WO2011039124A1

WO2011039124A1 - Optical arrangement in a projection exposure apparatus for euv lithography

Info

Publication number: WO2011039124A1
Application number: PCT/EP2010/064198
Authority: WO
Inventors: Viktor Kulitsky; Bernhard Gellrich; Stefan Xalter; Yim-Bun-Patrick Kwan; Peter Deufel; Andreas Wurmbrand
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2009-09-30
Filing date: 2010-09-24
Publication date: 2011-04-07
Also published as: US9298111B2; US20120188523A1; JP5490243B2; CN105137718B; CN102549503A; CN105137718A; DE102009045223A1; JP2013506281A; EP2483747A1; EP2483747B1; CN102549503B

Abstract

The invention concerns an optical arrangement in a projection exposure apparatus for EUV lithography, comprising a multiplicity of optical elements (101, 102) and a carrier structure (100, 300) which carries the optical elements (101, 102), wherein the carrier structure is composed of at least two releasably interconnected modules (110-140, 310-340, 510, 610), and wherein each module (110-140, 310-340, 510, 610) is composed of at least one carrier structure subelement (121-124, 421, 511 -514, 612-614), wherein a subhousing is produced by a multiplicity of carrier structure subelements (121-124, 421, 511-514, 612-614) and/or modules (110-140, 310, 340, 510, 610), and wherein said subhousing has a geometry that varies, at least in regions, in correspondence to a usable beam path in said projection exposure apparatus, said usable beam path being defined as an envelope of all light bundles which can propagate from all field points in a field plane to an image plane of the projection exposure apparatus.

Description

Optical arrangement in a

projection exposure apparatus for EUV lithography

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of German Patent Application DE 10 2009 045 223.0, filed on Sept. 30, 2009. The content of this application is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the invention

The present invention concerns an optical arrangement in a projection exposure apparatus for EUV lithography. State of the art

Microlithography is used for the production of microstructured components such as for example integrated circuits or LCDs. The microlithography process is carried out in what is referred to as a projection exposure apparatus which has an illumination system and a projection objective. The image of a mask (=reticle) illuminated by means of the illumination system is projected in that case by means of the projection objective onto a substrate (for example a silicon wafer) which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection objective in order to transfer the mask structure onto the light-sensitive coating on the substrate.

In projection exposure apparatuses designed for the EUV range, that is to say at wavelengths of for example about 13 nm or about 7 nm, mirrors are used as optical components for the imaging process due to the lack of availability of suitable translucent refractive materials. In that respect in practice operation under EUV conditions requires implementing a multiplicity of functionalities and fulfilling demanding requirements. Firstly as the service life of the mirrors or the projection exposure apparatus designed for operation under EUV conditions is limited due to contaminating particles or gases, in particular hydrocarbon compounds, operation of the projection exposure apparatus is required under vacuum conditions (for example at total pressures of 10^"3 mbars or below). In that respect the problem arises that the contaminants which spread in the system can adhere to the surfaces of the optical elements, which in turn results in an adverse effect on the optical properties of the elements such as for example a loss of reflection in respect of the mirrors.

WO 2008/034582 A2 discloses inter alia an optical arrangement, in particular a projection exposure apparatus for EUV lithography, which, to reduce the adhesion of contaminants, in particular to reflective optical elements, has within an evacuated housing at least one further vacuum housing surrounding the optical surface of the respective reflective optical element. Associated with the vacuum housing is a contamination reduction unit which reduces the partial pressure of contaminating substances such as water and/or hydrocarbons at least in the immediate proximity of the optical surface. In that way a kind of "mini-environment" is generated around the optical surface, with a reduced number of contaminating particles, so that fewer particles can be deposited on the optical surface.

US 2009/0135386 A1 discloses inter alia the provision of a plurality of subchambers in an illumination system of a projection exposure apparatus within a vacuum chamber, the subchambers being separated from each other by way of separating walls provided with a passage opening therethrough and respectively arranged at positions of minimum light cross-sectional area or in the proximity thereof, and respectively evacuated by associated vacuum pumps. In addition in operation with globally or locally high levels of light power density the problem arises that the increase in temperature of the optical elements such as for example mirrors, lenses or holder elements, that is involved with the high light power density and absorption, can result in a different respect in an adverse effect on the imaging properties of the optical system. An example of this is the adverse effect of temperature-sensitive elements present in the optical system such as for example position sensors. It is known for example in projection objectives designed for the EUV range, in addition to a carrier structure which carries mirrors and mirror actuators, to provide a measurement structure which is typically arranged outside the carrier structure and which is intended to ensure thermally and mechanically stable fixing of position sensors or other measurement systems for determining the mirror positions. The problem of an unwanted rise in temperature of that measurement structure is correspondingly more serious as the spacing between the position sensors and the mirrors which rise in temperature in operation of the projection exposure apparatus is relatively small (and for example can be in the range of between 5 and 100 mm).

It is known from US 2005/0018154 A1 to provide in a microlithographic projection exposure apparatus at least one heat shield which is intended to catch the heat given off by the mirrors and/or the carrier structure thereof, wherein that heat is dissipated by a heat transport circuit which is in mechanical contact with the heat shield.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an optical arrangement in a projection exposure apparatus for EUV lithography, which permits the provision of a carrier structure for optical elements of the system in structural space- saving fashion and with simultaneous and flexible implementation of further functionalities which are to be implemented by the projection exposure apparatus.

That object is attained by the features of the independent claims.

According to an aspect of the present invention, an optical arrangement in a projection exposure apparatus for EUV lithography comprises:

- a multiplicity of optical elements, and

- a carrier structure which carries the optical elements and which is composed of at least two releasably interconnected modules,

- wherein each module is composed of at least one carrier structure subelement,

- wherein a subhousing is produced by a multiplicity of carrier structure subelements and/or modules, and

- wherein said subhousing has a geometry that varies, at least in regions, in correspondence to a usable beam path in said projection exposure apparatus, said usable beam path being defined as an envelope of all light bundles which can propagate from all field points in a field plane to an image plane of the projection exposure apparatus.

The invention is based in particular on the concept of constructing a carrier structure for carrying the optical elements in modular fashion from the outset so that further functionalities to be implemented by the optical system can be implemented in a structural space-optimizing fashion and so-to-speak 'in one go'. The fact that more specifically the carrier structure has the above- described modular construction provides increased flexibility which in turn has the result that functionalities such as for example ensuring protection from contamination can be afforded for the optical elements by the provision of the above-described 'mini-environments' or subhousings or the provision of a heat shield for temperature-sensitive components such as sensors while minimizing or eliminating the requirement for additional components. In other words the functionalities which are referred to hereinbefore and possibly further functionalities are already linked together by the construction of the carrier structure.

The invention particularly involves the concept to combine the afore-mentioned 'mini-environment', i.e. a close-fitting or 'tight' housing of the usable beam path, with a force frame, i.e. a structure that serves to carry away mechanical loads, in particular due to gravity as well as load moments in actuated systems, and to actively carry the mirrors of the optical system. With other words, several carrier structure subelements are joined together in order to thereby form a massive, solid and tight encapsulation of a beam path in operation of the optical system which also absorbs mechanical forces acting on at least one of said optical elements.

The usable beam path in the projection exposure apparatus can be defined as an envelope of all light bundles which can propagate from all field points to the image plane of the projection exposure apparatus. The light bundles usually have a conical or cone-shaped geometry, and the beam path (due to the kidney-shaped geometry of the field) can particularly be kidney-shaped or elliptical. In view of the resulting complex and 3-dimensional overall-geometry of the usable beam path, the inventive arrangement of carrier structure subelements is particularly advantageous, since difficulties in forming the envelope of the usable beam path that would otherwise result from the complexity of said usable beam path can be avoided.

In some embodiments, openings in the respective carrier structure subelements can be formed as conical or cone-shaped bores that may serve as segments of the enclosure or environment, respectively, of the beam path. Moreover, the several carrier structure subelements can also have different sizes or dimensions, such that several carrier structure subelements may e.g. end up at positions where mirrors are to be mounted in order to build up the optical system. With other words, at least one of the carrier structure subelements may have a reduced cross-sectional size compared to other carrier structure subelements, whereby a mounting position of one of said mirrors is provided.

The several carrier structure subelements can furthermore be configured such that folded beam paths or beam paths in which light rays propagate, at least region-wise, back and forth on their way to the image plane can be 'encapsulated' in an at least almost optimum manner.

In particular for example in comparison with a carrier structure which is rigid or which is established from the outset, the modules according to the invention can already be so designed with a specific aim in mind that apertures or openings necessary for the beam passage which takes place in operation of the optical system are already adapted to the beam configuration, that is to say the carrier structure in the finished condition of being assembled from the modules already precisely allows the beam to pass through, in a structural space-optimizing fashion, without a proportion worth mentioning of unused structural space remaining. In that respect in particular it is also possible to build up the above-mentioned 'mini-environments' in one go without separate separating walls or housing portions being necessary for that purpose.

In addition, as regards the heat shield which was referred to in the opening part of this specification and which is generally also necessary, the modular structure can be used for example at the same time from the outset to provide cooling passages serving for example as the heat shield, on the one hand, insofar as the carrier structure subelements can already be so formed that portions of such cooling passages are already integrated so that when the carrier structure subelements are assembled the said cooling passages are virtually 'automatically' produced. On the other hand however, as is also described in greater detail hereinafter, it is also possible in a flexible manner to implement an optimum arrangement and possibly interconnection of those cooling passages and thus suitable multiple utilization of coolant circuits in regard to the specific factors and requirements in the respective optical system.

A further advantage of the assembly according to the invention comprising a plurality of assembled carrier structure subelements is that the individual carrier structure subelements (for example in regard to the surfaces of their inside contours) can be respectively ideally adapted, by virtue of the modular mode of construction, to the demands respectively existing in a specific system, in terms of the reflection of stray light, wherein the choice of the respectively appropriate surface treatment process such as mechanical treatment or coating can be specifically targeted ly and selectively adapted to the respective local factors or demands in the optical system. In that respect, in regions of the optical system in which stray light is particularly critical, it is possible to apply more complicated and costly surface treatment procedures whereas surfaces in less critical regions can be more easily produced or can even be left substantially unmodified.

It is to be pointed out that the optical elements can be carried by the carrier structure according to the invention both actively and also passively or indirectly (for example in the sense of being carried by actuators which in turn can carry the optical elements such as for example mirrors).

In addition it is to be noted that the invention is not limited to optical systems with a heat shield or systems with cooling passages. Rather the modular structure according to the invention is also advantageous in optical systems in which such heat shields are not necessary (for example as a consequence of components such as for example sensors not being involved in thermal expansion or because such thermal expansion does not cause any further problem).

In an embodiment at least one of the modules is composed of at least two carrier structure subelements, in particular at least three carrier structure subelements, further particularly at least four carrier structure subelements, thereby providing a further increase in flexibility both in regard to adaptation to the beam path in operation of the optical system and also in regard to the specifically targeted influencing of given regions of the beam path.

In an embodiment, said usable beam path is surrounded by said subhousing such that there is a maximum spacing of not more than 10 mm, more particularly not more than 5 mm, between said usable beam path and the subhousing.

In an embodiment at least one of the carrier structure subelements has at least two openings to permit a beam to pass through in operation of the optical system. In addition at least two carrier structure elements can have a different number of openings to permit a beam to pass through in operation of the optical system, wherein in addition at least two carrier structure subelements can differ in respect of the size and/or positioning of their openings.

In an embodiment the arrangement of the openings is adapted to the configuration of a beam passing through the optical system in operation.

In an embodiment said usable beam path comprises light bundles that at least partially penetrate each other.

In an embodiment said usable beam path is a folded beam path.

In an embodiment a beam passing through the optical system in operation traverses in succession different openings in at least one of the carrier structure subelements. In an embodiment at least two carrier structure subelements have at least region-wise a different surface treatment, for example by mechanical machining, coating or the like, in particular at their inside contour towards the beam path in operation of the optical system. In that way the flexibility of the modular arrangement according to the invention can be utilized insofar as the surface can be respectively matched to the local factors and requirements in the optical system (and for example in regions of the optical system in which stray light is particularly critical, more complicated and expensive surface treatment operations can be applied).

In an embodiment at least two carrier subelements have mutually corresponding surface portions which after assembly of said carrier structure subelements form with each other a cooling passage portion through which a cooling medium can flow in operation of the optical system. In that way when the carrier structure is assembled the above-mentioned cooling passages or heat shields can also be provided in one go. This concept of a cooling passage portion being formed by at least two carrier subelements is not limited to the above discussed aspect of forming a subhousing having a geometry that varies in correspondence to a usable beam path in said projection exposure apparatus, but can also be advantageously realized independently of this aspect. Accordingly, the invention, according to a further aspect, also relates to an optical arrangement in a projection exposure apparatus for EUV lithography, comprising:

- a multiplicity of optical elements; and

- wherein each module is composed of at least one carrier structure subelement, and

- at least two carrier subelements have mutually corresponding surface portions which after assembly of said carrier structure subelements form with each other a cooling passage portion through which a cooling medium can flow in operation of the optical system. In an embodiment at least one cooling medium circuit is constructed by means of a multiplicity of such cooling passage portions. In particular a multiplicity of cooling medium circuits which can be selectively connected together are constructed by a multiplicity of such cooling passage portions. In that way and having regard to the available typically limited supply of cooling medium, it is possible to achieve a heat shielding or an action which is optimally matched in regard to the specific factors and demands in the system.

In an embodiment at least one porous structure is arranged in the region of at least one of the cooling medium circuits, whereby the introduction of flow- induced vibration from the carrier structure into the mirrors or into the actuators carrying those mirrors can be reduced or prevented.

In an embodiment at least two carrier structure subelements are fluid-tightly sealed off relative to each other by way of at least one sealing element. In that way fluid-tight sealing integrity can also be implemented with integration of the cooling passages when connecting the carrier structure subelements themselves, for example by way of simple clamping connections or screw means.

In an embodiment the sealing element is in the form of a cover plate, wherein preferably that sealing plate and at least one of the carrier structure subelements are made from the same material. The cover plate can involve in particular a plate which covers a cooling passage and which for example can be welded in place. Using identical materials avoids electrochemical potentials which are different from each other (entailing different materials) and electrochemical corrosion caused in connection with the typically electrolytic cooling medium (especially as O-rings which are also possibly provided and which comprise non-electrically conductive material such as for example rubber also cannot cause any electrochemical corrosion). The invention further concerns a microlithographic projection exposure apparatus comprising an illumination system and a projection objective, wherein the illumination system and the projection objective has an optical arrangement having the above-described features.

The invention further concerns a process for the production of an optical system of a projection exposure apparatus for EUV lithography, wherein the optical system is constructed from a multiplicity of optical elements carried by a carrier structure, and wherein the carrier structure is composed of at least two releasably interconnected modules, and wherein each module is composed of at least one carrier structure subelement. In regard to preferred configurations and advantages of the process reference is directed to the foregoing description in connection with the arrangement according to the invention. Further configurations of the invention are set forth in the description and the appendant claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described in greater detail hereinafter by means of embodiments by way of example illustrated in the accompanying drawings in which: Figure 1 shows a diagrammatic view to illustrate the principle of the structure of an optical arrangement in accordance with an embodiment of the invention,

Figures 2 shows a diagrammatic plan view of a carrier structure subelement by way of example which can be used in the carrier structure of the Figure 1 arrangement, Figure 3 shows a diagrammatic view to illustrate the principle of integration of cooling passages in a carrier structure according to the invention, Figure 4 shows a diagrammatic plan view of a carrier structure subelement by way of example which can be used in the Figure 3 carrier structure, with incorporated cooling passage,

Figure 5 shows a diagrammatic view to illustrate an embodiment relating to the connection of carrier structure subelements to afford a carrier structure with integrated cooling passages, and

Figures 6 shows a diagrammatic view of a further embodiment relating to the connection of carrier structure subelements to afford a carrier structure with integrated cooling passages.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The concept of the invention is firstly described hereinafter with reference to the diagrammatic view showing the principles involved in Figure 1.

Figure 1 a shows a multiplicity of modules 1 10, 120, 130, 140 (it will be appreciated that the number thereof as four is only by way of example and can also be higher or lower) which jointly provide a carrier structure 100. The carrier structure 100 carries actively or passively optical elements such as for example mirrors 101 , 102 in a microphotolithographic projection exposure apparatus designed for EUV (wherein the carrier structure can be provided in the illumination system and/or in the projection objective of the projection exposure apparatus). Although two mirrors 101 , 102 are shown in the illustrated embodiment that number is also by way of example and can also be higher or lower, in which respect in the case of a carrier structure a projection objective typically involves more (for example six) mirrors. In addition the optical elements or mirrors 101 , 102 can also be carried indirectly, for example by way of actuators which in turn carry those mirrors (the actuators are not shown in Figure 1 for the sake of simplicity).

In the only diagrammatic view in principle in Figure 1 each of the modules 1 10- 140 is composed of four carrier structure subelements (for example the carrier structure subelements 121 -124). That number is only by way of example and can be higher or lower and can also be different for the individual modules 1 10- 140. The material of the carrier structure 100 can have or be for example a suitable metal, steel or an aluminum alloy, wherein the modules 1 10-140 can also be made from different materials. In addition the carrier structure subelements (for example 121-124), as described in greater detail hereinafter, can be joined together by way of different production processes to afford the modules 1 10- 140. Vacuum brazing, diffusion welding, clamping connection, screw connection and welding are particularly suitable. In that respect the connecting technology involved supports the demands for sufficiently high inherent frequency, damping and thermal conduction. The modules 1 10-140 can also be produced for example by welding plates or facets which can also be curved in a plate (possibly flexural) welded construction, to which in turn the cooling passages (to be described in greater detail hereinafter) can be applied (for example welded or soldered thereon), in which case the modules produced in that way are in turn connected together (for example by screwing). The modules 1 10-140 and carrier structure subelements according to Fig. 1 can be configured such that they form a subhousing having a geometry that varies, at least in regions, in correspondence to a usable beam path in the projection exposure apparatus. More particularly, the usable beam path can be surrounded by said subhousing such that there is a maximum spacing of not more than 10 mm, more particularly not more than 5 mm, between said usable beam path and the subhousing. Furthermore, a folded beam path which is schematically shown in Fig. 1 can be 'encapsulated' by said subhousing in an at least almost optimum manner.

Figure 2 shows a diagrammatic plan view of a carrier structure subelement 121 by way of example which can be used in the carrier structure according to the invention as shown in Figure 1 . In this example the carrier structure subelement 121 has in all three openings 121a, 121 b and 121 c as apertures for the beam to pass through. In this case the openings 121 a, 121 b and 121 c are so selected in respect of their geometry, arrangement and number in accordance with the ultimately intended placement of the respective carrier structure subelement 121 in the beam path so that when the carrier structure subelements or the modules in turn composed therefrom are joined together, the desired encapsulation of the light beam passing through the optical system in operation thereof or optionally the provision of the above-described 'mini- environments' is afforded.

Thus the regular or symmetrical arrangement of the openings or apertures 121a, 121 b and 121 c, shown in the example of Figure 2, is simplified as those openings are preferably so arranged at the respective positions of the beam passage therethrough that optimum geometrical approximation to the beam path is achieved. In general terms the carrier structure subelements, both in regard to their outside contour and also in regard to their inside contour, are thus of a geometry which is more complex for example in comparison with a round disk but also compared to the carrier structure subelement 121 illustrated in the embodiment by way of example. As is already apparent from Figure 1 that implies that carrier structure subelements with fewer openings or apertures are already provided in the simplified beam path diagrammatically shown there, depending on how often the beam path passes through the respective carrier structure subelement.

In addition the surfaces that can be seen in Figure 2 of the inside contour of each carrier structure subelement, by virtue of the modular structure, can be respectively ideally adapted to the demands in regard to reflection of stray light, insofar as respectively suitable surface treatment processes such as mechanical machining (for example for definedly roughening the surface to reduce or eliminate reflection phenomena) or coating in a suitable fashion are selected.

The internal geometry (which in fact at the same time also forms a 'mini- environment' within the optical system) can thus be individually produced, in which respect for example for specifically targetedly influencing the stray light properties in regions in which stray light is particularly critical, it is possible to apply more complex and expensive surface treatment operations and surfaces in less critical regions can be more easily produced or even left substantially unchanged.

Upon assembly of the carrier structure subelements to afford the carrier structure for example in Figure 1 the individual carrier structure subelements on the one hand can firstly be provided with the suitable openings and then stacked in mutually superposed relationship (and joined with the processes still described hereinafter), in which case that gives a stepped surrounding wall configuration for the beam to pass through, determined by the shape or plate geometry of the carrier structure subelements. Alternatively a plurality of carrier structure subelements can firstly be stacked in mutually superposed relationship to constitute the carrier structure before then the corresponding openings are produced for the beam to pass through. With reference to Figures 3 through 6 different possible ways of integrating cooling passages into the carrier structure are described hereinafter.

In per se known manner the fundamental purpose of such cooling passages, in a projection exposure apparatus designed for EUV, is to shield the thermal stresses which are involved with the radiation-induced rise in temperature of the mirrors and which occur in the region of the carrier structure from temperature-sensitive elements such as for example sensors. In regard to that heat shielding effect the modular configuration of the cooling passages according to the invention is also found to be advantageous in many respects, as described hereinafter.

Firstly, as indicated in the diagrammatic view in Figure 4, an implementation of cooling passages 450 of a comparatively complex configuration can be substantially reduced to two-dimensional structures insofar as cooling passages 450 are firstly produced for example by milling in the above- described carrier structure subelements 421 and are then closed by welding on cover plates. In addition, individual placement of the cooling passages within the carrier structure can also be effected for the purposes of specifically targeted control of thermal stresses in the optical system.

In that respect Figure 3 firstly shows a diagrammatic view in which associated with each of the modules 310-340 is its own or separate cooling circuit 315, 325, 335 and 345 respectively.

Now in further embodiments those cooling circuits can also be individually interconnected within the carrier structure. For example in a modification of the Figure 3 embodiment, cooling medium (for example water) which flows into the uppermost module 310 can be further used by interconnection with the lowermost module 340 in order to connect the modules 310, 340 together to form a single common cooling circuit, for example if they have to bear only comparatively slight thermal stresses. In addition, only one cooling circuit or also a plurality of cooling circuits can be associated with each module. The cooling circuits can therefore be placed individually in those regions where they are most needed so that those regions are supplied especially with cooling water. In that way, and having regard to the available typically limited supply of cooling medium, it is possible to achieve an action or heat screening effect which is optimally matched in regard to the specific factors or requirements involved.

A first embodiment relating to the integration of cooling passages in the carrier structure is described hereinafter with reference to the diagrammatic view in Figure 5. Referring to Figure 5 the carrier structure subelements 51 1 -514 (which are assembled to afford a module 510 similarly to Figure 1) are joined together by a connection involving intimate joining of the materials involved, insofar as after the carrier structure subelements 51 1-514 have been produced for example from aluminum or steel and after the regions for the cooling passages have been milled therein (of for example rectangular, round or oval cross-section) in the flat surfaces thereof, the mutually facing boundary surfaces of the carrier structure subelements 51 1 -514 are subjected to hard-vacuum brazing for sealing them off relative to each other and for achieving adequate sealing integrity in relation to the external (typically vacuum) environment of the cooling passages. A further suitable method of sealingly connecting the carrier structure subelements 51 1 -514, which is advantageous in regard to corrosion aspects which are considered in greater detail hereinafter, is diffusion welding in which the carrier structure subelements 51 1 -514 are welded directly on to each other. The monolithic modules 510,... which are accordingly obtained as described hereinbefore can then be screwed together to construct the carrier structure, similarly to Figure 1 . In the Figure 5 structure cooling medium 550 (for example cooling water) flows by way of a cooling medium feed 560 to the module 510 and is discharged again from the module 510 by way of a cooling medium discharge 570, in which respect the cooling passages extending in the direction of the plane of the paper (that is to say in the y-direction in the illustrated co-ordinate system) are denoted by '550a' and the through passages connecting those cooling passages 550a together in the z-direction are denoted by '550b'.

Preferably in that respect, in accordance with a further aspect of the invention, the configuration of the flow of cooling medium is implemented through the cooling passages 550a and the through passages 550b in such a way as to optimize the flow, with the aim of if possible not inducing any vibration from the carrier structure into the mirrors or into the actuators carrying the mirrors.

As a suitable measure for that purpose, the cooling passages 550a are as far as possible embodied without any bends in the flow path, as can be seen for example in Figure 4 by means of the cooling passage 450 indicated there. In order to counteract vibrations caused by eddies which nonetheless possibly occur, preferably the cooling passages 550a are implemented, particularly at the transitions between adjacent carrier structure subelements 51 1-514, with comparatively large radii or cross-sectional areas as the flow speed is lower in the larger volumes afforded thereby.

As a further suitable countermeasure in regard to flow-induced vibration to be avoided, flow rectifiers 580 in the form of porous structures (for example honeycomb structures, filter structures of porous materials or the like) are preferably incorporated (in particular in the passages 550b interconnecting the cooling passages 550a). Figure 6 shows a further embodiment relating to the connection of carrier structure subelements to form a carrier structure with integrated cooling passages.

As shown in Figure 6 carrier structure subelements 612-614 (assembled similarly to Figure 1 to form a module 610) are screwed together by way of screws 605. As that screwed connection only produces a clamping connection which is not fluid-tight in relation to the flow of cooling medium, sealing closure of the cooling passages 650a (which for example are again pre-milled) is then effected by way of sealing plates 690 which in turn are linked into the respective carrier structure subelements 612-614 by way of welded seams 696. A sealing effect at the transitions between the respective sealing plate 690 and the respectively adjoining carrier structure subelement 612-614 can be achieved by a further seal (which in the embodiment is in the form of a double O-ring seal 695).

The embodiment shown in Figure 6 is advantageous in particular in regard to corrosion aspects as identical materials (for example aluminum) can be used for production of the sealing plates 690 and the carrier structure subelements 612-614 and in addition the welding operations necessary for making the connection can also be carried out without additional materials so that the cooling passages can be produced substantially using one and the same material. Thus it is possible in the region of the cooling passages to at least substantially avoid the presence of different (for example soldering) materials with mutually different electrochemical potentials and electrochemical corrosion which is also involved therewith and with the typically electrolytic cooling medium. A further measure for reducing electrochemical corrosion within the cooling passages involves at least region-wise nickel-plating of the cooling passages. A further possible method of applying the cooling passages comprises laying on a foil (which preferably comprises the same material as the sheet material, for example steel or aluminum and which can be produced with a thickness, purely by way of example, of between 0.5 mm and 1 mm) which is fixed both at its periphery and also at suitable support points (for example by welding) and which is plastically deformed by way of the action of pressure to provide foils which are shaped in cushion form, the resulting cooling passages being provided with suitable connections for passing a cooling medium therethrough. It will be appreciated that different joining methods for joining the carrier structure subelements or modules together according to the invention to provide the carrier structure according to the invention can be used in combination, in which respect for example individual modules are milled out of solid material blocks (possibly with cooling passages being milled into the surface of the modules and with sealing joining using soldering or welding processes) and other individual modules comprising (possibly curved) facets are joined using soldering or welding processes, in which case the cooling passages can be welded or soldered on. Even if the invention has been described by reference to specific embodiments numerous variations and alternative embodiments will be apparent to the man skilled in the art, for example by combination and/or exchange of features of individual embodiments. Accordingly it will be appreciated by the man skilled in the art that such variations and alternative embodiments are also embraced by the present invention and the scope of the invention is limited only in the sense of the accompanying claims and equivalents thereof.

Claims

An optical arrangement in a projection exposure apparatus for EUV lithography, comprising:

• a multiplicity of optical elements (101 , 102); and

• a carrier structure (100, 300) which carries the optical elements (101 , 102) and which is composed of at least two releasably interconnected modules (1 10-140, 310-340, 510, 610);

• wherein each module (1 10-140, 310-340, 510, 610) is composed of at least one carrier structure subelement (121-124, 421 , 51 1- 514, 612-614);

• wherein a subhousing is produced by a multiplicity of carrier structure subelements (121-124, 421 , 51 1-514, 612-614) and/or modules (1 10-140, 310, 340, 510, 610); and

• wherein said subhousing has a geometry that varies, at least in regions, in correspondence to a usable beam path in said projection exposure apparatus, said usable beam path being defined as an envelope of all light bundles which can propagate from all field points in a field plane to an image plane of the projection exposure apparatus.

An optical arrangement as set forth in claim 1 , characterized in that said usable beam path is surrounded by said subhousing such that there is a maximum spacing of not more than 10 mm, more particularly not more than 5 mm, between said usable beam path and the subhousing.

An optical arrangement as set forth in claim 1 or 2, characterized in that at least one of the modules (1 10-140, 310-340, 510, 610) is composed of at least two carrier structure subelements (121 -124, 421 , 51 1 -514, 612-614), in particular at least three carrier structure subelements, further particularly at least four carrier structure subelements.

4. An optical arrangement as set forth in anyone of the claims 1 to 3, characterized in that at least one of the carrier structure subelements (121 -124, 51 1-514, 612-614) has at least two openings (121 a-121 c, 421 a- 421 c) to permit a beam to pass through in operation of the optical system.

5. An optical arrangement as set forth in claim 4, characterized in that at least two carrier structure subelements (121-124, 421 , 51 1 -514, 612-614) have a different number of openings (121 a-121 c, 421 a-421 c) to permit a beam to pass through in operation of the optical system.

6. An optical arrangement as set forth in claim 4 or claim 5, characterized in that at least two carrier structure subelements (121 -124, 421 , 51 1 -514, 612-614) differ in respect of the size, cross-sectional geometry and/or positioning of their openings (121 a-121 c, 421 a-421 c).

7. An optical arrangement as set forth in one of the claims 4 to 6, characterized in that the arrangement of the openings (121a-121 c, 421 a- 421 c) is adapted to the configuration of a beam passing through the optical system in operation.

8. An optical arrangement as set forth in anyone of the preceding claims, characterized in that said usable beam path comprises light bundles that at least partially penetrate each other.

9. An optical arrangement as set forth in anyone of the preceding claims, characterized in that said usable beam path is a folded beam path.

10. An optical arrangement as set forth in one of the preceding claims, characterized in that a beam passing through the optical system in operation traverses in succession different openings in at least one of the carrier structure subelements.

1 1. An optical arrangement as set forth in one of the preceding claims, characterized in that said optical elements are mirrors.

12. An optical arrangement as set forth in one of the preceding claims, characterized in that at least two carrier structure subelements (121-124, 421 , 51 1 -514, 612-614) have at least region-wise a different surface treatment, for example by mechanical machining, coating or the like.

13. An optical arrangement as set forth in one of the preceding claims, characterized in that at least two carrier subelements (121 -124, 421 , 51 1- 514, 612-614) have mutually corresponding surface portions which after assembly of said carrier structure subelements form with each other a cooling passage portion (450, 550a, 650a) through which a cooling medium (550, 650) can flow in operation of the optical system.

14. An optical arrangement in a projection exposure apparatus for EUV lithography, comprising:

• a multiplicity of optical elements (101 , 102); and

• a carrier structure (100, 300) which carries the optical elements (101 , 102) and which is composed of at least two releasably interconnected modules (1 10-140, 310-340, 510, 610),

• wherein each module (1 10-140, 310-340, 510, 610) is composed of at least one carrier structure subelement (121-124, 421 , 51 1- 514, 612-614), and

• wherein at least two carrier subelements (121-124, 421 , 51 1 -514, 612-614) have mutually corresponding surface portions which after assembly of said carrier structure subelements form with each other a cooling passage portion (450, 550a, 650a) through which a cooling medium (550, 650) can flow in operation of the optical system.

15. An optical arrangement as set forth in claim 13 or 14, characterized in that at least one cooling medium circuit (315, 315, 335, 345) is constructed by means of a multiplicity of such cooling passage portions.

16. An optical arrangement as set forth in claim 15, characterized in that a multiplicity of cooling medium circuits (315, 325, 335, 345) which can be selectively connected together are constructed by a multiplicity of such cooling passage portions.

17. An optical arrangement as set forth in claim 15 or claim 16, characterized in that at least one porous structure is arranged in the region of at least one of the cooling medium circuits.

18. An optical arrangement as set forth in one of the preceding claims, characterized in that at least two carrier structure subelements (612, 613, 614) are fluid-tightly sealed off relative to each other by way of at least one sealing element.

19. An optical arrangement as set forth in claim 18, characterized in that the sealing element is in the form of a cover plate (690).

20. An optical arrangement as set forth in claim 19, characterized in that at least one of the carrier structure subelements (612, 613, 614) and the cover plate (690) are made from the same material.

21. A microlithographic projection exposure apparatus comprising an illumination system and a projection objective, wherein the illumination system and/or the projection objective has an optical arrangement as set forth in one of the preceding claims.

22. A process for the production of an optical system of a projection exposure apparatus for EUV lithography, wherein the optical system is constructed from a multiplicity of optical elements (101 , 102) carried by a carrier structure, wherein the carrier structure (100, 300) is composed of at least two releasably interconnected modules (1 10-140, 310-340, 510, 610), and wherein each module (1 10-140, 310-340, 510, 610) is composed of at least one carrier structure subelement (121-124, 421 , 51 1 -514, 612-614), wherein a subhousing is produced by a multiplicity of carrier structure subelements (121 -124, 421 , 51 1-514, 612-614) and/or modules (1 10-140, 310, 340, 510, 610) such that said subhousing has a geometry that varies, at least in regions, in correspondence to a usable beam path in said projection exposure apparatus, said usable beam path being defined as an envelope of all light bundles which can propagate from all field points in a field plane to an image plane of the projection exposure apparatus.