WO2015090862A1

WO2015090862A1 - Euv lithography system and transport device for transporting a reflective optical element

Info

Publication number: WO2015090862A1
Application number: PCT/EP2014/075550
Authority: WO
Inventors: Moritz Becker; Dirk Heinrich Ehm; Peter Marek; Akbarinia ALIREZA
Original assignee: Carl Zeiss Smt Gmbh
Priority date: 2013-12-19
Filing date: 2014-11-25
Publication date: 2015-06-25
Also published as: TW201537305A; DE102013226678A1

Abstract

The invention relates to an EUV lithography system (1) comprising: at least one gas nozzle (18) with a nozzle opening for the emergence of a gas stream (19) for removing contaminating substances from a surface (8a-14a) of the EUV lithography system (1) and/or for deflecting contaminating substances, with the gas stream (19) forming at least one gas vortex in the EUV lithography system (1). The invention also relates to a transport device for transporting a reflective optical element for EUV lithography, comprising: a receptacle element for receiving the optical element, a movement device for moving the receptacle element and an outflow device for generating gas curtains flowing along the surface on both sides of the optical element.

Description

EUV lithography system and transport device for transporting a reflective optical element

Cross-reference to related application

This application claims priority to German Patent Application No. 10 2013 226 678, filed December 19, 2013, the entire disclosure of which is considered part of and is incorporated by reference in the disclosure of this application.

Background of the invention

The invention relates to an EUV lithography system comprising: at least one gas nozzle with a nozzle opening for the emergence of a gas stream for removing contaminating substances from a surface arranged in the EUV lithography system and/or for deflecting contaminating substances in the EUV lithography system. Furthermore, the invention relates to a transport device for transporting a reflective optical element for an EUV lithography system, in particular for an EUV lithography system as described above.

Within the meaning of this application, an EUV lithography system is understood to mean an optical system for EUV lithography, i.e. an optical system which may be used in the field of EUV lithography. In addition to an EUV lithography apparatus, which serves for producing semiconductor components, the optical system may be e.g. an inspection system for inspecting a photomask (also referred to as reticle below) used in an EUV lithography apparatus, for inspecting a semiconductor substrate to be structured (also referred to as wafer below) , or a metrology system which is used for measuring an EUV lithography apparatus or parts thereof, for example for measuring a projection system. Reflective optical elements for the EUV wavelength range (at wavelengths between approximately 5 nm and approximately 20 nm) , such as e.g. mirrors or photomasks, have optical surfaces which are intended to be protected from the deposition of contaminating substances in order to avoid a reduction in the reflectivity, imaging aberrations and shadows and exposure errors on the wafer connected therewith. Here, the contaminating substances, e.g. in the form of (nano-) particles, are typically preferably deposited on surfaces around which comparatively slowly flowing gases flow. It is possible that such depositions accumulate on the surfaces and become a contamination risk if these are released in cumulative fashion in the case of e.g. small disruptions (pressure variations, vibrations) .

The presence of contaminating substances in the residual gas atmosphere of an EUV lithography system cannot be completely avoided. By way of example, the contaminating substances may be polymers, which originate from vacuum pumps or which are outgassed from adhesives. The contaminating substances may also be residues of photoresists, which are applied to the wafer and which are outgassed from the photoresist under the influence of operating radiation and which may lead to carbon contaminations on the optical elements of the EUV lithography system.

In order to prevent or reduce the deposition of contaminating substances, avoiding surfaces which promote particle depositions, for example inner edges which have not been rounded, or only slightly rounded, and surfaces with high roughness, is known. Moreover, materials promoting particle depositions and electrostatic charges should be avoided to the greatest possible extent. However, for design reasons this cannot be implemented without restrictions. Moreover, replacing certain materials on which contaminating substances tend to adhere with other materials may lead to an increased weight or to undesirable material properties (e.g. a lower rigidity).

WO 2008/034582 A2 , by the applicant, has disclosed the practice of locally housing components of an EUV lithography system that run the risk of contamination in a housing part with a restricted part volume (mini- environment) , which housing part is purged by a purge gas in order to hinder the ingress of contaminating substances from the environment of the housing part. Particles that are released within the mini-environment are intended to be taken along by the purge gas stream and transported to the environment.

DE 10 2012 213 927 Al describes an EUV lithography system with a device for generating a gas curtain for deflecting contaminating substances. In particular, the gas curtain may be formed at an opening between two vacuum chambers of the EUV lithography system in order to prevent contaminating substances from crossing over from one vacuum chamber into the other vacuum chamber. A tube-shaped housing may be provided in the region of the opening. In order to generate the gas curtain, a gas nozzle can open into the tube-shaped housing.

WO 2010/115526 Al describes a method and a device for preventing the passage of contaminating gaseous substances through an opening in a housing of an EUV lithography apparatus . The contaminating gaseous substances are generated in a pulsed manner under the influence of the EUV radiation. In order to deflect the contaminating substances, a pulsed gas stream is generated in such a way that, in the region of the opening, the gas pulses overlap in time with the pulses of the contaminating substances.

In addition to the deflection of contaminating substances, it is likewise known to remove contaminating substances from optical surfaces with the aid of a gas nozzle or a plurality of gas nozzles, as is described in, for example, WO 2009/059614 Al by the applicant. To this end, the gas nozzle is aligned with the surface to be cleaned and the surface to be cleaned is brought into contact with a cleaning-gas gas stream, for example in the form of activated hydrogen or hydrogen radicals . In order to optimize the cleaning process, the gas stream can be generated in a pulsed manner, for example by pulsed supply of the cleaning gas. By way of example, this can avoid a maximum temperature on the surface to be cleaned from being exceeded.

The contamination may also occur during transport or handling of optical elements in the EUV lithography system by means of transport devices provided to this end, since the optical elements are, in the process, typically moved through the correspondingly contaminated chambers of the EUV lithography system and therefore at a particularly high risk of contamination. There is an increased risk of contamination during unprotected transport of optical elements, particularly outside of the protected vacuum environment of EUV lithography systems, that is to say, for example, at atmospheric pressure.

EP 0 174 877 A2 has disclosed a device for x-ray irradiation using an x-ray radiation source, which is arranged in a vacuum chamber and which generates a plasma emitting soft x-ray radiation and which also releases contaminating particles. A thin gas curtain of a gas transparent to soft x-ray radiation is arranged between a target and a mask in order to keep the particles away from the mask. By arranging the mask in the vicinity of the gas curtain, but far enough away from the latter in order to prevent an interaction, the gas curtain can be used for cooling the mask. For the purposes of cooling the mask, use can also be made of two gas curtains, with the mask being arranged therebetween .

Object of the invention

It is an object of the invention to provide an EUV lithography system and a transport device, which enable a more effective removal of contaminating substances from a surface and/or a more effective protection from contaminating substances than is the case in the prior art .

Subject matter of the invention In accordance with one aspect, this object is achieved by an EUV lithography system of the type set forth at the outset, wherein the gas stream forms at least one gas vortex, i.e. a rotating gas stream, in the EUV lithography system.

The gas stream emerging from the nozzle opening may form the vortex itself, i.e. from its own volumetric flow. However, the gas stream also forms a vortex within the meaning of the invention if the vortex is generated not only by the volumetric flow of the gas stream itself but, moreover, at least in part by an interaction with the volumetric flow of a further gas, for example of a surrounding gas. The volumetric flow of the gas stream and the volumetric flow of the further gas may mix or flow together in the process . The gas stream which forms the at least one gas vortex promotes the removal of contaminating substances already deposited on an optical surface of the EUV lithography system since the gas vortex increases the cleaning effectiveness (i.e. the cleaning effect per amount of purge gas or the cleaning effect per flow rate of the purge gas) and the cooling effectiveness (i.e. the cooling effect per amount of purge gas). Overall, this enables a more effective prevention of particle depositions and a more effective and simpler detachment of particles from surfaces.

The gas vortex can be generated not only during normal operation of the EUV lithography system but also outside of normal operation, for example in the case of purge processes occurring outside of normal operation, in order to more easily detach particles from specific surfaces by a targeted flow thereon or by flow guidance or flow manipulation. Furthermore, the gas stream which forms the gas vortex can advantageously improve the deflection of contaminating substances, e.g. in a gas curtain. The gas vortex generated in this manner can be used in a targeted manner for increasing the range of the gas stream forming the gas curtain. In one embodiment of the EUV lithography system, the gas nozzle is embodied to generate the gas vortex under stationary flow conditions within the gas nozzle. Within the meaning of this application, stationary flow conditions are understood to, mean conditions of the flow which do not change over time, i.e., for example, time-constant pressure, temperature and velocity conditions of the flow within the gas nozzle. In particular, stationary flow conditions are understood to mean no pulsed supply of gas into the gas nozzle, which leads to the generation of a pulsed gas stream. In a development of the preceding embodiment, the gas nozzle comprises a flow cross section extending asymmetrically in relation to the nozzle longitudinal axis. Such an asymmetrically extending flow cross section promotes the generation of velocity or pressure gradients and therefore the occurrence of gas flow velocities with different magnitudes within the gas nozzle; this promotes the formation of gas vortices and contributes to a (locally) improved cleaning effectiveness. For the asymmetric formation of the flow cross section, the gas nozzle, in particular the expansion funnel of the gas nozzle, may have an asymmetric form, i.e. the latter does not extend in a rotationally symmetric manner in relation to the nozzle longitudinal axis .

In one further development, the gas nozzle for generating the gas vortex comprises flow guiding elements, in particular extending in a thread-like manner. The flow guiding elements already put the gas stream flowing through the gas nozzle into rotation within the gas nozzle (and in a region adjoining the outlet) . As a result of the rotating gas vortex, the extent of the gas stream, e.g. when using the gas stream in a gas curtain, can be extended or the gas stream can be distributed in an improved manner. Larger optical surfaces in the EUV lithography system can be protected from particle contamination in this manner. The flow guiding elements extending in a thread-like manner may have a spiral embodiment and be arranged in an expansion funnel of the gas nozzle. A gas vortex rotating around the longitudinal axis of the gas nozzle is generated by the flow guiding elements. The flow guiding elements are preferably attached to the gas nozzle in an immobile or rigid manner. However, it is also possible to embody the flow guiding elements in a movable manner in order to be able to influence the degree of vortex formation in a targeted manner.

In a further development, the gas nozzle comprises at least one inlet opening laterally into the gas nozzle. The generation of gas vortices is likewise promoted by one or more lateral inlets into the gas nozzle, in particular if one or more inlets are arranged asymmetrically in relation to the nozzle longitudinal axis or if a plurality of inlets arranged with rotational symmetry in relation to the nozzle longitudinal axis are operated with mutually deviating flow conditions. By way of example, a first inlet into the gas nozzle can be operated at first pressure, temperature and/or velocity conditions and a different, second inlet can be operated at second pressure, temperature and/or velocity conditions deviating therefrom such that the gas stream generated in the interior of the gas nozzle by the combination of the individual streams entering through the inlets generates the gas vortex in the gas nozzle. In particular, the inlets open into an expansion funnel of the gas nozzle. The two or more inlets can be spaced apart from one another to a different extent, in particular in the circumferential direction, and open into the expansion funnel of the gas nozzle at different positions along the nozzle longitudinal axis.

In a further embodiment of the EUV lithography system, the gas nozzle is embodied for generating a pulsed vortex-type gas stream. A pulsed vortex-type gas stream can be generated by means of e.g. a valve which opens and closes periodically in the gas supply. Here, the nozzle can be shaped as described above. In a development, use is made of a de Laval nozzle in order to accelerate the gas to supersonic speeds . In the de Laval nozzle, pressure and temperature of the gas behave inversely to the speed. Here, the gas flow increases until the ratio of the pressures on the input side (Pin) and output side (P_out) the nozzle exceed a specific value. This value (Pin/Pout) is 1.899 for hydrogen and 2.049 for helium. Therefore, by increasing the gas flow, it is possible to generate a high velocity gas shock with increasing strength. Subsequently, the gas supply is once again choked.

In principle, the above-described gas nozzles can be operated with a stationary gas supply. However, it is also possible to operate the gas nozzles in a non- stationary manner, i.e. the gas supply to the gas nozzle may be pulsed, as a result of which individual vortex pulses can be generated, further increasing the efficiency of the vortex formation.

In a further embodiment, the gas nozzle is embodied for activating a cleaning gas contained in the gas stream, in particular for activating hydrogen. Since the vortex formed in the gas nozzle dwells for longer in a gas nozzle used for activating the cleaning gas than in the case of conventional gas nozzles, more time is available for activating gases contained in the gas stream such that the activation in accordance with this embodiment is advantageously amplified. A gas stream or gas beam with vortices also increases the dwell time and hence the cleaning effect on the surface to be cleaned of the cleaning gas (e.g. of the activated hydrogen) activated by the gas nozzle and contained in the gas stream. Gas nozzles which are embodied for activating a cleaning gas contained in the gas stream (also referred to as "hydrogen radical generator") have, for example, been disclosed in WO 2009/059614 Al by the applicant. By way of example, hydrogen can be activated by virtue of a molecular hydrogen beam being conveyed past an electrically heated filament, as a result of which the molecular hydrogen H₂ is partly split into radicals H* , i.e. excited individual atoms. Such an activated hydrogen gas beam is particularly suitable for removing carbon-based contaminants from an optical surface. Cleaning takes place outside of the operation of the EUV lithography system at irregular intervals (e.g. days to months) , depending on how strongly a carbon layer, caused by gaseous hydrocarbon contaminants, on the respective optical surface has grown.

A gas nozzle embodied for activating a cleaning gas and for forming at least one gas vortex can also be used during (normal) operation of the EUV lithography system for directing a gas beam of a purging gas onto an in particular comparatively large optical surface in order to protect the latter from contaminating substances. Conventional gas nozzles for activating a cleaning gas are typically embodied or arranged in such a way that the gas beam generated thereby is incident substantially perpendicular on the optical surface to be cleaned. As a result of the straight- lined gas beam extending substantially perpendicular to the surface, the gas emergence occurring in a conventional gas nozzle is unsuitable, or only suitable to restricted extent, for also protecting the optical surface from contaminating substances or particles during normal operation since particles which are carried along by a gas beam extending in a straight line are accelerated in the direction of the optical surface. By contrast, due to the centrifugal force, a gas beam rotating about, in particular, a nozzle longitudinal axis is more likely to be suitable for keeping contaminating substances away from the optical surface. The device for activating the cleaning gas, e.g. in the form of the filaments, is switched off during normal operation of the EUV lithography system.

In a further embodiment, the gas nozzle for removing the contaminating substances is arranged next to the optical surface in order to generate a gas stream extending along the optical surface with gas vortices conveyed along the optical surface . Conveying the gas vortices along the optical surface prevents a particle deposition in a particularly effective manner or causes particularly effective detachment of contaminating substances already deposited on the surface. The gas vortices moving over the surface can also effect an effective heat transport or an effective cooling of locally particularly strongly heated regions of the optical surface. Such regions may be created, in particular, at positions at which the EUV radiation is incident on the optical surface in a highly focussed, for example in an approximately punctiform manner.

In order to realize a conveyance of the gas vortices along the optical surface, the gas nozzle, in particular a longitudinal axis of the gas nozzle, is preferably aligned at an angle of between 45° and 90° with respect to the surface normal of the optical surface .

A further embodiment comprises at least one flow guiding element which promotes vortices and is arranged outside of the gas nozzle, in particular a preferably tapered edge, onto which the gas stream flows. Such a vortex-promoting flow guiding element can advantageously form a gas vortex which, for example, can serve for deflecting contaminating substances. The gas vortex can, in particular, be formed in the direct vicinity of a gas curtain in order to take and deflect contaminating particles such that the latter cannot advance into regions of the EUV lithography system where they could cause damage. By positioning the tapered edge in a targeted manner in the volume region through which the gas stream flows, it is possible to form a gas vortex at a suitable position, e.g. in the region of an opening, so as to prevent the ingress of contaminating particles into the opening.

An embodiment of the EUV lithography system additionally comprises an in particular tube-shaped housing extending across the gas stream, into which housing the nozzle opening opens and on which housing a collection opening for collecting the gas stream is arranged opposite to the nozzle opening at a distance to be bridged by the gas stream, with an edge, which serves as flow guiding element, onto which the gas stream flows being formed between the collection opening and a collection opening-side housing wall in order to form a gas vortex in the housing. Contaminating substances or particles can advantageously be deflected by the gas vortex or vortices formed in the housing. In particular, the gas vortex or vortices can particularly efficiently prevent a crossing of contaminating substances through the gas curtain.

The gas vortex generated e.g. above and/or below the gas curtain is created by a tangential impulse transfer from the gas forming the gas curtain or the gas stream to the surrounding gas entering via the pipe-shaped housing from above and below, which surrounding gas contains the contaminating substances . The edge preferably has an acute design (with an acute angle, i.e. an angle a of less than 90°, in particular of less than 45°) in order to promote vortex formation. However, in principle, it is also possible to generate gas vortices by a flow onto edges with comparatively small rounded edge forms (small rounding radii) . The formation of a gas vortex can also be promoted by the provision of a tapering edge between the nozzle opening and the nozzle opening-side housing wall.

The vortex formation can be promoted by the generation of a positive pressure region next to the gas curtain in the vicinity of the nozzle opening and the generation of a negative pressure region next to the gas curtain in the vicinity of the collection opening. This can ensure, in particular, that the gas vortex conveys contaminating particles away from the gas curtain and/or into the collection opening.

A negative pressure region in the vicinity of the nozzle opening and a positive pressure in the vicinity of the collection opening can be generated by a gas nozzle which is embodied for generating a subsonic gas stream if the pressure conditions are selected in a suitable manner; see, for example, Figures 3a and 3b of DE 10 2012 213 927 Al , cited at the outset. In particular, the gas can overexpand within a portion of the gas nozzle expanding from a constriction even in the case of very high flow velocities in the supersonic range such that the static pressure of said gas becomes smaller than that of the gas in the environment. This negative pressure may remain locally restricted to the region of the nozzle opening or the outlet of the gas nozzle. A positive pressure region can be created in the region of the collection opening, which positive pressure region promotes the vortex formation all the more as the collection opening becomes smaller and as the design of the edges delimiting the opening becomes sharper or less rounded off. In one development of the preceding embodiment, the flow cross section of the gas stream at the collection opening is smaller than the entry cross section of the collection opening. This is particularly the case if the gas nozzle generates an overexpanded gas stream, i.e. a gas stream in which upon emergence from the gas nozzle has a lower pressure than the static surrounding pressure. In this case, the gas stream is constricted when it encounters surrounding gas, and so the gas curtain only expands a little and is completely received by the opposite collection opening. Optionally, the gas stream can in this case drag additional surrounding gas with it into the collection opening and develop a pumping effect. In this manner, the surrounding gas containing the contaminating substances can be suctioned at least in part, wherein the suctioning effect can still be increased by the gas vorte .

Particularly when generating an overexpanded gas beam, influencing variables such as e.g. the size of the collection opening, the size of the nozzle opening, the distance to be bridged and the shape of the edge approached by the flow are ideally matched to one another in such a way that the gas curtain or the gas stream is completely, i.e. to 100%, suctioned by the collection opening and surrounding gas is optionally also dragged along. The static surrounding pressure and the emergence pressure at the gas nozzle (from which the emergence speed of the gas stream from the gas nozzle arises) can also, together with the aforementioned influencing variables, be matched to one another in such a way that the formation of one or more gas vortices for deflecting the contaminating substances is promoted.

In one development, the EUV lithography system is embodied to suction a portion of between 50% and 150% of the gas stream emerging at the nozzle opening at the opposite collection opening. The inventors have recognized that the gas vortex formation is promoted in the case of such a suction portion or such a passage probability. In the case of a suction portion between approximately 100% and 150%, the whole gas stream and part of the surrounding gas are suctioned through the collection opening, which can be achieved by the above- described overexpansion of the gas stream. In the case of an underexpanded gas stream, which is typically generated in the case of short gas nozzles and/or subsonic speeds, the gas emerging from the gas nozzle is not constricted but diverges strongly and typically does not completely reach the collection opening lying opposite to the nozzle opening. However, such a gas stream likewise promotes the vortex formation if the gas portion escaping into the environment, i.e. the gas portion missing the collection opening, is not too great and if provision is made for vortex-promoting edges. Gas curtains where well over 100% are received or suctioned by the collection opening and gas curtains where only a portion of well below 100% reaches the collection opening make the vortex formation more difficult or can completely prevent the vortex formation. The suction portion of the gas stream, i.e. the portion of the gas stream collected by the collection opening, mainly depends on the distance to be bridged, the type of gas, the flow velocity and the flow rate. For details in this respect, reference is made to DE 10 2012 213 927 Al, cited at the outset. In a further development, a static surrounding pressure in a vacuum environment of the EUV lithography system lies between 0.1 Pa and 100 Pa. Typically, gas vortices can only form in the viscous flow and pressure range. From below, this pressure range is restricted by molecular flow and above said pressure range possibly extends far beyond the pressure range typically used in EUV lithography systems. The boundary to the molecular flow range is described by the Knudsen number, which is defined as the ratio of the mean free path length of the gas molecules to a characteristic length such as e.g. the diameter of the available free space or the diameter of the vortex. Vortex formation is typically only possible in the case of Knudsen numbers smaller than one, i.e. if the vortex diameter is greater than the mean free path length of the molecules. In addition to the temperature and the type of gas used, the Knudsen number only depends on the pressure. In the case of hydrogen, the mean free path length at room temperature under pressure of approximately 1 Pa is approximately 12 mm, so that there should not be a drop below this pressure in the case of small channels or housings. In the case of relatively large optical surfaces or spatial regions which are available for vortex formation, a smaller pressure of e.g. 0.1 Pa may also be sufficient for vortex formation.

The vacuum environment of the EUV lithography system, in which the advantageous pressure region is to be aimed at, may for example prevail in a first and/or second vacuum chamber of the EUV lithography system. This vacuum environment can also be chambers between which deflection of contaminating particles should occur.

A development of the EUV lithography system comprises at least a first vacuum chamber and a second vacuum chamber, between which an opening for the passage of EUV radiation is formed, at which opening the gas nozzle for deflecting contaminating substances is formed. The dimension of the opening (in particular the width thereof) is typically selected in such a way that it can be bridged by the gas stream or the gas curtain. In general, at least one optical component which is intended to be protected from contaminating substances by the gas stream is arranged in at least one of the two vacuum chambers. Since the EUV radiation must pass through the gas stream, the gas stream or the gas curtain, due to the short range thereof, cannot be realized at any arbitrary position in the beam path, i.e. the gas stream should typically be used at locations where the EUV radiation has a small beam cross section. This is the case, in particular, in the region of an intermediate focus of the EUV radiation. The gas nozzle can, in particular, be arranged at an opening to a vacuum chamber for arranging a mask or for arranging a wafer.

In accordance with a second aspect, the object is achieved by a transport device for transporting a reflective optical element for EUV lithography, preferably a mask, in particular for an EUV lithography system as described above, comprising: a receptacle element for receiving the optical element, a movement device for moving the receptacle element and an outflow device for generating gas curtains flowing along the surface on both sides of the optical element. The reflective optical element can, in particular, be a plate- shaped optical element, for example a photomask for an EUV lithography system in the form of an inspection system, e.g. of an "actinic mask inspection tool", AIMS, in which a reflective photomask can be used. Instead of a reflective optical element, it is optionally also possible for a transmissive optical element to be transported by means of the transport device .

The deposition of contaminating substances on both the front side and the rear side of such a mask was found to be unfavourable. Contaminating substances deposited on the front side of the mask can lead to unwanted structures on the wafer and to defective semiconductor elements by disturbing the interference, while contaminating substances deposited on the rear side of the mask can lead to errors in the overlay of a plurality of semiconductor structures arranged over one another in layers . With the aid of the transport device, contaminating substances, which move toward the front and/or rear side of the reflective optical element and which threaten to be deposited on the optical element, can be taken by the gas curtains and deflected away from the surfaces at risk. In this manner, the risk of the deposition of contaminating substances or particles on the front side and rear side surfaces of the reflective optical elements and the risk of the corresponding negative consequences is removed or at least reduced.

The gas curtains can be generated not only during the transport of the optical element, e.g. from an exposure position to a storage or equipping position, but also in the resting state of the reflective optical element, i.e., for example, when the optical element is arranged in the exposure position or in the storage or equipping position. A further advantage of the transport device lies in the fact that the two gas curtains do not expand, or do not expand substantially, while flowing along the surface on the front side and rear side surface, as a result of which there is no local reduction in the gas temperature in the region of the surfaces and hence no temperature gradients set-in at the surfaces of the optical element or in the optical element. Therefore, overall, the transport device enables an improved contamination prevention and a more effective and more robust operation.

The flow rate or the volumetric flow of the outflow device can be set in such a way that, in particular, contaminating substances with specific size (typically expected in the corresponding application case) are taken and deflected. To this end, the outflow device can be operated with a flow rate or a volumetric flow of 1 to 500 mbar 1/s. The reflective optical element is mounted indirectly, e.g. by means of one or more contact elements, or directly on the receptacle element in order to receive the optical element. The receptacle element is typically connected to the movement device.

By way of example, the movement device can be embodied as a robot arm which can move the receptacle element (and hence the optical element) about one or more rotational and/or translational axes. At least part of the transport device, i.e. at least the receptacle element with the outflow device, can be arranged in vacuum environment (for example in a vacuum chamber of an EUV lithography system) with a static surrounding pressure of e.g. 0.1 to 100 Pa. It is understood that the transport device can, in principle, also be operated for transporting optical elements under normal conditions, i.e. in a static atmospheric pressure of approximately 0.9 bar to 1.1 bar.

In a development of the transport device, the outflow device comprises at least one nozzle for generating the gas curtains. By means of the nozzle or nozzles, the gas curtains flowing along the surface on both sides of the optical element can be generated and suitably formed. Forming the flow of the gas curtains and hence influencing the deflecting or diverging effect of the gas curtains can, for example, be effected by the shape of the nozzles (typically the flow cross sections thereof) and/or the number of nozzles. In principle, provision can be made for a single nozzle or provision can be made for a plurality of, for example two, nozzles for generating the gas curtains. In particular, the nozzles can have a slit-shaped emergence opening, the long side of which may for example extend over the whole width of the optical element.

In accordance with one development, the nozzle in each case comprises an emergence opening for generating one of the two gas curtains on both sides of the optical element. The emergence openings are typically arranged directly next to a side edge of the optical element. The respective emergence openings of the nozzle preferably have a constant emergence cross section in a direction extending across the gas emergence direction. In this manner, a uniform and planar flow around the front side and back side of the optical element can be achieved. Preferably, the emergence cross section of the front-side emergence opening and the emergence cross section of the rear-side emergence opening have the same size. By way of example, the emergence openings can be embodied as elongate slit openings with a constant slit width, which extend along the optical element across the gas emergence direction of the nozzle.

In one development, the nozzle comprises a flow- dividing central part and two outer guiding parts . The flow-dividing central part of the gas nozzle renders it possible to split an individual gas stream into at least two separate gas streams so as to generate the two gas curtains. To this end, the two gas streams separated by the central part open into the emergence openings arranged on both sides of the optical element. In order to introduce the gas curtain gas into the nozzle, provision can be made for a (single) nozzle inlet for supplying the gas curtain gas . The outer guiding parts can be arranged with mirror symmetry in relation to the flow-dividing central part.

In another development, a nozzle is in each case arranged on both sides of the optical element for generating the two gas curtains. In this development, nozzle inlets which have to be supplied with a gas for generating the gas curtains are provided on each nozzle .

In a further embodiment, the gas curtains emerge from the outflow device substantially tangentially or parallel to the mutually opposite, generally planar surfaces of the optical element. In this manner, the gas curtains experience no deflection, or almost no deflection, in a direction perpendicular to the surfaces of the optical element. Advantageously, as a result of this, the gas curtains flow along the surface of the optical element with a particularly stable manifestation.

In a further embodiment, the receptacle element is embodied as a frame-shaped holding element. Here, the frame-shaped holding element is typically matched in terms of its dimensions to the size of the reflective optical element, i.e. it is embodied with substantially the same size as the latter or embodied to be slightly larger, wherein the frame shape of the holding element substantially corresponds to the form or external geometry of the optical element. By way of example, the holding element can have a rectangular design if the optical element or the mask likewise has a rectangular form. The frame-shaped holding element need not necessarily have a closed form but can, for example, have a design that is open on one side, e.g. a U-shaped design. The reflective optical element is mounted indirectly or directly on the frame-shaped holding element .

A further embodiment of the transport device comprises a collection device for collecting the gas curtains generated by the outflow device. The collection device is embodied to collect and suction the gas curtains which emerged at the nozzle. This can firstly prevent substantial parts of the gas forming the gas curtains from escaping into the environment and, secondly, advantageously prevent an expansion of the gas curtain gas flowing along the surface of the front side and rear side of the optical element.

In a development of the preceding embodiment, the outflow device and the collection device are arranged on opposite lateral edges of the optical element. As a result, the gas curtains on both sides of the optical element flow along the shortest path from an outflow device-side boundary of the optical element, along the surface of the optical element, to a collection device- side edge of the optical element situated directly opposite thereto. In this manner, the risk of losing gas curtain gas to the environment can be minimized. The outflow device and the collection device are arranged on the receptacle element of the transport device. It is understood that the provision of a collection device can optionally be dispensed with such that the gas curtain gas can escape into the environment .

In a further embodiment, for the purposes of receiving the optical element or receiving a frame surrounding the optical element, contact elements are provided between the receptacle element and the optical element or between the receptacle element and the frame. The optical element can either be mounted directly on the contact elements or a frame connected to the optical element in a secure or optionally detachable manner can be mounted on the receptacle element via the contact elements. Preferably, provision is made for at least three contact elements for mounting the optical element. By way of example, the contact elements can be embodied as pins made of vibration-damping and/or wear- resistant material such that no particles can be produced there . Further features and advantages of the invention emerge from the following description of exemplary embodiments of the invention, on the basis, of the figures in the drawings which show the details essential to the invention and from the claims. The individual features can be implemented individually on their own or a number of them can be implemented in any combination in a variant of the invention.

Drawing

Exemplary embodiments are depicted ^'in the schematic drawing and explained in the following description. In detail : Figure 1 shows an illustration of an EUV lithography system with four gas nozzles for deflecting contaminating substances and with a gas nozzle for cleaning an optical surface, Figure 2 shows an illustration of a gas nozzle in accordance with Figure 1 for deflecting contaminating substances, comprising a nozzle opening for the emergence of a gas stream, which opens into a housing and comprises a collection opening for collecting the gas stream,

Figure 3 shows an illustration of a further gas nozzle comprising a housing embodied in a manner deviating from Figure 2, Figure 4 shows an illustration of a further gas nozzle opening into a housing, with flow lines of the gas stream and a surrounding gas depicted therein, Figure 5 shows an illustration analogous to Figure 4, with trajectories of contaminating particles,

Figure 6 shows an illustration of a gas nozzle in accordance with Figure 1 for the emergence of a gas stream for removing contaminating substances from an optical surface,

Figure 7 shows an illustration · of a further gas nozzle for removing contaminating substances by generating gas vortices which move along the optical surface,

Figure 8 shows an illustration of a cross section through a transport device for transporting a reflective optical element for EUV lithography,

Figure 9 shows a top view of the transport device from

Figure 8 ,

Figure 10 shows a front view of the transport device from Figure 8 and Figure 9, Figure 11 shows an illustration of a cross section through a further embodiment of a transport device for transporting a reflective optical element, and

Figure 12 shows a top view of the transport device in accordance with Figure 11. In the following description of the drawings, identical reference signs are used for identical or functionally identical components .

Figure 1 schematically shows an EUV lithography system 1 in the form of an EUV projection exposure apparatus, which comprises a beam generation system 2, an illumination system 3 and a projection system 4, which are housed in separate vacuum housings and arranged in succession in a beam path 6 emanating from an EUV light source 5 in the beam generation system 2. For simplification purposes, the reference signs for the three systems 2, 3, 4 are also used below for the respective vacuum housings or the vacuum environments formed therein.

By way of example, a plasma source, a free electron laser or a synchrotron can serve as EUV light source 5. The radiation in the wavelength range between approximately 5 nm and approximately 30 nm, emerging from the light source 5, is initially focussed in a collimator 7. With the aid of a subsequent monochromator 8, the desired operating wavelength λ_Β, which is at approximately 13.5 nm in the present example, is filtered out by varying the angle of incidence, as indicated by a double-headed arrow. The collimator 7 and the monochromator 8 are embodied as reflective optical elements. The radiation, treated in the beam generation system 2 in view of wavelength and spatial distribution, is introduced into the illumination system 3, which comprises a first and second reflective optical element 9, 10. The two reflective optical elements 9, 10 guide the radiation to a photomask 11 (reticle) as a further reflective optical element, which comprises a structure that is imaged on a wafer 12 with a reduced scale by means of the projection system 4. To this end, a third and fourth reflective optical element 13, 14 are provided in the projection system 4. It is understood that both the number of optical elements in the individual systems 2, 3, 4 and the arrangement thereof are only to be understood in an exemplary manner and that, in real systems, both the number and the arrangement of the optical elements may differ from the EUV lithography system 1 shown in Figure 1. The reflective optical elements 8, 9, 10, 11, 13, 14 each have an optical surface 8a, 9a, 10a, 11a, 13a, 14a, which is exposed to the EUV radiation 6 of the light source 5 and provided with a coating that reflects the EUV radiation 6. The optical elements 8, 9, 10, 11, 13, 14 are operated under vacuum conditions in a residual gas atmosphere, which has a (static) environmental pressure of a few Pascal, in the present example p₂ = 10 Pa. Furthermore, for simplification purposes, the assumption was made that the static pressure p₂ is the same in all three systems 2, 3, 4 and in a further vacuum chamber 15, in which the mask 11 is arranged. Typically, the static environmental pressure p₂, Pc in the vacuum environment of the EUV lithography system 1, i.e. in the individual vacuum housings 2, 3, 4, 15, lies between 0.1 Pa and 100 Pa. In the present example, a smaller surrounding pressure, which deviates from that in other vacuum chambers 2, 3, 4, 15, which is denoted by p₃ in Figure 1 and which may lie at e.g. approximately 5 Pa, prevails in a vacuum chamber 17 in which the wafer 12 is arranged. In the beam generation system 2, the surrounding pressure denoted by p_c in Figure 1 typically is of the same order, but may also be significantly larger and can be up to 100 Pa.

Since the interior of the EUV lithography system 1 cannot be baked out, the presence of residual gas components in the low-pressure environments in the individual vacuum housings 2, 3, 4, 15 cannot be completely avoided. In order to prevent residual gas components or other contaminating substances from depositing on the optical surfaces 8a, 9a, 10a, 11a, 13a, 14a of the optical elements 8, 9, 10, 11, 13, 14 and, as a result thereof, having an adverse effect on the reflectivity of said optical surfaces in relation to the EUV radiation, the EUV lithography system 1 respectively comprises a gas nozzle 20 for generating a gas stream 21 or a gas curtain 21, which extends across the EUV beam path 6, at the openings 16a-d for the passage of EUV radiation 6, which openings are formed between a respective first vacuum chamber 2, 3, 4, 15, 17 and a respectively adjacent second vacuum chamber 2, 3, 4, 15, 17, i.e. between the beam generation system 2 and the illumination system 3, between the illumination system 3 and the chamber 15 with the mask 11, between the chamber 15, in which the mask 11 is arranged, and the projection system 4, and between the projection system 4 and the chamber 17, in which the wafer 12 is arranged. Here, the opening 16a between the beam generation system 2 and the illumination system 3 lies in the region of an intermediate focus Z_F, at which the EUV radiation 6 only has a comparatively small diameter. A comparatively small diameter of the EUV beam path 6 is also present at the other openings 16b, 16c, 16d. The gas nozzles 20 respectively formed at the openings 16a-16d are not shown in Figure 1 and are described in detail below in relation to Figures 2 to 5. The gas streams 21 serve for deflecting contaminating substances (e.g. residual gas components) and in each case form at least one gas vortex in the EUV lithography system 1, as is described in more detail below. An exchange of contaminating substances between the vacuum housings 2, 3, 4, 15, 17 can be prevented in a particularly effective manner by the gas stream 21 or the vortex formation of the gas stream 21.

In order to remove contaminating substances already deposited on the optical surfaces 8a, 9a, 10a, 11a, 13a, 14a of the optical elements 8, 9, 10, 11, 13, 14, the EUV lithography system 1 comprises additional gas nozzles, of which one gas nozzle 18, arranged in front of the optical surface 10a of the second optical element 10 of the illumination system 3, is shown in Figure 1 in an exemplary manner. It is understood that typically such a gas nozzle 18 is also arranged at each further optical element 8, 9, 11, 13, 14 or at each further optical surface 8a, 9a, 11a, 13a, 14a. In order to remove the contaminating substances adhering to the optical surface 10a, the gas nozzle 18 likewise generates a gas stream 19, which forms at least one gas vortex, as is described in more detail below in conjunction with Figure 6 and Figure 7.

In the shown example, the gas nozzle 18 is embodied for activating hydrogen. In order to activate the hydrogen, the gas nozzle 18 has an activation device (not shown in any more detail) which serves to convert molecular hydrogen H₂ into activated hydrogen H* , for example by an electric field or by high temperatures, which, for example, can be generated by means of a filament. The activated hydrogen H* is able to remove the contaminating substances from the optical surface 10a in a particularly effective manner. The molecular hydrogen H₂ can be supplied to the gas nozzle 18 by means of a supply device 22, which projects into the vacuum housing 3 in a gastight manner. Together with the gas nozzle 18, the supply device 22 is displaceable in a direction 23 across the optical surface 10a in order to unblock the beam path 6 of the EUV lithography system 1 during operation and in order to displace the gas nozzle 18 relative to the optical surface 10a during cleaning so as to ensure a complete cleaning of the optical surface 10a. It is understood that the end of the hydrogen supply device 22 depicted by dashed lines in Figure 1 is connected to a reservoir (not depicted) for storing or for producing hydrogen.

It is possible to position the gas nozzle 18 in such a way that the latter does not project into the beam path 6 of the EUV lithography system 1 but nevertheless directs the gas stream 19 onto the optical surface 10a. Where applicable, the gas nozzle 18 can also be securely installed at a suitable position in the EUV lithography system 1. In addition to cleaning the optical surface 10a during an operational pause, the gas nozzle 18 can also be used during the operation of the EUV lithography system 1, to be precise for protecting the optical surface 10a from contaminating substances. In this case, the activation device present in the gas nozzle 18 is switched off and a purge gas, for example nitrogen N₂ or a different inert gas, is supplied to the gas nozzle 18 via the supply device 22, which purge gas is incident on the optical surface 10a in the form of a gas stream 19. As a result of the fact that the gas stream 19 has or forms a gas vortex, contaminating substances are accelerated outward by the centrifugal force and kept away from the optical surface 10a. A schematic design of a gas nozzle 20, which is used for generating the gas stream 21 in the form of a gas curtain generated in the region of one of the openings 16a-d, is explained in more detail below on the basis of Figure 2. The gas nozzle 20 has a nozzle opening 25 arranged at the end of an expansion funnel 24, through which nozzle opening the gas stream 21 for deflecting contaminating substances can emerge. The EUV lithography system 1 comprises a tube-shaped housing 26 extending across the gas stream 21, into which housing the nozzle opening 25 opens and on which housing a collection opening 28 for collecting the gas stream 21 is arranged opposite to the nozzle opening 25 at a distance 27 to be bridged by the gas stream 21. By way of example, the upper end 29, in Figure 2, of the pipe-shaped housing 26 can open into the vacuum housing of the beam generation system 2 and the lower end 30 of the tube-shaped housing 26 can open into the vacuum housing of the illumination system 3. In Figure 2, the optical axis of the EUV beam path 6 extends substantially along the longitudinal direction 31 of the tube-shaped housing 26 (from bottom to top in Figure 2) and a main flow direction 32 of the gas stream 21 extends perpendicular thereto (from left to right in Figure 2) . Proceeding from a comparatively small nozzle inlet 33, the gas stream 21 expands toward the larger nozzle opening 25 and subsequently flows further along the main flow direction 32 until it is collected by the collection opening 28.

Typically, a surrounding gas 34 (residual gas) is present in the region of the housing 26 adjoining the gas stream 21 from above in Figure 2. In the housing 26, a sharp edge 36, onto which the gas stream 21 flows for forming a gas vortex 37 arranged above the gas stream 21, is formed between the collection opening 28 and an upper collection opening-side housing wall 35. The formation of the gas vortex 37 is promoted by the flow-guiding effect of the edge 36, which enables a tangential impulse transfer from the gas stream 21 to the surrounding gas 34 which enters the tube-shaped housing 26 from above (see also Figures 4 and 5) . In the region of the edge 36, a positive pressure in relation to the surrounding pressure p_c is generated, which positive pressure, together with a negative pressure that is formed at a not rounded-off edge 41 at the upper boundary of the nozzle opening 25, likewise promotes a vortex formation.

By means of the gas vortex 37, contaminating substances, which are contained in the surrounding gas 34 entering from above in Figure 2 and flow downward along the housing 26, can be deflected such that these in turn flow back in the opposite direction (toward the top) . In this way, the gas vortex 37 can prevent contaminating substances from crossing through the housing 26. The gas nozzle 20 is operated under stationary flow conditions .

Surrounding gas 34 is likewise present in the region of the housing 26 adjoining the gas stream 21 from below in Figure 2. The transition region formed in the housing 26 between the collection opening 28 and a lower collection opening- side housing wall 35 has a rounded design in contrast to the upper edge 36, on which the gas vortex 37 is generated. A design of a lower edge 39, which would promote vortex formation, is depicted in Figure 2 using a dashed line. The nozzle opening-side transition region 40 from the expansion funnel 24 of the gas nozzle 20 to the lower nozzle opening- side housing wall 38 is also rounded off, in contrast to the upper, edged counterpart thereof. The formation of a gas vortex 37 below the gas stream 21 is prevented by the comparatively strongly rounded-off nozzle opening-side transition region 40, in which an edge formation (indicated by dashed lines) was deliberately avoided, and by the likewise strongly rounded-off collection opening- side transition region.

As shown in Figure 2, the formation of a gas vortex 37 can be promoted by influencing the geometry of the housing 26 in a respective transition region between the collection opening 28 and the collection opening- side housing wall 38 by virtue of forming edges 36, 39 (which are not rounded off) there. The same applies to the transition region between the nozzle opening 25 and the nozzle opening- side housing wall 38, on which the formation of an edge 41 likewise contributes to the formation of a vortex. As will be explained below on the basis of Figure 3, the vortex formation is promoted more strongly, as the design of the edges 36, 41 becomes more acute (as the angle between the housing wall 38 and the upper or lower part of the collection opening 28 decreases) .

The housing 26 of the EUV lithography system 1 depicted in Figure 3 differs from the housing 26 shown in Figure 2 in that the edge 36, which is arranged outside of the gas nozzle 20, on which the gas stream 21 flows and which acts as a vortex-promoting flow guiding element, has a tapered embodiment. Also, in contrast to Figure 2, the nozzle emergence- side upper housing wall 35 also comprises an edge 41 with a .correspondingly acute design. As a result of the edges 36, 41 being embodied more acute than in Figure 2, the gas vortex 37 formed above the gas stream 21 has an increased deflecting action (indicated by the greater number of vortex current lines) . The acute angle formed by the edges 36, 41 is less than 90°, preferably less than 45°, in particular less than 30°; the latter is the case in Figure 3. In order to promote the vortex formation, the housing 26 can, as shown in Figure 3, have a bulging design in particular, i.e. the housing walls 35, 38 can respectively have an outwardly curving (convex) section, along which the gas vortex 37 can flow.

Figure 4 depicts a further gas nozzle 20 and a further housing 26, which is embodied symmetrically in relation to a longitudinal axis 42 of the gas nozzle 20. The flow conditions in the gas nozzle 20 and in the housing 26 are set in such a way that the flow cross section 43 of the gas stream 21 at the collection opening 28 is smaller than the entry cross section 44 of the collection opening 28. For reasons of continuity, the volume flow of the gas stream 21 (cf. flow lines 45a to 45d) and the volume flow of the surrounding gas 34 (cf. flow lines 46a to 46c) therefore mix in the collection opening 28.

In contrast to the edges 36, 41 shown in Figures 2 and 3, the nozzle emergence- side and collection opening- side transition regions 47, 48 are slightly rounded off. In the flow conditions depicted in Figure 4, a gas vortex 37 can respectively be formed above and below the gas stream 21 despite the (slight) rounding off of the transition regions 47, 48. In Figure 4, the gas vortices 37 are substantially formed by the surrounding gas 34 present above and below the gas stream 21 (cf. corresponding flow lines 49a to 49c) . Here, the gas stream 21 generates the gas vortices 37 by the tangential impulse transfer to the surrounding gas 34. As a result of the flow cross section 43 of the gas stream 21 at the collection opening 28 being smaller than the entry cross section 44 of the collection opening 28, it is not only the whole gas stream 21, but also surrounding gas 34 dragged along thereby that is collected by the collection opening 28 (i.e., the collection opening 28 suctions more than 100% of the gas stream 21) . It is understood that, in principle, the flow conditions can also be set in such a way that the flow cross section 43 of the gas stream 21 at the collection opening 28 is greater than the entry cross section 44 of the collection opening 28 such that merely a portion of less than 100% of the gas stream 21 is collected by the collection opening 28, with the remaining portions of the gas stream 21 then, for example, escaping into the beam generation system- side and the illumination system- side regions of the housing 26. In-order to form gas vortices 37, which deflect the contaminating substances contained in the surrounding gas 34 and prevent a crossing over of the contaminating substances, the flow conditions in the gas nozzle 20 or in the housing 26 are preferably set in such a way that a portion of between 50% and 150% of the gas stream 21 emerging at the nozzle opening 25 is collected by the opposite collection opening 28.

Figure 5 shows different particle trajectories in the housing 26, as can result from the flow conditions in accordance with Figure 4. If contaminating substances or particles contained in the surrounding gas 34 find their way into the housing 26 and move in the direction of the gas stream 21, these reach one of the gas vortices 37, as a result of which the movement direction of said particles is substantially reversed in the shown example such that these find their way back into the beam generation system 2 or the illumination system 3, cf. particle or particle trajectory 50a and 50b, respectively. Particles further away from the gas vortices 37 are deflected and collected or suctioned by the collection opening 28, cf. particles or particle trajectories 51a and 51b, respectively. In each case, the passage of contaminating substances 50a, b; 51a, b through the housing 26 is prevented with the aid of the gas stream 21. Figure 6 shows a gas nozzle 18 with a nozzle opening 52 for the emergence of a gas stream 19 for removing contaminating substances from the optical surface 10a of the second optical element 10 in the illumination system 3 of the EUV lithography system 1. However, it is understood that instead of the optical surface 10a, any other optical surface 8a, 9a, 11a, 13a, 14a of the optical elements 8, 9, 11, 13, 14 (cf. Figure 1) or else, in principle, other (non-optical) surfaces, for example housing inner sides, can be purged of contaminating substances by means of a gas stream 19.

The gas nozzle 18 has a flow cross section extending asymmetrically in relation to the nozzle longitudinal axis 42 as a result of flow guiding elements 53 arranged or extending in a thread-like manner, and also has a lateral gas inlet 56. As a result of the spiral flow guiding elements 53, the gas nozzle 18 is embodied to generate the gas vortex 54 under stationary flow conditions. The gas stream 19 flowing out of the gas nozzle 18 generates a rotating gas vortex 54 in the EUV lithography system 1, the central axis of which gas vortex forms the nozzle longitudinal axis 42. The cleaning effect of the gas stream 19 can be increased by the gas vortex 54. The gas stream 19 can, in particular, be activated hydrogen H* , which is generated in the manner described above in conjunction with Figure 1. In the example shown in Figure 6, the gas nozzle 18 or the nozzle longitudinal axis 42 thereof is aligned at an angle a of approximately 45° in relation to the surface normal 55 in order to remove the contaminating substances from the optical surface 10a; however, it can also be aligned at a steeper angle a in relation to the surface normal 55, in particular at an angle a of between 45° and 90°. In particular, the gas nozzle 18 can also serve for generating a gas stream 19 of a purge gas forming a gas vortex 54 in the manner described above in conjunction with Figure 1, which gas stream serves to protect the optical surface 10a during the operation of the EUV lithography system 1.

The gas nozzle 18 schematically illustrated in Figure 7 has an asymmetric form with a central gas inlet 58 and an additional inlet 56, into which gas can likewise be let in, opening laterally into the gas nozzle 18, as a result of which a different pressure is set on opposite sides of the gas stream 19. The gas nozzle 18 thus generates a pulsed gas stream 19, i.e. the gas stream 19 · flowing out of the gas nozzle 18 forms a plurality of successive gas vortices 54 in a flow direction 57 of the gas stream 19. The gas nozzle 18 is arranged for removing the contaminating substances next to the optical surface 10a, wherein the flow direction 57 of the gas stream 19 extends at an angle of approximately 70° in relation to the surface normal 55 such that the gas stream 19 extends along the optical surface 10a and the gas vortices 54 are conveyed along the optical surface 10a. As a result of the gas vortices 54 moving along the optical surface 10a, contaminating substances can be transported away from the optical surface 10a. There can also be effective cooling or an effective heat transport away from the optical surface 10a with the aid of the non- stationary gas vortices 54, which was found to be advantageous, particularly in regions of the optical surface 10a where the latter is strongly heated locally due to EUV irradiation. Figures 8 to 10 show three illustrations of an exemplary embodiment of a transport device 60 for transporting a reflective (or optionally transmissive) optical element 61 for EUV lithography. The transport device 60 can be used to transport the optical element 61 from a work position, for example an exposure position, in which the optical element 61 is introduced into the EUV beam path of an EUV lithography system not depicted, for example of a metrology system, or of the EUV lithography system 1 shown in Figure 1, to a storage position outside of the EUV beam path. The optical element 61 can be embodied as an (exposure) mask or as a reticle and can be transported or moved in the EUV lithography system by means of the transport device 60. The optical element 61 can be removed from the EUV lithography system at the storage position, possibly through a vacuum lock.

The transport device 60 comprises a receptacle element, embodied as a frame-shaped holding element 63, for receiving the optical element 61 (cf. figure 9). For the purposes of receiving the optical element 61, contact elements 64 embodied as wear-resistant pins are arranged between the frame-shaped holding element 63 and the optical element 61. The holding element 63 has an open, U-shaped frame shape such that an optical element 61, which is supported in the storage position and freely accessible at the boundaries 65a, 65b thereof, can be engaged from below by means of the frame-shaped holding element 63 and lifted out of the storage position in order subsequently to be brought or transported into a different position. The optical element 61 shown in Figures 8 to 12 is embodied as a reflective rectangular mask with structures not shown in any more detail. In principle, it is possible for the optical element 61 to comprise an enclosure, for example a frame (not depicted) surrounding the optical element 61, which protects the optical element 61 from damage and simplifies the receiving by the holding element 63. In the case where the optical element 61 is surrounded by such a frame or such a enclosure, the contact elements 64 are typically arranged between the receptacle element embodied as the holding element 63 and the frame or the enclosure of the optical element 61. In order to move the receptacle element 63 embodied as a holding element, the transport device 60 comprises a movement device 66. By way of example, the movement device 66 depicted very schematically in Figure 8 can comprise a robotic arm, at the movable end of which the receptacle element 63 is fastened. By means of the movement device 66, the receptacle element 63, and, therewith, the optical element 61, can be moved about three rotational and three translational axes in a workspace, i.e. in a three-dimensional space, in which the transport device 60 is intended to move the optical element 61. By way of example, the vacuum housing 15 in Figure 1 can form such a workspace .

Since - as was described in conjunction with Figure 1 - contaminating substances or particles cannot be completely prevented in EUV lithography systems, it is also possible for such contaminations to be deposited on the reflective optical element 61. In principle, such a deposition can occur both in the work position and in the storage position. However, the risk of contamination is greater during a transport movement of the optical element 61 from a first position (e.g. the work position) into a second position (e.g. the storage position) since, in the process, the optical element 61 is moved through the workspace and, in the process, more contaminating substances present in the workspace can be deposited on said element.

In order to prevent a deposition of the contaminating substances on the optical element 61, the transport device 60 comprises an outflow device 67 for generating gas curtains (indicated by the arrows 68a and 68b) flowing along the surface on both sides of the optical element 61. The gas curtains 68a, 68b take and deflect contaminating substances which are moving toward a first surface 69a of the optical element 61 (front or top side) and toward a second surface 69b of the optical element 61 (rear or bottom side) and are threatening to be deposited on these surfaces 69a, 69b. In this manner, the risks resulting from a deposition are removed or at least reduced.

For the purposes of generating the gas curtains 68a, 68b, the outflow device 67 comprises a nozzle 70 which in each case comprises an emergence opening 71a, 71b for generating a respective gas curtain 68a, 68b on both sides of the optical element 61. The nozzle 70 comprises a flow-dividing central part 72 and two outer guiding parts 73. In order to generate the gas curtains 68a, 68b, a gas provision device 74 supplies the outflow device 67 or the nozzle 70 with gas that is under pressure in relation to the environment. From the gas provision device 74, the (purge) gas flows through a supply section 74 expanding in a slit-shaped manner into the nozzle 70 and emerges at the emergence openings 71a, 71b, which substantially extend over the whole length 76 of the nozzle 70 in order subsequently to flow along the surface on the first and second side or surface 69a, 69b of the optical element 61 (from left to right in Figure 9) .

The emergence openings 71a, 71b of the nozzle 70 are embodied as elongate slit openings with a constant slit width and extend across the gas emergence direction 68a, 68b of the nozzle 70 along the nozzle-side edge of the optical element 61. The gas forming the gas curtains 68a, 68b flows along the optical element 61 over the surface, i.e. uniformly over the first and second surface 69a, 69b. After the gas from the gas curtains 68a, 68b has reached the free boundary of the optical element 61, it escapes into the environment. Figure 10 depicts the transport device 60 in a side view (with a direction of view against the flow direction of the gas curtains 68a, 68b) .

Figure 11 and Figure 12 depict a further exemplary embodiment of the transport device 60. The transport device 60 is suitable for transporting the receptacle element 63 embodied as frame-shaped holding element, and hence the reflective optical element 61, from the work position (the exposure position) depicted in Figure 11 to another position, for example a transfer position, by means of the movement device 66. In order to transfer the optical element 61 to the EtTV lithography system or for removing the former from the EUV lithography system, provision can be made for a vacuum lock (not depicted) , into which the optical element 61 is placed by the transport device 60 for replacement or interchange purposes.

In contrast to Figures 8 to 10, the transport device 60 in Figures 11 and 12 comprises not only an outflow device 67 with a nozzle 70 and a corresponding flow- dividing central part 72 and two outer guiding parts 73, but also a collection device 77 for collecting the gas curtains 68a, 68b generated by the outflow device 67. The gas curtains 68a, 68b can be completely collected or suctioned by the collection device 77. This prevents the gas forming the gas curtains 68a, 68b from escaping into the environment. Furthermore, an expansion of the gas curtains 68a, 68b in a direction across the first and second sides 69a, 69b or the corresponding surfaces of the optical element 61 can largely be prevented. A substantially closed circuit for the gas forming the gas curtains 68a, 68b can be formed by the outflow device 67 and the collection device 77. The outflow device 67 and the collection device 77 are arranged on opposite lateral boundaries 65a, 65b of the optical element 61. In this manner, the laminar flow of the gas curtains 68a, 68b over the surfaces 69a, 69b of the optical element 61 is further promoted. In order to enable uniform suctioning of the gas curtains 68a, 68b, corresponding entry openings 78a, 78b of the collection device 77 (cf. Figure 11) are embodied as elongate slit openings with a constant slit width and extend along the collection device- side boundary 65b of the optical element 61 over substantially the whole length 79 of the boundary 65b of the optical element 61.

As an alternative to the illustrations above, the outflow device 67 can in each case comprise a nozzle for generating the two gas curtains 68a, 68b on the two sides of the optical element 61. The gas curtains 68a, 68b emerge from the outflow device 67 tangentially or parallel to the mutually opposite planar surfaces 69a, 69b of the optical element 61, both in the case of a single nozzle 70 and in the case of a plurality of nozzles, as a result of which the flow along the surface by the gas curtains 68a, 68b (from left to right in Figures 11 and 12) is promoted. It is understood that the transport device 60 in accordance with Figures 11 and 12 also comprises a gas provision device. The optical element 61 in Figures 11 and 12 is also mounted on the receptacle element 63 by means of contact elements 64 (contact pins) , which are arranged between the receptacle element 63 and the optical element 61. The gas used for generating the gas curtains 68a, 68b is substantially transparent to the EUV radiation, which is used for exposing the optical element 61 embodied as a mask and which propagates along an optical axis 80, and so there can be exposure of, or impact on, the optical element 61 by means of EUV radiation. In Figure 11, the receptacle element 63, together with the outflow device 67 and the collection device 77, is placed on a support surface 82 in the exposure position, wherein a conically expanding opening 81 is formed in said support surface for the passage of EUV radiation.

Claims

Patent claims

EUV lithography system (1) comprising:

at least one gas nozzle (18, 20) with a nozzle opening (25) for the emergence of a gas stream (19, 21) for removing contaminating substances from an optical surface (8a-14a) arranged in the EUV lithography system (1) and/or for deflecting contaminating substances in the EUV lithography system (1) ,

characterized

in that the gas stream (19, 21) forms at least one gas vortex (37; 54) in the EUV lithography system (1) .

EUV lithography system according to Claim 1, wherein the gas nozzle (18; 20) is embodied to generate the gas vortex (37; 54) under stationary flow conditions, preferably within the gas nozzle (18, 20) .

EUV lithography system according to Claim 2, wherein the gas nozzle (18; 20) comprises a flow cross section extending asymmetrically in relation to the nozzle longitudinal axis (42) .

EUV lithography system according to Claim 2 or 3, wherein the gas nozzle (18) for generating the gas vortex (54) comprises flow guiding elements (53) preferably extending in a thread-like manner.

EUV lithography system according to one of Claims 2 to 4 , wherein the gas nozzle (18) comprises at least one inlet (56) opening laterally into the gas nozzle (18) . EUV lithography system according to one of the preceding claims, wherein the gas nozzle (18) is embodied for generating a pulsed vortex-type gas stream (19) .

EUV lithography system according to one of the preceding claims, wherein the gas nozzle (18) is embodied for activating a cleaning gas contained in the gas stream (19) , in particular for activating hydrogen.

EUV lithography system according to one of the preceding claims, wherein the gas nozzle (18) for removing the contaminating substances is arranged next to the optical surface (8a-14a) in order to generate a gas stream (19) extending along the optical surface (8a-14a) . with gas vortices (54) conveyed along the optical surface (8a-14a) .

EUV lithography system according to one of the preceding claims, comprising at least one flow guiding element which promotes vortices and is arranged outside of the gas nozzle (18; 20), in particular a preferably tapered edge (36, 41) , onto which the gas stream (21) flows.

EUV lithography system according to one of the preceding claims, further comprising:

an in particular tube-shaped housing (26) extending across the gas stream (21) , into which housing the nozzle opening (25) opens and on which housing a collection opening (28) for collecting the gas stream (21) is arranged opposite to the nozzle opening (25) at a distance (27) to be bridged by the gas stream (21) , with an edge (36) onto which the gas stream (21) flows being formed between the collection opening (28) and a collection opening-side housing wall (35) in order to form a gas vortex (37) in the housing (26) .

EUV lithography system according to Claim 10, wherein the flow cross section (43) of the gas stream (21) at the collection opening (28) is smaller than the entry cross section (44) of the collection opening (28) .

EUV lithography system according to Claim 10 or 11, which is embodied to suction a portion of between 50% and 150% of the gas stream (21) emerging at the nozzle opening (25) at the opposite collection opening (28) .

EUV lithography system according to one of Claims 10 to 12, wherein a static environmental pressure (P2_/ Pc P3) in a vacuum environment (2, 3, 4) of the EUV lithography system (1) lies between 0.1 Pa and 100 Pa.

EUV lithography system according to one of Claims 10 to 13, further comprising: at least a first vacuum chamber (2, 3, 4, 15, 17) and a second vacuum chamber (2, 3, 4, 15, 17), between which an opening (16a-16d) for the passage of EUV radiation (6) is formed, at which opening the gas nozzle (20) for deflecting contaminating substances is formed.

Transport device (60) for transporting a reflective optical element (61) for EUV lithography, preferably a mask, in particular for an EUV lithography system (1) according to one of the preceding claims, comprising:

a receptacle element (63) for receiving the optical element (61) , a movement device (66) for moving the receptacle element (63) and

an outflow device (67) for generating gas curtains (68a, 68b) flowing along the surface on both sides of the optical element (61) .

Transport device according to Claim 15 , wherein the outflow device (67) comprises at least one nozzle (70) for generating the gas curtains (68a, 68b) .

Transport device according to Claim 16, wherein the nozzle (70) in each case comprises an emergence opening (71a, 71b) for generating a gas curtain (68a, 68b) on both sides of the optical element (61) .

Transport device according to Claim 17, wherein the nozzle (70) comprises a flow-dividing central part (72) and two outer guiding parts (73) .

Transport device according to Claim 17, wherein a nozzle - is in each case arranged on both sides of the optical element (61) for generating the two gas curtains (68a, 68b) .

Transport device according to one of Claims 15 to 19, wherein the gas curtains (68a, 68b) emerge from the outflow device (67) tangentially to the mutually opposite surfaces (69a, 69b) of the optical element (61) .

21. Transport device according to one of Claims 15 to 20, wherein the receptacle element (63) is embodied as a frame-shaped holding element. Transport device according to one of Claims 15 to 21, further comprising:

a collection device (77) for collecting the gas curtains (68a, 68b) generated by the outflow device (67) .

Transport device according to Claim 22, wherein the outflow device (67) and the collection device (77) are arranged on opposite edges (65a, 65b) of the optical element (61) .

Transport device according to one of Claims 15 to 23, wherein, for the purposes of receiving the optical element (61) or receiving a frame surrounding the optical element (61) , contact elements (64) are provided between the receptacle element (63) and the optical element (61) and/or between the receptacle element (63) and the frame.