OPTICAL ELEMENT MODULE WITH IMAGING ERROR AND POSITION CORRECTION

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent disclosure claims the benefit of International Patent Application Serial No. PCT/EP2006/004337 published as WO 2006/119970 A1 on November 16, 2006, and in- vented by Schoppach et al., the entire contents of which is hereby incorporated herein by reference.

This patent disclosure further claims the benefit of International Patent Application Serial No. PCT/EP2007/053382 filed April 5, 2007, and invented by Kugler et al., the entire contents of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to optical element modules used in exposure processes, in particular to optical element modules used in microlithography systems. It further relates to optical imaging arrangements which may be used in such microlithography systems. It further relates to a method of supporting an optical element. It also relates to an optical imaging method for transferring an image of a pattern onto a substrate. The invention may be used in the context of photolithography processes for fabricating microelectronic devices, in particular semiconductor devices, or in the context of fabricating devices, such as masks or reticles, used during such photolithography processes.

Typically, the optical systems used in the context of fabricating microelectronic devices such as semiconductor devices comprise a plurality of optical element modules comprising optical elements, such as lenses, mirrors, gratings etc., in the light path of the optical system. Those optical elements usually cooperate in an exposure process to illuminate a pattern formed on a mask, reticle or the like and to transfer an image of this pattern onto a substrate such as a wafer. The optical elements are usually combined in one or more functionally distinct optical element groups that may be held within distinct optical element units.

With such optical systems, typically, such optical element units are often built from a stack of optical element modules holding one or more - typically rotationally symmetric - optical elements. These optical element modules usually comprise an external generally ring shaped support structure supporting one or more optical element holders each, in turn, holding one or more optical elements.

Due to the ongoing miniaturization of semiconductor devices there is a permanent need for enhanced resolution of the optical systems used for fabricating those semiconductor devices. This need for enhanced resolution obviously pushes the need for an increased imaging accuracy of the optical system. Furthermore, to reliably obtain high-quality semiconductor devices it is not only necessary to provide an optical system showing a high degree of imaging accuracy. It is also necessary to maintain such a high degree of accuracy throughout the entire exposure process and over the lifetime of the system. As a consequence, the components of the optical system cooperating in the exposure process must be supported in a defined manner in order to provide and maintain a predetermined spatial relationship between said opti- cal system components which, in turn, guarantees a high quality exposure process.

It order to reduce imaging errors that may arise during operation of the optical system it is known to actively control the position of one or more of the optical elements of the optical system. Such an optical system is known, for example, from US 2005/000201 1 A1 (Sudoh), the entire disclosure of which is hereby incorporated herein by reference. However, such an active position control may not be sufficient to eliminate or compensate some of the imaging errors that may already exist or arise during operation of the optical system. For example, wavefront aberrations resulting from uneven loads acting on one or several of the optical elements of the optical system may not be satisfactorily compensated by merely displacing one or several optical elements of the optical system.

In order to deal which such imaging errors it has been proposed to actively deform one or several optical elements of the optical system. Such imaging error correction approaches are known, for example, from US 2003/0234918 A1 (Watson), US 6,842,277 B2 (Watson), US 6,884,994 B2 (Melzer et al.), US 2004/0144915 A1 (Wagner et al.), the entire disclosure of all of which is hereby incorporated herein by reference.

While US 2004/0144915 A1 (Wagner et al.) proposes to deform a mirror in order to correct wavefront aberrations and to displace a separate lens unit in order to compensate for further imaging errors, US 6,842,277 B2 (Watson) proposes to, both, deform and displace one single optical element using a plurality of active support elements kinematically acting in parallel onto the optical element. While most of the active support elements only serve to deform the

optical element, there are provided three so-called servos actively positioning the optical element. It order to deal with the problem that a position adjustment via the servos alters the load situation of the other active support elements and, thus, modifies the deformation of the optical element, it is proposed to use low stiffness actuators for these other active support elements. While the low stiffness of the actuators may reduce the alteration in the deformation of the optical element, there is still a need to actively compensate this alteration via the actuators.

SUMMARY OF THE INVENTION

It is thus an object of the invention to, at least to some extent, overcome the above disadvan- tages and to provide good and long term reliable imaging properties of a compact optical system used in an exposure process.

It is a further object of the invention to reduce the effort necessary for an optical system used in an exposure process while at least maintaining the imaging accuracy during operation of the optical system.

These objects are achieved according to the invention which is based on the teaching that a reduction of the effort, in particular the control effort, necessary for correcting imaging errors existing or arising during operation of the optical system is possible by providing a support to an optical element which allows kinematically independent position control and deformation control of the optical element. This kinematically independent position control and deforma- tion control of the optical element may be achieved by arranging the position control mechanism and the deformation control mechanism kinematically in series.

Thus, a very simple arrangement with simple imaging error correction is achieved. In particular, the position control does not influence the deformation of the optical element such that a position adjustment of the optical element does not necessarily require an adjustment of the deformation of the optical element. It will be appreciated that, in order to provide proper imaging error correction, an adjustment of the position of the optical element may be accompanied by an adjustment of the deformation of the optical element and vice versa. However, thanks to the kinematic independence, simple and predictable correction behavior is achieved.

Thus, according to a first aspect of the invention there is provided an optical element module comprising an optical element and a support structure supporting the optical element, the support structure comprising a first holding structure, an intermediate structure and a second holding structure. The first holding structure contacts the optical element and is adapted to adjustably introduce defined deformations into the optical element. The intermediate structure supports the first holding structure while the second holding structure supports the intermediate structure and is adapted to adjust the position of the intermediate structure.

According to a second aspect of the invention there is provided an optical imaging arrangement comprising a mask unit adapted to receive a pattern, a substrate unit adapted to re- ceive a substrate and an optical projection unit adapted to transfer an image of the pattern onto the substrate. The optical projection unit comprises at least one optical element and a support structure supporting the at least one optical element. The support structure comprises a first holding structure, an intermediate structure and a second holding structure. The first holding structure contacts the optical element and is adapted to adjustably introduce defined deformations into the optical element. The intermediate structure supports the first holding structure while the second holding structure supports the intermediate structure and is adapted to adjust the position of the intermediate structure.

According to a third aspect of the invention there is provided an optical imaging arrangement comprising a mask unit adapted to receive a pattern, a substrate unit adapted to receive a substrate and an optical projection unit adapted to transfer an image of the pattern onto the substrate. The optical projection unit comprises at least one optical element and a support structure supporting the at least one optical element. The support structure comprises a first holding structure and a second holding structure. The first holding structure contacts the optical element and is adapted to adjustably introduce defined deformations into the optical element. The second holding structure is adapted to adjust the position of the optical element. The first holding structure and the second holding structure are arranged kinematically in series, the second holding structure supporting the first holding structure.

According to a fourth aspect of the invention there is provided a method of supporting an optical element comprising providing an optical element and a support structure supporting the optical element, the support structure comprising a first holding structure contacting the optical element, an intermediate structure and a second holding structure; introducing defined deformations into the optical element via the first holding structure; supporting the first holding structure via the intermediate structure and adjusting the position of the intermediate structure via the second holding structure.

According to a fifth aspect of the invention there is provided an optical imaging method comprising providing a pattern, a substrate and an optical projection unit adapted to transfer an image of the pattern onto the substrate, the optical projection unit comprising at least one optical element, the optical projection unit comprising at least one optical element and a sup- port structure supporting the at least one optical element; the support structure comprising a first holding structure contacting the optical element, an intermediate structure supporting the first holding structure and a second holding structure, capturing an imaging error value representative of an imaging error of the optical projection unit, as a function of the imaging error value at least partially compensating the imaging error by at least one of introducing defined deformations into the optical element via the first holding structure and adjusting the position of the intermediate structure via the second holding structure and, finally, transferring the image of the pattern onto the substrate using the optical projection unit.

According to a sixth aspect of the invention there is provided a method of supporting an optical element comprising providing an optical element and a support structure supporting the optical element, the support structure comprising a first holding structure and a second holding structure, introducing defined deformations into the optical element via the first holding structure, and, kinematically independently from the introducing the defined deformations into the optical element via the first holding structure, adjusting the position of the optical element via the second holding structure.

According to a seventh aspect of the invention there is provided an optical imaging method comprising providing a pattern, a substrate and an optical projection unit adapted to transfer an image of the pattern onto the substrate, the optical projection unit comprising at least one optical element, the optical projection unit comprising at least one optical element and a support structure supporting the at least one optical element; the support structure comprising a first holding structure and a second holding structure, capturing an imaging error value representative of an imaging error of the optical projection unit, as a function of the imaging error value at least partially compensating the imaging error by at least one of introducing defined deformations into the optical element via the first holding structure, and, kinematically independently from the introducing the defined deformations into the optical element via the first holding structure, adjusting the position of the optical element via the second holding structure, and, finally, transferring the image of the pattern onto the substrate using the optical projection unit.

Furthermore, it will be appreciated that the above objects may also be achieved if the first support structure provides the position adjustment of the optical element while the second

support structure, via the intermediate structure and the first support structure, provides the adjustable deformation of the optical element.

Thus, according to an eighth aspect of the invention there is provided an optical element module comprising an optical element and a support structure supporting said optical ele- ment. The support structure comprises a first holding structure, an intermediate structure and a second holding structure, the first holding structure contacting said optical element, the intermediate structure supporting the first holding structure and the second holding structure supporting the intermediate structure. One of the first holding structure and the second holding structure is adapted to adjustably introduce defined deformations into the optical element while the other one of the first holding structure and the second holding structure is adapted to adjust the position of the optical element.

According to a ninth aspect of the invention there is provided a method of supporting an optical element comprising providing an optical element and a support structure supporting the optical element, the support structure comprising a first holding structure contacting the opti- cal element, an intermediate structure and a second holding structure; supporting the first holding structure via the intermediate structure and supporting the intermediate structure via the second holding structure; and introducing defined deformations into the optical element via one of the first holding structure and the second holding structure and adjusting the position of the optical element of via the other one of the first holding structure and the second holding structure.

Furthermore, it will be appreciated that, according to the invention, one of the defined deformation of the optical element and the position adjustment of the optical element may be omitted while still providing a very beneficial support to the optical element via the first holding structure, the second holding structure and the intermediate structure.

Thus, according to a tenth aspect of the invention there is provided and optical element module comprising an optical element and a support structure supporting the optical element. The support structure comprises a first holding structure, an intermediate structure and a second holding structure, the first holding structure contacting the optical element, the intermediate structure supporting the first holding structure, and the second holding structure supporting the intermediate structure. At least one of the first holding structure and the second holding structure is adapted to execute a function selected from the function group consisting of adjustably introducing defined deformations into the optical element and adjusting the position of the optical element.

According to an eleventh aspect of the invention there is provided a method of supporting an optical element comprising providing an optical element and a support structure supporting the optical element, the support structure comprising a first holding structure contacting the optical element, an intermediate structure and a second holding structure; supporting the first holding structure via the intermediate structure and supporting the intermediate structure via the second holding structure; executing at least one function via at least one of the first holding structure and the second holding structure, the at least one function being selected from the function group consisting of adjustably introducing defined deformations into the optical element and adjusting the position of the optical element.

Further aspects and embodiments of the invention will become apparent from the dependent claims and the following description of preferred embodiments which refers to the appended figures. All combinations of the features disclosed, whether explicitly recited in the claims or not, are within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a preferred embodiment of an optical imaging arrangement according to the invention which comprises an optical element module according to the invention and with which preferred embodiments of methods according to the invention may be executed;

Figure 2 is a schematic sectional representation of an optical element module of the opti- cal imaging arrangement of Figure 1 (section along line N-Il of Figure 3);

Figure 3 is a schematic top view of the optical element module of Figure 2;

Figure 4 is a block diagram of a preferred embodiment of an optical imaging method according to the invention comprising a method of supporting an optical element which may be executed with the optical imaging arrangement of Figure 1 ;

Figure 5 is a schematic sectional representation of a further preferred embodiment of an optical element module according to the invention that may be used in the optical imaging arrangement of Figure 1 ;

Figure 6 is a schematic sectional representation of a further preferred embodiment of an optical element module according to the invention that may be used in the optical imaging arrangement of Figure 1.

DETAILED DESCRIPTION OF THE INVENTION

First embodiment

In the following, a preferred embodiment of an optical imaging arrangement 101 according to the invention will be described with reference to Figures 1 to 3.

Figure 1 is a schematic and not-to-scale representation of the optical imaging arrangement in the form of an optical exposure apparatus 101. The optical exposure apparatus 101 com- prises an illumination unit 102 and an optical projection unit 103 adapted to transfer, in an exposure process, an image of a pattern formed on a mask 104.1 of a mask unit 104 onto a substrate 105.1 of a substrate unit 105. To this end, the illumination unit 102 illuminates the mask 104.1. The optical projection unit 103 receives the light coming from the mask 104.1 and projects the image of the pattern formed on the mask 104.1 onto the substrate 105.1 , e.g. a wafer or the like.

The optical projection unit 103 comprises a refractive optical element system including a plurality of refractive elements, such as lenses or the like. The optical element system is held by a stack of optical element modules including an optical element module 106 according to the invention with an optical element in the form of a lens 107.

Figure 2 and 3 show a schematic and not-to-scale sectional view and top view, respectively, of the optical element module 106. As can be seen from Figures 2 and 3, the lens 107 has a substantially rotationally symmetric lens body 107.1 with a spherical surface 107.2 that defines an axis 107.3 of rotational symmetry herein referred to as the optical axis 107.3 of the lens 107. The lens body 107.1 defines a radial direction R and a plane of main extension that are both substantially perpendicular to the optical axis 107.3.

The lens 107 is supported by a support structure 108 which in turn is connected to the other optical element modules of the optical projection unit 103. The support structure 108 comprises a first holding structure 109 contacting the lens 107, an intermediate structure in the form of a (preferably substantially rigid) first support ring 1 10 supporting the first holding

structure 109 and a second holding structure 1 11 in turn supporting the intermediate structure 1 10. Thus, in other words, the first holding structure 109 and the second holding structure 11 1 are arranged kinematically in series such that, for example, an alteration in the height (i.e. the dimension along the optical axis 107.3) of the first holding structure 109 does not influence the height of the second holding structure 1 11 and vice versa.

The first holding structure 109 comprises a plurality of first holding elements 109.1 as well as a plurality of second holding elements 109.2 (only one of each being shown in Figure 2 and 3, respectively, for reasons of clarity). The first holding elements 109.1 and the second holding elements 109.2 contact a surface 107.4 (in the embodiment shown, the lower surface 107.4) of the lens 107.

Both, the first holding elements 109.1 and the second holding elements 109.2 are evenly distributed at the outer circumference of the lens 107. However, it will be appreciated that, with other embodiments of the invention using reflective elements such as mirrors, a limitation to the outer circumference may not be necessary and an even distribution over the entire surface of the optical element (e.g. over the entire rear surface of the mirror) may be chosen.

Each of the first holding elements 109.1 exerts a first support force F1 on the lens 107 counteracting the gravitational force G acting on the lens 107, which, in the embodiment shown, acts in parallel to the optical axis 107.3. Similarly, each of the second holding elements 109.2 exerts a second support force F2 on the lens 107 counteracting the gravitational force G acting on the lens 107.

In the embodiment shown, the first and second support forces F1 and F2 act substantially in parallel to the gravitational force G. However, it will be appreciated that, with other embodiments of the invention, the first and second support forces F1 and F2 may have any other suitable orientation in space as long as they have a force component counteracting the gravi- tational force G in order to support the respective optical element.

To support the lens 107 with a defined second support force F2, each second holding element 109.2 comprises a passive resilient 109.4 element, such as a spring etc., exerting said second support force F2 on the lens 107. It will be appreciated that the passive second support force F2 may be adjusted by providing suitable adjustment means, such as adjustment screws or the like, allowing the adjustment of the pretension of the resilient element.

The first and second support forces F1 and F2 as well as the gravitational force G act on the lens 107 at different locations such that, as a function of the material properties of the lens

107, a certain deformation of the lens 107 (i.e. a certain deviation from the nominal geometry of the lens 107) arises.

As will be explained in further detail below, via the adjustment of the deformation of the lens 107 certain imaging errors, such as wavefront aberrations etc., of the optical projection unit 103 may be at least partly compensated or corrected as will be explained in further detail below.

In order to be able to actively adjust the deformation of the lens 107 each first holding element 109.1 comprises deformation adjusting device in the form of an active first actuator 109.3 supported on the first support ring 1 10. The first actuator 109.3 adjustably generates the respective first support force F1 exerted by the respective first holding element 107.1 on the lens 107. It will be appreciated that the first actuator 109.3 may be of any suitable design and may be working, for example, according to an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the first actuator 109.3 may be a piezo-actuator, a voice coil motor etc.

The deformation of the lens 107 that may be obtained depends, among others, on the number and distribution of the first holding elements 109.1 as well as the number and distribution of the second holding elements 109.2. Any total number of first and second holding elements 109.1 , 109.2 greater than three may be chosen depending on the type of deformation desired. Preferably, at least three first holding elements 109.1 as well as at least three sec- ond holding elements 109.2 are provided in order to achieve proper and sufficiently even support to the lens 107.

Furthermore, preferably, the number second holding elements 109.2 is equal to or greater than the number of the first holding elements 109.2. Thus, for example, along the circumference of the lens 107 every n-th holding element (with n>1 ) may be a first holding element 109.1. Typically, the number of first holding elements 109.2 is a function of the desired type of deformation of the lens 107 and, thus, a function of the type of imaging error to be corrected. For example, typically, the number of first holding elements 109.2 corresponds to the maximum order of lens deformation desired. However, it will be appreciated that, with other embodiments of the invention, the first support structure may comprise exclusively active holding elements adjustably generating support forces in order to provide the desired deformation of the optical element.

In the embodiment shown, an imaging error capturing device 1 12 is provided. This imaging error capturing device 112 captures one or more imaging errors of the optical element sys-

tern of the optical projection unit 103. For example, such an imaging error capturing device may use a part of the light of the illumination device 102 projected via all or part of the optical element system of the optical projection unit 103. As an alternative, light from a separate light source may be used. Furthermore, such a separate light source may operate at a wave- length which is identical to or different from the wavelength of the exposure light provided by the illumination device 102. Such imaging error capturing devices are well known in the art such that no further details will be given here in this respect.

The imaging error capturing device 112 is connected to a control device 1 13 and provides an imaging error signal representative of the respective imaging error captured to the control device. The control device 1 13, among others, is connected to the first actuators 107.3 of the first holding elements 107.1. The control device 1 13, as a function of the respective imaging error signal, controls the respective first support force F1 of the respective first actuator 107.3 in order to provide a deformation of the lens 107 at least partially compensating the respective imaging error.

As it becomes particularly clear from Figure 2, any alteration in the first support force F1 of the respective first holding element 109.1 causes an alteration of the second support force F2 of the respective second holding element 109.2 to reinstate the force equilibrium with the gravitational force G acting on the lens 107. Since the second holding elements 109.2 comprise simple passive spring elements 109.4 (changing their length as a function of the force applied) this also leads to an alteration in the position of the lens 107.

Such an alteration in the position of the lens 107 typically leads to a reduction in the imaging quality of the optical projection unit 103. In order to compensate for this effect the second support structure 1 11 is adapted to adjust the position of the first support ring 110 and, consequently, the position of the first support structure 109 as well as the position of the lens 107 held by the first support structure 109.

To this end, the second support structure 11 1 comprises a plurality of third holding elements

1 11.1 supported on an interface structure in the form of a second support ring 11 1.2. The third holding elements 1 11.1 support the first support ring 1 10. The second support ring

1 11.2 forms an interface of the second support structure 11 1 to and outer module housing 106.1 of the lens module 106.

Each third holding element 11 1.1 comprises a second actuator 11 1.3 adapted to adjust the length of the respective third holding element 11 1.1. It will be appreciated that the second actuator 11 1.3 may be of any suitable design and may be working, for example, according to

an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the second actuator 11 1.3 may be a piezo-actuator, a voice coil motor etc.

As can be seen from Figure 2 and 3, three holding element pairs 11 1.4 are provided, each comprising two third holding elements 11 1.1 arranged in the manner of a bipod.

The second support structure 11 1 supports the first support ring 110 in a statically determinate way in the manner of a hexapod. It will be appreciated that the bipods 1 11.4 - that are illustrated in a highly simplified manner in Figure 2 and 3 - may be used for generating a motion of the first support ring 1 10, thereby actively positioning the first support ring 110 and with it the first support structure 109 and the lens 107 in up to six degrees of freedom (DOF).

However, it will be appreciated that instead of the bipods 1 11.4, any other suitable second support structures may be provided to support the first support structure and the lens. Furthermore, it will be appreciated that, with other embodiments of the invention, position adjustment may be provided only in less than six degrees of freedom (DOF). For example, depending on the imaging error correction or compensation to be achieved, it may be sufficient that translational position adjustment parallel to the plane of main extension of the optical element (i.e. 2 DOF) and/or along the optical axis of the optical element (i.e. 3 DOF or 1 DOF) is provided.

As can be seen from Figure 3, the three holding element pairs 11 1.4 are evenly distributed at the outer circumference of the first support ring 110, i.e. they are mutually rotated about the optical axis 107.3 by an angle α=120° such that they are equiangularly distributed at the outer circumference of the first support ring 110. However, it will be appreciated that, with other embodiments of the invention any other suitable angle of rotation may be chosen between the holding element pairs.

In order to control the position adjustment operation of the second support structure 1 11 there is provided a position capturing device 114 capturing a position value representative of a relative position of the lens 107 with respect to a given reference. The reference may be any suitable real component or virtual component (e.g. an optical plane etc.) of the exposure apparatus 101.

The position capturing device 114 provides a position signal representative of the position value to the control device 113. The control device 113 in turn controls the second actuators

1 11.3 as a function of the position signal in order to properly position the lens 107 via the first support ring 1 10 and the first support structure at 109.

It will be appreciated that the position capturing device may be of any suitable design providing the desired position signal. For example, with certain embodiments of the invention, the first actuators 109.3 and the second actuators 1 11.3 may form part of the position capturing device 114, each providing a signal representative of the actual length of the respective first and third holding element and, thus, providing an information on the position of the lens 107 in relation to the interface structure 1 11.2.

However, it will be appreciated that, with other embodiments of the invention, the position of the lens 107 may be controlled via the control device 1 13 and the second actuators 1 11.3 as a function of an imaging error signal provided by the imaging error capturing device 1 12. Furthermore, a position signal as described above may be used in addition to this imaging error signal.

The kinematically serial arrangement of the first support structure 109 and the second sup- port structure 1 1 1 has the advantage that an alteration in the position of the lens 107 may be obtained via the second support structure 11 1 without influencing the deformation of the lens 107 provided via the first support structure 109. For example, it is possible to compensate thermal expansion related motion of the lens 107 without influencing the deformation of the lens provided by the first support structure 109.

On the other hand, the deformation control of the lens 107 and a position control of the lens 107 may be provided independently but contemporaneously, thereby allowing rapid reaction to altered boundary conditions within the exposure apparatus, e.g. during an exposure process, as well as providing a defined desired deformation and/or position alteration of the lens 107.

It will be appreciated that, with other embodiments of the invention, instead of the standing arrangement of the first support structure 109 and the second support structure 11 1 shown in Figure 2, a hanging arrangement may be chosen for the first support structure and/or the second support structure. If a hanging arrangement is chosen for one of the first and second support structure, a very compact design may be achieved as can be seen from dashed con- tour 115 in Figure 2 indicating a hanging arrangement of the second support structure.

Furthermore, it will be appreciated that, with other embodiments of the invention, more than one optical element may be held as described above in the respective optical element mod-

ule. A very compact arrangement may be achieved if a mutually penetrating arrangement of the second support structures is chosen as it is disclosed in the International Patent Application Serial No. PCT/EP2005/005600 published as WO 2005/116773 A1 (Kugler et al.), the entire contents of which is incorporated herein by reference.

With the optical exposure apparatus 101 of Figure 1 a preferred embodiment of an optical imaging method according to the invention comprising a method of supporting an optical element according to the invention may be executed as it will be described in the following with reference to Figure 1 to 4.

In a step 116.1 , the components of the optical exposure apparatus 101 including the mask 104.1 with a pattern, the substrate 105.1 , the optical projection unit 103 adapted to transfer an image of the pattern of the mask 104.1 onto the substrate 105.1 and comprising the optical element unit 106 as well as the illumination unit 102 adapted to illuminate the pattern of the mask 104.1 are provided.

In a step 116.2, the components of the optical exposure apparatus 101 are put into a spatial relation to provide the configuration as it has been described in the context of Figures 1 to 3. In a step 116.3, the lens 107 is actively deformed and/or positioned via the first support structure 109 and the second support structure 1 11 as it has been described above.

In a step 116.4, the illumination system 102 is then used to illuminate the pattern of the mask 104.1 , such that the optical projection unit 103 transfers an image of the pattern of the mask 104.1 onto the substrate 105.1 as it has been described above.

It will be appreciated that active deformation and/or position control of the lens 107 provided in step 1 16.3 may occur on a regular basis or driven by certain events during an exposure process. Thus, in a step 1 16.5 it is determined if the processes to be stopped. If this is not the case, e.g. if a further exposure step is to be performed, the method jumps back to step 1 16.3. This may be the case, for example, in a step and scan exposure process, where step 1 16.3 may be executed between subsequent scan processes. Otherwise the process stops in a step 1 16.6.

It will be appreciated that, with other embodiments of the invention, the function of adjusting the position of the optical element and introducing a defined deformation into the optical ele- ment may be exchanged between the first holding structure and the second holding structure. For example, a modified second holding structure supporting the intermediate structure could then be designed in the manner as it has been described above for the first holding

structure 109 while a modified first holding structure could then be designed in the manner as it has been described above for the second holding structure 11 1.

In this case, for example, the modified second holding structure would introduce a defined deformation into the intermediate structure which would then be transferred via the modified first holding structure into the optical element. To this end, the modified first holding structure would then preferably support the optical element on the intermediate structure in a statically overdeterminate way (e.g. by introducing one or more further bipods similar to the bipod 1 11.4) in order to be able to easily transfer the desired deformation of the intermediate structure into the optical element.

Second embodiment

In the following, a further preferred embodiment of an optical imaging arrangement according to the invention will be described with reference to Figures 1 and 5.

Figure 5 shows a schematic and not-to-scale sectional view of a further preferred optical element module 206 according to the invention holding a lens 207. The optical element module 206 may replace the optical element module 106 in the exposure apparatus 101 of Figure 1.

As can be seen from Figure 5, the lens 207 of the optical element module 206 has a substantially rotationally symmetric lens body 207.1 with a spherical surface 207.2 that defines an axis 207.3 of rotational symmetry herein referred to as the optical axis 207.3 of the lens 207. The lens body 207.1 defines a radial direction R and a plane of main extension that are both substantially perpendicular to the optical axis 207.3.

The lens 207 is supported by a support structure 208 which in turn is connected to the other optical element modules of the optical projection unit 103. The support structure 208 comprises a first holding structure 209 contacting the lens 207, an intermediate structure in the form of a (preferably substantially rigid) first support ring 210 supporting the first holding structure 209 and a second holding structure 21 1 in turn supporting the intermediate structure 210. Thus, in other words, the first holding structure 209 and the second holding structure 211 are arranged kinematically in series such that, for example, an alteration in the height (i.e. the dimension along the optical axis 207.3) of the first holding structure 209 does not influence the height of the second holding structure 21 1 and vice versa.

The first holding structure 209 comprises a plurality of first holding elements 209.1 as well as a plurality of second holding elements 209.2 (only one of each being shown in Figure 2 and

3, respectively, for reasons of clarity). Each of the first holding elements 209.1 has a contact element 209.5 rigidly contacting the lens 207, e.g. rigidly clamping the lens 207, at its outer circumference and a bipod 209.6 supporting the contact element 209.5. Each of the second holding elements 209.2 contacts the lower surface 207.4 of the lens 207.

Both, the first holding elements 209.1 and the second holding elements 209.2 are evenly distributed at the outer circumference of the lens 207. However, it will be appreciated that, with other embodiments of the invention using reflective elements such as mirrors, a limitation to the outer circumference may not be necessary and an even distribution over the entire surface of the optical element (e.g. over the entire back surface of the mirror) may be cho- sen.

Each of the first holding elements 209.1 exerts a first support force F1 on the lens 207 counteracting the gravitational force G acting on the lens 207, which, in the embodiment shown, acts in parallel to the optical axis 207.3. Similarly, each of the second holding elements

209.2 exerts a second support force F2 on the lens 207 counteracting the gravitational force G acting on the lens 207.

To support the lens 207 with a defined second support force F2, each second holding element 209.2 comprises a passive resilient 209.4 element, such as a spring etc., exerting said second support force F2 on the lens 207. It will be appreciated that the passive second support force F2 may be adjusted by providing suitable adjustment means, such as adjustment screws or the like, allowing the adjustment of the pretension of the resilient element.

The first and second support forces F1 and F2 as well as the gravitational force G act on the lens 207 at different locations such that, as a function of the material properties of the lens 207, a certain deformation of the lens 207 (i.e. a certain deviation from the nominal geometry of the lens 207) arises.

As will be explained in further detail below, via the adjustment of the deformation of the lens 207 certain imaging errors, such as wavefront aberrations etc., of the optical projection unit 203 may be at least partly compensated or corrected as will be explained in further detail below.

In order to be able to actively adjust the deformation of the lens 207 each first holding ele- ment 209.1 comprises deformation adjusting device in the form of two active first actuators

209.3 supported on the first support ring 210. Each first actuator 209.3 is connected to a first end of a first lever 209.7 the second end of which is rigidly connected to the contact element

209.5. One of the first levers 209.7 primarily extends substantially parallel to the radial direction R of the lens 207 while the other one of the first levers 209.7 primarily extends tangen- tially to the circumference of the lens 207.

The respective first actuator 209.3 via the associated first lever 209.7 adjustably generates the respective first support force F1 as well as a moment exerted via the respective contact element 209.5 on the lens 207. It will be appreciated that the first actuator 209.3 may be of any suitable design and may be working, for example, according to an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the first actuator 209.3 may be a piezo-actuator, a voice coil motor etc.

It will be further appreciated that the length and the elasticity of the respective first lever

209.7 is selected such that the first lever 209.7 provides a defined transmission of excursions between its first end and its second end via elastic deformation. Thus, very fine adjustments of the contact element 209.5 may be obtained from via the first actuators 209.3.

The deformation of the lens 207 that may be obtained depends, among others, on the num- ber and distribution of the first holding elements 209.1 as well as the number and distribution of the second holding elements 209.2. Any total number of first and second holding elements 209.1 , 209.2 greater than three may be chosen depending on the type of deformation desired. Preferably, at least three first holding elements 209.1 as well as at least three second holding elements 209.2 are provided in order to achieve proper and sufficiently even support to the lens 207.

Furthermore, preferably, the number second holding elements 209.2 is equal to or greater than the number of the first holding elements 209.2. Thus, for example, along the circumference of the lens 207 every n-th holding element (with n>1 ) may be a first holding element 209.1. Typically, the number of first holding elements 209.2 is a function of the desired type of deformation of the lens 207 and, thus, a function of the type of imaging error to be corrected. For example, typically, the number of first holding elements 209.2 corresponds to the maximum order of lens deformation desired. However, it will be appreciated that, with other embodiments of the invention, the first support structure may comprise exclusively active holding elements adjustably generating support forces in order to provide the desired defor- mation of the optical element.

In the embodiment shown, again, the imaging error capturing device 112 is used to capture one or more imaging errors of the optical element system of the optical projection unit 103 as it has been described above in the context of the first embodiment.

The imaging error capturing device 1 12 again provides an imaging error signal representative of the respective imaging error captured to the control device 113. The control device 1 13, among others, is now connected to the first actuators 207.3 of the first holding elements 207.1. The control device 113, as a function of the respective imaging error signal, controls the respective first support force F1 and the moment exerted on the lens 207 by the respective first actuator 207.3 in order to provide a deformation of the lens 207 at least partially compensating the respective imaging error.

Alterations in the orientation of the respective contact element 209.5 as well as alterations in the first support force F1 and the moments of the respective first holding element 209.1 may cause an alteration of the second support force F2 of the respective second holding element 209.2 to reinstate the force equilibrium with the gravitational force G acting on the lens 207. Since the second holding elements 209.2 comprise simple passive spring elements 209.4 (changing their length as a function of the force applied) this also may lead to an alteration in the position of the lens 207.

Such an alteration in the position of the lens 207 typically leads to a reduction in the imaging quality of the optical projection unit 203. In order to compensate for this effect the second support structure 211 is adapted to adjust the position of the first support ring 210 and, consequently, the position of the first support structure 209 as well as the position of the lens 207 held by the first support structure 209.

To this end, the second support structure 211 comprises a plurality of third holding elements

211.1 supported on an interface structure in the form of a second support ring 21 1.2. The third holding elements 211.1 support the first support ring 210. The second support ring

211.2 forms an interface of the second support structure 21 1 to and outer module housing 206.1 of the lens module 206.

Each third holding element 211.1 comprises a connecting element 211.5 connecting the first support ring 210 and a second support ring 21 1.2, two second actuators 211.3 supported on the second support ring 21 1.2 and two second levers 21 1.6 connecting the respective second actuator 211.3 and the connecting element 21 1.5.

Each second actuator 21 1.3 is connected to a first end of one of the second levers 21 1.6 the second end of which is rigidly connected to a central block 211.7 of the connecting element 211.5. One of the second levers 21 1.6 primarily extends substantially parallel to the radial direction R of the lens 207 while the other one of the second levers 21 1.6 primarily extends tangentially to the circumference of the lens 207.

Via the associated second lever 21 1.6 the respective second actuator 21 1.3 adjusts the orientation and location of the central block 21 1.7. Since the central block 21 1.7 is hinged to leaf spring elements 21 1.8 of the connecting element 21 1.5 the motion of the central block 211.7 causes a motion of the first support ring 210 and, thus, a position adjustment of the lens 207 in the manner as it has been disclosed in International Patent Application Serial No. PCT/EP2006/004337 mentioned initially.

It will be appreciated that the second actuator 21 1.3 may be of any suitable design and may be working, for example, according to an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the second actuator 21 1.3 may be a piezo-actuator, a voice coil motor etc.

It will be further appreciated that the length and the elasticity of the respective second lever 211.6 is selected such that the second lever 21 1.6 provides a defined transmission of excursions between its first end and its second end via elastic deformation. Thus, very fine adjustments of the connecting element 211.5 and, consequently, of the lens 207 may be ob- tained via the second actuators 21 1.3.

The second support structure 21 1 comprises three third holding elements 21 1.1 supporting the first support ring 210 in a statically determinate way. It will be appreciated that the third holding elements 21 1.1 may be used for generating a motion of the first support ring 210, thereby actively positioning the first support ring 210 and with it the first support structure 209 and the lens 207 in up to six degrees of freedom (DOF).

However, it will be appreciated that instead of the third holding elements 21 1.1 , any other suitable second support structures may be provided to support the first support structure and the lens. Furthermore, it will be appreciated that, with other embodiments of the invention, position adjustment may be provided only in less than six degrees of freedom (DOF). For example, depending on the imaging error correction or compensation to be achieved, it may be sufficient that translational position adjustment parallel to the plane of main extension of the optical element (i.e. 2 DOF) and/or along the optical axis of the optical element (i.e. 3 DOF or 1 DOF) is provided.

The three third holding elements 21 1.1 are evenly distributed at the outer circumference of the first support ring 210, i.e. they are mutually rotated about the optical axis 207.3 by an angle α=120° such that they are equiangularly distributed at the outer circumference of the first support ring 210. However, it will be appreciated that, with other embodiments of the

invention any other suitable angle of rotation may be chosen between the third holding elements.

In order to control the position adjustment operation of the second support structure 211 there is provided a position capturing device 1 14 capturing a position value representative of a relative position of the lens 207 with respect to a given reference. The reference may be any suitable real component or virtual component (e.g. an optical plane etc.) of the exposure apparatus 101.

The position capturing device 1 14 provides a position signal representative of the position value to the control device 113. The control device 213 in turn controls the second actuators 211.3 as a function of the position signal in order to properly position the lens 207 via the first support ring 210 and the first support structure at 209.

It will be appreciated that the position capturing device 114 may be of any suitable design providing the desired position signal. For example, with certain embodiments of the invention, the first actuators 209.3 and the second actuators 21 1.3 may form part of the position capturing device de 114, each providing a signal representative of the actual length of the respective first and third holding element and, thus, providing an information on the position of the lens 207 in relation to the interface structure 211.2.

However, it will be appreciated that, with other embodiments of the invention, the position of the lens 207 may be controlled via the control device 113 and the second actuators 211.3 as a function of an imaging error signal provided by the imaging error capturing device 1 12. Furthermore, a position signal as described above may be used in addition to this imaging error signal.

The kinematically serial arrangement of the first support structure 209 and the second support structure 211 has the advantage that an alteration in the position of the lens 207 may be obtained via the second support structure 21 1 without influencing the deformation of the lens 207 provided via the first support structure 209. For example, it is possible to compensate thermal expansion related motion of the lens 207 without influencing the deformation of the lens provided by the first support structure 209.

On the other hand, the deformation control of the lens 207 and a position control of the lens 207 may be provided independently but contemporaneously, thereby allowing rapid reaction to altered boundary conditions within the exposure apparatus, e.g. during an exposure proc-

ess, as well as providing a defined desired deformation and/or position alteration of the lens 207.

It will be appreciated that, with other embodiments of the invention, instead of the standing arrangement of the first support structure 209 and the second support structure 21 1 shown in Figure 5, a hanging arrangement may be chosen for the first support structure and/or the second support structure. If a hanging arrangement is chosen for one of the first and second support structure, a very compact design may be achieved as it has already been explained in the context of the first embodiment.

Furthermore, it will be appreciated that, with other embodiments of the invention, more than one optical element may be held as described above in the respective optical element module. A very compact arrangement may be achieved if a mutually penetrating arrangement of the second support structures is chosen as it is disclosed in the International Patent Application Serial No. PCT/EP2005/005600 published as WO 2005/116773 A1 (Kugler et al.), the entire contents of which is incorporated herein by reference.

It will be appreciated that with the optical exposure apparatus 101 of Figure 1 incorporating the optical element module 206 of Figure 5 the optical imaging method as it has been described above in the context of Figure 4 may be executed. Thus it is here only referred to the explanations given above in the context of the first embodiment.

Third embodiment

In the following, a further preferred embodiment of an optical imaging arrangement according to the invention will be described with reference to Figures 1 and 6.

Figure 6 shows a schematic and not-to-scale sectional view of a further preferred optical element module 306 according to the invention holding a lens 307. The optical element module 306 may replace the optical element module 106 in the exposure apparatus 101 of Figure 1.

As can be seen from Figure 6, the lens 307 of the optical element module 306 has a substantially rotationally symmetric lens body 307.1 with a spherical surface 307.2 that defines an axis 307.3 of rotational symmetry herein referred to as the optical axis 307.3 of the lens 307. The lens body 307.1 defines a radial direction R and a plane of main extension that are both substantially perpendicular to the optical axis 307.3.

The lens 307 is supported by a support structure 308 which in turn is connected to the other optical element modules of the optical projection unit 103. The support structure 308 comprises a first holding structure 309 contacting the lens 307, an intermediate structure in the form of a (preferably substantially rigid) first support ring 310 supporting the first holding structure 309 and a second holding structure 311 in turn supporting the intermediate structure 310. Thus, in other words, the first holding structure 309 and the second holding structure 311 are arranged kinematically in series such that, for example, an alteration in the dimensions of the first holding structure 309 does not influence the dimensions of the second holding structure 311 and vice versa.

The first holding structure 309 comprises a plurality of first holding elements 309.1 as well as a plurality of second holding elements 309.2 (only one of each being shown in Figure 2 and 3, respectively, for reasons of clarity). The first holding elements 309.1 and the second holding elements 309.2 contact the lower surface 307.4 of the lens 307.

Both, the first holding elements 309.1 and the second holding elements 309.2 are evenly distributed at the outer circumference of the lens 307. However, it will be appreciated that, with other embodiments of the invention using reflective elements such as mirrors, a limitation to the outer circumference may not be necessary and an even distribution over the entire surface of the optical element (e.g. over the entire back surface of the mirror) may be chosen.

Each of the first holding elements 309.1 exerts a first support force F1 on the lens 307 counteracting the gravitational force G acting on the lens 307, which, in the embodiment shown, acts in parallel to the optical axis 307.3. Similarly, each of the second holding elements 309.2 exerts a second support force F2 on the lens 307 counteracting the gravitational force G acting on the lens 307.

To support the lens 307 with a defined second support force F2, each second holding element 309.2 comprises a passive resilient 309.4 element in the form of a leaf spring exerting said second support force F2 on the lens 307. It will be appreciated that the passive second support force F2 may be adjusted by providing suitable adjustment means, such as adjustment screws or the like, allowing the adjustment of the pretension of the resilient element.

The first and second support forces F1 and F2 as well as the gravitational force G act on the lens 307 at different locations such that, as a function of the material properties of the lens 307, a certain deformation of the lens 307 (i.e. a certain deviation from the nominal geometry of the lens 307) arises.

As will be explained in further detail below, via the adjustment of the deformation of the lens 307 certain imaging errors, such as wavefront aberrations etc., of the optical projection unit 303 may be at least partly compensated or corrected as will be explained in further detail below.

In order to be able to actively adjust the deformation of the lens 307 each first holding element 309.1 comprises deformation adjusting device in the form of an active first actuator 309.3 supported on the first support ring 310 and acting via a first lever 309.5 on a leaf spring 309.6 supporting the lens 307. The first actuator 309.3 adjusts the respective first support force F1 exerted by the respective first holding element 307.1 on the lens 307. It will be ap- preciated that the first actuator 309.3 may be of any suitable design and may be working, for example, according to an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the first actuator 309.3 may be a piezo- actuator, a voice coil motor etc.

The deformation of the lens 307 that may be obtained depends, among others, on the num- ber and distribution of the first holding elements 309.1 as well as the number and distribution of the second holding elements 309.2. Any total number of first and second holding elements 309.1 , 309.2 greater than three may be chosen depending on the type of deformation desired. Preferably, at least three first holding elements 309.1 as well as at least three second holding elements 309.2 are provided in order to achieve proper and sufficiently even support to the lens 307. Further preferably, a large number of second holding elements 309.2 is provided in order to achieve as even nominal support as possible to the lens 307.

Furthermore, preferably, the number second holding elements 309.2 is equal to or greater than the number of the first holding elements 309.2. Thus, for example, along the circumference of the lens 307 every n-th holding element (with n>1 ) may be a first holding element 309.1. Typically, the number of first holding elements 309.2 is a function of the desired type of deformation of the lens 307 and, thus, a function of the type of imaging error to be corrected. For example, typically, the number of first holding elements 309.2 corresponds to the maximum order of lens deformation desired. However, it will be appreciated that, with other embodiments of the invention, the first support structure may comprise exclusively active holding elements adjustably generating support forces in order to provide the desired deformation of the optical element.

In the embodiment shown, again, the imaging error capturing device 112 is used to capture one or more imaging errors of the optical element system of the optical projection unit 103 as it has been described above in the context of the first embodiment.

The imaging error capturing device 1 12 again provides an imaging error signal representative of the respective imaging error captured to the control device 1 13. The control device 1 13, among others, is now connected to the first actuators 307.3 of the first holding elements 307.1. The control device 1 13, as a function of the respective imaging error signal, controls the respective first support force F1 exerted on the lens 307 by the respective first holding element 309.1 in order to provide a deformation of the lens 307 at least partially compensating the respective imaging error.

Any alteration in the first support force F1 of the respective first holding element 309.1 causes an alteration of the second support force F2 of the respective second holding ele- ment 309.2 to reinstate the force equilibrium with the gravitational force G acting on the lens 307. Since the second holding elements 309.2 comprise simple passive spring elements 309.4 (changing their shape as a function of the force applied) this also leads to an alteration in the position of the lens 307.

Such an alteration in the position of the lens 307 typically leads to a reduction in the imaging quality of the optical projection unit 303. In order to compensate for this effect the second support structure 311 is adapted to adjust the position of the first support ring 310 and, consequently, the position of the first support structure 309 as well as the position of the lens 307 held by the first support structure 309.

To this end, the second support structure 311 comprises a plurality of third holding elements 311.1 connected to an interface structure in the form of a second support ring 311.2. The third holding elements 31 1.1 hold the first support ring 310. The second support ring 311.2 forms an interface of the second support structure 311 to and outer module housing 306.1 of the lens module 306.

Each third holding element 31 1.1 comprises a connecting element 31 1.5 cardanically hinged to the first support ring 310 and to the second support ring 311.2, a second actuator 311.3 supported on the second support ring 311.2 and a second lever 31 1.6 connecting the second actuator 31 1.3 and the connecting element 31 1.5.

The second actuator 31 1.3 is connected to a first end of the second lever 31 1.6 the second end of which is rigidly connected to the connecting element 31 1.5. The second lever 311.6 is angled and has a one main extension parallel to the radial direction R of the lens 307.

Via the second lever 311.6 the respective second actuator 31 1.3 adjusts the orientation and location of the connecting element 31 1.5. Since the connecting element 31 1.5 is hinged to

the first support ring 310 and the second support ring 31 1.2 the motion of the connecting element of 311.5 causes a motion of the first support ring 310 and, thus, a position adjustment of the lens 307 in the manner as it has been disclosed in International Patent Application Serial No. PCT/EP2006/004337 mentioned initially.

It will be appreciated that the second actuator 31 1.3 may be of any suitable design and may be working, for example, according to an electric, an electromechanical, a pneumatic or a hydraulic working principle or any combination thereof. For example, the second actuator 31 1.3 may be a piezo-actuator, a voice coil motor etc.

It will be further appreciated that the length and the elasticity of the respective second lever 311.6 is selected such that the second lever 311.6 provides a defined transmission of excursions between its first end and its second end via elastic deformation. Thus, very fine adjustments of the connecting element 31 1.5 and, consequently, of the lens 307 may be obtained via the second actuators 31 1.3.

The second support structure 311 comprises three third holding elements 31 1.1 supporting the first support ring 310 in a statically determinate way. It will be appreciated that the third holding elements 31 1.1 may be used for generating a motion of the first support ring 310, thereby actively positioning the first support ring 310 and with it the first support structure 309 and the lens 307 in up to six degrees of freedom (DOF).

However, it will be appreciated that instead of the third holding elements 31 1.1 , any other suitable second support structures may be provided to support the first support structure and the lens. Furthermore, it will be appreciated that, with other embodiments of the invention, position adjustment may be provided only in less than six degrees of freedom (DOF). For example, depending on the imaging error correction or compensation to be achieved, it may be sufficient that translational position adjustment parallel to the plane of main extension of the optical element (i.e. 2 DOF) and/or along the optical axis of the optical element (i.e. 3 DOF or 1 DOF) is provided.

The three third holding elements 311.1 are evenly distributed at the outer circumference of the first support ring 310, i.e. they are mutually rotated about the optical axis 307.3 by an angle α=120° such that they are equiangularly distributed at the outer circumference of the first support ring 310. However, it will be appreciated that, with other embodiments of the invention any other suitable angle of rotation may be chosen between the third holding elements.

In order to control the position adjustment operation of the second support structure 311 there is provided a position capturing device 1 14 capturing a position value representative of a relative position of the lens 307 with respect to a given reference. The reference may be any suitable real component or virtual component (e.g. an optical plane etc.) of the exposure apparatus 101.

The position capturing device 1 14 provides a position signal representative of the position value to the control device 1 13. The control device 313 in turn controls the second actuators 311.3 as a function of the position signal in order to properly position the lens 307 via the first support ring 310 and the first support structure at 309.

It will be appreciated that the position capturing device 1 14 may be of any suitable design providing the desired position signal. For example, with certain embodiments of the invention, the first actuators 309.3 and the second actuators 311.3 may form part of the position capturing device de 1 14, each providing a signal representative of the actual length of the respective first and third holding element and, thus, providing an information on the position of the lens 307 in relation to the interface structure 311.2.

However, it will be appreciated that, with other embodiments of the invention, the position of the lens 307 may be controlled via the control device 1 13 and the second actuators 311.3 as a function of an imaging error signal provided by the imaging error capturing device 1 12. Furthermore, a position signal as described above may be used in addition to this imaging error signal.

The kinematically serial arrangement of the first support structure 309 and the second support structure 311 has the advantage that an alteration in the position of the lens 307 may be obtained via the second support structure 31 1 without influencing the deformation of the lens 307 provided via the first support structure 309. For example, it is possible to compensate thermal expansion related motion of the lens 307 without influencing the deformation of the lens provided by the first support structure 309.

On the other hand, the deformation control of the lens 307 and a position control of the lens 307 may be provided independently but contemporaneously, thereby allowing rapid reaction to altered boundary conditions within the exposure apparatus, e.g. during an exposure proc- ess, as well as providing a defined desired deformation and/or position alteration of the lens 307.

It will be appreciated that, compared to the other embodiments with their standing or hanging arrangement of the first support structure 309 and the second support structure 31 1 , the arrangement shown in Figure 6 with its substantially coplanar first and second structures provides a design that is very compact in the direction of the optical axis 307.3 of the lens 307.

It will be appreciated that with the optical exposure apparatus 101 of Figure 1 incorporating the optical element module 306 of Figure 6 the optical imaging method as it has been described above in the context of Figure 4 may be executed. Thus it is here only referred to the explanations given above in the context of the first embodiment.

In the foregoing, the invention has been described solely in the context of embodiments where the optical axis of the optical element to be supported is substantially parallel to the direction of the gravitational force acting on the optical element. However, it will be appreciated that, with other embodiments of the invention, any other orientation of the optical axis defined for the optical element with respect to the gravitational force may be given.

Furthermore, in the foregoing, the invention has been described solely in the context of purely refractive systems, in particular, comprising spherical lenses. However, it will be appreciated that, with other embodiments of the invention, the invention may be used in the context of exclusively reflective or diffractive optical systems as well as optical systems comprising any combination of reflecting elements, refractive and/or diffractive elements. Furthermore, any type and design of optical element may be used. For example, optical ele- ments with spherical, aspherical or planar optical surfaces may be used.

In the foregoing, the invention has been described solely in the context of embodiments where one of the first holding structure and the second holding structure provides position adjustment of the optical element while the other one of the first holding structure and the second holding structure provides a defined deformation of the optical element. However, has mentioned initially, it will be appreciated that, with other embodiments of the invention, one of the defined deformation of the optical element and the position adjustment of the optical element may be omitted while still providing a very beneficial support to the optical element via the first holding structure, the second holding structure and the intermediate structure. For example, in the embodiments outlined above, this may be done by providing a simple rigid support via one of the holding structures or by providing the same function (i.e. position adjustment or defined deformation) via both the first holding structure and the second holding structure.

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