Exposure apparatus

Abstract

Disclosed herein is an exposure apparatus (LA) for exposing a substrate (W) with patterned radiation, the exposure apparatus (LA) comprising: a patterning device (MA) configured to pattern radiation; a thermal conditioner (50) configured to thermally condition the patterning device (MA); and a controller (41) configured to vary a setting of the thermal conditioner and to control actuation of at least one of the patterning device (MA), an optical element of the exposure apparatus and the substrate (W) based on temperature data (T1) indicative of a temperature of the patterning device (MA) and / or deformation data indicative of a deformation of the patterning device (MA).

Description

EXPOSURE APPARATUSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority of EP application 24186835.5 which was filed on 05 July, 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to an exposure apparatus and a method of controlling 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). If not compensated for, all reticle shape deformations may increase distortions in the patterned substrate (e.g., overlay errors).

[0006] Reticle heating and / or cooling can cause changes in properties of gas through which radiation propagates that can affect the radiation beam path (e.g., focus) and cause distortions in the patterned substrate (e.g., overlay errors).SUMMARY

[0007] There is a general need to better reduce or compensate for the effects of reticle heating and / or cooling.

[0008] According to a first aspect of the invention, there is provided an exposure apparatus for exposing a substrate with patterned radiation, the exposure apparatus comprising: a patterning device configured to pattern radiation; a thermal conditioner configured to thermally condition the patterning device; and a controller configured to vary a setting of the thermal conditioner and to control actuationof at least one of the patterning device, an optical element of the exposure apparatus and the substrate based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.

[0009] According to a second aspect of the invention, there is provided a method for controlling a exposure apparatus, the method comprising: varying a setting of thermal conditioning of a patterning device of the exposure apparatus; and controlling actuation of at least one of the patterning device, an optical element of the exposure apparatus and a substrate to be exposed by the exposure apparatus based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.

[0010] According to a third aspect of the invention, there is provided 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 according to the second 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] 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.

[0012] 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

[0013] 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.

[0014] FIG. 1 is a schematic illustration of a lithographic apparatus, according to an exemplary aspect.

[0015] FIG. 2A is a schematic illustration of a lithographic cell, according to an exemplary aspect.

[0016] FIG. 2B is a schematic illustration of holistic lithography including a computer system to optimize a lithographic process, according to an exemplary aspect.

[0017] FIG. 3A is a schematic bottom perspective illustration of a reticle stage and a reticle, according to an exemplary aspect.

[0018] FIG. 3B is a schematic bottom plan illustration of the reticle stage shown in FIG. 3A.

[0019] FIG. 4 is a schematic diagram of control an exposure apparatus.

[0020] FIG. 5 is a graph showing the relationship between time and a setpoint temperature of gas conditioning the reticle.

[0021] 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

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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, the term “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).

[0026] 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.

[0027] 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 ICchip). 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.

[0028] 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.

[0029] 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.

[0030] 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 adjusting feed-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.

[0031] 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. PatentNo. 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.

[0032] 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.

[0033] 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).

[0034] 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 from computing devices, processors, controllers, or other devices executing the firmware, software, routines, instructions, etc.

[0035] 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.

[0036] Exemplary Lithographic System

[0037] 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. Thelithographic 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.

[0038] 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.

[0039] 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).

[0040] 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.

[0041] Exemplary Lithographic Cell

[0042] 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 / Ol, I / 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.

[0043] 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.

[0044] 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).

[0045] Exemplary Computer System

[0046] 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).

[0047] 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.

[0048] 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).

[0049] 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.

[0050] Exemplary Reticle Stage and Reticle

[0051] FIGS. 3A and 3B show schematic illustrations of reticle stage 200, according to exemplary aspects. FIG. 3A 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.

[0052] 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. 3 A and 3B, reticle 300 can be disposed at a center of bottom stage surface 202 and secured by reticle cages 224 adjacent to each corner of reticle 300.

[0053] 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.

[0054] As shown in FIGS. 3 A 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. 3A and 3B, one or more alignment marks 310 can be disposed in the corners 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.

[0055] Exemplary Exposure Control Methods

[0056] Figure 4 is a schematic diagram of an exposure apparatus. As shown in Figure 4, in an embodiment the exposure apparatus is a lithographic apparatus LA. For example, the exposure apparatus may be a lithographic apparatus LA of the type shown in Figure 1. The exposure apparatus is configured to expose a substrate W with patterned radiation.

[0057] As shown in Figure 4, in an embodiment the exposure apparatus comprises a patterning device MA. The patterning device MA is configured to pattern radiation. For example, as shown in Figure 4, in an embodiment the exposure apparatus comprises a radiation source SO. The radiation source SO is configured to direct radiation to the patterning device MA. The patterning device MA is configured to pattern the radiation supplied by the radiation source SO.

[0058] As shown in Figure 4, in an embodiment the exposure apparatus comprises a thermal conditioner 50. The thermal conditioner 50 is configured to thermally condition the patterning device MA. In an embodiment the thermal conditioner 50 is configured to induce flow of a thermal conditioning fluid for thermally conditioning the patterning device MA. For example, in an embodiment the thermal conditioner 50 is configured to induce a gas flow 51. The gas flow 51 may be across the patterning device MA. For example, the gas flow may be located between the radiation source SO and the patterning device MA. For example, the thermal conditioner 50 may be configuredto blow the gas flow 51 across a surface of the patterning device MA. In an embodiment the patterning device MA is located between the gas flow 51 and the substrate W.

[0059] However, it is not essential for the thermal conditioner 50 to induce a gas flow 51. In an alternative embodiment the thermal conditioner 50 may comprise at least one channel for the flow of thermal conditioning fluid. The thermal conditioning fluid may be a liquid such as water. The thermal conditioning channels may be provided in the support structure MT, for example.

[0060] In an embodiment the thermal conditioner 50 comprises a gas supply configured to output the gas flow 51. The gas supply may comprise a blower configured to blow the gas flow 51 across the patterning device MA. The gas supply may comprise a nozzle.

[0061] In an embodiment the thermal conditioner 50 comprises a gas extractor configured to extract the gas flow. For example, the gas extractor may be in fluid communication with a source of under pressure for inducing the gas flow 51.

[0062] The gas flow 51 may be for thermally conditioning the patterning device MA. For example, the gas flow 51 may cool the patterning device MA. Cooling the patterning device MA may comprise reducing the extent by which the temperature of the patterning device MA rises during use of the exposure apparatus. While the thermal conditioner 50 cools the patterning device MA, the temperature of the patterning device MA may continue to increase, albeit by a lesser extent. The gas flow 51 may facilitate removal of heat away from the patterning device MA.

[0063] As shown in Figure 4, in an embodiment the exposure apparatus comprises a controller 40. The controller 40 is configured to control one or more functions of the exposure apparatus. As shown in Figure 4, in an embodiment the controller 40 comprises the thermal conditioner 50. Alternatively, the thermal conditioner 50 may be separate from the controller 40. The controller 40 may be configured to control the thermal conditioner 50.

[0064] The thermal conditioner 50 may be configured to reduce the extent of errors caused by heating of the patterning device MA. For example, heat exchange between the patterning device MA and the gas adjacent to the patterning device MA can cause unpredictable variations of the refractive index of the gas. The variation in the refractive index can cause distortion of the image projected onto the substrate W. This can cause errors such as increased overlay.

[0065] In general, the patterning device MA heats up during use of the exposure apparatus. The patterning device MA may absorb radiation from the radiation source SO. The absorbed radiation causes the patterning device MA to heat up. When the patterning device MA heats up, the patterning device MA may thermally deform (e.g. change in shape). When the patterning device MA deforms, the image projected on the substrate W may be deformed. This can contribute to undesirable overlay.

[0066] As shown in Figure 4, in an embodiment the controller 40 is configured to control actuation 47 of at least one of the patterning device MA, an optical element of the exposure apparatus and the substrate W. The optical element may be a lens of the exposure apparatus. For example, Figure 4 showsthat the controller 40 may comprise a central controller 41. The central controller 41 may be configured to control the actuation 47.

[0067] Figure 4 shows three arrows of actuation 47 corresponding to actuation of the patterning device MA (top arrow), actuation of a lens of the exposure apparatus such as a lens of the projection system PS (middle arrow) an actuation of the substrate W (bottom arrow).

[0068] In an embodiment the controller 40 is configured to control the actuation 47 based on deformation data indicative of a deformation of the patterning device MA. By controlling the actuation 47 based on the deformation data, the deformation of the patterning device MA may be at least partly compensated for. For example, the controller 40 may be configured to control the actuation 47 so as to control alignment between two or more of the patterning device MA, the projection system PS and the substrate W.

[0069] As shown in Figure 4, in an embodiment the thermal conditioner 50 and the controlled actuation 47 are integrated with each other. For example, as shown in Figure 4, in an embodiment the controller 40 is configured to control the actuation 47 based on temperature data 44 indicative of a temperature of the patterning device MA. For example, as shown in Figure 4 in an embodiment the exposure apparatus comprises at least one temperature sensor 52-54, which may be referred to as a thermometer.

[0070] In an embodiment the exposure apparatus comprises a thermometer configured to measure a temperature of the patterning device to obtain the temperature data 44. For example the temperature sensor 52-54 may be provided. In an embodiment the controller 40 is configured to estimate the deformation of the patterning device MA based, at least in part, on the measurement of the temperature of the patterning device MA.

[0071] In an embodiment the exposure apparatus comprises a nozzle sensor 52 configured to measure the temperature of the gas flow 51 as it is output by the thermal conditioner 50. The nozzle sensor 52 may provide data indicative of the temperature of the gas flow 51, which in turn is indicative of the temperature of the patterning device MA that is conditioned by the gas flow 51. A model may be used for predicting or determining the temperature of the patterning device MA based on the temperature measured by the nozzle sensor 52 and optionally further information such as the time for which the patterning device MA has been used to expose series of substrates W.

[0072] Additionally or alternatively, the exposure apparatus may comprise a region sensor 53. The region sensor 53 may be located proximal to the patterning device MA. The region sensor 53 may be configured to measure the temperature of the gas in the region between the radiation source SO and the patterning device MA. The region sensor 53 may output data of the temperature of the gas proximal to the patterning device MA, which may be indicative of the temperature of the patterning device MA.

[0073] Additionally or alternatively, the exposure apparatus may comprise an output sensor 54. The output sensor 54 is configured to measure the temperature of gas output from the exposure apparatus. For example, the output sensor 54 may be configured to measure the temperature of gas that is extractedfrom the region between the radiation source SO and the patterning device MA. The temperature of the output gas may be indicative of the temperature of the patterning device MA.

[0074] As shown in Figure 4, in an embodiment the controller 40 is configured to receive the temperature data 44. For example, as shown in Figure 4, in an embodiment the controller 40 comprises an estimator 43. The estimator 43 is configured to receive the temperature data 44. The estimator 43 is configured to receive the deformation data 45. For example, the deformation data 45 may be derived from one or more sensors configured to determine the positions of markers associated with the patterning device MA.

[0075] The controller 40 may be configured to use the temperature data 44 and the deformation data 45 so as to control the actuation 47. For example, as shown in Figure 4, the estimator 43 may be configured to output combined data 46 to the central controller 41. The combined data 46 may comprise the temperature data 44 combined with the deformation data 45. The central controller 41 may be configured to control the actuation 47 based on the combined data 46.

[0076] By integrating the thermal conditioner 50 with the control of the actuation 47, the overall error caused by heating of the patterning device MA may be reduced. An embodiment of the invention is expected to reduce errors such as overlay error.

[0077] The error caused by the variation of the refractive index of the gas adjacent to the patterning device MA may be referred to as a non-moving average error. The non-moving average error is unpredictable.

[0078] The error due to deformation of the patterning device MA is, to an extent correctable. The deformation of the patterning device MA may comprise one or more different modes of deformation. For example, the change in shape of the patterning device MA may comprise contributions from one or more of a translational movement of the patterning device MA, an expansion of the patterning device MA, a skew of the patterning device MA etc. Some modes of deformation may be corrected, or at least compensated for, by controlling the actuation 47. The error caused by the deformation of the patterning device MA may be at least partly uncorrectable by the control of the actuation 47. For example, one or more modes of deformation (change and shape) of the patterning device MA may not be corrected for by actuating any of the patterning device MA, the projection system PS or the substrate W.

[0079] In an embodiment the at least one temperature sensor 52-54 is configured to perform temperature measurements substantially continuously. The temperature data 44 may be generated substantially continuously. The substantially continuous measurements of the temperature are used in combination with at least one position / deformation (local) measurement. The deformation measurement may be performed at the start of exposing a substrate W, for example. The temperature data 44 and the deformation data are provided to the estimator 43. The estimator 43 is configured to estimate the thermal deformation of the whole patterning device MA. The estimator 43 may be configured to estimate the thermal deformation of the patterning device MA substantially continuously.

[0080] In an embodiment the controller 40 is configured to categorize the deformation of the patterning device MA into a correctable category and non-correctable category. The deformation of the patterning device MA is categorized as correctable when the effect of the deformation on the exposure process is correctable by the actuation 47. The deformation of the patterning device MA is categorized as non- correctable when the effect of the deformation on the exposure process is not correctable by the actuation 47.

[0081] In other words, the controller 40 may be configured to classify the deformation of the patterning device MA into a first class of deformation that can be corrected for by the control of the actuation 47 and a second class of deformation that cannot be corrected for by the control of the actuation 47. In an embodiment the controller 40 is configured to control the actuation 47 based on the first class of deformation.

[0082] In an embodiment the estimator 43 is configured to output to the central controller 41 of the controller data 46 of the non-correctable deformations and the thermal effect of the gas heating up below the patterning device MA. In an embodiment the central controller 41 is configured to minimize both effects of (a) non-correctable deformations and (b) the thermal effect of the gas heating up below the patterning device MA. In an embodiment the central controller 41 is configured to control the actuation 47 and control the temperature of the gas flow 51 over the patterning device MA. In an embodiment the central controller 41 is configured to control the temperature of the gas flow 51 ignoring the correctable deformation.

[0083] In an embodiment the controller 40 is configured to vary the setting of the thermal conditioner 50, e.g. to vary the setting of the thermal conditioner 50 over time, based on a combined error caused by (a) distortion of refractive index of gas adjacent to the patterning device MA and (b) deformation of the patterning device MA that cannot be corrected for by the control of the actuation 47. The sum of the non-correctable deformation and the non-moving average error due to distortion of refractive index are the input for control of the thermal conditioner 50. The central controller 41 is configured to reduce or minimize the sum of the non-correctable deformation and the non-moving average error by controlling the thermal conditioner 50, for example by controlling the temperature of the gas blown from the nozzle of the gas supply. In an embodiment the controller 40 is configured to vary the setting of the thermal conditioner 50 so as to minimize the combined error. Alternatively, the controller 50 is configured to vary the setting of the thermal conditioner 50 based on a distortion error caused by distortion of refractive index of gas adjacent to the patterning device MA, or a deformation error caused by deformation of the patterning device MA that cannot be corrected for by the control of the actuation 47.

[0084] As shown in Figure 4, in an embodiment the central controller 41 is configured to output a temperature control signal T i to the thermal conditioner 50 for controlling the thermal conditioner 50. The temperature control signal T i may indicate the temperature of the gas to be output be the gas supply, for example. As shown in Figure 2, in an embodiment the nozzle sensor 52 is configured to providefeedback data such as a feedback temperature signal T2. The feedback temperature signal T2 may indicate the actual temperature of gas supplied by the gas supply. The thermal conditioner 50 may be controlled based on the temperature control signal Ti and the feedback temperature signal T2 so as to control the temperature of the gas flow 51.

[0085] The effect of the constantly changing thermal conditioner temperature is incorporated in the estimator model. The controller 40 can react to changes in this temperature, because the controller 40 uses the output of the estimator model.

[0086] Meanwhile, the controller 40 may be configured to control the actuation 47 so as to correct the correctable deformation. In an embodiment the controller 40 is configured to control the actuation 47 of at least one of the patterning device MA, an optical element of the exposure apparatus and the substrate W to be exposed by the exposure apparatus based on the deformation data. The optical element may be a lens of the exposure apparatus.

[0087] In an embodiment the exposure apparatus comprises at least one sensor configured to measure at least one of a position and a shape of the patterning device MA to obtain the deformation data. In an embodiment the at least one sensor comprises an interferometric sensor system. For example the interferometric sensor system may be an Integrated Lens Interferometry At Scanner “ILIAS” sensor system. Alternatively, the interferometric sensor system may be a Parallel ILIAS “PARIS” sensor system. Alternatively the sensor system may be a Transmission Image Sensor “TIS” system. The controller 40 is configured to estimate the deformation of the patterning device MA based on the measurement of the at least one of the position and the shape of the patterning device MA.

[0088] As shown in Figure 4, in an embodiment the exposure apparatus is configured such that a path of the radiation extends through a volume of gas adjacent to the patterning device MA. As a result the exposure process is affected significantly by any change in refractive index of the gas. The undesirable effect can be reduced by thermally conditioning the patterning device MA.

[0089] Figure 5 is a graph showing the relationship between time during use of the exposure apparatus and the ideal temperature of gas flow 51 blown across the patterning device MA. Here, the ideal temperature means the temperature of the gas flow 51 that would minimize the combined error of the undesirable effect of the varying refractive index and the non-correctable deformations.

[0090] The three lines of Figure 5 represent different use cases of the exposure apparatus. The top line represents open loop control of the thermal conditioner 50. In open loop control, the control of the thermal conditioner 50 does not take into account any data obtained during use of the exposure apparatus. As shown in Figure 5, the temperature of the gas supplied for the gas flow is constant. The middle lane and the bottom line represent full field and narrow field, respectively. Full field means that substantially the whole field of the patterning device MA is irradiated. Narrow field means that only a portion of the field is irradiated.

[0091] The patterns shown in Figure 5 represent control of the thermal conditioner 50 when the nonmoving average error and the non-correctable deformation are taken into account. The correctable deformation may be corrected for by controlling the actuation 47.

[0092] 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.

[0093] 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.

[0094] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. An exposure apparatus for exposing a substrate with patterned radiation, the exposure apparatus comprising: a patterning device configured to pattern radiation; a thermal conditioner configured to thermally condition the patterning device; and a controller configured to vary a setting of the thermal conditioner and to control actuation of at least one of the patterning device, an optical element of the exposure apparatus and the substrate based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.2. The exposure apparatus of clause 1 , wherein the controller is configured to vary the setting of the thermal conditioner based on a distortion error caused by distortion of refractive index of gas adjacent to the patterning device, or a deformation error caused by deformation of the patterning device that cannot be corrected for by the control of the actuation.3. The exposure apparatus of clause 1, wherein the controller is configured to vary the setting of the thermal conditioner based on a combined error caused by (a) distortion of refractive index of gas adjacent to the patterning device and (b) deformation of the patterning device that cannot be corrected for by the control of the actuation.4. The exposure apparatus of clause 3, wherein the controller is configured to vary the setting of the thermal conditioner so as to minimise the combined error.5. The exposure apparatus of any preceding clause, comprising: at least one sensor configured to measure at least one of a position and a shape of the patterning device to obtain the deformation data; wherein the controller is configured to estimate the deformation of the patterning device based on the measurement of the at least one of the position and the shape of the patterning device.6. The exposure apparatus of any preceding clause, comprising: a thermometer configured to measure a temperature of the patterning device to obtain the temperature data;wherein the controller is configured to estimate the deformation of the patterning device based on the measurement of the temperature of the patterning device.7. The exposure apparatus of any preceding clause, wherein the controller is configured to classify the deformation of the patterning device into a first class of deformation that can be corrected for by the control of the actuation and a second class of deformation that cannot be corrected for by the control of the actuation, wherein the controller is configured to control the actuation based on the first class of deformation.8. The exposure apparatus of any preceding clause, wherein the thermal conditioner is configured to cause a gas flow across a surface of the patterning device.9. The exposure apparatus of clause 8, wherein the setting of the thermal conditioner is a temperature of the gas flow.10. The exposure apparatus of clause 9, wherein the temperature data comprises the temperature of the gas flow.11. The exposure apparatus of any preceding clause, wherein the temperature data comprises a temperature measurement adjacent to the patterning device.12. The exposure apparatus of any preceding clause, configured such that a path of the radiation extends through a volume of gas adjacent to the patterning device.13. A method for controlling a exposure apparatus, the method comprising: varying a setting of thermal conditioning of a patterning device of the exposure apparatus; and controlling actuation of at least one of the patterning device, an optical element of the exposure apparatus and a substrate to be exposed by the exposure apparatus based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.14. 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 described in clause 13, 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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 alternative applications, 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.

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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. An exposure apparatus for exposing a substrate with patterned radiation, the exposure apparatus comprising: a patterning device configured to pattern radiation; a thermal conditioner configured to thermally condition the patterning device; and a controller configured to vary a setting of the thermal conditioner and to control actuation of at least one of the patterning device, an optical element of the exposure apparatus and the substrate based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.

2. The exposure apparatus of claim 1 , wherein the controller is configured to vary the setting of the thermal conditioner based on a distortion error caused by distortion of refractive index of gas adjacent to the patterning device, or a deformation error caused by deformation of the patterning device that cannot be corrected for by the control of the actuation.

3. The exposure apparatus of claim 1, wherein the controller is configured to vary the setting of the thermal conditioner based on a combined error caused by (a) distortion of refractive index of gas adjacent to the patterning device and (b) deformation of the patterning device that cannot be corrected for by the control of the actuation.

4. The exposure apparatus of claim 3, wherein the controller is configured to vary the setting of the thermal conditioner so as to minimise the combined error.

5. The exposure apparatus of claim 1, comprising: at least one sensor configured to measure at least one of a position and a shape of the patterning device to obtain the deformation data; wherein the controller is configured to estimate the deformation of the patterning device based on the measurement of the at least one of the position and the shape of the patterning device.

6. The exposure apparatus of claim 1 , comprising: a thermometer configured to measure a temperature of the patterning device to obtain the temperature data; wherein the controller is configured to estimate the deformation of the patterning device based on the measurement of the temperature of the patterning device.

7. The exposure apparatus of claim 1, wherein the controller is configured to classify the deformation of the patterning device into a first class of deformation that can be corrected for by the control of the actuation and a second class of deformation that cannot be corrected for by the control of the actuation, wherein the controller is configured to control the actuation based on the first class of deformation.

8. The exposure apparatus of claim 1, wherein the thermal conditioner is configured to cause a gas flow across a surface of the patterning device.

9. The exposure apparatus of claim 8, wherein the setting of the thermal conditioner is a temperature of the gas flow.

10. The exposure apparatus of claim 9, wherein the temperature data comprises the temperature of the gas flow.

11. The exposure apparatus of claim 1 , wherein the temperature data comprises a temperature measurement adjacent to the patterning device.

12. The exposure apparatus of claim 1, configured such that a path of the radiation extends through a volume of gas adjacent to the patterning device.

13. A method for controlling a exposure apparatus, the method comprising: varying a setting of thermal conditioning of a patterning device of the exposure apparatus; and controlling actuation of at least one of the patterning device, an optical element of the exposure apparatus and a substrate to be exposed by the exposure apparatus based on temperature data indicative of a temperature of the patterning device and / or deformation data indicative of a deformation of the patterning device.

14. 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 claim 13, 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.

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