WO2025181116A1

WO2025181116A1 - Method for regulating the temperature of an optical module for microlithography

Info

Publication number: WO2025181116A1
Application number: PCT/EP2025/055113
Authority: WO
Inventors: Markus BOHLEN; Kurt Stephan WISSEL; Ondrej Hybl; Alexander Kaniut; Bjoern Liebaug; Hubert Holderer
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2024-03-01
Filing date: 2025-02-26
Publication date: 2025-09-04
Anticipated expiration: 2026-09-01
Also published as: DE102024201937A1; TW202542656A

Abstract

A method for regulating the temperature of an optical module (24) for microlithography is presented and described. In order to provide a method which enables faster and more precise, preferably highly accurate, adjusting or in some cases in the first place successful adjusting of an optical element (25) in a projection exposure apparatus (1), the method comprises the following steps: a) providing an optical module (24), wherein the optical module (24) has an optical element (25) to be temperature regulated, b) regulating the temperature of the optical module (24), in particular of the optical element (25) to be temperature regulated, c) installing the optical module (24) in a projection exposure apparatus (1), and d) adjusting at least one optical element, preferably adjusting the optical element (25) to be temperature regulated, in the projection exposure apparatus (1), wherein step b) takes place at least for a time before and/or during step d).

Description

Method for regulating the temperature of an optical module for microlithography

The invention relates to a method for regulating the temperature of an optical module for microlithography, comprising the following steps: a) providing an optical module, wherein the optical module has an optical element to be temperature regulated, b) regulating the temperature of the optical module, in particular of the optical element to be temperature regulated, c) installing the optical module in a projection exposure apparatus, and d) adjusting at least one optical element, preferably adjusting the optical element to be temperature regulated, in the projection exposure apparatus, wherein step b) takes place at least for a time before and/or during step d) .

The subject matter of the German patent application 10 2024201937.2 is hereby incorporated by reference into the present disclosure.

Microlithography is used to produce microstructured components, such as for example integrated circuits. The microlithography process is performed for example using a projection exposure apparatus, which inter alia comprises an illumination optical unit and/or a projection optical unit. The structure of a mask (reticle) illuminated by means of the illumination optical unit is projected here by means of the projection optical unit onto a substrate, for example a wafer, in particular silicon wafer, which is coated with a light-sensitive layer (photoresist) and arranged in the image plane of the projection optical unit, in order to transfer the mask structure to the light-sensitive coating of the substrate.

One of the aims in the development of projection exposure apparatuses is to lithographically produce structures having smaller and smaller dimensions on the substrate, for example to obtain greater integration densities in semiconductor components. One approach consists in working with shorter wavelengths of electromagnetic radiation. For example, optical systems have been developed which use electromagnetic radiation from the so-called "deep ultraviolet" (DUV) range, in particular with operating wavelengths in the range between 150 nm and 400 nm, in particular 365 nm, 248 nm or 193 nm, or from the extreme ultraviolet (EUV) range, in particular with operating wavelengths in the range between 5 nm and 30 nm, in particular at 13.5 nm.

Often, after some time in exposure operation, it may be necessary to exchange individual optical modules, for example in order to repair the projection exposure apparatus. In this case, the exchange of individual optical modules should advantageously take place without demounting and installation of the entire illumination optical unit or projection optical unit, and preferably at the operating site of the projection exposure apparatus. After an optical module has been exchanged, adjusting of the optical units, in particular comprising adjusting of at least one optical element of an optical module, is additionally required in order to attain an optimum field position and pupil position for exposure operation. In this case, a position of the field plane is referred to as field position. In this case, the field plane corresponds to the object plane of the projection optical unit, preferably the mask (reticle) of the projection exposure apparatus being arranged in the object plane. Moreover, a position of an entrance pupil of the illumination optical unit of the projection exposure apparatus is referred to as pupil position. Without adjusting described above, it is often additionally the case that proper functioning of the projection exposure apparatus is not ensured at all, since incorrect exposure of a wafer otherwise occurs, for example. Corresponding adjusting may likewise be required in the course of the initial installation of an optical module in a projection exposure apparatus during the production of the projection exposure apparatus.

DE 102017 219 170 B3 describes for example a method for re-establishing an illumination system for an EUV lithography apparatus. In this case, the method comprises adjusting a pose of mirror modules of an illumination system of the EUV lithography apparatus. In this case, the initial installation, the exchange and the adjusting of an optical module or an optical element should each take up as short a duration as possible. Reducing the duration of the initial installation and in particular of the subsequent adjusting makes it possible to lower the production costs for the projection exposure apparatus. Reducing the duration of the exchange and in particular of the subsequent adjusting makes it possible to reduce the outage time of the projection exposure apparatus and thus to attain a higher production performance with the projection exposure apparatus. For sufficiently precise adjusting, in particular highly accurate adjusting with little variation and a small offset from the respective target value, and fast adjusting of the optical units, it is advantageous in this case if the optical elements of the optical modules, in particular the optical modules as a whole, have a sufficiently stable temperature during adjusting. In some cases, sufficiently precise, in particular highly accurate, adjusting is additionally not possible at all without a sufficiently stable temperature.

It should be taken into consideration here that the temperature conditions present during installation or exchange of an optical module in a projection exposure apparatus may not be sufficiently stable. By way of example, when an optical module is exchanged at the end customer, the temperature conditions present may deviate in some instances greatly from the target temperature striven for. In this case, these temperature deviations may lead to unwanted deformations of individual component parts of the optical module or even of the entire optical module. By way of example, different component parts of the optical module may additionally have different coefficients of thermal expansion, which at different temperatures in each case may lead to deformation states in the optical module that are foreseeable only with difficulty. Such deformations may in turn lead to an unwanted shift in the field position and/or pupil position and thus corrupted measurement results of the optical metrology, which in turn results in corrupted adjusting. Therefore, the invention is based on the object of providing a method which enables faster and more precise, preferably highly accurate, adjusting or in some cases in the first place successful adjusting of an optical element in a projection exposure apparatus.

This object is achieved by the method according to Patent Claim 1.

The present method for regulating the temperature of an optical element for microlithography in this case comprises step a): providing an optical module, wherein the optical module has an optical element to be temperature regulated. The optical element to be temperature regulated can be for example a lens element and/or a mirror. Besides the optical element to be temperature regulated, however, the optical module can have even further component parts. In this case, the optical module is installable in and/or demountable from a projection exposure apparatus.

The method additionally comprises step b) : regulating the temperature of the optical module, in particular of the optical element to be temperature regulated. By way of regulating the temperature of the optical module, in particular of the optical element to be temperature regulated, the optical element to be temperature regulated and/or some other component part of the optical module, preferably substantially the entire optical module, can be brought to a specific target temperature or at least close to a specific target temperature. If the optical element to be temperature regulated and/or the optical module are/is or substantially are/is ata corresponding target temperature, adjusting of an optical element, in particular of the optical element to be temperature regulated, of the projection exposure apparatus is simplified, and often actually made possible in the first place. This is because unwanted deformations which may lead to an unwanted shift in the field position can be avoided by way of regulating the temperature. In the present case, regulating the temperature is understood to mean heating and/or cooling. In step b), therefore, the optical module, in particular of the optical element to be temperature regulated, is heated and/or cooled. During step b), provision can advantageously be made for regulating the temperature of the optical element to be temperature regulated and/or of substantially the entire optical module.

The method additionally comprises step c): installing the optical module in a projection exposure apparatus. By way of the installing, the optical module is brought to the envisaged place in the projection exposure apparatus. The installing can involve the initial installation of an optical module in a projection exposure apparatus or alternatively the installation of an optical module in a projection exposure apparatus for the purpose of exchanging some other optical module.

Furthermore, the method comprises step d): adjusting at least one optical element, preferably adjusting the optical element to be temperature regulated, in the projection exposure apparatus. By way of adjusting an optical element, this optical element can be brought into its target pose, which enables optimum, often in the first place any satisfactory, operation of the projection exposure apparatus. The optical element can be a lens element and/or a mirror, as in the case of the optical element to be temperature regulated. A multiplicity of optical elements, comprising or not comprising the optical element to be temperature regulated, can additionally be adjusted in step d).

In the present case, "adjusting” should be understood to mean that the orientation and/or the position of the optical element, in particular of the optical element to be temperature regulated, are/is changed in order to bring the optical element into the corresponding target pose. If the optical element is not in the target pose but rather in an actual pose deviating therefrom, the field position and/or the pupil position do(es] not, for example, satisfy the specifications, in particular illumination specifications, required for exposure operation.

In the present case, the "position” of the optical element, in particular of the optical element to be temperature regulated, is understood to mean the coordinates of the optical element or the coordinates of a measurement point provided on the optical element with respect to the x-direction, the y-direction and the z-direction, also called spatial directions. In the present case, the "orientation” of the optical element, in particular of the optical element to be temperature regulated, is understood to mean the rotation of the optical element about at least one of the three spatial directions. That is to say that the optical element can be rotated about the x-direction, the y- direction and/or the z-direction. This gives six degrees of freedom for the position and/or orientation of the optical element. In this case, the "pose”, inter alia the target pose and/or actual pose, of the optical element, in particular of the optical element to be temperature regulated, comprises the position and the orientation of the optical element.

The present method additionally provides for step b) to take place at least for a time before and/or during step d). In the present case, “at least for a time” is understood to mean "at least for a period of time". Regulating the temperature is thus intended to take place at least for a period of time before and/or during the adjusting. As a result of this, the adjusting can be carried out particularly fast and precisely, in particular highly accurately. Often it is as a result of this that targeted adjusting is made possible in the first place. If the temperature of the optical module is regulated during the adjusting, the optical module can be brought to the target temperature during the adjusting and/or the target temperature can be kept stable atthe optical module during the adjusting. This makes it easier, in particular in a short time, to carry out precise, in particular highly accurate, adjusting or in some cases in the first place to conclude the adjusting with a satisfactory result. If the temperature of the optical module is in turn already regulated before the adjusting, the optical module is preferably already at the target temperature or substantially the target temperature after installation and thus before the start of the adjusting. This enables the adjusting to be already begun shortly after installation of the optical module, since no or only a short heating-up phase and/or cooling-down phase to the target temperature are/is required during the adjusting. Unwanted deformations which are present if the optical module is not at substantially the target temperature are additionally avoided. This shortens the duration of the adjusting and additionally improves the precision during the adjusting. In this case, step b] need not take place with continuity, in particular with continuity before and/or during step d). Specifically, provision can be made for step b) to take place in a plurality of, in particular temporally separate, segments. It is appropriate here in particular to divide step b) into different, preferably temporally separate, segments, preferably comprising a segment before step d] and/or a segment during step d). This is advantageous for example if regulating the temperature takes place in differing ways during different phases of the method.

The present method advantageously provides for step a] to take place at least for a time, preferably substantially completely, before step b), step c] and/or step d). Alternatively or additionally, step d) preferably takes place at least for a time, preferably substantially completely, after step a), step b), and/or step c).

Step a), step b), step c] and/or step d] can additionally take place at least for a time, preferably substantially completely, in a clean room.

In accordance with a first configuration of the method, provision is made for step b] to take place at least for a time before, during and/or after step c). It is often by virtue of regulating the temperature at least for a time before and/or during installation that targeted adjusting is made possible in the first place. Moreover, the installation or exchange of the optical module can possibly be temporally shortened, since a temperature-regulating phase after step c) can then possibly be dispensed with. Specifically, by virtue of correspondingly regulating the temperature, the optical module, in particular the optical element to be temperature regulated, can already be at the target temperature before the start of the adjusting or the temperature of the optical module can be at least in the region of the target temperature. A heating-up phase and/or cooling-down phase to the target temperature at the beginning of the adjusting are/is therefore not necessary, or are/is necessary only to a shortened extent. It is often by virtue of regulating the temperature after installation that targeted adjusting is made possible and/or the precision during the adjusting is improved in the first place. In this regard, for example, the time between installation and the adjusting can be used for regulating the temperature, such that on account thereof likewise a heating-up phase and/or cooling-down phase to the target temperature at the beginning of the adjusting are/is not necessary, or are/is necessary only to a shortened extent. Moreover, regulating the temperature after installation can also include regulating the temperature during the adjusting, such that the optical module is brought to the target temperature during the adjusting and/or the target temperature is kept stable at the optical module during the adjusting. This makes it easier, preferably in a short time, to achieve precise, in particular highly accurate, adjusting or in some cases even actually makes it possible in the first place to conclude the adjusting with a satisfactory result. In this case, step b) need not take place with continuity, in particular with continuity before, during and/or after step c). Specifically, provision can be made for step b] to take place in a plurality of, in particular temporally separate, segments. It is appropriate here in particular to divide step b) into different, preferably temporally separate, segments, preferably comprising a segment before step c), a segment during step c] and/or a segment after step c). This is advantageous for example if regulating the temperature takes place in differing ways during different phases of the method.

A further configuration of the method is distinguished by the fact that the optical module has a mount and/or a frame, and that, preferably, the temperature of the mount and/or of the frame is regulated in step b). The corresponding component parts of the optical module simplify in particular the receiving and mounting of the optical element to be temperature regulated and also of the optical module. By means of the mount, the optical element to be temperature regulated is received and/or mounted, inter alia, in the optical module. The frame in turn makes it possible inter alia to receive and/or mount the optical module in a projection exposure apparatus. However, the mount and/or the frame can also fulfil even further tasks. By virtue of the temperature of the mount and/or of the frame being regulated in step b], the adjusting is additionally simplified further. Particularly in the case of relatively complex and/or relatively large optical modules, on account of the interactions of the individual component parts it is not sufficient to regulate the temperature of only one specific component part of the optical module, rather it is necessary to regulate the temperature of a plurality of, preferably all, component parts of the optical module in order to attain a stable target pose of the optical element, in particular of the optical element to be temperature regulated, of the corresponding optical module during the adjusting. In this regard, different component parts of the optical module may have different coefficients of thermal expansion, which at different temperatures in each case may lead to deformation states in the optical module that are foreseeable only with difficulty. Particularly in the case of relatively large optical modules, the temperatures of the different component parts of the optical module are matched only rather slowly. Adjusting would then be possible only with very great difficulty or might not be possible at all.

A further configuration of the method provides that, before step c), some other optical module is demounted from the projection exposure apparatus. This creates space in the projection exposure apparatus for the optical module to be installed in step c). The method thus comprises the exchange of optical modules. An exchange may be necessary after some time of exposure operation, owing to the occurrence for example of aging, contamination and/or damage of an optical module in the projection exposure apparatus. In this context, it can be advantageous if the optical module installed in step c), and preferably provided in step a), is substantially structurally identical to the other optical module that is demounted, and/or fulfils substantially the same function in the projection exposure apparatus as the other optical module that is demounted. This simplifies fast reactivation of the projection exposure apparatus. Alternatively or additionally, it can be provided that, in step c), the optical module is installed substantially at the same location in the projection exposure apparatus as the other optical module that is demounted.

In accordance with one configuration of the method, provision is made for the method to comprise at least one of the following steps: al) providing at least one, preferably external and/or mobile, temperature-regulating device for regulating the temperature of the optical module, a2) providing a, preferably mobile, storage device for receiving and/or transporting the optical module, and/or a3) providing at least one temperature-regulating element, wherein the temperature-regulating element is connectable to the optical module. By virtue of providing corresponding devices and elements, regulating the temperature of the optical module can be simplified, often actually made possible in the first place, and possibly accelerated.

By virtue of providing a temperature-regulating device, a device which simplifies reliable temperature regulation is provided. Regulating the temperature by way of heating up and/or cooling down by way of the ambient air and/or by way of heat transfer from other component parts of the projection exposure apparatus alone would take up a relatively long time. By contrast, a temperature-regulating device leads to faster temperature regulation. Regulating the temperature to a specific target temperature can additionally be effected. The temperature-regulating device can be configured as an external and/or mobile temperature-regulating device. In the present case, an external temperature -regulating device is understood to mean that the temperature-regulating device is not a component part, in particular not an integral component part, of the projection exposure apparatus; preferably, the temperature-regulating device in this case is also not a component part of a clean room. Specifically, projection exposure apparatuses in some instances have an integrated temperature-regulating device, where this may also be the case for the present projection exposure apparatus in which the optical module is installed in step c). What is disadvantageous here, however, is that regulating the temperature of the optical module by means of the integrated temperature-regulating device would take too long, since in general the temperatures of a multiplicity of modules and component parts of the projection exposure apparatus are regulated simultaneously by means of the integrated temperature-regulating device. The set-up of the optical module composed of a plurality of component parts, for example the frame, the mount and/or the optical element, having low heat transfer coefficients among one another, likewise intensifies this disadvantage, since regulating the temperature of one of the component parts by means of the integrated temperature-regulating device would hardly influence the temperature of the other component parts. A relatively long time would elapse before the temperature of the optical module had been regulated to the target temperature by the integrated temperature-regulating device. This would result in a delay until or during the adjusting, which would in turn prolong the duration of production or repair of the projection exposure apparatus. In step b), provision can be made in this case for the thermal energy used for regulating the temperature to be provided at least for a time substantially exclusively by the, preferably external and/or mobile, temperature-regulating device. Alternatively or additionally moreover, it can be provided that, in step b), the thermal energy used for regulating the temperature is provided at least for a time, preferably at the same time, by the, preferably external and/or mobile, temperature-regulating device and the integrated temperature-regulating device. The use of a mobile temperature-regulating device has in turn the advantage that the corresponding temperature-regulating device can be used at different locations and/or for different projection exposure apparatuses. Advantageously, the temperature-regulating device is configured for separately regulating the temperature, in particular during step b), of the optical module. The temperature-regulating device can additionally preferably comprise a heat exchanger.

By virtue of providing a, preferably mobile, storage device for receiving and/or transporting the optical module, firstly providing the optical module is simplified. Moreover, given a corresponding configuration of the storage device, a device which prevents condensation on the optical module can likewise be provided. This is achieved for example by the optical module being received, preferably substantially completely, in the storage device and/or the storage device surrounding, preferably substantially completely, the optical module. It can be advantageous if the storage device forms a substantially sealed space vis-a-vis the surrounding atmosphere. Alternatively or additionally, the storage device can moreover be opened and/or closed. Since the storage device can moreover be configured for transporting the optical module, the storage device can also be configured as a transport device. Condensation can moreover be prevented even better if the temperature of the optical module is regulated in the storage device. This will also be discussed below. By virtue of providing at least one temperature-regulating element, wherein the temperature-regulating element is connectable to the optical module, a device which simplifies, in particular accelerates, reliable temperature regulation is likewise provided. By virtue of the temperature -regulating element being connectable to the optical module, thermal energy can be transferred directly from the temperatureregulating element to the optical module in a structurally simple manner. This simplifies and accelerates the heating and/or cooling of the optical module. In this case, the temperature-regulating element can be connected to a temperatureregulating line, in particular cooling lines, of the optical module. The temperatureregulating element can for example regulate the temperature of the optical module on its own. However, provision can advantageously be made for the temperatureregulating element to regulate the temperature of the optical module by means of the temperature-regulating device. Moreover, at least two temperature-regulating elements can be provided, which are preferably configured as described above.

In accordance with a further configuration of the method, it is provided that, in step b], the temperature of the optical module is regulated at least for a time by means of the temperature-regulating device, and/or that the temperature -regulating device is connected to the optical module at least for a time in step b). It is thereby possible to regulate the temperature of the optical module to the target temperature in a targeted manner and rapidly. As already explained above, for example, regulating the temperature by way of heating up and/or cooling down by way of the ambient air and/or by way of heat transfer from other component parts of the projection exposure apparatus would take up significantly more time and/or lead to the temperature of the optical module being regulated to an incorrect temperature. A connection between the optical module and the temperature -regulating device additionally simplifies the transfer of thermal energy.

A further configuration of the method provides that, in step b), in particular before step cj and/or before step d), the temperature of the optical module is regulated at least for a time by means of the temperature -regulating device in the storage device, and/or that the temperature-regulating device is connected to the storage device at least for a time in step b), in particular before step c] and/or before step d). It is thereby possible to make it easier to regulate the temperature before installation in the projection exposure apparatus, and to shorten the duration of the adjusting. In this regard, by way of regulating the temperature in the storage device, the optical module can be brought substantially to the target temperature, even if the surroundings around the storage device are subject to temperature fluctuations. Consequently, regulating the temperature can also already take place before the optical module is introduced into a clean room. The connection between storage device and temperature-regulating device additionally simplifies the targeted transfer of thermal energy. If the temperature of the optical module is regulated by means of the temperature-regulating device in the storage device, advantageously the storage device is closed and/or the optical module is insulated from the atmosphere surrounding the storage device. Otherwise, satisfactory or even successful temperature regulation is often not possible at all.

In accordance with a further configuration of the method, it is provided that, in step b], in particular during step c), after step c] and/or during step d), the temperature of the optical module is regulated at least for a time by way of the temperatureregulating element by means of the temperature-regulating device, and/or that the temperature-regulating element is connected to the optical module and/or the temperature-regulating device at least for a time, in particular during step c), after step cj and/or during step d). It is thereby possible to make it easier to regulate the temperature during installation in the projection exposure apparatus and/or during the adjusting, and moreover preferably to shorten the duration of the adjusting. In this case, the temperature-regulating element can be provided as an adapter between optical module and temperature-regulating device and thus simplifies the transfer of thermal energy between these components. In this case, the temperature-regulating element can be connected to the frame and/or the mount of the optical module. Alternatively or additionally, the temperature-regulating element can be releasably connected to the optical module and/or the temperature -regulating device.

A further configuration of the method provides for the optical module to be received and/or to be transported in the storage device at least for a time during step b). It is thereby possible for the optical element to be brought to the projection exposure apparatus in a simple and secure manner. Moreover, regulating the temperature can take place in the storage device during transport and thus already before installation of the optical module in the projection exposure apparatus.

In accordance with one configuration of the method, provision is made for the optical module to be removed from the storage device before step c), preferably after the other optical module has been demounted from the projection exposure apparatus. Particularly in the latter case, the optical module is prevented from being cooled down or heated up too much before step cj. It is advantageous if the optical module is removed from the storage device at most 24 h, more preferably at most 1 h, in particular at most 0.5 h, before step c). In this case, the removing should take place just before step c] as much as possible.

A further configuration of the method comprises the following step: e) measuring a field position and/or a pupil position of the projection exposure apparatus. Measuring the corresponding characteristic values makes it possible to carry out the adjusting in step d) very precisely, in particular highly accurately.

A further configuration of the method provides that step e) takes place at least for a time before, during and/or after step d], and/or that steps d] and e] are carried out iteratively, in particular are carried out iteratively until the field position and/or the pupil position satisfy a required specification. A corresponding configuration makes it possible to simplify as precise, in particular highly accurate, adjusting as possible. Measuring field position and/or pupil position before step d), i.e. the adjusting, can be used to determine an initial state, on the basis of which subsequent adjusting steps are determined. Measuring during and/or after step d) makes it easier to track the influence of the adjusting on the field position and/or the pupil position and to determine possibly further required adjusting steps. In this case, iteratively carrying outsteps d) and e) combines the abovementioned effects that were described in connection with carrying out step e) at least for a time before, during and/or after step d). In the present case, the specification is the tolerance range within which the field position and/or the pupil position ought to lie. For the field position, said tolerance range is advantageously at most 250 gm, preferably at most 100 gm, in particular at most 10 pm.

In accordance with a further configuration of the method, it is provided that, in step d), an orientation and/or a position of an optical element, preferably of the optical element to be temperature regulated, of the projection exposure apparatus are/is adjusted, in particular depending on the field position and/or pupil position measured in step e). Precise, in particular highly accurate, adjusting of the optical element is simplified as a result of this. By virtue of the adjustment depending on at least one of the values measured in step e), the adjusting is further simplified since the required adjusting steps can be determined particularly simply on the basis of the measured value(s).

A further configuration of the method is distinguished by the fact that step b) begins at least 1 h, preferably at least 5 h, more preferably at least 10 h, more preferably at least 20 h, in particular at least 40 h, before step c] and/or before step d). This makes it possible to regulate the temperature of the optical element over a sufficiently long period of time, such that the optical element is at the target temperature or at least a temperature near the target temperature for installation and/or the adjusting. Moreover, given a sufficiently early beginning, the temperature regulation can be carried out more gently for the materials of the optical module. Advantageously, provision can be made for step b) additionally to begin at least 48 h before step c] and/or before step d). Alternatively or additionally, a primary phase of step b] can begin at least 40 h, in particular at least 48 h, before step c) and/or a secondary phase of step b) can begin at least 1 h and/or at most 5 h before step d).

A further configuration of the method provides that, in step b), the temperature of the optical module is regulated to a target temperature, that, preferably, the target temperature is at least 10°C, preferably at least 15°C, in particular at least 20°C and/or at most 35°C, preferably at most 30°C, in particular at most 25°C, and/or that, preferably, the temperature regulation to the target temperature takes place with a deviation of at most 1°C, preferably at most 0.5°C, in particular at most 0.2°C. A temperature regulation to corresponding values simplifies precise, in particular highly accurate, adjusting. It is particularly preferred in this case if the target temperature is between 20°C and 24°C, in particular approximately 22°C, and/or the temperature regulation to the target temperature takes place with a deviation of at most 0.1°C.

The invention is explained in greater detail below with reference to a drawing illustrating just one preferred exemplary embodiment. In the drawing:

Figure 1 schematically shows a meridional section of a projection exposure apparatus for EUV projection lithography,

Figure 2 shows an optical module in a plan view.

Figure 3 shows the optical module from Figure 2 after having been received in a storage device in a front view, and

Figure 4 shows the optical module from Figure 2 during installation in a projection exposure apparatus in a front view.

The essential component parts of a microlithographic projection exposure apparatus 1 are described in exemplary fashion below, initially with reference to Figure 1. The description of the basic set-up of the projection exposure apparatus 1 and the component parts thereof should be understood here to be non-limiting.

One embodiment of an illumination system 2 of the projection exposure apparatus 1 has, in addition to a light 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 light 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 comprise the light source 3.

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 by way of a reticle displacement drive 9, in particular in a scanning direction.

A Cartesian xyz-coordinate system is depicted in Figure 1 for explanation purposes. The x-direction runs perpendicularly to the plane of the drawing into the latter. The y- direction runs horizontally, and the z-direction runs vertically. The scanning direction runs along the y-direction in Figure 1. The z-direction runs perpendicularly to the object plane 6.

The projection exposure apparatus 1 comprises a projection optical unit 10. The projection optical unit 10 serves for imaging 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 that differs from 0° between the object plane 6 and the image plane 12 is also possible.

A structure on the reticle 7 is imaged onto a light-sensitive layer of a wafer 13 arranged in the region of the image field 11 in the image plane 12. The wafer 13 is held by a wafer holder 14. The wafer holder 14 is displaceable by way of a wafer displacement drive 15, in particular along the y-direction. The displacement, firstly, of the reticle 7 by way of the reticle displacement drive 9 and, secondly, of the wafer 13 by way of the wafer displacement drive 15 can be implemented so as to be synchronized with one another.

The radiation source 3 is an EUV radiation source. The radiation source 3 emits in particular EUV radiation 16, which is also referred to below as used radiation, illumination radiation or illumination light. The used radiation has in particular a wavelength in the range of between 5 nm and 30 nm. The radiation source 3 can be a plasma source, for example an LPP (Laser Produced Plasma) source or a GDPP (Gas Discharge Produced Plasma) source. It can also be a synchrotron-based radiation source. The radiation source 3 can be a free electron laser (FEL).

The illumination radiation 16 emerging from the radiation source 3 is focused by a collector 17. The collector 17 can be a collector with one or with a plurality of ellipsoidal and/or hyperboloidal reflection surfaces. The illumination radiation 16 can be incident on the at least one reflection surface of the collector 17 with grazing incidence (GI), i.e. at angles of incidence of greater than 45°, or with normal incidence (NI), i.e. at angles of incidence of less than 45°. The collector 17 can be structured and/or coated firstly to optimize its reflectivity for the used radiation and secondly to suppress extraneous light.

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 can constitute a separation between a radiation source module, comprising the radiation source 3 and the collector 17, and the illumination optical unit 4.

The illumination optical unit 4 comprises a deflection mirror 19 and, disposed downstream thereof in the beam path, a first facet mirror 20. The deflection mirror 19 can be a plane deflection mirror or, alternatively, a mirror with a beam-influencing effect that goes beyond the purely deflecting effect. Alternatively or additionally, the deflection mirror 19 can be embodied as a spectral filter separating a used light wavelength of the illumination radiation 16 from extraneous light having a wavelength that deviates therefrom. If the first facet mirror 20 is arranged in a plane of the illumination optical unit 4 that is optically conjugate to the object plane 6 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 20 comprises a multiplicity of individual first facets 21, which are also referred to below as field facets. Figure 1 illustrates only some of these facets 21 by way of example.

The first facets 21 can be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate edge contour or an edge contour of part of a circle. The first facets 21 can be embodied as plane facets or alternatively as convexly or concavely curved facets.

As known for example from DE 10 2008 009 600 Al, the first facets 21 themselves can also be composed in each case of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 20 can be configured in particular as a microelectromechanical system (MEMS system). For details, reference is made to DE 10 2008 009 600 Al.

Between the collector 17 and the deflection mirror 19, the illumination radiation 16 travels horizontally, i.e. along the y-direction.

In the beam path of the illumination optical unit 4, a second facet mirror 22 is disposed downstream of the first facet mirror 20. If the second facet mirror 22 is arranged in a 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 at a distance from a 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 2006/0132747 Al, EP 1 614008 Bl, and US 6,573,978.

The second facet mirror 22 comprises 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. The second facets 23 can likewise be macroscopic facets, which can for example have a round, rectangular or else hexagonal boundary, or can alternatively be facets composed of micromirrors. In this regard, reference is likewise made to DE 10 2008 009 600 Al.

The second facets 23 can have plane or alternatively convexly or concavely curved reflection surfaces.

The illumination optical unit 4 consequently forms a doubly faceted system. This fundamental principle is also referred to as a fly's eye condenser (fly's eye integrator).

It can be advantageous to arrange the second facet mirror 22 not exactly in a plane that is optically conjugate to a pupil plane of the projection optical unit 10. In particular, the pupil facet mirror 22 can be arranged so as to be tilted relative to a pupil plane of the projection optical unit 7, as described for example in DE 10 2017 220 586 Al.

With the aid of the second facet mirror 22, the individual first facets 21 are imaged into the object field 5. The second facet mirror 22 is the last beam-shaping mirror or actually the last mirror for the illumination radiation 16 in the beam path upstream of the object field 5.

In a further embodiment (not illustrated) of the illumination optical unit 4, a transfer optical unit contributing in particular to the imaging of the first facets 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, alternatively, two or more mirrors, which are arranged in succession in the beam path of the illumination optical unit 4. The transfer optical unit can in particular comprise one or two normal-incidence mirrors (NI mirrors) and/or one or two grazingincidence mirrors (GI mirrors). In the embodiment shown in Figure 1, downstream of the collector 17 the illumination optical unit 4 has exactly three mirrors, specifically the deflection mirror 19, the field facet mirror 20 and the pupil facet mirror 22.

In a further embodiment of the illumination optical unit 4, the deflection mirror 19 can also be omitted, so that downstream of the collector 17 the illumination optical unit 4 can then have exactly two mirrors, specifically the first facet mirror 20 and the second facet mirror 22.

The imaging of the first facets 21 into the object plane 6 by means of the second facets 23 or using the second facets 23 and a transfer optical unit is routinely only approximate imaging.

The projection optical unit 10 comprises a plurality of mirrors Mi, which are consecutively numbered in accordance with their arrangement in the beam path of the projection exposure apparatus 1.

In the example illustrated in Figure 1, the projection optical unit 10 comprises six mirrors Ml to M6. Alternatives with four, eight, ten, twelve or any other number of mirrors Mi are likewise possible. The projection optical unit 10 is a doubly obscured optical unit. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 16. The projection optical unit 10 has an imageside numerical aperture which is greater than 0.5 and which can also be greater than 0.6 and, for example, can be 0.7 or 0.75.

Reflection surfaces of the mirrors Mi can be embodied as freeform surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape, just like the mirrors of the illumination optical unit 4, the mirrors Mi can have highly reflective coatings for the illumination radiation 16. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optical unit 10 has a large object-image offset in the y-direction between a y-coordinate of a centre of the object field 5 and a y-coordinate of the centre of the image field 11. This object-image offset in the y-direction can be of approximately the same magnitude as a z-distance between the object plane 6 and the image plane 12.

In particular, the projection optical unit 10 can have an anamorphic configuration. In particular, it has different imaging scales px, y in the x- and y-directions. The two imaging scales Px, Py of the projection optical unit 10 are preferably (Px, Py) = (+/- 0.25, +/-0.125). A positive imaging scale p means imaging without image inversion. A negative sign for the imaging scale p means imaging with image inversion.

The projection optical unit 10 consequently leads to a reduction in size with a ratio of 4:1 in the x-direction, i.e. in a direction perpendicular to the scanning direction.

The projection optical unit 10 leads to a reduction in size of 8:1 in the y-direction, i.e. in the scanning direction.

Other imaging scales are likewise possible. Imaging scales with the same signs and the same absolute values in the x-direction and y-direction, for example with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x-direction and in the y-direction in the beam path between the object field 5 and the image field 11 can be the same or can be different depending on the embodiment of the projection optical unit 10. Examples of projection optical units with different numbers of such intermediate images in the x- and y-directions are known from US 2018/0074303 Al. In each case one of the pupil facets 23 is assigned to exactly one of the field facets 21 for the purpose of forming a respective illumination channel for illuminating the object field 5. In particular, this can produce illumination according to the Kohler principle. The far field is decomposed into a multiplicity of object fields 5 with the aid of the field facets 21. The field facets 21 generate a plurality of images of the intermediate focus on the pupil facets 23 respectively assigned thereto.

The field facets 21 are each imaged by an assigned pupil facet 23 onto the reticle 7 in a manner overlaid on one another in order to illuminate the object field 5. The illumination of the object field 5 is in particular as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by overlaying different illumination channels.

The illumination of the entrance pupil of the projection optical unit 10 can be defined geometrically by way of an arrangement of the pupil facets. The intensity distribution in the entrance pupil of the projection optical unit 10 can be set by selecting the illumination channels, in particular the subset of the pupil facets which guide light. This intensity distribution is also referred to as illumination setting or illumination pupil filling.

A likewise preferred pupil uniformity in the region of portions of an illumination pupil of the illumination optical unit 4 which are illuminated in a defined manner can be achieved by a redistribution of the illumination channels.

Further aspects and details of the illumination of the object field 5 and in particular of the entrance pupil of the projection optical unit 10 are described below.

The projection optical unit 10 can have a homocentric entrance pupil, in particular.

The latter can be accessible. It can also be inaccessible. The entrance pupil of the projection optical unit 10 generally cannot be illuminated exactly by means of the pupil facet mirror 22. In the case of imaging of the projection optical unit 10 which telecentrically images the centre of the pupil facet mirror 22 onto the wafer 13, the aperture rays often do not intersect at a single point. However, it is possible to find an area in which the spacing of the aperture rays that is determined in pairs becomes minimal. This area represents the entrance pupil or an area conjugate thereto in real space. In particular, this area exhibits a finite curvature.

It may be the case that the projection optical unit 10 has different positions of the entrance pupil for the tangential beam path and for the sagittal beam path. 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. With the aid of this optical element, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

In the arrangement of the components of the illumination optical unit 4 illustrated in Figure 1, the pupil facet mirror 22 is arranged in an area conjugate to the entrance pupil of the projection optical unit 10. The field 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 an arrangement plane defined by the deflection mirror 19.

The first facet mirror 20 is arranged so as to be tilted with respect to an arrangement plane defined by the second facet mirror 22.

Figure 2 shows an optical module 24 in a plan view. In this case, the optical module 24 comprises an optical element 25, a mount 26 and a frame 27. The optical element 25 shown in the present case is also referred to as optical element 25 to be temperature regulated. By means of the mount 26, the optical element 25 to be temperature regulated is received and mounted in the optical module 24. The frame 27 is in turn provided for receiving and mounting the optical module 24 in a projection exposure apparatus 1. For this purpose, the frame 27 can have adapter elements, for example, in which case the adapter elements can be connected to a mounting unit of the projection exposure apparatus 1, for example a hexapod.

In this case, the optical module 24 illustrated in Figure 2 can be used in the projection exposure apparatus 1 described above and illustrated in Figure 1. By way of example, the optical module 24 can be used as deflection mirror 19, as first facet mirror 20, as second facet mirror 22 or as one of the mirrors Ml to M6. However, the optical module 24 can also be used in a different projection exposure apparatus 1, having a DUV radiation source for example.

Figure 3 shows the optical module 24 from Figure 2 after having been received in a storage device 28 in a front view. In the present case, the optical module 24 is completely surrounded by the storage device 28. In order to introduce the optical module 24 into the storage device 28 and take it out again, the storage device 28 can be opened and closed. This is done by way of a flap 29 in the case of the storage device 28 illustrated.

In the embodiment shown in the present case, the storage device 28 additionally serves as a transport device. In the present case, therefore, the storage device 28 is configured in such a way that it can be arranged and transported on a pallet 30. However, the storage device 28 can also be transported without a pallet 30, for example.

In order to regulate the temperature of the optical module 24, in particular of the optical element 25 to be temperature regulated, of the mount 26 and of the frame 27, in a targeted manner to the target temperature or at least close to the target temperature as early as before installation in the projection exposure apparatus 1 and before the adjusting, the storage device 28 illustrated is connected to a temperatureregulating device 31. In this case, the temperature-regulating device 31 regulates the temperature of the optical module 24 within the storage device 28. In order that the temperature of the optical module 24 is regulated for a sufficiently long time in the course of installation or the adjusting, regulating the temperature of the optical module 24 is begun for example as early as at least 40 h before installation in the projection exposure apparatus 1.

The temperature -regulating device 31 used in the present case is an external and mobile temperature -regulating device 31, such that the temperature regulation can also take place during transport of the optical module 24. Moreover, this temperatureregulating device 31 can also be used for temperature regulation without the storage device 28.

Figure 4 shows the optical module 24 from Figure 2 during installation in a projection exposure apparatus 1 in a front view. The optical module 24 has been removed from the storage device 28 for installation. In order to prevent the temperature of the optical module 24 from deviating from the target temperature too much after removal from the storage device 28, the temperature of the optical module 24 continues to be regulated by means of a temperature-regulating device 31. The temperatureregulating device 31 used can be the external and mobile temperature-regulating device 31 already described above. In order to simplify the temperature regulating in this case, at least one temperature -regulating element 32 is provided which is connected both to the optical module 24 and to the temperature-regulating device 31. The temperature -regulating element 32 thus serves inter alia as an adapter between the optical module 24 and the temperature-regulating device 31. In the present case, regulating the temperature in this way takes place both during installation in the projection exposure apparatus 1 and during the adjusting. This ensures that the optical module 24 is at the target temperature in a stable manner during the adjusting as well. It is not absolutely necessary to regulate the temperature continuously during the adjusting. By way of example, it is possible to adjust, subsequently to regulate the temperature, then to measure the field position and/or the pupil position and thereafter to regulate the temperature again. The installation of the optical module 24 in the projection exposure apparatus 1 is illustrated merely schematically in Figure 4. During installation, the optical module 24 is moved to the projection exposure apparatus 1 by means of an installation assistance device 33, illustrated schematically as a movable cart in the present case, and is then received in the projection exposure apparatus 1. In this case, the module 24 is received in a merely schematically illustrated mounting 34 of the projection exposure apparatus 1. Before, during and after installation, the temperature of the optical module 24 is regulated by means of the temperature-regulating device 31. Moreover, some other, preferably structurally identical, optical module 24 may already have been demounted before installation of the optical module 24.

Once the optical module 24 has been installed, at least one optical element of the projection exposure apparatus 1, in particular the optical element 25 to be temperature regulated, is adjusted. An orientation and/or a position of the corresponding optical element are/is adjusted for this purpose. This takes place here depending on measurement values of the field position and/or pupil position, wherein the measurement values are ascertained before, during and/or after the adjusting. The temperature of the optical module 24 continues to be regulated during the adjusting. This is done here by the external and mobile temperature-regulating device 31 already explained. This is indicated schematically by the tube 35 depicted using dashed lines, the tube 35 in the present case being a component part of the temperature-regulating device 31. By virtue of the temperature regulating also carried out during the adjusting, unwanted deformations of the optical module 24 are avoided. In this case, the adjusting and measuring are carried out until the field position and/or the pupil position satisfy a required specification.

Once the adjusting has been concluded, the temperature-regulating device 31 and the temperature-regulating element 32 are separated again from the optical module 24 and the projection exposure apparatus 1 can preferably be activated. List of reference

1 Projection exposure apparatus

2 Illumination system

3 Radiation source or EUV radiation source

4 Illumination optical unit

5 Object field

6 Object plane

7 Reticle

8 Reticle holder

9 Reticle displacement drive

10 Projection optical unit

11 Image field

12 Image plane

13 Wafer

14 Wafer holder

15 Wafer displacement drive

16 Illumination radiation or EUV radiation

17 Collector

18 Intermediate focal plane

19 Deflection mirror

20 First facet mirror or field facet mirror

21 First facets or field facets

22 Second facet mirror or pupil facet mirror

23 Second facets or pupil facets

24 Optical module

25 Optical element

26 Mount

27 Frame

28 Storage device

29 Flap 30 Pallet

31 Temperature-regulating device

32 Temperature-regulating element

33 Installation assistance device 34 Mounting

35 Tube

Ml to M6 Mirrors

Claims

P a t e n t C l a i m s

1. Method for regulating the temperature of an optical module (24) for microlithography, comprising the following steps: a) providing an optical module (24),

- wherein the optical module (24) has an optical element (25) to be temperature regulated, b) regulating the temperature of the optical module (24), in particular of the optical element (25) to be temperature regulated, c) installing the optical module (24) in a projection exposure apparatus (1), and d) adjusting at least one optical element, preferably adjusting the optical element (25) to be temperature regulated, in the projection exposure apparatus (1),

- wherein step b) takes place at least for a time before and/or during step d).

2. Method according to Claim 1, characterized in that step b) takes place at least for a time before, during and/or after step c).

3. Method according to Claim 1 or Claim 2, characterized in that the optical module (24) has a mount (26) and/or a frame (27), and in that, preferably, the temperature of the mount (26) and/or of the frame (27) is regulated in step b).

4. Method according to any of Claims 1 to 3, characterized in that before step c), some other optical module is demounted from the projection exposure apparatus (1).

5. Method according to any of Claims 1 to 4, characterized in that the method comprises at least one of the following steps: al) providing at least one, preferably external and/or mobile, temperatureregulating device (31) for regulating the temperature of the optical module (24), a2) providing a, preferably mobile, storage device (28) for receiving and/or transporting the optical module (24), and/or a3) providing at least one temperature-regulating element (32), wherein the temperature-regulating element is connectable to the optical module (24).

6. Method according to Claim 5, characterized in that in step b), the temperature of the optical module (24) is regulated at least for a time by means of the temperature-regulating device (31), and/or in that the temperature -regulating device (31) is connected to the optical module (24) at least for a time in step b).

7. Method according to Claim 5 or Claim 6, characterized in that in step b), in particular before step c) and/or before step d), the temperature of the optical module (24) is regulated at least for a time by means of the temperature -regulating device (31) in the storage device (28), and/or in that the temperature -regulating device (31) is connected to the storage device (28) at least for a time in step b), in particular before step c) and/or before step d).

8. Method according to any of Claims 5 to 7, characterized in that in step b), in particular during step c), after step c) and/or during step d), the temperature of the optical module (24) is regulated at least for a time by way of the temperature-regulating element (32) by means of the temperature-regulating device (31), and/or in that the temperature -regulating element (32) is connected to the optical module (24) and/or the temperature-regulating device (31) at least for a time, in particular during step c), after step c) and/or during step d).

9. Method according to any of Claims 5 to 8, characterized in that the optical module (24) is received and/or is transported in the storage device (28) at least for a time during step b).

10. Method according to Claim 9, characterized in that the optical module (24) is removed from the storage device (28) before step c), preferably after the other optical module has been demounted from the projection exposure apparatus (1).

11. Method according to any of Claims 1 to 10, characterized in that the method comprises the following step: e) measuring a field position and/or a pupil position of the projection exposure apparatus (1).

12. Method according to Claim 11, characterized in that step e) takes place at least for a time before, during and/or after step d), and/or in that steps d) and e) are carried out iteratively, in particular are carried out iteratively until the field position and/or the pupil position satisfy a required specification.

13. Method according to any of Claims 1 to 12, characterized in that in step d], an orientation and/or a position of an optical element, preferably of the optical element [25] to be temperature regulated, of the projection exposure apparatus (1) are/is adjusted, in particular depending on the field position and/or pupil position measured in step e).

14. Method according to any of Claims 1 to 13, characterized in that step b) begins at least 1 h, preferably at least 5 h, more preferably at least 10 h, more preferably at least 20 h, in particular at least 40 h, before step c) and/or before step d).

15. Method according to any of Claims 1 to 14, characterized in that in step b], the temperature of the optical module (24] is regulated to a target temperature, in that, preferably, the target temperature is at least 10°C, preferably at least 15°C, in particular at least 20°C and/or at most 35°C, preferably at most 30°C, in particular at most 25°C, and/or in that, preferably, the temperature regulation to the target temperature takes place with a deviation of at most 1°C, preferably at most 0.5°C, in particular at most 0.2°C.