DUV Lithography System

Abstract

The present invention relates to a DUV lithography apparatus comprising a light source generating DUV radiation at at least one operating wavelength in the DUV wavelength range, a photomask, and an optical element (44) transparent to the DUV radiation (8), spaced from the photomask and provided with an absorbing coating (32). The absorbing coating (32) has absorbing microstructures (34) covering a surface area percentage (F) of the surface area (26, 26a) provided with the absorbing coating (32) that is less than 0.1% and preferably greater than 0.01%.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from German Patent Application No. 10 2021 210 243.3, filed September 16, 2021, the entire disclosure content of which is incorporated herein by reference.

[0002] The present invention relates to an optical apparatus for DUV lithography, in particular a DUV lithography apparatus, comprising a light source for generating DUV radiation at at least one operating wavelength in the DUV wavelength range, and an optical element that is transparent to DUV radiation and is provided with an absorptive coating. [Background technology]

[0003] Within the meaning of the present application, the DUV wavelength range is understood to be the wavelength range of electromagnetic radiation between 150 nm and 370 nm. The DUV wavelength range is particularly important for microlithography. Radiation in the DUV wavelength range is therefore used, for example, in projection exposure apparatus and wafer or mask inspection apparatus. In such apparatuses, both transmissive optical elements, for example in the form of lens elements or plane plates, and reflective optical elements, for example in the form of mirrors, are used, which are for example integrated into the projection or illumination system of the DUV lithography apparatus. In DUV lithography apparatuses, the light source is generally designed to generate DUV radiation having a single operating wavelength. In wafer or mask inspection apparatuses, the light source can be designed to generate broadband radiation of multiple operating wavelengths or of one operating wavelength spectrum.

[0004] Patent document 1 describes a lithographic apparatus comprising a temperature setting device having first and second temperature control sections each serving to set the temperature distribution of an optical element of a projection system. Using the first and / or second temperature control sections, changes in aberrations of the projection system during or outside of an exposure operation are reduced. The two temperature control sections may comprise heating elements in the form of heating wires configured in an arc shape and extending along the outer edge regions of the lens elements. The heating elements may be arranged at a distance from the optical element or may be in contact with the optical element.

[0005] Patent Document 2 describes a microlithography projection exposure apparatus comprising an optical correction system having a primary illumination system for generating projection light, a projection lens, and a secondary illumination system for generating correction light. The correction system can be configured to use the correction light to heat a partial region of a correction element containing a heating material in order to perform local wavefront manipulation by generating locally different optical path lengths. The heating material of the correction element can be a coating on the correction element or on a substrate of the correction element. All lens elements through which both the correction light and the projection light pass are manufactured from a lens element material having a lower absorption coefficient for the correction light than the heating material contained in the correction element. The material of the lens element(s) should have a very low absorption coefficient for both the wavelength of the projection light (operating wavelength) and the wavelength of the correction light that is different from the wavelength of the projection light, while the heating material of the correction element should have a low absorption coefficient for the wavelength of the projection light but a high absorption coefficient for the wavelength of the correction light.

[0006] Furthermore, as mentioned above, when using the correction element described in Patent Document 2, the heating material must have a high absorption coefficient for the wavelength of the correction light. In the case of a correction element whose body is made of synthetic silica glass (SiO2), the body only has sufficient absorption at wavelengths on the order of about 2.6 μm or greater. Many dielectric coating materials used for anti-reflection coatings at operating wavelengths in the DUV wavelength range of 193 nm, 248 nm, or 365 nm, such as MgF2, LaF3, Al2O3, HfO2, and TiO2, also only absorb radiation at wavelengths greater than about 3 μm to about 10 μm.

[0007] Patent Document 2 describes an optical device in which radiation from a light source impinges on an optical element in a non-rotationally symmetric manner. The optical element has an absorbing coating whose absorption distribution is at least approximately complementary to the non-rotationally symmetric intensity distribution of the incident radiation from the light source. The energy absorbed in the absorbing coating is intended to cause additional heating of the optical element, which leads to a more rotationally symmetric temperature distribution. In one example, the additional heating is achieved by absorption of the projection light, with a small percentage of the projection light being absorbed by the coating. In yet another example, the light source comprises a projection light source and a compensation light source, and radiation from the compensation light source is directed toward the absorbing coating. The absorption coefficient of the coating can be adapted to the emission wavelength of a known light source, for example, a laser diode. The degree of additional heating can be set by the radiation power of the compensation light source.

[0008] In Patent Document 2, both during the absorption of the projection light and during the absorption of the radiation from the compensation light source, the central region of the optical element through which the projection light beam passes is not covered with an absorbing coating, or only its outer edge is covered with an absorbing coating, so that it is not possible to predefine or set with high precision or spatial resolution the temperature distribution of the optical element in the surface region on which the projection beam is incident. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 2020 / 0409276 [Patent Document 2] U.S. Patent No. 8,773,638 Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to provide an optical device of the aforementioned type in which the temperature distribution of the transmissive optical element can be predefined or set with high precision. [Means for solving the problem]

[0011] This object is achieved by an optical device as described above, in which the absorbing coating has absorbing microstructures covering a surface area percentage of the surface area provided with the absorbing coating that is less than 0.1% and preferably greater than 0.01%.

[0012] The present invention proposes providing a structured absorbing coating on a transmissive optical element. The structured absorbing coating comprises absorbing microstructures that cover only a small surface area percentage of the total surface area covered by the absorbing coating. The surface area percentage of less than 0.1% means that the microstructures are not concentrated in specific areas of the surface area covered by the absorbing coating, but rather the microstructures of the surface area are distributed over the entire surface area covered by the absorbing coating. The small surface area percentage covered by the absorbing coating also allows the absorbing coating to be applied within the surface area that is irradiated with DUV radiation without the DUV radiation being excessively attenuated by the absorbing coating.

[0013] The microstructures are typically arranged in island-like localized regions, with the distance between two adjacent microstructures generally being no greater than 5 mm. The microstructures can be distributed in particular in a grid-like manner, i.e., equidistant from one another, over the surface area provided with the absorbing coating. This facilitates the setting of a temperature distribution when the absorbing coating is irradiated with heating radiation (see below). However, a uniform distribution of the microstructures over the surface area is not necessarily required. The absorbing microstructures absorb radiation in the DUV wavelength range, in particular at the operating wavelength and / or heating radiation at wavelengths below approximately 1550 nm (see below).

[0014] A structured absorbing coating can be formed on a surface region by first applying a coating containing or consisting of an absorbing material to the surface region over a large area. The structuring of the absorbing coating can be carried out by applying a structured protective resist, which is generally carried out using lithography methods, followed by wet chemical etching or dry etching in a reactive gas atmosphere. Alternatively, to form the absorbing microstructures, the material of the absorbing coating can be locally removed by laser ablation. In this case, a laser beam can be focused onto a beam spot on the absorbing coating applied over a large area, the dimensions of which correspond to the desired structure size of the microstructures. In this case, the laser beam is guided over the surface region and scanned across the surface region, for example with regular interruptions at positions where the formation of the absorbing microstructures is intended.

[0015] The transmitting optical element provided with an absorptive coating may be an optical element that contributes to imaging, for example a lens element, but it may also be a corrective element, for example in the form of a plane plate, that performs no optical function other than the correction of wavefront aberrations.

[0016] In one embodiment, the surface area having the absorbing coating comprises or forms a surface area of ​​a transmissive optical element that is exposed to DUV radiation. As mentioned above, the absorbing coating covers only a surface area percentage of the coated surface area that is less than 0.1%, allowing the absorbing coating to be applied to (also) the surface area that is exposed to DUV radiation.

[0017] It is possible to apply the absorbing coating only to the illuminated surface area. However, it is also possible for the absorbing coating to encompass the illuminated surface area and also extend to the non-illuminated surface area of ​​the transmissive optical element adjacent to the illuminated surface area, in order to adapt or set the temperature distribution at the edge of the illuminated surface area. In principle, it is also possible to apply the absorbing coating only to a partial area of ​​the illuminated surface area. However, in this case, the temperature distribution in the illuminated surface area cannot be set more precisely than if the absorbing coating were applied to the entire illuminated surface area.

[0018] In yet another embodiment, the microstructures have an average structure width of less than 20 μm, preferably less than 10 μm. The average structure width is defined as the arithmetic mean of the structure widths of all microstructures of the absorbing coating. The structure width of each microstructure is understood to mean the maximum extent of the microstructure on the surface area, i.e., the longest straight line interconnecting two (any) points along the perimeter of the microstructure. The structure width of the microstructures can be predefined or set during structuring of the absorbing coating. All microstructures can have a uniform structure width, but it is also possible for the structure width of the microstructures to vary from location to location. In order to prevent the imaging properties of the optical device from being adversely affected by the microstructures, it is advantageous for the microstructures to have a relatively small structure width, in particular smaller than the operating wavelength. Such an adverse effect on the imaging properties can occur, for example, when transmissive optical elements are arranged in the projection optical unit of a DUV lithography device, which serves to image the structures on the mask onto the wafer.

[0019] In yet another embodiment, the absorbing coating is configured as a metallic coating. Due to the relatively small surface area fraction or low coverage of the surface area with the absorbing microstructure, it is advantageous or necessary for the absorbing coating to have a high absorption, and thus a high absorption coefficient, in the DUV wavelength range in order to generate sufficient heating power. Metallic materials are generally highly absorbing for radiation in the DUV wavelength range, and thus in the range of operating wavelengths of optical devices. Metallic materials also generally absorb radiation in wavelength ranges less than about 1550 nm, and are therefore also suitable for absorbing heating radiation irradiated on the absorbing coating at heating wavelengths outside the DUV wavelength range, for example, in the wavelength range from about 370 nm or 400 nm to about 1550 nm.

[0020] In one development, the absorbing coating comprises at least one material selected from the group comprising Cr, Al, Au, and Ag. These metals have a high absorption coefficient for radiation in the DUV wavelength range. However, it goes without saying that the absorbing coating can also comprise other metallic materials, provided that they have a particularly high absorption coefficient for radiation in the DUV wavelength range. In principle, the absorbing coating can also comprise non-metallic materials, provided that their absorption is sufficient and they are suitable for structuring. The absorbing coating generally comprises only a single (e.g., metallic) layer, but in some cases can also comprise two or more (e.g., metallic) layers.

[0021] In yet another embodiment, the absorbing coating (or absorbing microstructure) has a thickness of 50 nm to 200 nm. In order to introduce maximum heating power into the absorbing coating despite a small surface area fraction of less than 0.1%, the absorbing coating, or more precisely the absorbing microstructure, should be optically dense, i.e., practically opaque to radiation at the operating or heating wavelength (see below). The thickness required to create an optically dense coating depends on the operating or heating wavelength and the absorption coefficient of the absorbing material of the coating, usually a metallic material. For the wavelengths and absorbing materials used here, the thickness of the absorbing coating or microstructure should be of the order specified above.

[0022] In yet another embodiment, an anti-reflective coating for DUV radiation at the operating wavelength is applied to the absorbing coating. The anti-reflective coating can include a surface area covered with the absorbing coating and a further area on the surface of the transmissive optical element. The anti-reflective coating is generally applied to both the first entrance surface and the second exit surface of the transmissive optical element. In contrast, the absorbing coating is usually only applied to the entrance surface of the transmissive optical element, not to the exit surface of the transmissive optical element. However, in principle, it is also possible to apply an absorbing coating to the exit surface of the transmissive optical element or to apply an absorbing coating to both the entrance and exit surfaces.

[0023] In yet another embodiment, the surface area fraction of the microstructure varies from location to location, particularly depending on the intensity distribution of DUV radiation in the surface region provided with the absorbing coating. In this embodiment, the absorption of the absorbing coating for DUV radiation is typically predefined depending on the local intensity or intensity distribution of DUV radiation incident on the surface region. In this way, for a given or known intensity distribution, it is possible to predefine a predetermined static temperature distribution in the transmissive optical element, and therefore a predetermined static wavefront or wavefront correction, without requiring a heating radiation source for this purpose.

[0024] The surface area proportion of the absorbing microstructures can be selected to be greater in subregions of the surface region where the local intensity of DUV radiation in the DUV wavelength range is low than in subregions of the surface region where the local intensity of DUV radiation is high. In this way, the additional absorption of DUV radiation in the absorbing coating allows for a temperature distribution that is as uniform as possible in the transmitting optical element, and thus for a wavefront that is as constant as possible when passing through the transmitting optical element. However, it is also possible to specifically predefine a desired wavefront that deviates from a flat or constant wavefront by varying the surface area proportion of the absorbing microstructures over time, for example to compensate for wavefront or imaging aberrations caused by other optical elements of the optical device. The surface area proportion of the absorbing microstructures can be varied by varying the structure width of the microstructures over time and / or by varying the distance between adjacent microstructures over time.

[0025] In yet another embodiment, the transmissive optical element is positioned at or near the pupil plane. Positioning at (or near) the pupil plane is advantageous, particularly in the aforementioned cases where the local absorption or surface area fraction of the microstructures varies depending on the intensity distribution of the incident DUV radiation. In this case, the local surface area fraction of the microstructures can be adapted to the illumination settings of the illumination system of the optical device or optimized for illumination settings that generate a specific intensity distribution of DUV radiation on the optical element positioned at the pupil plane. Within the meaning of the present application, the expression "near the pupil plane" is understood to mean that the transmissive optical element is positioned at a distance from the pupil plane such that the imaged image point illuminates more than 50% of the surface area fraction of the optically transparent surface or illuminated surface area of ​​the transmissive optical element.

[0026] In one development, the optical apparatus further comprises a magazine having a plurality of transmissive optical elements each having a different change in the surface area proportion of the microstructure in the surface region covered with the absorbent coating over time, a transport device for transporting one of the transmissive optical elements from the magazine to the beam path of the optical apparatus and vice versa, and a control device for controlling the transport device preferably in accordance with the illumination settings of the DUV lithography apparatus.

[0027] In this development, the transmitting optical elements, each having an absorbing coating with the aforementioned absorbing microstructures, are stored in a magazine. The transmitting optical elements differ in the spatial variation of the surface area percentage of the absorbing microstructures. The control device serves to select one of the transmitting optical elements that is particularly suitable for the subsequent operation of the optical arrangement and to introduce it into the beam path or to replace it with another, less suitable transmitting optical element.

[0028] In this case, the spatial variation of the surface area fraction of the absorbing microstructures can be adapted or optimized to one of a plurality of different illumination settings of an illumination system, in particular of a DUV lithography apparatus. In this case, the control device can select one of the transmissive optical elements optimized for the selected illumination setting depending on the selected illumination setting. The illumination setting of the illumination system can be, for example, dipole illumination, quadrupole illumination, ring field illumination, etc. The control device can be configured in the form of a suitable programmable device (hardware and / or software) having a processor and a memory.

[0029] In yet another embodiment, the optical apparatus comprises a heating device having at least one heating light source that emits heating radiation onto a surface region of a transmissive optical element that is coated with an absorptive coating. As previously mentioned, the absorptive coating can be used to achieve radiative heating of the transmissive optical element at heating wavelengths that are not absorbed or only slightly absorbed by the material of the transmissive optical element and the anti-reflective coating. In this case, the absorption of the heating radiation occurs in a structured absorptive coating that absorbs the heating wavelength(s).

[0030] In yet another embodiment, the heating light source is configured to emit heating radiation to the surface region at at least one heating wavelength in the wavelength range of 400 nm to 1550 nm. As mentioned above, absorption of the heating radiation in an absorbing coating allows the use of a heating light source, for example in the form of a high power diode, such as those standard in telecommunications applications in the above specified wavelength range.

[0031] In yet another embodiment, the heating device includes a scanner device that aligns the heating radiation of the heating light source to different positions on the absorbing coating and / or a grid arrangement of heating light sources that irradiate different positions on the absorbing coating. The different positions to which the heating radiation is aligned can be, in particular, the positions of the absorbing microstructures. Using the scanner device, for example, it is possible to scan the entire surface area covered with the absorbing coating, and the power or intensity of the heating light source, e.g., a laser, can be varied over the location to generate a desired intensity distribution over the surface area covered with the absorbing coating. In this case, the power of the heating light source can be reduced to virtually zero in some cases at positions on the surface area located between the absorbing microstructures. When multiple heating light sources, e.g., in the form of (laser) diodes, are arranged in an array, each heating light source is typically assigned to a position on the surface area where at least one absorbing microstructure is located. In this particular embodiment, it is advantageous if the absorbing microstructures in the surface area are also arranged in a grid. Furthermore, in this case, it is generally advantageous if all absorbing microstructures have the same structure width, i.e., if their surface area proportion does not vary over the location.

[0032] The above-mentioned concept for localized radiative heating of a transmissive optical element using a structured absorbing coating can also be combined with other concepts that allow a temperature distribution, e.g., resistive heating, to be predefined or set using a heating element, e.g., in the form of a heating wire, as described, for example, in the above-mentioned patent document 1.

[0033] Further features and advantages of the present invention will become apparent from the following description of exemplary embodiments of the invention, with reference to the figures of the drawings which show the details essential to the invention, and from the claims. Each of the individual features can be implemented alone or in any combination of several in a variant of the invention.

[0034] Exemplary embodiments are shown in the schematic drawings and explained in the following description. [Brief explanation of the drawings]

[0035] [Figure 1] 1 shows a schematic diagram of a DUV lithography apparatus. [Figure 2a] 1 shows a schematic diagram of a transmissive optical element having an absorbing coating with a plurality of absorbing microstructures with varying structure widths. [Figure 2b] A schematic diagram similar to FIG. 2a is shown in which heating radiation of spatially varying intensity is irradiated onto an absorbing microstructure. DETAILED DESCRIPTION OF THE INVENTION

[0036] In the following description of the drawings, the same reference numerals are used for components that are the same or have the same function.

[0037] 1 shows a schematic diagram of a DUV lithography apparatus 1 comprising a beam shaping and illumination system 2 and a projection system 4. The beam shaping and illumination system 2 and the projection system 4 may be arranged in a vacuum housing and / or surrounded by a machine room with corresponding drive devices.

[0038] The DUV lithography apparatus 1 comprises a DUV light source 6. For example, a DUV light source 6 having an operating wavelength λ 1 in the DUV wavelength range, for example 193 nm. B An ArF excimer laser emitting DUV radiation 8 of λ 1 can be provided as the DUV light source 6. Alternatively, a different operating wavelength λ 2 in the DUV wavelength range can be provided. B A DUV light source 6 can be used that emits DUV radiation 8 at, for example, 248 nm or 365 nm.

[0039] 1 directs DUV radiation 8 onto a photomask 10. The photomask 10 is configured as a transmissive optical element and can be located external to the systems 2, 4. The photomask 10 contains structures that are imaged by the projection system 4 in reduced form onto, for example, a wafer 12.

[0040] The projection system 4 includes a plurality of lens elements 16 and / or mirrors 18 for imaging the photomask 10 onto the wafer 12. In this case, the individual lens elements 16 and / or mirrors 18 of the projection system 4 may be arranged symmetrically with respect to the optical axis 14 of the projection system 4. It should be noted that the number of lens elements and mirrors in the DUV lithography apparatus 1 is not limited to the number shown; more or fewer lens elements and / or mirrors may be provided. Furthermore, the mirrors generally have a curved front surface for beam shaping.

[0041] The air gap between lens element 16 and wafer 12 can be replaced with a liquid medium 20 having a refractive index greater than 1. The liquid medium can be, for example, high-purity water. Such an arrangement, also referred to as immersion lithography, improves resolution during imaging of photomask 10 onto wafer 12.

[0042] One of the transmissive lens elements 16 of the projection system 4, which is arranged in the pupil plane 22 of the projection system 4, is shown in detail in Figure 2a. The lens element 16 comprises a body 24 made of synthetic quartz glass (SiO2), which in the example shown is transparent to DUV radiation 8. The body 24 has, on both sides thereof, a first entrance surface 26 and a second exit surface 28 through which the DUV radiation 8 passes. A beam path 30 of the DUV radiation 8, or more precisely the outer edge of said beam path, is shown by a dashed line in Figure 2a. As can be seen in Figure 2a, the DUV radiation 8 is emitted onto the first surface 26 of the lens element 16 in a surface area 26a that does not cover the entire first surface 26 of the lens element 16, i.e., an outer partial area of ​​the first surface 26 is not struck by the DUV radiation 8.

[0043] As can also be seen in Figure 2a, a structured absorbing coating 32 is applied to the surface area 26a to be irradiated with DUV radiation 8. In the example shown in Figure 2a, the structured absorbing coating 32 comprises a plurality of absorbing microstructures 34, shown as solid rectangles in Figure 2a. The absorbing microstructures 34 do not completely cover the surface area 26a to which the absorbing coating 32 is applied, but rather only cover said surface area over a surface area fraction F, which is between 0.01% and 0.1% of the total area A of the irradiated surface area 26a. The small surface area fraction F of the structured absorbing coating 32 ensures that only a small proportion of the DUV radiation 8 is absorbed by the absorbing microstructures 34, ensuring that the transmittance of the optical element 16 is only slightly reduced as a result of the absorbing coating 34.

[0044] In the example shown in FIG. 2a, the structured absorbing coating 32, or more precisely the absorbing microstructures 34, is oriented at the operating wavelength λ B The absorbing microstructure 34 or absorbing coating 32 should be optically dense to the DUV radiation 8, i.e., virtually transparent to the DUV radiation 8. To achieve this, the absorbing microstructure 34 or absorbing coating 32 should have a sufficient thickness d, which should typically be on the order of 50 nm to 200 nm. Furthermore, the absorbing microstructure 34 should comprise a material that has a maximum absorption coefficient for the DUV radiation 8.

[0045] In the example shown in FIG. 2a, the absorbing coating 32 is configured as a metallic coating, i.e., the absorbing microstructures 34 are made of a metallic material. This is advantageous because metallic materials generally have a high absorption coefficient in the DUV wavelength range from about 150 nm to about 370 nm. In the illustrated example, the metal constituting the absorbing microstructures 34 is Cr, but it could also be a different metal with a high absorption coefficient, such as Al, Au, or Ag. As also shown in FIG. 2a, an anti-reflective coating 35a against DUV radiation 8 is applied to a large area of ​​the absorbing coating 32 on the first surface 26. An anti-reflective coating 35b against DUV radiation 8 is similarly applied to the second surface 28. The anti-reflective coatings 35a and 35b are made of a fluoride or oxide material that has relatively low absorption of DUV radiation 8, such as MgF2, LaF3, Al2O3, HfO2, or TiO2.

[0046] The absorbing microstructures 34 are formed by first depositing an absorbing coating made of metal, in the example described here made of chromium, over a large area of ​​the surface region 26a. Conventional coating methods are used for this deposition. In the example shown, for structuring the absorbing coating 32, a structured protective resist is applied to the metal coating, which acts as an etching mask for a subsequent etching method that removes the metal coating in areas not covered by the protective resist, so that only the absorbing microstructures 34 remain in the surface region 26a. The etching method can be a wet chemical etching method, but dry etching in a reactive gas atmosphere is also possible. Alternatively, the absorbing microstructures 34 can be produced by laser ablation on a large area of ​​the metal coating or layer.

[0047] In order not to adversely affect the quality of imaging of the structures of the photomask 10 onto the wafer 12, the absorbing microstructures 34 must not have too large a structure width b. In the example shown in FIG. 2b, the structure width b of the absorbing microstructures 34 varies from location to location, but the average structure width b of all the microstructures 34 is less than 20 μm, more precisely less than 10 μm. In FIG. 2a, the absorbing microstructures 34 are not arranged with a precisely uniform distribution, i.e., the distance D between the centers of adjacent absorbing microstructures 34 is not constant but varies from location to location. Therefore, in the example shown in FIG. 2a, the surface area fraction F of the absorbing microstructures 32 varies from location to location, i.e., depending on the position P on the illuminated surface area 26a.

[0048] The variation in surface area fraction F of absorbing microstructures 34 along irradiated surface region 26a varies in response to the variation in intensity distribution I(x) of DUV radiation 8 along irradiated surface region 26a in the X direction. Of course, the intensity distribution of DUV radiation 8 also varies in the Y direction, but this is not discernible in the cross-sectional view of lens element 16 in Figure 2a. In the example shown in Figure 2a, the locally variable power density or intensity distribution I(x) of DUV radiation 8 incident on surface region 26a is represented by arrows of different widths, with wider arrows corresponding to higher power densities or local intensities I(x) and narrower arrows corresponding to lower power densities or local intensities I(x).

[0049] As can be seen in FIG. 2 a, the surface area fraction F of the absorbing microstructures 34 at low-intensity irradiation positions P, where the local intensity I(x) of DUV radiation 8 is low, is larger than at positions P, where the local intensity I(x) of DUV radiation 8 is higher. The greater heating of the body 24 at positions P, where the intensity I(x) of DUV radiation 8 is higher, is compensated for by the fact that more DUV radiation 8 is absorbed by the coating 32 at positions P, where the intensity I(x) of DUV radiation 8 is lower, due to the larger surface area fraction F of the absorbing microstructures 34. A uniform temperature distribution and therefore a uniform refractive index can be generated in the body 24 in this way. When the DUV radiation 8 passes through the lens element 16, a plane wavefront 36, shown by the dashed-dotted line in FIG. 2 a, can be generated or obtained in this way. Needless to say, wavefronts 36 of essentially any geometric shape can be generated by appropriately adapting the spatial variation of the surface area fraction F of the absorbing microstructures 34 on the lens element 16.

[0050] Needless to say, the desired wavefront 36 can only be generated for a specific intensity distribution I(x) of the incident DUV radiation 8. If the intensity distribution I(x) changes, for example due to a change in the illumination settings of the beam shaping and illumination system 2, a wavefront 36 with a geometry that deviates from the desired geometry will be generated.

[0051] 1 also includes a magazine 38 storing a plurality of transmissive optical elements 16' each having a different variation in the surface area fraction F of the microstructures 34 in the surface region 26a provided with the absorbing coating 32. In this case, each transmissive optical element 16', or more precisely, the variation in the surface area fraction F, is optimized for each of a plurality of illumination settings S1, S2, ... of the beam shaping and illumination system 2. To exchange a lens element 16 arranged in the beam path 30 for one of the lens elements 16' stored in the magazine 38, the DUV lithography apparatus includes a transport device 40, which may be, for example, a lever arm. For controlling the transport device 40, the DUV lithography apparatus 1 includes a control device 42. The control device 42 is configured to replace the lens element 16 arranged in the beam path 30 with one of the lens elements 16' stored in the magazine 38, whose spatial variation in the surface area fraction F is optimized for each illumination setting S1, S2, ..., in the event of a change in the illumination settings S1, S2, ... of the beam shaping and illumination system 2.

[0052] In the case of the lens element 16 described in Fig. 2a, the desired temperature distribution in the body 24, and therefore the desired wavefront 36, is generated by the local variation of the surface area fraction F of the absorbing microstructures 34. The transmitting optical element 44 shown in Fig. 2b differs from the optical element 16 shown in Fig. 2a primarily in that it is a plate-like optical element (a plane-parallel plate). Furthermore, the absorbing microstructures 34 in the case of the plate-like optical element 44 shown in Fig. 2b are arranged in a grid pattern at equal distances D from one another and have the same structure width b. Therefore, in the case of the optical element 44 shown in Fig. 2b, the surface area fraction F of the absorbing microstructures 34 does not vary with location but is constant.

[0053] In order to generate a desired temperature distribution in the body 24 of the optical element 44 in the example shown in Figure 2b, a heating device 46 for radiative heating of the optical element 44 is used (see Figure 1). In the example shown in Figure 1, the heating device 46 has a heating wavelength λ HThe heating device 46 comprises a heating light source 48 comprising a laser, for example in the form of a high-power laser diode, which generates a heating radiation 50 of 1000 kJ / cm. The heating device 46 also comprises a scanner device 52 with one or more scanner mirrors which deflect the heating radiation 50 coupled into the beam path 30 of the projection system 4. The heating radiation 50 impinges on the plate-like optical element 44, which is the first optical element in the beam path 30 of the projection system 4. Using the scanner device 52, it is possible to change the position P of the heating radiation 50 on the plate-like optical element 44. The power of the heating light source 48 is adjustable so that a location-dependent intensity distribution I of the heating radiation 50 at the first surface 26 of the plate-like optical element 44 is obtained. H 2b, the surface area irradiated with the heating radiation 50 and provided with the absorbing coating 32 is the entire first surface 26 of the plate-shaped optical element 44, which includes the surface area 26a irradiated with the DUV radiation 8. The control device 42 controls the intensity distribution I H To predefine (x), one can act to control the heating light source 48 .

[0054] 1, the heating device 46 may have a grid arrangement 54 of heating light sources 48, e.g., in the form of laser diodes, as shown in FIG. 2b. The power of the heating radiation 50 generated by each heating light source 48 may be individually set, as indicated by the arrows of different widths in FIG. 2b. In the example shown in FIG. 2b, each heating light source 48 is aligned with a respective absorbing microstructure 34. However, it will be appreciated that in general each heating light source 48 will be aligned with multiple absorbing microstructures 34. The individual setting of the power of the heating light sources 49 allows for a location-dependent intensity distribution I of the heating radiation 50 at the first surface 26. H It is also possible to create or set (x).

[0055] Intensity distribution of heating radiation 50 I HBy being able to actively influence (x), a desired temperature distribution in the body 24 of the plate-like optical element 44 can be generated, which distribution generates a desired geometric shape of the wavefront 36. In this way, the optical element 44 shown in Figure 2b can be used to actively set or correct the wavefront 36 of the projection system 4 of the DUV lithography apparatus 1, in particular to compensate for wavefront aberrations occurring in the other optical elements 16, 18 of the projection system 4.

[0056] Both the heating light source 48 shown in FIG. 1 and the heating light source 48 of the grating arrangement 52 of FIG. 2b emit a heating wavelength λ in the wavelength range of 400 nm to 1550 nm. H The heating light source(s) 48 are configured to emit heating radiation 50 onto the plate-shaped optical element 44. This is possible because the absorbing coating 32 also absorbs radiation in the designated wavelength range. Thus, conventional high-power diodes, such as those common in telecommunications applications, can be used as the heating light source(s) 48.

Claims

1. An optical apparatus for DUV lithography, in particular a DUV lithography apparatus (1), comprising: At least one operating wavelength (λ) in the DUV wavelength range Ｂ a light source (6) for generating DUV radiation (8) of a transmissive optical element (16, 44) having an absorbing coating (32) for transmitting said DUV radiation (8); In an optical device (1) comprising: the absorbent coating (32) has absorbent microstructures (34) covering a surface area percentage (F) of less than 0.1% and greater than 0.01% of the surface area (26, 26a) covered by the absorbent coating (32); and The optical apparatus further comprises a heating device (46) having at least one heating light source (48) that emits heating radiation (50) onto the surface region (26) of the transmissive optical element (44) that is provided with the absorbing coating (32).

2. 2. The optical device of claim 1, wherein the surface area provided with the absorbing coating (32) comprises or forms a surface area (26a) of the transmissive optical element (16) that is irradiated with the DUV radiation (8).

3. 3. An optical device according to claim 1 or 2, wherein the absorbing microstructures (34) have an average structure width (b) of less than 20 μm, preferably less than 10 μm.

4. 3. An optical device according to claim 1 or 2, wherein the absorbing coating (32) is configured as a metallic coating.

5. 5. The optical device of claim 4, wherein the absorbing coating (32) comprises at least one material selected from the group consisting of Cr, Al, Au, and Ag.

6. 3. An optical device according to claim 1 or 2, wherein said absorbing coating (32) has a thickness (d) of between 50 nm and 200 nm.

7. 3. The optical device according to claim 1, wherein the at least one operating wavelength (λ Ｂ ) an anti-reflective coating (35a) against said DUV radiation (8) is applied to said absorbing coating (32).

8. 2. The optical device according to claim 1, wherein the surface area fraction (F) of the absorbing microstructures (34) varies from location to location depending on the intensity distribution (I(x)) of the DUV radiation (8) in the surface region (26a) provided with the absorbing coating (32).

9. 2. The optical device of claim 1, wherein the transmissive optical element (16) is positioned at or near a pupil plane (22).

10. 10. The optical device according to claim 8, a magazine (38) having a plurality of transmitting optical elements (16') each having a different surface area percentage (F) of the absorbing microstructures (34) in the surface region (26a) provided with the absorbing coating (32); a transport device (40) for transporting one of the transmissive optical elements (16') from the magazine (38) into the beam path (30) of the optical device (1); a control device (42) for controlling the transport device (40); The optical device further comprises:

11. 3. An optical device according to claim 1 or 2, wherein the transmitting optical element is an imaging optical element, in particular a lens element (16).

12. 3. The optical device according to claim 1, wherein the transmitting optical element is a correcting element (44) for correcting wavefront aberration.

13. 3. The optical device according to claim 1, wherein the heating light source (48) emits at least one heating wavelength (λ ) in a wavelength range of 400 nm to 1550 nm. Ｈ an optical device configured to irradiate the surface area (26) with heating radiation (50) at a wavelength of 1000 nm;

14. 3. The optical device according to claim 1, wherein the heating device (46) provides a spatially variable intensity distribution (I Ｈ (x)) an optical device configured to irradiate the heating radiation (50) onto the surface area (26) of the transmissive optical element (44).

15. 3. The optical apparatus according to claim 1, wherein the heating device (46) comprises a scanner device (52) for aligning the heating radiation (50) of the heating light source (48) with different positions (P) of the absorbing coating (32) and / or a grid arrangement (54) of heating light sources (48) for irradiating different positions (P) of the absorbing coating (32).

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