Method of controlling exposure apparatus

Abstract

Disclosed herein is a method of controlling an exposure apparatus configured to expose one or more substrates, the method comprising: determining, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement (23) measuring a parameter of a component of the exposure apparatus or of the at least one substrate based on a determined predictability of the parameter.

Description

METHOD OF CONTROLLING EXPOSURE APPARATUSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of EP application 24186834.8 which was filed on 5 July 2024 which is incorporated herein in their entirety by reference.FIELD

[0002] The present disclosure relates to a method of controlling an exposure apparatus and a controller configured to control an exposure apparatus.BACKGROUND

[0003] A lithographic apparatus is a machine constructed to apply a desired pattern onto a substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). A lithographic apparatus may, for example, project a pattern of a patterning device (e.g., a mask, a reticle) onto a layer of radiation-sensitive material (resist) provided on a substrate.

[0004] To project a pattern on a substrate a lithographic apparatus may use electromagnetic radiation. The wavelength of this radiation determines the minimum size of features which can be formed on the substrate. A lithographic apparatus, which uses extreme ultraviolet (EUV) radiation, having a wavelength within the range 4-20 nm, for example 6.7 nm or 13.5 nm, may be used to form smaller features on a substrate than a lithographic apparatus which uses, for example, deep ultraviolet (DUV) radiation with a wavelength of 157 nm or 193 nm or 248 nm.

[0005] A lithographic apparatus can include a reticle stage to hold a patterning device (e.g., a reticle) to transfer a pattern to a substrate. Reticle heating and / or cooling can cause changes in reticle properties that can affect the radiation beam path (e.g., focus) and cause distortions in the patterned substrate (e.g., overlay errors).

[0006] The shape of a reticle may also be deformed by other effects, such as the applied clamping force to the reticle. If not compensated for, all reticle shape deformations may increase distortions in the patterned substrate (e.g., overlay errors).

[0007] Deformations can be measured. Measured deformations can be compensated for. The measurements take time.SUMMARY

[0008] There is a general need to increase the frequency of exposures, without unduly increasing errors such as in focus or overlay. This may increase the fabrication throughput and yield of exposure processes.

[0009] According to a first aspect of the invention, there is provided a method of controlling an exposure apparatus configured to expose one or more substrates, the method comprising: determining,for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter of a component of the exposure apparatus, or of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.

[0010] According to a second aspect of the invention, there is provided method of forming a semiconductor device comprising the steps of processing a substrate with a layer of material to be patterned and illuminating the layer with a pattern, wherein the step of illuminating further comprises illuminating the layer using the method according to the first aspect of the invention, the method further comprising a step of introducing a structure corresponding to at least part of the pattern to a layer of the semiconductor device, wherein a portion of the layer of material to be patterned is being removed.

[0011] According to a third aspect of the invention, there is provided a controller configured to control an exposure apparatus that is configured to expose substrates, the controller configured to: determine, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter of a component of the exposure apparatus, or of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.

[0012] Implementations of any of the techniques described above may include an EUV light source, a DUV light source, a system, a method, a process, a device, and / or an apparatus. The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

[0013] Further features and exemplary aspects of the aspects, as well as the structure and operation of various aspects, are described in detail below with reference to the accompanying drawings. It is noted that the aspects are not limited to the specific aspects described herein. Such aspects are presented herein for illustrative purposes only. Additional aspects will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein.BRIEF DESCRIPTION OF THE DRAWINGS / FIGURES

[0014] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate the aspects and, together with the description, further serve to explain the principles of the aspects and to enable a person skilled in the relevant art(s) to make and use the aspects.

[0015] FIG. 1 is a schematic illustration of a lithographic apparatus, according to an exemplary aspect.

[0016] FIG. 2A is a schematic illustration of a lithographic cell, according to an exemplary aspect.

[0017] FIG. 2B is a schematic illustration of holistic lithography including a computer system to optimize a lithographic process, according to an exemplary aspect.

[0018] FIG. 3A is a schematic bottom perspective illustration of a reticle stage and a reticle, according to an exemplary aspect.

[0019] FIG. 3B is a schematic bottom plan illustration of the reticle stage shown in FIG. 3A.

[0020] FIG. 4 is a graph showing measurements made during exposure of a series of substrates.

[0021] FIG. 5 is a graph showing the relationship between the sequence of substrates within a series and the temperature of the reticle.

[0022] FIG. 6 is a graph showing distributions within a relationship between time and drift of a parameter.

[0023] FIG. 7 is a schematic diagram of predicting a parameter.

[0024] The features and exemplary aspects of the aspects will become more apparent from the detailed description set forth below when taken in conjunction with the drawings, in which like reference characters identify corresponding elements throughout. In the drawings, like reference numbers generally indicate identical, functionally similar, and / or structurally similar elements. Additionally, generally, the left-most digit(s) of a reference number identifies the drawing in which the reference number first appears. Unless otherwise indicated, the drawings provided throughout the disclosure should not be interpreted as to-scale drawings.DETAILED DESCRIPTION

[0025] This specification discloses one or more aspects that incorporate the features of this present invention. The disclosed aspect(s) merely exemplify the present invention. The scope of the invention is not limited to the disclosed aspect(s). The present invention is defined by the claims appended hereto.

[0026] The aspect(s) described, and references in the specification to “one aspect,” “an aspect,” “an example aspect,” “an exemplary aspect,” etc., indicate that the aspect(s) described may include a particular feature, structure, or characteristic, but every aspect may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same aspect. Further, when a particular feature, structure, or characteristic is described in connection with an aspect, it is understood that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other aspects whether or not explicitly described.

[0027] Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “on,” “upper” and the like, may be used herein for ease of description to describe one element or feature’s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly.

[0028] The term “about” or “substantially” or “approximately” as used herein indicates the value of a given quantity that can vary based on a particular technology. Based on the particular technology, theterm “about” or “substantially” or “approximately” can indicate a value of a given quantity that varies within, for example, 1-15% of the value (e.g., ±1%, ±2%, ±5%, ±10%, or ±15% of the value).

[0029] The term “parasitic thermal effects” as used herein indicates induced or internal stresses and / or deformations of a reticle, for example, due to heating and / or cooling the reticle (e.g., by resistive heating, gas flow cooling, exposing the reticle to a dose of radiation, etc.) or mechanical pressures and / or deformations from clamping and / or holding the reticle on the reticle stage.

[0030] The term “non-production substrate” as used herein indicates a substrate (e.g., a wafer) that is not part of a production lot and is not fabricated by a lithographic process into a device (e.g., an IC chip). For example, a non-production substrate can be a chuck temperature conditioning (CTC) wafer or calibration wafer for a reticle calibration method, for example, to calibrate a reticle heating model and to acclimate the reticle by exposing the reticle and the CTC wafer to a dose of radiation and measuring a reticle alignment and / or a reticle temperature.

[0031] The term “production substrate” as used herein indicates a substrate (e.g., a wafer) that is part of a production lot and is fabricated by a lithographic process into a device (e.g., an IC chip). For example, a production substrate can be a wafer (e.g., silicon) for fabrication and inline real-time calibration of a reticle heating model, for example, by exposing the reticle and the wafer to a dose of radiation and measuring a reticle alignment and / or a reticle temperature.

[0032] The term “reticle heating model” as used herein indicates a modal deformation approach (e.g., analysis of different reticle mode shapes) to determine reticle heating effects based on reticle alignment and / or reticle shape deformations and a finite element model (FEM) (e.g., COMSOL). For example, the reticle heating model can be deterministic (e.g., no random future states) or non-deterministic (e.g., including random future states) reticle heating effects. Further, the reticle heating model can be deemed a reticle heating execution algorithm (RHEA) that uses inline modal calibrations to determine the baseline reticle heating dynamics. The reticle heating model can be calibrated by exposing a reticle and a non-production substrate to a dose of radiation for inline real-time calibration of the reticle heating model. In some aspects, for example, the reticle heating model can be calibrated by exposing a reticle and a production substrate to a dose of radiation for inline real-time calibration of the reticle heating model. Other reticle heating models utilize a sensor-based approach (e.g., using RTS measurements) to calibrate the reticle heating model. This is described in further detail in U.S. Patent No. 10,429,749, U.S. Patent No. 10,281,825, and U.S. Publication No. 2020 / 0166854, which are incorporated by reference herein in their entireties.

[0033] Reticle heating causes changes in reticle properties that can affect the radiation path and cause fabrication errors (e.g., overlay). Reticle mechanical deformations (e.g., based on reticle temperature) can be calculated and decomposed into k-parameters. Each thermo-mechanical mode (e.g., eigenvector) can be modeled in time using modal participation factor p and time constant r. Measured overlay and / or alignment can be used to model the related k-parameter drifts, which can be used to calculate adjustments to the feed-forward parameters p and r. The reticle heating model can also include adjustingfeed-forward parameters p and r. This is described in further detail in U.S. Patent No. 10,429,749, U.S. Publication No. 2020 / 0166854, and WIPO Publication No. 2021 / 043519, which are incorporated by reference herein in their entireties.

[0034] The term “finite element model” or “FEM” as used herein indicates a method for numerically solving differential equations arising in the reticle heating model (e.g., heat transfer equations, structural analysis equations, fluid flow equations, etc.). For example, baseline reticle heating dynamics can be analyzed with the FEM through finite element analysis. This is described in further detail in U.S. Patent No. 10,429,749, U.S. Patent No. 10,281,825, and U.S. Publication No. 2020 / 0166854, which are incorporated by reference herein in their entireties.

[0035] The term “key performance indicators” or “KPIs” or “k-parameters” as used herein indicates coefficients of polynomials that are fit to distortions of reticle alignment marks and / or edge alignment marks. The k-parameters parameterize the distortion of the imaging across the field of each substrate. For example, each k-parameter can describe a certain image distortion component (e.g., scaling error, barrel distortion, pincushion distortion, etc.). For example, two important k-parameters are k4 (e.g., k4 / my shown in FIG. 7) that represents distortion in Y-axis magnification and kl8 (e.g., kl8 / cshpy shown in FIG. 8) that represents distortion in Y-axis barrel shape. The k-parameters can be used as input to a lithographic process (e.g., lithographic apparatus LA, lithographic cell LC, control system CL) to correct the distortion. This is described in further detail in U.S. Patent No. 10,429,749, U.S. Publication No. 2020 / 0166854, and WIPO Publication No. 2021 / 043519, which are incorporated by reference herein in their entireties.

[0036] The term “inline real-time calibration” as used herein indicates calibration of the reticle heating model during actual fabrication of production substrates. For example, a calibration lot of production substrates can be avoided and rework of production substrates for calibration purposes can be reduced or avoided. The calibration can be done inline by exposing a reticle and a production substrate to a dose of radiation. Further, the calibration can be done in real-time (e.g., at a real-time frame rate or a computing rate of 2.56 seconds or less).

[0037] Aspects of the disclosure may be implemented in hardware, firmware, software, or any combination thereof. Aspects of the disclosure may also be implemented as instructions stored on a machine-readable medium, which may be read and executed by one or more processors. A machine- readable medium may include any mechanism for storing or transmitting information in a form readable by a machine (e.g., a computing device). For example, a machine -readable medium may include read only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other forms of propagated signals (e.g., carrier waves, infrared signals, digital signals, etc.), and others. Further, firmware, software, routines, and / or instructions may be described herein as performing certain actions. However, it should be appreciated that such descriptions are merely for convenience and that such actions in fact result fromcomputing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0038] Before describing such aspects in more detail, however, it is instructive to present example environments in which aspects of the present disclosure may be implemented.

[0039] Exemplary Lithographic System

[0040] FIG. 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV and / or a DUV radiation beam B and to supply the EUV and / or DUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT (e.g., a mask table, a reticle table, a reticle stage) configured to support a patterning device MA (e.g., a mask, a reticle), a projection system PS, and a substrate table WT configured to support a substrate W.

[0041] The illumination system IL is configured to condition the EUV and / or DUV radiation beam B before the EUV and / or DUV radiation beam B is incident upon the patterning device MA. Thereto, the illumination system IL may include a faceted field mirror device 10 and a faceted pupil mirror device 11. The faceted field mirror device 10 and faceted pupil mirror device 11 together provide the EUV and / or DUV radiation beam B with a desired cross-sectional shape and a desired intensity distribution. The illumination system IL may include other mirrors or devices in addition to, or instead of, the faceted field mirror device 10 and faceted pupil mirror device 11.

[0042] After being thus conditioned, the EUV and / or DUV radiation beam B interacts with the patterning device MA. This interaction may be reflective (as shown), which may be preferred for EUV radiation. This interaction may be transmissive, which may be preferred for DUV radiation. As a result of this interaction, a patterned EUV and / or DUV radiation beam B’ is generated. The projection system PS is configured to project the patterned EUV and / or DUV radiation beam B’ onto the substrate W. For that purpose, the projection system PS may comprise a plurality of mirrors 13, 14 which are configured to project the patterned EUV and / or DUV radiation beam B’ onto the substrate W held by the substrate table WT. The projection system PS may apply a reduction factor to the patterned EUV and / or DUV radiation beam B’, thus forming an image with features that are smaller than corresponding features on the patterning device MA. For example, a reduction factor of 4 or 8 may be applied. Although the projection system PS is illustrated as having only two mirrors 13, 14 in FIG. 1, the projection system PS may include a different number of mirrors (e.g. six or eight mirrors).

[0043] The substrate W may include previously formed patterns. Where this is the case, the lithographic apparatus LA aligns the image, formed by the patterned EUV and / or DUV radiation beam B’, with a pattern previously formed on the substrate W.

[0044] Exemplary Lithographic Cell

[0045] FIG. 2A shows a lithographic cell LC, also sometimes referred to as a lithocell or cluster. Lithographic apparatus LA may form part of lithographic cell LC. Lithographic cell LC may also include one or more apparatuses to perform pre- and post-exposure processes on a substrate. Conventionally these include spin coaters SC to deposit resist layers, developers DE to develop exposed resist, chill plates CH, and bake plates BK. A substrate handler, or robot, RO picks up substrates from input / output ports I / O 1 , 1 / O2, moves them between the different process apparatuses and delivers them to the loading bay LB of the lithographic apparatus LA. These devices, which are often collectively referred to as the track, are under the control of a track control unit TCU which is itself controlled by a supervisory control system SCS, which also controls the lithographic apparatus LA via lithography control unit LACU. Thus, the different apparatuses can be operated to maximize throughput and processing efficiency.

[0046] In order for the substrates W exposed by the lithographic apparatus LA to be exposed correctly and consistently, it is desirable to inspect substrates to measure properties of patterned substrates, for example, overlay errors between subsequent layers, line thicknesses, critical dimensions (CD), etc. For this purpose, inspection tools (e.g., metrology tool MT) may be included in lithographic cell LC and / or lithographic apparatus LA. If errors are detected, adjustments, for example, may be made to exposures of subsequent substrates or to other processing steps that are to be performed on the substrates W, especially if the inspection is done before other substrates W of the same batch or lot are still to be exposed or processed.

[0047] An inspection apparatus, which may also be referred to as a metrology apparatus or metrology tool MT, is used to determine properties of the substrates W, and in particular, how properties of different substrates W vary or how properties associated with different layers of the same substrate W vary from layer to layer. The inspection apparatus may alternatively be constructed to identify defects on the substrate W and may, for example, be part of lithographic cell LC, integrated into lithographic apparatus LA, and / or be a stand-alone device. The inspection apparatus may measure the properties on a latent image (e.g., image in a resist layer after the exposure), on a semi-latent image (e.g., image in a resist layer after a post-exposure bake step), on a developed resist image (e.g., image in which the exposed or unexposed parts of the resist have been removed), or on an etched image (e.g., image after a pattern transfer step, such as etching).

[0048] Exemplary Computer System

[0049] FIG. 2B shows a computer system CL, also referred to as a controller or processor. Computer system CL may be part of lithographic cell LC, integrated into lithographic apparatus LA, and / or be a stand-alone device. Computer system CL is configured to optimize a lithographic process, for example, calibrate a reticle heating model. Typically the patterning process in lithographic apparatus LA is one of the most critical steps in the processing, which requires high accuracy of dimensioning and placement of structures on the substrate W. To ensure this high accuracy, three systems can be combined in a so-called “holistic” control environment as schematically depicted in FIG. 2B. As shown in FIG. 2B, the “holistic” environment can include lithographic apparatus LA, computer system CL, and metrology tool MT. For example, lithographic apparatus LA (a first system) can be connected to computer system CL (a second system) and metrology tool MT (a third system).

[0050] The key of such holistic lithography is to optimize the cooperation between these three systems to optimize a lithographic process, for example, to enhance the overall process window and provide tight controls loops to ensure that the patterning performed by lithographic apparatus LA stays within a process window. The process window defines a range of process parameters, for example, dose, focus, overlay, etc., within which a specific manufacturing process yields a defined result, for example, a functional semiconductor device — typically within which the process parameters in the lithographic process or patterning process are allowed to vary.

[0051] Computer system CL may, for example, use (e.g., part of) the design layout to be patterned to predict which resolution enhancement techniques to use and to perform computational lithography simulations and calculations, for example, to determine which mask layout and lithographic apparatus settings achieve the largest overall process window of the patterning process (shown in FIG. 2B by the double arrow in the first scale SCI). Typically, the resolution enhancement techniques are arranged to match the patterning possibilities of lithographic apparatus LA. Computer system CL may also be used to detect where within the process window lithographic apparatus LA is currently operating (e.g., using input from metrology tool MT) to predict whether defects may be present, for example, due to sub- optimal processing (shown in FIG. 2B by the arrow pointing “0” in the second scale SC2).

[0052] Metrology tool MT may provide input to computer system CL, for example, to enable accurate simulations and predictions. For example, metrology tool MT may provide alignment information. Metrology tool MT may provide feedback (e.g., via computer system CL) to lithographic apparatus LA to identify possible drifts, for example, in a calibration status of lithographic apparatus LA (shown in FIG. 2B by the multiple arrows in the third scale SC3). In lithographic processes, it is desirable to make frequent measurements of the structures created, for example, for process control and verification. Different types of metrology tools MT can be used, for example, to measure one or more properties relating to lithographic apparatus LA, a substrate W to be patterned, and / or reticle alignment. This is described in further details in U.S. Patent No. 11,099,319 and WIPO Publication No. 2021 / 043519, which are incorporated by reference herein in their entireties.

[0053] Exemplary Reticle Stage and Reticle

[0054] FIGS. 3A and 3B show schematic illustrations of reticle stage 200, according to exemplary aspects. FIG. 3 A is a schematic bottom perspective illustration of reticle stage 200 and reticle 300, according to an example aspect. FIG. 3B is a schematic bottom plan illustration of reticle stage 200 and reticle 300 shown in FIG. 3A.

[0055] Reticle stage 200 (e.g., support structure MT) can be used in a lithographic apparatus (e.g., lithographic apparatus LA) to hold a patterning device (e.g., patterning device MA). Reticle stage 200 can include bottom stage surface 202, top stage surface 204, side stage surfaces 206, clamp 250, reticle cage 224, and / or reticle 300. In some aspects, reticle stage 200 with reticle 300 can be implemented in lithographic apparatus LA. For example, reticle stage 200 can be support structure MT in lithographic apparatus LA. In some aspects, reticle 300 can be disposed on bottom stage surface 202 and held by clamp 250. For example, as shown in FIGS. 3A and 3B, reticle 300 can be disposed on clamp 250 (e.g., an electrostatic clamp) at a center of bottom stage surface 202 with reticle frontside 302 facing perpendicularly away from bottom stage surface 202. In some aspects, reticle cage 224 can be disposed on bottom stage surface 202. For example, as shown in FIGS. 3A and 3B, reticle 300 can be disposed at a center of bottom stage surface 202 and secured by reticle cages 224 adjacent to each comer of reticle 300.

[0056] In some lithographic apparatuses, for example, lithographic apparatus LA, reticle stage 200 with clamp 250 can be used to hold and position reticle 300 for scanning or patterning operations. In some aspects, as shown in FIGS. 3A and 3B, reticle stage 200 can include first encoder 212 and second encoder 214 for positioning operations. For example, first and second encoders 212, 214 can be interferometers. First encoder 212 can be attached along a first direction, for example, a transverse direction (i.e., X-direction) of reticle stage 200. And second encoder 214 can be attached along a second direction, for example, a longitudinal direction (i.e., Y-direction) of reticle stage 200.

[0057] As shown in FIGS. 3A and 3B, reticle 300 can include reticle frontside 302, alignment mark 310, and / or edge alignment mark 320. Alignment mark 310 is configured to measure a reticle alignment between reticle 300 and a substrate (e.g., substrate W, non-production substrate, production substrate). In some aspects, as shown in FIGS. 3 A and 3B, one or more alignment marks 310 can be disposed in the comers and / or the center of reticle 300 for an RA measurement. Edge alignment mark 320 is configured to measure a reticle shape deformation of reticle 300 due to thermal expansion when reticle 300 is not within a predetermined temperature (e.g., at 22 °C ± 0.2 °C). In some aspects, as shown in FIGS. 3 A and 3B, one or more edge alignment marks 320 can be disposed along the perimeter edges (e.g., horizontal and vertical edges) of reticle 300 for a reticle shape deformation (RSD) measurement. In some aspects, the results of the RA measurement and / or the RSD measurement can be converted to a reticle temperature, for example, by a FEM that solves for temperature based on reticle alignment and / or reticle deformation.

[0058] Exemplary Exposure Control Methods

[0059] The lithographic apparatus LA is an example of an exposure apparatus configured to expose one or more substrates W. However, it is not essential for the exposure apparatus to be a lithographic apparatus. The exposure apparatus is configured to expose one or more substrates W with radiation. Inan embodiment the radiation is patterned radiation. For example, the radiation may be patterned with a patterning device MA of the exposure apparatus.

[0060] The exposure apparatus may comprise a controller. For example, such a controller may be part of the computer system CL shown in Figure 2B . The controller may be configured to control operations of the exposure apparatus. For example, the controller may be configured to control measurements performed by the exposure apparatus.

[0061] During use of the exposure apparatus, the exposure apparatus may expose a series of substrates W. For example, the exposure apparatus may be configured to expose a plurality of substrates W, in turn. A measurement of a parameter may be performed per substrate W. For example, the measurement may be for obtaining data indicative of a deformation of the patterning device MA. The measurement may be referred to as an inline measurement. An inline measurement is a measurement that is made during a time period in which the exposure apparatus is being used to expose at least one substrate of a series of substrates W.

[0062] In an embodiment the controller is configured to determine whether to perform an inline measurement. In an embodiment a method of controlling the exposure apparatus comprises determining, for at least one substrate W of a series of substrates W exposed by the exposure apparatus, whether to perform an inline measurement of a parameter based on a determined predictability of the parameter. The parameter may be a parameter of a component of the exposure apparatus. For example, the component may be the patterning device MA. Alternatively, the parameter may be a parameter of the substrate W.

[0063] By determining whether to perform the inline measurement, it is possible to skip one or more inline measurements. By basing the determination on a determined predictability of the parameter, one or more inline measurements may be skipped on the basis of information such that errors are not unduly introduced by skipping an inline measurement.

[0064] For example, inline measurements may be skipped based on information from heating models of the patterning device MA, one or more lenses of the projection system PS and / or the substrate W. The determination may be performed based on the state of the patterning device MA and / or on the state of one or more lenses of the projection system PS. It is not necessary to rely fully on heating models.

[0065] An embodiment of the invention is expected to improve throughput, without unduly introducing errors into the exposure processes. Inline measurements may be performed intermittently. By reducing the frequency of inline measurements, the amount of time taken up by performing such inline measurements may be reduced. By reducing the time for performing inline measurements, throughput may be improved.

[0066] By basing the decision of whether to perform an inline measurement on the predictability of the parameter, it is possible to maintain the accuracy of the exposure processes. For example, when it is determined that the parameter is predictable, i.e. that there is a high level of confidence about thevalue of the parameter, then the inline measurement may not be necessary. The inline measurement may be skipped.

[0067] When the inline measurement is skipped, the prediction of the parameter may be used instead of performing the inline measurement. The prediction of the parameter may be expected to be relatively accurate, such that the possibility of introducing errors is not unduly increased. Meanwhile, if the predictability of the parameter is determined to be low, then the inline measurement may be performed. The result of the inline measurement may then be used for controlling the exposure process.

[0068] Figure 4 is a graph showing the relationship between a sequence of substrates W, i.e. a series of substrates W, and temperature of the patterning device MA. During exposure of the series of substrates W, the patterning device MA may heat up. For example, the patterning device MA may absorb some of the radiation that is incident on it. Part of the DUV exposure radiation is absorbed by the patterning device MA. As a result, the patterning device MA warms up.

[0069] Heating of the patterning device MA can cause errors in the exposure processes. For example, heat may be exchanged between the patterning device MA and gas adjacent to the patterning device MA. Heating of the gas can cause the refractive index of the gas to change. The change in refractive index can cause distortion of an image projected onto the substrate W. Overlay error can be undesirably increased. Additionally or alternatively, heating of the patterning device MA can cause the patterning device MA to thermally deform. When the patterning device MA deforms, the image to be projected onto the substrate W may be deformed.

[0070] In an embodiment, inline measurements of a parameter (or a plurality of parameters) are performed. For example, by measuring the deformation of the patterning device MA, the deformation can be at least partly compensated for. By measuring the temperature of the patterning device MA, the varying temperature and its effects on the image projected onto the substrate W may be at least partly compensated for.

[0071] Figure 4 shows that the temperature of the patterning device MA generally tends to increase as the series of substrates W are exposed. That is, the temperature of the patterning device MA is expected to be higher for the second substrate W than for the first substrate W. Similarly, the temperature of the patterning device MA for exposure of the third substrate is expected to be greater than for exposure of the second substrate W, and so on.

[0072] As shown in Figure 4, the patterning device MA may undergo heating 21. The heating 21 may be caused by absorption by the patterning device MA of the exposure radiation during exposure of the substrate W. Immediately following exposure of the substrate W, the patterning device MA may undergo cooling 22. The patterning device MA may reduce in temperature when the exposure radiation is not incident on the patterning device MA. For example, during the cooling 22, the substrate W may be exchanged with a subsequent substrate W to be exposed.

[0073] As shown in Figure 4, in general, the extent by which the patterning device MA heats up during the heating 21 is expected to be greater than the extent by which the patterning device MA reduces intemperature during the cooling 22. The time period for exposing the substrate W (which may correspond to the period of heating 21) may be longer than the time period for exchanging the substrate W (which may correspond to the period of cooling 22). In general, the patterning device MA may increase in temperature with each substrate W of the series of substrates W.

[0074] As shown in Figure 4, inline measurements 23 may be performed during the time period of exposing the series of substrates W. As shown in Figure 4, in an embodiment the inline measurement 23 is performed during the period of exchanging the substrate W. The inline measurement may be, for example, a measurement of the temperature of the patterning device MA.

[0075] As shown in Figure 4, in an embodiment the inline measurements 23 are performed intermittently. The inline measurement 23 may be performed for a subset, but not all, of the series of substrates W. For example, Figure 4 shows that the inline measurement 23 is performed for the first, third and fifth substrates but not for the second or fourth substrates. The time that would have been taken up by performing the inline measurement for the second and fourth substrates W may be saved. The overall time required for exposing the series of substrates W may be reduced.

[0076] Figure 5 is a graph showing the relationship between a sequence of substrates W, i.e. a series of substrates W, and temperature of the patterning device MA, according to a comparative example. In the example shown in Figure 5, the inline measurement 23 is performed for every single substrate W. As a result, the total time required for performing the inline measurements 23 is increased compared to what is shown in Figure 4.

[0077] Measuring the temperature of the patterning device MA is only one example of an inline measurement of a parameter. Additionally or alternatively, the inline measurement may be a measurement of a deformation of the patterning device MA. For example, the measurement may be of a position and / or shape of the patterning device MA. For example, one or more sensors may be configured to determine a location of corresponding markers of the patterning device MA. Additionally or alternatively, the inline measurement may be a measurement of the position and / or orientation of at least one lens of the projection system of the exposure apparatus and / or the position and / or the shape of the substrate W.

[0078] In an embodiment, when it is determined, for at least one substrate W of the series of substrates W to skip the inline measurement (i.e. not perform the inline measurement 23), the method comprises controlling exposure of the at least one substrate W dependent on a prediction of the parameter. By using the prediction of the parameter, the thermo-mechanical deformations can be compensated for even when the inline measurement 23 is not performed.

[0079] In an embodiment, the method of controlling the exposure apparatus comprises actuating at least one of the patterning device MA, an optical element of the exposure apparatus and the substrate W exposed by the exposure apparatus so as to account for the prediction of the parameter. The optical element may be a lens. For example, the exposure apparatus may comprise at least one actuator configured to actuate the patterning device MA, for example by actuating the support structure MT.Additionally or alternatively, the exposure apparatus may comprise at least one actuator configured to actuate the substrate W, for example by actuating the substrate table WT.

[0080] Actuation of the patterning device MA and / or the substrate W may be performed so as to align the patterning device MA and the substrate W relative to each other. Such alignment may help to compensate for any deformation. As another example, the exposure apparatus may comprise at least one actuator configured to actuate at least one lens of the projection system of the exposure apparatus. By actuating the lens of the projection system PS, the thermo-mechanical deformations may be at least partly compensated for.

[0081] The control of the actuation may be performed based on the inline measurements 23. When an inline measurement 23 is skipped, the control of the actuation may be performed based on the prediction of the parameter.

[0082] In an embodiment the controller is configured to use one or more prediction models to predict the intra-substrate thermo-mechanical deformations caused by the patterning device MA, optical element and / or substrate W. The optical element may be a lens. A combination of models and measurements may be used.

[0083] In an embodiment it is determined to perform the inline measurement 23 when the predictability is below a threshold and it is determined to skip the inline measurement 23 when the predictability is at least the threshold. The predictability is an estimate of the accuracy in the prediction of the parameter. In an embodiment the threshold can be selected, for example by a user. Such a user selectable threshold enables the user to choose between potential overlay impact and throughput. For example, when greater throughput is desired, the threshold may be lowered such that a greater proportion of the inline measurements 23 are skipped. When it is desirable to prioritise reducing overlay, then the threshold may be increased such that the proportion of inline measurements 23 that are skipped is reduced and more inline measurements are performed.

[0084] In an embodiment, the user can toggle on / off the determination of whether to perform an inline measurement 23. For example, the determination may be toggled off in which case the inline measurement 23 is performed for each substrate W without needing to consider the predictability of the parameter. When the determination is toggled on, then the controller determines whether to perform the inline measurement 23 based on the predictability of the parameter.

[0085] In an embodiment the method comprises determining the predictability of the parameter may be determined based on a rate of change of state of the component. The choice to perform an inline measurement 23 or not may depend on the estimate of accuracy and the prediction, based on the rate of change in the lens state and / or the rate of change in the state of the patterning device MA. The state of a lens and / or the state of the patterning device MA may depend on not only heating of the component but also other generic drifts.

[0086] In an embodiment the controller is configured to determine the predictability of the parameter by considering past data to characterise the present drift. The drift is the change over time of theparameter. For example, the drift may be the change over time of a temperature, position or shape of a component of the exposure apparatus or the substrate W. For example, in an embodiment the method comprises determining the predictability of the parameter based on data of a plurality of distributions 51-54 of previous measurements of the parameter.

[0087] Figure 6 is a schematic graph of the relationship between time t and drift D. The drift D varies over time t. For example, the temperature of the patterning device MA may vary over time.

[0088] As shown in Figure 6, in an embodiment the drift may be characterised by a plurality of distributions 51-54. For example, for distributions 51-54 are shown in Figure 6. In general, each distribution may correspond to a time period of the use of the exposure apparatus. As shown in Figure 6, there may be some overlap in time of the different distributions 51-54.

[0089] In an embodiment, the data of each distribution 51-54 (on which the determination of the predictability of the parameter is based) comprises at least one of a mean value of the parameter, a variance of the parameter and a class of the distribution. For example the class of the distribution may be a normal distribution, a Gaussian distribution, a linear distribution, a polynomial distribution or an exponential distribution.

[0090] As shown in Figure 6, the distribution may vary during use of the exposure apparatus. For example, when the patterning device MA is started to be used, then the distribution that characterises the variation in temperature of the patterning device MA may be exponential. However, once the exposure apparatus has been used for a substantial length of time, then the temperature of the patterning device MA may reach a substantially steady state. Accordingly, the distribution may no longer be exponential.

[0091] Based on, for example, the variance of the parameter and the class of the distribution, the controller may determine the predictability of the parameter at a given point in time . Based on the mean value of the parameter, the variance of the parameter and the class of the distribution, the controller may be configured to determine a prediction for the parameter at a given point in time.

[0092] In an embodiment the controller is configured to use Bayesian active inferencing techniques so as to determine the predictability and / or prediction of the parameter. In an embodiment, the method comprises inferring the data of each distribution 51-54 from the previous measurements of the parameter. In an embodiment the controller functions as a moving average filter guided by means of Bayesian active -inferencing. The controller may be considered to be a filter because the controller is configured to output predictions of the parameter based on input inline measurements of the parameter.

[0093] In an embodiment, the method comprises updating the data of the plurality of distributions 51- 54 when a measurement of the parameter is performed. Accordingly, future predictions can take into account the measurement of the parameter. The past data that is used to characterise the present drift is actively updated. Whenever there are measurements made, both predictions and the data on which the predictions are based are updated. This allows trends, jumps and non-uniform sampling to be navigated.

[0094] As shown in Figure 6, in an embodiment the method comprises predicting what the value of the drift D will be at a time ti . The prediction may be based on the distribution 51. As shown in Figure 6, in an embodiment the method comprises predicting what the value of the drift D will be at a time t2. The prediction may be based on the distribution 52. As shown in Figure 6, in an embodiment the method comprises predicting what the value of the drift D will be at a time L. The prediction may be based on the distribution 53. As shown in Figure 6, in an embodiment the method comprises predicting what the value of the drift D will be at a time L. The prediction may be based on the distribution 54.

[0095] In an embodiment, the controller is learning-based. For example, the controller may be configured to learn using the Bayesian active inferencing techniques. In an embodiment the controller is configured to learn using the so-called free-energy principle.

[0096] Figure 7 is a schematic diagram illustrating function of the controller 70. The controller 70 may be part of the computer system CL described elsewhere, for example.

[0097] In an embodiment the method comprises a learning phase in which inline measurements of the parameter are used to infer the data of each distribution 51-54 from the measurements of the parameter. The learning phase is before the determination of whether to perform an inline measurement 23 of a parameter based on the predetermined predictability of the parameter. The learning phase is an initial phase before predictions and determination of predictability of the parameter are used. During the initial learning phase, the controller is configured to learn the distributions of the parameter. After the initial learning phase, the controller is configured to determine whether to perform inline measurements 23.

[0098] As shown in Figure 7, in an embodiment the function of the controller 70 comprises learning 75 and prediction 76. In an embodiment the controller 70 is configured to use an information bank 71. The information bank contains the data from previous measurements of the parameter. The information bank contains data of how the parameter drifts over time. In an embodiment the information bank 71 is actively updated. Whenever there are measurements, both predictions and the information bank 71 are updated.

[0099] By providing that the controller is configured to actively learn, it is not necessary to provide a base line model in order to characterise the drift. In an embodiment the predictability is determined independently of any physical model.

[0100] The controller 70 may receive as an input measured values ytof the parameter. The controller 70 may provide as an output predicted values yt. The output values may be a moving average value.

[0101] In an embodiment the controller 70 is configured to make decisions (i.e. determination of whether to perform an inline measurement 23) guided by means of Bayesian active-inferencing. The information bank 71 stores a finite amount of measured data from the past. The drift information stored in the information bank 71 allows the controller to determine whether to form an inline measurement 23. The controller 70 is configured to take into account the current measurement data and the past data so as to predict the parameter such that variations in the signal (i.e. the noise) is maximised. Bymaximising the noise component in the data, in an ideal situation, irrespective of the type of noise, the rest of the signal should be the “real” drift.

[0102] During the initial phase of learning 75, the controller 70 is configured to determine the free- energy at each past time 72. Each past time may correspond to a time at which a measurement of the parameter was made. The controller 70 may be configured to determine the posteriori 73 of the free energy. In an embodiment the controller 70 is configured to provide feedback 77 so as to update the information bank 71 based on the present prediction.

[0103] In an embodiment, the controller 70 is configured to, during prediction 76, determine the firee- energy 74 at the present time. The controller 70 is configured to output as the prediction of the parameter the moving-average of the parameter.

[0104] An embodiment of the invention is expected to provide improved predictions of the parameter over time.

[0105] In an embodiment the controller 70 is configured to determine that a measured value for the parameter is an anomalous result. In an embodiment the controller 70 is configured to flag an anomalous result and / or not store the anomalous result in the information bank 71. By flagging anomalous results, the anomalous measurement result may be prevented from reducing the accuracy of future predictions.

[0106] An embodiment of the invention is expected to be able to handle any type of drift. The controller 70 does not depend on any baseline models. The controller 70 can differ in shape between anomalous results and genuine measurements.

[0107] In an embodiment the exposure apparatus comprises a thermal conditioner configured to thermally condition the patterning device MA. By thermally conditioning the patterning device, the undesirable influence of changes in temperature of the patterning device MA may be reduced. For example, the thermal conditioner may be configured to reduce the extent by which the temperature of the patterning device MA increases over time.

[0108] For example, in an embodiment the thermal conditioner is configured to induce a flow of gas across the patterning device MA. The flow of gas may help to remove heat from the patterning device MA. In an alternative embodiment, the thermal conditioner may comprise one or more channels for flowing thermal conditioning fluid adjacent to the patterning device MA. For example, the channels may be formed in the support structure MT. The thermal conditioning fluid may be, for example, a liquid such as water or a gas. The temperature of the thermal conditioning fluid may be controlled so as to control thermal conditioning of the patterning device MA.

[0109] Embodiments may be used with any type of lithographic system. For example, the lithographic system may be an EUV system or a DUV system. The lithographic system may be any design and is not restricted to the specific types of system shown in Figures 1 to 2B.

[0110] In all embodiments, the described determinations may be performed by algorithms implemented in a computer system. The computer system may also determine and apply process corrections for controlling the operation of a lithographic system in dependence on the determinations.

[0111] Although specific reference can be made in this text to the use of lithographic apparatus in the manufacture of ICs, it should be understood that the lithographic apparatus described herein may have other applications, such as the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, LCDs, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternative applications, any use of the terms “wafer” or “die” herein may be considered as synonymous with the more general terms “substrate” or “target portion”, respectively. The substrate referred to herein may be processed, before or after exposure, in for example a track unit (a tool that typically applies a layer of resist to a substrate and develops the exposed resist), a metrology unit and / or an inspection unit. Where applicable, the disclosure herein may be applied to such and other substrate processing tools. Further, the substrate may be processed more than once, for example in order to create a multi-layer IC, so that the term substrate used herein may also refer to a substrate that already contains multiple processed layers.

[0112] Although specific reference may have been made above to the use of aspects in the context of optical lithography, it will be appreciated that aspects may be used in other applications, for example imprint lithography, and where the context allows, is not limited to optical lithography. In imprint lithography a topography in a patterning device defines the pattern created on a substrate. The topography of the patterning device may be pressed into a layer of resist supplied to the substrate whereupon the resist is cured by applying electromagnetic radiation, heat, pressure or a combination thereof. The patterning device is moved out of the resist leaving a pattern in it after the resist is cured.

[0113] It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0114] The term “substrate” as used herein describes a material onto which material layers are added. In some aspects, the substrate itself may be patterned and materials added on top of it may also be patterned, or may remain without patterning.

[0115] The following examples are illustrative, but not limiting, of the aspects of this disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the relevant art(s), are within the spirit and scope of the disclosure.

[0116] Although specific reference may be made in this text to the use of the apparatus and / or system in the manufacture of ICs, it should be explicitly understood that such an apparatus and / or system has many other possible applications. For example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, LCD panels, thin-film magnetic heads, etc. The skilled artisan will appreciate that, in the context of such alternativeapplications, any use of the terms “reticle,” “wafer,” or “die” in this text should be considered as being replaced by the more general terms “mask,” “substrate,” and “target portion,” respectively.

[0117] While specific aspects have been described above, it will be appreciated that the aspects may be practiced otherwise than as described. The description is not intended to limit the scope of the claims.

[0118] It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary aspects as contemplated by the inventor(s), and thus, are not intended to limit the aspects and the appended claims in any way.

[0119] The aspects have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0120] The foregoing description of the specific aspects will so fully reveal the general nature of the aspects that others can, by applying knowledge within the skill of the art, readily modify and / or adapt for various applications such specific aspects, without undue experimentation, without departing from the general concept of the aspects. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed aspects, based on the teaching and guidance presented herein. Other aspects of the invention are set-out as in the following numbered clauses.1. A method of controlling an exposure apparatus configured to expose one or more substrates, the method comprising: determining, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter• of a component of the exposure apparatus, or• of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.2. The method of clause 1, comprising: when it is determined, for at least one substrate of the series of substrates, to skip the inline measurement, controlling exposure of the at least one substrate dependent on a prediction of the parameter.3. The method of clause 2, wherein the controlling of the exposure apparatus comprises: actuating at least one of a patterning device of the exposure apparatus, an optical element of the exposure apparatus and the substrate exposed by the exposure apparatus so as to account for the prediction of the parameter.The method of any preceding clause, wherein it is determined to perform the inline measurement when the predictability is below a threshold and it is determined to skip the inline measurement when the predictability is at least the threshold. The method of clause 4, comprising: the threshold being selectable by a user. The method of any preceding clause, comprising: determining the predictability of the parameter based on a rate of change of state of the component. The method of any preceding clause, comprising: determining the predictability of the parameter based on data of a plurality of distributions of previous measurements of the parameter. The method of clause 7, wherein the data of each distribution comprises at least one of a mean value of the parameter, a variance of the parameter and a class of the distribution. The method of clause 7 or 8, comprising: inferring the data of each distribution from the previous measurements of the parameter. The method of any of clauses 7-9, comprising: updating the data of the plurality of distributions when a measurement of the parameter is performed such that future predictions take into account the measurement of the parameter. The method of any of clauses 7-10, comprising: a learning phase in which the measurements of the parameter are used to infer the data of each distribution from the measurements of the parameter, the learning phase being before the determination of whether to perform an inline measurement of a parameter based on the determined predictability of the parameter. The method of any preceding clause, wherein the predictability is determined independently of any physical model. The method of any preceding clause, wherein the parameter is at least one of a shape, a size, a position and a temperature of the component. The method of any preceding clause, wherein the component is one of a patterning device of the exposure apparatus, an optical element of the exposure apparatus and the substrate exposed by the exposure apparatus. The method of any preceding clause, comprising: after determining, for at least one substrate of the series of substrates, to skip the inline measurement, performing the inline measurement for at least one subsequent substrate of the series of substrates.16. The method of any preceding clause, wherein exposure of each substrate comprises: illuminating a or the patterning device of the exposure apparatus with radiation so as to pattern the radiation; and projecting the patterned radiation onto the substrate.17. A method of forming a semiconductor device comprising the steps of processing a substrate with a layer of material to be patterned and illuminating the layer with a pattern, wherein the step of illuminating further comprises illuminating the layer using the method as claimed in one of the clauses 1 to 16, the method further comprising a step of introducing a structure corresponding to at least part of the pattern to a layer of the semiconductor device, wherein a portion of the layer of material to be patterned is being removed.18. A controller configured to control an exposure apparatus that is configured to expose substrates, the controller configured to: determine, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter• of a component of the exposure apparatus, or• of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.19. An exposure apparatus comprising the controller of clause 18.20. The exposure apparatus of clause 19, comprising: a patterning device; and a thermal conditioner configured to thermally condition the patterning device.

[0121] The breadth and scope of the aspects should not be limited by any of the above-described exemplary aspects, but should be defined only in accordance with the following claims and their equivalents.

Claims

CLAIMS1. A method of controlling an exposure apparatus configured to expose one or more substrates, the method comprising: determining, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter• of a component of the exposure apparatus, or• of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.

2. The method of claim 1, comprising: when it is determined, for at least one substrate of the series of substrates, to skip the inline measurement, controlling exposure of the at least one substrate dependent on a prediction of the parameter.

3. The method of claim 2, wherein the controlling of the exposure apparatus comprises: actuating at least one of a patterning device of the exposure apparatus, an optical element of the exposure apparatus and the substrate exposed by the exposure apparatus so as to account for the prediction of the parameter.

4. The method of any preceding claim, wherein it is determined to perform the inline measurement when the predictability is below a threshold and it is determined to skip the inline measurement when the predictability is at least the threshold.

5. The method of any preceding claim, comprising: determining the predictability of the parameter based on a rate of change of state of the component.

6. The method of any preceding claim, comprising: determining the predictability of the parameter based on data of a plurality of distributions of previous measurements of the parameter.

7. The method of any preceding claim, wherein the predictability is determined independently of any physical model.

8. The method of any preceding claim, wherein the parameter is at least one of a shape, a size, a position and a temperature of the component.

9. The method of any preceding claim, wherein the component is one of a patterning device of the exposure apparatus, an optical element of the exposure apparatus and the substrate exposed by the exposure apparatus.

10. The method of any preceding claim, comprising: after determining, for at least one substrate of the series of substrates, to skip the inline measurement, performing the inline measurement for at least one subsequent substrate of the series of substrates.

11. The method of any preceding claim, wherein exposure of each substrate comprises: illuminating a or the patterning device of the exposure apparatus with radiation so as to pattern the radiation; and projecting the patterned radiation onto the substrate.

12. A method of forming a semiconductor device comprising the steps of processing a substrate with a layer of material to be patterned and illuminating the layer with a pattern, wherein the step of illuminating further comprises illuminating the layer using the method as claimed in one of the claims 1 to 11, the method further comprising a step of introducing a structure corresponding to at least part of the pattern to a layer of the semiconductor device, wherein a portion of the layer of material to be patterned is being removed.

13. A controller configured to control an exposure apparatus that is configured to expose substrates, the controller configured to: determine, for at least one substrate of a series of substrates exposed by the exposure apparatus, whether to perform an inline measurement measuring a parameter• of a component of the exposure apparatus, or• of the at least one substrate, based on a determined predictability of the parameter, the inline measurement being a measurement that is made during a time period in which the exposure apparatus is being used to expose one or more substrates.

14. An exposure apparatus comprising the controller of claim 13.

15. The exposure apparatus of claim 14, comprising: a patterning device; and a thermal conditioner configured to thermally condition the patterning device.

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