Optical Diffractive Components

Abstract

The optical diffractive element (39) has a periodic grating structure profile. The arrangement of the diffractive structure levels is such that a wavelength range around two different target wavelengths diffracted by the grating structure profile has three radiation components with different phases that destructively interfere with each other. The diffractive structure levels (N0, N1, N2) predefine the topography of the grating period (P) of the diffractive grating structure profile, which is regularly repeated along the period progression direction x. These include a neutral diffractive structure level (N0), a positive diffractive structure level (N1) that is higher than the neutral diffractive structure level, and a negative diffractive structure level (N2) that is lower than the neutral diffractive structure level. Within the grating period (P), the neutral diffractive structure level (N0) has an extension along the period progression direction (x) that is less than 50% of the extension of the grating period (P). The difference between the two target wavelengths is less than 50%. This results in an optical diffractive element with expanded application possibilities, particularly for stray light suppression.

Description

[Technical field]

[0001] This patent application claims priority from German patent application DE 10 2019 213 063.1, the content of which is incorporated herein by reference.

[0002] The present invention relates to diffractive optical components.

[0003] Furthermore, the invention relates to an EUV collector of a projection exposure apparatus comprising such an optical diffractive element, an illumination system comprising such an EUV collector, an optical system comprising such an illumination system, a projection exposure apparatus comprising such an optical system, and a method for producing a structured element using such a projection exposure apparatus, as well as a structured element produced in this manner. [Background technology]

[0004] An EUV collector including an optical diffractive component in the form of an optical grating is known from WO2017 / 207401A1 and WO2014 / 114405A2. An embodiment of an optical grating for suppressing IR wavelengths in an EUV projection exposure apparatus is known from the publication "Multilayer EUV optics with integrated IR-suppression gratings", T. Feigl et al., 2016 EUVL Workshop, Berkeley, June 13-16, 2016. EP1540423B1 describes a grating-based spectral filter for suppressing radiation outside the band of use in an EUV lithography system. US Patent Application Publication No. 2014 / 0131586 describes a phase grating for a mask inspection system. DE102009044462A1 describes an optical filter element including a grating structure for diffracting infrared radiation in an EUV illumination system. The technical paper "Multilevel blazed gratings in resonance domain: an alternative to the classical fabrication approach" by M. Oliva et al., OPTICS EXPRESS, Vol. 19, No. 15, 2011, pages 1473 to 1475, and the technical paper "Highly efficient three-level blazed grating in the resonance domain" by M. Oliva et al., OPTICS LETTERS Vol. 35, No. 16, 2010, pages 2774 to 2776, describe various variations of blazed gratings.The technical article "Diffractive elements designed to suppress unwanted zeroth order due to surface depth error" by V. Kettunen et al., Journal of Modern Optics 51, 14, 2111-2123, 2004, discloses diffractive elements for suppressing unwanted zeroth order diffraction due to profile depth errors. US Pat. No. 9,551,941 (B2) discloses an illumination system for an EUV lithography apparatus and a facet mirror for the illumination system. WO 96 / 13942 A1 discloses an illumination system for a display panel. US Pat. No. 5,162,943 discloses an image reading device with a diffraction grating. US Patent Application Publication No. 2009 / 0289205 discloses a mirror for an EUV production method in the form of an EUV collector mirror. DE 102018218981 A1 discloses an optical grating for an EUV collector of a projection exposure apparatus.

[0005] Optical gratings can be used to suppress stray light of wavelengths different from that of the used light, where the stray light can be diffracted (made to diffract) by the optical grating towards a light trap (beam dump) while the used light follows a different path. Summary of the Invention

[0006] The aim of the invention is to develop an optical diffractive element of the type mentioned in the introduction in such a way as to expand its application possibilities, in particular for stray light suppression.

[0007] This object is achieved according to the invention by means of a diffractive optical element having the features specified in claim 1.

[0008] According to the invention, it is understood that in the case of a three-level structure, the spread ratio between the spread of the neutral diffraction structure level and the total spread of the grating period constitutes a degree of freedom that can be used in a targeted manner to realize the suppression of different target wavelengths with predefined suppression requirements. In this case, a relatively small adaptation compared to an arrangement of diffraction structure levels in which the neutral diffraction structure level within a grating period is exactly 50% of the spread of the grating period surprisingly gives rise to the possibility of controlling different target wavelengths with wavelengths that differ to a relatively small extent.

[0009] To satisfy the condition of destructive interference of three out-of-phase radiation components, the structural depth d 0 can be within a quarter of the mean target wavelength (λ / 4), and the positive diffraction structure level has a structure depth d 0 The higher or negative diffraction structure level, respectively, has a structure depth d 0 The spread of the diffractive structure levels and the structure depth can be selected according to the two target wavelengths such that three different phases are suppressed for both wavelengths. The spread of the neutral diffractive structure levels within the grating period can be less than 49.95% of the spread of the grating period, can be less than 49%, can be less than 45%, can be less than 40%, can be less than 35%, can be less than 30%, can be less than 25%, can be less than 20%, can be less than 15% of the spread of the grating period. The spread of the neutral diffractive structure levels within the grating period can be more than 5% of the spread of the grating period.

[0010] The difference between two target wavelengths that differ by a relatively small amount is less than 50%. If a first, larger target wavelength is designated as λ1 and a second, smaller target wavelength is designated as λ2, then λ1-λ2 is less than 0.5λ1.

[0011] An alternative difference criterion between two target wavelengths λ1 and λ2 that differ to a relatively small extent is (λ1-λ2) 2 / (λ1+λ2) 2 <20% which criterion should be respected by the optical diffractive component according to the invention and can replace the above criterion "less than 50% difference between the two target wavelengths".

[0012] Here, the following equation, (λ1-λ2) 2 / (λ1+λ2) 2 <15%, <12%, <10%, <8%, <5%, <4%, <3%, <2%, or otherwise less than 1% (<1%) can be true.

[0013] In an alternative embodiment of the optical diffractive component embodied to suppress two wavelengths that differ to a greater extent, it is true that the difference between the two target wavelengths that differ to a greater extent is greater than 50%, in which case it is true that λ1-λ2 is greater than 0.5λ1.

[0014] This difference may be greater than 60%, may be greater than 70%, or may be greater than 80%.

[0015] This criterion for suppression of two wavelengths that differ to a greater extent can also be expressed as follows, similar to the previous criterion "wavelengths that differ to a relatively small extent." (λ1-λ2) 2 / (λ1+λ2) 2 >20%

[0016] This difference ((λ1-λ2) 2 / (λ1+λ2) 2 could be even greater, possibly exceeding 30%, possibly exceeding 50%, and possibly exceeding 80%.

[0017] The optical diffractive component may be designed to suppress three different target wavelengths with two different target wavelengths that meet either the above criteria "relatively small difference" or "larger difference." Alternatively, two of the three target wavelengths can be controlled to meet one criterion "larger difference," and the other two of the three target wavelengths can be controlled to meet the other criterion "larger difference."

[0018] The two target wavelengths or two of the three target wavelengths may be, for example, 10.2 μm and 10.6 μm, and / or 10.6 μm and 1.046 μm.

[0019] The fact that the spread of one positive diffraction structure level and the spread of the other negative diffraction structure level within a grating period are the same as each other as described in claim 2 brings about good suppression results for both target wavelengths.

[0020] Correspondingly, the same applies for the same absolute structure depth as claimed in claim 3.

[0021] Radiation with two different target wavelengths according to claims 4 and 5 may be jointly suppressed by an optical diffractive element. The difference may be more than 5%, may be more than 10%, may be more than 15%, may be more than 20%, may be more than 25%, may be more than 30%, may be more than 35%, may be more than 40%, may be more than 45%. The difference between the two target wavelengths is less than 50%, may be less than 10%. The two target wavelengths may be, for example, within a wavelength band between 1 μm and 10.1 μm.

[0022] The spread of the grating period as claimed in claim 6 simplifies the production of the optical diffractive component.

[0023] A mirror-symmetrical arrangement of the diffractive structure levels as claimed in claim 7 likewise leads to a simplified manufacture.

[0024] The advantages of the EUV collector as claimed in claim 8 correspond to those already explained above with respect to the optical diffractive component, which are particularly evident when used in combination with an EUV light source in which the plasma is created by laser-induced discharge.

[0025] This applies in particular to an EUV collector mirror as claimed in claim 9. The radiation at least one target wavelength is also called stray light.

[0026] The advantage of the illumination system according to claim 10 corresponds to the advantage already explained above for the EUV collector according to the invention: the EUV used light is not exactly suppressed by the optical diffractive component, i.e. has a different wavelength than the stray light to be suppressed.

[0027] The illumination system can be made with an optical diffractive component embodied as described above so as to provide a uniform distribution of stray light in the region of a stray light removal location, for example in the region of a beam dump provided for this purpose. Alternatively or additionally, it is possible to ensure a predefined distribution function of the used light, in particular in a specific section of the illumination beam path of the illumination system, for example in the region of the pupil plane.

[0028] The advantages of the optical system according to claim 11, the projection exposure apparatus according to claim 12, the production method according to claim 13 and the microstructured or nanostructured component according to claim 14 correspond to the advantages already explained above for the collector according to the invention.

[0029] In particular, semiconductor components, for example memory chips or chips for processing data, can be produced using projection exposure apparatus.

[0030] Exemplary embodiments of the invention are explained in more detail below with reference to the drawings, in which: [Brief description of the drawings]

[0031] [Figure 1] 1 illustrates a schematic representation of a projection exposure apparatus for EUV microlithography; [Diagram 2] FIG. 1 shows a detail of the light source of a projection exposure apparatus in the environment of an EUV collector for directing EUV light from a plasma source region to a field facet mirror of an illumination optical unit of a projection exposure apparatus, where EUV is shown in a meridional section. [Diagram 3] FIG. 4 shows, in a more abstract manner compared to FIG. 3, firstly the guidance of the EUV light used and secondly the guidance of stray light components of different wavelengths in the case of reflection / diffraction at the EUV collector. [Figure 4] FIG. 1 is a side view of an optical diffractive component with a periodic grating structure profile having a diffractive structure with exactly three diffractive structure levels, greatly enlarged with respect to structure depth, where within a grating period, a neutral diffractive structure level has an extent along the period running direction that is less than 50% of the extent of the grating period along the period running direction. [Diagram 5] FIG. 5 diagrammatically shows the wavelength-dependent reflectance (dashed-dotted line) of the diffractive element according to FIG. 4 in comparison with another optical diffractive element not according to the invention. [Figure 6] In a similar figure to Figure 4, a further embodiment of an optical diffractive component, again with three diffractive structure levels, is shown embodied to suppress a first target wavelength in the 10 μm region and a second target wavelength in the 1 μm region by a diffractive structure level of a first asymmetric layout. [Figure 7]FIG. 7 shows, in a similar view to FIG. 4, an embodiment of a diffractive optical component which corresponds to the diffractive optical component according to FIG. 6, except that there are diffractive structure levels with a symmetrical layout. [Figure 8] In a similar view to FIG. 4, a further embodiment of an optical diffractive component is shown, again with three diffractive structure levels designed to suppress a first target wavelength in the 10 μm region and a second target wavelength in the 1 μm region. [Figure 9] In a similar view to FIG. 4, a further embodiment of an optical diffractive component is shown, again with three diffractive structure levels designed to suppress a first target wavelength in the 10 μm region and a second target wavelength in the 1 μm region. [Figure 10] In a diagram similar to FIG. 5, the wavelength-dependent reflectance R in the region of a first target wavelength of an optical diffractive component according to FIGS. 6 and 7 (solid lines), an optical diffractive component according to FIG. 8 (dotted line) and an optical diffractive component according to FIG. 9 (dashed line) are shown in comparison with an optical diffractive component not according to the invention (dashed line). [Figure 11] In a figure similar to FIG. 10, the wavelength-dependent reflectance in the region of the second target wavelength of the optical diffractive component according to FIGS. 6 / 7, 8 and 9 is shown in comparison with an optical diffractive component not according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] The projection exposure apparatus 1 for microlithography comprises a light source 2 for illumination or imaging light 3, which will be explained in more detail below. The light source 2 is for example an EUV light source which produces light in the wavelength range between 5 nm and 30 nm, in particular between 5 nm and 15 nm. In the following, the illumination or imaging light 3 is also referred to as EUV used light.

[0033] In particular, the light source 2 can be a 13.5 nm wavelength light source or a 6.9 nm wavelength light source. Other EUV wavelengths are possible. The beam path of the illumination light 3 is shown very diagrammatically in FIG.

[0034] An illumination optical unit 6 is used to guide illumination light 3 from the light source 2 to an object field 4 in an object plane 5. The illumination optical unit comprises a field facet mirror FF, which is shown very diagrammatically in Fig. 1, and a pupil facet mirror PF, which is also shown very diagrammatically and is arranged downstream in the beam path of the illumination light 3. A field-forming mirror 6b for grazing incidence (GI mirror, grazing incidence mirror) is arranged in the beam path of the illumination light 3 between the pupil facet mirror PF arranged in a pupil plane 6a of the illumination optical unit and the object field 4. Such a GI mirror 6b is not essential.

[0035] The pupil facets of the pupil facet mirror PF (not shown in any more detail) are part of a transfer optical unit, which transfers, in particular images, the field facets of the field facet mirror FF (also not shown) so as to overlap one another into the object field 4. Embodiments known from the prior art can be used on the one hand for the field facet mirror FF and on the other hand for the pupil facet mirror PF. By way of example, such an illumination optical unit is known from DE 10 2009 045 096 A1.

[0036] Using a projection or imaging optical unit 7, the object field 4 is imaged at a predefined reduced scale into an image field 8 in an image plane 9. Projection optical units which can be used for this purpose are known, for example, from DE 10 2012 202 675 A1.

[0037] In order to facilitate the description of the various embodiments of the projection exposure apparatus 1 and of the projection optical unit 7, a Cartesian xyz coordinate system is shown in the figures, from which the respective positional relationships of the components shown in the figures become apparent. In figure 1, the x-direction runs perpendicularly to the plane of the drawing towards the rear. The y-direction runs towards the left in figure 1 and the z-direction runs towards the top in figure 1. An object plane 5 extends parallel to the xy-plane.

[0038] The object field 4 and the image field 8 are rectangular. Alternatively, it is also possible for the object field 4 and the image field 8 to have a bent or curved embodiment, i.e. in particular to be partially ring-shaped. The object field 4 and the image field 8 have an x / y aspect ratio greater than 1. The object field 4 thus has a long object field dimension in the x direction and a short object field dimension in the y direction. These object field dimensions extend along the field coordinates x and y.

[0039] One of the exemplary embodiments known from the prior art can be used for the projection optical unit 7. What is imaged in this case is a part of a reflective mask 10, also called a reticle, which coincides with the object field 4. The reticle 10 is held by a reticle holder 10a. The reticle holder 10a is displaced by a reticle displacement drive 10b.

[0040] Imaging by the projection optical unit 7 is implemented on the surface of a substrate 11 in the form of a wafer, which is held by a substrate holder 12. The substrate holder 12 is displaced by a wafer or substrate displacement drive 12a.

[0041] 1 shows diagrammatically a beam 13 of illumination light 3 entering the projection optical unit 7 between a reticle 10 and a projection optical unit 7, and a beam 14 of illumination light 3 exiting the projection optical unit 7 between the projection optical unit 7 and a substrate 11. The numerical aperture (NA) on the image field side of the projection optical unit 7 is not reproduced to scale in FIG.

[0042] The projection exposure apparatus 1 is an apparatus of the scanner type. During operation of the projection exposure apparatus 1, both the reticle 10 and the substrate 11 are scanned in the y-direction. A stepper-type projection exposure apparatus 1 is also possible, in which stepwise displacements in the y-direction of the reticle 10 and the substrate 11 are performed between the individual exposures of the substrate 11. These displacements are performed synchronously with one another by suitable activation of the displacement drives 10b and 12a.

[0043] FIG. 2 shows the light source 2 in detail.

[0044] The light source 2 is a laser produced plasma (LPP) light source. For the purpose of creating a plasma, tin droplets 15 are generated by a tin droplet generator 16 as a series of continuous droplets. The trajectory of the tin droplets 15 extends transversely to the main beam direction 17 of the EUV application light 3. Here, the tin droplets 15 fall freely between the tin droplet generator 16 and a tin capture device 18, said droplets passing through a plasma source region 19. The EUV application light 3 is emitted by the plasma source region 19. When the tin droplets 15 reach within the plasma source region 19, they are impinged there by a pump light 20 from a pump light source 21. The pump light source 21 may be, for example, a CO 2 It may be an infrared laser light source in the form of a laser. Different IR laser sources are also possible, in particular solid-state lasers, for example Nd:YAG lasers. The pump light source 21 may comprise a light source unit for producing an optical pre-pulse and a light source unit for producing a main optical pulse. The optical pre-pulse on the one hand and the main optical pulse on the other hand may have different optical wavelengths.

[0045] The pump light 20 is transmitted to the plasma source region 19 via a mirror 22, which may be a mirror that can be tilted in a controlled manner, and via a focusing lens element 23. A plasma emitting the EUV use light 3 is created by the pump light impinging from the tin droplets 15 that arrive in the plasma source region 19. In FIG. 2 the beam path of the EUV use light 3 between the plasma source region 19 and the field facet mirror FF is shown in the extent to which the EUV use light is reflected by a collector mirror 24, which is also called EUV collector 24 in the following. The EUV collector 24 comprises a central passage aperture 25 for the pump light 20, which is focused towards the plasma source region 19 via the focusing lens element 23. The collector 24 is embodied as an ellipsoidal mirror and transmits the EUV use light 3 emitted by the plasma source region 19, which is located at one ellipsoidal focus of the collector 24, to an intermediate focus 26 of the EUV use light 3, which is located at the other ellipsoidal focus of the collector 24.

[0046] The field facet mirror FF is located downstream of the intermediate focus 26 in the beam path of the EUV use light 3 , in the region of the far field of the EUV use light 3 .

[0047] The EUV collector 24, as well as further components of the light source 2, which may be the tin droplet generator 16, the tin capture device 18 and the focusing lens element 23, are arranged in a vacuum housing 27. The vacuum housing 27 has a passage opening 28 in the region of the intermediate focus 26. The vacuum housing 27 comprises, in the region of the entrance of the pump light 20 into the vacuum housing 27, a pump light entrance window 29 for the light pre-pulse and the main light pulse.

[0048] 3 shows, in a very abstract way, firstly the guidance of the EUV used light, i.e. the illumination light 3, and secondly the guidance of the stray light 30, in particular of long-wave radiation, for example IR radiation with the wavelength of the optical prepulse and / or the main optical pulse, between the plasma source region 19 of the light source 2 and the intermediate focal plane 26a, in which the intermediate focus 26 is located. At the same time, FIG. 3 shows a variant of the lateral guidance of the pump light 20 into the plasma source region 19, i.e. guidance that does not require a passage opening of the type of the passage opening 25 in the EUV collector 24. Both the used light 3 and the stray light 30 originate from the plasma source region 19. Both the used light 3 and the stray light 30 are incident on surface sections 31, 32 over the impact surface 33 of the EUV collector 24. The surface sections 31, 32 are sections of a grating surface of the EUV collector 24, also indicated by 33 in the figure, on which an optical grating for diffractively dumping the stray light radiation 30 is arranged. An embodiment of the optical grating is described below. The grating surface may be positioned exclusively at the location of the surface sections 31, 32 where the stray light 30 impinges, or alternatively it may cover a larger section of the impingement surface 33, or in a further variant it may cover the entire impingement surface 33.

[0049] FIG. 4 shows an embodiment of an optical diffractive component 34 for suppressing two different target wavelengths, i.e. the waves of the optical prepulse from one light source 2 and the wavelength of the main optical pulse from the other light source 2. The optical diffractive component 34 is embodied as an optical grating with a grating period P along the periodicity direction x. FIG. 4 shows the structure height d of the optical grating 34 plotted against the periodicity direction x. The structure depth d is shown with a greatly enlarged scaling compared to the periodicity direction x. Typical orders of magnitude of the structure depth d are a few micrometers. Typical orders of magnitude of the period P are in the millimeter range, for example in the range of 0.5-10 mm, for example in the range of 1 mm-4 mm.

[0050] In some cases, the structure depth value d is given below with calculated precision, and when given in micrometers, rounding to two decimal places is usually sufficient.

[0051] The grating structure profile of the optical diffractive element 34 is shown in FIG. 0 , N 1 , and N 2 The diffraction structure has exactly three diffraction structure levels, denoted by 0 ~N 2 is the structure depth d relative to the reference plane (d=0). Ni is predefined. Diffractive structure level N 1 is the structural depth (structural height) d N1 =d 0 is 2.59904 μm (or 2.60 μm). 0 is the structural depth d N0 is embodied as a neutral diffraction structure level where n is 0. Therefore, the diffraction structure level N 0 is at the level of the reference plane. Diffractive structure level N 2 is embodied as a negative diffraction structure level, and a neutral diffraction structure level N 0 The absolute structural depth d is 2.59904 μm. N2 =-d 0 Therefore, the negative diffraction structure level N2 For the structural depth of N2 =-2.59904μm.

[0052] The diffractive structure of the optical grating 34 is arranged such that a wavelength range around two target wavelengths, λ1, e.g., an optical pre-pulse, and λ2, e.g., a main optical pulse, that is diffracted (made to diffract) by the grating structure profile has radiation components with three different phases that destructively interfere with each other.

[0053] Diffractive structure level N 0 ~N 2 predefines the topography of the grating period of the grating structure profile, which is regularly repeated along the period progression direction x.

[0054] The illustrated embodiment according to FIG. 4 has different diffractive structure levels N i The following sequence of N 0 , N 1 , N 0 , N 2 It is also possible to cyclically permute or mirror this order.

[0055] Within the grating period P, the neutral diffraction structure level N 0 is the total extent a along the period progression direction x that is less than 50% of the extent of the total lattice period P 0 Therefore, the positive diffraction structure level N 1 The spread of a 1 and the negative diffraction structure level N 2 The spread of a 2 The sum of these is the neutral diffraction structure level N 0 is greater than the entire extent of

[0056] In FIG. 4, the optical grating 34 has different diffractive structure levels N i This is illustrated by the ideal steep sidewalls between the

[0057] N different diffractive structure levels within a grating period P iThe spread of each 0 , a 1 , a 2 Diffractive structure level N i In this regard, for example, a displacement of the positive diffractive structure level N 1 is defined as two neutral diffraction structure levels N 0 As a result, a positive diffraction structure level N 1 The upstream and downstream neutral diffraction structure levels of have different extents from each other along the period progression direction. Two neutral diffraction structure levels N 0 Instead of , there is exactly one neutral diffractive structure level N 0 In this case, the extent a of the exactly one neutral diffractive structure level along the periodic progression direction x is 0 is less than 50% of the x-extent of the grating period P.

[0058] The basic characteristics of the diffractive optical element 34 are given in the table below. [Table 1]

[0059] In this case, a0 is the neutral diffraction structure level N in the grating period P. 0 represents the ratio between the total extent of the grating and the extent of the grating period P.

[0060] a1 (=a2) is the positive diffraction structure level N within the grating period P for the entire extent of the grating period P 1 Spread of and negative diffraction structure level N 2 The spread a1 of one positive diffraction structure level N1 and the spread a2 of the other negative diffraction structure level N2 along the periodic progression direction x are strictly equal.

[0061] d 0 is the positive diffraction structure level N 1and the absolute structure depth of the negative diffraction structure level N 2 represents the absolute structural depth of the

[0062] λ1, λ2 represent the two target wavelengths to be suppressed.

[0063] Diffractive structure level N 0 , N 1 , N 2 The spread of a 0 , a 1 , and a 2 , and structural depth d 0 is the diffraction structure level N for both target wavelengths λ1 and λ2. i The three radiation components with different phases, which are generated on reflection from the grating structure profile due to the lattice structure profile, are chosen so that destructive interference occurs in each case when added. In the arrow diagram showing the real and imaginary parts of the radiation components, the three contributions sum to zero when the wavelength corresponds to one of the two target wavelengths.

[0064] Parameter d 0 , a 0 , a 1 , and a 2 is designed such that the following equation is satisfied for both target wavelengths λ1 and λ2:

number

[0065] This formula applies to the case of normal incidence of radiation on the grating. The adaptation of the parameters for non-normal incidence will be clear to one skilled in the art. This adaptation may vary from component to component.

[0066] FIG. 5 shows diagrammatically the wavelength-dependent reflectivity R of various grating variants in the wavelength range 10.0-11.0 μm. The reflectivity 35 of the optical diffractive element 34 is shown by a dashed-dotted line. For the two target wavelengths λ1 and λ2, suppression of more than 10 orders of magnitude (10 -11 ) occurs.

[0067] For comparison, Figure 5 also shows the reflectivity of further optical diffractive elements not according to the invention, in particular the reflectivity of a binary grating, i.e. a grating with exactly two coextensive diffraction structure levels within a grating period (reflectivity 36), the reflectivity of an optical diffractive element with three diffraction structure levels whose neutral diffraction structure level is exactly 50% of the extent of the entire grating period and has a structure depth of 2.65 μm 37, and the reflectivity of a corresponding optical diffractive element with three diffraction structure levels whose neutral diffraction structure level is again exactly 50% of the extent of the entire grating period and has a structure depth d = 2.60 μm 38.

[0068] Reflectance 36 shows narrowband suppression at the target wavelength λ2. Reflectances 37 and 38 show broaderband suppression, first at the target wavelength λ2 (reflectance 37) and second at 10.4 μm (reflectance 38).

[0069] 6-9 show further embodiments of diffractive optical components.

[0070] In this case, Figs. 6 and 7 show three diffractive structure levels N 0 , N 1 , N 2 1 shows two embodiments of a first design of a spread distribution of , in which the neutral diffractive structure levels have a relatively small total spread compared to the total spread of the grating period P.

[0071] In this case, FIG. 6 shows three diffractive structure levels N i 1 shows an optical diffractive element 39 having an asymmetric design of 0 After that, the first positive diffraction structure level N 1 , then the negative diffraction structure level N 2 continues.

[0072] Therefore, in the case of the design according to FIG. 6, there is exactly one neutral diffractive structure level N 0 exists.

[0073] In the case of the optical diffractive component 40 according to FIG. 7, for a grating period P, the diffractive structure levels N i are mutually N 0 , N 1 , N 0 , N 2 In terms of sequence, this therefore corresponds to the embodiment of the optical diffractive component 34 according to FIG.

[0074] In the case of the design according to FIG. 7, the positive diffraction structure level N 1 is again a neutral diffraction structure level N with equal length extension. 0 Located symmetrically between them.

[0075] The diffractive optical components 41, 42 according to Figs. 8 and 9 differ from the diffractive optical component 34 according to Fig. 4 only in parameter details.

[0076] The basic parameters of the diffractive optical components 39 to 41 are given in the following table in a manner corresponding to the table above for the diffractive optical component 34. [Table 2]

[0077] The optical gratings 39-42 according to Figures 6-9 are designed to suppress two significantly different target wavelengths λ1, λ2, i.e. a first target wavelength λ1 in the region of 10.6 μm and a second target wavelength λ2 in the region of 1.046 μm.

[0078] In Figures 10 and 11, the suppression performance of optical diffractive elements 39-42 with three diffractive structure levels designed to suppress exactly one target wavelength, namely wavelength λ1 at 10.6 μm, is shown, again in comparison with an optical grating not according to the present invention.

[0079] FIG. 10 shows the reflectance R in the wavelength range of 10 μm to 11 μm, and FIG. 11 shows the reflectance in the wavelength range of 1.0 μm to 1.1 μm.

[0080] The two designs resulting in the optical diffractive elements 39, 40 according to Figures 6 and 7 produce the same suppression effect, shown as reflectance 43 in Figures 10 and 11. -7 Better suppression occurs at both target wavelength λ1 (FIG. 10) and target wavelength λ2 (FIG. 11).

[0081] The reflectivity 44 of the optical diffractive element 41 has similarly good suppression at the two target wavelengths, with additional suppression occurring in the region of 1.07 μm (side minimum 45) for this design of the optical diffractive element 41 .

[0082] The optical diffractive element 42 also has a suppression comparable to the reflectance (reflectance 46) of the optical diffractive elements 39, 40 in the region of the two target wavelengths λ1, λ2, with a further side minimum 47 of suppression additionally present at a wavelength of approximately 1.02 μm.

[0083] For the diffractive optical elements 41,42 the suppression in the region of the target wavelengths λ1,λ2 has a somewhat broader bandwidth compared to the diffractive optical elements 39,40.

[0084] The structuring of the optical grating described above may have the effect that stray radiation having, for example, infrared wavelengths reflected by the EUV collector 24 destructively interferes in the zeroth order and thus the stray light intensity is suppressed in the zeroth order. In this case, the optical diffractive element described above is typically used as a reflective element.

[0085] The body of the EUV collector 24 may be fabricated from aluminum. Alternative materials for this body are copper, alloys containing constituent copper and / or aluminum, or alloys of copper and aluminum oxide or silicon made by powder metallurgy.

[0086] To produce micro- or nanostructured components, the projection exposure apparatus 1 is used as follows: First, a reflective mask 10 or reticle and a substrate or wafer 11 are provided. Subsequently, with the aid of the projection exposure apparatus 1, the structure on the reticle 10 is projected onto a photosensitive layer of the wafer 11. Then, by developing the photosensitive layer, the micro- or nanostructures and thus the microstructured components are produced on the wafer 11.

Claims

1. - exactly three diffractive structure levels (N) that predefine different structure depths (d) relative to the reference plane (d=0); 0 , N 1 , N 2 Diffractive optical components (34, 39, 40, 41, 42) having a periodic grating structure profile with a diffractive structure having the arrangement of the diffractive structure is such that the wavelength range around two different target wavelengths (λ1, λ2) diffracted by the grating structure profile has radiation components with three different phases that destructively interfere with each other, - the diffraction structure level (N 0 , N 1 , N 2 ) predefines a topography of a grating period (P) of the grating structure profile, which is regularly repeated along a period progression direction (x), - the three diffraction structure levels (N 0 , N 1 , N 2 )but, -- Neutral diffraction structure level corresponding to structure depth 0 (N 0 )and, -- the neutral diffraction structure level (N 0 ) with a high positive diffraction structure level (N 1 )and, -- the neutral diffraction structure level (N 0 ) with respect to the low negative diffraction structure level (N 2 )and Including, Within the grating period (P), the neutral diffraction structure levels (N 0 ) has a spread (a) along the period progression direction (x) that is less than 50% of the spread of the grating period (P). 0 ) the difference between the two target wavelengths is less than 50%, i.e. if a first, larger, target wavelength is designated λ1 and a second, smaller, target wavelength is designated λ2, then λ1-λ2 is less than 0.5λ1; - an optical diffractive element (34, 39, 40, 41, 42), said two target wavelengths (λ1, λ2) differing by at least 1%.

2. The positive diffraction structure level (N 1 ) and the negative diffraction structure level (N 2 2. The optical diffractive element according to claim 1, characterized in that a1 = a2) have the same extent along the periodic progression direction (x).

3. The positive diffraction structure level (N 1 ) and the negative diffraction structure level (N 2 ) has the same absolute structure depth (d 0 3. A diffractive optical element according to claim 1, characterized in that it has a refractive index of 1 / 2.

4. 4. A diffractive optical element according to any one of claims 1 to 3, characterized in that the two target wavelengths differ by at least 10%.

5. 5. An optical diffractive element according to any one of the preceding claims, characterized in that the grating period (P) has an extent along the period progression direction (x) in the range of 0.5 mm to 5 mm.

6. The diffraction structure level (N 0 , N 1 , N 2 The diffraction structure levels (N 0 , N 1 , N 2 6. The optical diffractive element according to claim 1 , characterized in that:

7. An EUV collector (24) for use in an EUV projection exposure apparatus comprising an optical diffractive component (34, 39, 40, 41, 42) according to any one of the preceding claims.

8. 8. The EUV collector mirror according to claim 7, characterized in that the collector mirror is embodied in such a way that it directs EUV radiation (3) towards a focal region (26) and the optical diffractive component is embodied in such a way that it directs radiation (30) of at least one target wavelength away from the focal region (26).

9. 9. An illumination system comprising an EUV collector (24) according to claim 7 or 8 and comprising an illumination optical unit (6) for illuminating an object field (4) in which an object (10) to be imaged can be arranged with EUV use light as illumination light (3).

10. 10. An optical system comprising an illumination system according to claim 9, comprising a projection optical unit (7) for imaging the object field (4) into an image field (8) in which a substrate (11) can be arranged, on which a part of the object (10) to be imaged is imaged.

11. A projection exposure apparatus (1) comprising an optical system according to claim 10 and comprising an EUV light source (2).

12. The next method steps are: providing a reticle (10) and a wafer (11); The projection exposure apparatus according to claim 11 is used to project a structure on the reticle (10) into a - projecting onto a photosensitive layer of said wafer (11); - creating micro- and / or nano-structures on said wafer (11); A method for creating a structured component, comprising:

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