JP5654793B2 - Radiation detection element and method for manufacturing radiation detection element - Google Patents

Description

  The present invention relates to a radiation detection element and a method for manufacturing the radiation detection element. In particular, the present invention relates to a radiation detection element that detects radiation such as gamma rays and X-rays, and a method for manufacturing the radiation detection element.

  As a conventional radiation detector, one detection element is a radiation detector in which three or more detection units forming a channel are provided along one direction, and the detection unit located at the end of the detection element is: A radiation detector whose volume is larger than the volume of an adjacent detector is known (for example, see Patent Document 1). In the radiation detector described in Patent Document 1, signal readout electrodes of a plurality of channels are configured by a plurality of anode electrodes, and a bias application electrode is configured by one cathode electrode. An electrode dividing groove for dividing the anode electrode is formed between the anode electrodes.

  According to the radiation detector described in Patent Literature 1, it is possible to provide a radiation detector that can make the detection sensitivity of a plurality of channels uniform.

JP 2009-259859 A

  Here, in the radiation detector according to Patent Document 1, the cross-sectional shape of the electrode dividing groove for dividing the anode electrode is substantially rectangular. When the cross-sectional shape of the electrode dividing groove is rectangular, electrons and holes generated in the area immediately below the electrode dividing groove cannot be collected by the electrode, and the area becomes a dead area where radiation cannot be detected. obtain. It is desirable to reduce the insensitive area from the viewpoint of improving the detection sensitivity of radiation.

  Therefore, an object of the present invention is to provide a radiation detection element capable of improving the detection sensitivity of radiation and a method for manufacturing the radiation detection element.

  In order to achieve the above object, the present invention provides a semiconductor substrate made of a compound semiconductor capable of detecting radiation, a groove provided on the surface of the semiconductor substrate, and having a gradually narrowing width from the surface side toward the inside of the semiconductor substrate, There is provided a radiation detection element including an electrode provided on each of a flat region on a surface of a semiconductor substrate and a surface opposite to the surface of the semiconductor substrate.

  In the radiation detection element, the compound semiconductor may be CdTe or CdTeZn.

  In the radiation detection element, the groove preferably has a V shape or a U shape in cross section.

  In the radiation detection element, the electrode provided in the flat region on the surface of the semiconductor substrate is configured to include an In layer and a Ti layer from the flat region side of the surface of the semiconductor substrate, and The electrode provided on the opposite surface may be made of Pt.

  In order to achieve the above object, the present invention provides a semiconductor substrate preparation step of preparing a semiconductor substrate made of a compound semiconductor, a surface electrode formation step of forming a surface electrode on the surface of the semiconductor substrate, and a back surface on the back surface of the semiconductor substrate. The back surface electrode forming step for forming the electrode, and a blade whose cross-sectional width is gradually narrowed toward the tip are brought into contact with the surface electrode, and a groove whose width is gradually narrowed from the front surface toward the inside of the semiconductor substrate is formed on the surface of the semiconductor substrate. A method for manufacturing a radiation detection element is provided.

  Moreover, in the said manufacturing method of a radiation detection element, CdTe or CdTeZn may be sufficient as a compound semiconductor.

  Moreover, in the manufacturing method of the said radiation detection element, the front-end | tip part of a braid | blade may have V shape or circular arc shape in a cross section.

  Moreover, in the manufacturing method of the said radiation detection element, even if a surface electrode formation process forms In layer and Ti layer from the surface side of a semiconductor substrate, and a back surface electrode formation process forms a Pt layer on the back surface of a semiconductor substrate. Good.

  According to the radiation detection element and the method for manufacturing the radiation detection element according to the present invention, it is possible to provide a radiation detection element capable of improving the radiation detection sensitivity and a method for manufacturing the radiation detection element.

It is a perspective view of a radiation detector provided with a radiation detection element concerning an embodiment of the invention. It is a perspective view of a radiation detection element concerning an embodiment of the invention. (A) expands and shows the outline of the cross section of the groove | channel of the radiation detection element which concerns on embodiment of this invention, (b) expands and shows the outline of the cross section of the groove | channel of the radiation detection element concerning a prior art. It is a figure which shows the flow of the manufacturing process of the radiation detection element which concerns on embodiment of this invention. It is sectional drawing of the radiation detection element which concerns on the modification of embodiment of this invention.

[Embodiment]
FIG. 1 shows an example of a perspective view of a radiation detector including a radiation detection element according to an embodiment of the present invention.

(Outline of configuration of radiation detector 1)
The radiation detector 1 including the radiation detection element 10 according to the present embodiment is a radiation detector that has a card shape and detects radiation such as γ rays and X rays. In FIG. 1, the radiation 200 enters from the upper side to the lower side of the page. That is, the radiation 200 propagates along the direction from the radiation detection element 10 of the radiation detector 1 toward the card holder 30 and the card holder 31 and reaches the radiation detector 1. In the radiation detector 1, the radiation 200 is incident on the side surface of the radiation detection element 10 (that is, the surface facing upward in FIG. 1). Therefore, the side surface of the radiation detection element 10 is an incident surface of the radiation 200. Thus, the radiation detector in which the side surface of the radiation detection element 10 is the incident surface of the radiation 200 is referred to as an edge-on type radiation detector in the present embodiment. The radiation detector 1 detects a plurality of radiations 200 through a collimator having a plurality of openings through which the radiation 200 incident along a specific direction (for example, a direction toward the radiation detector 1) passes. The radiation detector 1 can be used as a radiation detector 1 for a radiation detection apparatus configured by arranging the radiation detectors 1 side by side.

  Specifically, the radiation detector 1 supports the substrate 20 by sandwiching the substrate 20 between a pair of radiation detection elements 10 capable of detecting the radiation 200, a thin substrate 20, and adjacent portions of the pair of radiation detection elements 10. Card holder 30 and card holder 31 are provided. As an example, four pairs of radiation detection elements 10 are fixed to the substrate 20 at positions where the substrate 20 is sandwiched. That is, the pair of radiation detection elements 10 of each set is fixed to a symmetric position with the substrate 20 as a symmetry plane on each of one surface and the other surface of the substrate 20.

  The substrate 20 is supported by being sandwiched between a card holder 30 and a card holder 31. The card holder 30 and the card holder 31 are formed to have the same shape, and the protruding portion 36 of the card holder 31 is fitted into the grooved hole 34 of the card holder 30 and the grooved hole of the card holder 31 is fitted. The board | substrate 20 is supported by the projection part 36 (not shown) which the card holder 30 has fitting to 34 (not shown).

  The elastic member mounting portion 32 and the recess 32a are fixed by pressing the radiation detector 1 against the radiation detector stand when the radiation detector 1 is inserted into the radiation detector stand supporting the plurality of radiation detectors 1. This is a portion where an elastic member such as a leaf spring is provided. The radiation detector stand has a connector into which the card edge portion 29 is inserted. In the radiation detector 1, the card edge portion 29 is inserted into the connector, and the connector and the pattern 29a are electrically connected. Thus, the circuit is electrically connected to a control circuit as an external electric circuit, an external power supply line, a ground line, and the like.

  Further, the radiation detector 1 includes a wiring pattern (radiation detection element) that electrically connects each of the electrodes of each radiation detection element 10 and the plurality of substrate terminals 22 to the opposite side of the substrate 20 of the pair of radiation detection elements 10. 10 further includes a flexible substrate 40 having electrodes on the element surface opposite to the substrate 20 and a wiring pattern on the radiation detection element 10 side of the flexible substrate 40 (not shown).

  The flexible substrate 40 is provided on both the one radiation detection element 10 side and the other radiation detection element 10 side of the pair of radiation detection elements 10 (in the present embodiment, four pairs of radiation detection elements 10). The flexible substrate 40 is provided on each of the one radiation detection element 10 side and each of the other radiation detection element 10 side). Then, one end of each of the plurality of wiring patterns of the flexible substrate 40 is electrically connected to the substrate terminal 22. The substrate terminal 22 is provided on the surface of the substrate 20 and is electrically connected to the wiring pattern of the substrate 20.

(Details of substrate 20)
The substrate 20 is a thin substrate (for example, a glass epoxy substrate such as FR4) on which a conductive thin film (for example, copper foil) made of a conductive material such as a metal conductor is formed, and is made of an insulating material such as a solder resist. It is formed with flexibility by being sandwiched between insulating layers. As an example, the substrate 20 is formed to have a thickness of 0.2 mm or less. The substrate 20 has a wiring pattern that is electrically connected to the electrode of the radiation detection element 10. A conductive silver paste is provided on a part of the surface of the wiring pattern, and the electrodes of the radiation detection element 10 are electrically connected to the wiring pattern through the silver paste.

  The wiring pattern of the substrate 20 that is electrically connected to the electrode of the radiation detection element 10 is formed so as to be electrically connected to the pattern 29 a of the card edge portion 29. The substrate 20 has a wiring pattern that electrically connects the substrate terminal 22 and the pattern 29 a of the card edge portion 29. Thereby, on the substrate 20, an electrode (surface electrode 116 described later) on the surface of the radiation detection element 10 on the substrate 20 side is electrically connected to the pattern 29 a of the card edge portion 29 by the wiring pattern of the substrate 20. Further, an electrode on the opposite side of the substrate 20 side of the radiation detection element 10 (a back surface electrode 118 described later) is a card via the wiring pattern of the flexible substrate 40, the substrate terminal 22, and the wiring pattern of the substrate 20. It is electrically connected to the pattern 29 a of the edge portion 29. Here, for example, the electrode on the substrate 20 side of the radiation detection element 10 is an anode electrode, and the electrode on the opposite side of the radiation detection element 10 on the substrate 20 side is a cathode electrode. In this case, the signal from the anode electrode and the signal from the cathode electrode are respectively guided to the pattern 29a of the card edge portion 29 and output to an external electric circuit via the pattern 29a.

(Details of radiation detection element 10)
FIG. 2 shows an example of a perspective view of the radiation detection element according to the exemplary embodiment of the present invention.

  The radiation detection element 10 mainly composed of a compound semiconductor is formed in a substantially rectangular parallelepiped shape. That is, the radiation detection element 10 is formed in a substantially square shape in plan view. A plurality of grooves 120 are provided on the element surface 10a, which is one surface perpendicular to the surface on which the radiation of the radiation detection element 10 is incident. Here, the groove 120 is provided with a shape in which the width gradually decreases from the element surface 10 a side toward the inside of the radiation detection element 10. For example, the groove 120 is formed to have a V shape in a sectional view. The width of the groove 120 (the width of the longest part) is about 0.2 mm.

  And it is the surface of the radiation detection element 10 on which the radiation is incident, and is delimited by a virtual perpendicular from each groove 120 to the surface opposite to the surface on which the groove 120 is provided (that is, the element surface 10b). A region and a region delimited by the virtual perpendicular and the end of the radiation detection element 10 are referred to as a pixel region. The radiation detection element 10 has (n−1) grooves 120 to form n pixel regions. In addition, a surface electrode 116 is provided on each of the plurality of element surfaces 10a as a flat region between the plurality of grooves 120, and a back electrode 118 is provided on the element surface 10b. Each of the plurality of pixel regions corresponds to one pixel (pixel) that detects radiation. Thereby, one radiation detection element 10 has a plurality of pixels.

  As an example, when one radiation detector 1 includes eight radiation detection elements 10 (four pairs of radiation detection elements 10) and each radiation detection element 10 has eight pixel regions, one radiation detection is performed. The device 1 will have a resolution of 64 pixels. By increasing or decreasing the number of grooves 120, the number of pixels of one radiation detection element 10 can be increased or decreased. As an example, the radiation detection element 10 has a width of about 1.2 mm, a length of about 11.2 mm, and a height of about 5 mm.

As the compound semiconductor constituting the radiation detection element 10, for example, CdTe can be used. Further, the radiation detection element 10 is not limited to the CdTe element as long as radiation such as γ rays can be detected. For example, a compound semiconductor element such as a CdZnTe (CZT) element or an HgI ₂ element can be used as the radiation detection element 10.

  FIG. 3A is an enlarged view of the outline of the groove of the radiation detection element according to the embodiment of the present invention, and FIG. 3B is an outline of the section of the groove of the radiation detection element according to the prior art. Enlarged view.

  As shown in FIG. 3A, the surface electrode 116 is provided on the element surface 10a of the radiation detection element 10 according to the present embodiment as described above. Specifically, the surface electrode 116 includes the first electrode 112 and the second electrode 114 in this order from the flat region side of the element surface 10a. The surface electrode 116 can be made of a material that is Schottky bonded to the radiation detection element 10. The first electrode 112 can be composed of, for example, an In layer, and the second electrode 114 can be composed of, for example, a Ti layer. A back electrode 118 is provided on the element surface 10b. The back electrode 118 is made of a material that makes ohmic contact with the radiation detection element 10. For example, the back electrode 118 can be made of Pt.

  Here, when an electric field is generated between the front electrode 116 and the back electrode 118, an electric field 130a from the element surface 10a toward the element surface 10b, and an electric field from the element surface 10a along the side surface of the groove 120 toward the element surface 10b. 130b occurs. That is, since the groove 120 has a cross-sectional shape whose width gradually decreases from the element surface 10a toward the element surface 10b, the electric field 130b passing through the vicinity of the groove 120 is linear from the element surface 10a to the element surface 10b. The direction is along the side surface of the groove 120, not in the direction toward.

  Then, due to the presence of the electric field 130b oriented along the side surface of the groove 120, the electrons 300 generated near or directly below the groove 120 by the incidence of the radiation 200 propagate to the surface electrode 116 side and are generated by the incidence of the radiation 200. The hole 310 propagates to the back electrode 118 side. Thereby, the electrons 300 and the holes 310 generated near or directly below the groove 120 by the radiation 200 can be appropriately collected by the front electrode 116 and the back electrode 118, and the detection sensitivity of the radiation 200 is improved.

  On the other hand, as shown in FIG. 3B, in the case of the groove 122 having a rectangular cross section, the width of the groove 122 is substantially constant from the element surface 10 a to the bottom of the groove 122. When the cross-sectional shape of the groove 122 is rectangular, the electric field 130a from the element surface 10a toward the element surface 10b is linear, and the electric field 130c in the vicinity of the groove 122 hardly follows the side surface of the groove 122. Therefore, there is almost no electric field immediately below the groove 122. That is, when the cross-sectional shape of the groove 122 is rectangular, the area immediately below the groove 122 becomes a dead area 400 where the radiation 200 cannot be detected. When the radiation 200 is incident on the insensitive region 400, the electrons 300 and the holes 310 generated by the incidence of the radiation 200 may not be collected by the front electrode 116 and the back electrode 118. However, since the radiation detection element 10 according to the present embodiment includes the groove 120 having a V-shaped cross section, the region where the radiation 200 cannot be detected can be reduced as compared with the case where the groove has a rectangular cross section.

(Manufacturing method of radiation detecting element 1)
FIG. 4 shows an example of the flow of the manufacturing process of the radiation detection element according to the embodiment of the present invention.

  First, for example, a semiconductor substrate 100 made of a compound semiconductor such as CdTe capable of detecting radiation is prepared (semiconductor substrate preparation step, FIG. 4A). Next, the surface electrode 116 is formed on the element surface 10a as the surface of the semiconductor substrate 100 (surface electrode forming step, FIG. 4B). In the surface electrode forming step, for example, an In layer and a Ti layer are formed in this order from the element surface 10a side of the semiconductor substrate 100. Further, a back electrode 118 is formed on the element surface 10b as the back surface of the semiconductor substrate 100 (back electrode forming process, FIG. 4B). In the back electrode forming step, for example, the Pt layer is formed as the back electrode 118. Note that the front surface electrode forming step and the back surface electrode forming step can be performed by vapor deposition, sputtering, or the like.

  Subsequently, the blade 50 whose cross-sectional width is gradually narrowed toward the tip is brought into contact with the surface electrode 116, and the groove 120 whose width is gradually narrowed toward the inside of the semiconductor substrate 100 made of a compound semiconductor from the element surface 10a side is formed on the semiconductor substrate. 100 is formed on the element surface 10a (groove forming step, FIG. 4C). Here, the tip 50a of the blade has, for example, a V shape in cross section. Further, a plurality of radiation detection elements 1 are manufactured from the semiconductor substrate 100 by cutting (that is, full cutting) from the element surface 10a to the element surface 10b at a predetermined position of the semiconductor substrate 100 (element separation step). be able to.

(Effect of embodiment)
Since the radiation detection element 10 according to the embodiment of the present invention has the groove 120 having a V-shaped cross section as a groove for dividing the surface electrode 116, the direction of the electric field from the element surface 10 a to the element surface 10 b is changed to the groove 120. Can be bent along the side. Thereby, since the dead area which cannot detect a radiation can be reduced, the detection sensitivity of the radiation of the radiation detection element 10 can be improved.

  Further, in the radiation detection element 10 according to the embodiment of the present invention, the groove 120 is formed in the semiconductor substrate 100 using the blade 50 having the blade tip 50a whose cross-sectional width gradually decreases toward the tip. When the tip of the blade is flat, the side surface of the tip of the blade contacts the semiconductor substrate 100 during rotation of the blade, and stress is likely to accumulate in the semiconductor substrate 100. In contrast, in the present embodiment, since the cross-sectional width of the blade tip 50a gradually narrows toward the tip, stress is unlikely to occur between the side surface of the blade tip 50a and the semiconductor substrate 100. Thereby, accumulation of mechanical stress in the region of the groove 120 can be suppressed. Therefore, it is possible to suppress the occurrence of damage such as cracks in the manufactured radiation detection element 10, and it is possible to suppress a decrease in detection sensitivity of the radiation detection element 10.

[Modification of Embodiment]
FIG. 5 shows an outline of a cross section of a radiation detection element according to a modification of the embodiment of the present invention.

  The radiation detection element 1a according to the modification of the embodiment has substantially the same configuration and function as the radiation detection element 10 according to the embodiment, except that the cross-sectional shape of the groove 120a is different. Therefore, a detailed description is omitted except for differences.

  That is, the groove 120a has a shape that gradually decreases in width from the element surface 10a side toward the inside of the radiation detection element 1a, and has a curved surface. For example, the groove 120a is formed to have a U shape in a sectional view. As an example, the groove 120a can be formed using a blade having an arc-shaped tip in cross section.

  While the embodiments of the present invention have been described above, the embodiments described above do not limit the invention according to the claims. In addition, it should be noted that not all the combinations of features described in the embodiments are essential to the means for solving the problems of the invention.

DESCRIPTION OF SYMBOLS 1 Radiation detector 1a Radiation detection element 10 Radiation detection element 10a, 10b Element surface 20 Board | substrate 22 Board | substrate terminal 29 Card edge part 29a Pattern 30, 31 Card holder 32 Elastic member mounting part 32a Recessed part 34 Grooved hole 36 Projection part 40 Flexible board 50 Blade 50a Blade tip 100 Semiconductor substrate 112 First electrode 114 Second electrode 116 Front electrode 118 Back electrode 120, 120a Groove 122 Groove 130a, 130b, 130c Electric field 200 Radiation 300 Electron 310 Hole 400 Dead area

Claims (6)

A semiconductor substrate made of a compound semiconductor capable of detecting radiation; and
A groove having a V-shape in cross section , which is provided on the surface of the semiconductor substrate and gradually decreases in width from the surface side toward the inside of the semiconductor substrate;
A surface electrode provided in a flat region of the surface of the semiconductor substrate; and a back electrode provided on a back surface opposite to the surface of the semiconductor substrate;
The groove is a groove that does not divide the back electrode by dividing the surface electrode, the back electrode Ri 1 Tsudea, the width of the longest portion of the groove is narrower than the width of the divided said surface electrode <br/> A radiation detection element characterized by the above. The radiation detection element according to claim 1, wherein the compound semiconductor is CdTe or CdTeZn. The surface electrode is configured to have an In layer and a Ti layer from the flat region side of the surface of the semiconductor substrate,
The radiation detection element according to claim 1 , wherein the back electrode is made of Pt . A semiconductor substrate preparation step of preparing a semiconductor substrate made of a compound semiconductor;
A surface electrode forming step of forming one surface electrode on the surface of the semiconductor substrate;
A back electrode forming step of forming one back electrode on the back surface of the semiconductor substrate;
The cross-sectional width is gradually narrowed toward the tip, a V-shaped blade is brought into contact with the surface electrode at the tip, and the width gradually narrows from the surface side toward the inside of the semiconductor substrate. A groove forming step of forming a groove having a V shape on the surface of the semiconductor substrate by dividing the surface electrode and not dividing the back electrode,
The method for manufacturing a radiation detection element, wherein, in the groove forming step, a width of a longest portion of the groove is narrower than a width of the divided surface electrode . The method for manufacturing a radiation detection element according to claim 4, wherein the compound semiconductor is CdTe or CdTeZn . The surface electrode forming step forms an In layer and a Ti layer from the surface side of the semiconductor substrate,
The method for manufacturing a radiation detection element according to claim 4, wherein the back electrode forming step forms a Pt layer on the back surface of the semiconductor substrate .

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