OPTICAL SYSTEM, LITHOGRAPHING FACILITY AND METHOD FOR ADJUSTING A CONTROL PARAMETER

Abstract

An optical system (200) comprising a force frame (204), a sensor frame (208) which is motion-decoupled and / or vibration-decoupled from the force frame (204), a first optical element (202) which is supported on the force frame (204) and which is position-controllable relative to the sensor frame (208) by means of a first position control (212) in order to follow a movement of the first optical element (202) to a movement of the sensor frame (208), at least a second optical element (203) which is supported on the force frame (204) and which is position-controllable relative to the first optical element (202) by means of a second position control (212) in order to follow a movement of the at least second optical element (203) to a movement of the first optical element (202), wherein a control parameter of the first position control (212), in particular dynamically, as a function of at least one on the optical system (200) is adaptable to the acting disturbance variable (214),in order to reduce a rule error of the second position rule (212).

Description

[0001] The present invention relates to an optical system, a lithography system with such an optical system and a method for adjusting a control parameter of a position control of an optical element of 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, which includes an illumination system and a projection system. The image of a mask (reticule) illuminated by the illumination system is projected by the projection system onto a substrate, such as a silicon wafer, coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0003] Driven by the pursuit of ever smaller structures in the fabrication 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 of this wavelength, such EUV lithography systems must use reflective optics, i.e., mirrors, instead of the refracting optics, i.e., lenses, used previously.

[0004] In EUV lithography, mirrors are used in projection systems that can be actively manipulated in all six degrees of freedom. The manipulators are responsible, among other things, for maintaining the position, orientation, and spacing of the mirrors relative to each other, thus minimizing image errors, especially overlay errors and line of sight (LoS) errors.

[0005] In lithography, multiple masks must be applied sequentially to the same wafer, with each mask containing a pattern for a different layer of the circuitry. An overlay defect means that these layers are not precisely aligned, which can lead to malfunctions in the chip. The causes of overlay defects can vary and include, for example, mechanical vibrations of the equipment, thermal expansion of the wafer, and / or inaccuracies in mask positioning.

[0006] Line-of-sight (LoS) errors are specific to lithographic processes where patterns are exposed onto the wafer by direct line of sight. These errors can occur when certain areas of the wafer are not exposed correctly, for example, because they are blocked by textures or masks. This results in the desired structures not being transferred accurately to the wafer.

[0007] To minimize such errors and external disturbances, high demands are typically placed on the control quality of the mirrors. The control bandwidth (CV) is often used as a measure for this. However, several factors can make increasing the control bandwidth undesirable or even impossible. These can include increased costs for implementing the controlled system (e.g., more complex actuation, greater use of mirror material, etc.). Furthermore, other constraints, such as available installation space or the size and / or geometry of the mirror, can limit the control bandwidth.

[0008] If only a small control bandwidth is available for a mirror, this can result in all other mirrors in the lithography system having to follow the mirror with the small control bandwidth in order to maintain their distances as stable as possible relative to it. The choice of a suitable control method for the mirror with the small control bandwidth therefore has a significant impact on the resulting line-of-sight (LoS) error, as all other mirrors mimic its movement, potentially leading to error propagation.

[0009] If, however, a high control bandwidth is possible for a mirror, this mirror can better compensate for disturbances by precisely following the movement of the sensor frame (SF). Thus, the essential movement of this mirror results from its precise imitation of the movement of the sensor frame (SF).

[0010] If cooling of the mirrors is desired during active operation, the control of the mirrors faces further challenges, since the active cooling of a mirror by a cooling medium causes additional unwanted movements of the mirror, which must be compensated for by the control system.

[0011] Against this background, one object of the present invention is to provide an improved optical system.

[0012] Accordingly, an optical system is proposed. The optical system comprises a force frame, a sensor frame which is motion-decoupled and / or vibration-decoupled from the force frame, a first optical element which is supported on the force frame and which is position-controllable relative to the sensor frame by means of a first position control in order to follow a movement of the first optical element to a movement of the sensor frame, and at least one second optical element which is supported on the force frame and which is position-controllable relative to the first optical element by means of a second position control in order to follow a movement of the at least second optical element to a movement of the first optical element.In this process, a control parameter of the first position control, in particular dynamically, can be adapted depending on at least one disturbance variable acting on the optical system in order to reduce a control error of the second position control.

[0013] By reducing the control error of the second position control element, an error in the optical system can be reduced. This, in turn, reduces the influence of disturbances on the optical system. As a result, image defects, particularly overlay errors and line of sight (LoS) errors, can be minimized. Ultimately, this leads to a reduction in rejects, as wafers can be processed with fewer defects. The optical system in question also reduces consequential errors in the position control of the second optical element. By optimally selecting the first position control element, the hardware requirements can be derived directly from the control parameter. Compared to a non-optimized optical system, this can result in lower requirements and thus lower manufacturing costs. Furthermore, over-engineering can be more effectively avoided.

[0014] It is understood that the optical system can also have more than two optical elements. In that case, it is preferred if the additional optical elements are each positionally controllable relative to the first optical element.

[0015] Dynamically adjustable means that the control parameter is preferably adjustable depending on the type and effect of the disturbance variable during system operation, especially in real time.

[0016] For example, the first optical element follows the movement of the sensor frame in order to preferably maintain a positional deviation relative to the sensor frame at or near zero. In this way, the first optical element preferably always maintains a substantially constant distance from the sensor frame, even if the latter is excited to movement, for example, by external influences such as oscillation. The second optical element, on the other hand, is controlled in its position relative to the first optical element, since the first position control may, for example, have a smaller control bandwidth than the second. Thus, a distance between the first and second optical elements can preferably be kept constant. The second optical element preferably follows the movement of the first optical element if the first position control has a comparatively smaller control bandwidth.

[0017] The control parameter can have a control bandwidth and / or an integrator cutoff frequency. The control bandwidth of the position control preferably refers to a range within which the position control can operate effectively to keep the controlled variable (the signal to be controlled or the output quantity) within a specific target range. The control bandwidth is preferably used in terms of the frequencies that the position control can process. The control bandwidth preferably describes the frequency range in which the position control can effectively respond to changes in the input signal or to disturbances to ensure stable control. The integrator cutoff frequency of the position control is a parameter that refers to the frequency at which the integrator of the position control begins to influence its effect on the overall system.This frequency defines the point at which the integrator significantly alters the behavior of the optical element, particularly with respect to phase shift and gain. A position control integrator is a component that sums the input signal over time. The integrator is used to eliminate steady-state control errors, i.e., deviations that accumulate over time as the system transitions to a steady state. The corner frequency (often also called the cutoff frequency) is the frequency at which the controller's gain drops to a specific value. In the case of an integrator, the corner frequency preferably means that the system experiences strong gain from the integrator for frequencies below this frequency, while the gain decreases for higher frequencies.

[0018] Preferably, the control parameter can be adapted depending on the disturbance variable. Depending on the disturbance variable and its effect, the control parameter can be adapted in various ways.

[0019] The influence of some disturbances (first group) can be reduced, for example, by increasing the control parameter, particularly the control bandwidth, to enable highly dynamic position control. The controllability of the first optical element preferably results from the product of the system sensitivity (i.e., how susceptible the optical system is to the disturbance) and the disturbance excitation caused by the disturbance. For example, the higher the control bandwidth of the first position control, the lower the system sensitivity. This reduces the contribution of the first optical element to the line-of-sight error.

[0020] For other disturbances (second group), the opposite is true. While a higher control bandwidth reduces the control error between the sensor frame and the first optical element, this also means that the first optical element must move at a high frequency if the sensor frame is moving at a high frequency. This, however, increases the control errors in the position control of the second optical element, which attempts to follow the first.

[0021] Therefore, it is preferable to modify the first position control as little as possible for such disturbances. The lower limit of controllability is preferably determined by the degrees of freedom and range of motion of the actuators. Overall, with the control strategy chosen in EUV systems, it is optimal to keep the first optical element as free from forces as possible. This is particularly important at high frequencies, as subsequent optical elements are less able to follow the first one, or may even be unable to do so at all. By reducing the forces on the first optical element, its accelerations are reduced, allowing the other optical elements to follow more effectively. In other words, the accelerations acting on the first optical element can be compared relatively easily, and the control parameter can be selected to reduce them, at least temporarily.

[0022] According to one embodiment, the control parameter of the at least second position control is also adaptable, in particular dynamically, depending on at least one disturbance variable acting on the optical system and / or the control parameter of the first position control, in order to further reduce a control error of the second position control.

[0023] By dynamically adjusting the control parameter of the at least second position control, the resulting errors in the position control of the at least second optical element can be further reduced. This creates an additional degree of freedom in adjusting the controllability.

[0024] According to one embodiment, the control parameter has a control bandwidth. The first position control has a smaller control bandwidth compared to the at least second position control, wherein the control bandwidth of the first position control is limited by a mass of the first optical element and / or an intrinsic dynamic of the first optical element and / or a geometry of the first optical element.

[0025] The controllability of the first position control can be limited, for example, by the mass and / or inherent dynamics of the optical element. For instance, the inertia of a heavy mirror can prevent it from being moved arbitrarily quickly by the position control actuators, thus reducing the control bandwidth. This is particularly problematic because high-frequency movements of the sensor frame, which require fast actuators from the first optical element, cannot be tracked due to the lack of inherent dynamics in the optical element. The first optical element is preferably controlled as a rigid body. With very thin optical elements, sufficiently accurate position control cannot be guaranteed at high frequencies because the optical element no longer behaves rigidly. This limitation is primarily determined by the first natural frequency of the first optical element.

[0026] According to one embodiment, the at least one disturbance variable includes an external excitation of the force frame and / or the sensor frame by a dynamic connection of a cooling device of the optical system and / or a flow-induced vibration of a coolant acting at least on the first optical element and / or the sensor frame for cooling the optical system and / or an acoustic excitation of the coolant acting in the dynamic connection and / or the force frame and / or at least the first optical element and / or the sensor frame and / or a movement of a wafer platform of the optical system transmitted via the force frame to the sensor frame.

[0027] The disturbances can preferably be divided into two groups.

[0028] A first group relates to disturbances that arise primarily due to fluid cooling (e.g., water cooling) of the optical elements. Excitations of the force frame can occur, which are transmitted to the respective optical element via both the actuator and a dynamic connection (e.g., the fluid cooling system). These excitations can be caused, for example, by movement of the wafer stage and / or by fluid cooling of the force frame. Flow-induced excitations can also occur, which are transmitted to the optical element via the dynamic connection. Acoustic excitations from the fluid column of the cooling system can also affect the respective optical element and the dynamic connection.

[0029] A second group relates to disturbances acting on the sensor frame, exciting it to move and thus disrupting its resting position. These can include, for example, excitations originating from movement of the wafer stage and / or fluid cooling of the force frame, transmitted to the sensor frame via a dynamic connection and / or decoupling elements. Excitations related to the cooling of the sensor frame, such as flow-induced vibrations and / or acoustic excitations from the fluid column of the cooling system, can also cause disturbances.

[0030] According to one embodiment, the control parameter of the first position control and / or the control parameter of the at least second position control can be adapted on the basis of a simulation model of the optical system, by which in particular an influence of the at least one disturbance variable on the optical system, especially on the first optical element and / or on the at least second optical element and / or on the sensor frame and / or on the force frame, can be simulated.

[0031] This describes a model-based approach. Disturbances that directly affect the first optical element and disturbances that manifest as movements of the sensor frame are preferably compared in the simulation model as a function of frequency, and an optimal control parameter for the first optical element is preferably selected based on this frequency. This can preferably be done before delivery of the optical system, or at least at intervals during the optical system's operation. The simulation model preferably includes a model of the disturbances and a model of the system behavior with respect to the disturbances. Specific domain knowledge is utilized in the model creation process.

[0032] According to one embodiment, the optical system has a measuring device, wherein the measuring device preferably has force sensors and / or pressure sensors and / or acceleration sensors configured to measure forces and / or pressures and / or accelerations of the first optical element and / or the at least second optical element and / or the sensor frame and / or the force frame.

[0033] In principle, other sensors are also conceivable, so the list should not be considered restrictive. For example, voltage and / or current sensors can also be used. Pressure sensors, for instance, allow pressure measurement in a flowing medium, whereby a resulting force can be calculated using a known flow cross-section.

[0034] According to one embodiment, the control parameter of the first position control and / or the control parameter of the at least second position control can be adapted based on measurement results of the measuring device, by which an influence of the at least one disturbance variable on the optical system, in particular on the first optical element and / or on the at least second optical element and / or on the sensor frame and / or on the force frame, in particular in isolation, can be measured.

[0035] Based on the measurement information provided by the measuring device, the first and / or second position control can be optimized. This allows the respective position control of the optical system to be calibrated, preferably as a function of disturbances. The measurements can be performed, for example, in a dynamic test setup for the optical system. The measurements can also be carried out as acceptance tests. The measuring device preferably allows for the measurement of transfer functions of the optical system. Furthermore, the measuring device preferably allows the effects of the occurring disturbances on the optical system to be considered separately.This preferably allows a direct comparison of the forces, pressures, and / or accelerations occurring within the optical system, thus enabling the optimal adjustment of the control parameter for the first and / or second position control, particularly for a given disturbance condition. Such measurements can also be performed at the optical system's final operating location to account for location-specific disturbances when adjusting the position control using the control parameter. Since some disturbances are system-specific and / or location-specific, the position control can be precisely tailored.

[0036] According to one embodiment, the optical system has a disturbance influence estimator which is configured to statistically and / or analytically determine an influence, in particular a non-measurable influence, of the at least one disturbance on a movement of the first optical element and / or the at least second optical element, and to adjust the first position control and / or the at least second position control on this basis.

[0037] The disturbance influence estimator preferably allows all non-measurable effects of the disturbance on the optical system to be estimated, particularly through time series analysis or similar methods, and incorporated into the optimization of the position control. For example, if the control parameter is set based on measurement results, and it is subsequently observed over time that the controller behavior deviates from the expected behavior, the disturbance influence estimator can estimate this deviation and include it in the adjustment of the control parameter. The disturbance influence estimator can, for example, reduce external forces on the optical elements caused by the at least one disturbance. The sensor frame can also be actively controllable, for example, to virtually increase its mass.The disturbance influence estimator can also be configured to estimate acceleration information from the optical elements and / or the sensor frame without measuring it. This may eliminate the need for a measuring device. Alternatively, the estimates can be used to reduce noise contributions from the measured acceleration information, for example, by performing a comparison. Furthermore, this allows for a simple combination of multiple acceleration sensor readings from the optical elements, the sensor frame, and / or other relevant locations.

[0038] According to one embodiment, the sensor frame has acceleration sensors for measuring acceleration information of the sensor frame and preferably a sensor frame position control for reducing accelerations of the sensor frame.

[0039] With the additional acceleration information from the sensor frame, a reference position for the first optical element can preferably be selected such that it remains largely fixed or motionless in space. This means that the other optical elements preferably follow a low-frequency motion signal, which is easier to implement from a control engineering perspective. For this purpose, the acceleration of the sensor frame is preferably integrated twice to obtain its position. At startup, a zero adjustment is preferably performed using the position of the sensor frame. This zero position is used as a reference for the first optical element. The first optical element attempts to maintain this reference. This allows the first optical element to be controlled with a high control bandwidth, resulting in good noise suppression. Furthermore, the influence of the sensor frame's movement can be reduced.

[0040] According to one embodiment, the acceleration information can be converted into position information by multiple integration and made available to the first position control for adjusting a reference position of the first optical element relative to the sensor frame.

[0041] According to one embodiment, the first optical element has acceleration sensors by which acceleration information of the first optical element can be measured, wherein the acceleration information can be provided to the at least second position control as an input variable, or wherein position information of the first optical element can be converted into acceleration information by multiple derivation, wherein the derived acceleration information can be provided to the at least second position control as an input variable.

[0042] The accelerometers are preferably arranged distributed across the optical element or integrated within it. Preferably, the accelerometers are arranged on the first optical element, which has a lower control bandwidth relative to the at least second optical element. The acceleration information thus measurable or obtained through integration can preferably be used in a feedthrough control structure for improved control of the at least second optical element.

[0043] As an alternative to the acceleration information measured by the accelerometers, the position signal from the first optical element can be derived twice. Low-noise position signals are preferred. The aim is to evaluate the optimal noise requirement for a corresponding system design and to compare the approaches to position and acceleration measurement in order to define an optimal system configuration.

[0044] According to one embodiment, the acceleration information from the sensor frame can be provided as an input variable to the first position control and / or the at least second position control.

[0045] Thus, for example, the first and / or second optical element can be controlled at low frequencies with reference to the acceleration information from the sensor frame. For this purpose, the acceleration information from the sensor frame is provided to the first position control and / or at least the second position control in a feedthrough control structure. This improves the performance of the position control, particularly in the low-frequency range. The acceleration sensors are preferably already present in a known optical system.

[0046] This embodiment describes an addition to the feedback loop of the optical element position control system by means of a feedforward control signal. For this purpose, the sensor frame has accelerometers that measure the accelerations of the sensor frame. Since the sensor frame preferably behaves like a rigid body up to a certain threshold frequency, the accelerometers preferably measure not only the acceleration of the sensor frame itself, but also the accelerations of encoder heads arranged on the sensor frame. The acceleration information is preferably used as feedforward control, preferably combined with a mass matrix of the optical elements to generate force signals, in addition to the encoder signals in the feedback loop of the optical element position control system. Thus, a control error caused by the acceleration of the sensor frame can be compensated for by the software before the position control system "detects" such an error.Thus, a servo error of the optical system can preferably be improved by a predetermined factor in at least one (dominant) spatial direction. The embodiment allows the existing acceleration measurement signal of the sensor frame to be used to improve controllability through a combination of feedback and feedforward control.

[0047] According to one embodiment, the first optical element and / or the at least second optical element has a mirror.

[0048] Furthermore, a lithography system with such an optical system is proposed. The optical system is preferably a projection optic of the projection exposure system. However, the optical system can also be an illumination system. The 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. The projection exposure 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.

[0049] Furthermore, a method for adjusting a control parameter of a first position control of a first optical element of an optical system for a lithography system is proposed. The method comprises the following steps: a) Providing the optical system, comprising a force frame, a sensor frame which is motion-decoupled and / or vibration-decoupled from the force frame, the first optical element which is supported on the force frame and which is position-controllable relative to the sensor frame by means of a first position control in order to follow a movement of the first optical element to a movement of the sensor frame, and at least one second optical element which is supported on the force frame and which is position-controllable relative to the first optical element by means of a second position control in order to follow a movement of the at least second optical element to a movement of the first optical element; and b) in particular dynamic adjustment of the control parameter of the first position control as a function of at least one disturbance variable acting on the optical system in order to reduce a control error of the second position control.

[0050] The term "one" here is not necessarily to be understood as restricting the number to exactly one element. Rather, it can also refer to multiple elements, such as two, three, or more. Similarly, every other counter used here should not be interpreted as restricting the number to the exact number stated. Instead, numerical deviations, both higher and lower, are possible unless otherwise specified.

[0051] The embodiments and features described for the optical system apply accordingly to the proposed method and vice versa.

[0052] Other possible implementations of the invention also include combinations of features or embodiments described previously or subsequently with regard to the exemplary embodiments, even if not explicitly mentioned. In such cases, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

[0053] Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the following description.

[0054] Exemplary embodiments of the invention. The invention will now be explained in more detail with reference to preferred embodiments and the accompanying figures. Fig. Figure 1 shows a schematic meridional section of a projection exposure system for EUV projection lithography; Fig. Figure 2 shows an optical system according to one embodiment; Fig. Figure 3 shows a control loop of a position control of an optical system according to a further embodiment; Fig. 4 shows a control loop of a position control of an optical system according to a further embodiment; Fig. Figure 5 shows a control error (servo error) of a control loop of the second optical element, with and without the provision of acceleration information from a first optical element and with different control parameter settings; and Fig. Figure 6 shows a spectral power density of an accelerometer.

[0055] In the figures, identical or functionally equivalent elements have been labelled with the same reference symbols, unless otherwise indicated. Furthermore, it should be noted that the representations in the figures are not necessarily to scale.

[0056] Fig. Figure 1 shows an embodiment of a projection exposure system 1 (lithography system), in particular an EUV lithography system. One embodiment of the illumination system 2 of the projection exposure system 1 has, in addition to a light or radiation source 3, an illumination optic 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 rest of the illumination system 2. In this case, the illumination system 2 does not include the light source 3.

[0057] A reticule 7 arranged in the object field 5 is exposed. The reticule 7 is held by a reticule holder 8. The reticule holder 8 can be moved, particularly in a scanning direction, via a reticule displacement drive 9.

[0058] In the Fig. 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 scan direction runs in the Fig. 1 along the y-direction y. The z-direction z runs perpendicular to the object plane 6.

[0059] The projection exposure system 1 comprises a projection optic 10. The projection optic 10 serves to image the object field 5 onto an image field 11 in an image plane 12. The image plane 12 is 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.

[0060] A structure on the reticulum 7 is imaged onto a photosensitive layer of a wafer 13 located in the image plane 12 within the image field 11. The wafer 13 is held by a wafer holder 14. The wafer holder 14 can be moved, particularly along the y-direction y, via a wafer transfer drive 15. The movement of the reticulum 7 via the reticulum transfer drive 9 and of the wafer 13 via the wafer transfer drive 15 can be synchronized.

[0061] Light source 3 is an EUV radiation source. Specifically, light source 3 emits EUV radiation 16, which is also referred to as useful radiation, illumination radiation, or illumination light. The useful radiation 16 has a wavelength in the range between 5 nm and 30 nm. 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. Light source 3 can be a free-electron laser (FEL).

[0062] 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 hyperboloid reflective surfaces. The at least one reflective surface of the collector 17 can be illuminated by the illumination radiation 16 at grazing incidence (GI), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 17 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0063] 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.

[0064] The illumination optics 4 comprise a deflecting mirror 19 and, downstream in the beam path, a first faceted mirror 20. The deflecting mirror 19 can be a planar deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 19 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation 16 from stray light of a different wavelength. If the first faceted mirror 20 is arranged in a plane of the illumination optics 4 that is optically conjugate to the object plane 6 as the field plane, it is also referred to as a field faceted mirror. The first faceted mirror 20 comprises a plurality of individual first facets 21, which can also be referred to as field facets. Of these first facets 21, the following are in the Fig. 1 only some examples are shown.

[0065] The first facets 21 can be designed as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or semicircular border contour. The first facets 21 can be designed as planar facets or alternatively as convexly or concavely curved facets.

[0066] As is known, for example, from DE 10 2008 009 600 A1, the first facets 21 can themselves each 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.

[0067] Between the collector 17 and the deflecting mirror 19, the illumination radiation 16 runs horizontally, i.e. along the y-direction y.

[0068] In the beam path of the illumination optics 4, a second faceted mirror 22 is arranged downstream of the first faceted mirror 20. If the second faceted mirror 22 is arranged in a pupil plane of the illumination optics 4, it is also referred to as a pupil faceted mirror. The second faceted 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 faceted mirror 20 and the second faceted 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 6,573,978.

[0069] 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.

[0070] The second facets 23 can also be macroscopic facets, which may, for example, have round, rectangular, or hexagonal edges, or alternatively, facets composed of micromirrors. Reference is also made to DE 10 2008 009 600 A1 in this regard.

[0071] The second facets 23 can have planar or alternatively convex or concave curved reflective surfaces.

[0072] The illumination optics 4 thus form a double-faceted system. This basic principle is also known as a honeycomb condenser (English: Fly's Eye Integrator).

[0073] It can be advantageous not to arrange the second faceted mirror 22 exactly in a plane that is optically conjugate to a pupil plane of the projection optics 10. In particular, the second faceted 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.

[0074] The second faceted mirror 22 images the individual first facets 21 into the object field 5. The second faceted mirror 22 is the last beam-shaping, or indeed the last, mirror for the illumination radiation 16 in the beam path before the object field 5.

[0075] In another embodiment of the illumination optics 4, not shown, a transmission optic can be arranged in the beam path between the second facet mirror 22 and the object field 5, which contributes in particular to imaging the first facets 21 into the object field 5. The transmission optic can have exactly one mirror, or alternatively two or more mirrors, arranged one behind the other in the beam path of the illumination optics 4. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (GI mirrors).

[0076] The lighting optics 4, in the version shown in the Fig. Figure 1 shows exactly three mirrors after the collector 17, namely the deflecting mirror 19, the first faceted mirror 20 and the second faceted mirror 22.

[0077] In a further embodiment of the lighting optics 4, the deflecting mirror 19 can also be omitted, so that the lighting optics 4 after the collector 17 can then have exactly two mirrors, namely the first faceted mirror 20 and the second faceted mirror 22.

[0078] The mapping of the first facets 21 by means of the second facets 23 or with the second facets 23 and a transmission optic into the object plane 6 is regularly only an approximate mapping.

[0079] The projection optics 10 comprise a plurality of mirrors Mi, which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0080] In the Fig. In the example shown, the projection optics 10 comprise six mirrors M1 to M6. Alternatives with four, eight, ten, twelve, or any other number of mirrors Mi are also possible. The projection optics 10 is a doubly obscured optic. The penultimate mirror M5 and the last mirror M6 each have an aperture 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.

[0081] The reflective surfaces of the mirrors Mi can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflective 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.

[0082] 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.

[0083] The projection optics 10 can be anamorphic. In particular, they have different magnifications βx, βy in the x and y directions. The two magnifications βx, βy of the projection optics 10 are preferably (βx, βy) = (+ / - 0.25, + / - 0.125). A positive magnification β indicates a projection without image inversion. A negative magnification β indicates a projection with image inversion.

[0084] The projection optics 10 thus lead to a reduction in the x-direction x, that is, in the direction perpendicular to the scan direction, in a ratio of 4:1.

[0085] The projection optics 10 lead to a reduction of 8:1 in the y-direction y, that is, in the scan direction.

[0086] Other magnification ratios are also possible. Magnification ratios with the same sign and absolute value in the x and y directions (x, y), for example with absolute values ​​of 0.125 or 0.25, are also possible.

[0087] 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, depending on the design of the projection optics 10, different. 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.

[0088] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form an illumination channel for illuminating the object field 5. This can result, in particular, in illumination according to Köhler's principle. The far field is divided into a multitude of object fields 5 by means of the first facets 21. The first facets 21 generate a plurality of images of the intermediate focus on the second facets 23 assigned to each of them.

[0089] The first facets 21 are each superimposed on a corresponding second facet 23 to illuminate the object field 5 on the reticle 7. The illumination of the object field 5 is particularly homogeneous. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0090] The illumination of the entrance pupil of the projection optics 10 can be geometrically defined by arranging the second facets 23. By selecting the illumination channels, in particular the subset of the second facets 23 that carry 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 filling.

[0091] Another preferred pupil uniformity in the area of ​​defined illuminated sections of an illumination pupil of the illumination optics 4 can be achieved by a redistribution of the illumination channels.

[0092] Further aspects and details of the illumination of the object field 5 and, in particular, the entrance pupil of the projection optics 10 are described below.

[0093] The projection optics 10 can, in particular, have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

[0094] The entrance pupil of the projection optics 10 cannot always be illuminated exactly by the second faceted mirror 22. When the projection optics 10 image the center of the second faceted mirror 22 telecentrically onto the wafer 13, the aperture rays often do not intersect at a single point. However, a surface can be found where the pairwise determined separation of the aperture rays is minimized. This surface represents the entrance pupil or a surface conjugate to it in real space. In particular, this surface exhibits a finite curvature.

[0095] The projection optics 10 may 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 faceted mirror 22 and the reticle 7. This optical element can accommodate the different positions of the tangential and sagittal entrance pupils.

[0096] During the Fig. In the arrangement of the components of the illumination optics 4 shown in Figure 1, the second faceted mirror 22 is arranged in a plane conjugate to the entrance pupil of the projection optics 10. The first faceted mirror 20 is arranged tilted relative to the object plane 6. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the deflecting mirror 19. The first faceted mirror 20 is arranged tilted relative to an arrangement plane defined by the second faceted mirror 22.

[0097] Fig. Figure 2 shows an optical system 200 according to an exemplary embodiment. The optical system 200 can, for example, be part of the in Fig. The optical system 200 can, for example, be a projection optical box (POB) of the lithography system 1 shown in Figure 1.

[0098] The optical system 200 comprises a first optical element 202 and a second optical element 203. The first optical element 202 can be a mirror. The second optical element 203 can be a mirror. The first optical element 202 can be one of the mirrors M1 to M6, in particular mirror M4, as shown in Fig. The second optical element 203 can be another of the mirrors M1 to M6, in particular mirror M3, as shown in 1. Fig. 1 is shown.

[0099] The optical system 200 has a force frame 204 for mounting the first optical element 202 and for adjusting the first optical element 202 relative to a sensor frame 208 of the optical system 200 by means of a first actuating device 206. The first optical element 202 is adjustable by an actuating force F of the first actuating device 206. The force frame 204 is further configured for mounting the second optical element 203 and for adjusting the second optical element 203 relative to the first optical element 202 and / or the sensor frame 208 by means of a second actuating device 207. The second optical element 203 is adjustable by an actuating force F of the second actuating device 207. The sensor frame 208 forms a reference structure of the optical system 200.

[0100] The first optical element 202 is supported on the force frame 204 and its position relative to the sensor frame 208 can be controlled by means of a first position control 210 in order to follow a movement of the first optical element 202 to a movement of the sensor frame 208, so that a distance A1 (see Fig. 1) between the first optical element 202 and the sensor frame 208 preferably remains constant.

[0101] The at least second optical element 203 is supported on the force frame 204 and its position relative to the first optical element 202 is controllable by a second position control 212 in order to follow a movement of the at least second optical element 203 to a movement of the first optical element 202, so that a distance A2 (see Fig. 1) preferably remains constant between the first optical element 202 and the second optical element 203.

[0102] In the present case, at least one control parameter of the first position control 210, in particular dynamically, can be adjusted depending on at least one disturbance variable 214 acting on the optical system 200 in order to reduce a control error of the second position control 212. Furthermore, at least one control parameter of the second position control 212, in particular dynamically, can be adjusted depending on at least one disturbance variable 214 acting on the optical system 200 and / or the control parameter of the first position control 210 in order to further reduce a control error of the second position control 212.

[0103] The force frame 204 can preferably be coupled to a support structure 218, for example an interface ring, by means of a decoupling device 216. The support structure can be connected to a reference structure 222 by means of a further decoupling device 220. The sensor frame is preferably decoupled from the force frame 204 by means of an actively controllable decoupling device 224.

[0104] The control parameter preferably has a control bandwidth. The first position control 220 has a smaller control bandwidth compared to the at least second position control 212. The control bandwidth of the first position control 210 is limited, for example, by the mass of the first optical element 202 and / or its inherent dynamics and / or its geometry. The first optical element 202 can, for example, be a very thin floating mirror.

[0105] The at least one disturbance variable 214 includes, for example, an external excitation of the force frame 204 and / or the sensor frame 208 by a dynamic connection of a cooling device of the optical system 200 and / or a flow-induced vibration of a coolant for cooling the optical system 200 acting at least on the first optical element 202 and / or the sensor frame 208 and / or an acoustic excitation of the coolant acting in the dynamic connection and / or the force frame 204 and / or at least the first optical element 202 and / or the sensor frame 208 and / or a movement B of a wafer platform of the optical system 200 transmitted via the force frame 204 to the sensor frame 208 (see Fig. 2) on.

[0106] The control parameter of the first position control 210 and / or the control parameter of the at least second position control 212 is, for example, adaptable on the basis of a simulation model of the optical system 200, by which in particular an influence of the at least one disturbance variable 214 on the optical system 200, in particular on the first optical element 202 and / or on the at least second optical element 203 and / or on the sensor frame 208 and / or on the force frame 204, can be simulated.

[0107] Alternatively or additionally, the optical system 200 comprises a measuring device 226. The measuring device 226 preferably comprises force sensors and / or pressure sensors and / or acceleration sensors 228, which are configured to measure forces and / or pressures and / or accelerations of the first optical element 202 and / or the at least second optical element 203 and / or the sensor frame 208 and / or the force frame 204.

[0108] This allows the control parameter of the first position control 210 and / or the control parameter of the at least second position control 212 to be adapted also on the basis of measurement results of the measuring device 226, by which an influence of the at least one disturbance variable 214 on the optical system 200, in particular on the first optical element 202 and / or on the at least second optical element 203 and / or on the sensor frame 208 and / or on the force frame 204, in particular in isolation, can be measured.

[0109] The optical system 200 can further include a disturbance influence estimator 230, which is designed to statistically and / or analytically determine an influence, in particular a non-measurable influence, of the at least one disturbance 214 on a movement of the first optical element 202 and / or the at least second optical element 203, and to adapt the first position control 210 and / or the at least second position control 212 on this basis.

[0110] Furthermore, the sensor frame 208 also includes acceleration sensors 232 for measuring acceleration information of the sensor frame 208 and preferably a sensor frame position control 234 for reducing accelerations of the sensor frame 208. The acceleration information can be converted into position information by multiple integration and made available to the first position control 210 for adjusting a reference position of the first optical element 202 relative to the sensor frame 208.

[0111] Furthermore, the first optical element 202 also has acceleration sensors 236, through which acceleration information of the first optical element 202 can be measured. The acceleration information can be provided as an input variable to the at least second position control 212. Alternatively, position information of the first optical element 202 can be converted into acceleration information by multiple derivations, whereby the derived acceleration information can be provided as an input variable to the at least second position control 212.

[0112] The acceleration information from sensor frame 208 is available, as shown in Fig. 4 shown, which can be provided as an input variable to the first position control 210 and / or the at least second position control 212.

[0113] Fig. Figure 3 shows a control loop 300 for controlling the position of the first optical element 202 relative to the sensor frame 208 and for controlling the second optical element 203 relative to the first optical element 202 according to a further embodiment. The control loop 300 comprises, on a first control path 302, the first position control 210 for controlling the position of the first optical element 202. The first position control 210 preferably receives as its input a target position PS of the first optical element 202. Furthermore, the actual position PI of the first optical element 202 relative to the sensor frame 208 is measured and fed back to the input in inverted form. The first position control 210 controls such that the target position PS corresponds to the actual position. The first position control 210 has the task of maintaining a constant distance between the first optical element 202 and the sensor frame 208.

[0114] Furthermore, the measured actual position PI is used for the control of the second optical element 203. For this purpose, the actual position PI is processed by a computing unit 304 to calculate the target position PS2 of the second optical element 203. This target position PS2 of the second optical element is then used as an input variable in the feedback control of the second position control 212 of the second optical element 203. Additionally, the actual position PI2 of the second optical element 203 is measured relative to the first optical element 203 and fed back to the input in inverted form. The first position control 210 regulates the position so that the target position PS2 corresponds as closely as possible to the actual position PI2. The second position control 212 is responsible for maintaining a distance between the second optical element 203 and the first optical element 202 as constant as possible.

[0115] Fig. Figure 3 shows a control loop 400 for controlling the position of the first optical element 202 relative to the sensor frame 208 and for controlling the second optical element 203 relative to the first optical element 202 according to a further embodiment. The position-dependent control of the second optical element 203 is based on the actual position PI of the first optical element 202 and is extended by acceleration information BoE of the first optical element 202 and further by the acceleration information BSF of the sensor frame 208. The respective acceleration information BoE and BSF are each converted into forces to the second optical element 203 by means of a mass matrix 402. The resulting forces are fed to the second position control 312 in a feedthrough control. In this way, the position control of the second optical element can be improved.

[0116] Fig. Figure 5 shows a Bode plot. Fig. Figure 5 shows a control error (servo error) of a control loop of the second optical element 203, with provision of acceleration information of the first optical element 202 according to the first curve 500. Fig. Figure 5 further shows a control error (servo error) of a control loop of the second optical element 203 without providing acceleration information from the first optical element 202, as shown by the second curve 502. The servo error is higher in this case. Furthermore, two curves 504 and 506 with different control parameter settings are shown. This feedthrough control, as described in Fig. As shown in Figure 4, improvements can be achieved in the relevant frequency range.

[0117] Fig. Figure 6 shows a Bode plot. Fig.Figure 6 shows the spectral power density (PSD) of an accelerometer. Minimizing noise in accelerometers is desirable, as noise acts as an additional source of interference in the control loop (400), leading to power loss. Analyses have shown that accelerometers with a defined PSD are preferred.

[0118] The optical system can also be used, for example, in a DUV lithography system.

[0119] Although the present invention has been described using exemplary embodiments, it can be modified in many ways. REFERENCE MARK LIST 1 Projection exposure system 2 Lighting system 3 light source 4 Lighting optics 5 object field 6 Object level 7 reticles 8 label holders 9 Reticle displacement drive 10 Projection optics 11 Image field 12 Image plane 13 wafers 14 wafer holders 15 wafer transfer drive 16 Lighting radiation 17 Collector 18 Intermediate focus plane 19 deflecting mirrors 20 first faceted mirror 21 first facet 22 second faceted mirror 23 second facet 200 optical system 202 optical element 203 optical element 204 power frames 206 Actuator 207 Actuator 208 sensor frames 210 Position control 212 Position control 214 Disturbance variable 216 Decoupling device 218 Support structure 220 decoupling device 222 Reference structure 224 Decoupling device 226 Measuring device 228 acceleration sensors 230 Disturbance Impact Estimators 232 acceleration sensors 234 Sensor frame position control 236 acceleration sensors 300 control loop 302 Control section 304 computing unit 400 control loop 402 Mass matrix 500 curve 502 Curve 504 Curve 506 Curve 600 power density spectrum A1 distance A2 distance B Movement BoE acceleration information BSF Acceleration Information M1 mirror M2 mirrors M3 mirror M4 mirrors M5 mirror M6 mirrors PI Actual Position PI2 Actual Position PS Target Position PS2 Target Position QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 009 600 A1 [0066, 0070] US 2006 / 0132747 A1

[0068] EP 1 614 008 B1

[0068] US 6,573,978

[0068] DE 10 2017 220 586 A1

[0073] US 2018 / 0074303 A1

[0087]

Claims

[1] Optical system (200) comprising a force frame (204), a sensor frame (208) which is motion-decoupled and / or vibration-decoupled from the force frame (204), a first optical element (202) which is supported on the force frame (204) and which is position-controllable relative to the sensor frame (208) by means of a first position control (212) in order to follow a movement of the first optical element (202) to a movement of the sensor frame (208), at least a second optical element (203) which is supported on the force frame (204) and which is position-controllable relative to the first optical element (202) by a second position control (212) in order to follow a movement of the at least second optical element (203) to a movement of the first optical element (202), wherein a control parameter of the first position control (212), in particular dynamically, is adaptable depending on at least one disturbance variable (214) acting on the optical system (200) in order to reduce a control error of the second position control (212). [2] Optical system according to claim 1, wherein a control parameter of the at least second position control (212), in particular dynamically, is adaptable depending on at least one disturbance variable (214) acting on the optical system (200) and / or the control parameter of the first position control (212) in order to further reduce a control error of the second position control (212). [3] Optical system according to claim 1 or 2, wherein the control parameter has a control bandwidth, and wherein the first position control (210) has a smaller control bandwidth compared to the at least second position control (212), wherein the control bandwidth of the first position control (212) is limited by a mass of the first optical element (202) and / or an intrinsic dynamic of the first optical element (202) and / or a geometry of the first optical element (202). [4] Optical system according to one of claims 1-3, wherein the at least one disturbance variable (214) comprises an external excitation of the force frame (204) and / or the sensor frame (208) by a dynamic connection of a cooling device of the optical system (200) and / or a flow-induced vibration of a coolant acting on at least the first optical element (202) and / or the sensor frame (208) for cooling the optical system (200) and / or an acoustic excitation of the coolant acting in the dynamic connection and / or the force frame (204) and / or at least the first optical element (202) and / or the sensor frame (208) and / or a movement of a wafer platform of the optical system (200) transmitted via the force frame (204) to the sensor frame (208). [5] Optical system according to one of claims 1-4, wherein the control parameter of the first position control (212) and / or the control parameter of the at least second position control (212) is adaptable on the basis of a simulation model of the optical system (200), by which in particular an influence of the at least one disturbance variable (214) on the optical system (200), in particular on the first optical element (202) and / or on the at least second optical element (203) and / or on the sensor frame (208) and / or on the force frame (204) can be simulated. [6] Optical system according to any one of claims 1-5, wherein the optical system (200) comprises a measuring device (226), wherein the measuring device (226) preferably comprises force sensors and / or pressure sensors and / or acceleration sensors (228) configured to measure forces and / or pressures and / or accelerations of the first optical element (202) and / or the at least second optical element (203) and / or the sensor frame (208) and / or the force frame (204). [7] Optical system according to claim 6, wherein the control parameter of the first position control (212) and / or the control parameter of the at least second position control (212) is adaptable on the basis of measurement results of the measuring device (226), by which an influence of the at least one disturbance variable (214) on the optical system (200), in particular on the first optical element (202) and / or on the at least second optical element (203) and / or on the sensor frame (208) and / or on the force frame (204), in particular in isolation, can be measured. [8] Optical system according to one of claims 1-7, wherein the optical system (200) has a disturbance influence estimator (230) configured to statistically and / or analytically determine an influence, in particular not measurable, of the at least one disturbance (214) on a movement of the first optical element (202) and / or the at least second optical element (203), and to adapt the first position control (210) and / or the at least second position control (212) on the basis thereof. [9] Optical system according to one of claims 1-8, wherein the sensor frame (208) has acceleration sensors (232) for measuring acceleration information of the sensor frame (208) and preferably a sensor frame position control (234) for reducing accelerations of the sensor frame (208). [10] Optical system according to claim 9, wherein the acceleration information can be converted into position information by multiple integration and can be made available to the first position control (212) for adjusting a reference position of the first optical element (202) relative to the sensor frame (208). [11] Optical system according to one of claims 1-10, wherein the first optical element (202) has acceleration sensors (236) by which acceleration information of the first optical element (202) can be measured, wherein the acceleration information of the at least second position control (212) can be provided as an input variable, or wherein position information of the first optical element (202) can be converted into acceleration information by multiple derivation, wherein the derived acceleration information of the at least second position control (212) can be provided as an input variable. [12] Optical system according to one of claims 1-11, wherein the acceleration information of the sensor frame (208) can be provided as an input variable to the first position control (212) and / or the at least second position control (212). [13] Optical system according to one of claims 1-12, wherein the first optical element (202) and / or the second optical element (203) comprises a mirror. [14] Lithography system (1), comprising an optical system (200) according to any one of claims 1-13. [15] Method for adjusting a control parameter of a first position control (212) of a first optical element (202) of an optical system (200) for a lithography system (1), comprising the steps: a) Providing the optical system (200), comprising a force frame (204), a sensor frame (208) which is motion-decoupled and / or vibration-decoupled from the force frame (204), the first optical element (202) which is supported on the force frame (204) and which is position-controllable relative to the sensor frame (208) by means of a first position control (212) in order to follow a movement of the first optical element (202) to a movement of the sensor frame (208), and at least one second optical element (203) which is supported on the force frame (204) and which is position-controllable relative to the first optical element (202) by means of a second position control (212) in order to follow a movement of the at least second optical element (203) to a movement of the first optical element (202); and b) in particular dynamically adjusting the control parameter of the first position control as a function of at least one disturbance variable (214) acting on the optical system (200) in order to reduce a control error of the second position control (212).

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