X-ray source

Abstract: An X-ray source comprises a thin film X-ray target (22) for generating X-rays in response to the application of electron beams, and a capillary tubular element (20) for allowing the X-rays to pass. The capillary tubular element (20) has such a diameter that the beams of the X-rays impinging on the inner surfaces of the capillary tubular element (20) are totally reflected. Additionally, a thin film (24) is provided for absorbing the electron beams, but allowing the X-rays to penetrate.

Description: The following relates to an X-ray source, especially an X-ray source as it may be used in X-ray photoelectron spectroscopy (XBS) or X-ray fluorescent spectroscopy or X-ray lithography. In such applications, it is necessary to generate small diameter X-ray beams. The document US-A-4.194.123 describes an X-ray source for use in X-ray lithography which source comprises: a means for generating electrons; a target film of a material producing X-rays when being irradiated by said electrons; and a plate comprising parallelly arranged capillary tubes through which X-rays may pass. In this arrangement, the plate is irradiated by radiation from a layer of radioactive material provided on one main surface of the plate. The radioactive radiation generates secondary electrons within the capillary tubes of the plate. These electrons are accelerated from the plate to the target film, in which film the energy of the accelerated electrons is transformed into X-radiation. The X-radiation returns through the capillary tubes of the plate and the layer of radioactive material and irradiates onto a specimem arranged behind the plate. Thereby, an area of the specimen corresponding to the area of the plate is irradiated with highly parallel X-rays. The document US-A-2.638.554 describes an X-ray source for providing highly focused X-rays for treatment of the human body. For this purpose, a plate comprising capillary tubes which all point towards a common point is provided. A target film for generating X-rays is provided on one main surface of the plate. This target film is irradiated by electrons. To be able to irradiate a target film of rather extended area, the means for generating the electrons may be a means for generating an electron beam which is scanned over the target film. It is the object of the present invention, to provide a X-ray source for generating narrow X-ray beams to be irradiated onto a specimen, said source having simple construction. The X-ray source of the present invention comprises the above listed features of the firstly discussed prior art source, and it is characterized in that: said target film is arranged on one main surface of said plate; said means for generating electrons is arranged to provide an electron beam having selectively a diameter in a range from less than the diameter of one capillary tube to a plurality of said diameters, and for scanning said electron beam along said main surface of said plate which is provided with said target film; an absorber film made of metal is provided on the other main surface of said plate for absorbing electrons; and a power source is provided for biasing said absorber film with a positive voltage. With this arrangement it is possible to scan a narrow X-ray beam over a specimen. This is done with a plate arrangement according to the plate arrangement as known from the document US-A-4.194.123, however, electrons and X-rays have the same radiation direction, whereas in the prior art plate arrangement they have opposite directions. To prevent that electrons moving in the direction of the X-radiation may irradiate from the plate, the plate is covered with an absorber film on the output side of the X-radiations for absorbing electrons. The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein; FIG. 1 is a cross-sectional view of an X-ray source according to a preferred embodiment of the present invention; FIG. 2 is an enlarged cross-sectional view of a single capillary tubular element used for the X-ray source of FIG. 1; FIG. 3 shows a schematic distribution of the X-ray beams generated from a thin film X-ray target in the X-ray source of FIG. 1; FIG. 4 is a cross-sectional view of the single capillary tubular element, showing the transmission of the X-ray beam in the capillary tubular element; and FIG. 5 is a cross-sectional view of the outlet of the single capillary tubular element, showing the emission of the X-ray beam from the outlet; and FIG. 1 is a cross-sectional view of an X-ray source according to a preferred embodiment of the present invention. In the X-ray source, a great number of capillary tubular element 20 are bundled so that their edges are aligned to provide a plate 21. Preferably, the diameter of each of the great number of capillary tubular elements is about 10 - 20 µm and the length is about 0.5 - 1.0 mm. The number of the capillary tubular elements bundled is in the order of ten thousand or less, about several tens thousand, or one hundred thousand or more, depending on the usage of the X-ray source. A thin film X-ray target 22 is provided at the side of the plate 21 comprising the great number of capillary tubular elements 20. Preferably, the thin film X-ray target 22 may be an aluminum layer of about 5 µm in thickness. Alternatively it may be a thin film of magnesium. Additionally, a thin film 24 is provided at the opposing side of the plate 21 for passing the X-ray beams generated from the X-ray target 22 and absorbing the electron beams possibly generated within the tubular element 20. Preferably, the thin film 24 is a thin aluminum film of, say, about 2 µm thinner than the thin film target 22 when the thin film target 22 is an aluminum layer. The thin film 24 may alternatively be a beryllium layer, a carbon layer, or a high polymer layer coated with an aluminum layer or the like. Further, the thin film 24 is biased with a positive voltage supplied from a power source, so that the electrons generated in the capillary tubular element can be gathered and removed efficiently. A sufficiently converging electron beam 26 is applied to the thin film X-ray target 22. Preferably, the diameter of a suitable electron beam 26 is about 5µm (the acceleration voltage is about 20 keV and the current is about 10 µ A), which can be easily generated. The diameter of the electron beam 26 is controlled to be smaller than the diameter of the capillary tubular element 20. X-rays 28 are generated from the thin film X-ray target 22 and penetrates through the thin film 24, thereby being emitted outside. The X-rays 28 are applied toward a specimen 25, so that the specimen 25 emits photoelectrons, which are detected by an electron spectrometer 29. The analyzer analyzes the energy of the photoelectrons. After being amplified, the energy of the photoelectrons is recorded in terms of the binding energy vs. the intensitiy. FIG. 2 is an enlarged cross-sectional view of a single capillary tubular element 20 used for the X-ray source of FIG. 1. The electron beau 26 is incident on the X-ray target 22 of the single tubular element 20 to produce X-rays 28 irradiating through thin film 24. The generation of the X-rays 28 will be described in detail. When the electron beam 26 becomes incident on the thin film X-ray target 22, this target generates characteristic X-rays ( in this preferred embodiment, Kα line of aluminum ), which irradiate from both sides of the thin film X-ray target 22, e.g. to the inside and the outside of the capillary tubular element 20. With respect to the beams of the X-rays 28 emitting to the inside of the thin film X-ray target 22, the angle of directing the X-rays 28 is distributed as shown in FIG. 3. Among the beams of the X-rays 28 within the inside of the capillary tubular element 20, the beams of the X-rays 28 not impinging on the inner faces of the capillary tubular element 20 and the beams of the X-rays 28 totally reflected by the inner faces of the element 20 can emit outside through the thin film 24 with a small solid angle as shown in FIG. 4. Therefore, the beams of the X-rays 28 emitted through the thin film 24 are scattered with having a distribution diameter similar to the diameter of the capillary tubular element 20. Owing to the total reflection of the capillary tubular element 20, the beams of the X- rays 28 can focus at a distance outside the outlet of the element 20. The distance depends on the diameter and the length of the capillary tubular element 20, and the wavelength of the X-ray 28. Since the thin film 24 absorbs the electron beams possibly generated from the inner side of the thin film X-ray target 22 and the inner surfaces of the capillary tubular element 20, those electron beams cannot emit outside through the thin film 24. Thus, the scanning of the small electron beam 26 toward the thin film X-ray target 22 produces the X-ray beams 28. It may be possible that the diameter of the electron beam 26 impinging on the thin film X-ray target 22 can cover a plurality of capillary tubular elements 20 at the same time, whereby substantially parallel beams of the X-rays 28 with large diameters can be generated from the thin film 24. While only certain embodiments of the present invention have been described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the claims.

Claims: An X-ray source comprising: a means for generating electrons (26); a target film (22) of a material producing X-rays when being irradiated by said electrons; and a plate (21) comprising parallelly arranged capillary tubes (20) through which X-rays may pass; characterized in that said target film (22) is arranged on one main surface of said plate (21); said means for generating electrons is arranged to provide an electron beam (26) having selectively a diameter in a range from less than the diameter of one capillary tube (20) to a plurality of said diameters, and for scanning said electron beam along said main surface of said plate which is provided with said target film; an absorber film (24) made of metal is provided on the other main surface of said plate for absorbing electrons; and a power source (30) is provided for biasing said absorber film with a positive voltage. The X-ray source of claim 1, wherein said X-ray target film (22) is made of aluminum or magnesium. The X-ray source of one of the claims 1 or 2, wherein said absorber film (24) comprises a film of aluminum. The X-ray source of one of the claims 1 to 3, wherein said absorber film (24) is thinner than said target film (22). Use of a X-ray source according to one of the claims 1 to 4 in X-ray photoelectron spectroscopy (XBS).

Inventors: SOEZIMA HIROYOSHI, SOEZIMA, HIROYOSHI
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1986
Main classification: H01J35
IPC codes: G21K1, G21K5, H05G1, H01L21, H01J35, G03F7, G21K7