Method for manufacturing a mirror for a microlithographic projection exposure apparatus

Abstract

The present invention relates to a method for manufacturing a mirror (26) for a microlithography projection exposure apparatus (1), comprising providing a first mirror part (27) and a second mirror part (28), the first mirror part (27) and the second mirror part (28) being in contact in the region of a first connecting surface (29) of the first mirror part (27) and a second connecting surface (30) of the second mirror part (28), the first mirror part (27) and the second mirror part (28) being heated to a holding temperature of at least 400°C and held at the holding temperature for a holding time in order to form a durable connection between the first mirror part (27) and the second mirror part (28), after which the first mirror part (27) and the second mirror part (28) are cooled to a first cooling temperature at a first cooling rate of at most 100 K / h.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a mirror for a microlithographic projection exposure apparatus, and also to a mirror for a microlithographic projection exposure apparatus, an illumination optical unit, a projection optical unit, and a microlithographic projection exposure apparatus. [Background technology]

[0002] Microlithography projection exposure apparatuses are used, in particular, in the manufacture of semiconductors and generally comprise an illumination optical unit and a projection optical unit. The illumination optical unit generates a desired light distribution from light of a light source for illuminating a reticle, often also referred to as a mask. Light in this case should be understood in the general sense of radiation, i.e., not limited to a specific wavelength. Therefore, the terms "light" and "radiation" are used synonymously below, i.e., the light source may also be referred to as a radiation source, and the light distribution may also be referred to as a radiation distribution, and so forth. Using the projection optical unit, the reticle is imaged onto a photosensitive material, for example, applied to a wafer or another substrate, in particular of semiconductor material. In this way, the photosensitive material is structured and exposed to a predetermined pattern by the reticle. Because the reticle has microstructures intended to be transferred to the substrate with high precision, the illumination optical unit must precisely and reproducibly generate the desired light distribution, and imaging by the projection optical unit must be precise and reproducible.

[0003] In addition to other optical elements, the illumination optical unit and the projection optical unit may have at least one mirror in the optical path, which deflects the light in a predetermined way by reflection on an optical surface. The specific deflection of the light depends on the formation of the optical surface, in particular its shape. The optical surface may be formed, for example, as a metal layer or as a series of layers with alternating reflectivity. Regardless of the formation of the optical surface, perfect reflection is impossible, so some light is always absorbed, causing the mirror to heat up. The heating is accompanied by thermal expansion and the resulting deformation of the mirror, in particular the optical surface, which may ultimately change the optical properties of the mirror.

[0004] In order to minimize the effect of heating on the optical properties of the mirror, the mirror can be made from a material with an extremely low coefficient of thermal expansion. Such materials may have a zero-cross temperature near which thermal expansion is particularly low, ideally even zero. Therefore, when using such materials, one generally tries to operate the mirror at or near its zero-cross temperature. This means that the zero-cross temperature should correspond as accurately as possible to the temperature that the mirror will assume under the intended operating conditions, or should be somewhat above this temperature. A zero-cross temperature somewhat above the expected operating temperature of the mirror has the advantage that local heating of the mirror due to maximum light intensity values ​​leads to only a slight expansion of the mirror.

[0005] From US Pat. No. 5,629,499 it is known that heat treatment influences the thermal expansion coefficient of doped quartz glass and its increase with temperature.

[0006] For example, if the mirror is intended to have cooling channels or to be larger than the blank of material available for its manufacture, it may be advantageous or even necessary to form the mirror from two or more parts.

[0007] A multi-component mirror with cooling channels is known from unpublished German patent application no. 102020208648.6.

[0008] A problem with mirrors made from two or more parts is the connection of the individual parts of the mirror in a way that meets the high requirements for lithography optics. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] US Patent Application Publication No. 10427974 Summary of the Invention [Problem to be solved by the invention]

[0010] The invention is based on the object of making a multi-component mirror of a microlithographic projection exposure apparatus in such a way that it meets very high optical requirements and has high dimensional stability under the intended operating conditions, in particular the mirror is intended to have very little thermal deformation under the intended operating conditions. [Means for solving the problem]

[0011] This object is achieved by the combination of features set forth in claim 1.

[0012] In a method for manufacturing a mirror for a microlithography projection exposure apparatus according to the invention, a first mirror part and a second mirror part are provided, which are in contact in the region of a first connecting surface of the first mirror part and a second connecting surface of the second mirror part. In order to form a durable connection between the first and second mirror parts, the first and second mirror parts are heated to a holding temperature of 400°C or higher and kept at the holding temperature for a holding time. After the holding time has elapsed, the first and second mirror parts are cooled to a first cooling temperature at a first cooling rate of up to 100 K / h.

[0013] The method according to the invention has the advantage that a very durable connection can be formed between mirror parts. The process of forming this connection is also referred to as bonding in the following. A further advantage of the method according to the invention is that the mirrors of the microlithography projection exposure apparatus manufactured by this method can be formed to meet very high optical requirements and have high dimensional stability under the intended operating conditions. In particular, the mirrors can be formed so that they undergo very little thermal deformation under the intended operating conditions. This can be achieved by forming the mirror with a zero-cross temperature that, averaged over the relevant volume, hardly deviates from a predetermined value and / or is very uniform within this relevant volume, with only slight spatial variations. Of particular interest here are regions of the mirror's volume that are located at a small distance from its optical surface, which could cause the mirror to deform to an unacceptable extent.

[0014] An important finding of the present invention is that the heat treatment used to join the mirror components can affect the mirror's zero-cross temperature, which should be taken into account when planning the heat treatment, in order to be able to produce particularly high-quality mirrors. In other words, the zero-cross temperature of the material from which the mirror components are made can be changed by joining, even though it was set to a desired value with considerable effort. For this reason, in the method of the present invention, a relatively low cooling rate is selected, for example, so that the heat treatment process can be monitored precisely over the entire volume of the mirror component as much as possible at any time.

[0015] A low cooling rate has the advantage that, for example, the temperature difference in different regions of the mirror element volume is relatively small when there is a change in the cooling rate. As a result, the non-uniformity of the zero-cross temperature of the mirror is also relatively small. A further advantage is that temperature errors in the furnace that keeps the mirror element at a certain temperature or in the mirror element itself do not have a strong influence on the uniformity of the zero-cross temperature. A low cooling rate generally has a larger effect on the absolute value of the zero-cross temperature than a high cooling rate. However, this can already be taken into account during the manufacturing of the material of the mirror element.

[0016] The heat treatment can be carried out in air or in an inert gas atmosphere, it is equally possible to carry out the heat treatment under vacuum conditions.

[0017] The first and second mirror components may be prepared in the form of an intermediate product manufactured by wringing the first connecting surface of the first mirror component with the second connecting surface of the second mirror component. This facilitates the heat treatment because it is not necessary to handle the mirror components individually and does not require the effort of accurately positioning the mirror components relative to each other during the heat treatment. Furthermore, since the connecting surfaces of the mirror components must be brought very close to each other during bonding and the connecting surfaces must meet the same prerequisites as for wringing in the case of bonding, successful wringing in advance is likely to result in successful bonding. Furthermore, the intermediate product may be inspected for defects before the heat treatment. A defect may be, for example, an inclusion between the connecting surfaces. If a defect is found, the intermediate product may be rejected or subjected to some other treatment. As a result, it is possible to avoid performing a thorough heat treatment on a defective intermediate product.

[0018] During the ringing, the first and second mirror parts can be brought together so that initially a partial area of ​​the first connecting surface and a partial area of ​​the second connecting surface come into contact to form a common contact surface, which expands as the first and second mirror parts continue to come together in the rolling direction.

[0019] The transition area between the common contact surface where the second mirror element is already ringed to the first mirror element and the un-ringed area of ​​the first and second connecting surfaces is also referred to as the ringing front. The effect of continuing to bring the first and second mirror elements together is that the ringing front advances in the rolling direction under supervision. This continuous ringing has the advantage that the relative alignment of the two mirror elements relative to each other can be monitored very precisely throughout the entire ringing motion, avoiding undesirable spontaneous ringing. Furthermore, at any point during the ringing motion, there is always a fluid connection between the ringing front area and the surrounding area, thus ensuring that gas can escape from this area, thereby substantially preventing gas mixing between the connecting surfaces.

[0020] The first and second mirror parts can be brought together in such a way that contact with the first mirror part occurs in a region of the second connecting surface adjacent to the outer contour of the second mirror part. It is equally possible to bring the first and second mirror parts together in such a way that contact with the first mirror part occurs in a central region of the second connecting surface. This allows the wringing action to be adapted to each situation, in particular the configuration of the second mirror part.

[0021] An optical surface forming region may be provided on the second mirror component on the side opposite to the second connecting surface.

[0022] The first connecting surface of the first mirror element and / or the second connecting surface of the second mirror element may have a curvature. A curved first connecting surface and / or second connecting surface is advantageous, particularly when a curved optical surface is to be formed on the second mirror element, since it allows, for example, a constant thickness of the second mirror and therefore a uniform deformability. Furthermore, a constant distance between the cooling channel and the optical surface can be achieved with little effort. The curvature of the first connecting surface and / or second connecting surface can correspond to the curvature of the target optical surface of the mirror.

[0023] The first mirror component may have a first connecting surface that is planar or has a large mean radius of curvature along at least one direction, particularly a mean radius of curvature greater than 10 mm. In this case, a thin second mirror component having a planar second connecting surface, particularly a second mirror component with a thickness of 0.5 mm to 10 mm, may be used. If the second mirror component has cooling channels, the thickness is measured from the bottom of the cooling channels. Such a thin second mirror component has the advantage that its second connecting surface can be deformed to fit the shape of the first connecting surface of the first mirror component. This means that the effort required to manufacture a second mirror component with a curved second connecting surface is unnecessary.

[0024] For a wavelength λ of 633 nm, the shape of the first connecting surface of the first mirror element and / or the second connecting surface of the second mirror element may deviate from a predetermined shape by less than λ / 2, preferably less than λ / 10. The first connecting surface of the first mirror element and / or the second connecting surface of the second mirror element may have a roughness of less than 5 nm, preferably less than 1 nm. The term "roughness" in this case encompasses randomly distributed deviations from a smooth surface. A precisely shaped, smooth connecting surface facilitates ringing and bonding, reduces the risk of gas ingress, and increases the load-bearing capacity of the connection. Before ringing or bonding, one of the two connecting surfaces can be adapted to the actual shape of the other of the two connecting surfaces. In this way, even greater precision can be achieved.

[0025] The curvature of the first connecting surface can be convex and the curvature of the second connecting surface can be concave, or the curvature of the first connecting surface can be concave and the curvature of the second connecting surface can be convex, and during the joining of the first and second mirror parts, the convex curvature has a mean radius of curvature whose absolute value is smaller than the absolute value of the mean radius of curvature of the concave curvature. This has the advantage that the greater the distance from the ringing front, the greater the distance between the two connecting surfaces, ensuring localized ringing continuity. The risk of undesired ringing at positions far from the ringing front is reduced. Furthermore, the risk of gas ingress is reduced.

[0026] Before heating to the holding temperature, the intermediate product can be stored at a storage temperature between 80°C and 400°C for a storage time of at least 2 hours, preferably at least 12 hours, and particularly preferably at least 24 hours. The interpolation temperature is preferably at least 160°C, particularly preferably at least 250°C. Furthermore, the interpolation temperature is preferably at most 350°C. Storage at these temperatures has the advantage that excess moisture diffuses from the area of ​​the connecting surfaces of the mirror components, increasing their strength. In particular, anhydrous materials promote the formation of covalent bonds during a subsequent heat treatment at the holding temperature. If a relatively low holding temperature in the range of approximately 400°C to 550°C is selected, prolonged storage at lower temperatures, for example at a holding temperature of up to 250°C for 1 to 2 weeks, is possible.

[0027] In particular, the first and second mirror parts are heated to a holding temperature of at least 500° C., preferably at least 600° C., particularly preferably at least 700° C. Using a high holding temperature, a particularly large number of covalent bonds are formed, so that a particularly durable connection of the mirror parts can be achieved.

[0028] The first and second mirror parts can be heated to a holding temperature of up to 900° C. In addition to the mentioned advantages, a higher holding temperature also comes with the disadvantage that the influence of the heat treatment on the zero cross temperature is increased. A good compromise can be achieved with the mentioned maximum values ​​for the holding temperature.

[0029] The first and second mirror parts may be heated to the holding temperature at a heating rate of up to 150 K / h, preferably up to 100 K / h. A slow heating rate has the advantage that less stress is formed between the inner and outer regions of the mirror parts, leaving more time available for the outward diffusion of water.

[0030] The holding time can be 8 hours or more, preferably 12 hours or more, and particularly preferably 20 hours or more. A longer holding time has the advantage that more covalent bonds are formed, thereby increasing the tensile strength of the connection between the mirror components. To enable efficient production, the holding time is preferably up to 72 hours, particularly preferably up to 48 hours.

[0031] The first cooling temperature may be 700°C or less. In particular, the first cooling temperature may be 600°C or less. The first cooling rate is preferably 50 K / h or less. In particular, the first cooling rate is between 1 K / h and 20 K / h. A low cooling rate has the advantage that the first and second mirror parts are cooled relatively uniformly throughout their volume. High spatial temperature gradients are avoided and temperature variations over time are similar throughout the volume. This further leads to a relatively uniform distribution of the zero cross temperature of the mirror.

[0032] After cooling to the first cooling temperature at the first cooling rate, the first and second mirror components may be cooled to a second cooling temperature lower than the first cooling temperature at a second cooling rate higher than the first cooling rate. The second cooling temperature may be 500°C or lower, preferably 400°C or lower. The second cooling rate may be 150 K / h or lower. In particular, the second cooling rate is between 5 K / h and 100 K / h. After cooling to the second cooling temperature, the first and second mirror components may be further cooled toward room temperature. This further cooling may be performed, at least initially, at a third cooling rate higher than the second cooling rate. The use of a high cooling rate at a low cooling temperature significantly accelerates the heat treatment without significantly compromising the mirror quality, since the cooling profile has a much smaller effect on the mirror's zero-cross temperature at a low cooling temperature than at a high cooling temperature.

[0033] The first and second mirror components can be cooled so that the moving average cooling rate, formed in 20 K temperature intervals, throughout the entire volume of the first and / or second mirror components has the same relative variation over time in the temperature range of 900°C to 700°C, with a deviation of up to 2 K / h. That is, cooling can be performed so that the difference in the variation over time of this moving average at all positions on the first and / or second mirror components is no more than 2 K / h, taking into account potential time differences. Preferably, the deviation of the moving average over the temperature range of 900°C to 700°C is no more than 1 K / h. Furthermore, the deviation of the moving average over the temperature range of 700°C to 500°C can be no more than 4 K / h, preferably no more than 2 K / h. This specification allows for a consistently high quality of the manufactured mirrors. In this case, a somewhat larger tolerance at low temperatures can accelerate the heat treatment without significant adverse effects. Furthermore, the first and second mirror parts can be cooled such that the mirror zero-cross temperature non-uniformity due to the heat treatment is at most + / - 1 K, preferably at most + / - 0.5 K. These tolerances should be maintained in particular within a volume area of ​​the mirror that laterally overlaps the optical surface of the mirror and extends from the optical surface to the depth of the cooling channels, i.e., from the optical surface to the start of the cooling channels. These tolerances can equally be maintained within a volume area of ​​the mirror that laterally overlaps the optical surface of the mirror and extends from the optical surface to a depth of 1 cm below the cooling channels.

[0034] The first and / or second cooling rates may be selected depending on the material composition of the first and second mirror components. In particular, the first and / or second cooling rates may be selected depending on the OH content and / or titanium content of the first and / or second mirror components. Since the effect of the heat treatment on the zero cross temperature of the mirror varies depending on the material composition of the mirror components, the achievable accuracy with respect to the properties of the mirror, in particular its zero cross temperature, can be improved by taking the material composition into account when designing the heat treatment.

[0035] The first and / or second cooling rates may be selected according to a desired average zero-cross temperature of the mirror, which allows for the manufacture of mirrors with very small deviations of the average zero-cross temperature from a predetermined value. In particular, the first and / or second cooling rates may be selected according to a desired average zero-cross temperature within a volumetric area of ​​the mirror that laterally overlaps the optical surface of the mirror and extends from the optical surface to a depth of 1 cm below the cooling channel.

[0036] To determine the first and / or second cooling rates, a material sample of the material from which the first and / or second mirror component is manufactured can be analyzed. In particular, the material sample can be subjected to all of the heat treatments of the material of the first and / or second mirror component in the same way. In this way, the first and / or second cooling rates can be very closely tailored to the material composition of the first and / or second mirror component without risking damage to the mirror component, thereby achieving very high precision and low variance in the average zero cross temperature of the manufactured mirror.

[0037] The present invention also relates to a mirror for a microlithography projection exposure apparatus, comprising a first mirror element, a second mirror element, and a light-reflecting optical surface. The first and second mirror elements are durably connected to one another by a heat treatment in the region of a first connecting surface of the first mirror element and a second connecting surface of the second mirror element. The mirror has an average zero cross temperature within a volumetric area that laterally overlaps the optical surface and extends to a depth of 1 cm from the optical surface, with a deviation of at most + / - 1 K from a predetermined value. Within this volumetric area, the predetermined value can decrease with increasing distance from the optical surface.

[0038] By interconnecting the first and second mirror parts using the method according to the invention, such a precise average zero cross temperature can be achieved, despite the influence of the heat treatment on the zero cross temperature, preferably with a deviation of at most + / - 0.5 K, particularly preferably at most + / - 0.2 K from the predetermined value.

[0039] Achieving such high accuracy would be nearly impossible if the method according to the invention did not take into account the effect on the mirror zero cross temperature of the heat treatment used to interconnect the mirror components.

[0040] The first connecting surface of the first mirror part and / or the second connecting surface of the second mirror part may have a curvature, where the curvature of the first connecting surface of the first mirror part may not be rotationally symmetric and therefore may have a different mean curvature, and / or the curvature of the second connecting surface of the second mirror part may not be rotationally symmetric and therefore may have a different mean curvature.

[0041] Cooling channels may be formed in the first and / or second mirror components. In this case, the mirror may have, within a volumetric area laterally overlapping its optical surface and extending from the optical surface to the depth of the cooling channels, i.e., from the optical surface to the start of the cooling channels, a mean zero-cross temperature that deviates from a predetermined value by at most + / −1 K, preferably at most + / −0.5 K, and particularly preferably at most + / −0.2 K. If the mirror has cooling channels, this condition may be replaced by the aforementioned condition for a volumetric area extending from the optical surface to a depth of 1 cm, regardless of the cooling channels, so that the depth of the volumetric area in the case of a mirror with cooling channels may be less than 1 cm. It is equally possible for the mirror to have, within a volumetric area laterally overlapping its optical surface and extending from the optical surface to a depth of 1 cm below the cooling channels, a mean zero-cross temperature that deviates from a predetermined value by at most + / −1 K, preferably at most + / −0.5 K, and particularly preferably at most + / −0.2 K. For the mentioned volume area, the predetermined value may in each case decrease with increasing distance from the optical surface. The cooling channels may be formed to open towards the first connecting surface of the first mirror element and / or the second connecting surface of the second mirror element.

[0042] The cooling channels may each be arranged transversely within the region for the optical surface for the majority of its longitudinal extent, allowing for efficient cooling of the region that has the greatest influence on temperature-induced deformation of the optical surface.

[0043] Furthermore, the cooling channels may extend parallel to the optical surface, which allows for particularly uniform cooling of the optical surface. In particular, the cooling channels may extend to the optical surface within a distance of 1 mm to 6 mm. The shape deviation between the second connecting surface of the second mirror element and the optical surface may be no more than 3 mm, preferably no more than 20 μm.

[0044] In one refinement, the edge-to-edge distance between adjacent cooling channels is 15 mm or less, preferably 5 mm or less. A small distance between the cooling channels allows for efficient and uniform cooling and facilitates deformability during ringing, especially in the case of a rolling direction across the cooling channels of the second mirror part. In particular, the values ​​of the width of the cooling channels, the edge-to-edge distance between adjacent cooling channels and the distance between the cooling channels and the optical surface may be approximately the same.

[0045] The cross-sectional dimension of the cooling channel may be between 0.2 mm and 10 mm. The depth of the cooling channel, i.e., the cross-sectional dimension approximately perpendicular to the first connecting surface of the first mirror element or the second connecting surface of the second mirror element, may be greater than the width of the cooling channel, i.e., the cross-sectional dimension perpendicular to the depth. In particular, the depth of the cooling channel may be greater than twice the width of the cooling channel. As a result, the surface area ratio of the cavity formed by the cooling channel parallel to the optical surface area is smaller than in the case of a wide cooling channel with a small depth, so that for the same flow cross-section, the risk of deformation of the optical surface of the mirror due to the pressure of the fluid in the cooling channel is reduced.

[0046] The first mirror element may have a greater thickness than the second mirror element, which allows for efficient cooling of the optical surface and increases the mechanical stability of the mirror.

[0047] The invention also relates to an illumination optical unit comprising a mirror formed according to the invention and / or manufactured by a method according to the invention.

[0048] The invention also relates to a projection optical unit comprising a mirror formed according to the invention and / or manufactured by a method according to the invention.

[0049] Finally, the invention relates to a microlithographic projection exposure apparatus comprising an illumination optical unit according to the invention and / or a projection optical unit according to the invention.

[0050] The invention will now be explained in more detail on the basis of exemplary embodiments shown in the drawings. [Brief explanation of the drawings]

[0051] [Figure 1] 1 shows an exemplary embodiment of a projection exposure apparatus for EUV projection lithography in schematic meridional section; [Figure 2] 1 shows an exemplary embodiment of a projection exposure apparatus for DUV projection lithography in meridional section; [Figure 3] 1 shows in schematic cross section an exemplary element of a mirror manufactured by the method according to the invention; [Figure 4] 4 shows yet another schematic cross-sectional view of the first exemplary embodiment of the mirror shown in FIG. 3; [Figure 5] 3 shows a flow chart illustrating the procedure according to the invention when connecting a lower part and an upper part; [Figure 6] 10 shows a schematic cross-sectional view of a snapshot during the ringing of the upper part onto the lower part. DETAILED DESCRIPTION OF THE INVENTION

[0052] FIG. 1 shows an exemplary embodiment of a projection exposure apparatus 1 for EUV projection lithography in schematic meridional section.

[0053] In the following text, the essential components of a microlithography projection exposure apparatus 1 will first be described by way of example with reference to Figure 1. The description here of the basic structure of the projection exposure apparatus 1 and its components should not be construed as limiting.

[0054] An embodiment of the illumination system 2 of the projection exposure apparatus 1 comprises, in addition to the light source or radiation source 3, an illumination optical unit 4 for illuminating an object field 5 in an object plane 6. In an alternative embodiment, the radiation source 3 can also be provided as a module separate from the rest of the illumination system. In this case, the illumination system does not include the radiation source 3.

[0055] A reticle 7 arranged in the object field 5 is exposed. The reticle 7 is held by a reticle holder 8. The reticle holder 8 is displaceable, in particular in the scanning direction, by a reticle displacement drive 9.

[0056] For illustrative purposes, a Cartesian xyz coordinate system is shown in Figure 1. The x direction extends perpendicular to the plane of the drawing. The y direction extends horizontally and the z direction extends vertically. In Figure 1, the scanning direction extends along the y direction. The z direction extends perpendicular to the object plane 6.

[0057] The projection exposure apparatus 1 comprises a projection optical unit 10. The projection optical unit 10 serves to image the object field 5 into an image field 11 in an image plane 12. The image plane 12 extends parallel to the object plane 6. Alternatively, an angle other than 0° between the object plane 6 and the image plane 12 is also possible.

[0058] It is shown that structures on a reticle 7 are imaged onto a photosensitive layer of a wafer 13 or of some other substrate arranged in the region of an image field 11 of an image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable, in particular along the y direction, by a wafer displacement drive 15. The displacement of the reticle 7 by the reticle displacement drive 9 on the one hand and the displacement of the wafer 13 by the wafer displacement drive 15 on the other hand can be performed synchronously with respect to one another.

[0059] The radiation source 3 is an EUV radiation source. The radiation source 3 emits illumination radiation 16, hereinafter also referred to as working radiation or illumination light. In the illustrated exemplary embodiment, the illumination radiation 16 has a wavelength in the EUV range, in particular in the range of 5 nm to 30 nm. The radiation source 3 can be a plasma source, for example an LPP source (laser produced plasma) or a GDPP source (gas discharge plasma). It can also be a synchrotron-based radiation source. Likewise, the radiation source 3 can be a free electron laser (FEL).

[0060] The illumination radiation 16 leaving the radiation source 3 is focused by the collector 17. The collector 17 may be a collector with one or more ellipsoidal and / or hyperbolic reflecting surfaces. The illumination radiation 16 may be incident on at least one reflecting surface of the collector 17 at grazing incidence (GI), i.e. at an angle of incidence greater than 45°, or at normal incidence (NI), i.e. at an angle of incidence smaller than 45°. The collector 17 may be structured and / or coated to optimize its reflectivity for the illumination radiation 16 on the one hand and to suppress extraneous light on the other hand.

[0061] Downstream of the collector 17, the illumination radiation 16 propagates through an intermediate focus in an intermediate focal plane 18. The intermediate focal plane 18 may represent the separation between the source module comprising the radiation source 13 and the collector 17 and the illumination optics unit 4.

[0062] The illumination optical unit 4 comprises a deflection mirror 19 and a first facet mirror 20 arranged downstream thereof in the beam path. The deflection mirror 19 can be a plane deflection mirror or a mirror with a beam-influencing effect beyond a pure deflection effect. Alternatively or additionally, the deflection mirror 19 can be embodied as a spectral filter that separates the used optical wavelength of the illumination radiation 16 from extraneous light of wavelengths deviating therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate with the object plane 6 as the field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a plurality of individual first facets 21, also referred to as field facets in the following. Only some of these first facets 21 are shown by way of example in FIG. 1 .

[0063] The first facet 21 may be embodied as a macroscopic facet, in particular as a rectangular facet, or in the form of a facet having an arcuate or part-circular peripheral contour. The first facet 21 may be embodied as a planar facet or as a convexly or concavely curved facet.

[0064] The first facet 21 itself can also consist of a number of individual mirrors, in particular a number of micromirrors, as is known, for example, from DE 10 2008 009 600. The first facet mirror 20 can in particular be formed as a microelectromechanical system (MEMS system). See DE 10 2008 009 600 for further details.

[0065] Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, ie along the y direction.

[0066] A second facet mirror 22 is arranged downstream of the first facet mirror 20 in the beam path of the illumination optical unit 4. If the second facet mirror 22 is arranged in the pupil plane of the illumination optical unit 4, it is also referred to as a pupil facet mirror. The second facet mirror 22 can also be arranged away from the pupil plane of the illumination optical unit 4. In this case, the combination of the first facet mirror 20 and the second facet mirror 22 is also referred to as a specular reflector. Specular reflectors are known from US Patent Application Publication No. 2006 / 0132747, EP 1 614 008 and US 6,573,978.

[0067] The second facet mirror 22 includes a plurality of second facets 23. In the case of a pupil facet mirror, the second facets 23 are also referred to as pupil facets.

[0068] The second facet 23 may likewise be a macroscopic facet, which may have, for example, a circular, rectangular or hexagonal perimeter, or a facet made up of a micromirror. In this respect, reference is also made to DE 10 2008 009 600 A1.

[0069] The second facet 23 may have a flat reflecting surface or a convexly or concavely curved reflecting surface.

[0070] The illumination optical unit 4 results in a double-faceted system, the basic principle of which is also called a honeycomb condenser (fly's eye integrator).

[0071] It may be advantageous not to arrange the second facet mirror 22 exactly in a plane that is optically conjugate with the pupil plane of the projection optical unit 10. In particular, as described in DE 10 2017 220 586 A1, the second facet mirror 22 may be arranged so that it is tilted with respect to the pupil plane of the projection optical unit 10.

[0072] The individual first facets 21 are imaged into the object field 5 by means of a second facet mirror 22. The second facet mirror 22 is the last beam-shaping mirror in the beam path upstream of the object field 5 or indeed the final mirror for the illumination radiation 16.

[0073] In a further embodiment of the illumination optical unit 4, not shown, a transfer optical unit, which in particular contributes to the imaging of the first facet 21 into the object field 5, can be arranged in the beam path between the second facet mirror 22 and the object field 5. The transfer optical unit can have exactly one mirror or two or more mirrors arranged one behind the other in the beam path of the illumination optical unit 4. The transfer optical unit can in particular include one or two mirrors for normal incidence (NI mirrors) and / or one or two mirrors for grazing incidence (GI mirrors).

[0074] In the embodiment shown in FIG. 1, the illumination optical unit 4 comprises exactly three mirrors downstream of the collector 17 , in particular a deflection mirror 19 , a field facet mirror 20 and a second facet mirror 22 .

[0075] In yet another embodiment of the illumination optical unit 4, the deflection mirror 19 is not required, so that the illumination optical unit 4 can then have exactly two mirrors downstream of the collector 17, specifically a first facet mirror 20 and a second facet mirror 22.

[0076] The imaging of the first facet 21 onto the object plane 6 by the second facet 23 or by means of the second facet 23 and the transfer optical unit is often only an approximate imaging.

[0077] The projection optical unit 10 comprises a number of mirrors Mi, which are numbered according to their position in the beam path of the projection exposure apparatus 1 .

[0078] 1, the projection optical unit 10 includes six mirrors M1-M6. Four, eight, ten, twelve, or any other number of mirrors Mi are equally possible. The projection optical unit 10 is a double-shielded optical unit. The penultimate mirror M5 and the final mirror M6 each have a through aperture through which radiation contributing to the exposure process passes on its way from the reticle 7 to the wafer 13 during exposure of the wafer 13. The projection optical unit 10 has an image-side numerical aperture that is greater than 0.5, may be greater than 0.6, and may be, for example, 0.7 or 0.75.

[0079] The reflective surface of the mirror Mi can be embodied as a freeform surface without an axis of rotational symmetry. Alternatively, the reflective surface of the mirror Mi can be designed as an aspheric surface, in which case the reflective surface shape has exactly one axis of rotational symmetry. Like the mirrors of the illumination optical unit 4, the mirror Mi can have a coating that is highly reflective with respect to the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

[0080] Projection optical unit 10 has a large object-image offset in the y direction between the y coordinate of the center of object field 5 and the y coordinate of the center of image field 11. This object-image offset in the y direction may be approximately the same size as the z distance between object plane 6 and image plane 12.

[0081] In particular, the projection optical unit 10 can have an anamorphic form. In particular, it has different imaging scales βx, βy in the x and y directions. The two imaging scales βx, βy of the projection optical unit 10 are preferably (βx, βy)=(+ / -0.25, + / -0.125). A positive imaging scale β means imaging without image inversion. A negative sign of the imaging scale β means imaging with image inversion.

[0082] The projection optical unit 10 results in a size reduction in the x-direction, ie perpendicular to the scanning direction, by a ratio of 4:1.

[0083] The projection optical unit 10 provides a size reduction of 8:1 in the y-direction, ie the scan direction.

[0084] Other imaging scales are possible as well, including imaging scales of the same sign and magnitude in the x and y directions, for example 0.125 or 0.25.

[0085] The number of intermediate image planes in the x and y directions in the beam path between the object field 5 and the image field 11 may be the same or may differ depending on the embodiment of the projection optical unit 10. An example of a projection optical unit 10 with a different number of such intermediate images in the x and y directions is known from US Patent Application Publication No. 2018 / 0074303.

[0086] Each of the second facets 23 is assigned to exactly one of the first facets 21 to form a respective illumination channel that illuminates the object field 5. This makes it possible, in particular, to generate illumination according to the Köhler principle. The far field is decomposed into a plurality of object fields 5 by means of the first facets 21. The first facets 21 generate a plurality of images of intermediate foci on the respectively assigned second facets 23.

[0087] By means of the assigned second facets 23, the first facets 21 are imaged onto the reticle 7 in an overlapping manner in order to illuminate the object field 5. The illumination of the object field 5 is in particular as uniform as possible. Its uniformity error is preferably less than 2%. By overlapping the different illumination channels, field uniformity can be obtained.

[0088] The illumination of the entrance pupil of the projection optical unit 10 can be geometrically defined by the arrangement of the second facets 23. By selecting the illumination channels to be guided, and in particular a subset of the second facets 23, the intensity distribution at the entrance pupil of the projection optical unit 10 can be set. This intensity distribution is also referred to as the illumination setting or illumination pupil filling.

[0089] A similarly favorable pupil uniformity in the region of a defined illuminated portion of the illumination pupil of the illumination optical unit 4 can be achieved by redistribution of the illumination channels.

[0090] Further aspects and details of the illumination of the object field 5, in particular the entrance pupil of the projection optical unit 10, are explained below.

[0091] In particular, the projection optical unit 10 may have a concentric entrance pupil, which may be accessible, or which may be inaccessible.

[0092] The entrance pupil of the projection optical unit 10 cannot always be illuminated exactly by the second facet mirror 22. In the case of imaging by the projection optical unit 10, which telecentrically images the center of the second facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find a surface at which the distance determined for the pair of aperture rays is minimal. This surface represents the entrance pupil or a real space surface conjugate to it. In particular, this surface has a finite curvature.

[0093] The projection optical unit 10 may have different entrance pupil positions for the tangential and sagittal beam paths. In this case, an imaging element, in particular an optical component of the transfer optical unit, should be provided between the second facet mirror 22 and the reticle 7. This optical element can be used to take into account the difference in the relative positions of the tangential and sagittal entrance pupils.

[0094] In the arrangement of the components of the illumination optical unit 4 shown in Figure 1, the second facet mirror 22 is arranged in a plane conjugate with the entrance pupil of the projection optical unit 10. The first facet mirror 20 is arranged so as to be tilted with respect to the object plane 6. The first facet mirror 20 is arranged so as to be tilted with respect to the arrangement plane defined by the deflection mirror 19.

[0095] The first facet mirror 20 is disposed so as to be inclined with respect to the disposition plane defined by the second facet mirror 22 .

[0096] 2 shows in a schematic diagram an exemplary embodiment of a projection exposure apparatus 1 for DUV projection lithography, where DUV stands for "deep ultraviolet." In particular, the projection exposure apparatus 1 can be designed to operate at a wavelength of 193 nm.

[0097] The projection exposure apparatus 1 comprises an illumination optical unit 4 and a projection optical unit 10. The internal structure of the illumination optical unit 4 and the internal structure of the projection optical unit 10, each of which may include, for example, optical components, sensors, manipulators, etc., are not shown in detail. In the case of the projection optical unit 10, a mirror M is shown as a representative of its optical components. The mirror M may be cooled using a cooling medium supplied by a cooling device 24. The cooling medium is a fluid, for example water. Additionally or alternatively, the illumination optical unit 4 may comprise a cooled mirror M and an associated cooling device 24. The projection optical unit 10 and / or the illumination optical unit 4 may also comprise multiple cooled mirrors M and cooling devices 24. In the case of the illumination optical unit 4 and in the case of the projection optical unit 10, lenses and further mirrors, cooled or uncooled, may be present, for example, as further optical components.

[0098] Likewise, in the exemplary embodiment of the projection exposure apparatus 1 shown in FIG. 1, at least one cooling device 24 may be provided, which may for example be connected to the mirror M3.

[0099] The radiation required for the operation of the projection exposure apparatus 1 is generated by a radiation source 3. The radiation source 3 can in particular be an excimer laser, for example an argon fluoride laser, which generates illumination radiation 16 of a wavelength of 193 nm.

[0100] Between the illumination optical unit 4 and the projection optical unit 10 there is arranged a reticle holder 8, on which a reticle 7, also called a mask, is fixed. The reticle holder 8 has a reticle displacement drive 9. Downstream of the projection optical unit 10 in the radial direction there is arranged a wafer holder 14, which carries a wafer 13 or some other substrate and has a wafer displacement drive 15.

[0101] 2 also shows a control device 25 connected to the illumination optical unit 4, the projection optical unit 10, the cooling device 24, the radiation source 3, the reticle holder 8 or reticle displacement drive 9, and the wafer holder 14 or wafer displacement drive 15. Similarly, the projection exposure apparatus of FIG. 1 may also have a control device 25 which may be connected to corresponding components.

[0102] The projection exposure apparatus 1 serves the purpose of imaging a reticle 7 with high precision onto a wafer 13. For this purpose, the reticle 7 is illuminated using an illumination optical unit 4, and the illuminated reticle 7 is imaged onto the wafer 13 using a projection optical unit 10. Specifically, the following procedure is adopted:

[0103] The illumination optical unit 4 converts the illumination radiation 16 generated by the radiation source 3 in a precisely defined manner by means of its optical components and directs it towards the reticle 7. Depending on the embodiment, the illumination optical unit 4 can be configured to illuminate the entire reticle 7 or only a partial area of ​​the reticle 7. The illumination optical unit 4 can illuminate the reticle 7 in such a way that there are substantially identical illumination conditions at each illumination point of the reticle 7. In particular, the light intensity and angular distribution of the incident illumination radiation 16 are substantially identical at each illumination point of the reticle 7.

[0104] The illumination optical unit 4 can illuminate the reticle 7 with illumination radiation 16, possibly with several different angular distributions. These angular distributions of illumination radiation 16 are also referred to as illumination settings. The desired illumination setting is generally selected depending on the structural elements formed on the reticle 7. For example, dipole or quadrupole illumination settings are used more frequently, in which case illumination radiation 16 is incident on each illumination point on the reticle 7 from two or four different directions, respectively. Depending on the form of the illumination optical unit 4, different illumination settings can be generated, for example, by different diffractive optical elements in combination with a zoom axicon optical unit, or by a mirror array, which has several small mirrors arranged side by side and each of which can be individually adjusted in terms of its angular position.

[0105] The reticle 7 may for example be formed as a glass plate transparent to the illumination radiation 16 provided by the illumination optical unit 4 and provided with an opaque structure, for example in the form of a chrome coating.

[0106] The projection exposure apparatus 1 can be configured such that the entire reticle 7 is simultaneously illuminated by the illumination optical unit 4 and completely imaged onto the wafer 13 by the projection optical unit 10 in a single exposure step.

[0107] Alternatively, the projection exposure apparatus 1 can be configured such that only partial areas of the reticle 7 are illuminated simultaneously by the illumination optical unit 4, and the reticle displacement drives 9 are controlled by the control device 25 such that, during exposure of the wafer 13, the reticle 7 is moved relative to the illumination optical unit 4, resulting in the illuminated partial areas moving across the entire reticle 7. The wafer 13 is moved synchronously by appropriately coordinated control actions of the wafer displacement drives 15, which also take into account the imaging properties of the projection optical unit 10, so that each illuminated partial area of ​​the reticle 7 is imaged onto a corresponding partial area of ​​the wafer 13. This movement of the reticle 7 and the wafer 13 is also referred to as scanning.

[0108] In both variants of the projection exposure apparatus 1, a photosensitive layer is applied to the wafer 13 in order to be able to transfer the latent image produced by exposure of the wafer 13 into a physical structure. The image of the reticle 7 is formed in this photosensitive layer by exposure, and subsequent chemical processes can be used to create permanent structures on the wafer 13 therefrom.

[0109] The reticle 7 is generally imaged not just once but multiple times side by side on the wafer 13. For this purpose, after each imaging of the reticle 7 on the wafer 13, the wafer holder 14 is laterally displaced in a manner that corresponds to the size of the image of the reticle 7 on the wafer 13. The imaging of the reticle 7 can here be performed individually as a whole or sequentially by scanning. Chemical treatment of the wafer 13 is initiated only after the desired number of imaging of the reticle 7 on the wafer 13 has been performed.

[0110] FIG. 3 shows in a schematic cross-sectional view an exemplary embodiment of a mirror 26 manufactured by a method according to the present invention. FIG. 4 shows the same exemplary embodiment of mirror 26 in yet another schematic cross-sectional view taken along section line AA shown in FIG. 3. In order to show as much detail of mirror 26 as possible, section line AA is laterally offset as it passes through mirror 26. In FIG. 3, the cross-section is taken along section line BB shown in FIG. 4. In FIGS. 3 and 4, the depiction of mirror 26 and its components is not to scale and is very abstract in order to show the invention as clearly as possible, as is the case with all other figures.

[0111] In the case of one of the projection exposure apparatuses 1 shown in FIGS. 1 and 2, a mirror 26 can be used, which has a lower part 27 and an upper part 28, each made of quartz glass, Ti-doped quartz glass, or glass ceramic. The terms "lower part" and "upper part" are chosen because the lower part 27 is generally made much thicker than the upper part 28 and therefore, so to speak, supports the upper part 28. However, these terms have no bearing on the orientation of the mirror 26 with respect to the direction of gravity in its mounted state. During operation of the projection exposure apparatus 1, the upper part 28 can be arranged above, below, or to the side of the lower part 27 with respect to the direction of gravity, or can take any other relative position thereto. The lower part 27 is also referred to as the first mirror part 27, and the upper part 28 is also referred to as the second mirror part 28.

[0112] The lower part 27 and the upper part 28 are rigidly connected to each other in the region of the connecting surface 29 of the lower part 27 and the connecting surface 30 of the upper part 28 by the method according to the invention, which will be described in more detail below. In the illustrated exemplary embodiment, the connecting surface 29 of the lower part 27 is formed concavely curved. The curvature can be formed spherically, aspherically, or according to a free-form surface. The connecting surface 30 of the upper part 28 is curved complementarily to the connecting surface 29 of the lower part 27 and thus has a convex curvature that can be formed spherically, aspherically, or according to a free-form surface. As a result, the connecting surface 30 of the upper part 28 and the connecting surface 29 of the lower part 27 can fit tightly together. As an alternative to being curved, the connecting surface 29 of the lower part 27 and the connecting surface 30 of the upper part 28 can also be formed flat.

[0113] On the side opposite the connecting surface 29, shown in the lower part of FIG. 3, the lower part 27 is flat. On the side opposite the connecting surface 30, shown in the upper part of FIG. 3, the upper part 28 is concavely curved and has a reflecting optical surface 31 with the same curvature. This curvature can be spherical, aspherical, or freeform, and can in particular correspond to the curvature of the connecting surface 30 of the upper part 28. Even if the connecting surfaces 29 and 30, the surface of the upper part 28 opposite the connecting surface 30, and the optical surface 31 are each rotationally symmetrical, the cross sections in FIGS. 3 and 4 are taken at different distances from the centers of these surfaces, resulting in slightly different curvatures. However, the difference in distance compared to the absolute value of the radius of curvature is in each case very small, so that the difference in curvature is not noticeable in the illustrations in FIGS. 3 and 4.

[0114] Alternatively, the optical surface 31 can also be formed planar, which is the case in particular if the connecting surface 29 of the lower part 27 and the connecting surface 30 of the upper part 28 are formed planar.

[0115] The optical surface 31 is embodied as a coating applied to the upper part 28. The formation of the coating depends on the wavelength for which the optical surface 31 is intended to exert its reflective effect. If reflection in the DUV range is desired, i.e. in the case of mirror M of FIG. 2, the coating can be formed as an aluminum layer. On the other hand, if reflection in the EUV range is intended, as for example in the case of mirror M3 of FIG. 1, the coating can be formed in particular from alternating successive layers of silicon and molybdenum, and possibly one or more further layers of different composition, acting for example as protective layers.

[0116] The upper part 28 also has a plurality of elongated cooling channels 32 that extend parallel to one another and to the optical surface 31, laterally in the region of the optical surface 31, and possibly slightly beyond it. Therefore, in the illustrated exemplary embodiment, the cooling channels 32 are curved. The cooling channels 32 extend to within approximately 1 mm to 6 mm of the optical surface 31 and open toward the connecting surface 30 of the upper part 28. The cooling channels 32 therefore have elongated cooling channel openings 33 in the region of the connecting surface 30 of the upper part 28. The transverse dimensions of the cooling channels 32 can be approximately 0.2 mm to 10 mm, and the depth of the cooling channels 32, i.e., the dimension generally perpendicular to the connecting surface 30 of the upper part 28, is generally significantly greater than the width, i.e., the dimension generally parallel to the connecting surface 30 of the upper part 28. For example, the depth of the cooling channels 32 can be more than twice the width of the cooling channels 32. The edge-to-edge distance between adjacent cooling channels 32 is 15 mm or less, preferably 5 mm or less. The width of the cooling channels 32, the edge-to-edge distance between adjacent cooling channels 32, and the distance between the cooling channels 32 and the optical surface 31 may have substantially the same value.

[0117] If the connecting surface 30 of the upper part 28 is not rotationally symmetrical, its mean radius of curvature may vary with azimuth, or in other words, with direction. In this case, the region of the connecting surface 30 of the upper part 28 in which the absolute value of the mean radius of curvature is smallest may extend transversely, in particular perpendicularly, to the longitudinal extent of the cooling channel opening 33. Adjacent regions of the connecting surface 29 of the lower part 27 and the connecting surface 30 of the upper part 28 may have slightly different mean radii of curvature in the unconnected state, the mean radius of curvature of the region of the convexly formed surface generally being smaller in absolute value than the mean radius of curvature of the corresponding region of the concavely formed surface.

[0118] The lower component 27 has a plurality of distribution channels 34 and return channels 35, which extend into the lower component 27 from the connecting surface 29 of the lower component 27 in a direction opposite to the connecting surface 29 of the lower component 27. Within the lower component 27, the distribution channels 34 communicate with a fluid distribution section 36, and the return channels 35 communicate with a fluid return section 37. The distribution channels 34 and the return channels 35 each widen in a stepped manner toward the connecting surface 29 of the lower component 27, where they overlap with both ends of two cooling channel openings 33. In other words, one distribution channel 34 overlaps with one end of each of the two cooling channel openings 33, and one return channel 35 overlaps with the two other ends of the same two cooling channel openings 33. Thus, one distribution channel 34 is fluidly connected at one end to the fluid distribution section 36 and at the other end to two cooling channels 32. Similarly, one collection channel 35 is fluidly connected at one end to a fluid collection section 37 and at the other end to two cooling channels 32 .

[0119] Thus, a fluid, for example, water, can be supplied to the cooling channels 32 through the fluid distribution section 36 and the distribution channels 34, with each distribution channel 34 supplying fluid to two cooling channels 32, and the fluid distribution section 36 supplying water to all of the distribution channels 34. The fluid flows through the cooling channels 32 and then flows via the return channels 35 into the fluid return section 37, through which the fluid can be removed. In this case, fluid flows into one return channel 35 for every two cooling channels 32, and the fluid in all return channels 35 flows into the fluid return section 37. The supply of fluid to the fluid distribution section 36 and the removal of fluid from the fluid return section 37 can be achieved using the cooling device 24, which can be connected to the fluid distribution section 36 and the fluid return section 37 for this purpose.

[0120] By adjusting the temperature of the supplied fluid to a temperature lower than that of the upper part 28, the effect of heat extraction from the upper part 28 as the fluid flows through the cooling channels 32 can be achieved. This heat extraction is intended, in particular, to compensate for heat input due to radiation incident on the optical surface 31 during operation of the lithography system. Since the optical surface 31 does not completely reflect the incident radiation, some of the radiation is absorbed by the optical surface 31 and, depending on the shape of the optical surface 31, also by the upper part 28 and converted into heat. Since the optical surface 31 and the upper part 28 have a certain thermal conductivity, some of this heat is guided into the cooling channels 32, where it is absorbed and carried away by the fluid. In this way, the temperature rise of the mirror 26 caused by radiation can be limited, and deformation of the optical surface 31 caused by thermal expansion effects can be reduced compared to an uncooled mirror 26. As a result, imaging aberrations caused by the deformation are also reduced.

[0121] The formation and arrangement of the cooling channels 32, distribution channels 34, return channels 35, fluid distribution sections 36 and fluid return sections 37 can be varied in various ways. For example, the cooling channels 32 can be arranged in the lower part 27 and formed so as to open towards the connecting surface 29 of the lower part 27, so that the cooling channels 32 have elongated cooling channel openings 33 in the region of the connecting surface 29 of the lower part 27. The distribution channels 34 and return channels 35 may not be necessary, and the fluid distribution sections 36 and fluid return sections 37 may be connected directly to the cooling channels 32, etc.

[0122] To manufacture the mirror 26, the lower and upper components 27 and 28 are manufactured as separate components and then connected to each other. The optical surface 31 is generally formed only after the lower and upper components 27 and 28 are connected to each other, in order to achieve the highest possible precision, particularly with regard to its shape, and to avoid damaging the optical surface 31 during the connection process. Materials with very low thermal expansion coefficients are used to manufacture the lower and upper components 27 and 28. Suitable materials are, for example, quartz glass, quartz glass doped with titanium oxide, or special glass ceramics. The lower and upper components 27 and 28 can be cut from a common material blank. However, if the lower and upper components 27 and 28 differ too much from each other in terms of material parameters, it is also possible to use different material blanks for them.

[0123] For example, quartz glass mixed with titanium oxide and having a zero-cross temperature averaged over the volume of lower part 27 of 22°C to 25°C can be used to manufacture lower part 27. The zero-cross temperature is adjusted here to match the expected temperature of lower part 27 taking into account the cooling of mirror 26 during operation of the lithography system. Depending on the method of manufacturing the material used for lower part 27, the increase in the thermal expansion coefficient at 22°C can be about 1.35 ppb / K. 2 At least within the region of lateral overlap with optical surface 31 in the finished mirror 26, the zero cross temperature exhibits a uniformity of better than + / - 5K, and this uniformity is better in the region of connecting surface 29 of lower part 27 than on the opposite surface.

[0124] The lower part 27 is cut out from a material blank and then machined by grinding and polishing. The connecting surface 29 of the lower part 27 can here in particular be shaped to approximately correspond to the intended shape of the optical surface 31 to be subsequently formed on the upper part 28. The shape deviation between the connecting surface 29 of the lower part 27 and the optical surface 31 is a maximum of 3 mm, preferably 200 μm or less. If the connecting surface 29 of the lower part 27 has a circular periphery, its diameter is generally 20 cm to 100 cm, with a sag of 3% or less of the diameter. Any desired function can be superimposed on the spherical basic shape of the connecting surface 29 of the lower part 27, so that freeform surfaces can be obtained.

[0125] For a wavelength λ of 633 nm used for the measurements, polishing of the connecting surface 29 of the lower component 27 can be performed with deviations from the predetermined shape (design shape) of less than λ / 2, preferably less than λ / 10. Furthermore, roughness of less than 5 nm, preferably less than 1 nm, can be achieved in this case. The term "roughness" in this case encompasses randomly distributed deviations from a smooth surface. Shape deviations or deviations from the design shape are considered to include both long-wave deviations from the predetermined shape and short-wave deviations that are not randomly distributed but are more localized. Long-wave shape deviations may be slightly larger than the above values ​​λ / 2 and λ / 10. However, for short-wave deviations, the above values ​​are maintained as much as possible. For example, deviations with spatial frequencies of a few centimeters do not have such destructive effects. Deviations with spatial frequencies of less than 100 μm are generally much more destructive.

[0126] To avoid drying of abrasive and polishing residues, the lower part 27 is rinsed immediately after grinding and polishing. Additionally, mechanical wet cleaning can be performed. The surface of the lower part 27 can be further cleaned with solvents, organic and inorganic cleaners, or by plasma treatment, etc.

[0127] During processing of the lower part 27, deep damage must be avoided because small amounts of water, other process agents such as abrasives, or contaminants may remain in the microcracks, which may evaporate upon heating of the lower part 27 and lead to localized blistering. To avoid or eliminate possible deep damage, dry and / or wet etching steps or other suitable optical processing steps can be used. Furthermore, stepwise grinding steps can be used, or a polishing step can be performed after non-contact removal, e.g., by oxygen plasma etching. The absence of deep damage can be demonstrated by a short etching step, e.g., with hydrofluoric acid, which does not result in localized etch pits. A hydrofluoric acid bath is suitable, along with a cleaning step to remove hydrocarbons.

[0128] After grinding and polishing or lapping, distribution channels 34 and return channels 35 and fluid distribution portions 36 and fluid return portions 37 are formed in lower part 27, as needed. Depending on the formation of lower part 27, cooling channels 32 may also be formed in lower part 27. Distribution channels 34 and return channels 35 and fluid distribution portions 36 and fluid return portions 37 generally have transverse dimensions, i.e., dimensions transverse to the direction of fluid flow, that are much larger than the corresponding dimensions of cooling channels 32.

[0129] The channels can be formed by milling, grinding, drilling, laser ablation, ultrasonic ablation, or etching, or a combination of these methods, and in all cases, as a final method step, etching with hydrofluoric acid can be performed to give the channels a slightly roughened surface to avoid subsequent crack propagation and to promote flow.

[0130] In order to protect the processed, in particular polished, surface of the lower part 27 from chipping of edges and similar damage, for example around the cooling channel openings 33, a protective resist can be applied to the surface of the lower part 27 before the formation of the channels. Edge chipping that occurs despite this precaution can be locally smoothed or eliminated, for example by a bevel extending around the cooling channel openings 33. However, this bevel is disadvantageous in terms of flow and strength due to a notch effect and should be avoided as far as possible.

[0131] As an alternative to the above procedure, it is possible to first form the channels in the lower component 27 and then process the surface of the lower component 27 by grinding, lapping, and / or polishing. However, for example, abrasive disks have limited rigidity and bulge into the cooling channel openings 33 or other openings, resulting in some rounding of the edges of the cooling channel openings 33 or other openings. This rounding of the edges can be eliminated by inserting or cementing a placeholder made of the same material as the lower component 27 into the cooling channel openings 33 or other openings. The placeholder, along with the connecting surface 29 of the lower component 27, is ground and polished to reduce the width of the gap created by the cooling channel openings 33 or other openings. The gap remaining between the placeholder and the surrounding material of the lower component 27 can also be filled with glass or ceramic powder-filled putty, so that even if there is slight bulging during polishing, there is little edge rounding. Alternatively, localized reworking can be performed by robotic polishing or ion beam polishing to minimize edge rounding. After processing the surface of the lower part 27, the placeholder and, if applicable, the potting material are again removed.

[0132] To avoid or at least reduce edge rounding, ablation or etching methods can be used as an alternative to mechanical surface processing. In these methods, if a resist mask is applied to areas not to be processed, under-etching of the peripheral areas of the resist mask can occur. The adverse effects of this under-etching can be counteracted by appropriate mechanical, laser ablation, or etching reprocessing.

[0133] Materials having the same or similar properties as those described for lower component 27 can be used to manufacture upper component 28. The material properties of upper component 28 can deviate only within certain limits from the material properties of lower component 27. For example, since lower components 27 and 28 are rigidly connected to each other, it is problematic for lower component 27 and upper component 28 to have significantly different thermal expansion behaviors.

[0134] After cutting out the upper part 28 from the material blank, the surfaces of the upper part 28, in particular the connecting surface 30, can be processed in the same manner as described for the lower part 27 and must meet similar requirements regarding form deviation and roughness. If the upper part 28 is relatively thin, the requirements regarding form deviation can be relaxed somewhat.

[0135] Depending on the embodiment variant, the upper part 28 may have cooling channels 32 and / or other channels, such as distribution channels 34 and recovery channels 35. All of these channels may be made in a similar manner as described for the lower part 27, and similar measures may be used to reduce edge rounding, etc.

[0136] The upper part 28 is generally 10 mm to 40 mm thick, but can have a smaller thickness under certain conditions. Depending on the thickness, the upper part 28 may need to be cemented or ringed onto a glass substrate as a carrier material for processing in order to achieve sufficient rigidity for precise processing.

[0137] Tools having the same or very similar nominal curvature as the tools for machining the connecting surface 29 of the lower component 27 can be used to machine the connecting surface 30 of the upper component 28 by grinding, lapping, and / or polishing. In some cases, a further step may follow in which the actual shapes of the connecting surface 29 of the lower component 27 and the connecting surface 30 of the upper component 28 are measured and the connecting surface 30 of the upper component 28 is locally adapted to the connecting surface 29 of the lower component 27 by robotic polishing, plasma etching, ion beam ablation, or compressive high-energy irradiation.

[0138] In the case of an embodiment of the mirror 26 in which the connecting surface 29 of the lower part 27 is substantially flat or has such a small curvature that the absolute value of the mean radius of curvature for at least one azimuth angle is greater than 10 m, it is possible to use a relatively thin upper part 28 having a thickness of 0.5 mm to 10 mm and to form the connecting surface 30 of the upper part 28 in a flat shape. In this case, the upper part 28 can deform during connection to the lower part 27, so that the connecting surface 30 of the upper part 28 can be adapted to the shape of the connecting surface 29 of the lower part 27. For the necessary processing before connection, the upper part 28 can be cemented to a sufficiently rigid carrier material or can be ringed on the carrier material.

[0139] As an alternative to using an upper part 28 cut from a material blank, a thin upper part 28 can also be manufactured from titanium-doped quartz glass, for example, by pouring onto molten metal (float glass), pouring over a long breakaway edge, pressure sintering glass soot, or indirectly by gray body. These methods have the advantage that the upper part 28 can be manufactured from a sheet a few millimeters thick, which allows for good uniformity in terms of material parameters and may eliminate machining. To achieve a thermal expansion behavior similar to that of the lower part 27 in an upper part 28 made from such a sheet, the OH content of the sheet should deviate by a maximum of 5% from that of the lower part 27, and the titanium content of the sheet should deviate by a maximum of 0.05% from that of the lower part 27. For very thin sheets from which upper parts 28 with a thickness of less than 2 mm are manufactured, these requirements can be relaxed somewhat.

[0140] Once the lower part 27 and the upper part 28 are completed, they can be connected to each other in the region of their connecting surfaces 29, 30. The connection is performed in two steps. In the first step, the upper part 28 is ringed onto the lower part 27, i.e., brought very close to the lower part 27, so that the upper part 28 adheres to the lower part 27 as a result of van der Waals forces between the atoms of the lower part 27 and the atoms of the upper part 28. In this first step, which can be performed at room temperature, an intermediate product is produced, including the lower part 27 and the upper part 28. In the second step, the connection between the upper part 28 and the lower part 27 is strengthened by a bonding process, whereby covalent bonds are formed between the atoms of the lower part 27 and the atoms of the upper part 28, so that the upper part 28 and the lower part 27 are connected to each other very strongly and durably. The steps in the bonding process according to the invention and the preparations therefor are described in more detail below.

[0141] 5 shows a flow chart illustrating the procedure according to the invention when connecting the lower part 27 and the upper part 28. The lower part 27 and the upper part 28 can be manufactured in the manner described above in processes that proceed substantially in parallel or that proceed completely independently of each other in spatially and / or temporally separate processes.

[0142] To enable the formation of a durable connection, in step S1 the lower part 27 and the upper part 28 are cleaned, activated and dried, particularly in the area of ​​the connecting surfaces 29, 30. For example, the connecting surface 29 of the lower part 27 and the connecting surface 30 of the upper part 28 can be simultaneously cleaned, ablated and activated, for example by etching with hydrofluoric acid, sputtering or plasma treatment with a hydrogen or oxygen plasma.

[0143] In step S2, which follows step S1, the upper component 28 is ringed onto the lower component 27. To ring onto the lower component 27, the connecting surface 30 of the upper component 28 is brought very close to the connecting surface 29 of the lower component 27, so that a strong attractive force is generated as a result of van der Waals forces between atoms near the surface of the upper component 28 and atoms near the surface of the lower component 27, ultimately connecting the upper component 28 and the lower component 27 to each other. Because van der Waals forces only act over a very short distance, the connecting surface 30 of the upper component 28 and the connecting surface 29 of the lower component 27 must be brought very close together. This is possible within a relatively large surface area only if the connecting surfaces 30 of the upper component 28 and the connecting surfaces 29 of the lower component 27 are very smooth, have nearly identical shapes, and are largely free of contaminants. It is also very important to bring the connecting surfaces 30 of the upper component 28 and the connecting surfaces 29 of the lower component 27 close enough to prevent, as much as possible, the infiltration of air or other gases between the connecting surfaces 30, 29. These gas inclusions may also have adverse effects during subsequent use of the mirror 28. A possible ringing procedure is illustrated in Figure 6, which shows in schematic cross section a snapshot during the ringing of the upper part 28 onto the lower part 27, the cross section being taken along the section line CC shown in Figure 4, and therefore perpendicular to the longitudinal extent of the cooling channel 32.

[0144] In the illustrated exemplary embodiment, the connecting surface 29 of the lower component 27 and the connecting surface 30 of the upper component 28 have at least approximately complementary curvatures. As can be seen in FIG. 6 , rather than the connecting surface 30 of the upper component 28 being drawn to the connecting surface 29 of the lower component 27 in parallel alignment over the entire surface area, the connecting surfaces 29, 30 form an angle with respect to each other as they are brought together, initially meeting only in the peripheral area shown on the left side of FIG. 6 . The angle is exaggerated in FIG. 6 so that the effect can be seen. When the connecting surfaces are brought together, initially, contact between the upper component 28 and the lower component 27 is only in a small area of ​​the connecting surfaces 29, 30, so that initially only a relatively small contact surface 28 is formed between the upper component 28 and the lower component 27. Because van der Waals forces create an attractive effect within the contact surface 38, ringing of the connecting surface 30 of the upper component 28 against the connecting surface 29 of the lower component 27 occurs in the area of ​​the contact surface 38.

[0145] The upper part 28 then continues to pivot further toward the lower part 27, thereby moving closer to the lower part 27, resulting in an increase in the size of the contact surface 38. Accordingly, the surface area over which the upper part 28 rings against the lower part 27 also increases. The linear transition between the ringing region of the connecting surfaces 29, 30 and the non-ringing region of the connecting surfaces 29, 30 is hereinafter referred to as the ringing front. In the illustration of FIG. 6 , the ringing front extends perpendicular to the plane of the drawing and approximately parallel to the longitudinal extent of the cooling channel 32. This applies at least to the region where the ringing front passes through the plane of the drawing. The ringing front can be shaped as a straight line or a slight curve and moves from left to right as the upper part 28 is drawn to the lower part 27, i.e., the approach of the upper part 28 to the lower part 27 progresses continuously from left to right. The gradual approaching is also referred to below as "rolling", so in the illustration of Figure 6, the upper part 28 is rolled from left to right relative to the lower part 27. The direction of the rolling motion is indicated by an arrow in Figure 6 and is referred to below as the rolling direction 39.

[0146] The continuous wringing with the gradually moving linear wringing front has the effect that gas is continuously displaced from the intermediate space between the connecting surface 30 of the upper part 28 and the connecting surface 29 of the lower part 27, thereby significantly reducing the risk of gas ingress. The wringing action ends when the connecting surface 30 of the upper part 28 has wringed against the connecting surface 29 of the lower part 27 over its entire surface area.

[0147] In the case of exemplary embodiments in which the connecting surface 30 of the upper part 28 and the connecting surface 29 of the lower part 27 are not formed rotationally symmetrically, the connecting surface 30 of the upper part 28 is preferably rolled relative to the connecting surface 29 of the lower part 27 parallel to the direction in which the connecting surfaces 29, 30 have the smallest absolute value of the mean radius of curvature.

[0148] The escape of gas from the intermediate space between the connecting surface 30 of the upper part 28 and the connecting surface 29 of the lower part 27 can be facilitated to some extent by the fact that the connecting surface 30 of the upper part 28 and the connecting surface 29 of the lower part 27 do not have exactly the same curvature.

[0149] As can be seen in Figure 6, the rolling direction 39 extends transversely, in particular perpendicularly, to the longitudinal extent of the cooling channel openings 33 and the cooling channels 32. Because the thickness of the upper part 28 is significantly reduced in the region of the cooling channels 32, these regions act like joints, making the upper part 28 more flexible in these regions. As a result, only a relatively small force is required to temporarily keep the upper part 28 at a sufficiently large distance from the lower part 27 outside the contact surface 38 to prevent ringing from occurring there, and to keep the connecting surface 30 of the upper part 28 close to the connecting surface 29 of the lower part 27. Furthermore, in the region of the contact surface 38, a sufficient engagement is achieved with the connecting surface 30 of the upper part 28 tightly against the connecting surface 29 of the lower part 27, resulting in a very reliable ringing.

[0150] It is likewise possible to draw the upper part 28 onto the lower part 27 so that the rolling direction 39 runs parallel to the cooling channel openings 33 and the longitudinal extent of the cooling channels 32. In this embodiment, particularly reliable venting of the intermediate space between the upper part 28 and the lower part 27 is ensured, since the gas can escape along the cooling channel openings 33. The deformability in the rolling direction is reduced to some extent compared to the above-mentioned embodiment.

[0151] The wringing of the upper part onto the lower part in step S2 has the effect of producing an intermediate product comprising a lower part 27 and an upper part 28 rigidly connected to each other in the region of their respective connecting surfaces 29, 30. The intermediate product must meet various quality requirements and is only passed to a heat treatment, which will be described in more detail below, if it does not. Otherwise, the intermediate product is reworked or rejected. The quality requirements relate, for example, to the occurrence of inclusions between the connecting surfaces 29 and 30.

[0152] In step S3, which follows step S2, the intermediate product is stored at a storage temperature for a storage time. The storage time may be, for example, 24 hours. The storage temperature may be higher than room temperature, for example, 80°C, or preferably between 160°C and 400°C. In particular, the storage temperature may be between 250°C and 350°C. A heat lamp combined with storage at a constant storage temperature is also possible. Storage at high temperature has the effect that excess moisture diffuses away from the area of ​​the connecting surfaces 29, 30, especially via the cooling channel openings 33. Depending on the pre-treatment of the lower part 27 and the upper part 28 before ringing and the time between the production and further use of the intermediate product, step S3 may not be necessary, especially if the edge-to-edge distance between adjacent cooling channels 32 is small.

[0153] In step S4, which follows step S3, a heat treatment begins to form a highly durable connection between the lower part 27 and the upper part 28. The formation of the connection by heat treatment is also referred to below as bonding. In step S4, the intermediate product is placed in a bonding furnace, which ensures a temperature uniformity, for example better than 2 K. An air or inert gas atmosphere can be supplied to the bonding furnace. It is also possible to evacuate the bonding furnace and perform the heat treatment under vacuum conditions. In the bonding furnace, the intermediate product is heated to a holding temperature at a heating rate of less than 150 K / h, preferably less than 100 K / h. The holding temperature is in the range of 400 °C to 900 °C, with temperatures above 500 °C, in particular above 600 °C, and more particularly above 700 °C being preferred.

[0154] This is followed by a step S5 in which the intermediate product is kept at a holding temperature for a holding time, which may be 8 hours or more, in particular 12 hours or more or 20 hours or more.

[0155] In step S6, the intermediate product is cooled and its temperature is reduced from the holding temperature. Cooling can be performed in multiple stages, with different cooling rates. For example, the temperature of the intermediate product can be initially reduced at a cooling rate of less than 100 K / h or less than 50 K / h, particularly between 1 K / h and 20 K / h, until a temperature of 700°C or 600°C is reached. Below 700°C or 600°C, the temperature can be reduced more rapidly, for example, at a cooling rate of less than 150 K / h, particularly between 5 K / h and 100 K / h or between 20 K / h and 100 K / h. Once a temperature of, for example, 500°C or 400°C is reached, the cooling rate restriction can be completely abandoned, and cooling can continue at any cooling rate until room temperature is reached. Cooling can be performed in either case, for example, by reducing the temperature of the gas surrounding the intermediate product and / or the temperature of other surrounding areas to a value below the temperature of the intermediate product. Step S6 completes the flow chart.

[0156] When setting the heat treatment parameters, particularly the holding temperature and cooling rate, it should be noted that these parameters can affect the zero-cross temperature and the increase in the thermal expansion coefficient of the mirror 26 manufactured using these parameters. These material properties are generally already set to desired values ​​during the manufacturing of the materials used for the lower part 27 and the upper part 28, but they can change again during the heat treatment. Therefore, if low tolerances are required for the zero-cross temperature and the increase in the thermal expansion coefficient of the mirror 26, it is not enough to simply use a material that meets these manufacturing requirements. Additionally, it is necessary to carefully plan the heat treatment of the intermediate product, taking into account the possible influence of the mentioned parameters. In this regard, it should be noted that the influence of the heat treatment on the zero-cross temperature and the increase in the thermal expansion coefficient depends on the material composition of the intermediate product, particularly its OH and titanium content. Therefore, to achieve low tolerances, the OH and titanium content should be taken into account. If this is not known accurately enough, measurements can be performed in the method according to the present invention to determine the OH and titanium content. Furthermore, measurements can be performed before the heat treatment to determine the actual zero-cross temperature and the actual thermal expansion coefficient of the intermediate product. Some of these measurements are not non-destructive and are therefore performed not on the intermediate product itself but on an associated test specimen, i.e., a piece of material from which the intermediate product is made. The associated test specimen undergoes the same heat treatment as the intermediate product, and if the lower part 27 and the upper part 28 are already heat treated before the intermediate product is formed, this is also performed on the associated test specimen. If the lower part 27 and the upper part 28 are made from different blanks, test specimens can be prepared for the lower part 27 and the upper part 28, respectively.

[0157] The heat treatment profile, i.e. the intended change in temperature of the intermediate product over time, is then determined individually for each intermediate product or for a group of intermediate products with similar material properties from the known or measured material properties, where the cooling profile, in particular the cooling rate used, is of particular importance.

[0158] In this way, mirrors 26 can be manufactured with average zero-cross temperatures that deviate from the desired zero-cross temperature by a maximum of + / - 1 K. Maximum deviations of + / - 0.5 K or + / - 0.2 K are also possible. In each case, these values ​​relate to the zero-cross temperature averaged over a volumetric area of ​​mirror 26 that laterally overlaps optical surface 31 and extends from optical surface 31 to a depth of 1 cm. This volumetric area can equally extend from optical surface 31 to a depth of 1 cm below cooling channel 32 or cooling channel 31. In the illustration of FIG. 3, extending to cooling channel 32 means extending to the upper edge of cooling channel 32, and extending 1 m below cooling channel 32 means extending 1 cm below the lower edge of cooling channel 32. In this volumetric area, the predetermined value can in each case increase with increasing distance from optical surface 31.

[0159] A further challenge in heat treatment is ensuring that the entire volume of the intermediate product is treated according to the intended heat treatment profile. For example, the peripheral regions of the intermediate product respond much faster to cooling applied from the outside than the core region, and therefore cool much faster. This problem is somewhat mitigated in that it is not necessary to achieve approximately the same temperature throughout the volume of the intermediate product at all times during cooling. Indeed, the predetermined cooling profile, i.e., the time-dependent decrease in temperature, should be maintained as precisely as possible at each location of the intermediate product. However, time differences between individual locations are also acceptable. Therefore, cooling is controlled so that the cooling profile is maintained locally in each case. To this end, the cooling rate is adapted stepwise during cooling, possibly multiple times over several hours, to achieve this goal. This adaptation can last, for example, from 1 to 6 hours.

[0160] In particular, it should be ensured that the moving average value of the cooling rate, formed in 20 K temperature intervals, throughout the volume of the intermediate product has the same relative variation over time in the temperature range from 900 °C to 700 °C, with a deviation of at most 2 K / h. That is, cooling should be performed so that the difference in the variation over time of this moving average value at all locations of the intermediate product, taking into account potential time differences, is at most 2 K / h. Preferably, the deviation of the moving average value in the temperature range from 900 °C to 700 °C is at most 1 K / h. Furthermore, the deviation of the moving average value in the temperature range from 700 °C to 500 °C may be at most 4 K / h, preferably at most 2 K / h. The ultimate goal of these measures is to achieve a zero-cross temperature nonuniformity due to the heat treatment of at most + / - 1 K, preferably at most + / - 0.5 K, within the volume area of ​​the mirror 26 that laterally overlaps with the optical surface 31 and extends to a depth of 1 cm below the optical surface 31. It is equally possible for this volume area to extend up to the cooling channel 32 or up to 1 cm below the cooling channel 32 .

[0161] The heat treatment is intended to achieve a tensile strength of the connection between the lower part 27 and the upper part 28 of 50 MPa or more.

[0162] In one variant, the lower part 27 and the upper part 28 are crimped together during the heat treatment.

[0163] The joining process described above is equally possible without wringing: in that case the procedure is analogously identical, and the individual steps must be performed on the lower part 27 and the upper part 28, which are not intermediate products but are not connected to each other by wringing.

[0164] After the joining process, the upper part 28 may be machined to a thickness of 2 mm to 10 mm above the cooling channels 32 .

[0165] After or instead of the processing step of reducing the thickness of the upper part 28, the upper part 28 is reprocessed so that the side opposite the connecting surface 30, on which the optical surface 31 will be formed, has a highly precise shape and meets predetermined roughness criteria. The optical surface 31 is then formed there. This can be done, for example, by applying an aluminum layer or by applying alternate layers of molybdenum and silicon. [Explanation of symbols]

[0166] 1. Projection exposure equipment 2. Lighting system 3 Radiation source 4. Illumination optical unit 5 Object field of view 6 Object plane 7 Reticle 8 Reticle Holder 9 Reticle Displacement Drive 10 Projection optical unit 11 Image field 12 Image plane 13 wafers 14 wafer holder 15 Wafer Displacement Drive 16 Lighting Radiation 17 Collector 18 Intermediate focal plane 19 Deflecting mirror 20 First Facet Mirror 21 First Facet 22 Second Facet Mirror 23 Second Facet 24 Cooling device 25 Control device 26. Mirror 27 Lower parts 28 Upper part 29 Connection Surface 30 Connection Surface 31 Optical surface 32 cooling channels 33 Cooling channel opening 34 Distribution Channels 35 Collection Channel 36 Fluid distribution section 37 Fluid recovery section 38 Contact surface 39 Rolling Direction M mirror M1 mirror M2 mirror M3 mirror M4 mirror M5 mirror M6 mirror

Claims

1. A method for manufacturing a mirror (26) of a microlithography projection exposure apparatus (1), comprising the steps of: providing a first mirror part (27) and a second mirror part (28), the first mirror part (27) and the second mirror part (28) being in contact in the region of a first connecting surface (29) of the first mirror part (27) and a second connecting surface (30) of the second mirror part (28); heating the first mirror component (27) and the second mirror component (28) to a holding temperature of 400°C or more and holding the first mirror component (27) and the second mirror component (28) at the holding temperature for a holding time to form a durable bond between the first mirror component (27) and the second mirror component (28); After the hold time has elapsed, the first mirror part (27) and the second mirror part (28) are cooled to a first cooling temperature at a first cooling rate of up to 100 K / h.

2. 2. The method according to claim 1, wherein the first mirror part (27) and the second mirror part (28) are provided in the form of an intermediate product produced by wringing together a first connecting surface (29) of the first mirror part (27) and a second connecting surface (30) of the second mirror part (28).

3. 3. The method according to claim 1 or 2, wherein, prior to heating to the holding temperature, the intermediate product is stored at a storage temperature of 80°C or higher and 400°C or lower for a storage time of 2 hours or longer.

4. The method according to any one of claims 1 to 3, wherein the first mirror part (27) and the second mirror part (28) are heated to a holding temperature of up to 900°C.

5. The method according to any one of claims 1 to 4, wherein the first mirror part (27) and the second mirror part (28) are heated to the holding temperature at a heating rate of up to 150 K / h.

6. 6. The method according to any one of claims 1 to 5, wherein the holding time is 8 hours or more.

7. The method according to any one of claims 1 to 6, wherein the first cooling temperature is 700°C or less.

8. 8. The method according to any one of claims 1 to 7, wherein after cooling to the first cooling temperature at the first cooling rate, the first mirror part (27) and the second mirror part (28) are cooled to a second cooling temperature lower than the first cooling temperature at a second cooling rate higher than the first cooling rate.

9. 9. The method according to any one of claims 1 to 8, wherein the first mirror part (27) and the second mirror part (28) are cooled in such a way that, over the entire volume of the first mirror part (27) and / or the second mirror part (28), a moving average value of the cooling rate formed in a temperature interval of 20 K has the same relative variation over time in the temperature range from 900 °C to 700 °C, except for a deviation of up to 2 K / h.

10. 10. The method according to any one of claims 1 to 9, wherein the first cooling rate and / or the second cooling rate are selected depending on a material composition of the first mirror part (27) and / or the second mirror part (28).

11. The method of any one of the preceding claims, wherein the first cooling rate and / or the second cooling rate are selected in response to a desired average zero cross temperature of the mirror (26).

12. The method according to any one of claims 1 to 11, wherein a material sample of the material from which the first mirror part (27) and / or the second mirror part (28) are manufactured is analyzed to determine the first cooling rate and / or the second cooling rate.

13. A mirror of a microlithography projection exposure apparatus (1), comprising: a first mirror component (27); a second mirror component (28); an optical surface (31) that reflects light; wherein the first mirror component (27) and the second mirror component (28) are durably connected to each other by heat treatment in the region of a first connecting surface (29) of the first mirror component (27) and a second connecting surface (30) of the second mirror component (28), The mirror (26) has, within a volumetric area laterally overlapping the optical surface (31) and extending to a depth of 1 cm from the optical surface (31), an average zero cross temperature that deviates from a predetermined value by a maximum of + / - 1 K.

14. An illumination optical unit comprising a mirror (26) manufactured by the method of any one of claims 1 to 12 and / or formed as claimed in claim 13.

15. A projection optical unit comprising a mirror (26) manufactured by the method of any one of claims 1 to 12 and / or formed as claimed in claim 13.

16. 16. A microlithography projection exposure apparatus comprising an illumination optical unit (4) according to claim 14 and / or a projection optical unit (10) according to claim 15.

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