Methods and systems to reduce effects of uncertain conditions for reticle heating

Abstract

A lithographic apparatus is configured to perform a lithographic process. The lithographic apparatus comprises an illumination system configured to illuminate a reticle and a projection system configured to project an image of the reticle onto a substrate, wherein the illuminating and projection comprise the lithographic process. The lithographic apparatus further comprises a controller configured to reduce effects of non-uniformity of the reticle in the lithographic process. The controller is configured to determine a status of the reticle, identify a model from a plurality of models based on the status, and predict, using the identified model, a thermal deformation associated with the reticle.

Description

METHODS AND SYSTEMS TO REDUCE EFFECTS OF UNCERTAIN CONDITIONS FOR RETICLE HEATINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of US application 63 / 622,768 which was filed on 19 January 2024 and which is incorporated herein in its entirety by reference.FIELD

[0002] The present disclosure relates to lithographic apparatuses, systems, and methods, for example, lithographic apparatuses, systems, and methods to reduce effects of uncertain conditions in a lithographic process.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 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 and cause distortions in the patterned substrate. Further, reticles can include a variety of different features that can cause non-uniform reticle absorption of the radiation beam during exposure. Changes in reticle properties can be modeled and corrected with a reticle heating model. Current reticle heating models assumes that a reticle is in a cold state, but this is generally not the case. In some examples, this approach can be inaccurate and inefficient, introduce errors and delays, and require rework of substrates.SUMMARY

[0006] Accordingly, there is a need to account for uncertainties, avoid rework of substrates, decrease overlay errors, and increase throughput, yield, and accuracy of the lithographic process.

[0007] In some aspects, a method includes determining a status of a lithographic element, identifying, based on the status, a model from a plurality of models, and predicting, using the identified model, a thermal deformation associated with the lithographic element.

[0008] In some aspects, a lithographic apparatus can perform a lithographic process. The lithographic apparatus can include an illumination system, a projection system, and a controller. The illumination system can illuminate a reticle. The projection system can project an image of the reticle onto a substrate. The illuminating and projection can include the lithographic process. The controller can reduce effects of non-uniformity of the reticle in the lithographic process. The controller can determine a status of the reticle and can identify a model from a plurality of models based on the status. The controller can also predict a thermal deformation associated with the reticle using the identified model.

[0009] In some aspects, a non-transitory computer readable medium program can include computer readable instructions configured to cause a processor to determine a status of a lithographic element, identify based on the status, a model from a plurality of models, and predict, using the identified model, a thermal deformation associated with the lithographic element.

[0010] 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.

[0011] 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

[0012] 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.

[0013] FIG. 1 is a schematic illustration of a lithographic system, according to an exemplary aspect.

[0014] FIG. 2A is a schematic illustration of a lithographic cell, according to an exemplary aspect.

[0015] FIG. 2B is a schematic illustration of holistic lithography including a computer system to optimize a lithographic process, according to an exemplary aspect.

[0016] FIG. 3A is a schematic bottom perspective illustration of a reticle stage and a reticle, according to an exemplary aspect.

[0017] FIG. 3B is a schematic bottom plan illustration of the reticle stage shown in FIG. 3A.

[0018] FIG. 4 A is a schematic top perspective illustration of a reticle exchange apparatus, according to an exemplary aspect.

[0019] FIG. 4B is a schematic partial cross-sectional illustration of the reticle exchange apparatus shown in FIG. 4A.

[0020] FIG. 5 is a schematic that shows an overlay error that may be caused by a temperature of the reticle, according to an exemplary aspect.

[0021] FIG. 6 is a block diagram of a deterministic reticle heating model, according to an exemplary aspect.

[0022] FIG. 7 is a schematic that shows exemplary reticle moves, according to an exemplary aspect.

[0023] FIG. 8 is a flowchart of a method for predicting a thermal deformation, according to an exemplary aspect.

[0024] FIG. 9 is an example computer system useful for implementing various embodiments.

[0025] 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

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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).

[0030] The term “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 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.

[0031] 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 initialized (e.g., setting initial values) and / or calibrated by exposing a reticle to a dose of radiation and measuring a non-uniformity map of the reticle (e.g., 2D transmission map, 2D reflectance map, 2D reflectivity map, etc.) 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 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 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.

[0032] 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.

[0033] The term “non-uniformity” or “non-uniform” as used herein indicates a parameter or a property of an object (e.g., a reticle) in a lithographic process that is not uniform and varies spatially and / or over time. In some aspects, non-uniformity can include thermal effects, thermomechanical effects, heating, absorption, transmission, transmittance, reflectance, reflectivity, emissivity, transparency, opacity, pattern density, design layout, or a combination thereof.

[0034] The term “reflectance map” or “2D reflectance map” as used herein indicates a measurement (e.g., percentage) of reflectance and / or absorption of an object (e.g., a reticle) or a portion of the object relative to an incoming dose of radiation. In some aspects, the reflectance map can include an absorption map based on DUV radiation. In some aspects, the reflectance map can include a reflectance map based on EUV radiation. In some aspects, the reflectance map can include an absorption map based on DUV radiation and a reflectance map based on EUV radiation.

[0035] The term “object heating model” as used herein indicates a modal deformation approach (e.g., analysis of different object mode shapes) to determine object heating effects based on object shape deformations and a FEM (e.g., COMSOL). In some aspects, the object of the object heating model can include a reticle, a lens, a substrate, a mirror, a filter, a combination thereof, or any other component of a lithographic process that exhibits a non-uniformity. In some aspects, the object heating model can include a reticle heating model, a lens heating model, a substrate heating model, or a combination thereof. For example, the object heating model can be deterministic (e.g., no random future states) or non-deterministic (e.g., including random future states) object heating effects. Further, the object heating model can utilize inline modal calibrations to determine the baseline object heating dynamics. The object heating model can be initialized (e.g., setting initial values) and / or calibrated by exposing an object (e.g., reticle, lens, substrate, etc.) to a dose of radiation and measuring a non-uniformity map of the object (e.g., 2D transmission map, 2D reflectance map, 2D reflectivity map, etc.) for inline realtime calibration of the object heating model. In some aspects, for example, the object heating model can be similar to the reticle heating model and the technique to reduce and / or compensate for non- uniformity (e.g., non-uniform heating) can be applied to other objects (e.g., a lens, a substrate, a mirror, a filter, etc.).

[0036] Object heating causes changes in object properties (e.g., reticle, lens, substrate, mirror, filter, etc.) that can affect the radiation path and cause fabrication errors (e.g., overlay). Object mechanical deformations (e.g., based on object 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 object heating model can also include adjusting feed-forward parameters p and r.

[0037] The term “finite element model” or “FEM” as used herein indicates a method for numerically solving differential equations arising in the reticle heating model or object heating model (e.g., heat transfer equations, structural analysis equations, fluid flow equations, etc.). For example, baseline reticle heating dynamics or object 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.

[0038] 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, linear magnification distortion, curvature distortion, etc.). For example, two important k-parameters are k4 that represents distortion in Y-axis magnification and kl8 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.

[0039] The term “inline calibration” or “inline real-time calibration” as used herein indicates calibration of the reticle heating model or object heating model during actual fabrication of substrates. For example, a calibration lot of substrates can be avoided and rework of substrates for calibration purposes can be reduced or avoided. The calibration can be done inline by exposing a reticle, a substrate, and / or an object (e.g., a lens, a mirror, a filter, etc.) 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). In some aspects, inline calibration can include reticle alignment (RA) results.

[0040] 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.

[0041] 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.

[0042] Exemplary Lithographic System

[0043] 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 masktable, 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 (e.g., a substrate stage) configured to support a substrate W.

[0044] 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.

[0045] 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).

[0046] 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.

[0047] In some aspects, support structure MT (e.g., a reticle stage) can include a transmission sensor TS. For example, as shown in FIG. 1, transmission sensor TS can be coupled to support structure MT and opposite patterning device MA (e.g., a reticle). Transmission sensor TS can be configured to measure a non-uniformity map (e.g., a 2D transmission map) of patterning device MA (e.g., a reticle) during exposure of EUV and / or DUV radiation beam B.

[0048] In some aspects, transmission sensor TS can include a spot sensor, for example, a photodetector, photosensor, photodiode, CCD, power meter, energy monitor, or any other power measuring device capable of measuring transmission of patterning device MA. In some aspects, transmission sensor TS can scan an area of a backside of patterning device MA (e.g., a reticle) to measure a 2D transmission map. In some aspects, transmission sensor TS can be scanned relative to patterning device MA. In some aspects, patterning device MA can be scanned relative to transmission sensor TS. In some aspects, theEUV and / or DUV radiation beam B can be scanned relative to transmission sensor TS and patterning device MA.

[0049] In some aspects, substrate table WT (e.g., a substrate stage) can include a reflectivity sensor RS. For example, as shown in FIG. 1, reflectivity sensor RS can be coupled to substrate table WT and opposite substrate W. Reflectivity sensor RS can be configured to measure a non-uniformity map (e.g., a 2D reflectivity map) of patterning device MA (e.g., a reticle) during exposure of EUV and / or DUV radiation beam B.

[0050] In some aspects, reflectivity sensor RS can include a spot sensor, for example, a photodetector, photosensor, photodiode, CCD, power meter, energy monitor, or any other power measuring device capable of measuring reflectivity of patterning device MA. In some aspects, reflectivity sensor RS can scan an area of a frontside of patterning device MA (e.g., a reticle) to measure a 2D reflectivity map. In some aspects, reflectivity sensor RS can be scanned relative to patterning device MA. In some aspects, patterning device MA can be scanned relative to reflectivity sensor RS. In some aspects, the EUV and / or DUV radiation beam B can be scanned relative to reflectivity sensor RS and patterning device MA.

[0051] Exemplary Lithographic Cell

[0052] FIG. 2A shows a lithographic cell LC, also sometimes referred to as a lithocell or cluster. Lithographic apparatus LA can form part of lithographic cell LC. Lithographic cell LC can 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.

[0053] 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.

[0054] 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 defectson 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).

[0055] Exemplary Computer System

[0056] FIG. 2B shows a computer system CL, also referred to as a controller or processor. Computer system CL can 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).

[0057] 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.

[0058] 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 can 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).

[0059] Metrology tool MT can 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 inFIG. 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.

[0060] Exemplary Reticle Stage and Reticle

[0061] FIGS. 3 A 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.

[0062] 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, a clamp controller 260, 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. Clamp controller 260 can be coupled to clamp 250 and be configured to control a position of 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.

[0063] 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.

[0064] 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). 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 a reticle alignment (RA) measurement. Edge alignment mark 320 is configured to measure a reticle shape deformation of reticle 300 due to thermal expansion, for example, when reticle 300 is not within apredetermined temperature (e.g., at 22 °C ± 0.2 °C). In some aspects, as shown in FIGS. 3A 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.

[0065] Exemplary Reticle Exchange Apparatus

[0066] FIGS. 4A and 4B show schematic illustrations of reticle exchange apparatus 100, according to exemplary aspects. FIG. 4 A is a schematic top perspective illustration of reticle exchange apparatus 100, according to an exemplary aspect. FIG. 4B is a schematic partial cross-sectional illustration of reticle exchange apparatus 100 shown in FIG. 4A.

[0067] Reticle exchange apparatus 100 can be configured to reduce reticle exchange time and thermal stresses in reticle 300 to increase overall throughput, for example, in lithographic apparatus LA. In some aspects, reticle exchange apparatus 100 can reduce stress in reticle 300 by removing reticle 300 from reticle stage 200 to in-vacuum robot (IVR) 400. For example, reticle exchange apparatus 100 can quickly unclamp reticle 300 from reticle cages 224 and clamp 250 and transfer reticle 300 to IVR 400 to release thermal stress in reticle 300. In some aspects, reticle exchange apparatus 100 can reduce stress in reticle 300 and increase throughput by unclamping and transferring reticle 300 from reticle stage 200 to IVR 400 and quickly returning and clamping reticle 300 back to reticle stage 200. As shown in FIGS. 4A and 4B, reticle exchange apparatus 100 can include reticle stage 200, clamp 250, and IVR 400.

[0068] IVR 400 can include reticle handler 402 with one or more reticle handler arms 404. In some aspects, reticle handler 402 can be a rapid exchange device (RED), which is configured to efficiently rotate and minimize reticle exchange time. Reticle handler arm 404 can include reticle baseplate 406 configured to hold an object, for example, reticle 300. In some aspects, reticle baseplate 406 can be an extreme ultraviolet inner pod (EIP) for reticle 300. Reticle baseplate 406 includes reticle baseplate frontside 407, and reticle 300 includes reticle backside 304.

[0069] As shown in FIGS. 4A and 4B, reticle baseplate 406 can hold reticle 300 such that reticle baseplate frontside 407 and reticle backside 304 each face bottom stage surface 202 and clamp frontside 252. For example, reticle baseplate frontside 407 and reticle backside 304 can be facing perpendicularly away from bottom stage surface 202 and clamp frontside 252. As shown in FIG. 4B, reticle exchange apparatus 100 can include reticle exchange area 410, which is the cross-sectional area between clamp 250, reticle 300, reticle baseplate 406, and reticle handler arm 404 during a reticle exchange process.

[0070] In one example, during a reticle exchange process, reticle handler arm 404 of reticle handler 402 positions reticle 300 on reticle baseplate 406 towards clamp 250 in reticle exchange area 410. As described above, a reticle handoff from reticle handler 402 to clamp 250 and vice-versa can release thermal stress in reticle 300 and reduce parasitic thermal effects in reticle 300.

[0071] FIG. 5 is a schematic that shows the overlay error that may be caused by the temperature of the reticle, according to exemplary aspects. In the time period Al, a reticle is used and it is heated. In thetime period B, the reticle is not used and it cools down. In the time period A2, the reticle is re-used. As shown in FIG. 5, when the time period B is short, the reticle is unable to cool down to the same cold state as at the start of time period Al. If the reticle heating model assumes that the reticle at the start of time period A2 is in the cold state, then the modelled deformation of the reticle will be inaccurate because of a change in the thermos-mechanical boundary conditions. The process for compensating for the heating of the reticle will therefore also be inaccurate (e.g., corrected position of the reticle with respect to the substrate, and / or the position of one or more optical components in the system). This may be referred to as an ABA lot sequence problem, or fast lot transition problem.

[0072] FIG. 6 is a deterministic reticle heating model, according to exemplary aspects. The model comprises a reticle heating execution algorithm (RHEA) 604, a reticle heating module 612, and an uncertainty module 608. RHEA 604 can include a modal deformation approach with the modelled deformation dependent on RA measurements.

[0073] In some aspects, inputs to RHEA 604 can include a reference state 602 and feedback data 610. Reference state 602 can comprise data describing the initial state of a reticle. Reference state 602 can be retrieved from a library. Feedback data 610 can comprise operational data, such as the applied dose. A RHEA output 614 can comprise heating dynamics determined by RHEA 604. RHEA output 614 can be provided to reticle heating module 612. Uncertainty module 608 can represent contributions to the actual deformation of a reticle that the deterministic heating module is unable to predict. In particular, the uncertainties may include events such as timing changes, or changes that result in different boundary conditions. The reticle reference model may output to RHEA 604 information indicating an upcoming ABA uncertainty.

[0074] Reticle heating module 612 can determine and output mode shapes 606 that are a determination of the reticle deformation. Process corrections for changing the operation of the lithographic apparatus may be determined in dependence on the output of the reticle heating model to at least partially compensate for the reticle deformation (e.g., change in a reticle position).

[0075] In some aspects, a problem with the reticle heating module described in FIG. 6 is that accuracy of the model depends on reference state 602 that describes the initial state of the reticle. However, reference state 602 assumes that reticle 300 is conditioned. The accuracy of the reticle heating model decreases if the reticle is not conditioned. In some aspects, reference state 602 can be obtained from a reticle reference model. The reticle reference model may track reticle 300 while it is present in the lithographic apparatus and input to the RHEA 604 information indicating a thermal state of reticle 300 based on corresponding thermal properties of different locations where the reticle 300 can go to (as further described with reference to FIG. 7) and the total time duration at each location.

[0076] FIG. 7 is a schematic that shows exemplary reticle moves, according to exemplary aspects. For example, when reticle A from a first lot A is not used, reticle A can travel through multiple locations (e.g., during time period B). Each possible location for the reticle may have different thermosmechanical characteristics. In some aspects, reticle 300 can move between different components withina lithographic apparatus. Such components may include a library 702, a robot 714, a turret robot 706, a stage 708, a turret stage 710, a conditioning device 712, and an inspection apparatus 704. According to some embodiments, the lithographic apparatus or a controller of the lithographic apparatus may perform a load / conditioning sequence. During the load / conditioning sequence, reticle 300 can travel through one or more locations. For example, robot 714 can transport reticle 300 to / from library 702, to / from inspection apparatus 704, to / from conditioning device 712, and to / from turret robot 706. Turret robot 706 can transport reticle 300 to / from robot 714, to / from turret stage 710, and to / from stage 708. It can be appreciated that the temperature of reticle 300 can be subject to change due to the transfer and inspection or other processes at different locations. For example, robot 714 can cause the reticle temperature to increase during transfer.

[0077] As discussed above, a problem with the reticle heating module described in FIG. 6 is that accuracy of the model depends on reference state 602 that describes the initial state of the reticle. However, reference state 602 assumes that reticle 300 is conditioned. The accuracy of the reticle heating model decreases if the reticle is not conditioned. In some aspects, reference state 602 can be obtained from the reticle reference model.

[0078] Embodiments described herein provide techniques for switching models based on an outcome from the reticle reference model. In some aspects, different reticle heating models may be used during different regimes of reticle heating during an ABA sequence. For example, a first model may be used to predict thermal deformation of reticle 300 during time period Al and a second model may be used to predict thermal deformation of reticle 300 during time period A2 (e.g., when reticle 300 is reused during time period A2).

[0079] In some aspects, the model may be identified based on the logistic information of reticle 300 (e.g., where reticle 300 resides). Inputs to RHEA 604 and / or the reticle reference model may also include reticle handling data that may be received from the reticle handler 402. The reticle handling data may include data on how the reticle has been handled. The reticle handling data may include location data that describes the location where the reticle has been. The reticle handling data may include time data that describes how long the reticle has been at each location. The reticle handling data may include thermal data that describes the temperature at each location that the reticle has been. The reticle handling data may include data on the thermal properties of the reticle at each location. In some aspects, the inputs may include information about each lithographic process performed with reticle 300 (e.g., when each lithographic process starts and ends). In some aspects, the inputs to the reticle reference model may include current or previous outputs from RHEA 604. In some aspects, the inputs may include deformation data. The reticle reference model may output a status of reticle 300.

[0080] A model from the plurality of models is identified based on the status of reticle 300. For example, a determination is made whether the lot is ABA category or not. The model is identified based on the determination. For example, when a reticle is first loaded onto a reticle stage (e.g., reticle stage 200), the model (e.g., the heating model) is selected based on the assumption that the reticle is in a coldstate. The cold state is the state of a reticle that has been appropriately conditioned by conditioning device 712. In some aspects, a first model associated with a cold state is identified and used to determine the thermal deformation associated with the reticle. When the reticle is reused, a determination is made of the status of the reticle based on at least the reticle handling data. If the reference reticle model determines that the reticle is in a hot state, a second model is identified and used to determine the thermal deformation associated with the reticle. If the reticle reference model determines that the reticle is in a cold state then the first model is reused to determine the thermal deformation associated with the reticle.

[0081] In some aspects, the plurality of models may be stored in a database. In some aspects, one or more models of the plurality of models may be a reticle deformation model that may be FEM, such as a thermomechanical FEM. Each model may generate deformation data corresponding to the thermal deformation of reticle 300. The deformation data may include the deformation effects at all location on reticle 300.

[0082] As discussed above, a different model is associated with each different status of the lithographic element (e.g., as opposed to changing internal states of the same model). This provides the advantage of providing a generic approach for different systems. In some aspects, the overlay sensitivity may be reduced while increasing the throughput.

[0083] In some aspects, the models may have different gain and different initial conditions. In some aspects, latent variables of each model may be updated based on measurements during the lithography process.

[0084] In some aspects, the first model may be a function of a first constant (kl) and the second model may be a function of a second constant (k2) (different from the first constant). In some aspects, an initial condition of the model may represent the state of reticle 300 at time of a change of the reticle. In some aspects, the initial condition may be determined using another model. For example, an initial condition for the second model may be determined using the first model at a time t, where time t represents the end of time period Al as an example.

[0085] In some aspects, one or more models of the plurality of models may model a spatial behavior of reticle 300. Depending on the moves of reticle 300 in the lithographic apparatus, a shape of reticle 300 may change and is modelled accordingly (e.g., the shape of reticle 300 is not constant). For example, a shape of reticle 300 can change from a first shape to a second shape. In some aspects, constants kl and k2 may depend on a location of reticle 300. For example, if reticle 300 is located in reticle stage 200 then the first model is used. If reticle 300 is located in the turret, then the second model with k2.

[0086] Exemplary Flow Diagrams

[0087] FIG. 8 shows method steps (e.g., using one or more processors) for performing a method 800 including functions described herein, according to some embodiments. The method 800 of FIG. 8 can be performed in any conceivable order and it is not required that all steps be performed. Moreover, the method steps of FIG. 8 described above merely reflect an example of steps and are not limiting.

[0088] In some embodiments, method 800 illustrates a method for predicting a thermal deformation of a lithographic element. As discussed above, the lithographic element can be a patterning device, an optical element, or a wafer.

[0089] In some aspects, in 802, a status of the lithographic element is determined. In some aspects, the status of the lithographic element can include a thermal condition. The thermal condition of the lithographic element can be determined based on a previous location of the lithographic element. The thermal condition can be a hot thermal condition (hot state) or a cold thermal condition (cold state).

[0090] In some aspects, a status of an exchange of a first reticle for a second reticle in a reticle stage is determined. The thermal condition may be determined based on the status of the exchange.

[0091] In some aspects, the status can be determined based on one or more of location data that describes a first location where the lithographic element is and a second location where the lithographic element has been, time data that describes how long the lithographic element has been at the first location and at the second location, and thermal data and deformation data. The thermal data and deformation data can be obtained from measurement and simulations. For example, if the location data indicates that reticle 300 was at conditioning device 712 and the time data indicates that the time spent at conditioning device 712 exceeds a threshold (e.g., location data and time data indicate that reticle 300 is appropriately conditioned) then the thermal condition of reticle 300 is determined to be in cold thermal condition.

[0092] In 804, a model is identified from a plurality of models (e.g., reticle heating models, lens heating models, substrate heating models) based on the status. The plurality of models may be reduced order state-space models. This provides the advantage of reduction in the usage of computational resources. Each model of the plurality of models can have a different respective gain constant or a different respective initial condition. For example, a first model is identified in response to determining that the thermal condition of the lithographic element is the hot thermal condition. In some aspects, the plurality of models may include a plurality of reticle heating models, a plurality of lens heating models, a plurality of substrate heating models.

[0093] In 806, a thermal deformation associated with the lithographic element is predicted. In some aspects, an operation of the lithographic process is controlled based on the predicted thermal deformation.

[0094] In 808, based on the predicted thermal deformation, the lithography process can be corrected by changing the configuration and / or operation of process performed with reticle 300 to at least partially compensate for the overlay error that would otherwise be caused by the deformation of the reticle shape (e.g., effect of the deformation). For example, the change in the configuration and / or operations may include changing one or more of a location of a stage lens, changing a parameter of a scanning lens, and moving an object stage. Thus, by improving the accuracy of predicted thermal deformation, the corrections to the lithographic process are also improved, which leads to an improved overlay performance, for example.

[0095] A controller of the lithographic apparatus (e.g., a computer system CL) may determine the correction of a positioning of the substrate with respect to reticle 300. The controller may then control a position of the substrate (e.g., by controlling the substrate table WT with respect to the reticle support MT) with respect to reticle 300. In some aspects, the controller may adjust lens parameters of projection system and / or illumination system based on the predicted deformation to improve the imaging performance. In some aspects, the controller may adjust one or more parameters in the illumination system IL to change a distribution of radiation intensity based on the predicted deformations. In some aspects, the deformations may include distortions that have a negative effect on the focus performance of the lithographic apparatus. The controller may calculate and apply a correction in the lithographic process based on the distortions of reticle 300, the effects of the actual distortion can at least partially be compensated to improve the focus performance of the lithographic process. In some aspects, the correction provided by the controller can be applied in any suitable way to improve the overlay performance of the lithographic apparatus. The correction may be applied before a batch of substrates being radiated with a pattern of reticle 300, and / or between two subsequent substrates of such batch being processed in the lithographic apparatus.

[0096] Various embodiments may be implemented, for example, using one or more well-known computer systems, such as computer system 900 shown in FIG. 9. One or more computer systems 900 can be used, for example, to implement any aspect of the disclosure discussed herein, as well as combinations and sub-combinations thereof.

[0097] Computer system 900 can include one or more processors (also called central processing units, or CPUs), such as a processor 904. Processor 904 can be connected to a communication infrastructure or bus 906.

[0098] Computer system 900 can also include customer input / output device(s) 903, such as monitors, keyboards, pointing devices, etc., which may communicate with communication infrastructure 906 through customer input / output interface(s) 902.

[0099] One or more of processors 904 can be a graphics processing unit (GPU). In an embodiment, a GPU may be a processor that is a specialized electronic circuit designed to process mathematically intensive applications. The GPU may have a parallel structure that is efficient for parallel processing of large blocks of data, such as mathematically intensive data common to computer graphics applications, images, videos, etc.

[0100] Computer system 900 can also include a main or primary memory 908, such as random access memory (RAM). Main memory 908 can include one or more levels of cache. Main memory 908 can have stored therein control logic (i.e., computer software) and / or data.

[0101] Computer system 900 can also include one or more secondary storage devices or memory 910. Secondary memory 910 can include, for example, a hard disk drive 912 and / or a removable storage device or drive 914. Removable storage drive 914 can be a floppy disk drive, a magnetic tape drive, a compact disk drive, an optical storage device, tape backup device, and / or any other storage device / drive.

[0102] Removable storage drive 914 can interact with a removable storage unit 918. Removable storage unit 918 can include a computer usable or readable storage device having stored thereon computer software (control logic) and / or data. Removable storage unit 918 can be a floppy disk, magnetic tape, compact disk, DVD, optical storage disk, and / any other computer data storage device. Removable storage drive 914 can read from and / or write to removable storage unit 918.

[0103] Secondary memory 910 can include other means, devices, components, instrumentalities or other approaches for allowing computer programs and / or other instructions and / or data to be accessed by computer system 900. Such means, devices, components, instrumentalities or other approaches may include, for example, a removable storage unit 922 and an interface 920. Examples of the removable storage unit 922 and the interface 920 can include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM or PROM) and associated socket, a memory stick and USB port, a memory card and associated memory card slot, and / or any other removable storage unit and associated interface.

[0104] Computer system 900 can further include a communication or network interface 924. Communication interface 924 can enable computer system 900 to communicate and interact with any combination of external devices, external networks, external entities, etc. (individually and collectively referenced by reference number 928). For example, communication interface 924 can allow computer system 900 to communicate with external or remote devices 928 over communications path 926, which may be wired and / or wireless (or a combination thereof), and which may include any combination of LANs, WANs, the Internet, etc. Control logic and / or data may be transmitted to and from computer system 900 via communication path 926.

[0105] Computer system 900 can also be any of a personal digital assistant (PDA), desktop workstation, laptop or notebook computer, netbook, tablet, smart phone, smart watch or other wearable, appliance, part of the Internet-of-Things, and / or embedded system, to name a few non-limiting examples, or any combination thereof.

[0106] Computer system 900 can be a client or server, accessing or hosting any applications and / or data through any delivery paradigm, including but not limited to remote or distributed cloud computing solutions; local or on-premises software (“on-premise” cloud-based solutions); “as a service” models (e.g., content as a service (CaaS), digital content as a service (DCaaS), software as a service (SaaS), managed software as a service (MSaaS), platform as a service (PaaS), desktop as a service (DaaS), framework as a service (FaaS), backend as a service (BaaS), mobile backend as a service (MBaaS), infrastructure as a service (laaS), etc.); and / or a hybrid model including any combination of the foregoing examples or other services or delivery paradigms.

[0107] Any applicable data structures, file formats, and schemas in computer system 900 may be derived from standards including but not limited to JavaScript Object Notation (JSON), Extensible Markup Language (XML), Yet Another Markup Language (YAML), Extensible Hypertext Markup Language (XHTML), Wireless Markup Language (WML), MessagePack, XML User InterfaceLanguage (XUL), or any other functionally similar representations alone or in combination. Alternatively, proprietary data structures, formats or schemas may be used, either exclusively or in combination with known or open standards.

[0108] In some embodiments, a tangible, non-transitory apparatus or article of manufacture comprising a tangible, non-transitory computer useable or readable medium having control logic (software) stored thereon may also be referred to herein as a computer program product or program storage device. This includes, but is not limited to, computer system 900, main memory 908, secondary memory 910, and removable storage units 918 and 922, as well as tangible articles of manufacture embodying any combination of the foregoing. Such control logic, when executed by one or more data processing devices (such as computer system 900), may cause such data processing devices to operate as described herein.

[0109] Based on the teachings contained in this disclosure, it will be apparent to persons skilled in the relevant art(s) how to make and use embodiments of this disclosure using data processing devices, computer systems and / or computer architectures other than that shown in FIG. 9. In particular, embodiments can operate with software, hardware, and / or operating system implementations other than those described herein.

[0110] Various embodiments of the present systems and methods are disclosed in the subsequent list of numbered clauses:1. A method, comprising: determining a status of a lithographic element; identifying, based on the status, a model from a plurality of models; and predicting, using the identified model, a thermal deformation associated with the lithographic element.2. The method of clause 1 , wherein the lithographic element is a patterning device, an optical element, or a wafer.3. The method of clause 1, wherein determining a status of the lithographic element comprises: determining a thermal condition of the lithographic element based on a previous location of the lithographic element.4. The method of clause 3, wherein the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the method further comprising: in response to determining that the thermal condition is the hot thermal condition, identifying the model as the first model.5. The method of clause 1, wherein the lithographic element is a reticle, and wherein determining the status further comprises: determining a status of an exchange of a first reticle for a second reticle in a reticle stage.6. The method of clause 5, further comprising: determining a thermal condition of the reticle based on the status of the exchange.7. The method of clause 1, further comprising: controlling an operation of a lithographic process that uses the lithography element based on the predicted thermal deformation.8. The method of clause 1, wherein the plurality of models are reduced order state-space models.9. The method of clause 1, wherein determining the status of the lithographic element is based on one or more of: location data that describes a first location where the lithographic element is and a second location where the lithographic element has been; time data that describes how long the lithographic element has been at the first location and at the second location; and thermal data and deformation data.10. The method of clause 1, wherein each model of the plurality of models has a different respective gain constant or a different respective initial condition.11. A lithographic apparatus configured to perform a lithographic process, the lithographic apparatus comprising: an illumination system configured to illuminate a reticle; a projection system configured to project an image of the reticle onto a substrate; wherein the illuminating and projection comprise the lithographic process; and a controller configured to reduce effects of non-uniformity of the reticle in the lithographic process, the controller configured to: determine a status of the reticle; identify a model from a plurality of models based on the status; and predict, using the identified model, a thermal deformation associated with the reticle.12. The lithographic apparatus of clause 11, wherein the controller is further configured to: determine a thermal condition of the reticle based on a previous location of the reticle.13. The lithographic apparatus of clause 12, wherein the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the controller is further configured to: identify the model as the first model in response to determining that the thermal condition is the hot thermal condition.14. The lithographic apparatus of clause 11, further comprising: a reticle stage, and wherein the controller is further configured to: determine a status of an exchange of a first reticle for a second reticle in the reticle stage.15. The lithographic apparatus of clause 11, wherein the plurality of models are reduced order statespace models.16. The lithographic apparatus of clause 11, wherein each model of the plurality of models has a different respective gain constant or a different respective initial condition.17. A non-transitory computer readable medium program comprising computer readable instructions configured to cause a processor to: determine a status of a lithographic element; identify based on the status, a model from a plurality of models; and predict, using the identified model, a thermal deformation associated with the lithographic element.18. The non-transitory computer readable medium program of clause 17, wherein the lithographic element is a patterning device, an optical element, or a wafer.19. The non-transitory computer readable medium program of clause 17, wherein the processor is further configured to: determine a thermal condition of the lithographic element based on a previous location of the lithographic element.20. The non-transitory computer readable medium program of clause 19, wherein the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the processor is further configured to: identify the model as the first model in response to determining that the thermal condition is the hot thermal condition.

[0111] Although specific reference may be made in this text to the use of the apparatus, system, and / or lithographic apparatus in the manufacture of ICs, it should be explicitly understood that such an apparatus, system, and / or lithographic apparatus described herein may have other possible applications, for example, it can be employed in the manufacture of integrated optical systems, guidance and detection patterns for magnetic domain memories, flat-panel displays, 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” herein may be considered as synonymous with the more general terms “mask,” “substrate,” and “target portion,” respectively.

[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. The substrate referred to herein may be processed, beforeor after exposure, for example, in a track unit (e.g., 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, 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.

[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] 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.

[0117] 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.

[0118] 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.

[0119] 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.

[0120] 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, comprising: determining a status of a lithographic element; identifying, based on the status, a model from a plurality of models; and predicting, using the identified model, a thermal deformation associated with the lithographic element.

2. The method of claim 1, wherein the lithographic element is a patterning device, an optical element, or a wafer.

3. The method of claim 1, wherein: determining a status of the lithographic element comprises determining a thermal condition of the lithographic element based on a previous location of the lithographic element; the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the method further comprises in response to determining that the thermal condition is the hot thermal condition, identifying the model as the first model.

4. The method of claim 1, wherein: the lithographic element is a reticle, and wherein determining the status further comprises determining a status of an exchange of a first reticle for a second reticle in a reticle stage; and the method further comprises determining a thermal condition of the reticle based on the status of the exchange.

5. The method of claim 1, further comprising: controlling an operation of a lithographic process that uses the lithography element based on the predicted thermal deformation.

6. The method of claim 1 , wherein the plurality of models are reduced order state-space models.

7. The method of claim 1, wherein determining the status of the lithographic element is based on one or more of: location data that describes a first location where the lithographic element is and a second location where the lithographic element has been;time data that describes how long the lithographic element has been at the first location and at the second location; and thermal data and deformation data.

8. The method of claim 1, wherein each model of the plurality of models has a different respective gain constant or a different respective initial condition.

9. A lithographic apparatus configured to perform a lithographic process, the lithographic apparatus comprising: an illumination system configured to illuminate a reticle; a projection system configured to project an image of the reticle onto a substrate; wherein the illuminating and projection comprise the lithographic process; and a controller configured to reduce effects of non-uniformity of the reticle in the lithographic process, the controller configured to: determine a status of the reticle; identify a model from a plurality of models based on the status; and predict, using the identified model, a thermal deformation associated with the reticle.

10. The lithographic apparatus of claim 9, wherein: the controller is further configured to determine a thermal condition of the reticle based on a previous location of the reticle; the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the controller is further configured to identify the model as the first model in response to determining that the thermal condition is the hot thermal condition.

11. The lithographic apparatus of claim 9, further comprising: a reticle stage, and wherein the controller is further configured to determine a status of an exchange of a first reticle for a second reticle in the reticle stage.

12. The lithographic apparatus of claim 9, wherein the plurality of models are reduced order state-space models or each model of the plurality of models has a different respective gain constant or a different respective initial condition.

13. A non-transitory computer readable medium program comprising computer readable instructions configured to cause a processor to: determine a status of a lithographic element;identify based on the status, a model from a plurality of models; and predict, using the identified model, a thermal deformation associated with the lithographic element.

14. The non-transitory computer readable medium program of claim 13, wherein the lithographic element is a patterning device, an optical element, or a wafer.

15. The non-transitory computer readable medium program of claim 13, wherein: the processor is further configured to determine a thermal condition of the lithographic element based on a previous location of the lithographic element; and the thermal condition is a hot thermal condition or a cold thermal condition and the plurality of models include a first model and a second model, and the processor is further configured to identify the model as the first model in response to determining that the thermal condition is the hot thermal condition.

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