Method for exchanging optical elements of an apparatus for semiconductor technology

Abstract

The invention relates to a method for exchanging optical elements (25) of an apparatus for semiconductor technology, the optical elements being designed for a productive wavelength and at least one part of the product beam path (40) in the apparatus passing through a region with an artificially generated atmosphere (90), comprising the following steps: a) exchanging at least one optical element (25, 25'); b) positioning and orienting at least the optical element (25') exchanged in the preceding step; c) carrying out a wavefront measurement along a beam path (140) comprising at least one exchanged optical element (25') without an artificially generated atmosphere (90) in the region provided therefor with a predefined wavelength different from the productive wavelength; d) if the wavefront measurement yields a wavefront aberration: adapting the positioning and orientation of at least the exchanged optical element (25') and repeating step (c); and e) if the wavefront measurement does not yield an aberration: producing the artificially generated atmosphere (90) in the region provided therefor.

Description

CZVS171PW0Method for exchanging optical elements of an apparatus for semiconductor technology

[0001] The invention relates to a method for exchanging optical elements of an apparatus for semiconductor technology.

[0002] In the prior art, apparatuses for semiconductor technology are understood to be apparatuses that are used for the production or testing of microstructured component parts or the components required for this purpose. An example of such an apparatus is a photolithographic projection exposure apparatus .

[0003] Photolithography is used for producing microstructured component parts, such as for example integrated circuits. The projection exposure apparatus used in the process comprises an illumination system and a projection system. The image of a mask (also referred to as a reticle) illuminated by the illumination system is projected so as to reduce the size of the former onto a substrate, for example a silicon wafer, which is coated with a light-sensitive layer and arranged in the image plane of the projection system, using the projection system in order to transfer the mask structure to the light-sensitive coating of the substrate.

[0004] Both in illumination systems and in the projection systems, in particular of projection exposure apparatuses designed for the EUV range, i.e. at exposure wavelengths of 5 nm to 30 nm, as a rule a plurality of optical elements, in particular mirrors, are provided in order to achieve the desired imaging of the mask onto the substrate. On account of the required accuracy, it is necessary to ensure, especially in projection systems, that the individual optical elements, with high accuracy, are situated in the correct position withrespect to one another and in relation to the mask and the substrate during operation of the proj ection exposure apparatus .

[0005] Especially in the case of EUV proj ection exposure apparatuses , the position of some of the optical elements is adj ustable with the aid of actuators in order in this way to be able to compensate for deviations from the ideal position of the respective optical element that arise on account of heat inputs , for example , even during the use of the proj ection exposure apparatus . For this purpose , a measuring apparatus coordinated with the exposure wavelength can be integrated in the proj ection exposure apparatus , and can be used to determine a possible wavefront aberration along the beam path used for the exposure . I f a corresponding wavefront aberration is ascertained, a suitable closed-loop control can attempt to correct this wavefront aberration by targeted alteration of the position of the individual adj ustable optical elements .

[0006] I f an optical element needs to be exchanged, for example on account of damage or degradation of the reflective surface , the proj ection exposure apparatus has to be opened in order to be able to exchange the optical element in question . Upon insertion of the new optical element , care must be taken to ensure that a newly inserted optical element is positioned with a suf ficient accuracy in relation to the other optical elements , since wavefront aberrations that arise on account of inaccurate positioning can be compensated for by the adj ustability of the optical elements of the proj ection exposure apparatus only to a certain extent . This holds true irrespective of whether or not an optical element to be exchanged is itsel f arranged adj ustably in the proj ection exposure apparatus . I f there is not suf ficient "basic accuracy" in the position of an exchanged optical element , the position thereof must besuitably corrected, e . g . by suitable spacers being arranged in the region of the securing of the optical element .

[0007] In the case of known proj ection exposure apparatuses , in particular in the case of those for the EUV range , the optical elements are situated in a region of the proj ection exposure apparatus that is evacuated to the greatest possible extent , in order that the radiation used for the exposure is not absorbed by dust particles or gas molecules along the beam path . For the actual exchange of an optical element in the region that is evacuated for the operation of the proj ection exposure apparatus , the region in question has to be regularly brought to ambient pressure ; however, for checking the wavefront with the mirror having been exchanged with the aid of the measuring apparatus situated in the proj ection exposure apparatus , the region in question then likewise has to be regularly evacuated again .

[0008] Especially the evacuation of the region in question that is necessary after the exchange takes up a considerable amount of time and is furthermore very energy-intensive . I f , once evacuation has taken place , on the basis of a wavefront aberration determined by the measuring apparatus integrated in the proj ection exposure apparatus , it is ascertained that the position of the exchanged component does not satis fy the accuracy requirements , the region in question must once again be brought to ambient pressure in order to alter the position of the exchanged optical element before the region is subsequently evacuated again . In this case , in particular, exchanging an optical component is associated with considerable expenditure of time and energy .

[0009] It is an obj ect of the present invention to provide a method for exchanging an optical element of aphotolithographic proj ection exposure apparatus in which the disadvantages known from the prior art no longer occur or occur only to a reduced extent .

[0010] This obj ect is achieved by a method according to Claim 1 . The dependent claims relate to advantageous developments .

[0011] Accordingly, the invention relates to a method for exchanging optical elements of an apparatus for semiconductor technology, the optical elements being designed for a productive wavelength and at least one part of the product beam path in the apparatus passing through a region with an arti ficially generated atmosphere , comprising the following steps : a ) exchanging at least one optical element to be exchanged of the apparatus for semiconductor technology; b ) positioning and orienting at least the optical element exchanged in the preceding step ; c ) carrying out a wavefront measurement along a beam path comprising at least one exchanged optical element without an arti ficially generated atmosphere in the region provided therefor with a predefined wavelength that is di f ferent from the productive wavelength; d) i f wavefront measurement yields a wavefront aberration : adapting the positioning and orientation of at least the exchanged optical element and repeating step ( c ) ; and e ) i f wavefront measurement does not yield an aberration : producing the arti ficially generated atmosphere in the region provided therefor .

[0012] Firstly, some terms used in connection with the invention are explained.

[0013] In association with the present invention, "apparatus for semiconductor technology" denotes any apparatus that can be used for the production or testing of microstructured component parts or the components required for this purpose. Besides photolithographic projection exposure apparatuses, this in particular also encompasses inspection apparatuses and metrology systems. In the case of inspection apparatuses for masks or wafers, e.g. the variability of the illumination can be increased with the aid of one or more MEMS micromirror units, which can result in higher-contrast or totally new image representations of the surface of a mask or wafer, which can be advantageous for the inspection of mask or wafer. This comparably also applies to metrology systems that can be used to measure masks, wafers or any other optical elements, such as mirrors, in particular, in which case an increased variability in the illumination can improve the measurement results .

[0014] "Optical elements" of an apparatus for semiconductor technology, i.e. e.g. of a projection exposure apparatus, in particular the illumination system thereof and / or the projection system thereof, are in particular beam-modifying elements, i.e. mirrors or lenses, inter alia. "Optical element to be exchanged" according to step a) means an optical element that is removed from the apparatus. "Optical element exchanged" according to step b) means an optical element that is newly inserted into the apparatus in exchange for the optical element to be exchanged or the removed optical element. "Positioning and orienting at least the optical element exchanged in the preceding step" means in other words: "positioning andorienting at least one optical element exchanged for the optical element to be exchanged in the preceding step".

[0015] The "productive wavelength" is that wavelength which is used or employed for the respectively envisaged purpose during the proper use of an apparatus for the semiconductor industry. The optical elements of the apparatus are designed for this wavelength, in principle, even if they can, of course, regularly also transform radiation having a different wavelength. The productive wavelength can also be a wavelength range. If the apparatus for the semiconductor industry is a photolithographic projection exposure apparatus, the productive wavelength corresponds to the exposure wavelength with which a reticle is imaged onto a radiation-sensitive layer designed for this purpose, in order to bring about chemical reactions in the radiation-sensitive layer. Customary exposure wavelengths are e.g. 193 nm or 13.5 nm.

[0016] The productive radiation having the productive wavelength is generated by a radiation source and is reshaped and / or deflected by suitable optical elements in order to achieve the effect desired for the respective apparatus, e.g. to image a mask arranged in an object plane into an image plane. In this case, the path taken by the productive radiation proceeding from the radiation source is referred to as the "productive beam path". In the case of a projection exposure apparatus as apparatus for semiconductor technology, the productive beam path regularly runs from a radiation source via optical elements of an exposure system, the reticle and optical elements of a projection system to a substrate provided with light-sensitive coating.

[0017] If the productive radiation would be absorbed in an air atmosphere too much to allow the desired effect to be achievedtherewith, it is known to guide the productive beam path at least partly through one or more regions with an arti ficially generated atmosphere within the apparatus for semiconductor technology . It is often the case that even the entire productive beam path passes in a region with an arti ficially generated atmosphere within the apparatus for semiconductor technology, for which purpose all components relevant to the productive beam path, such as optical elements , are then also arranged in said region . The arti ficially generated atmosphere can in particular also be distinguished by a particularly low pressure practically corresponding to a vacuum, preferably with a residual amount of hydrogen, and / or a hydrogen plasma . In other applications , the arti ficially generated atmosphere can also be a nitrogen atmosphere .

[0018] The invention has recogni zed that , i f an arti ficial atmosphere ( such as e . g . also a vacuum) basically present has to be eliminated during an exchange of an optical element in an apparatus for semiconductor technology, a check as to whether the positioning of an exchanged optical element is correct with a predefined accuracy, for which the arti ficial atmosphere must first be re-established, is disadvantageous - especially i f it turns out that the position of the exchanged optical element needs to be corrected, for which purpose the arti ficial atmosphere then has to be eliminated again at times . For checking the correct position of an exchanged element of apparatuses for the semiconductor industry, the prior art involves carrying out a wavefront measurement along the productive beam path . Re-establishing the arti ficial atmosphere is regularly necessary in that case since in principle radiation having the productive wavelength is used for the wavefront measurement according to the prior art .

[0019] The invention fundamentally departs from the procedure known from the prior art . Instead of a wavefront measurement with the productive wavelength over the entire productive beam path, the invention provides for carrying out the wavefront measurement with a wavelength that is di f ferent from the productive wavelength . Taking into consideration the optical properties of the optical elements of the apparatus for semiconductor technology, it is possible to choose in particular a wavelength which, for carrying out the wavefront measurement , does not require a special arti ficial atmosphere , but rather undergoes no or only insigni ficant absorption by air, for example . Moreover, the wavefront measurement does not have to be carried out over the entire productive beam path . Even though the latter is of course possible , it is already suf ficient according to the invention i f the wavefront measurement takes place along a beam path comprising at least one exchanged optical element . The beam path for the wavefront measurement in the method according to the invention often will correspond to the greatest possible extent to at least one portion of the productive beam path and / or will comprise the optical elements arranged upstream and downstream of an exchanged optical element along the productive beam path; that is not absolutely necessary, however .

[0020] I f optical elements - exchanged or not - involved in the beam path for the wavefront measurement carried out according to the method according to the invention are adj ustable by adj usting units , the adj ustable optical elements are adj usted suitably for the beam path . In other words , the adj ustable optical elements are intended to be adj usted such that the beam path required and desired for the wavefront measurement is also actually attained . Optical elements that are adj ustable e . g . with regard to their position and / or orientation by adj usting units can be provided in apparatuses forsemiconductor technology in order to be able to compensate for position and / or pose alterations that occur during the use of the apparatus . In order to be able to check the positioning and orientation of an exchanged optical element , it is necessary or at least expedient to move the optical elements which are involved in the beam path provided for this purpose and which are adj ustable into a typical or basic position and / or orientation for the later use of the apparatus for semiconductor technology .

[0021] In this case , it is particularly preferred i f the adj ustable optical elements , during the wavefront measurement , are adj usted depending on the currently determined wavefront aberration within predefined limits by a control device in order to reduce a wavefront aberration possibly ascertained . Proceeding from the assumption that with a static positioning and orientation of the optical elements the required accuracy cannot be achieved or at least cannot be permanently maintained over the operation of an apparatus , e . g . in order to achieve a desired imaging quality, i f adj usting units present in apparatuses for the semiconductor industry are used for adj usting the position and orientation of optical elements in order to reduce wavefront aberrations that otherwise occur, this functionality can also be used to reduce wavefront aberrations during the method according to the invention . In this case , however, limits , e . g . for the adj ustment of the individual optical elements , are preferably predefined which even after reduction of the wavefront aberration during the present method still permit suf ficient latitude to compensate for wavefront aberrations that occur or are ascertained during the actual operation of the apparatus for semiconductor technology .

[0022] Since an apparatus for semiconductor technology may not have the radiation source and / or wavefront sensor required for the wavefront measurement provided according to the invention, it is preferred i f , for the wavefront measurement , a radiation source for the predefined wavelength and / or a wavefront sensor are / is arranged in or on the apparatus for semiconductor technology prior to the wavefront measurement being carried out . A correspondingly secured radiation source and / or wavefront sensor are / is preferably removed again at least partly prior to the production - concluding the present method - of the artificially generated atmosphere in the region provided therefor . The radiation source and / or wavefront sensor are / is preferably secured dynamically stably to the apparatus for semiconductor technology .

[0023] Irrespective of whether the radiation source used for the wavefront measurement is part of the apparatus for semiconductor technology or is arranged in or on the apparatus at times , it is preferred i f the radiation source is tunable and is settable to the predefined wavelength .

[0024] The wavefront sensor or the wavefront measuring device can be in particular of an interferometric type , for example designed as a lateral shearing interferometer, or of a Shack- Hartmann type . The wavefront sensor can preferably comprise a 2D image capturing sensor and, arranged at a distance in front thereof , a lens mask, preferably a perforated sheet or a microlens array . The determination of wavefronts or wavefront aberrations in conj unction with corresponding sensors , i . e . in particular in conj unction with Hartmann or perforated sheet sensors and Shack-Hartmann sensors , is known to a person skilled in the art .

[0025] If an optical element along the beam path provided for the wavefront measurement is a reticle, it is preferred if the reticle is designed specifically for the wavefront measurement. If the apparatus for semiconductor technology is designed e.g. for reticles that are reflective in principle away from the structure to be imaged, preferably a fully reflective reticle without any structure is provided for the wavefront measurement .

[0026] It is also possible to provide a self-luminous reticle, which can then serve as a radiation source.

[0027] The apparatus for semiconductor technology is preferably a photolithographic projection exposure apparatus. The artificial atmosphere along the productive beam path, which artificial atmosphere is required for the ultimate use of the projection exposure apparatus, can be a vacuum in this case.

[0028] The invention will now be described by way of example on the basis of an advantageous exemplary embodiment with reference to the accompanying drawings, in which:Figure 1: shows a schematic illustration of a photolithographic projection exposure apparatus; andFigure 2: shows a schematic illustration of carrying out the method according to the invention on the projection exposure apparatus according to Figure 1.

[0029] Figure 1 illustrates a schematic meridional section through a photolithographic projection exposure apparatus 1 as an example of an apparatus for semiconductor technology. In this case, the projection exposure apparatus 1 comprises an illumination system 10 and a projection system 20.

[0030] An object field 11 in an object plane or reticle plane 12 is illuminated with the aid of the illumination system 10. To this end, the illumination system 10 comprises an exposure radiation source 13, which, in the illustrated exemplary embodiment, emits illumination radiation at least comprising used light in the EUV range, that is to say with a wavelength of between 5 nm and 30 nm in particular. The exposure radiation source 13 can be a plasma source, for example an LPP (laser produced plasma) source or a GDPP (gas discharge produced plasma) source. It can also be a synchrotron-based radiation source. The exposure radiation source 13 can also be a free electron laser (PEL) .

[0031] The illumination radiation emerging from the exposure radiation source 13 is initially focused in a collector 14. The collector 14 can be a collector with one or with a plurality of ellipsoidal and / or hyperboloidal reflection surfaces. The illumination radiation can be incident on the at least one reflection surface of the collector 14 with grazing incidence (GI) , that is to say at angles of incidence of greater than 45°, or with normal incidence (NI) , that is to say at angles of incidence of less than 45°. The collector 14 can be structured and / or coated on the one hand for optimizing its reflectivity for the used radiation and on the other hand for suppressing extraneous light.

[0032] Downstream of the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is constructed in a modular design, the intermediate focal plane 15 can be used, in principle, for the separation - including the structural separation - of the illumination system 10 into a radiation source module, comprising the exposure radiation source 13 and the collector 14, and the illumination opticalunit 16 described below . In the case of a corresponding separation, radiation source module and illumination optical unit 16 then j ointly form a modularly constructed illumination system 10 .

[0033] The illumination optical unit 16 comprises a deflection mirror 17 . The deflection mirror 17 can be a plane deflection mirror or alternatively a mirror with a beam-influencing effect going beyond the pure deflection ef fect . Alternatively or additionally, the deflection mirror 17 can be embodied as a spectral filter separating a used light wavelength of the illumination radiation from extraneous light having a wavelength that deviates therefrom .

[0034] The deflection mirror 17 is used to deflect the radiation emanating from the exposure radiation source 13 to a first facet mirror 18 . I f - as in the present case - the first facet mirror 18 is arranged in a plane of the illumination optical unit 16 which is optically conj ugate to the reticle plane 12 as a field plane , this facet mirror is also referred to as a field facet mirror .

[0035] The first facet mirror 18 comprises a multiplicity of micromirrors 18 ' that are individually pivotable about two mutually perpendicular axes in each case , for the purpose of controllably forming facets which are each configured with an orientation sensor (not depicted here ) for determining the orientation of the micromirror 18 ' . The first facet mirror 18 is thus a microelectromechanical system (MEMS system) , as also described in DE 10 2008 009 600 Al , for example .

[0036] A second facet mirror 19 is arranged downstream of the first facet mirror 18 in the beam path of the illumination optical unit 16 , with the result that this yields a doublyfaceted system, the fundamental principle of which is also referred to as a fly ' s eye integrator . I f the second facet mirror 19 - as in the depicted exemplary embodiment - is arranged in a pupil plane of the illumination optical unit 16 , it is also referred to as a pupil facet mirror . However, the second facet mirror 19 can also be arranged at a distance from a pupil plane of the illumination optical unit 16 , as a result of which a specular reflector arises from the combination of the first and the second facet mirror 18 , 19 , for example as described in US 2006 / 0132747 Al , EP 1 614 008 Bl and US 6 , 573 , 978 .

[0037] The second facet mirror 19 need not necessarily be constructed from pivotable micromirrors , but rather can comprise individual facets formed from one mirror or a manageable number of mirrors which are signi ficantly larger than micromirrors , which facets are either stationary or tiltable only between two defined end positions . It is however - as illustrated - also possible , in the second facet mirror 19 , to provide a microelectromechanical system having a multiplicity of micromirrors 19 ' that are individually pivotable about two mutually perpendicular axes in each case , each preferably comprising an orientation sensor .

[0038] The individual facets of the first facet mirror 18 are imaged into the obj ect field 11 with the aid of the second facet mirror 19 , with this regularly only being approximate imaging . The second facet mirror 19 can be the last beam-shaping mirror or else actually the last mirror for the illumination radiation in the beam path upstream of the obj ect field 11 .

[0039] In each case , one of the facets of the second facet mirror 19 is assigned to exactly one of the facets of thefirst facet mirror 18 for the purpose of forming an illumination channel for illuminating the object field 11. This can in particular result in illumination according to the Kohler principle .

[0040] The facets of the first facet mirror 18 are imaged overlaid on one another by way of a respective assigned facet of the second facet mirror 19, for the purpose of illuminating the object field 11. Here, the illumination of the object field 11 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different illumination channels.

[0041] By selecting the ultimately used illumination channels, which is possible without problems by way of a suitable setting of the micromirrors 18' of the first facet mirror 18, it is still possible to set the intensity distribution in the entrance pupil of the projection system 20 described below. This intensity distribution is also referred to as illumination setting. Incidentally, it may be advantageous here to arrange the second facet mirror 19 not exactly in a plane that is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil facet mirror 19 can be arranged so as to be tilted relative to a pupil plane of the projection system 20, as is described in DE 10 2017 220 586 Al, for example .

[0042] In the arrangement of the components of the illumination optical unit 16 as illustrated in Figure 1, however, the second facet mirror 19 is arranged in an area conjugate to the entrance pupil of the projection system 20. Deflection mirror 17 and the two facet mirrors 18, 19 are arranged tilted both vis-a-vis the object plane 12 and vis-a-vis one another in each case.

[0043] In an alternative embodiment (not illustrated) of the illumination optical unit 16, a transfer optical unit comprising one or more mirrors can additionally be provided in the beam path between the second facet mirror 19 and the object field 11. The transfer optical unit can in particular comprise one or two normal-incidence mirrors (NI mirrors) and / or one or two grazing-incidence mirrors (GI mirrors) . Using an additional transfer optical unit, it is possible in particular to take account of different poses of the entrance pupil for the tangential and for the sagittal beam path of the projection system 20 described below.

[0044] It is alternatively possible for the deflection mirror 17 illustrated in Figure 1 to be dispensed with, for which purpose the facet mirrors 18, 19 should then be suitably arranged vis-a-vis the radiation source 13 and the collector 14.

[0045] The object field 11 in the reticle plane 12 is transferred to the image field 21 in the image plane 22 with the aid of the projection system 20.

[0046] To this end, the projection system 20 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1. The mirrors M±are optical elements 25.

[0047] In the example illustrated in Figure 1, the projection system 20 comprises six mirrors Mi to M6as optical elements 25. Alternatives with four, eight, ten, twelve or any other number of mirrors M±are likewise possible. The penultimate mirror M5and the last mirror M6each have a passage opening for the illumination radiation, as a result of which the illustrated projection system 20 is a doubly obscured opticalunit. The projection system 20 has an image-side numerical aperture that is greater than 0.3 and can also be greater than 0.6, and can be for example 0.7 or 0.75.

[0048] The mirrors Mx to M4and M6are arranged on respective adjusting units 26, which enable the optical elements 25 to be adjusted in each case in terms of their position and / or orientation within certain limits. By means of a control unit (not illustrated in Figure 1) , the adjusting units 26 are controlled during the operation of the projection exposure apparatus 1 so as to result in as optimum as possible imaging of the reticle 30 onto the wafer 35.

[0049] The reflection surfaces of the mirrors M4can be in the form of freeform surfaces without an axis of rotational symmetry. However, the reflection surfaces of the mirrors M4can alternatively also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optical unit 16, the mirrors M4can have highly reflective coatings for the illumination radiation. These reflective coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0050] The projection system 20 has a large object-image offset in the y-direction between a y-coordinate of a centre of the object field 11 and a y-coordinate of the centre of the image field 21. This object-image offset in the y-direction can be of approximately the same magnitude as a z-distance between the object plane 12 and the image plane 22.

[0051] In particular, the projection system 20 can be designed to be anamorphic, that is to say it has different imaging scales px, pyin the x- and y-directions in particular. The twoimaging scales px, pyof the projection system 20 are preferably (px, py) = ( + / -0.25, / + -0.125) . An imaging scale p of 0.25 corresponds here to a reduction with a ratio 4:1, while an imaging scale p of 0.125 results in a reduction with a ratio of 8:1. A positive sign in the case of the imaging scale p means imaging without image inversion; a negative sign means imaging with image inversion.

[0052] Other imaging scales are likewise possible. Imaging scales px, pywith the same sign and the same absolute magnitude in the x- and y-directions are also possible.

[0053] The number of intermediate image planes in the x-direc- tion and in the y-direction in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the embodiment of the projection system20. Examples of projection systems 20 with different numbers of such intermediate images in the x-direction and y-direction are known from US 2018 / 0074303 Al.

[0054] In particular, the projection system 20 can comprise a homocentric entrance pupil. The latter can be accessible. However, it can also be inaccessible.

[0055] A reticle 30 (also referred to as mask) arranged in the object field 11 is exposed by the illumination system 10 and transferred by the projection system 20 onto the image plane21. The reticle 30 is held by a reticle holder 31. The reticle holder 31 is displaceable by way of a reticle displacement drive 32 in particular in a scanning direction. In the exemplary embodiment illustrated, the scanning direction runs in the y-direction.

[0056] The reticle 30 can have an aspect ratio of between 1:1 and 1:3, preferably between 1:1 and 1:2, and particularly preferably of 1:1 or 1:2. The reticle 30 can be substantially rectangular and is preferably 5 to 7 inches (12.70 to 17.78 cm) long and wide, further preferably 6 inches(15.24 cm) long and wide. As an alternative thereto, the reticle 30 can have a length of 5 to 7 inches (12.70 cm to 17.78 cm) and a width of 10 to 14 inches (25.40 cm to 35.56 cm) , preferably a length of 6 inches (15.24 cm) and a width of 12 inches (30.48 cm) .

[0057] A structure on the reticle 30 is imaged onto a lightsensitive layer of a wafer 35 arranged in the region of the image field 21 in the image plane 22. The wafer 35 is held by a wafer holder 36. The wafer holder 36 is displaceable by way of a wafer displacement drive 37 in particular along the y-di- rection. The displacement, firstly, of the reticle 30 by way of the reticle displacement drive 32 and, secondly, of the wafer 35 by way of the wafer displacement drive 37 can be synchronized with one another.

[0058] The projection exposure apparatus 1 illustrated in Figure 1 or its illumination system 10, the above description of which reflects substantially known prior art, is distinguished by the fact that the entire productive beam path 40 illustrated by dotted lines runs from the exposure radiation source 13 as far as the wafer 35 in a vacuum as artificial atmosphere 90. This ensures that the productive wavelength in the EUV range, here 13.5 nm, actually also passes from the exposure radiation source 13 as far as the wafer 35 and is not absorbed by an atmosphere. In order to be to ensure that the productive beam path passes exclusively through the artificial atmosphere 90 or the vacuum, all illustrated components of the projection exposure apparatus 1 are arranged in the evacuable space inwhich the artificial atmosphere 90 or the vacuum can be created. The space has a corresponding volume, which is why creating the artificial atmosphere 90 in the space is associated with considerable expenditure of time and energy, inter alia.

[0059] Figure 2 illustrates carrying out the method according to the invention.

[0060] In this case, Figure 2 shows the projection exposure apparatus 1 in the state after the first two method steps have already been concluded, specifically the exchange of at least one optical element 25 and the initial positioning and orientation of the exchanged optical element 25' : In the example illustrated, the mirror M4has been exchanged (cf. reference sign 25' , M4' ) and has been arranged on the associated adjusting unit 26 with the aid of securing elements and spacers for fundamentally producing the productive beam path 40.

[0061] In order to be able to actually exchange the optical element 25, M4, the artificial atmosphere 90 required for the use of the projection exposure apparatus 1, namely the vacuum, has been eliminated beforehand, and moreover has not yet been re-established at the point in time illustrated in Figure 2. The optical elements 25, 25' are thus exposed to the atmosphere surrounding the projection exposure apparatus 1, in this case the filtered air of the clean room in which the projection exposure apparatus 1 is situated.

[0062] Once the artificial atmosphere 90 has been eliminated and before or after the exchange of the mirror M4, an arrangement 100 for wavefront measurement is temporarily inserted into the projection exposure apparatus 1. Besides a control device 110, the functioning of which will also be discussedlater, the arrangement 100 comprises a radiation source 120 and a wavefront sensor 130 .

[0063] In the present exemplary embodiment , the radiation source 120 has the outer shape of a reticle 30 ( cf . Figure 1 ) to such an extent that the radiation source 120 can be secured on the reticle holder 31 and as necessary can even be positioned highly precisely with the aid of the reticle displacement drive 32 . In the exemplary embodiment illustrated, the radiation source 120 is of sel f-luminous design and for this purpose comprises a planar light-emitting diode that emits radiation with a wavelength that is visible to the human eye and thus di f fers from the productive wavelength in the EUV range . The radiation source 120 of the exemplary embodiment shown is not tunable , even though that may be preferred in principle .

[0064] The wavefront sensor 130 - in a manner comparable to the radiation source 120 - has the outer shape of a wafer 35 ( cf . Figure 1 ) to such an extent that the wavefront sensor can be secured on the wafer holder 36 instead of a wafer 35 and can be finely positioned by way of the wafer displacement drive 37 . The wavefront sensor 130 is designed for the wavelength of the radiation source 120 and is configured as a Shack-Hartmann sensor in the present exemplary embodiment . The wavefront sensor 130 thus comprises a 2D image capturing sensor 131 with, arranged at a distance in front thereof , a lens mask 132 in the form of a microlens array . The functioning of the wavefront sensor 130 and also the evaluation of the images captured by the 2D image capturing sensor 131 in order to determine a possible wavefront aberration are known to a person skilled in the art and need no further explanation at this j uncture .

[0065] The control device 110 is connected both to the radiation source 120 and to the wavefront sensor 130. Furthermore, the control device 110 is connected to the various adjusting units 26 for the optical elements 25, 25' and also to the reticle and wafer displacement drives 32, 37, respectively. The control device 110 can be a separate component that is introduced into the projection exposure apparatus 1 together with the other components of the arrangement 100, i.e. the radiation source 120 and the wavefront sensor 130. In this case, the control device 110 is then connected either directly to the adjusting units 26 and the displacement drives 32, 37, or else to an interface of the controller of the projection exposure apparatus 1, such that the control device 110 can also actually control the components mentioned. An alternative is to model the control device 110, e.g. in the form of a computer program product, in the controller of the projection exposure apparatus 1. In this case, radiation source 120 and wavefront sensor 130 should then be linked to the controller of the projection exposure apparatus 1 in order that they can be controlled by the control device 110.

[0066] In order to carry out a wavefront measurement, once radiation source 120 and wavefront sensor 130 have been positioned sufficiently accurately with the aid of the displacement drives 32, 37, firstly the optical elements 25, 25' are each brought, with the aid of the adjusting units 26 by way of the control unit 110, firstly into a position and orientation suitable for the productive beam path 40 (cf. Figure 1) fundamentally provided by way of these optical elements 25, 25' . The beam path 140 which then fundamentally arises after the radiation source 120 has been switched on by the control unit 110, and which leads as far as the wavefront sensor 130, is illustrated by dashed lines in Figure 2.

[0067] The wavefront determined by the wavefront sensor 130 (or the point pattern representing the wavefront) is then examined for wavefront aberrations by the control device 110.

[0068] If a wavefront aberration is ascertained, the control device 110 controls the adjusting units 26 in a systematic and targeted manner in order to reduce the wavefront aberration to the greatest possible extent. The control strategies to be pursued here by the control unit 110 are known in principle to a person skilled in the art or can be determined with manageable effort at least for the respective configuration of the projection exposure apparatus 1.

[0069] The adjustment of the optical elements 25, 25' by the control device 110 takes place here while the wavefront continues to be measured, in order thus to be able to directly monitor the effect of the adjustment on the wavefront aberration. The adjustment of the individual optical elements 25, 25' takes place here exclusively within predefined limits, which in principle are made narrower than the adjustment possibilities available in principle for the individual adjusting units 26. This ensures that during later operation of the projection exposure apparatus 1, remaining adjustment possibilities on each of the adjusting units 26 are still sufficient to be able to carry out adaptations of the position and / or orientation of individual optical elements 25, 25' that may be necessary during operation 1.

[0070] If an ascertained wavefront aberration cannot be reduced or cannot be sufficiently reduced by way of the control device 110 with the aid of the adjusting units 26 within the scope of the predefined limits, the position and orientation of the exchanged optical element 25' must be adapted manually. For this purpose, in the present exemplary embodiment, themirror M4' would be detached from the adjusting unit 26 and secured thereto again with the aid of altered securing elements and / or spacers. The results of the control device 110 from the wavefront measurement may yield indicators here as to what securing elements and / or spacers should potentially be used.

[0071] Once the adaptation of the position and / or orientation of the exchanged optical element 25' has taken place, the described wavefront measurement is carried out again in order to check whether a wavefront aberration that is not able to be compensated for still exists.

[0072] If a wavefront aberration is no longer ascertainable or a wavefront aberration present can be compensated for by the adjusting units 26, the arrangement 100 is at least partly removed again from the projection exposure apparatus 1, that is to say at least radiation source 120 and wavefront sensor 130 are demounted. Whether the control unit 110 can or needs to be removed depends on the individual case. If the control unit 110 is modelled purely in terms of software in the controller of the projection exposure apparatus 1, it need e.g. only be deactivated, but not completely removed.

[0073] Once the arrangement 100 has accordingly been removed, the artificial atmosphere 90 (cf. Figure 1) or the vacuum can be produced and the projection exposure apparatus 1 can be used properly again. On account of the method according to the invention, the time-consuming and energy-intensive production of the artificial atmosphere 90 takes place only once it is ensured that the projection exposure apparatus can be operated with the required accuracy despite the exchange of an optical component 25' .

Claims

25Patent Claims1. Method for exchanging optical elements (25) of an apparatus for semiconductor technology, the optical elements (25) being designed for a productive wavelength and at least one part of the product beam path (40) in the apparatus passing through a region with an artificially generated atmosphere (90) , comprising the following steps: a) exchanging at least one optical element (25) to be exchanged of the apparatus for semiconductor technology; b) positioning and orienting at least one optical element ( 25 ’ ) exchanged in the preceding step; c) carrying out a wavefront measurement along a beam path (140) comprising at least one exchanged optical element ( 25 ’ ) without an artificially generated atmosphere (90) in the region provided therefor with a predefined wavelength that is different from the productive wavelength; d) if the wavefront measurement yields a wavefront aberration: adapting the positioning and orientation of at least the exchanged optical element ( 25 ’ ) and repeating step (c) ; and e) if the wavefront measurement does not yield an aberration: producing the artificially generated atmosphere (90) in the region provided therefor.

2. Method according to Claim 1, characterized in that at least some of the optical elements (25, 25' ) along the beam path (140) provided for the wavefront measurement areadjustable by adjusting units (60) and are adjusted suitably for the beam path (140) .

3. Method according to Claim 2, characterized in that the adjustable optical elements (25, 25' ) , during the wavefront measurement, are adjusted depending on the currently determined wavefront aberration preferably within predefined limits by a control device (110) in order to reduce a wavefront aberration possibly ascertained.

4. Method according to any of the preceding claims, characterized in that, for the wavefront measurement, a radiation source (120) for the predefined wavelength and / or a wavefront sensor (130) are / is arranged in or on the apparatus for semiconductor technology prior to the wavefront measurement being carried out and / or are / is removed at least partly prior to the production of the artificially generated atmosphere (90) in the region provided therefor.

5. Method according to any of the preceding claims, characterized in that the radiation source (120) is tunable and is settable to the predefined wavelength.

6. Method according to any of the preceding claims, characterized in that the wavefront sensor (130) comprises a 2D image capturing sensor (131) and, arranged at a distance in front thereof, a lens mask (132) , preferably a perforated plate or a microlens array.. Method according to any of the preceding claims, characterized in that at least one optical element (25, 25' ) along the beam path provided for the wavefront measurement is a reticle de- signed therefor.

8. Method according to any of the preceding claims, characterized in that the apparatus for semiconductor technology is a projection exposure apparatus (1) for semiconductor lithography.

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