Method for Producing a Diffractive Optical Element and Diffractive Optical Element

Abstract

A method for producing a diffractive optical element and a diffractive optical element are disclosed. In an embodiment a method for producing a diffractive optical element includes generating a surface structure by implanting ions into a material of a substrate, a layer or a layer system, wherein the surface structure includes a structure height of less than 10 nm.

Claims

1.-15. (canceled)

16. A method for producing a diffractive optical element, the method comprising: generating a surface structure by implanting ions into a material of a substrate, a layer or a layer system, wherein the surface structure comprises a structure height of less than 10 nm.

17. The method according to claim 16, wherein the surface structure is generated with the structure height varying in lateral direction.

18. The method according to claim 16, wherein implanting ions comprises implanting ions through a patterned mask layer.

19. The method according to claim 16, wherein implanting ions comprises implanting ions by a laterally confined ion beam, and wherein a ion fluence of an ion beam is varied during the ion implantation.

20. The method according to claim 16, wherein the ions are implanted to an implantation depth between 10 nm and 500 nm, inclusive.

21. The method according to claim 16, wherein an ion energy during the ion implantation is between 2 keV and 100 keV.

22. The method according to claim 16, wherein the structure height of the surface structure is a non-integer multiple of a lattice plane spacing of the material or a non-integer multiple of a thickness of a single layer of the layer system of the diffractive optical element.

23. The method according to claim 16, wherein the structure height of the surface structure is smaller than a grating plane spacing of the material at the surface or is smaller than a thickness of a single layer of the layer system of the diffractive optical element.

24. A diffractive optical element comprising: a surface structure in a material of a substrate, a layer or a layer system, wherein the surface structure comprises a laterally varying structure height of less than 10 nm, and wherein the substrate, the layer or the layer system comprises an ion implantation region below the surface structure.

25. The diffractive optical element according to claim 24, wherein the diffractive optical element is a reflection diffraction grating.

26. The diffractive optical element according to claim 24, wherein a ion implantation depth is between 10 nm and 500 nm, inclusive.

27. The diffractive optical element according to claim 24, wherein the structure height of the surface structure is a non-integer multiple of a lattice plane spacing of the material at the surface or a non-integer multiple of a thickness of a single layer of the layer system of the diffractive optical element.

28. The diffractive optical element according to claim 24, wherein the structure height of the surface structure is less than a grating plane spacing of the substrate or is less than a thickness of a single layer of the layer system.

29. The diffractive optical element according to claim 24, wherein the substrate is a single crystal or an amorphous substrate.

30. The diffractive optical element according to claim 24, wherein the layer or the layer system is a mirror for EUV radiation or X-rays.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The method and the diffractive optical element are explained in more detail below by means of examples in connection with FIGS. 1 to 4.

[0023] In the Figures:

[0024] FIG. 1 shows a schematic illustration of a method step in the method for producing the diffractive optical element;

[0025] FIG. 2 shows a schematic illustration of a cross-section through an example of the diffractive optical element;

[0026] FIG. 3 shows an atomic force microscopy image of a section of the surface structure in an example of a diffractive optical element; and

[0027] FIG. 4 shows an illustration of a height profile of the example of FIG. 3.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0028] Components which are identical or have the same effect are marked with the same reference signs in the figures. The components shown as well as the proportions of the components among each other are not to be regarded as true to scale.

[0029] In the method step for producing a diffractive optical element shown in FIG. 1, ions 2 are implanted into the surface of a substrate 1. The substrate 1 is preferably a single crystal. For example, the substrate 1 is a silicon substrate. In the example, the substrate comprises lattice planes with a lattice plane spacing a in the vertical direction. However, the method can alternatively be applied to amorphous substrates.

[0030] In the example shown here, the ions 2 are implanted directly into the substrate 1. Alternatively, however, it would also be possible for a layer or layer system to be applied to the substrate 1 prior to the ion implantation. In this case, the ions 2 are implanted into the layer, layer system or underlying substrate. For example, a layer or layer system for reflecting EUV or X-rays can be applied to the substrate 1.

[0031] In the method, the ions 2 are advantageously implanted into the substrate 1 in a location-dependent manner. In particular, an implantation profile varying in lateral direction, i.e. parallel to the surface of the substrate 1, is generated. For this purpose, a mask layer 5 is advantageously applied prior to ion implantation. The mask layer 5 can be a metal layer that is not penetrated by the ions during ion implantation. For example, the mask layer 5 is a chromium layer or a gold layer. However, the mask layer may also comprise other materials such as metal oxides, polymers or resists. As an alternative to the use of a mask layer 5, it is possible for a laterally limited ion beam to be guided over the substrate surface in a location-dependent manner with varying ion fluence. In FIG. 1, for a simplified illustration of the principle, only one opening in the mask layer 5 is shown, with which an elevation of the surface structure to be generated is produced. In fact, the mask layer 5 may comprise a plurality of such openings, which may in particular form a periodic lattice structure. The lattice structure may comprise, for example, a lattice constant in the region of 50 nm to 500 nm.

[0032] FIG. 2 illustrates the substrate 1 after implantation of the ions 2. The ions 2 implanted in the substrate 1 cause the formation of a surface structure 3. In particular, the surface is raised above an ion implantation region 4. The elevation occurs by volume change due to the creation of defects in the crystal lattice of the substrate 1 and the resulting changes in bond lengths and/or density. The achievable structure height of the surface structure 3 thus depends on the spatial extent as well as the depth position of the ion implantation region 4 and is conditioned by the type of crystal defects (e.g. point defects such as vacancies, interstitial and substitutional atoms, dislocations, stacking faults, amorphized regions).

[0033] In FIG. 2, a depth profile of the implanted ions 2 is schematically illustrated next to the substrate 1. The concentration of the implanted ions 2 as a function of depth can be precisely and specifically adjusted by the choice of implantation parameters (ion type, ion energy, ion fluence, irradiation temperature) or by subsequent temperature treatment. The ion implantation depth is preferably between 10 nm and 500 nm. The ion implantation depth is understood here to be the depth t at which the ion concentration comprises its maximum. The ion implantation depth depends in particular on the ion energy of the ions used. This is preferably between 2 keV and 100 keV. The implanted ions can be, for example, noble gas ions such as argon ions or helium ions, which do not affect the further physical properties of the material, or substitution atoms of the material of the substrate, the layer or the layer system.

[0034] By a location-dependent implantation of the ions 2, an elevation of the surface can be structured with high local resolution and thus the surface structure 3 can be generated. When using a single crystal substrate 1, the method can advantageously obtain the crystal structure at the surface of the substrate 1. By controlling the implantation parameters, the parameters of a subsequent temperature treatment, and taking advantage of the smoothing properties of a crystalline layer overlying the ion implantation region 4, the tension of the lattice planes in the direction towards the surface can be controlled.

[0035] In the method, a structure height h corresponding to a non-integer multiple of the lattice plane spacing a of the material of substrate 1 can advantageously be realized. The structure height his preferably between 0.1 nm and 10 nm. In particular, the structure height may be less than 5 nm or even less than 1 nm. An advantage of the method described herein is, in particular, that such low structure heights of the surface structure 3 can be produced with high accuracy and spatial resolution. This would not be readily possible with an etching process. In particular, the produced structure height h can be smaller than the lattice plane spacing a of the substrate 1. In contrast, with an etching process, only structure heights that are not smaller than the lattice plane spacing a can be obtained.

[0036] In particular, the substrate 1 with the surface structure 3 produced with the method forms a diffractive optical element 10.

[0037] FIG. 3 illustrates an atomic force microscopy image showing a section of a surface structure 3 which may be part of a diffractive optical element 10. The image section shows an area of 5 μm×5 μm. The surface structure 3 comprises four lines with stripe structures whose structure height increases from bottom to top in the FIG. 3.

[0038] A height profile of the surface structures 3 is illustrated in FIG. 4. In FIG. 4 it can be seen that the surface structures 3 comprise structure heights h of less than 2 nm (top row) to less than 1 nm (bottom row).

[0039] The invention is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses any new feature as well as any combination of features, which in particular includes any combination of features in the patent claims, even if that feature or combination itself is not explicitly specified in the patent claims or exemplary embodiments.