DE102018214559A1 - Optical arrangement and EUV lithography device with it - Google Patents

Abstract

The invention relates to an optical arrangement comprising: a first reflective optical element for the EUV wavelength range, which has a first multi-layer system extending over a first surface on a first substrate, wherein the first multi-layer system has first, alternately arranged layers, wherein Irradiation at a constant angle of incidence forms a first reflectivity profile (R1 (A)) as a function of the wavelength (A), and a second reflective optical element for the EUV wavelength range, which comprises a second multilayer system extending over a second surface on a second substrate wherein the second multilayer system has second, alternately arranged layers, a second reflectivity profile (R2 (A)) being formed as a function of the wavelength (A) when irradiated at a constant angle of incidence, wherein Str reflected by the first reflective optical element At the second reflective optical element meets. The optical arrangement (13) has a resulting transmission profile (T (λ)) with a 20% width (B) as a function of the wavelength (λ), an integral (Fb, 1 + Fb, 2) of the resulting transmission profile (T (λ)) over wavelengths (λ) in the EUV wavelength range outside the 20% width (B) not more than 6.5% of an integral (Fa) of the resulting transmission curve (T (λ)) over wavelengths within the 20th % Width (B ') is.

Description

Background of the invention

The invention relates to an optical arrangement comprising: a first reflective optical element for the EUV wavelength range, which has a first multi-layer system extending over a first surface on a first substrate, wherein the first multi-layer system comprises first, alternately arranged layers of at least two materials having a different real part of the refractive index at a wavelength in the EUV wavelength range, which forms a first Reflektivitätsverlauf under irradiation at a constant angle of incidence, and a second reflective optical element for the EUV wavelength range, which extends over a second surface second multilayer system on a second substrate, the second multi-layer system having second, alternately arranged layers of at least two materials with different real part of the refractive index at a wavelength in the EUV wavelength range, wherein be i radiation under a constant angle of incidence forms a second Reflektivitätsverlauf, and wherein the first reflective optical element and the second reflective optical element are arranged such that the first reflective optical element reflected radiation impinges on the second reflective optical element.

Such an optical arrangement or such an optical system is known from DE 10 2016 224 111 A1 known. There, it is proposed that a first half-width of the first reflectivity profile should not amount to more than 4% of a first wavelength at which the first reflective optical element has a maximum reflectivity. A second half-width of the second reflectivity profile of the second optical element is greater than the first half-width of the first reflective optical element. By providing the first reflectivity profile with the (low) first half-width, interference radiation in the EUV wavelength range is to be suppressed, thereby reducing the thermal load on optical elements following in the beam path. The second reflective optical element has a broader bandwidth than the first reflective optical element in order to additionally reduce the heat input due to the absorption of incident radiation by reflecting more radiation from the second reflective optical element.

In EUV lithography devices, especially in EUV lithography equipment for wafer exposure, the power of the EUV light source is usually very large and may for example be several hundred watts (in the EUV Nutzwellenlängenbereich). This is problematic since the majority of this radiation does not reach the wafer, but is absorbed within the lithography system and there leads to a heat input. This is particularly problematic in the illumination system of the EUV lithography system, which follows in the beam path to the EUV light source, especially in the so-called field facet mirror, which is the first reflective optical element in the illumination system or in the EUV beam path and which is thus exposed to the highest heat load , In addition, the field facet mirror has a large number of small movable components (facet mirror and / or micromirrors) and is thus difficult to cool.

In the EP1938150B1 is described a lighting system with a collector and with a field facet mirror. In order to produce a substantially rectangular, as homogeneous as possible illumination in a plane in which the facet mirror is arranged, an aspherical mirror can be arranged in the light path from the EUV light source to the facet mirror. The aspheric mirror transforms the substantially annular illumination produced by the collector into the substantially rectangular illumination in the plane of the collector mirror. Also the DE 10 2007 041 004 A1 describes an illumination optics for EUV microlithography with an optical correction element for homogenizing the illumination of the first optical element of a facet optic.

By such an aspherical mirror or by such an optical correction element can be achieved that the illumination of the field facet mirror is quasi homogeneous. In this way it is prevented that some of the field facets in the center of the field facet mirror are exposed to a high heat load and possibly degrade ("melt"), while most other field facets are still below their critical temperature. It should be noted that in a typical far field, i. with a non-homogeneous illumination, an intensity difference of up to a factor of 4 is present.

In addition to the spatial shaping of the radiation incident on the facet mirror, spectral shaping of the radiation can also contribute to minimizing the heat input into the field facet mirror. At the same time, however, the transmission of the EUV lithography system and thus the power of the useful radiation arriving at the wafer should be reduced as little as possible.

Object of the invention

The object of the invention is to provide an optical arrangement and an EUV lithography apparatus with such an optical arrangement, which make it possible to reduce the heat load of the radiation passing through the optical arrangement to subsequent optical elements, without significantly reducing the useful power.

Subject of the invention

This object is achieved by an optical arrangement of the aforementioned type which has a transmission profile resulting from the first reflectivity profile and from the second reflectivity profile with a 20% width as a function of the wavelength, wherein an integral of the resulting transmission profile over wavelengths in the EUV Wavelength range outside the 20% width is not more than 6.5%, preferably not more than 3%, in particular not more than 1% of an integral of the resulting transmission profile over wavelengths within the 20% width. The resulting transmission profile is the product of the first reflectivity profile of the first reflective optical element and the second reflectivity profile of the second reflective optical element. Below the 20% width, reference is made to those wavelengths (20% points) at which the transmission profile has dropped to 20% of the maximum transmission. The 20% or 20% width is a better indicator of the behavior of the flanks of a transmission path than the 50% points or the half width. According to the invention, it is proposed to shape a resulting transmission profile as a function of the wavelength and thus a resulting spectrum of the radiation reflected by the second reflective optical element of the optical arrangement in such a way that the resulting transmission profile and thus the resulting spectrum is as box-shaped as possible, ie the resulting transmission profile has as steeply sloping edges as possible. The inventors have recognized that a suitable geometry of the spectral profile with steeply sloping edges and not - as would be expected - a change or reduction of the half width or the 20% width of the spectral profile to a low heat load at high efficiency on Wafer leads.

A measure of the steepness of the resulting transmission profile is the ratio between the integral, i. the area under the resulting transmission curve, for wavelengths outside the 20% width, to the integral, i. to the area under the resulting transmission curve, for wavelengths that are within the 20% width. Since the two reflective optical elements may also have a residual reflectivity for other wavelengths than in the EUV wavelength range, only the resulting transmission profile within the EUV wavelength range is used for the integration outside of the resulting 20% width nm and about 20 nm, ie these two wavelengths represent the lower limit or the upper limit of the interval used for the integration. The measure of the steepness of the resulting transmission curve defined in this way makes it possible to take into account the presence of secondary maxima at wavelengths outside the 20% width which are usually present in reflective optical elements for the EUV wavelength range.

The generation of a box-shaped transmission profile, which fulfills the condition given above, is not readily possible by means of a single reflective optical element, without the maximum reflectivity or transmission of the optical arrangement decreasing too much. The inventors therefore propose that the reflectivity profiles of two reflective optical elements be coordinated with one another in such a way that the result is a possible box-shaped resulting transmission profile and thus a corresponding spectrum of the radiation reflected by the second reflective optical element. A respectively suitable reflectivity profile as a function of the wavelength can be determined by a suitable design of the multi-layer systems, in particular the thicknesses of the layers of the multi-layer systems, the two reflective optical elements, optionally alternatively or additionally, the materials of the layers of the multi-layer systems can be suitably selected.

In another embodiment, the resulting transmission profile at one wavelength has a maximum transmission and a wavelength interval in which the resulting transmission profile decreases from 80% to 20% of the maximum transmission is not more than 60% of the 20% width. In addition to the above-mentioned measure of the steepness of the transmission curve, which takes into account in particular the secondary maxima, the width of the wavelength interval in which the transmission drops from 80% to 20% also represents a measure of the steepness of the transmission curve. When determining the width the wavelength interval, the widths of the two subintervals at smaller wavelengths than the Wavelength with maximum transmission and summed up at wavelengths greater than the wavelength with maximum transmission.

In one embodiment, an integral of the first reflectivity profile over wavelengths in the EUV wavelength range greater than a maximum wavelength of the 20% width of the resulting transmission profile is less than a quarter of an integral of the first reflectivity profile over wavelengths in the EUV wavelength range which are smaller as a minimum wavelength of the 20% width of the resulting transmission profile and an integral of the second reflectivity profile over wavelengths in the EUV wavelength range which are smaller than a minimum wavelength of the 20% width of the resulting transmission profile is less than one quarter of an integral of the second reflectivity profile over wavelengths in the EUV wavelength range greater than a maximum wavelength of the 20% width of the resulting transmission profile, or vice versa.

In this embodiment, the secondary maxima of the first reflectivity profile on one side of the 20% width of the resulting transmission profile, for example at smaller wavelengths than the wavelengths within the 20% width, are deliberately suppressed. The suppression of the sub-maxima at this side, however, takes place at the expense of an increase in the secondary maxima on the other side of the 20% width, for example at longer wavelengths than a maximum wavelength of the 20% width. For a suppression of the secondary maxima on both sides, therefore, the second reflectivity profile is designed such that the secondary maxima of the second reflectivity profile are suppressed at the other side of the 20% width, for example at wavelengths greater than the wavelengths within the 20% width. Since the resulting transmission curve represents the product of the first and second reflectivity curve, the secondary transmission maxima on both sides of the 20% width are suppressed in the resulting transmission curve.

It will be understood that the roles of the first and second reflective optical elements can also be reversed, i. In the first reflectivity pattern, side maxima at wavelengths are suppressed (and satisfy the above condition) larger than a maximum wavelength of the 20% width of the resulting transmission characteristic, and at the second reflectivity pattern secondary wavelengths at wavelengths are suppressed (and the above condition is satisfied), which is smaller are considered to be a minimum wavelength of the 20% width.

In an alternative embodiment, at least one maximum wavelength at which a local maximum of the first reflectivity profile occurs outside a first 20% width of the first reflectivity profile coincides with at least one minimum wavelength at which a local minimum of the second reflectivity profile is outside a second 20% width of the second Reflektivitätsverlaufs occurs, or vice versa. By coincidence of the maximum wavelength with the minimum wavelength is meant that the two wavelengths have a wavelength difference of not more than 0.02 nm. In this embodiment, the resulting transmission profile is reduced outside the respective 20% width of the first reflective optical element or the second reflective optical element in that the wavelength of at least one secondary maximum coincides with the wavelength of at least one secondary minimum. In this way, the resulting transmission path of the optical device outside the resulting 20% width can also be effectively suppressed and a box profile approximated, particularly if the reflectivity of the respective reflective optical element at the local minimum is practically zero.

In this embodiment, in particular, those secondary maxima can be suppressed which lie immediately to the left / right immediately adjacent to the first / second 20% width of the first / second reflective optical element. The suppression of precisely these secondary maxima is favorable because the reflectivity at these secondary maxima is greater than at secondary maxima farther from the respective 20% width. By suitably adapting the thicknesses and, where appropriate, the materials of the layers of the multi-layer systems, additional secondary maxima further removed from the wavelength with maximum reflectivity can additionally be suppressed in order to approach the spectral box geometry as precisely as possible.

In a further embodiment, a first wavelength with maximum reflectivity of the first reflectivity profile and a second wavelength with maximum reflectivity of the second reflectivity curve deviate from one another by no more than 1%. In order to ensure a sufficient transmission of the optical arrangement at the useful wavelength, the wavelengths with maximum reflectivity of the first and the second reflectivity curve should not deviate too much from one another. The deviation is understood to be the ratio of the difference between the two wavelengths to the sum of the two wavelengths.

In a development, the first 20% width of the first reflectivity profile is not more than 4% of the first wavelength and / or the second 20% width of the second reflectivity profile is not more than 4% of the second wavelength. In addition to the steepness of the reflectivity curve, the 20% width of the respective reflectivity profile also has an influence on the heat input of reflective optical elements following in the beam path. Therefore, the 20% widths of the reflectivity curves of the two reflective optical elements should not be chosen too large.

In another embodiment, the first 20% width and the second 20% width do not deviate from each other by more than 5%. The deviation is understood to mean the ratio of the difference between the two 20% widths to the sum of the two 20% widths. Unlike in the cited above DE 10 2016 224 111 A1 In the present optical arrangement, it is not necessary for the second 20% width to be greater than the first 20% width, since the second reflective optical element does not generally need to be additionally protected against heat input. In addition, it is favorable for the production of the box profile, if the amount of the two 20% widths substantially matches.

In one embodiment, the alternately arranged first layers of the first multi-layer system have no periodically recurring thicknesses and / or the alternately arranged second layers of the second multi-layer system have no periodically recurring thicknesses. Conversely, conventional EUV wavelength region reflective optical elements typically have stacks of alternating layers of a larger refractive index material of real material and a smaller refractive index real material, with the thicknesses of the layers of the two materials of the stacks of layers repeating such that the multi-layer system has a periodicity. Multi-layer systems in which the thicknesses of the layers have no periodicity make it possible to change the shape of the spectral reflectivity curve, in particular the 20% width and the steepness of the flanks of the reflectivity profile, and in this way to produce a desired reflectivity profile.

Preferably, one or more first and / or second layers comprise as lower refractive index material one or more of molybdenum, ruthenium, rhodium, palladium, zirconium, titanium, yttrium, niobium, lanthanum, cerium, their alloys and compounds, for example Borides, carbides, silicides, oxides and nitrides.

In addition, one or more first and / or second layers preferably have, as a material with a higher refractive index, one or more materials from the group consisting of silicon, carbon, boron, silicon boride, silicon carbide and boron carbide. Especially in connection with the aforementioned materials for layers of the material with the lower refractive index can be realized on the basis of said materials narrow-band multi-layer systems, which also have a large slope of the flanks of the Reflektivitätsverlaufs.

In one embodiment, the material having the lower real part of the refractive index of the first layers agrees with the material having the lower real part of the refractive index of the second layers and / or the material having the higher real part of the refractive index of the first layers agrees with the material having the higher real part the refractive index of the second layers match. In particular, the first multi-layer system and the second multi-layer system can be formed of the same materials, for example of silicon and molybdenum.

In a further embodiment, the first reflective optical element is designed as a collector mirror. As described above, the collector mirror is typically the first reflective optical element in the beam path after the EUV light source. Interference radiation can therefore be absorbed on the collector mirror before it strikes the subsequent optical elements and possibly damages them. This has a favorable effect that the collector mirror can be well cooled as a rule, for example, by this with a cooling medium, in particular with a cooling fluid, is applied.

In one embodiment, the second reflective optical element has a free-form surface as the second surface. In this case, the second reflective optical element may be arranged in the beam path after the collector mirror. The free-form surface, which may be, for example, a (rotationally symmetric) aspherical surface - but need not act - makes it possible to produce a substantially rectangular, as homogeneous as possible illumination of a subsequent facet mirror in the beam path. In addition, the free-form mirror together with the collector mirror can be used to produce a box-shaped spectral profile of the radiation striking the field facet mirror.

Another aspect of the invention relates to an EUV lithography apparatus having an optical assembly formed as described above. The two reflective optical elements of the optical arrangement may be, for example, the collector mirror described above and the free-form mirror. However, it is understood that the first and the second reflective optical element can also be other reflective optical elements of the EUV lithography device, which typically follow one another directly in the beam path. The EUV lithography device need not necessarily be an EUV lithography system, but may also be another type of device that uses EUV wavelength radiation, such as a wafer or mask inspection device ,

In an embodiment, the EUV lithography device comprises a field facet mirror arranged such that radiation reflected by the second reflective optical element strikes the field facet mirror. As already described above, the field facet mirror represents the first optical element of the illumination system (possibly after the free-form mirror) and is therefore exposed to a high heat load. In addition, the field facet mirror is difficult to cool, so that it is favorable if the heat load on the field facet mirror can be reduced by the optical arrangement described above, which is arranged in the beam path in front of the field facet mirror.

Further features and advantages of the invention will become apparent from the following description of embodiments of the invention, with reference to the figures of the drawing, which show details essential to the invention, and from the claims. The individual features can be realized individually for themselves or for several in any combination in a variant of the invention.

list of figures

• 1 eine schematische Darstellung einer EUV-Lithographieanlage,
• 2a,b schematische Darstellungen eines ersten und eines zweiten reflektiven optischen Elements, die jeweils ein Viellagensystem aufweisen,
• 3 schematische Darstellungen von unterschiedlich steilen Verläufen eines wellenlängenabhängigen Abschwächungskoeffizienten,
• 4a-d schematische Darstellungen eines Wärmeeintrags in ein optisches Element und einer Nutzleistung in Abhängigkeit von spektralen Parametern des Abschwächungskoeffizienten,
• 5a-c Reflektivitätsverläufe in Abhängigkeit von der Wellenlänge bei reflektiven optischen Elementen gemäß dem Stand der Technik,
• 6a-c Reflektivitätsverläufe in Abhängigkeit von der Wellenlänge für ein erstes reflektives optisches Element und ein zweites reflektives optisches Element sowie eines daraus resultierenden Transmissionsverlaufs, wobei Nebenmaxima oberhalb bzw. unterhalb einer 20%-Breite des resultierenden Transmissionsverlaufs in den beiden Reflektivitätsverläufen unterdrückt werden,
• 7a-c Reflektivitätsverläufe in Abhängigkeit von der Wellenlänge für ein erstes reflektives optisches Element, bei dem zwei Nebenmaxima bei den gleichen Wellenlängen auftreten wie zwei Nebenminima bei einem zweiten reflektiven optischen Element, sowie eines daraus resultierenden Transmissionsverlaufs.

Embodiments are illustrated in the schematic drawing and will be explained in the following description. It shows

• 1 a schematic representation of an EUV lithography system,
• 2a, b schematic representations of a first and a second reflective optical element, each having a multilayer system,
• 3 schematic representations of different steep gradients of a wavelength-dependent attenuation coefficient,
• D-4a schematic representations of a heat input into an optical element and a useful power as a function of spectral parameters of the attenuation coefficient,
• 5a-c Reflectivity curves as a function of the wavelength in reflective optical elements according to the prior art,
• 6a-c Reflectivity gradients as a function of the wavelength for a first reflective optical element and a second reflective optical element and a resulting transmission curve, wherein secondary maxima are suppressed above or below a 20% width of the resulting transmission curve in the two Reflektivitätsverläufen,
• 7a-c Reflectivity curves as a function of the wavelength for a first reflective optical element, in which two secondary maxima occur at the same wavelengths as two secondary minima in a second reflective optical element, and a resulting transmission profile.

In the following description of the drawings, identical reference numerals are used for identical or functionally identical components.

In 1 schematically is an EUV lithography device in the form of an EUV lithography system 1 shown. The EUV lithography system 1 has a beam generating system 2 , a lighting system 3 and a projection system 4 accommodated in separate vacuum housings and consecutively in one of an EUV light source 5 of the beam-forming system 2 outgoing beam path from the EUV light source 5 emitted EUV radiation 6 are arranged. As an EUV light source 5 For example, a plasma source or a synchrotron can serve. In the example shown, it is a laser-based plasma source. The EUV lithography system 1 is operated under vacuum conditions, so that the EUV radiation 6 is absorbed as little as possible in their interior.

The of the light source 5 emitted EUV radiation 6 In the wavelength range between about 5 nm and about 20 nm is using a collector mirror 7 focused on an intermediate focus. The EUV radiation 6 gets out of the beam generation system 2 about the intermediate focus in the lighting system 3 introduced. The lighting system 3 has a free-form mirror 8th and a facet optic with two further reflective optical elements in the form of a field facet mirror 9 and a pupil facet mirror 10 on. The free-form mirror 8th serves to after reflection on the collector mirror 7 essentially annular or circular beam profile of the EUV radiation 6 in a substantially rectangular beam profile in the plane of the field facet mirror 9 to transform.

The field facet mirror 9 and the pupil facet mirror 10 direct the radiation onto a photomask 11 which has a structure applied to a wafer 12 should be displayed. At the photomask 11 It is also a reflective optical element for the EUV wavelength range, which can be changed depending on the exposure process. With the help of the projection system 4 gets the from the photomask 11 reflected EUV radiation on the wafer 12 projects and thereby the structure on the photomask 11 on the wafer 12 displayed. These are in the projection system 4 two additional reflective optical elements 28 . 29 intended. It should be noted that both the projection system 4 as well as the lighting system 3 each may have only one or more than two or three, four, five, six, seven, eight, nine or ten mirrors. Some of these mirrors may be designed as grazing incidence mirrors.

2a, b schematically show a first reflective optical element in the form of the collector mirror 7 and a second reflective optical element 8th in the form of the free-form mirror 8th , which together form an optical arrangement 13 form. The collector mirror 7 is for normal incidence of EUV radiation 6 formed and has a first reflective coating in the form of a first multi-layer system 14 on. Also the free-form mirror 8th is for normal incidence of EUV radiation 6 formed and has a second reflective coating in the form of a second multi-layer system 15 on. In the first multi-day system 14 they are alternately applied or arranged layers 16 . 17 a material with a higher real part of the refractive index at a useful wavelength λ _N , in which, for example, the exposure is performed (also Spacer 16 called) and a lower refractive index material at the use wavelength λ _N (also absorber 17 called). An absorber-spacer pair forms a (first) stack 18 , Accordingly, the second multi-layer system also has 15 alternately arranged spacer layers 19 and absorber layers 20 put on a (second) stack 21 form.

The terminology spacer and absorber is common in some areas of X-ray optics and is therefore also used in the following. Ideally, however, neither spacer nor absorber will absorb useful radiation, i.e., any absorption of useful radiation in the absorber will be undesirable, but inevitable due to the properties of the materials available.

The first or second surface 22 . 23 are on a respective first and second substrate 24 . 25 educated. Typical substrate materials for reflective optical elements for the EUV wavelength range are, for example, silicon, silicon carbide, silicon-infiltrated silicon carbide, quartz glass, titanium-doped quartz glass, glass and glass ceramic. The respective substrate 24 . 25 may also be formed of copper, aluminum, a copper alloy, an aluminum alloy or a copper-aluminum alloy.

The thicknesses of the individual first layers 16 . 17 and the individual second layers 19 . 20 as well as the first and the second stack 18 . 21 can over the entire first or second multilayer system 14 . 15 be constant or over a respective first or second surface 22 . 23 vary on which the respective multilayer system 14 . 15 is applied. In this case, the thicknesses can be determined as a function of a desired angle-dependent or spectral reflectivity profile, depending on which spectral or angle-dependent reflection profile or which maximum reflectivity is to be achieved at the operating wavelength. The reflection profile can also be selectively influenced by the basic structure of absorber 17 and spacers 16 is supplemented by more more and less absorbing materials to increase the maximum possible reflectivity at the respective operating wavelength. This can be done in some stacks 18 . 21 Absorber and / or spacer materials are exchanged for each other or the stacks 18 . 21 be built up from more than one absorber and / or spacer material. Furthermore, additional layers can also act as diffusion barriers between at the transition of spacer layers 16 to absorber layers 17 and / or at the transition from absorber to spacer layer 17 . 16 be provided. Diffusion barriers can be known to increase reflectivity, even over extended periods of time or under heat, to real multi-layer systems by reducing the effect of density change due to structural change.

Also, optional on the the substrate 24 . 25 opposite side of the multi-layer system 14 . 15 a cover layer 26 . 27 (Vfl. 2a, b ), which can also be designed in several layers. Between the multi-day system 14 . 15 and the substrate 24 . 25 it is also possible to provide a substrate protection layer (not illustrated) and / or a stress-reducing layer which, inter alia, comprises the substrate 24 . 25 from radiation damage caused by the EUV radiation 6 protects and / or that of the multilayer system 14 . 15 can compensate for applied layer stresses. Design options, as described above for the design of the layers of absorber and / or spacer materials, for example, a location dependence of the layer thickness, can be applied mutatis mutandis to other layers such as cover layers.

The substrate protective layer may comprise one or more of the group consisting of iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), vanadium (V), copper (Cu), silver (Ag), gold ( Au), platinum (Pt), iridium (Ir), ruthenium (Ru), palladium (Pd), rhodium (Rh), germanium (Ge), tungsten (Wo), molybdenum (Mo), tin (Sn), zinc ( Zn), indium (In) and tellurium (Te).

The stress relieving layer may comprise one or more of the group consisting of iron (Fe), nickel (Ni), cobalt (Co), chromium (Cr), vanadium (V), copper (Cu), silver (Ag), gold (Au), platinum (Pt), iridium (Ir), ruthenium (Ru), palladium (Pd), rhodium (Rh), germanium (Ge), tungsten (Wo), molybdenum (Mo), tin (Sn), zinc (Zn), indium (In) and tellurium (Te).

The substrate protective layer may also be formed as a stress-reducing layer. Next to the top layer 26 . 27 for the multi-day system 14 . 15 can / can also be formed as a multi-layer system, the substrate protective layer and / or the voltage-reducing layer.

Further explanations, in particular for periodic and aperiodic arrangements, relate in particular only to the multi-layer system 14 . 15 ie, topcoats 26 . 27 , Protective and similar layers are not considered here. The multi-day system 14 . 15 can be differentiated from the other layers, for example, by the fact that it already has a relevant reflectivity on its own, eg a reflectivity of more than 30%, but further addition of equivalent layers leads to no significant increase in the reflectivity anymore.

In the presentation of 2a is the first area 22 attached to the collector mirror 7 is formed, for simplicity, shown as a flat surface, but this is typically an ellipsoidal segment. The second surface is the same 23 at the free-form mirror 8th is formed in 2 B shown plan, but it is a free-form surface, for example, an aspherical surface. As described above, the geometry of the freeform surface is selected such that the field facet mirror 9 from the EUV radiation 6 is illuminated as homogeneously as possible.

wobei Q(λ) die von der Wellenlänge λ abhängige spektrale Verteilung der Leistung der EUV-Lichtquelle 5, T(λ) die Gesamttransmission durch die EUV-Lithographieanlage 1 und α(λ) einen zusätzlichen wellenlängenabhängigen Abschwächungskoeffizienten bezeichnen. Dieser wellenlängenabhängige Abschwächungskoeffizient α(λ) beschreibt die erfindungsgemäße Wirkung.The in the beam path to the optical arrangement 13 with the first optical element 7 and the second optical element 8th the following field facet mirrors 9 has a variety of micromirrors and is therefore difficult to cool. It is therefore advantageous if the on the field facet mirror 9 impinging EUV radiation 6 has a spectral distribution whose heat input W on the field facet mirror 9 as low as possible. On the other hand, the spectral distribution should be chosen such that the net power N at the wafer 12 as big as possible. For the net power N on the wafer 12 applies: $$N={\displaystyle \int \alpha \left(\lambda \right)T\left(\lambda \right)Q\left(\lambda \right)d\lambda }$$

in which Q (λ) the of the wavelength λ dependent spectral distribution of the power of the EUV light source 5 . T (λ) the total transmission through the EUV lithography system 1 and α (λ) denote an additional wavelength-dependent attenuation coefficient. This wavelength-dependent attenuation coefficient α (λ) describes the effect according to the invention.

wobei R(λ) die wellenlängenabhängige Reflektivität des Feldfacettenspiegels 9 bezeichnet.For the heat input W in the first reflective optical element of the EUV lithography system or in the present example in the field facet mirror 9 applies: $$W={\displaystyle \int \alpha \left(\lambda \right)\left[1-R\left(\lambda \right)\right]Q\left(\lambda \right)d\lambda }$$

in which R (λ) the wavelength-dependent reflectivity of the field facet mirror 9 designated.

The wavelength-dependent attenuation coefficient α (λ) should be chosen so that on the one hand the net power N as large as possible and on the other hand the heat input W as small as possible. These two requirements are opposite at first glance.

For the following considerations, a simplified model is used in which the performance Q (λ) the EUV light source 5 is constant, ie does not depend on the wavelength, since the plasma is less dependent on wavelength for the relevant EUV wavelength range λ as the first layers 16 . 17 or the second layers 19 . 20 of the two multi-level systems 14 . 15 having. For the transmission T (λ) becomes a typical spectrum on the wafer 12 accepted. For the reflectivity R (λ) in equation (2), R (λ) = T (λ) ^{1/7 is} set, according to a simplified model of the EUV lithography equipment 1 of seven reflective optical elements each having the same wavelength-dependent reflectivity profile R (λ) ,

und hängt somit von den beiden Parametern σ, welcher ein Maß für die spektrale Breite des Abschwächungskoeffizienten α(λ) ist, und p, welcher ein Maß für die Steilheit der Spektralverteilung des Abschwächungskoeffizienten α(λ) darstellt, ab. Wie anhand von 3 ersichtlich ist, nimmt die Steilheit der Spektralverteilung des Abschwächungskoeffizienten α(λ) mit zunehmendem p zu, d.h. je größer der Supergauß-Parameter p, desto mehr nähert sich die Spektralverteilung des Abschwächungskoeffizienten α(λ) einem Kastenpotential an.The attenuation coefficient to be optimized α (λ) is modeled as a supergaussian distribution, ie as $$\alpha \left[\lambda \right]=exp\left[\frac{{\left|\lambda -{\mathrm{<figure-callout\; id="0"\; label="\lambda "\; filenames="DE102018214559A1\_0006.png,DE102018214559A1\_0007.png"\; state="\{\{state\}\}">\lambda </figure-callout>}}_0\right|}^p}{{\sigma }^p}\right]$$

and thus depends on the two parameters σ , which is a measure of the spectral width of the attenuation coefficient α (λ) is and p , which is a measure of the steepness of the spectral distribution of the attenuation coefficient α (λ) represents, off. As based on 3 is apparent, the slope of the spectral distribution of the attenuation coefficient decreases α (λ) with increasing p too, ie the larger the supergauss parameter p The more the spectral distribution of the attenuation coefficient approaches α (λ) a box potential.

There are thus two input parameters for the modeling σ . p as well as two output parameters N . W , D-4a all show the same data obtained in the modeling in a different representation. As in particular in 4c It is easy to see that it is necessary to achieve sufficient net output N on the wafer 12 required that the width σ is sufficiently large, for example greater than 0.15 nm. By increasing the steepness p can at substantially constant heat input W (see. 4d ) an increase in net power N on the wafer 12 (see. 4c ) can be achieved. A change in the width σ, however, changes the heat input W in the optical element and the net power N on the wafer 12 essentially similar.

From the above model it follows that there is not a change, in particular a reduction, in the width σ of the spectral distribution of the attenuation coefficient α (λ) is advantageous, but rather an increase in the steepness of the spectral distribution of the attenuation coefficient α (λ) , which is parameterized by the supergauss parameter p in the simplified model used here. To achieve the desired spectral distribution at the field facet mirror 9 is used in the EUV lithography system 1 from 1 with the help of the optical arrangement 13 from the first and second reflective optical elements 7 . 8th a wavelength-dependent transmission profile T (λ) generated, which approximates a spectral box profile.

To such a box-shaped transmission course T (λ) It is necessary to generate the wavelength-dependent first reflectivity profile R1 of the first reflective optical element 7 and the wavelength-dependent second reflectivity profile R2 of the second reflective optical element 8th suitable to choose. The following is based on 5a-c explains how the wavelength-dependent reflectivity curve R (λ) an (arbitrary) optical element, for example the first reflective optical element 7 , by a suitable choice of the thicknesses of the layers 16 . 17 or the thickness of a respective stack 18 of the (first) multi-day system 14 can be influenced.

For the following considerations it is assumed that the useful wavelength λ _N the EUV lithography system 1 at about 13.5 nm. A combination of materials which is customary in this case represents molybdenum as the absorber material and silicon as the spacer material.

5a shows a Reflektivitätsverlauf R (λ) depending on the wavelength λ a reflective optical element 7 which is a periodic sequence of eighty stacks 18 from alternating spacer layers 16 made of silicon with uniform thickness ds (here: ds = 4.274 nm) and absorber layers 17 of molybdenum of uniform thickness d _A (here: d _A = 2.636 nm). The reflectivity course R (λ) points at a wavelength λ _MAX of about 13.5 nm maximum reflectivity R _MAX on, which is about 72%. The reflectivity R increases starting from the maximum reflectivity R _MAX slowly and the Reflektivitätsverlauf R (λ) points Nebenmaxima with a comparatively low value of the maximum reflectivity R on. The in 5a and the reflectivity profile R (λ) shown in the following illustrations applies to a constant angle of incidence γ on the first surface 22 , which is close to 0 °, eg at about 3 °.

Indicates the multilayer system 14 more than fifty piles 18 from alternating spacer layers 16 and absorber layers 17 on, one has the freedom, by a deviation from the periodicity, the form of the spectral Reflektivitätsverlaufs R (λ) to change. In the simplest case, two differently thick stacks can be used 18 with a different thickness d _A the absorber location 17 and ds the spacer layer 16 used in the multilayer system 14 be arranged one above the other and two subsystems of the multi-layer system 14 form. In the reflective optical element 7 which the in 5b shown Reflektivitätsverlauf R (λ) are, for example, starting from the first surface 22 forty stacks 18 with a thickness d _A the absorber location 17 of 3.291 nm and a thickness ds of the spacer layer 16 of 3,874 nm applied, as well as forty more stacks 18 with a thickness d _A the absorber location 17 of 2.906 nm and a thickness ds of the spacer layer 16 of 4.052 nm. As in 5b it can be seen, the reflectivity R of the secondary maxima, which is at longer wavelengths than the wavelength λ _MAX with the highest reflectivity R _MAX are significantly higher.

Further improvement can be achieved by using a completely aperiodic multilayer system 14 is used, in which the alternately arranged first layers 16 . 17 no periodically recurring thicknesses d _A , ds, ie at each individual stack 18 are the thickness d _A the absorber location 17 and the thickness ds of the spacer layer 16 differently. 5c shows a wavelength-dependent reflectivity profile R (λ) for such aperiodic multi-layer system, in which the thicknesses d _A , ds of the layers 16 . 17 from Si or from Mo are shown in Table 1 below. Table 1 substratum Mo 1,000 nm Si 3,855 nm Mo 3,172 nm Mo 3,433 nm Si 2,786 nm Mo 3.023 nm Si 3,814 nm Si 3.401 nm Mo 3,275 nm Si 3,981 nm Mo 3,187 nm Mo 3,669 nm Si 3,244 nm Mo 3,171 nm Si 3,772 nm Si 3.446 nm Mo 1.059 nm Si 3,710 nm Mo 1.776 nm Mo 3.478 nm Si 1,024 nm Mo 3,313 nm Si 1000 nm Si 2,550 nm Mo 1724 nm Si 3,747 nm Mo 1,000 nm Mo 1,000 nm Si 3,728 nm Mo 3,267 nm Si 3,217 nm Si 1000 nm Mo 2,995 nm Si 3,713 nm Mo 3,215 nm Mo 1,331 nm Si 2,636 nm Mo 3,321 nm Si 3,811 nm Si 1000 nm Mo 1.008 nm Si 3,713 nm Mo 3,186 nm Mo 1,000 nm Si 1,033 nm Mo 3,298 nm Si 3,816 nm Si 2.411 nm Mo 2,635 nm Si 3.019 nm Mo 3,147 nm Mo 3,642 nm Si 4,175 nm Mo 1,000 nm Si 3,862 nm Si 3.562 nm Mo 2.515 nm Si 1000 nm Mo 3.092 nm Mo 3,631 nm Si 3,631 nm Mo 2.019 nm Si 3,895 nm Si 3,582 nm Mo 3,354 nm Si 3,700 nm Mo 3.065 nm Mo 3.511 nm Si 4,639 nm Mo 3,319 nm Si 3,917 nm Si 3.498 nm Mo 2.611 nm Si 3,717 nm Mo 3.047 nm Mo 3,383 nm Si 2.429 nm Mo 3,282 nm Si 3,932 nm Si 3.485 nm Mo 4.121 nm Si 3,735 nm Mo 3.032 nm Mo 3,376 nm Si 4,166 nm Mo 3,266 nm Si 3,948 nm Si 3,568 nm Mo 3.558 nm Si 3,743 nm Mo 3,008 nm Mo 3,425 nm Si 2.077 nm Mo 3,251 nm Si 3,966 nm Si 3,655 nm Mo 3.090 nm Si 3,763 nm Mo 2,987 nm Mo 2.303 nm Si 3,772 nm Mo 3,236 nm Si 3,977 nm Si 1000 nm Mo 2.558 nm Si 3,767 nm Mo 2,969 nm Mo 1,000 nm Si 3,612 nm Mo 3,261 nm Si 3,993 nm Si 2,852 nm Mo 2.548 nm Si 3,751 nm Mo 2,943 nm Mo 2.319 nm Si 4,998 nm Mo 3,254 nm Si 4,021 nm Si 1000 nm Mo 2.314 nm Si 3,821 nm Mo 2,909 nm Mo 1,000 nm Si 1.809 nm Mo 3,269 nm Si 4.054 nm Si 2,938 nm Mo 2.440 nm Si 1725 nm Mo 2,870 nm Mo 3,362 nm Si 4,881 nm Mo 1,000 nm Si 4.084 nm Si 3,837 nm Mo 3,327 nm Si 1.175 nm Mo 2,832 nm Mo 3,206 nm Si 2,956 nm Mo 3,122 nm Si 4,112 nm Si 3,728 nm Mo 3,838 nm Si 3,782 nm Mo 2,795 nm Mo 2,163 nm Si 4.063 nm Mo 3,181 nm Si 4140 nm Si 1.001 nm Mo 3.096 nm Si 3,806 nm Mo 2,758 nm Si 4,174 nm Si 4,205 nm Si 1000 nm Mo 2,724 nm Mo 2.319 nm surface

The in 5c shown associated Reflektivitätsverlauf R (λ) has steeper pronounced flanks than in 5a shown Reflektivitätsverlauf R (λ) However, more pronounced secondary maxima occur on both sides of the maximum wavelength λ _MAX on. As in 5b, c can also be seen, the value of the maximum reflectivity can be R _MAX of the multi-day system 14 by an aperiodic design of the thickness ds, d _A the layers 16 . 17 do not improve.

The above in connection with 5a-c described behavior of the Reflektivitätsverlaufs R (λ) is not random, rather usually results in any deviation of the thicknesses d _A , ds of the layers 16 . 17 from a perfectly periodic sequence that the secondary maxima are undesirably more pronounced. After reflection on such a reflective optical element 7 indicates the EUV radiation 6 Therefore, still comparatively much energy in the secondary maxima, which is absorbed on the following reflective optical elements, in particular for the above-described case of poorly coolable Feldfacettenspiegels 9 unfavorable.

Nevertheless, the desired box-shaped spectral distribution of the on the field facet mirror 9 incident EUV radiation 6 therefore, they become a first reflectivity curve R1 (λ) of the first reflective optical element 7 and a second reflectivity profile R2 (λ) of the second reflective optical element 8th changed together in such a way that the optical arrangement 13 from the two reflective optical elements 7 . 8th a resulting transmission profile T (λ ), which approximately corresponds to the desired box-shaped course.

6a shows the first reflectivity course R1 (λ) at the first reflective optical element 7 . 6b the second reflectivity course R2 (λ) on the second reflective optical element 8th and 6c the two Reflektivitätsverläufe R1 (λ), R2 (λ) and the resulting transmission curve T (λ) the optical arrangement 13 , which is the product of the two Reflektivitätsverläufen R1 (λ) . R2 (λ) represents, ie T (λ) = R1 (λ) × R2 (λ).

The in 6a shown first Reflektivitätsverlauf R1 (λ) is from a first multi-day system 14 produced in which the spacer layers 16 and the absorber layers 17 Thicknesses ds or d _A have, which are shown in Table 2 below. Table 2 substratum Si 3,771 nm Si 4,160 nm Si 3,670 nm Mo 3,909 nm Mo 2.555 nm Mo 2,775 nm Mo 1,932 nm Si 3,615 nm Si 3,993 nm Si 3,814 nm Si 1000 nm Mo 3,715 nm Mo 2,989 nm Mo 3.088 nm Mo 1,000 nm Si 2,732 nm Si 2,195 nm Si 3,803 nm Si 3.020 nm Mo 1.613 nm Mo 1,000 nm Mo 3.576 nm Mo 3 482 nm Si 1,032 nm Si 1.209 nm Si 3.462 nm Si 3,642 nm Mo 1.025 nm Mo 2,313 nm Mo 3.065 nm Mo 3,130 nm Si 2.597 nm Si 3,736 nm Si 4,086 nm Si 4.074 nm Mo 3,168 nm Mo 4,219 nm Mo 2.454 nm Mo 3,143 nm Si 3,380 nm Si 2,645 nm Si 4,563 nm Si 3,711 nm Mo 3,357 nm Mo 2.509 nm Mo 3.047 nm Mo 1.883 nm Si 3,998 nm Si 3.504 nm Si 3,773 nm Si 1000 nm Mo 3,356 nm Mo 1,000 nm Mo 3,279 nm Mo 1,000 nm Si 4,187 nm Si 1.407 nm Si 3,809 nm Si 3,332 nm Mo 3.036 nm Mo 1.680 nm Mo 2,936 nm Mo 3.005 nm Si 4.054 nm Si 3.033 nm Si 3,999 nm Si 4,134 nm Mo 3,824 nm Mo 2.316 nm Mo 3,239 nm Mo 2,976 nm Si 3,182 nm Si 3,941 nm Si 3,759 nm Si 3,965 nm Mo 3,222 nm Mo 2,716 nm Mo 3,164 nm Mo 3.025 nm Si 3,533 nm Si 3,865 nm Si 3,607 nm Si 3,891 nm Mo 1.695 nm Mo 2.097 nm Mo 2.225 nm Mo 3,177 nm Si 3.022 nm Si 4,367 nm Si 1000 nm Si 3,835 nm Mo 1,000 nm Mo 3,327 nm Mo 1,000 nm Mo 3.042 nm Si 2,434 nm Si 4,511 nm Si 2,951 nm Si 3,860 nm Mo 2.027 nm Mo 2,796 nm Mo 3,309 nm Mo 2,918 nm Si 3,193 nm Si 3,088 nm Si 3,701 nm Si 4,268 nm Mo 3.492 nm Mo 2.321 nm Mo 3,353 nm Mo 2.514 nm Si 3,962 nm Si 4.043 nm Si 3,657 nm Si 4,362 nm Mo 2,975 nm Mo 3,000 nm Mo 3,435 nm Mo 2,692 nm Si 4,485 nm Si 3,870 nm Si 3,878 nm Si 4.085 nm Mo 2,842 nm Mo 2,943 nm Mo 2,949 nm Mo 3.051 nm Si 3,688 nm Si 4,235 nm Si 3,968 nm Si 3,888 nm Mo 3,662 nm Mo 3,315 nm Mo 3,289 nm Mo 3.031 nm Si 3.502 nm Si 3,348 nm Si 3,783 nm Si 4.011 nm Mo 2,815 nm Mo 3.455 nm Mo 2,941 nm Mo 2,652 nm Si 3,727 nm Si 3,818 nm Si 4.058 nm Si 4,203 nm Mo 3,103 nm Mo 2,829 nm Mo 3,206 nm Mo 2.504 nm Si 3,840 nm Mo 1,000 nm Si 4,266 nm surface Mo 1,000 nm Si 3,947 nm Mo 2.271 nm Si 1000 nm Mo 2.401 nm Si 1000 nm

As in 6a can be seen, the first reflectivity profile R1 (λ) at a first maximum wavelength λ _1MAX of about 13.55 nm a maximum (first) reflectivity R _1MAX of about 70%. At the in 6a shown first Reflektivitätsverlauf R1 (λ) are the secondary maxima at longer wavelengths than the maximum wavelength λ _1MAX suppressed. In order to determine a measure for the suppression of the secondary maxima, the (first) area F1a becomes below the reflectivity profile R1 (λ) at wavelengths λ in the EUV wavelength range smaller than a minimum wavelength λ _BMIN (here: about 13.2 nm) a 20% width B of in 6c determined resulting transmission profile T (λ), ie at wavelengths λ, for which applies: λ _{EUV, MIN} (here: 5 nm) <λ <λ _BMIN , where λ _{EUV, MIN} denotes the minimum wavelength of the EUV wavelength range.

In addition, a (second) area F2b becomes below the first reflectivity profile R1 (λ) at wavelengths λ in the EUV wavelength range greater than a maximum wavelength λ _BMAX (here: approx. 13.8 nm) of the 20% width B of the in 6c shown resulting transmission curve T (λ) is determined, that is, at wavelengths λ, for which: λ _BMAX <λ <λ _{EUV, MAX,} wherein λ _{EUV, MAX} the maximum wavelength of the EUV wavelength range referred to (here: λ _{EUV, MAX} = 20 nm). The second area F1b is at the in 6a shown first reflectivity profile R1 (λ) not more than about a quarter of the first surface area F1b, ie it holds: F1b <0.25 F1a. The ratio between the two areas F1a, F1b thus represents a measure of the degree of suppression of the secondary maxima, which at longer wavelengths λ than the maximum wavelength λ _MAX lie.

As in 6a can also be seen, is the suppression of secondary maxima at longer wavelengths λ as the maximum wavelength λ _M1MAX only at the expense of increasing the secondary maxima at smaller wavelengths λ as the maximum wavelength λ _1MAX possible. For a bilateral suppression of the secondary maxima, therefore, the in 6b shown second reflectivity course R2 (λ) of the second reflective optical element 8th from a second multi-day system 15 produced, in which the thicknesses ds or d _A the layers 16 . 17 are selected according to the following Table 3: Table 3 substratum Si 3,200 nm Si 3,826 nm Si 3,511 nm Mo 2.519 nm Mo 3,350 nm Mo 3,285 nm Mo 3,434 nm Si 1000 nm Si 1431 nm Si 4,383 nm Si 3,554 nm Mo 1,000 nm Mo 1,065 nm Mo 1.442 nm Mo 3,274 nm Si 1,092 nm Si 1,562 nm Si 1,521 nm Si 3,958 nm Mo 1,000 nm Mo 2,785 nm Mo 1.169 nm Mo 3.042 nm Si 1000 nm Si 3,245 nm Si 3,102 nm Si 3,802 nm Mo 2.529 nm Mo 3.050 nm Mo 2.057 nm Mo 3,193 nm Si 3.253 nm Si 3,652 nm Si 4,701 nm Si 3,872 nm Mo 4,442 nm Mo 3,760 nm Mo 4.001 nm Mo 3,426 nm Si 5,000 nm Si 3.030 nm Si 3.523 nm Si 1429 nm Mo 5,000 nm Mo 1,108 nm Mo 3,337 nm Mo 1,000 nm Si 5,000 nm Si 1.647 nm Si 3,626 nm Si 1.121 nm Mo 3,982 nm Mo 2.063 nm Mo 2,971 nm Mo 3.086 nm Si 3,349 nm Si 4,309 nm Si 3.523 nm Si 4,123 nm Mo 3,633 nm Mo 3.058 nm Mo 3.563 nm Mo 2,865 nm Si 3,302 nm Si 3.052 nm Si 3,620 nm Si 3,961 nm Mo 3,111 nm Mo 3,189 nm Mo 1.104 nm Mo 3.022 nm Si 1.284 nm Si 4,109 nm Si 1000 nm Si 4,107 nm Mo 1,000 nm Mo 1.825 nm Mo 1.206 nm Mo 2,745 nm Si 1.805 nm Si 4,855 nm Si 3,337 nm Si 4,332 nm Mo 2.568 nm Mo 1,108 nm Mo 3.428 nm Mo 2,795 nm Si 3,282 nm Si 1,551 nm Si 4.064 nm Si 3,842 nm Mo 4,957 nm Mo 1,000 nm Mo 3,300 nm Mo 1,000 nm Si 4,552 nm Si 3,147 nm Si 3,310 nm Si 1000 nm Mo 3.586 nm Mo 2,774 nm Mo 3,436 nm Mo 1.075 nm Si 2,877 nm Si 4,762 nm Si 3,893 nm Si 4,147 nm Mo 2,758 nm Mo 5,000 nm Mo 3,206 nm Mo 2,460 nm Si 4.064 nm Si 4,844 nm Si 3.501 nm Si 4,232 nm Mo 4111 nm Mo 3.093 nm Mo 3,105 nm Mo 1,000 nm Si 2,782 nm Si 1,932 nm Si 3,868 nm Si 1000 nm Mo 3,890 nm Mo 1,000 nm Mo 1,000 nm Mo 1,000 nm Si 3,073 nm Si 1.608 nm Si 1000 nm Si 3,926 nm Mo 3,772 nm Mo 2,137 nm Mo 1.469 nm Mo 2,709 nm Si 4,342 nm Mo 1,000 nm Si 4,573 nm Mo 2.316 nm Mo 2,388 nm Si 4,634 nm Mo 1,000 nm Si 4,689 nm Si 4,590 nm Mo 2.018 nm Si 1000 nm Mo 2,111 nm Mo 2,385 nm Si 4,670 nm Mo 1,000 nm Si 1000 nm Si 4,299 nm Mo 2,240 nm Si 4,788 nm surface Mo 1,000 nm Si 4,669 nm Mo 2,021 nm Si 1000 nm Mo 2,090 nm Si 5,000 nm

As in 6b can be seen, serves the second Reflektivitätsverlauf R2 (λ) for suppression of secondary maxima, those at smaller wavelengths λ as a second maximum wavelength λ _2MAX of about 13.6 nm, at which the second reflective optical element 8th a maximum reflectivity R _2MAX of about 70%. An integrated value F2a of the second reflectivity profile R2 (λ) at wavelengths λ, for which the following applies: λ _{EUV, MIN} (here: 5 nm) <λ <ABMIN is at the in 6b less than a quarter of a wavelength λ, for which applies: λ _BMAX <λ <λ _{EUV, MAX} integrated value F2b, ie it applies F2a <0.25 F2b.

Due to the suppression of secondary maxima at wavelengths λ above the maximum wavelength λ _1MAX of the first reflectivity course R1 (λ) and the suppression of the sub-maxima at wavelengths λ below the maximum wavelength λ _2MAX of the second reflectivity profile R2 (λ) results in a 6c shown by a solid line resulting transmission curve T (λ) of the optical arrangement 13 in which the secondary maxima on both sides of a maximum wavelength λ _MAX (here: 13.6 nm) of the transmission curve T (λ) are suppressed, in which the optical arrangement 13 a maximum transmission T _MAX reached by about 50%. An integral value Fb, 1 + Fb, 2 over all wavelengths λ in the EUV wavelength range which lie outside the resulting 20% width B, ie for which λ _{EUV, MIN} <λ <λ _BMIN , corresponding to a first partial integral Fb, 1 or for which: λ _BMAX <λ <λ _{EUV, MAX} , corresponding to a second partial integral Fb, 2, is not more than 6.5% of an integral value or area Fa within the resulting 20% width B, ie, Fb, 1 + Fb, 2 <0.065 Fa. In the example shown, even Fb, 1 + Fb, 2 <0.03 Fa, more specifically Fb, 1 + Fb, 2 <0.01 Fa, ie Secondary maxima are suppressed particularly well. As a result of the suppression of the secondary maxima, a box-shaped resulting transmission profile T (λ) is approximated.

In addition, the in 6c shown resulting transmission curve T (λ) steeply sloping flanks: In 6c are two wavelength intervals W1 . W2 shown, in which the resulting transmission profile T (λ) each of 80% of the maximum transmission T _MAX to 20% of the maximum transmission T _MAX decreases (corresponding to the minimum wavelength λ _BMIN or the maximum wavelength λ _BMAX the 20% width B ), where the two wavelength intervals W1 . W2 at smaller or at larger wavelengths λ than the maximum wavelength λ _MAX occur. In the example shown, the widths of the two wavelength intervals W1 . W2 in sum a value W = W1 + W2 = 0.4 nm, which does not exceed 60% of the resulting 20% width B of approximately 0.6 nm (between ABMIN = 13.2 nm and λ _BMAX = 13, 8 nm).

Another possibility for generating a substantially box-shaped transmission profile T (λ) of the optical arrangement 13 by the suppression of secondary maxima is described below by means of 7a-c described. 7a shows analogously to 6a a first reflectivity course R1 (λ) from a first multi-day system 14 is generated, in which the spacer layers 16 and the absorber layers 17 Thicknesses ds or d _A which are shown in Table 4 below: TABLE 4 substratum Si 1000 nm Si 1000 nm Si 4,971 nm Mo 3,604 nm Mo 1,000 nm Mo 1,000 nm Mo 1,935 nm Si 2,188 nm Si 3.289 nm Si 2,773 nm Si 2,875 nm Mo 1,000 nm Mo 3.492 nm Mo 3,197 nm Mo 3,752 nm Si 1000 nm Si 2,868 nm Si 3,886 nm Si 3,690 nm Mo 2,808 nm Mo 1,000 nm Mo 3,104 nm Mo 4,631 nm Si 3.462 nm Si 1000 nm Si 4,610 nm Si 3,887 nm Mo 3,809 nm Mo 2.530 nm Mo 3,234 nm Mo 1.688 nm Si 3,671 nm Si 3,385 nm Si 3,791 nm Si 1,345 nm Mo 2,162 nm Mo 2.402 nm Mo 2,984 nm Mo 1,147 nm Si 2,941 nm Mo 3,664 nm Si 4,301 nm Mo 3.044 nm Mo 1.417 nm Si 4,110 nm Mo 1,553 nm Si 3,966 nm Si 3.541 nm Mo 1,930 nm Si 1000 nm Mo 2,863 nm Mo 1,000 nm Si 3,367 nm Mo 1,000 nm Si 4.031 nm Si 1.791 nm Mo 1.013 nm Si 3,172 nm Mo 1,120 nm Mo 1826 nm Si 1014 nm Mo 3,150 nm Si 1000 nm Si 3,889 nm Mo 2.312 nm Si 3,963 nm Mo 1,000 nm Mo 2.475 nm Si 3.476 nm Mo 2,898 nm Si 3,794 nm Si 4,207 nm Mo 3.563 nm Si 3,969 nm Mo 2,890 nm Mo 2.409 nm Si 4.039 nm Mo 2,860 nm Si 4.074 nm Si 3,573 nm Mo 3,175 nm Si 4.075 nm Mo 2,897 nm Mo 1,922 nm Si 2,934 nm Mo 2,898 nm Si 4.012 nm Si 1000 nm Mo 2,382 nm Si 4.073 nm Mo 2,875 nm Mo 1,000 nm Si 1.003 nm Mo 2,881 nm Si 4140 nm Si 3.402 nm Mo 1.442 nm Si 4.066 nm Mo 2,718 nm Mo 2,957 nm Si 2,801 nm Mo 2,893 nm Si 4,207 nm Si 3,686 nm Mo 3,465 nm Si 4,083 nm Mo 2,705 nm Mo 3.403 nm Si 3.508 nm Mo 2,886 nm Si 4,198 nm Si 3,618 nm Mo 3,009 nm Si 4.017 nm Mo 2,699 nm Mo 3,333 nm Si 4,479 nm Mo 1.011 nm Si 4,208 nm Si 3,816 nm Mo 2,945 nm Si 1000 nm Mo 2.684 nm Mo 3,116 nm Si 3,607 nm Mo 1.011 nm Si 4,224 nm Si 2,949 nm Mo 3,311 nm Si 3,988 nm Mo 2,690 nm Mo 1,000 nm Si 3,578 nm Mo 2,861 nm Si 4,287 nm Si 1000 nm Mo 3,329 nm Si 4,142 nm Mo 2.594 nm Mo 2,290 nm Si 4.037 nm Mo 2,839 nm Si 4,283 nm Si 3,539 nm Mo 2,793 nm Si 4.084 nm Mo 2.256 nm Mo 3,301 nm Si 3,747 nm Mo 2,890 nm Si 1000 nm Si 3,923 nm Mo 3,253 nm Si 4.036 nm surface Mo 3,131 nm Si 4137 nm Mo 2,955 nm Si 3,753 nm Mo 2,366 nm Si 3,960 nm

As in 7a can be seen, the first Reflektivitätsverlauf points R1 (λ) at a first maximum wavelength λ _1MAX of about 13.51 nm a maximum (first) reflectivity R _1MAX of about 70%. A first 20% width B1 of the first reflectivity profile R1 (λ), which is at a value of R _1MAX × 0.2, has an amount of B1 = about 0.85 nm. Outside the first 20% width B1, the first reflectivity curve points R1 (λ) a first local maximum R _{N1a, MAX} at a first maximum wavelength λ _{N1a, MAX} of about 12.9 nm and a second local maximum R _{N1b, MAX} at a second maximum wavelength λ _{N1b, MAX} of about 14.0 nm. The first reflectivity profile R1 (λ) has correspondingly local minima at a first minimum wavelength λ _{N1a, MIN} of about 13.0 nm and at a second minimum wavelength λ _{N1b, MIN} of about 14.1 nm.

The in 7b shown second reflectivity course R2 (λ) is from a second multi-day system 15 produced in which the spacer layers 19 and the absorber layers 20 Thicknesses ds or d _A have, which are shown in Table 5 below. Table 5 substratum Si 1.262 nm Si 3,951 nm Si 1000 nm Mo 3.556 nm Mo 3,140 nm Mo 1.809 nm Mo 1.503 nm Si 3,578 nm Si 4,079 nm Si 3,674 nm Si 3.437 nm Mo 4,998 nm Mo 4,105 nm Mo 2,189 nm Mo 2,993 nm Si 5,000 nm Si 4,793 nm Si 4,553 nm Si 4.258 nm Mo 5,000 nm Mo 5,000 nm Mo 3,746 nm Mo 2.010 nm Si 5,000 nm Si 5,000 nm Si 4,104 nm Si 4,539 nm Mo 5,000 nm Mo 3,740 nm Mo 3,150 nm Mo 2.341 nm Si 4,803 nm Si 3.851 nm Si 3,427 nm Si 4,169 nm Mo 4,200 nm Mo 3.559 nm Mo 1,118 nm Mo 2,993 nm Si 3,749 nm Si 3,399 nm Si 1000 nm Si 2,917 nm Mo 3,414 nm Mo 3.070 nm Mo 1.465 nm Mo 1.018 nm Si 3.541 nm Si 3,905 nm Si 3,625 nm Si 1,040 nm Mo 3.458 nm Mo 2.009 nm Mo 3.034 nm Mo 2.423 nm Si 3.506 nm Si 1000 nm Si 3,911 nm Si 3,681 nm Mo 3,352 nm Mo 1,000 nm Mo 3,108 nm Mo 2,140 nm Si 3,435 nm Si 2,833 nm Si 3,704 nm Si 4,455 nm Mo 3,411 nm Mo 3,477 nm Mo 3,378 nm Mo 2,834 nm Si 3,693 nm Si 3.059 nm Si 3,671 nm Si 2,854 nm Mo 2,974 nm Mo 3.406 nm Mo 3.072 nm Mo 2,997 nm Si 3.543 nm Si 4,384 nm Si 4,263 nm Si 1.005 nm Mo 3,189 nm Mo 3.645 nm Mo 2,862 nm Mo 1.443 nm Si 1614 nm Si 4,895 nm Si 3.221 nm Si 3.020 nm Mo 1,000 nm Mo 4122 nm Mo 1.603 nm Mo 3.419 nm Si 4.050 nm Mo 1.507 nm Si 4.053 nm Mo 1,000 nm Mo 3,186 nm Si 1000 nm Mo 2,736 nm Si 1000 nm Si 3,422 nm Mo 1,000 nm Si 4,714 nm Mo 1.122 nm Mo 3.596 nm Si 3,372 nm Mo 1849 nm Si 4,135 nm Si 3,923 nm Mo 3,308 nm Si 3,927 nm Mo 2,702 nm Mo 2,961 nm Si 3.602 nm Mo 1,000 nm Si 4.229 nm Si 3,948 nm Mo 3,394 nm Si 1000 nm Mo 2658 nm Mo 3.005 nm Si 3,664 nm Mo 1.674 nm Si 4.254 nm Si 3,890 nm Mo 3,172 nm Si 3,960 nm Mo 2,650 nm Mo 3,101 nm Si 3,896 nm Mo 2,715 nm Si 4.252 nm Si 3,778 nm Mo 3.039 nm Si 4,183 nm Mo 2,672 nm Mo 1.824 nm Si 3,879 nm Mo 2,821 nm Si 4,225 nm Si 1000 nm Mo 3,162 nm Si 4,105 nm Mo 2.302 nm Mo 1,000 nm Si 3,846 nm Mo 2,802 nm Si 1000 nm Si 3,154 nm Mo 2,770 nm Si 4.095 nm surface Mo 3,166 nm Si 4,333 nm Mo 2,898 nm Si 3,841 nm Mo 2,764 nm Si 3,775 nm

As in 7b can be seen, the second Reflektivitätsverlauf points R2 (λ) at a second maximum wavelength λ _2MAX of about 13.51 nm a maximum (second) reflectivity R _2MAX of about 70%. A second 20% width B2 of the second reflectivity profile R2 (A) that are at a value of R _2MAX × 0.2, has an amount of B2 = about 0.75 nm. Outside the second 20% width B2 has the second Reflektivitätsverlauf R2 (λ) a first local maximum R _{N2a, MAX} at a first maximum wavelength λ _{N2a, MAX} of about 13.0 nm and a second local maximum R _{N2b, MAX} at a second maximum wavelength λ _{N2b, MAX} of about 14.1 nm. The second reflectivity profile R2 (λ) has correspondingly local minima at a first minimum wavelength λ _{N2a, MIN} of about 12.9 nm and at a second minimum wavelength λ _{N2b, MIN} of about 14.0 nm.

At the in 7a, b shown Reflektivitätsverläufen R1 (A) . R2 (λ) thus agree the two maximum wavelengths λ _{N1a, MAX} . λ _{N1b, MAX} of the first reflectivity profile R1 (λ) with the two minimum wavelengths λ _{N2a, MIN} . λ _{N2b, MIN} of the second reflectivity profile R2 (λ) match. Accordingly, the two minimum wavelengths are also correct λ _{N1a, MIN} . λ _{N1b, MIN} of the first reflectivity course R1 (λ) with the two maximum wavelengths λ _{N2a, MIN} , λ _{N2B, MIN of} the second reflectivity _curve R2 (λ) match.

The from the two Reflektivitätsverläufen R1 (λ) . R2 (λ) resulting transmission course T (λ) the optical arrangement 13 in which the secondary maxima on both sides of a maximum wavelength λ _MAX (here: 13.5 nm) are suppressed in 7c shown. At the maximum wavelength λ _MAX has the optical arrangement 13 a maximum transmission T _MAX from about 50% up. An integral value Fb, 1 + Fb, 2 over all wavelengths A in the EUV wavelength range which are outside the resulting 20% width B, ie for which either: _{T EUV} , MIN <λ <λ _BMIN , corresponding to a first partial integral Fb , 1 or for which: ABMAX <λ <λ _{EUV, MAX} , corresponding to a second partial integral Fb, 2, is not more than 6.5% of an integral value Fa within the resulting 20% width B, ie Fb, 1 + Fb, 2 <0.065 Fa, even the conditions Fb, 1 + Fb, 2 <0.03 Fa and Fb, 1 + Fb, 2 <0.01 Fa are fulfilled. By suppressing the secondary maxima is thus also in the in 7a-c example, a box-shaped resulting transmission profile T (λ) approximated. It is understood that more or fewer than two secondary maxima of the first reflectivity profile R1 (λ) can also coincide with secondary minima of the second reflectivity profile R2 (λ), and vice versa. As based on 7c can be seen, but it is usually sufficient, in each case a secondary maximum or a secondary minimum at smaller and larger than the respective maximum wavelength λ _1MAX . λ _2MAX to suppress, if they are in close proximity to the 20% width B to produce the desired, substantially box-shaped transmission profile T (λ).

For the generation of the essentially box-shaped transmission profile T (λ), the first and second 20% widths B1, B2 of the first and second reflectivity profiles R1 (A), R2 (λ) should not differ by more than 5%, ie it should apply: | B1-B2 | / (B1 + B2) ≤ 0.05. Accordingly, the first maximum wavelength should be λ _1MAX and the second maximum wavelength λ _2MAX the first and the second Reflektivitätsverlaufs R1 (λ) . R2 (λ) do not differ by more than 1%, ie it should be: | λ _1MAX - λ _2MAX | / (λ _1MAX + λ _2MAX ) ≤ 0.01.

In summary, in the manner described above, an approximately box-shaped resulting transmission profile T (λ) the optical arrangement 13 be generated to the heat input W on the field facet element following in the beam path 9 to reduce, without affecting the useful power N on the wafer 12 decreases significantly. In addition to generating a transmission profile T (λ) with steep flanks, it is favorable if the transmission profile T (λ) a small 20% width B having. This can be achieved if, as in the two examples above, for the first 20% width B1 or for the second 20% width B2 that this does not exceed 4% of the respective first or second wavelength λ _1MAX . λ _2MAX with maximum first and second reflectivity R _1MAX . R _2MAX is.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102016224111 A1 [0002, 0019]
• EP 1938150 B1 [0004]
• DE 102007041004 A1 [0004]

Claims (15)

An optical assembly (13) comprising: a first EUV wavelength region reflective optical element (7) having a first multilayer system (14) extending over a first surface (22) on a first substrate (24), the first one The multilayer system (14) has first, alternately arranged layers (16, 17) of at least two materials with different real part of the refractive index at a wavelength (λ) in the EUV wavelength range, wherein a first reflectivity profile (λ) occurs when irradiated at a constant angle of incidence (γ). R1 (A)) depending on the wavelength (A), and a second reflective optical element (8) for the EUV wavelength range, which comprises a second multilayer system (15) extending over a second surface (23) on a second substrate (25), wherein the second multi-layer system (15) second, alternately arranged layers (19, 20) of at least two materials with different m real part of the refractive index at a wavelength (λ) in the EUV wavelength range, wherein when irradiated at a constant angle of incidence (γ) a second reflectivity curve (R2 (A)) depending on the wavelength (A) is formed, of the first Reflected reflective element (7) reflected radiation (6) on the second reflective optical element (8), characterized in that the optical arrangement (13) from the first Reflektivitätsverlauf (R1 (A)) and from the second Reflektivitätsverlauf (R2 (A)) having a 20% width (B) as a function of the wavelength (A), an integral (Fb, 1 + Fb, 2) of the resulting transmission profile (T (λ )) over wavelengths (λ) in the EUV wavelength range outside the 20% width (B) no more than 6.5% of an integral (Fa) of the resulting transmission profile (T (λ)) over wavelengths (λ) within the 20% -Width (B) is. Optical arrangement according to Claim 1 in which the resulting transmission profile (T (λ)) has a maximum transmission (T _MAX ) at a wavelength (λ _MAX ) and at which a wavelength interval (W1 + W2) in which the resulting transmission profile (T (λ)) of 80% to 20% of the maximum transmission (T _MAX ) decreases, not more than 60% of the 20% width (B) is. Optical arrangement according to Claim 1 or 2 in which an integral (F1b) of the first reflectivity profile (R1 (A)) has wavelengths (λ) in the EUV wavelength range which are greater than a maximum wavelength (λ _BMAX ) of the 20% width (B) of the resulting transmission _profile ( _FIG. T (λ)) is less than one quarter of an integral (F1a) of the first reflectivity profile (R1 (A)) over wavelengths (λ) in the EUV wavelength range smaller than a minimum wavelength (λ _BMIN ) of the 20% width ( B) of the resulting transmission profile (T (λ)), and in which an integral (F2a) of the second reflectivity profile (R2 (A)) over wavelengths (λ) in the EUV wavelength range which are smaller than a minimum wavelength (λ _BMIN ) of the 20% width (B2) of the resulting transmission profile (T (λ)) is less than one quarter of an integral (F2b) of the second reflectivity profile (R2 (A)) over wavelengths (λ) in the EUV wavelength range that are greater than a maximum wavelength (λ _BMAX ) of 20% width (B) of the resulting transmission curve (T (λ)), or vice versa. Optical arrangement according to Claim 1 or 2 in which at least one maximum wavelength (λ _{N1a, MAX} , λ _{N1b, MAX} ) at which a local maximum (R _{N1a, MAX} , R _{N1b, MAX} ) of the first reflectivity _profile (R1 (A)) is outside of a first 20 % Width (B1) of the first reflectivity profile (R1 (A)) coincides with at least one minimum wavelength (λ _{N2a, MIN} , λ _{N2b, MIN} ) at which a local minimum (R _{N2a, MIN} , R _{N2b , MIN} ) of the second reflectivity profile (R2 (A)) is outside a second 20% width (B2) of the second reflectivity profile (R2 (A)), or vice versa. Optical arrangement according to one of the preceding claims, _wherein a first wavelength (λ _1MAX ) with maximum reflectivity (R _1MAX ) of the first reflectivity _curve (R1 (A)) and a second wavelength (λ _1MAX ) with maximum reflectivity (R _2MAX ) of the second Reflectivity course (R2 (A)) by no more than 1%. Optical arrangement according to Claim 5 in which the first 20% width (B1) of the first reflectivity profile (R1 (A)) is not more than 4% of the first wavelength (λ _1MAX ) and / or in which the second 20% width (B2) of the second one Reflectivity curve (R2 (A)) is not more than 4% of the second wavelength (λ _2MAX ). An optical arrangement according to any one of the preceding claims, wherein the first 20% width (B1) and the second 20% width (B2) do not deviate from each other by more than 5%. Optical arrangement according to one of the preceding claims, in which the alternately arranged first layers (16, 17) of the first multi-layer system (14) have no periodically recurring thicknesses and / or in which the alternately arranged second layers (19, 20) of the second multilayer system (14) 15) have no periodically recurring thicknesses. An optical arrangement according to any one of the preceding claims, wherein one or more first and / or second layers (17; 20) comprises, as a lower refractive index material, one or more of molybdenum, ruthenium, rhodium, palladium, zirconium, titanium, yttrium , Niobium, lanthanum, cerium, their alloys and compounds, in particular borides, carbides, silicides, oxide and nitrides. An optical arrangement according to any one of the preceding claims, wherein one or more first and / or second layers (16, 19) comprise as a higher refractive index material one or more of silicon, carbon, boron, silicon boride, silicon carbide and boron carbide. An optical assembly according to any one of the preceding claims, wherein the material having the lower real part of the refractive index of the first layers (16) coincides with the material having the lower real part of the refractive index of the second layers (19) and / or the material having the higher one Real part of the refractive index of the first layers (17) coincides with the material with the higher real part of the refractive index of the second layers (20). Optical arrangement according to one of the preceding claims, in which the first reflective optical element is designed as a collector mirror (7). Optical arrangement according to one of the preceding claims, in which the second reflective optical element (8) has a free-form surface as the second surface (23). An EUV lithography apparatus (1) comprising: an optical assembly (13) according to any one of the preceding claims. EUV lithography device according to Claim 14 , further comprising: a field facet mirror (9) arranged such that radiation (6) reflected by the second reflective optical element (8) meets the field facet mirror (9).

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