Sensor device for a microlithography projection exposure system, and method for operating a sensor device

Abstract

The invention relates to a sensor device (100) for a microlithography projection exposure system (600, 700), comprising a measurement object (101), at least one sensor (102) which is paired with the measurement object, and an analysis unit. The sensor (102) is produced in the form of a distance sensor (103), wherein an auxiliary mass (105) which is suspended on the measurement object (101) by means of an elastic element (104) is provided as a reference for the sensor (102). The sensor (102) is designed to detect the distance between the auxiliary mass (105) and the measurement object (101) along a first measuring axis. The invention additionally relates to a method for operating a sensor device (100).

Description

[0001] Sensor device for a microlithographic projection exposure apparatus and method for operating a sensor device

[0002] This application claims priority from German patent application 10 2023 204 733.0 filed on May 22, 2023. The entire disclosure of this patent application is incorporated by reference into this application.

[0003] The invention relates to a sensor device for a microlithographic projection exposure apparatus according to the features of claim 1.

[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, particularly acceleration sensors, are used to increase image positioning accuracy and image quality. These are used, for example, in the illumination device and / or the projection lens of the microlithographic projection exposure system. In particular, such sensors are used for the active damping of a vibration isolation system of a sensor frame having at least one position sensor.Alternatively or additionally, acceleration sensors can be used in the feedforward control to actively dampen vibrations of optical elements and frames, such as sensor frames or force frames. Acceleration sensors can also be used to support the position control of optical elements, especially mirrors. Furthermore, accelerometers can be used to reduce line-of-sight errors and thus overlay errors.

[0006] In order to enable the most precise positioning and control of the optical elements, a sensor frame is provided to which position sensors are attached. The position sensors measure the position of the optical element relative to the sensor frame. The sensor frame is mechanically decoupled from the environment by means of a vibration isolation system in order to increase the accuracy of the sensors. The vibration isolation system decouples the sensor frame from external vibrations, such as floor vibrations, but also internal vibrations that are generated, for example, by the movements of the wafer stage or the reticle stage. The decoupling is achieved via a suspension using one or preferably a plurality of springs or air springs, preferably on a force frame coupled to the optical element or on a bearing.To enable active damping of the vibration isolation system, especially at its resonant frequency, acceleration sensors are used to measure the acceleration of the sensor frame. The movement of the sensor frame or an optical element, i.e., the acceleration to be measured, is often very small, typically in the picometer range or mm / s. 2 The use of conventional acceleration sensors from the prior art, such as piezoceramic sensors, is only possible to a very limited extent in this frequency range of 1 Hz to 100 Hz, as they exhibit excessive noise and thus a poor signal-to-noise ratio. Therefore, the object of the present invention is to provide a sensor device and a method for operating a sensor device that exhibit an improved signal-to-noise ratio even at low frequencies.

[0007] The object relating to the sensor device is achieved by a sensor device having the features of claim 1. The object relating to the method for operating the sensor device is achieved by a method having the features of claim 13. Advantageous embodiments with expedient further developments are specified in the subclaims.

[0008] The sensor device according to the invention is characterized in that the at least one sensor is designed as a displacement sensor, that an auxiliary mass suspended from the measurement object by means of a resilient element is provided as a reference for the sensor, and that the sensor is configured to repeatedly detect the distance between the auxiliary mass and the measurement object along a first measurement axis, i.e., the position of the measurement object relative to the auxiliary mass. The resilient element mechanically decouples the auxiliary mass from the measurement object and serves as a motionless reference for the sensor for measuring the distance or position of the measurement object relative to the auxiliary mass. The resilient element preferably acts parallel to the first measurement axis.The use of a displacement sensor instead of an acceleration sensor leads to an improved signal-to-noise ratio and thus to more precise position detection at a lower measurement frequency range, i.e. in the range between 1 Hz and 100 Hz.

[0009] According to the invention, the evaluation unit is configured to numerically calculate the first derivative and / or the second derivative of the distances detected by the displacement sensor. It is particularly advantageous if the evaluation unit is configured to forward the speed or acceleration values ​​thus generated to a control unit, which is configured to initiate further measures. Preferably, the control unit can initiate actuators to change the position or attitude of the measurement object, even periodically. The evaluation unit can itself be part of a control unit, in particular a microcontroller, or actuators can initiate counterforces proportional to the determined speed signal to the movements detected by the displacement sensor in order to dampen the measurement object or to reduce or eliminate the influence of disturbances.

[0010] It is particularly preferred if the displacement sensor is designed as an optical encoder. The optical encoder preferably comprises a scale attached to the auxiliary mass and a light source, as well as a grating attached to the side of the measurement object opposite the scale. 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-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 measurement object and thus a change in the distance of the measurement object from the auxiliary mass changes the interference pattern displayed on the scale. Alternatively, the displacement sensor can also be designed as a capacitive sensor, with a first electrode attached to the auxiliary mass and the other electrode attached to the side of the measurement object opposite the first electrode. Furthermore, in another alternative embodiment, it is advantageous if the displacement sensor is designed as an interferometer.

[0011] In order to decouple the auxiliary mass from the measuring object, it is preferred if the resilient element 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.

[0012] In order to be able to measure the movement of the measurement object in all six rigid body degrees of freedom, it is advantageous if a second sensor formed as a displacement sensor is present, which is configured to detect the distance between the measurement object and the auxiliary mass along a second measuring axis arranged linearly independently, in particular perpendicular or approximately perpendicular to the first measuring axis, and / or that a third sensor formed as a displacement sensor is present, which is configured to detect the distance between the measurement object and the auxiliary mass along a third measuring axis arranged linearly independently, in particular perpendicular or approximately perpendicular to the first measuring axis and the second measuring axis.In this context, it is advantageous to have an additional spring element on the second measuring axis or parallel to the second measuring axis, and an additional spring element on the third measuring axis or parallel to the third measuring axis, on which the auxiliary mass is suspended relative to the measuring object. This enables mechanical decoupling of the auxiliary mass from the measuring object.

[0013] The resilient element can preferably be formed as a leaf spring or as a spiral spring. However, more complex geometries of the resilient element are also possible, with the resilient element being designed in such a way that a predetermined stiffness is specifically realized in the measuring axes and the other axes. Alternatively or additionally, it is also possible for the resilient element to be formed as a permanent-magnet gravitational compensator. 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. 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 from the measurement object. Furthermore, it is also possible for the resilient element to be formed as a combination of a leaf spring or a coil spring with a permanent magnetic gravitational compensator. Alternatively, the resilient element can also be formed as a plurality of coil springs and / or leaf springs coupled to one another.In particular, it is advantageous if the resilient element is formed as a gravitational compensator in the direction of gravity, while the resilient elements parallel to the other measuring axes are formed as springs.

[0014] Furthermore, it is particularly preferred if, in addition to the at least one displacement sensor, at least one acceleration sensor is present for detecting the acceleration of the measurement object along a first measurement axis. 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 three measurement axes, i.e., for the total of three translational degrees of freedom of the measurement object. The acceleration sensor is preferably also attached to the measurement object. The movement of the measurement object can be detected by both the acceleration sensor and the displacement sensor.

[0015] Since the signal-to-noise ratio for the displacement sensor below approximately 100 Hz is better than the signal-to-noise ratio of an acceleration sensor and conversely the signal-to-noise ratio for the acceleration sensor above approximately 100 Hz is better than for a displacement sensor, it is advantageous if a low-pass filter is assigned to the at least one displacement sensor for attenuating the detected signal of the displacement sensor 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 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 acceleration sensor and the displacement sensor is approximately 1. The cut-off 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 measurement object that (Fourier-transformed) are smaller than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the displacement sensor (distances or distances differentiated once or twice) are preferably used. For larger movements of the measurement object that are greater than a cutoff frequency or a cutoff frequency range, the measurement data recorded by the acceleration sensor is used. The larger movements recorded by the displacement sensor that are greater than the cutoff frequency or the cutoff frequency range are damped using the low-pass filter, and the smaller movements recorded by the acceleration sensor that are smaller than the cutoff frequency or the cutoff frequency range are preferably damped using the high-pass filter.

[0016] Within the scope of the invention, it is advantageous if the measurement object is an optical element of the microlithographic projection exposure system, for example a mirror or a lens.

[0017] Alternatively or additionally, it is preferred if the measurement object is formed as a sensor frame, wherein the sensor frame has at least one position sensor for the optical element. 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 distances of the sensor frame along a measuring axis with respect to the auxiliary mass can be determined repeatedly or continuously by means of at least one displacement sensor, and the first derivative over time of the distance function determined in this way can be numerically calculated by means of the evaluation unit.The speed of the sensor frame determined in this way can be forwarded to a control unit, and actuators can be caused to initiate a counterforce directed opposite to the determined speed. Furthermore, it is also possible for the evaluation unit to numerically calculate the second derivative over time of the measured distances. The acceleration of the sensor frame determined in this way can be forwarded to a control unit, and actuators can be caused to initiate a counterforce directed opposite to the determined accelerations. Alternatively, the vibration isolation system can additionally have a viscous damper to dampen unwanted vibrations of the vibration isolation system. The sensor frame is preferably suspended from a force frame. Furthermore, it is also possible for the evaluation unit to numerically calculate the second derivative over time of the measured distances.Alternatively or additionally, it is preferred if the measurement object is a force frame for an optical element of 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.

[0018] The invention further relates to a method for operating a previously described sensor device for a microlithographic process, comprising the following steps: a. Multiple detection of the distance between the measurement object and the auxiliary mass along a first measurement axis by means of the at least one displacement sensor, and b. Forwarding the distances detected by the sensor to an evaluation unit.

[0019] The advantages and embodiments described in connection with the sensor device are also applicable to the method comprising the sensor device.

[0020] According to the invention, the method comprises the following step: c. Forming the first derivative and / or the second derivative of the distances over time.

[0021] Furthermore, it is preferred if the speeds and / or accelerations thus determined are forwarded from the evaluation unit to a control unit to initiate appropriate measures. Within the scope of the method, it is further advantageous if the control unit causes actuators to introduce counterforces proportional to the detected speed / acceleration for the active damping of the measurement object, or to eliminate disturbances or adjust the position of the optical elements. The sampling rate of the measurements is preferably at least 100 Hz, more preferably at least 1 kHz, and most preferably at least 20 kHz.Within the scope of the method, it is preferred if a second sensor formed as a displacement sensor repeatedly detects the distance between the measurement object and the auxiliary mass in a second measuring axis that is linearly independent of the first measuring axis, and that a third sensor formed as a displacement sensor repeatedly detects the distance between the measurement object and the auxiliary mass along a third measuring axis that is linearly independent of the first and second measuring axes.

[0022] In order to be able to record movements of the measurement object above 100 Hz with a good signal-to-noise ratio over a wide frequency range, it is preferred if the recorded signals - i.e. movements - which are greater than a predetermined or predeterminable cut-off frequency or a cut-off frequency range of the displacement sensor are damped by means of a low-pass filter, and if the recorded signals - i.e. movements - which are smaller than a predetermined or predeterminable cut-off frequency or cut-off frequency range of the acceleration sensor are damped by means of a high-pass filter, whereby the sum of the transfer function of the signals from the displacement sensor and the acceleration sensor is approximately 1.In other words, the signals detected by the displacement sensor are preferably used for smaller movements of the measurement object below the cutoff frequency or below the cutoff frequency range, and the measurement signals detected by the acceleration sensor are used for larger movements of the measurement object above the cutoff frequency and above the cutoff frequency range. The larger movements detected by the displacement sensor, which are greater than the cutoff frequency or the cutoff frequency range, are dampened using the low-pass filter, and the smaller movements detected by the acceleration sensor, which are less than the cutoff frequency or the cutoff frequency range, are preferably dampened using a high-pass filter.

[0023] The advantages, embodiments and previously described configurations of the sensor device are transferable to the method for operating the sensor device.

[0024] 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. The embodiments described below are merely examples and do not limit the subject matter of the invention. They show:

[0025] Figure 1a is a schematic representation of a microlithographic projection exposure system designed for operation in the EUV,

[0026] Figure 1 b is a schematic representation of a microlithographic projection exposure system designed for operation in DUV,

[0027] Figure 2 is a schematic representation of a first embodiment of a sensor device,

[0028] Figure 3 is a schematic representation of a second embodiment of a sensor device,

[0029] Figure 4 is a schematic representation of a third embodiment of a sensor device,

[0030] Figure 5 is a schematic representation of a fourth embodiment of a sensor device,

[0031] Figure 6 is a schematic representation of a fifth embodiment of a sensor device, and

[0032] Figure 7 shows a schematic representation of the signal processing in an embodiment with both at least one acceleration sensor and a displacement sensor. 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.

[0033] 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 sensor device according to the invention can be used in the projection lens or in an illuminator of an EUV projection exposure system.

[0034] 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.

[0035] 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.

[0036] Figure 2 shows a first embodiment of a sensor device 100 for a microlithographic projection exposure system 600, 700 or an illumination device with a measurement object 101, at least one sensor 102 assigned to the measurement object 101, and an evaluation unit (not shown in detail), which is preferably designed as a control unit or as an executable program on a microcontroller. In order to achieve a good signal-to-noise ratio when determining the movement of the measurement object 101, even for small movements, particularly in the picometer range, the sensor 102 is designed as a displacement sensor 103. An auxiliary mass 105 suspended from the measurement object 101 by means of a resilient element 104 and thus motionless serves as a reference for the sensor 102.

[0037] The sensor 102 is configured to measure the distance between the auxiliary mass 105 and the measurement object 101 along a first measurement axis. For simpler signal processing, the evaluation unit is configured to numerically calculate the first derivative and / or the second derivative of the distances measured by the displacement sensor 103. The first derivative and / or the second derivative of the distances measured multiple times by the displacement sensor 103, i.e., a distance function, is preferably calculated numerically by the evaluation unit or an additional control unit, e.g., by dividing the difference quotient by the difference quotient x(t) « , where T is the sampling time. This determines the velocities and / or accelerations analogously to the values ​​typically recorded for sensors in a microlithographic projection exposure system.

[0038] To decouple the auxiliary mass 105 from the measurement object 101, the auxiliary mass is suspended from the measurement object 101 by means of a resilient element 104. 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. This very soft suspension allows good decoupling between the measurement object 101 and the auxiliary mass to be achieved. The resilient element 104 can be formed as a leaf spring or as a spiral spring. Furthermore, it is also possible for the resilient element 104 to be formed as a permanent magnetic gravity compensator (not shown in detail). Furthermore, the resilient element can also be formed as a combination of different springs or as a combination of at least one spring with a magnetic gravity compensator.

[0039] The measurement object 101 can be formed as an optical element, for example as one of the mirrors 603, 604, 605, 606, 607, 651, 652, 653, 654, 655, 656 or lenses of the projection lens of the projection exposure system 600, 700.

[0040] Alternatively or additionally, the measurement object 101 is formed as a sensor frame (not shown in detail), which is suspended from a force frame coupled to the optical element, wherein the sensor frame has at least one position sensor for the optical element. Based on the sensor frame, the position of the optical elements is checked by means of the at least one position sensor. The sensor frame is preferably decoupled in order to decouple it from the environment, in particular from floor vibrations or vibrations due to the movement of the wafer stage. By means of the sensor device and in particular by using the displacement sensors 103, even small movements of the sensor frame, i.e. movements of the sensor frame in the frequency range between 1 Hz and 100 Hz, can be detected with a good signal-to-noise ratio. The speeds determined by forming the first derivative of the detected distances or movement frequencies, or by forming the secondThe acceleration determined from the recorded distances or movement frequencies can then be forwarded to a control unit in order to take measures, for example to dampen the sensor frame more or less, and to cause actuators to adjust the sensor frame or to introduce counterforces, etc. The position sensors of the sensor frame can also be designed as displacement sensors, the signal of which is differentiated once or twice.

[0041] Alternatively or additionally, the measurement object 101 can be formed as a force frame (not shown in detail) that is connected to an optical element, with at least one actuator being arranged on the force frame on the side facing the optical element. The actuator can be used to adjust the position and / or deform the optically active surface of the optical element. In the present case, it is preferred if the evaluation unit is configured to numerically determine the second derivative of the distances detected by the displacement sensor.

[0042] The embodiment according to Figure 3 differs in that a second sensor 108 formed as a displacement sensor 103 is present, which is configured to detect the distance between the measurement object 101 and the auxiliary mass 105 along a second measuring axis arranged perpendicular to the first measuring axis.

[0043] In this case, the auxiliary mass is also decoupled from the measurement object 101 parallel to the second measuring axis by means of a resilient element 104. In order to be able to detect a change in movement along all three translational degrees of freedom, a third sensor (not shown in detail) designed as a displacement sensor 103 can also be present, which is configured to detect the distance between the measurement object 101 and the auxiliary mass 105 along a third measuring axis arranged perpendicular to the first measuring axis and the second measuring axis. The auxiliary mass 105 is then preferably decoupled from the measurement object 101 along this measuring axis by a resilient element 104 (not shown in detail), which is arranged parallel to the third measuring axis or acts parallel to the third measuring axis.

[0044] In the embodiment shown in Figure 4, the displacement sensor 103 is formed as an optical encoder 107, which comprises a scale 107b arranged on the auxiliary mass and an optical system 107b arranged opposite the scale 107b on the measurement object, comprising a light source and at least one grating. Alternatively, the displacement sensor can also be formed as an interferometer or as a capacitive sensor.

[0045] The embodiment according to Figure 5 differs from that according to Figure 4 in that two optical encoders 107 are provided, wherein one optical encoder 107 measures along a first measuring axis and the second optical encoder measures along a second measuring axis arranged perpendicular to the first measuring axis.

[0046] The embodiment according to Figure 6 differs in that, in addition to the displacement sensors 103, acceleration sensors 109 are present. A low-pass filter is assigned to the displacement sensor 103. This filter attenuates signal frequencies from the displacement sensor 103 above a predetermined cutoff frequency or a cutoff frequency range. In other words, larger movements or higher frequencies, which are better detected by an acceleration sensor 109, are attenuated, and only those signal frequencies / movements are detected by the displacement sensor that are in a frequency range of preferably less than 100 Hz. Conversely, a high-pass filter is assigned to the acceleration sensors 109. This filter enables attenuation of the measured signal frequencies / movements below a predetermined cutoff frequency or a cutoff frequency range.The filters are selected such that the sum of the transfer function of the signals from the acceleration sensor 109 and the displacement sensor 103 is approximately 1.

[0047] The method for operating a sensor device 100 for a microlithographic projection exposure system 600, 700 comprises the following steps: First, the distance between a measurement object 101 and an auxiliary mass 105 along a first measurement axis is detected multiple times by means of at least one displacement sensor 103. Analogously but optionally, a second sensor 108 formed as a displacement sensor 103 can also detect the distance between the measurement object 101 and the auxiliary mass 105 multiple times along a second measurement axis perpendicular to the first measurement axis, and / or a third sensor formed as a displacement sensor 103 can detect the distance between the measurement object 101 and the auxiliary mass 105 multiple times along a third measurement axis perpendicular to the first and second measurement axes.

[0048] A distance function is created by repeatedly measuring the distances. An evaluation unit numerically determines the first derivative, i.e., the speed of the measurement object, and / or the second derivative, i.e., the acceleration, over time. The evaluation unit can also be implemented as a control unit or a microcontroller. The control unit or an additional control unit can then take action based on the determined speed or acceleration values. For example, the control unit can cause actuators to adjust the position of an optical element or deform the active surface of an optical element. Likewise, the control unit can cause a parameter change in a vibration isolation system of a sensor frame.Likewise, during the detection of vibrations, the alignment or deformation of the optical element can be adjusted using the control unit in order to reduce the imaging errors caused by vibrations or other disturbances.

[0049] Figure 7 schematically illustrates a signal processing sequence when the sensor device 100 comprises at least one displacement sensor 103 and at least one acceleration sensor 109 in addition to the at least one displacement sensor 103. The detected signals of the at least one displacement sensor 103, i.e., the distances derived once or twice that are greater than a predetermined or predeterminable cutoff frequency or a cutoff frequency range, are attenuated by a low-pass filter 110. Conversely, the signals detected by the acceleration sensor 109 that are smaller than a predetermined or predeterminable cutoff frequency or a cutoff frequency range are attenuated by a high-pass filter 111, wherein the sum of the transfer function of the signals of the displacement sensor 103 and the acceleration sensor 109 is approximately 1.In other words, the small movements below preferably 50 Hz to 500, preferably 70 Hz with 300 Hz and most preferably 100 Hz to 200 Hz are read out / detected by means of the displacement sensor 103, while the larger movements above this.

[0050] Limit frequency or this limit frequency range can be read / detected using acceleration sensors 109. This allows larger movements, as well as smaller movements in the picometer range or larger accelerations and smaller accelerations in mm / s 2 area of ​​a measurement object 101 can be detected with an optimal signal-to-noise ratio.

[0051] LIST OF REFERENCE SYMBOLS

[0052] 100 sensor device

[0053] 101 Measurement object

[0054] 102 Sensor

[0055] 103 displacement sensor

[0056] 104 spring element

[0057] 105 auxiliary mass

[0058] 107 encoders

[0059] 107a scale (encoder)

[0060] 107b Optics (Encoder)

[0061] 108 second sensor

[0062] 109 Accelerometer

[0063] 110 low-pass filter

[0064] 111 High Pass

[0065] 600 projection exposure system

[0066] 601 plasma light source

[0067] 602 collector mirror

[0068] 603 field facet mirror

[0069] 604 Pupillary facet mirror

[0070] 605 first telescope mirror

[0071] 606 second telescope mirror

[0072] 607 Deflecting mirror

[0073] 620 Mask table

[0074] 621 Mask

[0075] 651 Mirror (projection lens)

[0076] 652 mirror (projection lens)

[0077] 653 Mirror (projection lens)

[0078] 654 mirror (projection lens)

[0079] 655 Mirror (projection lens)

[0080] 656 mirrors (projection lens)

[0081] 660 wafer table

[0082] 661 coated substrate

[0083] 700 DUV lithography system 701 DUV light source

[0084] 702 DUV radiation / beam path

[0085] 703 Beam shaping and illumination system (DUV)

[0086] 704 photomask 705 projection system

[0087] 706 wafers

[0088] 707 lens

[0089] 708 mirrors

[0090] 709 optical axis

Claims

CLAIMS 1. Sensor device (100) for a microlithographic projection exposure system (600, 700), with a measurement object (101), at least one sensor (102) assigned to the measurement object and an evaluation unit, wherein the sensor (102) is designed as a displacement sensor (103), wherein an auxiliary mass (105) suspended from the measurement object (101) by means of a resilient element (104) is provided as a reference for the sensor (102), and wherein the sensor (102) is designed to detect the distance between the auxiliary mass (105) and the measurement object (101) along a first measuring axis, characterized in that the evaluation unit is designed to numerically form the first derivative and / or the second derivative of the distances detected by the displacement sensor (103).

2. Sensor device (100) according to claim 1, characterized in that the displacement sensor (103) is formed as an optical encoder (107).

3. Sensor device (100) according to claim 1, characterized in that the displacement sensor (103) is formed as a capacitive sensor or as an interferometer.

4. Sensor device (100) according to one of claims 1 to 3, characterized in that the resilient element (104) of the auxiliary mass (105) is selected such that the suspension frequency is between 0.1 Hz and 100 Hz, preferably between 0.1 and 50 Hz and very particularly preferably between 1 Hz and 30 Hz.

5. Sensor device (100) according to one of claims 1 to 4, characterized in that a second sensor (108) formed as a displacement sensor (103) is present, which is set up to detect the distance between the measurement object (101) and the auxiliary mass (105) in a second measuring axis arranged linearly independently with respect to the first measuring axis and / or that a third sensor formed as a displacement sensor (103) is present, which is set up is to detect the distance between the measuring object (101) and the auxiliary mass (105) in a third measuring axis arranged linearly independently with respect to the first measuring axis and the second measuring axis.

6. Sensor device (100) according to one of claims 1 to 5, characterized in that the resilient element (104) is formed as a leaf spring or as a spiral spring.

7. Sensor device (100) according to one of claims 1 to 6, characterized in that the resilient element (104) is formed as a magnetic gravitational compensator.

8. Sensor device (100) according to one of claims 1 to 7, characterized in that in addition to the at least one displacement sensor (103) there is an acceleration sensor (109) for detecting the acceleration of the measurement object (101) along a measurement axis.

9. Sensor device (100) according to claim 8, characterized in that a low-pass filter (110) is assigned to the at least one displacement sensor (103) for attenuating the detected signal of the displacement sensor (103) above a predetermined cut-off frequency or a cut-off frequency range, and in that a high-pass filter (111) is assigned to the at least one acceleration sensor (109) for attenuating the detected signal below a predetermined cut-off frequency or a cut-off frequency range, the sum of the transfer function of the signals from the acceleration sensor (109) and the displacement sensor (103) being approximately 1.

10. Sensor device (100) according to one of claims 1 to 9, characterized in that the measuring object (101) is formed as an optical element.

11. Sensor device (100) according to one of claims 1 to 10, characterized in that the measuring 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.

12. Sensor device (100) according to one of claims 1 to 11, characterized in that the measuring object (101) is formed as a force frame which is connected to an optical element, wherein at least one actuator is arranged on the force frame on the side facing the optical element.

13. A method for operating a sensor device (100) for a microlithographic projection exposure system (600, 700) according to one of claims 1 to 12, comprising the following steps: a. Multiple detection of the distance between a measurement object (101) and an auxiliary mass (105) along a first measurement axis by means of the at least one displacement sensor (103). b. Forwarding the distances detected by the sensor (102) to a c. Forming the first derivative and / or the second derivative of the distances over time.

14. The method according to claim 13, characterized in that a second sensor (108) formed as a displacement sensor repeatedly detects the distance between the measurement object (101) and the auxiliary mass (105) along a second measuring axis that is linearly independent of the first measuring axis, and in that a third sensor formed as a displacement sensor (103) repeatedly detects the distance between the measurement object (101) and the auxiliary mass (105) along a third measuring axis that is linearly independent of the first and second measuring axes.

15. Method according to one of claims 13 or 14, characterized in that the detected signals which are greater than a predetermined or predeterminable cut-off frequency or a cut-off frequency range of the at least one displacement sensor (103) are attenuated by means of a low-pass filter and the detected signals which are smaller than a predetermined or predeterminable cut-off frequency or cut-off frequency range of the at least one acceleration sensor (109) are attenuated by means of a high-pass filter, wherein the sum of the transfer function of the signals of the displacement sensor (103) and the acceleration sensor (109) is approximately 1.

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