EUV Collector

Abstract

The EUV collector (11) has a reflective surface (20) with a basic mirror shape of a spherical section. A diffraction grating (22) for the EUV use light (10) is attached to the reflective surface (20). The diffraction grating (22) is designed so that the EUV use light (10) emanating from the sphere center (21) of the spherical section is diffracted by the diffraction grating (22) toward a collection region (23). The collection region (23) is spatially separated from the sphere center (21). This creates an EUV collector that can effectively separate the EUV use light to be collected with the help of the collector from extraneous light having a wavelength different from the use light wavelength.

Description

[Technical Field]

[0001] This patent application claims priority to German patent application DE102020208298.7, the contents of which are incorporated herein by reference.

[0002] The present invention relates to an EUV collector. Furthermore, the present invention relates to a light source-collector module including such an EUV collector, an illumination optical unit for an EUV projection exposure apparatus including such an EUV collector, a projection exposure apparatus including such an illumination optical unit, a method for generating microstructured or nanostructured components using such a projection exposure apparatus, and components generated using such a method. [Background technology]

[0003] EUV collectors are known from U.S. Patent No. 9,541,685, U.S. Patent No. 7,084,412, and DE102017204312. Further design variations of EUV collectors are known from U.S. Patent No. 9,612,370 and DE102013002064. [Overview of the project]

[0004] The object of the present invention is to further develop an EUV collector that can effectively separate the EUV light to be collected with the help of the collector from extraneous light having a different wavelength from the light wavelength to be collected.

[0005] According to the present invention, this objective is achieved by an EUV collector having the features described in claim 1.

[0006] According to the present invention, it has been recognized that it is possible to design an EUV collector such that only EUV light used, i.e., EUV light having or having a wavelength bandwidth of the light used, is diffracted in the direction of the collection region, while non-diffracted light, i.e., external light having a different wavelength from the EUV light used, is retroreflected by the reflective surface of the collector due to the basic mirror shape of the spherical section. Spatial separation of the optical paths of the EUV light used and external light having a different wavelength can be achieved in this way. The diffraction grating can be designed such that, here, the expected external light wavelengths are not diffracted by the diffraction grating, and these external light wavelengths are reflected by the basic mirror shape of the reflective surface, and if these external light wavelengths belong to the external light rays emanating from the center of the sphere or passing through the center of the sphere, they are retroreflected by the reflective surface.

[0007] In the case of an EUV collector, the reflective surface having the basic mirror shape of the spherical section, i.e., the spherical surface, is designed to guide the EUV light used.

[0008] The diffraction grating may be radially symmetrical with respect to the connection line between the center of the sphere and the center of the collection region. The diffraction angle produced by the diffraction grating for EUV light, i.e., the angle between the beam of EUV light incident on the diffraction grating and the beam subsequently diffracted by the diffraction grating, may be in the range of 0° to 45°. This diffraction angle is preferably in the range of 2° to 45°, for example, 5° to 45°, or 5° to 40°.

[0009] Overall, it is possible to achieve an EUV collector with high diffraction efficiency for EUV light.

[0010] The change in lattice period described in claim 2 is matched to the geometric conditions of diffraction of EUV-used light toward the collection region. The change in lattice period may be continuous or stepwise. In particular, multiple diffraction grating surface sections at different distances from the connection line can be designed with continuous or stepwise changes in lattice period. These diffraction grating surface sections can be embodied in the form of a closed diffraction grating surface section around the connection line.

[0011] The lattice period described in claim 3 has proven to be of practical use, as such a lattice period is the result of corresponding geometric considerations and, in addition, has been found to be achievable with reasonable effort. Furthermore, such a lattice period is less than the typical coherence length of currently preferred EUV light sources, particularly plasma sources.

[0012] The lattice deformation described in claim 4 can exceed 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, and 90%, and can even exceed 95%, providing good diffraction efficiency for EUV-based light. Combinations of these lattice deformations are also possible.

[0013] The distance between the center of the sphere and the center of the collection region described in claim 5 ensures good spatial separation between the EUV light used and the external light reflected towards the center of the sphere.

[0014] The optical trap described in claim 6 ensures that external light is removed in a defined manner. The optical trap may have a symmetrical shape that conforms to the symmetry of the EUV collector and / or the symmetry of the diffraction effect of the diffraction grating. The optical trap may have a basic sleeve or tube shape. The tubular cross section of the optical trap between the trap inlet opening and the trap outlet opening may be designed to decrease, in particular to decrease linearly. The optical trap may have a frustoconical longitudinal section.

[0015] The basic mirror shape described in claim 7 avoids continuously curved surfaces, which may be advantageous in grid generation.

[0016] The number of polyhedral surfaces described in claim 8 allows for a manageable generation burden. This number can exceed 50 and can exceed 100. This number can be less than 10,000, and in particular, it can be less than 1,000. This number can be in the range of 50 to 500, or 100 to 250, or 250 to 500. Numbers in the range of 50 to 100, 250 to 1,000, or 500 to 1,000 are also possible.

[0017] The advantages of the light source-collector module described in claim 9 correspond to those already described above in relation to the EUV collector. The EUV light source can be a plasma source having an infrared pump laser in particular. If the source region of the light source is located in the region at the center of the sphere of the spherical section of the basic mirror shape of the collector's reflective surface, the pump light retroreflected by the reflective surface passes through the source region at least one more time, which can improve the pumping efficiency of the light source. The EUV diffraction grating is preferably designed so that the wavelength range of the pump light is not diffracted by the diffraction grating. Therefore, the pump light is external light that is not diffracted by the diffraction grating.

[0018] Compared to collectors that diffract higher wavelength external light, the diffraction grating structure of the collector according to the present invention, which diffracts EUV light, has a smaller structural depth, thereby shortening the etching time in the etching production process. Since the EUV light can be effectively separated from external light, lithography masks without protective films, especially without pellicles, can be used during projection exposure, which further reduces reflection loss.

[0019] The advantages of the illumination optical unit according to claim 10, the projection exposure apparatus according to claim 11, the method for producing a microstructured or nanostructured component according to claim 12, and the component produced by such a method correspond to those already described above with reference to the EUV collector or the light source - collector module. The produced component can be a microchip, particularly a memory chip.

[0020] Exemplary embodiments of the present invention will be described in more detail below with reference to the drawings.

Brief Description of the Drawings

[0021] [Figure 1] FIG. schematically shows a meridian cross - section of a projection exposure apparatus for EUV projection lithography. [Figure 2] FIG. shows a meridian cross - section through the collector of the projection exposure apparatus. [Figure 3] FIG. shows a cross - section perpendicular to the grating structure through an embodiment of a diffraction grating for EUV used light, the diffraction grating being attached to the reflective surface of the collector. [Figure 4] FIG. is a diagram showing a further embodiment of a diffraction grating for the collector, similar to FIG. 3. [Figure 5] FIG. is a diagram showing a further embodiment of a diffraction grating for the collector, similar to FIG. 3. [Figure 6] FIG. schematically shows a snapshot of substrate illumination as part of a method for producing a diffraction grating according to one of the embodiments according to FIGS. 3 to 5. [Figure 7] FIG. shows different embodiments for the design of the basic mirror shape of the collector, each figure being approximated to a spherical - section surface by an embodiment of a polyhedron, and in each case shown as an approximated global spherical - section surface, with only some of the sections being used for the collector. [Figure 8]The figures show different embodiments for designing the basic mirror shape of the collector, each of which is approximated by a spherical section surface by an embodiment of a polyhedron, and in each case is shown as an approximated whole-spherical section surface, of which only a portion of the section is used in the collector. [Figure 9] The figures show different embodiments for designing the basic mirror shape of the collector, each of which is approximated by a spherical section surface by an embodiment of a polyhedron, and in each case is shown as an approximated whole-spherical section surface, of which only a portion of the section is used in the collector. [Modes for carrying out the invention]

[0022] First, the schematic configuration of the microlithography projection exposure apparatus 1 will be described.

[0023] The Cartesian xyz coordinate system is used for explanation. In Figure 1, the x-axis extends perpendicular to the plane of the drawing into the drawing. The y-axis extends to the right. The z-axis extends downward. In relation to the explanation of individual components, the local Cartesian xyz coordinate system is used in Figure 2 and subsequent figures, in which the x-axis of the local coordinate system extends parallel to the x-axis of the global coordinate system according to Figure 1, and the x and y axes are positioned so that in both cases they span the principal plane approximated by the respective optical surfaces.

[0024] Figure 1 schematically shows a meridian cross-section of a microlithography projection exposure apparatus 1. The illumination system 2 of the projection exposure apparatus 1 includes an illumination optical unit 4 for exposing the object field of view 5 on the object plane 6, in addition to the radiation source 3. In this case, a reticle 6a placed in the object field of view 5 is exposed, and the reticle is held by a reticle holder 6b. The projection optical unit 7 plays the role of imaging the object field of view 5 onto the image field of view 8 on the image plane 9. The structure of the reticle is imaged onto the photosensitive layer of a wafer 9a placed in the region of the image field of view 8 on the image plane 9, and the wafer is held by a wafer holder 9b.

[0025] The reticle holder 6b is driven by the reticle displacement drive 9c, and the wafer holder 9b is driven by the wafer displacement drive 9d. The drives by the two displacement drives 9c and 9d are synchronized with each other along the y-direction.

[0026] Radiation source 3 is an EUV radiation source that emits radiation in the range of 5 nm to 30 nm. This can be a plasma source, such as a GDPP (gas discharge generated plasma) source or an LPP (laser generated plasma) source. For example, tin can be excited by a carbon dioxide laser operating at a wavelength of 10.6 μm, i.e., in the infrared region, to form a plasma. A synchrotron-based radiation source can also be used for radiation source 3. Those skilled in the art can find information on such radiation sources, for example, in U.S. Patent No. 6,859,515.

[0027] The EUV radiation 10 emitted from the radiation source 3 is focused by a collector 11, which will be described in more detail below. Downstream from the collector 11, the EUV radiation 10 propagates through the intermediate focal plane 12 and then enters a field facet mirror 13 having a number of field facets 13a. The field facet mirror 13 is positioned in the plane of the illumination optical unit 4, which is optically conjugate to the object plane 6.

[0028] EUV radiation 10 will also be referred to as illumination light or imaging light below.

[0029] Downstream from the field-of-view facet mirror 13, the EUV radiation 10 is reflected by a pupil facet mirror 14 having a number of pupil facets 14a. The pupil facet mirror 14 is positioned on the pupil plane of the illumination optical unit 4, which is optically conjugate to the pupil plane of the projection optical unit 7. With the help of the pupil facet mirror 14 and an imaging optical assembly in the form of a transfer optical unit 15 having mirrors 16, 17, and 18 designated in order in the beam path, the field-of-view facets 13a of the field-of-view facet mirror 13 are imaged into the object field of view 5 in a manner that they overlap each other. The last mirror 18 of the transfer optical unit 15 is a graze-induction (GI) mirror.

[0030] Figure 2 shows the collector 11 in more detail. When the radiation source 3 is implemented as an LPP light source, the collector has a through-aperture 19 for pump light to generate plasma. The pump light can have a pump light wavelength in the infrared wavelength range, for example, 10.6 μm.

[0031] The collector 11 has a reflective surface 20 with a basic mirror shape of a spherical section. This basic mirror shape is designed in the style of a spherical mirror. The spherical radius of this basic mirror shape of the reflective surface 20 is indicated by a in Figure 2. The spherical radius a is measured from the sphere center where the plasma source region 21 of the radiation source 3 is located. In principle, the sphere center is also located at the center of the plasma source region 21, and therefore, reference numeral 21 in Figure 2 also indicates the sphere center.

[0032] The basic mirror shape can accurately reproduce a spherical section. Alternatively, as described below, it is possible to approximate the surface of a spherical section using a polyhedron, for example. The "sphere center" of such a polyhedron corresponds to the sphere center of the approximated spherical section surface.

[0033] A diffraction grating 22 is attached to the reflective surface 20, which is not shown in detail in Figure 2, but is shown in Figure 3 with a greatly enlarged cross-section perpendicular to the series of grating structures.

[0034] The diffraction grating 22 shown in Figure 3 is a binary grating with a grating period d and a diffraction structure height h.

[0035] The diffraction grating 22 on the reflective surface 20 of the EUV collector 11 is designed so that the EUV illumination light 10 emitted from the source region 21 at the spherical center of the spherical section of the basic mirror shape of the reflective surface 20 is diffracted by the diffraction grating 22 toward the collection region 23, which is the intermediate focal point of the intermediate focal plane 12. The collection region 23 is spatially separated by a distance b from the source region 21 at the spherical center.

[0036] To determine the dimensions of the diffraction grating 22 with respect to the lattice period d and diffraction structure height h, the lattice surface sections 22 extend radially symmetrically around the rotational symmetry axis 24 of the diffraction grating 22. i This will be taken into consideration.

[0037] Figure 2 shows such a surface section 22 of the diffraction grating 22. i An example of the reflection conditions is shown. Surface section 22 from the axis 24 of rotational symmetry. i The distance is indicated by R in Figure 2. Spherical section shape surface section 22 i The radius is indicated by a. Surface section 22 for illumination light 10 emitted from source region 21 i The diffraction angle at β is denoted by β. The reference point R is at a distance R on the axis of rotational symmetry 24. i The distance between this reference point R and the source region 21 at the center of the sphere is shown by w in Figure 2. i This reference point R is also the point of collision of the illumination light 10 emitted from the source region 21 onto the diffraction grating 22, in the subsequent determination of the diffraction angle. i The distance between and the collection area 23 is shown by c in Figure 2.

[0038] The following applies to the diffraction angle β.

number

[0039] Next, each value of the diffraction angle β of the surface section 22 under consideration i can be inserted into the lattice formula of the lattice period d. d = λ / sinβ (2) Here, λ is the wavelength of the illumination light 10 used.

[0040] The diffraction structure height h at the wavelength λ of the illumination light 10 with λ = 13 nm is in the region where h ≈ 13 nm in the binary diffraction grating according to FIG. 3. The distance value R of 50 mm and the radius of 200 mm, as well as the distance b of 1000 mm between the light source region 21 and the collection region 23, result in a diffraction angle β of 12°, which results in a lattice period d of 62 nm at a wavelength λ of 13 nm.

[0041] The following table gives further assignments of the values of the diffraction angle β and the lattice period d for different values of R, a, and b. [Table 1]

[0042] Therefore, the lattice period d of the diffraction grating 22 depends, inter alia, on the distance R from the axis of rotational symmetry 24, that is, from the connecting line between the sphere center (light source region 21) and the collection region 23, for each lattice section 22 i and varies between the minimum lattice period and the maximum lattice period. The smaller the diffraction angle β, the larger the lattice period d can be.

[0043] The lattice period d of the diffraction grating 22 is for each surface section 22 under consideration from the axis of rotational symmetry 24 iDepending on the distance R, as well as the sphere radius a and the distance b between the source region 21 and the collection region 23, it can vary, for example, in the range of 10 nm to 4000 nm.

[0044] The maximum lattice period d is chosen to be smaller than the coherence length of radiation source 3.

[0045] The illumination light 10 is diffracted, for example, at a diffraction angle β in the range of 0° to 45°.

[0046] Distance b can be in the range of 50mm to 4000mm.

[0047] The diffraction efficiency of the binary diffraction grating 22 shown in Figure 3 can be in the 40% range. This diffraction efficiency represents the intensity ratio of the illumination light 10 diffracted by the diffraction grating 22 to the illumination light 10 incident on the diffraction grating 22.

[0048] Since the reflective surface 20 of the collector 11 is spherical, it is not diffracted by the diffraction grating 22, and light or radiation components emitted from the source region 21 at wavelengths different from the wavelength of light used by the illumination light 10 are reflected back by the reflective surface 20. In particular, the beam path of such foreign light 25, which is pump light but also other wavelengths generated in the plasma of the source region 21, is shown by a solid line to the source region 21 in Figure 2, and then by a dotted line at 26. If the foreign light 25 is pump light, the retroreflection of the pump light 25 at the reflective surface 20 and its subsequent new passage through the source region 21 can result in improved pumping efficiency, and therefore improved efficiency of the radiation source 3.

[0049] An optical trap 27 for the non-diffracted foreign light 25 is positioned further along the path of the foreign light beam. As can be seen in the embodiment of Figure 2, the optical trap 27 has a frustoconical longitudinal section. The optical trap 27 has an inlet opening 28 facing the reflective surface 20 and having an inlet opening cross section, and an outlet opening 29 facing the collection region 23 and having an outlet opening cross section smaller than the inlet opening cross section.

[0050] The inner wall 30 of the light trap 27 is designed to absorb external light 25. The light trap 27 can be thermally coupled to a heat sink.

[0051] The average reflectance of the collector 11 for illumination light 10 without a diffraction grating on the reflective surface 20 can be greater than 50%, greater than 52%, greater than 55%, greater than 60%, and even greater.

[0052] Further embodiments of the lattice structure of the diffraction grating 31 are described below with reference to Figure 4 and can be used in the collector 11 instead of the diffraction grating 22 shown in Figure 3. Components and functions corresponding to those already described above with reference to Figures 1 to 3 are given the same reference numerals and will not be discussed in detail again.

[0053] The diffraction grating 31 is an echelon grating with a total of four step levels N1, N2, N3, and N4. The level differences between adjacent steps N1 / N2, N2 / N3, and N3 / N4 are all the same size. Between adjacent steps N4 / N1, i.e., in the transition between two grating periods, there is a threefold level difference, specifically the height h of the entire diffraction structure. i The length in the y-direction is the same in all cases and is d / 4. The diffraction efficiency of the diffraction grating 31 can be in the range of 80%.

[0054] Further embodiments of the lattice structure of the diffraction grating 32 are described below with reference to Figure 5 and can be used in the collector 11 instead of the diffraction grating 22 shown in Figure 3. Components and functions corresponding to those already described above with reference to Figures 1 to 3 are indicated by the same reference numerals and will not be discussed in detail again.

[0055] The diffraction grating 32 corresponds to level N i It is an 8-step grating where the level difference between adjacent levels within the grating period d is h / 8. The diffraction efficiency of the diffraction grating 32 can be over 90% and can be in the range of 95%.

[0056] Figure 6 shows a snapshot of the diffraction grating of type 22 during its generation. Although schematically shown as a flat surface in Figure 6, the grating substrate 33, which is actually curved spherically like the reflective surface 20 of the collector 11, is illuminated by two coherent structural light sources 34, 35 having wavelengths in the range of 10 nm to 4000 nm. The structural light sources 34, 35 can be infrared light sources, visible wavelength spectrum light sources, excimer light sources, or EUV light sources.

[0057] The lattice substrate 33 has a photosensitive coating on the side facing the structural light sources 34 and 35, which includes a multilayer coating made of molybdenum / silicon.

[0058] The radiation 34a and 35a from the structural light sources 34 and 35 interfere with each other on the grating substrate 33, forming standing waves which can be used in the photosensitive layer of the grating substrate 33 for subsequent structuring, i.e., to generate the diffraction structure of the diffraction grating 22 by an etching step.

[0059] As an alternative to the lattice structuring described above, each diffraction grating 22, 31, and 32 can also be generated with the help of near-field mask illumination. Electron beam lithography or illumination at EUV wavelengths can also be used to generate the diffraction grating structure.

[0060] The basic mirror shape of the reflective surface 20 in the form of a spherical section can be approximated by a polyhedron on the surface of the spherical section. Examples of such polyhedra 36, ​​37, and 38 are shown in Figures 7 to 9.

[0061] Figure 7 shows a spherical polyhedron composed of triangles. The spherical polyhedron 37 shown in Figure 8 is bounded by lines corresponding to the Earth's longitude and latitude.

[0062] The spherical polyhedron 38 shown in Figure 9 is bounded by pentagons.

[0063] The hemispherical polyhedra corresponding to polyhedra 36-38 are used approximately as the basic shape of the reflective surface 20 of the collector 11. The hemispherical separation surface of polyhedron 37 can extend along the equator or along the meridian.

[0064] The diffraction gratings of the collector 11, such as diffraction gratings 22, 31, and 32, can also be designed as blazed diffraction gratings, in which the grating structure is tilted such that the tilt angle specifies the direction of reflection of the illumination light 10, which matches the diffraction angle β.

[0065] The number of faces of polyhedra 36, ​​37, and 38 is greater than 10, but less than 10,000, and especially less than 1,000.

[0066] With the help of the projection exposure apparatus 1, at least a portion of the reticle in the object field of view 5 is imaged onto a region of the photosensitive layer of the wafer in the image field of view 8 for lithography production of microstructured or nanostructured components, in particular semiconductor components, such as microchips. Depending on the embodiment of the projection exposure apparatus 1 as a scanner or stepper, the reticle and wafer are moved in the y-direction in a time-synchronized manner, continuously in scanner operation or step-by-step in stepper operation. [Explanation of symbols]

[0067] 1. Microlithography projection exposure system 2. Lighting System 3 Radiation source 4. Illumination Optical Unit 5 Object field of view 6 Object plane 6a Reticle 6b Reticle holder 7 Projection Optical Unit 8 Image field 9 Image plane 9a wafer 9b Wafer holder 9c Reticle Displacement Drive 9d Wafer Displacement Drive 10 EUV radiation, EUV illumination light, illumination light 11 Collector 12 Intermediate focal plane 13. Field of View Faceted Mirror 13a Visual field facets 14. Eye Facet Mirror 14a Pupil Facet 15. Transmission Optical Unit 16, 17, 18 Miller 19 Through-opening 20 reflective surface 21 Plasma source region, generation region 22 Diffraction gratings, binary diffraction gratings 22i Surface section, lattice surface section 23 Collection Area 24 Axes of rotational symmetry 25. External light, pump light 27 Light Trap 28 Entrance opening 29 Exit opening 30 Inner wall 31, 32 Diffraction gratings 33 Lattice substrate 34, 35 coherent structured light source, structured light source 34a, 35a radiation 36 Polyhedron 37, 38 Polyhedron, spherical polyhedron Distance of surface section 22i R i Reference point

Claims

1. - A reflective surface (20) having a basic mirror shape of a spherical section EUV collector (11), - Diffraction gratings (22, 31, 32) for EUV light (10) are attached to the reflective surface (20), and the diffraction gratings (22, 31, 32) are designed so that the EUV light (10) emitted from the spherical center (21) of the spherical section is diffracted by the diffraction gratings (22, 31, 32) toward the collection region (23). The collection region (23) is spatially separated from the sphere center (21), An EUV collector (11) is provided, in which a reflective surface (20) having the basic mirror shape of the spherical section is designed to guide the EUV light (10).

2. The lattice period d of the diffraction grating (22, 31, 32) is such that the lattice section (22) is separated from the connecting line (24) between the center of the sphere (21) and the center of the collection region (23). i The collector according to claim 1, characterized in that it changes between the minimum lattice period and the maximum lattice period depending on the distance R of the lattice.

3. The collector according to claim 2, having a lattice period in the range of 10 nm to 4000 nm.

4. The collector according to any one of claims 1 to 3, characterized in that the diffraction gratings (22, 31, 32) are designed as a binary grating (22), a multistep grating (31, 32), or a blazed grating.

5. The collector according to any one of claims 1 to 4, characterized in that the separation b between the center of the sphere (21) and the center of the collection region (23) is 50 mm to 4000 mm.

6. A collector according to any one of claims 1 to 5, characterized by at least one optical trap (27) for foreign light that is not diffracted by the diffraction gratings (22, 31, 32).

7. The collector according to any one of claims 1 to 6, characterized in that the basic mirror shape of the reflective surface (20) is approximated by a polyhedron (36, 37, 38) on the surface of a spherical section.

8. The collector according to claim 7, characterized in that the number of faces of the polyhedron (36, 37, 38) exceeds 10.

9. A light source-collector module having an EUV light source (3) and an EUV collector (11) according to any one of claims 1 to 8.

10. Illumination optical unit (4) for an EUV projection exposure apparatus (1) having an EUV collector (11) according to any one of claims 1 to 8.

11. A projection exposure apparatus for EUV projection lithography comprising an EUV light source (3), an illumination optical unit according to claim 10 for transmitting illumination light (10) from the light source (3) to an object field of view (5) in which a reticle (6a) having a structure to be imaged can be placed, and a projection optical unit (7) for imaging the object field of view (5) into an image field of view (8).

12. A method for generating microstructured or nanostructured components, - A step of preparing a substrate (9a) on which a layer made of a photosensitive material is at least partially applied, - A step of preparing a reticle (6a) having a structure to be imaged, - A step of projecting at least a portion of the reticle (6a) onto a region of the layer of the substrate (9a) made of the photosensitive material, with the help of the projection exposure apparatus described in claim 11. Methods that include...

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