JP2003004668A - X-ray inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an X-ray inspection apparatus in which a current flowing to a steering coil for X-ray deflection in an X-ray tube is adjusted easily and which can make the output of an X-ray detection device maximum. SOLUTION: Electrons are emitted from a cathode filament 1 to which a negative high voltage is applied, they are converged by a Wehnelt electrode 2, and they are accelerated to a high speed by an anode 3 so as to enter a hole in the center of the anode 3. Their electron beam is deflected by the steering coil 4, and it is converged by a focus coil 5 so as to collide with a target 6. Generated transmission-direction X-rays are incident on the X-ray image detection device 7 so as to enter a PC 8 as a luminance-output image signal. An X-Y deflection instruction signal is output by optical-axis auxiliary software 9, a current value flowing to the steering coil 4 via an X-ray controller 10 is changed, and an X-Y deflection value which makes the image signal maximum is set automatically.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray inspection apparatus, and more particularly, to a transmission type X-ray tube, which focuses an electron beam of the X-ray tube with a steering coil. The present invention relates to an X-ray inspection apparatus that deflects and converges with a coil, collides with a target, generates X-rays in a transmission direction, and performs inspection using an X-ray image detection apparatus. 2. Description of the Related Art Techniques for observing a fine internal structure by a nondestructive inspection method are required in various fields. 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 minute focus. The X-ray tube has an open structure, uses a thin tungsten plate as a target, shoots a focused electron beam into the target, and emits X-rays generated there. In order to observe the fine structure of the inspection component, a minute focal spot size is used. This X
The X-ray tube is called a micro-focus X-ray tube. An electron beam starting from a hot cathode in a vacuum vessel is converged by an electron lens and injected into a small area of 1 to 200 μm on a target. To use. Among the microfocus X-ray tubes, those having a particularly small focal dimension are of the type called an open type. The open type X-ray tube has a vacuum vessel opening / closing mechanism and a vacuum exhaust pump, and has a feature that a hot cathode and a target material can be exchanged. For this reason, in an open-type microfocus X-ray tube, the focal length is reduced by raising the temperature of the hot cathode of the cathode at the expense of the life of the hot cathode and the target, and reducing the focal size under conditions of high tube voltage and high tube current. It is possible to miniaturize. Open X-ray tubes are further 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 opposite sides when 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 an electron beam to a minute area on a target to reduce the focal size of X-rays. FIG. 4 shows a cross-sectional structure of an open transmission X-ray tube. This X-ray tube has a cathode filament 1 of a cathode portion,
Wehnelt electrode 2, anode 3 for accelerating the electron beam,
A steering coil 4 for deflecting the direction of the electron beam;
Focus coil 5 for focusing the deflected electron beam
And a target 6 provided on the X-ray transmission window. Each part is vacuum-tightly connected to each other by an O-ring (not shown) to form an X-ray tube container which is drawn in two steps by a turbo molecular pump and a rotary pump (not shown). A high-voltage cable is inserted into the cathode side, and the cathode filament 1 is sent from the X-ray controller 10a.
Is applied with a negative high voltage. The target 6 on the side of the anode 3 and the exterior of the X-ray tube container are kept at the ground potential. When a voltage is applied from a high-voltage cable (not shown) to the cathode filament 1 and a current flows and is heated, thermions are emitted and accelerated toward the anode 3 to form an electron beam. The electron beam passes through the Wehnelt electrode 2, is accelerated and enters a cylindrical portion provided at the center of the anode 3, and the traveling direction of the electron beam is adjusted by the steering coil 4 from the X-ray controller 10 a. The X-ray controller 10 a converges the electron beam with a small diameter by the focus coil 5 and enters the target 6. A target 6 is mounted inside an X-ray output window having a thickness T of aluminum of about 0.5 mm. As the target 6, for example, tungsten having a thickness of about 50 μm is used,
The target material is formed directly on the X-ray transmission window.
When an electron beam enters the target 6, X-rays are emitted there. Among the emitted X-rays, X-rays in a direction transmitting through the X-ray transmission window are irradiated on the sample, and the transmitted X-rays are incident on the X-ray image detecting device 7, so that an X-ray image can be obtained.
The X-ray conditions of the microfocus X-ray tube are as follows.
225kV, tube current ~ 2mA, focus size 1 ~
Those having a size of about 200 μm are used. [0004] The conventional X-ray inspection apparatus is configured as described above. However, the cathode filament 1 of the electron gun of this microfocus X-ray generator requires several hundred hours. It needs to be replaced because it has only a service life. At the time of replacement, the inside of the X-ray tube container is brought to atmospheric pressure, the cathode filament 1 of the electron gun at the cathode is taken out, and the cathode filament 1 is replaced with a new one. Then, the cathode filament 1 is attached to the X-ray tube container again, and the inside is evacuated to a vacuum. However, each time the cathode filament 1
Cannot be installed. Therefore, it is necessary to adjust the traveling direction of the electron beam by the steering coil 4 in order to correct the displacement of the electron beam due to the displacement of the mounting position after the cathode filament 1 is mounted and evacuated to a vacuum. This adjustment is performed by manually changing the optical axis by operating a button of the X-ray control device 10a while visually confirming the image from the X-ray image detection device 7, and transmitting the X-rays to the upper, lower, front and rear electromagnetic coils constituting the steering coil 4. By adjusting the deflection value and the current of the Y deflection value, the optical axis at which the brightness of the image is maximized has been found. This adjustment operation must be performed while visually checking the output image of the X-ray image detection device 7, and there is a disadvantage that the adjustment becomes difficult because the X-ray output is weak when the tube voltage is low. . Further, when the displacement of the electron beam is large and the electron beam deviates from the original opening, the output of the X-ray is lost, so that there is a disadvantage that the adjustment becomes extremely difficult. Since it is necessary to change the two axes, manual adjustment takes a very long time to find the optical axis, and since the screen brightness is a visual comparison, the optical axis must be moved in the wrong direction. There is a problem of scanning. The present invention has been made in view of such circumstances, and has as its object to provide an X-ray inspection apparatus that can easily adjust an electron beam to a predetermined position on a target. . In order to achieve the above object, an X-ray inspection apparatus according to the present invention causes an electron beam generated and accelerated in an electron generating section to collide with a target while being focused by a focusing means. An X-ray inspection apparatus comprising: an X-ray tube that generates X-rays through the X-ray tube; and an X-ray image detection device that irradiates the sample with X-rays generated from the X-ray tube and detects a transmission image. A deflecting means disposed between the focusing means and the focusing means for deflecting the electron beam two-dimensionally;
Scanning means for dimensional scanning, means for measuring the intensity of X-rays by the X-ray image detection device while scanning the electron beam by the scanning means, and the measured value obtained by the measuring means is the highest value Setting means for determining the amount of deflection by said deflecting means and setting the deflection amount in said deflecting means. [0007] The X-ray inspection apparatus of the present invention is configured as described above, and deflecting means for two-dimensionally deflecting the electron beam generated from the electron generating section is provided between the electron generating section and the focusing means. The X-ray intensity is measured by an X-ray image detecting device while the electron beam is two-dimensionally scanned while changing the X-deflection value and the Y-deflection value by scanning means provided outside the deflecting means. , The amount of deflection of the deflecting means at which the obtained measured value is the highest is obtained, and the X deflection value and Y
This is for setting a deflection value. Therefore, the X-deflection value and the Y-deflection value are set by the scanning means so as to obtain the highest X-ray intensity, so that the electron beam can be moved to a predetermined position on the target in a short time without visual observation as in the related art. The position can be easily adjusted. An embodiment of the X-ray inspection apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a configuration of an X-ray inspection apparatus according to the present invention. In this X-ray inspection apparatus, the electron beam emitted from the cathode filament 1 is focused by the Wehnelt electrode 2, accelerated by the anode 3, deflected by the steering coil 4, focused by the focus coil 5, and collides with the target 6. A transmission-type X-ray tube that emits X-rays in the transmission direction, an X-ray image detection device 7 that detects transmitted X-rays and outputs the image signals, and a personal computer PC that scans the output image.
8, an optical axis auxiliary software 9 installed in the PC 8, and a negative high voltage applied to the cathode filament 1, the anode 3 is set to the ground potential, and the optical axis auxiliary software 9
An X-ray controller 10 that receives the highest luminance XY deflection value found by the above and controls a current value flowing through the XY deflection coil of the steering coil 4 and focuses an electron beam by the focus coil 5. The X-ray inspection apparatus includes a steering coil 4
X-rays transmitted from a transmission type X-ray tube having the following are detected by the X-ray image detector 7 and output as image signals, and the images are automatically scanned by the PC 8 using the optical axis auxiliary software 9. The XY deflection value of the steering coil 4 having the highest brightness is input from the PC 8 to the X-ray controller 10 as an XY deflection instruction signal, and the X-ray controller 10
This device controls the current value flowing through the X-deflection coil and the current value flowing through the Y-deflection coil, which are optimal for use, and can be used with a higher luminance signal. The X-ray inspection apparatus comprises a cathode filament 1, a Wehnelt electrode 2, an anode 3 for accelerating an electron beam, a steering coil 4 for deflecting the direction of the electron beam, a deflected electron beam. A transmission type X-ray tube including a focus coil 5 for focusing a beam and a target 6 provided on an X-ray transmission window is used, and each part is vacuum-sealed with an O-ring (not shown). It is connected and forms an X-ray tube container which is drawn in two steps by a turbo molecular pump and a rotary pump (not shown). A high-voltage cable is inserted on the cathode side, and a negative high voltage is applied to the cathode filament 1 from the X-ray controller 10. The target 6 on the side of the anode 3 and the exterior of the X-ray tube container are kept at the ground potential. When a voltage is applied from a high-voltage cable (not shown) to the cathode filament 1 and a current flows and is heated, thermoelectrons are emitted and accelerated toward the anode 3 to form an electron beam. The electron beam passes through the Wehnelt electrode 2, is accelerated and enters a cylindrical portion provided at the center of the anode 3, and the traveling direction of the electron beam is adjusted by the steering coil 4 from the X-ray controller 10. The steering coil 4 deflects the traveling direction of the electron beam drawn out of the cathode filament 1 and accelerated by the anode 3. Electromagnetic coils are provided in front and rear and up and down, and deflect the electron beam by a magnetic field. The electron beam passes through the central electron beam passage, but spreads and travels in a bundle. The periphery of the bundle of electron beams is captured by surrounding electrodes and the like. If the electron beam is decentered with respect to the central axis of the X-ray tube, it will flow to the surrounding electrodes. Therefore, the deflection of the electron beam is controlled by the current flowing through the X deflection coil and the Y deflection coil, and the traveling direction of the electron beam can be freely adjusted by the deflection in the X and Y directions. The steering coil 4 generally deflects an electron beam by a magnetic field. However, the present invention is not limited to this. It is also possible to deflect the electron beam by an electric field. Then, the X-ray controller 10 controls the steering coil 4
The current value flowing to the X deflection coil and the current value flowing to the Y deflection coil which are most suitable for are controlled. The optimum XY deflection value is PC8
Is set by the optical axis assisting software 9 installed in the. Then, the beam is converged by the focus coil 5 from the X-ray controller 10 into an electron beam having a small diameter, and enters the target 6. The target 6 has a thickness T = aluminum of aluminum.
It is mounted inside an X-ray output window of about 0.5 mm. As the target 6, for example, tungsten having a thickness of about 50 μm is used, or a target material is formed directly on the X-ray transmission window. When an electron beam enters the target 6, X-rays are emitted there. X radiated
The sample is irradiated with X-rays out of the X-rays that pass through the X-ray transmission window, and the transmitted X-rays are incident on the X-ray image detection device 7,
A line image can be obtained. The X-ray conditions of the microfocus X-ray tube are as follows: a tube voltage of 5 to 225 kV and a tube current of 2
Those having a focal length of about 1 to 200 [mu] m are used. The X-ray image detector 7 is an X-ray image detector combining an image intensifier (II) and a CCD camera. Image intensifier (I.
I. ) Is captured by a CCD camera, and the output can be extracted as an X-ray image signal. An X-ray image detecting device 7 that receives transmitted X-rays and forms an X-ray image includes:
Although an image intensifier and a CCD camera are used, the image intensifier may be replaced with a semiconductor flat panel imaging device. An X-ray conversion film that normally converts X-rays into light, as an imaging device for a semiconductor flat panel;
A signal stored in each pixel is constituted by a photodiode array arranged in a matrix just below the photodiode array and switching elements connected to each photodiode array, and sequentially turning on each switching element after X-ray irradiation. It has a radiation sensor array composed of a conversion film that reads charges and forms an X-ray image and that directly outputs a charge signal corresponding to an incident dose in response to radiation,
Switching elements are connected to the electrodes arranged in a matrix just below the switching elements, and when the switching elements are sequentially turned on at the time of irradiation, the signal charges accumulated in each pixel are read to form an X-ray image. There is something. In either type, there is a type in which a data storage device is built in and an image is formed on an OFF line, and a type in which a signal is transmitted from an X-ray image detection unit on an ON line. When this semiconductor flat panel is used, it does not occupy a space like an image intensifier, so that the X-ray inspection apparatus becomes compact. Next, the X-ray image detecting device 7 automatically changes the X-deflection value and the Y-deflection value of the current flowing through the steering coil 4 of the present X-ray inspection apparatus using the optical axis auxiliary software 9. The luminance is measured based on the image signal of
The method of finding the deflection value / Y deflection value is shown in FIG.
This will be described with reference to FIG. FIG. 2 shows a flowchart of the optical axis assisting software 9 installed in the PC 8 of the X-ray inspection apparatus. 3A and 3B are diagrams showing an example of scanning by the optical axis auxiliary software 9, wherein FIG. 3A shows a first scanning range 11, FIG. 3B shows a second scanning range 12,
(C) is a diagram showing a third scanning range 13. First, PC
The optical axis assisting software 9 of FIG. 8 is activated to receive the image signal from the X-ray image detecting device 7 and to start the optical axis adjustment. First, (a) the first scanning range 11 for checking the luminance of the image is set large. The first scanning range 1
1 is naturally set to be larger than the threshold (the minimum scannable range). Then, the X deflection value and the Y deflection value are started from the minimum value, the luminance is measured, and the X deflection value and the Y deflection value are respectively increased, and the luminance is sequentially measured. If the X deflection value and the Y deflection value are smaller than the first scanning range 11, the luminance measurement is further continued. If the X deflection value and the Y deflection value are outside the first scanning range 11 by repeating the increase of the deflection value,
From the measurement results in the first scanning range 11, the scanning range is set small around the highest luminance XY deflection value 11a having the highest luminance, and (b) the second scanning range 12 is set. Second scanning range 1
2 is naturally larger than the threshold value (the minimum scannable range), so that the X deflection value and the Y deflection value at the start of scanning at that location are minimized, the luminance is measured, and the X deflection value and the Y deflection value are respectively increased. Then, the second scanning range 12 is sequentially scanned to measure the luminance. Then, the X deflection value and the Y deflection value are set to the second
If it is outside the scanning range 12, the scanning range is set small around the highest luminance XY deflection value 12 a having the highest luminance from the measurement results in the second scanning range 12, and (c) the third scanning range 13 is set. . Since the third scanning range 13 is still larger than the threshold value (the minimum scannable range), the X deflection value and the Y deflection value at the start of scanning at that location are set to the minimum value, the luminance is measured, and the X deflection value and the Y deflection value are measured. By increasing the deflection values respectively, the third
The scanning range 13 is sequentially scanned to measure the luminance. And
If the X deflection value and the Y deflection value are out of the third scanning range 13,
From the measurement results in the third scanning range 13, the scanning range is set small around the highest luminance XY deflection value 13a having the highest luminance, and the fourth scanning range is set. At this time, when the fourth scanning range reaches the threshold value (the minimum scanning range), the measurement result within the third scanning range 13 indicates that the highest luminance XY having the highest luminance is obtained.
The deflection value 13a is set as an optimum value, and this value is input from the PC 8 to the X-ray controller 10 as an XY deflection instruction signal,
The optical axes can be aligned. The X-ray inspection apparatus according to the present invention is constructed as described above. The electron beam of the X-ray tube is controlled by the optical axis assisting software installed in the PC which is the electron beam scanning means. Scans the X- and Y-deflection values of the deflecting means, measures the X-ray intensity with an X-ray image detector, and adjusts the X- and Y-deflection values so that the X-ray intensity becomes the highest. Since the optical axis of the electron beam is not found visually by manual scanning as in the related art, the user simply operates the switch for starting the optical axis adjustment of the X-ray control device. This can be performed in a short time, and the position of the electron beam can be easily adjusted to a predetermined position on the target without misidentifying the optical axis.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a view showing one embodiment of an X-ray inspection apparatus of the present invention. FIG. 2 is a flowchart showing an optical axis assisting software flowchart of the X-ray inspection apparatus of the present invention. FIG. 3 is a diagram showing a scanning example of the X-ray inspection apparatus of the present invention. FIG. 4 is a diagram showing a conventional X-ray inspection apparatus. [Description of Signs] 1 ... Cathode filament 2 ... Wehnelt electrode 3 ... Anode 4 ... Steering coil 5 ... Focus coil 6 ... Target 7 ... X-ray image detector 8 ... PC 9 ... Optical axis assisting software 10, 10a ... X-ray Control device 11: first scanning range 11a: maximum luminance XY deflection value 12: second scanning range 12a: maximum luminance XY deflection value 13: third scanning range 13a: maximum luminance XY deflection value

Claims (1)

1. An electron beam generated and accelerated by an electron generating section and collided with a target while being focused by a focusing means.
An X-ray inspection apparatus comprising: an X-ray tube that generates X-rays; and an X-ray image detector that irradiates a sample with X-rays generated from the X-ray tube and detects a transmission image. A deflecting means disposed two-dimensionally to deflect the electron beam two-dimensionally; a scanning means for two-dimensionally scanning the amount of deflection by the deflecting means; and the X-ray scanning means for scanning the electron beam with the scanning means. Means for measuring the intensity of X-rays by a line image detecting device, and setting means for determining the amount of deflection by the deflecting means at which the measured value obtained by the measuring means is the highest value and setting the amount of deflection by the deflecting means. An X-ray inspection apparatus characterized by the above-mentioned.