DE102010049994B3 - Resist structure for producing an X-ray optical lattice structure - Google Patents

Abstract

The present invention relates to a resist pattern for producing an X-ray optical grating structure. The invention includes stabilizing beams that are incorporated into the resist pattern. The webs of the Resisstruktur at a first angle α are mounted on a substrate and the stabilizing beams at a second angle β, wherein between α and β must be at least a distance of 20 ° and at most a distance of 70 ° may exist to the to obtain stabilizing effect. In particular, the production of X-ray optical grating structures with aspect ratios of more than 500 is to be made possible without the grid bars bending, or the stabilizing structure has an adverse effect on the visibility. The resist structures are particularly suitable for the production of X-ray optical grating structures made of gold.

Description

The present invention relates to a resist pattern for producing an X-ray optical grating structure.

For many applications, such as in medical diagnostics or material analysis, X-rays are used. Here, optical gratings are used whose structure and in particular their aspect ratio special requirements are made, since the quality of the imaging technique referred to in the jargon as differential phase contrast imaging (DPCI) with X-ray depends decisively on the height of the optical grating structures.

In order to achieve a high contrast relevant for medical applications, the absorption of the material deposited in the resist structure, in the web gaps (usually gold) in the range should be greater than 80%. Depending on the application, X-ray energies, for which the tomographic structure is optimally designed and termed design energies, are in the range from 20 keV to 60 keV, with the polychromatic radiation of the x-ray tube also carrying energies up to about 10 keV above the design energy are present. This means that the thickness of the absorbing gold must be at least 100 microns and thus the height of the resist structure over 100 microns.

Methods are known in the art for producing resist structures with heights of several hundred microns. In F. Pfeiffer et al., Nature Physics (2006) Advanced Online Publication, p. The possibilities of phase-contrast X-ray imaging with non-coherent X-ray sources are described. For the realization of these imaging systems, the production of lattice structures with a high aspect ratio is necessary. However, these demands on the dimensions of the absorbent structures, as well as their mechanical stability represent process engineering problems.

In E. Reznikova et al., Soft X-ray lithography of high aspect ratio SU8 submicron structures, Micro Syst. Techn. (2008) a method is described, which in principle allows the production of such structures. In the publication, however, it is also clear that at structural heights of greater than 60 μm, the webs of different lengths are bent and thus the aspect ratio is limited.

Known in J.Knowner, et al., Front and backside structuring of gratings for phase contrast imaging with x-ray tubes, Proc. SPIE, Vol. 7804, 780408 (2010), shows resist structures that have been attempted to prevent the problem of bending the grid bars by connecting the grid bars with fill bars. The disadvantage of this solution is that the gold bars are interrupted again and again by quasi transparent areas (filling bars). This results in fluctuating visibility values when analyzing the visibility V with a detector having a pixel size in the range of fewer grating periods and less. The visibility V is defined as follows V = (I _{max -I min} ) / (I _max + I _min ) where I _{max is} the maximum intensity value and I _{min is} the minimum intensity value in the generated X-ray image.

Proceeding from this, the object of the invention is to propose a resist structure for producing a roentgen optical lattice structure which avoids the disadvantages and limitations listed. In particular, the production of X-ray optical grating structures with aspect ratios of more than 500 is to be made possible without the grid bars bending, or the stabilizing structure has an adverse effect on the visibility.

The invention is based on the idea that stabilizing beams are introduced into the resist structure. The webs of the Resisstruktur are attached at a first angle α on the substrate and the stabilizing beam with a second angle β, wherein between α and β must be at least a distance of 20 ° and at most a distance of 70 ° may exist to the to obtain stabilizing effect.

Such resist structures are suitable for the production of X-ray optical grating structures. In the area of the stabilizing beam, the height of the material deposited in the web gaps is reduced by a maximum of the value d 'resulting from d '= d × 1 / cosβ where d is the perimeter diameter of the beam. The stabilizing effect of the bars is completely preserved, since the arrangement of the bars results in a stabilization of the entire area. Another advantage is that the height of the stabilizing beams can be repeated at will and thus significantly higher structures than previously possible. For N structures arranged one above the other, there is a height change of N × d, which corresponds to a few% of the total height and has only a marginal effect on the visibility.

With such structures, gratings for phase-contrast X-ray imaging of any height can be realized with approximately constant visibility over the entire area of the grating structure. This makes it possible to realize structures with energies of more than 40 keV, which have an absorption of 80% and more. This and the uniformity of the absorption allows a much better resolution in the phase contrast image.

The resist structures described above are also suitable for the production of gratings for neutron imaging because of their high aspect ratios.

The invention will be explained in more detail by means of examples and the figure.

1 schematically shows an embodiment of a resist structure whose webs 1 at an angle α = 90 ° on a substrate 2 are arranged and a field of cross-section round bars 3 that the webs 1 stabilized. The stabilizing bars 3 are at an angle β = 45 ° on the substrate 2 attached and cut the bars 1 in the embodiment shown in the 1 at an angle of 45 °.

The distance between two adjacent stabilizing beams must be in the range between double and 20 times the gap width for each direction, with the perimeter diameter of each beam between 1 μm and 10 μm. The beam circumference diameter is preferably 2 μm to 5 μm. Such an arrangement and dimensioning of the beams and the choice of the angle causes that in a web gap of the resist structure and thus in the later webs of the lattice structure, the total height of the stabilizing beams a maximum of 20% of the grid height and preferably at most 10% of the grid height and thus the Visibility only slightly influenced.

The resist structures explained in the example are particularly suitable for the production of X-ray optical grating structures made of gold.

Claims (9)

Resist structure for producing an X-ray optical grating structure comprising a multiplicity of webs ( 1 ) with a height (h) and a width (b), as well as web columns with a width (b ') and the webs ( 1 ) stabilizing bars ( 3 ) with a circumference diameter (d), wherein the webs ( 1 ) and the webs ( 1 ) stabilizing bars ( 3 ) on a substrate ( 2 ) are arranged, characterized in that the webs ( 1 ) at an angle α on the substrate ( 2 ) are arranged and the webs ( 1 ) stabilizing bars ( 3 ) are arranged at an angle β, wherein the angles α and β are not equal. A resist pattern for producing an X-ray optical grating structure according to claim 1, wherein the angles α and β have a difference of at least 20 ° to a maximum of 70 °. A resist pattern for producing an X-ray optical grating structure according to claim 1, wherein the angles α and β have a difference of 40 ° to 50 °. A resist pattern for making an X-ray optical grating structure according to claim 1, wherein each stabilizing beam ( 3 ) at least 2 bars ( 1 ) penetrates. Resist structure for producing an X-ray optical grating structure according to one of claims 1 to 4, wherein the height (h) of the webs ( 1 ) to the width (b ') of the web gaps has a ratio of 10 to 500. Resist structure for producing an X-ray optical grating structure according to claim 1 to 5, wherein the distance between two stabilizing beams ( 3 ) is at least twice the width (b ') and at most 20 times the width (b'). Resist structure for producing an X-ray optical grating structure according to claim 1 to 6, wherein the radius of circumference of a beam ( 3 ) is between 1 μm and 10 μm. A resist pattern for producing an X-ray optical grating structure according to claims 1 to 7, wherein the resist pattern is made of a negative resist material. Resist structure for producing a X-ray optical grating structure according to claim 1 to 8, wherein in addition to the stabilizing beam ( 3 ), which are arranged at an angle β, further stabilizing bars ( 3 ) are arranged at an angle β ', and wherein the angle β' does not have the same value as one of the angles α or β.

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