Projection exposure system with cooling water including polymer additives

Abstract

The invention relates to a projection exposure system (1) for photolithography for imaging a mask (30) illuminated by an illumination system (10) onto a substrate (35) using a projection system (20), wherein at least one component (M4) of the projection exposure system (1) has at least one fluid channel (26) for conveying a temperature control medium, and a temperature control system (100) is connected to the at least one fluid channel (26) such that a closed temperature control circuit (105) for the temperature control medium is formed. The temperature control medium is liquid and contains at least one polymer additive to achieve the Toms effect.

Description

[0001] The invention relates to a projection exposure system for photolithography.

[0002] Photolithography is used to manufacture microstructured components, such as integrated circuits. The projection exposure system used comprises an illumination system and a projection system. The image of a mask (also called a reticulum) illuminated by the illumination system is projected in a reduced size onto a substrate, such as a silicon wafer, coated with a photosensitive layer and positioned in the image plane of the projection system. This transfers the mask structure onto the photosensitive coating of the substrate.

[0003] Both illumination and projection systems, particularly those designed for EUV applications (i.e., exposure wavelengths from 5 nm to 30 nm), typically employ multiple optical elements, especially mirrors, to achieve the desired image of the mask onto the substrate. Due to the required accuracy, it is crucial, especially in projection systems, to ensure that the position of the individual optical elements relative to each other, as well as to the mask and the substrate, changes only within extremely small tolerances, if at all, during operation of the projection system. Furthermore, the shape of the optical elements, particularly the mirror surfaces, must not change, or only within a predefined range. Any change in the position and / or shape of one or more optical elements can lead to a decrease in the image quality of the projection system.

[0004] Corresponding changes in the position and / or shape of one or more optical elements can occur due to heat input into the optical elements or into the structure supporting them. Such heat input inevitably occurs, for example, due to the absorption of illumination radiation by the optical elements, the absorption of interfering radiation, particularly in the infrared range, and the heat loss from electrical components in the projection system. Electrical actuators are known to compensate for changes in the position of the optical elements to a certain extent; however, these actuators themselves emit heat.To avoid or at least minimize changes in the shape of the optical elements from a target shape and to dissipate heat introduced into the projection exposure system, in particular its projection system, it is known to provide at least some of the optical elements and / or other components of the projection exposure system and in particular the projection system with fluid channels for the passage of a temperature control fluid - in particular demineralized water.

[0005] Even though the temperature of individual components can be well regulated by passing a temperature control fluid through parts of the projection exposure system, thus reducing or even completely preventing changes in the position and / or shape of one or more optical elements due to heat input, it has been shown that passing temperature control fluid through the designated fluid channels introduces vibrations into the components of the projection exposure system, which can lead to a decrease in image quality, especially when occurring in the projection system.

[0006] The cause of these vibrations introduced by the temperature control fluid includes flow-induced vibrations (FIV), which result from the interaction of a turbulent flow with the wall of the flow channel.

[0007] Even if it may be possible to minimize the flow-induced vibrations introduced by the passage of temperature control fluid through a suitable choice of cross-section and other design of the fluid channels, the resulting vibrations may still reduce the image quality of a projection exposure system beyond a permissible level.

[0008] The object of the present invention is to provide an alternative or additional possibility for reducing the vibrations generated by a temperature control fluid in a projection exposure system.

[0009] This problem is solved by a projection exposure system according to claim 1. Advantageous further developments are the subject of the dependent claims.

[0010] Accordingly, the invention relates to a projection exposure system for imaging a mask illuminated by an illumination system onto a substrate using a projection system, wherein at least one component of the projection exposure system has at least one fluid channel for passing through a temperature control medium and a temperature control system is connected to the at least one fluid channel in such a way that a closed temperature control circuit for the temperature control medium is formed, wherein the temperature control medium is liquid and contains at least one polymer additive to achieve the Toms effect.

[0011] The invention has recognized that the Toms effect achievable by adding a polymer additive to a provided temperature control medium has an advantageous effect on the vibrations caused by the flow of the temperature control medium through the channels provided for this purpose in a projection exposure system, in particular reducing them.

[0012] According to the Toms effect, first described in the article "Some observations on the flow of linear polymer solutions through straight tubes at large Reynolds numbers" by B.A. Toms in the proceedings "Proceedings of the 1st International Congress on Rheology (North-Holland, Amsterdam, 1948)" (Volume 2, pages 135-141) and subsequently named after its discoverer, the wall friction in turbulent flow can be significantly reduced, sometimes by up to 80%, by adding a small amount of a polymer to a Newtonian fluid. This reduction in wall friction due to the Toms effect is also reflected, among other things, in a reduction of the coefficient of friction c. f(or the pipe friction factor λ in the case of flow in a straight pipe), which can easily be verified experimentally. First, the wall friction, the coefficient of friction c, is determined for any liquid to which no polymer additive has yet been added. f or the pipe friction factor λ is determined in turbulent flow, and under the same test conditions, but after adding a small amount of a polymer additive in continued turbulent flow, a lower wall friction, a lower friction coefficient c, is observed. f If a lower pipe friction coefficient λ is observed, it can be concluded that the polymer additive caused the Toms effect. If, after adding the polymer additive under otherwise constant test conditions, turbulent flow no longer occurs or the wall friction does not decrease, then the polymer, in the added quantity, does not cause the Toms effect.

[0013] The Toms effect can be generated for a variety of liquids using different polymer additives. In the article "Turbulent drag reduction by polymer additives: Fundamentals and recent advances" by Li Xi in "Physics of Fluids", Vol. 31, 121302 (2019), the Toms effect is described in detail with numerous references to further publications. This provides those skilled in the art with sufficient starting points for selecting a polymer additive potentially suitable for generating the Toms effect in a specific liquid, as well as determining the required quantity. Independently of this, the presence of a Toms effect in a liquid with a polymer additive can be determined by measuring the wall friction and the coefficient of friction c. f or easily verify the pipe friction coefficient λ of the liquid with and without polymer additive.

[0014] While the Toms effect is primarily used in the prior art to reduce pressure loss in pipelines, e.g., in the transport of crude oil, or in fire-fighting water systems, the invention recognizes that the well-known reduction of pressure loss can also achieve a reduction, at least, of flow-induced vibrations during the passage of temperature control medium through the cooling channels of a projection exposure system. Thanks to the Toms effect, polymer additives can fundamentally reduce the production of turbulent flow fluctuations and the corresponding fluctuation energy, thereby—as the invention has recognized—reducing not only the pressure loss but also the energy introduced into the walls of the cooling channel in the form of vibration.

[0015] Adding a polymer additive to the temperature control medium can reduce flow-induced vibrations in a projection exposure system caused by the flow of the temperature control medium. Reducing these vibrations improves image quality.

[0016] It is preferred that the average molecular mass of the polymer additive is greater than the average molecular mass of the temperature control medium by a factor of 2, preferably by a factor of 200. The term "average molecular mass" takes into account the possibility that both the polymer additive and the temperature control medium may comprise different molecules and / or isotopes of one or more molecules. In this case, the weighted arithmetic mean of the individual molecular masses in the polymer additive and / or temperature control medium is assumed to be the "average molecular mass." If the polymer additive and / or temperature control medium comprises only one specific molecule, the average molecular mass corresponds to the molecular mass of that particular molecule.If one of the preferred molecular mass ratios is present, there is a very high probability, if not certainty, that the addition of the polymer additive will produce the desired Toms effect and result in a noticeable reduction in flow-induced vibrations.

[0017] Preferably, the polymer additive comprises linear macromolecules, which preferably have a deformable backbone. The "backbone" is defined as the continuous series of covalently bonded atoms that form the "backbone" of a macromolecule. A "linear macromolecule" possesses such a backbone. The polymer additive can also consist exclusively of such macromolecules. The presence of such macromolecules in the polymer additive promotes the occurrence and magnitude of the Toms effect. It is also possible for the polymer additive to have hyperbranched polymers and / or spherical structures. Such structures can also influence the near-wall flow dynamics and promote the occurrence of the Toms effect.

[0018] While not strictly necessary, it is preferable for the temperature control medium to be polymer-free apart from the polymer additive. In other words, the temperature control medium itself, and before the addition of the polymer additive, should not contain any polymer molecules, so that any occurrence of the Toms effect after the addition of the polymer additive can be directly attributed to the polymer additive. However, even if the temperature control medium already contains polymer molecules in its initial state, the investigation of turbulent flow of the temperature control medium with and without the polymer additive, as described above, can determine whether the polymer additive causes a Toms effect or not.

[0019] It is preferred that the temperature control medium be water, preferably demineralized or distilled. Water has proven to be an advantageous temperature control medium for use in projection exposure systems because, within the regularly occurring temperature range, which is only a few degrees Celsius around a standard room temperature of 21°C, no phase changes are to be expected, the heat transfer properties and flowability are sufficient, and the corrosion behavior of materials used in projection exposure systems with water as the corrosion medium is well known. Furthermore, water is not a hazardous substance. If the water is demineralized or distilled, undesirable deposits of salts or similar substances in the cooling channel are also avoided. Should, in addition to the polymer additive provided according to the invention, further chemical and / or physical properties of the water, such as...Where electrical conductivity-modifying additives are required or desirable, it is preferred that these additives are first added to demineralized or distilled water. This ensures that only the intended additives are present in the water.

[0020] It is preferred that the pH value of the temperature control medium with polymer additive is between 5 and 8, preferably between 6 and 7.5. A suitable pH value of the temperature control medium containing the polymer additive prevents chemical reactions with the materials lining the walls of the fluid channel for conveying the temperature control medium, which can occur upon contact with acidic or basic liquids. This is particularly relevant in cases where an existing projection exposure system designed for pure (fully demineralized) water as the temperature control medium is to be subsequently upgraded to a projection exposure system according to the invention by adding a suitable polymer additive to the temperature control medium.

[0021] The use of the term "additive" already makes it clear that, according to the invention, the polymer is to be added to the temperature control medium only in small quantities. The actual required or optimal quantity necessary to achieve or maximize the desired Toms effect depends on a multitude of parameters, but in particular on the composition of both the temperature control medium and the polymer additive. Both the determination of the fundamental occurrence of the Toms effect and its optimization as a function of the ratio of temperature control medium to polymer additive can be achieved by a person skilled in the art through a manageable number of experiments, as already described above.Regardless, for the present application of a projection exposure system, it is advantageous if the concentration of the at least one polymer additive in the water is preferably between 0.05 ppm and 1000 ppm, or between 2 ppm and 100 ppm. Due to the very small amounts of polymer additive, the flow and heat transfer properties of the temperature control medium do not change practically, or at least not measurably.

[0022] It is preferred if the average molecular mass of the polymer additive is between 10 g / mol and 100,000 g / mol, preferably between 40 g / mol and 50,000 g / mol, and / or the average molecular mass of the tempering medium is between 15 g / mol and 20 g / mol, preferably between 17 g / mol and 19 g / mol.

[0023] It is preferred if the polymer additive comprises polyacrylamide (PAM), polyethylene glycol (PEG) and / or hydroxypropyl methylcellulose (HPMC). It is particularly preferred if the polymer additive consists practically exclusively (i.e., more than 90% by weight, preferably 95% by weight, and further preferably more than 97.5% by weight) of one of the aforementioned substances.

[0024] Preferably, the temperature control circuit comprises at least one circulation pump and / or an element for actively controlling the temperature of the temperature control medium. The circulation pump can cause and / or precisely control the flow of the temperature control medium through the designated fluid channel. The element for actively controlling the temperature of the temperature control medium, which is, for example, a heat exchanger with a connected controllable heat / cold source such as a heat pump and / or an electric heating element, enables precise temperature adjustment of the temperature of the temperature control medium, which ultimately allows for precise temperature control of at least the components of the projection system through which the temperature control medium flows.

[0025] The projection exposure system is preferably designed for exposure with a wavelength in the EUV range – that is, with exposure wavelengths from 5 nm to 30 nm. With a correspondingly designed projection exposure system, particularly small structures can be imaged onto a substrate. With such small structures, vibrations, especially in the area of ​​the optical elements of the projection system, can have a significant impact on image quality, which is why they must be minimized as much as possible. For a projection exposure system to be able to expose with EUV, in addition to a suitable EUV radiation source, all optical elements in the exposure and projection systems – i.e., all elements that deflect or modify the exposure radiation or parts thereof – must be designed for the relevant wavelength range. It is known that only reflective optical elements are suitable for EUV radiation.Suitable optical elements or their coatings are known from the prior art.

[0026] The invention will now be described by way of example using an advantageous embodiment with reference to the accompanying drawings. These show: Fig. 1: a schematic representation of a projection exposure system according to the invention for photolithography; and Fig. 2: a detailed section of the Fig. 1.

[0027] In Fig. Figure 1 shows a projection exposure system 1 for photolithography in a schematic meridional section. The projection exposure system 1 comprises a lighting system 10 and a projection system 20.

[0028] The illumination system 10 illuminates an object field 11 in an object plane or reticulum plane 12. The illumination system 10 comprises an illumination radiation source 13, which, in the illustrated embodiment, emits illumination radiation comprising at least useful light in the EUV range, i.e., in particular with a wavelength between 5 nm and 30 nm. The illumination radiation source 13 can be a plasma source, for example, an LPP source (laser-produced plasma) or a DPP source (gas-discharge-produced plasma). It can also be a synchrotron-based radiation source. The illumination radiation source 13 can also be a free-electron laser (FEL).

[0029] The illumination radiation emanating from the light source 13 is first focused in a collector 14. The collector 14 can be a collector with one or more ellipsoidal and / or hyperboloid reflective surfaces. The at least one reflective surface of the collector 14 can be illuminated at grazing incidence (GI), i.e., with angles of incidence greater than 45°, or at normal incidence (NI), i.e., with angles of incidence less than 45°. The collector 14 can be structured and / or coated to optimize its reflectivity for the useful radiation and to suppress stray light.

[0030] After the collector 14, the illumination radiation propagates through an intermediate focus in an intermediate focal plane 15. If the illumination system 10 is to be constructed in a modular manner, the intermediate focal plane 15 can, in principle, be used for the separation – including 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 optics 16 described below. With such a separation, the radiation source module and the illumination optics 16 then together form a modularly constructed illumination system 10.

[0031] The illumination optics 16 include a deflecting mirror 17. The deflecting mirror 17 can be a flat deflecting mirror or, alternatively, a mirror with an effect that influences the beam shape beyond the mere deflection effect. Alternatively or additionally, the deflecting mirror 17 can be designed as a spectral filter that separates a useful wavelength of the illumination radiation from stray light of a different wavelength.

[0032] The deflecting mirror 17 deflects the radiation from the illumination radiation source 13 onto a first faceted mirror 18. If the first faceted mirror 18 is arranged – as in the present case – in a plane of the illumination optics 16 that is optically conjugate to the reticular plane 12 as a field plane, it is also referred to as a field faceted mirror.

[0033] The first faceted mirror 18 comprises a plurality of micromirrors 18' that can be individually pivoted about two mutually perpendicular axes for the controllable formation of facets, each preferably equipped with an orientation sensor (not shown) for determining the orientation of the micromirror 18'. The first faceted mirror 18 is thus a microelectromechanical system (MEMS system), as described, for example, in DE 10 2008 009 600 A1.

[0034] In the beam path of the illumination optics 16, a second faceted mirror 19 is arranged downstream of the first faceted mirror 18, resulting in a double-faceted system, the basic principle of which is also known as a honeycomb condenser (fly's eye integrator). If the second faceted mirror 19 is arranged in a pupil plane of the illumination optics 16 – as in the illustrated embodiment – ​​it is also referred to as a pupil faceted mirror. However, the second faceted mirror 19 can also be arranged at a distance from a pupil plane of the illumination optics 16, in which case the combination of the first and second faceted mirrors 18, 19 results in a specular reflector, as described, for example, in US 2006 / 0132747 A1, EP 1 614 008 B1, and US 6,573,978.

[0035] The second faceted mirror 19 need not be constructed from pivotable micromirrors, but can instead comprise individual facets formed from one or a manageable number of mirrors that are significantly larger than micromirrors, and which are either fixed or tiltable only between two defined end positions. However, as shown, it is also possible to provide the second faceted mirror 19 with a microelectromechanical system comprising a plurality of micromirrors 19' that are individually pivotable about two axes perpendicular to each other, each preferably including an orientation sensor.

[0036] With the aid of the second faceted mirror 19, the individual facets of the first faceted mirror 18 are projected onto the object field 11, although this is regularly only an approximate projection. The second faceted mirror 19 can be the last beam-shaping or even the last mirror for the illumination radiation in the beam path before the object field 11.

[0037] Each of the facets of the second faceted mirror 19 is assigned to exactly one of the facets of the first faceted mirror 18 to form an illumination channel for illuminating the object field 11. This can result in illumination according to Köhler's principle.

[0038] The facets of the first faceted mirror 18 are each superimposed by a corresponding facet of the second faceted mirror 19 to illuminate the object field 11. The illumination of the object field 11 is as homogeneous as possible. It preferably exhibits a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

[0039] By selecting the illumination channels ultimately used, which is easily achieved by appropriately adjusting the micromirrors 18' of the first faceted mirror 18, the intensity distribution in the entrance pupil of the projection system 20 described below can also be adjusted. This intensity distribution is also referred to as the illumination setting. Furthermore, it can be advantageous not to arrange the second faceted mirror 19 exactly in a plane that is optically conjugate to a pupil plane of the projection system 20. In particular, the pupil faceted mirror 19 can be tilted relative to a pupil plane of the projection system 20, as described, for example, in DE 10 2017 220 586 A1.

[0040] In the Fig. In the arrangement of the components of the illumination optics 16 shown in Figure 1, the second faceted mirror 19 is arranged in a surface conjugate to the entrance pupil of the projection system 20. Deflection mirror 17 and the two faceted mirrors 18, 19 are arranged at an angle both to the object plane 12 and to each other.

[0041] In an alternative embodiment of the illumination optics 16, not shown, a transmission optic comprising one or more mirrors can be provided in the beam path between the second faceted mirror 19 and the object field 11. The transmission optic can, in particular, comprise one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (GI mirrors). With an additional transmission optic, different positions of the entrance pupil for the tangential and sagittal beam paths of the projection system 20 described below can be accommodated.

[0042] Alternatively, it is possible that on the in Fig. The deflecting mirror 17 shown in Figure 1 is dispensed with, for which the faceted mirrors 18, 19 are then to be arranged appropriately opposite the radiation source 13 and the collector 14.

[0043] Using the projection system 20, the object field 11 in the reticulum plane 12 is transferred to the image field 21 in the image plane 22.

[0044] The projection system 20 comprises a plurality of mirrors M. i , which are numbered according to their arrangement in the beam path of the projection exposure system 1.

[0045] In the Fig. In the example shown, projection system 20 comprises six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors M are possible. i are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage for the illumination radiation, making the depicted projection system 20 a doubly obscured optic. The projection system 20 has an image-side numerical aperture that is greater than 0.3 and can also be greater than 0.6, for example, 0.7 or 0.75.

[0046] The reflective surfaces of the mirrors M i can be designed as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflective surfaces of the mirrors M can be i but can also be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflecting surface shape. The mirrors M i Like the mirrors of the lighting optics 16, they can 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.

[0047] The projection system 20 has a large object-image offset in the y-direction between a y-coordinate of the center of the object field 11 and a y-coordinate of the center of the image field 21. This object-image offset in the y-direction can be approximately as large as a z-distance between the object plane 12 and the image plane 22.

[0048] The projection system 20 can in particular be anamorphic, i.e. it has in particular different image scales β x , β y in the x and y directions. The two image scales β x , β y of the projection system 20 are preferably located at (β x , β y ) = (+ / - 0.25, / +- 0.125). A magnification β of 0.25 corresponds to a reduction in the ratio of 4:1, while a magnification β of 0.125 results in a reduction in the ratio of 8:1. A positive sign for the magnification β indicates a magnification without image inversion, a negative sign indicates a magnification with image inversion.

[0049] Other magnification ratios are also possible. Magnification ratios with the same sign and those with the same absolute value β are also possible. x , β y In the x and y directions, adjustments are possible.

[0050] The number of intermediate image planes in the x- and y-directions in the beam path between the object field 11 and the image field 21 can be the same or different, depending on the design of the projection system 20. Examples of projection systems 20 with different numbers of such intermediate images in the x- and y-directions are known from US 2018 / 0074303 A1.

[0051] Projection system 20 can, in particular, have a homocentric entrance pupil. This may be accessible. However, it may also be inaccessible.

[0052] A reticle 30 (also called a mask) arranged in the object field 11 is exposed by the lighting system 10 and transferred to the image plane 21 by the projection system 20. The reticle 30 is held by a reticle holder 31. The reticle holder 31 can be moved, particularly in a scanning direction, by means of a reticle displacement drive 32. In the illustrated embodiment, the scanning direction is in the y-direction.

[0053] A structure on the reticulum 30 is imaged onto a photosensitive layer of a wafer 35 located in the image plane 22 within the image field 21. The wafer 35 is held by a wafer holder 36. The wafer holder 36 can be displaced, particularly along the y-direction, via a wafer transfer drive 37. The displacement of the reticulum 30 via the reticulum transfer drive 32 and of the wafer 35 via the wafer transfer drive 37 can be synchronized.

[0054] The Fig. 1 The projection exposure system 1 shown, or its projection system 20, the above description of which essentially reflects the known prior art, is characterized by the fact that a temperature control system 100 is provided, with which various components of the projection system 20 can be kept at a set temperature, in order to avoid or at least minimize changes in the position and / or shape of the mirrors M1 to M6.

[0055] In Fig. 1 and Fig. 2, which is merely an enlargement of part of the Fig. For the sake of clarity, the temperature control system 100 is shown only schematically in Figure 1, limited to mirror M4. As indicated, among other things, by the additional inlets and outlets shown with dotted lines, the temperature control system 100 can also extend to other mirrors M1, M2, M3, M5, and / or M6, as well as other components not shown, such as the support structure to which mirrors M1 to M6 are attached. It is also possible that the temperature control system 10 controls components of the exposure system 10. However, the exposure system 10 may also have its own temperature control system.

[0056] The temperature control system 100 comprises fluid lines 101 for conveying a temperature control medium, a circulation pump 102 for pumping the temperature control medium through the fluid lines 101, and a controllable heat / cold source as element 103 for actively temperature control of the temperature control medium. The fluid lines 101 are connected to a fluid channel 26 passing through the mirror M4 to be temperature controlled, such that a closed temperature control circuit 105 is formed for the temperature control medium.

[0057] The circulation pump 102 circulates the temperature control medium, which can be actively regulated to a desired temperature by means of element 103, along or through various components, such as the mirror M4, where heat exchange occurs, so that the respective components gradually approach the actively regulated temperature of the temperature control medium. This is well known in the prior art.

[0058] Element 103 for active temperature control of the temperature control medium can be provided as a heat pump with an electrically operated heating element, which is designed to supply or remove heat from the temperature control medium flowing through a heat exchanger.

[0059] To prevent vibrations from the circulation pump 102 and / or the active temperature control element 103 from being transmitted through the structure, the circulation pump 102 and / or the active temperature control element 103 are generally mechanically decoupled from the projection system 10 as much as possible and positioned away from it. For this reason, the circulation pump 102 and / or the active temperature control element 103 are also regularly located outside the evacuable space provided for the optical elements of the projection exposure system 1. The system boundary between the evacuable space and the area with ambient conditions is defined in Fig. 1 and Fig. 2 indicated by the dotted line 90.

[0060] In addition to the elements 101, 102, and 103 shown, the temperature control system 100 can include further elements, such as controllable valves. If several components of the projection exposure system 1 are supplied with temperature control medium in different parallel temperature control circuits 105 using the temperature control system 100, valves can be used to individually adjust the flow rate in the individual temperature control circuits 105.

[0061] All elements 101, 102, 103 of the temperature control system 100, as well as the fluid channels 26 through components of the projection exposure system 1, are designed to generate as few flow-induced vibrations as possible.

[0062] In the illustrated projection exposure system 1 according to the invention, a temperature control medium containing a polymer additive is used to achieve the Toms effect. In the illustrated embodiment, the temperature control medium is demineralized water to which 10 ppm of linear polyethylene glycol molecules (PEG) are added as a polymer additive.

[0063] With a suitably modified temperature control medium, the desired Toms effect occurs, which can be easily determined by comparing the wall friction of a turbulent flow of the temperature control medium with and without the polymer additive. It has been shown that, along with the onset of the Toms effect, at least the flow-induced vibrations can also be reduced. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2008 009 600 A1

[0033] US 2006 / 0132747 A1

[0034] EP 1 614 008 B1

[0034] US 6,573,978

[0034] DE 10 2017 220 586 A1

[0039] US 2018 / 0074303 A1

[0050] Cited non-patent literature

[0000] Some observations on the flow of linear polymer solutions through straight tubes at large Reynolds numbers” by BA Toms in the conference proceedings “Proceedings of the 1st International Congress on Rheology (North-Holland, Amsterdam, 1948)” (Volume 2, pages 135-141

[0012] Turbulent drag reduction by polymer additives: Fundamentals and recent advances“ von Li Xi in „Physics of Fluids“, Jg. 31, 121302 (2019

[0013]

Claims

[1] Projection exposure system (1) for imaging a mask (30) illuminated by an illumination system (10) onto a substrate (35) with the aid of a projection system (20), wherein at least one component (M4) of the projection exposure system (1) has at least one fluid channel (26) for conducting a temperature control medium and a temperature control system (100) is connected to the at least one fluid channel (26) in such a way that a closed temperature control circuit (105) for the temperature control medium is produced, characterized by that the tempering medium is liquid and contains at least one polymer additive to achieve the Toms effect. [2] Projection exposure apparatus according to claim 1, characterized by that the average molecular mass of the polymer additive is a factor of 2, preferably a factor of 200, greater than the average molecular mass of the temperature control medium. [3] Projection exposure system according to one of the preceding claims, the polymer additive comprises linear macromolecules, preferably with a deformable main chain. [4] Projection exposure system according to one of the preceding claims, characterized by that the temperature control medium is polymer-free apart from the polymer additive. [5] Projection exposure system according to one of the preceding claims, characterized by that the tempering medium is water, preferably demineralized water. [6] Projection exposure system according to one of the preceding claims, characterized by that the pH value of the tempering medium with polymer additive(s) is between 5 and 8, preferably between 6 and 7.

5. [7] Projection exposure system according to one of the preceding claims, characterized by that the concentration of the at least one polymer additive in the water is preferably between 0.05 ppm and 1000 ppm, between 2 ppm and 100 ppm. [8] Projection exposure system according to one of the preceding claims, characterized by that the average molecular mass of the polymer additive is between 10 g / mol and 100,000 g / mol, preferably between 40 g / mol and 50,000 g / mol, and / or the average molecular mass of the temperature control medium is between 15 g / mol and 20 g / mol, preferably between 17 g / mol and 19 g / mol. [9] Projection exposure system according to one of the preceding claims, characterized by that the or at least one polymer additive is polyacrylamide (PAM), polyethylene glycol (PEG) or hydroxypropylmethylcellulose (HPMC). [10] Projection exposure system according to one of the preceding claims, characterized by that the temperature control system (100) comprises at least one circulation pump (102) and / or one element (103) for actively controlling the temperature control medium. [11] Projection exposure system according to one of the preceding claims, characterized bythat the projection exposure system (1) is designed for exposure with a wavelength in the EUV range.

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