JP2001319608A - Micro-focusing x-ray generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a micro-focusing X-ray generator that can easily adjust position of an electron beam at a prescribed position of a target. SOLUTION: An electron beam 10 emitted from an electron source 1 by a grid electrode 2 is deflected by a deflector 3 to correct the axis of the electron beam. An outer peripheral portion of the electron beam 10 is incident on a measuring plate 4 sectored into three or more electrodes provided at an aperture portion. Currents of sectored electrodes are different according to an eccentric state of the electron beam axis, and a deflector 3 is adjusted with the measured values. Furthermore, by electrically insulating the target 8 from an X-ray transmission window 7, current that flows in the target 8 is measured to be regarded as the X-ray intensity, and the electron beam 10 can be subject to position adjustment on the target 8 by adjusting the deflector 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmission or reflection type X-ray generator and, more particularly, to a device for exchanging filaments.
The present invention relates to an open-type microfocus X-ray generator that adjusts the direction of an electron beam using a deflector.

[0002]

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. This X-ray tube has an open structure, uses a thin tungsten plate as a target, emits a focused electron beam into the target, and emits X-rays generated therefrom. 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 minute area having a size of 1 μm to 200 μm on a target. To use.

[0003] Of the microfocus X-ray tubes, those of which the focal dimension can be made particularly small are of the type called open type. The open type X-ray tube includes 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 or the target, or by reducing the focal length under high tube voltage and high tube current conditions. Can be miniaturized.

[0004] Open-type 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 the electron beam to a minute area on the target to reduce the focal size of X-rays.

As an example, FIG. 5 shows a cross-sectional structure of an open transmission X-ray tube. The X-ray tube includes an electron source 1 in a cathode section, a grid electrode 2, and a deflector 3 for adjusting the direction of an electron beam.
And an aperture 5 for converging the adjusted electron beam 10, an electron lens 6 for converging, an X-ray output window 7 for supporting the target 8, and a target 8 in the anode section. Each part is vacuum-tightly connected to each other by an O-ring (not shown), and the X-ray tube container 9 is drawn in two steps by a turbo pump and a rotary pump (not shown).
Is formed. A high voltage cable is inserted into the cathode section, and a negative high voltage is applied to the electron source 1 composed of a filament. The exterior of the target 8 and the X-ray tube container 9 at the anode section are kept at the ground potential. When a voltage is applied from a high-voltage cable (not shown) to the filament and a current flows and is heated, thermions are emitted and accelerated toward the anode to form an electron beam 10.

The electron beam 10 passes through the grid electrode 2,
The traveling direction of the electron beam 10 is adjusted by the deflector 3. Then, the light is converged by the aperture 5 and the electron lens 6 into an electron beam 10 having a small diameter, and enters the target 8. A target 8 is mounted inside an X-ray output window 7 having a thickness T of aluminum of about 0.5 mm. For example, the target 8 is made of tungsten having a thickness of about 50 μm, or the target material is made of an X-ray output window 7.
Or directly on the substrate. When an electron beam 10 enters this target 8, X-rays 11 are emitted there. X of the emitted X-rays 11 in the direction transmitting through the X-ray output window 7
Line 11 is used. X of microfocus X-ray tube
Line conditions are as follows: tube voltage is 5 to 225 kV, tube current is 2 mA
The focal size is about 1 to 200 μm.

[0007]

Although the conventional microfocus X-ray generator is constructed as described above, the filament of the electron source 1 of this microfocus X-ray generator has a life of only several hundred hours. No replacement of the filament is required. At the time of replacement, the inside of the X-ray tube container 9 is brought into the atmospheric pressure state, and the electron source 1 at the cathode of the X-ray tube container 9 is replaced.
Is taken out and the filament of the electron source 1 is replaced with a new one. Then, the electron source 1 is attached to the X-ray tube container 9 again, and the inside is evacuated to a vacuum. However, it is not possible to attach the filament or the electron source 1 itself at the same position every time. Therefore, it is necessary to adjust the traveling direction of the electron beam 10 by the deflector 3 in order to correct the displacement of the electron beam due to a shift in the mounting position after mounting the electron source 1 and evacuating to a vacuum. This adjustment has been performed manually by adjusting the currents flowing through the upper, lower, front and rear electromagnetic coils constituting the deflector 3 while observing the output of an X-ray detector such as an X-ray camera.

This adjustment operation requires an X-ray detector, and has a drawback that it is difficult to adjust the X-ray output when the tube voltage is low, since the output is weak. Further, when the displacement of the electron beam is large and the electron beam is out of the hole of the aperture portion, the output of the X-ray is lost, so that there is a disadvantage that the adjustment becomes extremely difficult.

The present invention has been made in view of such circumstances, and detects the electron beam 10 and easily adjusts the position of the converged electron beam 10 to a predetermined position on the target 8. It is an object of the present invention to provide a microfocus X-ray generator capable of performing the above.

[0010]

In order to achieve the above object, a microfocus X-ray generator according to the present invention determines the direction of electrons emitted from a cathode filament by a deflector, accelerates the electrons with a high voltage, and accelerates the electron lens. In a microfocus X-ray generator that generates X-rays by converging with the anode target and generating X-rays, a current measuring plate of three or more divisions is provided in an aperture portion where an electron beam is incident, and flows through each electrode of the current measuring plate. The current can be measured.

According to a second aspect of the present invention, there is provided a microfocus X-ray generator, wherein the direction of electrons emitted from a cathode filament is determined by a deflector, accelerated by a high voltage, converged by an electron lens, and collided with an anode target. In a microfocus X-ray generator for generating X-rays, the anode target is electrically insulated from ground potential,
It can measure the amount of electron beam current reaching the anode target.

The microfocus X-ray generator according to the present invention is configured as described above, and is provided with a current measuring plate having three or more divisions in the aperture where the electron beam enters, and a current flowing through each electrode of the current measuring plate. Is measured, the deflector is adjusted according to the measured value, the direction of the electron beam is determined, and the electron beam is converged to a predetermined target position.An insulating layer that electrically insulates the anode target is provided. A current detecting means is provided between the ground potentials, the current flowing through the anode target is measured, the direction of the electron beam is determined by a deflector so that the measured value is maximized, and the electron beam is converged to a predetermined target position. is there.

Therefore, if the deflector is adjusted while calculating the position of the electron beam from the amount of the electron beam hitting each electrode of the current measuring plate, many electrons can be collected at the center of the aperture. Then, since the X-ray intensity is proportional to the amount of electrons hitting the target, and the amount of electrons hitting the target is proportional to the target current, the X-ray intensity can be determined by measuring the target current. Therefore, even if there is no X-ray detector, if the adjustment lens is adjusted while measuring the target current, the position of the electron beam can be adjusted to a predetermined position at a position where the target current is maximized.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a microfocus X-ray generator according to the present invention will be described with reference to FIG. FIG. 1 is a diagram showing a cross-sectional structure of a microfocus X-ray generator according to the present invention. This device is an electron source 1 that emits electrons.
A grid electrode 2 for shaping the emitted electrons as an electron beam; a deflector 3 for adjusting the traveling direction of the emitted electron beam 10; and a deflector 3 for narrowing the deflector 3 and the electron beam 10. Measurement plate 4 for current of three or more divisions provided between aperture 5 (incident aperture section)
An aperture 5 for narrowing the electron beam 10 that has passed through the central opening (the electron beam passage hole 12 shown in FIG. 2) of the measurement plate 4, an electron lens 6 for focusing, and a metal such as an Al plate. A target 8 mounted on an X-ray output window 7 made and electrically conductive, an X-ray tube container 9 for accommodating the above-described components in a vacuum, and a negative high voltage applied to the electron source 1 in the cathode section. The X-ray tube container 9 includes a high-voltage generating unit (not shown) for supplying a high voltage with a ground potential, and a vacuum pump (not shown) for evacuating the X-ray tube container 9 to a vacuum. .

FIG. 2 shows the structure of the measurement plate 4 as viewed from the aperture side of the electron beam 10. The measurement plate 4 includes three or more divided electrodes provided in the entrance aperture of the electron beam 10. Here, four divided measurement electrodes 13 are arranged via an insulator 14, and an electron beam passage hole 12 of an opening through which the electron beam 10 passes is formed in the center. Lead wires (not shown) are led out from the divided measurement electrodes 13 to measure the current from each lead wire to determine the traveling direction of the electron beam 10.

The deflector 3 deflects the traveling direction of the electron beam 10 drawn from the electron source 1. Electromagnetic coils are provided at the front, rear, upper and lower sides, and the electron beam 10 is deflected by a magnetic field. The deflection is caused by the split measurement electrodes 13 of the measurement plate 4.
, And the traveling direction of the electron beam 10 can be freely adjusted by deflection in the XY directions. Although the deflector 3 generally deflects an electron beam by a magnetic field, the present invention is not limited to this, and it is of course possible to deflect the electron beam by an electric field.

The deflection control of the electron beam 10 is performed as follows. The electron source 1 with the updated filament is mounted, the X-ray tube container 9 is evacuated to a vacuum, and electrons are emitted from the electron source 1. The emitted electron beam 10 travels toward the target 8. At that time, the electron beam 1
Most of the zeros pass through the electron beam passage hole 12 at the center of the measuring plate 4, but the electron beam 10 spreads and travels in a bundle. The periphery of the bundle of electron beams 10 is captured by the divided measurement electrodes 13 provided on the measurement plate 4. If the electron beam 10 is eccentric with respect to the center axis of the X-ray tube, the current flowing through each divided measurement electrode 13 is different. The eccentric position of the electron beam 10 is calculated based on the measured current value, and the deflector 3 is adjusted so that the electron beam 10 is returned to the center axis of the X-ray tube. That is, if the deflector 3 is adjusted while calculating the position of the electron beam 10 from the amount of the electron beam impinging on each divided measurement electrode 13 of the current measurement plate 4, many electrons can be collected at the center of the aperture.

FIG. 3 shows a second embodiment of the microfocus X-ray generator according to the present invention. The intensity of the X-rays 11 is proportional to the amount of the electron beam impinging on the target 8. Therefore, if the target current is measured, the intensity of the X-rays 11 can be determined. Therefore, the present apparatus is provided with an insulating layer 15 and an ammeter 16 for electrically insulating the anode target 8 from the X-ray output window 7, and measuring a current flowing between the insulated anode target 8 and the ground potential. The current measuring means for adjusting the deflector 3 to determine the direction of the electron beam 10 so as to micro-focus at a predetermined target 8 position is not limited to the ammeter 16 so that the potential of the resistor can be maximized. May be measured. Therefore, even if there is no X-ray detector, if the deflector 3 is adjusted while measuring the target current, the position of the electron beam can be adjusted to a predetermined position at the position where the target current is maximized. Although the insulating layer 15 is provided in the above embodiment, the X-ray output window 7 with the target 8 may be insulated without providing the insulating layer 15. Further, an X-ray output window 7 made of an insulating material may be used. FIG. 4 shows a reflection type microfocus X-ray generator. In this case, since the target 8 can be easily insulated, the same measurement of the target current can be performed.

In the above embodiment, the case where the measurement plate 4 is provided on the electron beam 10 has been described. However, the electrodes of the aperture 5 may be divided and used as measurement electrodes. Further, in order to measure the current of each divided measurement electrode 13 of the measurement plate 4 and adjust the current of the deflector 3 based on the measured value, an external control device is provided, the operation is automatically calculated, and the adjustment is performed by the feedback circuit. You can do it. Similarly, in order to measure the target current while insulating the target 8 with the insulating layer 15 and adjust the deflector 3 so as to maximize the current, similarly, an external control device is provided, and the adjustment is automatically performed by the feedback circuit. It can be carried out.

[0020]

The microfocus X-ray generator of the present invention is constructed as described above. When the filament is replaced, the center axis of the electron beam is adjusted by a deflector to microfocus on a predetermined target position. For this purpose, a current measuring plate having three or more divisions is provided in the course of the electron beam, and the deflector is adjusted while calculating the position of the electron beam from the amount of the electron beam (aperture current) hitting each electrode of the current measuring plate. Many electrons can be collected at the center of the aperture. Therefore, the adjustment work of the electron beam axis can be completed in a short time.

Further, since an insulating layer for electrically insulating the anode target from the X-ray output window is provided and the current flowing through the insulated anode target is measured to detect the X-ray intensity, the X-ray detector is used. Even if there is no, the target current corresponding to the X-ray output is linked with the beam adjustment, and by adjusting the deflector, the position of the electron beam can be adjusted to a predetermined position at the position where the target current is maximized. I can do it.

In the conventional adjustment work, an X-ray detector is required. Further, adjustment under a condition where the tube voltage is low is difficult because the X-ray output is weak and the adjustment is difficult. In some cases, there was no output from the X-ray detector, so that the adjustment could not be performed. On the other hand, the present device can determine the direction of the electron beam by adjusting the deflector without requiring the X-ray detector, and can easily microfocus on the position of the target.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of a microfocus X-ray generator according to the present invention.

FIG. 2 is a diagram showing a structure of a divided measurement electrode provided in an aperture portion of an electron beam of the microfocus X-ray generator according to the present invention.

FIG. 3 is a diagram showing another embodiment of the microfocus X-ray generator according to the present invention.

FIG. 4 is a diagram showing another embodiment of the microfocus X-ray generator according to the present invention.

FIG. 5 is a diagram showing a conventional microfocus X-ray generator.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electron source 2 ... Grid electrode 3 ... Deflector 4 ... Measuring plate 5 ... Aperture 6 ... Electron lens 7 ... X-ray output window 8 ... Target 9 ... X-ray tube container 10 ... Electron beam 11 ... X-ray 12 ... Electron beam Passing hole 13: Split measuring electrode 14: Insulator 15: Insulating layer 16: Ammeter

Claims (2)

[Claims] 1. A micro-focus X-ray generator for determining the direction of electrons emitted from a cathode filament by a deflector, accelerating at a high voltage, converging by an electron lens, and colliding with an anode target to generate X-rays. A microfocus X-ray generator, wherein a current measuring plate having three or more divisions is provided in an aperture part where an electron beam is incident, and a current flowing through each electrode of the current measuring plate can be measured. 2. A micro-focus X-ray generator for determining the direction of electrons emitted from a cathode filament by a deflector, accelerating with a high voltage, converging with an electron lens, and colliding with an anode target to generate X-rays. A microfocus X-ray generator, wherein an anode target is electrically insulated from a ground potential, and a current amount of an electron beam reaching the anode target can be measured.