NL2038244A - Methods and systems to reduce non-uniform thermomechanical effects - Google Patents

Abstract

A method of reducing non-uniform thermomechanical effects of a reticle in a lithographic process includes defining a non-uniformity map of the reticle, calibrating a reticle heating model based on the non-uniformity map, and reducing a non-uniformity of the reticle based on the calibrated reticle heating model. The non-uniformity map can include a transmission map, a reflectance map, a transparency map, a pattern density map, and/or a reflectivity map of the reticle. The non-uniformity can include a spatially varying absorption profile of the reticle. Advantageously the method can reduce and/or compensate for non-uniform thermomechanical effects of the reticle, account for non-uniform pattern density of the reticle, reduce uncertainties in the lithographic process, increase calibration accuracy and speed of the reticle heating model, avoid rework of substrates, decrease overlay errors, and increase throughput, yield, and accuracy of the lithographic process.

Description

METHODS AND SYSTEMS TO REDUCE NON-UNIFORM THERMOMECHANICAL EFFECTS

FIELD

[0001] The present disclosure relates to calibration apparatuses, systems, and methods, for example, reticle calibration apparatuses, svstems, and methods to reduce non-uniform thermomechanical effects in a lithographic process.

BACKGROUND

[0002] 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.

[0003] 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.

[0004] 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 assume a uniform reticle absorption, 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

[0005] Accordingly, there is a need to. e.g, reduce and/or compensate for non-uniform thermomechanical effects of a reticle, account for non-uniform pattern density of the reticle, reduce uncertainties in a lithographic process, increase calibration accuracy and speed of a reticle heating model, avoid rework of substrates, decrease overlay errors, and increase throughput, yield, and accuracy of the lithographic process.

[0006] In some aspects, a method of reducing and/or compensating for non-uniform thermomechanical effects of a reticle can include defining a non-uniformity map of the reticle in a lithographic process. In some aspects, the method can further include calibrating a reticle heating model based on the non-

uniformity map. In some aspects, the method can further include reducing a non-uniformity of the reticle based on the calibrated reticle heating model.

[0007] In some aspects, defining the non-uniformity map can include measuring a transmission map and/or a reflectance map of the reticle. In some aspects, measuring the transmission map and/or the reflectance map of the reticle can include exposing the reticle to a dose of radiation and scanning an area of a backside and/or a frontside of the reticle with a sensor. In some aspects, the dose of radiation can include DUV radiation. In some aspects, the dose of radiation can include EUV radiation. In some aspects, the dose of radiation can include DUV and EUV radiation. In some aspects, the sensor can include a spot sensor (e.g.. photodetector, photosensor, photodiode, CCD, power meter, energy monitor, or any other power measuring device). In some aspects, scanning can include scanning the sensor relative to the reticle, scanning the reticle relative to the sensor, scanning the dose of radiation relative to the reticle and the sensor, or a combination thereof.

[0008] In some aspects. defining the non-uniformity map can include measuring a two-dimensional (2D) transmission map of the reticle. In some aspects, measuring the 2D transmission map of the reticle can include exposing the reticle to a dose of radiation and scanning an area of a backside of the reticle with a sensor. In some aspects, the dose of radiation can include DUV radiation. In some aspects, the reticle can be scanned relative to the sensor. In some aspects, the sensor can be scanned relative to the reticle. In some aspects, the 2D transmission map can include a high density of data points, for example, at least 5.000 points. In some aspects, the sensor can be part of a reticle stage configured to support the reticle.

[0009] In some aspects, defining the non-uniformity map can include measuring a 2D reflectance map of the reticle. In some aspects, measuring the 2D reflectance map can include measuring a 2D absorption map based on DUV radiation. In some aspects, measuring the 2D reflectance map can include measuring a 2D reflectance map based on EUV radiation. In some aspects, measuring the 2D reflectance map can include measuring a 2D absorption map based on DUV radiation and measuring a 2D reflectance map based on EUV radiation. In some aspects, measuring the 2D reflectance map of the reticle can include exposing the reticle to a dose of radiation and scanning an area of a frontside of the reticle with a sensor. In some aspects, the dose of radiation can include EUV radiation. In some aspects, the reticle can be scanned relative to the sensor. In some aspects, the sensor can be scanned relative to the reticle. In some aspects, the 2D reflectance map can include a high density of data points, for example, at least 5,000 points. In some aspects, the sensor can be part of a substrate table configured to support a substrate for patterning.

[0010] In some aspects, defining the non-uniformity map can include defining a transparency map and/or a pattern density map of the reticle. In some aspects, defining the transparency map and/or the pattern density map of the reticle can include defining a 2D reflectivity map of the reticle. In some aspects, defining the non-uniformity map can include defining a 2D transparency map of the reticle. In some aspects, defining the 2D transparency map (e.g., image) of the reticle can include defining a 2D alpha compositing map of the reticle (e.g., each pixel has an additional numeric value stored in its alpha channel). In some aspects, defining the non-uniformity map can include defining a 2D pattern density map of the reticle. In some aspects, defining the 2D pattern density map of the reticle can include defining a 2D design layout (e.g., chrome pattern) of the reticle (e.g., binary file format, GDS, GDSII,

CAD, AutoCAD, OASIS, or any other electronic design automation (EDA) format).

[0011] In some aspects, calibrating the reticle heating model can include initializing the reticle heating model (e.g, setting initial values) based on the non-uniformity map. In some aspects, calibrating the reticle heating model can further include predicting modal deformation shapes of the reticle based on the non-uniformity map. In some aspects, predicting the modal deformation shapes can include using a finite element model (FEM) based on the non-uniformity map. In some aspects, calibrating the reticle heating model can further include measuring a reticle alignment (RA) between the reticle and a substrate. In some aspects, calibrating the reticle heating model can further include adjusting the modal deformation shapes of the reticle based on the measured reticle alignment (RA).

[0012] In some aspects, reducing the non-uniformity of the reticle can include reducing a spatially varying absorption profile of the reticle. In some aspects, reducing the non-uniformity of the reticle can include compensating for a spatially varving absorption profile of the reticle. In some aspects, reducing the non-uniformity of the reticle can further include applying a correction to a substrate in the lithographic process. In some aspects, reducing the non-uniformity of the reticle can further include applying a correction to a subsequent substrate in the lithographic process. In some aspects, reducing the non-uniformity of the reticle can further include applying a correction to a subsequent lot (e.g, twenty-five wafers) in the lithographic process.

[0013] In some aspects, a method of reducing and/or compensating for non-uniform thermomechanical effects of an object can include defining a non-uniformity map of the object in a lithographic process.

In some aspects, the method can further include calibrating an object heating model based on the non- uniformity map. In some aspects. the method can further include reducing a non-uniformity of the object based on the calibrated object heating model.

[0014] In some aspects, defining the non-uniformity map can include measuring a transmission map and/or a reflectance map of the object when exposed to a dose of radiation. In some aspects, the dose of radiation can include DUV radiation. In some aspects, the dose of radiation can include EUV radiation. In some aspects. the dose of radiation can include DUV and EUV radiation. In some aspects, measuring the transmission map and/or the reflectance map of the object can include exposing the object to a dose of radiation and scanning an area of a backside and/or a frontside of the object with a sensor.

In some aspects, measuring the reflectance map can include measuring an absorption map based on

DUV radiation. In some aspects. measuring the reflectance map can include measuring a reflectance map based on EUV radiation. In some aspects, measuring the reflectance map can include measuring an absorption map based on DUV radiation and measuring a reflectance map based on EUV radiation.

In some aspects, the sensor can include a spot sensor (e.g., photodetector, photosensor, photodiode,

CCD, power meter, energy monitor, or any other power measuring device). In some aspects, scanning can include scanning the sensor relative to the object, scanning the object relative to the sensor, scanning the dose of radiation relative to the object and the sensor, or a combination thereof. In some aspects, defining the non-uniformity map can include defining a transparency map and/or a pattern density map of the object.

[0015] In some aspects, calibrating the object heating model can include initializing the object heating model (e.g, setting initial values) based on the non-uniformity map. In some aspects, calibrating the object heating model can further include predicting modal deformation shapes of the object using a

FEM. In some aspects, predicting the modal deformation shapes can include using a FEM based on the non-uniformity map of the object. In some aspects. calibrating the object heating model can further include adjusting the modal deformation shapes of the object based on inline calibration of the lithographic process. In some aspects. the inline calibration can include measuring a reticle alignment (RA) between a reticle and a substrate of the lithographic process. In some aspects, the inline calibration can include measuring an alignment (e.g., overlay) of a substrate of the lithographic process. In some aspects, the inline calibration can include measuring a parameter (e.g., focus, beam shape, curvature, k- parameter, etc.) of a lens of the lithographic process.

[0016] In some aspects, reducing the non-uniformity of the object can include reducing a spatially varying absorption profile of the object. In some aspects. the object can include a reticle. In some aspects, the object can include a lens. In some aspects, the object can include a mirror. In some aspects, the object can include a substrate (¢.g., wafer). In some aspects, the object heating model can include a reticle heating model. In some aspects, the object heating model can include a lens heating model. In some aspects, the object heating model can include a mirror heating model. In some aspects, the object heating model can include a substrate heating model (e.g.. wafer heating model).

[0017] In some aspects. a lithographic apparatus can include an illumination system, a projection system, and a controller. In some aspects, the illumination system can be configured to illuminate a reticle. In some aspects, the projection system can be configured to project an image of the reticle onto a substrate. In some aspects, the controller can be configured to reduce effects of non-uniformity of the reticle in a lithographic process. In some aspects, the controller can be configured to define a non- uniformity map of the reticle, calibrate a reticle heating model based on the non-uniformity map, and reduce a non-uniformity of the reticle based on the calibrated reticle heating model.

[0018] In some aspects, a non-transitory computer readable medium program can include computer readable instructions configured to cause a processor to define a non-uniformity map of a reticle in a lithographic process. calibrate a reticle heating model based on the non-uniformity map. and reduce a non-uniformity of the reticle based on the calibrated reticle heating model.

[0019] 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.

[0020] 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 5 thatthe 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 QF THE DRAWINGS

[0021] 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.

[0022] FIG. 1 is a schematic illustration of a lithographic system, according to an exemplary aspect.

[0023] FIG. 2A is a schematic illustration of a lithographic cell, according to an exemplary aspect.

[0024] FIG. 2B is a schematic illustration of holistic lithography including a computer system to optimize a lithographic process, according to an exemplary aspect.

[0025] FIG. 3A is a schematic bottom perspective illustration of a reticle stage and a reticle, according to an exemplary aspect.

[0026] FIG. 3B is a schematic bottom plan illustration of the reticle stage shown in FIG. 3A.

[0027] FIG. 4A is a schematic top plan illustration of a reticle with a first pattern area, according to an exemplary aspect.

[0028] FIG. 4B is a schematic top plan illustration of a reticle with a second pattern area, according to an exemplary aspect.

[0029] FIG. 5 is a schematic illustration of a reticle measurement system for measuring a non- uniformity map of the reticle in the lithographic system shown in FIG. 1, according to an exemplary aspect.

[0030] FIG. 6 is a plot of a 2D transmission map of the reticle, according to an exemplary aspect.

[0031] FIG. 7 is a schematic illustration of a reticle heating model based on the 2D transmission map shown in FIG. 6. according to an exemplary aspect.

[0032] FIG. 8 is a vector plot of overlay due to non-uniform heating of the reticle. according to an exemplary aspect.

[0033] FIG. 9 is a vector plot of corrected overlay based on the reticle heating model shown in FIG. 7, according to an exemplary aspect.

[0034] FIG. 10 is a plot of a 2D reflectivity map of the reticle. according to an exemplary aspect.

[0035] FIG. 11 isa plot of a finite element model (FEM) of the reticle based on the 2D reflectivity map shown in FIG. 10, according to an exemplary aspect.

[0036] FIG. 12 is a schematic illustration of a reticle heating model based on the 2D reflectivity map shown in FIG. 10, according to an exemplary aspect.

[0037] FIG. 13 is a vector plot of overlay due to non-uniform heating of the reticle, according to an exemplary aspect.

[0038] FIG. 14 is a vector plot of corrected overlay based on the reticle heating model shown in FIG. 12, according to an exemplary aspect.

[0039] FIG. 15 is a flow diagram for reducing a non-uniformity of a reticle in a reticle heating model, according to an exemplary aspect.

[0040] FIG. 16 is a flow diagram for reducing a non-uniformity of an object in an object heating model, according to an exemplary aspect.

[0041] 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

[0042] 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.

[0043] 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.

[0044] 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 features 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.

[0045] 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).

[0046] 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 (¢.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.

[0047] 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 bv reference herein in their entireties.

[0048] 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 u and time constant tT. 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 u and 7. The reticle heating model can also include adjusting feed-forward parameters u and 7. 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.

[0049] The term “non-uniformity” or “non-uniform™ as used herein indicates a parameter or a property of an object (eg. 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.

[0050] 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.

[0051] 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 real- time 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.).

[0052] 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 u and time constant z. 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 u and 7.

The object heating model can also include adjusting feed-forward parameters u and 7.

[0053] 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.

[0054] 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 k18 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.

[0055] 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 (¢.g., a lens, a mirror, a filter, etc.) to a dose of radiation. Further, the calibration can be done in real-time (¢.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.

[0056] 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.

[0057] 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.

[0058] Exemplary Lithographic System

[0059] FIG. 1 shows a lithographic system comprising a radiation source SO and a lithographic apparatus LA. The radiation source SO is configured to generate an EUV and/or a DUV radiation beam

B and to supply the EUV and/or DUV radiation beam B to the lithographic apparatus LA. The lithographic apparatus LA comprises an illumination system IL, a support structure MT (e.g., a mask table, a reticle table. a reticle stage) configured to support a patterning device MA (e.g., a mask, a reticle), a projection system PS, and a substrate table WT (e.g.. a substrate stage) configured to support a substrate W.

[0060] 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.

[0061] 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).

[0062] 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.

[0063] 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) durmg exposure of EUV and/or DUV radiation beam B.

[0064] 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 patteming device MA. In some aspects, patterning device MA can be scanned relative to transmission sensor TS. In some aspects, the

EUV and/or DUV radiation beam B can be scanned relative to transmission sensor TS and patterning device MA.

[0065] 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.

[0066] 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.

[0067] Exemplary Lithographic Cell

[0068] 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/O1, 1/02. 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.

[0069] 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.

[0070] 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).

[0071] Exemplary Computer System

[0072] 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 ofthe 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).

[0073] 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.

[0074] 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).

[0075] 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.

[0076] Exemplary Reticle Stage and Reticle

[0077] 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.

[0078] Reticle stage 200 (e.g.. support structure MT) can be used in a lithographic apparatus (e.g., lithographic apparatus LA) to hold a patterning device (e.g., patterning device MA). Reticle stage 200 can include bottom stage surface 202, top stage surface 204. side stage surfaces 206, clamp 250, reticle cage 224, and/or reticle 300. In some aspects, reticle stage 200 with reticle 300 can be implemented in lithographic apparatus LA. For example, reticle stage 200 can be support structure MT in lithographic apparatus LA. In some aspects, reticle 300 can be disposed on bottom stage surface 202 and held by clamp 250. For example, as shown in FIGS. 3A and 3B, reticle 300 can be disposed on clamp 250 (e.g., an electrostatic clamp) at a center of bottom stage surface 202 with reticle frontside 302 facing perpendicularly away from bottom stage surface 202. In some aspects, reticle cage 224 can be disposed on bottom stage surface 202. For example, as shown in FIGS. 3A and 3B, reticle 300 can be disposed at a center of bottom stage surface 202 and secured by reticle cages 224 adjacent to each corner of reticle 300.

[0079] 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.

[0080] 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 comers 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 a predetermined 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.

[0081] Exemplary Reticle Pattern Non-Uniformity

[0082] FIG. 4A is a schematic top plan illustration of reticle 300 with first pattern area 400A, according to an exemplary aspect. FIG. 4B is a schematic top plan illustration of reticle 300 with second pattern area 400B, according to an exemplary aspect.

[0083] As shown in FIG. 4A. reticle 300 can include frontside 302 and backside 304. and frontside 302 can be patterned with first pattern area 400A. First pattern area 400A can include a metal (e.g., chromium) on frontside 302 of reticle 300 to form one or more patterns for lithographic processes. First pattern area 400A can include transparent area 402 (e.g., no pattern) and high density area 410 (e.g., 50% pattern density). In some aspects. first pattern area 400A can be used for a memory pattern area in a lithographic process. As discussed above. the pattern non-uniformity between transparent area 402 (e.g.. no pattern) and high density area 410 (e.g., 30% pattern density) of first pattern area 400A can cause non-uniform reticle absorption of a radiation beam (e.g., EUV and/or DUV radiation beam B) during exposure, leading to non-uniform reticle heating.

[0084] As shown in FIG. 4B, reticle 300 can include frontside 302 and backside 304, and frontside 302 can be patterned with second pattern area 400B. Second pattern area 400B can include a metal (e.g, chromium) on frontside 302 of reticle 300 to form one or more patterns for lithographic processes.

Second pattern area 400B can include transparent area 402 (e.g., no pattern), medium density area 420 (e.g.. 30% pattern density). and low density area 422 (e.g., 10% pattern density). In some aspects, second pattern area 400B can be used for a logic pattern area in a lithographic process. As discussed above, the pattern non-uniformity between transparent area 402 (e.g., no pattern), medium density area 420 (e.g., 30% pattern density), and low density area 422 (e.g., 10% pattern density) of second pattern area 400B can cause non-uniform reticle absorption of a radiation beam (e.g., EUV and/or DUV radiation beam B) during exposure, leading to non-uniform reticle heating.

[0085] Exemplary Reticle Non-Uniformity Maps

[0086] FIG. 5 is a schematic illustration of reticle measurement system 300 for measuring a non- uniformity map (e.g.. 2D transmission map 600, 2D reflectivity map 1000, etc.) of reticle 300 in the lithographic system shown in FIG. 1, according to an exemplary aspect. FIG. 6 is a plot of 2D transmission map 600 of reticle 300, according to an exemplary aspect. FIG. 10 is a plot of 2D reflectivity map 1000 of reticle 300, according to an exemplary aspect. FIG. 11 is a plot of finite element model (FEM) 1100 of reticle 300 based on 2D reflectivity map 1000 shown in FIG. 10, according to an exemplary aspect.

[0087] FIG. 5 illustrates reticle measurement system 500, according to an exemplary aspect. Reticle measurement system 300 can be configured to measure a non-uniformity map (e.g., 2D transmission map 600, 2D reflectivity map 1000, reflectance map, transparency map, pattern density map, etc.) of reticle 300. Reticle measurement system 500 can be further configured to measure a non-uniformity map (e.g., transmission map. reflectivity map. reflectance map, transparency map, pattern density map, etc.) of an object, for example, a reticle (e.g.. reticle 300), a lens (e.g., lens in lithographic apparatus

LA). a mirror (e.g., first mirror 13), or a substrate (e.g., substrate W). Although reticle measurement system 300 is shown in FIG. 3 as a stand-alone system and/or method. the aspects of this disclosure can be used with other apparatuses, systems, and/or methods, such as, but not limited to, lithographic apparatus LA, lithographic cell LC, computer system CL, metrology tool MT, support structure MT, substrate table WT, reticle stage 200, reticle 300, reticle heating model 700, reticle heating model 700’, flow diagram 1300, and/or flow diagram 1600.

[0088] As shown in FIG. 5, reticle measurement system 500 can include reticle stage 200, reticle stage actuator 502 (e.g., linear XYZ motor), reticle 300, transmission sensor TS, transmission sensor actuator 504 (e.g linear XYZ motor), substrate table WT, and/or reflectivity sensor RS. In some aspects, reticle measurement system 500 can be part of the lithographic system (e.g., lithographic apparatus LA) shown in FIG. 1. In some aspects, reticle measurement system 500 can utilize transmission sensor TS to measure a transmission map of reticle 300 (e.g., 2D transmission map 600) during exposure by EUV and/or DUV radiation beam B. In some aspects, reticle measurement system 500 can utilize reflectivity sensor RS to measure a reflectance map of reticle 300 and/or a reflectivity map of reticle 300 (e.g., 2D reflectivity map 1000) during exposure by EUV and/or DUV radiation beam B.

[0089] Reticle stage 200 can be configured to support reticle 300 and control motion (e.g., scanning) of reticle 300 relative to EUV and/or DUV radiation beam B. Reticle stage 200 can include reticle stage actuator 502 (e.g, linear XYZ motor) configured to move reticle stage 200 relative to EUV and/or DUV radiation beam B. In some aspects, reticle stage 200 can include transmission sensor TS. For example, as shown in FIG. 5, transmission sensor TS can be coupled to reticle stage 200. In some aspects, transmission sensor TS can move with reticle stage 200 during a scan of reticle 300. In some aspects, transmission sensor TS can move independent of reticle stage 200 during a scan of reticle 300. For example, transmission sensor TS can include transmission sensor actuator 504 (e.g., linear XYZ motor) that can move relative to reticle stage 200. In some aspects, transmission sensor TS can be separate and independent from reticle stage 200.

[0090] Transmission sensor TS can be configured to measure a transmission map of reticle 300 (e.g, 2D transmission map 600 shown in FIG. 6) during exposure of EUV and/or DUV radiation beam B. 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 a transmission of reticle 300. Transmission sensor TS can include transmission sensor actuator 504 (e.g., linear XYZ motor) configured to scan backside 304 of reticle 300 to measure a 2D transmission map. In some aspects, transmission sensor TS can be scanned relative to reticle 300 (e.g., via transmission sensor actuator 504). In some aspects. reticle 300 can be scanned relative to transmission sensor TS (e.g., via reticle stage actuator 502). In some aspects, the EUV and/or DUV radiation beam B can be scanned relative to transmission sensor TS and reticle 300. In some aspects, transmission sensor TS can scan a high density of data points of reticle 300. for example, at least 5,000 points.

[0091] Reflectivity sensor RS can be configured to measure a reflectance map of reticle 300 and/or a reflectivity map of reticle 300 (e.g., 2D reflectivity map 1000 shown in FIG. 10} during exposure of

EUV and/or DUV radiation beam B. 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 a reflectance and/or a reflectivity of reticle 300. In some aspects, substrate table WT can include reflectivity sensor RS. For example, as shown in FIG. 5, reflectivity sensor RS can be coupled to substrate table WT. In some aspects, substrate table WT can include an actuator (¢.g., a linear XYZ motor) configured to move substrate table WT relative to EUV and/or DUV radiation beam B. In some aspects, reflectivity sensor RS can work in conjunction with reticle stage 200 to scan frontside 302 of reticle 300 to measure a 2D reflectance map and/or a 2D reflectivity map. For example. as shown in FIG. 5, with substrate W removed from substrate table WT, reticle stage 200 can scan reticle 300 relative to EUV and/or DUV radiation beam B while reflectivity sensor RS measures a reflectance and/or a reflectivity from reticle 300 for a scanned area. In some aspects, reflectivity sensor RS can be scanned relative to reticle 300 (e.g., via substrate table WT actuator). In some aspects, reticle 300 can be scanned relative to reflectivity sensor RS (e.g., via reticle stage actuator 502). In some aspects, the EUV and/or DUV radiation beam B can be scanned relative to reflectivity sensor RS and reticle 300. In some aspects, reflectivity sensor RS can scan a high density of data points of reticle 300, for example, at least 5,000 points.

[0092] As shown in FIG. 6, 2D transmission map 600 shows a percentage (%) of transmission (a.u.) of EUV and/or DUV radiation beam B through reticle 300 for a scanned area of backside 304 of reticle 300 {e.g., XY), for example, 100 mm x 100 mm. In some aspects. 2D transmission map 600 can include a high density of data points, for example, at least 5,000 points. In some aspects, 2D transmission map 600 can be determined (e.g., measured) by transmission sensor TS in reticle measurement system 500.

As shown in FIG. 6, 2D transmission map 600 can include non-uniformity data (¢.g., non-uniform transmission) of reticle 300, for example, showing deviations (e.g., non-uniformity) of transmission from 0% to 100% for different patterns (e.g., chrome patterns) on reticle 300. In some aspects, 2D transmission map 600 can be used to calibrate (e.g., initialize) a reticle heating model (e.g., reticle heating model 700 shown in FIG. 7) for a lithographic process.

[0093] As shown in FIG. 10, 2D reflectivity map 1009 shows a percentage (%) of reflectivity (a.u.) of

EUV and/or DUV radiation beam B from reticle 300 for a scanned area of frontside 302 of reticle 300 (e.g.. XY), for example, 100 mm x 100 mm. In some aspects, 2D reflectivity map 1000 can include a high density of data points, for example, at least 5,000 points. In some aspects. 2D reflectivity map 1000 can be determined (e.g., measured) by reflectivity sensor RS in reticle measurement system 500.

As shown in FIG. 10, 2D reflectivity map 1000 can include non-uniformity data (e.g., non-uniform reflectivity) of reticle 300. for example, showing deviations (e.g., non-uniformity) of reflectivity from 0% to 100% for different patterns (e.9g chrome patterns) on reticle 300. In some aspects, 2D reflectivity map 1000 can be used to calibrate (e.g., initialize) a reticle heating model (e.g, reticle heating model 700" shown in FIG. 12) for a lithographic process.

[0094] As shown in FIG. 11, FEM plot 1100 shows simulated reticle temperature (°C) of reticle 300 based on 2D reflectivity map 1000 for the scanned area (e.g., XY), for example, 100 mm x 100 mm. In some aspects, FEM plot 1100 can include a high density of data points, for example, at least 5,000 points. In some aspects, FEM plot 1100 can be determined {e.g., calculated) using 2D reflectivity map 1000 and reticle recipe data (e.g., image size, position on reticle, etc.) in a finite element model (FEM), for example. as part of a reticle heating model. As shown in FIG. 11. FEM plot 1100 can include non- uniformity data (e.g., non-uniform heating) of reticle 300, for example, showing deviations (e.g., non- uniformity) of reticle temperature from 15 °C to 45 °C for different patterns (e.g., chrome patterns) on reticle 300. In some aspects. FEM plot 1100 can be used to calibrate (¢.g., optimize) a reticle heating model (e.g.. reticle heating model 700' shown in FIG. 12) for a lithographic process.

[0095] Exemplary Reticle Heating Models

[0096] As discussed above, 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). Further. reticles can include a variety of different features (e.g., chrome patterns) that can cause non-uniform reticle absorption of the radiation beam during exposure (¢.g., non-uniform reticle heating).

[0097] Reticles can have different features (e.g., pattern densities) in different pattern areas for different applications (e.g., memory pattern area, logic pattern area, server pattern area, etc.), which may require different reflectivity at different positions on the reticle. For example, for a logic chip, the logic pattern area of the reticle may have a different reflectivity than a cache and memory pattern area.

This difference between bright reflective features (e.g.. chrome area) and dark absorptive features (e.g.,

transparent area) can lead to large differences in local power absorption of the radiation beam on the reticle. For example, a transparency and/or pattern density (e.g., chrome pattern) of the reticle can cause non-uniform reticle absorption during exposure (e.g., spatially varying absorption profile).

[0098] Changes in reticle properties can be modeled and corrected with a reticle heating model. Current reticle heating models assume a uniform reticle absorption. but, in reality, this is generally not the case and one or more non-uniformities may exist in the system that can negatively impact a lithographic process (e.g., non-uniform reticle heating can cause an overlay error of about 3 nm). In some examples, this approach can be inaccurate and inefficient, introduce errors and delays, and require rework of substrates.

[0099] A non-uniformity map (e.g., non-uniform reticle transmission map) can include higher-order reticle deformations (e.g., modal deformation shapes) as a result of non-uniform power absorption during exposure (e.g.. non-uniform reticle heating). This non-uniformity map can be used to initialize and calibrate the reticle heating model to account for reticle non-uniformities (e.g., non-uniform thermomechanical effects, non-uniform absorption, non-uniform heating, etc.) and provide a more accurate and efficient reticle heating model, decrease errors and delays (e.g.. decrease overlay errors), and apply corrections to avoid rework of substrates.

[0100] Aspects of reticle calibration apparatuses, systems, and methods as discussed below can reduce and/or compensate for non-uniform thermomechanical effects of a reticle, account for non-uniform pattern density of the reticle, reduce uncertainties in a lithographic process, increase calibration accuracy and speed of a reticle heating model, avoid rework of substrates, decrease overlay errors, and increase throughput, vield, and accuracy of the lithographic process.

[0101] FIGS. 7-9 and 12-14 illustrate reticle heating models 700, 700’, according to various exemplary aspects. FIG. 7 is a schematic illustration of reticle heating model 700 based on 2D transmission map 600 shown in FIG. 6, according to an exemplary aspect. FIG. 8 is a vector plot of overlay 800 due to non-uniform heating of reticle 300, according to an exemplary aspect. FIG. 9 is a vector plot of corrected overlay 900 based on reticle heating model 700 shown in FIG. 7. according to an exemplary aspect.

FIG. 12 is a schematic illustration of reticle heating model 700" based on 2D reflectivity map 1000 shown in FIG. 10, according to an exemplary aspect. FIG. 13 is a vector plot of overlay 1300 due to non-uniform heating of reticle 300, according to an exemplary aspect. FIG. 14 is a vector plot of corrected overlay 1400 based on reticle heating model 700' shown in FIG. 12, according to an exemplary aspect.

[0102] FIG. 7 illustrates reticle heating model 700, according to an exemplary aspect. Reticle heating model 700 can be configured to reduce and/or compensate for non-uniform thermomechanical effects of reticle 300 in a lithographic process. Reticle heating model 700 can be further configured to reduce and/or compensate for non-uniformity (e.g., non-uniform thermomechanical effects) of an object (e.g., a reticle, a lens, a mirror, a filter, a substrate. etc.) in the lithographic process. Reticle heating model 700 can be further configured to increase calibration accuracy and speed. decrease overlay errors. and increase fabrication throughput and yield of the lithographic process. Although reticle heating model 700 is shown in FIG. 7 as a stand-alone system and/or method, the aspects of this disclosure can be used with other apparatuses, systems. and/or methods, such as. but not limited to, lithographic apparatus LA, lithographic cell LC, computer system CL, metrology tool MT, support structure MT, substrate table

WT, reticle stage 200, reticle 300, reticle measurement system 500, reticle heating model 700", flow diagram 1500, and/or flow diagram 1690.

[0103] As shown in FIG. 7, reticle heating model 700 can include reticle recipe database 710, non- uniformity map database 720 (e.g.. reticle transmission map database), finite element model (FEM) 730, principle component analysis (PCA) 740, inline calibration 750, and reticle heating feed-forward 760. In some aspects. reticle heating model 700 can reduce and/or compensate for non-uniform thermomechanical effects of reticle 300 in a lithographic process. In some aspects, reticle heating model 700 can be calibrated (e.g., initialized) with non-uniformity map database 720 (e.g., 2D transmission map 600 shown in FIG. 6). In some aspects, reticle heating model 700 can decrease overlay errors in a lithographic process and avoid rework of substrates. In some aspects, reticle heating model 700 can be used for an object (e.g., a reticle, a lens, a mirror, a filter, a substrate, etc.) of a lithographic process in an object heating model.

[0104] Reticle recipe database 710 can be configured to provide reticle recipe data 712 (e.g., image size, position on reticle, etc.) to FEM 730. Reticle recipe database 710 can be further configured to provide reticle non-uniformity data 714 (e.g.. one or more reticle transmission maps) to FEM 730 based on one or more reticle transmission maps (¢.g., 2D transmission map 600). As shown in FIG. 7, reticle recipe database 710 can send reticle recipe data 712 and reticle non-uniformity data 714 to FEM 730.

In some aspects, reticle non-uniformity data 714 can include reticle transmission map 722 to initialize

FEM 730 and account for non-uniformities in the specific area (e.g., first pattern area 400A) of reticle 300 during exposure.

[0105] Non-uniformity map database 720 can be configured to retain one or more non-uniformity maps (e.g., transmission maps) of reticle 300. Non-uniformity map database 720 can be further configured to calibrate (e.g.. initialize) FEM 730 and account for non-uniformities in reticle 300 during exposure. In some aspects, non-uniformity map database 720 can include one or more transmission maps (e.g., 2D transmission map 600) of reticle 300. In some aspects. non-uniformity map database 720 can include an average of a plurality of transmission maps (¢.g.. 2D transmission map 600) of reticle 300. As shown in FIG. 7, non-uniformity map database 720 can send reticle transmission map 722 (e.g.. 2D transmission map 600) that can be combined with reticle recipe database 710 to form reticle non- uniformity data 714 to FEM 730.

[0106] In some aspects, non-uniformity map database 720 can include one or more non-uniformity maps (e.g., transmission map, reflectivity map, reflectance map, transparency map, pattern density map, etc.) of reticle 300 of a lithographic process. In some aspects, non-uniformity map database 720 can include one or more non-uniformity maps (e.g., transmission map. reflectivity map, reflectance map,

transparency map, pattern density map. etc.) of an object of a lithographic process, for example, a reticle (e.g., reticle 300), a lens (e.g, lens in lithographic apparatus LA), a mirror (eg. first mirror 13), or a substrate (¢.g., substrate W).

[0107] FEM 730 can be configured to model {e.g., simulate) non-uniform thermomechanical effects of reticle 300 for a selected recipe (e.g.. selected reticle pattern area). As shown in FIG. 7, FEM 730 can receive reticle recipe data 712 (e.g. image size, position on reticle, etc.) and reticle non-uniformity data 714 (e.g., reticle transmission map 722), simulate corresponding non-uniform thermomechanical effects through finite element analysis (e.g.. thermodynamic equations). and send simulated reticle heating data 732 to PCA 740.

[0108] PCA 740 can be configured to determine (e.g., extract) modal deformation shapes and amplitudes of modal deformation shapes of simulated reticle heating data 732 from FEM 730. In some aspects, modal deformation shapes can include spatially varying absorption profiles of reticle 300. In some aspects, modal deformation shapes can include deflection patterns (e.g., thermal expansion patterns) associated with particular modal frequencies of reticle 300. As shown in FIG. 7, PCA 740 can send simulated amplitudes of modal deformation shapes 742 to inline calibration 750, and send modal deformation shapes 744 to reticle heating feed-forward 760.

[0109] Inline calibration 756 can be configured to compare simulated amplitudes of modal deformation shapes 742 with actual alignment results of reticle 300. Inline calibration 750 can be further configured to calibrate simulated amplitudes of modal deformation shapes 742. In some aspects, inline calibration 750 can include reticle alignment (RA) measurements between reticle 300 and a substrate (e.g, substrate W). In some aspects, inline calibration 750 can include adjusting simulated amplitudes of modal deformation shapes 742 based on measured reticle alignment (RA). As shown in FIG. 7, inline calibration 750 can send calibrated amplitudes of modal deformation shapes 752 to reticle heating feed- forward 760.

[0110] Reticle heating feed-forward 760 can be configured to reduce and/or correct non-uniform thermomechanical effects of reticle 300. Reticle heating feed-forward 760 can be further configured to apply corrections to substrate W and/or subsequent substrates based on modal deformation shapes 744 and calibrated amplitudes of modal deformation shapes 752 of reticle 300 for the selected recipe. As shown in FIG. 7, reticle heating feed-forward 760 can receive modal deformation shapes 744 from PCA 740 and calibrated amplitudes of modal deformation shapes 752 from inline calibration 750. In some aspects, reticle heating feed-forward 760 can reduce and/or compensate for a non-uniformity of reticle 300 (e.g.. non-uniform thermal heating). In some aspects, reticle heating feed-forward 760 can reduce a spatially varying absorption profile of reticle 300. In some aspects, reticle heating feed-forward 760 can apply a correction to a substrate and/or a subsequent substrate in a lithographic process. In some aspects, reticle heating feed-forward 760 can decrease overlay errors in a lithographic process.

[0111] As shown in FIG. 8. vector plot of overlay 800 shows overlay deformations (e.g., errors) due to non-uniform heating of reticle 300. In some aspects, vector plot of overlay 800 can include non-

uniform thermomechanical effects of reticle 300 as well as reticle alignment (RA) noise. As shown in

FIG. 8, vector plot of overlay 800 can include overlay deformations in both X- and Y-directions. for example, showing an average X-direction deformation of Ax = 2.747 nm and an average Y-direction deformation of Ay = 0.588 nm.

[0112] As shown in FIG. 9, vector plot of corrected overlay 900 shows corrected overlay deformations (e.g.. errors) based on reticle heating model 700 shown in FIG. 7. In some aspects, vector plot of corrected overlay 900 can include corrections from reticle heating feed-forward 760 based on modal deformation shapes 744 and calibrated amplitudes of modal deformation shapes 752. As shown in FIG. 9. vector plot of corrected overlay 900 can include corrected overlay deformations in both X- and Y- directions, for example, showing an average X-direction corrected deformation of Ax = 0.738 nm (e.g., 73% decrease in overlay error) and an average Y-direction corrected deformation of Ay = 0.810 nm (e.g.. 38% increase in overlay error).

[0113] FIG. 12 illustrates reticle heating model 700’, according to certain aspects. The aspects of reticle heating model 700 shown in FIG. 7, for example, and the aspects of reticle heating model 700" shown in FIG. 12 may be similar. Similar reference numbers are used to indicate features of the aspects of reticle heating model 700 shown in FIG. 7 and the similar features of the aspects of reticle heating model 700" shown in FIG. 12. One difference between the aspects of reticle heating model 700 shown in FIG. 7 and the aspects of reticle heating model 700' shown in FIG. 12 is that reticle heating model 700" utilizes non-uniformity map database 720' (e.g., reflectivity maps) and sends reticle reflectivity map 722' (e.g., 2D reflectivity map 1000 shown in FIG. 10) to initialize FEM 730, rather than non- uniformity map database 720 {e.g., transmission maps) that sends reticle transmission map 722 (e.g., 2D transmission map 600 shown in FIG. 6) to initialize FEM 730 shown in FIG. 7. Although reticle heating model 700" is shown in FIG. 12 as a stand-alone system and/or method, the aspects of this disclosure can be used with other apparatuses, systems, and/or methods, such as, but not limited to, lithographic apparatus LA, lithographic cell LC, computer system CL, metrology tool MT, support structure MT, substrate table WT, reticle stage 200, reticle 300, reticle measurement system 500, reticle heating model 700. flow diagram 1500. and/or flow diagram 1600.

[0114] As shown in FIG. 12, reticle heating model 700' can include non-uniformity map database 720' (e.g.. reticle reflectivity map database) to send reticle reflectivity map 722' (e.g., 2D reflectivity map 1000 shown in FIG. 10) to initialize FEM 730. In some aspects, reticle heating model 700' can reduce and/or compensate for non-uniform thermomechanical effects of reticle 300 in a lithographic process.

In some aspects, reticle heating model 700’ can be calibrated (e.g., initialized) with non-uniformity map database 720' (e.g., 2D reflectivity map 1000 shown in FIG. 10). In some aspects, reticle heating model 700" can decrease overlay errors in a lithographic process and avoid rework of substrates. In some aspects, reticle heating model 700' can be used for an object (e.g., a reticle, a lens, a mirror, a filter, a substrate, etc.) of a lithographic process in an object heating model.

[0115] Non-uniformity map database 720' can be configured to retain one or more non-uniformity maps (e.g., reflectivity maps) of reticle 300. Non-uniformity map database 720' can be further configured to calibrate (e.g., initialize) FEM 730 and account for non-uniformities in reticle 300 during exposure. In some aspects, non-uniformity map database 720' can include one or more reflectivity maps (e.g, 2D reflectivity map 1000) of reticle 300. In some aspects, non-uniformity map database 720' can include an average of a plurality of reflectivity maps (e.g., 2D reflectivity map 1000) of reticle 300. As shown in FIG. 12, non-uniformity map database 720' can send reticle reflectivity map 722' (e.g.. 2D reflectivity map 1000) that can be combined with reticle recipe database 710 to form reticle non- uniformity data 714 to FEM 730.

[0116] In some aspects. non-uniformity map database 720' can include one or more non-uniformity maps (e.g., transmission map, reflectivity map, reflectance map, transparency map, pattern density map, etc.) of reticle 300 of a lithographic process. In some aspects, non-uniformity map database 720' can include one or more non-uniformity maps (e.g., transmission map, reflectivity map, reflectance map, transparency map, pattern density map, etc.) of an object of a lithographic process, for example, a reticle (e.g. reticle 300), a lens (e.g., lens in lithographic apparatus LA). a mirror (e.g.. first mirror 13), or a substrate (¢.g., substrate W).

[0117] As shown in FIG. 13, vector plot of overlay 1300 shows overlay deformations (e.g., errors) due to non-uniform heating of reticle 300. In some aspects, vector plot of overlay 1300 can include non- uniform thermomechanical effects of reticle 300 as well as reticle alignment (RA) noise. As shown in

FIG. 13, vector plot of overlay 1300 can include overlay deformations in both X- and Y-directions, for example, showing an average X-direction deformation of Ax = 0.92 nm and an average Y-direction deformation of Ay = 1.45 nm.

[0118] As shown in FIG. 14. vector plot of corrected overlay 1400 shows corrected overlay deformations (e.g., errors) based on reticle heating model 700’ shown in FIG. 12. In some aspects, vector plot of corrected overlay 1400 can include corrections from reticle heating feed-forward 760 based on modal deformation shapes 744 and calibrated amplitudes of modal deformation shapes 752. As shown in FIG. 14, vector plot of corrected overlay 1400 can include corrected overlay deformations in both X- and Y-directions, for example, showing an average X-direction corrected deformation of Ax = 0.35 nm (e.g.. 62% decrease in overlay error) and an average Y-direction corrected deformation of Ay = 0.43 nm (e.g., 70% decrease in overlay error).

[0119] Exemplary Flow Diagrams

[0120] FIGS. 15 and 16 illustrate flow diagrams for reticle heating models 700, 700, according to various exemplary aspects. FIG. 15 illustrates flow diagram 1500 for reducing a non-uniformity of a reticle (e.g. reticle 300) in a reticle heating model (e.g., reticle heating models 700, 700%. It is to be appreciated that not all steps in FIG. 15 are needed to perform the disclosure provided herein. Further,

some of the steps may be performed simultaneously. sequentially, and/or in a different order than shown in FIG. 15. Flow diagram 1500 shall be described with reference to FIGS. 5-14. However, flow diagram 1500 is not limited to those example aspects.

[0121] In step 1502, as shown in the example of FIGS. 5-14, a non-uniformity map (e.g., 2D transmission map 600, 2D reflectivity map 1000, etc.) of reticle 300 can be defined in a lithographic process. In some aspects, defining the non-uniformity map can include measuring a transmission map of reticle 300 (e.g., 2D transmission map 600 shown in FIG. 6). In some aspects, defining the non- uniformity map can include measuring a reflectance map of reticle 300. In some aspects. defining the non-uniformity map can include measuring a reflectivity map of reticle 300 (e.g.. 2D reflectivity map 1000 shown in FIG. 10). In some aspects, defining the non-uniformity map can include defining a transparency map of reticle 300. In some aspects, defining the non-uniformity map can include defining a pattern density map of reticle 300.

[0122] In step 1504, as shown in the example of FIGS. 5-14, a reticle heating model (e.g., reticle heating models 700. 700") can be calibrated based on the non-uniformity map. In some aspects, calibrating the reticle heating model includes initializing the reticle heating model based on the non- uniformity map. In some aspects, calibrating the reticle heating model further includes predicting modal deformation shapes (e.g., modal deformation shapes 744) of reticle 300 using a finite element model (e.g., FEM 730) based on the non-uniformity map. In some aspects, calibrating the reticle heating model further includes measuring a reticle alignment (RA) between reticle 300 and a substrate (e.g., substrate

W) and adjusting the modal deformation shapes of reticle 300 based on the measured reticle alignment (RA) (e.g., inline calibration 750).

[0123] In step 1506, as shown in the example of FIGS. 5-14, a non-uniformity (e.g., non-uniform reticle heating) of reticle 300 can be reduced and/or corrected based on the calibrated reticle heating model (¢.g., reticle heating feed-forward 760). In some aspects, reducing the non-uniformity can include reducing a spatially varying absorption profile of reticle 300. In some aspects, correcting the non- uniformity can include correcting an overlay deformation profile of reticle 300.

[0124] In step 1508, optionally. as shown in the example of FIGS. 5-14, a correction can be applied to a substrate and/or a subsequent substrate in the lithographic process. In some aspects, the correction can decrease an overlay error of the lithographic process.

[0125] FIG. 16 illustrates flow diagram 1600 for reducing a non-uniformity of an object (e.g., a reticle, a lens, a mirror, a filter, a substrate. etc.) in an object heating model (e.g.. reticle heating models 700, 700". It is to be appreciated that not all steps in FIG. 16 are needed to perform the disclosure provided herein. Further, some of the steps may be performed simultaneously. sequentially, and/or in a different order than shown in FIG. 16. Flow diagram 1600 shall be described with reference to FIGS. 5-14.

However, flow diagram 1600 is not limited to those example aspects.

[0126] In step 1602, as shown in the example of FIGS. 5-14, a non-uniformity map (e.g.. 2D transmission map 600, 2D reflectivity map 1000, etc.) of an object (¢.g., a reticle, a lens, a mirror, a filter, a substrate. etc.) can be defined in a lithographic process. In some aspects, defining the non- uniformity map can include measuring a transmission map of the object (e.g.. 2D transmission map 600 shown in FIG. 6). In some aspects, defining the non-uniformity map can include measuring a reflectance map of the object. In some aspects, defining the non-uniformity map can include measuring a reflectivity map of the object (e.g.. 2D reflectivity map 1000 shown in FIG. 10). In some aspects, defining the non-uniformity map can include defining a transparency map of the object In some aspects, defining the non-uniformity map can include defining a pattern density map of the object.

[0127] In step 1604. as shown in the example of FIGS. 5-14, an object heating model (e.g.. reticle heating models 700, 700" can be calibrated based on the non-uniformity map. In some aspects, calibrating the object heating model includes initializing the object heating model based on the non- uniformity map. In some aspects, calibrating the object heating model further includes predicting modal deformation shapes (e.g.. modal deformation shapes 744) of the object using a finite element model (e.g.. FEM 730) based on the non-uniformity map. In some aspects, calibrating the object heating model further includes measuring a reticle alignment (RA) between reticle 300 and a substrate (e.g., substrate

W) and adjusting the modal deformation shapes of the object based on the measured reticle alignment (RA) (e.g., inline calibration 750).

[0128] In step 1606. as shown in the example of FIGS. 5-14. a non-uniformity (e.g., non-uniform object heating) of the object can be reduced and/or corrected based on the calibrated object heating model (e.g, reticle heating feed-forward 760). In some aspects, reducing the non-uniformity can include reducing a spatially varying absorption profile of the object. In some aspects, correcting the non- uniformity can include correcting an overlay deformation profile of the object.

[0129] In step 1608, optionally, as shown in the example of FIGS. 5-14, a correction can be applied to a substrate and/or a subsequent substrate in the lithographic process. In some aspects, the correction can decrease an overlay error of the lithographic process.

[0130] Various embodiments of the present apparatuses, systems and methods are disclosed in the subsequent list of numbered clauses: 1. A method comprising: defining a non-uniformity map of a reticle in a lithographic process; calibrating a reticle heating model based on the non-uniformity map; and reducing a non-uniformity of the reticle based on the calibrated reticle heating model. 2. The method of clause 1, wherein the defining the non-uniformity map comprises measuring a transmission map and/or a reflectance map of the reticle. 3. The method of clause 2, wherem the measuring the transmission map and/or the reflectance map of the reticle comprises exposing the reticle to a dose of radiation and scanning an area of a backside and/or a frontside of the reticle with a sensor. 4. The method of clause 1, wherein the defining the non-uniformity map comprises defining a transparency map and/or a pattern density map of the reticle.

5. The method of clause 4. wherein the defining the transparency map and/or the pattern density map of the reticle comprises defining a two-dimensional reflectivity map of the reticle. 6. The method of clause 1, wherein the calibrating the reticle heating model comprises initializing the reticle heating model based on the non-uniformity map.

7 The method of clause 6, wherein the calibrating the reticle heating model further comprises predicting modal deformation shapes of the reticle using a finite element model (FEM) based on the non-uniformity map.

8. The method of clause 7. wherein the calibrating the reticle heating model further comprises: measuring a reticle alignment (RA) between the reticle and a substrate; and adjusting the modal deformation shapes of the reticle based on the measured reticle alignment (RA). 9. The method of clause 1, wherein the reducing the non-uniformity of the reticle comprises reducing a spatially varying absorption profile of the reticle. 10. The method of clause 9, wherein the reducing the non-uniformity of the reticle further comprises applying a correction to a substrate in the lithographic process. 11. A method comprising: defining a non-uniformity map of an object in a lithographic process; calibrating an object heating model based on the non-uniformity map: and reducing a non-uniformity of the object based on the calibrated object heating model. 12. The method of clause 11, wherein the defining the non-uniformity map comprises measuring a transmission map and/or a reflectance map of the object when exposed to a dose of radiation. 13. The method of clause 11, wherein the defining the non-uniformity map comprises defining a transparency map and/or a pattern density map of the object. 14. The method of clause 11, wherein the calibrating the object heating model comprises initializing the object heating model based on the non-uniformity map. 15. The method of clause 14, wherein the calibrating the object heating model further comprises predicting modal deformation shapes of the object using a finite element model (FEM). 16. The method of clause 15, wherein the calibrating the object heating model further comprises adjusting the modal deformation shapes of the object based on inline calibration of the lithographic process. 17. The method of clause 11, wherein the reducing the non-uniformity of the object comprises reducing a spatially varying absorption profile of the object. 18. The method of clause 11, wherein the object comprises a reticle. 19. The method of clause 11, wherein the object comprises a lens. 20. The method of clause 11, wherein the object comprises a substrate. 21. A 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: and a controller configured to reduce effects of non-uniformity of the reticle in a lithographic process, the controller configured to: define a non-uniformity map of the reticle; calibrate a reticle heating model based on the non-uniformity map; and reduce a non-uniformity of the reticle based on the calibrated reticle heating model. 22. A non-transitory computer readable medium program comprising computer readable instructions configured to cause a processor to: define a non-uniformity map of a reticle in a lithographic process: calibrate a reticle heating model based on the non-uniformity map; and reduce a non-uniformity of the reticle based on the calibrated reticle heating model.

[0131] 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.

[0132] 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.

[0133] 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 isto be interpreted by those skilled in relevant art(s) in light of the teachings herein.

[0134] 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, before or 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 herem 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.

[0135] 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.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] The foregoing description of the specific aspects will so fully reveal the general nature of the aspects that others can, by applving 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.

[0140] 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 (14)

CONCLUSIONS 1. A method comprising: determining a non-uniformity map of a patterning device in a lithographic process; calibrating a heating model for a patterning device based on the non-uniformity map; and reducing a non-uniformity of the patterning device based on the calibrated heating model for the patterning device. 2. The method of claim 1, wherein: determining the unevenness map comprises measuring a transmission map and/or a reflection map of the patterning device; and measuring the transmission map and/or the reflection map of the patterning device comprises exposing the patterning device to a radiation dose and scanning an area of a back side and/or a front side of the patterning device with a sensor. 3. The method of claim 1, wherein: determining the unevenness map comprises determining a transparency map and/or a pattern density map of the patterning device; and determining the transparency map and/or the pattern density map of the patterning device comprises determining a two-dimensional reflectivity map of the patterning device. The method of claim 1, wherein: calibrating the patterning device heating model comprises triggering the patterning device heating model based on the nonuniformity map; calibrating the patterning device heating model further comprises predicting modal deformation shapes of the patterning direction using a finite element model (FEM) based on the nonuniformity map, and calibrating the patterning device heating model further comprises: measuring a reticle alignment (RA) between the patterning device and a substrate; and adjusting the modal deformation shapes of the patterning device based on the measured reticle alignment (RA). 5. The method of claim 1, wherein: reducing the non-uniformity of the patterning device comprises reducing a spatially varying absorption profile of the patterning device; reducing the non-uniformity of the patterning device further comprises applying gene correction to a substrate in the lithographic process. 6. A method comprising: determining a non-uniformity map of an object in a lithographic process; calibrating a heating model for an object based on the non-uniformity map; and reducing a non-uniformity of the object based on the calibrated heating model for an object. 7. A method according to claim 6, wherein determining the non-uniformity map comprises measuring a transmission map and/or a reflection map of the object when exposed to a radiation dose. 8. The method of claim 6, wherein determining the unevenness map comprises determining a transparency map and/or a pattern density map of the object. 9. The method of claim 6, wherein: calibrating the heating model for the object comprises initiating the heating model for the object based on the nonuniformity map: 10. The method of claim 9, wherein calibrating the heating model for the object further comprises predicting deformation shapes of the object using a finite element model (FEM). 11. The method of claim 10, wherein calibrating the heating model for the object further comprises adjusting the modal deformation shapes of the object based on inline calibration of the lithographic process. 12. The method of claim 6, wherein reducing the non-uniformity of the object comprises reducing a spatially varying absorption profile of the object. 13. The method of claim 6, wherein the object comprises a patterning device, a lens or a substrate. 14. Lithographic apparatus. comprising: an illumination system configured to illuminate a patterning device; a protection system configured to project an image of the patterning device onto a substrate; and a controller configured to reduce effects of patterning device unevenness in a lithographic process, the controller being configured: to determine a patterning device unevenness map; to calibrate a patterning device heating model based on the unevenness map; and to reduce a patterning device unevenness based on the calibrated patterning device heating model.