JP2849491B2 - X-ray tomography method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for tomography of a sample using transmitted X-rays, and more particularly to an X-ray tomography method and an apparatus suitable for measuring the internal structure of a circuit board. is there.

[0002]

2. Description of the Related Art A device described in US Pat. No. 4,926,452 is known as a device for detecting a tomographic image at a certain focal plane inside a sample by using transmitted X-rays. In this case, the X-rays are scanned by scanning the focused electron beam on the target, and the detector for detecting the X-rays transmitted through the sample is scanned in synchronization with the focused electron beam, thereby scanning the sample. The tomographic image at a certain focal plane inside is
The image other than the focal plane is detected in a blurred state.

[0003]

However, in the case of the prior art, the focused electron beam is scanned on the target,
Since the X-rays are scanned, the diameter of the X-ray source irradiated on the sample cannot be reduced to a small value, and the tomographic image is detected as a blurred state.

A first object of the present invention is to provide an X-ray tomography method in which a tomographic image at a focal plane inside a sample is sharp, and an image other than the focal plane can be detected as a blurred state. To serve. A second object of the present invention is to provide an X-ray tomography apparatus in which a tomographic image at a focal plane inside a sample is sharp and an image other than the focal plane can be detected as a blurred state. is there.

[0005]

The first object of the present invention is basically to rotate a sample around a predetermined axis of rotation with respect to a fixed X-ray source and to rotate the sample in a fixed attitude state. By detecting transmitted X-rays from
This is achieved by obtaining a tomographic image at the focal plane inside the sample. The second object is basically to detect a transmitted X-ray from a sample in a predetermined manner when the sample is rotationally driven with respect to a fixed X-ray source in a position variable around a predetermined rotation axis and in an invariable posture state. This is achieved by configuring for processing.

[0006]

When the sample is rotated relative to a fixed X-ray source with a variable position around a predetermined rotation axis and the posture state is invariable, while transmitting X-rays from the sample are detected at each sample rotation driving position, At each of these rotational drive positions, the image on the focal plane inside the sample is always detected as the same position on the X-ray detection plane, but the image on the plane other than the focal plane inside the specimen has different positions on the X-ray detection plane. When cumulative addition processing or cumulative accumulation processing is performed on the transmitted X-ray images detected at each of the sample rotation drive positions, the tomographic image on a surface other than the focal plane inside the sample is blurred. The tomographic image at the focal plane inside the sample can be clearly detected.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to FIGS. Before describing the present invention in detail, the principle of the X-ray tomographic imaging will be briefly described.
It shows the principle of line tomography. In this case,
The focal plane (present inside the sample) 1 and the film 2 are synchronously driven to rotate about the same rotation axis. FIG. 2 shows the rotational movement of the sample at this time as a plane.
As shown in the figure, the sample 3 is driven to rotate around a rotation axis including the fixed X-ray source 4 with a constant radius, and the center position thereof is variable as if it exists on the circumference. Are rotationally driven invariably. Such a situation is the same for the film 2 which is driven to rotate in synchronization with the sample 3. Therefore, assuming that the sample 3 and the film 2 are synchronously driven around the same rotation axis as described above, the point C on the focal plane 1 is always photographed at the same position on the film 2. The other points A and B which do not exist on the focal plane 1 are not photographed at the same position on the film 2. This means that the points A and B are blurred and a tomographic image on the focal plane 1 is obtained. Moreover, at that time, sample 3
When the turning radius of the sample 3 is set to be variable so that the incident angle of X-rays to the sample can be changed, a tomographic image on the focal plane 1 is obtained as a variable depth of focus.

FIG. 3 also shows X based on such a principle.
1 shows a principle configuration of an example of a line tomography apparatus. In this case, the target 6 is irradiated with the electron beam 5 in a converging state, so that the fixed X-ray source 4
It functions as. The X-rays generated by the target 6 by the irradiation of the electron beam 5 are detected as a two-dimensional image by the X-ray detector 7 corresponding to the above-described film 2 via the sample 3. Are not rotationally driven, but are instead provided on the same circumference in a plurality corresponding to the predetermined rotational drive positions of the sample 3. Therefore, when the sample 3 is sequentially driven to rotate at each of the predetermined rotational drive positions, the X-ray transmission images are sequentially formed at the X-ray detectors 7 provided corresponding to each of the rotational drive positions, and the X-ray transmission images are sequentially focused on the inside of the sample 3. This can be detected as a tomographic image on the surface 1. However, in each of these tomographic images, the image on the plane other than the focal plane 1 has not been blurred yet, so that the tomographic images are sequentially cumulatively added by the image adding circuit 8 in order to blur the image on the plane other than the focal plane 1. It is something to be done. The image on the plane other than the focal plane 1 is blurred by the cumulative addition, and the tomographic image on the focal plane 1 is clearly obtained and can be displayed on the monitor 10.
In this example, two X-ray detectors 7 are provided, but two or more X-ray detectors 7 are generally provided at equal circumferential angles on the circumference.

As described above, the principle of X-ray tomography and X-ray
The principle configuration of the line tomography apparatus has been described. next,
If the X-ray tomography apparatus according to the present invention is specifically described,
FIG. 4 shows a specific configuration in one example. According to this, in the electron irradiation system, the electrons generated by the filament 13 in the high heat state are accelerated by the accelerating tube 14 and irradiated onto the target 6 as an electron beam converged by the converging lens 15. Has become. As a result, X-rays are generated from the target 6. In this case, the wavelength of the generated X-rays depends on the acceleration voltage of the electron beam.
Given the wavelength of the line, it is desirable that the acceleration voltage is variable, and it is sufficient if the variable range is set to 10 to 200 kV. As a material of the target 6, a heavy element and a material having a high melting point are desirable, and for example, tungsten is suitable. Further, in order to prevent the target 6 itself from being melted by the heat generated in the target 6, heat from the target 6 is transferred to a tank 32 through a cooling rod (a material is suitably a metal having a high thermal conductivity such as copper). Care must be taken to escape the cooling medium 31 inside, for example, liquid nitrogen. On the other hand, the electron irradiation system is housed inside a vacuum vessel so as to be placed in a vacuum atmosphere. The inside of the vacuum vessel is evacuated by a vacuum pump 22 through a valve 23, so that the electron irradiation system is placed in a vacuum atmosphere. Configurable. However, it is necessary that the target 6 itself be thin in order to improve the resolution of the X-ray image. This is because the smaller the thickness, the smaller the X-ray generation area and closer to the point light source, so that the resolution of the X-ray image is improved accordingly. Therefore, in order to appropriately satisfy conflicting demands such as improvement of the mechanical strength and resolution of the target 6 itself, an X-ray extraction window separating the vacuum and the atmosphere is provided separately from the target 6, or the sample chamber is also provided. It is conceivable to place it in a vacuum atmosphere.

Now, X-rays are generated from the target 6 by electron beam irradiation, and the X-rays pass through the sample 3 which is in a rotationally driven state, and a photoelectric conversion film (a part of an electron optical system) is formed. For example, metals such as gold and silver, CsI, KCl, Cs
(A thin film of Br or the like) 16. Although the sample 3 is placed on the stage 11, the sample 3 is in a rotationally driven state because the stage 11 is rotationally driven by the drive circuit 12.
At this time, since the stage 11 is of the X-ray transmission type, its presence does not hinder the X-ray optical path. In any case, when the transmitted X-rays from the sample 3 are irradiated on the photoelectric conversion film 16, photoelectrons are generated as a photoelectron image from the X-ray irradiation region of the photoelectric conversion film 16 by the photoelectric effect. In this way, the photoelectron image generated on the photoelectric conversion film 16 is then formed on the fluorescent screen 19 by a lens (either an electrostatic type or a magnetic field type can be used) 18. If the coil 17 is driven by the drive circuit 12 in synchronization with the rotational drive scanning of the stage 11 by the drive 12, the photoelectron images at each position on the photoelectric conversion film 16 are successively displayed on the fluorescent screen 19.
By forming an image on the top, a tomographic image of the inside of the sample 3 is obtained. In addition, in order to accommodate the electron optical system in a vacuum atmosphere, a vacuum container therefor is evacuated by a vacuum pump 22 through a valve 24, so that the electron optical system is placed in a vacuum atmosphere. At this time, the photoelectric conversion film 16 and the fluorescent plate 19 can be used as a part of the partition wall separating the vacuum and the atmosphere.

As described above, the photoelectron image is converted into an optical image on the fluorescent screen 19,
A phosphor that emits fluorescence when irradiated with electrons, for example, P-
46, YAG (Yttrium Aluminum Garnet), YAP (Ytt
rium Aluminum Pero-vskite) is preferred. The optical image on the fluorescent screen 19 is detected by the TV camera 21 via the lens 20 and can be observed on the monitor 10. The lens 20 used at that time has a large numerical aperture and is bright, for example, a microscope. Is preferable, and the TV camera 21 is required to have high sensitivity. For example, an SIT (Silicon intensifier Tar
get Tube) cameras are preferred.

FIGS. 5 and 6 show the construction of an X-ray detecting section (electro-optical system) for enabling the X-ray tomography apparatus to detect X-rays with high sensitivity. Generally, X-rays generated by electron beam excitation are weak, so that transmitted X-rays from the sample 3 need to be detected with high sensitivity. In the configuration shown in FIG.
By using a camera 21 with high sensitivity, transmitted X-rays from the sample 3 are detected with high sensitivity as a result, but in the example shown in FIG. The photoelectron image is multiplied by 33 and converted into an optical image by the fluorescent screen 19. Also in this case, it is desirable to use a high-sensitivity TV camera 21. FIG.
In this case, the photoelectron image on the photoelectric conversion film 16 is formed and multiplied by the microchannel plate 33 via the lens 18 and then detected by the two-dimensional sensor 34 such as a CCD or an image pickup tube. ing.

FIG. 7 shows a specific configuration of another example of the X-ray tomography apparatus according to the present invention, which is a more specific example of the basic configuration of the X-ray tomography apparatus according to the present invention shown in FIG. Things. The point substantially different from that shown in FIG.
Is selectively detected by the two-dimensional X-ray detector 7 arranged on the circumference. In this case, as the X-ray detector 7, an X-ray image
A combination of an intensifier and a TV camera, or an X-ray imaging tube has been used. At this time, the synchronization circuit 29 synchronizes the rotation of the sample 3 by the drive circuit 12 with the switching by the changeover switch 35. Thus, while the sample 3 is driven by one rotation, the X-rays transmitted through the sample 3 are sequentially detected two-dimensionally in each of the plurality of X-ray detectors 7 and are obtained from the changeover switch 35. . Changeover switch 35
The X-ray images sequentially obtained through the image adder 8 are cumulatively added by an image adding circuit 8, and then the blurred image other than the focal plane is deleted by the image processing device 9, so that the image is monitored as one X-ray tomographic image. 10 is displayed.

FIG. 8 shows a specific configuration of another example of the X-ray tomography apparatus according to the present invention. In this example, the X-ray transmitted through the sample 3 is converted into an optical image by the fluorescent screen 25, and is detected by the TV camera 21 via the group of lenses 26 and the group of shutters 27 arranged on the circumference. It is that you are. While the sample 3 is rotationally driven by the synchronization circuit 29 via the drive circuit 12 and the stage 11, each time the sample 3 is sequentially rotated to a predetermined rotational drive position, a shutter corresponding to the rotational drive position is opened. Thus, the optical images corresponding to the respective predetermined rotational drive positions on the fluorescent screen 25 are sequentially accumulated by the TV camera 21. One X-ray tomographic image is obtained as a state in which an image other than the focal plane is blurred by accumulative addition of a plurality of optical images, and can be displayed on the monitor 10.

FIG. 9 shows the structure of another different example of the X-ray tomography apparatus according to the present invention. In this case, the sample 3 is rotationally driven through the stage 11, but the X-ray transmitted through the sample 3 is fixed on the X-ray detector 7 according to each predetermined rotational drive position of the sample 3. Are detected two-dimensionally in different areas. That is, in the configuration shown in FIG. 7, a plurality of X-ray detectors 7 are required, but in this example, a transmitted X-ray image is detected on the fixed X-ray detector 7 having a large detection surface. It has become something. In the image processing device 36, the detected transmission X-ray image is collected and accumulated as if the X-ray detector 7 was rotationally driven in synchronization with the sample 3, and the transmitted transmission X-ray image was collected in the image addition circuit 8. X-ray images are cumulatively added. From the cumulatively added transmission X-ray images, the blurred image other than the focal plane is deleted by the image processing device 9 and displayed on the monitor 10 as one tomographic image on the focal plane. ing.

The X-ray tomography method and apparatus according to the present invention have been described above. However, other methods for obtaining an X-ray tomographic image are also conceivable. For example, even if the sample and the X-ray detecting means are synchronized and tilted, or the sample and the X-ray detecting means are linearly driven in synchronization with each other in the opposite direction while maintaining a parallel state, This is because an X-ray tomographic image can be obtained as a desired state. Incidentally, a method for obtaining an X-ray tomographic image by synchronizing and tilting the sample and the X-ray detection means will be described below.

FIG. 10 shows the principle of the X-ray tomography. As shown, the focal plane 1 inside the sample and the film 2 are tilted synchronously. In this case as well, the point C on the focal plane 1 is at the same position on the film 2 regardless of the tilt state. Other points A and B which are photographed but not on the focal plane 1 are photographed at positions corresponding to the inclined state, and cannot be photographed at the same position on the film 2 regardless of the inclined state. ing. As a result, the image in the area other than the focal plane 1 is
An X-ray tomographic image can be obtained. FIG. 11 shows a principle configuration of an X-ray tomography apparatus based on the X-ray tomography principle. As shown, the focal plane 1 inside the sample and the X-ray detector 7 are tilted in synchronization with each other, but the X-rays transmitted through the sample in each tilt state are transmitted X-ray images by the X-ray detector 7. Is detected in two dimensions,
By accumulating the transmitted X-ray images in the image addition circuit 8, the images other than the focal plane 1 are blurred.
An X-ray tomographic image on the focal plane 1 is obtained, and the monitor 10
It is displayed above. FIG. 12 shows the specific configuration. As shown, the sample 3 and the X-ray detector 7 are tilted synchronously by the drive circuit 12, and each time the tilt state is updated, the transmitted X-rays are sequentially detected and accumulated by the X-ray detector 7. The images are cumulatively added by the image adding circuit 8. Cumulatively added transmission X
The X-ray tomographic image on the focal plane 1 is displayed on the monitor 10 by removing the blurred image of the line image other than the focal plane by the image processing device 9.

[0018]

As described above, according to claims 1 to 5,
The tomographic image at the focal plane inside the sample is sharp, and the image at other than the focal plane is detectable as a blurred state.
In the case of the line tomography method according to claims 6 to 11, the tomographic image at the focal plane inside the sample is sharp, and the image other than the focal plane is detectable as a blurred state. An X-ray tomography apparatus can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the principle of X-ray tomography according to the present invention.

FIG. 2 is a view for explaining a rotational movement of a sample on the principle of X-ray tomography according to the present invention;

FIG. 3 is a diagram showing a basic configuration of an example of the X-ray tomography apparatus according to the present invention;

FIG. 4 is a diagram showing a specific configuration of an example of an X-ray tomography apparatus according to the present invention.

FIG. 5 is a diagram showing another configuration of an X-ray detection unit in the X-ray tomography apparatus.

FIG. 6 is a diagram showing another configuration of the X-ray detector in the X-ray tomography apparatus.

FIG. 7 is a diagram showing a specific configuration of another example of the X-ray tomography apparatus according to the present invention.

FIG. 8 is a diagram showing a specific configuration of another example of the X-ray tomography apparatus according to the present invention.

FIG. 9 is a diagram showing a specific configuration of still another different example of the X-ray tomography apparatus according to the present invention.

FIG. 10 is a view for explaining another principle of X-ray tomography different from the principle of X-ray tomography according to the present invention;

FIG. 11 is a diagram showing a basic configuration of an example of an X-ray tomography apparatus based on another principle of X-ray tomography;

FIG. 12 is a diagram showing a specific configuration of an example of an X-ray tomography apparatus based on another principle of X-ray tomography;

[Explanation of symbols]

1 focal plane, 2 film, 3 sample, 4 X-ray source, 5
... Electron beam, 6 ... Target, 7 ... X-ray detector, 8 ... Image addition circuit, 9 ... Image processing device, 10 ... Monitor, 11 ... Stage, 12 ... Drive circuit, 13 ... Filament, 14 ...
Accelerator tube, 15: converging lens, 16: photoelectric conversion film, 17:
Coil, 18 lens, 19 fluorescent plate, 20 lens,
21: TV camera, 22: vacuum pump, 23: valve,
Reference numeral 24: bulb, 25: fluorescent plate, 26: lens group, 27:
Shutter group, 28 ... Driver, 29 ... Synchronous circuit, 30 ...
Cooling rod, 31 cooling medium, 32 tank, 33 microchannel plate, 34 two-dimensional sensor, 35 changeover switch, 36 image processing device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04N 5/30-5/335 G01N 23/00-23/227 G01B 15/00-15/08

Claims (11)

(57) [Claims] An X-ray from a fixed X-ray source is detected by an X-ray detecting means via a sample, and the sample and the X-ray detecting means are positioned in different planes around the same rotation axis, and are variable in position and posture. An X-ray tomography method in which a tomographic image at a focal plane inside the sample is detected by synchronously rotating and driving as a state invariant. 2. A sample is fixed at a variable position around a predetermined rotation axis and in a constant posture state so that X-rays from a fixed X-ray source are detected by a plurality of fixed X-ray detecting means via the sample. Each time the angle rotation is driven, the tomographic image at the focal plane inside the sample is detected by the fixed X-ray detection means provided corresponding to the fixed angle rotation drive position, and the fixed X-ray detection means An X-ray tomography method in which a tomographic image at a focal plane inside a sample is detected by sequentially accumulating the detected tomographic images. 3. In a state in which the sample is rotated around a predetermined rotation axis so as to be variable in position and invariable in attitude so that X-rays from a fixed X-ray source are detected through the sample, the sample is rotated. An X-ray tomography method in which a transmitted X-ray is once photoelectrically converted and then subjected to electro-optical conversion so that a tomographic image at a focal plane inside the sample is detected. 4. Each time the sample is sequentially driven to rotate at a constant angle as a variable position and a constant posture state around a predetermined rotation axis so that X-rays from a fixed X-ray source are detected through the sample. The X-rays passing through the sample are converted into optical images, and the optical images corresponding to each rotational drive position of the sample at a constant rotation angle are sequentially accumulated and accumulated, so that a tomographic image on the focal plane inside the sample is detected. X-ray tomography method to be performed. 5. A sample is assumed to be variable in position around a predetermined rotation axis and invariable in attitude so that X-rays from a fixed X-ray source are detected as a tomographic image at a focal plane inside the sample via the sample. An X-ray tomography method wherein the sample is driven to rotate with a variable radius of rotation when the sample is driven to rotate. 6. A fixed X-ray source for generating X-rays, photoelectric conversion means for generating photoelectrons by irradiation of X-rays transmitted through a sample from the X-ray source, and optically converting the photoelectrons from the photoelectric conversion means. An electron optical system that forms an image, a means for rotating the sample around a predetermined rotation axis, a means for rotating and rotating the sample in an invariable state, and synchronizing photoelectrons from the photoelectric conversion means with the rotation of the sample. X-ray tomography apparatus comprising: a scanning unit. 7. A fixed X-ray source for generating X-rays, means for rotating a sample around a predetermined rotation axis in a variable position and in an invariable posture state, and means for rotating the sample by a fixed angle. The transmission X from the sample at the fixed angle rotation drive position
An X-ray tomography apparatus comprising: a plurality of fixed X-ray detecting means for detecting a line as a two-dimensional image; and image adding means for sequentially accumulating and adding image detection outputs from each of the X-ray detecting means. 8. A fixed X-ray source for generating X-rays, means for rotating the sample around a predetermined rotation axis in a variable position and invariable posture state, and rotating the sample from the fixed X-ray source. Optical image conversion means for converting transmitted X-rays into an optical image;
A plurality of imaging means for forming an optical image on the common image detection surface by the conversion means, and an optical path opening / closing means for opening / closing an optical path of the imaging means at a position corresponding to each fixed angle rotation drive position of the sample,
Storage type detecting means for detecting an image sequentially formed on the common image detecting surface by each of the image forming means.
Line tomography equipment. 9. A fixed X-ray source for generating X-rays, photoelectric conversion means for generating photoelectrons by irradiation of X-rays transmitted through a sample from the X-ray source, and optically converting the photoelectrons from the photoelectric conversion means. An electron optical system for forming an image, a photomultiplier for multiplying photoelectrons in relation to the optical system, and the sample is rotated around a predetermined rotation axis so that its position is variable and its posture state is invariable. An X-ray tomography apparatus comprising: a scanning unit that scans the photoelectrons from the photoelectric conversion unit in synchronization with the rotation of the sample. 10. A fixed X-ray source for generating X-rays, photoelectric conversion means for generating photoelectrons by irradiation of X-rays transmitted through a sample from the X-ray source, and optically converting the photoelectrons from the photoelectric conversion means. An electron optical system that forms an image, a means for rotating the sample around a predetermined rotation axis, a means for rotating and rotating the sample in an invariable state, and synchronizing photoelectrons from the photoelectric conversion means with the rotation of the sample. An X-ray tomography apparatus comprising: a scanning unit; and an optical image detecting unit configured to detect an image formed as an optical image by the electron optical system. 11. A fixed X-ray source for generating X-rays, photoelectric conversion means for generating photoelectrons by irradiation of X-rays transmitted through a sample from the X-ray source, and optically converting the photoelectrons from the photoelectric conversion means. An electron optical system for forming an image, a photomultiplier for multiplying photoelectrons in relation to the optical system, and the sample is rotated around a predetermined rotation axis so that its position is variable and its posture state is invariable. Means, and means for scanning the photoelectrons from the photoelectric conversion means in synchronization with the rotational drive of the sample,
An X-ray tomography apparatus having an optical image detecting means for detecting an image formed as an optical image by the electron optical system.