JPH03186710A - X-ray tomography method, equipment, and target for generating X-rays - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a tomography method using transmitted X-rays, an apparatus thereof, and an X-ray generation target, and is particularly suitable for measuring the internal structure of a circuit board. X-ray tomography method and equipment,
Furthermore, the present invention relates to a target that is included in the apparatus for generating X-rays.

[Prior Art] Until now, as an apparatus for enlarging and observing a transmitted X-ray image, one described in Japanese Patent Application Laid-open No. 70304/1984 has been known. In this case, an X-ray image transmitted through a sample is converted into a photoelectron image by a photoelectric conversion film, and then enlarged and projected onto a fluorescent screen by an electron lens.

[Problems to be Solved by the Invention] However, in the case of the prior art, when a sample is irradiated with X-rays, an image transmitted through the sample, that is, a projected image, is detected, so the tomographic image of the sample is detected. In order to obtain an image, it is necessary to reconstruct a tomographic image from the projected image. This reconstruction processing is called CT (computer tomography), but it requires a huge amount of calculation processing to obtain a tomographic image.

SUMMARY OF THE INVENTION An object of the present invention is to provide an X-ray tomography method in which a tomographic image of a sample at the focal plane can be detected in a state where images at other than the focal plane are blurred, simply and easily.

Another object of the present invention is to provide an X-ray tomography apparatus having a simple and easy configuration in which a tomographic image of a sample in the focal plane can be detected while images in areas other than the focal plane are blurred. .

Still another object of the present invention is to provide an X-ray generation target whose X-ray tomographic image can be detected with high resolution.

[Means for solving the problem] The above purpose is basically to deflect a focused electron beam and irradiate it onto a target, and to detect the X-rays generated by the target through the sample. This is achieved by detecting a tomographic image at that focal plane while blurring the image at that point.

Another purpose is to irradiate a target with a focused electron beam and detect the X-rays generated from the X-ray source through the sample with a photoelectric conversion film. This is achieved by scanning the target with a convergent electron beam and scanning photoelectrons from the photoelectric conversion film in synchronization with the scanning of the convergent electron beam. In addition, X-rays generated from an X-ray source by irradiating a target with a focused electron beam
The rays are detected by multiple X-ray detectors through the sample, and the X-rays that passed through the sample were detected two-dimensionally as image signals by the X-ray detectors at positions corresponding to the scanning positions of the convergent electron beam. This can be achieved by configuring it to be added. Furthermore,
By irradiating the target with a focused electron beam, the X-rays generated from the X-ray source are detected as an optical image through the sample. This is achieved by configuring the device to be detected by an accumulation-type detection means via a storage type detection means.

Another purpose is that the X-ray generating target used in an X-ray tomography apparatus is basically configured as a multilayer structure of two or more types including a thin X-ray generating layer. achieved.

[Function] First, the principle of the X-ray tomography method according to the present invention is to move the X-ray source and the transmission image detection surface in synchronization so that only the layer of interest is in focus. The explanation is as follows.

That is, as shown in FIG. 2, if the X-ray source 1 and the film 2 are moved linearly in opposite directions in synchronization, the point C on the focal plane 3 will be the same on the film 2. The other points A and B, which are not on the focal plane 3, are photographed at different positions on the film 2. This means that an image on the focal plane 3, that is, a tomographic image on the focal plane 3, is obtained with points A and B blurred.

At this time, the motion of the X-ray source 1 and the film 2 is not necessarily limited to linear motion, but may be other motions such as circular motion or arc motion.

Now, next, X according to the present invention based on such a principle.
To explain the basic configuration of the line tomography apparatus with reference to FIG. 3, if the electron beam 4 is irradiated onto the target 5 in a converged state and the electron beam 4 is scanned in a circular orbit as much as possible, the target 5 will be exposed. After the generated X-rays pass through a sample (not shown), they are converted into a photoelectron image by a charge conversion film 6. If this photoelectron image is scanned in a circular orbit by the coil 7 in synchronization with the scanning of the electron beam 4, the photoelectron image will be formed on the screen 9. As shown, point C on the focal plane 3 is imaged at the same position on the screen 9, but other points A, B
are arranged so that they are not imaged at the same position on the screen 9. As a result, the image on the non-focal plane is blurred, and only the image on the focal plane 3 is obtained.

FIG. 4 also shows an X-ray tomography apparatus having another example of the basic configuration for obtaining tomographic images. The difference from the previous example is that in this example, the X-rays generated by target 5 are directed toward the sample (
(not shown) and then detected by the X-ray detector 10 instead of by the photoelectric conversion film. Although a plurality of X-ray detectors 10 are provided, as shown in the figure, when the electron beam 4 is irradiated to the point P1 position,
The X-ray image detected by the X-ray detector 10 located at
X detected by the X-ray detector 10 located at
If the line image and the line image are added by the addition circuit 11, the images at the focal plane 3 are blurred, and the tomographic image at the focal plane 3 as a result of the addition is displayed on the monitor 12. It is said to be observable. Although the number of X-ray detectors 10 is two in this example, it may be three or more.

Although other fundamental configurations of the X-ray tomography apparatus can be considered, the specific configuration based on this will be described later. Further, in order to obtain a high-resolution tomographic image, it is desirable that the thickness of the target be as thin as possible, but this will also be described later.

[Example] Hereinafter, the present invention will be explained with reference to FIGS.

First, the X-ray tomography apparatus according to the present invention will be described. FIG. 1 shows the configuration of an example thereof. In this case, the electrons generated by the filament 13 in a high temperature state are accelerated by the accelerator tube 14, and are converged by the converging lens 15 so as to be irradiated onto the target 5 as an electron beam. X-rays are generated from the target 5 by this irradiation, but the wavelength of the generated X-rays depends on the accelerating voltage of the electron beam, and since there is an appropriate X-ray wavelength depending on the sample, It has become desirable for the acceleration voltage to be variable.

For example, it is sufficient if the variable range is set to 10 to 200 kV. The material for the target 5 is preferably a heavy element with a high melting point; for example, tungsten is suitable as the material. More preferably, in order to prevent the target 5 from melting due to the heat generated by the target 5, the heat may be released to a cooling medium in the tank, such as liquid nitrogen, through the cooling rod 40. As the cooling rod 40, copper, which is considered to have good heat conduction, is suitable. By the way, since the electron irradiation system needs to be housed and maintained in a vacuum atmosphere, it is housed inside a vacuum container. The vacuum container can be evacuated by a vacuum pump 21 via a valve 22 to obtain a vacuum atmosphere. In this case, the target 5 may be configured as part of a vacuum container that separates the vacuum from the atmosphere. As for the target 5 itself, if its thick film is made thinner, the X-ray generating region will be sandwiched closer to the point light source, and the resolution of the X-ray image will be improved. Based on this, it can be said that it is desirable that the film thickness of the target 5 is thin, but since atmospheric pressure is applied to the target 5, there is a limit to how thin it can be in terms of mechanical strength. ing. This problem can be solved by providing an X-ray extraction window separate from the target 5 to separate the vacuum from the atmosphere, or by placing the sample chamber in a vacuum atmosphere as well.

Now, when the electron beam is in a convergent state, the coil 16 is connected to the drive circuit 2.
4, the target 5 is scanned along a circular orbit, and the X-rays generated from the target 5 during this scanning pass through the sample 32 placed on the stage 17, and undergo photoelectric conversion. The film 6 is irradiated with light. At this time, the stage 17 is of a transmission type, and the optical path of the X-rays is not obstructed, but when the photoelectric conversion film 6 is irradiated with the X-rays, photoelectrons are generated from the photoelectric conversion film 6 due to the photoelectric effect. It looks like this. As the photoelectric conversion film 6, for example, metals such as gold and silver, and films such as CsI, KCI, and CsBr are used.

The photoelectron image on the photoelectric conversion film 6 is formed on the fluorescent screen 18 by the lens 8. At this time, the coil 7 is driven by the drive circuit 24 in synchronization with the scanning of the electron beam by the coil 16. , the photoelectron images at each position on the photoelectric conversion film 6 are sequentially formed on the fluorescent screen 18, so that the sample 3
The tomographic image in 2 is obtained. As the lens 8 at that time, either an electrostatic type or a magnetic field type may be used.
For example, immersion objective electro
Static lenses are now being used. Note that since the photoelectronic imaging system also needs to be housed and maintained in a vacuum atmosphere, it is housed in a vacuum container. The inside of the vacuum container is connected to the vacuum pump 2 via the valve 23.
It is designed to be exhausted at 1. In this case, the photoelectric conversion film 6 and the fluorescent screen 18 can be used as part of the partition wall separating the vacuum and the atmosphere.

As described above, the fluorescent screen 18 is converted into a photoelectronic image or an optical image.The fluorescent screen 18 is made of a fluorescent substance that emits fluorescence when irradiated with electrons, such as P-46, P-20, or YAG ( Yttrium Aluminum
m Garn-et), Y A P (Yttrium
A single crystal of aluminum perovskite is preferred. The optical image on the fluorescent screen 18 is the lens 1
9 is detected by the TV camera 20, and the monitor 12
However, the lens 19 is preferably one with a large numerical aperture and is bright, such as an objective lens for a microscope, and the TV camera 20 is required to have high sensitivity. S I T (Silicon
1ntensifier Target Tube)
A camera is preferred.

As described above, the optical image on the fluorescent screen 18, that is, the sample 32
The tomographic image inside is displayed on the monitor 12, and the depth of focus of the tomographic image can be easily changed by changing the diameter of the trajectory (circular orbit) on the target 5 of the convergent electron beam irradiated onto the target 5. It has become something that can be done. That is, if the diameter is made smaller, the depth of focus becomes deeper, and if the diameter is made larger, the depth of focus becomes shallower. Needless to say, at this time, the excitation force of the coil 7 can be changed together with the excitation force of the coil 16. The height of the tomographic image can be changed by moving the stage 17 up and down, or by changing the excitation force of the coil 7 and changing the radius of rotation of the photoelectron image. Also, sample 3
2 is large, an image of the entire surface of the sample 32 can be obtained by moving the stage 17 within the XY plane. Furthermore, although the electron beam is scanned in a circular trajectory in the above description, the electron beam may be scanned in a trajectory other than this, for example, a linear trajectory.

Here, to explain an example of a target that generates X-rays, in order to improve the resolution of the detected X-ray image,
As already mentioned, it is necessary to miniaturize the X-ray source. Since the X-ray generation area depends on the electron scattering area within the target, in order to reduce the X-ray generation area, the thickness of the target must be reduced. In order to reduce the X-ray generation area to 1 μm or less, the target itself should have a thickness of 1 μm, but such a thickness cannot be said to have sufficient mechanical strength. Particularly when the target is used as a barrier between a vacuum and the atmosphere, atmospheric pressure is directly applied to the target, which requires considerable mechanical strength. Furthermore, considering that most of the energy of the electron beam irradiated onto the target is converted into heat, the thinness of the target is disadvantageous from the viewpoint of heat conduction as well. In order to solve these problems, it is sufficient to configure the target as shown in FIG.

That is, FIG. 5 shows a cross section of the target, and as can be seen from this, the target has a sufficiently thin X-ray generating layer 25 and a layer 25 for increasing the mechanical strength of the X-ray generating layer 25. It is composed of a holding layer 26. The X-ray generation layer 25 is made of a heavy element, and the retention layer 26 is made of a light element. However, since the amount of X-ray generation is proportional to the atomic number of the target, the retention layer 26 is made of a heavy element compared to the X-ray generation layer 25.
The amount of X-rays generated is negligible. Therefore, it is considered that X-rays are generated in the X-ray generation layer 25, which is a narrow region, and moreover, the X-rays from the X-ray generation layer 25 are not absorbed at all in the retention layer 26, which is a light element, and are transmitted as they are. It has become. In this way, although the X-ray generating layer 25 itself is thin and its strength is not sufficient,
The mechanical strength is reinforced by the holding layer 26, and the generated heat is conducted to the holding layer 26, so that although the X-ray generation area is small, the target has sufficient mechanical strength and is resistant to heat. That's what you get. The X-ray generating layer 25 itself may be directly or indirectly cooled with liquid nitrogen. Incidentally, heavy metals such as tungsten, gold, and molybdenum are preferred as specific constituent elements of the X-ray generation layer 25, and as constituent materials of the retention layer 26, in addition to silicon and aluminum, nitride compounds ( silicon nitride (SiN), boron nitride (BN)), silicon carbide (SiC), beryllium, organic materials (
A single layer film or a composite film of polyimide, etc.) is suitable.

FIG. 6 shows the configuration of an X-ray detection section that detects X-rays with high sensitivity. Since the X-rays generated by electron beam excitation are weak, the X-rays generally need to be detected with high sensitivity.

In the example shown in FIG. 1, the sensitivity was improved by using a highly sensitive TV camera 20, but in this example, a microchannel plate 27 is arranged in front of the fluorescent screen 18, High sensitivity has been achieved by multiplying the electron image. Even in this case,
It is better to use a highly sensitive TV camera 20.

FIG. 7 shows another configuration of the X-ray detection section which can be used as a highly sensitive X-ray detector.

As shown in the figure, the photoelectron image on the photoelectric conversion film 6 is formed on a microchannel plate 27 via a lens 8, multiplied, and then detected by a two-dimensional sensor 28. As the two-dimensional sensor, a CCD, a photodetector tube, etc. are being used.

FIG. 8 shows the configuration of another example of the X-ray tomography apparatus according to the present invention. In this example, the target is irradiated with a focused electron beam, and until the target generates X-rays, the first
It is similar to the one shown in the figure. A substantial difference is that the X-rays that have passed through the sample 32 are selectively detected by a plurality of X-ray detectors 29 arranged on the circumference. In this case, each X-ray detector 29 is a two-dimensional X-ray detector, such as a combination of an X-ray image intensifier and a TV camera, or an X-ray imaging tube. The synchronous circuit 31 includes a drive circuit 30 that drives the coil 16 and a changeover switch 3.
By synchronizing with the switching in step 3, X-rays transmitted through the same point in the sample 32 can be detected from among the outputs of each of the multiple X-ray detectors 29 according to the X-ray generation point. ,
Either one can be selectively obtained by a changeover switch 33. If the convergent electron beam is made to circle around the target 5 by the coil 16, the changeover switch 3
Since the switching at 3 is also repeated once, X-ray detection images corresponding to the number of X-ray detectors 29 can be sequentially obtained from the changeover switch 33. These images are sequentially added by the image addition circuit 34 to obtain a single image, which is then displayed on the monitor 12. However, in the image obtained in this way, images other than the focal plane are blurred. It is obtained as a tomographic image. Note that the overall arrangement of the plurality of X-ray detectors 29 corresponds to the scanning trajectory of the convergent electron beam,
A circular array may be used for a circular orbit, and a linear array may be used for a straight orbit.

FIG. 9 shows the configuration of still another example of the X-ray tomography apparatus according to the present invention. In this example, as in the previous example, the target is irradiated with a convergent electron beam, and the
The process is similar to that shown in FIG. 1 until lines are generated. The substantial difference is that the X-rays that have passed through the sample 32 are irradiated onto the fluorescent screen 35, and an optical image is formed on the fluorescent screen 35, but this optical image is arranged on the circumference. It is configured to be detected by the TV camera 20 through a lens 36 group and a shutter 37 group.

At that time, in the synchronous circuit 31, the drive circuit 30 and the driver 38
By operating these in synchronization, one of the plurality of shutters 37 can be selectively opened depending on the X-ray generation point. When the convergent electron beam makes one revolution around the target 5, the plurality of shutters 37 are also opened one after another, so that the shutters 37 are also placed in the exposure state one after another in the direction of one revolution. be. The TV camera 20 is configured to accumulate and detect images for one round in order to obtain a tomographic image, and then display the images on the monitor 12. In this example, an image fiber group may be used instead of the lens 36, and a plurality of PLZT shutters, liquid crystal shutters, mechanical shutters, etc. may be used as the shutter group 37; By rotating the board,
A similar effect can be obtained. Furthermore, as the TV camera 20, a high-sensitivity camera, such as an SIT camera, is used.
For example, YAG or YAP single crystal is suitable for the fluorescent screen 35. An X-ray image intensifier may be used instead of the fluorescent screen 35.

[Effects of the Invention] As explained above, in the cases according to claims 1 to 4, the tomographic image of the sample at the focal plane can be easily and easily changed from the tomographic image of the sample at the focal plane to the image at other than the focal plane. An X-ray tomography method is obtained in which a blurred state can be detected in real time, and especially in the case according to claim 4, a tomographic image is detected as a variable depth of focus.

Further, according to claims 5 to 9, the X-rays are configured such that the tomographic image of the sample at the focal plane can be detected in real time in a state where the tomographic image of the sample at the focal plane is blurred. A tomography device will be obtained.

Furthermore, claim 9. In the case of IO, an X-ray tomographic image can be detected with high resolution, and an X-ray generating target with high mechanical strength can be obtained.

[Brief explanation of drawings]

1, 8, and 9 are diagrams each showing a specific configuration of an X-ray tomography apparatus according to the present invention, and FIGS. 2, 3, and 4 are diagrams showing an X-ray tomography apparatus according to the present invention. Principles of photography methods,
FIG. 5 is a diagram for explaining the principle configuration of an X-ray tomography apparatus, and FIG. 6 is a diagram illustrating an example configuration of an X-ray generation target according to the present invention. FIG. 7 is a diagram showing a more desirable partial configuration of an X-ray tomography apparatus using a photoelectric conversion film. 4... (Convergent) electron beam, 5... Target (for X-ray generation), 6... Photoelectric conversion film, 7... Coil (for photoelectron scanning), 12... Monitor, 16...・Coil (for focused electron scanning), 18.35... Fluorescent screen, 19... Lens, 20... TV camera, 25... X-ray generation layer,
26... Retaining layer, 27... Microchannel plate, 29... X-ray detector, 32... Sample, 33...
...Selector switch, 34...Image addition circuit, 36...
・Lens, 37...Shutter, 40...Cooling rod, 4
1...Liquid nitrogen

Claims (1)

[Claims] 1. A focused electron beam is deflected and irradiated onto a target, and the X-rays generated from the target are detected through the sample, thereby blurring the image outside the focal plane, An X-ray tomography method in which a tomographic image at the focal plane is detected. 2. An X-ray tomography method for obtaining a tomographic image of a sample by irradiating a target with a focused electron beam and detecting X-rays generated from the target through the sample, the method comprising: deflection of the focused electron beam; While scanning the focused electron beam over the target, the transmitted X-rays from the sample were first photoelectrically converted and then electro-optically converted, thereby blurring the image outside the focal plane whose position was variable. An X-ray tomography method in which a tomographic image at the focal plane is detected in a state where 3. An X-ray tomography method for obtaining a tomographic image of a sample by irradiating a target with a focused electron beam and detecting X-rays generated from the target through the sample, the method comprising: deflection of the focused electron beam; The convergent electron beam is scanned over the target by scanning the target, while the transmitted X-rays from the sample are sequentially detected two-dimensionally at positions corresponding to each scanning position of the convergent electron beam, and then added, thereby changing the position. An X-ray tomography method in which a tomographic image at a focal plane is detected while images at focal planes other than the focal plane are blurred. 4. The X according to any one of claims 1 to 3, wherein the incident angle of the convergent electron beam with respect to the sample is variably set, so that a tomographic image at the focal plane is detected as a variable depth of focus. Linear tomography method. 5. An X-ray source that generates X-rays by irradiating a target with a focused electron beam, and a photoelectric conversion film that generates photoelectrons when irradiated with X-rays that have passed through a sample from the X-ray source. , an electron optical system for forming photoelectrons from the photoelectric conversion film as an optical image; a means for scanning a convergent electron beam on a target; and a means for synchronizing the photoelectrons from the photoelectric conversion film with the scanning of the convergent electron beam. An X-ray tomography apparatus comprising: scanning means; 6. An X-ray source that generates X-rays by irradiating a target with a focused electron beam, means for scanning the target with the focused electron beam, and 2 at positions corresponding to each scanning position of the convergent electron beam.
A plurality of X-ray detection means for dimensionally detecting image signals, means for sequentially selecting the output of the X-ray detection means according to each scanning position of the convergent electron beam, and X-ray detection from the means. An X-ray tomography apparatus comprising: means for sequentially adding outputs. 7. An X-ray source that generates X-rays by irradiating a target with a focused electron beam, means for scanning the target with the focused electron beam, and means for converting into an optical image; a plurality of imaging means for forming the optical images of the means onto an image detection surface; and opening and closing of the optical path of the imaging means at positions corresponding to respective scanning positions of the convergent electron beam. An X-ray tomography apparatus comprising: a means for detecting an image formed by the image forming means; and an accumulation type detecting means for detecting an image formed by the image forming means. 8. The X-ray tomography apparatus according to claim 5, wherein the electron optical system that forms the photoelectrons as an optical image is provided with means for multiplying the photoelectrons. 9. The X-ray tomography apparatus according to claim 5, further comprising means for detecting an image formed as an optical image by the electron optical system. 10. An X-ray generation target used in the X-ray tomography apparatus according to any one of claims 5 to 9, which has a multilayer structure of two or more types including a thin X-ray generation layer. Target for generating X-rays. 11. The X-ray generating target according to claim 10, comprising a thin X-ray generating layer and a holding layer for reinforcing the mechanical strength of the X-ray generating layer. 12. The X-ray generating target according to claim 10, comprising a thin X-ray generating layer and a retaining layer having good thermal conductivity. 13. The X-ray generator according to any one of claims 10 to 12, wherein the thin X-ray generating layer is coolable with liquid nitrogen.
Target for line generation.