JP2009245727A - X-ray source - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an X-ray source 11, capable of solving problems about electrode 31, such as stagnation of gas around it 31, difficulty of wiring to it 31, and high cost, with its performance and functions maintained. <P>SOLUTION: The electrodes 31 of an electrostatic lens 17 are pinched and held by two insulating plates 33. The insulating plates 33 are equipped with grooves 34, which join the electrodes 31 through a brazing material 35. When the electrodes 31 are joined to two insulating plates 33, the electrodes 31 are held with a jig to keep their axial and parallel accuracy, and then connected to the two insulating plates 33. Since both sides of the electrodes 31 intersecting an arrangement direction of the insulating plates 33 are made open, gas emitted from the electrodes 31 resulting from incident electron beams 15 hardly collects between the electrodes 31, and further, wiring for electrodes is also facilitated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an X-ray source that emits X-rays.

  In general, an X-ray source having a micro focus has been already commercialized as a micro focus X-ray source, and is widely used in a nondestructive inspection apparatus for inspecting a micro area of an object with high resolution. . In this X-ray source, an electron beam emitted from an electron gun is converged by an electromagnetic lens and focused on a narrow area of the target surface on the order of μm or less, and the X-ray emitted there A configuration in which light is transmitted through and released is employed (for example, see Patent Document 1).

  In order to focus the electron beam to a small spot with a certain amount of current value, it is important to design the electron gun and electromagnetic lens by matching, but now, by making various efforts A microfocus X-ray source approaching 0.1 μm has been achieved.

  The X-ray tube which is the main body of this X-ray source can be classified into a magnetic lens system composed of electromagnets and an electrostatic lens system composed of a plurality of electrodes as its focusing mechanism (lens). While it is easy to cope with voltage acceleration, it is large, and the latter is characterized by being small at an acceleration voltage of 50 kV or less.

  The micro-focus X-ray tube, which is a low-voltage acceleration electrostatic lens system capable of emitting X-rays up to the energy range of soft X-rays, has recently been used in product fields and pharmaceutical fields where organic materials are frequently used. Furthermore, since there is an increasing demand for high-resolution inspections of minute objects composed of light elements that reach cells, industrial demand can be expected to increase rapidly.

  When an electrostatic lens for converging an electron beam is configured, a plurality of electrodes each having a hole through which the electron beam passes are arranged in series in the axial direction while maintaining insulation. In order to maintain insulation between the electrodes, a cylindrical insulating cylinder formed of an insulating material such as ceramics is used, and a stacked structure is adopted in which insulating cylinders are arranged between a plurality of electrodes. Since a general X-ray tube is baked at a high temperature, a bonding method such as brazing is used to bond the electrode and the insulating cylinder in order to withstand this temperature.

  In order to exhibit the focusing performance as designed by the optical design with respect to the electron beam, it is necessary to configure an electrostatic lens in which the axial accuracy and parallelism of the electrodes stacked in the axial direction are sufficiently maintained. Therefore, in the case of an electrostatic lens having a stacked structure, it is necessary to use parts such as an electrode and an insulating tube processed and manufactured with sufficient accuracy, and the electrode and the insulating tube are fitted to ensure axial accuracy. It is necessary to take measures and measures such as using a special jig when forming such a shape.

In addition, since the voltage applied between the electrodes is equivalent to the acceleration voltage of the electron beam at the maximum, an insulating cylinder having an insulation distance that does not cause spatial dielectric breakdown and creeping dielectric breakdown with respect to this voltage is provided. It will be necessary.
JP 2004-28845 A (page 4-5, FIG. 1)

  In general, in the case of a microfocus X-ray tube that converges an electron beam to a size of 1 μm or less on the target surface, an axial accuracy of the electrodes constituting the electrostatic lens is required to be approximately ± 10 μm. In this way, in the electrostatic lens having a stacked structure, it is required to increase the processing accuracy of the parts as described above, and this also applies to the insulating cylinder that is difficult to process. For this reason, the manufacturing cost of the insulating cylinder is very high. Furthermore, when a sufficient creepage insulation distance cannot be secured with respect to the length of the insulating cylinder, it is necessary to perform uneven processing on the inner and outer walls of the insulating cylinder. It will be something.

  Further, the gas released when the electron beam is incident on the electrode is likely to stagnate between the insulating cylinder and the electrode, that is, it has an undesired structure in terms of conductance. As a result, the degree of vacuum locally deteriorates inside the vacuum vessel of the X-ray tube, and this hinders the stable maintenance of the electron beam trajectory.

  In addition, in the electrostatic lens having a stacked structure, wiring to the intermediate electrode sandwiched between the insulating cylinders is difficult.

  In addition, the electrode of the electron gun is also supported using an insulating cylinder, and there is a problem similar to that of an electrostatic lens.

  The present invention has been made in view of such points, and while maintaining the performance and function of the electrode, X-rays that can solve the problems of gas stagnation near the electrode, difficulty of wiring to the electrode, and high cost. The purpose is to provide a source.

  The present invention includes an electron gun having an electrode and generating an electron beam, an electrostatic lens having an electrode for converging the electron beam generated by the electron gun, and at least one electrode of the electron gun and the electrostatic lens And a plurality of insulators that sandwich and hold them.

  The present invention also provides an electron gun having an electrode and generating an electron beam, an electrostatic lens having an electrode for converging the electron beam generated by the electron gun, and at least one of the electron gun and the electrostatic lens An electrode support to which the electrode is attached, and a plurality of insulators that sandwich and hold the electrode support.

  According to the present invention, since at least one electrode of the electron gun and the electrostatic lens is sandwiched and held by a plurality of insulators, gas stagnation in the vicinity of the electrode, It can solve the difficulty of wiring and the problem of high price.

  Further, according to the present invention, the electrode support is sandwiched and held by a plurality of insulators, and at least one electrode of the electron gun and the electrostatic lens is attached to the electrode support, so that the performance and function of the electrode are maintained. However, it is possible to solve the problems of gas stagnation near the electrodes, difficulty in wiring to the electrodes, and high cost, and the degree of freedom of usable electrodes is increased, thereby improving the convergence characteristics.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 and 2 show a first embodiment.

  The X-ray source 11 is a microfocus X-ray tube having a vacuum vessel 12 in which the inside is held in vacuum, and also serves as an X-ray emission window for emitting X-rays 13 to the outside at one end of the vacuum vessel 12. A target 14 is disposed.

  In the vacuum vessel 12, an electron gun 16 that generates an electron beam 15 toward the target 14, an electrostatic lens 17 that converges the electron beam 15 to enter the target 14, and the electron gun 16 and the electrostatic lens 17 An insulation introduction terminal 18 and the like for connecting to the outside are disposed.

  The electron gun 16 includes an electron source (emitter) 21 that generates an electron beam 15, a suppression electrode (referred to as a Wehnelt electrode or a suppressor electrode) 22 as an electrode that forms a crossover and accelerates at a target voltage, and An insulating cylinder 23 that supports the suppression electrode 22 on the vacuum vessel 12 is provided. The suppression electrode 22 is cup-shaped and has a hole 24 through which the electron beam 15 passes.

  In addition, the electrostatic lens 17 is configured by using a plurality of metal electrodes 31, and in this example, three electrodes 31 (first electrode 31a, second electrode 31b, and third electrode 31c). As an example, a three-pole lens configuration using a lens is used. In general, a voltage close to the acceleration voltage is applied to the second electrode 31b disposed in the middle, and a ground potential or a voltage close thereto is applied to the first and third electrodes 31a and 31c. These electrodes 31 have a rectangular plate shape, and a hole 32 through which an electron beam passes is formed at the center.

  These electrodes 31 are sandwiched and held between two insulating plates 33 as a plurality of insulators. These insulating plates 33 are made of ceramics for soldering to the metal electrode 31, and a plurality of grooves 34 are formed on the surface sandwiching the electrodes 31, and the edges of the three electrodes 31 are brazed to the grooves 34. It is fitted and fixed together with the material 35. The number of grooves 34 is larger than the number of electrodes 31. In FIG. 2, the grooves 34 other than the groove 34 into which the electrode 31 is fitted are omitted. The insulating plate 33 holding the electrode 31 is supported on the vacuum vessel 12 side.

  When joining the three electrodes 31 and the two insulating plates 33, the two insulating plates 33 are attached to the three electrodes 31 held by using a jig for ensuring the axial accuracy and parallelism of the electrodes 31. Because of the joining, the two insulating plates 33 do not contribute to the installation accuracy but simply serve to support and fix the three electrodes 31. Therefore, the insulating plate 33 does not require high shape accuracy and can be made inexpensive.

  Since the brazing material 35 directly joins the metal electrode 31 and the ceramic insulating plate 33, it is preferable to use an active brazing material that does not require metallization treatment on the ceramic joining surface.

  In the X-ray source 11, the electron beam 15 emitted from the electron source 21 in the electron gun 16 forms a crossover once in the vicinity of the hole 24 of the suppression electrode 22 and is accelerated at a target voltage. A focusing action is received by the electrostatic lens 17 and a focal point is formed on the surface of the target 14. X-rays 13 are generated from the focal portion of the target 14, pass through the target 14, and are emitted outside the X-ray source 11.

  Since the electrostatic lens 17 of the X-ray source 11 thus configured has a structure in which both side surfaces intersecting with the direction in which the two insulating plates 33 of the electrode 31 are arranged are open, an electron beam is applied to the electrode 31. The gas released by the incidence of 15 is less likely to accumulate between the electrodes 31, and the connection of wiring for determining the potential of the intermediate second electrode 31b is facilitated.

  Therefore, by adopting a structure in which the electrode 31 of the electrostatic lens 17 is sandwiched and held between the two insulating plates 33, the gas stagnation near the electrode 31 and the electrode 31 are maintained while maintaining the performance and function of the electrode 31. It can solve the difficulty of wiring and the problem of high price.

  Next, FIG. 3 shows a second embodiment.

  This is an example in which the configuration in which the electrode 31 is sandwiched and held by two insulating plates 33 as in the electrostatic lens 17 of the first embodiment is also applied to the electron gun 16.

  The suppression electrode 22 of the electron gun 16 is sandwiched and held by two insulating plates 33 and supported on the vacuum container 12 side. On the outer surface of the suppression electrode 22, a plate portion 41 is provided so as to be fitted in the groove 34 of the insulating plate 33 and joined with the brazing material 35. Also on the vacuum container 12 side, a plate portion 42 is provided so as to be fitted in the groove 34 of the insulating plate 33 and joined by the brazing material 35.

  Since the electron gun 16 has a structure in which both side surfaces intersecting with the direction in which the two insulating plates 33 of the suppression electrode 22 are arranged are open, the electron beam 15 is emitted by being incident on the suppression electrode 22. This makes it easier for the gas to be discharged, and makes it difficult to accumulate in the vicinity of the suppression electrode 22.

  The X-ray source 11 that is a microfocus X-ray tube is characterized in that many of the electron beams 15 emitted from the electron gun 16 are cut immediately before entering the electrostatic lens 17, and the cause is the electron gun. It is conceivable that the electron beam 15 emitted from 16 enters the suppression electrode 22 and the amount of gas emitted increases, and it is effective to make it easier to discharge the gas and prevent it from collecting near the suppression electrode 22. Become.

  In this way, the X-ray source 11 with improved countermeasures against gas emission can be provided.

  Next, FIGS. 4 and 5 show a third embodiment.

  In the electrostatic lens 17, it is possible to increase the creeping insulation distance between the electrodes 31 by forming the grooves 34 in the insulating plate 33, which is more effective by increasing the number of the grooves 34 between the electrodes 31. Can be increased.

  In order to form the high-strength electrostatic lens 17, it is required to form a high electric field between the electrodes 31, and therefore it is not necessary to increase the length of the insulating plate 33 in order to maintain the creeping insulation distance. This is undesirable in terms of electron optical design. For the electron beam 15 accelerated at a particularly high voltage, the method of forming the groove 34 that can increase the creeping insulation distance without changing the distance between the electrodes 31 is a compact X-ray source 11 while maintaining the lens strength. It is effective in constructing.

  However, it is necessary to consider the creepage distance with respect to the path (discharge path) in the entire circumferential direction of the insulating plate 33 between the electrodes 31. Therefore, not only the surface of the insulating plate 33 that sandwiches the electrode 31, It is necessary to continuously form grooves 34 on the back and side surfaces.

  As a result, the creeping insulation distance can be increased without changing the inter-electrode distance, and the electrostatic lens 17 having high strength can be provided.

  The same applies to the insulating plate 33 of the electron gun 16.

  Thus, the X-ray source 11 can be provided that maintains a compact size even at a high acceleration voltage.

  Next, FIGS. 6 and 7 show a fourth embodiment.

  It is characterized by a structure employing a two-step joining method in which an electrode support plate 51 as an electrode support is first joined to two insulating plates 33, and then an electrode 31 is joined to the electrode support plate 51. is there. The electrode support plate 51 has the same outer shape as the electrode 31, and an opening 52 that is slightly smaller than the outer shape of the electrode 31 is formed inside.

  In order to improve the convergence performance of the electrostatic lens 17, it is not sufficient that the electrodes 31 constituting the electrostatic lens 17 be a planar type, and it is required to apply some of them having various three-dimensional shapes such as cup shapes. In order to meet these requirements, the electrode support plate 51 and the electrode 31 connected to the insulating plate 33 are separated so that the electrode 31 having a three-dimensional structure can be easily attached, and a structure that can be joined and assembled in order. Shall be taken.

  6 and 7, the second electrode 31b in the middle of the electrostatic lens 17 is formed in a cup shape, whereby an electrostatic lens 17 with small surface aberration can be formed, and the electron beam 15 It is possible to improve the convergence characteristics.

  As described above, it is possible to provide the X-ray source 11 having the electrostatic lens 17 and the electron gun 16 with improved aberration characteristics and improved focus size performance.

It is sectional drawing of the X-ray source which shows the 1st Embodiment of this invention. It is a perspective view of the electrostatic lens of an X-ray source same as the above. It is sectional drawing of the X-ray source which shows the 2nd Embodiment of this invention. It is sectional drawing of the electrostatic lens of the X-ray source which shows the 3rd Embodiment of this invention. It is an A arrow view of FIG. 4 same as the above. It is sectional drawing of the decomposition | disassembly state of the electrostatic lens of the X-ray source which shows the 4th Embodiment of this invention. It is sectional drawing of the assembly state of an electrostatic lens same as the above.

Explanation of symbols

11 X-ray source
15 electron beam
16 electron gun
17 Electrostatic lens
22 Suppression electrode as electrode
31 electrodes
33 Insulation plate as an insulator
34 Groove
51 Electrode support plate as electrode support

Claims (5)

An electron gun having an electrode and generating an electron beam;
An electrostatic lens having an electrode for converging the electron beam generated by the electron gun;
An X-ray source comprising: a plurality of insulators that sandwich and hold at least one electrode of the electron gun and the electrostatic lens. An electron gun having an electrode and generating an electron beam;
An electrostatic lens having an electrode for converging the electron beam generated by the electron gun;
An electrode support to which at least one electrode of the electron gun and the electrostatic lens is attached;
An X-ray source comprising: a plurality of insulators that sandwich and hold the electrode support. The X-ray source according to claim 1, wherein the insulator is provided with a groove for fitting the electrode. The X-ray source according to claim 2, wherein a groove for fitting the electrode support is provided in the insulator. The X-ray source according to claim 3 or 4, wherein the groove of the insulator is provided on the entire circumference of the insulator.

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