Laser light source, especially for use in a microlithographic projection exposure system

Abstract

Laser light source, especially for use in a microlithographic projection exposure system, with • a laser module (105, 305) for generating a multitude of light pulses; and • an optical pulse stretcher (110, 310) for stretching the pulse length of the light pulses generated by the laser module (105, 305); • wherein the optical pulse extender (110, 310) comprises a plurality of mirrors (111, 112, 113, 114, 200, 311, 312, 313, 314) each with a mirror substrate (210) and a reflective layer system (220); and • wherein the mirror substrate (210) is at least one of these mirrors (111, 112, 113, 114, 200, 311, 312, 313, 314) made of silicon (Si).

Description

BACKGROUND OF THE INVENTION Area of ​​the invention

[0001] The invention relates to a laser light source, in particular for use in a microlithographic projection exposure system. State of the art

[0002] Microlithography is used to manufacture microstructured electronic components. The microlithography process is carried out in a projection exposure system, which includes an illumination unit and a projection lens. The image of a mask (= reticulum) illuminated by the illumination unit is projected by the projection lens onto a substrate (e.g., a silicon wafer) coated with a photosensitive layer (photoresist) and positioned in the image plane of the projection lens. This transfers the mask structure onto the photosensitive coating of the substrate.

[0003] In a projection exposure system designed for operation in the DUV range (e.g. at working wavelengths of less than 250 nm, especially less than 200 nm), laser light sources in the form of excimer lasers, especially krypton fluoride excimer lasers at a working wavelength of 248 nm or argon fluoride excimer lasers at a working wavelength of 193 nm, are typically used.

[0004] Challenges arising in the development of projection exposure systems include, on the one hand, increasing accuracy requirements for the microlithographic production of ever smaller structures and their positioning on the wafer, and on the other hand, a desirable increase in the throughput achieved with the respective projection exposure system from a cost perspective.

[0005] Regarding the aforementioned increase in throughput achieved with the respective projection exposure system, one problem is that there are limits to increasing the pulse energy and / or repetition rate, which would be desirable for increasing the output power of the laser light source. Increasing the repetition rate, and thus the frequency of electrical discharges within the laser light source's resonator, which is a possible way to increase the output power, can lead to acoustic resonances and ultimately cause the spectral bandwidth to increase beyond an acceptable level. Conversely, increasing the pulse energy leads to higher radiation exposure of optical components within the laser light source, as well as greater stress on electronic assemblies.

[0006] One well-known approach is to stretch pulses generated by the laser light source (e.g., with a pulse length of 20 ns) to a longer duration of, for example, (100-450) ns by using optical pulse stretchers, thus reducing the degradation of subsequent optical components accordingly.

[0007] A problem that arises during the operation of such an optical pulse extender or a corresponding laser light source, particularly when the output power of the laser light source is increased, is the occurrence of undesired wavefront aberrations. These aberrations are caused, on the one hand, by unwanted changes in the refractive index of the gas medium near the respective mirror surface of the mirrors, which heat up through thermal absorption, as the light passes through the optical pulse extender. On the other hand, they are also caused by thermally induced deformation or "warping" of the mirrors themselves. In particular, the heating of purge gas (e.g., nitrogen) located in the region of the respective mirror surface leads to the generation of thermal schlieren, which disrupts the wavefront of the light passing through the optical pulse extender and reflected by the respective mirror.Furthermore, the aforementioned undesirable change in refractive index upon heating leads to a thermal lensing effect and a concomitant defocusing of the light in question.

[0008] For the state of the art, reference is made only by way of example to DE 10 2022 202 241 A1 and DE 10 2022 107 633 B3. SUMMARY OF THE INVENTION

[0009] It is an object of the present invention to provide a laser light source, in particular for use in a microlithographic projection exposure system, which enables an increase in the output power of the laser light source while at least partially avoiding the problems described above.

[0010] This problem is solved by the laser light source according to the features of independent claim 1.

[0011] According to the invention, a laser light source, particularly for use in a microlithographic projection exposure system, has the following features: - a laser module for generating a large number of light pulses; and - an optical pulse stretcher for stretching the pulse length of the light pulses generated by the laser module; - wherein the optical pulse stretcher comprises a plurality of mirrors, each with a mirror substrate and a reflective layer system; and - wherein the mirror substrate of at least one of these mirrors is made of silicon (Si).

[0012] The invention is based in particular on the concept of designing at least one mirror of an optical pulse stretcher of a laser light source with a mirror substrate made of silicon (Si), thus combining a comparatively low coefficient of thermal expansion of the mirror substrate material with a comparatively high thermal conductivity. The mirror substrate material according to the invention can be monocrystalline silicon (Si), polycrystalline silicon (Si), or amorphous silicon (Si).

[0013] The invention involves a deliberate departure from the mirror substrate materials conventionally used in an optical pulse stretcher of a laser light source. One such conventionally used mirror substrate material is, in particular, calcium fluoride (CaF2), which, due to its comparatively large energy band gap and typically high purity, exhibits a generally advantageous low absorption in terms of lifetime and, moreover, when fluoride materials are also typically used in the reflective layer system of the respective mirrors, generally offers the advantage of comparable values ​​for the respective coefficients of thermal expansion of the mirror substrate on the one hand and the reflective layer system on the other.

[0014] Against the foregoing background, the use of silicon (Si) as a mirror substrate material according to the invention, which is not intuitive in light of the operating wavelengths in the DUV range (e.g. 193 nm) particularly envisaged in the invention, absorbs light passing through the reflective layer system to the mirror substrate to a significant extent and which also differs in its coefficient of thermal expansion from the fluoride materials possibly used in the reflective layer system of the respective mirrors, is now based on the consideration that, due to a significantly improved heat dissipation in the mirror substrate material according to the invention, the disadvantages that are generally accepted with the dispensing with a transparent mirror substrate material and with the aforementioned, comparatively large difference in the coefficient of thermal expansion can be avoided.

[0015] In other words, although the invention accepts that the (residual) light which usually inevitably reaches the mirror substrate through the reflective layer system is absorbed to a significant extent in the mirror substrate, the heat generated as a result in the mirror substrate by the conversion of the radiant energy can be dissipated comparatively well, thereby largely avoiding the wavefront aberrations mentioned in the introduction, both due to thermal schlieren formation and due to thermally induced mirror deformations.Furthermore, according to the invention, it is accepted that the coefficient of thermal expansion for the silicon (Si) used as a mirror substrate material according to the invention differs comparatively greatly from the coefficient of thermal expansion of the fluoride materials possibly used in the reflective layer system of the respective mirrors, which generally results in the formation of thermally induced stresses in the coating process.

[0016] The acceptance of the aforementioned disadvantages according to the invention is based on the consideration that the thermal conductivity of silicon (Si) has a value of approximately 140 W*m. -1 *K -1 is significantly greater than, for example, the thermal conductivity of calcium fluoride (CaF2) with a value of approximately 9.71 W*m -1 *K -1 or the thermal conductivity of quartz glass (SiO2) with a value of approximately 1.38 W*m -1 *K -1Furthermore, the coefficient of thermal expansion of silicon (Si) is approximately 2.7*10 -6 K -1 significantly smaller than the coefficient of thermal expansion of calcium fluoride (CaF2) with a value of approximately 18.85*10 -6 K -1 . These properties (i.e., comparatively high thermal conductivity and comparatively small coefficient of thermal expansion) are each advantageous with regard to the desired minimization of local thermal warping and mirror heating (as well as the associated schlieren formation and thermal lensing effect).

[0017] For the aforementioned quartz glass (SiO2), the coefficient of thermal expansion is approximately 0.5*10 -6 K -1even lower than for the silicon (Si) used as a mirror substrate material according to the invention, however, for quartz glass (SiO2) as a mirror substrate material, the mirror temperature is increased due to the comparatively low thermal conductivity relative to the silicon (Si) used according to the invention, which in turn has a detrimental effect on the contributions to wavefront aberrations discussed at the beginning, namely thermally induced local mirror deformations and thermal schlieren formation.

[0018] The concept according to the invention of using silicon (Si) as a mirror substrate material has the further advantage that, due to the particularly efficient heat dissipation, a comparatively complex active cooling of the mirror in question (and the associated cooling fluid connections, cooling fluid channels, etc.) can be dispensed with. Furthermore, according to the invention, requirements regarding conventionally used directional cooling via a directed gas flow can also be relaxed, whereby, as described below, such directional cooling can optionally be completely avoided in embodiments of the invention without any loss of performance.

[0019] Another advantage is that the concept according to the invention can be implemented in existing (e.g. lithography) systems without significant modifications.

[0020] Further advantages result from the wide availability and the relatively low material costs (e.g., compared to the use of calcium fluoride as a mirror substrate material), as well as from the comparatively good machinability in terms of manufacturing aspects.

[0021] According to one embodiment, the mirror substrate of at least two, in particular at least three, and further in particular all mirrors of the optical pulse extender is made of silicon (Si).

[0022] According to one embodiment, at least some of the mirrors of the optical pulse stretcher are arranged in positions offset from each other with respect to the direction of gravity, with the at least one mirror being arranged in the last of these positions with respect to the direction of gravity.

[0023] For a mirror of the optical pulse extender located in this position, the inventive design with a mirror substrate made of silicon (Si) is particularly advantageous insofar as the problem of (purge) gas heating solved according to the invention is particularly serious for this mirror in view of the gas that may rise and thus enter the other optically used area of ​​the optical pulse extender.

[0024] In further embodiments, the at least one mirror made of silicon (Si) can also be a concave mirror with a concavely curved optical surface pointing in the direction of gravity. For a mirror arranged in this way, any gas heated in the region of the optical surface cannot escape, or can only escape with difficulty, without additional purging, so that here too the advantageous effect achieved according to the invention of preventing such heating is particularly evident.

[0025] According to one embodiment, the reflective layer system of the at least one mirror has a multilayer structure consisting of a plurality of individual layers, wherein the number of these individual layers is at least twenty, in particular at least thirty, further in particular at least forty, and further in particular at least fifty. These individual layers can be layers of stacks of individual layers or functional layers (e.g., in the form of barrier layers or adhesive layers).

[0026] According to one embodiment, the reflective layer system of the at least one mirror has a transmittance of less than 3%, in particular less than 2%, and further in particular less than 1%.

[0027] In the aforementioned embodiments with a comparatively large number of individual layers in the multilayer structure or a comparatively low transmittance of the reflective layer system, the absorbing property of the mirror substrate material used according to the invention is further compensated for by reducing the proportion of light reaching the mirror substrate through the reflective layer system. In a further embodiment, an absorbing layer in the form of a substrate protection layer or a corresponding absorbing layer system can be provided in the layer structure, either additionally or alternatively to a comparatively large number of individual layers in the multilayer structure.

[0028] According to one embodiment, the reflective layer system of the at least one mirror has a reflectivity of at least 98% over a spectral bandwidth of at least 10 nm.

[0029] According to one embodiment, the at least one mirror has an optical surface, wherein at least one surface normal on this optical surface is arranged at an angle in the range of 80° to 100°, in particular at an angle in the range of 85° to 95°, and further in particular at an angle of 90° to the direction of gravity.

[0030] For such a mirror, with its optical surface arranged essentially “vertically” (i.e. not “lying down”), a problem solved with conventional directional cooling via a directed gas flow for essentially “horizontally” or “lying down” arranged mirrors, namely the deposition of particles on the optical surface of the mirror, is greatly reduced, so that the invention allows for the elimination of such directional cooling with a directed gas flow without any overall loss.

[0031] According to one embodiment, the optical pulse extender is arranged such that the angle between the direction of light entry into the optical pulse extender and the direction of gravity is in the range of 85° to 95°.

[0032] According to one embodiment, the optical pulse extender has an output power of more than 1 watt (W), in particular more than 10 watts (W), and further in particular more than 40 watts (W).

[0033] At such high output powers of the optical pulse extender, the thermal problems described in the introduction are particularly relevant, so that the advantages of the inventive design of the optical pulse extender due to the design of one or more mirrors with silicon (Si) as mirror substrate material then come to the fore in a particularly effective way.

[0034] According to one embodiment, the optical pulse stretcher is designed to stretch light pulses generated in the laser light source by the laser module with a pulse length of at least 20 nanoseconds (ns) to a pulse length of at least 100 nanoseconds (ns).

[0035] According to one embodiment, the optical pulse stretcher is designed to stretch light pulses generated in the laser light source by the laser module with a pulse length of at least 20 ns to a pulse length of less than 10,000 ns, in particular less than 1,000 ns, and further in particular less than 750 ns.

[0036] According to one embodiment, the laser light source is designed for a working wavelength of less than 360 nm, in particular for a working wavelength of less than 250 nm, and further in particular for a working wavelength of less than 200 nm.

[0037] According to one embodiment, the laser light source is designed for a working wavelength of more than 120 nm, in particular more than 150 nm.

[0038] The invention further relates to a microlithographic projection exposure system, comprising a laser light source, an illumination device and a projection lens, wherein, during operation of the projection exposure system, the illumination device illuminates an object plane of the projection lens with light from the laser light source and the projection lens maps this object plane onto an image plane, wherein the laser light source is configured according to the features described above.

[0039] Further embodiments of the invention can be found in the description and the dependent claims.

[0040] The invention is explained in more detail below with reference to exemplary embodiments shown in the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] They show: Fig. 1 a schematic representation to illustrate the possible basic structure of a laser light source according to the invention; Fig. 2 a schematic representation to illustrate the possible structure of a mirror present in an optical pulse stretcher of a laser light source according to the invention; Fig. 3 a schematic representation to illustrate the possible basic structure of a laser light source according to the invention in a further embodiment; and Fig. 4 A schematic representation to explain the possible setup of a microlithographic projection exposure system designed for operation in DUV. DETAILED DESCRIPTION OF PREFERRED EXECUTION FORMS

[0042] In the following, embodiments of the present invention will be described with reference to the schematic representations of Fig. 1-3 explained.

[0043] Fig. Figure 1 shows a schematic representation of the possible basic structure of a laser light source 100 according to the invention. The laser light source 100 has a laser module 105, which is only schematically indicated and designed in a conventional manner, for generating a plurality of light pulses. These light pulses can, by way of example (and without limiting the invention to this), each have a pulse length on the order of 30 nanoseconds (ns) and enter an optical pulse stretcher designated "110". The optical pulse stretcher 110 has a beam splitter 115 and a plurality of mirrors 111-114, of which in Fig. Figure 1 shows only four mirrors for the sake of simplicity. The invention is not limited to a specific number of mirrors within the optical pulse extender, although this number can typically range from eight to twelve in exemplary embodiments. The arrow "101" indicates the direction of gravity.

[0044] As a result of the Fig. Following the repeated reflection of the light component coupled out by the beam splitter 115 (dashed arrows) at the respective optical surfaces of the mirrors 111-114, this coupled-out light component experiences a time delay relative to the light component transmitted by the beam splitter 115, before the coupled-out light component, after reflection at the beam splitter 115, follows the transmitted light component. The overall time extension achieved can be achieved conventionally by cascading several stages according to this principle, each with a different time delay. In the example of Fig. 1 exactly three beams are emitted, or exactly three beams emerge from the optical pulse extender 110 (although only two are shown in the illustration).

[0045] By way of example only (and without limiting the invention to this), the extension of the pulse length achieved in the optical pulse extender 110 can be carried out to a pulse length in the range of 100 nanoseconds (ns) to 750 nanoseconds (ns).

[0046] Fig. Figure 2 shows a schematic representation to illustrate a possible embodiment of a mirror in the optical pulse stretcher 110 of a laser light source 100 according to the invention. The mirror according to the invention has a mirror substrate 210 and a reflective layer system 220, wherein additional functional layers (not shown) e.g. in the form of barrier layers or adhesive layers can also be provided in the layer structure of the mirror 200.

[0047] The reflective layer system 220 comprises a multilayer structure consisting of a plurality of alternatingly arranged individual layers 221, 222, wherein these individual layers can, for example, comprise a fluoride material in a manner known per se. This material can be, for example, aluminum fluoride (AlF3), gadolinium fluoride (GdF3), lanthanum fluoride (LaF3), magnesium fluoride (MgF2), sodium aluminum fluoride (NaAlF3), or ytterbium fluoride (YbF3).

[0048] The number of individual layers is typically (without the invention being limited thereto) at least twenty and can, in embodiments of the invention, preferably at least thirty, more particularly at least forty, and more particularly at least fifty. These individual layers can be layers of individual layer stacks or also functional layers (e.g., in the form of barrier layers or adhesive layers).

[0049] The at least one mirror 200 provided according to the invention in the optical pulse stretcher of the laser light source 100 is characterized in particular by the fact that silicon (Si) is used as the mirror substrate material of the mirror substrate 210. This results – in addition to other advantages already discussed – in particular in a significant reduction of wavefront aberrations by reducing the occurrence of the disturbance factors already discussed in the introduction, namely thermally induced local mirror deformations and thermal schlieren formation.

[0050] Wavefront experiments conducted by the inventors show that the local thermally induced deformation or warping of silicon (Si) as a mirror substrate material is significantly reduced compared to calcium fluoride (CaF2) as a mirror substrate material when irradiated with laser light at a working wavelength of approximately 193 nm. In these wavefront experiments, the surface of the respective samples was scanned with a 633 nm laser beam, and the wavefront of the light reflected from each sample was measured with a wavefront sensor. Despite the comparatively higher total absorption (approximately 0.2%) of the silicon (Si) sample compared to the total absorption of the calcium fluoride (CaF2) sample (approximately 0.1%), the silicon (Si) sample exhibits significantly less thermally induced deformation or warping. The experiment involved measuring the (each in arbitrary units, auThe PV (peak-to-valley) value (in arbitrary units) was reduced from 3.9 for the calcium fluoride (CaF2) sample to a PV value of 0.43 for the silicon (Si) sample.

[0051] Fig. Figure 3 shows a schematic representation to illustrate the possible basic structure of a laser light source according to the invention in a further embodiment, wherein, in comparison to Fig. One analogous or essentially functionally identical component is designated with reference numerals increased by "200". This is in accordance with... Fig. 3 of the optical pulse extenders 310 compared to Fig. 1 rotated by 90°, which according to Fig. 3 is achieved, by way of example, using two additional deflecting mirrors 316, 317 in the optical beam path. As a result of this arrangement, the mirrors 311-314 in the optical pulse extender 310 are arranged with their respective optical surfaces essentially "vertically" (i.e., not "lying down"). This has the effect of greatly reducing a problem that is solved with conventional directional cooling via a directed gas flow when the mirrors are arranged essentially "horizontally" or "lying down," namely the deposition of particles on the optical surface of the mirror. Therefore, the invention allows for the elimination of such directional cooling with a directed gas flow without any overall drawbacks.

[0052] Fig. Figure 4 shows a possible basic structure of a microlithographic projection exposure system 400 designed for operation in DUV as an application example of a laser light source according to the invention.

[0053] The projection exposure system 400 according to Fig. 4 comprises a lighting device 410 and a projection lens 420. The lighting device 410 serves to illuminate a structure-bearing mask (reticule) 415 with light from a light source unit 405, which includes a laser light source, for example in the form of an ArF excimer laser for a working wavelength of about 193 nm (or also in the form of an XeF excimer laser for a working wavelength of about 351 nm, in the form of a KrF excimer laser for a working wavelength of about 248 nm or in the form of an F2 excimer laser for a working wavelength of about 157 nm) and a beam shaping optic that generates a parallel light beam.

[0054] The lighting device 410 has an optical unit 411, which, in the illustrated example, includes a deflecting mirror 412. The optical unit 411 can, for example, include a diffractive optical element (DOE) and a zoom-axicon system to generate different lighting settings (i.e., intensity distributions in a pupil plane of the lighting device 410). Downstream of the optical unit 411, a light mixing device (not shown) is located in the beam path, which, for example,The device may, in a manner known per se, have an arrangement of micro-optical elements suitable for achieving light mixing, as well as a lens group 413, behind which a field plane with a reticle masking system (REMA) is located. This system is imaged by a REMA lens 414, which follows in the direction of light propagation, onto the structure-bearing mask (reticule) 415 arranged in a further field plane, thereby limiting the illuminated area on the reticule. The structure-bearing mask 415 is imaged by the projection lens 420 onto a lens substrate or a wafer 430 provided with a photosensitive layer (photoresist). The projection lens 420 can be designed, in particular, for immersion operation, in which case an immersion medium is located in front of the wafer or its photosensitive layer with respect to the direction of light propagation. Furthermore, it can, for example, have a numerical aperture NA greater than 0.85, especially greater than 1.1.

[0055] Even though the invention has been described with reference to specific embodiments, numerous variations and alternative embodiments are apparent to the person skilled in the art, for example, through the combination and / or exchange of features of individual embodiments. Accordingly, it is understood to the person skilled in the art that such variations and alternative embodiments are included in the present invention, and that the scope of the invention is limited only in accordance with the appended claims and their equivalents.

Claims

[1] Laser light source, especially for use in a microlithographic projection exposure system, with • a laser module (105, 305) for generating a multitude of light pulses; and • an optical pulse stretcher (110, 310) for stretching the pulse length of the light pulses generated by the laser module (105, 305); • wherein the optical pulse extender (110, 310) comprises a plurality of mirrors (111, 112, 113, 114, 200, 311, 312, 313, 314) each with a mirror substrate (210) and a reflective layer system (220); and • wherein the mirror substrate (210) is at least one of these mirrors (111, 112, 113, 114, 200, 311, 312, 313, 314) made of silicon (Si). [2] Laser light source according to claim 1, characterized by, that the mirror substrate (210) of at least two, in particular of at least three, further in particular of all mirrors (111, 112, 113, 114, 200, 311, 312, 313, 314) of the optical pulse extender (110, 310) is each made of silicon (Si). [3] Laser light source according to claim 1 or 2, characterized by , that at least some of the mirrors of the optical pulse stretcher (110, 310) are arranged in positions offset from each other with respect to the direction of gravity, wherein the at least one mirror (111, 112, 113, 114, 200, 311, 312, 313, 314) is arranged in the last of these positions with respect to the direction of gravity. [4] Laser light source according to any one of claims 1 to 3, characterized by, that the reflection layer system (220) of the at least one mirror (111, 112, 113, 114, 200, 311, 312, 313, 314) has a multilayer structure consisting of a plurality of individual layers (221, 222), wherein the number of these individual layers (221, 222) is at least twenty, in particular at least thirty, further in particular at least forty, further in particular at least fifty. [5] Laser light source according to any one of the preceding claims, characterized by , that the reflection layer system (220) of the at least one mirror (111, 112, 113, 114, 200, 311, 312, 313, 314) has a transmittance of less than 3%, in particular less than 2%, and further in particular less than 1%. [6] Laser light source according to any one of the preceding claims, characterized by, that the reflection layer system (220) of the at least one mirror (111, 112, 113, 114, 200, 311, 312, 313, 314) has a reflectivity of at least 98% over a spectral bandwidth of at least 10 nm. [7] Laser light source according to any one of the preceding claims, characterized by , that the at least one mirror (311, 312, 313, 314) has an optical surface, wherein at least one surface normal on this optical surface is arranged at an angle in the range of 80° to 100°, in particular at an angle in the range of 85° to 95°, and further in particular at an angle of 90° to the direction of gravity. [8] Laser light source according to any one of the preceding claims, characterized by , that the optical pulse extender (110, 310) is arranged such that an angle between the direction of light entry into the optical pulse extender (110) and the direction of gravity lies in the range of 85° to 95°. [9] Laser light source according to any one of the preceding claims, characterized by , that the optical pulse extender (110, 310) has an output power of more than 1 watt (W), in particular more than 10 watts (W), and further in particular more than 40 watts (W). [10] Laser light source according to any one of the preceding claims, characterized by , that the optical pulse stretcher (110, 310) is designed to stretch light pulses generated in the laser light source (100, 300) by the laser module (105, 305) with a pulse length of at least 20 nanoseconds (ns) to a pulse length of at least 100 nanoseconds (ns). [11] Laser light source according to any one of the preceding claims, characterized by, that the optical pulse stretcher (110, 310) is designed to stretch light pulses generated in the laser light source (100, 300) by the laser module (105, 305) with a pulse length of at least 20 ns to a pulse length of less than 10,000 ns, in particular less than 1,000 ns, and further in particular less than 750 ns. [12] Laser light source according to any one of the preceding claims, characterized by that it is designed for a working wavelength of less than 360 nm, in particular for a working wavelength of less than 250 nm, and further in particular for a working wavelength of less than 200 nm. [13] Laser light source according to any one of the preceding claims, characterized by that it is designed for a working wavelength of more than 120 nm, in particular more than 150 nm. [14] Microlithographic projection exposure system, comprising a laser light source (100, 300, 405), an illumination device (410) and a projection lens (420), wherein the illumination device (410) illuminates an object plane of the projection lens (420) with light from the laser light source (100, 300, 405) during operation of the projection exposure system (400) and the projection lens (420) maps this object plane onto an image plane, characterized by , that the laser light source (100, 300, 405) is configured according to one of the preceding claims.

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