X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
2001-05-29
2003-06-03
Dunn, Drew A. (Department: 7882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S070000, C378S085000, C378S145000
Reexamination Certificate
active
06574306
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a channel-cut monochromator which can be used in a high-resolution X-ray diffractometer.
The high-resolution X-ray diffractometer has developed based on a certain technique called “double crystal method”. With the double crystal method, a rocking curve (a graph indicating a relationship between an X-ray diffraction intensity and a diffraction angle for a certain diffraction peak) of a single crystal sample can be measured in such a manner that X-rays are diffracted by the first crystal to become a monochromatic beam and then it irradiates the sample (the second crystal). The first crystal may be usually a perfect-crystal of silicon (Si) or germanium (Ge). In the double crystal method, it is known that the angular resolution of the rocking curve becomes highest when the first crystal is the same as the sample crystal and also the diffraction plane of the first crystal is coincident with the object lattice plane of the sample crystal (i.e., the same d-value which is an interplaner spacing of lattice planes). Such an X-ray optics, in which the first crystal and the sample crystal have the same d-value, is called “parallel arrangement”. With this ideal arrangement, the full width at half maximum intensity (FWHM) of a measured rocking curve becomes narrowest and the shape of the rocking curve is almost coincident with the theoretically-predicted shape.
Alternatively, even when the first crystal and the sample crystal are not perfectly the same, a high resolution is obtained using the first crystal having the d-value which is nearly equal to that of the object lattice plane of the sample crystal, this optics being called “quasi parallel arrangement”. For example, the first crystal may be a germanium perfect-crystal with {400} reflection for obtaining the rocking curve of {400} reflection of GaAs single crystal or InP single crystal.
A large difference in d-value between the first crystal and the second crystal lowers resolution because the wavelength dispersion effect is added in a manner of convolution, so that the FWHM of a measured rocking curve becomes broader. It is desirable therefore, for measuring the highest-resolution rocking curve using the double crystal method, to select the first crystal having a d-value most closest to that of the sample crystal, the d-value of the sample crystal depending upon the kind of the crystal and the Miller indices of the object lattice plane of reflection. Accordingly, it is necessary to change the first crystal frequently in response to the kind of the sample crystal and its object Miller indices and further to conduct X-ray optical alignment whenever the first crystal is changed.
It is troublesome, however, to conduct the optical alignment again by altering the crystal arrangement based on the double crystal method and such alignment operation needs skill. Therefore, some improvements have developed for easy alignment: for example, the second crystal can be adjusted by rotation around the first crystal or the X-ray source can be adjusted by rotation around the first crystal as disclosed in, for example, Japanese patent publication No. JP 1-86100 A (1989). Such improvements, however, still need crystal exchange operation and alignment operation. Thus, such improvements still need troublesome operation and are not so efficient.
The first crystal is usually a flat crystal, but it is known that it may be a channel-cut monochromator which is manufactured by processing a groove on a monolithic single crystal block. X-rays may be diffracted plural times at the side walls of the groove to become a monochromatic parallel beam as disclosed in, for example, Japanese patent publication No. JP 9-49899 A (1997). If X-rays are diffracted even-number (e.g., two) times at the channel-cut monochromator, the output X-ray beam becomes a monochromatic parallel beam and travels in a direction parallel to the incident X-ray beam. If the output X-ray beam from the first crystal is parallel to the incident X-ray beam as mentioned above, an output X-ray beam from the first crystal after exchange of the first-crystal is to become parallel to the former output X-ray beam before the exchange. Accordingly, even when the first crystal is exchanged, it is not necessary, for alignment operation, to “rotate” the X-ray tube or the sample unit (i.e., goniometer unit) so that the system space can be minimized, noting that a translational movement is needed for alignment operation.
The channel-cut monochromator produces an output X-ray beam which is basically identical with one from a flat crystal monochromator with single reflection. However, when X-rays are diffracted “plural times” at the channel-cut monochromator, the reflection coefficient curve of the output X-ray beam has skirts with extremely reduced intensities, this being the effect of the plural times of diffraction. Also using the channel-cut monochromator, it is necessary, for obtaining the highest-resolution rocking curve, to exchange the monochromator to one having an optimum d-value in response to the kind of the sample crystal and its object Miller indices. And the exchange of the channel-cut monochromator requires in general alignment operation with a translational movement of the sample unit.
A further improvement, which requires no translational movement of the sample unit either, is to use a four-crystal monochromator as disclosed in, for example, Japanese patent publication Nos. JP 59-108945 A (1984) and JP 4-264299 A (1992). The four-crystal monochromator is composed of two channel-cut monochromators arranged to be mirror-symmetrical. The four-crystal monochromator produces a highly-monochromatic and highly-parallel output X-ray beam which is also on the extension line of the incident X-ray beam. Using the X-ray beam produced by the four-crystal monochromator, a high-resolution rocking curve of a sample is always obtained without depending upon the kind of the sample crystal and its object Miller indices. Using the four-crystal monochromator however, the output X-ray beam inadvantageously has a very low intensity which would be about one hundredth of that produced by the double crystal method. Thus the use of the four-crystal monochromator has some problems: (1) it requires a high-power X-ray source which is expensive; and (2) it takes a long time to measure the rocking curve for accumulating the intensity. Therefore, the four-crystal monochromator would be limited to have only such reflecting surfaces that its Miller indices can produce a high-intensity X-ray beam.
Next, the state of art in X-ray analysis using a high-resolution X-ray diffractometer is described below. As a thin film technique spreads, object samples of the high-resolution X-ray diffractometer spread from the conventional bulk crystals toward film crystals on substrates. The crystal state of the film is in variety and classified to (1) a perfect epitaxial layer (pseudomorphic layer), (2) an epitaxial layer in which dislocations occur in a boundary between a substrate crystal and the epitaxial layer for strain relaxation, (3) an epitaxial layer having an orientation distribution (mosaicity), (4) a polycrystalline thin film having strong preferred orientation, (5) a polycrystalline thin film having no preferred orientation and (6) an amorphous thin film. Under the circumstances, the high-resolution X-ray diffractometer has been expected to have various functions so as to measure not only the rocking curves mentioned above but also reflection coefficient (near the total reflection region with glancing incident angles) and polycrystalline film X-ray diffraction.
Therefore, various incident optical systems have to be prepared to regulate, according to the sample state, the parallelism and the wavelength range of X-rays which are incident on a sample. Such an incident optical system may be a module-type incident optical unit which can be exchanged for another or an incident optical system which can be switched to another state without removing a crystal as disclosed in
Dunn Drew A.
Frishauf Holtz Goodman & Chick P.C.
Rigaku Corporation
Thomas Courtney
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