JP2005203708A - X-ray imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provided an X-ray imaging device capable of detecting X-ray of large energy range using the same device having a simple structure. <P>SOLUTION: An X-ray imaging device 1 comprises a CCD 10 and a scintillation portion 30. The CCD 10 has a highly-concentrated p<SP>+</SP>-type semiconductor layer 19 and a semiconductor substrate 23 comprising a p-type epitaxial layer 21 deposited on the front surface side of the p<SP>+</SP>-type semiconductor layer 19. An imaging portion 2 is structured by a region corresponding to a plurality of transfer electrodes 27 in the semiconductor substrate 23 (p-type epitaxial layer 21). The scintillation portion 30 is formed such that a region (the bottom surface of a recess 29) on the rear surface side of the semiconductor substrate 23 corresponding to the imaging portion 2 is covered with it. The scintillation portion 30 comprises a scintillator 31 and a protection film 33. The scintillator 31 converts incident hard X-ray to visible light of a wavelength band of 550 nm to which a photoelectric conversion device of the imaging portion 2 has sensitivity. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an X-ray imaging device.

  An X-ray imaging device using a charge coupled device (hereinafter referred to as “CCD”) is an imaging device having excellent energy resolution and position resolution. In particular, an X-ray imaging device using a back-illuminated CCD is excellent in X-ray detection efficiency with a small energy because the X-ray to be detected is not blocked by the charge transfer electrode. For this reason, an X-ray imaging device using a back-illuminated CCD can detect X-rays in a predetermined energy band (for example, X-rays of 0.1 to 20 keV (hereinafter referred to as “soft X-rays”)).

  Since a CCD is manufactured using silicon (Si), the absorption of X-rays in an energy band higher than X-rays in a predetermined energy band (for example, 20 to 100 keV X-rays (hereinafter referred to as “hard X-rays”)) is extremely high. It becomes low. For this reason, hard X-rays pass through the CCD without being detected by the CCD. Therefore, in order to detect hard X-rays, an X-ray imaging device provided with a scintillator that converts X-rays into visible light can only be used. X-rays (soft X-rays) having a wide energy range with the same imaging device. And hard X-rays) could not be detected.

As an apparatus for detecting X-rays in different energy bands with the same apparatus, there is known a radiation detection apparatus having a configuration in which a plurality of PIN photodiodes, each detecting X-rays in different energy bands, are stacked via an insulator. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 9-275223

  However, in the radiation detection apparatus described in Patent Document 1, since a plurality of photodiodes are stacked, the structure becomes complicated.

  In view of the above circumstances, an object of the present invention is to provide an X-ray imaging element capable of detecting X-rays in a wide energy range with the same element having a simple structure.

  An X-ray imaging device according to the present invention is formed on the incident surface side of a detected X-ray of a semiconductor substrate and has sensitivity to X-rays in a predetermined energy band and visible light in a predetermined wavelength band. An imaging unit that captures an image of the visible light, and an X of an energy band higher than an X-ray of a predetermined energy band are disposed so as to cover at least a region corresponding to the imaging unit on the side opposite to the incident surface of the semiconductor substrate. And a scintillator that emits visible light in a predetermined wavelength band by absorbing the line.

  In the X-ray imaging device according to the present invention, when X-rays in a predetermined energy band are incident, an X-ray image in the predetermined energy band is captured by the imaging unit. On the other hand, when X-rays in an energy band higher than X-rays in a predetermined energy band are incident, the X-rays are converted into visible light in a predetermined wavelength band by a scintillator, and the converted visible light image in the predetermined wavelength band is an imaging unit. Is imaged. As a result, X-ray images over a wide range from the predetermined energy band to a higher energy band can be taken. In addition, a simple structure in which an imaging unit is formed on the incident surface side of the detected X-ray of the semiconductor substrate, and a scintillator is disposed so as to cover at least a region corresponding to the imaging unit on the opposite surface side of the incident surface of the semiconductor substrate. Thus, an X-ray image in a wide energy band can be taken.

  The imaging unit preferably includes a plurality of photoelectric conversion elements arranged in a two-dimensional manner.

Moreover, the scintillator preferably _includes a Bi ₄ Ge _{3 O 12.} Since Bi ₄ Ge ₃ O ₁₂ forms a columnar crystal, the determination accuracy of the X-ray incident position can be improved. Moreover, the scintillator comprising Bi ₄ Ge ₃ O ₁₂ is for high light emission amount can be obtained, it is possible to obtain high energy resolution as X-ray imaging device. Since Bi ₄ Ge ₃ O ₁₂ exhibits a high light emission amount even when cooled to about −100 ° C., a high scintillator light emission amount can be obtained even when the X-ray imaging device is used in a cooled state, and a high energy resolution. Can be obtained.

  The scintillator preferably contains CsI. Since CsI forms a columnar crystal, the determination accuracy of the X-ray incident position can be improved. Moreover, since the scintillator containing CsI can obtain a high light emission amount, the X-ray imaging device can obtain a high energy resolution.

The scintillator preferably contains Gd ₂ O ₂ S (gadolinium oxysulfide). Since Gd ₂ O ₂ S forms a columnar crystal, the determination accuracy of the X-ray incident position can be improved. Further, since the scintillator including Gd 2 _O 2 _S high light emission amount can be obtained, the X-ray imaging device can obtain high energy resolution.

  Further, it is preferable that a reflective film that reflects visible light in a predetermined wavelength band is provided behind the scintillator in the X-ray incident direction. When configured in this way, the light traveling from the scintillator toward the opposite side to the detected X-ray incidence side is reflected by the reflective film, so that the detection sensitivity is improved without escaping the generated light. Can do.

  Further, the semiconductor substrate preferably has a thinned area corresponding to the imaging unit. When comprised in this way, the fall of the detection sensitivity with respect to the light which generate | occur | produced with the scintillator can be suppressed.

  According to the present invention, it is possible to provide an X-ray imaging device capable of detecting X-rays in a wide energy range with the same device having a simple structure.

  An X-ray imaging device according to an embodiment of the present invention will be described with reference to the drawings. In the description, the same reference numerals are used for the same elements or elements having the same function, and redundant description is omitted.

  FIG. 1 is a schematic diagram for explaining a cross-sectional configuration of the X-ray imaging device according to the present embodiment. In the following description, the incident surface (upper surface in FIG. 1) side of the detected X-ray is referred to as the front surface side, and the opposite surface (lower surface in FIG. 1) side is referred to as the back surface side. The X-ray imaging device 1 includes a CCD unit 10 and a scintillation unit 30.

The CCD unit 10 has a semiconductor substrate 23. The semiconductor substrate 23 includes a high concentration p ⁺ type semiconductor layer 19 and a p type epitaxial layer 21 deposited on the surface side of the p ⁺ type semiconductor layer 19. An insulating layer 25 is provided on the surface side of the semiconductor substrate 23 (p-type epitaxial layer 21). A plurality of transfer electrodes 27 made of polysilicon are provided in the insulating layer 26 on the surface side of the insulating layer 25. An insulating layer 28 and a pad electrode 17 described later are provided on the surface side of the insulating layer 26. An imaging unit 2 to be described later is configured by a region corresponding to the plurality of transfer electrodes 27 in the semiconductor substrate 23 (p-type epitaxial layer 21). A silicon oxide film 24 is formed on the back side of the semiconductor substrate 23.

The p ⁺ type semiconductor layer 19 is made of a silicon substrate doped with boron. The thickness of the p ⁺ type semiconductor layer 19 is about 300 μm. The p type epitaxial layer 21 is formed on the p ⁺ type semiconductor layer 19. The p-type epitaxial layer 21 has a high resistance of about several kΩcm and a thickness of about 50 to 100 μm. The insulating layer 25 is made of a silicon oxide film and has a thickness of about 0.1 μm. The insulating layer 26 is made of a silicon oxide film, a silicon nitride film, or a composite region thereof.

A region corresponding to the imaging unit 2 in the semiconductor substrate 23 (p ⁺ type semiconductor layer 19) is thinned from the back side, and a recess 29 is formed. The depth of the recess 29 has a substantially same depth as the p ⁺ -type semiconductor layer 19, a thin region of the p ⁺ -type semiconductor layer 19 functions as an accumulation layer. The thickness of the thinned region of the p ⁺ type semiconductor layer 19 is about 1 μm.

  Next, the CCD unit 10 will be described in detail with reference to FIG. FIG. 2 is a schematic plan view of the X-ray imaging device according to the first embodiment. In the CCD unit 10, a full frame transfer (FFT) type CCD is configured. The CCD unit 10 includes a vertical shift register portion 3 corresponding to the imaging unit 2 and a horizontal shift register portion 5. The imaging unit 2 includes a light receiving area 7, an optical black area 9, and an isolation area 11. A plurality of electrode pads 17 are arranged at the end of the CCD unit 10.

  A plurality of photoelectric conversion elements (pixels) are two-dimensionally arranged in the light receiving area 7. Each photoelectric conversion element is configured in a region corresponding to each vertical shift register portion 3 in the p-type epitaxial layer 21. The photoelectric conversion element is sensitive to soft X-rays and visible light in a wavelength band near 550 nm. For this reason, the imaging unit 2 captures a soft X-ray image and a visible light image in the wavelength band.

  The optical black area 9 is located outside the light receiving area 7. In the optical black area 9, photoelectric conversion elements that are configured not to receive light are arranged so as to surround the light receiving area 7. In addition, the isolation area 11 is disposed between the light receiving area 7 and the optical black area 9 in order to electrically separate the light receiving area 7 and the optical black area 9. The isolation area 11 and the optical black area are used as a dark current reference in a normal front-illuminated CCD, but are not necessarily required in this embodiment.

  The input unit 13 inputs an electrical signal to the vertical shift register part 3 and the horizontal shift register part 5. The charges accumulated in the potential well over the charge accumulation period are sequentially transferred during the charge transfer period by the vertical shift register portion 3 and the horizontal shift register portion 5 to be a time series signal. The transferred charge is converted into a voltage at the output unit 15 and output as an image signal.

  The vertical shift register portion 3, the horizontal shift register portion 5, the input unit 13, and the output unit 15 are electrically connected to corresponding electrode pads 17 by wiring electrodes (not shown). The electrode pad 17 is used to supply a DC voltage or a clock to the CCD unit 10 (vertical shift register unit 3, horizontal shift register unit 5 or input unit 13) and to extract a signal output from the imaging unit 2. is there. The electrode pad 17 is electrically connected to an external substrate or the like by electrically connecting a bonding wire (not shown).

  With reference to FIG. 1 again, the scintillation unit 30 will be described. The scintillation unit 30 is formed so as to cover a region on the back surface side of the semiconductor substrate 23 corresponding to the imaging unit 2 (the bottom surface of the recess 29). The scintillation unit 30 includes a scintillator 31 and a protective film 33. The scintillator 31 converts the incident hard X-rays into visible light having a wavelength band of 550 nm where the photoelectric conversion element of the imaging unit 2 is sensitive. The scintillator 31 is grown and formed on the substrate back surface (bottom surface portion of the recess 29) corresponding to the imaging unit 2, and is made of CsI. The thickness of the scintillator 31 is about 100 to 500 μm.

  A protective film 33 is coated on the back side of the scintillator 31. The protective film 33 is formed by laminating an organic film 33a made of polyparaxylene and a reflective thin film 33b made of aluminum or the like. The organic film 33a prevents the scintillator 31 from coming into contact with air and prevents deterioration in light emission efficiency due to deliquescence. The reflective thin film 33 b reflects light traveling in the direction opposite to the X-ray incident direction among the light generated by the scintillator 31. The reflective thin film 33b blocks direct light from the outside. The thickness of the organic film 33a is about several to several tens of micrometers. The thickness of the reflective thin film 33b is about 1 μm.

  Next, the operation of the X-ray image sensor 1 will be described. First, X-rays to be detected enter from the surface side of the X-ray imaging element 1. When the incident X-ray to be detected is a soft X-ray, the photoelectric conversion element of the imaging unit 2 has sensitivity to the soft X-ray, and therefore the incident soft X-ray is depleted in the CCD unit 10 p-type epitaxial. Electrons are generated in the layer 21 by photoelectric conversion. The generated electrons are accumulated in the potential well of the charge transfer channel formed under the insulating layer 25 for a certain time. As a result, the soft X-rays are detected by the CCD unit 10 (see FIG. 3A). The number of electrons stored in each photoelectric conversion element is a number proportional to the energy of the incident soft X-ray, and an image signal corresponding to the soft X-ray image is obtained.

  On the other hand, when the detected X-ray incident from the surface side of the X-ray image pickup device 1 is a hard X-ray, the photoelectric conversion element of the image pickup unit 2 has no sensitivity to the hard X-ray. The light passes through the portion 10 (transfer electrode 27, insulating layer 25, semiconductor substrate 23) and reaches the scintillator 31 disposed on the back surface side of the thinned semiconductor substrate 23 (bottom surface of the recess 29). The hard X-rays are absorbed by the scintillator 31, converted into visible light having sensitivity by the photoelectric conversion element of the imaging unit 2, and emitted in proportion to the amount of hard X-rays reaching the scintillator 31. Of the emitted visible light, the light traveling toward the front surface is incident on the photoelectric conversion element of the imaging unit 2 from the back surface of the semiconductor substrate 23 (the bottom surface of the recess 29) (the CCD unit 10 functions as a so-called back-illuminated CCD). ). The light traveling toward the back surface side is reflected by the reflective thin film 33b of the protective film 33, passes through the scintillator 31, and enters the photoelectric conversion element of the imaging unit 2 from the back surface of the semiconductor substrate 23 (the bottom surface of the recess 29) (FIG. 3 ( b)). For this reason, almost all of the light generated by the scintillator 31 enters the imaging unit 2.

  Since the photoelectric conversion element is sensitive to the emitted visible light, an electric signal corresponding to the amount of visible light is generated by photoelectric conversion and accumulated for a certain period of time. Since the amount of visible light corresponds to the amount of incident hard X-rays, the number of electrons stored in each photoelectric conversion element is proportional to the amount of incident hard X-rays. An image signal corresponding to the line image is obtained.

  The image signals accumulated in the photoelectric conversion elements are sequentially output from the electrode pad 17 via a signal line (not shown) and transferred to the outside of the CCD unit 10. An X-ray image can be obtained by processing this image signal with an external processing device (not shown).

  As described above, in this embodiment, when soft X-rays are incident, an image of soft X-rays is directly captured by the imaging unit 2 of the CCD unit 10. On the other hand, when hard X-rays enter, the hard X-rays are converted into visible light by the scintillator 31, and an image of the converted visible light is captured by the imaging unit 2. As a result, both soft X-rays and hard X-rays, that is, X-ray images in an extremely wide energy band of 0.1 to 100 keV can be taken efficiently.

  In the present embodiment, the imaging unit 2 is formed on the front surface side of the semiconductor substrate 23, and the scintillator 31 is disposed so as to cover at least a region corresponding to the imaging unit 2 on the back surface side of the semiconductor substrate 23. Depending on the structure, an X-ray image of a wide energy band can be taken.

  In this embodiment, a scintillator made of CsI is used as the scintillator 31. Since CsI forms a columnar crystal, high determination accuracy of the X-ray incident position can be obtained. Moreover, since the scintillator 31 containing CsI can obtain a high light emission amount, the X-ray imaging device 1 using the scintillator 31 can obtain high energy resolution.

  In the present embodiment, the reflective thin film 33 b is provided behind the scintillator 31 in the detected X-ray incident direction. Thereby, the light which goes to the opposite side to the detected X-ray incident side among the light generated in the scintillator 31 is reflected by the reflective thin film 33b, and the detection sensitivity can be improved without escaping the generated light.

In the present embodiment, the semiconductor substrate 23 (p ⁺ type semiconductor layer 19) has a thinned area corresponding to the imaging unit 2. Since the semiconductor substrate 23 (p ⁺ -type semiconductor layer 19) is thinned, the light generated by the scintillator 31 is suppressed from being absorbed by the semiconductor substrate 23 (p ⁺ -type semiconductor layer 19). Become. As a result, it can suppress that the detection sensitivity of the light which generate | occur | produced in the scintillator 31 falls.

  The present invention is not limited to the embodiment described above. For example, although the semiconductor substrate 23 is p-type, the present invention is not limited to this, and the semiconductor substrate 23 may be n-type.

In the X-ray imaging device 1 of the present embodiment, a scintillator made of CsI is used as the scintillator 31, but is not limited to this, and includes Bi ₄ Ge ₃ O ₁₂ (hereinafter referred to as “BGO”) ( A scintillator may be used, which is not limited to the one made of BGO and may contain other substances, but the weight content of BGO is preferably 95 to 100%. Since BGO forms columnar crystals in the same manner as CsI, high determination accuracy of the X-ray incident position can be obtained. Moreover, since the scintillator using BGO can obtain a high light emission amount, the X-ray imaging device 1 can obtain a high energy resolution. In general, the X-ray image sensor is often used after being cooled in order to suppress thermal noise. In particular, since BGO exhibits a high light emission amount even when cooled at about −100 ° C., the X-ray image sensor 1 is cooled. Even if it is used, a high amount of emitted light of the scintillator 31 can be obtained, and a high energy resolution can be obtained.

A scintillator containing Gd ₂ O ₂ S may be used as the scintillator 31. Since Gd ₂ O ₂ S also forms columnar crystals in the same way as CsI, high determination accuracy of the X-ray incident position can be obtained. In addition, since a scintillator containing Gd ₂ O ₂ S can obtain a high light emission amount, an X-ray imaging device using the scintillator can obtain high energy resolution.

It is the schematic for demonstrating the cross-sectional structure of the X-ray image sensor which concerns on embodiment. It is a schematic plan view of the CCD unit of the X-ray imaging device according to the embodiment. (A) is a figure explaining the detection of the soft X-ray of the X-ray image sensor which concerns on embodiment. (B) is a figure explaining the detection of the hard X-ray of the X-ray image sensor which concerns on embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... X-ray image sensor, 2 ... Imaging part, 3 ... Vertical shift register part, 7 ... Light receiving area, 10 ... CCD part, 19 ... p ⁺ type semiconductor layer, 21 ... p type epitaxial layer, 23 ... Semiconductor substrate, 29 Recess, 30 ... scintillation part, 31 ... scintillator, 33 ... protective film, 33b ... reflective thin film, 33a ... organic film.

Claims (7)

An imaging unit that is formed on the incident surface side of the X-ray to be detected of the semiconductor substrate and has sensitivity to X-rays in a predetermined energy band and visible light in a predetermined wavelength band, and captures images of the X-rays and the visible light When,
The semiconductor substrate is disposed so as to cover at least a region corresponding to the imaging unit on the surface opposite to the incident surface, and absorbs X-rays in an energy band higher than the X-rays in the predetermined energy band, thereby An X-ray imaging device comprising: a scintillator that emits visible light in a wavelength band.   The X-ray imaging device according to claim 1, wherein the imaging unit includes a plurality of photoelectric conversion elements arranged two-dimensionally. The X-ray imaging device according to claim 1, wherein the scintillator includes Bi ₄ Ge ₃ O ₁₂ .   The X-ray imaging device according to claim 1, wherein the scintillator includes CsI. The X-ray imaging device according to claim 1, wherein the scintillator includes Gd ₂ O ₂ S.   The X-ray imaging according to claim 1, wherein a reflective film that reflects visible light in the predetermined wavelength band is provided behind the scintillator in the X-ray incident direction to be detected. element. The X-ray imaging device according to claim 1, wherein a region of the semiconductor substrate corresponding to the imaging unit is thinned.

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