Patent Description:
As one of industry nondestructive inspection apparatus, an X-ray image capture system is known. For example, an X-ray inspection apparatus having a micro focus X-ray tube is used for inspection of electronic devices represented by a semiconductor integrated circuit substrate. An X-ray tube is an X-ray source emitting an X-ray from a target by applying a high voltage with a predetermined potential difference in accordance with X-ray energy between an anode and a cathode and emitting electrons accelerated by this high voltage to the target.

The resolution in an X-ray image capture system is improved when the X-ray focal spot diameter is smaller. Thus, conventionally, various technologies for achieving a fine X-ray focal spot diameter have been proposed. Patent Literature <NUM> proposes a technology that, by providing a fine recess (X-ray low absorbance part) in a target having a large thickness so that an X-ray is unable to transmit to the opposite side to the irradiation side of an electron beam (which will be absorbed inside the target) even if the electron beam is emitted to a target and the X-ray is generated, achieves an X-ray focal spot diameter based on the diameter size of the X-ray low absorbance part regardless of the size of the incident region of the electron beam to the target (electron beam spot). Further, Patent Literature <NUM> proposes a technology that, by providing a shield layer that shields a target from an electron beam on the electron beam irradiation side of the target and providing a fine opening in the shield layer, achieves an X-ray focal spot diameter based on the diameter size of the opening regardless of the size of the spot diameter of the electron beam.

As discussed above, in the technologies disclosed in Patent Literature <NUM> and Patent Literature <NUM>, the X-ray focal spot diameter of an X-ray generation device is defined by a diameter size of a recess or an opening formed in advance in a target or a target stack structure. It is therefore necessary to apply fine processing of a desired X-ray focal spot diameter size to the target or the target stack structure.

<CIT> discloses microfocus X-ray equipment for enlarging radiographic short-time recordings, a focussed electron beam for the production of X-radiation impinges on the retarding material of a target. In this case, the retarding material in the focal spot passes over into the liquid aggregate state due to the high thermal loading. For this reason, the equipment is operated in pulsed operation, wherein the position of the focal spot on the target is, when each loading occurs, displaced relative to the previous position. The retarding material is arranged in a retarding layer on a carrier layer and the electron beam impinges on the retarding layer oriented perpendicularly to the electron beam. A control interrupts the irradiation at the latest when the carrier layer starts to melt.

As a method for achieving a fine X-ray focal spot diameter without depending on the size of such a recess or an opening, there is a method for reducing an incident region (spot) of an electronic beam to a target plane. The spot diameter of an electronic beam depends on X-ray emission conditions (a tube voltage and a tube current) and an applied voltage (focus voltage) to a convergence electrode that converges electrons moving from a cathode including an electron source to an anode including a target. Since the X-ray emission condition is determined in accordance with an object, the spot diameter of an electron beam is reduced by adjusting the focus voltage for a desired X-ray emission condition. Adjustment of the focus voltage is performed by applying various voltages to the convergence electrode under a desired X-ray emission condition to acquire X-ray transmission images, performing image processing on respective X-ray transmission images to finely compare the resolution, and determining a focus voltage providing the highest resolution (just focus voltage). However, such a method of adjusting the focus voltage requires significant efforts.

The present invention intends to provide an X-ray generation device that may easily reduce the X-ray focal spot diameter.

In accordance with the present invention, there is provided an X-ray generation device as recited by claim <NUM>. Preferred features are set out in the dependent claims.

According to the present invention, the X-ray focal spot diameter can be easily reduced.

A general configuration of an X-ray generation device according to a first embodiment of the present invention will be described with reference to <FIG> is a schematic sectional view illustrating a configuration example of an X-ray generation device according to the present embodiment.

As illustrated in <FIG>, an X-ray generation device <NUM> according to the present embodiment includes an X-ray tube <NUM>, a drive circuit <NUM>, a control unit <NUM>, an electron beam deflection unit <NUM>, and a storage device <NUM>. It is preferable that, among these components, at least the X-ray tube <NUM> and the drive circuit <NUM> be arranged in a housing container <NUM>. In the housing container <NUM>, an insulating oil <NUM> may be filled in order to ensure a dielectric voltage between components arranged therein. The insulating oil <NUM> is preferably an electric insulating oil such as a mineral oil, a silicone oil, a fluorine based oil, or the like. A resin may be used instead of an insulating oil. A mineral oil that is easy to handle is preferably applied to an X-ray generation device using the X-ray tube <NUM> whose rated tube voltage is around <NUM> kV.

The X-ray tube <NUM> includes an electron source <NUM>, a grid electrode <NUM>, a convergence electrode <NUM>, and an anode <NUM>. The cathode includes the electron source <NUM>. The anode <NUM> includes an anode member <NUM>, a target <NUM>, and a target support <NUM>. The electron source <NUM>, the grid electrode <NUM>, and the convergence electrode <NUM> are connected to the drive circuit <NUM> and desired control voltages are applied thereto from the drive circuit <NUM>, respectively. The anode <NUM> is connected to the housing container <NUM> maintained at a ground potential.

The electron source <NUM> is not particularly limited, and a hot cathode such as a tungsten filament or an impregnated type cathode or a cold cathode such as a carbon nanotube can be applied, for example. The material forming the target <NUM> is preferably a material having a high melting point and a high X-ray generation efficiency, and tungsten, tantalum, molybdenum, an alloy thereof, or the like can be applied, for example. The target <NUM> used in the present invention is a transmission type target having a thickness that enables a generated X-ray to transmit to the opposite side to the irradiation side of electrons. The target support <NUM> supports the target <NUM> and forms an X-ray transmission window used for emitting an X-ray from the target <NUM> to the outside. The material forming the target support <NUM> is preferably a material having a high X-ray transmissivity and a high thermal conductivity, and diamond can be applied, for example. A use of a material having a high thermal conductivity has an advantageous effect of suppressing a rise in temperature of the target <NUM> due to electron beam irradiation and reducing deterioration of the target <NUM>.

Electrons emitted from the electron source <NUM> are accelerated by a high voltage with respect to the anode <NUM> to generate an electron beam, this electron beam is collided to the target <NUM> provided in the anode <NUM>, and thereby an X-ray is generated at the target <NUM>. The X-ray dose emitted from the target <NUM> can be controlled by the electron beam amount emitted to the target <NUM>. The electron beam amount emitted to the target <NUM> can be controlled by a grid voltage applied to the grid electrode <NUM>. Further, the spot diameter of the electron beam can be controlled by a focus voltage applied to the convergence electrode <NUM>.

The electron beam deflection unit <NUM> is provided outside the tube (outside) of the X-ray tube <NUM> and between the cathode and the anode <NUM>. For example, the electron beam deflection unit <NUM> is provided between the convergence electrode <NUM> and the target <NUM>. Further, the electron beam deflection unit <NUM> has a function of causing a magnetic field to work on an electron beam generated inside the X-ray tube <NUM> and deflecting the trajectory of an electron beam entering the target <NUM> and is configured to be able to switch incident positions of the electron beam. The electron beam deflection unit <NUM> may be one or more permanent magnets or may be one or more electromagnets. For example, as illustrated in <FIG>, the electron beam deflection unit <NUM> may include two permanent magnets, and the two permanent magnets are arranged around the X-ray tube <NUM> such that the S-pole of one permanent magnet faces the N-pole of the other permanent magnet in the tube diameter direction. Alternatively, the electron beam deflection unit <NUM> may be a single permanent magnet arranged around the X-ray tube <NUM> such that the magnetic pole is oriented to the tube diameter direction.

Note that the electron beam deflection unit <NUM> may have any configuration as long as the position at which the electron beam enters the target <NUM> can be switched between two points. For example, the electron beam deflection unit <NUM> may be configured to be removable or may be configured to be rotatable. For example, when the electron beam deflection unit <NUM> is the permanent magnet, the electron beam deflection unit <NUM> may be configured to be removable with respect to the X-ray generation device <NUM> by being fixed by a screw or a spring. When being the electromagnet, the electron beam deflection unit <NUM> may be configured to be able to turn on and off a power source that flows current to the electromagnet. The electron beam deflection unit <NUM> may have a rotation mechanism, a motion mechanism, or the like having a motor or the like, and thereby the electron beam deflection unit <NUM> may be configured so as to be able to change the strength or the orientation of the magnetic field of the electron beam deflection unit <NUM> caused to work on the electron beam.

The drive circuit <NUM> includes a high voltage generator circuit, an electron source drive circuit, a grid voltage control circuit, a focus voltage control circuit, or the like (all of which are not illustrated). The high voltage generator circuit generates a high voltage to be applied between the anode <NUM> and the cathode (the electron source <NUM>) of the X-ray tube <NUM>. The electron source drive circuit controls the voltage or the current to be supplied to the electron source <NUM>. The grid voltage control circuit controls the grid voltage to be supplied to the grid electrode <NUM>. The focus voltage control circuit controls the focus voltage to be supplied to the convergence electrode <NUM>. The control unit <NUM> is connected to the drive circuit <NUM>. The control unit <NUM> supplies a control signal used for controlling the high voltage generator circuit, the electron source drive circuit, the grid voltage control circuit, the focus voltage control circuit, the electron beam deflection unit <NUM> (which may have a rotation mechanism or a motion mechanism), or the like to the drive circuit <NUM>. The storage device <NUM> stores a voltage table in which various X-ray emission conditions and just focus voltages under these conditions are stored in association with each other.

Next, the characteristic structure in the X-ray generation device of the first embodiment will be described with reference to <FIG> and <FIG>. <FIG> is a plan view illustrating the structure of the X-ray generation device <NUM> of the first embodiment. <FIG> illustrates a plan view of the X-ray generation device <NUM> of the first embodiment in a plane (a plane parallel to X-Y plane) perpendicular to the traveling direction (Z-axis direction) of the electron beam. The sectional view of the portion of the X-ray tube <NUM> of <FIG> corresponds to a sectional view taken along a line A-A' of <FIG>.

The target <NUM> provided in the X-ray generation device <NUM> in the first embodiment has a thin film portion <NUM> having a locally small thickness. Further, the thin film portion <NUM> is located on the extended line of the center axis (optical axis) of the convergence electrode <NUM>.

Furthermore, the X-ray generation device <NUM> in the first embodiment includes the electron beam deflection unit <NUM> configured to be able to switch a state of not causing a magnetic field to work on the electron beam traveling to the target <NUM> and a state of causing a magnetic field to work thereon. Since the thin film portion <NUM> is located on the extended line of the center axis (optical axis) of the convergence electrode <NUM>, when no magnetic field is caused by the electron beam deflection unit <NUM> to work on the electron beam converged by the convergence electrode <NUM>, the electron beam converged by the convergence electrode <NUM> enters the thin film portion <NUM> of the target <NUM>. On the other hand, when a magnetic field is caused by the electron beam deflection unit <NUM> to work on the electron beam converged by the convergence electrode <NUM>, the electron beam is forced to be deflected by Lorentz force and enters an electron beam irradiation portion <NUM>. In other words, the electron beam deflection unit <NUM> is a switching unit that switches the incident position of the electron beam to the target <NUM> between a first region (the thin film portion <NUM>) that is a region in which the thickness is locally small in the target <NUM> and a second region (the electron beam irradiation portion <NUM>) that is a region different from the first region in the target <NUM>.

The electron beam deflection unit <NUM> may have any configuration as long as it can switch the incident position of the electron beam between two points (the thin film portion <NUM> and the electron beam irradiation portion <NUM>) and is an electromagnet, for example. As another example, the electron beam deflection unit <NUM> may be a permanent magnet configured to be removable with respect to the X-ray generation device <NUM> by being latched by a screw or a spring. <FIG> illustrates the electron beam deflection unit <NUM> having two permanent magnets. The two permanent magnets are arranged around the X-ray tube <NUM> such that the S-pole of one permanent magnet faces the N-pole of the other permanent magnet in the tube diameter direction. Note that only one permanent magnet may be arranged around the X-ray tube <NUM>. As another example, a shield plate that blocks a magnetic field and is configured to be arrangeable / removable may be provided between the electron beam deflection unit <NUM> and the X-ray tube <NUM>.

<FIG> includes sectional views illustrating configuration examples of the target <NUM> having the electron beam irradiation portion <NUM> and the thin film portion <NUM>. The electron beam irradiation portion <NUM> has a film thickness through which an X-ray can transmit in the incident direction of the electron beam, that is, a film thickness through which the X-ray can be taken out on the target support <NUM> side of the opposite side to the incident plane of the electron beam. For example, the film thickness of the electron beam irradiation portion <NUM> is not more than <NUM> micrometers, and more preferably, not more than <NUM> micrometers.

On the other hand, the thin film portion <NUM> is not particularly limited as long as it is configured to have a thinner film thickness of the target <NUM> than the electron beam irradiation portion <NUM>. For example, as illustrated in <FIG> the thin film portion <NUM> may be formed of a recess <NUM> provided in the target <NUM>. Although formed on the side opposed to the target support <NUM> in <FIG>, the recess <NUM> may be present on the target support <NUM> side or may be present on both sides. Further, as illustrated in <FIG>, the thin film portion <NUM> may be formed of a through hole <NUM> provided in the target <NUM>. The through hole <NUM> corresponds to a case where the film thickness of the thin film portion <NUM> of the target <NUM> is zero.

It is desirable that the thickness of the target <NUM> in the thin film portion <NUM> of the present invention decrease continuously or stepwise toward the centroid (center axis) of the thin film portion <NUM>. With the thin film portion <NUM> having such a thickness, the relationship between the focus voltage and the X-ray dose, which will be described below in detail, becomes clear, and this facilitates determination of the just focus voltage. Further, it is desirable that the shape of the thin film portion <NUM> be rotational symmetry about the center axis. For example, the thin film portion <NUM> may be formed of the rectangular recess <NUM> or the through hole <NUM> as illustrated in <FIG>. Alternatively, the thin film portion <NUM> may be formed of the substantially spherical recess <NUM> or through hole <NUM> as illustrated in <FIG>.

The thin film portion <NUM> of the target <NUM> may be a portion formed in advance in the target <NUM> by mechanical processing before assembly of the X-ray generation device or may be formed by intentionally excessively irradiating the target <NUM> with an electron beam after assembly of the X-ray generation device. Since the thin film portion <NUM> of the present invention is not to directly define an X-ray focal spot diameter as described below in detail, the diameter (area) of the thin film portion <NUM> may be larger than or smaller than the spot diameter (area) of a desired electron beam. Therefore, it is not necessary to perform precise fine processing for forming a recess or an opening, which directly defines an X-ray focal spot diameter in the conventional art, in the target <NUM> or a target stack structure.

Next, the concept of the adjustment method for an X-ray focal spot diameter of the present invention will be described with reference to <FIG>.

The target <NUM> of the present invention has a film thickness through which an X-ray can transmit in the incident direction of an electron beam, that is, a film thickness through which an X-ray can be taken out on the target support <NUM> side of the opposite side to the incident plane of the electron beam. When such the target <NUM> is used, the focal spot diameter of the X-ray emitted from the X-ray tube <NUM> changes depending on the spot diameter of the electron beam entering the target <NUM>. That is, the larger the spot diameter of an electron beam is, the larger the X-ray focal spot diameter is, and the smaller the spot diameter of an electron beam is, the smaller the X-ray focal spot diameter is. To reduce the X-ray focal spot diameter, it is necessary to reduce the spot diameter of the electron beam entering the target <NUM>. Further, the spot diameter of the electron beam is the smallest in a state where the focal point of the electron beam is located on the target <NUM>.

<FIG> includes schematic diagrams illustrating that the focal point position of an electron beam <NUM> differs when different focus voltages are applied to the convergence electrode <NUM> by using the X-ray generation device <NUM> according to the first embodiment of the present invention in a state where the electron beam deflection unit <NUM> does not cause a magnetic field to work on the electron beam. <FIG> is a case where the focus voltage is A, which is a state (over focus state) where the focal point of the electron beam <NUM> is located on the electron source <NUM> side of the target <NUM>. <FIG> is a case where the focus voltage is B (just focus voltage), which is a state (just focus state) where the focal point of the electron beam <NUM> is located on the target <NUM>. <FIG> is a case where the focus voltage is C, which is a state (under focus state) where the focal point of the electron beam <NUM> is located at a position more distant from the electron source <NUM> than the target <NUM>.

The ratio of the thin film portion <NUM> in the spot of the electron beam is larger when the focus voltage is B (state of just focus) than when the focus voltage is A or C. The thin film portion <NUM> is a region where the recess <NUM> or the through hole <NUM> is provided in the target <NUM>, and the number of target atoms in the thin film portion <NUM> is smaller than the number of target atoms in a region around the thin film portion <NUM>. Therefore, as the focus voltage approaches B (just focus voltage), the X-ray dose emitted from the target <NUM> decreases.

<FIG> is a graph illustrating an example of a relationship between the X-ray dose emitted from the target <NUM> and the focus voltage applied to the convergence electrode <NUM> in a state where the electron beam deflection unit <NUM> does not cause a magnetic field to work on the electron beam (that is, a state where an electron beam trajectory (the center axis of the electron beam) is fixed so that the electron beam enters the thin film portion <NUM> of the target <NUM>) in a use of the X-ray generation device <NUM> of the first embodiment of the present invention. As described above, as the focus voltage approaches B (just focus voltage), the X-ray dose emitted from the target <NUM> decreases. This is because the ratio of the thin film portion <NUM> in the spot of the electron beam increases as the spot of the electron beam decreases. When the thickness of the target <NUM> in the thin film portion <NUM> decreases continuous or stepwise toward the centroid (the center axis) of the thin film portion <NUM>, the change rate of the X-ray dose around the just focus voltage more increases, which enables easier determination of the just focus voltage.

On the other hand, <FIG> is a graph illustrating, as a comparative example, a relationship between the X-ray dose emitted from the target <NUM> and the focus voltage applied to the convergence electrode <NUM> in a state where the electron beam enters a target <NUM> having a constant thickness (that is, a target without the thin film portion <NUM> being formed therein). In such a case, the X-ray dose emitted from the target <NUM> is constant regardless of the focus voltage.

Therefore, a focus voltage that minimizes the X-ray dose emitted when the electron beam enters the thin film portion <NUM> of the target <NUM> is the just focus voltage that minimizes the spot diameter of the electron beam and, at the same time, minimizes the X-ray focal spot diameter.

That is, the adjustment method of the X-ray focal spot diameter in the present invention is as follows. <FIG> is a flowchart illustrating the adjustment method of the X-ray focal spot diameter in the X-ray generation device according to the present embodiment. First, an electron beam is caused to enter the thin film portion <NUM> of the target <NUM> (step S101). Next, a plurality of focus voltages are applied to the convergence electrode <NUM>, and each X-ray dose emitted from the X-ray generation device <NUM> is measured by an X-ray detector (a dosimeter or the like) provided outside the X-ray generation device <NUM>. Then, information on the plurality of focus voltages and information on a plurality of corresponding X-ray doses are acquired as multiple pieces of associated information (step S102). A focus voltage that minimizes the X-ray dose is determined as the just focus voltage based on the multiple pieces of associated information (step S103). When the just focus voltage is determined, a relationship between the focus voltage and the X-ray dose may be acquired to calculate the just focus voltage based on the multiple pieces of associated information.

Since the thin film portion <NUM> of the first embodiment is located on the extended line of the center axis (optical axis) of the convergence electrode <NUM>, switching of the incident position of the electron beam to the thin film portion <NUM> may be performed by removing the permanent magnet from the X-ray generation device <NUM> or may be performed by stopping the current applied to the electromagnet, for example.

Typically, a voltage table in which various X-ray emission conditions and just focus voltages for the conditions are recorded in association with each other is stored in an X-ray generation device. Conventionally, to create such a voltage table, it is necessary to acquire a plurality of X-ray transmission images with different focus voltages in various X-ray emission conditions, perform image processing on respective X-ray transmission images to finely compare the resolution, and determine a just focus voltage providing the highest resolution.

In contrast, in the X-ray generation device <NUM> according to the first embodiment, it is only required to find a focus voltage providing the least X-ray dose emitted when the electron beam enters the thin film portion <NUM> of the target <NUM> for each of the X-ray emission conditions. Therefore, in the X-ray generation device <NUM> according to the first embodiment, accurate image processing is not required in creating a voltage table, and creation of the voltage table can be simplified.

Further, since creation of a voltage table is easier, it is possible to regularly update the voltage table. Accordingly, even when the just focus voltage changes due to unexpected temporal change of the device, high resolution can be maintained over a long period.

On the other hand, when X-ray image capturing or the like is performed by using the X-ray generation device according to the first embodiment (in an X-ray generation mode), the electron beam emitted from the electron source <NUM> is deflected by the electron beam deflection unit <NUM>, and the incident position of the electron beam is switched to the electron beam irradiation portion <NUM> of the target <NUM> (that is, the electron beam trajectory (the center axis of the electron beam) is fixed so that the electron beam enters the thin film portion <NUM> of the target <NUM>). Further, the control unit <NUM> references the voltage table stored in the storage device <NUM> and applies the just focus voltage in accordance with a predetermined X-ray emission condition to the convergence electrode <NUM>.

Note that, although the case where the thin film portion <NUM> is irradiated with the electron beam not deflected by the electron beam deflection unit <NUM> and the electron beam irradiation portion <NUM> is irradiated with the electron beam deflected by the electron beam deflection unit <NUM> has been illustrated as an example in the present embodiment, the regions irradiated with the electron beam may be opposite.

As described above, according to the present embodiment, the X-ray focal spot diameter can be easily reduced.

An X-ray generation device according to a second configuration will be described with reference to <FIG>. The same components as those of the X-ray generation device in the first embodiment will be labeled with the same reference, and the description thereof will be omitted or simplified. <FIG> is a plan view illustrating a configuration example of an X-ray generation device according to the second configuration.

In the first embodiment, the incident position of the electron beam to the target <NUM> is switched in accordance with whether or not a magnetic field works on the electron beam converged by the convergence electrode <NUM>. In the second configuration, a configuration will be described in which the incident position of an electron beam to the target <NUM> is switched by changing the orientation of a magnetic field caused to work on the electron beam.

The electron beam deflection unit <NUM> according to the second configuration is configured so that the orientation of a magnetic field applied so as to deflect the electron beam can be rotated about the center axis (optical axis) of the convergence electrode <NUM> as an axis. For example, a pair of electron beam deflection units <NUM> interposing the X-ray tube <NUM> and facing each other may have a rotary mechanism having a motor or the like to rotate the electron beam deflection units <NUM> about the center axis of the convergence electrode <NUM> as an axis. With such a configuration, the orientation of the magnetic field occurring between the pair of the electron beam deflection units <NUM> can be rotated about the center axis of the convergence electrode <NUM> as an axis. <FIG> illustrates a case as an example where a pair of electron beam deflection units <NUM> interposing the X-ray tube <NUM> and facing each other is configured to be rotated by a step of <NUM> degrees about the center axis of the convergence electrode <NUM> as an axis.

When the electron beam deflection units <NUM> are located as illustrated in <FIG>, the electron beam emitted from the electron source <NUM> is forced to be deflected by Lorentz force and enters the electron beam irradiation portion <NUM> of the target <NUM>. The electron beam irradiation portion <NUM> changes in accordance with the position of the electron beam deflection units <NUM>. When the electron beam deflection units <NUM> are configured to be rotated by a step of <NUM> degrees, the position of the electron beam irradiation portion <NUM> is also located at a position rotated by a step of <NUM> degrees about the center axis of the convergence electrode <NUM> as an axis, as illustrated by black circles and a white circuit in <FIG>.

In the second configuration, the thin film portion <NUM> whose thickness is locally small is provided in any position that the electron beam may enter in response to rotation of the electron beam deflection units <NUM>. For example, a position that the electron beam enters when the electron beam deflection units <NUM> has moved to the position of the electron beam deflection units <NUM>' is defined as the thin film portion <NUM> in the example of <FIG>.

With such a configuration of the target <NUM>, with only a change of the orientation of the magnetic field applied to the electron beam by the electron beam deflection unit <NUM>, the position that the electron beam enters can be easily switched between the thin film portion <NUM> and the electron beam irradiation portion <NUM>. Further, when the electron beam irradiation portion <NUM> of the target <NUM> is deteriorated (that is, the film thickness is reduced) due to a long period of use, the deteriorated electron beam irradiation portion <NUM> may be used as a new thin film portion <NUM>. In such a case, a not-deteriorated target region that the electron beam deflected by the electron beam deflection units <NUM> may enter is set as a new electron beam irradiation portion <NUM>. Further, with only a change of the orientation of the magnetic field applied by the electron beam deflection unit <NUM>, the incident position of the electron beam can be switched to the new electron beam irradiation portion <NUM>.

Note that, although the example in which the electron beam deflection units <NUM> are formed of permanent magnets and a rotary mechanism is used to rotate the electron beam deflection units <NUM> has been illustrated in the present configuration, the electron beam deflection units <NUM> may be formed of electromagnets. Further, multiple pairs of the electron beam deflection units <NUM> formed of electromagnets may be arranged, and a magnetic field in a desired direction may be formed by supplying current to any of the electromagnets instead of rotating the electron beam deflection units <NUM>.

As described above, also in the second configuration, it is possible to easily reduce the X-ray focal spot diameter in the same principle in the first embodiment without performing accurate image processing.

In the first embodiment, the incident position of the electron beam to the target <NUM> is switched in accordance with whether or not a magnetic field works on the electron beam converged by the convergence electrode <NUM>. Further, in the second configuration, the incident position of the electron beam to the target <NUM> is switched by changing the orientation of a magnetic field caused to work on the electron beam. In a third configuration, an embodiment in which the incident position of the electron beam to the target <NUM> is switched by changing the magnitude of a magnetic field caused to work on the electron beam will be described.

The electron beam deflection unit <NUM> of the third configuration is configured so as to be able to change the magnitude of the magnetic field applied to deflect the electron beam. For example, it is possible to change the magnitude of the magnetic field caused to work on the electron beam by changing the current applied to the electromagnet or changing the number of permanent magnets to be installed. That is, when the electron beam deflection unit <NUM> is formed of permanent magnets, it is possible to increase the magnitude of the magnetic field caused to work on the electron beam by increasing the number of permanent magnets. When the electron beam deflection unit <NUM> is formed of an electromagnet, it is possible to increase the magnitude of the magnetic field caused to work on the electron beam by increasing the current applied to the electromagnet. With an increased magnitude of the magnetic field caused to work on the electron beam, Lorentz force applied to electrons becomes larger, and the deflection amount of the electron beam becomes much larger.

<FIG> schematically illustrates an irradiation position of the electron beam to the target <NUM> when the magnetic field applied by the electron beam deflection unit <NUM> is changed between a first magnitude and a second magnitude that is different from the first magnitude. <FIG> illustrates an example in which the magnetic field caused to work on the electron beam is set to the first magnitude to cause the electron beam to enter the thin film portion <NUM>, and the magnetic field caused to work on the electron beam is set to the second magnitude, which is larger than the first magnitude, to cause the electron beam to enter the electron beam irradiation portion <NUM>. In such a case, the thin film portion <NUM> is located on a side closer to the center axis of the convergence electrode <NUM> than the electron beam irradiation portion <NUM>.

The magnetic field caused to work on the electron beam may be set to the first magnitude to cause the electron beam to enter the thin film portion <NUM>, and the magnetic field caused to work on the electron beam may be set to the second magnitude that is smaller than the first magnitude to cause the electron beam to enter the electron beam irradiation portion <NUM>. In such a case, the thin film portion <NUM> is located on a side farther from the center axis of the convergence electrode <NUM> than the electron beam irradiation portion <NUM>.

With such a configuration of the target <NUM>, with only a change of the magnitude of the magnetic field applied to the electron beam by the electron beam deflection unit <NUM>, the position that the electron beam enters can be easily switched between the thin film portion <NUM> and the electron beam irradiation portion <NUM>.

As described above, also in the third configuration, it is possible to easily reduce the X-ray focal spot diameter in the same principle in the first embodiment without performing accurate image processing.

An X-ray image capture system according to a fourth configuration will be described with reference to <FIG> and <FIG>. The same components as those of the X-ray generation devices in the first embodiment and in the second configuration will be labeled with the same reference, and the description thereof will be omitted or simplified.

First, the general configuration of the X-ray image capture system according to the present configuration will be described with reference to <FIG> is a block diagram illustrating the general configuration of the X-ray image capture system according to the present configuration.

As illustrated in <FIG>, an X-ray image capture system <NUM> according to the present configuration includes the X-ray generation device <NUM>, an X-ray detection device <NUM>, an information acquisition unit <NUM>, a system control device <NUM>, and a display device <NUM>. The X-ray generation device <NUM> is the X-ray generation device of the first embodiment or the second configuration and includes the X-ray tube <NUM>, the drive circuit <NUM>, the control unit <NUM>, and the storage device <NUM>. The control unit <NUM> further has a function as a receiving unit that receives information including information on an X-ray dose acquired by the X-ray detection device <NUM> in addition to the functions described in the first embodiment and in the second configuration. The X-ray detection device <NUM> includes an X-ray detector <NUM>.

The system control device <NUM> is connected to the control unit <NUM> of the X-ray generation device <NUM>, the X-ray detector <NUM> of the X-ray detection device <NUM>, the information acquisition unit <NUM>, and the display device <NUM>.

Next, the characteristic structure of the X-ray image capture system of the fourth configuration will be described. The X-ray image capture system of the fourth configuration includes the information acquisition unit <NUM>. The information acquisition unit <NUM> has a function of acquiring the focus voltage applied to the convergence electrode <NUM> and the X-ray dose detected by the X-ray detector <NUM> when the focus voltage is applied as associated information. The information acquisition unit <NUM> may be of any configuration as long as it has such a function. For example, as illustrated in <FIG>, the information acquisition unit <NUM> may be formed of independent components connected to the X-ray generation device <NUM>, the X-ray detection device <NUM>, and the system control device <NUM>, respectively, or may be a part of any of the X-ray generation device <NUM>, the X-ray detection device <NUM>, and the system control device <NUM>.

Next, the outline of the operation of the X-ray image capture system <NUM> according to the present configuration will be described with reference to <FIG>.

The system control device <NUM> is responsible for overall control of the system including the X-ray generation device <NUM>, the X-ray detection device <NUM>, and the information acquisition unit <NUM>. The control unit <NUM> of the X-ray generation device <NUM> controls the drive circuit <NUM> in response to an instruction from the system control device <NUM> and outputs various control signals to the X-ray tube <NUM>. For example, the system control device <NUM> provides information on X-ray emission conditions (for example, a tube voltage and a tube current) to the control unit <NUM>. The control unit <NUM> that has received the information on the X-ray emission conditions references the voltage table stored in the storage device <NUM> and acquires a just focus voltage in the X-ray emission condition provided from the system control device <NUM>. The control unit <NUM> controls the drive circuit <NUM> and outputs various drive signals such as the tube voltage in accordance with the X-ray emission condition, the just focus voltage acquired from the voltage table, or the like to the X-ray tube <NUM>. Accordingly, the emission state of an X-ray emitted from the X-ray generation device <NUM> can be controlled.

An X-ray <NUM> emitted from the X-ray generation device <NUM> transmits through an object <NUM> and is detected by the X-ray detector <NUM>. The X-ray detector <NUM> may be of any form as long as it can measure the dose (exposure dose, absorbed dose, dose equivalent, radioactivity, or the like) of the X-ray emitted from the X-ray generation device <NUM> as two-dimensional information. The X-ray detector <NUM> has a plurality of detection elements (for example, a dosimeter or a counter tube) (not illustrated) and acquires a transmission X-ray image. Alternatively, the X-ray detector <NUM> having an image intensifier, a camera, or the like may be used to acquire information on the X-ray dose. The X-ray detector <NUM> converts an acquired transmission X-ray image into an image signal and outputs the image signal. A slit, a collimator, or the like (not illustrated) may be arranged between the X-ray tube <NUM> and the object <NUM> in order to suppress unnecessary X-ray irradiation.

The X-ray detector <NUM> performs predetermined signal processing on an image signal under the control of the system control device <NUM> and outputs the processed image signal to the system control device <NUM>. The system control device <NUM> outputs a display signal to the display device <NUM> in order to display an image on the display device <NUM> based on the processed image signal. The display device <NUM> displays a captured image of the object <NUM> based on a display signal on a screen.

Next, the adjustment method for the X-ray focal spot diameter in the X-ray image capture system <NUM> according to the present configuration will be described with reference to <FIG> and <FIG> is a flowchart illustrating the adjustment method for the X-ray focal spot diameter in the X-ray image capture system according to the present configuration.

The adjustment method for the X-ray focal spot diameter in the X-ray image capture system <NUM> according to the present configuration can be implemented when performed by the control unit <NUM> of the X-ray generation device <NUM> or the system control device <NUM> via the control unit <NUM> in accordance with the flowchart illustrated in <FIG>, for example. Each step illustrated in the flowchart of <FIG> can be implemented in a hardware-like manner by mounting circuit components, which are hardware components such as LSI or the like in which a program is embedded, on the control unit <NUM> or the system control device <NUM>. Alternatively, each step can be implemented in a software-like manner by causing a computer forming the control unit <NUM> or the system control device <NUM> to execute a program used for performing each step illustrated in the flowchart of <FIG>.

Alternatively, the program described above may be stored in a storage medium, and the program stored in the storage medium may be read as a code and executed by a computer. That is, a computer readable storage medium is also included in the scope of the present configuration. Further, not only the storage medium in which the program described above is stored but also the program itself is included in the scope of the present configuration. As the storage medium, for example, a floppy (registered trademark) disk, a hard disk, an optical disk, a magneto-optical disk, a CD-ROM, a magnetic tape, a nonvolatile memory card, or a ROM can be used. Further, the scope of the present configuration includes an example that operates on OS to perform a process in cooperation with another software or a function of an add-in board without being limited to an example that performs a process by a program alone stored in the storage medium.

The system control device <NUM> transitions to an adjustment mode to adjust the X-ray focal spot diameter in response to an instruction from a user or at a timing when a predetermined condition is met. The system control device <NUM> notifies the control unit <NUM> in the X-ray generation device <NUM> and the X-ray detection device <NUM> of the information indicating that transition to the adjustment mode to adjust the X-ray focal spot diameter has been made.

The predetermined condition may be, for example, that an accumulated irradiation time at a point of the target <NUM> irradiated with the electron beam has elapsed and exceeds a predetermined period, that the X-ray dose decreases below a predetermined value, or the like. In such a way, automatic transition to the adjustment mode to adjust the X-ray focal spot diameter is performed regularly and thereby high resolution can be maintained over a longer period.

In response to receiving information from the system control device <NUM>, the control unit <NUM> detects that transition to the adjustment mode to adjust the X-ray focal spot diameter has been made (step S201).

The control unit <NUM> that has detected the transition to the adjustment mode to adjust the X-ray focal spot diameter controls the electron beam deflection unit <NUM> so that the electron beam emitted from the electron source <NUM> enters a region including the thin film portion <NUM> of the target <NUM> (step S202).

Next, the control unit <NUM> sets the voltage value of the focus voltage applied to the convergence electrode <NUM> to a plurality of values and controls the drive circuit <NUM> so as to emit an X-ray from the X-ray tube <NUM> at each of the voltage values. For example, the control unit <NUM> sets the voltage values of the focus voltage applied to the convergence electrode <NUM> to a plurality of values in the X-ray emission conditions (the tube current and the tube voltage) specified by the system control device <NUM>. The information on the focus voltages set by the control unit <NUM> for the drive circuit <NUM> is transmitted to the information acquisition unit <NUM>.

The X-ray detector <NUM> of the X-ray detection device <NUM> detects the X-ray emitted from the X-ray generation device <NUM> caused by the electron beam entering the thin film portion <NUM> of the target <NUM>. The X-ray detection device <NUM> transmits information on the X-ray dose detected by the X-ray detector <NUM> to the information acquisition unit <NUM>.

The information acquisition unit <NUM> acquires information on the focus voltage received from the control unit <NUM> and information on the X-ray dose received from the X-ray detection device <NUM> as information associated with each other (step S203). That is, the information acquisition unit <NUM> associates the information on the voltage value of the focus voltage with the information on the X-ray dose obtained at that time. The information acquisition unit <NUM> or the system control device <NUM> determines a voltage value providing the smallest X-ray dose from the information in which the voltage values and the X-ray doses are associated with each other. The relationship between the focus voltage and the X-ray dose may be acquired from multiple pieces of information, and a voltage value that may provide the smallest X-ray dose may be calculated and determined based on the relationship (step S204). The voltage value determined in such a way is the voltage value providing the smallest spot diameter of the electron beam and, at the same time, a voltage value providing the smallest X-ray focal spot diameter (just focus voltage value).

The control unit <NUM> sets the focus voltage applied to the convergence electrode <NUM> to the just focus voltage value determined in step S104. Accordingly, the spot diameter of the electron beam entering the target <NUM> can be optimized.

The just focus voltage value determined in such a way can be associated with the X-ray emission conditions and stored as the voltage table in the storage device <NUM> of the X-ray generation device <NUM>. Alternatively, the voltage table that has already been stored may be updated with the newly acquired just focus voltage value.

Next, an image capture mode to capture a transmission X-ray image of the object <NUM> will be described. The system control device <NUM> causes the X-ray image capture system <NUM> to enter the image capture mode in response to an instruction from the user or at a timing when a predetermined condition is met (such as at the end of the adjustment mode for the X-ray focal spot diameter). The system control device <NUM> notifies the control unit <NUM> in the X-ray generation device <NUM> of the information indicating that transition to the image capture mode has been made. The control unit <NUM> that has detected the transition to the image capture mode controls the electron beam deflection unit <NUM> so that the electron beam emitted from the electron source <NUM> enters the electron beam irradiation portion <NUM> of the target <NUM>.

The control unit <NUM> references the voltage table stored in the storage device <NUM>, selects the just focus voltage in accordance with a predetermined X-ray emission condition, and controls the X-ray tube <NUM> via the drive circuit <NUM>. Accordingly, the spot diameter of the electron beam entering the target <NUM> can be optimized, and a fine focal spot diameter of the X-ray emitted from the X-ray tube <NUM> can be achieved.

As described above, according to the present configuration, it is possible to easily reduce an X-ray focal spot diameter without requiring efforts such as image processing. Accordingly, capturing of a transmission X-ray image with high resolution can be easily realized.

The present invention is not limited to the embodiment described above, and various modifications are possible.

Claim 1:
An X-ray generation device (<NUM>) comprising: a cathode including an electron source (<NUM>) that generates an electron beam; an anode (<NUM>) including a transmission type target configured to transmit, in an incident direction of the electron beam, an X-ray generated by collision of the electron beam; and a convergence electrode (<NUM>) that converges the electron beam toward the transmission type target,
wherein the transmission type target has a first region (<NUM>) having a locally small thickness and a second region (<NUM>) having a larger thickness than the first region (<NUM>),
wherein the X-ray generation device (<NUM>) further comprises an electron beam deflection unit (<NUM>) configured to switch an incident position of the electron beam to the transmission type target between the first region (<NUM>) and a second region (<NUM>) in accordance with whether or not a magnetic field is applied to the electron beam,
characterized in that the electron beam deflection unit (<NUM>) has an adjustment mode to adjust an X-ray focal spot diameter and an X-ray generation mode to generate an X-ray, wherein the electron beam deflection unit deflects the electron beam to enter the first region in the adjustment mode, and wherein the electron beam deflection unit deflects the electron beam to enter the second region in the X-ray generation mode,
wherein the X-ray generation device is arranged to acquire information on the X-ray dose measured by an X-ray detector provided outside the X-ray generation device (<NUM>), and
wherein the X-ray generation device is arranged to adjust the X-ray focal spot diameter by controlling a voltage applied to the convergence electrode when the electron enters the first region (<NUM>) to obtain the focus voltage leading to the least X-ray dose.