JP2008300089A - X-ray tube - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray tube of an X-ray fluoroscope with an area (a volume) breaking vacuum made as little as possible, in exchanging components such as a target and an aperture. <P>SOLUTION: The X-ray tube is provided with a filament 1 emitting electron beams, a grid electrode 2, an anode 3 accelerating the electron beams emitted, a magnetic field lens 5 focusing the electron beams, a target 6 fitted on an X-ray transmission window and an aperture 7 arranged at a lower part of the target, with a periphery of the filament 1 and a periphery of the electron beam line 9 from the filament 1 over to the target 6 maintained in a high vacuum state. A shutter 15 capable of opening and closing for partitioning a vacuum space of the electron beam line 9 is provided at an intermediate part of the electron beam line 9 from the anode 3 to the target 6, and further, a degassing valve 20 is provided for releasing the vacuum space at the target side partitioned by the shutter 15 to the atmosphere. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an open type X-ray tube used in an X-ray apparatus. Here, an open X-ray tube means that an accelerating electrode (anode) and a filament are arranged in a vacuum vessel maintained in a high vacuum state, an opening / closing mechanism is provided in the vacuum vessel, and a vacuum exhaust pump is connected thereto. An X-ray tube that keeps the inside of the container in a vacuum state during use as a ray tube, prevents the filament from burning out, and allows the inside of the vacuum container to be opened to the atmosphere when the filament or target is replaced. Say.

  A technique for observing the fine internal structure of an inspection object by a nondestructive inspection method is required in each field. For example, for the development of semiconductor packaging, mounting inspection, and quality assurance, internal defects and the like are examined using an X-ray tube having a micro focus. An X-ray tube having a micro focus uses a tungsten plate target having a small thickness, and a focused electron beam is injected into the target to emit X-rays generated there. Such an X-ray tube is called a microfocus X-ray tube, and an electron beam emitted from a filament (hot cathode) in a vacuum vessel is converged by a magnetic lens (deflection coil, converging coil) to be 1 to 1 on the target. An X-ray is generated by implanting into a minute region having a size of 200 μm.

  Among the microfocus X-ray tubes, X-ray tubes whose focal size can be miniaturized are of a type called an open type. The open X-ray tube is equipped with a vacuum container opening / closing mechanism and a vacuum exhaust pump. During use as an X-ray tube, the inside of the container is maintained in a high vacuum state, and the filament (hot cathode) is cut to remove the filament. When exchanging, or when exchanging an aperture that avoids collision of unnecessary electrons with the target or the target, the inside of the container can be opened to the atmosphere. (See Patent Document 1).

Open type X-ray tubes are classified into two types called transmission type and reflection type. In the transmission type, the electron beam and the output X-ray are located on the opposite side as viewed from the target surface, whereas in the reflection type, the electron beam and the output X-ray are located on the same side as viewed from the target surface. Both the transmission type and the reflection type have the same structure for converging the electron beam to a minute region on the target and miniaturizing the focal size of the X-ray.
JP 2003-115398 A

  In the conventional open type X-ray tube described above, it is unavoidable to replace the filament disposed at the center of the vacuum vessel, but even when replacing the target, aperture, and other parts on the tip side of the electron beam line. Since all the space in the vacuum vessel had to be opened to the atmosphere, it took time to evacuate and to evacuate after the replacement, and the replacement work was troublesome.

  Therefore, in the present invention, when replacing parts such as a target and an aperture on the front end side of the electron beam line, only a limited part including this region can be opened to the atmosphere so that the time and labor required for the replacement can be reduced. An object is to provide an X-ray tube of an X-ray fluoroscopic apparatus that can be shortened.

  The X-ray tube of the present invention made to solve the above problems includes a filament that emits an electron beam, a grid electrode, an anode that accelerates the emitted electron beam, a magnetic lens that focuses the electron beam, and an X-ray tube. An X-ray tube comprising a target provided on a line transmission window and an aperture disposed at a lower part of the target, wherein the periphery of the filament and the periphery of the electron beam line from the filament to the target are maintained in a high vacuum state, An openable / closable shutter that partitions the vacuum space of the electron beam line is provided at an intermediate portion of the electron beam line from the anode to the target, and the target-side vacuum space partitioned by the shutter is opened to the atmosphere. The air vent valve is provided.

  Here, the magnetic lens is generally called an electron lens or a focusing coil, and encompasses these. Further, the shutter may have any structure as long as it has a structure capable of blocking the vacuum space of the electron beam line from the anode to the target in a highly airtight state so as to be opened and closed. Further, the opening and closing of the shutter may be either electric or manual.

  According to the X-ray tube of the present invention, when replacing parts such as the target and the aperture, the vacuum space in the middle part of the electron beam line from the anode to the target is shut off by the shutter, and the partition side of the target side is separated. By opening the vacuum space to the atmosphere, the area where the vacuum is broken can be partially and reduced, thereby reducing the time and labor required for replacement.

(Means and effects for solving other problems)
In the above invention, the filament, grid electrode, and anode are housed in a vacuum vessel, the periphery of the electron beam line from the anode to the target is hermetically held by a pipe, and the shutter is provided in the middle of the pipe. It is desirable to do.
According to this, since the vacuum space of the electron beam line from the anode to the target can be formed with a thin diameter pipe, for example, with a diameter of 15 mm to 20 mm, the area where the vacuum is broken when the target is replaced, that is, the volume is reduced. In addition, the shutter can be easily assembled to the pipe.

In the above invention, the shutter includes a plunger penetrating the pipe from the side surface, a cylinder that slidably holds the outer surface of the plunger positioned outside the pipe, and a drive unit that reciprocates the plunger. It is good to have the structure comprised so that the vacuum space in a pipe may be divided | segmented and connected by the reciprocating motion of a plunger.
Thereby, an airtight shutter can be manufactured with a simple structure.

Furthermore, in the above invention, the plunger is provided with a ball valve which is biased toward the anode side by a spring and seals the divided anode side pipe opening, and a beam passage hole along the electron beam line. It is desirable that the reciprocating motion of the plunger can be selected between a closed position where the ball valve fits into the pipe opening and an open position where the beam passage hole is continuous with the pipe inner hole.
As a result, when the vacuum space of the electron beam line is interrupted, the ball valve is elastically fitted into the pipe opening by the spring pressure of the spring to seal the opening, and the vacuum on the filament side from the shutter is more reliably maintained. can do.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment, It cannot be overemphasized that various aspects are included in the range which does not deviate from the meaning of this invention.

  FIG. 1 is a diagram illustrating a configuration example of an X-ray fluoroscopic apparatus using an open X-ray tube. The X-ray fluoroscopic apparatus mainly includes an open X-ray tube A, a sample stage 13 on which a sample 12 is placed, and an X-ray detector 14.

  The open X-ray tube A is disposed between a filament 1 (hot cathode) that emits thermoelectrons by heating, an anode 3 that accelerates the emitted thermoelectrons, and the filament 1 and the anode 3. A grid electrode 2 (Wernert electrode) that restricts the emitted thermoelectrons toward the anode 3, a deflection coil 4 that deflects the direction of the electron beam formed by the thermoelectrons, and a magnetic field that focuses the deflected electron beam. The lens (converging coil) 5, a target 6 provided on the X-ray transmission window, and an aperture 7 disposed below the target 6 in order to avoid unnecessary electrons from colliding with the target 6. Yes. The grid electrode 2 may have any shape that can limit the thermoelectrons emitted from the filament. However, it is preferable that the grid electrode 2 function as a Wehnelt electrode in a mortar shape so as to converge the electrons.

The filament 1, grid electrode 2 and anode 3 in the open X-ray tube 10 are sealed with a vacuum vessel 8, and the periphery of a thin electron beam line 9 from the anode 3 to the target 6 is kept airtight. In this embodiment, the periphery of the electron beam line 9 from the anode 3 to the target 6 is hermetically maintained by the pipe 10 and the magnetic lens 5. The pipe 10 is formed of a thin pipe having a diameter of 15 mm to 20 mm, preferably a diameter of 16 mm.
The vacuum vessel 8 is provided with an evacuation pump 11, and the electron beam line 9 from the anode 3 to the target 6 is maintained in a high vacuum state by evacuation by the pump. .

  An X-ray detector 14 is disposed opposite to the outside of the target 6 of the open X-ray tube A with a sample stage 13 on which the sample 12 is placed, and detects X-rays irradiated from the target 6. It is made to be able to. The detection signal of the X-ray detector 14 is subjected to image processing by an image generation unit of a control system (not shown) to generate an X-ray luminance signal and displayed on the monitor screen. Alternatively, when a flat panel detector in which the X-ray detector main body and the image creation unit are integrated is used as the X-ray detector 14, the X-ray luminance signal ( Image data) is created and displayed on the monitor screen. The filament 1 is connected to a power source (not shown) via a power cable.

Furthermore, an openable / closable shutter 15 is provided in the middle portion of the electron beam line 9 from the anode 3 to the target 6 to partition the vacuum space of the electron beam line. The shutter 15 may have any structure as long as it has an excellent airtightness. In this embodiment, as shown in FIGS. 2 and 3, a plunger 16 penetrating the pipe 10 from the side surface is provided. And a cylinder 17 that slidably holds the outer surface of the plunger 16 and a drive unit 22 that reciprocates the plunger 16. The plunger 16 is provided with a ball valve 18 that seals an opening of the lower pipe 10 that is always urged downward by a spring and divided, and a beam passage hole 19 along the electron beam line 9. The closed position shown in FIG. 2 and the open position shown in FIG. 3 can be selected by reciprocating movement of the plunger 16. In addition, an air vent valve 20 is provided in the pipe 10 for opening the vacuum space of the pipe 10 on the target 6 side partitioned by the shutter 15 to the atmosphere.
The drive unit 22 for driving the plunger 16 is preferably a solenoid using an electromagnet, but may be a mechanical unit combining a motor and a gear. Alternatively, the drive unit 22 may be manually opened and closed as a manual operation grip.
Further, the sliding contact surface between the plunger 16 and the cylinder 17 and the joint surface between the pipe 10 and the cylinder 17 are sealed with a sealing material 21 such as an O-ring to maintain airtightness.

  The open X-ray tube A, the sample stage 13 on which the sample 12 is placed, and the X-ray detector 14 are stored in an X-ray protective box (not shown) for protecting scattered X-rays. .

In such an X-ray tube A, when a current is passed through the filament 1 and thermoelectrons are emitted, the thermoelectrons are accelerated toward the target 6 by the acceleration electrode 3 to form an electron beam.
The electron beam passes through the central opening of the anode 3, and the traveling direction of the electron beam is adjusted by the deflection coil 4. Then, the magnetic lens 5 converges the electron beam with a small diameter and enters the target 6.
For the target 6, for example, tungsten having a thickness of about 50 μm is used. Alternatively, the target material is formed directly on the line transmission window. When an electron beam enters the target 6, X-rays are emitted. Of the radiated X-rays, an X-ray beam in a direction that passes through the X-ray transmission window is irradiated onto the sample 12 placed on the sample stage 13, and the transmitted X-rays that have passed through the sample are detected by the X-ray detector 14. The The detection signal is sent to a control system (not shown), an X-ray luminance signal is created by signal processing, and is displayed on the monitor as an X-ray image.

  The target 6 and the aperture 7 in the X-ray tube need to be removed when the dirt is washed or replaced with a new one. In particular, the aperture 7 needs to be replaced with an aperture having a different opening area prepared separately when adjusting the collision area in accordance with the resolution and brightness. In such a case, the vacuum space at the intermediate portion of the electron beam line 9 from the anode 3 to the target 6 is blocked by the shutter 15, and the target-side vacuum space that is partitioned is opened to the atmosphere by the air vent valve 20. The area for breaking the vacuum can be suppressed to a small volume from the shutter 15 to the target 6, and the time required for replacement can be shortened.

  The plunger 16 of the shutter 15 shown in the above embodiment is provided with a ball valve 18 in order to improve the airtightness. However, as shown in FIG. 4, the sliding contact surface between the plunger 16 and the cylinder 17 and the pipe The ball valve 18 described above can be omitted if the joint surface between the cylinder 10 and the cylinder 17 can be reliably maintained airtight by the sealing material 21 such as an O-ring.

  The present invention can be used for an X-ray fluoroscopy device or an X-ray inspection apparatus equipped with an open X-ray tube.

1 is a partial cross-sectional view illustrating a configuration of an X-ray fluoroscopic apparatus that is an embodiment of the present invention. It is an expanded sectional view showing the shutter part of the X-ray tube in the present invention, and shows the closed position of a shutter. It is an expanded sectional view showing the above-mentioned shutter part, and shows the open position of a shutter. The expanded sectional view which shows the other Example of the said shutter part.

Explanation of symbols

A: X-ray tube 1: Filament 2: Grid electrode 3: Anode 5: Magnetic lens 6: Target 7: Aperture 8: Vacuum container 9: Electron beam line 10: Pipe 15: Shutter 16: Plunger 17: Cylinder 18: Ball Valve 19: Beam passage hole 20: Air vent valve 22: Drive unit

Claims (4)

Filament that emits an electron beam, grid electrode, anode that accelerates the emitted electron beam, a magnetic lens that focuses the electron beam, a target provided on the X-ray transmission window, and an aperture disposed below the target An X-ray tube in which the periphery of the filament and the periphery of the electron beam line from the filament to the target are maintained in a high vacuum state,
An openable / closable shutter that partitions the vacuum space of the electron beam line is provided at an intermediate portion of the electron beam line from the anode to the target, and the target-side vacuum space partitioned by the shutter is opened to the atmosphere. An X-ray tube comprising an air bleeding valve for opening.   The filament, grid electrode, and anode are housed in a vacuum vessel, the periphery of an electron beam line from the anode to the target is hermetically held by a pipe, and the shutter is provided in the middle of the pipe. X-ray tube as described.   The shutter includes a plunger penetrating the pipe from a side surface, a cylinder that slidably holds an outer surface of the plunger located outside the pipe, and a drive unit that reciprocates the plunger. The X-ray tube according to claim 2, wherein the X-ray tube is formed so as to divide and communicate the vacuum space in the pipe by reciprocal movement.   The plunger is provided with a ball valve which is biased toward the anode side by a spring and seals the divided opening of the pipe on the anode side, and a beam passage hole along the electron beam line. The X-ray tube according to claim 3, wherein a reciprocating motion of the X-ray tube allows selection between a closed position where the ball valve fits into the pipe opening and an open position where the beam passage hole continues to the pipe inner hole.

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