Structured grating component, imaging system and manufacturing method

Abstract

The invention relates to a method of manufacturing a structured grating, a corresponding structured grating component (1) and an imaging system. The method comprising the steps of: providing (110, 120, 130) a catalyst (30) on a substrate (20), the catalyst (20) having a grating pattern; growing (140) nanostructures (50) on the catalyst (30) so as to form walls (52) and trenches (54) based on the grating pattern; and filling (160) the trenches (54) between the walls (52) of nanostructures (50) using an X-ray absorbing material (70). The invention provides an improved method for manufacturing a structured grating and such structured grating component (1), which is particularly suitable for dark-field X-ray imaging or phase-contrast imaging.

Claims

1. A method of manufacturing a structured grating, the method comprising: providing a catalyst on a substrate, the catalyst having a grating pattern; growing nanostructures on the catalyst so as to form walls and trenches based on the grating pattern; and filling the trenches between the walls of nanostructures using an X-ray absorbing material.

2. The method according to claim 1, wherein the nanostructures are grown using a material having a lower X-ray absorbance than the X-ray absorbing material.

3. The method according to claim 1, wherein the nanostructures comprise carbon nanotubes.

4. The method according to claim 1, further including applying a passivation layer prior to filling the trenches using the X-ray absorbing material.

5. The method according to claim 4, wherein applying the passivation layer includes a chemical vapor deposition.

6. The method according to claim 4, wherein the passivation layer is applied to a defined distance from the substrate, wherein the defined distance particular less than 2 μm.

7. The method according to claim 4, wherein filling the trenches comprises electroplating.

8. The method according to claim 1, wherein filling the trenches comprises at least one of: mechanical filling using mechanical stress, high temperature and underpressure; filling the trenches with a metal powder embedded in a binder substance and baking the binder substance to achieve solid filling of the trenches; and imprinting the grating structures using the grown nanostructures.

9. The method according to claim 1, further comprising bending the grating structure to adjust the grating structure to a cone beam of an X-ray source.

10. A structured grating component, comprising: a substrate; a catalyst on the substrate, the catalyst having a grating pattern; nanostructures on the substrate forming walls and trenches based on the grating pattern; and X-ray absorbing material filling the trenches between the walls of nanostructures, wherein the nanostructures include carbon nanotubes.

11. The structured grating component according to claim 10, further comprising: a passivation layer arranged between the X-ray absorbing material and the nanostructures.

12. The structured grating component according to claim 10, wherein the substrate is in direct contact with the X-ray absorbing material.

13. The structured grating component according to claim 10, wherein the nanostructures comprise support elements joining two adjacent walls, wherein the support elements are provided at different positions in a longitudinal direction on two opposite sides of a wall, respectively.

14. An imaging system, comprising a structured grating component according to claim 10.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following drawings:

(2) FIG. 1A-1F schematically and exemplarily illustrate steps of a method according to the invention,

(3) FIG. 2 schematically and exemplarily illustrates a top view on an unfilled structured grating component, and

(4) FIG. 3 schematically and exemplarily illustrates a perspective view of a cross-sectional cut through a structured grating.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) FIGS. 1A to 1F schematically and exemplarily illustrate the various steps of the method of manufacturing a structured grating according to the present invention.

(6) As illustrated in FIG. 1A, in a step 110, a substrate 20 is provided with a catalyst 30 on a surface thereof. Substrate 20 can be a rigid substrate like conductive silicon with a plating base, comprising for instance Cu, Ni, Au, wherein the catalyst 30 forms a sublayer for the growing process of nanostructures 50 described below, such as carbon nanotubes (CNT). Substrate 20 can also be or comprise a conductive foil including nickel foil, copper foil, and the like.

(7) In FIG. 1B, a lithography step 120 of applying a photo mask 40 having a grating structure, i.e. comprising the geometric structure with which the catalyst 30 is to be patterned, is applied.

(8) In an etching step 130, which is schematically and exemplarily illustrated in FIG. 1C, light is subjected onto the arrangement such that all parts of the catalyst 30, which are not covered by photo mask 40, are removed or etched. Steps 110 to 130 can be summarized as geometric preparation of a catalyst 30 having a grating pattern on a substrate 20.

(9) In FIG. 1D, a step 140 of growing nanostructures 50 on catalyst 30 is schematically and exemplarily illustrated. Walls 52 and trenches 54 located between two adjacent walls 52 are thus formed. Walls 52 grow on top of catalyst 30 based on the grating pattern provided for this purpose.

(10) Preferentially, nanostructures 50 comprise or consist of carbon nanotubes (CNT). Thus, the growing step 140 is specifically adapted for the growth of CNT. CNT allow the deposition and growth of walls 52 with a very high aspect ratio, i.e. a very high ratio of a thickness 53 to a height 55 of the walls 52, respectively. The grating pattern is formed such that thickness 53 approximately corresponds to a distance 57 between two adjacent walls 52.

(11) FIG. 1E schematically and exemplarily illustrates an optional step 150 of preparing the structures for filling with X-ray absorbing materials. More specifically, a passivation layer 60 is applied including the infiltration of nanostructures 50 at the side surfaces of the walls 52 and the topside of the walls 52. Passivation layer 60 is applied, for instance, using atomic layer deposition (ALD) or comparable technologies. The infiltration is precisely controlled to stop also at a defined depth as well as the passivation layer 60 on the sidewalls of the walls 52 is precisely controlled to stop in a defined distance from substrate 20, preferably below 2 microns, before covering the ground of the trench 54 and thus contact substrate 20. Thus, electronic and conductivity properties of substrate 20 are not obstructed by passivation layer 60.

(12) FIG. 1F schematically and exemplarily illustrates a step 160 of filling the trenches 54 between walls 52 of nanostructures 50 using an X-ray absorbing material 70. A plurality of alternatives for filling the trenches 54 in step 160 is described in the following.

(13) The passivation material of passivation layer 60 preferentially comprises at least one of Al2O3, TiO2, and SiO2.

(14) Step 160 preferentially comprises a step of electroplating. Electroplating allows for a complete and reliable filling of the trenches 54 with X-ray absorbing material 70.

(15) An alternative to electroplating for step 160 includes mechanical filling using mechanical stress, high temperature and underpressure, as described in the above cited article by Lei et al., 2016. An even further approach includes filling the trenches in step 160 using a fine powder of metal, for instance in a binder matrix that can be baked at the end, in order to achieve a solid filling with X-ray absorbing material 70 of the trenches 54. A further alternative method of step 160 includes the use of the nanostructures 50 for imprinting of the grating structures. This alternative depends on mechanical properties of the material system. A similar concept, but approached different from this method is described by the above cited article by Yashiro et al. 2014.

(16) The X-ray absorbing material 70 comprises for example Au, Pb, Bi, or any combination or alloy thereof. In particular, the composition of X-ray absorbing material 70 can be chosen in order to have the most favorable X-ray absorbance for the intended application.

(17) Step 150 is strictly required in case the electroplating is employed as an implementation of step 160 for filling the trenches 54. In the alternative versions of step 160, passivation of step 150 may not be required for all implementations. For these methods, in several examples, it is more important to guarantee wettability of the nanostructures 50 with the filling material forming X-ray absorbing material 70 to avoid defects in filling due to differences in respective material properties. Therefore, step 150 can, for other methods of filling in step 160 apart from electroplating, additionally or alternatively employ the deposition of an optional nanolayer over all on the nanostructures 50, so as to improve the wettability of the respective nanostructures 50.

(18) After filling the trenches 54 in step 160, manufacturing of a structured grating component 1 is completed.

(19) FIG. 2 schematically and exemplarily illustrates a topview on structured grating component 1 corresponding to the result of the method explained in FIGS. 1A to 1F. A plurality of longitudinal and parallel walls 52 can be seen as extending in the direction illustrated as vertical in FIG. 2, wherein X-ray absorbing material 70 is illustrated in the trenches between respective walls 52. At respective different positions along the extension direction of walls 52, support elements 58 are provided, which join or link adjacent walls 52. Thus, a mechanical stability of structured grating component 1 is increased.

(20) Preferentially, the thickness of walls and trenches, respectively, is in the range of 1 to 10 microns, preferably between 7 and 9 microns, wherein a deviation from the standard or average thickness is preferentially less than 10%. Thus, the thickness of walls and trenches can be considered to be approximately constant.

(21) FIG. 3 schematically and exemplarily illustrates structured grating component 1 in a perspective, cross-sectional view such that the extension of walls 52 and trenches 54 in a normal direction on substrate 20 can be seen. The heights 55 of walls 52 are larger than their respective widths or thickness, wherein the aspect ratio is larger than 5, preferably larger than 10 and most preferably at least 15.

(22) For the integration of such structured grating component 1 in an X-ray imaging system, substrate 20 can preferably be bent to a defined radius to match a focus to the focal spot distance. Preferentially, substrate 20 can be bent after manufacturing structured grating component 1 according to the method as described with reference to FIG. 1, wherein stable structures of a bottom layer at the interface between substrate 20 and nanostructures 40 will support the bending.

(23) Infiltration and step 160, including electroplating or any other method of filling the trenches 54 with nanostructures 70, could stabilize the mechanical interface depending on an optimization recipe. Preferentially, substrate 20 can be bent using a mechanical frame setup. In some examples, substrate 20 can also be patterned in tiles to form subareas, which can be individually used for bending.

(24) While the main focus of the concepts according to the invention as described above is medical X-ray imaging, in particular phase-contrast imaging and dark-field imaging, other use cases for the inventive concepts are manifold. Apart from medical imaging, application of the inventive concepts is also beneficial, for instance, in nondestructive testing (NDT).

(25) Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

(26) In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality.

(27) A single unit or device may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

(28) Any reference signs in the claims should not be construed as limiting the scope.