WO2009124590A1

WO2009124590A1 - Optical aperture device

Info

Publication number: WO2009124590A1
Application number: PCT/EP2008/054311
Authority: WO
Inventors: Hermann Bieg; Uy-Liem Nguyen
Original assignee: Carl Zeiss Smt Ag
Priority date: 2008-04-09
Filing date: 2008-04-09
Publication date: 2009-10-15

Abstract

There is provided an optical module comprising an aperture device and a support structure supporting the aperture device, the aperture device defining an aperture edge and an aperture plane. The aperture edge is adapted to define a geometry of a light beam passing the aperture device along an optical axis. The support structure is adapted to hold the aperture device in a defined manner when the aperture plane is inclined with respect to a horizontal plane. A temperature distribution prevails within the aperture device and at least one of the aperture device and the support structure is adapted to maintain at least one of a relative position of the aperture edge with respect to the optical axis and a geometry of the aperture edge substantially unaltered upon an introduction of a thermal energy into the aperture device, the thermal energy being adapted to cause an alteration in the temperature distribution.

Description

OPTICAL APERTURE DEVICE

BACKGROUND OF THE INVENTION

The invention relates to an optical module that may be used within an optical device used in exposure processes, in particular in microlithography systems. It further relates to an optical imaging arrangement comprising such an optical module. It further relates to a method of defining the geometry of a light beam used within such an optical device. 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. Further components of such optical systems are aperture devices defining the geometry of the light beam used in the exposure process.

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 optical system components which, in turn, guarantees a high quality exposure process. In 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 2005/0002011 A1 (Sudoh), the entire disclosure of which is hereby incorporated herein by reference.

A further source of such imaging errors may be an alteration in the relative position of an aperture device used within the optical system with respect to the optical axis defined by the optical elements system. For example, a telecentricity error may result from such an alteration in the relative position. A reason for such an alteration in the relative position of the aperture of the aperture device may be a thermally induced alteration within the geometry of components the aperture device (i.e. a positive or negative expansion of these components).

In particular, within the microlithography systems mentioned above, due to the high radiation power of the light used in the exposure process, a high thermal load due to absorption of the exposure light acts on the aperture device. This is the case at any location within the optical exposure system. However, particularly high thermal loads typically occur in the illumination system of the optical exposure system. In particular, in so-called EUV systems (working with exposure light in the extreme UV range at a wavelength below 20 nm, typically in the range of 13 nm) a rather high thermal load acts on the components due to the high absorption rate at these wavelengths.

In order to deal which such imaging errors resulting from an alteration within the position of the aperture of the aperture device with respect to the optical axis typical aperture devices (having a horizontal orientation) are supported using a support configuration with three pins having spherical end surfaces, each end surface running in a substantially V-shaped groove extending in a horizontal plane as it is known, for example, from WO 2005/050322 A1 (Bieg et al.), the entire disclosure of which is incorporated herein by reference. Typically, the longitudinal axes of the grooves intersect at the thermal center of the aperture device. Due to the gravitational force acting on the aperture device, a self centering design is achieved where the aperture maintains its relative position with respect to the optical axis.

While this configuration may be suitable for a configuration with a horizontally oriented aperture device, any susceptible inclination with respect to the horizontal plane renders this solution unsuitable since the self centering effect due to the gravitational force is not reliably present anymore due to the component of the gravitational force acting parallel to the plane of the aperture. SUMMARY OF THE INVENTION

It is thus an object of the invention to, at least to some extent, overcome the above disadvantages and to provide good and long term reliable imaging properties of an optical device used in an exposure process and comprising an aperture device, even if the aperture device has a non-horizontal orientation.

It is a further object of the invention to reduce the effort necessary for an optical device comprising an aperture device used in an exposure process while at least maintaining the imaging accuracy during operation of the optical device even if the aperture device has a non-horizontal orientation.

These objects are achieved according to the invention which is based on the teaching that it is possible to maintain at least one of the a relative position of the aperture edge with respect to the optical axis and a geometry of the aperture edge substantially unaltered upon an introduction of a thermal energy into the aperture device even if the aperture plane of the aperture device has a non-horizontal orientation by suitably designing either the support structure holding the aperture device in a defined manner or the aperture device itself.

Thus, according to a first aspect of the invention there is provided an optical module comprising an aperture device and a support structure supporting the aperture device, the aperture device defining an aperture edge and an aperture plane. The aperture edge is adapted to define a geometry of a light beam passing the aperture device along an optical axis. The support structure is adapted to hold the aperture device in a defined manner when the aperture plane is inclined with respect to a horizontal plane. A temperature distribution prevails within the aperture device and at least one of the aperture device and the support structure is adapted to maintain at least one of a relative position of the aperture edge with respect to the optical axis and a geometry of the aperture edge substantially unaltered upon an introduction of a thermal energy into the aperture device, the thermal energy being adapted to cause an alteration in the temperature distribution.

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 receive a substrate, an illumination unit adapted to illuminate the pattern and an optical projection unit adapted to transfer an image of the pattern onto the substrate. Each of the illumination unit and the optical projection unit comprises a system of optical elements, the system of optical elements defining an optical axis. At least one of the illumination unit and the optical projection unit comprises an optical module, the optical module comprising an aperture device and a support structure supporting the aperture device. The aperture device defines an aperture edge, the aperture edge defining an aperture plane and being adapted to define a geometry of a light beam provided by a light source of the illumination unit and passing the aperture device along the optical axis. The support structure is adapted to hold the aperture device in a defined manner when the aperture plane is inclined with respect to a horizontal plane. A temperature distribution prevails within the aperture device and at least one of the aperture device and the support structure is adapted to maintain at least one of a relative position of the aperture edge with respect to the optical axis and a geometry of the aperture edge substantially unaltered upon an introduction of a thermal energy into the aperture device when the aperture plane is inclined with respect to a horizontal plane, the thermal energy being adapted to cause an alteration in the temperature distribution.

According to a third aspect of the invention there is provided a method of defining the geometry of a light beam passing an aperture device along an optical axis, the method comprising providing and, via a support structure, supporting the aperture device defining an aperture edge such that the aperture edge defines the geometry of the light beam passing the aperture device; introducing a thermal energy into the aperture device, the thermal energy being adapted to cause an alteration in a temperature distribution within the aperture device, via at least one of the aperture device and the support structure, maintaining at least one of a relative position of the aperture edge with respect to the optical axis and a geometry of the aperture edge substantially unaltered upon the introduction of the thermal energy into the aperture device when the aperture plane is inclined with respect to a horizontal plane.

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 QF THE DRAWINGS

Figure 1 is a schematic representation of a preferred embodiment of an optical imaging arrangement according to the invention which comprises an arrangement for an optical device 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 module according to the invention being a part of the optical imaging arrangement of Figure 1 (along line M-Il of Figure 3);

Figure 3 is a schematic top view of the optical module of Figure 2 along line Ill-Ill of Figure 2;

Figure 4 is a block diagram of a preferred embodiment of a method of defining the geometry of a light beam which may be executed with the optical imaging arrangement of Figure 1.

Figure 5 is a schematic top view of a further preferred embodiment of an optical module according to the invention;

Figure 6 is a schematic sectional view of a further preferred embodiment of an optical module according to the invention;

Figure 7 is a schematic top view of a further preferred embodiment of an optical module according to the invention;

Figure 8 is a schematic sectional view of a part of the optical module along line VIII-VIII of Figure 7;

Figure 9 is a schematic top view of a part of a further preferred embodiment of an optical module according to the invention (along line IX-IX of Figure 10);

Figure 10 is a schematic sectional view of a part of the optical module along line X-X of Figure 9.

DETAILED DESCRIPTION OF THE INVENTION

First embodiment

In the following, a first preferred embodiment of an optical imaging arrangement 101 according to the invention will be described with reference to Figures 1 to 4. Figure 1 is a schematic and not-to-scale representation of the optical imaging arrangement in the form of an optical exposure apparatus 101 used in a microlithography process during manufacture of semiconductor devices. The optical exposure apparatus 101 comprises a first optical device in the form of an illumination unit 102 and a second optical device in the form of 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 illumination unit 102 comprises an optical element system 106 (only shown in a highly simplified manner in Figure 1) including a plurality of optical element units such as optical element unit 106.1. The optical projection unit 103 comprises a further optical element system 107 including a plurality of optical element units 107.1. The optical element units of the optical element systems 106 and 107 are aligned along a folded optical axis 101.1 of the optical exposure apparatus 101.

In the embodiment shown, the optical exposure apparatus works with light in the EUV range at a wavelength of 13 nm. Thus, the optical elements used within the illumination unit 102 and the optical projection unit 103 are exclusively reflective optical elements. However, it will be appreciated that, with other embodiments of the invention working at different wavelengths, any type of optical element (refractive, reflective or diffractive) may be used alone or in an arbitrary combination.

The optical element system 107 further comprises an optical module 108 according to the invention. The optical module 108 comprises an aperture device in the form of a aperture stop 109 and a support structure 110 supporting the aperture stop 109.

The aperture stop 109 is a ring shaped element defining an aperture edge 109.1 which in turn defines the geometry of a light beam passing the aperture stop 109 along the optical axis 101.1 during an exposure process. In order to provide a high imaging accuracy during the exposure process the aperture edge 109.1 has to have a defined position with respect to the optical axis 101.1. In the embodiment shown, the aperture edge 109.1 defines an aperture center 109.2 (here the area center of gravity of the aperture defined by the aperture edge 109.1) and the aperture plane 109.3 (i.e. a plane of main extension of the aperture edge 109.1). This aperture center 109.2, in the embodiment shown, has to be located as close as possible to the optical axis to provide proper imaging results. However, it will be appreciated that, with other embodiments of the invention, any other desired relative position of the aperture edge (and an aperture center defined by this aperture edge) with respect to the optical axis may be chosen depending on the needs of the actual optical system.

During an exposure process the aperture stop 109 absorbs a considerable amount of radiation energy provided by the light incident on the aperture stop 109. As a consequence, the temperature distribution within the aperture stop 109 successively changes due to the thermal energy introduced into the aperture stop 109 via the absorbed radiation energy. Typically, the part of the aperture stop 109 exposed to the incident light experiences a considerable increase in its temperature. This temperature increase leads to a thermal expansion of at least parts of the aperture stop 109 which (unless counteracted) in turn might lead to an undesired alteration of the relative position between the aperture edge 109.1 and the optical axis 101.1.

With aperture devices known in the art having a horizontal orientation of the aperture plane such an alteration in the relative position between the aperture edge and the optical axis typically is counteracted by a support arrangement being formed by three pins having spherical end surfaces, each end surface running in a substantially V-shaped groove extending in a horizontal plane. Typically, the longitudinal axes of the grooves intersect at the thermal center of the aperture device. Due to the gravitational force acting on the aperture device, a self centering design is achieved where the aperture maintains its relative position with respect to the optical axis.

However, as may be seen from Figure 1 and 2, in the embodiment shown, the aperture plane 109.3 is inciined with respect to the horizontal plane such that the known support configuration (due to a component of the gravitational force acting in parallel to the aperture plane 109.3) may not provide reliable results any more.

Thus, to avoid a change in the relative position between the aperture edge 109.1 and the optical axis 101.1 , the support structure 110 comprises an outer support ring 110.1 and a holding device 110.2 fixedly connected thereto and holding the aperture stop 109 at three holding locations 110.3. To this end, the holding device 110.2 comprises three identical holding elements in the form of leaf spring elements 110.4 fixedly connected to the aperture stop 109.

Each leaf spring element 1 10.4 extends tangential to the circumferential direction of the aperture stop 109 and is arranged such that the holding device 110.2 is compliant in the radial direction of the aperture stop 109 (within the aperture plane 109.3) and substantially rigid in a direction perpendicular to the aperture plane 109.3 (i.e. along the optical axis 101.1). Furthermore, the leaf spring elements 110.4 are evenly distributed at the outer circumference of the aperture stop 109.

With this arrangement a fixed connection between the aperture stop 109 and the support structure 110 is achieved which is not subject to uncertainties with respect to the relative position between the support structure 110 and the aperture stop 109. Furthermore, it is achieved that on the one hand (due to the high rigidity of the holding device 110.2 along the optical axis 101.1) the position of the aperture stop 109 along the optical axis 101.1 is well- defined.

On the other hand, the radial compliance of the holding device 1 10.2 provided by the three identical leaf spring elements 110.4 makes it possible that the holding device 1 10.2 follows the position alteration of the respective holding location 110.3 which occurs due to the thermal expansion of the aperture stop 109 (resulting from the change in the temperature distribution within the aperture stop 109). In other words, the radial compliance of the holding device 110.2 (achieved by the bending of the leaf spring elements 110.4) allows the aperture stop 109 to radially expand without altering the relative position of the aperture center 109.2 with respect to the optical axis 101.1.

It will be appreciated that, in the embodiment shown, this effect is achieved if a symmetrical alteration of the temperature distribution within the aperture stop 109 occurs. However, in cases where no such symmetrical alteration of the temperature distribution of the aperture stop 109 occurs during normal operation of the exposure device 101 an alteration of the relative position between the aperture center 109.2 and the optical axis 101.1 may nevertheless be avoided by adapting the compliance of the holding device 110.2 to the thermal situation to be expected during operation. For example, a different (asymmetrical) distribution of (identical) leaf spring elements may be chosen and/or leaf spring elements of different design, in particular, different compliance, may be used.

Furthermore, it will be appreciated that any desired and suitable different number of holding elements may be used with other embodiments of the invention. Furthermore, it will be appreciated that the respective holding element does not necessarily have to be or comprise (one or more) leaf spring sections. Rather any other component or arrangement elastically bending or otherwise deforming and, thus, providing a suitable compliance in the radial direction of the aperture stop may be used. The support ring 110.1 itself is supported in a well-defined self centering manner on a support element, here a part 103.2 of the housing 103.1 of the optical projection unit 103. To this end is supported via four pins 110.5, two of them cooperating with V-shaped grooves 110.6 provided within the support ring 110.1. However, it will be appreciated as any other suitable and, preferably, self centering support to the support ring 110.1 may be selected.

In order to provide a stable position of the aperture center 109.2 with respect to the optical axis 101.1 , the support ring 110.1 is thermally uncoupled from the aperture stop 109 in order to avoid (as for as possible) and alteration in the position of the support ring 110.1. This thermal uncoupling, in the embodiment shown, is mainly achieved via the small cross-section of the leaf spring elements 110.4 which leads to a reduced heat transfer from the aperture stop 109 to the support ring 110.

However, it will be appreciated that a thermal uncoupling may also be provided via parts of the holding device 110.2 having a sufficiently low thermal conductivity and, thus, preventing or at least reducing heat transfer to the support ring 110.1 via the holding device 110.2. The thermal conductivity of these thermal uncoupling parts is preferably smaller than the thermal conductivity of the aperture stop 109.

In order to further reduce heat transfer from the aperture stop 109 to the support ring (e.g. via radiation) a heat shielding element may be provided between the support ring 110.1 and the aperture stop 109 as it is indicated in Figure 2 and 3 by the dashed contour 111,

Furthermore, in order to further reduce heat transfer from the aperture stop 109 to the support ring 110.1 (e.g. via radiation), for example, a heat sink element (such as e.g. an actively and/or passively cooled optical element, in particular a pupil mirror) may be located closely adjacent to the aperture stop 109 in order to receive at least a considerable part of the heat emitted by the aperture stop 109.

However, it will be appreciated that, with other embodiments of the invention, a passive and/or active thermal stabilization of the support ring 110.1 may be chosen as well (e.g. passive tempering/cooling elements such as tempering/cooling ribs etc or active tempering/cooling devices such as a tempering/cooling circuit etc).

Furthermore, it will be appreciated that, with other embodiments of the invention, the aperture stop itself may be designed such that it prevents or reduces an alteration in the relative position of the aperture edge 109.1 with respect to the optical axis 101.1. For example, the aperture stop may be made of a material having a near zero coefficient of thermal expansion (CTE), thus largely avoiding thermal expansion of the aperture stop 109. Such materials are for example Invar, Zerodur, etc.

Furthermore, it will be appreciated that, with other embodiments of the invention, the aperture stop itself may be designed such that it prevents or reduces an alteration in the relative position of the aperture edge 109.1 with respect to the optical axis 101.1 by avoiding or at least reducing a change in the temperature distribution within the aperture stop 109.

To this end, for example, passive thermal balancing device may be used providing improved heat removal from the aperture stop 109. Such passive means may be, for example, a suitable surface of the aperture stop 109 providing increased heat removal by providing increased radiation. Preferably such increased radiation is provided as directed radiation in order to avoid undesired heating of other temperature sensitive components of the imaging device 101.

Furthermore, an active thermal balancing device in the form of an active temperature control circuit 109.4 of the aperture stop 109 may be provided (Figure 3). Such an active temperature control circuit 109.4 may for example use a fluidic coolant or electric cooling elements such as Peltier elements etc.

With the optical exposure apparatus 101 of Figure 1 a preferred embodiment of a method of defining the geometry of a light beam 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 112.1 , the components of the optical exposure device 101 as they have been described above are provided and 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 112.2, the optical exposure device 101 is used to expose one or several images of the pattern formed on the mask 104.1 onto the substrate 105.1 as it has been described above. During this step the aperture stop 109 defines the geometry of the light beam passing it along the optical axis 101.

At this occasion, in a step 112.3, a thermal energy is introduced into the aperture stop 109, the thermal energy causing an alteration in a temperature distribution within the aperture stop In a step 115.4, the aperture stop 109 in response to the introduction of the thermal energy expands and the support structure 110 maintains the relative position of the aperture edge 109.1 with respect to the optical axis 101.1 substantially unaltered by following the expansion of the aperture stop 109.

Second embodiment

In the following, a second embodiment of the optica! module 208 according to the invention will be described with reference to Figure 5. The optical module 208 in its basic design and functionality largely corresponds to the optical module 108 and may replace the optical module 108 in the optical imaging device 101 of Figure 1, Thus, it is here mainly referred to the explanations given above and only the differences with respect to the optical module 108 will be explained in further detail. In particular, similar parts are given the same reference numeral raised by the amount 100 and (unless explicitly described in the following) in respect to these parts reference is made to the explanations given above in the context of the first embodiment.

The only difference with respect to the optical module 108 lies within the fact that the optical module 208 comprises three active holding elements 210.4 each contacting the aperture stop 209 at a holding location 210.3 and connecting the aperture stop 209 to the outer support ring 210.1 of the support structure 210.

The support structure 210 comprises a capturing device 210.7 and a control device 210.8 connected thereto. The capturing device 210.7, in the embodiment shown, comprises one or a plurality of temperature sensors (only one of which being shown in Figure 5) distributed over the aperture stop 209 and capturing a value representative of the actual temperature of the aperture stop 209 at the location of the respective sensor.

The capturing device 210.7 provides corresponding signals to the control device 210.8. The control device 210.8 uses a temperature behavior model previously established for the aperture stop 209 (and stored within the control device 210.8). The temperature behavior model allows to determine the position of the respective holding location 210.3 with respect to the optical axis 101.1 as a function of the values captured by the capturing device 210.7.

Using the temperature behavior model the control device 210.8 establishes control signals for actuator devices 210.9 of the active holding devices 210.4 and provides these control signals to the actuator devices 210.9. The actuator devices 210.9, in response to the control signals adjust the length and/or orientation of the respective holding element 210.4 such that the holding elements 210.4 follows the alteration in the position of the holding location 210.3 resulting from a change in the temperature distribution within the aperture stop 209, thereby maintaining the relative position between the aperture center 209.3 and the optical axis 101.1 unchanged.

It will be appreciated that the capturing device, with other embodiments of the invention, does not necessarily have to capture temperature values. Rather, and a value may be captured that has an influence on the temperature distribution within the aperture stop. For example, a historical record of the radiant power provided by the illumination unit 102 may be used as a basis for the temperature behavior model used by the control device.

Furthermore, it will be appreciated that any desired number of such values representative or indicative of the actual temperature distribution and, thus, the actual position of the holding locations may be used. In particular, a value regularly captured had one single location may be sufficient. For example, even one single temperature sensor may be sufficient if, for example, a symmetrical temperature distribution is to be expected under any operating conditions.

Furthermore, it will be appreciated that, with other embodiments of the invention, it is not necessary to use such a temperature behavior model. Rather, a simple position control of the aperture stop capturing an actual position and/or geometry or an alteration in the actual position and/or geometry of the aperture stop may be used.

Third embodiment

In the following, a third embodiment of the optical module 308 according to the invention will be described with reference to Figure 6. The optical module 308 in its basic design and functionality largely corresponds to the optical module 208 and may replace the optical module 108 in the optical imaging device 101 of Figure 1. Thus, it is here mainly referred to the explanations given above and only the differences with respect to the optical module 208 will be explained in further detail. In particular, similar parts are given the same reference numeral raised by the amount 100 and (unless explicitly described in the following) in respect to these parts reference is made to the explanations given above in the context of the first embodiment.

The only difference with respect to the optical module 208 lies within the fact that the optical module 308 comprises one single active holding element 310.4 clamping the aperture stop 209 at one single holding location 210.3 and connecting the aperture stop 209 to the outer support element 103.2.

The support structure 310 comprises a capturing device 310.7 and a control device 310.8 connected thereto. The capturing device 310.7, in the embodiment shown, comprises one or a plurality of temperature sensors (only one of which being shown in Figure 6) distributed over the aperture stop 309 and capturing a value representative of the actual temperature of the aperture stop 309 at the location of the respective sensor.

The capturing device 310.7 provides corresponding signals to the control device 310.8. The control device 310.8 uses a temperature behavior model previously established for the aperture stop 309 (and stored within the control device 310.8). The temperature behavior model allows to determine the position of the respective holding location 310.3 with respect to the optical axis 101.1 as a function of the values captured by the capturing device 310.7.

Using the temperature behavior model the control device 310.8 establishes control signals for actuator devices 310.9 of the active holding devices 310.4 and provides these control signals to the actuator devices 310.9. The actuator devices 310.9, in response to the control signals adjust the length and/or orientation of the respective holding element 310.4 such that the holding elements 310.4 follows the alteration in the position of the holding location 310.3 resulting from a change in the temperature distribution within the aperture stop 309, thereby maintaining the relative position between the aperture center 309.3 and the optical axis 101.1 unchanged.

It will be appreciated that, here as well, the capturing device, with other embodiments of the invention, does not necessarily have to capture temperature values. Furthermore, it will be appreciated that, with other embodiments of the invention, it is not necessary to use such a temperature behavior model. Rather, a simple position control of the aperture stop capturing an actual position and/or geometry or an alteration in the actual position and/or geometry of the aperture stop may be used.

A further difference with respect to the second embodiment lies within the fact that the active holding device 310.4 may be controlled by the control device 310.8 to remove the aperture stop 309 from its location and, thus, from the light path and to replace it with another, second aperture stop. Fourth embodiment

In the following, a fourth embodiment of the optical module 408 according to the invention will be described with reference to Figure 7 and 8. The optical module 408 in its basic design and functionality largely corresponds to the optical module 108 and may replace the optical module 108 in the optical imaging device 101 of Figure 1. Thus, it is here mainly referred to the explanations given above and only the differences with respect to the optical module 108 will be explained in further detail. In particular, similar parts are given the same reference numeral raised by the amount 300 and (unless explicitly described in the following) in respect to these parts reference is made to the explanations given above in the context of the first embodiment.

The difference with respect to the optical module 108 lies within the fact that the aperture stop is made of a plurality of (circumferentially overlapping) aperture stop elements of 409.5, each being held by a separate holding element 410.4.

Each holding element 410.4 is made of the first structural part 410.10 connected, at its first end, to the support ring 410.1 and a second structural part 410.11 connected, at its first end, to the second end of the first structural part 410.10 and, at its second end, to the aperture stop element 409.5.

The respective holding element 410.4 has a folded back arrangement, i.e. the second end of the second structural part 410.1 1 , in the radial direction of the aperture stop 409, is located between the first and second end of the first structural part 410.10. By this means it is possible to select radial length and/or the respective coefficient of thermal expansion (CTE) of the respective structural part 410.10, 410.11 such that the thermal expansions of the aperture stop element 409.5, the first structural part 410.10 and the second structural part 410.1 1 eliminate each other such that the aperture edge 409.1 maintains its position with respect to the optical axis 101.1 upon a given change in the temperature distribution within the aperture stop 409 (to be expected during normal operation of the optical exposure device 101).

Fifth embodiment

In the following, a fifth embodiment of the optical module 508 according to the invention will be described with reference to Figure 5. The optical module 508 in its basic design and functionality largely corresponds to the optical module 108 and may replace the optical module 108 in the optical imaging device 101 of Figure 1. Thus, it is here mainly referred to the explanations given above and only the differences with respect to the optical module 108 will be explained in further detail. In particular, similar parts are given the same reference numeral raised by the amount 400 and (unless explicitly described in the following) in respect to these parts reference is made to the explanations given above in the context of the first embodiment.

Here again, as may be seen from Figure 9 and 10, in the embodiment shown, the aperture plane 509.3 (defined by the aperture edge 509.1) is inclined with respect to the horizontal plane such that a previously known support configuration (due to a component of the gravitational force acting in parallel to the aperture plane 109.3) may not provide reliable results any more.

Again, the support ring 510.1 supporting the aperture stop 509 is supported (not shown in Figure 9 and 10) in the well-defined self centering manner as it has been described in the context of the optical module 108 (i.e. the first embodiment). The only difference with respect to the optical module 108 lies within the fact that the optical module 508 comprises six holding elements 510.4 and 510.12 each contacting the aperture stop 509 at a holding location 510.3 and connecting the aperture stop 509 to the outer support ring 510.1 of the support structure 510.

Three of the six holding elements are designed as pins 510.4 mounted to the support ring 510.1. Each pin 510.4 has a spherical end surface contacting a planar surface 510.13 of the aperture stop 509. The spherical end surfaces of the three pins 510.4 define a contact plane that runs perpendicular to the optica! axis 101.1 such that the planar surface 510.13 also runs perpendicular to the optical axis 101.1

The other three holding elements 510.12 are designed as (substantially rigid) radial guide elements each contacting a lateral surface of a contact pin 510.14 mounted to the aperture stop 509. Each contact pin 510.14 slidably contacts the associated guide element 510.12. Each guide element 510.12 is arranged such that the associated contact pin 510.14 may slide along a line of guidance 510.15. The three lines of guidance 510.15 intersect at the optical axis 101.1 such that the aperture center 509.2 is also located on the optical axis 101.1.

If the aperture stop 509 radially expands or contracts due to a change within its temperature distribution in the respective contact pin 510.14 is guided along the respective line of guidance 510.15. Consequently, the aperture center 509.2 does not change its position with respect to the optical axis 101.1. The three guide elements 510.12 may be arranged in an arbitrary manner as long as the lines of guidance 510.15 defined by the guide elements intersect at a common point of intersection located in a desired spatial relationship with respect to the optical axis 101.1 and as long as the contact forces acting at the contact points provide a self adjusting configuration with one single state of equilibrium (where the aperture center 509.2 is located at its desired location).

It will be appreciated that, in the embodiment shown, this effect is achieved if a symmetrical alteration of the temperature distribution within the aperture stop 109 occurs. However, in cases where no such symmetrical alteration of the temperature distribution of the aperture stop 509 occurs during normal operation of the exposure device 101 an alteration of the relative position between the aperture center 509.2 and the optical axis 101.1 may nevertheless be avoided by adapting the alignment of the lines of guidance 510.15 to the thermal situation to be expected during operation. For example, a different alignment of the lines of guidance 510.15 with no common point of intersection may be chosen and/or an at least partially curved shape of at least one of the lines of guidance 510.15 may be provided. Furthermore, it will be appreciated that any desired and suitable different number of holding elements may be used with other embodiments of the invention.

In order to provide a stable position of the aperture center 509.2 with respect to the optical axis 101.1 , the support ring 510.1 is thermally uncoupled from the aperture stop 509 in order to avoid {as for as possible) and alteration in the position of the support ring 1 10.1. This thermal uncoupling, in the embodiment shown, is mainly achieved via the small contact surface between the holding elements 510.4 and 510.12 and the aperture stop 509 which leads to a reduced heat transfer from the aperture stop 509 to the support ring 510.

However, it will be appreciated that a thermal uncoupling may also be provided via parts of the holding device 510.2 having a sufficiently low thermal conductivity and, thus, preventing or at least reducing heat transfer to the support ring 510.1 via the holding device 510.2. The thermal conductivity of these thermal uncoupling parts is preferably smaller than the thermal conductivity of the aperture stop 509.

In the foregoing, the invention has been described in the context of embodiments and where the optical module according to the invention is using the optical projection unit. However, it will be appreciated that the optical module according to the invention may provide its beneficial effects as well in the illumination unit since, there, a high absorption of radiation energy by aperture devices used is to be expected. In the foregoing, the invention has been described in the context of embodiments working in the EUV range. However, it will be appreciated that the invention may also be used at any other wavelength of the exposure light, e.g. in systems working at 193 nm etc.

Although, in the foregoing, the invention has been described solely in the context of microlithography systems. However, it will be appreciated that the invention may also be used in the context of any other optical device using aperture devices.

Claims

What is claimed is:

1. An optical module comprising

- an aperture device and

- a support structure supporting said aperture device; - said aperture device defining an aperture edge and an aperture plane,

- said aperture edge being adapted to define a geometry of a light beam passing said aperture device along an optical axis;

- said support structure being adapted to hold said aperture device in a defined manner when said aperture plane is inclined with respect to a horizontal plane, - a temperature distribution prevailing within said aperture device and at least one of said aperture device and said support structure being adapted to maintain at least one of a relative position of said aperture edge with respect to said optical axis and a geometry of said aperture edge substantially unaltered upon an introduction of a thermal energy into said aperture device, said thermal energy being adapted to cause an alteration in said temperature distribution.

2. The optical module according to claim 1 , wherein

- said support structure comprises at least one holding device holding said aperture device at at least one holding location;

- said at least one holding device being adapted to follow a thermally induced alteration in a position of said at least one holding location resulting from a thermal expansion of said aperture device in response to said alteration in said temperature distribution, thereby preventing an alteration in said position of said aperture edge with respect to said optical axis.

3. The optical module according to claim 2, wherein - said at least one holding device comprises at least one holding element;

- said at least one holding element being adapted to be elastically deformed such that said at least one holding element follows said thermally induced alteration in said position of said at least one holding location.

4. The optical module according to claim 3, wherein

- said at least one holding device comprises a plurality of holding elements;

- said holding elements being substantially evenly distributed at an outer circumference of said aperture device.

5. The optical module according to claim 3, wherein

- said at least one holding element comprises at least one leaf spring section;

- said at least one leaf spring section being adapted to be bent in response to said thermally induced alteration in said position of said at least one holding location.

6. The optical module according to claim 2, wherein - said support structure comprises at least one outer support device;

- said at least one holding element connecting said aperture device to said at least one outer support device;

- at least one thermal uncoupling arrangement being provided;

- said at least one thermal uncoupling device being adapted to restrict a heat transfer from said aperture device to said outer support device.

7. The optical module according to claim 6, wherein at least one of

- at least a part of said thermal uncoupling arrangement is formed by a thermal uncoupling section of said at least one holding element and - at least a part of said thermal uncoupling arrangement is formed by a thermal shielding device arranged between said outer support device and said aperture device.

8. The optical module according to claim 7, wherein said thermal uncoupling section having at least one of - a first thermal conductivity which is smaller than a second thermal conductivity of said aperture device and - a first cross-section which is smaller than a second cross-section of said at least one holding element.

9. The optical module according to claim 2, wherein

- said at least one holding device is an active holding device comprising a capturing device, a control device connected to said capturing device and an actuator device connected to said control device;

- said capturing device being adapted to capture at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of said holding location;

- said capturing device being adapted to provide said actual value of said at least one variable to said control device;

- said control device being adapted to generate at least one control signal as a function of said actual value of said at least one variable and to provide said at least one control signal to said actuator device;

- said actuator device, in response to said at least one control signal, adjusting a position of said holding location such that said at least one holding device follows a thermally induced alteration in said position of said holding location.

10. The optical module according to claim 9, wherein said at least one variable captured by said capturing device is at least one of a temperature of said aperture device and a radiant power provided by a light source providing said light beam.

11. The optical module according to claim 9, wherein

- said control device comprises a temperature behavior model of said aperture device; - said temperature behavior model being a previously established model representative of a position of said holding location with respect to said aperture edge as a function of said at least one variable captured by said capturing device;

- said control device being adapted to generate said least one control signal using said temperature behavior model.

12. The optical module according to claim 9, wherein - said support structure comprises a plurality of said active holding devices;

- said active holding devices being substantially evenly distributed at an outer circumference of said aperture device.

13. The optical module according to claim 9, wherein - said aperture device is a first aperture device and

- said at least one active holding device is adapted to remove said first aperture device from its position with respect to said optical axis and to replace said first aperture device with a second aperture device by placing said second aperture device at a defined position with respect to said optical axis, thereby altering said geometry of said light beam passing said second aperture device.

14. The optical module according to claim 1 , wherein

- said aperture device comprises at least one aperture edge element defining said aperture edge;

- said at least one aperture edge element being made of a material having a coefficient of thermal expansion which is sufficiently low to maintain at least one of said relative position of said aperture edge with respect to said optical axis and said geometry of said aperture edge substantially unaltered upon an alteration in said temperature distribution to be expected during operation of said optical module.

15. The optical module according to claim 1, wherein

- said aperture edge element being made of a material selected from the group consisting of titanium (Ti), Invar, Zerodur, quartz (SiO₂)....

16. The optical module according to claim 1 , wherein

- said aperture device comprises at least one first structural element, at least one second structural element and at least one aperture edge element defining said aperture edge;

- said at least one first structural element showing a first thermal expansion behavior and being connected to said support structure; - said at least one second structural element showing a second thermal expansion behavior and connecting said at least one aperture edge element to said at least one first structural element;

- said second thermal expansion behavior being adapted to said first thermal expansion behavior such that, upon said alteration within said temperature distribution of said aperture device, a second thermal expansion of said second structural element compensates a first thermal expansion of said first structural element such that at least one of said geometry and said position of said aperture edge remains unchanged.

17. The optical module according to claim 16, wherein

- said first structural element is a ring shaped element having a first coefficient of thermal expansion and

- a plurality of second structural elements is provided, each having a second coefficient of thermal expansion; - each second structural element, at a first end, being connected to said first structural element and, at a second end located radially inwards of said first end, being connected to said at least one aperture edge element;

- said the second coefficient of thermal expansion being adapted to said first coefficient of thermal expansion such that, upon said alteration within said temperature distribution of said aperture device, said second thermal expansion of said second structural element compensates said first thermal expansion of said first structural element.

18. The optical module according to claim 1 , wherein

- said aperture device comprises at least one first structural element, at least one second structural element, at least one aperture edge element, a capturing device and a control device;

- said at least one first structural element being connected to said support structure;

- said at least one second structural element comprising at least one actuator device connecting said at least one aperture edge element to said at least one first structural element;

- said at least one aperture edge element defining said aperture edge; - said capturing device being adapted to capture at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of said at least one aperture element; - said capturing device being adapted to provide said actual value of said at least one variable to said control device;

- said control device being adapted to generate at least one control signal as a function of said actual value of said at least one variable and to provide said at least one control signal to said actuator device; - said actuator device, in response to said at least one control signal, adjusting a position of said aperture edge element such that, upon said alteration within said temperature distribution of said aperture device, a thermal expansion of said first structural element is compensated such that at least one of said geometry and said position of said aperture edge remains unchanged.

19. The optical module according to claim 18, wherein said at least one variable captured by said capturing device is at least one of a temperature of said aperture device and a radiant power provided by a light source providing said light beam.

20. The optical module according to claim 18, wherein

- said control device comprises a temperature behavior model of said aperture device;

- said temperature behavior model being a previously established model representative of a position of said aperture edge element with respect to said first structural element as a function of said at least one variable captured by said capturing device; - said control device being adapted to generate said least one control signal using said temperature behavior model.

21. The optical module according to claim 1 , wherein

- a thermal balancing device is provided;

- said a thermal balancing device maintaining a heat balance of said aperture device such that said temperature distribution within said aperture device remains substantially constant.

22. The optical module according to claim 20, wherein said thermal balancing device comprises a passive heat transfer device providing enhanced heat transfer from said aperture device to the surroundings of said aperture device.

23. The optical module according to claim 22, wherein said passive heat transfer device 5 is adapted to provide directed heat transfer.

24. The optical module according to claim 23, wherein

- said passive heat transfer device comprises a heat transfer surface of said aperture device,

- said heat transfer surface having a geometry adapted to provide heat radiation in ao predetermined direction.

25. The optical module according to claim 21 , wherein said thermal balancing device comprises an active heat transfer device providing controlled heat transfer from said aperture device.

26. The optica! module according to claim 25, wherein s - said thermal balancing device comprises at least one temperature control circuit connected to said aperture device;

- said at least one temperature control circuit working according to at least one of a fluidic working principle and an electric working principle.

27. The optical module according to claim 1, wherein o - said aperture edge defines an aperture center;

- at least one of said aperture device and said support structure being adapted to maintain at least a relative position of said aperture center with respect to said optical axis substantially unaltered upon an introduction of said thermal energy into said aperture device. 5

28. An optical imaging arrangement comprising

- a mask unit adapted to receive a pattern,

- a substrate unit adapted to receive a substrate; - an illumination unit adapted to illuminate said pattern;

- an optical projection unit adapted to transfer an image of said pattern onto said substrate;

- each of said illumination unit and said optical projection unit comprising a system of optical elements, said system of optical elements defining an optical axis;

• at least one of said illumination unit and said optical projection unit comprising an optical module, said optical module comprising an aperture device and a support structure supporting said aperture device;

- said aperture device defining an aperture edge, said aperture edge defining an aperture plane and being adapted to define a geometry of a light beam provided by a light source of said illumination unit and passing said aperture device along said optical axis;

- said support structure being adapted to hold said aperture device in a defined manner when said aperture plane is inclined with respect to a horizontal plane, - a temperature distribution prevailing within said aperture device and at least one of said aperture device and said support structure being adapted to maintain at least one of a relative position of said aperture edge with respect to said optical axis and a geometry of said aperture edge substantially unaltered upon an introduction of a thermal energy into said aperture device when said aperture plane is inclined with respect to a horizontal plane, said thermal energy being adapted to cause an alteration in said temperature distribution.

29. The optical imaging arrangement according to claim 28, wherein

- said support structure comprises at least one holding device holding said aperture device at at least one holding location; - said at least one holding device being adapted to follow a thermally induced alteration in a position of said at least one holding location resulting from a thermal expansion of said aperture device in response to said alteration in said temperature distribution, thereby preventing an alteration in said position of said aperture edge with respect to said optical axis.

30. The optical imaging arrangement according to claim 29, wherein

- said at least one holding device is an active holding device comprising a capturing device, a control device connected to said capturing device and an actuator device connected to said control device; - said capturing device being adapted to capture at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of said holding location;

31. The optical imaging arrangement according to claim 29, wherein

- said control device comprises a temperature behavior model of said aperture device; - said temperature behavior model being a previously established model representative of a position of said holding location with respect to said aperture edge as a function of said variable captured by said capturing device;

32. The optical imaging arrangement according to claim 30, wherein said at least one variable captured by said capturing device is at least one of a temperature of said aperture device and a radiant power provided by said light source of said illumination unit.

33. The optical imaging arrangement according to claim 30, wherein - said aperture device is a first aperture device and - said at least one active holding device is adapted to remove said first aperture device from its position with respect to said optical axis and to replace said first aperture device with a second aperture device by placing said second aperture device at a defined position with respect to said optical axis, thereby altering said geometry of said light beam passing said second aperture device.

34. The optical imaging arrangement according to claim 28, wherein

35. The optical imaging arrangement according to claim 28, wherein

- said at least one first structural element showing a first thermal expansion behavior and being connected to said support structure;

- said at least one second structural element showing a second thermal expansion behavior and connecting said at least one aperture edge element to said at least one first structural element;

36. The optical imaging arrangement according to claim 28, wherein

- said aperture device comprises at least one first structural element, at least one second structural element, at least one aperture edge element, a capturing device and a control device; - said at least one first structural element being connected to said support structure;

- said at least one aperture edge element defining said aperture edge; - said capturing device being adapted to capture at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of said at least one aperture element;

- said actuator device, in response to said at least one control signal, adjusting a position of said aperture edge element such that, upon said alteration within said temperature distribution of said aperture device, a thermal expansion of said first structural element is compensated such that at least one of said geometry and said position of said aperture edge remains unchanged.

37. The optical imaging arrangement according to claim 36, wherein said at least one variable captured by said capturing device is at least one of a temperature of said aperture device and a radiant power provided by said light source providing said light beam.

38. The optical imaging arrangement according to claim 36, wherein

- said temperature behavior model being a previously established model representative of a position of said aperture edge element with respect to said first structural element as a function of said at least one variable captured by said capturing device;

39. The optical imaging arrangement according to claim 28, wherein

- a thermal balancing device is provided;

- said thermal balancing device maintaining a heat balance of said aperture device such that said temperature distribution within said aperture device remains substantially constant.

40. The optical imaging arrangement according to claim 39, wherein said thermal balancing device comprises at least one of a passive heat transfer device providing enhanced heat transfer from said aperture device to the surroundings of said aperture device and an active heat transfer device providing controlled heat transfer from said aperture device.

41. The optical imaging arrangement according to claim 28, wherein

- said aperture edge defines an aperture center;

- at least one of said aperture device and said support structure being adapted to maintain at least a relative position of said aperture center with respect to said optical axis substantially unaltered upon an introduction of said thermal energy into said aperture device.

42. A method of defining the geometry of a light beam passing an aperture device along an optical axis, said method comprising

- providing and, via a support structure, supporting said aperture device defining an aperture edge such that said aperture edge defines said geometry of said light beam passing said aperture device;

- introducing a thermal energy into said aperture device, said thermal energy being adapted to cause an alteration in a temperature distribution within said aperture device,

- via at least one of said aperture device and said support structure, maintaining at least one of a relative position of said aperture edge with respect to said optical axis and a geometry of said aperture edge substantially unaltered upon said introduction of said thermal energy into said aperture device when said aperture plane is inclined with respect to a horizontal plane.

43. The method according to claim 42, wherein - said support structure holds said aperture device at at least one holding location;

- said support structure following a thermally induced alteration in a position of said at least one holding location resulting from a thermal expansion of said aperture device in response to said alteration in said temperature distribution, thereby preventing an alteration in said position of said aperture edge with respect to said optical axis.

44. The method according to claim 43, wherein at least one holding element holds said aperture device at said at least one holding location and is elastically deformed such that it follows said thermally induced alteration in said position of said at least one holding location.

45. The method according to claim 43, wherein said aperture device is held via a plurality of holding elements substantially evenly distributed at an outer circumference of said aperture device.

46. The method according to claim 43, wherein said aperture device is held such that a heat transfer from said aperture device to said support structure is restricted by thermally uncoupling said aperture device and said support structure;

47. The method according to claim 43, wherein

- at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of said holding location is captured, - at least one control signal is generated as a function of said actual value of said at least one variable, and,

- in response to said at least one control signal, a position of said holding location is adjusted such that said support structure follows a thermally induced alteration in said position of said holding location.

48. The method according to claim 47, wherein said at least one variable captured by said capturing device is at least one of a temperature of said aperture device and a radiant power provided by a light source providing said light beam.

49. The method according to claim 47, wherein - a temperature behavior model of said aperture device is used to generate sad control signal;

- said temperature behavior model being a previously established model representative of a position of said holding location with respect to said aperture edge as a function of said at least one variable captured;

50. The method according to claim 43, wherein, in a further step,

- said aperture device being a first aperture device is removed from its position with respect to said optical axis and

• said first aperture device is replaced with a second aperture device by placing said second aperture device at a defined position with respect to said optical axis such that said second aperture device defines said geometry of that light beam, thereby altering said geometry of said light beam.

51. The method according to claim 42, wherein

- at least one aperture edge element is provided to define said aperture edge;

- said at least one aperture edge element being made of a material having a coefficient of thermal expansion which is sufficiently low to maintain at least one of said relative position of said aperture edge with respect to said optical axis and said geometry of said aperture edge substantially unaltered upon an alteration in said temperature distribution to be expected during operation of said aperture device.

52. The method according to claim 42, wherein

- at least one aperture edge element defining said aperture edge is held via at least one first structural element and at least one second structural element;

53. The method according to claim 42, wherein

- at least one actual value of at least one variable representative of at least one of an actual status of said temperature distribution within said aperture device and an actual position of at least one aperture edge element defining said aperture edge is captured; - at least one control signal is generated as a function of said actual value of said at least one variable, and,

- in response to said at least one control signal, a position of said at least one aperture edge element is adjusted such that, upon said alteration within said temperature distribution of said aperture device, at least one of said geometry and said position of said aperture edge remains unchanged.

54. The method according to claim 53, wherein said at least one variable captured is at least one of a temperature of said aperture device and a radiant power provided by a light source providing said light beam.

55. The method according to claim 53, wherein - a temperature behavior model of said aperture device is used to generate said at least one control signal;

- said temperature behavior model being a previously established model representative of a position of said aperture edge element with respect to said optical axis as a function of said at least one variable captured.

56. The method according to claim 42, wherein a heat balance of said aperture device is maintained via a heat balancing device such that said temperature distribution within said aperture device remains substantially constant upon said introduction of said thermal energy.

57. The method according to claim 56, wherein said heat transfer from said aperture device is actively controlled.

58. The method according to claim 42, wherein

- said aperture edge defines an aperture center and,

- via at least one of said aperture device and said support structure, at least a relative position of said aperture center with respect to said optical axis is maintained substantially unaltered upon said introduction of said thermal energy into said aperture device.

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