Method for determining the tightness of an optical module of an optical assembly, optical assembly, and projection exposure system having an optical assembly

Abstract

The invention relates to a method for determining the tightness of a first optical module (101, 2011-5) of an optical assembly (100, 200), having the following steps: a) providing a first operating pressure in the interior of the housing (103, 203) of the optical assembly (100, 200), the first operating pressure being lower than a second operating pressure in a closed cavity (111, 211) of the first optical module (101, 201.1-5), b) providing a first purge gas flow (112) having a purge gas and a first detector gas in the closed cavity (111, 211) of the first optical module (101, 201.1-5) by means of a first purge device (113, 114, 213, 214), c) determining the content of detector gas in the interior of the housing (102, 202) by means of a detector (116, 216), and d) comparing the determined content of the first detector gas with at least one content target value of the first detector gas in order to determine the tightness of the connecting region of the first optical module (101, 201.1-5).

Description

[0001] Method for determining the tightness of an optical assembly of an optical arrangement, optical arrangement, projection exposure system with optical arrangement

[0002] Reference to related registration

[0003] This application claims priority over German patent application 102024208828.5 dated September 17, 2024, the entire disclosure of which is incorporated by reference into this application.

[0004] Field of invention

[0005] The invention relates to a method for determining the tightness of an optical assembly of an optical arrangement by providing a detector gas into a cavity of the optical arrangement and determining a proportion of the detector gas in an interior space of the optical arrangement separated from the cavity.

[0006] The invention further relates to an optical arrangement with at least one optical assembly, a housing and at least one purging device, wherein the optical assembly has at least one optomechanical element that is at least partially received by a support structure, forms a cavity with it and wherein a purging gas stream comprising a purging gas and a detector gas can be provided by the purging device.

[0007] The invention further relates to a projection exposure system for EUV lithography.

[0008] State of the art

[0009] Projection exposure systems for semiconductor lithography are used to fabricate microstructured devices using a photolithographic process. In this process, a structure-bearing mask, the so-called reticulum, is projected onto a photosensitive layer using projection optics or a projection system. The minimum feature size that can be imaged using such projection optics is determined by the wavelength of the imaging light. The smaller the wavelength of the imaging light, the smaller the structures that can be imaged. Currently, imaging light with a wavelength of 193 nm or imaging light with a wavelength in the extreme ultraviolet (EUV) range, i.e., at least 5 nm and at most 30 nm, is primarily used.When using imaging light with a wavelength of 193 nm, both refractive and reflective optical elements are used within the projection imaging system. When using imaging light with a wavelength in the EUV range, only reflective optical elements, especially mirrors, are used, which are typically operated under vacuum conditions in a vacuum environment.

[0010] Such optical elements typically have a reflective surface, that is, a reflective coating applied to a substrate of the optical element. If the wavelength of the imaging light used is in the EUV range between 5 nm and 30 nm, the reflective coating typically comprises several individual layers consisting of alternating materials with different refractive indices. Such a multilayer system can, for example, have alternating silicon and molybdenum layers. During operation of the projection exposure system, the reflective coating is exposed to EUV radiation, which promotes a chemical reaction between the layer materials and gaseous substances present in a residual gas atmosphere within the interior of the projection exposure system.This process causes a degradation of the layer materials used, which leads to a reduction in layer reflection and thus impairs the transmission of the overall system.

[0011] To protect the individual layers from degradation, a topcoat, which may consist of ruthenium, for example, is typically applied to the reflective coating. For a possible structure of the topcoat, reference is made to DE 10 2014 204660 A1. Degradation, such as oxidation, can also occur on such a topcoat through a chemical reaction with residual gas present in the vacuum environment, whereby the chemical reaction is triggered or at least promoted by EUV radiation. This degradation of the topcoat during operation of the projection exposure system also leads, in particular, to an undesirable reduction in the reflectivity of the respective optical element and thus to a reduction in its overall transmission.From the prior art, DE 10 2010 041 468 A1 describes an optical assembly of an optical arrangement of an EUV projection exposure system for EUV lithography, comprising a plurality of optical elements. These optical elements can each be actuated or controlled by an actuator assigned to the respective optical element. The respective actuator is designed to generate a variable magnetic field and, for this purpose, is arranged in a vacuum-tight housing separate from the respective optical element, since some of the electronic components required for the actuator's operation cannot be used in a vacuum environment.For the operation of the projection exposure system, a first operating pressure (typically a technical vacuum of an inert or reducing atmosphere) is provided in the area of ​​the optical elements, which differs from a second operating pressure within the vacuum-tight housing with the actuators in such a way that the first operating pressure is smaller than the second operating pressure.

[0012] This creates the risk that, in the event of a leak in the housing, some of the housing atmosphere could enter the area of ​​the actuated optical elements, thus increasing the initial operating pressure. Typically, however, standard materials (e.g., paints or plastics) are used inside the housing, which are not suitable for use under EUV conditions. Oxidizing components such as oxygen may also be present in the housing atmosphere. These substances promote the previously described degradation of the coating, meaning that a potential leak in the housing directly affects the reflectivity of the optical elements.

[0013] In the case of smaller leaks, such as those increasing the initial operating pressure by 0.01–10%, it is difficult to detect them by changing the initial or secondary operating pressure. However, even these types of leaks increase the risk of coating degradation. Similarly, direct monitoring of the gas composition in the optical element area with regard to degrading species, such as oxygen, has proven insufficiently sensitive.

[0014] The object of the invention is therefore to provide an improved method for operating an optical arrangement for an EUV projection exposure system, which improves the determination of the tightness of the optical arrangement. This should reduce the risk of degradation of optical layers of the optical arrangement.

[0015] This problem is solved according to the features of independent claim 1.

[0016] The inventive method for determining the tightness of a first optical assembly of an optical arrangement comprises the following steps:

[0017] - Providing a first operating pressure in an interior space of an optical arrangement housing, wherein the first operating pressure is lower than a second operating pressure in a sealed cavity of the first optical assembly,

[0018] - Providing a first purge gas stream comprising a purge gas and a first detector gas in the enclosed cavity of the first optical assembly by means of a first purge device

[0019] - Determination of the proportion of the first detector gas inside the housing by a detector

[0020] - Comparison of the determined proportion of the first detector gas with at least one target proportion of the first detector gas for determining the tightness of the first optical assembly.

[0021] In one variant, the method according to the invention comprises, as a step preceding the steps mentioned above: providing the optical arrangement with the first optical assembly.

[0022] In a variant of the method according to the invention, several optical assemblies can also be connected in such a way that the sealed cavities of the individual optical assemblies form a common cavity. The first purge gas stream, containing the purge gas and the first detector gas, is thus supplied to all optical assemblies, typically with a flow rate of 0.5–5 l / min, thereby enabling the simultaneous leak testing of several optical assemblies.

[0023] For the method according to the invention, nitrogen or another inert gas, different from the first detector gas, is typically provided as the purge gas. The purge gas in the first purge gas stream serves to reduce substances within the sealed cavity that promote the degradation of optical elements. The first detector gas in the first purge gas stream is advantageously selected such that it is not present, or only present in very small quantities, within the atmosphere of the housing interior at the first operating pressure. This enables a very sensitive leak test. The target proportion of the first detector gas is typically based on empirical values. For a detector gas that is not present in the housing interior, this value can be approximately one order of magnitude higher than the detector's detection limit for that detector gas.

[0024] According to one embodiment of the method, the tightness of at least one second optical assembly of the optical arrangement is determined independently of the first optical assembly. This embodiment of the method therefore requires that the optical arrangement comprises at least two optical assemblies. The first operating pressure provided inside the housing is also lower than a third operating pressure in a sealed cavity of the second optical assembly. In addition to the method according to the invention, this embodiment includes the following steps:

[0025] - Providing a second purge gas stream comprising a purge gas and a second detector gas in the enclosed cavity of the second optical assembly by means of a second purge device

[0026] - Determination of the proportion of the second detector gas inside the housing by the detector

[0027] - Comparison of the determined proportion of the second detector gas with at least one target proportion of the second detector gas for determining the tightness of the second optical assembly.

[0028] The second purge device allows the at least two optical assemblies to be treated independently with their respective purge gas and the first or second detector gas. Since the optical assemblies may differ in their design, purge gas and / or detector gas flows tailored to each individual assembly can be provided. The first and second detector gases can be the same, enabling, for example, the separate testing of multiple optical assemblies. Thus, using the same gas as both the first and second detector gas allows for the independent testing of several optical assemblies.

[0029] In a particularly advantageous embodiment of the method for independently verifying the leak tightness of at least two optical assemblies using at least two purge devices, a second detector gas different from the first is used. Naturally, more than two different detector gases can be used by employing more than two purge devices or correspondingly more dosing devices within a purge device. This allows the leak tightness verification steps for the first and second optical assemblies to be performed independently and simultaneously, enabling particularly efficient verification. This is achieved by exploiting the fact that different detector gases can be detected independently of one another by the detector in their respective purge gas streams.For example, if a residual gas analyzer is used as a detector, it is advantageous that the different detector gases have different masses.

[0030] According to one embodiment of the method according to the invention, the proportion of the first and / or second detector gas is determined with time resolution. If several optical assemblies, connected in series, are tested for leaks using a first purge device, this embodiment allows for localization within the volume to be tested. Knowing the flow rate of the purge gas stream, which contains the purge gas and the detector gas(es), as well as the volumes of the individual connected, sealed cavities, it is possible to estimate, based on the temporal measurement, how far the detector gas has reached in the purge gas stream. In this way, in the case of several optical assemblies connected in series, it is possible, for example, to easily identify the affected optical assembly.For this embodiment of the method according to the invention, it is advantageous if the respective rinsing device comprises at least two metering devices, so that the proportion of the respective detector gas in the rinsing gas stream can be varied.

[0031] According to a further embodiment of the method according to the invention, the composition of the first and / or second detector gas in the respective purge gas stream is varied over time. Particularly for time-resolved measurements, this offers a further possibility of improving localized detection, as the variation of the first and / or second detector gas during the time-resolved measurement allows the detector to repeatedly detect increases and / or decreases in the concentrations of the various components of the first and / or second detector gas. For this embodiment of the method according to the invention, it is advantageous if the respective purge device comprises several metering devices, such that each component is assigned its own metering device.

[0032] According to one embodiment, the inventive method is carried out temporarily or permanently before commissioning a projection exposure system. For the purposes of this application, commissioning means the commencement of the supply of EUV light to the EUV projection exposure system, which passes through the optical arrangement section by section. Before commissioning, the required operating pressures are already supplied both inside the housing and in the sealed cavity(ies) of the optical assembly(s). Likewise, the purge gas flow(s) is supplied, consisting of the purge gas and the first detector gas or the first and second detector gases. Particularly immediately before commissioning the projection exposure system, there is a risk of degradation of the optical elements, as contaminants adhere especially easily during this phase.This method can also be used to verify whether the existing sealing properties of one or more optical assemblies have been maintained by the prior integration of optical arrangements into the projection exposure system. For economic reasons, a temporary check may suffice.

[0033] According to one embodiment, the inventive method is carried out intermittently or continuously during operation of the projection exposure system. Particularly during operation of the projection exposure system, it may be necessary to continuously check the tightness. At particularly critical points, this can be done continuously. Where the risk is lower, the check can be carried out intermittently for economic reasons.

[0034] According to one embodiment of the method according to the invention, a pressure between 1 and 25 Pa is provided as the first operating pressure inside the housing, and a pressure between 85 and 110 kPa is provided as the second and / or third operating pressure in the cavities. The first operating pressure is advantageously provided by a hydrogen atmosphere. In the simplest case, the second and / or third operating pressure can initially be provided by connecting the sealed cavity of the optical assembly to an external atmosphere. In the further course of the method, the second and each subsequent operating pressure of a sealed cavity of an optical assembly is provided and / or maintained by the respective purge gas flow.The operating pressures in the cavities are advantageously chosen in such a way as to ensure damage-free operation of the electronics required for the optomechanical components.

[0035] According to a further embodiment of the method according to the invention, a gas from the group comprising helium, argon, krypton, xenon, CO2, CF4, and / or SFe is selected as the first and / or second, as well as any further possible, detector gas. The respective total proportion is 0.1–5%, in particular 1.5–3.5%, of the respective purge gas stream. These gases, as well as mixtures thereof, are chemically inert and available in high purity. These gases can also be very well distinguished from one another by a detector, in particular a residual gas analyzer.

[0036] According to a further embodiment of the method according to the invention, the proportion of the first detector gas and / or the second detector gas, as well as any other possible detector gas, in the interior of the housing is determined as partial pressure, sum of partial pressures, and / or leakage rates. For this purpose, pre-calibrated gas-specific sensors can be used, for example. In particular, the use of a residual gas analyzer enables the detection of corresponding partial pressures or equivalent quantities that allow for conversion into partial pressures.

[0037] According to a further embodiment of the method according to the invention, the at least one target value of the first detector gas and / or the at least one target value of the second detector gas each corresponds to a pre-warning value. A pre-warning value refers to a fraction of the detector gas that indicates an increased risk of degradation of the optical surfaces, but still ensures at least temporary, safe operation of the optical arrangement. If at least one of these pre-warning values ​​is exceeded by the respective determined fraction of the first detector gas or any other detector gas, a remaining service life of the affected optical assembly is determined in a further step. This allows for better planning of particularly time-consuming maintenance and replacement of optical assemblies within optical arrangements and enables them to be combined with other regularly required maintenance measures.This allows for a particularly advantageous reduction in operating downtime of the projection exposure system.

[0038] According to a further embodiment of the method according to the invention, the at least one setpoint value of the first detector gas and / or the at least one setpoint value of the second detector gas each corresponds to an exchange value. An exchange value represents a proportion of one of the detector gases that indicates a criticality for potential degradation of the optical surfaces, necessitating the immediate replacement of the affected optical assembly. The exchange value indicates a leakage in the affected optical assembly that could cause irreversible degradation of the corresponding optical elements. Therefore, in a further step, if at least one of these exchange values ​​is exceeded by the determined proportion of one of the detector gases, an immediate replacement of the affected optical assembly is indicated.By immediately replacing the affected optical assembly, the loss of this optical assembly can be avoided, or at least the effort required for its repair can be significantly reduced.

[0039] Furthermore, it is an object of the invention to provide an optical arrangement with at least one optical assembly for an EUV projection exposure system, which ensures reliable monitoring and control of the tightness of this at least one optical assembly.

[0040] The optical arrangement according to the invention for an EUV projection exposure system comprises a first optical assembly and a housing that at least partially encloses the first optical assembly and further encapsulates a section of an EUV beam path within the EUV projection exposure system. The first optical assembly comprises a support structure and at least one optomechanical element for controlling an optical element, wherein the optomechanical element is at least partially received by the support structure and forms a sealed cavity with the support structure. This creates a connection between the sealed cavity and an interior space of the housing, sealing them from one another. The optical arrangement also includes a detector designed to determine the composition of the atmosphere within the housing.Furthermore, the optical arrangement comprises a first purge device for providing a first purge gas stream within the enclosed cavity of the first optical assembly. The optical arrangement is characterized in that the first purge gas stream comprises a purge gas and a first detector gas.

[0041] The optomechanical element is typically an actuator for generating a variable magnetic field, which can be a piezoelectric actuator or a coil with an electric current through it. The optomechanical element ensures the actuation of the associated optical element, which is designed to reflect EUV light. The first optical assembly can comprise a multitude of optomechanical elements, each with its own associated optical elements. These elements can be arranged in a matrix within the first optical assembly, whereby the sum of the individual optical surfaces of the elements forms a complete optical surface for the first optical assembly.

[0042] Since the materials and substances used in the operation of the optical arrangement for the at least one optomechanical element promote degradation of the at least one optical element and thus reduce its reflectivity, the at least one optomechanical element is at least partially enclosed by the supporting structure. The resulting cavity advantageously encapsulates these materials and substances, thereby reducing degradation of the optical element. The first optical assembly within the optical arrangement is formed by the at least one optomechanical element, the supporting structure, and the optical element. The enclosure of the at least one optomechanical element by the supporting structure creates a connection area that vacuum-tightly separates the formed cavity from the interior of the housing surrounding the first optical assembly.For the purposes of this application, "vacuum-tight" preferably means a tightness against a vacuum of at least 10⁻³ mbar*l / s, in particular at least 10⁻⁶ mbar*l / s. This vacuum-tight separation further improves the prevention of degradation of the optical element.

[0043] Additionally, the optical arrangement includes the first purge device, which provides the purge gas and the first detector gas within the sealed cavity of the first optical assembly. Typically, the purge gases used are inert gases such as nitrogen or noble gases. The purge gas of the first purge gas stream advantageously removes materials and substances, such as paints and plastics, present in the gas phase of the sealed cavity used for optomechanical elements. Furthermore, the proportion of oxidizing species such as oxygen can be reduced by the purge gas of the first purge gas stream.Overall, the first purge gas stream provided by the first purge device further improves the prevention of degradation of the at least one optical element during operation, as the proportion of the aforementioned species within the enclosed cavity is reduced, thus also reducing the entry into the interior of the housing in the event of a leak.

[0044] However, due to the constantly increasing demands on EUV projection exposure systems, in the event of leaks, especially smaller leaks that increase the operating pressure inside the housing by a maximum of 0.01 - 10%, a critical proportion of the aforementioned species can enter the interior of the housing, potentially leading to degradation of the optical elements.

[0045] To improve leak detection and control, the first purge gas stream also includes the first detector gas. This first detector gas can be determined by the detector, which monitors the atmosphere inside the housing, after any leakage from the first optical assembly into the sealed cavity. Advantageously, a detector gas is used that is not present in the atmosphere inside the housing and is itself chemically inert. For example, the first detector gas that can be provided by the first purge device is helium, argon, krypton, xenon, CO2, CF4, or SFe. In the simplest case, the first detector gas can be supplied, for example, via a metering device of the first purge device as a mixture with the purge gas from a reservoir. For monitoring the interior of the housing, the detector can be directly integrated into the housing.In this case, the detector is advantageously attached to the housing. Alternatively, the detector can be indirectly associated with the housing by being placed on an outer housing that encloses the housing of the optical arrangement. The detector is typically a residual gas analyzer. The residual gas analyzer allows for the targeted monitoring of specific mass ranges of the first detector gas. In the case of a non-isotopically pure first detector gas, the isotopic ratios can also be used for detection.

[0046] This arrangement allows for the detection of leaks during operation of the optical system, particularly small leaks that increase the operating pressure inside the housing by, for example, 0.01–10%. This enables the early detection of a leak that is critical for the degradation of the optical elements of the first optical assembly. Depending on the detected leak rate, this allows for the immediate or prompt replacement of the first optical assembly to be planned. By planning for a prompt replacement, the downtime of the EUV projection system can be advantageously reduced by combining it with other maintenance work.

[0047] According to one embodiment, the first purge device comprises a first and at least one second metering device. The first and second metering devices of the first purge device allow the purge gas to be supplied separately from the first detector gas. This makes it possible to adjust and vary the overall proportion of the first detector gas in the purge gas flow, for example, between 0.1 and 5%, as desired. Thus, different sensitivities for leak detection can be set. If the first purge device comprises more than two metering devices, mixtures of any composition, in particular of the gases already mentioned, can also be supplied as the first detector gas, or switching between different gases is possible. In these cases, it is advantageous if the different gas species or components that constitute the first detector gas have a signature that is at least partially, and in particular completely, distinguishable in the detector.

[0048] According to one embodiment, the optical arrangement 2-12 comprises optical assemblies. For improved imaging capabilities, it may be necessary for the optical arrangement 2-12, in particular 4-10, and further, in particular 6, to comprise optical assemblies. Each individual optical assembly, as described, comprises at least one optomechanical element with an associated optical element. However, each of the optical assemblies can also comprise a plurality of these components, as described. To check the tightness of all assemblies, the first purge device can, for example, be connected to the optical assemblies in series or parallel. For this purpose, the first purge device is connected to several optical assemblies that are continuously connected to one another, or the first purge device is connected to each individual optical assembly in parallel.The first purge gas stream can thus be supplied to several optical assemblies. A combination of series or parallel connections can also be used, or the first purge device can be assigned to only some of the optical assemblies. Each of these arrangements allows for the simultaneous leak tightness testing of multiple optical assemblies. In this embodiment, the first purge device can also comprise a first and at least one second metering device.

[0049] According to an advantageous embodiment of the optical arrangement with 2-12 optical assemblies, this optical arrangement comprises at least two purging devices assigned to different optical assemblies. Each of the at least two purging devices can comprise a first and at least one second metering device, as described. This embodiment allows the optical assemblies to be checked for leaks individually or in groups independently of one another. Sampling can be performed, for example, using a gas species as a detector gas, which can be supplied to the individual optical assemblies or groups of optical assemblies via the respective purging gas stream at different times. A leak can be attributed to a specific optical assembly based on the time of detection of this detector gas.It is also possible to provide different gas species as detector gas for individual optical assemblies or groups of optical assemblies via the respective purge gas flows. The leak tightness of various optical assemblies can be checked simultaneously, since the detection of a specific gas species as detector gas can be assigned to a specific optical assembly. In one variant of the optical arrangement, the connection area is formed by a closing element of the optomechanical element and a sealing element. The closing element is pressed against a body of the optomechanical element by the sealing element, thus encapsulating the interior of the body from the interior of the housing. Since the interior of the body of the optomechanical element is in contact with the sealed cavity, or rather...As part of this enclosed cavity, the end element, together with the sealing element, encapsulates the enclosed cavity from the interior of the housing. The sealing element typically comprises an elastomeric plastic, while the end element typically comprises a ceramic material. If the at least one optical assembly comprises several optomechanical elements, then consequently several connection areas are formed, each consisting of a sealing element and an end element.

[0050] The invention further relates to a projection exposure system with an optical arrangement having the features described above.

[0051] The invention will now be explained in more detail with reference to the drawings.

[0052] This shows

[0053] Figure 1 shows an optical arrangement for an EUV projection exposure system comprising a first optical assembly, a housing, a detector and a first purging device according to an exemplary embodiment.

[0054] Figure 2 shows an optical arrangement for an EUV projection exposure system with several optical assemblies, a housing, a detector and two rinsing devices, wherein both rinsing devices are assigned to different optical assemblies, according to an exemplary embodiment.

[0055] Figure 3 shows a process flow of the method according to the invention. Figure 4 shows an optical arrangement for an EUV projection exposure system with several optical assemblies, a housing, a detector, and a first purge device during a step of the method according to the invention, and a time-resolved signal profile with varying detector gas according to an exemplary embodiment.

[0056] Figure 5 shows an optical arrangement for an EUV projection exposure system with an optical arrangement according to an exemplary embodiment.

[0057] Figure 1 shows an embodiment of an optical arrangement 100 according to the invention. A cross-sectional view is shown. The optical arrangement 100 comprises a first optical assembly 101 which is at least partially enclosed by a housing 102. This forms an interior space 103 of the housing 102 containing the first optical assembly 101. The first optical assembly 101 comprises a support structure 104 and optomechanical elements 105 which are at least partially received by the support structure 104. By receiving the optomechanical elements 105 in the support structure 104, a connection area is formed, which in the embodiment of Figure 1 is formed by a closing element 106 and a sealing element 107. The sealing element 107 typically comprises an elastomeric plastic. The closing element 106 typically comprises a ceramic material.

[0058] The optomechanical element 105 is designed to control an optical element 108. The optical element 108 has an optical surface 109 designed to reflect EUV light 110.

[0059] Furthermore, the support structure 104, by accommodating the optomechanical elements 105, forms a sealed cavity 111 within the support structure 104. This design allows for different operating pressures and atmospheric compositions in the interior of the housing 103 and the sealed cavity 111. For example, a first operating pressure required for EUV operation can be provided as a technical vacuum in the interior 103 of the housing 102, while a second operating pressure, required for the operation of the electronics of the optomechanical elements 105, can be provided in the sealed cavity 111, in the range of atmospheric pressure. Thus, the first operating pressure for the operation of the optical arrangement 100 is lower than the second operating pressure. Typically, the first operating pressure is 1–25 Pa and the second operating pressure is 85–110 kPa.

[0060] In the event of a leak in the optical arrangement 101, particularly in the connection area formed by the end element 106 and the sealing element 107, gaseous components from the sealed cavity 111 will enter the interior of the housing 103 during operation. These include substances and materials such as paints or plastics, as well as oxidizing species such as oxygen or water, which are unsuitable for EUV operation. These can cause or promote degradation of the optical surface 109 of the optical elements 108.

[0061] Therefore, the optical arrangement 100 is associated with a first purge device for providing a first purge gas flow 112 within the enclosed cavity. The first purge device comprises an inlet 113 and an outlet 114, which are connected to the enclosed cavity 111 of the optical assembly 101. In the embodiment shown in Figure 1, the inlet 113 and the outlet 114 are located within the housing 102, so that the supply for providing the first purge gas flow 112 is provided from outside the housing 102. For this purpose, the first purge device has a first metering device 115 at the inlet for providing a purge gas for the first purge gas flow 112. Typically, an inert gas, such as nitrogen or a noble gas, is chosen as the purge gas.The described critical materials and substances can be continuously removed from the enclosed cavity 111 through the outlet 114 of the first purge device by means of the purge gas of the first purge gas stream 112, and their proportion can be advantageously reduced.

[0062] Nevertheless, there is a risk that, in the event of a leak, a still critical proportion of the described substances and materials could enter the interior 103. Therefore, the optical arrangement 100 is designed such that the tightness of the first optical assembly 101 can be checked temporarily or permanently. For this purpose, a detector 116 for determining the composition of the atmosphere in the interior 103 of the housing 102 is assigned to the optical arrangement 100. The detector can, for example, be designed as a residual gas analyzer or a gas-specific sensor. Since the detector 116 has insufficient sensitivity for the described critical substances and materials, which cause degradation even in very small quantities, as well as for the purge gas of the first purge gas stream 112, detecting a leak solely by directly detecting these substances with the detector 116 is insufficient.Therefore, the first purge device of the exemplary embodiment of the optical arrangement 100 according to Figure 1 comprises a second metering device 117 for supplying a first detector gas for the purge gas stream. Advantageously, the first detector gas is itself a chemically inert gas that is not present in the atmosphere of the interior 103 or only occurs in very small quantities. Examples are helium, argon, krypton, xenon, CO2, CF4, or SFe. In the event of a leak, the first detector gas thus also enters the interior 103 and can be detected by the detector 116. A proportion of the first detector gas determined in this way can then be compared with a target value for the first detector gas, so that the criticality of a potential leak of the first optical assembly 101 can be determined.

[0063] In the embodiment shown in Figure 1, the optical arrangement 100 comprises a first optical assembly 101 connected to the first purge device. It is also possible for the optical arrangement 100 to comprise, in addition to this first optical assembly 101, further optical assemblies connected to the first purge device. In order to check the tightness of all optical assemblies, particularly simultaneously, the first purge device can then be assigned to the optical assemblies, for example, by a series or parallel connection, or a combination thereof. Furthermore, the first purge device of the optical arrangement can have additional metering devices (not shown). This advantageously allows mixtures of different components, particularly variable over time, of the first detector gas to be provided.

[0064] Figure 2 shows a further embodiment of the optical arrangement 200 according to the invention. A perspective top view is shown. The optical arrangement 200 comprises ten optical assemblies 201.1–201.10 which are at least partially enclosed by a housing 202. This forms an interior space 203 of the housing 202 containing the optical assemblies 201.1–10. A detector 2016 is arranged on the housing 202 to determine the composition of the atmosphere of the interior space 203 of the housing 202. The optical assemblies 201.1–10 each comprise a support structure and optomechanical elements 205 that are at least partially received by the respective support structure. These elements are arranged in rows and columns, as shown by way of example for optical assembly 201.3.By incorporating the optomechanical elements 205 into the respective supporting structure, a connection area and a closed cavity 211 are formed within the optical assembly (shown for 201 .3).

[0065] Furthermore, the optical arrangement 200 comprises a first and a second purge device for reducing substances and materials that promote the degradation of optical surfaces. The first purge device includes an inlet 213 with a first metering device 215 and a second metering device 217, as well as an outlet 214. The inlet 213 is connected via a series connection with connecting pieces to the sealed cavities (example 211 for 201.3) of the optical assemblies 201.1-5. The first metering device 215 serves to supply a purge gas for a first purge gas stream, and the second metering device 217 serves to supply a first detector gas for the first purge gas stream into the cavities of the associated optical assemblies (201.1-5).

[0066] The second purge device comprises an inlet 220 with a first metering device 221, a second metering device 222, and a third metering device 223, as well as an outlet 224, which are connected to the sealed cavities of the optical assemblies 201.6–201.10. The first metering device 221 serves to supply a purge gas of a second purge gas stream 212, and the second metering device 222 serves to supply a second detector gas for the second purge gas stream 212 into the cavities of the associated optical assemblies (201.6–10). The third metering device 223 enables, for example, the supply of a further component of the second detector gas if a mixture, particularly one that can be varied over time, of detector gases is desired.

[0067] In the embodiment shown in Figure 2, the inlets 213, 220 and the outlets 214, 224 are also housed within the casing 202, so that the purge gas flows are supplied from outside the casing 202. In this embodiment, the optical assemblies 201.1-5 and 201.6-10 can each be independently tested for leak tightness in groups by means of the first and second purge devices of the optical arrangement 200. For example, when using the same detector gas, the first and second purge devices allow for the separation of the tests by determining the leak tightness of the respective groups. When different gas species are supplied as the first and second detector gas by the respective second metering devices 217 and 222 into the respective purge gas flows, the leak tightness of the two groups of optical assemblies 201.1-5 and 201.6-10 can be determined independently of each other.Six to ten simultaneous and independent measurements are possible. For this to work, the different first and second detector gases should be sufficiently distinguishable by the detector used. For example, in a residual gas analyzer, the detector must have different masses. Simultaneous, independent determination of the leak tightness allows for particularly efficient testing.

[0068] In the embodiment shown in Figure 2, the optical arrangement 200 comprises two flushing devices, each assigned to a group of optical assemblies. It is also possible for the optical arrangement 200 to comprise further flushing devices, in particular for each individual optical assembly to have its own separate flushing device. Such an arrangement allows for the efficient and direct identification of a leaking optical assembly, thereby further reducing the time required for replacement. Likewise, it is conceivable that the optical arrangement 200 comprises more or fewer than ten optical assemblies, in particular 2 to 12 optical assemblies.

[0069] Figure 3 shows an embodiment of the inventive method for determining the tightness of at least one first and one second optical assembly of an optical arrangement. The method according to the invention can be applied to the optical arrangement according to the invention.

[0070] In a first step, an initial operating pressure is established within the interior of an optical assembly housing. This initial operating pressure is typically 1–25 Pa and is generated, for example, by a reducing atmosphere, particularly hydrogen. This enables the propagation of EUV light within the optical assembly while simultaneously suppressing contamination. This initial operating pressure is lower than a second operating pressure within a sealed cavity of the first optical assembly. Typically, the second operating pressure is 85–110 kPa and, in the simplest case, can be achieved by a pressureless connection between the sealed cavity and the external atmosphere.The pressure range of the second operating pressure ensures damage-free operation of the electronics required for the function of optomechanical elements within the sealed cavity of the first optical assembly. In the event of a leak, components from the sealed cavity of the first optical assembly will therefore enter the interior of the optical arrangement's housing.

[0071] Therefore, in a second step b of the inventive method, a first purge gas stream is provided in the sealed cavity of the first optical assembly, comprising a purge gas and a first detector gas. Typically, the purge gases used are inert gases such as nitrogen or noble gases. The purge gas of the first purge gas stream advantageously removes or at least reduces materials and substances, such as paints and plastics, that are necessary for the use of optomechanical elements in the gas phase of the sealed cavity of the first optical assembly but would promote degradation in the event of a leak. A purge gas flow rate of 0.5–5 l / min can be selected. Furthermore, a first detector gas is provided for the first purge gas stream in this step.Advantageously, a detector gas is used that is not present in the atmosphere of the interior or only in small quantities and is itself chemically inert. Examples of detector gases include helium, argon, krypton, xenon, CO2, CF4, or SFe. The first detector gas can be provided at a concentration of 0.1–5%, particularly 1.5–3.5%. If a device according to the embodiment of Figure 1 is selected, the purge gas of the first purge gas stream 112 can be provided by the first metering device 115 of the first purge device, and the first detector gas of the first purge gas stream 112 can be provided by the second metering device 117 of the first purge device.

[0072] In a third step c, a detector determines the proportion of the first detector gas inside the housing. For example, a residual gas analyzer or a gas-specific sensor can be used as the detector. The proportion of the first detector gas can be determined as partial pressure, sum of partial pressures, and / or leak rates. The detector may also be designed to detect components of the purge gas or critical materials and substances. However, the detector typically detects the described critical substances and materials, which cause degradation of optical surfaces even in very small quantities, as well as components of the purge gas, with insufficient sensitivity. Only the detector gas provides sufficient sensitivity for verifying the tightness of an optical assembly using the method according to the invention.

[0073] To determine the tightness of the first optical assembly, in a fourth step d, the measured proportion of the first detector gas is compared with at least one target value for the first detector gas. This target value is typically based on empirical values ​​and, as a limit, generally indicates a tightness class of the first optical assembly and its criticality for potential degradation of optical surfaces. If the measured proportion of the first detector gas exceeds the target value, this criticality is indicated.

[0074] For example, the determined target value of the first detector gas in step d can correspond to a pre-warning value. A pre-warning value represents a proportion of the first detector gas that indicates an increased risk of degradation of optical surfaces, but still ensures safe operation of the optical arrangement, at least temporarily. If the pre-warning value is exceeded by the determined proportion of the first detector gas, a remaining operating time for the affected optical assembly is determined in step h. This makes particularly time-consuming maintenance and replacement of optical assemblies within optical arrangements easier to plan and allows them to be combined with other routine maintenance measures. This can significantly reduce downtime for the projection exposure system.

[0075] Similarly, the target value in step d can correspond to a replacement value. A replacement value refers to a fraction of the detector gas that indicates a criticality for the degradation of optical surfaces, necessitating the immediate replacement of the affected optical assembly. This replacement value indicates a leak in the affected optical assembly that could cause irreversible degradation of the corresponding optical surfaces. Therefore, in step i, if the replacement value is exceeded by the determined fraction of the detector gas, an immediate replacement of the affected optical assembly is indicated. Such a replacement can prevent the loss of this optical assembly or at least significantly reduce the effort required for its repair.

[0076] Steps a-d, including h and i, in Figure 3 of the embodiment of the method according to the invention are not limited to a first optical assembly. By connecting the first purge device in series or parallel, several optical assemblies can be jointly tested for leaks, and the first purge gas stream, containing the purge gas and the first detector gas, is provided accordingly in several optical assemblies. Likewise, the first purge device can include a third and further metering devices, so that, for example, a first detector gas with different components can be provided.

[0077] For the independent determination of the tightness of the at least one second optical assembly, a fifth step e of the embodiment of the inventive method according to Figure 3 involves providing a second purge gas stream, comprising a purge gas and a second detector gas, in a sealed cavity of the at least one second optical assembly. For the same reasons as for the first optical assembly, a third operating pressure in the sealed cavity of the second optical assembly is greater than the first operating pressure in the interior of the housing of the optical arrangement. Typically, for the second purge gas stream, inert gases such as nitrogen or noble gases are used for the purge gas stream to reduce contaminants. The second purge gas stream is provided by the second purge device independently of the first purge gas stream.Furthermore, in this step, a second detector gas is provided for the second purge gas stream. Advantageously, helium, argon, krypton, xenon, CO2, CF4, and / or SFe are also used as the detector gas. The second detector gas can also be provided with a proportion of 0.1–5%, particularly 1.5–3.5%. If a device according to the embodiment of Figure 2 is selected, the purge gas of the second purge gas stream 212 can be provided by the first metering device 221 of the second purge device, and the second detector gas of the second purge gas stream 212 can be provided by the second metering device 222 of the second purge device.

[0078] The second purge gas stream is supplied by the second purge device independently of the first purge gas stream. The first and second detector gases can be the same, allowing, for example, the at least one first and at least one second optical assemblies to be tested separately and thus independently of each other. Likewise, the first and second detector gases can be different, enabling independent, parallel testing of the leak tightness of the at least one first and at least one second optical assemblies.

[0079] In a sixth step f, the detector determines the proportion of the second detector gas inside the housing, thereby achieving sufficient sensitivity for verifying the tightness of the second optical assembly using the inventive method. The proportion of the second detector gas can be determined as partial pressure, sum of partial pressures, and / or leak rates.

[0080] To determine the tightness of the second optical assembly, in a seventh step (g), the measured proportion of the second detector gas is compared with at least one target value for the proportion of the second detector gas. This target value is also typically based on empirical values ​​and, as a limit value, generally indicates a tightness class of the second optical assembly and its criticality for potential degradation of optical surfaces.

[0081] For example, the target value of the second detector gas in step g can correspond to an early warning value. An early warning value refers to a proportion of the second detector gas that indicates an increased risk of degradation of optical surfaces, but still ensures safe operation of the optical arrangement, at least temporarily. If this early warning value is exceeded by the determined proportion of the second detector gas, a remaining service life of the affected second optical assembly is determined in step h, thus yielding the same advantages regarding maintenance planning already described for the first optical assembly. Similarly, the target value of the second detector gas in step g can correspond to a replacement value.An exchange value refers to a fraction of the second detector gas that indicates a criticality for the degradation of optical surfaces, necessitating the immediate replacement of the affected second optical assembly. This exchange value indicates a leak in the affected second optical assembly that could cause irreversible degradation of the corresponding optical surfaces. Therefore, in step i, if the exchange value is exceeded by the determined fraction of the second detector gas, an immediate replacement of the affected optical assembly is indicated. Such a replacement can prevent the loss of this second optical assembly or at least significantly reduce the effort required for its repair.

[0082] The target values ​​for the proportions of the first and second detector gases, for example as a warning value or as an exchange value, can be the same, especially if the same gas is used. However, different values ​​can also be used, particularly if different detector gases are used or if a specific design of the respective optical assembly is taken into account.

[0083] Steps e-g, including h and i in Figure 3, are not limited to a second optical assembly. By connecting the second purge device in series or parallel, several optical assemblies can be jointly tested for leaks, and the second purge gas stream, containing the purge gas and the second detector gas, is provided accordingly in several optical assemblies.

[0084] The embodiment of the method according to the invention, as shown in Figure 3, can be carried out temporarily or permanently before commissioning a projection exposure system. Particularly immediately before commissioning the projection exposure system, there is a risk of degradation of the optical elements, as contaminants adhere especially easily during this phase. This method can also be used to test whether the existing sealing properties of one or more optical assemblies have been maintained by their prior integration into the projection exposure system. The method according to Figure 3 can also be carried out temporarily or permanently during the operation of a projection exposure system.

[0085] Figure 4 shows a section of the embodiment of the optical arrangement of Figure 2 with respect to the group of optical assemblies 201.6-10 during a phase of an embodiment of the method according to the invention. Figure 4 shows the distribution of two different components 225, 227 of the second detector gas of the second purge gas stream 212 at time t3 of this embodiment of the method according to the invention.

[0086] The second metering device 222 of the second purge device supplied a first component 225 (symbolized by triangles) of the second detector gas of the second purge gas stream 212 to the connected, sealed cavities of the optical assemblies 201.6–201.10. The optical assembly 201.6 has a leak 226. The first component 225 of the second detector gas escaped from the leak 226 and was detected by the detector 216 (the escaped components of the second detector gas are not shown in Figure 4 for simplification). After a certain time (not shown), the supply of the first component 225 of the second detector gas in the second purge gas stream was discontinued, and the supply of a second component 227 (symbolized by circles) of the second detector gas in the second purge gas stream immediately followed.The first component 225 and the second component 227 of the second detector gas have different compositions and are distinguishable from the detector 216. For example, the first and second components 225 and 227 are different gas species. The first component 225 of the second detector gas of the second purge gas stream 212 was transported as far as the optical assembly 201.7, while up to time t3 it was displaced from the first optical assembly 201.6 by the second component 227 of the second detector gas. From time t2 onwards, the proportion of the first component 225 of the second detector gas escaping from the leak 226 therefore decreased, while the proportion of the second component 227 of the second detector gas increased.

[0087] Accordingly, the upper part of Figure 4 shows time-resolved signal profiles 228 and 229 determined by detector 216 of the first component 225 and second component 227 of the second detector gas in the second purge gas stream. The intensity I of the signal profiles 228 and 229 can be determined as partial pressure, sum of partial pressures, and / or leak rates. The signal profile 228 of the first component of the second detector gas 225 begins at a level corresponding to a detection limit or background signal of the first component 225 of the second detector gas in the second purge gas stream for this test setup. At time t1, when the first component 225 of the second detector gas reaches the leakage 226 in the optical assembly 201.6, the signal of profile 228 begins to rise to a level that correlates with the size of the leakage 226.After the first component 225 of the second detector gas is no longer supplied and is replaced by the second component 227 of the second detector gas, the first component 225 is displaced from the first optical assembly 201.6 by the second component 227. From time t2 onwards, the intensity of the signal curve 228 of the first component 225 of the second detector gas therefore decreases, while the signal curve 229 of the second component 227 of the second detector gas increases. The signal curve 228 tends again towards the detection limit or the background signal of the first component 225 of the second detector gas. The signal curve 229 rises to a level which, for the second component 227 of the second detector gas, also correlates with the size of the leakage 226.

[0088] By determining the components 225 and 227 of the second detector gas over time, and knowing the purge gas flows of the purge gas and the second detector gas as the second purge gas stream, as well as the volumes of the individual connected sealed cavities of the optical assemblies 201.6-10, the determined time points t1 and t2 can be used to estimate the location to which each component of the second detector gas has reached. In this way, the location of the leak 226 can be easily determined by identifying the affected optical assembly 201.6. Furthermore, by changing the proportions of the detector gases, additional time points Btx can be determined, thus further refining the localization of the leak.

[0089] Figure 5 shows a simplified representation of a projection exposure system 400, in particular an EUV projection exposure system, for microlithography. The projection exposure system 400 has a housing 401 enclosing an interior space and at least one, in this case several, optical components 402 to 412 arranged in the housing 401.

[0090] According to the exemplary embodiment, the projection exposure system 400 further comprises a radiation source 413, in particular an EUV light source, an illumination system 414 for illuminating an object field 415 in an object plane 416, and a projection system 417. The illumination system 414 illuminates a reticle 418 arranged or arrangable in the object field 415, which is held by a reticle holder 419. The projection system 417 serves to image the object field 415 onto an image field 420 in an image plane 421. A structure of the reticle 418 is imaged onto a photosensitive layer of a wafer 422 arranged in the image plane 421 within the area of ​​the image field 420 and held by a wafer holder 423. The wafer is made, in particular, of a semiconductor material, for example, silicon.

[0091] The radiation source 413 emits EUV radiation 424, particularly in the range between 5 nm and 30 nm, especially 13.5 nm. To control the radiation path of the EUV radiation 424, preferably at least one of the optical components 402 to 412, in particular each of the optical components 402 to 412, is controllable, in particular for respective alignment or positioning.

[0092] The EUV radiation 424 generated by the radiation source 413 is aligned by means of a collector mirror integrated into the radiation source 413 (not shown) such that the EUV radiation 424 passes through an intermediate focus 425 in the region of an intermediate focus plane before the EUV radiation 424 then strikes a first of the optical components 402, in this case a field facet mirror 402. After the field facet mirror 404, the EUV radiation 424 is directed to a second of the optical components 403, in this case a pupil facet mirror 403. Subsequently, the light is guided through the further optical components 404, 405, 406 to the object field 415.

[0093] The reticle 418 arranged or arrangable in the object field 415 is, for example, a reflective photomask having reflective and non-reflective, or at least less strongly reflective, areas for generating at least one structure to be imaged. Alternatively, the reticle 418 is formed by a plurality of micromirrors arranged in a one- or multi-dimensional configuration and preferably movable about at least one axis. The reticle 418 reflects a portion of the EUV radiation 424 coming from the illumination system 414 into the projection system 417 and shapes the light reflected into the projection system 417 such that the information about the structure of the reticle 418 is transferred to the image plane 420 by means of the projection system 417.

[0094] In the present embodiment, the projection lens 417 has, without being limited to this number, six optical components or optical elements 407 to 412.

[0095] The projection exposure system 400 further comprises sub-housings 426, 427, 428 arranged in the housing 401, each of which at least partially encloses one of the optical components 402, 403, 404. The sub-housings 426, 427, 428 serve to prevent or at least minimize contamination of the area at least partially enclosed by the sub-housings 426, 427, 428, in particular contamination of the optical components 402, 403, 404. The sub-housings 426, 427, 428 are at least partially connected to each other, so that the sub-housings 426, 427, 428 encapsulate the beam path of the EUV light 424 formed by the optical components 402, 403, 404 within the illumination system 414.

[0096] In the present example of a projection exposure system, the optical component 402 comprises at least one optical assembly with a sealed cavity, as is implemented in the embodiments of the optical arrangements (100, 200) from Figure 1 or 2. The reflective surface of the optical component 402, used for the reflection and structuring of the EUV light 424, is therefore formed by a plurality of controllable micromirrors. The components required for control are accordingly placed in the sealed cavity. The materials present within the cavity (e.g., paints or plastics, or oxidizing components such as oxygen or water) promote degradation of the optical surface of the optical component 402. Therefore, a cleaning device 429 is associated with the optical component 402. The cleaning device 429 can be configured as a single or multiple cleaning device.This allows for the addressing of individual, multiple, or all optical assemblies of the optical component 402. The purge device 429 thus enables the adjustment of a first purge gas flow, comprising a purge gas and at least one first detector gas. The purge gas reduces the substances that promote degradation.

[0097] To detect a leak in the optical component 402, a detector 430 for determining the atmosphere of the interior of the sub-housing 426 is assigned to the sub-housing 426. To enable this determination, a detector gas for the first purge gas flow is supplied via the purge device 429, as described for the embodiments according to Figures 1 and 2, into at least one described sealed cavity of the optical component 402. Due to the leak, the detector gas enters the interior of the sub-housing 426 and can be detected by the detector 430.

[0098] As described, the sub-housings 426, 427, 428 partially enclose the respective optical components 402, 403, 404 of the illumination system 414 and are interconnected. Since the interior of these sub-housings 426, 427, 428 is continuously flushed, the sub-housings are not hermetically sealed from the interior of the illumination system 414. Thus, parts of the atmosphere from the interior of sub-housing 426 can enter the interior of the illumination system 414 and can be detected by a detector 431 located therein. Such an arrangement generally does not allow for a specific determination of the tightness of the optical component 402 of sub-housing 426 and is less sensitive due to the fact that only a portion of the atmosphere from the interior of sub-housing 426 enters the separate interior of the illumination system 414.However, such an arrangement can be advantageous if, for example, due to space constraints or specific pressure conditions, it is not possible or only possible with difficulty to attach a detector directly to a partial housing. Therefore, detector 431 can be provided as an alternative to detector 430. However, both detectors can also be combined, as shown for the projection exposure system according to Figure 5.

[0099] The representation and positioning of the partial housing 426 with the flushing device 429 and the detector 430 in Figure 5 is to be understood as exemplary. Optionally, other optical components can also be tested for leak tightness using such an arrangement. Reference numerals

[0100] 100 Optical Arrangement

[0101] 101 First Optical Assembly

[0102] 102 cases

[0103] 103 Interior of the case

[0104] 104 Supporting structure

[0105] 105 optomechanical element

[0106] 106 Final element

[0107] 107 Sealing element

[0108] 108 optical element

[0109] 109 optical surface

[0110] 110 EUV light

[0111] 111 enclosed cavity

[0112] 112 first purge gas stream

[0113] 113 Access to the first flushing device

[0114] 114 Outlet of the first flushing device

[0115] 115 first dosing device of the first rinsing device

[0116] 116 Detector

[0117] 117 second dosing device of the first rinsing device

[0118] 200 Optical Arrangement

[0119] 201.1-10 Optical Assemblies

[0120] 202 cases

[0121] 203 Interior of the case

[0122] 205 optomechanical element 211 enclosed cavity

[0123] 212 second purge gas stream

[0124] 213 Access to the first flushing device

[0125] 214 Outlet of the first flushing device

[0126] 215 first dosing device of the first rinsing device

[0127] 216 Detector

[0128] 217 second dosing device of the first rinsing device

[0129] 220 Access to the second flushing device

[0130] 221 first dosing device of the second rinsing device

[0131] 222 second dosing device of the second flushing device

[0132] 223 third dosing device of the second flushing device

[0133] 224 Outlet of the second flushing device

[0134] 225 first component of a second detector gas

[0135] 226 Leakage

[0136] 227 second component of a second detector gas

[0137] 228 Signal profile of the first component of the second detector gas

[0138] 229 Signal profile of the second component of the second detector gas t1-3 Time points of a signal I ai Steps of an embodiment of the method according to the invention

[0139] 400 EUV projection system

[0140] 401 Housing

[0141] 402 - 412 optical components

[0142] 413 Radiation source

[0143] 414 Lighting system

[0144] 415 Object field Object plane Projection optics Reticle Reticle holder Image field Image plane Wafer Wafer holder EUV radiation Intermediate focus - 428 (Partial) housing Flushing device Detector Detector

Claims

Patent claims 1. Method for determining the tightness of a first optical assembly (101, 201.1-5) of an optical arrangement (100, 200), comprising the following steps: a) providing a first operating pressure in an interior of a housing (103, 203) of the optical arrangement (100, 200), wherein the first operating pressure is less than a second operating pressure in a sealed cavity (111, 211) of the first optical assembly (101, 201.1-5); b) providing a first purge gas stream (112) comprising a purge gas and a first detector gas in the sealed cavity (111, 211) of the first optical assembly (101, 201.1-5).1-5) by a first purging device (113, 114, 213, 214), c) determination of a proportion of the first detector gas in the interior of the housing (102, 202) by a detector (116, 216), d) comparison of the determined proportion of the first detector gas with at least a target proportion of the first detector gas for determining the tightness of the connection area of ​​the first optical assembly (101 , 201.1 -5), wherein in a step a) preceding the optical arrangement (100, 200) with the first optical assembly (101 , 201.1-5) is provided.

2. The method of claim 1, wherein a tightness of at least one second optical assembly (201.6-10) of the optical arrangement (200) is determined independently of the first optical assembly and the first operating pressure in the interior of the housing (203) is less than a third operating pressure in a sealed cavity (211) of the second optical assembly (201.6-10), further comprising the following steps: 34 e) Providing a second purge gas stream (212) comprising a purge gas and a second detector gas in the enclosed cavity (211) of the second optical assembly (201.6-10) by means of a second purge device (220, 224), f) Determining a proportion of the second detector gas in the interior of the housing (203) by means of the detector (216), g) Comparing the determined proportion of the second detector gas with at least one target proportion of the second detector gas for determining the tightness of the second optical assembly (201.6-10).

3. Method according to claim 2, characterized in that a second detector gas different from the first detector gas is used.

4. Method according to claims 1-3, characterized in that the proportion of the first and / or second detector gas in step c or f is determined with time resolution.

5. Method according to claims 1-4, characterized in that the composition of the first and / or second detector gas is varied over time.

6. Method according to claims 1-5, characterized in that the method is carried out temporarily or permanently before commissioning a projection exposure position (400).

7. Method according to claims 1-6, characterized in that the method is carried out temporarily or permanently during operation of the projection exposure system (400).

8. Method according to one of claims 1-7, characterized in that in step a the first operating pressure in the interior of the housing (103, 203) is provided between 1-25 Pa and the second and / or third operating pressure in the cavities (111, 211) is between 85 and 110 kPa.

9. Method according to one of claims 1-8, characterized in that in step b and / or e a gas from the group comprising helium, argon, krypton, xenon, CO2, CF4 and / or SFe is selected as the first and / or second detector gas and the respective total proportion is 0.1 - 5%, in particular 1.5- 3.5% of the first and second purge gas stream (112, 212).

10. Method according to one of claims 1-9, characterized in that the proportion of the first detector gas in step c and / or the second detector gas in step f in the interior of the housing (103, 203) is determined as partial pressure, sum of partial pressures and / or leak rates.

11. Method according to one of claims 1-10, characterized in that in step d at least one setpoint fraction of the first detector gas and / or in step g at least one setpoint fraction of the second detector gas each corresponds to a pre-warning value and in step h when one of these pre-warning values ​​is exceeded by the fraction of the first detector gas determined in step c and / or the fraction of the second detector gas determined in step f a remaining operating time of the affected optical assembly (101 , 201.1 -10) is determined.

12. Method according to one of claims 1-11, characterized in that in step d at least one setpoint value of the first detector gas and / or in step g at least one setpoint value of the second detector gas each corresponds to an exchange value. and in step i, when one of these exchange values ​​is exceeded by the proportion of the first detector gas determined in step c and / or the proportion of the second detector gas determined in step f, an immediate exchange of the affected optical assembly (101 , 201.1 -10) is indicated.

13. Optical arrangement (100, 200) for an EUV projection exposure system (400), comprising a first optical assembly (101, 201.1-10) and a housing (102, 202) at least partially enclosing the first optical assembly (101, 201.1-19), which further encapsulates a section of an EUV beam path (110, 424) within the EUV projection exposure system (400), wherein the first optical assembly (101, 201.1-10) a support structure (104) and at least one optomechanical element (105, 205) for controlling an optical element (108), wherein the optomechanical element (105, 205) is at least partially received by the support structure (104) and forms a closed cavity (111, 211) with the support structure (104), wherein a connecting area (106, 107) formed thereby seals the closed cavity (111, 211) and an interior of the housing (103) from each other, wherein the optical arrangement (100, 200) is associated with a detector (116, 216) for determining a composition of an atmosphere of the interior of the housing (103, 203), wherein the optical arrangement (100, 200) includes a first rinsing device (113, 114, 213, 214) for providing a first purge gas stream (112) within the enclosed cavity (111 , 211 ) is characterized in that the first purge gas stream comprises a purge gas and a first detector gas.

14. Optical arrangement according to claim 13, characterized in that the first rinsing device comprises a first (115, 117) and at least one second (117, 217) dosing device.

15. Optical arrangement according to claim 13 or 14, characterized in that the optical arrangement comprises 2-12 optical assemblies (201.1 - 201.10).

16. Optical arrangement according to claim 15, characterized in that the optical arrangement (200) comprises at least two rinsing devices (213, 214, 220, 224) which are assigned to different optical assemblies (201.1-5; 201.6-10).

17. Projection exposure system (400) with an optical arrangement (100, 200) according to one of claims 13-16.

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