillator elements 31. For the filler 34, a resin such as an epoxy resin, an ultraviolet curable resin, or a polyimide resin can be used. Furthermore, if these resins are filled with a mixture of heavy metal powders such as tungsten and molybdenum, the radiation shielding effect between the scintillator elements 31 can be enhanced, and the occurrence of crosstalk can be further prevented.

  An upper surface reflecting material 35 is formed on the surface of the scintillator element 31 opposite to the surface facing the semiconductor light detection element 21. As the side surface of the scintillator, the upper surface reflecting material 35 may be formed by sequentially forming a base material 32 and a metal reflecting material 33, or titanium oxide powder or the like used as a reflecting material in a conventional radiation detector is epoxy. A white paint kneaded with a resin may be used.

  Next, the manufacturing method of the radiation detector according to the present embodiment will be described with reference to FIGS.

First, in step 1, grooves are formed in a lattice pattern at a substantially constant pitch on a Gd ₂ O ₂ S scintillator substrate 5 processed to a desired size (FIG. 3A).

  Next, in step 2, the grooved scintillator substrate 5 is dipped in SSG solution 6 of HSG-R7-13 manufactured by Hitachi Chemical Co., Ltd., and the SOG solution 6 is filled into the groove formed in the scintillator substrate 5. (FIG. 3B). Instead of filling the SOG liquid 6 into the groove of the scintillator substrate 5 by such a dip coating method, filling may be performed using a method such as a screen printing method, a spin coating method, or a dispensing method.

  If the wettability between the SOG liquid 6 and the scintillator substrate 5 is poor, a pretreatment for improving wettability such as HMDS (hexamethyldisilazane) treatment or oxygen plasma irradiation is performed before filling the groove with the SOG liquid 6. You can do it. Furthermore, when the SOG liquid 6 in the groove is excessive, the SOG liquid 6 is shaken off using centrifugal force, or the SOG liquid 6 is sucked off with a non-woven fabric (Asahi Kasei Fibers Co., Ltd., Bencott). The SOG liquid 6 may be removed.

  When the viscosity of the SOG liquid 6 is increased, bubbles are likely to be entrained when filling the groove, and uniform filling becomes difficult. Therefore, the viscosity of the SOG liquid 6 is considered to be experimentally appropriate. It is preferable to prepare. In the present embodiment, an example in which the SOG liquid 6 having a viscosity of 15 cP (0.015 Pa · s) is used will be described.

  Next, in step 3, the SOG liquid 6 is baked to form a base material 32 containing silicon oxide. An electric furnace is used for firing, the temperature is raised from room temperature, and the temperature is kept at a predetermined temperature for a predetermined time. The oxygen concentration during firing is sufficiently reduced, for example, 1000 ppm or less. By this firing, the base material 32 containing silicon oxide is formed on the groove processing surface, and the surface roughness of the groove processing surface is reduced. In the present embodiment, the substrate is baked at 400 ° C. for 30 minutes, the thickness of the base material 32 on the groove processing surface is 0.1 to 2 μm, and the surface roughness Ra of the groove processing surface is 500 nm or less. (FIG. 3C) was obtained.

  In the present embodiment, the SOG liquid 6 is filled in the groove of the scintillator substrate 5 and baked to form the base material 32 containing silicon oxide. However, a base material containing another inorganic oxide may be formed. . For example, the base material 32 containing titanium oxide may be formed by filling a precursor liquid of titanium oxide into the groove of the scintillator substrate 5 and baking it. Even when another oxide precursor liquid is used, the viscosity of the liquid is preferably 20 cP (0.020 Pa · s) or less from the viewpoint of easy filling into the grooves.

  By using the base material 32 containing an inorganic oxide, it becomes difficult for the metal to segregate from the organometallic compound liquid 7 on the base material 32 in the next step, and the uniform metal reflector 33 can be obtained. This effect is considered to be because the base material 32 containing an inorganic oxide hardly reacts with the organic solvent contained in the organic compound liquid 7, and the starting point for segregation of the metal hardly occurs.

  Next, in step 4, the scintillator substrate 5 on which the base material 32 is formed is immersed in the organometallic compound solution 7, and the organometallic compound solution 7 is filled in the grooves of the scintillator substrate 5. In an example of the present embodiment, as the organometallic compound solution 7, Nano Dotite XA-9069 manufactured by Fujikura Kasei Co., Ltd., which is an organic silver compound solution, is used (FIG. 3D).

  In this embodiment, the organometallic compound liquid 7 is filled in the groove of the scintillator substrate 5 by the dip coating method, but it may be filled by using other methods such as a screen printing method, a spin coating method, and a dispensing method. good. Furthermore, when the organometallic compound liquid 7 in the groove is excessive, the organometallic compound liquid 7 is shaken off using centrifugal force, or the non-woven fabric (Asahi Kasei Fibers Co., Ltd., Bencott) is used. The excess organometallic compound liquid 7 may be removed by sucking off the liquid.

  When the viscosity of the organometallic compound liquid 7 is increased, bubbles are likely to be entrained when filling the grooves, and uniform filling becomes difficult. 6 is preferably prepared. In this embodiment, the organometallic compound liquid 7 having a viscosity of 15 cP (0.015 Pa · s) is used.

  Next, in step 5, the organometallic compound 7 is baked to form a metal reflector 33 containing Ag. For baking, a hot plate is used and held at a predetermined temperature (for example, 150 ° C.) for a predetermined time (for example, 30 minutes). The organometallic compound 7 before firing is colorless and transparent, but when Ag particles are deposited during firing, the color changes to brown, and then the Ag particles are bonded together to form a silver continuous film. The thickness of the metal reflecting material 33 in the groove containing this Ag is 0.1 to several μm (FIG. 3E).

  In the present embodiment, the metal metal compound liquid 7 is filled in the groove of the scintillator substrate 5 and fired to form the metal reflector 33 containing Ag. However, the embodiment of the present invention is not limited to this, A metal fine particle paste containing Ag, Au, Al, Ni, etc., which has a relatively high light reflectance with respect to visible light, is filled in the groove of the scintillator substrate 5 and fired to obtain a fired metal fine particle. Alternatively, the metal reflector 33 containing may be formed. Even when such a metal fine particle paste is used, the viscosity of the paste is preferably 20 cP (0.020 Pa · s) or less because of easy filling into the grooves.

  Next, in step 6, the filler 34 is filled into the grooves of the scintillator substrate 5. In the present embodiment, an epoxy resin mixed with a curing agent is used as the filler 34 and the grooves of the scintillator substrate 5 are filled by screen printing. In addition, it may replace with the example which fills an epoxy resin using a screen printing method, and may use other filling methods, such as a dispensing method. Furthermore, it is more preferable that the epoxy resin is filled in a reduced-pressure atmosphere so that no bubbles remain inside the epoxy resin. Then, this epoxy resin is heated and cured for a predetermined time in an electric oven set at a predetermined temperature (FIG. 3 (f)).

  Next, in step 7, the surface of the scintillator substrate 5 is ground. By grinding the substrate surface (grooved surface), the base material 32, the metal reflector 33, and the filler 34 adhered to the surface of the scintillator substrate 5 are removed (FIG. 3G).

  Next, in step 8, the top reflector 35 is formed. In the present embodiment, the upper surface reflecting material 35 is made of epoxy resin mixed with a curing agent and further mixed with titanium oxide powder to form a white paint, and screen printing is performed on the surface (grooved surface) of the scintillator substrate 5. It will be applied by the method. In addition, instead of the example of applying the white paint by the screen printing method, other application methods such as a dispensing method may be used. Further, the white paint is heated and cured for a predetermined time in an electric oven set at a predetermined temperature (FIG. 3 (h)).

  In the present embodiment, a white paint in which an epoxy resin and titanium oxide powder are kneaded is used as the upper surface reflecting material 35. Instead, white powder that reflects visible light emitted by the scintillator element 31, such as silicon oxide or A white paint using aluminum oxide powder or titanium oxide powder coated with silicon oxide may be used. Moreover, you may form a base material and a metal reflective material in order on the conditions similar to the process 2-the process 6 without using a white coating material.

  Next, in step 9, the back surface of the scintillator substrate 5 (the surface opposite to the groove processing surface) is ground to remove the base material 32, the metal reflector 33, and the filler 34 attached to the back surface of the scintillator substrate 5. As a result, the scintillator substrate 5 is separated into a plurality of columnar scintillator elements 31, and the scintillator array 3 is formed (FIG. 3 (i)).

  Finally, in step 10, alignment is performed so that the plurality of scintillator elements 31 and the plurality of semiconductor light detection elements 21 face each other, and the opposite surface of the upper surface reflecting material 35 of the scintillator array 3 and the semiconductor light detection element array 2. The surface is bonded through an adhesive layer 4. The adhesive layer 4 is bonded to the scintillator array 3 and the semiconductor photodetecting element array 2 by using an optical adhesive and heating the adhesive layer 4 for a predetermined time in an electric furnace set at a predetermined temperature. Thus, the radiation detector 1 of the present embodiment is completed (FIG. 3 (j)).

Example 1
Next, examples of the present invention will be described. In this embodiment, the interval between adjacent scintillator elements 31 is set to 100 μm or less.

First, in step 1, a Gd ₂ O ₂ S scintillator substrate 5 machined to a width of 73 mm, a height of 22 mm, and a thickness of 2.0 mm is machined to form grooves having a width of 80 μm and a depth of 1.7 mm at a pitch of 1 mm. (FIG. 3A).

  Next, in step 2, the grooved scintillator substrate 5 is dipped in SSG solution 6 of HSG-R7-13 manufactured by Hitachi Chemical Co., Ltd., and the SOG solution 6 is filled into the groove formed in the scintillator substrate 5. (FIG. 3B).

  In this embodiment, the SOG liquid 6 is filled in the groove of the scintillator substrate 5 by the dip coating method, but it may be filled by using a screen printing method, a spin coating method, a dispensing method, or the like.

  If the wettability between the SOG liquid 6 and the scintillator substrate 5 is poor, a pretreatment for improving wettability such as HMDS (hexamethyldisilazane) treatment or oxygen plasma irradiation is performed before filling the groove with the SOG liquid 6. You can do it. Furthermore, when the SOG liquid 6 in the groove is excessive, the SOG liquid 6 is shaken off using centrifugal force, or the SOG liquid 6 is sucked with a non-woven fabric (Asahi Kasei Fibers Co., Ltd., Bencott). Excess SOG liquid 6 may be removed.

  When the viscosity of the SOG liquid 6 is increased, bubbles are easily involved when filling the groove, and uniform filling becomes difficult. As a result of making and studying SOG liquids 6 having various viscosities, the present inventor has found that if the viscosity of the SOG liquid 6 is 20 cP (0.020 Pa · s) or less, it can be uniformly filled without entraining bubbles. In this example, the SOG liquid 6 having a viscosity of 15 cP (0.015 Pa · s) was used with sufficient margin.

  Next, in Step 3, the SOG liquid 6 was baked to form a base material 32 containing silicon oxide. An electric furnace was used for firing, and the temperature was raised from room temperature and held at 400 ° C. for 30 minutes. The oxygen concentration during firing was set to 1000 ppm or less. After firing, a base material 32 containing silicon oxide was formed on the groove processing surface, and the surface roughness of the groove processing surface was alleviated. The thickness of the base material 32 on the groove processed surface was 0.1 to 2 μm, and the surface roughness Ra of the groove processed surface was 500 nm or less (FIG. 3C). Here, the surface roughness Ra is measured by using an atomic force microscope, that is, an AFM (Digital Instruments: Nano Scope III), and the surface of the groove processing surface in the region of 5 μm square (5 mm × 5 mm) in the tapping mode and the probe. The distance was measured, and the difference in the irregularities on the surface of the grooved surface was calculated.

  In this embodiment, the SOG liquid 6 is filled in the groove of the scintillator substrate 5 and baked to form the base material 32 containing silicon oxide. However, even if a base material containing another inorganic oxide is formed in the same manner, good. For example, the base material 32 containing titanium oxide may be formed by filling a precursor liquid of titanium oxide into the groove of the scintillator substrate 5 and baking it. Even when another oxide precursor liquid is used, the viscosity of the liquid is preferably 20 cP (0.020 Pa · s) or less from the viewpoint of easy filling into the grooves.

By using the base material 32 containing an inorganic oxide, in the next step, the metal is less likely to segregate from the organometallic compound liquid 7 on the base material 32, and a uniform metal reflector 33 can be obtained. This effect is considered to be because the base material 32 containing an inorganic oxide hardly reacts with the organic solvent contained in the organic compound liquid 7, and the starting point for segregation of the metal hardly occurs.
However, the base material 32 is selected from those that are not dissolved by the organometallic compound liquid described below. For example, when a silicon resin coating material is used as the base material 32, the silicon resin coating material is dissolved in the organometallic compound liquid. Accordingly, here, the base material 32 containing silicon oxide or other inorganic oxide is formed by using a material such as SOG liquid 6 containing silicon dioxide or other inorganic oxide without containing silicone resin. To do.

  Next, in step 4, the scintillator substrate 5 on which the base material 32 was formed was immersed in the organometallic compound solution 7, and the organometallic compound solution 7 was filled in the grooves of the scintillator substrate 5. In this example, as the organometallic compound liquid 7, Nano Dotite XA-9069 manufactured by Fujikura Kasei Co., Ltd., which is an organic silver compound liquid, was used (FIG. 3 (d)).

  In this embodiment, the organometallic compound liquid 7 is filled in the groove of the scintillator substrate 5 by the dip coating method, but it may be filled by a method such as a screen printing method, a spin coating method, or a dispensing method. Furthermore, when the organometallic compound liquid 7 in the groove is excessive, the organometallic compound liquid 7 is shaken off using centrifugal force, or the non-woven fabric (Asahi Kasei Fibers Co., Ltd., Bencott) is used. The excess organometallic compound liquid 7 may be removed by sucking off the liquid.

  When the viscosity of the organometallic compound liquid 7 is increased, air bubbles are easily involved when filling the groove, and uniform filling becomes difficult. The inventor of the present application made organometallic compound liquids 7 having various viscosities, and as a result of repeated examination, as long as the viscosity of the organometallic compound liquid 7 is 20 cP (0.020 Pa · s) or less, it is uniform without entraining bubbles. In this example, the organometallic compound liquid 7 having a viscosity of 15 cP (0.015 Pa · s) was used with a sufficient margin.

  Next, in step 5, the organometallic compound 7 was fired to form a metallic reflector 33 made of Ag. For baking, a hot plate was used and held at 150 ° C. for 30 minutes. The organometallic compound 7 before firing was colorless and transparent, but when the Ag particles were precipitated during firing, the color turned brown, and then the Ag particles were combined to form a silver continuous film. The thickness of the metal reflecting material 33 in the groove made of Ag was 0.1 to several μm (FIG. 3E).

FIG. 4 is an SEM image of the surface of the metal reflector 33 after firing, and FIG. 11 is an image obtained by adjusting the contrast of FIG. 4 to make the grain noticeable. A continuous Ag microstructure as shown in FIG. 4 (or FIG. 11) was formed by thermal decomposition of organic silver. When the light reflectance and light transmittance on the surface of the metal reflector 33 were measured at a wavelength of 500 nm, the light reflectance was 95.26% and the light transmittance was 0%. As the metal reflector 33 used in the radiation detector 1, It was confirmed that the light reflection characteristics were sufficient.
By improving the light reflectivity, the ability to confine the visible light emitted by the scintillator element inside the scintillator element is improved, and the visible light emitted by the scintillator element is efficiently guided to the semiconductor photodetector element. The output of the radiation detector can be increased.

(Example 2)
Next, examples in which the firing temperature in step 5 is varied will be described. First, the metal reflector 33 is obtained by holding for 30 minutes on a hot plate set at a plurality of different firing temperatures. Then, 5 lines having a length of 2 microns are drawn from the SEM image of the metal reflector 33 at each firing temperature, and the average number is obtained by counting the number of Ag grains on the line, and 2 microns is divided by the average number. The results of calculating the particle size are shown below.
140 ° C firing: (Cannot be counted in a continuous film state)
150 degreeC baking: 38.4 counts, average particle diameter 52nm.
160 degreeC baking: 25.6 counts, average particle diameter 78nm.
180 degreeC baking: 17.6 counts, average particle diameter 114nm.
200 degreeC baking: 28.2 counts, average particle diameter 71nm.
250 degreeC baking: 16.2 counts, average particle diameter 123nm.
From this example, it can be concluded that the higher the firing temperature, the smaller the count value and the larger the average particle size. Note that the light reflectance measured at a wavelength of 500 nm exceeds 90%, for example, 93% or more, and preferably 95% or more, can be said to be sufficient light reflection characteristics as the metal reflector 33 used in the radiation detector 1. According to the observation of the SEM image, the reflectance decreases as the area of the recesses formed between the Ag grains increases, but it has been found from experiments that the recesses tend to be conspicuous when the average particle size is 100 nm or more. Therefore, the reflectance characteristics as described above are achieved when the average particle size is less than 100 nm. Further, it has been confirmed that when the particle size of the structure of the metal reflective film is about 1/10 or less of the light wavelength of 500 nm, scattering is further suppressed and it contributes to an improvement in reflectance. Therefore, more preferable reflectance characteristics are achieved when the average particle diameter is less than 60 nm. Moreover, it is also preferable that the tissue is joined to form an integrated Ag film. Therefore, from the above example, the firing temperature in step 5 is preferably 140 ° C. and 200 ° C. or less, more preferably 140 ° C. and less than 160 ° C., for example, about 150 ° C. Is preferred.
FIG. 5 is an SEM image of the surface of the metal reflector 33 obtained by firing the organometallic compound 7 by holding it on a hot plate at 250 ° C. for 30 minutes, and FIG. 12 is adjusted for contrast so that the granularity in FIG. 5 is conspicuous. Is. By increasing the firing temperature, the Ag microstructure became large and irregular in comparison with FIG. 4 (or FIG. 11). Moreover, the area of the recessed part between particle | grains has also increased. When the light reflectance and light transmittance on the surface of the metal reflector 33 were measured at a wavelength of 500 nm, the light transmittance was 0%, but the light reflectance was 92.54%. It was confirmed that the light reflectance of the reflecting material 33 was lowered.
In addition, the SEM image of FIG. 4, 5 (or FIG. 11, 12) was observed with the sample for a measurement produced on the same conditions. That is, in the configuration of FIG. 2, force was continuously applied along the surface of the metal reflector 33, the base material 32 was cleaved, and the exposed surface was observed with an SEM to obtain a fine microstructure photograph of Ag. Is.

  FIG. 6 shows the relationship between the light reflectance of the metal reflector 33 measured at a wavelength of 500 nm and the firing temperature. As the firing temperature increased, the light reflectance of the metal reflector 33 tended to decrease.

  The reason why the light reflection characteristics of the metal reflector 33 are changed with respect to the firing temperature is considered to be due to the difference in the metal reflector structure with respect to the firing temperature. When the organometallic compound 7 is baked at a low temperature, the decomposition reaction of the organic silver is slow. Therefore, the precipitated Ag particles are bonded over time to form a continuous fine structure. It is thought that the structure of large and irregular particles is formed because the Ag particles precipitated before the formation of a continuous fine structure is fast and the reaction is completed. Accordingly, the temperature for firing the organometallic compound 7 is preferably as low as possible within the temperature range in which the thermal decomposition reaction occurs.

  In this embodiment, the metal metal compound liquid 7 is filled in the groove of the scintillator substrate 5 and baked to form the metal reflector 33 made of Ag. Similarly, the metal fine particle paste is put into the groove of the scintillator substrate 5. The metal reflector 33 made of a fired metal fine particle may be formed by filling and firing. The metal fine particles used for the metal fine particle paste are preferably metal fine particles containing Ag, Au, Al, Ni, etc., which have a high light reflectance with respect to visible light. Even when a metal fine particle paste is used, the viscosity of the paste is preferably 20 cP (0.020 Pa · s) or less because of easy filling into the grooves.

  Next, in step 6, the filler 34 was filled into the grooves of the scintillator substrate 5. In the present embodiment, as the filler 34, a scintillator substrate manufactured by Three Bond Co., Ltd., a main agent 2023, and a curing agent 2131D mixed with a main agent 100: a curing agent 30 (weight ratio) is used. 5 grooves were filled. In this embodiment, the epoxy resin is filled using a screen printing method, but other filling methods such as a dispensing method may be used. Furthermore, it is more preferable that the epoxy resin is filled in a reduced-pressure atmosphere so that no bubbles remain inside the epoxy resin. The epoxy resin was cured by heating at 100 ° C. for 1 hour in an electric oven (FIG. 3 (f)).

  Next, in step 7, the surface of the scintillator substrate 5 was ground. By grinding the substrate surface (grooved surface), the base material 32, the metal reflector 33, and the filler 34 adhered to the surface of the scintillator substrate 5 were removed (FIG. 3G).

Next, in step 8, a top reflector 35 was formed. In this example, as the upper surface reflecting material 35, an epoxy resin of a main agent 2023 and a curing agent 2131D manufactured by Three Bond Co., Ltd. mixed with a main agent 100: a curing agent 30 (weight ratio) is mixed with an average particle size of about 0.1. A white paint obtained by kneading 3 μm titanium oxide powder was applied to the surface (grooved surface) of the scintillator substrate 5 by screen printing. In this embodiment, the white paint is applied by the screen printing method, but other application methods such as a dispensing method may be used. The white paint was cured by heating in an electric oven at 100 ° C. for 1 hour. (FIG. 3 (h)).
Here, the base material 32 and the metal reflecting material 33 formed up to step 6 are formed under conditions optimal for forming between the scintillator elements. For this reason, the base material and the metal reflector formed on the upper surface are thick on the upper surface side, and cracks may be formed at the bent corners and may be peeled off. Therefore, the base material 32 and the metal reflecting material 33 adhering to the upper surface side of the scintillator substrate 5 are temporarily removed in step 7, and then the upper surface reflecting material 35 is re-formed in step 8.

  In this example, a white paint kneaded with an epoxy resin and titanium oxide powder was used as the upper surface reflector 35, but white powder that reflects visible light emitted by the scintillator element 31, for example, silicon oxide or aluminum oxide powder, You may use the white coating material which used the powder which coat | coated the silicon oxide to the powder of titanium oxide. Moreover, you may form a base material and a metal reflective material in order on the conditions similar to the process 2-the process 6 without using a white coating material.

  Next, in step 9, the back surface of the scintillator substrate 5 (the surface opposite to the groove processing surface) was ground. The base material 32, the metal reflector 33, and the filler 34 attached to the back surface of the scintillator substrate 5 are removed, and the scintillator substrate 5 is ground until the thickness of the scintillator substrate 5 is reduced from 2.0 mm to 1.7 mm. 5 was separated into a plurality of columnar scintillator elements 31 to form a scintillator array 3 (FIG. 3 (i)).

  Finally, in step 10, the opposite surface of the upper surface reflector 35 of the scintillator array 3 and the surface of the semiconductor light detection element array 2 are bonded so that the plurality of scintillator elements 31 and the plurality of semiconductor light detection elements 21 face each other. Bonded through layer 4. The adhesive layer 4 is made of Epoxy Technologies, Epo-Tek301 optical adhesive, and heated in an electric furnace at 80 ° C. for 1 hour, so that the scintillator array 3 and the semiconductor photodetector array 2 are cured and bonded. And the radiation detector 1 was completed (FIG.3 (j)).

(Example 3)
Next, the crosstalk between the radiation detector of the present invention and a conventional radiation detector using a reflective material of white paint was compared. In this example, radiation detectors having different scintillator element intervals of 20 μm to 150 μm were produced by the same manufacturing method as in Example 1. In addition, as a comparative example, a radiation detector having the same scintillator element size as in the present embodiment and a different scintillator element interval of 20 μm to 150 μm was manufactured using an epoxy resin made of Three Bond Co., Ltd. It was prepared using a white paint reflecting material in which titanium oxide powder having an average particle size of about 0.3 μm was kneaded with the mixture of the agent 30 (weight ratio).

  Semiconductor photodetection attached to the scintillator element irradiated with X-rays by irradiating the single scintillator elements of the radiation detectors of this embodiment and the comparative example thus manufactured with X-rays condensed to a diameter of about 100 μm. The crosstalk was calculated from the ratio between the output current of the element and the output current of the semiconductor photodetecting element attached to the adjacent scintillator element.

  FIG. 7 shows the relationship between the scintillator element interval and crosstalk. In the radiation detector of the comparative example using white paint as the light reflecting material, the crosstalk increased as the scintillator element interval narrowed. However, in the radiation detector of the present example using the metal reflecting material, the scintillator element interval was Even if it becomes narrow, crosstalk is kept small. From the above, it was confirmed that the radiation detector of the present example was superior in crosstalk as compared with the radiation detector of the comparative example.

1 radiation detector,
2 semiconductor photodetector array,
21 semiconductor light detection element,
3 scintillator array,
31 scintillator elements,
32 Base material,
33 metal reflector,
34 filler,
35 top reflector,
4 Adhesive layer,
5 Scintillator board,
6 SOG liquid,
7 Organometallic compound solution.

Claims (5)

A step of forming a processing groove having a grid shape of 100 μm or less on one side of the scintillator substrate;
A step of forming an inorganic oxide base material and a metal reflecting material in order on the processed groove side surface, which is a base material having optical transparency at the emission wavelength of the scintillator element;
Processing a surface opposite to the groove processing surface of the scintillator substrate to form a scintillator array including a plurality of scintillator elements;
Bonding a semiconductor light detection element array including a plurality of semiconductor light detection elements and the scintillator array so that the respective semiconductor light detection elements and the scintillator elements face each other;
With
A method of manufacturing a radiation detector, comprising filling the processed groove with an inorganic oxide precursor solution and baking the solution to form the base material. An inorganic oxide precursor solution is filled in the processed groove by one of a dip coating method, a screen printing method, a spin coating method, and a dispensing method, and baked to form the base material. The manufacturing method of the radiation detector of Claim 1 . Method of manufacturing a radiation detector according to claim 1 or 2, characterized in that less 20cP viscosity of the precursor solution of the inorganic oxide. Filling the processed groove in which the base material is formed by any one of a dip coating method, a screen printing method, a spin coating method, and a dispensing method and firing the solution to form the metal reflector. The manufacturing method of the radiation detector as described in any one of Claim 1 to 3 characterized by these. The method of manufacturing a radiation detector according to claim 4 , wherein the viscosity of the organometallic compound solution is 20 cP or less.

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