EP3827444A1

EP3827444A1 - Mirror for a microlithographic projection exposure system, and method for operating a deformable mirror

Info

Publication number: EP3827444A1
Application number: EP19737007.5A
Authority: EP
Inventors: Johannes Lippert; Toralf Gruner; Kerstin HILD; Philip LUCKE; Mohammadreza NEMATOLLAHI
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2018-07-26
Filing date: 2019-06-24
Publication date: 2021-06-02
Also published as: US20210149310A1; JP2021531510A; US11187990B2; DE102018212508A1; KR20210040045A; JP7438185B2; WO2020020550A1

Abstract

The invention relates to a mirror for a microlithographic projection exposure system, and to a method for operating a deformable mirror. According to one aspect of the invention, a mirror has an active optical area (11), a mirror substrate (12), a reflective layer stack (21) for reflecting electromagnetic radiation impinging on the active optical area (11), and at least one piezoelectric layer (16), which is arranged between the mirror substrate (12) and the reflective layer stack (21) and which, via a first electrode arrangement situated on the side of the piezoelectric layer (16) facing the reflective layer stack (21) and via a second electrode arrangement situated on the side of the piezoelectric layer (16) facing the mirror substrate (12), can be exposed to an electrical field for generating a locally variable deformation, this piezoelectric layer (16) having a plurality of columns spatially separated from one another by column boundaries, wherein a mean column diameter of said columns is in the range of from 0.1 µm to 50 µm.

Description

Mirror for a microlithographic

Proiektionsbelichtunqsanlaqe. and method for operating a

deformable mirror

The present application claims the priority of the German patent application DE 10 2018 212 508.2, filed on July 26, 2018. The content of this DE application is incorporated into the present application text by reference (“incorporation by reference”).

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to a mirror for a microlithographic projection exposure system and to a method for operating a deformable mirror.

State of the art

Microlithography is used to produce microstructured components, such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure system, which has an illumination device and a projection objective. The image of a mask illuminated by the illumination device (= reticle) is here projected by means of the projection lens onto a substrate coated with a light-sensitive layer (= photoresist) and arranged in the image plane of the projection lens (for example a silicon wafer). jected to transfer the mask structure onto the light-sensitive coating of the substrate.

In projection lenses designed for the EUV area, i.e. at wavelengths of e.g. 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 being applied across this piezoelectric layer by applying an electrical voltage to both sides Piezoelectric layer arranged electrodes is generated. If the piezoelectric layer is deformed locally, the reflective layer stack of the adaptive mirror also deforms, so that, for example, imaging errors (possibly also imaging errors that change over time) can be at least partially compensated for by suitable control of the electrodes.

With regard to the above-mentioned piezoelectric layer used to compensate for optical aberrations, it is fundamentally desirable that a certain electrical voltage applied to the electrodes can also predict the proportional and as high a deformation as possible of the piezoelectric layer and thus of the reflective layer stack of the adaptive mirror Consequence. The coefficient which 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 which is responsible for the linear expansion in the direction perpendicular to the optical active surface.

A problem that arises in practice here, however, is that the linear expansion described above in the direction perpendicular to the optical active surface in the (essentially volume-preserving) piezoelectric Material whose contraction in the lateral direction results, this effect can be described by the d _3i coefficient or the corresponding component of the dielectric tensor.

The effect described above is illustrated in the schematic representations of FIGS. 7a-7e, where the mirror substrate is denoted by “70” and the piezoelectric layer by “71” (although for the sake of simplicity no further functional layers have been shown here ). The mechanical tension (FIG. 7c) built up in the lateral direction within the piezoelectric layer 71 when an electric field (FIG. 7b) is applied is in turn transferred to the firmly grown (and comparatively more flexible or relatively flexible to the piezoelectric layer 71) softer) mirror substrate 70 (FIG. 7c) with the result that the mirror substrate 70 deviates in the direction facing away from the piezoelectric layer 71 (FIG. 7d). As indicated in FIG. 7e, the above-described effect ultimately results in the piezoelectric layer 71 sinking into the mirror substrate 70 and ultimately undesirably leads to the result of the application of the electric field Overall pass effect is reduced accordingly in comparison to the linear expansion described by the d ₃₃ coefficient.

Another problem that occurs in practice is that the adjustment accuracy that can ultimately be achieved with an adaptive mirror with the structure shown in FIG. 1, for example, is limited by flysteresis effects occurring within the piezoelectric layer 16. By “hysteresis” it is meant here that the deflection ultimately achieved at a certain value of the applied electrical voltage (corresponding to the “travel path” of the piezoelectric layer in the direction perpendicular to the optical active surface) is dependent on the previous history, in other words Cyclic traversal of a voltage range (eg according to the diagram shown in Fig. 5) yield different values of the deflection or the travel path for “outward” and “return” with regard to the values of the applied electrical voltage. All in all, the implementation of sufficiently large deflections with high adjustment accuracy of an adaptive mirror is therefore a demanding challenge in practice.

With regard to the prior art, reference is only made to DE 10 2013 219 583 A1 and DE 10 2015 213 273 A1 by way of example.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a mirror for a microlithographic projection exposure system and a method for operating a deformable mirror, which enable the realization of sufficiently large deflections with high adjustment accuracy.

This object is achieved in accordance with the features of the independent patent claims.

A mirror according to the invention for a microlithographic projection exposure system, the mirror having an optical active surface, has:

- a mirror substrate,

a stack of reflective layers for reflecting electromagnetic radiation impinging on the optical active surface, and

- At least one piezoelectric layer which is arranged between the mirror substrate and the reflection layer stack and via a first electrode arrangement located on the side of the piezoelectric layer facing the reflection layer stack and a second one on the side of the piezoelectric layer facing the mirror substrate located electrode arrangement can be acted upon with an electric field to generate a locally variable deformation,

this piezoelectric layer has a plurality of columns spatially separated from one another by column boundaries,

- With an average column diameter of these columns in the range of 0.1 pm to 50pm.

According to one embodiment, the average column spacing of adjacent columns is in the range from 2% to 30% of the average column diameter.

The invention is initially based on the observation that the piezoelectric layer present in an adaptive mirror, which can be acted upon with an electric field to produce a locally variable deformation, is typically not perfectly homogeneous, but rather, depending on the respective manufacturing process, in a kind of “column structure” of a large number crystalline columns.

Based on this knowledge, the invention is based, in particular, on the concept of selecting the mean column diameter of these columns in such a way that the best possible compromise is achieved between the travel path that can be realized with the adaptive mirror on the one hand and the setting accuracy that can be achieved on the other hand ,

As far as the travel path or the linear extension in the direction perpendicular to the optical active surface is concerned, the invention is based on the consideration that the effect described above of sinking the piezoelectric layer into the mirror substrate (ie the aforementioned “identification Effect ”) can be reduced or largely eliminated by minimizing the mean column diameter. This can be explained by the fact that when the piezoelectric layer is composed of comparatively small columns (e.g. with a medium diameter knife in the range of 0.5 m) there is a largely free mobility of these columns in the lateral direction and therefore no significant mechanical stresses are transmitted between adjacent columns, which could cause the piezoelectric layer to sink into the mirror substrate.

On the other hand, with regard to the setting accuracy that can be achieved with the adaptive mirror, the invention is based on the consideration that, with regard to the hysteresis effect that also limits this setting accuracy and is also described at the beginning, a comparatively larger value of the mean column diameter is favorable. This fact is due to the fact that the said hysteresis effect partly is caused by friction effects occurring between adjacent columns or at the column boundaries and is therefore particularly pronounced when, due to a small mean column diameter, there are a particularly large number of friction surfaces within the piezoelectric layer.

As a result, based on the above considerations, the invention now includes the principle of choosing a suitable compromise value or range of values for the mean column diameter, so that both the travel path achieved with the adaptive mirror and the achievable entry accuracy I each do this can meet the required specification.

According to one embodiment, a ratio between the average column diameter and the height of the columns is in the range from 50: 1 to 1: 200, in particular in the range from 10: 1 to 1:10.

The invention also relates to a mirror for a microlithographic projection exposure system, the mirror having an optical active surface with

- a mirror substrate, a stack of reflective layers for reflecting electromagnetic radiation striking the optical active surface, and

- At least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and via a first one, on the side of the piezoelectric layer facing the reflection layer stack

Electrode arrangement located in the layer and a second electrode arrangement located on the side of the piezoelectric layer facing the mirror substrate can be acted upon with an electric field to produce a locally variable deformation,

- With an average column spacing of these columns in the range of 2% to 30% of the average column diameter. The invention also relates to a mirror for a microlithographic

Projection exposure system, the mirror having an optical active surface with

- a mirror substrate,

a stack of reflective layers for reflecting electromagnetic radiation striking the optical active surface, and

- At least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and via an first electrode arrangement located on the side of the piezoelectric layer facing the reflection layer stack and a second electrode arrangement located on the side of the piezoelectric layer facing the mirror substrate with an electric field Generation of a locally variable deformation can be applied,

this piezoelectric layer has a plurality of columns spatially separated from one another by column boundaries, - A ratio between the average column diameter and the height of the columns in the range from 50: 1 to 1: 200, in particular in the range from 10: 1 to 1:10.

According to one embodiment, the piezoelectric layer has at least two regions which differ from one another by at least 30% in terms of the mean column diameter.

In embodiments of the invention, these two regions can correspond to different layer layers of the piezoelectric layer, a first of these layer layers being arranged closer to the mirror substrate than a second layer layer of these layer layers.

The first layer layer preferably has the area with a smaller average column diameter. This embodiment has the advantage that said first layer layer acts relatively flexible due to the relatively smaller mean column diameter compared to the second layer layer and thus the mechanical coupling in the direction of the layer stack between the second layer layer, which has the comparatively larger mean column diameter, and the Mirror substrate reduced. At the same time, a reduced hysteresis contribution can be achieved via the second layer layer due to the smaller number of column boundaries there.

In further embodiments of the invention, the two regions with different mean column diameters can also represent regions that are laterally separated from one another within the same layer position of the piezoelectric layer. With this configuration, the fact can be taken into account that areas are typically present in the adaptive mirror in which, for example, the disadvantageous effect of the “sinking effect” described above (ie, the “indentation”) is differently pronounced, so that according to the invention approximately in Areas with a comparatively lower level of this sinking effect due to greater “static certainty” (which are only examples) Edge areas and / or through components such as bushings or the like. mechanically supported areas of the mirror), the mean column diameter can be chosen to be correspondingly larger, in order to achieve a greater restriction of the hysteresis effect and thus a greater setting accuracy.

- a mirror substrate;

a stack of reflective layers for reflecting electromagnetic radiation impinging on the optical active surface; and

- At least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and via an first electrode arrangement located on the side of the piezoelectric layer facing the reflection layer stack and a second electrode arrangement located on the side of the piezoelectric layer facing the mirror substrate with an electric field Generation of a locally variable deformation can be applied;

- This piezoelectric layer has a plurality of columns spatially separated from one another by column boundaries;

- The piezoelectric layer has at least two regions which differ from one another by at least 30% in terms of the mean column diameter.

According to one embodiment, the piezoelectric layer has at least two regions which differ from one another in terms of the mean column diameter by at least 40%, more particularly by at least 50%.

According to one embodiment, the piezoelectric layer has at least two regions, which differ in terms of the average column spacing differ from each other by at least 10%, in particular by at least 20%.

- a mirror substrate;

- The piezoelectric layer has at least two areas which differ from one another in terms of the mean column spacing by at least 10%, in particular by at least 20%.

In other applications, a mirror according to the invention can also be used e.g. be used in a system for mask metrology.

According to one embodiment, the mirror is designed for a working wavelength of less than 30 nm, in particular less than 15 nm. However, the invention is not limited to this, so that in further applications the invention can also be advantageously implemented in an optical system with a working wavelength in the VUV range (for example less than 200 nm). The invention also relates to a method for operating a deformable mirror, the mirror comprising:

- a mirror substrate,

a stack of reflective layers for reflecting electromagnetic radiation impinging on an optical active surface of the mirror, and

the method comprising the following steps:

- Determination of an expected hysteresis contribution to the deformation behavior of the mirror, the linear expansion of the piezoelectric layer along the surface normal to the optical active surface when the first electrode arrangement and / or the second electrode arrangement is acted upon by a predetermined voltage distribution U (x , y) deviates from the product of the relevant linear expansion coefficient d ₃₃ (x, y) of the piezoelectric layer with the respective value of the electrical voltage; and

- Applying a modified voltage distribution to the first electrode arrangement and / or the second electrode arrangement such that this hysteresis contribution is at least partially compensated for.

According to one embodiment, the expected hysteresis contribution is determined based on the model after the hysteresis behavior of the mirror has been measured beforehand. According to one embodiment, the expected hysteresis contribution is determined on the basis of a measurement of the electrical permittivity of the piezoelectric layer.

According to one embodiment, the method has the step of applying an electrical bias (bias voltage) to the first electrode arrangement and / or the second electrode arrangement.

According to one embodiment, a unipolar alternating electrical field is generated in the piezoelectric layer along the direction of the surface normal to the optical active surface before the mirror is put into operation and / or during at least one break in order to align Weiss areas.

The invention further relates to a method for operating a deformable mirror, the mirror comprising:

- a mirror substrate,

- At least one piezoelectric layer, which is arranged between the mirror substrate and the reflection layer stack and has an electrical field via a first electrode arrangement located on the side of the piezoelectric layer facing the reflection layer stack and a second electrode arrangement located on the side of the piezoelectric layer facing the mirror substrate Generation of a locally variable deformation can be applied,

- In which a unipolar alternating electric field is generated along the direction of the surface normal to the optical active surface before the mirror is put into operation and / or during at least one break to align Weiss areas in the piezoelectric layer.

The frequency of the unipolar alternating electrical field can be, for example, in an interval from 1 mFIz to 100 mFIz. The invention further relates to an illumination device or a projection lens of a microlithographic projection exposure system with at least one mirror with the features described above, and also to a microlithographic projection exposure system.

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

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

BRIEF DESCRIPTION OF THE DRAWINGS

Show it:

Figure 1 is a schematic representation for explaining the structure of an adaptive mirror according to an embodiment of the invention;

FIG. 2 shows a diagram for explaining a concept on which the invention is based according to one aspect;

FIG. 3-4 schematic representations to explain further embodiments of the invention;

FIG. 5 shows a diagram for explaining a further concept on which the invention is based;

Figure 6 is a schematic representation to explain the possible

Construction of a microlithographic projection exposure system designed for operation in the EUV; and FIGS. 7a-7e are schematic representations to explain a problem on which the invention is based and which occurs in a conventional adaptive mirror.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 shows a schematic representation to explain the exemplary structure of a mirror according to the invention. The mirror 10 in particular comprises a mirror substrate 12 which is made from any suitable mirror substrate material. Suitable mirror substrate materials include titanium dioxide (Ti0 ₂₎ -doped quartz glass, and only by way of example (and would be limited without limiting the invention thereto) (Corning Inc.) or Zerodur ^® the designations under the trademark ULE ^® (manufactured by Schott AG) distributed materials are usable. Furthermore, the mirror 10 has, in a manner known per se, a reflection layer stack 21, which in the illustrated embodiment comprises a molybdenum-silicon (Mo-Si) layer stack only by way of example. Without the invention being restricted to specific configurations of this layer stack, a structure which is only suitable as an example can comprise approximately 50 layers or layer packages of a layer system composed of molybdenum (Mo) layers with a layer thickness of 2.4 nm each and silicon (Si) layers with a layer thickness of 3.3nm each.

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

The exposure of the optical active surface 11 of the mirror 10 to electromagnetic EUV radiation during operation of the optical system (indicated by an arrow in FIG. 1) may result in an inhomogeneous volume change of the mirror substrate 12 due to the temperature distribution, which results from the absorption of inhomogeneous radiation impinging on the optical active surface 11. The mirror 10 is adaptively designed to correct such an undesirable change in volume or also to correct other aberrations which occur during operation of the microlithographic projection exposure system, as will be explained in more detail below. In addition, the mirror 10 according to the invention has a piezoelectric layer 16, which in the exemplary embodiment is made of lead zirconate titanate (Pb (Zr, Ti) 0 ₃ , PZT). In further embodiments, the piezoelectric layer 16 can also be made from another suitable material (for example aluminum nitride (AIN), aluminum scandium nitride (AIScN), lead magnesium niobate (PbMgNb) or vanadium-doped zinc oxide (ZnO)) his. The piezoelectric layer 16 can, for example, have a thickness of less than 5 pm, more particularly a thickness in the range from 1 pm to 4 pm. In embodiments, the performance of the piezoelectric layer 16 can be increased by introducing a calcium niobate layer (CaNbOs layer) at a suitable point in the layer stack. The increase in performance is achieved in that the piezoelectric layer 16 preferably grows in the [001] crystal direction.

Above or below the piezoelectric layer 16 are electrode arrangements, via which the mirror 10 can be acted upon with an electric field in order to generate a locally variable deformation. Of these electrode arrangements, the second electrode arrangement facing the mirror 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 of which has an electrical voltage relative to the electrode 14 via a lead 19 are acted upon. The electrodes 20 are embedded in a common smoothing layer 18, which is made, for example, of quartz (S1O ₂ ) and is used to flatten the electrode arrangement formed from the electrodes 20. Furthermore, the mirror 10 according to FIG. 1 has an optional adhesive layer 13 (in the example made of titanium, Ti) between the mirror substrate 12 and the lower electrode 14 facing the mirror substrate 12. Furthermore, “15” denotes an existing buffer layer between the electrode 14 facing the mirror substrate 12 and the piezoelectric layer 16. This PUF ferschicht 15 serves to further support the growth of PZT in an optimum crystalline structure and uniform polarization characteristics of the piezoelectric layer 16 to ensure over the service life, and can be made of, for example, LaNiO _ß.

1, 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). This mediator layer 17 serves to “mediate” between the electrodes 20 in the potential, wherein it has only a low electrical conductivity (preferably less than 200 Siemens / meter (S / m) with the result that one between adjacent electrodes 60 existing voltage difference essentially drops across the mediator layer 17.

When the mirror 10 or an optical system having this mirror 10 is in operation, the application of an electrical voltage to the electrodes 14, 20 leads to a deflection of this piezoelectric layer via the electrical field which is formed in the region of the piezoelectric layer 16 16. In this way, an actuation of the mirror 10 can be achieved to compensate for optical aberrations.

As already described at the beginning, depending on the manufacturing process, the piezoelectric layer is typically not perfectly homogeneous, but is built up in a kind of “column structure” from a large number of crystalline columns. An influencing or targeted control of the average column diameter is possible here via various parameters of the manufacturing process, in particular the laser clock frequency set in a method of laser deposition, the mirror substrate temperature during the waxing process, the Design of a growth layer present between the mirror substrate and the piezoelectric layer and the gas composition within the chamber during the coating are to be mentioned. The mean size of the crystalline columns that ultimately arises can be influenced in a targeted manner by one or more of the parameters mentioned above.

This influencing of the average column diameter now takes place according to the invention, as shown schematically in the diagram in FIG. 2, in such a way that both the “sinking effect” (English “indentation”) and the increasing average diameter increase with increasing average column diameter Column diameter decreasing hysteresis effect is taken into account.

In the diagram of FIG. 2, exemplary qualitative profiles are shown both with regard to the dependence of the hysteresis effect on the average column diameter (dotted curve) and with regard to the dependence of the sinking effect on the average column diameter (dashed curve). As indicated in FIG. 2, the targeted setting of the mean column diameter in the marked value interval according to the invention has the result that both effects (i.e. both the hysteresis effect and the sinking effect) are below a threshold value specified by the respective specification.

3 and FIG. 4 show schematic and highly simplified representations for explaining further possible configurations of a piezoelectric layer present in an adaptive mirror according to the invention, with different embodiments of the piezoelectric layer being present in these embodiments, which differ with regard to the mean column diameter differ significantly (in particular by at least 40%, further in particular by at least 50%). In this way, the fact can be taken into account that, depending on the specific design of the adaptive mirror, areas may be present in which, for example, the “sinking effect” described above (for example as a result of a mechanical support of the mirror substrate) is less critical, so that in such areas the mean column diameter can be chosen larger in favor of reducing the hysteresis effect and thus increasing the setting accuracy. In the exemplary scenario of FIG. 3, a piezoelectric layer 30 in a radially outer edge region of the piezoelectric layer 30 or the adaptive mirror has an area 32 with a larger mean column diameter compared to a radially further inside first area 31 on.

According to FIG. 4, the above-mentioned regions of a piezoelectric layer 40 with different average column diameters correspond to different layer positions of the piezoelectric layer, the first layer layer 41, which is arranged closer to the mirror substrate than the second layer layer, in the illustrated embodiment 42, due to a comparatively smaller mean column diameter, becomes relatively flexible and thus the mechanical coupling in the direction of the layer stack between the second layer layer 42 and the (not shown) mirror substrate is reduced. 4, the “sinking effect” described above is alleviated on the one hand and, on the other hand, a reduced hysteresis contribution is achieved via the second layer layer due to the smaller number of column boundaries there.

According to a further aspect of the present invention, in addition or as an alternative to the setting of the mean column diameter within the piezoelectric layer described above with reference to FIGS. 2-4, one or more further suitable measures are taken in order to reduce the previously described hysteresis contribution of the piezoelectric layer and thus the increase the setting accuracy achieved with the adaptive mirror.

A first of these measures includes the model-based prediction of the hysteresis, the results obtained in this prediction being integrated from the outset into the travel paths implemented in the adaptive mirror. in order to achieve increased positioning accuracy as a result. In particular, based on a measurement of the hysteresis behavior of the component (ie the adaptive mirror or the piezoelectric layer), characteristic parameters can be determined and processed in corresponding models, with models suitable for hysteresis prediction (without the invention being restricted to this), for example, that Preisach model, the Prandtl-Ishlinskii model, the Duhem model, the Bouc-Wen model, the Coleman-Hodgdon model and the Jiles-Atherton model.

In further embodiments, the expected hysteresis contribution can also be made on the basis of a measurement of the electrical permittivity of the piezoelectric layer, in order in turn to achieve at least partial compensation of the hysteresis contribution by correspondingly applying a modified voltage distribution to the electrode arrangements. Here, the invention makes use of a linear relationship between the piezoelectric expansion on the one hand and the change in permittivity, on the other hand, with the publication Y. Ishikiriyama “Improvement of Self-sensing Piezoelectric Actuator Control Using Permittivity Change Detection”, Journal of Advanced Mechanical Design, Systems and Manufacturing, Volume 4, No. 1, 2010, pages 143-149.

In further embodiments, the respective electrode arrangement can be subjected to an electrical bias (“bias voltage”). As a result, the so-called Weiss areas can be aligned before the adaptive mirror is actually put into operation, and thus a reduction in the hysteresis effect.

Such a “bias voltage” is applied before the adaptive mirror according to the invention is operated or during breaks in operation. Furthermore, according to FIG. 5, such a “bias voltage” can be maintained continuously even during the operation of the adaptive mirror. Furthermore, an alignment of the Weiss districts and thus a reduction in the hysteresis can also be achieved by applying a “bias voltage” to the piezoelectric layer during its production in the cooling step.

The set values of the electrical bias can in particular exceed the voltage values actually used for actuation. As indicated in FIG. 5, a “working point” which is improved with regard to the undesired hysteresis effect can also be selected by applying a suitable electrical voltage. For example, by changing from the voltage range according to curve “C” to the voltage range according to curve “D”, only by way of example in accordance with FIG. 5 can the hysteresis reduction, taking advantage of the non-linear course of the curve, also exceed the effect of reducing the travel distance that is also obtained , in other words "effectively less hysteresis deviation per set nanometer surface deformation" occurs.

When the "bias voltage" and the deformation-effective, variable control voltage work together, it is possible to design the variable voltage component between 0V and a predetermined maximum value. Alternatively, it can be designed so that the variable voltage lies between specified (non-zero) minimum and maximum values or in such a way that its maximum value is 0V and it is in the negative voltage range. For example, the “bias voltage” can be 50V and the variable voltage can vary between 0V and 50V. Alternatively, the bias voltage can be selected to be 70V and the variable voltage can be between -20V and + 30V. Furthermore, in this example the bias voltage can be 100V and the variable voltage between -50V and 0V.

In FIG. 5, each of these situations could describe operation in the area delimited by the curves labeled D. The difference is that a comparatively high “bias voltage” constantly, ie also during breaks in operation, maintains a strong polarization of the domains or Weiss districts. However, it is possible that a consistently high voltage places higher demands on the insulation of the structures. ever the operating point is selected based on which aspect is more significant in the specific application. There is the possibility of adapting the complete working area (ie in FIG. 5 the area which is delimited by curves D) as well as the respective choice of the “bias voltage” to the current operating conditions. With a low required amplitude, a focus can be placed on low hysteresis and thus high accuracy, so that the tendency is to work with a comparatively high “bias voltage”. If, on the other hand, large travels are required with reduced accuracy requirements, a comparatively low "bias voltage" is selected.

In further embodiments, a unipolar alternating electric field can be applied to align the Weiss districts before the adaptive mirror is put into operation and / or during breaks in operation. The frequency of this unipolar alternating electric field can e.g. are in an interval from 1 mHz to 100 mHz.

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. Arranged in the light path downstream is a deflecting mirror 607, which directs the radiation striking 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 objective in an image plane in which one with a light-sensitive one Layer (photoresist) coated substrate 661 is located on a wafer table 660.

Of the mirrors 651-656 of the projection lens, only by way of example the mirrors 651 and 652, which are arranged in relation to the optical beam path in the initial region of the projection lens, can be designed in the manner according to the invention, since the effect achieved results in compensation for thermal deformations which is then particularly pronounced on these mirrors 651, 652 due to the still comparatively low total reflection losses and therefore the relatively high light intensities.

Although the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments, 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 appended claims and their equivalents.

Claims

claims

1. Mirror for a microlithographic projection exposure system, the mirror having an optical active surface (11) with

• a mirror substrate (12);

• a reflection layer stack (21) for reflecting electromagnetic radiation incident on the optical active surface (11); and

• at least one piezoelectric layer (16), which is arranged between the mirror substrate (12) and the reflection layer stack (21) and via a first, on the side of the piezoelectric layer (16) facing the reflection layer stack (21) and a second electrode arrangement , on the side of the piezoelectric layer (16) facing the mirror substrate (12) electrode arrangement can be acted upon by an electric field to produce a locally variable deformation;

• wherein this piezoelectric layer (16) has a plurality of columns spatially separated from one another by column boundaries;

• where an average column diameter of these columns is in the range from 0.1 pm to 50 pm.

2. Mirror according to claim 1, characterized in that the average column spacing of adjacent columns is in the range of 2% to 30% of the average column diameter.

3. Mirror for a microlithographic projection exposure system, the mirror having an optical active surface (11) with

• a mirror substrate (12);

• at least one piezoelectric layer (16), which between Mirror substrate (12) and reflection layer stack (21) are arranged and via a first electrode arrangement located on the side of the piezoelectric layer (16) facing the reflection layer stack (21) and a second one on the side facing the mirror substrate (12) piezoelectric layer (16) located electrode arrangement can be acted upon with an electric field for generating a locally variable deformation;

• wherein this piezoelectric layer (16) has a plurality of columns spatially separated from one another by column boundaries; and

• where an average column spacing of these columns is in the range of 2% to 30% of the average column diameter.

4. Mirror according to one of claims 1 to 3, characterized in that a ratio between the average column diameter and the height of the columns is in the range from 50: 1 to 1: 200, in particular in the range from 10: 1 to 1:10.

5. mirror for a microlithographic projection exposure system, the mirror having an optical active surface (11) with

• a mirror substrate (12);

• at least one piezoelectric layer (16), which is arranged between the mirror substrate (12) and the reflection layer stack (21) and via a first, on the side of the piezoelectric layer (16) facing the reflection layer stack (21) and a second electrode arrangement , on the side of the piezoelectric layer (16) facing the mirror substrate (12) electrode arrangement can be acted upon by an electric field to produce a locally variable deformation; • wherein this piezoelectric layer (16) has a plurality of columns spatially separated from one another by column boundaries;

• a ratio between the mean column diameter and the height of the columns in the range from 50: 1 to 1: 200, in particular in the range from 10: 1 to 1:10.

6. Mirror according to claim 5, characterized in that a ratio between the average column diameter and the height of the columns is in the range of 10: 1 to 1:10.

7. Mirror according to one of the preceding claims, characterized in that the piezoelectric layer (16) has at least two regions which differ from one another by at least 30% in terms of the mean column diameter.

8. Mirror for a microlithographic projection exposure system, the mirror having an optical active surface (11) with

• a mirror substrate (12);

• at least one piezoelectric layer (16, 30, 40), which is arranged between the mirror substrate (12) and the reflection layer stack (21) and via a first, on the side of the piezoelectric layer (16, 30, 40) facing the reflection layer stack (21) ) located electrode arrangement and a second electrode arrangement located on the side of the piezoelectric layer (16, 30, 40) facing the mirror substrate (12) can be acted upon by an electric field to produce a locally variable deformation;

• wherein this piezoelectric layer (16, 30, 40) has a plurality of columns spatially separated from one another by column boundaries; • The piezoelectric layer (16, 30, 40) has at least two areas which differ from one another by at least 30% in terms of the mean column diameter.

9. Mirror according to one of the preceding claims, characterized in that the piezoelectric layer (16, 30, 40) has at least two regions which differ in terms of the mean column diameter by at least 40%, further in particular by at least 50% of - distinguish each other.

10. Mirror according to one of claims 7 to 9, characterized in that these two regions correspond to different layer layers of the piezoelectric layer (16), a first layer layer (41) of these layer layers being arranged closer to the mirror substrate than a second layer layer (42 ) of these layers.

11. Mirror according to claim 10, characterized in that the first layer layer (41) has the area with a smaller average column diameter.

12. Mirror according to one of claims 7 to 11, characterized in that these two areas are within one and the same layer position of the piezoelectric layer (16), laterally separated areas (31, 32).

13. Mirror according to one of the preceding claims, characterized in that the piezoelectric layer (16, 30, 40) has at least two regions which differ from one another in terms of the mean column spacing by at least 10%, in particular by at least 20%.

14. Mirror for a microlithographic projection exposure system, the mirror having an optical active surface (11) with • a mirror substrate (12);

• wherein this piezoelectric layer (16, 30, 40) has a plurality of columns spatially separated from one another by column boundaries;

• wherein the piezoelectric layer (16, 30, 40) has at least two areas which differ from one another by at least 10% in terms of the average column spacing.

15. Mirror according to claim 14, characterized in that the piezoelectric layer (16, 30, 40) has at least two regions which differ from one another by at least 20% in terms of the mean column spacing.

16. Mirror according to one of the preceding claims, characterized in that the mirror is designed for a working wavelength of less than 30 nm, in particular less than 15 nm.

17. Mirror according to one of the preceding claims, characterized in that it is a mirror for a microlithographic projection exposure system.

18. A method of operating a deformable mirror, the mirror comprising:

A mirror substrate (12),

• a reflective layer stack (21) for reflecting electromagnetic radiation striking an optical active surface (11) of the mirror, and

At least one piezoelectric layer (16), which is arranged between the mirror substrate (12) and the reflection layer stack (21) and is arranged via a first electrode arrangement on the side of the piezoelectric layer (16, 30, 40) facing the reflection layer stack (21). voltage (20) and a second electrode arrangement (14) located on the side of the piezoelectric layer (16, 30, 40) facing the mirror substrate (12) can be subjected to an electric field to generate a locally variable deformation;

d a d u r c h g e k e n n z e i c h n e t, d a s s

the process comprises the following steps:

a) determining an expected hysteresis contribution to the deformation behavior of the mirror, the linear extent of the piezoelectric layer (16, 30, 40) along the surface normal to the optical active surface (11) when the first electrode arrangement (20 ) and / or the second electrode arrangement (14) with a predetermined voltage distribution U (x, y) from the product of the relevant linear expansion coefficient d ₃₃ (x, y) of the piezoelectric layer (16, 30, 40) with the respective value deviates from the electrical voltage; and

b) loading the first electrode arrangement (20) and / or the second electrode arrangement (14) with a modified voltage distribution such that this hysteresis contribution is at least partially compensated for.

19. The method according to claim 18, characterized in that the determination of the expected hysteresis contribution is model-based after the previous one The hysteresis behavior of the mirror is measured.

20. The method according to claim 18 or 19, characterized in that the hysteresis contribution to be expected is determined on the basis of a measurement of the electrical permittivity of the piezoelectric layer (16, 30, 40).

21. The method according to any one of claims 18 to 20, characterized in that it comprises the step of applying an electrical bias (bias voltage) to the first electrode arrangement (20) and / or the second electrode arrangement (14).

22. The method according to any one of claims 18 to 21, characterized in that prior to putting the mirror into operation and / or during at least one break in order to align Weiss areas in the piezoelectric layer, an unipolar alternating electric field is generated along the direction of the surface normal to the optical active surface becomes.

23. A method for operating a deformable mirror, the mirror comprising:

A mirror substrate (12),

characterized in that Before the mirror is put into operation or / and during at least one break in order to align Weiss areas in the piezoelectric layer, a unipolar alternating electric field is generated along the direction of the surface normal to the optical active surface.

24. Illumination device of a microlithographic projection exposure system, characterized in that the optical system has a mirror according to one of claims 1 to 17.

25. Projection objective of a microlithographic projection exposure system, characterized in that the optical system has a mirror according to one of claims 1 to 17.

26. Microlithographic projection exposure system (400) with an illumination device and a projection objective, characterized in that the projection exposure system has an optical system according to claim 25.