JPH08190880A - X-ray image pickup tube and its operating method - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain an X-ray image pickup tube having a target image pickup tube capable of obtaining a high-sensitivity and high-quality X-ray image without white spot-like screen defects. An X-ray transparent insulating substrate 2, a target electrode 4 made of a crystalline Si thin plate, a hole injection blocking layer 6, a conductive film 7 and a scanning electron beam landing layer 8 as an image pickup tube target portion and The scanning electron beam generator 11 constitutes an X-ray image pickup tube.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-sensitivity X-ray image pickup tube in which the target portion of the X-ray image pickup tube is improved and a method of operating the same.

[0002]

2. Description of the Related Art An X-ray image pickup tube is effective for nondestructive inspection of semiconductor ICs, diagnosis of inside of living body, crystal analysis, material analysis, etc. because it can be observed in real time and high resolution can be obtained. Therefore, it is widely used in fields such as industry, measurement, and academic fields.

An X-ray image pickup tube is usually an X-ray or a γ-ray (hereinafter,
An image pickup tube target part in which a target electrode and a photoconductive film are deposited on a face plate which easily transmits X-rays), and a scanning electron beam generating part provided facing the photoconductive film via a vacuum. , Incident X-rays are absorbed by the photoconductive film and converted into electric charges, which are directly extracted as electric signals by the scanning electron beam.

In the X-ray image pickup tube, a metal beryllium thin plate that easily transmits X-rays has been conventionally used as a face plate of a target portion of the image pickup tube, and a boron nitride (BN) thin plate X is used.
A line image pickup tube is also disclosed (for example, Japanese Patent Application No. 2-230658).
Specification). Further, a glass thin plate may be used as the face plate for the soft X-ray band having relatively high energy (for example, Technical Report of Television Society, Vol. 17, No. 22, 13).
Pp. 18, 1993). Further, recently, the inventors have proposed to use a crystalline Si thin plate having a good surface smoothness as a face plate material (Japanese Patent Application No. 5-264710).

For the target electrode, the conductive face plate itself, A
A metal electrode such as 1 and an oxide electrode such as SnO ₂ are used.

A conventionally known semiconductor material such as lead oxide (PbO), amorphous selenium (Se), or cadmium telluride (CdTe) is used for the photoconductive film. Among them, amorphous selenium has high resolution, and it is known that an avalanche multiplication phenomenon of charges occurs inside when a high electric field is applied.
A line imaging tube has been proposed (for example, Proceedings of National Conference of the Television Society of Japan, pp. 15-16, 1989).

Further, in the X-ray image pickup tube as well as in a general image pickup tube, the stray capacitance of the target electrode is reduced to increase the SN ratio, and the false signal caused by the landing abnormality of the scanning electron beam on the photoconductive film is also generated. In order to suppress the above, the target electrode is formed only in the electron beam scanning region, and is connected to the target electrode pin provided through the face plate outside the scanning region of the face plate (for example, Japanese Patent Application No. No. 2-230658) is disclosed. Furthermore, in the peripheral portion of the target electrode, by providing a peripheral potential control electrode electrically separated from the target electrode, and by setting a constant potential,
A method for stabilizing high voltage operation (Japanese Patent Application No. 5-264710) is disclosed.

[0008]

In the conventional X-ray image pickup tube described above, it is difficult to polish the surface of the thin plate metal beryllium or boron nitride with high precision, and therefore white spots caused by the unevenness of the surface of the face plate. -Like local image defects are likely to occur, especially in the avalanche multiplication type X-ray image pickup tube used in a high electric field,
In addition to a marked increase in white dot image defects, dark current is also likely to increase, resulting in image deterioration.

In addition, in the method (Japanese Patent Application No. 5-264710) of adopting the crystalline Si thin plate having good surface smoothness proposed by the inventors as a face plate material, (1) Be, BN, etc. In the method of holding the vacuum with the X-ray window material and using the Si thin plate itself or adding the metal electrode as the target electrode, it is necessary to open a new hole in the side surface of the glass outer tube to take out the target potential. Becomes complicated,
(2) In the method of holding a vacuum by the Si thin plate itself, the Si thin plate cannot be made sufficiently thin due to the vacuum being held, and a large amount of X-rays are absorbed by the Si thin plate in the low energy region. Has the drawback of being narrow. Furthermore, since Si is a semiconductor, it is not sufficient in terms of insulation to form the target electrode only in the electron beam scanning region or to form another electrode region outside the scanning region to provide a different potential. There was a problem that was.

The object of the present invention is to use an X-ray having a wide applicable energy range, even if an electric field high enough to cause an avalanche multiplication phenomenon is applied, without use of the above-mentioned white dot image defect and increase of dark current. It is to provide an image pickup tube.

Another object of the present invention is to provide a method of manufacturing an X-ray image pickup tube capable of suppressing a false signal due to an abnormal landing of an electron beam even under an electric field high enough to cause an avalanche multiplication phenomenon. Especially.

[0012]

In the present invention, in order to achieve the above object, an X-ray image pickup tube is provided at least with a photoconductive film formed on an X-ray transparent substrate and in a vacuum. A scanning electron beam generator disposed opposite to the photoconductive film is used, an insulating BN thin plate is used as the substrate, and a crystalline Si thin plate directly bonded to the substrate is used as the target electrode.

Further, in order to achieve the above-mentioned other objects,
Limiting the position and size of the target electrode mainly to the position and size corresponding to the scanning area of the scanning electron beam,
Alternatively, a peripheral potential control electrode made of a single crystal Si thin plate electrically insulated from the target electrode is provided on the same surface as the target electrode in the peripheral portion of the target electrode.

[0014]

The target electrode made of a single-crystal Si thin plate can have its surface smoothed to the order of 1 nm by using a recent processing technique. Therefore, a high electric field is applied to the photoconductive film made of amorphous Se. When the avalanche multiplication operation is performed, a high-sensitivity image can be obtained without causing white spot-like local image defects due to unevenness of the interface.

The insulating substrate made of a BN thin plate is used to hold the target electrode in a limited position and size, or to provide a peripheral potential control electrode around the target electrode so as to be insulated from the target electrode. Acts as a support substrate. Further, the BN plate is an insulating material having the best X-ray transparency, and the applicable energy region can be widened by making it thin within a range in which the mechanical strength as a vacuum holding substrate can be maintained.

The target electrode made of a single-crystal Si thin plate and the insulating substrate made of a BN thin plate can be easily joined with an adhesive or the like. By using this joined plywood, the above-mentioned object can be achieved while maintaining the conventional image pickup tube structure. Can be achieved.

[0017]

1 is a schematic sectional view showing the basic structure of an X-ray image pickup tube of the present invention. 1 is a reinforcing plate with an X-ray transmission window, 2 is an insulating substrate, 3 is an adhesive, 4 is a target electrode made of crystalline Si, 5 is a peripheral potential control electrode, 6 is a hole injection blocking layer, and 7 is photoconductive. A film, 8 is a scanning electron beam landing layer, 9 is a mesh electrode, 10 is a scanning electron beam, 11 is a scanning electron beam generator (electron gun), 12 is a target potential extracting electrode, and 13 is for sealing in vacuum. Indium, 14 is a metal ring, 15 is a coil for deflecting the scanning electron beam, and 16 is a glass outer tube of the image pickup tube.

A glass plate or the like is used as the reinforcing plate 1 with an X-ray transmission window. The insulating substrate 2 is preferably a BN thin plate. Adhesive 3
Is an epoxy adhesive or the like. When a crystalline Si thin plate is used for the peripheral potential control electrode 5 similarly to the target electrode 4, it can be manufactured simultaneously with the target electrode, and thus the manufacturing is easy, but the crystalline Si thin plate is not necessarily required. CeO ₂ or the like is used for the hole injection blocking layer 6. A semiconductor material such as PbO, Se, CdT is used for the photoconductive film 7. Among them, Se has a high resolution, and sensitivity can be increased by utilizing avalanche multiplication of charges. For the scanning electron beam landing layer 8, porous Sb ₂ S ₃ or the like is used.

The basic structure of the X-ray image pickup tube according to the present invention is shown in FIG.
As described above, an example of the structure in the vicinity of the target portion including at least the insulating substrate, the target electrode, and the photoconductive film in the X-ray imaging tube will be described below.

(Embodiment 1) Embodiment 1 in the vicinity of a target portion of an X-ray image pickup tube according to the present invention is shown in FIGS. 2A is a cross-sectional view, FIG. 2B is a top view of a target electrode position, and FIG. 3 is an explanatory view showing a manufacturing process.

First, (1) in order to obtain a target electrode made of a crystalline Si thin plate, it is polished with high precision to obtain a thin Si film.
SOI (Silicon On In In) bonded to each other through an O ₂ layer
sulater) substrate 20 is prepared, and Si is formed on the substrate 20 by the CVD method.
The Nx film 19 is formed. Here, as the SOI substrate,
Si thin layer 21 is 10 μm, SiO ₂ layer 22 is 1 μm, S
A substrate having an i base layer 23 of 300 μm and a diameter of 26 mm was used. Next, (2) a photoresist is applied on the SiNx film, and a desired etching pattern is formed by using photolithography. Next, (3) pattern etching is performed using a 30% NaOH aqueous solution. Next, (4) a SiNx film is formed again on the etched sample by the CVD method, and the exposed SiO ₂ layer is covered with the SiNx film 17.

Next, (5) the sample obtained by this work, the BN thin plate 2 and the glass reinforcing plate 1 provided with a window for X-ray transmission are adhered using an epoxy adhesive and then the target potential is drawn out. As a hole, a hole is formed at a predetermined position of the glass reinforcing plate by ultrasonic processing, and then the silver epoxy resin 12 is filled. Here, a BN thin plate 2 having a thickness of 0.5 mm and a glass reinforcing plate 1 having a thickness of 2.0 mm are used, and a window hole for X-ray transmission is located at a position corresponding to the scanning region of the scanning electron beam so as to be slightly larger than the scanning region. Set to.

Further, (6) First, the Si base layer 23 is changed to Na.
After etching with a 30% OH aqueous solution, the SiO ₂ layer 22
Is etched with a mixed solution of ammonium fluoride and hydrofluoric acid. At this time, the SiO ₂ layer functions as a stopper during Si etching, and the Si thin plate functions as a stopper during SiO ₂ layer etching. Further, (7) CeO ₂ of 20 nm is used as the hole injection blocking layer 6, and amorphous Se is used as the photoconductive film 7.
After vacuum-depositing the film in a thickness of 5 to 50 μm, Sb ₂ S ₃ as the electron beam landing layer 8 is formed to a thickness of 100 nm in an Ar gas atmosphere of 0.3 Torr to obtain an image pickup tube target portion.

The image pickup tube target portion obtained as described above is set in an image pickup tube glass outer tube 16 having a mesh electrode 9 and an electron gun 11 therein, as shown in FIG. Then, crimping is performed via the In ring 13 integrated with the metal ring 14,
The inside was evacuated and vacuum-sealed to obtain an X-ray imaging tube.

The obtained X-ray image pickup tube was incorporated into a camera and operated. As a result, for example, the photoconductive film thickness 30
Even if a high voltage of 3 kV was applied to the target electrode with respect to μm, white dot-shaped screen defects did not occur, and a high-sensitivity and high-quality X-ray image was obtained. During high voltage operation, the peripheral potential control electrode had the same potential as the cathode of the electron gun.

(Embodiment 2) FIG. 4 shows the vicinity of the target portion in Embodiment 2 of the X-ray imaging tube according to the present invention. FIG.
(a) is sectional drawing, (b) is a top view of a target electrode position.

In the second embodiment (FIG. 4), the peripheral potential control electrode is not formed by being bonded to the insulating substrate made of the BN thin plate, but the shield electrode 18 is separately provided.

The manufacturing method of the target portion of this embodiment is the same as that of the manufacturing method of the target portion of the first embodiment except that the pattern is changed so that the peripheral potential control electrode is not formed.

As shown in FIG. 1, the image pickup tube target portion obtained as described above is set in the glass tube 16 of the image pickup tube in which the mesh electrode 9 and the electron gun 11 are incorporated so as to be sandwiched between the shield electrodes 18. Then, it was pressure-bonded through the In ring 13 integrated with the metal ring 14, and the inside was evacuated and vacuum-sealed to obtain an X-ray imaging tube.

The X-ray image pickup tube thus obtained was incorporated into a camera and evaluated in the same manner as in Example 1. As a result, with respect to the photoconductive film thickness of 40 μm, white dot-shaped screen defects did not occur up to a high voltage of 4 kV on the target electrode, and a high-sensitivity and high-quality X-ray image was obtained. During high voltage operation, the shield electrode had the same potential as the cathode of the electron gun.

[0031]

According to the present invention, since a Si single crystal thin plate which has excellent surface smoothness and can be arranged on a substrate is used as a target electrode of an image pickup tube, an electric field high enough to cause an avalanche multiplication phenomenon is obtained. Is applied, there is an effect that an X-ray image pickup tube that can be used without a white dot image defect and an increase in dark current is obtained. Further, since the Si single crystal plate is sufficiently thin and is directly bonded to the BN thin plate having good X-ray transparency as an insulating substrate, there is an effect that a wide applicable energy range can be secured. In addition, by using the peripheral potential control electrodes and the like, high SN
It is also possible to suppress spurious signals due to the digitization and electron beam landing abnormality. Therefore, the X-ray image pickup apparatus using the X-ray image pickup tube of the present invention can obtain a high-quality X-ray image with high sensitivity and high resolution.

[Brief description of drawings]

FIG. 1 is a sectional view showing a basic structure of an X-ray image pickup tube of the present invention.

FIG. 2 is a cross-sectional view showing the vicinity of an X-ray image pickup tube target portion according to an embodiment of the present invention and a top view of target electrode positions.

FIG. 3 is an explanatory view showing a manufacturing process of an X-ray image pickup tube target portion of one embodiment of the present invention.

FIG. 4 is a cross-sectional view showing the vicinity of an X-ray image pickup tube target portion of one embodiment of the present invention and a top view of target electrode positions.

[Explanation of symbols]

2 ... Insulating substrate, 3 ... Adhesive, 4 ... Target electrode, 5
... peripheral potential control electrode, 6 ... hole injection blocking layer, 7 ... photoconductive film, 8 ... scanning electron beam landing layer, 11 ... scanning electron beam generator.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tadaaki Hirai 1-280 Higashi Koikekubo, Kokubunji, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (72) Inventor Mitsuo Usami 1-280 Higashi Koikeku, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor Takashi Tase 1-280, Higashi Koigokubo, Kokubunji, Tokyo Hitachi Ltd. Central Research Laboratory (72) Inventor Toru Tohso 3434-1, Kamibasaya, Obuchizawa-machi, Kitashikoma-gun, Yamanashi Hitachi Electronics Obuchi Sawa Factory

Claims (8)

[Claims] 1. An X-ray transparent insulating substrate, a target electrode made of a crystalline Si thin plate bonded on the insulating substrate, a hole injection blocking layer formed on the target electrode, and the positive electrode. An X-ray image pickup tube comprising: an image pickup tube target section including a photoconductive film formed on a hole injection blocking layer; and a scanning electron beam generation section opposed to the photoconductive film via a vacuum. 2. The X-ray image pickup tube according to claim 1, wherein the X-ray transparent insulating substrate is a BN thin plate. 3. The X-ray image pickup tube according to claim 2, wherein the position and size of the target electrode are limited to the position and size mainly corresponding to the scanning region of the scanning electron beam. 4. The method according to claim 3, wherein at least a surface of the peripheral portion of the target electrode that is in contact with the hole injection blocking layer,
An X-ray imaging tube provided with a peripheral potential control electrode made of a crystalline Si thin plate electrically separated from the target electrode. 5. The X-ray imaging tube according to claim 1, 2, 3, or 4, wherein at least a part of the photoconductive film is made of an amorphous semiconductor layer containing Se as a main component. 6. The image pickup tube according to claim 1, wherein a voltage is applied to the target electrode such that avalanche multiplication of charges occurs inside the photoconductive film. Method of operating a line pickup tube. 7. An X-ray imaging apparatus using the X-ray imaging tube according to claim 1. 8. The method of operating an X-ray image pickup device according to claim 7, wherein a voltage is applied to the target electrode of the image pickup tube such that avalanche multiplication of charges occurs inside the photoconductive film.