METHOD FOR PRODUCING A MIRROR FOR A LITHOGRAPHY SYSTEM

Description

[0001] The invention relates to a method for producing a mirror for a lithography system. The lithography system is, in particular, an EUV or DUV lithography system.

[0002] Reference is made to the content of priority applications DE 10 2015 204 454.8 and DE 10 2015 224 281.1.

[0003] Lithography systems are used, for example, in the manufacture of integrated circuits (ICs) to image a mask pattern in a mask (also called a reticle) onto a substrate, such as a silicon wafer. In particular, such lithography systems comprise an illumination device and a projection lens. The image of the mask illuminated by the illumination device is projected by the projection lens onto the substrate coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection lens, in order to transfer the mask pattern onto the light-sensitive layer of the substrate.

[0004] In projection lenses designed for the EUV range, i.e., at wavelengths of approximately 13 nm, for example, mirrors are used as optical components for the imaging process due to the lack of suitable translucent materials. One problem that arises is that the mirrors heat up and experience associated thermal deformation due to the absorption of the radiation emitted by the EUV light source (exposure of the mask) as well as due to other heat sources. These thermal deformations—both locally in the area of ​​the optical surface being exposed and in the entire mirror—result as a function of the heat flux distribution and the material-dependent thermal expansion coefficient. These optical deformations, in turn, can impair imaging using the projection lens. The problem of thermal deformation is not limited to EUV lithography systems.Rather, this problem also exists in conventional lithography systems that, for example, use ArF excimer lasers and, in particular, operate with a wavelength of 192 nm and a combination of corresponding lenses and mirrors as optical elements.

[0005] WO 2014 / 139763 A2 shows a reflector device with a reflector and an arrangement of thermoelectric heat pumps that are thermally connected to the reflector. Furthermore, the reflector device comprises a control device configured to control the thermoelectric heat pumps and determine a temperature of the reflector from a measured voltage at at least one of the thermoelectric heat pumps. Furthermore, DE 10 2013 201 805 A1 shows a lithography system comprising an optical element, a cooling device for cooling the optical element with at least one cooling element, and an actuator for displacing the cooling element and the optical element relative to one another.

[0006] Furthermore, EP 0 532 236 A1 shows a system for stabilizing the shapes of optical elements, an exposure device using this system and a method for manufacturing semiconductor devices.

[0007] Against this background, it is an object of the present invention to provide a method for producing a mirror in which the deformation of the mirror in the exposure process of the lithography system is as small as possible.

[0008] This problem is solved by the features of the independent claim. A method for producing a mirror for a lithography system is proposed, comprising the following steps. In a first step a), an expected heat flow distribution on the mirror is determined. In a second step b), a plurality of heating zones are formed on the mirror depending on the determined heat flow distribution. In a third step c), a respective heating zone is provided with a respective heating device for heating the respective heating zone depending on a detected temperature of the respective heating zone or the expected heat flow distribution on the mirror.

[0009] Advantageously, with a mirror manufactured in this way, the temperature in all heating zones of the mirror can be kept constant or nearly constant. This allows mirror deformations due to heating, especially due to varying degrees of heating in different heating zones of the mirror, to be avoided or almost avoided. In particular, different heating zones can be preheated to different degrees (if necessary only shortly before "starting exposure") before the wafer is exposed to the lithography system, thus heating the mirror by the radiation from the lithography system for exposure. The different heating zones can be preheated both before the wafer exposure is switched on for the first time and before or during switching between two different illumination settings and / or reticle changes, or the heating of the heating zones can be adjusted.

[0010] In the first step a), the expected heat flow distribution on the mirror is determined, preferably through calculations and / or simulations based on models. The expected heat flow distribution on the mirror is therefore the distribution determined using models and calculations and / or simulations based on these models. This allows the heating zones on the mirror to be selected in the second step b) so that areas with particularly high temperatures, so-called heat flow poles, are appropriately distributed among the heating zones. This then makes it possible to achieve a constant temperature distribution in the mirror body of the mirror by appropriately heating the individual heating zones. Using the heating devices provided in the third step c) for heating the respective heating zones, each heating zone can be heated depending on the respectively recorded temperature or depending on the expected heat flow distribution.This allows a constant temperature to be achieved in each heating zone. If a heat flow distribution has been determined for each heating zone, the heating system can respond to the heat flow distribution with an appropriate heating pattern.

[0011] The mirror body of the mirror can additionally be cooled by means of a device for reducing the mirror temperature in order to reduce or adjust the temperature level of the mirror body as a whole.

[0012] In other words, one of the insights underlying the present invention is that typical heat flow distributions on the mirror during exposure operation of the lithography system correspond to a pattern that can be easily divided into a few distinctly hot and (in comparison) distinctly cold zones. The temperature of a respective (heating) zone can then be detected with little effort (just one temperature sensor per heating zone may be sufficient) and controlled by heating and / or cooling in such a way that the deformation of the mirror and thus any image aberration of the mirror are minimized. IR cameras can also be used for temperature measurement. Alternatively, the temperature is not measured; instead, the expected heat flow distribution is used to adjust the temperature of the individual heating zones accordingly.

[0013] The expected heat flow distribution is determined based on the structure to be imaged on the wafer. Depending on the reticle and the structures to be imaged on the wafer using the lithography system, a different heat flow or heat flow distribution on the mirror results.

[0014] The expected heat flow distribution encompasses several heat flow poles. By using multiple heating zones, the heat flow distribution can be individually addressed with one or more heat flow poles. The heat flow poles are a few zones with high heat input that stand out clearly from the surrounding zones with lower heat input.

[0015] Each heating zone is assigned exactly one heat flow pole. Advantageously, each heat flow pole can be located in a separate heating zone. This allows the temperature of each heating zone to be kept constant, as heating of a heating zone can be tailored to each heat flow pole. Furthermore, each heating zone can be assigned exactly one heat flow pole.

[0016] According to a further embodiment of the method, the expected heat flow distribution has an X-dipole, a Y-dipole, and / or a DRAM profile. The expected heat flow distribution can, in principle, be any desired heat flow pattern.

[0017] According to a further embodiment of the method, between 3-10, 3-20, 3-30 or 3-100 heating zones are formed. It is also possible to form 3-200 heating zones. In principle, it is desirable to ensure the most constant temperature distribution possible within the mirror volume with as few heating zones as possible. The fewer heating zones formed, the simpler the thermal conditioning of the mirror and thus the production of the conditioning unit. In most cases, a good result can be achieved with 3-10 heating zones. For example, each heating zone can have an area greater than 5 cm², preferably greater than 10 cm², and even more preferably greater than 100 cm².

[0018] According to a further embodiment of the method, the mirror has an optically active region and an optically inactive region, and preferably one or more heating zones are formed in the optically active region and / or the optically inactive region. Both the optically active region and the optically inactive region can have one or more heating zones. The aim is to achieve the most constant temperature distribution possible throughout the entire mirror body by using multiple heating zones.

[0019] According to a further embodiment of the method, between 3 and 10 ,Preferably, between 4 and 9 heating zones are formed, and / or at least one heating zone is formed in the optically inactive region. Generally, this number of heating zones is sufficient to achieve a constant temperature throughout the entire mirror body. For example, seven heating zones can be formed on the front side of the mirror, two heating zones on the side of the mirror, and five heating zones on the back of the mirror. This results in a total of fourteen heating zones.

[0020] According to a further embodiment of the method, the mirror comprises a mirror body which has the optically active region on its end face, wherein an annular edge region comprising the optically active region, a lateral surface of the mirror body and / or an end face opposite the end face has the optically inactive region.

[0021] Each heating zone is equipped with a temperature sensor to measure the temperature of that heating zone. The temperature sensors can be used to determine the temperature of each heating zone. If multiple temperature sensors are used per heating zone or a thermal camera is used to measure the temperature of a heating zone, the temperature distribution within that heating zone can also be determined. The thermal camera can be an infrared camera, in particular.

[0022] According to a further embodiment of the method, the mirror is provided with a device for reducing the mirror temperature for cooling a mirror body of the mirror. Due to the heating of the individual heating zones, the temperature of the mirror body of the mirror is increased overall. To lower the overall temperature level of the mirror body, a device for reducing the mirror temperature can be provided. The device for reducing the mirror temperature can be designed as a heat sink arranged at a distance from the mirror body. Alternatively or additionally, the device for reducing the mirror temperature can also be designed as an enlargement of the surface of the mirror.

[0023] Furthermore, a method for operating a lithography system is proposed, wherein the lithography system comprises at least one mirror manufactured according to the method for manufacturing the mirror as described. The method for operating a lithography system comprises the following step. In this step, the respective heating zone is heated by means of the respective heating device such that the temperature of each heating zone remains constant.

[0024] If necessary, each heating zone can be heated to a specified temperature.

[0025] Advantageously, with the lithography system operated in this way, the temperature of the mirror can be kept constant or nearly constant in all heating zones of the mirror, and thus in the mirror volume. This allows mirror deformations or imaging errors due to heating, particularly heating to varying degrees in different heating zones of the mirror, to be avoided or nearly avoided. In particular, different heating zones can be preheated to different degrees before (especially shortly before) the exposure of the wafer of the lithography system begins, thus heating the mirror by the radiation from the lithography system for exposure begins.

[0026] The expression "the temperature of each heating zone remains constant" means that the temperature difference that occurs when the wafer is exposed for the first time as well as when switching between two different illumination settings is less than 15K, preferably less than 5K and even more preferably less than 1K.

[0027] According to one embodiment of the method, each heating zone is heated independently of any other heating zone. This ensures that each heating zone can be heated individually so that the temperature of the mirror body remains constant overall in all heating zones.

[0028] According to a further embodiment of the method, heating is carried out at variable times for one or more of the heating zones. Advantageously, the heating of the heating zones can be adjusted as needed to keep the temperature of the mirror, in particular of the entire mirror body, constant.

[0029] According to a further embodiment of the method, the heating zones are heated during an exposure operation of the lithography system. Furthermore, the heating zones can be heated before the start of the exposure and / or after the start of the exposure.

[0030] According to a further embodiment of the method, the heating zones are preheated before exposure. The heating zones can be preheated to varying degrees before the wafer is exposed in the lithography system, and thus before the mirror is heated by the radiation from the lithography system for exposure. This ensures that no significant temperature jumps occur on or in the mirror when the wafer is exposed. The heat input in the heating zones can be adjusted at any time to achieve optimal optical performance.

[0031] According to a further embodiment of the method, at least one heating device heats the corresponding heating zone with a pattern. Advantageously, the pattern precisely corresponds to the heat flow distribution, so that the temperature within the heating zone can be kept constant.

[0032] According to a further embodiment of the method, the pattern has a ring profile or part of a ring profile. Heating with such a pattern advantageously allows the temperature of one or more heating zones or of the mirror body to be kept constant.

[0033] The mirror for a lithography system produced by the method has a plurality of heating zones which are formed depending on an expected heat flow distribution, and a plurality of heating devices, wherein each heating zone is assigned a heating device for heating the respective heating zone depending on a detected temperature of the respective heating zone or the expected heat flow distribution on the mirror.

[0034] Advantageously, the temperature can be kept constant or nearly constant in all heating zones of the mirror. This allows mirror deformations or imaging errors due to heating, especially due to varying degrees of heating in different heating zones of the mirror, to be avoided or virtually avoided. In particular, different heating zones can be preheated to different degrees before the exposure of the wafer of the lithography system, and thus the heating of the mirror, begins.

[0035] According to one embodiment, at least one heating device comprises a heat radiator and / or a heating resistor. Advantageously, the heating device can heat the corresponding heating zone of the mirror using heat rays and / or a heating resistor.

[0036] The manufactured mirror comprises a temperature sensor for each heating zone for detecting the temperature of a respective heating zone. Advantageously, the temperature of a heating zone can be measured with one temperature sensor.

[0037] According to a further embodiment, the mirror to be manufactured comprises a mirror body and a device for reducing the mirror temperature for cooling the mirror body. Advantageously, the temperature level of the mirror body can be lowered by means of the device for reducing the mirror temperature.

[0038] According to a further embodiment, the device for reducing the mirror temperature comprises a heat sink arranged at a distance from the mirror body. Heat can be transferred from the mirror body to the heat sink via a gas atmosphere and / or via thermal radiation. Advantageously, the mirror body and the heat sink are not in mechanical contact with one another in order to avoid mechanical contact between the heat sink and the mirror body, so that, for example, no vibrations can be transferred from the heat sink to the mirror body. According to a further embodiment, the mirror body has several zones. Furthermore, the heat sink is divided into several segments in order to cool the individual zones separately. Advantageously, the individual segments can be arranged such that a uniform temperature level can be achieved in the mirror body.

[0039] According to a further embodiment, the device for reducing the mirror temperature comprises a region of the mirror in which a surface is enlarged compared to a smooth surface due to the shape of the surface. Advantageously, the larger the surface area of ​​the mirror, the better it can dissipate heat.

[0040] The embodiments and features described for the proposed methods apply correspondingly to the manufactured mirror, and vice versa. The manufactured mirror can be used in a projection system for a lithography system.

[0041] The lithography system comprises the manufactured mirror as described and / or a projection system with the manufactured mirror. In particular, the lithography system can also comprise multiple mirrors as described. Further possible implementations of the invention also include combinations of features or embodiments described previously or below with respect to the exemplary embodiments that were not explicitly mentioned. In this case, the person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention. The invention is defined by the appended claims.

[0042] Advantageous embodiments and aspects of the invention are the subject of the dependent claims and the exemplary embodiments of the invention described below. The invention will be explained in more detail below using preferred embodiments with reference to the accompanying figures. Fig. 1 shows a schematic view of an EUV lithography system; Fig. 2 shows a comparison of the RMS deformation of the optical surface of two mirrors; Fig. 3 shows a further comparison of the RMS of the deformation of the optical surface of two mirrors; Fig. 4 shows a principle of preheating; Fig. 5A, 5B and 5C show different heat flow distributions of a mirror; Fig. 6 shows a mirror with several heating zones; Fig. 7 shows a section VII - VII from Fig. 6 ; Fig. 8 shows the mirror Fig. 6 and 7 in the vicinity of a lens of a lithography system; Fig. 9 shows a schematic representation of a mirror with different heating zones; Fig. 10 shows a section X - X from Fig. 9 ; Fig. 11 shows several heating zones on the back of the Fig. 9 und 10 depicted mirror; Fig. 12 shows a flow chart of a method for producing a Fig. 6 , 7 , 9, 10 and 11 depicted mirror; Fig. 13 shows a mirror in the vicinity of a lens of a lithography system as in Fig. 8 with a heat sink; Fig. 14 shows the mirror in the vicinity of a lens of a lithography system from Fig. 13 with a heat sink divided into several segments; Fig. 15 shows an enlarged view of area XV of the mirror from Fig. 13 ; and Fig. 16 shows an enlarged view of area XV of the mirror from Fig. 13 with an alternative interface.

[0043] Unless otherwise indicated, identical reference numerals throughout the figures designate identical or functionally equivalent elements. Furthermore, it should be noted that the illustrations in the figures are not necessarily to scale.

[0044] Fig. 1 shows a schematic view of an EUV lithography system 100 according to an embodiment, which includes a beam-shaping system 102, an illumination system 104, and a projection system 106. The beam-shaping system 102, the illumination system 104, and the projection system 106 are each provided in a vacuum housing, which is evacuated using an evacuation device (not shown in detail). The vacuum housings are surrounded by a machine room (not shown in detail), in which the drive devices for mechanically moving or positioning one or more optical elements are provided. Furthermore, electrical controls and the like can also be provided in this machine room.

[0045] The beam-shaping system 102 comprises an EUV light source 108, a collimator 110, and a monochromator 112. The EUV light source 108 can be, for example, a plasma source or a synchrotron, which emits radiation in the EUV range (extreme ultraviolet range), i.e., e.g., in the wavelength range from 0.1 nm to 30 nm. The radiation emitted by the EUV light source 108 is first focused by the collimator 110, after which the desired operating wavelength is filtered out by the monochromator 112. Thus, the beam-shaping system 102 adjusts the wavelength and spatial distribution of the light emitted by the EUV light source 108. The EUV radiation 114 generated by the EUV light source 108 has a relatively low transmissivity through air, which is why the beam guidance spaces in the beam shaping system 102, the illumination system 104 and the projection system 106 are evacuated.

[0046] In the illustrated example, the illumination system 104 comprises a first mirror 116 and a second mirror 118. These mirrors 116, 118 can be configured, for example, as facet mirrors for pupil shaping and direct the EUV radiation 114 onto a photomask 120.

[0047] The photomask 120 is also designed as a reflective optical element and can be arranged outside the systems 102, 104, 106. The photomask 120 has a structure that is imaged in a reduced size onto a wafer 122 or the like by means of the projection system 106. For this purpose, the projection system 106 has, for example, a third mirror 124 and a fourth mirror 126 in the beam guidance space. It should be noted that the number of mirrors of the EUV lithography system 100 is not limited to the number shown, and more or fewer mirrors can also be provided. Furthermore, the mirrors are usually curved at their front side for beam shaping.

[0048] The projection optics in projection system 106 are shown in an extremely simplified manner with the two mirrors 124, 126. The projection optics preferably comprise several mirrors, e.g., six to nine mirrors. The frontmost mirror 124 of a projection optics in the beam path after the reticle 120 heats up particularly rapidly. This is partly because the light impinges on it perpendicularly (normal incident mirror). Therefore, the following will discuss the frontmost mirror 124 (hereinafter referred to as mirror 124) of the projection optics.

[0049] Fig. 2 shows a comparison of the deformation of two mirrors 124. A mirror 124 that is not thermally manipulated is compared with a mirror 124 that uses the "Advanced Wavefront Correction" method. "Advanced Wavefront Correction" means that a thermoelastic deformation of the mirror 124 occurs to compensate for imaging errors. Fig. 2 The root-mean-square (RMS) of the deviation d of the surface deformation of the optical surface from its deformation at time t = 0 is plotted against time t. The deformation at time t = 0 is set to zero. The greater the deformation, the greater the deviation d. At time t = 0, the exposure by the EUV radiation of the two mirrors 124 to be compared begins. The upper curve in Fig. 2 is the curve of the non-thermally manipulated mirror. How to Fig. 2 As can be seen, the non-thermally manipulated mirror experiences a strong deformation or a strong change in deformation after the onset of EUV exposure. This strong deformation or change in deformation is due to the formation of heat flux poles. As the lower curve shows, the deformation or change in deformation can be reduced using the "Advanced Wavefront Correction" method. Thus, the lower curve can remain below a maximum permissible value of the RMS(d), which is Fig. 2 symbolized by the dashed line.

[0050] Fig. 3 shows a further comparison of the deformation of two mirrors 124. Shown is the root mean square (RMS) deviation d of the surface deformation of the optical surface from its deformation at time t = 0 for a mirror 124 that is not preheated (upper curve) and for a mirror 124 that is preheated (lower curve). "Preheated" means that the mirror 124 is heated before the EUV exposure of the mirror 124 begins, i.e., before time t = 0, so that the temperature difference when the exposure starts is not so great. An initial strong deformation or change in deformation of the mirror 124 that is not preheated can be seen. If the mirror 124 is preheated, the initial deformation or change in deformation of the mirror 124 is significantly weaker.

[0051] Fig. 4 shows a principle of preheating. Before a mirror 124 is exposed, ie in the time range t < 0, the mirror 124 is heated with a heat flow Q̇ MPH (mirror pre-heating, MPH). At time t = 0, the exposure of the mirror 124 begins. The exposure of the mirror 124 results in a heat flow Q̇ EUV (extreme ultraviolet, EUV) onto the mirror 124. To ensure that the heat flow onto the mirror 124 is always constant, the heat flow Q̇ MPH at time t = 0 by the amount Δ Q̇ MPH reduced. The heat flow Q̇ EUV increases by Δ Q̇ EUV . The total heat flux absorbed by mirror 124 changes in such a way that the mirror temperature does not change, if possible.

[0052] The Figuren 5A, 5B and 5Cshow EUV heat flux distributions 518 on a mirror 124. The mirror 124 has a mirror body 500. On the mirror body 500, an optically active region 502 and an optically inactive region 504 can be seen. The optically active region 502 is the region of the mirror 124 where the EUV radiation is reflected. Furthermore, the Figuren 5A, 5B and 5C The mirror 124 shown has three holding devices 506, with a bore 508 leading through each holding device 506 for fastening the mirror 124 to a mirror holder.

[0053] Depending on the structure to be imaged on the wafer 122, a different heat flow distribution 518 results on the mirror 124. Fig. 5A shows a mirror 124 with an X-dipole 512 heat flow distribution 518 and Fig. 5B shows a mirror 124 with a Y-dipole 514 heat flow distribution 518. Further shows Fig. 5C a mirror 124 with a "DRAM 516 heat flow distribution 518," i.e., with a heat flow distribution 518 that arises during the exposure of a wafer 122 for the production of DRAM. Calculations and / or simulations based on models can be used to determine which heat flow distribution 518 is to be expected on the mirror 124. The expected heat flow distribution 518 is the heat flow distribution 518 that is determined based on models as well as calculations and / or simulations based on these models.

[0054] Based on the knowledge of the expected heat flow distribution 518, heating zones HZ can be selected to match this heat flow distribution 518. Fig. 6 shows a mirror 124 with several heating zones HZ1 - HZ8. As in Fig. 6 As can be seen, the optically active area 502 is divided into five heating zones HZ1 - HZ5. The heating zones HZ6 - HZ8 are located in the optically inactive area 504. The heating zone HZ6 and the heating zone HZ7 are arranged in a ring around the optically active area 502. The heating zone HZ6 is located to the right and left of the optically active area 502. In contrast, the heating zone HZ7 is located above and below the Fig. 6 The heating zone HZ6 can be divided into two heating zones, HZ6a and HZ6b, and the heating zone HZ7 can be divided into two heating zones, HZ7a and HZ7b. The heating zone HZ8 is formed as an outer ring around the ring of heating zones HZ6 and HZ7.

[0055] By knowing the expected heat flux distribution 518, the heating zones HZ1-HZ8 can be formed on the mirror such that heat flux poles 510, i.e., regions with particularly high temperatures, are suitably distributed among the heating zones HZ1-HZ8. The present example shows a heat flux distribution 518 with an X and a Y dipole 512, 514, which results from a wafer-specific illumination setting. Each heat flux pole 510 is assigned to exactly one heating zone HZ2-HZ5. The remaining heating zones, in contrast, are "cold" heating zones, i.e., they do not contain a heat flux pole 510 during exposure operation.

[0056] Thus, by appropriately heating the individual heating zones HZ1-HZ8, a constant temperature distribution can be achieved in the mirror body 500 of the mirror 124. "Constant" here means that the temperature of a heating zone, as measured by a temperature sensor, remains within a specific temperature difference. The maximum temperature difference that may occur when the wafer exposure is first switched on, before and after switching on, as well as when switching between two different illumination settings, is less than 15 K, preferably less than 5 K, and even more preferably less than 1 K. A temperature difference within the optically active region 502 is less than 3 K, preferably less than 0.5 K, and particularly preferably less than 0.1 K. This prevents thermally induced imaging errors of the mirror 124 that exceed a specified value.

[0057] In particular, the individual heating zones HZ1 - HZ8 can be heated separately. Furthermore, the individual heating zones HZ1 - HZ8 can be heated at variable times, e.g., the individual heating zones HZ1 - HZ8 can be preheated.

[0058] Fig. 7 shows a section VII - VII from Fig. 6 . The mirror 124 with the mirror body 500 is shown. The mirror body 500 can be designed as a monolith. On the left side of the Fig. 7 A holding device 506 with an associated bore 508 is shown. The mirror body 500 contains several bores 700 in the form of blind holes, which are introduced into the mirror body 500 from a rear end face (opposite the front end face with the optically active region 502). Temperature sensors 702 are located in the bores 700. The temperature sensors 702 are mounted close to the respective heating zone HZ1 - HZ8 so that they can measure the temperature of the respective heating zone HZ1 - HZ8 as accurately as possible.

[0059] As in Fig. 7 As shown, a temperature sensor 702 is provided for each heating zone HZ1 - HZ8. This allows a temperature to be determined for each heating zone HZ1 - HZ8. Alternatively, multiple temperature sensors 702 can be used per heating zone HZ1 - HZ8. With multiple temperature sensors 702 for a heating zone HZ1 - HZ8, a temperature profile for this heating zone HZ1 - HZ8 can be created. By knowing the temperature profile of a heating zone HZ1 - HZ8, this heating zone HZ1 - HZ8 can be heated with an appropriate heating pattern. Such an approach can even better prevent temperature fluctuations within a heating zone HZ1 - HZ8. A heating pattern can also extend across multiple heating zones HZ1 - HZ8.

[0060] Alternatively or in addition to the temperature sensors 702, a thermal camera can record the temperature distribution for one or more heating zones HZ1 - HZ8. A thermal camera can also be used to create a temperature profile for one or more heating zones HZ1 - HZ8.

[0061] Fig. 8 shows the mirror 124 from Fig. 6 and 7 in the vicinity of a lens of a lithography system. A housing 800 is also shown. The beam path is located within the housing 800 in the so-called mini-environment. The radiation that strikes the mirror 124 during the exposure of a wafer 122 generates a heat flow. Q̇ EUV. This radiation strikes the optically active region 502 of the mirror 124 and heats it, since the radiation is not completely reflected. To prevent thermally induced deformation of the mirror 124 over time, the temperature of the entire mirror 124, i.e., all temperatures of the individual heating zones HZ1 - HZ8, should be constant. For this purpose, the individual heating zones HZ1 - HZ8 are individually heated with the respective heating devices HE1 - HE8, in particular with heat radiators 804, so that all heating zones HZ1 - HZ8 of the mirror 124 have the same temperature before, during, and after exposure of the wafer 122 (nevertheless, the temperatures in different heating zones HZ1 - HZ8 can be different). The individual heating devices HE1 - HE8 can be combined in heating devices 802. In Fig. 8 Two heating devices 802 are shown. The first heating device 802 contains the heating devices HE1 - HE4, and the second heating device 802 contains the heating devices HE5 - HE8. Each heating zone HZ1 - HZ8 is assigned a heating device HE1 - HE8. Furthermore, the arrangement of the heating devices 802 is also possible on the side or on the back of the mirror 124. Furthermore, the mirror body 500 can be transparent or partially transparent to the heat emitted by the heating devices 802, and the heat can be absorbed at the optical surface.

[0062] Below the mirror body 500, a heating device HE13 is also shown for heating the rear end face (opposite the front end face with the optically active region 502). The heating device HE13 can consist of several individual heating devices, for example, to heat a rear side 906 of the mirror 124, as shown in Fig. 11 is shown.

[0063] The heating devices HE1 - HE13 can be equipped with a VCSEL (vertical cavity surface emitting laser). VCSELs that emit radiation in the infrared range can be used in particular.

[0064] Fig. 9 und Fig. 10 show a schematic representation of a mirror 124 with different heating zones HZ9 - HZ13. In Fig. 9 1 shows a plan view of the end face 900 of the mirror 124. The heating zone HZ9 is delimited by the optically active region 502. As previously described, the optically active region 502 can also be divided into several heating zones. The lateral surface 904 forms a heating zone HZ10, the holding devices 506 form a heating zone HZ11, and an annular edge region 902 forms a heating zone HZ12. In a heating device 802, which is only shown schematically, four heating devices HE9 - HE12 are shown, which can heat the corresponding heating zones HZ9 - HZ12.

[0065] Fig. 10 shows a section X - X from Fig. 9 . In this illustration, the end face 906 opposite the end face 900 of the mirror 124 can be seen. The end face 906, ie the back of the mirror 124, forms a heating zone HZ13.

[0066] Accordingly, it is preferable to heat not only the optically active region 502, but also one or more other regions. The goal is to maintain a temperature as constant as possible throughout the entire mirror body 500. A change in temperature with location or over time is undesirable, as this can lead to deformation of the mirror 124. The heating zones HZ9 - HZ13 can be heated all together or only partially. They can be heated simultaneously, sequentially, or at different time intervals. They can be heated with constant heat flows or with a specific heat flow pattern. They can be heated before the exposure of the wafer 122, during the exposure of the wafer 122, and after the exposure of the wafer 122. Each heating zone HZ9 - HZ13 is heated with a separate heating device HE9 - HE13. One or more heat radiators 804 can be used per heating zone HZ9 - HZ13.Multiple heating zones HZ9–HZ13 can be heated with just one 802 heater. Heating zones HZ9–HZ13 can be heated using either heat radiators or thermal resistors. IR heating heads can be used for the heat radiators.

[0067] Fig. 11 shows several heating zones HZ13a - HZ13i on the back of the Fig. 9 und 10 The heating zone HZ13 is thus divided into several individual heating zones HZ13a - HZ13i. The mirror 124 can have no, one, or several heating zones HZ13a - HZ13i on its rear side 906. The heating zones HZ13a - HZ13i are heated individually as described above in order to achieve the most constant temperature possible in the mirror body 500.

[0068] Fig. 12 shows a flow chart of a method for producing a Fig. 6 , 7 , 9, 10 and 11shown mirror 124. In a first step S1, an expected heat flow distribution 518 on the mirror 124 is determined.

[0069] This depends on which structure is to be imaged on the wafer 122 using the projection system 106. This is determined through calculations and / or simulations based on models. This allows the heat flow distribution 518 on the mirror 124 to be estimated. The expected heat flow distribution 518 on the mirror 124 is the distribution determined based on models as well as calculations and / or simulations based on these models.

[0070] In a second step S2, a plurality of heating zones HZ1-HZ13 are formed on the mirror 124 depending on the determined heat flow distribution 518. Preferably, the heating zones HZ1-HZ13 on the mirror 124 are selected such that regions with particularly high temperatures, so-called heat flow poles 510, are suitably distributed among the heating zones HZ1-HZ13. By appropriately heating the individual heating zones HZ1-HZ13, a constant temperature distribution can then be achieved in the mirror body 500 of the mirror 124, both temporally and spatially.

[0071] In a third step S3, a respective heating zone HZ1 - HZ13 is provided with a respective heating device HE1 - HE13 for heating the respective heating zone HZ1 - HZ13. The respective heating zone is heated depending on a detected temperature of the respective heating zone HZ1 - HZ13 or the expected heat flow distribution 518 on the mirror 124.

[0072] Fig. 13 shows a mirror 124 in a housing 800, as it is also shown in Fig. 8 In contrast to the Fig. 8 The mirror 124 shown in Fig. 13 The mirror 124 shown includes, in addition to the mirror body 500, a device 1300 for reducing the mirror temperature for cooling the mirror body 500. Overall, the aim is to achieve the most homogeneous temperature distribution possible throughout the entire mirror body 500.

[0073] The described preheating of mirror 124, i.e., the heating of multiple heating zones HZ1-HZ13, increases the mirror temperature. For example, the temperature level of mirror body 500 of mirror 124 can increase from approximately 45°C to approximately 65°C. The increased mirror temperature can have a detrimental effect on the mirror coating (e.g., a sequence of layers of molybdenum and silicon) and the adhesive applied to mirror 124 (e.g., for connecting mirror 124 to temperature sensors 702 or holding devices 506). Furthermore, a spatially inhomogeneous thermal expansion coefficient of the material of mirror body 500 becomes increasingly pronounced the higher the temperature rises.

[0074] A reference temperature of, for example, 22°C may apply in the lithography system 100. The cooling water temperature of the lithography system 100 is therefore 22°C. Lowering the temperature level of the mirror 124 by reducing the temperature of the cooling water of the lithography system 100 would result in neighboring elements of the mirror 124 being inadvertently cooled. Therefore, the mirror 124 can have a separate cooling device 1300 for reducing the mirror temperature.

[0075] The device 1300 for reducing the mirror temperature can be a heat sink 1302 arranged at a distance from the mirror body 500. The heat sink 1302 has a lower temperature than the mirror body 500. The temperature of the heat sink 1302 can be within a temperature range of 20°C to -60°C, 0°C to -40°C, or -10°C to -30°C.

[0076] The heat sink 1302 is positioned at a suitable location between the mirror body 500 and the housing 800. As in Fig. 13 As shown, the heat flow Q̇ EUV is applied centrally to the mirror body 500. This will cause the mirror body 500 to heat up primarily in the center. To achieve the most homogeneous temperature distribution possible throughout the entire mirror body, the heat sink 1302 can be arranged centrally to the mirror body 500. However, a heat sink 1302 is also conceivable at any other position between the mirror body 500 and the housing 800.

[0077] How Fig. 13 shows, the heat sink 1302 can be designed as a plate 1304. In principle, the heat sink 1302 can have any geometry. Furthermore, the plate 1304 can, as in Fig. 13 shown, extend along a portion of the back side 906 of the mirror body 500. Alternatively, the plate 1304 may also extend along the entire back side 906 of the mirror body 500.

[0078] It is advantageous if there is no mechanical contact between the mirror body 500 and the plate 1304. This prevents the transmission of vibrations from the plate 1304 to the mirror body 500. The heat is transferred from the mirror body 500 to the plate 1304 via a gas atmosphere and / or via thermal radiation.

[0079] The plate 1304 can be attached to the housing 800 to be held thereby. The housing 800 can be thermally insulated from the plate 1304. Heat exchange can then take place primarily between the mirror body 500 and the plate 1304.

[0080] Furthermore, the plate 1304 can be connected to a Peltier element 1306. The Peltier element 1306 can also be connected to the housing 800. This allows the plate 1304 to be cooled by the Peltier element, with the heat being transferred from the plate 1304 to the housing 800 via the Peltier element 1306. The plate 1304 and the housing 800 can be made of a thermally conductive material such as steel or aluminum.

[0081] Alternatively or additionally, the plate 1304 can be cooled by means of a cooling fluid. The temperature of the cooling fluid can be adjusted to the temperature of the mirror body 500. A separate cooling circuit can be provided for this purpose. Water or glycol, for example, can be provided as the cooling fluid. The cooling fluid is guided to the plate 1304 via a supply line 1308 and removed from the plate 1304 via a discharge line 1310. Furthermore, the cooling fluid can flow through a pipe system in the plate 1304 to cool it. Alternatively, the pipe system can also be attached to the outside of the plate 1304. The supply line 1308 and the discharge line 1310 are each guided through the housing 800 at a feedthrough 1312.

[0082] Alternatively, the plate 1304 can also be held by the supply line 1308 and the discharge line 1310. In this case, the supply line 1308 and the discharge line 1310 are designed to be stable, for example, from a material that includes a metal. In a further alternative, elements can also be provided that pass through the housing 800 and hold the plate 1304. In this case, the supply line 1308 and the discharge line 1310 can only have the function of conducting the cooling fluid.

[0083] Alternatively, plate 1304 can also be cooled using two-phase cooling. For this purpose, liquid carbon dioxide (CO2) can be fed to plate 1304 via supply line 1308 and evaporated there. The required evaporation energy is extracted from plate 1304. This cools plate 1304. The partially evaporated carbon dioxide is then removed via discharge line 1310. The temperature of the carbon dioxide remains constant. This allows the temperature of plate 1304 to be kept virtually constant even with fluctuations in the heat dissipated by plate 1304.

[0084] Furthermore, the surface 1314 of the heat sink 1302 can be coated in such a way that it effectively absorbs thermal radiation. For this purpose, the surface 1314 of the heat sink 1302 can be black. This particularly applies to the side 1316 of the heat sink 1302 facing the rear side 906 of the mirror body 500.

[0085] Alternatively or additionally, the inner side 1318 of the housing 800 may be coated such that the housing 800 is not unnecessarily cooled due to the heat sink 1302.

[0086] Fig. 14 shows the mirror 124 in the housing 800 of Fig. 13 with a heat sink 1302 divided into several segments 1400. The individual segments 1400 can be formed as plate-shaped elements 1402. The mirror body 500 can have several zones Z1 - Z4. The zones Z1 - Z4 can be heated differently. The individual segments 1400 can be arranged such that they cool a zone Z1 - Z4 separately. For example, as in Fig. 14 shown, one segment 1400 is arranged below each zone Z1 - Z4.

[0087] All segments 1400 can be cooled separately or together. Furthermore, the individual segments 1400 can be mechanically in contact with one another or arranged mechanically separately from one another. Only some segments 1400 can be in contact with one another. In this case, other segments 1400 are not mechanically in contact with one another.

[0088] As in Fig. 14 As shown, the segments 1400 are arranged below the rear side 906 of the mirror body 500. In principle, however, the segments 1400 can also be arranged around the entire mirror body 500.

[0089] Fig. 15 shows an enlarged view of the area XV of the mirror 124 from Fig. 13 . A surface 1500 is visible, which is formed as a smooth surface 1502. Surface 1500 can be coated, for example, on the back side 906 of mirror 124, in such a way that it radiates heat particularly well. The coating can comprise nickel. Furthermore, the coating can be black.

[0090] Fig. 16 shows an enlarged view of the area XV of the mirror 124 from Fig. 13 with an alternative surface 1500. The device 1300 for reducing the mirror temperature may comprise a region 1600 of the mirror 124 in which the surface 1500 is enlarged due to the shape of the surface 1500 compared to a smooth surface 1502. As in Fig. 16 As can be seen, the surface 1500 has ribs 1602. Due to the ribs 1602, the surface 1500 is made of Fig. 15 enlarged. In principle, the surface 1500 can have any shape that enlarges the surface 1500 compared to the smooth surface 1502. Due to the larger surface 1500, heat can be better dissipated and / or radiated from the mirror body 500 toward the plate 1304. Alternatively or additionally, the surface 1314 of the plate 1304 can also be enlarged to increase the heat absorption of the plate 1304.

[0091] In a further alternative, the surface 1314 of the plate 1304 and / or the surface 1500 of the mirror 124 may be further enlarged by increasing the surface roughness.

[0092] The manufacture and application of the mirror 124 of the lithography system 100 have been explained. However, the illustrated embodiments can of course also be applied to any other mirror of the lithography system 100.

[0093] Furthermore, the mirror 124 of an EUV lithography system, with a working light wavelength between 0.1 and 30 nm, was discussed. However, the invention is not limited to EUV lithography systems, but can also be applied to other lithography systems, for example, DUV ("deep ultraviolet") lithography systems, with a working light wavelength between 30 and 250 nm.

[0094] Although the invention has been described using various embodiments, it is by no means limited thereto, but can be modified in many ways within the scope of the appended claims. LIST OF REFERENCE SYMBOLS

[0095] 100 EUV lithography system 102 Beam shaping system 104 Illumination system 106 Projection system 108 EUV light source 110 Collimator 112 Monochromator 114 EUV radiation 116 First mirror 118 Second mirror 120 Photomask 122 Wafer 124 Third mirror 126 Fourth mirror 500 Mirror body 502 Optically active area 504 Optically inactive area 506 Holding device 508 Hole in the holding device 510 Heat flux pole 512 X-dipole 514 Y-dipole 516 D-RAM profile 518 Heat flux distribution 700 Hole in the mirror body 702 Temperature sensor 800 Housing 802 Heater 804 Heat radiator 900End face 902Annular edge area 904Shell surface 906End face opposite the end face (rear) 1300Device for reducing the mirror temperature 1302Heat sink 1304Plate 1306Peltier element 1308Supply line 1310Discharge line 1312Feedthrough 1314Surface of the heat sink 1316Side of the heat sink 1318Inside of the housing 1400Segment 1402Plate-shaped element 1500Surface of the mirror 1502Smooth surfaceof the mirror 1600Area of ​​the mirror 1602Rib Q̇ Heat flow HZ1 Heating zone 1 HZ2 Heating zone 2 HZ3 Heating zone 3 HZ4 Heating zone 4 HZ5 Heating zone 5 HZ6 Heating zone 6 HZ6a First heating zone of the divided heating zone 6 HZ6b Second heating zone of the divided heating zone 6 HZ7 Heating zone 7 HZ7a First heating zone of the divided heating zone 7 HZ7b Second heating zone of the divided heating zone 7 HZ8 Heating zone 8 HZ9 Heating zone 9 HZ10 Heating zone 10 HZ11 Heating zone 11 HZ12 Heating zone 12 HZ13 Heating zone 13 HZ13a - HZ13ivarious heating zones within heating zone 13 HE1 Heating device 1 HE2 Heating device 2 HE3 Heating device 3 HE4 Heating device 4 HE5 Heating device 5 HE6 Heating device 6 HE7 Heating device 7 HE8Heating device 8 HE9Heating device 9 HE10Heating device 10 HE11Heating device 11 HE12Heating device 12 HE13Heating device 13 Z1Zone 1 Z2Zone 2 Z3Zone 3 Z4Zone 4

Claims

1. Method for producing a mirror (124) for a lithography apparatus (100), with the steps of: ascertaining an expected heat flux distribution (518) on the mirror (124) in an exposure operation of the lithography apparatus (100) in dependence on a structure to be imaged on the wafer (122), wherein the expected heat flux distribution (518) comprises a plurality of heat flux poles (510), forming a plurality of heating zones (HZ1 - HZ13) on the mirror (124) in dependence on the ascertained heat flux distribution (518), assigning in each case exactly one heat flux pole (510) of the plurality of heat flux poles (510) to in each case one of the plurality of heating zones (HZ1 - HZ13), attaching exactly one temperature sensor (702) to a respective heating zone (HZ1 - HZ13) allocated for capturing a temperature of the respective heating zone (HZ1 - HZ13), and providing the respective heating zone (HZ1 - HZ13) with a respective heating device (HE1 - HE13) for heating the respective heating zone (HZ1 - HZ13) in dependence on a temperature of the respective heating zone (HZ1 - HZ13) captured by means of the respective temperature sensor (702) or the expected heat flux distribution (518) on the mirror (124).

2. Method according to Claim 1, wherein the mirror (124) has an optically active region (502) and an optically inactive region (504) and wherein one or more heating zones (HZ1 - HZ13) are formed in the optically active region (502) and / or in the optically inactive region (504).

3. Method according to Claim 1 or 2, wherein at least one heating device (HE1 - HE13) has a thermal emitter (804) and / or a heat resistor.

4. Method according to one of Claims 1 to 3, wherein the mirror (124) is provided with a device (1300) for reducing the mirror temperature for cooling a mirror body (500) of the mirror (124).

5. Method according to Claim 4, wherein the device (1300) for reducing the mirror temperature has a heat sink (1302) that is arranged at a distance from the mirror body (500).

6. Method according to Claim 5, wherein the mirror body (500) has a plurality of zones (Z1 - Z4) and the heat sink (1302) is divided into a plurality of segments (1400) in order to cool the individual zones (Z1 - Z4) separately.

7. Method according to one of Claims 4 to 6, wherein the device (1300) for reducing the mirror temperature has a region (1600) of the mirror (124) in which a surface (1500) is enlarged, due to the shape of the surface (1500), as compared to a smooth surface (1502).