X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-07-16
2001-07-10
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S085000, C378S034000
Reexamination Certificate
active
06259764
ABSTRACT:
TECHNICAL FIELD
This invention relates to the focusing of X-rays and. more particularly, to the utilization of microminiature periodic structures for focusing hard X-rays.
BACKGROUND OF THE INVENTION
In a number of applications of practical importance, it is necessary to be able to focus rays emanating from an X-ray source into a small spot size. For so-called hard or relatively high-energy X-rays, this is a particularly difficult and challenging task. Various techniques for fabricating optical elements capable of focusing hard X-rays are described in a paper entitled “Microfocusing Optics for Hard X-Rays Fabricated by X-Ray Lithography” by A. A. Krasnoperova et al, SPIE Proc., vol. 2516, pages 15-26, 1995.
In particular, a number of structures made by integrated-circuit fabrication processes and suitable for focusing hard X-rays have been priorly proposed. Among these are a variety of periodic structures including Fresnel zone plates.
Heretofore, Fresnel zone plates for hard X-rays have been formed in a layer whose thickness is specified by a particular phase-shift requirement. In practice, the thickness of such a layer from which phase-type zone plates are fabricated has typically been at least about several micrometers (&mgr;m).
To achieve an extremely small or high-resolution spot size with a Fresnel zone plate onto which X-rays of a specified energy impinge, the smallest feature of the zone plate structure must have a width that is comparable in size to the desired spot size. Thus, for example, if the features of the zone plate are formed in a three-&mgr;m-thick layer and an aspect ratio (thickness-to-width dimensions) of about ten is manufacturable, the smallest feature that can be defined in the zone plate structure is approximately 0.3 &mgr;m [or about 300 nanometers (nm)]. In that case, the zone plate is capable of focusing the specified hard X-rays to a spot size having a diameter of the order of
300
nm. But, as the energy of the incident X-rays increases, i.e. for harder X-rays, the required thickness of the zone plate increases in order to ensure the correct phase shift between adjacent zones. Given the same manufacturable aspect ratio, this results in thicker zone plates with larger feature sizes and hence larger spot sizes.
Accordingly, efforts have continued by workers skilled in the art directed at trying to devise improved structures suitable for focusing hard X-rays to a small spot size. It was recognized that such efforts, if successful, would provide an important instrumentality for use in various practical applications such as in non-destructively examining small features in integrated circuits.
SUMMARY OF THE INVENTION
In accordance with the principles of the present invention, a layer of a single-crystal material is formed on a substrate made of a substance that does not satisfy the Bragg condition for reflection when the layer of single-crystal material does. The substrate can even be of single-crystal material; the only requirement is that the substrate and the thin single-crystal layer do not simultaneously satisfy the Bragg condition.
In particular, in accordance with the invention, the single-crystal layer is patterned to define a periodic structure such as a multi-element amplitude-type Fresnel zone plate. In the periodic structure, selected portions of the single-crystal layer are totally removed to reveal the underlying substrate. A portion of the incident X-rays above a threshold energy level and directed at the zone plate at a specified angle is reflected from the elements of the zone plate. Specifically, the reflected rays constructively converge to form a focused spot.
In further accordance with the invention, the width of the narrowest element of such an amplitude-type zone plate, and thus the size of the focused spot, may be decreased while maintaining an achievable aspect ratio simply by decreasing the thickness of the single-crystal layer. Correspondingly, as the thickness of the single-crystal layer decreases, the intensity of the focused spot also decreases.
REFERENCES:
patent: 5272744 (1993-12-01), Itou et al.
patent: 5719915 (1998-02-01), Koike et al.
patent: 6128364 (2000-10-01), Niemann
“Microfocusing Optics for Hard X-Rays Fabricated by X-Ray Lithography” by A.A. Krasnoperova et al, SPIE vol. 2516, pp. 15-26.
Evans-Lutterodt Kenneth
Kim Chang-yong
Agere Systems Guardian Corp.
Dunn Drew A.
Porta David P.
LandOfFree
Zone plates for X-rays does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Zone plates for X-rays, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Zone plates for X-rays will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2516982