Method for operating a lithography system, optical system and lithography system

Abstract

Method for operating a lithography system (1) comprising an optical system (100) with an optical element (102), comprising the steps: a) providing (S1) a plasma (108) in an environment (110) of an optically active surface (104) of the optical element (102) for modifying the optically active surface (104), b) Determining (S2) an actual value (F IST ) at least one parameter (F) of the optically active surface (104), and c) controlling (S4) the at least one parameter (F) of the optically active surface (104) based on the determined actual value (F IST ) and a predetermined target value (F SOLL ) by adjusting at least one plasma parameter (P1) of the provided plasma (108).

Description

[0001] The present invention relates to a method for operating a lithography system, an optical system and a lithography system with such an optical system.

[0002] Microlithography is used to manufacture microstructured components, such as integrated circuits. The microlithography process is carried out using a lithography system equipped with an illumination system and a projection system. The image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example, a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0003] Driven by the pursuit of ever smaller structures in the production of integrated circuits, EUV lithography systems are currently being developed that use light with a wavelength in the range of 0.1 nm to 30 nm, particularly 13.5 nm. Since most materials absorb light at this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the refractive optics, i.e., lenses, as was previously the case.

[0004] Optical elements of a lithography system, such as mirrors and lenses, feature high-precision optical materials and a high surface quality. The imaging quality of the lithography system depends largely on the nature and chemical purity of the optically active surfaces of its optical elements. However, these optical elements are sensitive components whose surface quality is subject to degradation during operation of the lithography system due to various processes, such as contamination.

[0005] Against this background, it is an object of the present invention to provide an improved method for operating a lithography system and an improved optical system for a lithography system.

[0006] According to a first aspect, a method for operating a lithography system is proposed. The lithography system comprises an optical system with an optical element. The method comprises the following steps: a) providing a plasma in an environment of an optically active surface of the optical element for modifying the optically active surface, b) determining an actual value of at least one parameter of the optically active surface, and c) Controlling the at least one parameter of the optically active surface based on the determined actual value and a predetermined target value by adjusting at least one plasma parameter of the provided plasma.

[0007] By providing a plasma in the environment of the optically active surface of the optical element, the optically active surface can be modified. In particular, the optically active surface is modified in such a way that degradation of the optically active surface is counteracted. Degradation of the optically active surface can occur, for example, through reactions of the optically active surface with species in the environment, through removal of material from the optically active surface due to such reactions, and / or through deposition of contaminant species from the environment onto the optically active surface. This degradation is counteracted with the help of the provided plasma; for example, the reverse reaction is intensified in reversible degradation reactions.

[0008] An actual state of the optically active surface can therefore change over time, e.g., degrade in various ways. Actual values ​​of one or more parameters of the optically active surface therefore change over time. By (e.g., repeatedly and / or continuously) determining the actual value of at least one parameter of the optically active surface, this change can be monitored. Taking the determined actual value into account, one or more plasma parameters of the provided plasma can be adjusted based on a control system, such that the provided plasma modifies the optically active surface such that the at least one parameter of the optically active surface is controlled to the predetermined target value.

[0009] This can improve the imaging quality of the optical system with the optical element and / or maintain sufficient imaging quality of the optical system. In particular, an unfavorable change in the beam path in the optical system due to degradation of the optically active surface(s) can be prevented and / or reduced.

[0010] The lithography system (projection exposure system) can be an EUV lithography system. EUV stands for "Extreme Ultraviolet" and refers to a wavelength of the working light between 0.1 nm and 30 nm, especially 13.5 nm. The lithography system can also be a DUV lithography system. DUV stands for "Deep Ultraviolet" and refers to a wavelength of the working light between 30 nm and 250 nm.

[0011] The optical system is, for example, a projection system of the lithography system. However, the optical system can also be, for example, an illumination system of the lithography system. In the microlithography process, the image of a mask (reticle) illuminated by the illumination system is projected by the projection system onto a substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection system, for example, a silicon wafer, in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0012] The optical element is, for example, a reflective optical element (e.g., a mirror) or a transmissive optical element (e.g., a lens) of the lithography system. The optically active surface is, in particular, an optically active surface of the optical element. The optically active surface is, for example, a reflective surface. However, the optically active surface can also be a transmissive surface. The optically active surface can have a circular, oval, angular, and / or freeform surface.

[0013] The plasma contains, for example, ions, free electrons, and / or radicals. The plasma can contain, for example, various ionic species and / or various radical species. The plasma is generated, for example, using a plasma source.

[0014] The environment of the optically active surface of the optical element is, in particular, a space (three-dimensional space) in which the optically active surface is arranged. In other words, the plasma provided in the environment of the optically active surface comes into physical contact with the optically active surface. One can also say that the plasma is provided at the optically active surface.

[0015] The provided plasma modifies the optically active surface in such a way that an optical property of the optical element and thus of the optical system is improved. For example, the imaging quality of the optical system is improved.

[0016] The provided plasma (e.g., the plasma particles, i.e., the ions, electrons, radicals, etc.) interacts specifically with the optically active surface to modify the optically active surface. For example, if it is determined in step b) that contamination layers have deposited (e.g., locally) on the optically active surface, ions and radicals of the plasma can be continuously generated to selectively etch and remove the contaminants without, however, attacking the actual optically active surface.

[0017] The at least one parameter of the optically active surface is, in particular, at least one parameter on which an optical property of the optical element depends. In other words, the at least one parameter of the optically active surface is, in particular, at least one parameter that is indicative of an optical property of the optical element.

[0018] The actual value of the at least one parameter of the optically active surface characterizes an instantaneous value of the at least one parameter of the optically active surface. The actual value of the at least one parameter of the optically active surface is determined, for example, using a measuring device.

[0019] Controlling the at least one parameter of the optically active surface comprises, in particular, determining a deviation of the determined actual value of the at least one parameter of the optically active surface from the target value of the at least one parameter of the optically active surface. Furthermore, the control comprises determining, based on the determined deviation, a manipulated variable for adjusting the at least one plasma parameter of the provided plasma. The at least one plasma parameter is thus adjusted based on the determined manipulated variable. For example, a plasma source device of the optical system is controlled based on the determined manipulated variable.

[0020] The optical system comprises, for example, a control device configured to determine the deviation of the actual value from the target value, determine the manipulated variable based on the deviation, and, for example, control the plasma source device based on the determined deviation. The control device comprises, for example, a P, PI, and / or PID controller.

[0021] A deviation determination unit can also be provided. In this case, instead of the control device, the deviation determination unit can also be configured to determine the deviation of the actual value of the at least one parameter of the optically active surface from the predetermined target value and to transmit this determined deviation to the control device.

[0022] Furthermore, a transfer unit can optionally be provided to convert the recorded actual value into information that can be evaluated by the control system. A transfer function (further transfer function) can be applied for this purpose.

[0023] The control of the at least one parameter of the optically active surface is based in particular on feedback control. The control of the at least one parameter of the optically active surface is carried out in particular based on a (closed) control loop. The target value of the at least one parameter of the optically active surface corresponds to a reference variable of the control loop. In addition, the detected actual value of the at least one parameter of the optically active surface is fed in negative form to the control device (or a deviation determination unit) in order to determine a deviation between the actual value and the target value.

[0024] For example, the control of at least one parameter of the optically active surface can be performed continuously. In addition, a temporally discretized, interval-based control is also possible.

[0025] For example, steps a) to c) are carried out repeatedly and / or continuously.

[0026] In step b), the actual value of more than one parameter of the optically active surface can also be determined. Then, in step c), the control is performed separately for each of the multiple parameters of the optically active surface (i.e., based on a separate control loop). In this case, the control is based on several independent control loops.

[0027] Alternatively, if the actual value of more than one parameter of the optically active surface is determined in step b), the control in step c) can also be based on several interdependent control loops.

[0028] In step c), control can also be achieved by adjusting more than one plasma parameter of the provided plasma. Then, for example, a corresponding manipulated variable can be determined for each of several plasma parameters. For example, the multiple manipulated variables for the multiple plasma parameters are determined (e.g., calculated and / or derived) from the deviation of the actual value from the target value based on a model and / or simulation.

[0029] The optical system can also have more than one optical element. In this case, the method can optionally also modify the optically active surfaces of several of the optical elements of the optical system using a respective plasma. For this purpose, steps a) to c) are performed for each optically active surface or each optical element of the multiple optical elements. For example, the control in step c) is then carried out for each optically active surface or each optical element of the multiple optical elements based on a separate control loop.

[0030] According to one embodiment, the method comprises: Recording an instantaneous value of at least one plasma parameter, wherein the control of the at least one parameter of the optically active surface is carried out based on the detected instantaneous value of the at least one plasma parameter.

[0031] For example, the instantaneous value of at least one plasma parameter is measured and / or recorded experimentally.

[0032] For example, in step c), a value to be set for the at least one plasma parameter is determined based on the deviation of the actual value from the target value of the at least one parameter of the optically active surface (e.g., also based on a model or the like). Furthermore, a manipulated variable is determined, for example, based on the deviation of the actual value from the target value of the at least one parameter of the optically active surface and based on the detected instantaneous value of the at least one plasma parameter.

[0033] According to a further embodiment, steps a), b) and / or c) are carried out during operation and / or an exposure process of the lithography system.

[0034] This allows the optically active surface of the optical element to be modified during operation of the lithography system. In particular, the at least one parameter of the optically active surface can be monitored repeatedly and / or continuously during operation of the lithography system. Furthermore, the at least one plasma parameter can be adjusted repeatedly and / or continuously based on the control. Thus, sufficient optical quality of the optically active surface can be ensured during operation of the lithography system, e.g., also during the exposure process.

[0035] During operation of the lithography system, for example, a space within a vacuum housing in which the optical element is arranged is evacuated.

[0036] During the exposure process of the lithography system, the optical element, i.e. the optically active surface of the optical element, is irradiated with working light (e.g. EUV / DUV light).

[0037] According to a further embodiment, the optical element is arranged in a vacuum housing of the lithography system, and the plasma is provided within the vacuum housing.

[0038] This means that the optical element is treated with the plasma in the installed or arranged state in the optical system or in the lithography system.

[0039] According to a further embodiment: the plasma is generated within the vacuum housing and / or the vacuum housing forms a plasma chamber of a plasma source device for generating the plasma, or the plasma is generated outside the vacuum housing and fed into an interior of the vacuum housing and into the environment of the optically active surface.

[0040] In the first alternative of this embodiment, the plasma is generated within the vacuum housing. Thus, no separate plasma source and / or plasma source device is required. For example, the vacuum housing in which the optical element is arranged can also simultaneously form the plasma chamber of the plasma source device. Thus, an additional housing for forming the plasma chamber is not required. In the first alternative, the plasma can be generated, for example, in the vicinity of the optically active surface of the optical element.

[0041] In the second alternative of this embodiment, the plasma is generated outside the vacuum housing and fed, for example by means of a feed line, into an interior of the vacuum housing and into the environment of the optically active surface.

[0042] According to a further embodiment, modifying the optically active surface comprises cleaning, chemical modification and / or physical modification.

[0043] The chemical modification of the optically active surface comprises, for example, a chemical reaction of a material of the optically active surface (including a material from contaminants of the optically active surface) with one or more species and / or particle types of the provided plasma. The chemical modification of the optically active surface includes, for example, (e.g., wet-chemical) etching, oxidation, or reduction of the material of the optically active surface (including a material from contaminants of the optically active surface). By way of example only, carbon has accumulated on the optically active surface and is then etched away using the plasma.

[0044] The physical modification of the optically active surface comprises, for example, a physical interaction between a material of the optically active surface (including a material of contaminants of the optically active surface) and one or more species and / or particle types of the provided plasma. The physical modification of the optically active surface comprises, for example, a physical removal of this material. By way of example only, a particle has attached itself to the optically active surface by physisorption and is then removed with the aid of the plasma. Physisorption is a physical adsorption in which a physical bond occurs between an adsorbate (e.g., a contaminant) and an adsorbent (material of the optically active surface) (physical modification / degradation of the optically active surface).

[0045] According to a further embodiment, the at least one parameter of the optically active surface comprises an optical parameter, a reflectivity, a transmissivity, a surface parameter, a surface roughness, a binding energy, a degree of contamination, a composition of a contamination and / or a dimension of a contamination of the optically active surface.

[0046] Contamination of the optically active surface includes, for example, deposits and / or accumulations on the optically active surface. The deposits or accumulations can be caused by physisorption or chemisorption. Chemisorption is a chemical adsorption in which a chemical reaction occurs between an adsorbate (e.g., from the ambient atmosphere) and an adsorbent (material of the optically active surface) (chemical modification / degradation of the optically active surface).

[0047] The composition of the contamination, for example, includes a chemical composition of the contamination. The composition of the contamination includes, in particular, the components (species) of the contamination. The composition of the contamination is determined, for example, stoichiometrically.

[0048] The dimension of the contamination of the optically active surface is, for example, a layer thickness of a contamination layer and / or an area covered by the contamination.

[0049] The binding energy is in particular a (physical) binding energy of the optically active surface.

[0050] According to a further embodiment, determining the actual value of the at least one parameter of the optically active surface comprises: Surface analysis of the optically active surface, Detecting an optical property of the optical system which is indicative of the actual value of at least one parameter of the optically active surface, and / or Detecting a further instantaneous value of at least one further plasma parameter of the provided plasma, which is indicative of the actual value of the at least one parameter of the optically active surface.

[0051] Surface analysis of the optically active surface allows the optically active surface to be directly examined. Surface analysis of the optically active surface includes, for example, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and / or Raman spectroscopy.

[0052] Alternatively or in addition to a direct surface analysis of the optically active surface, the condition of the optically active surface can also be determined indirectly. For example, an optical property (e.g., an imaging property and / or a transmission) of the optical system can be recorded. From this, the actual value of at least one parameter of the optically active surface can be determined in the next step.

[0053] The transmission (total transmission) of the optical system is a value derived from a comparison of the radiation coupled into the optical system at the beginning of the overall beam path and the radiation coupled out of the optical system at the end of the overall beam path. The transmission (total transmission) of the optical system can be used to determine the condition (i.e., actual value) of the optically active surface of the optical element of the optical system. For example, a recorded total transmission of the optical system can also be compared with an initial total transmission of the optical system determined before the optical system and / or the lithography system was first put into operation.

[0054] Another example of an indirect determination of the state of the optically active surface is the recording of the instantaneous value of at least one further plasma parameter. The at least one further plasma parameter is preferably a composition of the plasma, from which a state of the optically active surface can be inferred.

[0055] The at least one further plasma parameter may be the same as the at least one plasma parameter set in step c) of the method or may be a different one.

[0056] A property / parameter that is indicative of the actual value of at least one parameter of the optically active surface means that the actual value of at least one parameter of the optically active surface can be derived and / or determined from this property or parameter. The derivation / determination can also be carried out, for example, based on a model, a simulation, and / or under certain assumptions.

[0057] According to a further embodiment, the instantaneous value of the at least one plasma parameter and / or the further instantaneous value of the at least one further plasma parameter is detected by means of spectroscopy, mass spectroscopy, plasma resonance spectroscopy and / or detecting a plasma characteristic curve.

[0058] For example, the instantaneous value and / or the further instantaneous value of the at least one (further) plasma parameter is recorded using a residual gas analyzer (RGA), a Langmuir probe for recording a plasma characteristic curve, optical emission spectroscopy (OES), in which the plasma is spectroscoped and analyzed from the outside through a window, a multipole resonance probe and / or a retarding field energy analyzer (RFEA).

[0059] In the case of the further instantaneous value of the at least one further plasma parameter, this can also be determined indirectly from an (in situ or ex situ) investigation of the optically active surface if the at least one further plasma parameter causes surface effects on the optically active surface from which the at least one further plasma parameter can be inferred.

[0060] According to a further embodiment, the at least one plasma parameter and / or the at least one further plasma parameter comprises an electron density, an electron temperature, an electron energy distribution function, a collision frequency, a plasma potential and / or a composition of the plasma.

[0061] The composition of the plasma, for example, shows a (relative) proportion of the various components (i.e. species / particle types) of the plasma.

[0062] According to a further embodiment, determining the actual value of the at least one parameter of the optically active surface comprises surface analysis of the optically active surface in situ or ex situ.

[0063] In-situ surface analysis of the optically active surface means that the optically active surface of the optical element is examined while the optical element is installed in the optical system. When the optical element is installed in the optical system, the optical element is arranged, for example, in a vacuum housing of the lithography system.

[0064] Ex situ surface analysis of the optically active surface, for example, means that a sample representative of the optically active surface (witness sample) is removed from the location of the optical element in the installed state and examined at a distance from it. For example, the optical element is arranged within a vacuum housing, and the witness sample is removed from the vacuum housing (e.g., ejected) for examination.

[0065] For example, the optical element has a first part with a first portion of the optically active surface and a second part with a second portion of the optically active surface. Furthermore, the second part is detachably attached to the first part. In this example, the second part with the second portion of the optically active surface represents the witness sample. To analyze the surface of the optically active surface of the optical element ex situ, the second part with the second portion of the optically active surface (i.e. the witness sample) is moved from the vacuum housing to outside the vacuum housing. The second portion of the optically active surface is then examined outside the vacuum housing, e.g. using a surface measuring device.

[0066] The second part with the second section of the optically active surface (i.e., the witness sample) can—in the installed state—be arranged, for example, outside a useful area of ​​the optically active surface. For example, the witness sample can be arranged when the working light has a diffraction order of two or greater. The useful area of ​​the optically active surface is, in particular, an area used for the lithographic beam path and / or lithographic imaging.

[0067] In the case of a facet mirror as an optical element, the second part with the second section of the optically active surface (ie the witness sample) can, for example, also be a facet of the facet mirror.

[0068] According to a further embodiment, a manipulated variable for adjusting the at least one plasma parameter is determined based on a deviation of the actual value from the target value by applying a transfer function and / or a model.

[0069] This makes it easier to determine how at least one plasma parameter must be adjusted in order to bring the state of the optically active surface from the actual value towards the target value.

[0070] The manipulated variable can, for example, also be determined based on the recorded instantaneous value of at least one plasma parameter by applying the transfer function, the model and / or a simulation calculation.

[0071] According to a further embodiment, setting the at least one plasma parameter comprises: Setting a power coupled into a plasma source, Applying a local modulation of the coupled power, setting one or more bias potentials of the plasma source, Applying a magnetic field and / or an electric field to the plasma provided in the vicinity of the optically active surface, Setting a pressure of the provided plasma in the vicinity of the optically active surface, Setting a composition of the provided plasma, Supplying one or more process gases into the environment, and / or Setting a chamber pressure in a plasma chamber of the plasma source device.

[0072] In particular, a plasma source device can be provided, which comprises a plasma source and a plasma chamber. The plasma source device can also comprise a magnetic field unit and / or an electric field unit for applying the (external) magnetic field or the (external) electric field to the plasma in the vicinity of the optically active surface.

[0073] The plasma source device can optionally also comprise a gas supply unit for supplying the one or more process gases to the environment of the optically active surface. By supplying the one or more process gases, chemical surface reactions of the optically active surface can be specifically controlled with reversible effects. For example, by supplying the one or more process gases, the number (relative proportion) of free radicals in the provided plasma can be increased.

[0074] The one or more process gases are, for example, one or more etching gases. The one or more etching gases include, for example, xenon difluoride (XeF2), sulfur hexafluoride (SF6), sulfur tetrafluoride (SF4), nitrogen trifluoride (NF3), phosphorus trifluoride (PF3), tungsten hexafluoride (WF6), tungsten hexachloride (WCl6), molybdenum hexafluoride (MoF6), hydrogen fluoride (HF), nitrogen oxygen fluoride (NOF), and / or triphosphorus trinitrogen hexafluoride (P3N3F6).

[0075] The one or more process gases may also contain other gases, such as carbon dioxide (CO2). Such gases, such as carbon dioxide, can also be referred to as background gases because they are present in the system at relatively low partial pressures. These are sometimes disruptive residual gases that cannot be completely removed from the chamber due to the technical vacuum, but are nevertheless ionized by the plasma.

[0076] According to a second aspect, an optical system for a lithography system is proposed. The optical system comprises: an optical element with an optically active surface, a plasma source device for providing a plasma in an environment of the optically active surface for modifying the optically active surface, a measuring device for detecting an actual value of at least one parameter of the optically active surface, and a control device for controlling the at least one parameter of the optically active surface based on the determined actual value and a predetermined target value by controlling the plasma source device to adjust at least one plasma parameter of the provided plasma.

[0077] The measuring device is designed in particular to directly or indirectly detect the actual value of at least one parameter of the optically active surface.

[0078] The respective unit, for example, the control device, the deviation detection unit, and the transfer unit, can be implemented in hardware and / or software. In a hardware implementation, the respective unit can be designed as a device or as part of a device, for example, as a computer or a microprocessor. In a software implementation, the respective unit can be designed as a computer program product, as a function, as a routine, as part of a program code, or as an executable object. Furthermore, the corresponding unit can also be designed as part of a higher-level control system of the lithography system.

[0079] In embodiments, the plasma source device comprises: a plasma source for generating an inductively coupled plasma, a plasma source for generating a plasma using direct current, a plasma source for generating a plasma by means of alternating voltage, and / or a plasma source for generating a plasma using microwaves and / or alternating voltage discharge.

[0080] The plasma source for generating an inductively coupled plasma (ICP) has, for example, a coil, in particular an induction coil.

[0081] The plasma source for generating the plasma using direct voltage or direct current (DC) is used to generate the plasma by direct current excitation.

[0082] The plasma source for generating the plasma using alternating voltage (e.g. an alternating voltage of 13.56 MHz) is used to generate the plasma by alternating current excitation.

[0083] For example, a frequency of 2.45 GHz is used in the plasma source for generating the plasma using microwaves and / or alternating voltage discharge.

[0084] According to a third aspect, a lithography system with an optical system as described above is proposed.

[0085] "One" in this case is not necessarily limited to a single element. Rather, multiple elements, such as two, three, or more, may also be included. Any other counting term used here should not be understood as implying a limitation to the exact number of elements stated. Rather, numerical deviations upwards and downwards are possible, unless otherwise stated.

[0086] The embodiments and features described for the method apply accordingly to the proposed optical system and vice versa.

[0087] Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0088] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography according to an embodiment; Fig. 2 shows an optical system of the projection exposure system from Fig. 1 according to a first embodiment; Fig. 3 shows a flow diagram of a method for operating the projection exposure apparatus of Fig. 1 according to one embodiment; Fig. 4 shows a control circuit for controlling at least one parameter of an optically active surface of an optical element of the optical system of Fig. 2; Fig. 5 shows an optical system of the projection exposure system from Fig. 1 according to a second embodiment; Fig. 6 shows an optical system of the projection exposure system from Fig. 1 according to a third embodiment; and Fig. 7 shows an optical system of the projection exposure system from Fig. 1 according to a fourth embodiment.

[0089] In the figures, identical or functionally equivalent elements are provided with the same reference numerals unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0090] Fig. 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of an illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optics 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the light source 3 can also be provided as a separate module from the remaining illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0091] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 can be displaced via a reticle displacement drive 9, in particular in a scanning direction.

[0092] In the Fig. For illustrative purposes, Figure 1 shows a Cartesian coordinate system with an x-direction x, a y-direction y, and a z-direction z. The x-direction x runs perpendicular to the plane of the drawing. The y-direction y runs horizontally, and the z-direction z runs vertically. The scanning direction runs in the Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0093] The projection exposure system 1 comprises a projection optics 10. The projection optics 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 runs parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0094] A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the image plane 12 in the region of the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be displaced, in particular along the y-direction y, via a wafer displacement drive 15. The displacement of the reticle 7, on the one hand, via the reticle displacement drive 9, and the displacement of the wafer 13, on the other hand, via the wafer displacement drive 15, can be synchronized with each other.

[0095] The light source 3 is an EUV radiation source. The light source 3 emits, in particular, EUV radiation 16, which is also referred to below as useful radiation, illumination radiation, or illumination light. The useful radiation 16 has, in particular, a wavelength in the range between 5 nm and 30 nm. The light source 3 can be a plasma source, for example, an LPP source (Laser Produced Plasma) or a DPP source (Gas Discharged Produced Plasma). It can also be a synchrotron-based radiation source. The light source 3 can be a free-electron laser (FEL).

[0096] The illumination radiation 16 emanating from the light source 3 is focused by a collector 17. The collector 17 can be a collector with one or more ellipsoidal and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 17 can be exposed to the illumination radiation 16 at grazing incidence (GI), i.e., at angles of incidence greater than 45°, or at normal incidence (NI), i.e., at angles of incidence less than 45°. The collector 17 can be structured and / or coated, on the one hand, to optimize its reflectivity for the useful radiation and, on the other hand, to suppress stray light.

[0097] After the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 can represent a separation between a radiation source module, comprising the light source 3 and the collector 17, and the illumination optics 4.

[0098] The illumination optics 4 comprises a deflecting mirror 19 and, downstream of this in the beam path, a first facet mirror 20. The deflecting mirror 19 can be a flat deflecting mirror or, alternatively, a mirror with a beam-influencing effect beyond the pure deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful light wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first facet mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugated to the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Of these first facets 21, Fig. 1 only some examples are shown.

[0099] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or partially circular edge contour. The first facets 21 can be designed as flat facets or, alternatively, as convexly or concavely curved facets.

[0100] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 themselves can also be composed of a plurality of individual mirrors, in particular a plurality of micromirrors. The first facet mirror 20 can, in particular, be designed as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 A1.

[0101] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0102] In the beam path of the illumination optics 4, a second facet mirror 22 is arranged downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged at a distance from a pupil plane of the illumination optics 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US 2006 / 0132747 A1, EP 1 614 008 B1, and US Pat. No. 6,573,978.

[0103] The second facet mirror 22 comprises a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0104] The second facets 23 can also be macroscopic facets, which can, for example, be round, rectangular, or hexagonal, or alternatively facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0105] The second facets 23 can have planar or alternatively convex or concave curved reflection surfaces.

[0106] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a fly's-eye integrator.

[0107] It may be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second facet mirror 22 can be arranged tilted relative to a pupil plane of the projection optics 10, as described, for example, in DE 10 2017 220 586 A1.

[0108] With the help of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-forming mirror or actually the last mirror for the illumination radiation 16 in the beam path before the object field 5.

[0109] In a further embodiment of the illumination optics 4 (not shown), a transmission optics can be arranged in the beam path between the second facet mirror 22 and the object field 5, which transmission optics contributes in particular to the imaging of the first facets 21 into the object field 5. The transmission optics can have exactly one mirror, but alternatively also two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 4. The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirrors, normal incidence mirrors) and / or one or two mirrors for grazing incidence (GI mirrors, grazing incidence mirrors).

[0110] The illumination optics 4 has in the version shown in the Fig. 1, after the collector 17 there are exactly three mirrors, namely the deflection mirror 19, the first facet mirror 20 and the second facet mirror 22.

[0111] In a further embodiment of the illumination optics 4, the deflection mirror 19 can also be omitted, so that the illumination optics 4 can then have exactly two mirrors after the collector 17, namely the first facet mirror 20 and the second facet mirror 22.

[0112] The imaging of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optics into the object plane 6 is usually only an approximate imaging.

[0113] The projection optics 10 comprises a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0114] In the Fig. In the example shown in Figure 1, the projection optics 10 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or a different number of mirrors M1 are also possible. The projection optics 10 is a doubly obscured optic. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optics 10 has an image-side numerical aperture that is greater than 0.5 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0115] Reflection surfaces of the mirrors Mi can be designed as freeform surfaces without a rotational symmetry axis. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one rotational symmetry axis of the reflection surface shape. The mirrors Mi, like the mirrors of the illumination optics 4, can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0116] The projection optics 10 has a large object-image offset in the y-direction y between a y-coordinate of a center of the object field 5 and a y-coordinate of the center of the image field 11. This object-image offset in the y-direction y can be approximately as large as a z-distance between the object plane 6 and the image plane 12.

[0117] The projection optics 10 can, in particular, be anamorphic. It has, in particular, different magnifications β, βy in the x and y directions x, y. The two magnifications βx βy of the projection optics 10 are preferably (βx βy = (+ / - 0.25, + / - 0.125). A positive magnification β means an image without image inversion. A negative sign for the magnification β means an image with image inversion.

[0118] The projection optics 10 thus leads to a reduction in the ratio 4:1 in the x-direction x, i.e. in the direction perpendicular to the scanning direction.

[0119] The projection optics 10 leads to a reduction of 8:1 in the y-direction y, i.e. in the scanning direction.

[0120] Other magnifications are also possible. Magnifications with the same sign and absolutely identical in the x and y directions (x, y), for example, with absolute values ​​of 0.125 or 0.25, are also possible.

[0121] The number of intermediate image planes in the x- and y-directions x, y in the beam path between the object field 5 and the image field 11 can be the same or can be different, depending on the design of the projection optics 10. Examples of projection optics with different numbers of such intermediate images in the x- and y-directions x, y are known from US 2018 / 0074303 A1.

[0122] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form a respective illumination channel for illuminating the object field 5. This can, in particular, result in illumination according to the Köhler principle. The far field is divided into a plurality of object fields 5 using the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to them.

[0123] The first facets 21 are each imaged onto the reticle 7 by an associated second facet 23, superimposed on one another, to illuminate the object field 5. The illumination of the object field 5 is, in particular, as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0124] By arranging the second facets 23, the illumination of the entrance pupil of the projection optics 10 can be geometrically defined. By selecting the illumination channels, in particular the subset of the second facets 23 that guide light, the intensity distribution in the entrance pupil of the projection optics 10 can be adjusted. This intensity distribution is also referred to as the illumination setting or illumination pupil fill.

[0125] A likewise preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by redistributing the illumination channels.

[0126] Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optics 10 are described below.

[0127] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0128] The entrance pupil of the projection optics 10 cannot usually be precisely illuminated with the second facet mirror 22. When imaging the projection optics 10, which images the center of the second facet mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found in which the pairwise determined distance of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in spatial space. In particular, this surface exhibits a finite curvature.

[0129] It is possible that the projection optics 10 have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 22 and the reticle 7. With the help of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

[0130] In the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second facet mirror 22 is arranged in a surface conjugate to the entrance pupil of the projection optics 10. The first facet mirror 20 is arranged tilted relative to the object plane 6. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the deflection mirror 19. The first facet mirror 20 is arranged tilted relative to an arrangement plane defined by the second facet mirror 22.

[0131] Fig. Figure 2 shows a cross-sectional view of an optical system 100 according to a first embodiment. The optical system 100 comprises at least one optical element 102. The optical element 102 is, for example, a mirror or a lens. By way of example, Fig. 2, a mirror is shown as the optical element 102. The optical element 102 has an optically active surface 104. In the example of Fig. 2, the optically active surface 104 is a reflective surface. Furthermore, in Fig. 2 a work light 106 (e.g. corresponding to the work light 16 in Fig. 1) is shown, which impinges on the optically active surface 104. As shown, in the case of a mirror as the optical element 102, the working light 106 is reflected by the optically active surface 104.

[0132] The imaging quality of the optical system 100 and the lithography system 1 with the optical system 100 depends to a large extent on the surface quality, surface texture, and chemical purity of the optically active surface 104 of the optical element 102 (and possibly other optical elements of the optical system 100). The surface quality of the optically active surface 104 can degrade during operation of the lithography system 1 due to various processes, e.g., contamination from the ambient atmosphere.

[0133] The following is based on reference to Fig. 3 a method for operating a lithography system 1 ( Fig. 1) with an optical system 100 ( Fig. 2) described.

[0134] In a first step S1 of the method, a plasma 108 ( Fig. 2) in an environment 110 of the optically active surface 104 of the optical element 102. The plasma 108 is provided, for example, by means of a plasma source device 120 with a plasma source 122. The plasma source device 120 is in Fig. 2 is shown purely schematically and any suitable plasma source device or plasma source (e.g. any plasma source device or plasma source described herein) may be used.

[0135] The environment 110 in which the plasma 108 is provided comprises, in particular, the optically active surface 104. The environment 110 in which the plasma 108 is provided is, in particular, a three-dimensional space in which the optically active surface 104 is arranged. Although not shown in the figures, the environment 110 in which the plasma 108 is provided can also accommodate the entire optical element 102.

[0136] The plasma 108 provided in step S1 serves to modify the optically active surface 104. For example, the optically active surface 104 is chemically and / or physically modified using the plasma 108. For example, the optically active surface 104 is cleaned using the plasma 108, e.g., to remove contaminants from the optically active surface 104.

[0137] In a second step S2 of the method, an actual value F IST at least one parameter F of the optically active surface 104 is determined.

[0138] The at least one parameter F of the optically active surface 104 is, for example, an optical parameter, e.g., a reflectivity (in the case of a reflective optically active surface) and / or a transmissivity (in the case of a transmissive optically active surface) of the optically active surface 104. The reflectivity is, for example, a degree of reflection at a specific wavelength and / or in a specific wavelength range, which indicates the mathematical relationship between the reflected and incident intensity of the radiation 106 reflected at the optically active surface 104. Furthermore, the transmissivity is, for example, a degree of transmission at a specific wavelength and / or in a specific wavelength range, which indicates the mathematical relationship between the transmitted and incident intensity of the radiation transmitted through an optically active surface of a transmissive optical element.

[0139] The at least one parameter F of the optically active surface 104 can, for example, also be a surface parameter, e.g., a surface roughness and / or a binding energy of the surface. A surface parameter also includes one or more parameters of a contamination of the optically active surface 104. Contamination is, for example, physical and / or chemical adsorption on the optically active surface 104. The one or more parameters F of a contamination of the optically active surface 104 include, for example, a degree of contamination, a composition of a contamination, and / or a dimension (e.g., layer thickness, covered area) of a contamination of the optically active surface 104.

[0140] The actual value F ISTof the at least one parameter F of the optically active surface 104 can be determined in step S2 by directly analyzing the optically active surface 104. For this purpose, a surface measuring device 112 can be provided, as in Fig. 2. Using the surface measuring device 112, a surface analysis of the optically active surface 104 can be performed. Any suitable surface analysis method can be used for this purpose (e.g., X-ray spectroscopy, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy).

[0141] The actual value F ISTHowever, in step S1, the at least one parameter F of the optically active surface 104 can also be determined indirectly—alternatively or in addition to the direct surface analysis. For example, an optical property T of the optical system 100 as a whole can be recorded. From the recorded optical property T, the actual value F can then be determined (e.g., computer-aided). IST of the at least one parameter F of the optically active surface 104. The optical property T of the optical system 100 as a whole is, for example, an imaging property and / or a so-called transmission of the optical system 100. A transmission of an optical system is understood here to be a quantity that is derived from radiation coupled into the optical system 100 at the beginning of the overall beam path (e.g., the working light 16 reflected by the reticle 7 in Fig. 1, which is coupled into the projection optics 10 as optical system 100) and a radiation coupled out at the end of the overall beam path (e.g. the working light 16 incident on the wafer 13 in Fig. 1, which is coupled out of the projection optics 10 as optical system 100). From the transmission T of the optical system 100, the state (ie actual value F IST ) of the optically active surface 104 of the optical element 102. Even with several optical elements, such as the several mirrors M1 to M6 of the projection optics 10, the state (ie actual value F IST ) of the optically active surface 104 of each individual optical element 102, M1 to M6.

[0142] Another example of an indirect determination of the actual value F ISTof at least one parameter F of the optically active surface 104 is the detection of an instantaneous value P2 IST at least one plasma parameter P2 of the provided plasma 108 (hereinafter “further instantaneous value P2 IST of the at least one further plasma parameter P2"). The at least one further plasma parameter P2 is preferably a composition Z of the plasma 108. From the composition Z of the plasma 108, for example, conclusions can be drawn about particles, atoms and / or molecules that have been released from a material of the optically active surface 104 and transferred into the plasma 108.

[0143] In an optional third step S3 of the method, an instantaneous value P 1 IST of at least one plasma parameter P1 of the provided plasma 108.

[0144] The at least one plasma parameter P1 and the above-described at least one further plasma parameter P2 can be, for example, an electron density D e , an electron temperature T e , an electron energy distribution function V e , a shock frequency F S , a plasma potential U P and / or a composition Z of the plasma 108.

[0145] The instantaneous value P1 IST of the at least one plasma parameter P1 is detected in step S3, for example, using a plasma measuring device 114, as in Fig. 2 is schematically sketched. The plasma measuring device 114 is, for example, configured to measure the instantaneous value P1 IST of the at least one plasma parameter P1 by means of spectroscopy, mass spectroscopy, plasma resonance spectroscopy and / or detecting a plasma characteristic. The plasma measuring device 114 can, for example, be located outside a (in Fig. 2 not shown) vacuum housing (see vacuum housing 316, 416 in Fig. 5, Fig. 6). The plasma measuring device 114 is arranged, for example, in a defined mechanical and / or optical contact with the vacuum housing. The plasma measuring device 114 can, for example, be mounted on an outer housing wall 115 (in Fig. 2 indicated by a dashed line), e.g. in direct physical contact with the outer housing wall 115 of a vacuum housing.

[0146] The additional instantaneous value P2 described above IST of at least one further plasma parameter P2 (see step S2) can be detected using the plasma measuring device 114.

[0147] In a fourth step S4 of the method, the at least one parameter F of the optically active surface 104 is set to a predetermined target value F SOLLIn particular, in step S4, the at least one parameter F of the optically active surface 104 is determined based on the determined actual value F IST and the predetermined target value F SOLL by adjusting at least one plasma parameter P1 of the provided plasma 108.

[0148] In Fig. 4 is a control circuit 200 for controlling the at least one parameter F of the optically active surface 104 of the optical element 102 ( Fig. 2) is shown.

[0149] The optical system 100 ( Fig. 2) and / or the lithography system 1 ( Fig. 1) may in particular comprise a control device 202 for controlling the at least one parameter F of the optically active surface 104, as in Fig. 4. In Fig. 4, the reference symbol r(t) denotes a reference variable of the control loop 200. The reference variable r(t) corresponds to the setpoint value F SOLLof at least one parameter F of the optically active surface 104 of the optical element 102. The target value r(t), F SOLL can be a variable dependent on time t or can be a temporally constant variable. The reference symbol y(t) denotes a controlled variable as a function of time t of the control loop 200. The controlled variable y(t) corresponds to the actual value F determined in step S2. IST of at least one parameter F of the optically active surface 104 of the optical element 102. Furthermore, in Fig. 4 illustrates a disturbance z(t) which leads to a control deviation e(t) of the determined actual value F IST from the predetermined target value F SOLL can lead to.

[0150] The control device 202 or a deviation determination unit 204 ( Fig. 4) is designed to calculate the deviation e(t) of the actual value F IST , y(t) of the at least one parameter F of the optically active surface 104 from the predetermined target value FSOLL , r(t). Furthermore, the control device 202 is configured to determine a manipulated variable u(t) based on the determined deviation e(t). The manipulated variable u(t) is a manipulated variable for adjusting the at least one plasma parameter P1 of the provided plasma 108. The manipulated variable u(t) can be determined by applying a transfer function g1 and / or a model. By applying the transfer function g1 and / or the model, a suitable adaptation of the at least one plasma parameter P1 to a desired at least one plasma parameter P1 SOLL , by which the optically active surface 104 is modified so that at least one parameter F adapts to the desired value F SOLL approaching, can be found more easily.

[0151] There may also be a transfer unit 214 ( Fig. 4) be provided to determine the actual value F IST, y(t) into information y'(t) that can be evaluated by the control device 202, as in Fig. 4. A further transfer function g2 can be applied.

[0152] The reference number 206 in Fig. 4 denotes a controlled system of the control loop 200. The controlled system 206 comprises a sensor 208 for determining the actual value F IST , y(t) of the at least one parameter F of the optically active surface 104 of the optical element 102. This allows an actual state of the optically active surface 104 to be determined. The sensor system 208 is, for example, connected to the surface measuring device 112 ( Fig. 2) and / or the plasma measuring device 114 ( Fig. 2) and / or a measuring device (not shown) for detecting the total transmission T of the optical system 100.

[0153] The control system 206 also includes an actuator 210 for adjusting the at least one plasma parameter P1 of the provided plasma 108. By adjusting the at least one plasma parameter P1 of the provided plasma 108, the optically active surface 104 is specifically modified (e.g., cleaned). The actuator 210 is, for example, controlled by an adjustment unit 121 of a plasma source device 120 ( Fig. 2) is realized. The controlled system 206 ( Fig. 4) also includes the optically active area 212, 104.

[0154] If the optional step S3 has been executed and the instantaneous value P1 IST of the at least one plasma parameter P1 has been detected, then the control of the at least one parameter F of the optically active surface 104 - in addition to the deviation e(t) - can be based on this detected instantaneous value P1 ISTof at least one plasma parameter P1. In particular, the control device 202 can use the detected instantaneous value P1 when determining the manipulated variable u(t) IST of at least one plasma parameter P1, as in Fig. 4 illustrates.

[0155] As in Fig. 2, for example, the surface measuring device 112 or another measuring device transmits a signal A relating to the detected actual value F IST of the at least one parameter F of the optically active surface 104 to the control device 202 (e.g. also via the unit 214 and / or 204, Fig. 4). Furthermore, the control device 202 transmits a control signal B relating to the manipulated variable u(t) to a setting unit 121 of the plasma source device 120.

[0156] If, merely by way of example, the at least one parameter F of the optically active surface 104 is (or comprises) a reflectivity, then a predetermined target value F SOLL for the reflectivity, for example, 70%. If in step S2, e.g., by means of the surface measuring device 112 ( Fig. 2) it is determined that an actual value F IST However, if the reflectivity, e.g. due to contamination z(t) of the optically active surface 104, is only 65%, then the control device 202 or the unit 204 will detect a control deviation e(t) of 5%. Based on this, for example, an electron density D e and / or another plasma parameter P1 of the provided plasma 108 can be specifically changed so that the contamination is reduced and / or removed and thus the actual value F IST the reflectivity to the predetermined target value F SOLL is approximated.

[0157] With this method it is possible to determine the state (FIST ) of the optically active surface 104 and to adapt the modification (e.g., cleaning) of the optically active surface 104 using the plasma 108 accordingly, repeatedly and / or continuously. This makes it possible to better ensure the required surface finish and / or a sufficiently high surface quality of the optically active surface 104.

[0158] For example, steps S1, S2, and S4 (and optionally S3) can be performed during operation and / or exposure of the lithography system 1. This allows undesired changes in the optically active surface 104 to be detected during the operation and / or exposure of the lithography system 1. Thus, such undesired changes in the optically active surface 104 during the operation and / or exposure of the lithography system 1 can be counteracted by appropriately modifying the provided plasma 108.

[0159] In Fig. 5 shows an optical system 300 according to a second embodiment. The illustration in Fig. 5 is a cross-sectional view except for a shown plasma source 322, which is drawn in perspective for illustrative purposes.

[0160] Similar to the optical system 100 in Fig. 2, the optical system 300 comprises at least one optical element 302, e.g., a mirror or a lens. Also in Fig. 5 shows a mirror as an example of an optical element 302. The optical element 302 has an optically active surface 304 onto which a working light 306 impinges. The optically active surface 304 has, similar to the optically active surface 104 in Fig. 2, at least one parameter F whose actual value F IST is determined in step S2 and in step S4 to a predetermined target value F SOLL The reference numeral 308 designates a plasma 308 with plasma parameters P1, P2 provided in an environment 310 of the optically active surface 304. The plasma 308 and the environment 310 are accordingly similar to the Fig. 2 and the surroundings 110. For example, a surface measuring device 312, similar to the surface measuring device 112 in Fig. 2, is provided.

[0161] As in Fig. 5, the surface measuring device 312 or another measuring device transmits a signal A relating to the detected actual value F IST of the at least one parameter F of the optically active surface 304 to the control device 302 (or to the unit 214 and / or 204, Fig. 4). Furthermore, the control device 302 transmits a control signal B relating to the manipulated variable u(t) to a setting device 321 of the plasma source device 320.

[0162] The optical element 302 in Fig. 5 is arranged in a vacuum housing 316 of the optical system 300 and / or the lithography system 1. During operation of the optical system 300 and / or the lithography system 1, an interior space 318 of the vacuum housing 316 is evacuated to a vacuum pressure.

[0163] Furthermore, Fig. 5 shows a plasma source device 320 for generating the plasma 308. The plasma source device 320 has a plasma source 322. By way of example, in Fig. 5 shows a plasma source 322 with a coil 324, in particular an induction coil, for generating an inductively coupled plasma 308. The plasma 308 is provided within the vacuum housing 316. Furthermore, in the embodiment of Fig. 5 the plasma 308 is also generated within the vacuum housing 316. In the example of Fig. 5, the vacuum housing 316 simultaneously forms a plasma chamber 326 of the plasma source device 320, with the coil 324 of the plasma source 322 being arranged externally around the vacuum housing 316. In particular, the coil 324 of the plasma source 322 surrounds the vacuum housing 316. In other words, the vacuum housing 316 is arranged within an internal cavity of the coil 324.

[0164] In Fig. 6 shows an optical system 400 according to a third embodiment. The illustration in Fig. 6 is a cross-sectional view except for a shown plasma source 422, which is drawn in perspective for illustrative purposes.

[0165] In the following, essentially only differences to the second embodiment ( Fig. 5) described.

[0166] Similar to the optical system 300 in Fig. 5, the optical system 400 comprises Fig. 6 at least one optical element 402 with an optically active surface 404. The reference numeral 408 denotes a plasma 408 provided in an environment 410 of the optically active surface 404. The optical element 402 is arranged in a vacuum housing 416. Also in Fig. 6, a plasma source device 420 is shown with a plasma source 422 with an exemplary coil 424 for generating the plasma 408. In contrast to the embodiment of Fig. 5, the plasma 408 in the embodiment in Fig. 6 is generated outside the vacuum housing 416. This means that the plasma source 422 with the plasma chamber 426 is arranged outside the vacuum housing 416. The plasma 408' generated outside the vacuum housing 416 is fed, e.g., via a feed channel 428, into an interior space 418 of the vacuum housing 416 and into the surrounding area 410 of the optically active surface 404.

[0167] Although in Fig. 6 is not shown, a measuring device for recording the actual value F IST similar to Fig. 2 and Fig. 5 (measuring device 112, 312).

[0168] Although in the Fig. 5 and Fig. 6 shows a plasma source 322, 422 with a coil 324, 424 for generating an inductively coupled plasma 308, 408, other types of plasma sources can also be used to generate the respective plasma 308, 408. For example, the respective plasma 308, 408 can also be generated by means of direct current excitation, alternating current excitation, microwaves and / or alternating voltage discharge. Fig. 2 may be generated with any plasma source device 320, 420 or plasma source 322, 422 described herein or any other suitable plasma source device or plasma source.

[0169] For setting the at least one plasma parameter P1 of the provided plasma 108, 308, 408 ( Fig. 2, Fig. 5, Fig. 6) can, for example, be a power L ( Fig. 2) can be set, a local modulation M of the injected power L can be applied and / or one or more bias potentials U B of the plasma source 122, 322, 422. In addition or instead, a pressure P P ( Fig. 2) the provided plasma 108, 308, 408 in the environment 110, 310, 410 of the optically active surface 104, 304, 404 can be set and / or a chamber pressure P K ( Fig. 6) in the plasma chamber 326, 426 of the plasma source device 120, 320, 420. Furthermore, in addition or instead, a composition Z of the provided plasma 108, 308, 408 can be set (e.g., starting from P IST modified).

[0170] In addition, to adjust the at least one plasma parameter P1 of the provided plasma 108, 308, 408 - in addition to or instead of one or more of the measures listed above - one or more process gases 430 can also be supplied into the environment 410 of the optically active surface 408. The one or more process gases 430 comprise, for example, one or more etching gases and / or other gases. Fig. 6 shows a gas supply device 432 with a reservoir 434 and a further supply channel 436. Each plasma source device 120, 320, 420 described herein ( Fig. 2, Fig. 5, Fig. 6) may optionally comprise a gas supply device similar to the gas supply device 432.

[0171] Furthermore, in order to adjust the at least one plasma parameter P1 of the provided plasma 108, 308, 408 - in addition to or instead of one or more of the measures listed above - the plasma 108, 308, 408 in the environment 110, 310, 410 of the optically active surface 104, 304, 404 can also be subjected to an external magnetic field and / or an external electric field E. By way of example, in Fig. 6 shows an electric field E generated by an electric field unit 438 of the plasma source device 420.

[0172] For setting the at least one plasma parameter P1 of the provided plasma 108, 308, 408 based on the control device 202 ( Fig. 4) determined manipulated variable u(t), the control device 202 controls a corresponding actuator 210 (e.g. unit 121, 321) of the plasma source device 120, 320, 420 described above ( Fig. 2, Fig. 5, Fig. 6) accordingly.

[0173] As in connection with Fig. 2, the actual value F IST of the at least one parameter F of the optically active surface 104, 304, 404 in step S1 of the method by analyzing the optically active surface 104, 304, 404 using the surface measuring device 112, 312.

[0174] In the Fig. 2 and Fig. Figure 5 illustrates an in-situ surface analysis of the optically active surface 104, 304. This means that the optically active surface 104, 304 of the optical element 102, 302 is examined in the installed state of the optical element 102, 302 in the optical system 100, 300.

[0175] The surface measuring device 112, 312 is arranged in particular such that a clearly defined optical path exists from the surface measuring device 112, 312 to the optically active surface 104, 304. For example, the surface measuring device 112, 312 is arranged within a vacuum housing 316. An arrangement of the surface measuring device 112, 312 within the vacuum housing 316 enables, in particular, an unobstructed optical path to the optically active surface 104, 304. Alternatively, the surface measuring device 112, 312 can also be arranged outside the vacuum housing 316, and the vacuum housing 316 can have a viewing window (not shown) through which an optical path to the optically active surface 104, 304 is provided.

[0176] Fig. Fig. 7 shows an optical system 500 according to a fourth embodiment in a cross-sectional view along line VII-VII in Fig. 5.

[0177] As in Fig. 7, can be used as an alternative to an in-situ surface analysis O IN also a surface analysis of the optically active surface 504 ex situ O EX This means, for example, that a sample 504" (witness sample) representative of the optically active surface 504 is removed from the location of the optical element 502 in the installed state and examined at a distance therefrom. For example, the optical element 502 is arranged within a vacuum housing 516, and the witness sample 504" is removed from the vacuum housing 516 for examination (e.g., discharged through a lock 538).

[0178] For example, the optical element 502 has a first part 502' with a first section 504' of the optically active surface 504 and a second part 502" with a second section 504" of the optically active surface 504. Furthermore, the second part 502" is detachably attached to the first part 502'. In this example, the second part 502" with the second section 504" of the optically active surface 504 represents the witness sample. In other words, the optical element 502 in this example is not monolithic, but has at least two parts 502', 502" that can be detachably attached to one another.

[0179] For ex situ surface analysis O EX the optically active surface 504 of the optical element 502, the second part 502" with the second section 504" of the optically active surface 504 (ie the witness sample) is moved from the vacuum housing 516 to outside the vacuum housing 516, as in Fig. 7 on the right. Then, the second section 504" of the optically active surface 504 is examined outside the vacuum housing 516 (e.g., with a measuring device 512 similar to the surface measuring device 112, 312).

[0180] Each of the optical systems 100, 300, 400 described herein may also comprise more than one optical element 102, 303, 404. In this case, the method according to Fig. 3 Optionally, the optically active surfaces of several of the optical elements of the optical system can also be modified by means of a respective plasma. For this purpose, steps S1, S2 and S4 (and optionally S3) are carried out for each optically active surface or each optical element of the plurality of optical elements. For example, the control in step S4 is then carried out for each optically active surface or each optical element of the plurality of optical elements based on a separate control loop similar to the control loop 200 in Fig. 2.

[0181] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. LIST OF REFERENCE SYMBOLS 1 projection exposure system 2 Lighting system 3 Light source 4 Lighting optics 5 Object field 6 Object level 7 reticles 8 reticle holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 Wafer relocation drive 16 Illumination radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirrors 20 first facet mirror 21 first facet 22 second facet mirror 23 second facet 100 systems 102 elements 104 area 106 work light 108 Plasma 110 Surroundings 112 Surface measuring device 114 Plasma measuring device 115 Housing wall 120 Plasma source device 121 units 122 Plasma source 200 control loop 202 Control device 204 Deviation Determination Unit 206 Control system 208 Sensor technology 210 Actuators 212 area 214 Transfer Unit 300 system 302 Element 304 Deviation Determination Unit 306 work light 308 Plasma 310 surroundings 312 Surface measuring device 316 vacuum housing 318 Interior 320 Plasma source device 321 units 322 Plasma source 324 coil 326 Plasma Chamber 400 system 402 Element 404 area 408, 408' Plasma 410 surroundings 416 Vacuum Housing 418 Interior 420 Plasma source device 422 Plasma source 424 coil 426 Plasma Chamber 428 feed channel 430 process gases 432 Gas supply device 434 storage containers 436 feed channel 438 electric field unit 500 system 502 Element 502', 502" part 504 area 504', 504" section 512 Surface measuring device 516 vacuum housing 538 Lock A Signal B Signal D e Electron density E electric field e(t) control deviation F Parameter F IST Actual value F SOLL Target value F S Shock frequency g1, g2 transfer function L Performance M Modulation M1-M6 mirrors O EX Surface analysis ex situ O IN In situ surface analysis P p Pressure P k Pressure P1 Plasma parameters P1 IST Instantaneous value P1 SOLL Value P2 plasma parameters P2 IST Instantaneous value r(t) reference variable S1-S4 process steps T Property T e Electron temperature U B Bias potential U p Plasma potential u(t) manipulated variable V e Electron energy distribution function y(t) controlled variable y(t)' controlled variable Z Composition z(t) disturbance variable QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] DE 10 2008 009 600 A1 [0100, 0104] US 2006 / 0132747 A1

[0102] EP 1 614 008 B1

[0102] US 6,573,978

[0102] DE 10 2017 220 586 A1

[0107] US 2018 / 0074303 A1

[0121]

Claims

[1] Method for operating a lithography system (1) comprising an optical system (100) with an optical element (102), comprising the steps: a) providing (S1) a plasma (108) in an environment (110) of an optically active surface (104) of the optical element (102) for modifying the optically active surface (104), b) Determining (S2) an actual value (F IST ) at least one parameter (F) of the optically active surface (104), and c) controlling (S4) the at least one parameter (F) of the optically active surface (104) based on the determined actual value (F IST ) and a predetermined target value (F SOLL ) by adjusting at least one plasma parameter (P1) of the provided plasma (108). [2] Method according to claim 1, comprising: Recording (S3) of an instantaneous value (P1 IST ) of at least one plasma parameter (P1), wherein the control of the at least one parameter (F) of the optically active surface (104) is based on the detected instantaneous value (P1 IST ) of at least one plasma parameter (P1). [3] Method according to claim 1 or 2, wherein steps a), b) and / or c) are carried out during an operation and / or an exposure process of the lithography system (1). [4] Method according to one of claims 1 to 3, wherein the optical element (302, 402) is arranged in a vacuum housing (316, 416) of the lithography system (1), and the plasma (308, 408) is provided within the vacuum housing (316, 416). [5] Method according to claim 4, wherein the plasma (308) is generated within the vacuum housing (316) and / or the vacuum housing (316) forms a plasma chamber (326) of a plasma source device (320) for generating the plasma (108), or the plasma (408, 408') is generated outside the vacuum housing (416) and is fed into an interior space (418) of the vacuum housing (416) and into the environment (410) of the optically active surface (404). [6] Method according to one of claims 1 to 5, wherein modifying the optically active surface (104) comprises cleaning, chemical modification and / or physical modification. [7] Method according to one of claims 1 to 6, wherein the at least one parameter (F) of the optically active surface (104) comprises an optical parameter, a reflectivity, a transmissivity, a surface parameter, a surface roughness, a binding energy, a degree of contamination, a composition of a contamination and / or a dimension of a contamination of the optically active surface (104). [8] Method according to one of claims 1 to 7, wherein the determination of the actual value (F IST) of the at least one parameter (F) of the optically active surface (104): Surface analysis of the optically active surface (104), Detecting an optical property (T) of the optical system (100) which is indicative of the actual value (F IST ) of the at least one parameter (F) of the optically active surface (104), and / or Recording another instantaneous value (P2 IST ) at least one further plasma parameter (P2) of the provided plasma (108), which is indicative of the actual value (F IST ) of the at least one parameter (F) of the optically active surface (104). [9] Method according to one of claims 2 to 8, wherein the instantaneous value (P1 IST ) of at least one plasma parameter (P1) and / or the further instantaneous value (P2 IST) of the at least one further plasma parameter (P2) is detected by means of spectroscopy, mass spectroscopy, plasma resonance spectroscopy and / or detecting a plasma characteristic curve. [10] Method according to one of claims 1 to 9, wherein the at least one plasma parameter (P1) and / or the at least one further plasma parameter (P2) is an electron density (D e ), an electron temperature (T e ), an electron energy distribution function (V e ), a shock frequency (F S ), a plasma potential (U P ) and / or a composition (Z) of the plasma (108). [11] Method according to one of claims 1 to 10, wherein the determination of the actual value (F IST ) of the at least one parameter (F) of the optically active surface (104), a surface analysis of the optically active surface (104) in situ (O IN ) or ex situ (O EX ). [12] Method according to one of claims 1 to 11, wherein a manipulated variable (u) for adjusting the at least one plasma parameter (P1) is based on a deviation (e) of the actual value (y, F IST ) from the target value (r, F SOLL ) of the at least one parameter (F) of the optically active surface (104) is determined by applying a transfer function (g1) and / or a model. [13] Method according to one of claims 1 to 12, wherein adjusting the at least one plasma parameter (P1) comprises: Setting a power (L) coupled into a plasma source (122), Applying a local modulation (M) of the injected power (L), Setting one or more bias potentials (U B ) of the plasma source (122), Applying a magnetic field and / or an electric field (E) to the provided plasma (408) in the vicinity (410) of the optically active surface (404), Setting a pressure (P P ) of the provided plasma (108) in the environment (110) of the optically active surface (104), Setting a composition (Z) of the provided plasma (108), Supplying one or more process gases (430) into the environment (410), and / or Setting a chamber pressure (P K ) in a plasma chamber (426) of the plasma source device (420). [14] Optical system (100) for a lithography system (1), comprising: an optical element (102) with an optically active surface (104), a plasma source device (120) for providing a plasma (108) in an environment (110) of the optically active surface (104) for modifying the optically active surface (104), a measuring device (112) for detecting an actual value (F IST ) at least one parameter (F) of the optically active surface (104), and a control device (202) for controlling the at least one parameter (F) of the optically active surface (104) based on the determined actual value (F IST ) and a predetermined target value (F SOLL ) by controlling the plasma source device (120) to adjust at least one plasma parameter (P1) of the provided plasma (108). [15] Lithography system (1) with an optical system (100) according to claim 14.

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