DE102023135411A1 - METHOD AND LASER SYSTEM FOR COMPENSATING MISALIGNMENTS - Google Patents

Abstract

The invention relates to a method (21) for operating a laser system (1) and to a correspondingly configured laser system (1). In the method (21), during normal operation of the laser system (1), the system is automatically and continuously monitored for misalignments (13). If a misalignment (13) is detected, at least one operating parameter (8) of the laser system (1) is determined, the change of which has an effect opposite to the respective misalignment (13). The at least one operating parameter (8) determined in this way is then automatically adjusted to compensate for the detected misalignment (13).

Description

The present invention relates to a method for operating a laser system and a correspondingly configured laser system.

Laser systems are used today for a wide variety of applications. Increasingly high demands are placed on them, for example, with regard to performance, precision, and reliability. However, today's laser systems, for example for industrial applications, can be extremely complex. This can lead to situations in which such a laser system does not operate precisely according to a specified target, for example, if it is misaligned, degraded, or misaligned. This can occur, for example, due to changing environmental conditions, degradation of individual components, or mechanical adjustment of passive optical elements, for example due to vibrations. Preventing this using conventional means is either impractical or could incur disproportionately high costs, so that regular manual maintenance measures are required or carried out instead. This may require the laser system to be shut down in whole or in part, or to be put into maintenance or adjustment mode, which incurs effort and costs and can lead to reduced overall efficiency and productivity. Improvements would therefore be desirable in this area.

The object of the present invention is to enable particularly robust operation and particularly high accuracy of a laser system in a particularly simple and efficient manner.

The problem is solved by the subject matter of the independent claims, or rather the main and secondary claims. Further possible embodiments of the invention are specified in the subclaims, the description, and the drawings. Features, advantages, and possible embodiments presented in the description for one of the subject matter of the independent claims are to be regarded at least analogously as features, advantages, and possible embodiments of the respective subject matter of the other independent claims, as well as any possible combination of the subject matter of the independent claims, optionally in conjunction with one or more of the subclaims.

The method according to the invention can be used for or during the operation of a laser system or laser installation. The method comprises several method steps that can be executed automatically during normal operation of the respective laser system. Normal operation here refers to operation of the laser system in regular, productive use, i.e., not during maintenance, testing, or setting or adjustment operations. The laser system can therefore be operated as intended during normal operation, for example, at full power and without any other restrictions.

In the method according to the invention, the laser system is continuously monitored for misalignments or misalignments. These can be deviations from a predefined target or desired behavior of the laser system, such as, for example, misalignment of a generated or emitted laser beam, so that it does not hit a predetermined target point. This can be detected, for example, by means of a corresponding surveillance camera and/or other sensors. Monitoring for misalignments can, for example, be carried out regularly at a predetermined frequency or continuously and/or can be triggered, for example, by one or more predefined trigger events.

Furthermore, in the method according to the invention, when a misalignment is detected, at least one operating parameter of the laser system is determined, the change of which has an effect opposite to the misalignment, i.e., a direction of the corresponding deviation from the desired behavior. Changing the operating parameter(s) here means changing the actual value and/or the desired value for this operating parameter. For example, a list, a table, a characteristic map, or the like can be specified, from which the automatically changeable, i.e., adaptable, operating parameters and corresponding effects or impacts can be determined or read out.

In a further method step of the method according to the invention, the at least one specific operating parameter is then automatically adjusted, i.e. changed, in order to completely or at least partially compensate for the detected misalignment.

The at least one operating parameter can therefore be used as a manipulated or controlled variable to fully or partially achieve or restore the specified target or desired behavior of the laser system. This can lead to the adjusted value of the at least one operating parameter ultimately deviating from a nominal target value of this operating parameter in the overall optimally adjusted state of the laser system, i.e. it can be set or adjusted differently.

Adjusting the at least one operating parameter may mean or include a one-time or individual adjustment or a continuous control. In the latter case, the laser system may, for example, have a corresponding controller, such as a PID or fuzzy controller, for the at least one operating parameter or for each operating parameter.

Since the method according to the invention allows an operating parameter to be determined and used to compensate for the misalignment, which can be automatically adjusted during normal operation of the laser system, the misalignment can be compensated or corrected non-invasively. This eliminates the need to shut down the laser system, and manual maintenance or readjustment is also not necessary. This ultimately enables particularly robust and reliable continuous, i.e., long-term, operation of the laser system with particularly high efficiency, i.e., a particularly high percentage of productive or useful time. This, in turn, can reduce the operating or manufacturing costs associated with the laser system compared to conventional approaches.

The present invention is based on the realization that today's laser systems, with their considerable complexity, often have a multitude of different adjustable operating parameters that can have a direct or indirect influence on various properties or an operating state of the laser system, thus enabling corresponding, at least indirect, control. The detected misalignment can thus be effectively remedied, for example, even if its actual cause does not lie in the ultimately adjusted operating parameter. By means of the present invention, effective, in particular uninterrupted operation or continued operation during or after a misalignment of the laser system can therefore be enabled, for example, even if the actual cause of the misalignment cannot be remedied easily or, for example, not without interrupting the operation of the laser system, but rather, for example, only as part of a maintenance or repair intervention. This can also be enabled or achieved in a particularly simple, low-effort, and cost-effective manner, since corresponding operating parameters that influence the behavior of the laser system can often already be automatically adjustable in conventional laser systems, or such automatic adjustability can be implemented with comparatively little effort. This can be achieved purely on a software basis, i.e., using a corresponding control or regulation program. However, additional necessary hardware, such as an additional electronic controller or valve, or a heating or cooling device, can often be installed in the laser system or retrofitted into an existing laser system relatively easily and cost-effectively, for example, compared to a design that is not susceptible to misalignment, including appropriate monitoring and control of the ambient conditions, or the use of more precise and robust servomotors for optical elements, or the like.

The present invention also relates to a laser system or a laser installation with at least one laser source, i.e. at least one light or beam source for laser light, a conditioning or influencing device for conditioning or influencing a laser beam generated by the laser source, and an optical system. The influencing device and the optical system are connected downstream of the laser source in a designated beam propagation direction of the laser beam within the laser system. Conditioning or influencing the laser beam in the present sense can mean or include, for example, its amplification or modulation, or a wavelength conversion or chopping into individual laser pulses and/or the like. The conditioning or influencing device can therefore be or include, for example, an amplifier and/or a modulator and/or a wavelength converter and/or a chopper. Furthermore, the laser system according to the invention comprises a monitoring device for automatically detecting misalignments of the laser system, in particular with regard to the alignment and/or predetermined properties of the laser beam, and a control device for controlling and/or regulating at least one operating parameter of the laser system. The laser system according to the invention is designed to carry out the method according to the invention, in particular automatically or semi-automatically. The laser system according to the invention can therefore be the laser system mentioned in connection with the method according to the invention or correspond thereto. Likewise, the laser system according to the invention can have further components or functions not explicitly mentioned here, such as an electrical power supply, an RF power source or an RF power supply (RF: radio frequency), a cooling system, a gas system and/or the like. These components can be additional devices of the laser system or, for example, be at least partly a component of the influencing device.

In one possible embodiment of the present invention, the laser system is configured to detect, as misalignments, an unintentional change in the alignment of the laser beam and/or the output caustic of the laser system and/or a laser power. A changed alignment of the laser beam, i.e., an incorrect alignment, can mean, for example, a shift or tilt of a corresponding optical axis of the laser system. Such a changed alignment can be determined in particular at or after an output of a drive or excitation laser or of an amplifier or preamplifier of the laser system. Likewise, the output caustic can be determined, in particular in the beam propagation direction, after a preamplifier or main amplifier, in particular after the amplifier of the laser system last passed through by the laser beam in the beam propagation direction. The laser power can also be determined after one or the last amplifier of the laser system. Likewise, the laser power can be determined, for example, at multiple points, in particular after and/or before several or all amplifiers of the laser system. The latter can enable a more precise localization of the misalignment and, if necessary, a better-coordinated reaction or measure, i.e., a correspondingly adapted selection and/or adjustment of the at least one operating parameter. This can, if necessary, enable or achieve compensation for the misalignment by means of a minimal adjustment. According to a finding underlying the present invention, the misalignments described here can typically be effectively influenced by one or more appropriately selected operating parameters and are thus particularly well suited for the application of the present invention.

In a further possible embodiment of the present invention, the influencing device comprises at least one amplifier for amplifying the laser beam, for example, its intensity or power. The laser system is then configured to determine and adapt at least one operating parameter of the amplifier as the at least one operating parameter. In particular, one or more operating parameters of the amplifier or of devices feeding or supplying it can be used exclusively to compensate for the respective misalignment. It has been shown that the amplifier or amplifiers can offer a wide range of options for effectively influencing the laser beam and thus compensating for misalignments. At the same time, by using one or more operating parameters of the amplifier, the misalignment can be compensated for without adjusting the optics or disrupting the laser source, i.e., the actual generation of the laser light. This can be particularly advantageous because the optics can often only be adjusted with less precision, or a precise adjustment option for the optics can lead to very high costs, and changing the operating parameters of the laser source is often not practically possible.

In a further possible embodiment of the present invention, the influencing device has a plurality of amplifiers, for example, a plurality of amplifiers or amplifier stages connected in series for amplifying the laser beam generated by the laser source. The laser system is then configured to automatically distribute the adjustment of the at least one operating parameter among the plurality of amplifiers. For example, the total scope of the adjustment of a specific operating parameter can be distributed among a plurality of amplifiers and/or different operating parameters can be adjusted for different amplifiers. The distribution can be uniform or uneven. If, for example, a specific operating parameter is to be changed by a total of 10% with an even distribution, the same operating parameter can be changed by 5% in a first amplifier and also by 5% in a second amplifier. If two different operating parameters are to be adjusted, for example, the first operating parameter can be changed, i.e. adjusted, in or on a first amplifier and the second operating parameter can be changed, i.e. adjusted, in or on a second amplifier. The embodiment of the present invention proposed here can, on the one hand, prevent the behavior of an individual amplifier from changing too significantly or unnecessarily. This allows the amplifiers to maintain robust function with exceptional reliability and avoids unexpected side effects from major changes to the operating parameters of a single amplifier. Furthermore, it allows for particularly extensive adjustments to be made or for particularly large misalignments to be compensated for. For example, the maximum adjustment or adjustment range for a specific operating parameter in an individual amplifier may be limited. By utilizing the possible adjustment or adjustment ranges of multiple amplifiers for the same and/or several different operating parameters, correspondingly stronger effects can be achieved.

According to a further possible embodiment of the present invention, the at least one operating parameter is or controls a property of the laser system, which is different from a mechanical position or angular position, i.e. the alignment of an optical element of the laser system that is acted upon by the laser beam, i.e. illuminated or irradiated. An optical element in the present sense can be a component of the optics, in particular a passive one, such as a mirror, a lens, or a prism. In other words, adjusting or changing the at least one operating parameter does not change the position or alignment of an optical element. Rather, the at least one operating parameter can be, for example, an electrical operating parameter and/or a thermal operating parameter and/or a material parameter. Due to the embodiment of the present invention proposed here, the laser system does not need to have a typically very complex or cost-intensive automatic precise adjustment option for the optical elements and can nevertheless enable automatic compensation of misalignments. This enables robust and reliable operation of the laser system in a particularly simple and cost-effective manner. Furthermore, this can potentially enable or support a particularly simple and compact design of the laser system.

In a further possible embodiment of the present invention, the laser system is configured to determine, i.e., select, the at least one operating parameter from a predefined list of operating parameters. This predefined list includes at least a gas composition, a gas exchange waiting time, a gas pressure, a gas volume flow, a gas temperature, a coolant temperature, a coolant volume flow, an RF power, an amplifier turn-off time, and a pre-pulse laser power. The gas composition, the gas exchange waiting time, the gas volume flow, the gas temperature, and the gas pressure can apply to volumes irradiated by the laser beam or laser light within the laser system. These operating parameters can influence, for example, a refractive index, a gain factor, contamination, or the like in order to influence the laser beam. Whether and, if so, which of these operating parameters can be adapted in a particular laser system can depend on its specific design. For example, the gas pressure can be continuously adjusted accordingly in a laser system with a continuous gas flow. In other laser systems, the gas pressure may be adjusted only or preferentially during a gas change, for example in combination with a gas analysis.

To adjust the gas composition, i.e., a gas mixture, additional helium can be introduced into the corresponding volume, for example. Adjusting the gas exchange waiting time can, for example, enable the exploitation of contamination and/or diffusion effects. To adjust, for example, the gas composition and/or the gas pressure and/or the gas temperature, a molecular sieve, such as a zeolite material, arranged in or on the respective gas volume can be used. This can, in particular, be equipped with a controllable heating and/or cooling device. This can, for example, automatically control an adsorption rate or a release of previously adsorbed molecules. The RF power can, for example, be an RF input power or RF supply power of the amplifier mentioned elsewhere and/or a reflected power. This can be adjusted, for example, by controlling a matching network between an RF power source and the device supplied with the RF power, in particular the amplifier. Likewise, an adaptation can be carried out or realized here, for example, by appropriately controlling a duty cycle of the RF power source, especially in the case of a non-continuously pumped amplifier.

Overall, the operating parameters mentioned here offer various relatively easy-to-implement and effective ways to compensate for misalignments. Adjusting at least some of the operating parameters mentioned can be achieved purely using software and can therefore be easily retrofitted to existing laser systems. Any hardware or components required to adjust some of the operating parameters mentioned, compared to conventional laser systems, can be integrated into existing laser system designs relatively inexpensively and easily.

In a further possible embodiment of the present invention, the laser system is configured to automatically limit the adjustment of the at least one operating parameter, so that the adjustment does not fall below a predetermined lower threshold value for a laser output power of the laser system. In other words, the laser system can be configured to define or implement the at least one operating parameter depending on or taking into account a power of the laser beam or laser light output by the laser system. The laser output power considered here can, for example, be the power of the laser beam at or immediately after the aforementioned, in particular the last, amplifier of the laser system or in a target zone into which the laser beam generated by the laser system is directed as intended. The laser system can also be configured here to control or limit the adjustment of at least one operating parameter such that the laser power is kept within a predetermined range. In other words, the laser system can then take into account not only a predetermined minimum power to be maintained, but also a predetermined maximum power of the laser beam to be maintained. Since the adjustment of various operating parameters can influence the laser output power, the adjustment or adjustment range of an operating parameter must be limited accordingly if necessary.

Should a larger adjustment or a larger range of adjustment of this operating parameter be nominally necessary to compensate for a specific misalignment, the laser system can be configured to additionally or alternatively determine and adjust at least one other operating parameter that has a smaller, no, or opposite influence on the laser output power. The maximum extent of the adjustment and/or the selection of the operating parameter(s) to be adjusted can therefore be limited by a predetermined minimum gain of one or more of the amplifiers of the laser system mentioned elsewhere. The predetermined threshold value can then, for example, effectively be predetermined for the minimum gain of the amplifier or be dependent on this, for example also taking into account or including losses occurring downstream of the amplifier. By taking the laser output power into account when compensating for a misalignment, as proposed in the embodiment of the present invention described here, it can be ensured that the laser system can always perform its intended task. For example, achieving at least the specified minimum laser output power or the corresponding minimum gain can be prioritized over completely compensating for a detected misalignment. Overall, the proposed embodiment of the present invention can also benefit particularly robust and reliable operation of the laser system.

In a further possible embodiment of the present invention, the laser system is configured to adjust several operating parameters of the laser system in combination with one another in order to compensate for the respective misalignment. The laser system can in particular be configured to do this depending on the size or strength of the respective detected misalignment. This can mean, for example, that several operating parameters are determined and adjusted to compensate for this misalignment only when the misalignment exceeds a predetermined size or strength, or when an individual operating parameter would have to be changed by more than a predetermined absolute or relative value or amount in order to fully compensate for the misalignment. This makes it easier to compensate for smaller misalignments, while larger misalignments can be compensated for without excessively changing a single operating parameter, thereby avoiding or reducing unwanted side effects. Furthermore, the embodiment of the present invention proposed here can also enable automatic compensation of misalignments that could not be fully compensated by adjusting only a single operating parameter. This ultimately makes it possible to achieve or ensure particularly robust, reliable, and precise operation of the laser system, possibly even particularly long-term.

In a further possible embodiment of the present invention, the laser system is configured to adapt the at least one operating parameter by means of a control system based on a predefined model, in particular a predictive control system. In other words, a model can be used here, for example, which can model or simulate the laser system or its behavior, i.e., in particular, the effects of an adjustment or change in one or more operating parameters of the laser system. This can then be used—if necessary in several differently parameterized simulations or model runs—to determine the at least one operating parameter to be adjusted and/or a scope or degree of adjustment of the at least one operating parameter necessary to compensate for the detected misalignment before an operating parameter of the laser system is actually adjusted. If necessary, the model can also use or consider a respective current operating state of the laser system as input or boundary condition. The embodiment of the present invention proposed here can enable particularly precise and reliable adjustment of the at least one operating parameter and thus enable or support particularly robust, intended, and low-interruption operation of the laser system.

As a basis or input for the model, for example, one or more sensitivity curves can be used for the laser system, which can indicate the effects of a change in one or more operating parameters, in particular depending on the magnitude of the respective change. Such sensitivity curves can, for example, be predetermined, determined during operation, or adapted or updated based on data recorded during operation. Corresponding data, such as measurement or sensor data recorded during operation, from which the sensitivity curves can be generated, can, for example, be obtained during operation of several laser systems. This means that corresponding data can be obtained particularly quickly and easily for a large number of different situations or conditions, so that the corresponding sensitivity curves can be correspondingly robust and cover a particularly large state or parameter space. Corresponding data can, if necessary, be obtained without special measurement or test operation of the laser system or systems, since variations or fluctuations in various operating parameters, the operating state, and the conditions under which the laser system or systems are operated are almost inevitable in practice. In other words, the corresponding data can be obtained based on natural or unavoidable variations in field use or productive operation of the laser system(s).

In a possible further development of the present invention, the model is based on operating data recorded during previous operation, for example measurement or sensor data, only for the respective laser system itself. In other words, for the model, i.e. for modeling or simulating the adjustments of one or more operating parameters, only data or sensitivity curves of the exact laser system in which a detected misalignment is to be compensated can be used. A system-specific or system-individual model can therefore be used for the respective laser system. This automatically takes into account individual properties or special features of the respective laser system, which are not necessarily known in detail but can determine or influence the behavior of the respective laser system. This in turn enables a particularly high level of model accuracy and thus a particularly precise determination of an adjustment of one or more operating parameters necessary to compensate for the respective misalignment. For this purpose, the laser system can be equipped with appropriate sensors or data acquisition devices to record current values or a temporal progression of one or more operating parameters of the respective laser system, as well as corresponding properties, behaviors, or operating states of the laser system as the basis or parameters of the model and/or the sensitivity curves underlying it. These can be, for example, sensors or data acquisition devices for the misalignments and operating parameters mentioned elsewhere.

In a further possible embodiment of the present invention, the laser system additionally comprises an adjustment device for adjusting the alignment of at least one, in particular passive, element of the optics. By means of the respective adjustment device, one or more of the optical elements mentioned elsewhere, for example, mirrors, lenses, prisms, or the like, can be automatically moved. This can mean or include, for example, a translation, a rotation, a tilt, and/or more of the like. The adjustment device can, for example, comprise a servomotor, in particular an electric one, a coil or an electromagnet for electromagnetic adjustment, a linear drive, and/or more of the like. In the embodiment of the present invention proposed here, the laser system is configured to compensate for the misalignment—at least as far as possible—additionally or alternatively by means of the adjustment device only if and only if a detected misalignment cannot be fully compensated by maximum adjustment, i.e., by fully utilizing the maximum range of change or adjustment of the at least one operating parameter. The adjustment device or the possibility of compensating for the misalignment by adjusting or changing the alignment of at least one element of the optics can therefore serve or be implemented as a fallback solution here. This can be used, for example, if compensating for the misalignment by means of corresponding settings or adjustments to one or more operating parameters of the at least one amplifier mentioned elsewhere would result in, for example, a predetermined minimum gain no longer being achieved. The embodiment of the present invention proposed here can, on the one hand, enable particularly precise and flexible compensation for correspondingly smaller misalignments. On the other hand, ultimately, even particularly large misalignments can be compensated for, at least if they manifest themselves in an incorrect alignment or propagation direction of the laser beam.

Further features of the invention can be seen from the following description of the figures and from the drawing. The above-mentioned The features and combinations of features mentioned in the description as well as the features and combinations of features shown below in the description of the figures and/or in the figures alone can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

• 1 eine schematische Darstellung eines Lasersystems mit automatischem Dejustierungsausgleich;
• 2 eine schematische Diagrammdarstellung zur Veranschaulichung der Einflüsse verschiedener Betriebsparameter des Lasersystems auf ein Laserstrahlalignment;
• 3 eine schematische Diagrammdarstellung zur Veranschaulichung eines Bereichs, in dem ein fehlerhaftes Laserstrahlalignment ausgeglichen werden kann; und
• 4 einen beispielhaften schematischen Ablaufplan für ein Verfahren zum Betreiben eines entsprechenden Lasersystems.

The drawing shows in:

• 1 a schematic representation of a laser system with automatic misalignment compensation;
• 2 a schematic diagram illustrating the influences of various operating parameters of the laser system on a laser beam alignment;
• 3 a schematic diagram illustrating an area in which an incorrect laser beam alignment can be compensated; and
• 4 an exemplary schematic flow chart for a method for operating a corresponding laser system.

Identical or functionally identical elements are provided with the same reference symbols in the figures.

1 shows a schematic and simplified representation of a laser system 1. The laser system 1 here comprises a laser source 2 that can generate one or more laser beams 3. The laser source 2 can be a single beam or light source or comprise multiple beams or light sources. Likewise, the laser source 2 can comprise one or more preamplifiers.

The generated laser beam 3 can be amplified within the laser system 1. For this purpose, the laser system 1 has at least one amplifier 4b. The amplifier 4b can be a single amplifier or, schematically, represent several amplifiers or amplifier stages, for example, connected in series.

The laser system 1 further comprises an optical system, which is indicated here by way of example by a passive optical element 5 positioned downstream of the amplifier 4b. The optical system may also comprise further optical elements 5, which may also be arranged, for example, between the laser source 2 and the amplifier 4b. The optical system may comprise, for example, one or more lenses and/or one or more mirrors or the like as optical elements 5. It may also contain further active optical elements, such as an acousto-optical and/or electro-optical modulator.

The laser system 1 can, for example, be designed for EUV light generation. Laser light can be directed onto a corresponding target or reaction material, such as a tin droplet, which can subsequently release EUV radiation. For this process to function efficiently and smoothly, precise irradiation of the reaction material with the laser light is required. Therefore, the laser system 1 is typically adjusted accordingly at its intended location. With correct adjustment, the laser beam 3 amplified by the amplifier 4b can be output by the laser system 1 as a correspondingly adjusted laser beam 6 and then impinge on a predetermined target 7, for example, the aforementioned reaction material or a corresponding spatial region.

Amplifying the laser beam 3 with the highest possible efficiency and amplification power in a practical wavelength range can be a complex task. Therefore, the laser system 1 can have or use a correspondingly large number of different operating parameters 8, indicated schematically here. Several operating parameters, which particularly relate to the amplifier 4b, are indicated here by way of example. These can be, for example, adjustable properties of a gas supply, an RF or high-frequency power supply, a cooling device, a heatable and/or coolable molecular sieve, and/or the like. To monitor and control or regulate these operating parameters 8 or actual and target values of the operating parameters 8, the laser system 1 also has a corresponding control device 9. The control device 9 can, for example, be coupled to devices and/or sensors assigned to the operating parameters 8 via corresponding interfaces 10. To carry out the measures or control sequences described here, the control device 9 can have corresponding electronics and/or circuit logic, which is schematically indicated here by a processor 11 and a computer-readable data memory 12 coupled thereto. The processor 11 can be, for example, a microprocessor, microchip, microcontroller, or the like. For example, a corresponding operating or computer program and, if applicable, a predefined model for the laser system 1 and/or other data can be stored in the data memory 12, which can then be executed or processed by the processor 11.

In practice, during the operation of complex systems such as Laser System 1, unwanted situations can occur again and again, in which deviations from the optimal adjustment of the respective system occur. This can be have various causes, such as a change in the ambient conditions, thermal effects which can lead, for example, to a changed thermal expansion of components of the laser system 1, a degradation or a defect in individual components, a mechanical adjustment, for example of the at least one passive optical element 5, an unintentional change or incorrect setting of one of the operating parameters 8 and/or the like. This can then lead to a misalignment 13, indicated schematically here. Such a misalignment 13 can then lead, for example, to a correspondingly misaligned laser beam 14 being produced instead of the adjusted laser beam 6, which is not directed at or hits the desired target 7, but rather a different, faulty or undesired incorrect target 15.

Such misalignments 13 can, in principle, be remedied or corrected by switching off the laser system 1 or placing it in a special adjustment mode and then performing a manual adjustment. However, since this is complex and may require an undesirable interruption of the productive operation of the laser system 1, the laser system 1 is configured here to automatically compensate for corresponding misalignments 13. This is achieved here by automatically adjusting settings or operating conditions of the laser system 1, i.e., in particular, the adjustable operating parameters 8 of the optical amplifier 4b, if necessary, taking into account specified requirements or boundary conditions.

To implement such automatic adjustment, the laser system 1 here also has a monitoring device 16 for automatically detecting misalignments 13. Furthermore, the control device 9 is configured to determine one or more of the operating parameters 8 that can be adjusted, i.e., their value can be changed, to compensate for the respectively detected misalignment 13, and then automatically adjust the corresponding at least one operating parameter 8 accordingly. In addition, the laser system 1 here also has an automatically controllable adjustment device 17 for adjusting, in particular mechanically or geometrically, the at least one optical element 5. This adjustment device 17 can also be automatically controlled by the control device 9.

Since it is not necessarily immediately obvious in which ranges the operating parameters 8 can be adjusted without hindering or excessively hindering the functionality or function of the laser system 1, and what concrete effects changes to one or more of the operating parameters 8 have on the properties or operation of the laser system 1, for example, on the laser beam alignment, a corresponding sensitivity analysis can first be carried out. This can be done in a corresponding measurement or test operation or based on fluctuations or variations in the operating parameters 8 occurring during ongoing productive operation of the laser system 1. For illustration purposes, 2 a schematic diagram. Here, a plane spanned by spatial x- and y-directions is shown, which, for example, can be perpendicular to the adjusted laser beam 6 in the area of the target 7. Accordingly, the target 7 is located in the center of the plane shown. Various sensitivity curves 18 are shown here as examples, each of which indicates for one of the adjustable operating parameters 8 how its change affects the laser beam alignment. It can be seen that adjustments to various operating parameters 8 can lead to different shifts in the x-direction and/or in the y-direction.

In practice, several of the operating parameters 8 can be adjusted simultaneously or in combination with each other. As shown schematically in 3 shown, this results in a corresponding possible adjustment or compensation range 19. This compensation range 19 indicates the area or spatial region in which misalignments 13 resulting from a misalignment can be compensated for by automatically adjusting one or more of the operating parameters 8. For further illustration, a displacement 20 associated with the misalignment 13 is shown here, which results in the corresponding misaligned laser beam 14 no longer hitting the target 7, but rather the corresponding incorrect target 15. The incorrect target 15 lies within the compensation range 19. This means that the corresponding misalignment 13 can be compensated for by suitably adjusting one or more of the operating parameters 8 according to the corresponding sensitivity curves 18, so that the target 7 is hit again.

If, in the case of a larger misalignment 13, the mistarget 15 were to lie outside the compensation range 19, the mistarget 15 could possibly be shifted closer to the target target 7 by appropriately adjusting one or more of the operating parameters 8, without ultimately achieving this completely.

For further illustration, 4 an exemplary schematic flow chart 21 for a method for operating the laser system 1. In a method step S1 First, data is recorded or collected that indicates the behavior and operating states of the laser system 1 at various values of the operating parameters 8. For example, the current ambient conditions and/or other variables can also be recorded. Depending on the requirements, the corresponding data can be recorded using only the laser system 1 itself or using one or more different such laser systems 1. As indicated here by a loop-shaped path, this method step S1 can be carried out repeatedly or continuously.

Based on the data collected in process step S1, the sensitivity curves 18 or the corresponding model of the laser system 1 can be generated in a process step S2.

In a method step S3, the possible compensation range 19 can then be determined.

During normal or productive operation of the laser system 1, monitoring for misalignments 13 can then be carried out continuously or regularly in a method step S4. For this purpose, for example, the target target 7 and a surrounding area, for example corresponding at least to the compensation area 19, can be observed by means of the monitoring device 16. For this purpose, the monitoring device 16 can be or comprise a camera, for example. Likewise, for this purpose, for example, a portion of the laser light can be directed to the monitoring device 16 or to the corresponding camera after leaving the amplifier, in particular after passing through the optics or the at least one optical element 5, in order to detect misalignments 13. Monitoring for other types of misalignments 13 can also be carried out by means of the monitoring device 16. For this purpose, the monitoring device 16 can, for example, monitor a power of the laser light at or after the output of the amplifier 4b using a corresponding sensor.

Upon detection of a misalignment 13, the control device 9 can then determine in a method step S5 which of the operating parameters 8 need to be adjusted, in what manner, or to what extent, in order to compensate for the detected misalignment 13, and the corresponding adjustment can be carried out automatically if necessary. If it is detected here that complete compensation of the misalignment 13 is not possible by adjusting one or more of the operating parameters 8, the adjustment device 17 can additionally or alternatively be automatically controlled to compensate for the misalignment 13. By combining the adjustment of at least one of the operating parameters 8 and the adjustment of the at least one optical element 5 by means of the adjustment device 17, the latter can be minimized if necessary. As a result, for example, when using an anisotropic optical element 5 or an optical element that acts depending on a direction of light incidence, a corresponding undesired influence on the laser light can be avoided or minimized.

The automatic adjustment of the operating parameters 8 and/or the adjustment device 17 can, for example, be carried out continuously or as a continuous control during ongoing operation of the laser system 1. For this purpose, the control device 9 can form or implement a corresponding controller, or the laser system 1 can have at least one corresponding controller.

According to the method proposed here, one or more manipulated or controlled variables of the laser system 1, in particular at the amplifier 4b, can be automatically adjusted in order to compensate for misalignments 13 at or after the output of the amplifier 4b, i.e., to correct them, without significantly influencing other important output variables. The latter can be achieved, for example, by appropriately limiting the compensation range 19 depending on corresponding predefined requirements or boundary conditions. During the automatic compensation of the misalignments 13 proposed here, their respective cause may or may not be remedied, which may depend on the respective cause and the control or adjustment options of the respective laser system 1.

Overall, the examples described show how laser beam alignment control can be implemented and applied on a laser system, for example via amplifier settings.

LIST OF REFERENCE SYMBOLS

1

Laser system

2

Laser source

3

laser beam

4

Influencing device

4b

amplifier

5

optical element

6

adjusted laser beam

7

Target goal

8

Operating parameters

9

Control device

10

interface

11

processor

12

Data storage

13

Maladjustment

14

misaligned laser beam

15

Missing target

16

monitoring device

17

adjustment device

18

Sensitivity curves

19

Compensation area

20

shift

21

Schedule

S1 - S5

Procedural steps

Claims (12)

Method (21) for operating a laser system (1), wherein during normal operation of the laser system (1) automatically - the laser system (1) is continuously monitored for misalignments (13), - upon a detected misalignment (13), an operating parameter (8) of the laser system (1) is determined, the change of which has an effect opposite to the misalignment (13), and - the determined operating parameter (8) is adjusted to compensate for the detected misalignment (13). Laser system (1), in particular for EUV light generation, comprising at least one laser source (2), an influencing device (4) for influencing a laser beam (3) generated by the laser source (2) and an optics (5) which are connected downstream of the laser source (2), a monitoring device (16) for detecting misalignments (13) of the laser system (1) and a control device (9), wherein the laser system (1) is designed to carry out the method (21) according to Claim 1 is set up. Laser system (1) according to Claim 2 , characterized in that the laser system (1) is designed to detect as misalignments (13) a change in the alignment of the laser beam (6, 14) and/or the output caustic and/or a laser power. Laser system (1) according to Claim 2 or 3 , characterized in that the influencing device (4) has an amplifier (4b) for amplifying the laser beam (3) and the laser system (1) is designed to determine and adapt an operating parameter (8) of the amplifier (4b) as the one operating parameter (8). Laser system (1) according to one of the Claims 2 until 4 , characterized in that the influencing device (4) has a plurality of amplifiers (4b) and the laser system (1) is designed to distribute the adaptation between the plurality of amplifiers (4b). Laser system (1) according to one of the Claims 2 until 5 , characterized in that the operating parameter (8) is or controls a property of the laser system (1) which is different from a mechanical position of an optical element (5) acted upon by the laser beam (6, 14). Laser system (1) according to one of the Claims 2 until 6 , characterized in that the laser system (1) is designed to determine the operating parameter (8) from the following list: gas composition, gas temperature, gas pressure, gas volume flow, gas exchange waiting time, coolant temperature, coolant volume flow, RF power, amplifier switch-off time, pre-pulse laser power. Laser system (1) according to one of the Claims 2 until 7 , characterized in that the laser system (1) is designed to limit the adjustment of the one operating parameter (8) so that a predetermined threshold value for a laser output power is not undercut. Laser system (1) according to one of the Claims 2 until 8 , characterized in that the laser system (1) is designed to adapt, in particular depending on the size of the detected misalignment (13), several operating parameters (8) in combination with one another in order to compensate for the misalignment (13). Laser system (1) according to one of the Claims 2 until 9 , characterized in that the laser system (1) is designed to adapt the operating parameter (8) by means of a control based on a predetermined model, in particular a predictive control. Laser system (1) according to Claim 10 , characterized in that the model is based on operating data recorded during previous operation only of the respective laser system (1) itself. Laser system (1) according to one of the Claims 2 until 11 , characterized in that the laser system (1) additionally comprises an adjusting device (17) for adjusting the alignment of at least of an element (5) of the optics (5) and is configured to compensate for the misalignment (13) additionally or alternatively by means of the adjusting device (17) only when a detected misalignment (13) cannot be completely compensated by maximum adjustment of the operating parameter (8).

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