EP1323170B1 - X-ray optical system - Google Patents

Abstract

The invention relates to an X-ray optics arrangement having an X-ray source, one element focussing X-rays and one element reflecting X-rays for the generation of a parallel X-radiation having a small beam cross section of high photon flux density. To solve this problem the X-radiation of the X-ray source is directed with the focussing element upon the convex, parabolic and reflecting surface of the reflecting element, and allowed to be advantageously employed in the X-ray analysis, e.g. with the X-ray diffraction measurement, reflectometry and/or fluoro-chemical analysis.

Description

The invention relates to an X-ray optical arrangement according to the preamble of claim 1. It can be special advantageous in X-ray analysis, e.g. in the X-ray diffractometry, reflectometry and / or the fluorescence analysis can be used.

In the X-ray analytics are for the most diverse Applications X-rays with high intensity, i.e. especially high photon density required. This can be done by focusing the x-rays be achieved. In many cases, however, it is cheaper X-radiation with very small divergence, in the best case, use as parallel X-rays to be able to.

It may also be necessary in X-ray analysis be to monochromatize the x-rays to to carry out certain analyzes.

In X-ray analysis, it is also desired a high surface sensitivity of the X-radiation on surfaces to be analyzed or in fluidic Samples present on substrate slides are to reach. In these cases, the X-rays preferably grazing, i. with relative small angles of incidence up to a few degrees of incidence angles or a few tenths of a degree angle of incidence, i.e. near the critical angle of total reflection, on a sample or a corresponding substrate surface directed and consequently the radiation cross section according to 1 / sin  projected onto the sample surface becomes. It is desired the photon density ever Increase the area on the projection surface or to focus on a smaller projection screen. The surface intensity and consequently also the photon density can be known by strong bundling parallel or nearly parallel X-rays are increased and consequently also the each locally detectable measurement signal of a sample increases become. In particular, the spatial resolution of Measuring signals, i. the most accurate assignment possible Measuring signals to the measuring location make high demands the test setup.

Usually, correspondingly small-sized Apertures in the beam path of the X-ray radiation arranged so that only part of the X-rays through the aperture to reach the site and so a locally defined assignment of the measurement signal is reached to the measuring location. Of course requires the use of such screens intensity losses the X-rays that are not for measurement can be exploited. This suffers the accuracy of measurement or it must be an increase in the required Measuring time can be accepted, which for many Use cases is not desired or even measurements impossible.

The mentioned disadvantages could also with X-ray optical Constructions in which multilayer systems with concave curvatures adapted period thicknesses, the are described for example in DE 44 43 853 A1, not completely eliminated and it is not succeeded, the beam cross section of the X-ray radiation reduce so much that in consequence of the required Iris occurring intensity losses, after as before, although occur in a reduced form.

In particular, in semiconductor technology the Miniaturization is progressing strongly and the step out of the Micro- and nanoscale requires analytics Ways to make certain elements and connections with high measuring accuracy, at the same time high To analyze spatial resolution in a short time.

It is therefore an object of the invention an X-ray optical To provide arrangement with the parallel, but at least approximately parallel X-rays with small beam cross section and accordingly high photon density provided can be.

According to the invention, this object is achieved with the features of claim 1. Advantageous embodiments and further developments of the invention can, with the features mentioned in the subordinate claims be achieved.

The X-ray optical arrangement according to the invention uses usual X-ray optical elements, like a suitable X-ray source, X-rays focusing and an X-ray reflecting Element. The X-ray radiation of the X-ray source on the focusing element directed, which is a lens effect reaching element, but cheaper to a corresponding shaped reflector can act. The of X-ray focused on this element is on directed an X-ray reflecting element, whose reflective surfaces are convex and is formed parabolic.

Due to this surface shape of the reflective element can simultaneously bundling (compression) X-radiation and its parallel alignment be obtained with negligible divergence, the on a suitably arranged and aligned Surface of a sample or a substrate directed can be.

Depending on the shape of the focusing element, the convergent X-ray radiation with punctiform, elliptical or line-shaped cross section are, of course, the surface contour of the X-ray reflecting Element is adapted to this geometry. For linear Beam cross sections can be focused and the reflective element have cylinder symmetry.

For many applications, the function of the used aperture and it is used for stray light suppression. However, in individual cases are still Apertures required to increase the spatial resolution, becomes a much smaller part of the X-ray intensity hidden from the aperture, because the photon density in the correspondingly compressed X-radiation is considerably higher than that of known Solutions is the case. So can an increase in intensity greater than 2 can be achieved.

At least the surface of the reflective element can be a single reflective layer, in In many cases, however, cheaper, a multilayer system exhibit.

If only a single reflective layer or a reflective element made of a suitably suitable material is used, the X-ray radiation from the focusing element can be directed onto the reflective element at an angle ≦ the critical angle  _{c of} the total reflection and the desired effect can be achieved.

In many cases, however, it is more favorable to use a gradient multilayer system in which the individual layers of the multilayer system, taking into account the different angles of incidence of the x-rays, have a correspondingly adapted thickness distribution with which the respective angles of incidence  _i and Bragg's for a predeterminable x-ray wavelength Satisfy equation on each surface element of the reflective element. The gradient layers have a double-layer thickness that changes over the length.

This can further increase the photon density and also an improved monochromatization of X-radiation can be achieved. The adjacent ones Single layers of a multilayer system point different X-ray optical refractive indices on.

The largest possible compression of the X-ray radiation can be obtained when focusing points F of focusing and reflective element with each other match, but at least in the immediate Are arranged close to each other.

The focusing element forms the X-ray source in a line focus, it is also advantageous the parabolic shape of the reflective element cylindrically symmetric to choose a linear To receive parallel radiation.

In addition to the already mentioned advantages, can with the X-ray optical arrangement according to the invention also at small angles of incidence of X-rays on the Samples achieved a higher spatial resolution of the measurement signals be, because at approximately the same number of photons reduces the projected area on the sample becomes.

In general, with the invention, the signal-to-noise ratio be improved because with the reflective Element an additional monochromator is arranged in the beam path.

In addition to shortening the measurement time can also be the dynamic Range of measurement can be increased, which is e.g. the information content of a measured reflectogram rises, possibly due to background signals covered diffraction orders are detected can.

By translational movement and / or pivoting around certain distances and angles of the focusing and / or reflective element, the X-radiation on certain small measuring locations / areas be directed.

The invention is based on an exemplary embodiment be explained.

Showing:

FIG. 1:

schematically an example of an X-ray optical Arrangement according to the invention in the divergent X-radiation of an X-ray source on a focusing Element directed and in parallel radiation converted with smaller beam cross section will and

FIG. 2:

in schematic form an example of a Arrangement, in the case of the parallel X-ray radiation directed to a focusing element and in parallel with clearly converted smaller beam cross section becomes.

In the example shown in Figure 1 becomes divergent X-radiation of an X-ray source 1 on a concave, elliptical or parabolic shape Surface, with for the X-ray radiation used reflective surface, in this case a Multilayer system, directed. The x-ray radiation is reflected from there and at the same time on the convex, parabolic reflective surface of the directed to the reflective element, the from the reflective element 3 reflected x-ray radiation simultaneously compressed and aligned in parallel becomes. The bundled parallel X-radiation can then for the different X-ray analysis techniques be used, wherein X-ray cross-sections in the range of less than 200 microns easily accessible are.

On the reflective surface of the reflective Element 3 can also be a multilayer system, in which the layer thicknesses of the individual layers locally, according to the different angles of incidence the incident X-ray considered are, be present. In this case, the parallel, reflected x-rays not only have a higher intensity, but they will also monochromatized.

In the example shown in Figure 2 of an inventive Arrangement becomes X-ray with less or no divergence in parallel form the concave, parabolic reflective surface a focusing element 2 directed. Of this Surface is the X-ray radiation accordingly reflected and focused at the same time and on the Surface of the reflective element 3 directed. From the representation is clearly visible that the Beam cross section b ', that of the reflective element 3 parallel reflected X-rays significantly smaller than the beam cross-section b, the original used parallel X-radiation is. from that follows that with sufficiently high reflectivity of (2) and (3) the photon density in the of the reflective Element 3 reflected X-radiation opposite the original parallel radiation increased has been.

Advantageously, the reflective element is again provided with a multilayer system on the reflective surface, wherein the period thickness d of the individual layers satisfy the Bragg equation λ = 2d _eff sin  (d _eff = the effective period thickness taking into account the dispersion).

Since the focused X-radiation predetermines different angles of incidence  _i on the reflecting surface of the reflecting element 3, it is accordingly also necessary to use a corresponding gradient multilayer system which has a different period thickness d _i at the corresponding X-ray wavelength corresponding to the respective angles of incidence.

Possibilities for the formation of such a multilayer system are in the unpublished DE 199 32 275, on their relevant disclosure be fully used should.

Both in Figure 1, as well as in Figure 2 is shown that the corresponding reflective surfaces the focusing element 2 and the reflective element 3 is formed and the two elements 2 and 3 are arranged to each other are that their focus points F coincide with each other.

In the examples of Figures 1 and 2, the reflective Surface of the focusing element 2 a parabolic shape (Figure 2), but it can also an elliptical contour (Figure 1) are used.

p/2 insbesondere die Gleichung b b' = Y E -Y A Y' E -Y' A = 2px E -2px A 2p'x' E -2p'x' A wobei die Parabelgleichungen Y=2px Y'=2p'x' zugrunde gelegt werden
bzw.In the example according to FIG. 2, in which parallel or nearly parallel output X-ray radiation is used, assuming x _A , x _E

p / 2 in particular the equation b b ' = Y e - Y A Y ' e - Y ' A = 2 px e - 2 px A 2 p'x ' e - 2 p'x ' A where the parabolic equations Y = 2 px Y ' = 2 p'x ' be based on
respectively.

Using ray-set and parabola equation, this may be too b b ' = p p '

be simplified, where p and p 'the respective Parabola parameter of focusing element 2 and reflective element 3 are.

It follows that an increase in the photon flux density can always be achieved if that with the product of the center reflectivities of focusing Element 2 R (2) and reflective element 3 R (3) multiplied ratio of beam cross sections R (2) * R (3) * b / b '> 1 becomes.

Claims (10)

1. X-ray optical arrangement having an x-ray source, an x-ray focusing element and an x-ray reflecting element for the purpose of producing parallel x-radiation with a small beam cross section and of high photon density, characterized in that the x-radiation of the x-ray source (1) is directed with the aid of the focusing element (2) onto the convex, parabolic and reflecting surface of the reflecting element (3).
2. X-ray optical arrangement according to Claim 1,
   characterized in that a reflecting layer or a multilayer system is present on the surface of the reflecting element (3).
3. X-ray optical arrangement according to Claim 1 or 2, characterized in that the individual layers of the multilayer system are gradient layers.
4. X-ray optical arrangement according to Claim 1 or 2, characterized in that the x-radiation is directed onto the reflecting element (3) at an angle ≤ critical angle _c of total reflection.
5. X-ray optical arrangement according to one of Claims 1 to 3, characterized in that the x-radiation is directed onto the multilayer system with gradient layers at incidence angles _i such that the Bragg equation is satisfied on each surface element of the reflecting element (3) for a prescribable x-radiation wavelength.
6. X-ray optical arrangement according to one of Claims 1 to 5, characterized in that the focal points F of the focusing element (2) and of the reflecting element (3) correspond.
7. X-ray optical arrangement according to one of Claims 1 to 6, characterized in that the focusing element (2) has a concave, parabolic or elliptical surface.
8. X-ray optical arrangement according to one of Claims 1 to 7, characterized in that the parabolic shape of the reflecting element (3) is cylindrically symmetrical.
9. X-ray optical arrangement according to one of Claims 1 to 8, characterized in that in each case, neighbouring individual layers of the multilayer system have different x-ray optical refractive indices.
10. Use of an x-ray optical arrangement according to one of Claims 1 to 9 in x-ray diffractometry, reflectometry and/or x-ray fluorescence analysis.

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