Patent Number: 062663925
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the soller slit according to the present invention will be described. Before describing the soller slit of the present invention in detail, the utilization of the soller slit will be described briefly. FIG. 5 illustrates a focusing type X-ray optical system that is an example of utilization of the soller slit. The X-ray optical system includes an X-ray focus `F` of a line type generating X-rays, a specimen `S` to be measured and an X-ray counter 1 for detecting X-rays diffracted by the specimen `s`. An incident side soller slit 2 and a divergence limiting slit 3 are arranged in the order between the X-ray focus `F` and the specimen `s`. A scatter limiting slit 4, a receiving side soller slit 6 and a receiving slit 7 are arranged in the order between the specimen `S` and the X-ray counter 1. Divergent X-rays generated from the X-ray focus `F` are directed to the incident side soller slit 2 to restrict divergence thereof in a vertical direction, that is height direction. The X-rays are subsequently incident on the divergence limiting slit 3 by which divergence thereof in a horizontal direction, that is width direction, is restricted. Then, the X-rays whose vertical and horizontal divergences are thus restricted are directed to the specimen `S`. When Bragg's diffraction condition is satisfied between crystal lattice plane of the specimen `S` and the incident X-rays, the X-rays are diffracted by the specimen `S`. X-rays diffracted by the specimen `S` passes through the scatter limiting slit 4 to remove scattered component thereof, and then through the receiving side soller slit 6 to limit divergence thereof in the height direction. Then, the diffracted X-rays are focused on the receiving slit 7. Portions of the focused diffracted X-rays that fall in areas defined by the receiving slit 7 passes therethrough and are received by the X-ray counter 1 to thereby calculate an intensity of X-rays. In the X-ray measurement mentioned above, it has been known that, when an X-ray component diverging in the height direction is taken in the X-ray counter 1, the so-called umbrella effect occurs, with which resolution is degraded. In order to avoid the degradation of resolution, the soller slits 2 and 6 prevent such X-ray component diverging in the height direction from being taken in the X-ray counter 1. FIG. 6 is a plan view of a parallel X-ray beam optical system that is another example of the utilization of the soller slit. This X-ray optical system includes an X-ray focus `F` of a line type generating X-rays, a specimen `S` to be measured and the X-ray counter 1 for detecting X-rays diffracted by the specimen `S`. An incident side soller slit 2 is arranged between the X-ray focus `F` and the specimen `S`. A receiving side soller slit 6 is arranged between the specimen `S` and the X-ray counter 1. Divergent X-rays generated from the X-ray focus `F` are transformed into parallel beams by the incident side soller slit 2 and is incident on the specimen `S`. X-rays diffracted by the specimen `S` is received in the X-ray counter 1 while its divergence is restricted by the receiving soller slit 6. And then, intensity of X-rays is calculated. The receiving side soller slit 6 functions to improve resolution in the X-ray measurement by restricting the divergence of X-rays diffracted by the specimen `S`. In the focusing type optical system shown in FIG. 5 and in the parallel beam optical system shown in FIG. 6, the incident side soller slit 2 is formed by laminating a plurality of metal foils 9 with interposing spacers 8 as shown in FIG. 1. This is also true for the receiving side soller slit 6. When diverging incident X-rays R1 are incident on the soller slit 2 or 6, divergence thereof in a vertical direction is restricted, resulting in parallel X-rays R2 on the receiving side. By rotating the soller slit 2 or 6 by an angle of 90.degree., it is possible to obtain parallel X-ray beams having a width in the lateral direction. As one of the optical characteristics of the soller slit 2 and 6, there have been known an opening angle .phi. shown in FIG. 2, which is defined by the following formula: EQU .phi.=2.times.tan.sup.-1 (t/L) where "L" is a length of the metal foil 9 and "t" is a gap between adjacent metal foils 9. The opening angle .phi. is an important element for defining the resolution of the X-ray optical system utilizing the soller slit. In this example, sintering a metal material such as tungsten (W) or molybdenum (Mo) forms the metal foils 9 of the soller slits 2 and 6. The total reflection of X-rays passing through the soller slits 2 and 6 is restricted by utilizing roughness of the surfaces of the metal foils, which is naturally provided by the sintering. According to the currently usable sintering processing, it is possible to effectively form a desired high harmonic surface roughness, that is, surface roughness having space period of, for example, not larger than 50 .mu.m, preferably 20.about.50 .mu.m, and having RMS value of, for example 20 nm.about.1 .mu.m, preferably 20.about.50 nm, on the material surfaces. The high harmonic surface roughness is very effective to restrict total reflection of X-rays. By restricting total refection of X-rays in this manner, it is possible to improve resolution in the X-ray measurement. Alternatively, the metal foils 9 of the soller slits 2 and 6 may be formed by using oxidized stainless steal or brass (Cu: Zn=5: 1), with improved resolution of the X-ray measurement. When stainless steal foil is oxidized, oxide material is formed on surfaces of the stainless steal foil, with which surface roughness having space period of, for example, not larger than 50 .mu.m, preferably 20.about.50 .mu.m, and having RMS value of, for example, 20 nm.about.1 .mu.m, preferably 20.about.50 nm, can be effectively formed on surfaces of the stainless steal foil. The high harmonic surface roughness is very effective to restrict total reflection of X-rays as mentioned previously. By restricting total reflection of X-rays in this manner, it is possible to improve resolution in the X-ray measurement. Embodiments of the soller slit according to the present invention will be described in detail. First Embodiment Metal foils 9 were prepared from tungsten plate formed by sintering and a soller slit 2 or 6 was fabricated by using the metal foils 9. Besides, metal foils 9 were prepared from a rolled stainless steal plate and a rolled brass plate. Further soller slits 2 or 6 of a prior art were fabricated by using the metal foils 9 and the brass foils 9, respectively. FIG. 3 shows X-ray intensity vs. diffraction angle characteristics curves obtained X-ray measurement performed using X-ray optical systems constructed with using the respective three soller slits. In this measurement, a peak broadening that is defined by FWHM (full width of half-maximum) intensity and a tailing is investigated. Incidentally, the term "tailing" means a width of a bottom portion T in the characteristic curve shown in FIG. 3. It was observed that the peak broadening was substantially smaller in the case (curve A) where the soller slit fabricated by sintering tungsten is used, compared with the cases where the soller slits fabricated by using the rolled stainless steal (curve B) and the rolled brass (curved C). This means that resolution when the soller slit fabricated by sintering tungsten is used is highest. Second Embodiment Metal foils 9 shown in FIG. 1 were prepared by the conventional method utilizing a rolled brass (Cu: Zn=5: 1) and then, soller slits 2 and 6 were fabricated by using the metal foils 9. Subsequently, an X-ray measurement was performed with using an X-ray optical system constructed by using of the soller slits thus formed. FIG. 4 shows an X-ray intensity vs. diffraction angle characteristic curve D obtained by an X-ray measurement performed with using X-ray optical systems constructed by using of the soller slits. Thereafter, the metal foils 9 of the soller slits 2 and 6 were disassembled from the latter and oxide material is formed on the surfaces of the metal foils 9 by oxidizing the latter with using dense nitric acid. Then, the oxidized metal foils 9 were re-assembled in the soller slits 2 and 6 and an X-ray measurement was performed with using thus re-assembled soller slits 2 and 6. The characteristic curve E shown in FIG. 4 is a result of the X-ray measurement. As compared the characteristic curve E corresponding to the oxidized metal foils and the characteristic curve D corresponding to the metal foils which are not oxidized, it is clear that the characteristic curve E is superior to the characteristic curve D in the peak broadening specified with both FWHM value and tailing. That is, when the soller slits fabricated by using the oxidized metal foils are employed, resolution of the X-ray measurement can be improved substantially. Other Embodiment Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited thereto and can be modified or changed variously within the scope of the present invention defined by the appended claims. For example, the soller slit according to the present invention can be applied to other X-ray optical system than the X-ray optical system shown in FIGS. 5 and 6. Further, the structure of the soller slit is not limited to that shown in FIG. 1 and can be any structure provided that the metal foils are arranged with a predetermined space between adjacent ones. For example, the spacers are not always arranged on both sides of each metal foil. It is possible to arrange the spacer on one side of each metal foil.