WO2021224036A1

WO2021224036A1 - Method for operating a deformable mirror, and optical system having a deformable mirror

Info

Publication number: WO2021224036A1
Application number: PCT/EP2021/060757
Authority: WO
Inventors: Hans Michael STIEPAN; Toralf Gruner; Kerstin HILD; Evgeny SAVELYEV
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2020-05-07
Filing date: 2021-04-23
Publication date: 2021-11-11
Also published as: DE102020205752A1

Abstract

The invention relates to a method for operating a deformable mirror and to an optical system having a deformable mirror, the mirror (10, 30) comprising a mirror substrate (12, 32), a reflection layer system (21, 41) for reflecting electromagnetic radiation impinging on an active optical area (11, 31) of the mirror, and at least one piezoelectric layer (16, 36) which is arranged between the mirror substrate and reflection layer system and which can be subjected to an electric field by means of a first electrode arrangement provided on the side of the piezoelectric layer facing the reflection layer system and a second electrode arrangement provided on the side of the piezoelectric layer facing the mirror substrate by voltage actuation of the first and/or second electrode arrangement in order to generate a locally variable deformation. A method according to the invention has the following steps: Determining a temperature distribution present in the region of the piezoelectric layer; and adjusting the voltage actuation of the first and/or the second electrode arrangement depending on the temperature distribution determined in step a).

Description

Method for operating a deformable mirror and an optical system with a deformable mirror

The present application claims the priority of the German patent application DE 10 2020 205 752.4, filed on May 7, 2020. The content of this DE application is incorporated by reference into the present application text.

BACKGROUND OF THE INVENTION

Field of invention

The invention relates to a method for operating a deformable mirror, and an optical system with a deformable mirror.

State of the art

Microlithography is used to manufacture microstructured components such as integrated circuits or LCDs. The microlithography process is carried out in what is known as a projection exposure system, which has an illumination device and a projection lens. The image of a mask (= reticle) illuminated by means of the illumination device is projected by means of the projection lens onto a substrate (e.g. a silicon wafer) coated with a light-sensitive layer (= photoresist) and arranged in the image plane of the projection lens, in order to create the mask structure on the light-sensitive Transfer coating of the substrate. In projection lenses designed for the EUV range, ie at wavelengths of, for example, about 13 nm or about 7 nm, mirrors are used as optical components for the imaging process due to the lack of availability of suitable translucent refractive materials.

It is also known to design one or more mirrors in an EUV system as an adaptive mirror with an actuator layer made of a piezoelectric material, an electric field with locally different strengths over this piezoelectric layer by applying an electrical voltage to both sides of the piezoelectric Layer arranged electrodes is generated. In the event of local deformation of the piezoelectric layer, the reflective layer system of the adaptive mirror is also deformed so that, for example, imaging errors (possibly also temporally variable imaging errors) can be at least partially compensated for by suitable control of the electrodes.

8 shows, in a merely schematic representation, a construction of a conventional adaptive mirror 80 that is possible in principle. The mirror 80 comprises in particular a mirror substrate 82 and a reflective layer system 91 and has a piezoelectric layer 86, which in the example is made of lead-zirconate-titanate (Pb ( Zr, Ti) 03, PZT) is made. Above or below the piezoelectric layer 86 are electrode arrangements, via which the mirror 80 can be subjected to an electric field for generating a locally variable deformation. Of these electrode arrangements, the second electrode arrangement facing the substrate 82 is designed as a continuous, flat electrode 84 of constant thickness, whereas the first electrode arrangement has a plurality of electrodes 90, each of which can be supplied with an electrical voltage relative to the electrode 84 via a lead 89 . The electrodes 90 are embedded in a common smooth layer 88 which is made, for example, of quartz (S1O2) and serves to level the electrode arrangement formed from the electrodes 90. Furthermore, the mirror 80 has between the mirror substrate 82 and the Mirror substrate 82 facing lower electrode 84 has an adhesive layer 83 (e.g. made of titanium, Ti) and a buffer layer 85 (e.g. made of LaNiC) arranged between the electrode arrangement facing the substrate 82 and the piezoelectric layer 86, which the growth of PZT in optimal, crystalline Structure further supported and ensures constant polarization properties of the piezoelectric layer 86 over the service life.

When the mirror 80 or an optical system having this mirror 80 is in operation, the application of an electrical voltage to the electrodes 90 or 84 and, via the electrical field that forms, leads to a deflection of the piezoelectric layer 86. In this way, - For example, to compensate for optical aberrations, for example as a result of thermal deformations in the case of EUV radiation impinging on the optical active surface 81, an actuation of the mirror 80 can be achieved.

According to FIG. 8, the mirror 80 also has a mediator layer 87. This mediator layer 87 is in direct electrical contact with the electrodes 90 (which are shown in plan view in FIG. 8a for illustration purposes only). This mediator layer 87 serves to “mediate” between these electrodes 90 in the potential, whereby it has only a low electrical conductivity with the result that a voltage difference existing between adjacent electrodes 90 essentially drops across the mediator layer 87.

However, a problem that arises when operating the adaptive mirror described above is that as a result of the absorption of the radiation emitted by the EUV light source, the associated heating of the EUV mirror also causes a corresponding heating of the piezoelectric mirrors present in the adaptive or deformable mirror Layer causes. Due to an existing temperature dependency of the piezoelectric effect (ie in particular the size of the spatial expansion of the piezoelectric layer achieved for a certain applied electrical voltage or the mirror deformation caused by this), a calculated without taking the above-mentioned heating into account Voltage control of the electrode arrangements in the adaptive mirror no longer leads exactly to the desired mirror deformation. This circumstance in turn results in a non-optimal or faulty wafer exposure when a microlithographic projection exposure system having the relevant deformable or adaptive mirror is in operation.

Regarding the state of the art, reference is made to DE 10 2013 219 583 A1 and DE 102015 213 273 A1 only by way of example.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method for operating a deformable mirror and an optical system with a deformier ble mirror which, based on the principle of locally varying deformation of a piezoelectric layer, provide the best possible correction of aberrations in an optical system Allow avoidance of the problems described above.

This object is achieved according to the features of the independent patent claims.

According to one aspect, the invention relates to a method for operating a deformable mirror, the mirror having:

- a mirror substrate,

a reflective layer system for reflecting electromagnetic radiation incident on an optical effective surface of the mirror, and

- At least one piezoelectric layer which is arranged between the mirror substrate and reflective layer system and has a first electrode arrangement located on the side of the piezoelectric layer facing the reflective layer system and a second electrode arrangement located on the side of the piezoelectric layer facing the mirror substrate Electrode arrangement can be acted upon by a voltage control of the first and / or the second electrode arrangement with an electric field for generating a locally variable deformation.

The method according to the invention has the following steps: a) determining a temperature distribution present in the region of the piezoelectric layer; and b) adapting the voltage control of the first and / or the second electrode arrangement as a function of the temperature distribution determined in step a).

In the context of the present application, the term “reflective layer system” is intended to include both multiple layer systems or reflective layer stacks and single layers.

The present invention is based in particular on the concept of adapting the voltage control of the electrode arrangements in a deformed mirror with a piezoelectric layer that can be acted upon via electrode arrangements with an electrical field to generate a locally variable deformation depending on a previously determined temperature distribution in the area of the piezoelectric layer In particular, the linear expansion of the material of the piezoelectric layer which is achieved as a function of the voltage for the relevant temperature distribution - which in turn can be determined in advance by means of a calibration - is taken into account. The coefficient that characterizes the voltage-dependent linear expansion of the material of the piezoelectric layer is also referred to as the d ₃₃ coefficient and corresponds to the relevant component of the dielectric tensor responsible for the linear expansion in the direction perpendicular to the effective optical surface.

In other words, the invention includes, inter alia, the principle that, in the case of a mirror deformed by means of a piezoelectric layer, initially a currently im Determine the temperature distribution in the area of this piezoelectric layer and then, knowing the values of the d ₃₃ coefficient of the piezoelectric layer that apply to the respective temperature distribution, apply the correct electrical voltage from the outset, taking into account the heating that has taken place, in order to achieve a desired deformation of the mirror .

The temperature distribution in the area of the piezoelectric layer can be determined in different ways. According to a preferred embodiment (but without the invention being restricted to this), the temperature distribution is determined by measuring a leakage current flowing between the electrode arrangements via the piezoelectric layer.

According to this aspect, the invention is based on the consideration that the piezoelectric layer has a typically relatively high but finite electrical resistance (usually in the megaohm to gigaohm range), so that an electrical leakage current between the electrode arrangements via the piezoelectric Layer occurs, which is of a comparatively small but measurable order of magnitude (typical values of this leakage current being in the microampere range).

The invention now makes use of the further knowledge that said leakage current has a significant temperature dependency and can consequently be used as an indicator of the currently existing temperature in the area of the piezoelectric layer.

Thus, the invention also includes the concept of using the (actually parasitic) leakage current via the piezoelectric layer for temperature determination and for correct voltage control of the electrodes with regard to this temperature or the corresponding piezoelectric properties of the piezoelectric layer. According to one embodiment, the temperature distribution is determined in step a) in a spatially resolved manner.

According to one embodiment, the temperature distribution is determined in step a) in a time-resolved manner.

According to one embodiment, the first or the second electrode arrangement has a plurality of electrodes, each of which can be subjected to an electrical voltage relative to the first other electrode arrangement via a supply line.

According to one embodiment, the voltage control in step b) is adapted in such a way that an electrical voltage is applied to these electrodes independently of one another as a function of a locally varying temperature distribution determined in step a).

According to one embodiment, the voltage control is adapted in step b) taking into account a calibration carried out beforehand, with this calibration determining a deformation of the piezoelectric layer for different temperatures.

According to one embodiment, this calibration is carried out in a calibration stand which has a heating device for setting different temperatures on the mirror, a unit for voltage control and leakage current measurement on the mirror and an interferometric measuring arrangement for measuring surface deformation of the mirror.

According to one embodiment, the determination of the temperature distribution in step a) comprises the measurement of a leakage current flowing between the electrode arrangements via the piezoelectric layer.

According to one embodiment, the measurement of the leakage current takes place in a spatially resolved manner. According to one embodiment, the determination of the temperature distribution in step a) comprises an impedance measurement to determine a temperature-dependent capacitance of the piezoelectric layer.

According to one embodiment, the first or the second electrode arrangement has a plurality of electrodes, these electrodes being brought to the same electrical potential before the leakage current is measured.

According to one embodiment, one of the electrode arrangements is assigned an intermediary layer for setting an at least regionally continuous course of the electrical potential along the respective electrode arrangement.

According to one embodiment, the temperature distribution is determined in step a) using at least one infrared camera, in which case the temperature distribution is inferred from a camera image recorded by this infrared camera.

According to one embodiment, the temperature distribution is determined in step a) using an arrangement of temperature sensors located in the mirror substrate.

The invention further relates to an optical system with

- A deformable mirror with an optical active surface, a mirror substrate, a reflective layer system for reflecting electromagnetic radiation impinging on the optical cal active surface, and at least one piezoelectric layer which is arranged between the mirror substrate and the reflective layer system;

- The piezoelectric layer having a first electrode arrangement located on the side of the piezoelectric layer facing the reflection layer system and a second electrode arrangement on the mirror substrate facing side of the piezoelectric layer located electrode arrangement can be acted upon with an electric field for generating a locally variable deformation;

- wherein the optical system has a device for determining a temperature distribution present in the region of the piezoelectric layer.

According to one embodiment, the device for determining a temperature distribution present in the region of the piezoelectric layer is designed based on the measurement of a leakage current flowing between the electrode arrangements via the piezoelectric layer.

According to one embodiment, the device for determining a temperature distribution present in the region of the piezoelectric layer is designed based on an impedance measurement to determine the temperature-dependent capacitance of the piezoelectric layer.

According to one embodiment, the device for determining a temperature distribution present in the region of the piezoelectric layer has an infrared camera for recording a camera image of the optical active surface.

According to one embodiment, the device for determining a temperature distribution present in the region of the piezoelectric layer has an arrangement of temperature sensors located in the mirror substrate.

According to one embodiment, the mirror is designed for a working wavelength of less than 30 nm, in particular less than 15 nm.

According to one embodiment, the optical system is a lighting device or a projection lens of a microlithographic projection exposure system.

The invention further relates to a microlithographic projection exposure system with an illumination device and a projection lens, wherein the Projection exposure system has an optical system with the features described above be.

Further embodiments of the invention can be found in the description and the subclaims.

The invention is explained in more detail below with reference to the exemplary embodiments shown in the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Show it:

FIG. 1 shows a schematic illustration to explain a determination of the temperature distribution taking place in an adaptive mirror in the region of the piezoelectric layer according to an embodiment of the invention;

FIG. 2 shows an equivalent circuit diagram for the adaptive mirror according to FIG. 1; FIG. 3 shows a schematic illustration to explain a determination of the temperature distribution in an adaptive mirror in the region of the piezoelectric layer according to a further embodiment of the invention;

FIG. 4 shows a schematic representation of a calibration stand which can be used in the method according to the invention;

FIG. 5 shows a diagram for explaining a possible sequence of a method according to the invention; FIG. 6 shows a schematic illustration to explain the possible structure of a microlithographic projection exposure system designed for operation in the EUV;

FIG. 7 shows a schematic illustration to explain the possible structure of a microlithographic projection exposure system designed for operation in the VUV; and

FIG. 8 shows a schematic illustration to explain the possible structure of a conventional adaptive mirror.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows a schematic illustration to explain the structure of a mirror according to the invention in an exemplary embodiment of the inven tion. In particular, the mirror 10 comprises a mirror substrate 12 which is produced from any suitable mirror substrate material. Suitable mirror substrate materials include titanium dioxide (Ti0 ₂₎ -doped quartz glass, which in way of example only (and without the invention being limited thereto) under the trade designation ULE ^® (manufactured by Corning Inc.) sold material can be used. Other suitable materials are Lithiumaluminosili- cate glass ceramics, for example, under the names Zerodur ^® (Schott AG) or Clearceram ^® (manufactured by Ohara Inc.) sold. In particular in applications outside of EUV microlithography, other materials such as silicon (Si) are also conceivable.

Furthermore, the mirror 10 has, in a manner known per se, a reflective layer system 21 which, in the embodiment shown, comprises a molybdenum-silicon (Mo-Si) layer stack merely by way of example. Without the invention being restricted to specific configurations of this reflective layer system, a suitable one can be used merely by way of example Structure comprise about 50 layers or layer packages of a layer system of molybdenum (Mo) layers with a layer thickness of 2.4 nm each and silicon (Si) layers with a layer thickness of 3.3 nm each. In further embodiments, the reflective layer system can also be a single layer.

The mirror 10 can in particular be an EUV mirror of an optical system, in particular of the projection objective or the lighting device of a microlithographic projection exposure system.

The mirror 10 has a piezoelectric layer 16, which in the example is made of lead zirconate titanate (Pb (Zr, Ti) 03, PZT). Above or below the piezoelectric layer 16 are electrode arrangements, via which the mirror 10 can be subjected to an electric field for generating a locally variable deformation. Of these electrode arrangements, the second electrode arrangement facing the substrate 12 is designed as a continuous, flat electrode 14 of constant thickness, whereas the first electrode arrangement has a plurality of electrodes 20, each with an electrical voltage relative to the electrode 14 via a lead 19 can be acted upon. The electrodes 20 are embedded in a common smooth layer 18, which is made of quartz (S1O2), for example, and is used to level the electrode arrangement formed by the electrodes 20. Furthermore, the mirror 10 has an adhesive layer 33 (e.g. made of titanium, Ti) between the mirror substrate 12 and the lower electrode facing the mirror substrate 12 and a buffer layer 15 (e.g. made of LaNiOs) arranged between the electrode arrangement facing the substrate 12 and the piezoelectric layer 16 ), which further supports the growth of PZT in an optimal, crystalline structure and ensures constant polarization properties of the piezoelectric layer over the service life.

In operation of the mirror 10 or one of these mirror 10 having optical system's, the application of an electrical voltage leads to the Electrodes 20 via the developing electric field to deflect the piezoelectric layer 16. In this way, an actuation of the mirror 10 can be achieved - e.g. to compensate for optical aberrations, e.g. .

According to the embodiment of FIG. 1 - but without the invention being restricted thereto - the mirror 10 also has a mediator layer 17. This mediator layer 17 is in direct electrical contact with the electrodes 20 (which are shown in Fig. 1 only for illustration in plan view) and serves to "mediate" between the electrodes 20 in potential, whereby they have only a low electrical conductivity ( preferably less than 200 Siemens / meter (S / m)), so that a voltage difference existing between adjacent electrodes 20 essentially drops over the mediating layer 17.

The embodiments described below have in common that in accordance with the invention to take into account a heating occurring during operation of the deformable mirror or the respective optical system and to ensure a nonetheless (ie taking into account the change in the piezoelectric properties associated with this heating) correct Voltage control a - preferably locally and temporally resolved - determination of the temperature distribution in the area of the piezoelectric layer of the deformable mirror takes place.

In a first preferred embodiment, this temperature determination takes place by measuring the leakage current flowing between the electrode arrangements across the piezoelectric layer, the invention showing a significant temperature dependence of this leakage current or the temperature dependence of the ohm, which is decisive for the magnitude of the leakage current ^. see resistance of the piezoelectric layer makes use of. Fig. 2 shows for explanation of this concept, an equivalent circuit diagram for the purpose described with reference to FIG. 1, structure of the deformable mirror 10. In this case, whoever the to the individual electrodes 20 of the reflection layer system 21 facing the electrode assembly, respectively voltages Ui, U _2, ..., U _n created. The mediator layer 17 present in the mirror 10 as described (but not mandatory in the context of the present invention) can be viewed as a continuous voltage divider from a plurality of ohms ^' resistors RML as shown in FIG. The electrode arrangement facing the substrate 12 is grounded according to FIG. 2, and the application of voltage to the electrodes 20 to achieve expansion of the piezoelectric layer 16 or an accompanying mirror deformation corresponds to the charging of the electrodes 20 of the first electrode arrangement, the electrode 14 of the second the electrode assembly as well as the intervening piezoelectric layer 16 formed capacitors C. the piezoelectric layer 16 is according to Fig. 2, see also as a voltage divider from Ohm ^'resistors RPZT viewed.

See Exemplary values of this ^ohmic resistance of the piezoelectric layer are in order of magnitude in the megohm range and have a significant temperature dependence. In a calculation example about accepts the Ohm ^'see resistance of the piezoelectric layer from a value Ri = 01/27 MW at a temperature Ti = 20 ° C to a value R 2 = 00:23 MW at a temperature T2 = 40 ° C from. From Ohm ^'s law, for an exemplary electrical voltage of U = 20V, an increase in leakage current associated with this temperature change from a value h = 16mA at Ti = 20 ° C to a value = 87mA at T2 = 40 ° C.

From the above considerations it follows that the measurement (also indicated in FIG. 2) of the leakage currents occurring at the individual electrodes 20 in turn enables a spatially resolved determination of the currently existing temperature distribution. A corresponding measuring device for measuring the leakage current is only indicated in FIG. 1 and denoted by “25”. Such a measuring device 25 can in particular per electrode 20 or Lead 19 have an ammeter, wherein the corresponding ammeter can also be housed away from the mirror 10, for example in an electronic module typically for the control of the electrodes 20 that is already present in the electronics module.

In practice, if there is a mediator layer in the deformable mirror (as described with reference to FIG. 1), it may be useful to apply the same electrical voltage to all electrodes 20 of the electrode arrangement in question during the above-mentioned leakage current measurement, so that no electrical current flows over during the leakage current measurement the mediator layer 17 flows. This can prevent the measurement of the leakage current from being disturbed by the occurrence of currents (typically two to three orders of magnitude higher) through the mediation layer or excessive “measurement noise” with regard to the leakage current to be determined. In particular, non-operating phases of the optical system or exposure pauses of the microlithographic projection exposure system can be selected for said control of the electrodes during the leakage current measurement.

In further embodiments, specifically provided measuring electrodes that are not in electrical contact with the mediation layer 17 or that are electrically insulated from this mediation layer 17 can also be provided for measuring the leakage current. Since no optically effective mirror deformation is achieved in the area of such measuring electrodes, the relative surface area of said measuring electrodes is preferably selected to be small (in particular less than 1%, further in particular less than 0.1%).

In further embodiments, a leakage current-based determination of the temperature distribution in the region of the piezoelectric layer 16 can also take place using the fact that the capacitance of the piezoelectric layer 16 also has a significant temperature dependency. For this purpose, an alternating electric field can be used temporarily via the electrode arrangements and for the purpose of determining the temperature according to the invention applied and an impedance measurement carried out. This alternating electric field can in particular have a frequency in the range from 10 Hz to 100 kHz, further in particular in the range from 100 Hz to 10 kHz.

In a calculation example, the dielectric constant e increases from a value ei (T) = 1286 at a temperature Ti = 20 ° C to a value S2 (T) = 1399 at a temperature T2 = 40 ° C. This is accompanied by an increase in the capacitance CPZT of the piezoelectric layer from a value CPZT _, I = 4.47nF to a value CPZT _, 2 = 4.86nF.

With regard to the determination of the temperature distribution present in the region of the piezoelectric layer, the concept according to the invention is not limited to the measurement of leakage currents described above.

In particular, in embodiments of the invention, the temperature distribution in the area of the piezoelectric layer can also be determined using temperature sensors which - as only indicated schematically in FIG. 3 - can be arranged, for example, within the mirror substrate and as close as possible to the piezoelectric layer . In FIG. 3, components that are analogous or essentially functionally the same as in FIG. 1 are denoted by reference numbers increased by “20”.

To achieve good spatial resolution when determining the temperature, it is advantageous to use as large a number of temperature sensors 45 as possible, with one temperature sensor being provided for each electrode 40 of the first electrode arrangement (composed of the individual electrodes 40).

The temperature sensors 45 can be equipped in particular in the form of temperature-dependent resistors or impedances coupling to the temperature field of the piezoelectric layer 36, bridge circuits known in the prior art can be used for high-precision resistance measurement. In further embodiments, the determination according to the invention of the temperature distribution present in the region of the piezoelectric layer can also be carried out using an infrared camera, in which case the temperature distribution can be inferred from a camera image recorded by this infrared camera.

After the determination of the temperature distribution in the area of the piezoelectric layer described above with reference to different embodiments, according to the invention the voltage control of the first and / or second electrode arrangement is adapted as a function of this temperature distribution, so that the mirror deformation achieved via this voltage control or that in the optical system is ultimately If the aberration correction is effected, the corresponding current temperature distribution and the resulting piezoelectric properties (in particular the value of the d33 coefficient) are taken into account.

To determine the suitable adaptation of the voltage control, the deformation of the piezoelectric layer for different temperatures is preferably determined in a preliminary calibration. A calibration stand that can be used for this purpose can, for example, have an interferometric structure in which the deformation of the piezoelectric layer is determined at a given electrical voltage and at different temperatures (e.g. set via an infrared heating source).

Fig. 4 shows a schematic representation of the possible structure of such a calibration stand. The expansion coefficient d33 is determined via the interferometric measurement of the surface deformation of the deformable mirror (labeled “54” in FIG. 4). A heating device 55 (eg an IR radiator) is used to set different temperatures on the mirror 54. The calibration stand also has an infrared camera 57 for temperature measurement and an electronic unit labeled “56” for voltage control and leakage current measurement. In the interferometric measurement setup 4 from a light source (not shown) generated measurement light via an optical fiber 51 and a beam splitter 52 on a Computergenerier th hologram (CGH) 53. By reflection of this CGH 53 emanating the electromagnetic radiation at a reference mirror 60 is a Reference wave is generated, whereas a test wave is generated by reflection of the electromagnetic radiation emanating from the CGH 53 on the mirror 54. The reference wave and the test wave reach a detector 59 (eg in the form of a CCD camera) via the beam splitter 52 and an ocular lens 58 and interfere there with one another, so that an interferogram for the Mirror surface of the mirror 54 is drawn on.

Fig. 5 shows a diagram to explain the possible sequence of a method according to the invention. 5 initially in an optional step S51 using a calibration stand (e.g. with the structure described above with reference to FIG. 4) for different temperatures and different electrical voltages applied to the electrode arrangements of the deformierba ren mirror, the electrode-resolved ( or spatially resolved) determination of the d33 coefficient or the deformation of the piezoelectric layer of the deformable mirror as a function of the leakage current.

In a subsequent step S52, the values of the d33 coefficient obtained for the respective electrodes of the deformable mirror are stored in a database (created for the individual mirror) as a function of the leakage current. Then, in step S53, a target profile of the relevant deformable mirror is specified when the microlithographic projection exposure system is in operation. In a step S54 the measurement of the respective leakage currents is carried out, whereupon in step S55 a location-dependent determination of the d33 coefficient takes place on the basis of the measured leakage currents and the aforementioned database. In the subsequent step S56, an electrical voltage required to set the desired target profile is determined. This electrical voltage is in step S57 to the Electrode arrangements of the deformable mirror applied. Optionally, according to step S58, a periodic control measurement of the leakage currents is carried out.

6 shows a schematic illustration of an exemplary projection exposure system designed for operation in the EUV, in which the present invention can be implemented.

According to FIG. 6, an illumination device in a projection exposure system 600 designed for EUV has 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 telescope mirror 605 and a second telescope mirror 606 are arranged in the light path after the pupil facet mirror 604. A deflecting mirror 607 is arranged in the light path below, which deflects the radiation hitting 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 with the aid of the projection lens in an image plane in which a substrate 661 coated with a light-sensitive layer (photoresist) is located on a wafer table 660.

7 shows a structure that is possible in principle for a microlithographic projection exposure system 700 designed for operation in the VUV. The projection exposure system 700 has an illumination device 710 and a projection objective 720. The lighting device 710 is used to illuminate a structure-bearing mask (reticle) 730 with light from a light source unit 701, which comprises, for example, an ArF excimer laser for a working wavelength of 193 nm and beam shaping optics that generate a parallel light bundle. The lighting device 710 has an optical unit 711 which, among other things, includes a deflecting mirror 712 in the example shown. The optical unit 711 can, for example, be a diffractive optical unit for generating different lighting settings (ie intensity distributions in a pupil plane of the lighting device 710) Element (DOE) and have a zoom axicon system. In the direction of light propagation after the optical unit 711 there is a light mixing device (not shown) in the beam path, which, for example, in a manner known per se, can have an arrangement of micro-optical elements suitable for achieving light mixing, as well as a lens group 713, behind which there is a field plane with a reticle masking system (REMA), which is imaged by a REMA lens 714 following in the direction of light propagation onto the structure-bearing mask (reticle) 730 arranged in a further field plane and thereby delimits the illuminated area on the reticle.

The structure-bearing mask 730 is imaged with the projection objective 720 on a substrate or a wafer 740 provided with a light-sensitive layer (photoresist). The projection objective 720 can in particular be designed for immersion operation, in which case an immersion medium is located in front of the wafer or its light-sensitive layer in relation to the direction of light propagation. Furthermore, it can, for example, have a numerical aperture NA greater than 0.85, in particular greater than 1.1.

In principle, any mirror of the projection exposure apparatus 600 or 700 described with reference to FIG. 6 or FIG. 7 can be configured as a deformable or adaptive mirror in the manner according to the invention.

If the invention has also been described on the basis of specific embodiments, numerous variations and alternative embodiments will be apparent to the person skilled in the art, e.g. by combining and / or exchanging features of individual embodiments. Accordingly, it is understood by a person skilled in the art that such variations and alternative embodiments are also encompassed by the present invention, and the scope of the invention is limited only within the meaning of the attached patent claims and their equivalents.

Claims

A method of operating a deformable mirror (10, 30), the mirror comprising:

• a mirror substrate (12, 32);

• a reflective layer system (21, 41) for reflecting on an optical active surface (11, 31) of the mirror impinging electromagnetic radiation treatment; and

• At least one piezoelectric layer (16, 36), which is arranged between the mirror substrate (12, 32) and the reflective layer system (21, 41) and over a first side of the piezoelectric layer (16, 16, 16, 41) facing the reflective layer system (21, 41) 36) located electrode arrangement and a second, on the mirror substrate (12, 32) facing side of the piezoelectric layer (16, 36) located by voltage control of the first and / or the second electrode arrangement with an electric field to generate a locally variable Deformation can be acted upon; d a d u r c h e k e n n n n z e i n e t, that the method has the following steps: a) determining a temperature distribution present in the region of the piezoelectric layer (16, 36); and b) adapting the voltage control of the first and / or the second electrode arrangement as a function of the temperature distribution determined in step a).

2. The method according to claim 1, characterized in that the determination of the temperature distribution in step a) takes place in a spatially resolved manner.

3. The method according to claim 1 or 2, characterized in that he averages the temperature distribution in step a) takes place time-resolved.

4. The method according to any one of claims 1 to 3, characterized in that the first or the second electrode arrangement has a plurality of electrodes (20, 40), which each via a supply line (19, 39) with an electrical voltage based on the respective other electrode arrangement be aufschlagbar.

5. The method according to claim 4, characterized in that the adjustment of the voltage control in step b) takes place in such a way that these electrodes (20, 40) depending on a locally varying temperature distribution determined in step a) independently of one another with an electrical voltage be applied.

6. The method according to any one of the preceding claims, characterized in that the adjustment of the voltage control in step b) takes place taking into account a calibration carried out in advance, with this calibration in each case a deformation of the piezoelectric layer (16, 36) is determined for different temperatures .

7. The method according to claim 6, characterized in that this Kalibrie tion is carried out in a calibration stand which has a heating device (55) for setting different temperatures on the mirror, a unit (56) for voltage control and leakage current measurement on the mirror and an interferometric measuring arrangement for measuring a surface deformation of the mirror.

8. The method according to any one of the preceding claims, characterized in that the determination of the temperature distribution in step a) comprises the measurement of a leakage current flowing between the electrode arrangements via the piezoelectric layer (16).

9. The method according to claim 8, characterized in that the measurement of the leakage current is spatially resolved.

10. The method according to claim 8 or 9, characterized in that the first or the second electrode arrangement has a plurality of electrodes (20, 40), these electrodes (20, 40) being brought to the same electrical potential before the measurement of the leakage current .

11. The method according to any one of claims 1 to 7, characterized in that the determination of the temperature distribution in step a) comprises an impedance measurement to determine a temperature-dependent capacitance of the piezoelectric layer (16).

12. The method according to any one of the preceding claims, characterized in that one of the electrode arrangements is assigned a mediator layer (17, 37) for setting an at least regionally continuous course of the electrical potential along the respective electrode arrangement.

13. The method according to any one of the preceding claims, characterized in that the determination of the temperature distribution in step a) takes place using at least one infrared camera, wherein the temperature distribution is inferred from a camera image recorded by this infrared camera.

14. The method according to any one of the preceding claims, characterized in that the determination of the temperature distribution in step a) takes place using an arrangement of temperature sensors (45) located in the mirror substrate (32).

15. Optical system, with

• a deformable mirror (10, 30) with an optical active surface (11, 31), a mirror substrate (12, 32), a reflective layer system (21, 41) for reflecting electromagnetic radiation incident on the optical active surface (11, 31) , and at least one piezoelectric layer (16, 36), which between mirror substrate (12, 32) and reflective layer system (21, 41) is arranged;

• the piezoelectric layer (16, 36) having a first electrode arrangement on the side of the piezoelectric layer (16, 36) facing the reflective layer system (21, 41) and a second electrode arrangement on the side facing the mirror substrate (12, 32) The electrode arrangement located on the side of the piezoelectric layer (16, 36) can be subjected to an electric field for generating a locally variable deformation; it is noted that the optical system has a device for determining a temperature distribution present in the region of the piezoelectric layer (16, 36).

16. Optical system according to claim 15, characterized in that the device for determining a temperature distribution present in the region of the piezoelectric layer (16) is designed based on the measurement of a leakage current flowing between the electrode arrangements via the piezoelectric layer (16).

17. Optical system according to claim 15, characterized in that the device is designed for determining a temperature distribution present in the region of the piezoelectric layer (16) based on an impedance measurement to determine the temperature-dependent capacitance of the piezoelectric layer (16).

18. Optical system according to one of claims 15 to 17, characterized in that the device for determining a temperature distribution present in the region of the piezoelectric layer has an infrared camera for recording a camera image of the optical active surface.

19. Optical system according to one of claims 15 to 18, characterized in that the device for determining a in the region of the piezo electrical layer present temperature distribution in a mirror substrate (32) located arrangement of temperature sensors (45).

20. Optical system according to one of claims 15 to 19, characterized in that the mirror is designed for a working wavelength of less than 30 nm, in particular less than 15 nm.

21. Optical system according to one of claims 15 to 20, characterized in that it is a lighting device or a projection lens of a microlithographic projection exposure system.

22. Microlithographic projection exposure system with an illumination device and a projection objective, characterized in that the projection exposure system has an optical system according to claim 21.