JP2002352754A - Transmission type x-ray target - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a transmission type X-ray target by which a clear X-ray image with a contrast can be obtained, even if a sample is thin or minute, or absorbs little X-rays. SOLUTION: A converged electron beam 1 collides with an evaporation target 6, consisting of thorium doped tungsten or tungsten rhenium alloy fabricated through CVD method. A ceramic member 5 or a glass member is used as an X-ray transmission window member, and X-rays 4 generated at the evaporation target 6 is transmitted through the ceramic member 5, without attenuation of the soft X-ray components. While the heat generated at the evaporation target 6 is radiated circumferentially from the ceramic member 5, the surface of tungsten is not made rough due to the diffusion of thorium, and deterioration of X-ray emission can be suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a target of a transmission type X-ray tube, and more particularly, to an X-ray non-destructive inspection and an X-ray tube using a soft X-ray generated by irradiating a target metal with electrons. The present invention relates to a transmission type X-ray target of a transmission type microfocus X-ray tube for performing analysis.

[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, shoots a focused electron beam into the target, and radiates X-rays generated therethrough from the back side. In order to observe the fine structure of the inspection component, a minute focal spot size is used.

FIG. 4 shows a sectional structure of an open transmission X-ray tube. The X-ray tube includes a cathode section 20 (lower section), an anode section 21 (middle section), and a target section 22 (upper section). Each section is connected to each other by an O-ring in a vacuum-tight manner. The vacuum chamber 11 is formed by a two-stage drawing by a rotary pump (not shown). The cathode section 20 is connected to the high-voltage cable insertion port 17.
, A high negative voltage is applied to the electrodes of the Wehnelt 9 and the filament 10. The anode unit 21, the target unit 22, and the exterior of the vacuum chamber 11 are kept at the ground potential. When a voltage is applied to the filament 10 from a high-voltage cable (not shown) and a current flows, the thermoelectrons are emitted and accelerated toward the anode 19 to form the electron beam 1. The anode part 21 is provided with the anode 19 and the pipe 26 on the lens holder 25.
It incorporates

The electron beam 1 passes through the hollow portion of the pipe 26 and is converged by the electron lens 8 of the target portion 22 into the electron beam 1 having a small diameter and enters the target metal 2. The target part 22 incorporates the electron lens 8 in the cylinder of the pole piece 27, and the X-ray transmission window base material 3 is provided between the upper part of the pole piece TOP 23 and the target holder 14.
As shown in FIG. 5, the target metal 2 is mounted inside the X-ray transmission window substrate 3 having a thickness t of about 0.5 mm of aluminum, as shown in FIG. The target metal 2 has a thickness of, for example, 50 μm.
m of tungsten or target metal 2
Is formed directly on the X-ray transmission window substrate 3. When the electron beam 1 enters the target metal 2, X
Emit line 4. The radiation direction is directional,
X-rays 4 in the transmitted direction are used. The X-ray conditions of the X-ray tube are as follows: a tube voltage of 5 to 160 kV and a tube current of 0.3 mA.
Degree, focal size is 1-20 by micro focus
Those having a thickness of about 0 μm are used.

[0005] Of the microfocus X-ray tubes, those whose focal dimensions can be miniaturized 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 a closed-type microfocus X-ray tube, the temperature of the hot cathode and the temperature of the hot cathode are sacrificed at the expense of the service life of the hot cathode and the target, and the focal size is reduced. It is possible to reduce the size.

[0006]

The conventional transmission type X-ray target is constructed as described above, and a part of the kinetic energy of the electrons colliding with the target metal 2 is converted into X-rays, and the intensity is I-ray. = K · i · Z · V ² . Here, I is the X-ray intensity, k is a constant, i is the tube current, Z is the atomic number of the target element, and V is the acceleration voltage. The target metal 2 is of a fixed type, a foil or a thin film having a constant thickness is attached to the X-ray transmission window base material 3, and the intensity of the generated X-ray has a wavelength distribution. It is determined by the material and thickness of the material. A thick metal (target metal 2 + X-ray transmitting window substrate 3) has a significantly different X-ray intensity in a region with low photon energy than a thin metal (target metal 2 + X-ray transmitting window substrate 3). This is the X in the low photon energy region
X-rays with a longer wavelength (soft X-rays)
This is because attenuation is larger due to internal absorption of the metal (target metal 2 + X-ray transmission window substrate 3) as compared with the line (hard X-ray). Therefore, the spectrum of the X-rays generated in the transmission type X-ray tube depends on the acceleration voltage V, the materials of the target metal 2 and the X-ray transmission window substrate 3, and the thickness of the target metal 2 and the X-ray transmission window substrate 3. It is determined. Soft X-rays have a large X-ray absorptivity and a small sample thickness,
For a sample with little line absorption, contrast is easily obtained, which is advantageous.

For this reason, the X-ray transmission window substrate 3 also requires a material having a good X-ray transmittance and an appropriate thickness. However,
The thickness of the X-ray transmission window base material 3 through which the X-rays 4 are transmitted is as thick as about 0.5 mm in the conventional aluminum plate, so that if the thickness is large, soft X-rays of 1 to 10 keV are blocked. . For this reason, various measures have been taken such as using a material having good X-ray transmission properties such as beryllium, or reducing the thickness of the X-ray transmission window substrate 3 as much as possible. However, as the material of the X-ray transmission window base material 3, there is no base material having aluminum or beryllium properties or more, and there is a limit in strength in reducing the thickness. Beryllium Be is a metal material having better X-ray transparency than aluminum, but beryllium is hard and brittle at room temperature, and is difficult to process such as rolling and elongation. In addition, since beryllium has an affinity for oxygen, the processing is performed at a high temperature in a hydrogen atmosphere or in a vacuum, etched with an acid, or polished with care for Be powder. . Since a beryllium plate is expensive and its processing is difficult as described above, a thin aluminum plate is generally used as the X-ray transmission window substrate 3. But,
With a thickness of about 0.5 mm of the conventional X-ray transmission window substrate 3,
The problem is that the soft X-ray component with a long wavelength is absorbed, and even if hard X-rays with a short wavelength are irradiated on a thin sample, the sample transmission ability is too high and it is difficult to obtain sufficient contrast of the internal structure. there were.

The present invention has been made in view of such circumstances, and it is possible to obtain a clear X-ray image with contrast for a sample having a small thickness, a sample having a small X-ray absorption, and a minute sample. It is an object of the present invention to provide a transmission type X-ray target that can be used.

[0009]

In order to achieve the above object, the transmission type X-ray target of the present invention accelerates and converges the electrons emitted from the filament of the cathode to form the X-ray target on the anode side X-ray transmission window substrate. Collision with the target metal provided in
A transmission type X-ray target of an X-ray tube for generating X-rays in a transmission direction, wherein ceramic or glass is used for the X-ray transmission window substrate, and the target metal is deposited on an inner surface of the X-ray transmission window substrate. It is.

Further, the transmission type X-ray target of the present invention comprises:
In a transmission type X-ray target of an X-ray tube which accelerates and converges electrons emitted from a cathode filament to collide with a target metal provided on an X-ray transmission window substrate on the anode side to generate X-rays in a transmission direction. And forming an antistatic film made of a metal other than the target metal on the inner surface of the X-ray transmission window substrate, using ceramic or glass for the X-ray transmission window substrate, and depositing the target metal on the antistatic film. It was done.

According to a third aspect of the present invention, there is provided a transmission type X-ray target in which alumina, aluminum nitride, silicon carbide, silicon nitride, or a ceramic mixture thereof is used for the X-ray transmission window substrate.

Further, the transmission type X-ray target according to claim 4 uses tungsten or a tungsten rhenium alloy as the target metal.

According to a fifth aspect of the present invention, there is provided a transmission type X-ray target wherein a metal obtained by doping thorium into tungsten or a tungsten rhenium alloy is used as the target metal.

According to a sixth aspect of the present invention, there is provided a transmission type X-ray target wherein aluminum, an aluminum alloy, or beryllium is used for the antistatic film made of a metal other than the target metal formed on the inner surface of the X-ray transmission window substrate. It is.

The transmission type X-ray target of the present invention is constituted as described above, and alumina, aluminum nitride, silicon carbide, silicon nitride or a mixture of the above ceramics or glass is coated on the X-ray transmission window substrate. Used, and a metal other than the target metal on the X-ray transmission window substrate,
For example, an antistatic film made of aluminum or an aluminum alloy or beryllium is formed, and then, on the antistatic film, tungsten or a tungsten rhenium alloy,
Alternatively, it is formed by vapor deposition of a target metal doped with thorium.

[0016] Therefore, the X-ray transmission window substrate is made of a ceramic which has a small attenuation of X-rays, a high strength and a good thermal conductivity.
Or, glass is used, soft X-ray absorption is low, and
By using tungsten or a tungsten-rhenium alloy as the target metal and further doping with thorium, thermal surface roughness due to electron impact on the target surface can be reduced, and reduction in X-ray radiation efficiency can be reduced. Further, since the antistatic film is provided so as not to charge up the electrons that have impacted on the target to the periphery, it can operate stably. Then, with respect to an X-ray having a large soft X-ray component and a sample having a small thickness or a sample having a small X-ray absorption, an X-ray image with contrast can be obtained.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the transmission type X-ray target of the present invention will be described with reference to FIG. FIG. 1 is a view showing a cross section of a transmission type X-ray target of the present invention. The transmission type X-ray target is provided on the anode 19 side in FIG. 4 and is a ceramic base 5 as an X-ray transmission window base for transmitting the X-rays 4 to the outside, and is formed by vapor deposition on the ceramic base 5. The electron beam 1 emitted from the cathode filament 10 shown in FIG. 4 is accelerated and converged, collides and collides, and emits X-rays 4 in the transmission direction. The present transmission type X-ray target is different from the conventional transmission type X-ray target in that the X-ray transmission window substrate of the conventional transmission type X-ray target uses an aluminum alloy plate, whereas The point is that ceramic or glass having good X-ray transparency, high strength, and good thermal conductivity is used as the X-ray transmission window substrate of the X-ray target. Thereby, a large amount of soft X-ray components can be emitted.

The target metal of the conventional transmission X-ray target is spot-welded with tungsten foil or tungsten is deposited, whereas the deposition target 6 of the transmission X-ray target is tungsten or tungsten. The point is that the tungsten rhenium alloy is formed by using the CVD method. Thereby, a dense metal layer can be formed. Further, the target metal material of the transmission type X-ray target is formed by doping thorium into tungsten or a tungsten rhenium alloy. As a result, thermal surface roughness due to electron impact on the target surface is reduced, and X-ray radiation efficiency can be increased.

The ceramic substrate 5 is used as an X-ray transmission window substrate, has good X-ray transparency, high strength, does not break even when locally heated to a high temperature, and has good thermal conductivity. Is used. For example, a ceramic of alumina, aluminum nitride, silicon carbide, silicon nitride, or a mixture thereof is used. Among them, aluminum nitride is most preferable because of its excellent thermal conductivity. The thickness is not limited, but t = 0.1 to
Any value between 1.0 mm is used. These materials have little attenuation to soft X-rays. Similar characteristics can be satisfied by using a glass substrate, particularly a hard glass substrate, instead of the ceramic substrate 5.

Since the vapor deposition target 6 functions as a target metal material, it has a large atomic number, has a high melting point because the accelerated electron beam 1 collides and locally rises in temperature, and has a high melting point. Tungsten or a tungsten rhenium alloy is used because of its low vapor pressure, good thermal conductivity for heat dissipation, and good electrical conductivity. The film thickness is manufactured to an arbitrary value of 0.1 to 15 μm, and the manufacturing method is a CVD method.

As the CVD method, a thermal CVD method of forming a thin film by a chemical reaction at a high temperature is used. When a film is formed at a high temperature, a dense film of a high-purity substance is obtained with an extremely high adhesion strength, and a film having little internal strain and pinholes is obtained, and a film having excellent adhesion is obtained. In the thermal CVD method, a volatile compound (source) of a material to be formed into a film is vaporized and sent so as to be as uniform as possible on a substrate heated at a high temperature, and then subjected to chemical treatment such as decomposition, reduction, oxidation and substitution on the substrate. The reaction is performed to form a thin film on the substrate. To form a tungsten thin film, halide WF ₆ or W (CO) ₆ is used as a volatile compound, and the volatile gas is vaporized and mixed with a carrier gas such as Ar or He, or WCl ₆ vaporized with, fed into the reaction chamber mixed with a carrier gas such as H _2, to form a thin film of tungsten by a vapor phase reaction.

In the present X-ray transmission type target, it is preferable that thorium is doped into tungsten or a tungsten rhenium alloy as a target metal material. When this focused thorium collides with the deposition target 6 on which the focused electron beam 1 is deposited, the temperature of the tungsten thin film layer becomes high and strain is generated between the tungsten crystal grains. The field diffuses to the surface, which spreads to form a monolayer of thorium. Therefore, the surface of the tungsten metal material is less likely to be rough. Thereby, it is possible to reduce a decrease in X-ray radiation efficiency (efficiency of converting electron beam energy to X-ray energy).

FIG. 2 shows another embodiment of the present X-ray transmission type target. FIG. 1 shows an example in which a deposition target 6 is deposited on a central portion of a ceramic base 5. The ceramic base 5 is an insulator, and the electron beam 1 collides with the deposition target 6, and the electron beam is irradiated. Flows on the surface to the peripheral portion, and a vapor deposition target 6a is formed over the entire area of the ceramic substrate 5 to improve the flow.

FIG. 3 shows another embodiment of the present X-ray transmission type target. In FIG. 3, instead of forming the deposition target 6a as shown in FIG. 2 over the entire area of the ceramic substrate 5, a thin film of a conductive antistatic film 7 having good X-ray transparency, for example, aluminum or aluminum alloy Alternatively, a beryllium thin film is formed, and thereafter, a deposition target 6 as a target metal material is formed by a CVD method. Thus, charge-up of electrons after collision with an insulator such as ceramic is eliminated, and stable operation can be performed. In this case, the ceramic substrate 5
Has strong strength, the antistatic film 7 can be reduced in thickness, and the absorption of soft X-ray components can be reduced.

As in the above embodiment, when the focused electron beam 1 collides with the vapor deposition target 6, most of the energy becomes heat, and the vapor deposition target 6 is locally heated to a high temperature. When thorium is doped into the tungsten of the vapor deposition target 6, the surface of the tungsten is prevented from being roughened, and the electrons after collision do not pass through the target and the antistatic film 7 to be charged up to the peripheral portion. Then, the X-rays 4 generated in the vapor deposition target 6 pass through the ceramic base material 5 having good X-ray transparency and are radiated to the outside without attenuating the soft X-ray component. The ceramic base material 5 as the X-ray transmission window base material has strength, reduces attenuation of soft X-ray components, and provides clear and sharp contrast for a sample having a small thickness, a sample having a small X-ray absorption, and a small sample. X-ray images can be obtained.

[0026]

The transmission type X-ray target of the present invention is constructed as described above. Since ceramic or glass is used for the X-ray transmission window base material, soft X-ray absorption is small and strength is improved. Strong and good thermal conductivity. When an antistatic film made of aluminum or the like is formed on the X-ray transmission window base material, and then a target metal obtained by doping thorium in tungsten or a tungsten-rhenium alloy is formed thereon, the impact may be applied to the target. The charged electrons do not charge up to the periphery, operate stably, and the thermal surface roughness due to electron collision is small, so that a decrease in X-ray radiation efficiency can be reduced. This makes it possible to obtain an X-ray image having a high contrast for a sample having a small soft X-ray component and a small X-ray absorption.

[Brief description of the drawings]

FIG. 1 is a view showing one embodiment of a transmission type X-ray target of the present invention.

FIG. 2 is a view showing an embodiment in which a vapor deposition target of a transmission type X-ray target of the present invention is vapor-deposited on the entire surface.

FIG. 3 is a view showing another embodiment of the transmission type X-ray target of the present invention.

FIG. 4 is a diagram showing a transmission type X-ray tube.

FIG. 5 is a view showing a conventional transmission X-ray target.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electron beam 2 ... Target metal 3 ... X-ray transmission window base material 4 ... X-ray 5 ... Ceramic base material 6, 6a ... Evaporation target 7 ... Antistatic film 8 ... Electronic lens 9 ... Wehnelt 10 ... Filament 11 ... Vacuum chamber DESCRIPTION OF SYMBOLS 12 ... Sample 14 ... Target holder 15 ... X-ray detector 17 ... High voltage cable insertion port 18 ... High voltage receptacle 19 ... Anode 20 ... Cathode part 21 ... Anode part 22 ... Target part 23 ... Pole piece TOP 25 ... Lens holder 26 … Pipe 27… pole piece

Claims (6)

[Claims] 1. An X-ray tube for generating X-rays in a transmission direction by accelerating and converging electrons emitted from a cathode filament to collide with a target metal provided on an anode-side X-ray transmission window base material. A transmission type X-ray target, wherein ceramic or glass is used for the X-ray transmission window substrate, and the target metal is deposited on an inner surface of the X-ray transmission window substrate. 2. An X-ray tube for generating X-rays in a transmission direction by accelerating and converging electrons emitted from a cathode filament to collide with a target metal provided on an anode-side X-ray transmission window base material. In a transmission type X-ray target, ceramic or glass is used for the X-ray transmission window substrate, and an antistatic film made of a metal other than the target metal is formed on the inner surface of the X-ray transmission window substrate. A transmission type X-ray target, wherein the target metal is deposited on the target. 3. An X-ray transmission window base material comprising alumina, aluminum nitride, silicon carbide, silicon nitride, or a ceramic of a mixture of said ceramics.
Alternatively, the transmission type X-ray target according to claim 2. 4. The method according to claim 1, wherein tungsten or a tungsten-rhenium alloy is used as the target metal.
Alternatively, the transmission type X-ray target according to claim 2. 5. The transmission type X-ray target according to claim 1, wherein a metal obtained by doping tungsten or tungsten rhenium alloy with thorium is used as the target metal. 6. The transmission type X according to claim 2, wherein aluminum, an aluminum alloy or beryllium is used for the antistatic film made of a metal other than the target metal formed on the inner surface of the X-ray transmission window substrate. Line target.