Vibration-correction unit, method for operating a vibration-correction unit, sensor and lithography apparatus having a sensor

Abstract

The invention relates to a vibration-correction unit (100) for an object (101) in a lithography apparatus (600, 700), having a sensor (102), which is connected to the object (101) and comprises an electromagnetic actuator (103) and an auxiliary mass (104), which is connected to at least one coil (106), protruding into a cavity (105) of the electromagnetic actuator (103), and is designed for linear movement along at least one measuring axis (116), wherein the electromagnetic actuator (103) is configured to generate a magnetic flux density in the region of the at least one coil (106), and having a control unit (107), which is configured to sense a measured variable of the coil (106) and to convert it into an acceleration acting on the auxiliary mass (104) along the measuring axis (116), and also having a compensation unit (108), which is configured to exert on the object (101) a counteracting force directed counter to the acceleration determined. The invention also additionally relates to a method for operating a vibration-correction unit (100), to a sensor and to a lithography apparatus having a sensor.

Description

[0001] Carl Zeiss SMT GmbH

[0002] Vibration correction unit, method for operating a vibration correction unit, sensor and lithography system with a sensor

[0003] The invention relates to a vibration correction unit for a lithography system, in particular for a microlithographic projection exposure system, and to a method for operating a vibration correction unit. Furthermore, the invention relates to a sensor for a lithography system and a lithography system, in particular a projection exposure system or an illumination system, comprising a sensor.

[0004] Projection exposure systems are used to create extremely fine structures, particularly on semiconductor devices or other microstructured components. The operating principle of these systems is based on creating extremely fine structures down to the nanometer range by means of a generally reduced-size image of structures on a mask, a so-called reticle, on an element to be structured, a so-called wafer, which is provided with photosensitive material. The minimum dimensions of the created structures depend directly on the wavelength of the light used. This light is shaped in an illumination optics for optimal illumination of the reticle. Recently, light sources with an emission wavelength in the range of a few nanometers, for example between 1 nm and 120 nm, particularly in the range of 13.5 nm, have been increasingly used. This wavelength range is also referred to as the EUV range.

[0005] In addition to systems operating in the EUV range, the microstructured components are also manufactured using the market-established DUV systems with a wavelength between 100 nm and 300 nm, particularly 193 nm. With the demand for ever smaller structures, the requirements for optical correction in the systems have continued to increase. With each new generation of projection exposure systems in the EUV or DUV range, throughput is increased to improve cost-effectiveness. A variety of sensors are used to increase image positioning accuracy and image quality. The sensors can detect the position of an object, its speed, or even the acceleration acting on the object.These sensors are used, for example, in the illumination device and / or the projection lens of the microlithographic projection exposure system, but can also be used in the measurement of optical elements for a lithography system. Furthermore, acceleration sensors or speed sensors, in particular, can be used for the active damping of a vibration isolation system of a sensor frame having at least one position sensor. Alternatively or additionally, the use of acceleration sensors or speed sensors in the feedforward control for the active damping of vibrations of optical elements and frames, such as sensor frames or force frames, is also possible. The positioning of objects in the lithography system, in particular of optical elements, can in turn be detected using position sensors.It is therefore also possible to reduce line-of-sight errors and overlay errors in the imaging of the lithography system by means of a large number of differently designed sensors, i.e. acceleration sensors and / or speed sensors and / or position sensors.

[0006] To enable the most precise positioning and control of the optical elements, a support structure is provided to which position sensors are attached. The position sensors measure the position of the optical element relative to the support structure. The support structure is mechanically decoupled from the environment to increase the accuracy of the sensors. The decoupling is achieved via a suspension using one or preferably a plurality of springs or air springs, preferably on another support structure or on a bearing. The movement performed by the support structures or an element of the lithography system, i.e. the acceleration to be measured, is often very small. The use of conventional acceleration sensors from the state of the art is only possible to a very limited extent, as they have excessive noise and thus a poor signal-to-noise ratio.

[0007] The German patent application filed under application number 10 2023 204 733.0 shows an acceleration sensor which is designed as a displacement sensor and has an evaluation unit which is configured to convert the detected distance into an acceleration by deriving it twice.

[0008] It is an object of the present invention to provide a vibration correction unit, a method for operating a vibration correction unit, a sensor and a lithography system with a sensor, which reduce the above-mentioned disadvantages.

[0009] The object relating to the vibration correction unit is achieved by a vibration correction unit having the features of claim 1. The object relating to the method for operating the vibration correction unit is achieved by a method having the features of claim 13. The object relating to the sensor is achieved by a sensor having the features of claim 18. The object relating to the lithography system is achieved by a lithography system having the features of claim 21. Advantageous embodiments with expedient further developments are specified in the subclaims.

[0010] The vibration correction unit according to the invention for an object in a lithography system with a sensor connected to the object, which comprises an electromagnetic actuator and an auxiliary mass which is connected to at least one coil projecting into a cavity of the electromagnetic actuator and is designed for a linear movement along at least one measuring axis, wherein the electromagnetic actuator, in particular its coil, is designed to generate a magnetic flux density in the region of the at least one coil, comprises a control unit which is designed to detect a measured variable of the coil and to convert it into an acceleration acting on the auxiliary mass along the measuring axis, and a compensation unit which is designed to exert a counterforce on the object which is opposite to the determined acceleration.This allows the force / acceleration acting on the auxiliary mass and thus on the object, i.e., the vibrations acting on the object, to be measured with an improved signal-to-noise ratio and to compensate for or at least reduce these. The control unit and the correction unit can be combined into a single component or be separate components. For a more precise determination of the acceleration, it is preferred if the auxiliary mass is connected to two spaced-apart coils extending into the cavity of the electromagnetic actuator.

[0011] In order to generate the magnetic flux density in the region of the at least one coil of the electromagnetic actuator, it is advantageous if the electromagnetic actuator has at least one permanent magnet or at least one further actuator coil.

[0012] Furthermore, the invention provides that the auxiliary mass is connected directly or indirectly to the object by means of a spring. The spring enables a linear movement of the auxiliary mass to be defined and enables the movement of the auxiliary mass to be linear in response to the vibrations. This, in turn, makes it possible to increase the sensitivity of the sensor in the frequency range between 1 Hz and 200 Hz. The auxiliary mass can be connected directly to the object or indirectly via, for example, a sensor housing. Furthermore, it is preferred if the spring of the auxiliary mass is selected such that the suspension frequency is between 0.1 Hz and 100 Hz, preferably between 0.1 Hz and 50 Hz, and most preferably between 1 Hz and 30 Hz. The spring can be formed as a leaf spring or as a spiral spring. Alternatively or additionally, it is also possible for the spring to be formed as a permanent magnetic gravitational compensator.In addition, more complex geometries can also be selected for the spring. For example, two magnets with the same magnetic orientation can be arranged at a distance from one another along an axis, which is preferably arranged parallel to the measuring axis. In the central region of this axial magnet arrangement, an outer circumferential magnet ring is provided, which at least partially encloses the inner magnets. The outer magnet ring has a magnetic orientation transverse to the inner magnets, so that the inner pole of the outer magnet is adjacent to a pole of the same name on the first inner magnet and to a pole of the opposite name on the second inner magnet. This results in a magnetic force along the longitudinal axis between the inner and outer magnets, which remains almost constant over a wide displacement range despite the relative displacement of the outer magnet to the inner magnets.This magnetic force can be used as a compensating force, thus decouples the auxiliary mass from the object. Furthermore, it is also possible for the spring to be formed as a combination of a leaf spring or a coil spring with a permanent magnetic gravitational compensator. Alternatively, the spring can also be formed as a plurality of interconnected coil springs and / or leaf springs. It is particularly advantageous if the spring is formed as a gravitational compensator in the direction of gravity.

[0013] Furthermore, it is preferred if the electromagnetic actuator has a housing made of a ferromagnetic material that at least partially encloses the cavity. This enables magnetic shielding of the remaining elements of the sensor from the magnetic field of the permanent magnet. The housing preferably has at least one opening through which the at least one coil protrudes into the cavity.

[0014] Within the scope of the invention, it is advantageous if the measured variable of the coil is a voltage induced in the at least one coil and the control unit is configured to determine a speed of the auxiliary mass based on the detected induced voltage and to convert this into an acceleration using the first derivative. This enables an indirect measurement of the acceleration of the auxiliary mass and thus of the object via the voltage induced in the coil. According to Faraday's law, the voltage induced in the coil is proportional to the speed and the magnetic flux density of the electromagnetic actuator. The movement of the auxiliary mass therefore displaces the coil within the electromagnetic actuator, changing the magnetic field and inducing a voltage in the at least one coil, which in turn is a measure of the speed at which the auxiliary mass is moving.In contrast to an acceleration sensor based on a displacement sensor, in which the measured value is derived twice to determine the acceleration, the present sensor only needs to be derived once, which enables a faster determination of the current acceleration of the object.

[0015] Alternatively, it is also preferred if the measured variable of the coil is a current or an electrical current supplied to the at least one coil of the electromagnetic actuator. The acceleration acting on the auxiliary mass and thus on the object is proportional to the magnetic flux density, the length of the at least one coil, and the supplied current. In one embodiment, an electrical resistor electrically connected to the coil and a detection unit are provided for detecting the electrical current.

[0016] Furthermore, it is advantageous to additionally include a displacement sensor configured to determine the position of the auxiliary mass. The auxiliary sensor is preferably connected to the object either indirectly, for example, via a housing, or directly.

[0017] Furthermore, it is preferred if a control structure is additionally present, wherein the control structure is configured to supply electrical current to the coil of the electromagnetic actuator such that the position of the auxiliary mass detected by the displacement sensor along the measuring axis is constant. By means of the control structure, the position of the auxiliary mass is kept constant, in particular stationary or at least stationary with respect to the at least one measuring axis. The current intensity supplied to the coil is consequently selected by means of the control structure such that the position of the auxiliary mass detected by the displacement sensor is constant. The current intensity supplied to the at least one coil within the framework of the control structure is in turn proportional to the acceleration acting on the object.

[0018] In this context, it is advantageous if the displacement sensor is an optical displacement sensor, for example an optical encoder or an interferometer. The optical encoder preferably comprises a scale, a light source, and a grating. Optical encoders usually comprise a beam splitter that splits the light emitted by the light source into two beams. The two beams strike the diffraction grating at two different positions and are diffracted there. The first beam is then projected via a 4-Ω plate onto a first mirror, and the second beam is projected via another 4-Ω plate onto a second mirror, where they are each reflected back onto the diffraction grating, diffracted there, and directed back onto the beam splitter. The movement of the object and thus a change in the distance between the object and the auxiliary mass changes the interference pattern displayed on the scale.Alternatively, the displacement sensor can also be designed as a capacitive sensor.

[0019] Furthermore, it is preferred if the sensor has a calibration unit for calibrating the sensor. In this case, it is particularly advantageous if the calibration unit is formed as an electromagnetic element which has a calibration coil that is connected to the auxiliary mass and projects into a cavity of the electromagnetic element, as well as a displacement or speed sensor for detecting the movement or speed of the auxiliary mass. The electromagnetic element is preferably formed as a permanent magnet, but can also be formed as a coil. The calibration unit is configured to energize the calibration coil with at least two different predetermined or predeterminable current intensities such that the calibration coil causes a movement of the auxiliary mass.The calibration unit is also preferably configured to detect the movement of the auxiliary mass using the displacement sensor and convert it into a speed, or to detect the speed of the auxiliary mass directly using the speed sensor (e.g., a Doppler interferometer). Furthermore, the calibration unit is configured to additionally detect the voltage induced in the electromagnetic actuator by the movement of the auxiliary mass. A calibration value is thus calculated as the value of the voltage induced in the coil of the electromagnetic actuator at a detected speed. This calibration value, i.e., the induced voltage divided by the speed, corresponds to the magnetic flux density multiplied by the length of the coil of the electromagnetic actuator. This calibration value or values ​​are preferably stored in a memory.For calibration, the induced voltage is preferably recorded at at least two different speeds and stored in a memory. Calibration can of course be performed multiple times at predetermined current intensities (speeds of the auxiliary mass). The voltmeter and / or displacement sensor of the sensor can also be designed as the voltmeter and / or displacement sensor of the calibration unit, i.e. the sensors used for vibration measurement are preferably also used for calibration. The calibration value(s) recorded in this way, i.e. the calibration unit, can be used both in the measuring arrangement in which the measured variable is the induced voltage and in the measuring arrangement in which the measured variable is the supplied current. Furthermore, the recorded or determined (converted) speed can of course be converted into an acceleration by forming the first derivative.

[0020] Alternatively, it is advantageous if the electromagnetic actuator itself is part of the calibration unit. In this case, no additional electromagnetic element is required for calibration. The calibration unit therefore comprises a voltmeter, a displacement or speed sensor, a voltage source, and a control and evaluation unit. The calibration unit is configured to energize the coil of the electromagnetic actuator with various current intensities in such a way that a movement of the auxiliary mass is induced, and (simultaneously) to determine the voltage induced in the electromagnetic actuator by the movement of the auxiliary mass using the voltmeter and the speed detected by the displacement sensor or the speed sensor.The calibration value(s) recorded in this way, i.e. the calibration unit, can be used both in the measuring arrangement in which the measured quantity is the induced voltage and in the measuring arrangement in which the measured quantity is the supplied current.

[0021] In a further alternative embodiment, in which the electromagnetic actuator itself is part of the calibration unit, the coil of the electromagnetic actuator is formed as a bifilar coil, such that a first winding of the coil forms a measuring coil of the sensor for vibration measurement, and a second winding of the coil forms the calibration coil. The calibration unit, in turn, is configured to energize the calibration coil (i.e., the second winding of the coil) with different current intensities, such that a movement of the auxiliary mass is initiated, which is detected by the displacement sensor and converted into a speed, or is detected directly by a speed sensor.In addition, the calibration unit is configured to measure the voltage induced in the measuring coil (i.e., the first winding of the coil) due to the movement of the auxiliary mass using a voltmeter. The measured or determined speeds are assigned to the values ​​of the induced voltage as calibration values ​​and stored in a memory. The calibration value(s) thus recorded, i.e., the calibration unit, can be used both in the measuring setup where the measured variable is the induced voltage and in the measuring setup where the measured variable is the applied current.

[0022] Within the scope of the invention, it is advantageous if the object is formed as a sensor frame, wherein the sensor frame has at least one position sensor for an optical element. An optical element can be suspended from the sensor frame. The sensor frame is preferably decoupled from the environment by means of a vibration isolation system, in particular by means of a spring or an air spring. Since vibration of the sensor frame can still occur despite the vibration isolation system, in particular at the resonance frequency of the vibration isolation system, the acceleration of the sensor frame can be determined by means of the at least one sensor according to the invention comprising the electromagnetic actuator, and a counterforce opposite to the determined acceleration can be introduced by means of an actuator. The actuator can be the electromagnetic actuator of the sensor or another actuator.Alternatively, the vibration isolation system can additionally comprise a viscous damper to dampen unwanted vibrations of the vibration isolation system. The sensor frame is preferably suspended from a force frame. Alternatively or additionally, it is preferred if the object is a force frame for an optical element of the lithography system, in particular the microlithographic projection exposure system, wherein the force frame is connected to the optical element or another optical element, and at least one actuator connected to the optical element is attached to the force frame for adjusting or deforming the optical element.

[0023] Alternatively, the object can also be an optical element of the lithography system, in particular the microlithographic projection exposure system, for example a mirror or a lens.

[0024] In order to be able to determine the acceleration of the object along multiple measurement axes or also with respect to a rotational axis, it is advantageous if at least one second sensor comprising an electromagnetic actuator and an auxiliary mass is present, which is configured to detect the acceleration acting on the object along a second axis deviating from the measurement axis. The axes can be linearly independent, in particular perpendicular. Alternatively, the first sensor and the second sensor can also be arranged parallel to each other at a distance L from each other. This also enables the determination of the acceleration along a rotational axis in addition to a translational degree of freedom.In order to be able to measure the movement of the object in all six rigid-body degrees of freedom, it is again advantageous if a total of six of the previously described sensors are present, each of which is configured to determine a measured value of the coil along different measuring axes. In particular, to determine the six rigid-body degrees of freedom, three arrangements, each with two sensors arranged parallel to each other at a distance L, can be provided. The three arrangements are arranged linearly independently of each other, preferably perpendicularly, on the object. In this case, spring suspension of the respective auxiliary masses can be dispensed with, since the auxiliary mass is held suspended by the electromagnetic actuator.

[0025] Furthermore, it is advantageous if a further acceleration sensor is additionally present, which is formed independently of an electromagnetic actuator, for determining the acceleration of the object along at least one axis. In this context, it is particularly preferred if the acceleration sensor is configured to determine the acceleration in a measurement frequency range that differs from the measurement frequency range of the sensor having the electromagnetic actuator, or to detect the acceleration in a measurement frequency range greater than 100 Hz. The at least one acceleration sensor is preferably designed as a piezoceramic sensor, although other types of acceleration sensors are also possible, in particular sensors designed as MEMS sensors (Micro-Electro-Mechanical sensors), preferably as MOEMS sensors (Micro-Opto-Electro-Mechanical sensors).In particular, it is advantageous if at least one acceleration sensor is present for each of the object's six rigid-body degrees of freedom. The acceleration sensor is preferably also mounted on the object. The object's movement can be detected by both the acceleration sensor and the sensor comprising the electromagnetic actuator.Since the signal-to-noise ratio for the sensor comprising the electromagnetic actuator is better below approximately 100 Hz than the signal-to-noise ratio of the further acceleration sensor and conversely the signal-to-noise ratio for the further acceleration sensor is better above approximately 100 Hz than for the sensor comprising the electromagnetic actuator, it is advantageous if a low-pass filter is present for attenuating the detected signal of the sensor comprising the electromagnetic actuator above a predetermined cut-off frequency or a cut-off frequency range and that a high-pass filter is assigned to the at least one further acceleration sensor for attenuating the detected signal below a predetermined cut-off frequency or a cut-off frequency range, and that the sum of the transfer function of the signals from the further acceleration sensor and the sensor comprising the electromagnetic actuator is approximately 1.The cutoff frequency is preferably approximately in the range 50 Hz to 500 Hz, particularly preferably between 70 Hz and 300 Hz and very particularly preferably between 100 Hz and 200 Hz. In other words, for smaller movements of the object which are (Fourier transformed) smaller than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the sensor comprising the electromagnetic actuator (distances or distances differentiated once or twice) are used, and for larger movements of the object which are greater than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the further acceleration sensor are used.The larger movements detected by the sensor comprising the electromagnetic actuator, which are larger than the cutoff frequency or the cutoff frequency range, are in turn damped by means of the low-pass filter, and the smaller movements detected by the further acceleration sensor, which are smaller than the cutoff frequency or the cutoff frequency range, are preferably damped by means of the high-pass filter.

[0026] The method for operating a vibration correction unit according to the invention comprises at least the following steps: a. Detecting a measured variable of a coil by means of the sensor comprising the electromagnetic actuator and the auxiliary mass, b. Determining the acceleration acting on the object along a measuring axis based on the detected measured variable of the coil, c. Generating a counterforce on the object opposite to the acceleration to compensate for vibrations.

[0027] The advantages, embodiments and previously described configurations of the vibration correction unit are transferable to the method for operating the vibration correction unit.

[0028] Within the scope of the method, it is particularly advantageous if the measured variable of the coil is a voltage induced in the at least one coil of the electromagnetic actuator. According to Faraday's law, the voltage induced in the at least one coil is proportional to the speed and the magnetic flux density B. The movement of the auxiliary mass consequently displaces the coil within the electromagnetic actuator, changing the magnetic field and inducing a voltage in the at least one coil, which in turn is a measure of the speed at which the auxiliary mass is moving.

[0029] In this context, it is advantageous to determine the acceleration by converting the voltage induced in at least one coil into a velocity and then deriving the velocity once with respect to time. Compared to a displacement sensor, the acceleration acting on the object only needs to be derived once, which makes it possible to determine the acceleration more quickly.

[0030] Alternatively, it is preferred if the measured variable of the coil is an electrical current supplied to the at least one coil of the electromagnetic actuator.

[0031] Preferably, the acceleration is determined by detecting the current intensity supplied to the at least one coil which is necessary to keep the position of the auxiliary mass constant, at least along the measuring axis, preferably to keep it stationary.In order to be able to detect movements of the object above 100 Hz with a good signal-to-noise ratio over a wide frequency range, it is preferred if the detected signals - i.e. the movements - which are greater than a predetermined or predeterminable cut-off frequency or a cut-off frequency range of the sensor comprising the electromagnetic actuator are damped by means of a low-pass filter, and if the detected signals - i.e. movements - which are smaller than a predetermined or predeterminable cut-off frequency or cut-off frequency range of the further acceleration sensor (for example a piezoceramic sensor) are damped by means of a high-pass filter, wherein the sum of the transfer function of the signals of the sensor comprising the electromagnetic actuator and the further acceleration sensor is approximately 1.In other words, for smaller movements of the object below the cutoff frequency or below the cutoff frequency range, the signals detected by the sensor comprising the electromagnetic actuator are preferably used, and for larger movements of the object above the cutoff frequency and above the cutoff frequency range, the measurement signals detected by the additional acceleration sensor are used. The larger movements detected by the sensor comprising the electromagnetic actuator, which are greater than the cutoff frequency or the cutoff frequency range, are dampened by means of the low-pass filter, and the smaller movements detected by the additional acceleration sensor, which are smaller than the cutoff frequency or the cutoff frequency range, are preferably dampened by means of a high-pass filter.

[0032] The sensor according to the invention for a lithography system for detecting a measured variable of an object has an electromagnetic actuator and an auxiliary mass, wherein the auxiliary mass is connected to at least one coil projecting into a cavity of the electromagnetic actuator and is configured for a linear movement along at least one measuring axis. The electromagnetic actuator is configured to generate a magnetic flux density in the region of the at least one coil. Furthermore, a control unit is provided which is configured to detect a measured variable of the coil. This enables the measured variable acting on the auxiliary mass and thus on the object to be detected. The sensor is or can be connected to the object directly or indirectly.In one embodiment, the control unit can be configured to convert the measured variable of the coil into an acceleration acting on the auxiliary mass along the measuring axis. This makes it possible to detect the acceleration or force acting on the auxiliary mass and thus on the object.

[0033] In particular, it is advantageous if the sensor is designed as a position sensor and if the control unit is configured to convert the detected measured variable, in particular by integration, into a position of the object.

[0034] Alternatively or additionally, it is advantageous if the sensor is designed as a speed sensor and if the control unit is configured to convert the measured value into a speed of the object.

[0035] For a more precise determination of the measured variable of the object, i.e. an acceleration or a speed or a position, it is preferred if the auxiliary mass is connected to two spaced-apart coils projecting into the cavity of the electromagnetic actuator.

[0036] In order to generate the magnetic flux density in the region of the at least one coil of the electromagnetic actuator, it is advantageous if the electromagnetic actuator has at least one permanent magnet or at least one further actuator coil.

[0037] Furthermore, it is advantageous if the auxiliary mass is connected directly or indirectly to the object by means of a spring. The spring makes it possible to define a linear movement of the auxiliary mass and enables the movement of the auxiliary mass to be linear in response to the vibrations. This, in turn, makes it possible to increase the sensitivity of the sensor in the frequency range between 1 Hz and 200 Hz. The auxiliary mass can be connected directly to the object or indirectly via, for example, a sensor housing. Furthermore, it is preferred if the spring of the auxiliary mass is selected such that the suspension frequency is between 0.1 Hz and 100 Hz, preferably between 0.1 Hz and 50 Hz, and most preferably between 1 Hz and 30 Hz. The spring can be formed as a leaf spring or as a spiral spring. Alternatively or additionally, it is also possible for the spring to be formed as a permanent magnetic gravitational compensator.In addition, more complex geometries can also be selected for the spring. For example, two magnets with the same magnetic orientation can be arranged at a distance from one another along an axis, which is preferably arranged parallel to the measuring axis. In the central region of this axial magnet arrangement, an outer circumferential magnet ring is provided, which at least partially encloses the inner magnets. The outer magnet ring has a magnetic orientation transverse to the inner magnets, so that the inner pole of the outer magnet is adjacent to a pole of the same name on the first inner magnet and to a pole of the opposite name on the second inner magnet. This results in a magnetic force along the longitudinal axis between the inner and outer magnets, which remains almost constant over a wide displacement range despite the relative displacement of the outer magnet to the inner magnets.This magnetic force can be used as a compensating force, thus decouples the auxiliary mass from the object. Furthermore, it is also possible for the spring to be formed as a combination of a leaf spring or a coil spring with a permanent magnetic gravitational compensator. Alternatively, the spring can also be formed as a plurality of interconnected coil springs and / or leaf springs. It is particularly advantageous if the spring is formed as a gravitational compensator in the direction of gravity.

[0038] Furthermore, it is preferred if the electromagnetic actuator has a housing made of a ferromagnetic material that at least partially encloses the cavity. This enables magnetic shielding of the remaining elements of the sensor from the magnetic field of the permanent magnet. The housing preferably has at least one opening through which the at least one coil protrudes into the cavity.

[0039] Within the scope of the invention, it is advantageous, on the one hand, if the measured variable of the coil is a voltage induced in the at least one coil, and the control unit is configured to determine a speed of the auxiliary mass based on the detected induced voltage. According to Faraday's law, the voltage induced in the coil is proportional to the speed and the magnetic flux density of the electromagnetic actuator. The movement of the auxiliary mass consequently displaces the coil within the electromagnetic actuator, changing the magnetic field and inducing a voltage in the at least one coil, which in turn is a measure of the speed at which the auxiliary mass is moving.In contrast to an acceleration sensor based on a displacement sensor, in which the measured value is derived twice to determine the acceleration, with this sensor it only needs to be derived once, which allows for faster determination of the object's current acceleration. If the sensor is designed as a speed sensor, the determined speed can be used. If the sensor is designed as an acceleration sensor, the measured speeds can be converted into an acceleration by taking the first derivative. This enables an indirect measurement of the acceleration of the auxiliary mass and thus of the object via the voltage induced in the coil. Alternatively, the determined acceleration can also be converted back into a speed by integration.If the sensor is designed as a position sensor, the determined accelerations can either be integrated twice and thus converted into a position of the object or the determined velocities of the object can be converted into a position by integration.

[0040] Alternatively, it is also preferred if the measured variable of the coil is a current intensity or an electrical current intensity supplied to the at least one coil of the electromagnetic actuator. The acceleration acting on the auxiliary mass and thus on the object is proportional to the magnetic flux density, the length of the at least one coil, and the supplied current intensity. In one embodiment, an electrical resistor electrically connected to the coil and a detection unit are provided for detecting the electrical current intensity. If the sensor is designed as a speed sensor, the control unit is configured to convert the determined acceleration into a speed of the object by integration. If, on the other hand, the sensor is designed as a position sensor, the control unit is configured to convert the determined acceleration into the position of the object by integration (twice integration).Furthermore, it is advantageous to additionally include a displacement sensor configured to determine the position of the auxiliary mass. The auxiliary sensor is preferably connected to the object either indirectly, for example, via a housing, or directly.

[0041] Furthermore, it is preferred if a control structure is additionally present, wherein the control structure is configured to supply electrical current to the coil of the electromagnetic actuator such that the position of the auxiliary mass detected by the displacement sensor along the measuring axis is constant. By means of the control structure, the position of the auxiliary mass is kept constant, in particular stationary or at least stationary with respect to the at least one measuring axis. The current intensity supplied to the coil is consequently selected by means of the control structure such that the position of the auxiliary mass detected by the displacement sensor is constant. The current intensity supplied to the at least one coil within the framework of the control structure is in turn proportional to the acceleration acting on the object. If the sensor is designed as a speed sensor, the control unit is configured to convert the determined acceleration into a speed of the object by integration.If, on the other hand, the sensor is designed as a position sensor, the control unit is set up to convert the determined acceleration into the position of the object by integrating it (integrating twice).

[0042] In this context, it is advantageous if the displacement sensor is an optical displacement sensor, for example an optical encoder or an interferometer. The optical encoder preferably comprises a scale, a light source, and a grating. Optical encoders usually comprise a beam splitter that splits the light emitted by the light source into two beams. The two beams strike the diffraction grating at two different positions and are diffracted there. The first beam is then projected via a 4-Ω plate onto a first mirror, and the second beam is projected via another 4-Ω plate onto a second mirror, where they are each reflected back onto the diffraction grating, diffracted there, and directed back onto the beam splitter. The movement of the object and thus a change in the distance between the object and the auxiliary mass changes the interference pattern displayed on the scale.Alternatively, the displacement sensor can also be designed as a capacitive sensor.

[0043] Within the scope of the invention, it is advantageous if the object is formed as a sensor frame, wherein the sensor frame has at least one position sensor for an optical element. An optical element can be suspended from the sensor frame. The sensor frame is preferably decoupled from the environment by means of a vibration isolation system, in particular by means of a spring or an air spring. Since vibration of the sensor frame can still occur despite the vibration isolation system, in particular at the resonance frequency of the vibration isolation system, the acceleration of the sensor frame can be determined by means of the at least one sensor according to the invention comprising the electromagnetic actuator, and a counterforce opposite to the determined acceleration can be introduced by means of an actuator. The actuator can be the electromagnetic actuator of the sensor or another actuator.Alternatively, the vibration isolation system can additionally comprise a viscous damper to dampen unwanted vibrations of the vibration isolation system. The sensor frame is preferably suspended from a force frame. Alternatively or additionally, it is preferred if the object is a force frame for an optical element of the lithography system, in particular the microlithographic projection exposure system, wherein the force frame is connected to the optical element or another optical element, and at least one actuator connected to the optical element is attached to the force frame for adjusting or deforming the optical element.

[0044] Alternatively, the object can also be an optical element of the lithography system, in particular the microlithographic projection exposure system, for example a mirror or a lens.

[0045] In order to be able to determine the measurand of the object along multiple measurement axes or also with respect to a rotational axis, it is advantageous if at least one second sensor comprising an electromagnetic actuator and an auxiliary mass is present, which is configured to detect the acceleration acting on the object along a second axis deviating from the measurement axis. The axes can be linearly independent, in particular perpendicular. Alternatively, the first sensor and the second sensor can also be arranged parallel to each other at a distance L from each other. This also enables the measurand of the object along a rotational axis in addition to a translational degree of freedom.In order to be able to measure the measurand, in particular the movement, of the object in all six rigid-body degrees of freedom, it is again advantageous if a total of six of the previously described sensors are present, each of which is configured to determine a measurand of the coil along differing measuring axes. In particular, to determine the six rigid-body degrees of freedom, three arrangements, each with two sensors arranged parallel to one another at a distance L, can be provided, wherein the three arrangements are arranged linearly independently of one another, preferably perpendicularly, on the object. In this case, spring suspension of the respective auxiliary masses can be dispensed with, since the auxiliary mass is held suspended by the electromagnetic actuator.

[0046] Furthermore, it is advantageous if a further acceleration and / or speed and / or position sensor is additionally present, which is formed independently of an electromagnetic actuator, for determining the measured variable of the object, i.e. an acceleration, speed or position of the object along at least one axis. In this context, it is particularly preferred if the further acceleration and / or speed and / or position sensor is configured to determine the acceleration in a measuring frequency range that differs from the measuring frequency range of the sensor having the electromagnetic actuator, or to detect the acceleration in a measuring frequency range greater than 100 Hz. The at least one acceleration sensor is preferably designed as a piezoceramic sensor, although other types of acceleration sensors are also possible, in particular MEMS sensors.Micro-electro-mechanical sensors (MOEMS) are sensors, preferably designed as MOEMS sensors (Micro-opto-electro-mechanical sensors). It is particularly advantageous if at least one additional acceleration and / or speed and / or position sensor is present for each of the object's six rigid-body degrees of freedom. This additional acceleration and / or speed and / or position sensor is preferably also attached to the object. The position or movement of the object can be detected both by the additional acceleration and / or speed and / or position sensor and by the sensor comprising the electromagnetic actuator.

[0047] Since the signal-to-noise ratio for the sensor comprising the electromagnetic actuator is better below approximately 100 Hz than the signal-to-noise ratio of the further acceleration and / or speed and / or position sensor, and conversely, the signal-to-noise ratio for the further acceleration and / or speed and / or position sensor is better above approximately 100 Hz than for the sensor comprising the electromagnetic actuator, it is advantageous if a low-pass filter is present to attenuate the detected signal of the sensor comprising the electromagnetic actuator above a predetermined cut-off frequency or a cut-off frequency range, and that a high-pass filter is assigned to the at least one further acceleration and / or speed and / or position sensor to attenuate the detected signal below a predetermined cut-off frequency or a cut-off frequency range,and that the sum of the transfer function of the signals from the further acceleration and / or speed and / or position sensor and the sensor comprising the electromagnetic actuator is approximately 1. The cutoff frequency is preferably approximately in the range 50 Hz to 500 Hz, particularly preferably between 70 Hz and 300 Hz, and most preferably between 100 Hz and 200 Hz. In other words, for smaller movements of the object, which (Fourier transformed) are smaller than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the sensor comprising the electromagnetic actuator (distances or even distances differentiated once or twice) are used, and for larger movements of the object, which are greater than a cutoff frequency or a cutoff frequency range,The measurement data acquired by the additional acceleration and / or speed and / or position sensor are used. The larger movements detected by the sensor comprising the electromagnetic actuator, which are greater than the cutoff frequency or the cutoff frequency range, are in turn attenuated by the low-pass filter, and the smaller movements detected by the additional acceleration and / or speed and / or position sensor, which are smaller than the cutoff frequency or the cutoff frequency range, are preferably attenuated by the high-pass filter.

[0048] A method for operating a sensor connected to an object preferably comprises at least the following steps: a. detecting a measured variable of the coil by means of the sensor comprising the electromagnetic actuator and the auxiliary mass, and b. determining the acceleration acting on the object along a measuring axis based on the detected measured variable of the coil.

[0049] The advantages, embodiments and previously described configurations of the sensor are transferable to the method for operating the sensor.

[0050] Within the scope of the method, it is particularly advantageous if the measured variable of the coil is a voltage induced in the at least one coil of the electromagnetic actuator. According to Faraday's law, the voltage induced in the at least one coil is proportional to the speed and the magnetic flux density B. The movement of the auxiliary mass consequently displaces the coil within the electromagnetic actuator, changing the magnetic field and inducing a voltage in the at least one coil, which in turn is a measure of the speed at which the auxiliary mass is moving.

[0051] In this context, it is advantageous if the acceleration is determined by converting the voltage induced in at least one coil into a velocity and then subdividing the velocity once with respect to time. Compared to a displacement sensor, the acceleration acting on the object only needs to be derived once, which allows for faster acceleration determination. If the sensor is designed as a position sensor, it is advantageous if the determined acceleration is converted into the object's position by integration.

[0052] Alternatively, it is preferred if the measured variable of the coil is an electrical current supplied to the at least one coil of the electromagnetic actuator. If the sensor is designed as a position sensor, it is advantageous if the determined acceleration is converted into a position of the object by integration. If the sensor is designed as a speed sensor, it is preferred if the determined acceleration is converted into a speed of the object by integration.

[0053] Preferably, the acceleration is determined by detecting the current intensity supplied to the at least one coil, which is necessary to keep the position of the auxiliary mass constant, at least along the measuring axis, preferably stationary. If the sensor is designed as a position sensor, it is advantageous if the determined acceleration is converted into a position of the object by integration. If the sensor is designed as a speed sensor, it is preferred if the determined acceleration is converted into a speed of the object by integration.

[0054] The lithography system according to the invention with a plurality of objects has at least one sensor according to the invention, which is connected or connectable to at least one object. The object is preferably an optical element, for example a mirror or a lens, or a support structure, for example a sensor frame or a force frame. The lithography system can also be an illumination device or a projection lens of a lithography system.

[0055] The advantages and embodiments described for the sensor are also applicable to the lithography system comprising at least one sensor.

[0056] Further features, properties, and advantages of the present invention are described in more detail below using embodiments with reference to the accompanying figures. All features described so far and below are advantageous both individually and in any combination with one another. The embodiments described below are merely examples which, however, do not limit the subject matter of the invention. Figure 1a shows a schematic representation of a microlithographic projection exposure system designed for operation in the EUV range.

[0057] Figure 1 b is a schematic representation of a microlithographic projection exposure system designed for operation in DUV,

[0058] Figure 2 is a schematic representation of a first embodiment of a vibration correction unit,

[0059] Figure 3 is a schematic representation of a second embodiment of a vibration correction unit,

[0060] Figure 4 is a schematic representation of a third embodiment of a vibration correction unit and

[0061] Figure 5 is a schematic representation of a sensor with a calibration unit.

[0062] Figure 1a shows a schematic representation of an exemplary projection exposure system 600 designed for operation in the EUV, in which the present invention can be implemented.

[0063] According to Fig. 1a, an illumination device in a projection exposure system 600 designed for EUV comprises a field facet mirror 603 and a pupil facet mirror 604. The light from a light source unit, which comprises a plasma light source 601 and a collector mirror 602, is directed onto the field facet mirror 603. A first telescopic mirror 605 and a second telescopic mirror 606 are arranged in the light path downstream of the pupil facet mirror 604. A deflection mirror 607 is arranged downstream in the light path, which deflects the radiation incident upon it onto an object field in the object plane of a projection objective comprising six mirrors 651-656. At the location of the object field, a reflective structure-bearing mask 621 is arranged on a mask table 620, which is imaged by means of the projection lens into an image plane in which a substrate 661 coated with a light-sensitive layer (photoresist) is located on a wafer table 660.The vibration correction unit according to the invention can be used in the projection lens or in an illuminator of an EUV projection exposure system.

[0064] The invention can also be used in a DUV system, as shown in Figure 1b. A DUV system is essentially constructed like the EUV system described above in Figure 1a, whereby mirrors and lenses can be used as optical elements in a DUV system, and the light source of a DUV system emits useful radiation in a wavelength range from 100 nm to 300 nm.

[0065] The DUV lithography system 700 shown in Figure 1b has a DUV light source 701. An ArF excimer laser, for example, can be provided as the DUV light source 701, which emits radiation 702 in the DUV range at, for example, 193 nm. A beam shaping and illumination system 703 directs the DUV radiation 702 onto a photomask 704. The photomask 704 is designed as a transmissive optical element and can be arranged outside the systems 703. The photomask 704 has a structure which is imaged in a reduced size onto a wafer 706 or the like by means of the projection system 705. The projection system 705 has a plurality of lenses 707 and / or mirrors 708 for imaging the photomask 704 onto the wafer 706. Individual lenses 707 and / or mirrors 708 of the projection system 705 can be arranged symmetrically to the optical axis 709 of the projection system 705.It should be noted that the number of lenses 707 and mirrors 708 of the DUV lithography system 700 is not limited to the number shown. More or fewer lenses 707 and / or mirrors 708 can also be provided. In particular, the beam shaping and illumination system 703 of the DUV lithography system 700 has a plurality of lenses 707 and / or mirrors 708. Furthermore, the mirrors are usually curved at their front side for beam shaping. An air gap 710 between the last lens 707 and the wafer 706 can be replaced by a liquid medium having a refractive index > 1. The liquid medium can be, for example, ultrapure water. Such a setup is also referred to as immersion lithography and has an increased photolithographic resolution.Figure 2 shows a first embodiment of a vibration correction unit 100 for an object 101 in a lithography system with a sensor 102 connected to the object 101, which has an electromagnetic actuator 103 and an auxiliary mass.

[0066] 104. The auxiliary mass 104 is connected to two spaced-apart coils 106 of the electromagnetic actuator 103, which are inserted into a cavity

[0067] 105 of the electromagnetic actuator 103. The auxiliary mass 104 is configured to perform a linear movement along a measuring axis 116, i.e., to guide the auxiliary mass 104 for a linear movement along the measuring axis 116. For this purpose, the auxiliary mass 104 is suspended from a spring 110, wherein the auxiliary mass 104 is connected directly or indirectly to the object 101 by means of the spring 110. The object 101 can be connected to the sensor at any location.

[0068] 102 and thus connected to the spring 110. The electromagnetic actuator

[0069] 103 is configured to generate a magnetic flux density B in the region of the coils 106. For this purpose, the electromagnetic actuator 103 in this case has a permanent magnet 109, but could alternatively also have another actuator coil not shown in detail. Furthermore, a control unit 107 is provided, which is configured to record a measured variable of the coils 106 relative to an absolute reference system 115. The control unit 107 is also configured to convert the recorded measured variable of the coil into an acceleration acting on the auxiliary mass 104 along the measuring axis 116. In addition, a compensation unit 108 is provided, which is configured to exert a counterforce on the object 101 that is opposite to the determined acceleration. The compensation unit 108 can comprise an actuator and can be attached at any location on the object 101.

[0070] The spring 110 of the auxiliary mass 104 is selected such that the suspension frequency is between 0.1 Hz and 100 Hz, preferably between 0.1 Hz and 50 Hz, and most preferably between 1 Hz and 30 Hz. The spring 110 can be formed as a leaf spring or as a spiral spring. Alternatively or additionally, it is also possible for the spring 110 to be formed as a permanent magnetic gravitational compensator. Furthermore, more complex geometries can also be selected for the spring 110. For example, two magnetically similarly oriented magnets can be arranged at a distance from one another along an axis that is preferably arranged parallel to the measuring axis 116. In the central region of this axial magnet arrangement, an outer circumferential magnet ring is provided, which at least partially encloses the inner magnets.The outer magnet ring has a magnetic orientation transverse to the inner magnets, so that the inner pole of the outer magnet is adjacent to a pole of the same name on the first inner magnet and to a pole of the opposite name on the second inner magnet. This results in a magnetic force along the longitudinal axis between the inner and outer magnets, which remains virtually constant over a wide displacement range despite the relative displacement of the outer magnet to the inner magnets. This magnetic force can be used as a compensating force, thus decouples the auxiliary mass 104 from the object 101. Furthermore, it is also possible for the spring 110 to be formed as a combination of a leaf spring or a coil spring with a permanent magnetic gravitational compensator. Alternatively, the spring 110 can also be formed as a plurality of coil springs and / or leaf springs coupled to one another.In particular, it is advantageous if spring 110 is formed as a gravitational compensator in the direction of gravity.

[0071] Figure 2 shows that the electromagnetic actuator 103 has a housing 111 that at least partially encloses the cavity 105 and is made of a ferromagnetic material. This enables magnetic shielding of the remaining elements of the sensor 102 from the magnetic field of the permanent magnet 109. Furthermore, the housing 111 leads to a concentration of the magnetic flux density in the region of the coil 106. The housing 111 has at least one opening through which the coils 106 protrude into the cavity 105. In this case, the sensor 102 also has a sensor housing 114 that at least partially encloses the sensor 102. The electromagnetic actuator 103 and the spring 110 of the auxiliary mass 104 are attached to the inside of the sensor housing 114. The outside of the sensor housing 114 can in turn be connected to the object 110.

[0072] In the embodiment according to Figure 2, the measured variable of the coil 106 detected by the control unit 107 is a voltage induced in the coils 106. The control unit 107 is also configured to determine a speed of the auxiliary mass 104 based on the detected induced voltage and to convert this into an acceleration using the first derivative. Thus, by measuring the voltage induced in the coils 106, it is possible to indirectly determine the speed and, by forming the first derivative of the speed with respect to time, to determine the acceleration of the auxiliary mass 104. The acceleration of the auxiliary mass 104 is in turn proportional to the force acting on the object 101, so that the compensation unit 108 is configured to introduce a counterforce opposite to the acceleration or force acting on the object 101, for example, by means of a separate actuator.The voltage induced in the coils 106 is proportional to the speed and the magnetic flux density according to Faraday's law. The movement of the auxiliary mass 104 consequently displaces the coils 106 within the cavity 105 of the electromagnetic actuator 103, changing the magnetic field and inducing a voltage in the at least one coil 106, which in turn is a measure of the speed at which the auxiliary mass 104 is moving. This allows the vibrations transmitted to the object to be determined more quickly and with an improved signal-to-noise ratio compared to the prior art.

[0073] If the sensor 102 is formed as a position sensor, the control unit is configured to either integrate the determined speed or to integrate the determined acceleration twice in order to determine the position of the object 101.

[0074] The object 101 can be formed as a sensor frame, wherein the sensor frame has at least one position sensor for an optical element. Additionally, an optical element can be suspended from the sensor frame. The sensor frame is preferably decoupled from the environment by means of a vibration isolation system, in particular by means of a spring or an air spring. Since vibration of the sensor frame can still occur despite the vibration isolation system, in particular at the resonance frequency of the vibration isolation system, the acceleration can be determined by means of the at least one sensor 102 according to the invention, and a counterforce opposite to the determined acceleration can be introduced by means of an actuator. The actuator can be the electromagnetic actuator 103 of the sensor 102 or another actuator.Alternatively, the vibration isolation system can additionally comprise a viscous damper to dampen unwanted vibrations of the vibration isolation system. The sensor frame is preferably suspended from a force frame. Alternatively or additionally, it is preferred if the object 101 is a force frame for an optical element of the lithography system, in particular the microlithographic projection exposure system, wherein the force frame is connected to the optical element and at least one actuator connected to the optical element is attached to the force frame for adjusting or deforming the optical element. Alternatively, the object can also be an optical element of the lithography system, in particular the microlithographic projection exposure system, for example a mirror or a lens.

[0075] Furthermore, an additional acceleration sensor 113 may also be provided, which is formed independently of an electromagnetic actuator 103, for determining the acceleration of the object 101 along at least one axis. This is preferably formed as a piezoceramic sensor, although other types of acceleration sensors are also possible, in particular MEMS sensors (micro-electro-mechanical sensors), preferably MOEMS sensors (micro-opto-electro-mechanical sensors). The movement of the object 101 can be detected both by the additional acceleration sensor 113 and by the sensor 102 comprising the electromagnetic actuator 103.

[0076] Since the signal-to-noise ratio for the sensor 102 comprising the electromagnetic actuator 102 is better below approximately 100 Hz than the signal-to-noise ratio of a piezoceramic sensor, and conversely, the signal-to-noise ratio for the piezoceramic sensor is better above approximately 100 Hz than for the sensor 102 comprising the electromagnetic actuator 103, a low-pass filter is provided to attenuate the detected signal from the sensor 102 comprising the electromagnetic actuator 103 above a predetermined cutoff frequency or a cutoff frequency range. A high-pass filter is assigned to the at least one further acceleration sensor 113 to attenuate the detected signal below a predetermined cutoff frequency or a cutoff frequency range, the sum of the transfer function of the signals from the further acceleration sensor 113 and the sensor 102 comprising the electromagnetic actuator 103 being approximately 1.The cutoff frequency is preferably approximately in the range 50 Hz to 500 Hz, particularly preferably between 70 Hz and 300 Hz and very particularly preferably between 100 Hz and 200 Hz. In other words, for smaller movements of the object which are (Fourier transformed) smaller than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the sensor 102 comprising the electromagnetic actuator 103 (distances or distances differentiated once or twice) are used, and for larger movements of the object 101 which are greater than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the further acceleration sensor 113 are used.The larger movements detected by the sensor 102 comprising the electromagnetic actuator 103, which are greater than the cutoff frequency or the cutoff frequency range, are in turn damped by means of the low-pass filter, and the smaller movements detected by the further acceleration sensor 113, which are smaller than the cutoff frequency or the cutoff frequency range, are preferably damped by means of the high-pass filter.

[0077] The exemplary embodiment according to Figure 3 differs in that the measured variable of the coil 106 is an electrical current supplied to the at least one coil 106 of the electromagnetic actuator 103, and in that a displacement sensor 112 is additionally present, which is configured to determine the position of the auxiliary mass 104. Furthermore, a control structure (not shown in detail) is present, which can also be part of the control unit 107 and is formed, for example, as a microcontroller. This control structure or control loop is configured to supply electrical current to the coils 106 of the electromagnetic actuator 103 such that the position of the auxiliary mass 104 detected by the displacement sensor 112 is constant at least along the measuring axis 116. The control structure keeps the position of the auxiliary mass 104 constant, in particular stationary, or at least constant with respect to the at least one measuring axis 116.By supplying electric current to the coils 106, the magnetic field of the electromagnetic actuator is changed, causing the coils 106 to be displaced in such a way that the movement of the auxiliary mass 104 caused, for example, by vibrations, is compensated by the supplied current. The current supplied to the coils 106 is proportional to the force acting on the auxiliary mass 104 and thus to the acceleration of the auxiliary mass 104, i.e., the object 101.

[0078] If the sensor 102 is formed as a position sensor, the control unit 107 is configured to integrate the determined acceleration twice in order to determine the position of the object 101.

[0079] If, however, the sensor 102 is designed as a speed sensor, the control unit 107 is configured to convert the determined acceleration into a speed of the object 101 by integration.

[0080] The displacement sensor 112 can be formed as an optical displacement sensor, for example, an optical encoder or an interferometer. The optical encoder comprises, in a simple form, a scale and a light source, as well as a grating. Optical encoders typically comprise a beam splitter that splits the light emitted by the light source into two beams. The two beams strike the diffraction grating at two different positions and are diffracted there. The first beam is then projected via a 4-μm plate onto a first mirror, and the second beam is projected via another 4-μm plate onto a second mirror, where they are each reflected back onto the diffraction grating, diffracted there, and directed back onto the beam splitter. The movement of the object 101 and thus a change in the distance of the object 101 from the auxiliary mass changes the interference pattern displayed on the scale.Alternatively, the displacement sensor 112 can also be designed as a capacitive sensor. The compensation unit 108 is presently designed as the electromagnetic actuator 103. However, an additional compensation unit can also be present.

[0081] Figure 4 shows a further exemplary embodiment, which differs in that two sensors 102, 102a, 102b according to the invention are arranged parallel to one another and spaced apart by a length L. This arrangement makes it possible to determine the acceleration of the auxiliary mass 104, i.e., the acceleration acting on the object, along a measuring axis 116 using one of the sensors 102a. The other of the sensors 102b determines the acceleration along an axis 117 deviating from the measuring axis. This makes it possible to determine (calculate) the rotational movement, i.e., the acceleration of the auxiliary mass 104 along a rotational axis. Such an arrangement thus makes it possible to detect the acceleration of the object along two degrees of freedom (one translational degree of freedom and one rotational degree of freedom).Thus, using three such arrangements according to Figure 4, i.e., with a total of six sensors according to the invention, whose measuring axes 116 differ from one another, it is possible to determine the acceleration along all six rigid body degrees of freedom. The axes can be linearly independent, in particular vertical.

[0082] The method for operating a vibration correction unit 100 according to the invention, as shown in Figures 2 to 4, comprises at least the following steps: First, the measured variable of the coil 106 is detected along a measuring axis 116 by means of the at least one sensor 102 comprising the electromagnetic actuator 103 and the auxiliary mass 104. The acceleration acting on the object 101 along the measuring axis 116 is determined based on the detected measured variable of the coil 106, and subsequently, a counterforce directed opposite to the determined acceleration is generated on the object 101 to compensate for or at least reduce vibrations acting on the object 101.

[0083] In order to be able to detect movements of the object above 100 Hz with a good signal-to-noise ratio over a wide frequency range, it is provided within the scope of the method that the detected signals - i.e. the movements - which are greater than a predetermined or predeterminable cut-off frequency or a cut-off frequency range of the displacement sensor 112 are attenuated by means of a low-pass filter, and if the detected signals - i.e. movements - which are smaller than a predetermined or predeterminable cut-off frequency or cut-off frequency range of a further acceleration sensor 113, which is formed independently of an electromagnetic actuator 103, are attenuated by means of a high-pass filter, wherein the sum of the transfer function of the signals of the sensor 102 comprising the electromagnetic actuator 103 and the further acceleration sensor 102 is approximately 1.In other words, for smaller movements of the object 101 below the cutoff frequency or below the cutoff frequency range, the signals detected by the sensor 102 comprising the electromagnetic actuator 103 are preferably used, and for larger movements of the object 101 above the cutoff frequency and above the cutoff frequency range, the measurement signals detected by the additional acceleration sensor 113 are used. The larger movements detected by the sensor 102 comprising the electromagnetic actuator 103, which are greater than the cutoff frequency or the cutoff frequency range, are dampened by means of the low-pass filter, and the smaller movements detected by the additional acceleration sensor 113, which are smaller than the cutoff frequency or the cutoff frequency range, are preferably dampened by means of a high-pass filter.

[0084] In the method for operating the vibration correction unit 100 according to Figure 2 or Figure 4, the measured variable of the coil 106 is a voltage induced in the at least one coil 106 of the electromagnetic actuator 103. According to Faraday's law, the voltage induced in the at least one coil 106 is proportional to the speed and the magnetic flux density B. The movement of the auxiliary mass 104 consequently displaces the at least one coil 106 within the cavity 105 of the electromagnetic actuator 103, changing the magnetic field and inducing a voltage in the at least one coil 106, which in turn is a measure of the speed at which the auxiliary mass 104 is moving. The acceleration is determined by converting the voltage induced in the at least one coil 106 into a speed and then subtracting the speed over time.Compared to an acceleration sensor based on a displacement sensor, the acceleration acting on the object only needs to be derived once, which means that the acceleration can be determined more quickly.

[0085] In the method for operating the vibration correction unit 100 according to Figure 3 or Figure 4, the measured variable of the coil 106 is an electrical current supplied to the at least one coil 106 of the electromagnetic actuator 103. The acceleration is determined by detecting the current that must be supplied to the at least one coil 106 in order to keep the position of the auxiliary mass 104 constant. This current is in turn proportional to the acceleration of the auxiliary mass 104 and thus to the acceleration of the object 101. Figure 5 shows an embodiment of the sensor 102 with a calibration unit 118. The calibration unit 118 is formed as a (further) electromagnetic element 119, which is arranged along the measuring axis 116. In the present case, the electromagnetic actuator 103 and the electromagnetic element 119 are arranged on opposite sides of the auxiliary mass 104.The calibration unit 118 has a calibration coil 120, which is connected to the auxiliary mass 104 and projects into a cavity 121 of the electromagnetic element 119, as well as a displacement or speed sensor 112 for detecting the movement or speed of the auxiliary mass 104. A voltmeter (not shown in detail) is also present, although the voltmeter of the sensor 102 can also be used here. The electromagnetic element 119 is preferably formed as a permanent magnet, but can also be formed as a coil. The calibration unit 118 is configured to energize the calibration coil 120 with at least two different predetermined or predeterminable current intensities, such that the calibration coil 120 causes a movement of the auxiliary mass 104.The calibration unit 120 is also preferably configured to detect the movement of the auxiliary mass 104 using the displacement sensor 112 and convert it into a speed, or to detect the speed of the auxiliary mass directly using the speed sensor (e.g., a Doppler interferometer). Furthermore, the calibration unit 118 is configured to additionally detect the voltage induced in the electromagnetic actuator 103 by the movement of the auxiliary mass 104. The detected values ​​of the voltage induced in the coil of the electromagnetic actuator 103 at at least two different speeds are stored as calibration values, preferably in a memory. This calibration value, i.e., the induced voltage divided by the speed, corresponds to the magnetic flux density multiplied by the length of the coil 106 of the electromagnetic actuator 103.The calibration can, of course, be performed multiple times at specified current intensities (speeds of the auxiliary mass). The calibration value(s) thus acquired, i.e., the calibration unit 118, can be used both with the measuring arrangement 100, in which the measured variable is the induced voltage, and with the measuring arrangement 100, in which the measured variable is the supplied current. Alternatively, and not shown in detail, the electromagnetic actuator 103 itself is part of the calibration unit. Consequently, no additional electromagnetic element is present. The calibration unit 118 then comprises a voltmeter, a displacement or speed sensor 112, a voltage source, and a control and evaluation unit.The calibration unit 118 is configured to energize the coil 106 of the electromagnetic actuator 103 with different current intensities such that a movement of the auxiliary mass 104 is induced, and (simultaneously) to determine the voltage induced in the electromagnetic actuator 103 by the movement of the auxiliary mass 104 by means of the voltmeter and the speed detected by means of the displacement sensor 112 or the speed sensor.

[0086] In a further embodiment not shown in detail, in which the electromagnetic actuator 103 itself is part of the calibration unit 118, the coil 106 of the electromagnetic actuator 103 is formed as a bifilar coil, such that a first winding of the coil forms a measuring coil 106 of the sensor for vibration measurement and a second winding of the coil forms the calibration coil 120. The calibration unit 118 is in turn configured to energize the calibration coil 120 (i.e., the second winding of the coil) with different current intensities, such that a movement of the auxiliary mass 104 is initiated, which movement is detected by the displacement sensor 112 and converted into a speed or is detected directly by a speed sensor.In addition, the calibration unit 118 is configured to detect the voltage induced in the measuring coil 106 (i.e., the first winding of the coil) due to the movement of the auxiliary mass 104 using a voltmeter, and to assign the detected or determined velocities to the values ​​of the induced voltage as calibration values ​​and store them in a memory. Furthermore, the detected or determined (converted) velocity can, of course, be converted into an acceleration by forming the first derivative. LIST OF REFERENCE SYMBOLS

[0087] 100 sensor device

[0088] 101 objects

[0089] 102 Sensor

[0090] 102a first sensor

[0091] 102b second sensor

[0092] 103 electromagnetic actuator

[0093] 104 Auxiliary mass

[0094] 105 Cavity

[0095] 106 coil

[0096] 107 Control Unit

[0097] 108 compensation unit

[0098] 109 Permanent magnet

[0099] 110 spring

[0100] 111 housings

[0101] 112 displacement sensor

[0102] 113 additional acceleration sensor

[0103] 114 Sensor housing

[0104] 115 Reference system

[0105] 116 first measuring axis

[0106] 117 Axis

[0107] 118 Calibration unit

[0108] 119 electromagnetic element (of the calibration unit)

[0109] 120 calibration coil

[0110] 121 Cavity (of the electromagnetic element)

[0111] 600 projection exposure system

[0112] 601 plasma light source

[0113] 602 collector mirror

[0114] 603 field facet mirror

[0115] 604 Pupillary facet mirror

[0116] 605 first telescope mirror

[0117] 606 second telescope mirror

[0118] 607 Deflecting mirror 620 Mask table

[0119] 621 Mask

[0120] 651 Mirror (projection lens)

[0121] 652 mirror (projection lens)

[0122] 653 Mirror (projection lens)

[0123] 654 mirror (projection lens)

[0124] 655 Mirror (projection lens)

[0125] 656 mirrors (projection lens)

[0126] 660 wafer table

[0127] 661 coated substrate

[0128] 700 DUV lithography system

[0129] 701 DUV light source

[0130] 702 DUV radiation / beam path

[0131] 703 Beam Forming and Illumination System (DUV)

[0132] 704 Photomask

[0133] 705 projection system

[0134] 706 wafers

[0135] 707 lens

[0136] 708 mirrors

[0137] 709 optical axis

Claims

CLAIMS 1 . Vibration correction unit (100) for an object (101) in a lithography system, comprising a sensor (102) connected to the object (101), which comprises an electromagnetic actuator (103) and an auxiliary mass (104) which is connected to at least one coil (106) projecting into a cavity (105) of the electromagnetic actuator (103) and is designed for a linear movement along at least one measuring axis (116), wherein the electromagnetic actuator (103) is designed to generate a magnetic flux density in the region of the at least one coil (106), and comprising a control unit (107) which is designed to detect a measured variable of the coil (106) and to convert it into an acceleration acting on the auxiliary mass (104) along the measuring axis (116), as well as a compensation unit (108) which is designed to apply a counterforce to the object which is opposite to the determined acceleration. (101 ), characterized in thatthat the auxiliary mass (104) is connected directly or indirectly to the object (101) by means of a spring (110).

2. Vibration correction unit (100) according to claim 1, characterized in that the auxiliary mass (104) is connected to two spaced-apart coils (106) projecting into the cavity (105) of the electromagnetic actuator (103).

3. Vibration correction unit (100) according to claim 1 or 2, characterized in that the electromagnetic actuator (103) has at least one permanent magnet (109) or a further actuator coil which is designed to generate the magnetic flux density in the region of the at least one coil (106).

4. Vibration correction unit (100) according to one of claims 1 to 3, characterized in that the electromagnetic actuator (103) has a housing (111) which at least partially encloses the cavity (105) and is formed from a ferromagnetic material.

5. Vibration correction unit (100) according to one of claims 1 to 4, characterized in that the measured variable is a voltage induced in the at least one coil (106) and the control unit (107) is configured to determine a speed of the auxiliary mass (104) on the basis of the detected induced voltage and to convert this into an acceleration by means of the first derivative.

6. Vibration correction unit (100) according to one of claims 1 to 4, characterized in that the measured variable is an electrical current supplied to the at least one coil (106) of the electromagnetic actuator (103).

7. Vibration correction unit (100) according to claim 6, characterized in that a displacement sensor (112) is additionally provided, which is configured to determine the position of the auxiliary mass (104).

8. Vibration correction unit (100) according to claim 7, characterized in that a control structure is additionally provided, wherein the control structure is configured to supply electrical current to the coil (106) of the electromagnetic actuator (103) such that the position of the auxiliary mass (104) detected by the displacement sensor (112) along the measuring axis (116) is constant.

9. Vibration correction unit (100) according to claim 7 or 8, characterized in that the displacement sensor (112) is an optical displacement sensor.

10. Vibration correction unit (100) according to one of claims 1 to 9, characterized in that the object (101) is formed as a sensor frame which is suspended from an optical element, wherein the sensor frame has at least one position sensor for an optical element.

11. Vibration correction unit (100) according to one of claims 1 to 10, characterized in that at least one second sensor (102b) comprising an electromagnetic actuator (103) and an auxiliary mass (104) is present, which is configured to detect the acceleration acting on the object (101) along a second axis (117) deviating from the measuring axis (116).

12. Vibration correction unit (100) according to one of claims 1 to 11, characterized in that in addition there is a further acceleration sensor (113) which is formed freely from an electromagnetic actuator (103) for detecting the acceleration of the object (101) along at least one axis.

13. A method for operating a vibration correction unit (100) for a lithography system (600, 700) according to one of claims 1 to 12, comprising the following steps: a. detecting a measured variable of the coil (106) by means of the at least one sensor (103) comprising the electromagnetic actuator (103) and the auxiliary mass (105) along a measuring axis (116), b. determining the acceleration acting on the object (101) along the measuring axis (116) based on the detected measured variable of the coil (106), and c. generating a counterforce on the object (101) opposite to the acceleration.

14. The method according to claim 13, characterized in that the measured variable is a voltage induced in the at least one coil (106) of the electromagnetic actuator (103).

15. The method according to claim 14, characterized in that the acceleration is determined by converting the voltage induced in the at least one coil (106) into a speed and deriving the speed once with respect to time.

16. The method according to claim 15, characterized in that the measured variable is an electrical current supplied to the at least one coil (106) of the electromagnetic actuator (103).

17. The method according to claim 16, characterized in that the acceleration is determined by detecting the current intensity supplied to the at least one coil (106) which is necessary to keep the position of the auxiliary mass (104) constant.

18. Sensor (102) for a lithography system (600, 700) for detecting a measured variable of an object (101), with an electromagnetic actuator (103) and an auxiliary mass (104) which is connected to at least one coil (106) projecting into a cavity (105) of the electromagnetic actuator (103) and is designed for a linear movement along at least one measuring axis (116), wherein the electromagnetic actuator (103) is designed to generate a magnetic flux density in the region of the at least one coil (106), and with a control unit (107) which is designed to detect a measured variable of the coil (106).

19. Sensor (102) according to claim 18, characterized in that the sensor (102) is formed as a position sensor, and that the control unit (107) is configured to convert the determined measured variable into a position.

20. Sensor according to (102) claim 18, characterized in that the sensor (102) is formed as a speed sensor, and that the control unit (107) is arranged to convert the measured variable into a speed.

21. Lithography system (600, 700) with a plurality of objects (101) and with at least one sensor (102) according to one of claims 19 to 21, which is connected or connectable to the at least one object (101).

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