Method for monitoring proper functioning of one or more components of lithographic system

Abstract

A method for monitoring that one or more components of a lithographic system are functioning properly is disclosed. The method includes determining a frequency response function of each of the one or more components during a production activity using the lithographic system at a time during which control requirements during the production activity are relatively not strict; evaluating each of the frequency response functions with respect to control data indicative of nominal lithographic system behavior; and predicting whether to perform a maintenance action on the lithographic system based on the evaluating step.

Description

Technical Field

[0001] The present invention claims priority from European application 22194094.3 filed on September 06, 2022, and the entire contents of this European application are incorporated herein by reference. Technical Field

[0002] The present invention relates to methods and apparatus which may be used, for example, for manufacturing devices by photolithographic techniques, and to methods of manufacturing devices using photolithographic techniques. The invention more particularly relates to fault detection for such devices. Background Art

[0003] A lithographic apparatus is a machine that applies a desired pattern to a substrate, usually to a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that case, a pattern forming device (which is alternatively referred to as a mask or reticle) can be used to produce a circuit pattern to be formed on a single layer of the IC. This pattern can be transferred to a target portion (e.g., a portion including a die, a die, or a number of dies) on a substrate (e.g., a silicon wafer). The transfer of the pattern is usually performed via imaging onto a layer of radiation-sensitive material (resist) disposed on the substrate. Typically, a single substrate will include a network of adjacent target portions that are patterned continuously. These target portions are typically referred to as "fields."

[0004] In the manufacture of complex devices, many lithographic patterning steps are typically performed, whereby functional features are formed in successive layers on a substrate. Therefore, a key aspect of the performance of a lithographic apparatus is the ability to properly and accurately place the applied pattern relative to features placed in a previous layer (either by the same apparatus or by a different lithographic apparatus). For this purpose, the substrate is provided with one or more sets of alignment marks. Each mark is a structure whose position can be measured later using a position sensor (usually an optical position sensor). The lithographic apparatus comprises one or more alignment sensors, by which the position of the mark on the substrate can be accurately measured. Different types of marks and different types of alignment sensors are known from different manufacturers and from different products of the same manufacturer.

[0005] In other applications, metrology sensors are used to measure exposed structures on the substrate (in the resist and / or after etching). A fast and non-invasive form of a specialized inspection tool is a scatterometer, in which a radiation beam is directed onto a target on the surface of the substrate and the properties of the scattered or reflected beam are measured. Examples of known scatterometers include angle-resolved scatterometers of the type described in US2006033921A1 and US2010201963A1. In addition to measurement of feature shapes by reconstruction, such devices can also be used to measure diffraction-based overlay, as described in published patent application US2006066855A1. Diffraction-based overlay metrology using dark field imaging of diffraction orders enables overlay measurement of smaller targets. Examples of dark field imaging metrology can be found in international patent applications WO 2009 / 078708 and WO 2009 / 106279, the documents of which are hereby incorporated by reference in their entirety. Further developments of the technology have been described in published patent publications US20110027704A, US20110043791A, US2011102753A1, US20120044470A, US20120123581A, US20130258310A, US20130271740A and WO2013178422A1. These targets may be smaller than the illumination spot and may be surrounded by product structures on the wafer. Composite grating targets may be used to measure multiple gratings in one image. The contents of all these applications are also incorporated herein by reference.

[0006] Lithography systems are extremely complex tools that include multiple components, many of which require very tight control to achieve patterning accuracy at nanometer scales and at acceptable speeds. Uptime of these systems is important, and any downtime represents a significant expense. However, currently it is necessary to take the system offline to measure the frequency response functions of system components in order to determine whether the system components are functioning correctly or whether maintenance action is required.

[0007] It would be desirable to improve such photolithography system maintenance methods. Summary of the invention

[0008] In a first aspect, the present invention provides a method for monitoring proper functioning of one or more components of a lithography system, the method comprising: determining a frequency response function of each of the one or more components during a production activity using the lithography system at a time when control requirements are relatively lax during the production activity; evaluating each of the frequency response functions relative to control data indicative of nominal lithography system behavior; and predicting whether to perform maintenance action on the lithography system based on the evaluating step.

[0009] A computer program and a lithography system are also disclosed, the computer program and the lithography system being operable to perform the method of the first aspect.

[0010] The above and other aspects of the invention will be understood from consideration of the examples described below. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0012] Figure 1 Describing lithographic equipment; and

[0013] Figure 2 Schematically illustrated Figure 1 Measurement and exposure process in the device. DETAILED DESCRIPTION

[0014] Before describing embodiments of the invention in detail, it is instructive to present an example environment that can be used to implement embodiments of the invention.

[0015] Figure 1 A lithographic apparatus LA is schematically depicted. The apparatus comprises an illumination system (illuminator) IL configured to condition a radiation beam B (e.g. UV radiation or DUV radiation), a patterning device support or support structure (e.g. mask table) MT configured to support a patterning device (e.g. mask) MA and connected to a first positioner PM configured to accurately position the patterning device according to certain parameters, two substrate tables (e.g. wafer stages) WTa and WTb each configured to hold a substrate (e.g. resist-coated wafer) W and each connected to a second positioner PW configured to accurately position the substrate according to certain parameters, and a projection system (e.g. refractive projection lens system) PS configured to project a pattern imparted by the patterning device MA to the radiation beam B onto a target portion C (e.g. comprising one or more dies) of the substrate W. A reference frame RF connects the various components and serves as a reference for setting and measuring the position of the patterning device and substrate and the positions of features on the patterning device and substrate.

[0016] The illumination system may include various types of optical components for directing, shaping, or controlling radiation, such as refractive, reflective, magnetic, electromagnetic, electrostatic, or other types of optical components, or any combination thereof.

[0017] The patterning device support MT holds the patterning device in a manner that depends on the orientation of the patterning device, the design of the lithographic apparatus, and other conditions (such as whether the patterning device is held in a vacuum environment). The patterning device support may use mechanical, vacuum, electrostatic or other clamping techniques to hold the patterning device. The patterning device support MT may be, for example, a frame or a stage, which may be fixed or movable as required. The patterning device support may ensure that the patterning device is in a desired position, for example relative to a projection system.

[0018] The term "patterning device" as used herein should be broadly interpreted as referring to any device that can be used to impart a radiation beam with a pattern in its cross-section so as to produce a pattern in a target portion of the substrate. It should be noted that, for example, if the pattern imparted to the radiation beam includes phase-shifting features or so called assist features, the pattern may not exactly correspond to the desired pattern in the target portion of the substrate. Typically, the pattern imparted to the radiation beam will correspond to a specific functional layer in a device (such as an integrated circuit) produced in the target portion.

[0019] As depicted herein, the apparatus is of the transmissive type (e.g., using a transmissive patterning device). Alternatively, the apparatus may be of the reflective type (e.g., using a programmable mirror array of the type mentioned above, or using a reflective mask). Examples of patterning devices include masks, programmable mirror arrays, and programmable LCD panels. Any use of the term "reticle" or "mask" herein may be considered synonymous with the more general term "patterning device". The term "patterning device" may also be interpreted as referring to a device that stores pattern information in digital form for controlling the programmable patterning device.

[0020] The term "projection system" as used herein should be broadly interpreted as covering any type of projection system suitable for the exposure radiation used or for other factors such as the use of an immersion liquid or the use of a vacuum, including refractive, reflective, catadioptric, magnetic, electromagnetic and electrostatic optical systems, or any combination thereof. Any use of the term "projection lens" herein may be considered synonymous with the more general term "projection system".

[0021] The lithographic apparatus may also be of a type in which at least a portion of the substrate may be covered by a liquid having a relatively high refractive index (e.g., water) so as to fill the space between the projection system and the substrate. Immersion liquid may also be applied to other spaces in the lithographic apparatus, such as the space between the mask and the projection system. Immersion techniques are well known in the art for increasing the numerical aperture of a projection system.

[0022] In operation, the illuminator IL receives a radiation beam from a radiation source SO. For example, when the source is an excimer laser, the source and the lithographic apparatus may be separate entities. In such a case, the source is not considered to form part of the lithographic apparatus, and the radiation beam is transferred from the source SO to the illuminator IL by means of a beam delivery system BD comprising, for example, suitable directing mirrors and / or a beam expander. In other cases, for example, when the source is a mercury lamp, the source may be an integral part of the lithographic apparatus. The source SO and the illuminator IL together with the beam delivery system BD (if necessary) may be referred to as a radiation system.

[0023] The illuminator IL may, for example, comprise an adjuster AD for adjusting the angular intensity distribution of the radiation beam, an integrator IN and a condenser CO. The illuminator may be used to condition the radiation beam, to have a desired uniformity and intensity distribution in its cross-section.

[0024] The radiation beam B is incident on a patterning device MA held on a patterning device support MT and is patterned by the patterning device. Having traversed the patterning device (e.g. a mask) MA, the radiation beam B passes through a projection system PS which focuses the beam onto a target portion C of the substrate W. With the aid of a second positioner PW and a position sensor IF (e.g. an interferometric device, a linear encoder, a 2-D encoder or a capacitive sensor), the substrate table WTa or WTb can be accurately moved, for example in order to position a different target portion C in the path of the radiation beam B. Similarly, the first positioner PM and a further position sensor (which is not in the Figure 1 ) can be used to accurately position the patterning device (eg, mask) MA relative to the path of the radiation beam B, for example after mechanical retrieval from a mask library or during scanning.

[0025] Mask alignment marks M1, M2 and substrate alignment marks P1, P2 can be used to align the pattern forming device (e.g., mask) MA and the substrate W. Although the substrate alignment marks occupy dedicated target portions as shown, the marks can be located in the spaces between the target portions (these marks are called scribe alignment marks). Similarly, where more than one die is provided on the pattern forming device (e.g., mask) MA, the mask alignment marks can be located between the dies. Small alignment marks can also be included in the die among the device features, in which case it is desirable to make the mark as small as possible and without requiring any imaging or process conditions that are different from adjacent features. An alignment system for detecting alignment marks is further described below.

[0026] The depicted apparatus can be used in a variety of modes. In scanning mode, the pattern forming device support (e.g., mask table) MT and the substrate table WT are scanned synchronously while a pattern imparted to the radiation beam is projected onto a target portion C (i.e., a single dynamic exposure). The speed and direction of the substrate table WT relative to the pattern forming device support (e.g., mask table) MT may be determined by the (re)magnification and image reversal characteristics of the projection system PS. In scanning mode, the maximum size of the exposure field limits the width of the target portion in a single dynamic exposure (in the non-scanning direction), while the length of the scanning movement determines the height of the target portion (in the scanning direction). Other types of lithographic apparatus and operating modes are possible, as is well known in the art. For example, stepping modes are known. In so-called "maskless" lithography, the programmable pattern forming device is held stationary, but with a changing pattern, and the substrate table WT is moved or scanned.

[0027] Combinations and / or variations on the above-described modes of use or entirely different modes of use may also be used.

[0028] The lithographic apparatus LA is of the so-called dual-platform type, which has two substrate tables WTa, WTb and two stations - exposure station EXP and measurement station MEA - between which the substrate tables can be exchanged. While one substrate on one substrate table is exposed at the exposure station, another substrate can be loaded onto the other substrate table at the measurement station and various preparatory steps are performed. This situation achieves a considerable increase in the throughput of the apparatus. The preparatory steps can include using a horizontal sensor LS to map the surface height profile of the substrate, and using an alignment sensor AS to measure the position of the alignment mark on the substrate. If the position sensor IF is not able to measure the position of the substrate table when the substrate table is at the measurement station and at the exposure station, a second position sensor can be provided to enable the position of the substrate table relative to the reference system RF to be tracked at the two stations. Instead of the dual-platform arrangement shown, other arrangements are known and available. For example, other lithographic apparatuses that provide substrate tables and measurement tables are known. These substrate tables and measurement tables are docked together when preparatory measurements are performed, and then detached when the substrate table undergoes exposure.

[0029] Figure 2 Diagram for exposing a target portion (e.g., die) to Figure 1200 , a new substrate W' is loaded into the apparatus by a mechanism not shown. The two substrates are processed in parallel to increase the throughput of the lithographic apparatus.

[0030] Reference is initially made to a newly loaded substrate W', which may be a previously unprocessed substrate, which is prepared with a new photoresist for the first exposure in the apparatus. However, typically, the lithographic process described will be only one step in a series of exposure and processing steps, so that the substrate W' has passed through this apparatus and / or other lithographic apparatus several times and may also be subject to subsequent processes. With particular regard to the problem of improving overlay performance, the task is to ensure that the new pattern is applied exactly in the correct position on a substrate that has been subjected to one or more cycles of patterning and processing. These processing steps gradually introduce deformations in the substrate, which must be measured and corrected to achieve satisfactory overlay performance.

[0031] Previous and / or subsequent patterning steps may be performed in other lithographic equipment, as just mentioned, and may even be performed in different types of lithographic equipment. For example, some layers in the device manufacturing process that are very demanding in terms of parameters such as resolution and overlay may be performed in more advanced lithographic tools than other layers that are less demanding. Thus, some layers may be exposed in immersion lithographic tools, while other layers are exposed in "dry" tools. Some layers may be exposed in tools operating at DUV wavelengths, while other layers are exposed using EUV wavelength radiation.

[0032] At 202, the alignment of the substrate relative to the substrate table WTa / WTb is measured and recorded using alignment measurements using substrate marks P1 etc. and an image sensor (not shown). In addition, a plurality of alignment marks across the substrate W' will be measured using an alignment sensor AS. In one embodiment, these measurements are used to establish a "wafer grid" that very accurately maps the distribution of the marks across the substrate, including any deformations from the nominal rectangular grid.

[0033] At step 204, a map of wafer height (Z) relative to XY position is also measured using a level sensor LS. Conventionally, height maps are only used to achieve accurate focus on the exposed pattern. Additionally, height maps can be used for other purposes.

[0034] When the substrate W' is loaded, the recipe data 206 are received, which define the exposure to be performed and also define the properties of the wafer and the previously generated pattern and the pattern to be generated on the substrate W'. The measurements of the wafer position, wafer grid and height map obtained at 202, 204 are added to these recipe data so that the complete set of recipe and measurement data 208 can be transferred to the exposure station EXP. The measurement of the alignment data includes, for example, the X position and Y position of the alignment target formed in a fixed or nominally fixed relationship with the product pattern as the product of the lithography process. These alignment data obtained just before the exposure are used to generate an alignment model, which has parameters that fit the model to the data. These parameters and the alignment model will be used during the exposure operation to correct the position of the pattern applied in the current lithography step. The model in use interpolates the position deviations between the measured positions. Conventional alignment models can include four, five or six parameters, which together define the translation, rotation and scaling of the "ideal" grid at different sizes. Advanced models using more parameters are known.

[0035] At 210, wafers W' and W are exchanged so that substrate W' to be measured becomes substrate W and enters exposure station EXP. Figure 1 In the example apparatus of , this exchange is performed by exchanging supports WTa and WTb within the apparatus so that the substrates W, W' remain accurately clamped and positioned on those supports to preserve the relative alignment between the substrate table and the substrate itself. Therefore, once the tables have been exchanged, in order to utilize the measurement information 202, 204 for the substrate W (formerly W') to control the exposure step, it is necessary to determine the relative position between the projection system PS and the substrate table WTb (formerly WTa). At step 212, reticle alignment is performed using mask alignment marks M1, M2. In steps 214, 216, 218, scanning movements and radiation pulses are applied at successive target positions across the substrate W to complete exposure of a plurality of patterns.

[0036] By using the alignment data and height map obtained at the measurement station in performing the exposure step, these patterns are accurately aligned relative to the desired positions, and in particular, accurately aligned relative to features previously placed on the same substrate. The exposed substrate is subjected to etching or other processes according to the exposed pattern.

[0037] Those skilled in the art will recognize that the above description is a simplified overview of the many very detailed steps involved in one example of a real manufacturing situation. For example, there will often be separate stages of coarse and fine measurements using the same or different markings, rather than measuring alignment in a single pass. The coarse and / or fine alignment measurement steps may be performed before or after the height measurement, or may be interleaved.

[0038] In lithography systems, an important issue that has a significant impact on system uptime and therefore productivity is the ability to quickly and efficiently detect and / or diagnose events or trends that may indicate irregular or abnormal behavior (e.g., therefore failure events). Of course, it is always preferred to detect problems before they cause machine failure (failure event) so that any maintenance and downtime can be planned and scheduled. Such predictive maintenance requires that diagnostics be performed at regular intervals in order to prevent unscheduled downtime.

[0039] Lithography systems are extremely complex and include a number of different modules (e.g., including, among others, a projection optics module, a wafer stage module, a reticle stage module, a reticle masking module), each of which can be monitored. When there is a problem with a lithography system, one way to determine the root cause is to measure the frequency response function of a component or module of the system (e.g., the signal response per frequency in the frequency domain). The frequency response can be compared to control data indicating nominal lithography system behavior (such as system population data from similar systems) and / or historical data from earlier measurements. Any significant difference in the frequency response can be used as an indicator of abnormal behavior; for example, indicating that the component is not functioning correctly.

[0040] For frequency response function analysis, component inputs and outputs can be measured simultaneously to determine how the system changes the input to derive the output. For example, if the system is linear (which is a common assumption), this change can be fully described by the frequency response function. In fact, for linear and stable systems, the response of the system to any input can be predicted based solely on the frequency response function. However, system linearity is not a requirement, and therefore there are many methods (such as optimal linear approximation methods) that can handle nonlinearities while still generating frequency response functions. Therefore, the methods disclosed in this article are equally applicable to linear (or assumed linear) and / or nonlinear systems. Therefore, the frequency response function is a (complex) transfer function represented in the frequency domain. Frequency response functions are well known in dynamic mechanical system or mechatronic integration analysis and will not be described in detail here.

[0041] To perform a frequency response function analysis, an excitation signal is injected into the system or component being analyzed and the output (signal response per frequency or frequency response) of the system or component is measured. Due to the need to inject the excitation signal, currently such frequency response function analysis is performed when production is not in progress, so that the excitation signal does not interfere with production performance and control accuracy during production. However, this means that system downtime needs to be scheduled for such analysis. Furthermore, this approach does not allow predictive maintenance, because the frequency response function analysis is currently only run during setup and when it is known that the system already has a problem. Especially when multiple measurements should be performed to obtain a good signal-to-noise ratio and good measurement quality, such diagnostic downtime can be significant.

[0042] Therefore, it is proposed to perform the frequency response function analysis during actual production and measure the frequency response function online. This approach appears to be an unnatural solution, because the necessary excitation signal needs to be added to the system input (or a component of the system), resulting in a disturbance in the system performance. However, the inventors have speculated that there is an opportunity during production when such a frequency response function analysis can be performed without negatively affecting the system performance and in particular without affecting the imaging positioning accuracy.

[0043] In particular, it is proposed to perform such a frequency response function analysis during periods during production when highly accurate control is not required (i.e., during periods when the required control accuracy may be less stringent than, for example, during exposure). In embodiments, this may include performing such a frequency response function analysis between exposures. For example, the frequency response function analysis may be performed during periods during production when actual (e.g., servo) performance is not required. For example, in case the system comprises two stages, this may be performed during chuck exchange (e.g., Figure 2 210, as described above). Other such periods may include performing a frequency response function analysis on the reticle stage when a wafer exchange occurs and / or performing a frequency response function analysis on the wafer stage when a reticle is loaded, depending on, for example, the specific components under consideration. There are also situations where the system may be exposure or measurement limited (depending on actual product details), in which case either the measurement or exposure chuck is waiting for the other to complete.

[0044] Other opportunities may include during regularly performed maintenance actions such as M(X) actions. Such maintenance actions are routinely performed to maintain proper system performance. Such actions may be related to, for example, any one or more of the following: drift control, clearing disk space, various minor calibrations, and / or (idle) situation monitoring actions.

[0045] Thus, during a suitable time during production, frequency response measurements (e.g., transfer measurements for determining the transfer function) can be performed simultaneously and in parallel with a planned activity (e.g., a chuck transfer). The frequency response measurement data can be distinguished from normal activity data. This can be done because there is a correlation between the (ideal) injected signal and the measured positioning signal during, for example, a move. However, the measured position signal also includes a contribution that is not correlated with the injected signal but is correlated with the actual move set point. By exploiting this correlation between the injected signal and the move signal, for example by calculating the cross or auto power spectral density, an appropriate frequency response can be calculated without additional bias or variance due to the move. Due to the nature of an activity such as a chuck transfer, the excitation signal and therefore the frequency response measurement should not have any significant impact on such an activity.

[0046] Since suitable (e.g., between exposures) activities such as chuck transfers are frequently performed, there is sufficient opportunity to repeat such measurements to enable averaging to obtain a good quality frequency response function (good signal-to-noise ratio). Thus, in an embodiment, it is proposed to repeat such measurements multiple times and average.

[0047] The frequency response function may be monitored, for example, in real time and / or during production. This may include comparing the frequency response function to control data (such as population data and / or historical data) to monitor for any deviations that indicate problems and / or problematic behavior. Based on the monitoring, a prediction may be made as to whether the system will continue to function correctly, normally, and / or within specifications (e.g., when the frequency response function does not deviate significantly from the control data), or whether a problem may be imminent and whether a service action should be scheduled. Thus, unscheduled outages may be prevented by including appropriate or suitable maintenance actions during scheduled outages as determined based on the frequency response function.

[0048] Additionally, if the system does in fact shut down, is unscheduled (or any other non-nominal lithography system behavior is detected), actual data (e.g., historical data, such as captured in parallel with the frequency response function data) will be available, enabling faster diagnosis.

[0049] Since the methods disclosed herein can generate a large amount of data, an optional step may include downsampling one or more of the measured frequency response functions, for example by performing a fit on the measured data. Such downsampling techniques are well known in the art, and any suitable downsampling technique may be used.

[0050] While specific embodiments of the invention have been described above, it will be appreciated that the invention may be practiced otherwise than as described.

[0051] Although the above may specifically refer to the use of embodiments of the invention in the context of optical lithography, it will be appreciated that the invention may be used in other applications (e.g., imprint lithography) and is not limited to optical lithography where the context permits. In imprint lithography, the topography in the patterning device defines the pattern produced on the substrate. The topography of the patterning device may be pressed into a layer of resist supplied to a substrate on which the resist is cured by applying electromagnetic radiation, heat, pressure, or a combination thereof. After the resist is cured, the patterning device is removed from the resist, leaving a pattern in the resist.

[0052] As used herein, the terms "radiation" and "beam" encompass all types of electromagnetic radiation, including ultraviolet (UV) radiation (e.g., having a wavelength of at or about 365 nm, 355 nm, 248 nm, 193 nm, 157 nm, or 126 nm) and extreme ultraviolet (EUV) radiation (e.g., having a wavelength in the range of 1 nm to 100 nm), as well as particle beams (such as ion beams or electron beams).

[0053] The term "lens" may refer to any one or combination of various types of optical components, including refractive, reflective, magnetic, electromagnetic and electrostatic types, as the context permits. Reflective components are likely to be used in devices operating in the UV and / or EUV range.

[0054] The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims

1. A method for monitoring the functioning of one or more components of a lithography system, the method comprising: determining a frequency response function of each of the one or more components during a production activity using the lithography system at a time during the production activity when control requirements are relatively less stringent; evaluating each of the frequency response functions relative to control data indicative of nominal lithography system behavior; and Whether to perform a maintenance action on the lithography system is predicted based on the evaluating step.

2. The method according to claim 1, comprising: If the evaluating step indicates a deviation from the control data, the maintenance action is scheduled and / or performed.

3. The method according to claim 1 or 2, comprising: If the evaluating step indicates no significant deviation from the control data, the maintenance action is not scheduled and / or not performed.

4. A method according to any preceding claim, wherein: Said determination of the frequency response function of each of said one or more components is performed between exposure actions during which at least one pattern is actually exposed onto the substrate.

5. A method according to any preceding claim, wherein: The determining of the frequency response function for each of the one or more components is performed during one or more periods during production when servo performance is not required.

6. A method according to any preceding claim, wherein: The determining of the frequency response function of each of the one or more components is performed during a chuck transfer action in which the chuck is transferred from a measurement side of the lithography system to an exposure side of the lithography system and / or the chuck is transferred from the exposure side of the lithography system to a measurement side of the lithography system.

7. A method according to any preceding claim, wherein: The determining of the frequency response function for each of the one or more components comprises one or both of: performing a frequency response function analysis on a mask stage during substrate exchange; and / or performing a frequency response function analysis on a wafer stage when a mask is loaded onto the mask stage.

8. A method according to any preceding claim, wherein: The determining of the frequency response function of each of the one or more components is performed during a maintenance action.

9. The method according to claim 8, wherein: The maintenance action includes one or more of the following: a drift control action, a disk space cleanup, a calibration action, and / or an idle state monitoring action.

10. A method according to any preceding claim, wherein: The determining of a frequency response function for each of the one or more components includes injecting an excitation signal into the one or more components and monitoring a frequency response of the one or more components.

11. The method according to claim 10, further comprising: determining a correlation between the injected excitation signal and the movement signal of the one or more components; and Each of the frequency response functions is determined based on the correlation to distinguish a frequency response attributable to the injected excitation signal from other signal contributions.

12. A method according to any preceding claim, wherein: The determining of a frequency response function for each of the one or more components includes performing the determining a plurality of times and averaging the determined frequency response functions for each component.

13. A method according to any preceding claim, comprising: At least one of the frequency response functions is downsampled.

14. A method according to any preceding claim, comprising: Diagnostic actions are performed using one or more of the frequency response functions in the event of non-nominal lithography system behavior and / or unscheduled downtime.

15. A computer program comprising program instructions operable, when run on a suitable device, to perform the method according to any one of claims 1 to 14.

16. A non-transitory computer program carrier comprising a computer program according to claim 15.

17. A processing device comprising: The non-transitory computer program carrier according to claim 16; and A processor operable to run the computer program included on the non-transitory computer program carrier.

18. A lithographic system operable to perform the method according to any one of claims 1 to 14.

19. An integrated circuit manufactured using the photolithography system of claim 18.

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