X-ray or gamma ray systems or devices – Specific application – Fluorescence
Reexamination Certificate
1999-11-17
2002-11-05
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Fluorescence
C378S003000, C378S006000, C378S143000
Reexamination Certificate
active
06477226
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention concerns an X-ray analysis device comprising an X-ray source for the illumination of a sample with X-rays, a sample support for receiving the sample, and a detector for detecting the diffracted or scattered X-radiation or fluorescent X-radiation emitted by the sample, wherein an X-ray optical construction element of semi-conductor material having a plurality of channels which are essentially transparent for X-rays is provided in the path of rays between the X-ray source and the detector.
An X-ray optical construction element with the above-mentioned described features is known from U.S. Pat. No. 4,933,557.
X-ray optical construction elements in the path of rays of the X-ray analysis device may be e.g. X-ray windows, X-ray collimators or X-ray lenses. The X-ray windows have to be sufficiently transparent also for soft X-radiation. For this reason, they have been produced up to now either from elements with a small z-value or having a very small thickness. Windows for X-ray tubes (e.g. for Cu-k&agr; rays) have been produced up to now from beryllium which has the large disadvantage that such tubes have to be disposed of as special waste, since beryllium is highly poisonous. Alternatively, also X-ray windows of CVD diamond layers have been examined which are, however, relatively expensive to produce.
It is known to use thin organic films (e.g. mylar, polypropylene etc.) as window layers for X-ray detectors, however, these X-ray windows have to be additionally supported by grid plates as support to withstand the pressure of the outer atmosphere with respect to the normally evacuated X-ray detector. From U.S. Pat. No. 5,416,821 it is e.g. known to produce such grid plates of anisotropically etched 110 silicon discs having collimating properties such that the construction element is given the combined function of an X-ray collimator window.
In contrast thereto, it is the object of the present invention to present an X-ray analysis device with the above described features, wherein one or several X-ray optical construction elements are used which are, on the one hand, not poisonous, but on the other hand are particularly transparent for X-rays, whereby it is tried to achieve a relatively high mechanical rigidity also for large openings and very short construction lengths and thus a particularly long service life and high pressure stability and density.
SUMMARY OF THE INVENTION
According to the invention, this complex object is achieved in a surprisingly simple but efficient manner in that the X-ray optical construction element comprises a semi-conductor wafer having micropores extending in the direction of the rays in an essentially parallel manner and comprising diameters of between 0.1 and 100 &mgr;m, preferably 0.5 to 20 &mgr;m which are formed by etching.
An X-ray optical construction element of such a semi-conductor wafer, when used e.g. as a vacuum seal, has a considerably higher density than the films of synthetic material used up to now. In contrast to X-ray windows of beryllium, such a construction component is not poisonous and can be produced with very high mechanical rigidity e.g. by silicon nitride sheets having an extremely small thickness of 50 nm, whereas beryllium windows usually have a minimum thickness of 25 &mgr;m. Due to the refined structures, the inventive X-ray optical construction element can be produced with a very short construction length which mainly corresponds to the wafer thickness (100 to 700 &mgr;m) whereas e.g. known X-ray collimators have minimum construction thicknesses in the range of several centimeters. Of course, the small construction thickness of the inventive X-ray optical construction element is highly advantageous also with respect to its function as X-ray window or X-ray lens, wherein there is no need to make concessions to the mechanical rigidity.
The article by V. Lehmann “The Physics of Micropore Formation in Low Doped n-Type Silicon”, Journal of the Electrochemical Society, Vol. 140, No. 10, 2836-2843 (1993) discloses an electro-chemical method of producing micropores in semi-conductor wafers. The holes referred to as “macropores” in said article having diameters of a magnitude of 10 &mgr;m are etched in such a manner that the walls between the generated pores are very thin (e.g. 2 &mgr;m) and that each respective pore tip is closed by a likewise thin layer (in general only a few &mgr;m) of silicon.
In a preferred embodiment of the inventive X-ray analysis device, the micropores of the X-ray optical construction element have not been etched continuously such that a ground surface having a thickness of between 1 to 100 &mgr;m, preferably between 5 and 20 &mgr;m remains. For this reason, the effective silicon layer for the penetrating X-ray light is very thin, which makes the X-ray optical construction component highly transparent. The grid of the pore walls, however, provides for a relatively high mechanical stability despite the apparently small wall thickness.
In a preferred further development of this embodiment, the inner side of the micropores is lined with a stabilizing layer which closes the micropores on one side of the semi-conductor wafer. This enhances the mechanical stability of the X-ray optical construction element without considerably impairing the transparency for X-radiation.
In order to further increase the X-ray transparency, in a particularly preferred further development, the ground surface of the semi-conductor wafer on the side on which the stabilizing layer closes the pores is etched down to the stabilizing layer. This selective etching of the wafer material leaves only a thin film of approximately 20 to 100 nm thickness of the stabilizing layer which covers the pore ground and thus generates an extremely thin window for the X-radiation. In the ideal case, the inventive X-ray optical construction element used as a window for X-ray fluorescence detectors may be transparent for energies of not more than around 100 eV.
In a particularly preferred manner, the stabilizing layer is disposed by means of CVD methods (chemical vapor deposition). CVD methods of this type are known per se. The layered material is thereby disposed onto the surface to be covered and, after cooling down, is subjected to compression thereby avoiding the formation of cracks.
It is preferred to use silicon nitride (Si
3
N
4
), boron nitride (BN), boron hydride (BH) or possibly also boron carbide or silicon carbide or even carbon as materials for the stabilizing layer. With these it is possible to produce extremely thin films which cover the ground of the pore, but still have sufficiently high mechanical rigidity and vacuum density when the inventive X-ray optical construction element is used as X-ray window.
One embodiment of the inventive X-ray analysis device is particularly preferred in which the semi-conductor wafer of the X-ray optical construction element consists of silicon. A varied and common technology for the micro-fine processing of this material is known from the production of electronic components.
The semi-conductor wafer according to the inventive X-ray optical construction element will have in general a thickness of between 10 &mgr;m and 1 mm, preferably between 100 and 700 &mgr;m.
It is the easiest to produce micropores having a circular cross-section with the processing methods known per se from semi-conductor technology. With modifications of the known methods, it is also possible to produce other cross-sectional shapes, e.g. elliptical cross-sections.
In the easiest case, the micropores may comprise a cross-section which is constant along the pore length. This geometrical shape will be sufficient for most cases of application.
When the inventive X-ray optical construction element is used e.g. as X-ray lens, it may be advantageous to provide the micropores with a cross-section that varies along the pore length.
One embodiment is particularly simple in which the micropore axis extends essentially perpendicularly to the surface of the semi-conductor wafer.
As an alternative, embodiments
Golenhofen Rainer
Lehmann Volker
Bruker AXS Analytical X-Ray Systems GmbH
Hobden Pamela R.
Porta David P.
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