WO2026006407A1

WO2026006407A1 - Defect reduction strategies using mechanical learnings from mechanical simulation

Info

Publication number: WO2026006407A1
Application number: PCT/US2025/035188
Authority: WO
Inventors: Yichi Zhang; Monica Sawkar Mathur
Original assignee: Lam Research Corp
Current assignee: Lam Research Corp
Priority date: 2024-06-26
Filing date: 2025-06-25
Publication date: 2026-01-02
Anticipated expiration: 2026-12-26

Abstract

A static mechanical simulation determines stress and deformation in a resist after development. The mechanical simulation takes patterned exposure data and post-exposure bake data as inputs to determine differential initial strain and stress in the resist. The initial strain is related to blanket volume loss that occurs in the resist as a result of exposure and post-exposure bake. Using the initial strain, film property, and geometry layout as inputs, the mechanical simulation determines or even quantifies a final stress and deformation in the resist after development. The final stress and deformation in the resist can be correlated to defect instances. Various strategies, including bulk mask optimization, pre-exposure operations, and enhanced optical proximity correction (OPC) that utilize the mechanical simulation learning, can be applied to reduce the initial strain or stress in the resist and thereby reduce defectivity after development.

Description

DEFECT REDUCTION STRATEGIES USING MECHANICAL LEARNINGS FROM MECHANICAL SIMULATION

RELATED APPLICATION(S)

[0000] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in its entirety and for all purposes.

FIELD

[0001] The present disclosure relates to modeling stress and deformation in a resist, and more particularly to modeling stress and deformation in a resist after development, which can be correlated to one or more defects in the resist after development. Using learnings from the modeling, various defect-reduction strategies can be designed to reduce the stress and deformation in the resist after development.

BACKGROUND

[0002] The fabrication of semiconductor devices, such as integrated circuits, is a multi-step process involving photolithography. In general, the process includes the deposition of material on a wafer, and patterning the material through lithographic techniques to form structural features (e.g., transistors and circuitry) of the semiconductor device. The steps of a typical photolithography process known in the art include: preparing the substrate; applying a photoresist, such as by spin coating; exposing the photoresist to light in a desired pattern, causing the more exposed areas of the photoresist to become more or less soluble in a developer solution; developing by applying a developer solution to remove either the more exposed or the less exposed areas of the photoresist; and subsequent processing to create features on the areas of the substrate from which the photoresist has been removed, such as by etching or material deposition.

[0003] The evolution of semiconductor design has created the need, and has been driven by the ability, to create ever smaller features on semiconductor substrate materials. This progression of technology has been characterized in “Moore’s Law” as a doubling of the density of transistors in dense integrated circuits every two years. Indeed, chip design and manufacturing has progressed such that modern microprocessors may contain billions of transistors and other circuit features on a single chip. Individual features on such chips may be on the order of 22 nanometers (nm) or smaller, in some cases less than 10 nm. [0004] One challenge in manufacturing devices having such small features is the ability to reliably and reproducibly create photolithographic masks having sufficient resolution. Current photolithography processes typically use 193 nm ultraviolet (UV) light to expose a photoresist. The fact that the light has a wavelength significantly greater than the desired size of the features to be produced on the semiconductor substrate creates inherent issues. Achieving feature sizes smaller than the wavelength of the light requires use of complex resolution enhancement techniques, such as multipatteming. Thus, there is significant interest and research effort in developing photolithographic techniques using shorter wavelength light, such as extreme ultraviolet radiation (EUV), having a wavelength of from 10 nm to 15 nm, e.g., 13.5 nm.

[0005] EUV photolithographic processes can present challenges, however, including low power output and loss of light during patterning. Traditional organic chemically amplified resists (CAR) similar to those used in 193 nm UV lithography have potential drawbacks when used in EUV lithography, particularly as they have low absorption coefficients in EUV region and the diffusion of photo-activated chemical species can result in blur or line edge roughness. Furthermore, in order to provide the etch resistance required to pattern underlying device layers, small features patterned in conventional CAR materials can result in high aspect ratios at risk of pattern collapse. Metal oxide resist has been proposed as an alternative to CAR materials because of its triple absorptivity under EUV. Metal oxide resist exhibit a high exposure latitude and can maintain a stable pattern down to even a half pitch of 16 nm and below. Metal oxide resist can demonstrate enhanced stability and is suitable for high volume manufacturing. In some instances, metal oxide resist offers environmental benefits, reducing waste and cost by 5-10 times compared to conventional CAR materials.

[0006] Some resists, such as metal oxide resists, may undergo shrinkage or deformation during exposure and post-exposure bake steps. The shrinkage or deformation can lead to increased defectivity in the resist following development. However, there is a lack of understanding associated with the mechanical response(s) of the resist to exposure and post-exposure bake and the relationship of such mechanical response(s) to defects that emerge in various geometry of the resist after development.

[0007] The background description provided herein is for the purpose of generally presenting the context of the present technology. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present technology. SUMMARY

[0008] Provided herein is a method of determining stress and deformation in a resist after development. The method includes receiving, in a mechanical simulation, experimental data sets regarding exposure and post-exposure bake performed on the resist as inputs, determining, using the mechanical simulation, an initial strain in the resist based at least in part on the experimental data sets, and determining, using the mechanical simulation, stress and deformation in the resist after development based at least in part on the initial strain and pattern geometry of the resist.

[0009] In some implementations, the resist is a negative tone resist. In some implementations, the resist includes a metal-oxide-containing EUV resist. In some implementations, determining the stress and deformation in the resist after development includes: constructing a geometric representation of the resist after development, meshing the geometric representation of the resist to form one or more meshes, applying the initial strain in the resist to the geometric representation of the resist, and performing calculations with governing equations in each of the meshes iteratively to obtain the stress and deformation in the resist after development. In some implementations, the method further includes correlating the stress and deformation in the resist to one or more defects in the resist after development. In some implementations, the experimental data sets include an aerial image of the resist after exposure, where the aerial image includes a planar intensity distribution of incoming EUV light observed by the resist. In some implementations, the experimental data sets include volume losses of the resist after post-exposure bake associated with conditions of the post-exposure bake. In some implementations, the method further includes determining a relationship between the volume losses of the resist after postexposure bake and lateral shrinkage, stress accumulation, and thickness loss after development. In some implementations, determining the initial strain in the resist includes calculating strain in the resist using an aerial image of the resist after exposure and using volume losses of the resist after post-exposure bake associated with conditions of the post-exposure. In some implementations, determining the stress and deformation in the resist after development includes quantifying the stress and deformation in the resist using a multi-step static mechanical simulation. In some implementations, the method further includes training the mechanical simulation using experimental defectivity data compared against the stress and deformation in the resist determined from the mechanical simulation.

[0010] Also provided herein is a mechanical simulation for determining stress and deformation in a resist after development comprising one or more non-transitory machine readable media comprising logic configured to implement: a static mechanical simulation configured to receive experimental data sets associated with exposure and post-exposure bake as inputs, configured to determine an initial strain in the resist based at least in part on the experimental data sets, and configured to determine the stress and deformation in the resist after development based at least in part on the initial strain in the resist.

[0011] In some implementations, the resist is a negative tone resist. In some implementations, the resist includes a metal-oxide-containing EUV resist. In some implementations, the static mechanical simulation configured to determine the stress and deformation in the resist is configured to construct a geometric representation of the resist after development, mesh the geometric representation of the resist to form one or more meshes, apply the initial strain in the resist to the geometric representation of the resist, and perform calculations with governing equations in each of the one or more meshes iteratively to obtain the stress and deformation in the resist after development. In some implementations, the static mechanical simulation is further configured to correlate the stress and deformation in the resist to one or more defects in the resist after development.

[0012] Also provided herein is a method of reducing detectivity in a resist. The method includes identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist includes bulk regions and local feature regions, and generating a photomask with one or more assist features to reduce patterning radiation exposure in the bulk regions of the resist, where the one or more assist features to the photomask reduce the mechanically-induced defects in the resist in the local feature region.

[0013] In some implementations, the one or more assist features to the photomask reduce a volume of the resist in the bulk regions and reduce an exposure dose to the resist. In some implementations, reducing patterning radiation exposure in the bulk regions is correlated with reducing an initial strain in the resist. In some implementations, the method further includes identifying one or more areas in the bulk region for removal that are not necessary to a patterned resist after development, and correlating the one or more areas in the bulk region for removal to the one or more assist features of the photomask. In some implementations, the method further includes determining, using the mechanical simulation, that the one or more areas in the bulk region for removal will reduce the initial strain in the resist in the local feature region.

[0014] Also provided herein is a method of reducing initial strain in a resist. The method includes identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist includes bulk regions and local feature regions, and selecting a pre-exposure operation that reduces the initial strain in the resist, where the pre-exposure operation includes blanket resist exposure to DUV, post-application bake, or deposition of a blended resist film for the resist.

[0015] In some implementations, the pre-exposure operation includes blanket resist exposure to DUV. In some implementations, the blanket resist exposure to DUV reduces a dose for the EUV exposure. In some implementations, the blanket resist exposure to DUV reduces a shrinkage contrast between exposed regions and unexposed regions of the resist after EUV exposure. In some implementations, the pre-exposure operation reduces a dose for the EUV exposure and reduces a shrinkage contrast between exposed regions and unexposed regions of the resist after the EUV exposure.

[0016] Also provided herein is a method of reducing detectivity in a resist. The method includes identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist includes bulk regions and local feature regions, identifying one or more areas with high stress in the local feature regions of the resist, and performing an optical proximity correction (OPC) operation on a photomask to reduce defectivity in the local feature regions.

[0017] In some implementations, performing the OPC operation is based at least in part on the initial strain in the resist. In some implementations, performing the OPC operation on the photomask makes corrections to the photomask according to geometric characteristics of a target pattern and reduction of mechanical defects in the resist that are associated with the initial strain. In some implementations, performing the OPC operation on the photomask to reduce the defectivity in the local feature regions is correlated with the initial strain in the resist.

BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 presents a flow diagram of an example patterning process flow involving an EUV resist according to some implementations.

[0019] Figure 2 presents a flow diagram of an example method of determining stress and deformation in a resist film after development according to some implementations.

[0020] Figure 3A presents a graph showing a fraction of light absorbed by an example 2-D representation of a resist film as a function of an x-direction of the resist film during an exposure step.

[0021] Figure 3B presents a graph showing a blanket volume loss percentage (%) as a result of performing a post-exposure bake step on a photoresist film as a function of dose. [0022] Figure 3C presents a graph showing an amount of volume remaining in the photoresist film as a function of an x-direction of the resist film after the exposure step and the post-exposure bake step.

[0023] Figure 4 presents an example reaction pattern between photoresist units according to some implementations.

[0024] Figure 5A shows a cross-sectional schematic illustration of an example resist film showing initial strain, deformation and stress as a result of the initial strain, in the resist film prior to development.

[0025] Figure 5B shows a cross-sectional schematic illustration of an example resist film showing lateral shrinkage and stress in the resist film after development.

[0026] Figure 6A shows an example geometric representation of a resist film in a finite element analysis.

[0027] Figure 6B shows an example mesh for the geometric representation of the resist film in the finite element analysis.

[0028] Figure 6C shows an example step of inputting initial strain into the geometric representation of the resist film.

[0029] Figure 6D shows an example step of solving governing equations in each mesh and communicating between meshes and iterating results until a converged solution is reached.

[0030] Figure 7A shows a cross-sectional schematic illustration of an example resist film after development, where the resist film comprises two features connected by a “spider web” of residual scum.

[0031] Figure 7B shows a cross-sectional schematic illustration of a resist film after development showing asymmetric shrinkage and displacement from its original location, when the resist film is connected by a “spider web.”

[0032] Figure 7C shows a cross-sectional schematic illustration of a resist film after development showing symmetric shrinkage, when the resist film is not connected by any “spider web.”

[0033] Figure 8A shows a geometric representation of a resist film with an inverse tip geometry after development.

[0034] Figure 8B shows a deformation and stress distribution in the geometric representation of the resist film with the inverse tip geometry after development. [0035] Figure 8C shows a magnified view of the deformation and stress distribution in the geometric representation of the resist film with the inverse tip geometry after development.

[0036] Figure 9A shows height deformation distribution and volume loss in a resist film prior to development.

[0037] Figure 9B shows a post height deformation distribution and volume loss in the resist film after development.

[0038] Figure 10 presents a flow diagram of an example process flow for applying a defectreduction strategy in a resist according to some implementations.

[0039] Figure 11 A presents a graph illustrating local shrinkage ratio of an EUV resist film as a function of an x-direction of the EUV resist film for different EUV exposure dose conditions.

[0040] Figure 1 IB shows a graph illustrating a relationship between an initial strain in a resist film and dose.

[0041] Figure 12A shows a top plan view of an example photoresist film comprising a bulk region and a local feature region, where stress in the photoresist film varies depending on the region of the photoresist film, according to some implementations.

[0042] Figure 12B shows a lateral deformation distribution in a magnified top plan view of a portion of an example photoresist film.

[0043] Figure 12C shows a lateral deformation distribution in a magnified top plan view of a portion of an example photoresist film formed with an assist feature in the bulk region according to some implementations.

[0044] Figure 13 A shows a stress distribution in a magnified top plan view of a portion of an example photoresist film prior to an enhanced optical proximity correction (OPC) operation.

[0045] Figure 13B shows a stress distribution in a magnified top plan view of the portion of the example photoresist film after an enhanced optical proximity correction (OPC) operation to address mechanical defects according to some implementations.

[0046] Figure 14 presents an example computer system that may be employed to implement certain embodiments described in the present disclosure.

DETAILED DESCRIPTION

[0047] The terms “semiconductor wafer,” “wafer,” “substrate,” “wafer substrate,” and “partially fabricated integrated circuit” are used interchangeably. One of ordinary skill in the art would understand that the term “partially fabricated integrated circuit” can refer to a semiconductor wafer during any of many stages of integrated circuit fabrication. A wafer or substrate used in the semiconductor device industry typically has a diameter of 200 mm, or 300 mm, or 450 mm. The following detailed description assumes the present disclosure is implemented on a wafer. However, the present disclosure is not so limited. The work piece may be of various shapes, sizes, and materials. In addition to semiconductor wafers, other work pieces that may take advantage of the present disclosure include various articles such as printed circuit boards and the like.

Introduction

[0048] Patterning of thin films in semiconductor processing is often an important step in the fabrication of semiconductors. Patterning involves lithography. In conventional photolithography, such as 193 nm photolithography, patterns are printed by emitting photons from a photon source onto a mask and printing the pattern onto a photosensitive photoresist, thereby causing a chemical reaction in the photoresist that, after development, removes certain portions of the photoresist to form the pattern.

[0049] Advanced technology nodes (as defined by the International Technology Roadmap for Semiconductors) include nodes 22 nm, 16 nm, and beyond. In the 16 nm node, for example, the width of a typical via or line in a Damascene structure is typically no greater than about 30 nm. Scaling of features on advanced semiconductor integrated circuits (ICs) and other devices is driving lithography to improve resolution.

[0050] EUV lithography can extend lithography technology by moving to smaller imaging source wavelengths than would be achievable with conventional photolithography methods. EUV light sources at approximately 10-20 nm, or 11-14 nm wavelength, for example 13.5 nm wavelength, can be used for leading-edge lithography tools, also referred to as scanners. The EUV radiation is strongly absorbed in a wide range of solid and fluid materials including quartz and water vapor, and so operates in a vacuum.

[0051] EUV lithography makes use of EUV resists that are patterned to form masks for use in etching underlying layers. EUV resists may be polymer-based chemically amplified resists (CARs) produced by liquid-based spin-on techniques. An alternative to CARs is directly photopatternable metal oxide-containing films, such as those available from Inpria, Corvallis, OR, and described, for example, in U.S. Patent Publication No. 2017/0102612, U.S. Patent Publication No. 2016/021660, and U.S. Patent Publication No. 2016/0116839, incorporated by reference herein at least for their disclosure of photopatternable metal oxide-containing films. Such films may be produced by spin-on techniques or dry vapor-deposited. The metal oxide-containing film can be patterned directly (i.e., without the use of a separate photoresist) by EUV exposure in a vacuum ambient providing sub-30 nm patterning resolution, for example as described in U.S. Patent 9,996,004, issued June 12, 2018 and titled “EUV PHOTOPATTERNING OF VAPOR- DEPOSITED METAL OXIDE-CONTAINING HARDMASKS,” and/or in International Patent Application No. PCT/US2019/31618, filed May 9, 2019, and titled “METHODS FOR MAKING EUV PATTERNABLE HARD MASKS,” the disclosures of which at least relating to the composition, deposition, and patterning of directly photopatternable metal oxide films to form EUV resist masks is incorporated by reference herein. Generally, the patterning involves exposure of the EUV resist with EUV radiation to form a photo pattern in the resist, followed by development to remove a portion of the resist according to the photo pattern to form the mask.

[0052] Directly photopatternable EUV resists may be composed of or contain metals and/or metal oxides mixed within organic components. The metals/metal oxides are highly promising in that they can enhance the EUV photon adsorption and generate secondary electrons and/or show increased etch selectivity to an underlying film stack and device layers.

[0053] To meet the requirements and demands of low dose-to-size (DtS) in photolithography, metal-containing or metal oxide-containing resists show promise due to its high absorptivity under EUV radiation compared to conventional chemically amplified resists. Metal oxide-containing resists exhibit high exposure latitude, maintains a stable pattern down to even a half pitch of 16 nm and below, eliminates the need for solvents, demonstrates enhanced stability, demonstrates suitability for high-volume manufacturing, and offers environmental benefits.

[0054] In some embodiments, metal oxide-containing resists are often utilized as a negative- tone-development (NTD) resist. With negative-tone-development resist, the less exposed regions are selectively removed while the more exposed regions are retained after development. Metal oxide-containing resists as negative-tone-development resist typically undergo greater shrinkage and deformation during an EUV exposure step and post-exposure bake (PEB) step compared to positive-tone-development resist. Such deformation and associated stress can potentially lead to increased defectivity in the resist mask following development, in certain 2D geometry. However, there is limited understanding of the mechanical deformation and stress, and their correlation with defect generation.

[0055] The present disclosure relates to a mechanical simulation designed for stress and deformation calculations in a resist such as a metal oxide-containing resist. Stress and deformation in the resist may occur after an exposure step and/or after a post-exposure bake step prior to development. In some implementations, the mechanical simulation utilizes the results of the stress and deformation calculations prior to development, along with the geometry change during the development, to determine a stress and deformation in the resist after development. The resulting stress and deformation in the resist after development can be utilized for the detection of weak points in the resist and for correlating defects. The mechanical simulation provides a comprehensive understanding of the mechanical response of the resist, such as the negative-tone- development resist. That way, the mechanical response can be correlated with defects in the resist after development and aids in the optimization of the photolithographic process and mask design.

[0056] Figure 1 presents a flow diagram of an example patterning process flow involving an EUV resist according to some implementations. Though the patterning process flow relates to an EUV-sensitive resist in Figure 1 , it will be understood that the mechanical simulation of the present disclosure is not limited to an EUV resist. The EUV resist is a resist that is sensitive to EUV radiation. The operations of a process flow 100 may be performed in different orders and/or with different, fewer, or additional operations. In some implementations, the operations of the process flow 100 may be implemented, at least in part, according to software stored in one or more non- transitory computer readable media.

[0057] The process flow 100 for patterning an EUV resist is performed on a substrate such as a semiconductor substrate. In some embodiments, the substrate is or includes a partially fabricated semiconductor device film stack. At block 104 of the process flow 100, an underlayer may be deposited on the substrate. In some embodiments, the underlayer may be deposited over a hard mask such as an ashable hard mark (AHM). The underlayer is configured to increase adhesion between the subsequently-formed EUV resist and the substrate. The underlayer is also configured to reduce EUV dose for effective EUV exposure of the EUV resist. The underlayer may include a vapor-deposited film of hydronated carbon doped with a non-carbon heteroatom such as oxygen (O), silicon (Si), nitrogen (N), tungsten (W), boron (B), iodine (I), chlorine (Cl), or a combination thereof. For example, an underlayer comprising a hydronated carbon film doped with iodine may improve generation of secondary electrons in the EUV resist upon exposure to EUV radiation. The underlayer may have a thickness equal to or less than about 25 nm, such as a thickness between about 2 nm and about 20 nm. In some implementations, the underlayer may be deposited using a vapor deposition technique such as PECVD or ALD.

[0058] At block 106 of the process flow 100, an EUV resist is deposited. The EUV resist may be deposited on the underlayer. Deposition of the EUV resist may be a dry deposition process such as a vapor deposition process or a wet process such as a spin-on deposition process. EUV lithography makes use of EUV resists, which may be metal oxide-based resists produced by dry vapor-deposited techniques. In some cases, the EUV resist may be a metal-containing EUV resist. The EUV resist may be an EUV-sensitive film, where the EUV-sensitive film can include one or more ligands (e.g., EUV labile ligands) that can be removed, cleaved, or cross-linked by radiation (e.g., EUV radiation). Accordingly, the EUV-sensitive film itself can be altered by exposure to such radiation. In some implementations, the EUV resist includes an organometallic material or metal-oxide-containing material. The EUV resist comprises a metal that can have a high patterning radiation absorption (e.g., an EUV absorption cross-section that is equal to or greater than IxlO⁷ cm²/mol). In some implementations, the metal is selected from a group consisting of tin (Sn), bismuth (Bi), tellurium (Te), cesium (Cs), antimony (Sb), indium (In), molybdenum (Mo), hafnium (Hf), iodine (I), zirconium (Zr), iron (Fe), cobalt (Co), nickel, (Ni), copper (Cu), zinc (Zn), silver (Ag), platinum (Pt), germanium (Ge), and lead (Pb). For example, the metal includes tin. As such, the EUV resist may include organotin oxide in some implementations.

[0059] Though not shown in the process flow 100, an optional cleaning process is performed to clean a backside and bevel edge of the substrate. This can be performed after deposition of the EUV resist and prior to EUV exposure. The backside and bevel edge clean may remove unintended deposits of the EUV resist from the backside and bevel edge of the substrate. The backside and bevel edge clean may be accomplished using wet cleaning techniques or dry cleaning techniques, or in combination with one another.

[0060] Though not shown in the process flow 100, an optional post-application bake (PAB) may be performed after deposition of the EUV resist and prior to EUV exposure. The PAB treatment may involve a combination of thermal treatment, chemical exposure, and moisture to increase the EUV sensitivity of the EUV resist, which can reduce the EUV dose to develop a pattern.

[0061] At block 108 of the process flow 100, the EUV resist is exposed to EUV radiation. Exposure to EUV radiation forms a photo pattern in the EUV resist. In some embodiments, EUV exposure may occur at doses ranging from about 10 mJ/cm² to about 100 mJ/cm². Generally speaking, EUV exposure causes a change in the chemical composition and cross-linking in the EUV resist, creating a contrast in latent image that can be exploited for subsequent development. The EUV resist may be photo patterned by exposing a region to EUV light, typically under relatively high vacuum. More exposed areas of the EUV resist are created through EUV photo patterning that have altered physical or chemical properties relative to less exposed areas. The difference in properties between more exposed and less exposed areas may be exploited in subsequent processing.

[0062] At block 110 of the process flow 100, the EUV resist is exposed to a post-exposure bake (PEB). The PEB treatment may further increase contrast in etch selectivity of the EUV resist after photo patterning by EUV exposure. During PEB, the EUV resist is thermally treated in the presence of various chemical species to facilitate cross-linking in the more EUV-exposed regions of the EUV resist. The PEB treatment temperature may be controlled to further increase etch contrast in the EUV resist, where the PEB treatment temperature may be between about 100°C and about 300°C, such as between about 170°C and about 290°C. The bake ambient may be controlled to further increase etch contrast in the EUV resist, where the bake ambient may control pressure as well as introduction of reactive gases such as air, H2O, H2O2, CO2, CO, O2, O3, CH4, CH3OH, N2, H2, NH3, N2O, NO, alcohol, acetyl acetone, formic acid, Ar, He, or their mixtures. The PEB treatment can be designed to drive evaporation of organic fragments that are generated during EUV exposure, oxidize the metal hydride species into metal hydroxide, and facilitate crosslinking between neighboring -OH groups and form a cross-linked metal oxide network.

[0063] At block 112 of the process flow 100, the EUV resist is developed to form a resist mask. In various embodiments, the more exposed regions are removed (positive tone) or the less exposed regions are removed (negative tone). For instance, development may involve selective removal of less exposed regions of the EUV resist relative to more exposed regions of the EUV resist. Development may be performed using wet or dry processes. A wet development process exposes the EUV resist to a solvent for selective removal of portions of the EUV resist. A dry development process exposes the EUV to an etch gas for selective removal of portions of the EUV resist. The dry development process may include a thermal (plasma- free) dry development process, a plasma dry development process, or a combination of a thermal dry development process and a plasma dry development process. In some embodiments, the etch gas can include a halide such as a hydrogen halide. Accordingly, development chemistries may include but are not limited to a halide-containing gas includes a hydrogen halide (e.g., HBr, HC1, etc.), hydrogen and halogen gas (e.g., H2 and CI2, H2 and Br2, etc.), boron trichloride, an organic halide, an acyl halide, a carbonyl halide, a thionyl halide, or mixtures thereof. An organic halide can include but is not limited to C_xHyF_z, CxHyClz, C_xHyBr_z, and C_xHyI_z, where x, y, and z are values equal to or greater than 0. An acyl halide can include but is not limited to CH3COF, CH3COCI, CHsCOBr, and CH3COI. A carbonyl halide can include but is not limited to COF2, COCI2, COBn, and COI2. A thionyl halide can include but is not limited to SOF2, SOCI2, SoBr2, and SOI2. In some embodiments, the etch gas may be flowed with or without inert/carrier gas such as He, Ne, Ar, Xe, and N2. In some embodiments, the dry development can involve a thermal process, a plasma process, or a combination of a thermal process and a plasma process. Parameters such as chamber pressure, gas flow rates, substrate temperature, and duration of exposure may be tuned. In some embodiments, a chamber pressure may be between about 20 mTorr and about 1000 mTorr. In some alternative embodiments, a chamber pressure may be between about 50 Torr and about 760 Torr. In some embodiments, a substrate temperature may be between about -60°C and about 300°C. In some embodiments where plasma is applied, the RF levels may be tuned at RF power levels equal to or less than about 1000 W. Selection of the development method along with optimization of the development parameters may influence development selectivity, roughness, descumming, and other characteristics of development.

[0064] Though not shown in the process flow 100, a post-development treatment may be performed after development and prior to pattern transfer etching. The treatment may be a thermal treatment, plasma treatment, chemical treatment, selective deposition treatment, or a combination of the aforementioned treatments. Thermal treatment may expose the resist mask to an elevated temperature reduce detectivity and LWR. Plasma treatment may expose the resist mask to plasma such as a direct (jn-situ) plasma or remote plasma in order to densify the resist mask, reduce LWR, and/or clear open area scum in a descumming process. Chemical treatment may expose the resist mask to reactive chemical species such as halide-based species to improve etch resistance, reduce outgassing, and increase line CD. Selective deposition treatment may expose the resist mask to chemical precursors for selectively depositing a protective coating on the resist mask to reduce DtS, improve etch resistance, reduce outgassing, and increase line CD. Any one or more of the foregoing treatments are applied to the resist mask after development to improve the performance of the resist mask during pattern transfer.

[0065] At block 114 of the process flow 100, pattern transfer is performed using the resist mask. During pattern transfer, one or more substrate layers are etched using the resist mask for pattern transfer. Such substrate layers are underlying the resist mask and may be removable by lithographic etching. Pattern transfer etching may etch materials to a desired depth to form a plurality of patterned features. In some embodiments, the one or more substrate layers include the hard mask and the underlayer. Any defects, roughness, or variations in CD in the resist mask are replicated in the material(s) being patterned during pattern transfer etching.

[0066] The process flow 100 illustrates some of the many steps that are performed in an example EUV photolithography workflow. After deposition of an EUV resist, the EUV photolithography workflow can typically proceed with EUV exposure, bake, and development prior to pattern transfer. Each of the many steps in the EUV photolithography workflow can be performed using different photoresist materials, different techniques (e.g., wet or dry), and different conditions (e.g., bake conditions, development chemistries, EUV dose, etc.). And variations in photoresist materials, techniques, and/or conditions can affect patterning outcomes such as CD, LWR, LER, DtS, and defects in the patterned resist mask.

[0067] With all these different steps and parameters that can be tuned, it can be particularly cumbersome and time-consuming to optimize an EUV photolithography process to achieve desired patterning outcomes. Extensive experimentation is required and time-intensive evaluations are needed to determine optimal parameters, materials, and processes for an EUV photolithography process. Performing such physical experiments to evaluate processes and materials can take weeks to months to achieve one cycle of learning. This lengthy process flow and evaluation flow is not only highly complex, but also time-consuming and cost-prohibitive.

[0068] Recent advances in EUV photolithography technology have necessitated resist materials with higher absorptivity and quantum efficiency as technology nodes scale to smaller feature sizes. Metal-containing EUV resists such as metal oxide-containing EUV resists are potential candidates to replace polymer-based chemically amplified resists for EUV lithography because of their higher absorptivity and quantum efficiency. However, a mechanistic understanding of the mechanical behaviors and interactions of metal oxide-containing EUV resists with respect to process and pattern geometry is scant. It is important to ascertain a mechanistic understanding of the behaviors and interactions of metal oxide-containing EUV resist. Specifically, it is important to ascertain a mechanistic understanding of defect generation in the resist and its correlation to mechanical responses taking place during various photolithography steps and patterning geometry. This understanding facilitates construction of computational methods and models that simulate patterned deformation and stress accumulation so that simulation results can be related and validated by experimental observation.

Mechanical Simulation For Post-Development Stress and Deformation Calculations

[0069] The photolithography process is a highly complex process. A resist (e.g., metal-oxide- containing EUV resist) undergoes a series of transformations and changes at each step of the EUV photolithography process. A resist material may have a certain absorption coefficient, which can affect how it responds to different exposures and different bake conditions. A resist material may have a certain thickness or density, which can influence its response to exposure (e.g., EUV exposure) and bake. Changes in the bake conditions can result in different patterning outcomes. Changes in a development chemistry or a development method can lead to changes in patterning outcomes. Changes in dose can lead to different development behaviors that result in different patterning performances. All this to say that variations in photons, materials, and processes can influence a patterning performance of a photolithography process.

[0070] Feature degradation and defects such as break defects are observed in resist masks after development. Such resist masks may exhibit unexpected geometry after development. The defects in the resist masks may be correlated to mechanical responses of the resist following various photolithography steps, including but not limited to exposure, post-exposure bake, and development. Mechanical responses of the resist are often observed as stress and deformation (e.g., shrinkage), and may be more pronounced in negative-tone-development resist such as metal oxide-containing negative-tone-development resist, with specific patterning geometries.

[0071] From a simulation perspective, current commercial software modules may be limited to modeling deformation only, which is unable to provide a complete implication to defects in a resist. Inputs into these modules remain constant under a fixed process operating condition. From an experimental perspective, process engineers are required to evaluate processes and film materials through patterning defectivity tests. The preparation of each test vehicle, the photolithographic process, and metrology, and the re-optimization of process and geometry, can take months to even complete one learning cycle.

[0072] A mechanical simulation of the present disclosure may calculate an initial strain in the resist after exposure and post-exposure bake, and may calculate a final stress and deformation in the resist after development. In some implementations, the mechanical simulation may be a static mechanical simulation for determining pre-development stress and strain in the resist and determining post-development stress and strain in the resist, whereby the post-development stress and strain are determined using the pre-development stress, strain, and developed geometry as input. The calculated post-development stress and deformation in the resist may be correlated with defects in the resist.

[0073] Figure 2 presents a flow diagram of an example method of determining stress and deformation in a resist film after development according to some implementations. The operations of a process 200 may be performed in different orders and/or with different, fewer, or additional operations. One or more operations of the process 200 may be implemented in accordance with any of the techniques, simulations, or models described in the present disclosure. In some implementations, the operations of the process 200 may be implemented, at least in part, according to software stored in one or more non-transitory computer readable media. An example of a system implementing software stored in one or more non-transitory computer readable media is described in Figure 14.

[0074] At block 210 of the process 200, experimental data sets are received as inputs in a mechanical simulation regarding exposure and post-exposure bake (PEB) performed on a resist. The mechanical simulation of the present disclosure can be a predictive model or simulation workflow that is able to receive inputs and generate predicted outputs regarding stress and deformation in a resist after development. Optionally, the mechanical simulation can determine defects in the resist after development and its relationship to process details such as exposure and PEB process conditions. The resist may be dry or wet deposited on a substrate. In some embodiments, the resist is a metal oxide-containing resist such as an organotin oxide resist. The metal oxide-containing resist may be an EUV-sensitive metal oxide-containing resist. In some embodiments, the resist is a negative-tone-development resist, or metal oxide-containing negative- tone-development resist.

[0075] The resist on the substrate may undergo various photolithographic operations prior to development. In some embodiments, the resist undergoes exposure such as EUV exposure to become a photopatterned resist. The photopattemed resist comprises more exposed and less exposed regions after exposure to radiation, where more exposed regions may also be referred to as exposed (e.g., EUV-exposed) regions and less exposed regions may also be referred to as unexposed (e.g., EUV-unexposed) regions. For example, at an EUV module or scanner, the resist is exposed to EUV light to cause photo patterning, thereby forming more EUV-exposed regions and less EUV-exposed regions. The exposure step may cause ligand cleavage and cross-linking in the more exposed regions of the resist relative to the less exposed regions. This may cause initial strain in the resist prior to development. Furthermore, stress and deformation may occur in the resist following the exposure step.

[0076] Inputs received by the mechanical simulation may include experimental data sets corresponding to exposure-related data. Exposure-related data may include but are not limited to dose (e.g., EUV dose) and aerial image of the photoresist from exposure. An aerial image may include a planar intensity distribution of incoming light that the substrate observes. It may be calculated by a rigorous lithography simulator such as HyperLith™ or PROLITH™, considering the light source, mask pattern, mask stack material, and focus, among other possible effects. Exposure-related data may also include data related to a material of the photoresist, which may include but is not limited to an absorption coefficient of the photoresist, an external quantum efficiency of the photoresist, a cluster size of the photoresist, a density of the photoresist, and a thickness of the photoresist. By way of illustration, higher EUV doses can lead to greater amounts of removal of ligand (R) groups and greater amounts of cross-linking.

[0077] Figure 3A presents a graph showing a 2D line/space (L/S) example of fraction of light absorbed by a photoresist film as a function of an x-direction of the photoresist film during an exposure step. The mechanical simulation can receive exposure data as input. In some cases, the exposure data can take the form of an aerial image, which shows an amount of light absorbed by the photoresist film across the photoresist film. The photoresist film is exposed to light to cause photo patterning and form more exposed areas and less exposed areas. Photons of the light (e.g., EUV light) are absorbed by the photoresist film, but photon absorption by the photoresist film is not necessarily evenly distributed across the photoresist film. Photon absorption can depend on a variety of factors, such as the absorption coefficient of the photoresist film, the density of the photoresist film, and the dose. An amount of photon absorption in the photoresist film may vary along the thickness of the film and along the plane of the film. As shown in Figure 3A, the amount of photon absorption is lowest at the center of the space, and highest in the center of the lines of the photoresist film. The amount of photon absorption gradually decreases closer to the boundaries between the line and the trench of the photoresist film. The aerial image in Figure 3 A shows a 1- dimensional distribution of light absorption in the photoresist film. The absorbed light distribution shown in Figure 3A shows the impact of light distribution along the x-direction. A general aerial image shows the impact of light distribution along both the x-direction and the y-direction. Thus, the experimental data sets received by the mechanical simulation may include an aerial image of the resist, where the aerial image of the resist may show a planar intensity distribution of incoming light observed by the resist. The exposure data may be used to calculate volume loss in the photoresist film after exposure.

[0078] The resist on the substrate may undergo additional photolithographic operations prior to development such as bake. In some embodiments, the resist undergoes post-exposure bake to further improve etch contrast. The post-exposure bake step may be performed after exposure and prior to development. The post-exposure bake step may cause more ligand cleavage and crosslinking. This may accentuate initial strain in the resist prior to development. Stress and deformation may also occur in the resist following the post-exposure bake step.

[0079] Inputs received by the mechanical simulation may include experimental data sets corresponding to PEB-related data. PEB-related data may include but are not limited to bake temperature, pressure, gas species, flow rates of gas species, and duration of exposure, among other bake-related conditions. By way of an example, higher bake temperatures and/or longer bake times can lead to greater amounts of removal of ligand (R) groups and greater amounts of cross-linking. PEB-related data may also include data related to a material of the photoresist, which may include but is not limited to a cluster size of the photoresist, a density of the photoresist, and a thickness of the photoresist. PEB-related data and exposure-related data may be accounted for to calculate pre-development data. Pre-development data may include volume loss observed in the photoresist film after exposure and post-exposure bake. That way, an amount of volume remaining across the photoresist film can be calculated after exposure and post-exposure bake.

[0080] Figure 3B presents a graph showing a blanket volume loss percentage (%) as a result of performing a post-exposure bake step on a photoresist film as a function of dose. During a bake step such as a post-exposure bake step, volume losses may occur in the photoresist film. As the dose increases, volume loss in the photoresist film increases. In some embodiments, as the dose increases, the volume loss in the photoresist film increases linearly or substantially linearly. The volume loss may be attributable to ligand cleavage and cross-linking in the photoresist film as a result of the exposure and post-exposure bake steps. For instance, shrinkage may occur predominantly in the more exposed (line) regions of the photoresist film, leading to volume loss in the photoresist film. Accordingly, the experimental data sets received by the mechanical simulation may include data associated with volume losses in the photoresist film prior to development.

[0081] Figure 3C presents a graph showing the 2D illustration of the corresponding amount of volume remaining in the photoresist film as a function of an x-direction of the resist film after the exposure step and the post-exposure bake step. Accounting for the aerial image in Figure 3A and the blanket volume loss after exposure and post-exposure bake in Figure 3B, an amount of volume remaining in the photoresist film can be calculated across the photoresist film. The mechanical simulation can calculate volume loss or volume remaining across the photoresist film. In some embodiments, such calculations can be based at least in part on an aerial image of the photoresist film indicative of the planar intensity distribution of light absorbed by the photoresist film following exposure and based at least in part on a blanket volume loss of the photoresist film following a post-exposure bake. Hence, the experimental data sets received by the mechanical simulation may include data associated with volume remaining in the photoresist film prior to development.

[0082] The process conditions in the experimental data sets may be utilized to determine an initial strain in the resist film after exposure and post-exposure bake, and may ultimately be evaluated to determine their impact on final stress and deformation. The process conditions in the experimental data sets may be varied to determine how process condition variations can impact the final stress and deformation in the resist film. The process conditions may also be evaluated to determine their impact on defect(s) generated in the resist film after development.

[0083] Returning to Figure 2, at block 220 of the process 200, an initial strain in the resist is determined using the mechanical simulation based at least in part on the experimental data sets. Strain is a measure of deformation in a material under the influence of an external force. Strain (e) can be calculated as a fractional or percentage change in length or other dimension. An initial strain can be determined based on initial deformation or local shrinkage in the resist prior to development. After the resist film undergoes exposure and post-exposure bake steps, ligand (R) cleavage and cross-linking occur that result in volume losses in the resist film. These volume losses create a differential initial strain in the resist film. In some embodiments, the initial strain in the resist film can be calculated using finite element analysis. In some embodiments, the mechanical simulation can determine both an initial strain and stress in the resist prior to development. [0084] A resist can be composed of several photoresist units. In some embodiments, the photoresist unit can include an organometal-oxy cage that includes metal atoms (M) and oxygen atoms (O), which form a network of M-O-M bonds. The metal atom can include but is not limited to indium, tin, bismuth, antimony, tellurium, hafnium, or zirconium. In some embodiments, the metal atom is tin. Tin itself can have different oxidation states. In particular embodiments, the metal atom is tin(II). In other embodiments, the metal atom is tin(IV). Attached to the metal atoms are ligands (R), which are responsive to radiation exposure. The ligands (R) can be removed, cleaved, or cross-linked by exposure to radiation. The ligands (R) are formed on the perimeter of the organometal-oxy cage. By way of an example, each R can be independently, H, halo, optionally substituted alkyl, optionally substituted cycloalkyl, optionally substituted cycloalkenyl, optionally substituted alkenyl, optionally substituted alkynyl, optionally substituted alkoxy (e.g., -OR¹, in which R¹ can be optionally substituted alkyl), optionally substituted alkanoyloxy, optionally substituted aryl, optionally substituted amino, optionally substituted bis(trialkylsilyl)amino, optionally substituted trialkylsilyl, oxo, an anionic ligand (e.g., oxido, chloride, hydrido, acetate, iminodiacetate, propanoate, butanoate, benzoate, etc.), a neutral ligand, or a multidentate ligand. The ligands (R) can surround the metal-oxy (e.g., Sn-O) cage made of M-O-M bonds.

[0085] Figure 4 presents an example reaction pattern between photoresist units according to some implementations. Metal-based precursors such as tin-based precursors may be surrounded by ligands (R). The ligands (R) on the perimeter of the organometal-oxy cage can be removable to enable cross-linking between photoresist unit clusters. Such cross-linking can take place during the course of exposure (e.g., EUV exposure) and/or bake (e.g., PEB). As individual photoresist units interact at a molecular level during exposure and bake operations, the photoresist units may undergo chemical reactions. The reaction mechanism in Figure 4 show that individual photoresist units may undergo cross-linking to create a network that is resistant to development. Furthermore, the reaction mechanism in Figure 4 shows that individual photoresist units may undergo ligand (R) cleavage. Ligand cleavage and cross-linking may occur at the molecular level during exposure steps and/or bake steps. Without being limited by any theory, the R-groups are cleaved and the elimination of ligands (R) leave an increased number of cross-linking points. In the presence of moisture and/or oxygen-containing counter-reactant, metal-hydroxyl (M-OH) bonds or metal- oxygen-metal (M-O-M) bonds form at the cross-linking points, where the metal-hydroxyl (M-OH) bonds may participate in further reactions to form metal-oxygen-metal (M-O-M) bonds. Crosslinking and ligand cleavage as a result of exposure may lead to volume losses and differential initial strain in the photoresist film. [0086] Figure 5A shows a cross-sectional schematic illustration of an example resist film showing initial strain, and deformation and stress as a result of the initial strain, in the resist film prior to development. The resist film prior to development may undergo exposure (e.g., EUV exposure) and bake (e.g., PEB) operations. The exposure and bake operations cause ligand cleavage and cross-linking within the resist film. As shown in Figure 5A, the resist film may be divided into “line” regions and “space” regions, where the line regions represent more exposed regions after photopatterning that will resist development in a negative-tone-development resist, and the space regions represent less exposed regions after photopatterning that will be removed upon development in the negative-tone-development resist. The center of the resist film in the cross-sectional illustration represents the space regions and the right and left sides of the resist film in the cross-sectional illustration represent the line regions.

[0087] Ligand cleavage and cross-linking within the resist film can result in several effects. Ligand cleavage and cross-linking cause internal strain because material is lost. As shown in Figure 5A, strain in the resist film can be represented by four arrows pointing to each other. The initial strain is more significant in the line regions of the resist film than the space regions of the resist film. This creates a differential initial strain in the resist film. Furthermore, stress occurs in the resist film before development. Without being limited by any theory, ligand cleavage creates empty space and photoresist unit clusters will pull together upon cross-linking. This pulling force is relaxed in the vertical direction, causing the resist film to change thickness (e.g., shrink) before development. As shown in Figure 5A, arrows pointing downwards show shrinkage in the thickness of the resist film. More shrinkage occurs in the line regions of the resist film than the space regions of the resist film. The vertical shrinkage is the height-direction manifestation of volume loss in the resist film prior to development. In addition, the differential initial strain also creates an asymmetric pulling force in the horizontal direction, which cannot be relaxed and causes residual stress to be accumulated in the resist film before development. As shown in Figure 5A, stress can be represented by horizontal arrows. The stress in the resist film following exposure and/or bake pulls the resist film from the space regions and pushes against the line regions. This stress does not immediately result in observable lateral shrinkage prior to development because the space region of the resist film has not been removed yet. However, the differential stress in the resist film will cause the resist film to have another mechanical response after development. The differential stress remains as residual stress mainly in the line regions or more exposed regions.

[0088] Figure 5B shows a cross-sectional schematic illustration of a 2D example resist film showing lateral shrinkage and stress in the resist film after development. Development selectively removes the space regions or less exposed regions relative to the line regions or more exposed regions, which makes the sidewall a new free surface. After development, the aggregated residual stress from the resist film creates pulling forces on local features. The pulling forces on local features lead to stress accumulation and feature deformation at the free surface. Lateral deformation may also be referred to as lateral shrinkage, which is another mechanical response of the resist film. As shown in Figure 5B, the final resist profile exhibits lateral shrinkage on the edges due to residual stress. Moreover, in some geometries, especially complex or two- dimensional designs, like tip-to-tip or more complicated industrial design, free surfaces are not created at all feature locations. As a result, the residual stress is not relaxed as lateral shrinkage, but accumulated in the local region instead.

[0089] As highlighted by Figure 5 A, the exposure and bake steps may cause initial strain, which is manifested as differential deformation and stress in the resist film prior to development. Volume loss or shrinkage may occur in a vertical direction as a result of exposure and bake, and stress may occur in a horizontal direction as a result of exposure and bake. As highlighted by Figure 5B, the development step may cause deformation to occur in the horizontal direction in the form of lateral shrinkage, and, in certain 2D geometries, stress may accumulate near the edges within the local features. Defects in the resist mask after patterning may be correlated to the mechanical responses of the resist following exposure, bake, and/or development.

[0090] Quantities such as initial strain, initial deformation, and initial stress in the resist film may be calculated prior to development in the mechanical simulation. Quantities such as final deformation and stress in the resist film may also be calculated after development in the mechanical simulation. In some embodiments, one or more of these quantities (post-development or pre-development) may be calculated using finite element analysis. Pre-development finite element analysis uses a non-developed geometry, and post-development finite element analysis uses a developed geometry. Finite element analysis provides a computerized method to model the effect of forces, vibrations, fluid flow, heat transfer, and other physical effects on an object. A typical area of interest to solve is structural analysis of an object to determine the object’ s behaviors under various real-world forces. Finite element analysis applies a numerical method for solving differential equations arising in engineering and mathematical modeling. To solve a problem, the numerical method in finite element analysis subdivides a large system into smaller, simpler parts referred to as finite elements. Details of applying finite element analysis to a resist film are discussed below.

[0091] Finite element analysis on the resist film may be applied using any suitable simulation software for simulation of physical systems and the interactions among them. For example, a suitable simulation software can include but is not limited to COSMOL Multiphysics®, which is a finite element analyzer, solver, and simulation software package for various physics and engineering applications.

[0092] An initial step in finite element analysis may include constructing a geometry. The geometry may reflect the relevant object or portions thereof to be modeled in a physical system. The constructed geometry may not necessarily include all the details of the object to save time and resources for meshing. Figure 6A shows an example geometric representation of a resist film in a finite element analysis. This is a top-down view of the post-developed simulation geometry. In some examples, this could serve as a second step in a multi-step (e.g., 2-step) static mechanical simulation. The geometry of the resist film shows the geometry of interest for modeling. The actual simulation geometry is a 3D rendering of the resist profile. In Figure 6A, the geometry of interest is a line-end geometry, where the grey regions represent the resist film and the white regions represent empty space. It will be understood that the geometry can be based on an original geometry design file or from a resist pattern simulation. It will also be understood that in a multi- step static mechanical simulation, where the mechanical simulation can implement at least two analysis steps or components, different geometries that represent the pre-developed resist film and the post-developed resist film are needed separately.

[0093] Another step in finite element analysis may include meshing. Meshing divides the geometry of interest into finite elements so that relevant physics representations and equations may be applied to each element. Meshing dissects the constructed geometry into smaller geometries. A mesh includes many elements that are connected by nodes, where nodes are coordinate locations in space that can vary by element type. Nodes represent the shape of the geometry. Finite element analyzers generally do not work with irregular shapes, but can readily operate with common shapes like cubes. Thus, meshing turns irregular geometries into recognizable shapes referred to as “elements.” Figure 6B shows an example mesh for the geometric representation of the resist film in the finite element analysis. Common types of meshing can include tetrahedral element meshing, hexahedral element meshing, or a hybrid of tetrahedral and hexahedral element meshing. In Figure 6B, a mesh is made of the constructed geometry using an automatic tetrahedral element meshing with physics-based resolution control. The mesh in Figure 6B can be converted for numerical calculations.

[0094] Another step in finite element analysis may include defining the physics and real-world conditions to be applied in the model. These physics and real- world conditions are applied to the geometric representation, on the boundary and bulk of the geometry. Figure 6C shows an example step of inputting physics and real-world conditions to pre-development simulations or post- development simulations. The initial strain can be inputted for pre-development simulations. The initial strain may be calculated and obtained from the experimental data sets as discussed earlier herein. The initial strain in the resist film may be computed based on ligand cleavage/removal and cross-linking that takes place in the resist film. The stress and displacement results from the predevelopment simulation can be inputted for post-development simulations. The pre-development or post-development simulations can be applied with finite element analysis with certain boundary conditions. For instance, some boundary conditions may specify a free surface, where the surface is freely deformable such as a sidewall or top surface of a resist film, and some boundary conditions may specify a fixed surface, where the surface cannot have deformation such as a bottom of the resist film interfacing with a substrate surface.

[0095] Another step in finite element analysis is to make calculations for every single element among the finite elements. The individual results are communicated and combined to provide a final result of the structure. Partial differential equations or governing equations are solved for each element to help predict the behavior of each element. Since the elements share nodes, the equations that solve them are linked together. Figure 6D shows an example step of solving governing equations in each node or element and communicating between nodes and elements, iterating results until a converged solution is reached. Here, one of the governing equations can include Hooke’s Law (F = -kx), where x represents a displacement and k represents a stiffness constant and F represents force. Stress (o) can be calculated as force per unit area: o = F/A. Strain (a) can be calculated as displacement over length: a = 5/L. Knowing the initial strain or displacement, and other film property and conditions, the model using the finite element analyzer can calculate quantities such as force in each element. The model can solve governing equations in each of the nodes or elements based on the initial conditions, and the result can be iterated until a converged simulation provides a balanced stress, deformation, or strain output. The solver can be a static solver, which solves the steady-state equilibrium solution, or a transient solver, which solves for the solution through time evolution.

[0096] Returning to Figure 2, at block 230 of the process 200, stress and deformation in the resist are determined using the mechanical simulation based at least in part on the initial strain and pattern geometry of the resist. The mechanical simulation can be a static multi-step mechanical simulation workflow. In a first step, the mechanical simulation can take an initial strain input and determine the balanced stress and deformation in the resist prior to development using the experimental data sets associated with exposure and post-exposure bake. This provides predevelopment results. In another step, the mechanical simulation can determine balanced stress and deformation in the resist after development. This step can determine the final stress and deformation using the pre-development results and pre-developed geometry as input. Thus, the mechanical simulation can simulate patterned deformation and stress accumulation for various geometry. The simulated results can be related to experimental observations and actual experimental defectivity data.

[0097] Quantities such as a final stress and deformation in the resist film may be calculated after development in the mechanical simulation. In some embodiments, one or more of these quantities may be calculated using finite element analysis. The finite element analysis and method is discussed above. Finite element analysis may be applied to a constructed geometry of a resist film prior to development. Finite element analysis may be applied to a constructed geometry of the resist film after development. The constructed geometry after development is different from the constructed geometry prior to development. In some embodiments of a negative-tone- development resist, the less exposed areas of the resist film are removed and the more exposed areas are retained after development. In some embodiments, stress and deformation calculated in the resist film prior to development may be applied as input in the finite element analysis for the resist film after development. A relationship between volume losses of the resist film after exposure and post-exposure bake (prior to development) may be determined with lateral shrinkage and thickness loss in the resist film after development.

[0098] At block 240 of the process 200, the stress and deformation in the resist are correlated with one or more defects in the resist after development. The mechanical simulation establishes a relationship between the mechanical responses of the resist as a result of exposure and postexposure bake steps to the final stress and deformation in the resist after development. Thus, the mechanical responses of the resist as a result of exposure and post-exposure bake steps can be correlated with the one or more defects in the resist after development. In some embodiments, defects may include but are not limited to line necking and line break defects. In some embodiments, other defects may include pinhole defects and bridge defects. Such defects may be attributed to the exposure conditions and/or bake conditions performed on the resist. Process optimizations and photomask improvement can be designed according to the specific learning from the aforementioned mechanical simulation strategy.

[0099] Depending on the problem statement that a user is trying to solve, the mechanical simulation of the present disclosure can be applied to a number of different situations. The mechanical simulation can produce insights and specific learnings for each situation and problem statement. That way, defects and problems that a user is observing in a resist film after development can be correlated to the geometries, exposure conditions, and post-exposure bake conditions. Some example problem statements are discussed below. Pillar spider web displacement problem

[0100] Local features in a resist can be depicted as pillars. In some cases, the pillars may be connected by “spider webs” that extend between adjacent pillars. Such “spider webs” may arise from development as scum that cannot be removed after a development process. For instance, a thermal dry development may remove most of the less exposed regions while retaining the more exposed regions as pillars. However, residue or scum can accumulate near the bottom that the thermal dry development was unable to remove. It was observed that unusual pillar deformations occur so that the pillars are tilted and are not centered in the region that they are printed. The mechanical simulation of the present disclosure can be applied to understand why this is occurring. In other words, the root cause of the pillar displacement defect can be understood using a qualitative static mechanical simulation of the present disclosure.

[0101] Figure 7A shows a cross-sectional schematic illustration of an example resist film after development, where the resist film comprises two features connected by a “spider web” of residual scum. The resist film 700 comprises two features or pillars 710 formed on an underlayer 720. The resist film 700 further comprises scum or spider-web 730 between the two pillars 710, where the spider-web 730 is connected to the adjacent pillars 710. In the mechanical simulation, a uniform initial strain 740 is applied to the resist film 700. The uniform initial strain can be determined from the resist shrinkage or volume loss after exposure and post-exposure bake steps, which is manifested after development.

[0102] Figure 7B shows a cross-sectional schematic illustration of a resist film after development showing asymmetric shrinkage and displacement from its original location, when the resist film is connected by a “spider web.” Upon application of the uniform initial strain to the resist film 700, the mechanical simulation can model effects of deformation after development. The mechanical simulation shows the simulated patterned resist film 750. The simulated patterned resist film 750 shows an asymmetric displacement and shrinkage response. Each of the pillars in the simulated patterned resist film 750 exhibits asymmetric shrinkage towards a space region where the spider-web 730 exists. The pillars in the simulated patterned resist film 750 are tilted and displaced from its original location.

[0103] Figure 7C shows a cross-sectional schematic illustration of a resist film after development showing symmetric shrinkage, when the resist film is not connected by any “spider web.” The mechanical simulation shows the simulated patterned resist film 760. The simulated patterned resist film 760 shows a symmetric shrinkage response. This can be compared to the asymmetric shrinkage response in the simulated patterned resist film 750 in Figure 7B that can be attributed to the presence of scum or spider-web 730. The critical dimension (CD) in both cases of Figure 7B and 7C do not change. However, the center point or centroid of the pillar shifts in the simulated patterned resist film 750 of Figure 7B compared to the simulated patterned resist film 760 of Figure 7C. Put another way, there is a displacement change in the pillars as a result of the presence of spider-web 730. Without being limited by any theory, the mechanical simulation can provide insight that a collateral force is exerted due to the presence of the spider-web 730 that causes the pillars 710 to shift towards a space region while the CD of the pillars remains the same. Such phenomenon is related to deteriorate CDU (critical dimension uniformity) and potential defectivity upon pattern transfer.

2-D asymmetric feature weak point

[0104] In this case, a resist film is shown with a general inverse tip geometry. The resist film is shown after development. It was observed in the general inverse tip geometry that break defects occur at locations near the tip. This was also observed similarly in resist films with a line end geometry. The location near the tip is observed as a high probability point for failure. The mechanical simulation of the present disclosure can be applied to understand why this is occurring. Specifically, a static mechanical simulation can be applied on the post-developed geometry of the resist film to understand the feature break defects that occur in the resist film with an inverse tip geometry or line end geometry.

[0105] Figure 8A shows a top-down view of the geometric representation of a resist film with an inverse tip geometry after development. The resist film 800 is shown after development and comprises mask regions 810 and space regions 820. The space regions 820 are designed as alternating staggered lines placed across the resist film 800. Three space regions 820 extend from a first side and three space regions 820 extend from a second side opposite the first side. Tips of the space regions 820 from the first side extend past tips of the space regions 820 from the second side, where such a distance (in a vertical direction between tips) may be labeled as D. A lateral distance between adjacent tips may be labeled L. In some embodiments, D may be the same or substantially similar as L. In the mechanical simulation, an initial strain may be applied to the resist film 800. The initial strain may be assumed to be the same throughout the resist film, where the initial strain may be determined from the resist shrinkage or volume loss after exposure and post-exposure bake.

[0106] Figure 8B shows a deformation on geometry and stress distribution in the geometric representation of the resist film with the inverse tip geometry after development. Figure 8C shows a magnified view of the deformation on geometry and stress distribution in the geometric representation of the resist film with the connector geometry after development. Upon application of the uniform initial strain to the resist film 800, the mechanical simulation can model effects of deformation and stress after development. This may be illustrated by a stress distribution map on the deformed geometry. The mechanical simulation shows the simulated patterned resist film 850. The simulated patterned resist film 850 shows asymmetric stress accumulation, particularly at connection regions 860. Much higher stress is exhibited at the connection regions 860 than in a remainder of the simulated patterned resist film 850. Line tilting is also observed in the simulated patterned resist film 850. The asymmetric stress accumulation and deformed pattern profile in the connection regions 860 can significantly contribute to line weakness. The bulk pulling strain and the local junction geometry lead to stress accumulation at the connection regions 860 and feature deformation and weakness.

Shrinkage and stress quantification

[0107] In this case, it may be desired to quantify stress and shrinkage in a resist film. Unlike qualitative mechanical simulations that can be performed in a single analysis step or component, quantification of stress and shrinkage can be performed by a multi-step (e.g., 2-step) static mechanical simulation. A multi-step static mechanical simulation serves to simulate both predevelopment geometry and post-development geometry for comparison with experimental data. It will be understood that the software or simulation of the present disclosure can be implemented in any number of steps. In one example implementation, the software or simulation may perform at least one analysis step or component with either pre-development geometry or post-development geometry. In another example implementation, the software or simulation may perform at least two analysis steps or components with both pre-development geometry and post-development geometry.

[0108] Figure 9A shows an initial stress distribution and volume loss in a resist film prior to development. The pre-development simulated resist film 900 may undergo exposure (e.g., EUV exposure) and bake (e.g., post-exposure bake). The pre-development simulated resist film 900 comprises more exposed line regions 910 and less exposed space regions 920. Due to ligand cleavage and cross-linking, there is more volume loss in the more exposed line regions 910 compared to the less exposed space regions 920. The strain and stress may be calculated as a result of the volume losses in the resist film pre-development simulated 900. The multi-step static mechanical simulation performs a pre-development simulation to determine a height change and residual stress in the resist film prior to development. The pre-development simulated resist film 900 can be compared against actual experimental data. The actual experimental data may include process conditions for exposure and post-exposure bake, which allows a user to connect shrinkage and stress information with process details. [0109] Figure 9B shows a post stress distribution and final deformation in the resist film after development. The multi-step static mechanical simulation uses the principal stresses and strain data from the pre-development simulated resist film 900 as a simulation starting point for a subsequent step. The multi-step static mechanical simulation performs a post-development simulation to determine a final deformation and stress in the resist film after development. Remaining or residual stress in the pre-development simulated resist film 900 gets released when the less exposed space regions 920 are removed. As a result, the resist film deforms again. The post-development simulated resist film 950 shows lateral shrinkage as a result of removal of the less exposed space regions 920. The multi-step static mechanical simulation outputs a final stress and deformation in the simulated post-development resist film 950. The final stress and deformation in the simulated post-development resist film 950 can be compared against actual experimental defectivity data. Using actual experimental defectivity data and comparing against the simulated results of stress and deformation, the multi-step static mechanical simulation can be trained for a more accurate model in more complicated 2D planar geometry. The multi-step static mechanical simulation is able to output quantifiable results for final deformation and accumulated stress. A first simulation provides an initial stress and strain in a resist film prior to development. A second simulation uses that initial stress and strain data along with a developed geometry to determine the final stress and deformation in the resist film after development. The final stress and deformation in the resist film after development can be correlated with defects in the resist film. The learnings and insights can be applied to optimize process details and photomask designs.

Strategies for Reducing Shrinkage Contrast and Defectivity

[0110] Metal oxide resist (MOR) offers many advantages as a photoresist, particularly for EUV lithography. With a high absorption coefficient and low blur radius compared to chemically amplified resist (CAR), the metal oxide resist presents a suitable photoresist material for printing features below a half-pitch of 14 nm. However, as discussed above, metal oxide resist encounters high defectivity problems with complex 2-D designs. The high defectivity problems are associated with mechanical responses following various photolithography steps, which can be observed as stress, deformation, and shrinkage in the metal oxide resist. Such mechanical responses are more pronounced in negative-tone-development (NTD) resist. Metal oxide resist in EUV lithography is often a negative-tone-development resist.

[0111] Strategies for reducing defectivity are generally more applicable to chemically amplified resist, which are frequently a positive-tone-development (PTD) resist. A common strategy or technique for reducing defectivity in 2-D geometric design is optical proximity correction (OPC). Image distortions may occur during sub-wavelength lithography, such as comer rounding and linewidth variations, due to an optical proximity effect. The optical proximity effect refers to the phenomenon of the printed design deviating from the intended design due to interference and diffraction effects of light waves. Optical proximity correction can correct image distortions caused by the optical proximity effect by moving edge locations or adding extra polygons (e.g., sub-resolution assist features) to the pattern on a photomask. The modified photomask has a corrected pattern to eliminate the optical proximity effect. In some instances, optical proximity correction can be driven by a rules-based optical proximity correction. Rules-based optical proximity correction is driven by pre-defined rules and patterns based on geometric properties of layout patterns to compensate for image distortions (e.g., comer rounding) during the printing of patterns.

[0112] Strategies such as optical proximity correction have been applied to positive-tone- development chemically amplified resist and negative-tone-development metal oxide resist. For example, with negative-tone-development metal oxide resist, optical proximity correction can be applied at the local feature level to increase the aerial light intensity where break defects have been observed in experimental results. However, implementing optical proximity correction can require sophisticated software and algorithms to model and correct for distortions and defects, which can be computationally expensive. The process is a complex process associated with many empirical design rules, heavy experimental and metrology requirements, and burdensome computational lithography. Furthermore, the corrected mask from optical proximity correction can suffer from drawbacks such as limitations in depth of focus and impacts from process variations.

[0113] In the present disclosure, strategies and techniques are employed to reduce defectivity in a resist based on the mechanical responses in the resist. Typically, optical proximity correction reduces defectivity associated with image distortions caused by diffraction effects of light waves. In other words, standard optical proximity correction focuses primarily on the lithography process and the interaction between light and the photoresist at a local feature level, whereas the defect reduction strategies of the present disclosure focus on the mechanical challenges and responses that occur at the bulk and local feature level. The present disclosure provides various strategies and techniques to reduce defectivity associated with mechanical responses induced in a resist that can be caused during exposure, bake, and/or development of the resist. By way of an example, pulling strains are generated from bulk features in the resist due to exposure and bake, which induces a shrinkage. Especially in negative-tone-development resist such as negative-tone- development metal oxide resist, the shrinkage contrast between exposed and unexposed regions can be relatively high. The pulling strains act on local thin connection features, which create high stress and deformation, and can ultimately lead to break defects. The strategies and techniques of the present disclosure reduce unnecessary cross-linking induced shrinkage in the bulk feature and reinforce local mechanical problem hot spots. In some implementations, the strategies and techniques for reducing defectivity in a resist based on mechanical responses can be combined with standard optical proximity correction. In some implementations, the strategies and techniques for reducing defectivity in a resist based on mechanical responses can enhance optical proximity correction, such as a rules-based optical proximity correction. In some implementations, the strategies and techniques for reducing defectivity in a resist based on mechanical responses can be done independent of standard optical proximity correction.

[0114] In some implementations, the defect reduction strategies of the present disclosure can fall into one of three categories: (1) process optimization, (2) mask optimization, and (3) enhanced optical proximity correction. Any of the defect reduction strategies described in these categories may be used in alone or in combination with one another. These defect reduction strategies provide various tuning knobs for mitigating mechanical obstacles and ultimately reducing break defects. The defect reduction strategies may be employed on one or both of the mask and photolithography process to reduce defects.

[0115] Figure 10 presents a flow diagram of an example process flow for applying a defectreduction strategy in a resist according to some implementations. The operations of a process 1000 may be performed in different orders and/or with different, fewer, or additional operations. One or more operations of the process 1000 may be implemented in accordance with any of the techniques or models described in the present disclosure. In some implementations, the operations of the process 1000 may be implemented, at least in part, according to software stored in one or more non-transitory computer readable media. An example of a system implementing software stored in one or more non-transitory computer readable media is described in Figure 14.

[0116] At block 1010 of the process 1000, mechanically-induced defects in a resist are identified using a mechanical simulation based at least in part on an initial strain and pattern geometry of the resist. Aspects of the mechanical simulation to identify mechanically-induced defects in a resist are discussed earlier herein and are not repeated for the sake of brevity. In some implementations, the resist may include bulk regions and local feature regions separate from the bulk regions.

[0117] In some cases, the initial strain in the resist may be calculated using the mechanical simulation. The mechanical simulation may calculate the initial strain in the resist using one or both of exposure-related data and PEB-related data. Shrinkage or volume losses may occur as a result of exposure and bake steps. Such shrinkage or volume losses may be attributable to ligand cleavage and cross-linking in the resist. The shrinkage or volume losses generate pulling strains that impact bulk features and localized features, creating high stress and deformation after development. The mechanical simulation can simulate the impact of the initial strain on the pattern geometry of the resist. In particular, the mechanical simulation can determine the final stress and deformation in the resist after development using pre-development strain and pre-development geometry as inputs. In some implementations, the determination can be made using finite element analysis. The mechanical simulation can identify the mechanically-induced defects from the final stress and deformation in the resist after development. Accordingly, the mechanical responses of the resist as a result of exposure and post-exposure bake steps can be simulated to identify mechanically-induced defects in the resist.

[0118] In some implementations, the resist includes a negative-tone-development (NTD) resist. In some implementations, the resist includes a metal oxide-containing resist such as a metal oxidecontaining EUV resist. For example, the metal oxide-containing resist may include an organometallic oxide such as organotin oxide.

[0119] At block 1020 of the process 1000, a defect-reduction strategy is applied to reduce the mechanically -induced defects in the resist, where the defect-reduction strategy includes one or more of the following: (i) process optimization, (ii) mask optimization, and (iii) enhanced optical proximity correction. Utilizing the information ascertained from the mechanical simulation, the defect-reduction strategy may serve to reduce the initial strain in the resist. High initial strain may occur due to ligand cleavage and cross-linking, resulting in hot spots of high stress after exposure and post-exposure bake. The defect-reduction strategy may mitigate or otherwise reduce the high initial strain in such areas. Process optimization may leverage pre-processing steps to reduce the exposure dose (e.g., EUV dose) required to pattern the resist. The lower the exposure dose, the lower the shrinkage contrast between exposed and unexposed regions after exposure. Examples of process optimization include but are not limited to blanket DUV treatment, post-application bake, and deposition of a blended resist film. Mask optimization may reduce initial strain in the resist by blocking or limiting unnecessary photons in a bulk region of the resist. The photomask for mask optimization may be modified to incorporate added or assist features that reduce unnecessary photons in the bulk region of the resist. In some implementations, the mask optimization may be combined with a standard optical proximity correction operation because mask optimization is implemented in the bulk region rather than the local feature region of the resist. Enhanced optical proximity correction may be implemented to modify a photomask that is tailored to address areas where mechanically-induced defects occur. This can be utilized as a design rule in an optical proximity correction operation to identify features that need strengthening. Whereas a standard optical proximity correction operation can modify a photomask to eliminate the optical proximity effect related to interference and diffraction effects of light waves, the enhanced optical proximity correction operation can modify the photomask to reduce mechanically -induced defects. Each of the aforementioned defect-reduction strategies are discussed in more detail below, with the process optimization strategy shown in block 1030, the mask optimization strategy shown in block 1040, and the enhanced optical proximity correction strategy shown in blocks 1050 and 1055.

[0120] At block 1030 of the process 1000, application of the defect-reduction strategy may include selecting a pre-exposure operation that reduces the initial strain in the resist, where the pre-exposure operation includes blanket resist exposure to DUV, post-application bake (PAB), or deposition of a blended resist film. Areas of relatively high final accumulated stress may be correlated with increased defectivity. One or more of these pre-exposure operations may be performed to reduce the intensity of exposure (e.g., EUV exposure) and post-exposure bake. Metal-containing resists such as metal oxide-containing resists encounter high shrinkage contrast between exposed and unexposed regions, which results in mechanically-induced defects formed by film stress. By implementing some of the aforementioned pre-exposure operations, shrinkage contrast between exposed and unexposed regions may be reduced by reducing the exposure dose (e.g., EUV dose) and/or intensity of the post-exposure bake step.

[0121] Regarding blanket resist exposure to DUV, the resist may be treated by exposure to blanket DUV to modify material properties of the resist such that radiation-sensitivity of the resist is increased. In some implementations, exposure to blanket DUV increases the sensitivity of the resist to EUV radiation. The exposure to blanket DUV occurs prior to formation of exposed and unexposed regions of the resist during photopatterning. Without being limited by any theory, the exposure to blanket DUV removes organic ligands (R-groups) in the resist and induces blanket level uniform shrinkage. This pre-exposure operation reduces exposure dose for photopatterning and results in a lower shrinkage contrast between exposed and unexposed regions, thereby reducing stress-induced defects. Thus, in some implementations, the blanket DUV treatment can reduce the EUV dose required for cross-linking in exposed regions without substantially causing cross-linking. In some implementations, the wavelength of blanket DUV exposure is less than about 300 nm. In some implementations, an intensity of the blanket DUV exposure is between about 1 mJ/cm² and about 100 mJ/cm², between about 10 mJ/cm² and about 80 mJ/cm², or between about 20 mJ/cm² and about 60 mJ/cm². In some implementations, treating the resist with blanket DUV exposure is accompanied by a thermal process with control of temperature, pressure, ambient bas chemistry, gas flow/ratio, and moisture. Aspects of blanket DUV treatment on a resist are described in further detail in International Application No. PCT/US2021/025111, filed March 31, 2021, entitled “PRE-EXPOSURE PHOTORESIST CURING TO ENHANCE EUV LITHOGRAPHIC PERFORMANCE,” which is incorporated herein by reference in its entirety and for all purposes.

[0122] The reduction in shrinkage contrast between exposed and unexposed regions following blanket DUV treatment is demonstrated in Figure 11 A. Figure 1 1A presents a graph illustrating local shrinkage ratio of an EUV resist film as a function of an x-direction of the EUV resist film for different EUV exposure dose conditions. A first curve 1110 plots the local shrinkage ratio along the x-direction of the EUV resist film at an EUV dose without any blanket DUV treatment. A second curve 1120 plots the local shrinkage ratio along the x-direction of the EUV resist film at an EUV dose with a blanket DUV treatment. By comparison, the second curve 1120 demonstrated a significantly reduced shrinkage contrast between the exposed and unexposed regions of the EUV resist film, where the second curve 1120 occurred at a lower EUV dose than the first curve 1110.

[0123] Returning to block 1030 of the process 1000, application of the defect- reduction strategy may include application of a post-application bake. The post-application bake is performed after deposition of the resist on the substrate and prior to exposure for photopatteming. The postapplication bake involves some combination of thermal treatment, chemical treatment, and moisture to modify the material properties of the resist such that radiation-sensitivity of the resist is increased. In some implementations, post-application bake increases the sensitivity of the resist to EUV radiation. The post-application bake reduces a dose-to-size for the resist. The postapplication bake reduces the exposure dose for photopatteming and results in a lower shrinkage contrast between exposed and unexposed regions, thereby reducing stress-induced defects. The post-application bake may remove organic ligands (R-groups) and achieve a desired amount of cross-linking. During the post-application bake, the resist may be exposed to an elevated temperature such as a temperature between about 100°C and about 300°C, or between about 100°C and about 220°C. In some implementations, the resist may be exposed to a reactive gas during the post-application bake. Examples of reactive gases include but are not limited to water, hydrogen, oxygen, ozone, hydrogen peroxide, carbon monoxide, carbon dioxide, ammonia, nitrous oxide, nitric oxide, an alcohol, acetyl acetone, formic acid, oxalyl chloride, pyridine, a carboxylic acid, an amine, and combinations thereof. Aspects of post-application bake on a resist are described in further detail in International Application No. PCT/US2020/070171, filed June 24, 2020, entitled “BAKE STRATEGIES TO ENHANCE LITHOGRAPHIC PERFORMANCE OF METALCONTAINING RESIST,” which is incorporated herein by reference in its entirety and for all purposes.

[0124] The post-application bake applies a thermal treatment to the resist prior to exposure. In some implementations, the post-application bake reduces shrinkage contrast between exposed and unexposed regions that form after exposure (e.g., EUV exposure). As with blanket DUV treatment, the reduced shrinkage contrast between exposed and unexposed regions can potentially lead to less accumulated stress and feature deformation between developed and undeveloped regions.

[0125] In some implementations of block 1030 of the process 1000, application of the defectreduction strategy may include deposition of a blended resist film. The “blended” resist film refers to a resist deposited using a mixture of different precursors. The resist may be deposited as a homogeneously blended film or a vertically heterogeneous film. In some cases, the mixture of different precursors may include a first metal precursor with a first organometal and a second metal precursor with no metal-carbon bonds or a second organometal. With a blended resist film, the composition of the resist may be finely tuned through selection of appropriate precursors and/or adjustment of ratios of the precursors during delivery to a process chamber. By fine-tuning the composition of the resist, the resist may have a desired level of cross-linking and may have increased sensitivity to radiation for photopatteming. In some implementations, the “blended” resist film may have increased sensitivity to EUV radiation. The desired level of cross-linking in the “blended” resist film provides pre-existing cross-linking in the resist so that the intensity of the exposure step and/or post-exposure bake step can be reduced. This results in a lower shrinkage contrast between exposed and unexposed regions, which reduces stress-induced defects. The “blended” resist film can exhibit not only improved properties such as sensitivity, but also improved properties in resolution and line-edge roughness. In some implementations, the “blended” resist film deposits the resist using a vapor deposition process such as a chemical vapor deposition (CVD) process, where the substrate is exposed to at least one first metal precursor, at least one second metal precursor, and a reactant. The first metal precursor may have at least one metal-carbon bond. The second metal precursor may have no metal-carbon bonds or may have at least one metal-carbon bond that is weaker than the metal-carbon bond of the first metal precursor. Aspects of deposition of a “blended” resist film are described in further detail in International Application No. PCT/US2024/052528, filed October 23, 2024, entitled “BLENDED AND VERTICAL COMPOSITION GRADIENT EUV RESISTS,” which is incorporated herein by reference in its entirety and for all purposes.

[0126] Figure 1 IB shows a graph illustrating a relationship between an initial strain in a resist film and dose. A pre-processing operation such as blanket DUV treatment, post-application bake, or deposition of a blended resist film, can remove organic ligands and/or achieve a desired level of cross-linking in the resist film prior to exposure for photopatteming and post-exposure bake. This can reduce shrinkage contrast between exposed and unexposed regions after photopatteming. This can also increase overall sensitivity to EUV radiation, thereby reducing the effective exposure dose necessary for photopatterning. As shown in Figure 11B, increases in EUV dose for photopatterning results in increased strain in the resist film and largely follows a linear relationship. For instance, an EUV dose of about 30 mJ/cm² results in an initial strain in the resist film of about 37%. However, reducing the EUV dose to about 21 mJ/cm² results in an initial strain in the resist film of about 30%. This shows that pre-processing the resist film, such as by blanket DUV treatment, post-application bake, or deposition of a blended resist film, reduces EUV dose to effectively reduce the initial strain in the resist film.

[0127] Returning to Figure 10, at block 1040 of the process 1000, application of the defectreduction strategy may include generating a photomask with one or more assist features to reduce patterning radiation exposure in bulk regions of the resist, where the one or more assist features to the photomask reduce the mechanically-induced defects in the resist in local feature regions of the resist. Mask optimization at 1040 may employ one or more assist features to block or reduce patterning radiation exposure in the bulk region of the resist. However, it will be understood that mask optimization at 1040 is not limited to employing one or more assist features, but may employ any appropriate modification to the photomask that blocks or otherwise limits patterning radiation exposure to the bulk region of the resist.

[0128] In semiconductor fabrication, a photomask is used to define patterns that are printed on a substrate during a photolithography process. Variations in the intended pattern may be induced by optical interference and diffraction effects. To prevent these effects, sub-resolution assist features (SRAFs) are included on the photomask as an application of optical proximity correction (OPC). For instance, one or more polygons may comprise sub-resolution assist features, also known as scattering bars, serifs, and/or simply assist features, that take advantage of the fact that edges of near- and sub-wavelength features located in dense areas of the photomask are typically resolved more sharply in a photolithographic system. The sub-resolution assist feature is typically printed near an existing local feature to improve the imaged resolution of the existing local feature, and the sub-resolution assist feature is typically so narrow that it does not appear on a substrate imaged by the photomask. In short, sub-resolution assist features on photomasks are conventionally placed at or near local features of the photomask to address optical interference and diffraction effects in optical proximity correction.

[0129] In contrast, the one or more assist features (or other modification) designed on the photomask at block 1040 are placed at bulk areas of the photomask to address mechanically - induced defects in a resist. These bulk areas of the photomask are separate and away from local features of the photomask. Ordinarily, in a negative-tone-development resist, exposed regions of a resist film remain after development while unexposed regions of the resist film are removed after development. Bulk areas of the photomask can represent large openings or large transparent areas through which patterning radiation passes through. In contrast, local feature areas can represent small opaque or non-transparent areas that block or reflect the patterning radiation. The local feature areas of the photomask define the local feature regions of the resist and the bulk areas of the photomask define the bulk regions of the resist. The one or more assist features may be polygons or other geometric shapes located in the bulk areas of the photomask. As a result, the one or more assist features cause reduced exposure in a bulk region of the resist. This is in contrast to typical sub-resolution assist features used in optical proximity correction that reduce exposure in local feature regions of a resist. This allows the mask optimization step at block 1040 to work in conjunction with optical proximity correction since the one or more assist features modify the photomask in a manner that affects the bulk regions of the resist rather than the local feature regions of the resist.

[0130] The one or more assist features reduce an amount of patterning radiation that the resist is exposed to. This causes the exposure dose (e.g., EUV dose) to the resist for photopatterning to be reduced. The one or more assist features prevent or reduce exposure in one or more areas of the resist that are unnecessary for defining a pattern in the resist. In some implementations of the block 1040, the process 1000 further includes identifying one or more areas in the bulk regions of the resist for removal that are not necessary to a patterned resist after development. These one or more areas that are not necessary to a patterned resist are not needed or not part of the printed design (e.g., printed circuitry) of the substrate. In other words, portions of the resist may be removed in negative-tone-development that do not otherwise interfere with the patterning of the resist in creating a desired pattern. However, these one or more areas may nonetheless contribute to the initial strain in the resist.

[0131] Identification of the one or more areas in the bulk regions for removal can be correlated to the one or more assist features of the photomask. The one or more assist features of the photomask block or otherwise reduce exposure to the one or more areas in the bulk regions that may be deemed superfluous to patterning the resist. With negative-tone-development, the one or more areas of the bulk regions are removed. Thus, the one or more assist features of the photomask reduce a volume of the resist in the bulk regions of the resist.

[0132] The one or more areas in the bulk regions of the resist that are deemed superfluous may contribute to initial strain in the resist. Removal of these one or more areas in the bulk regions of the resist will reduce the initial strain in the resist. In fact, the removal of these one or more areas in the bulk regions of the resist will result in the reduced accumulated stress in the local feature regions of the resist. Reducing the stress in the local resist feature can correlate to reduced defectivity in the resist. In some implementations of the block 1040, the process 1000 further includes determining, using the mechanical simulation, that the one or more areas in the bulk regions for removal will reduce the initial strain in the resist in the local feature regions of the region. The mechanical learning from the mechanical simulation can be leveraged to determine unnecessary dosage in bulk regions and unnecessary areas in the bulk regions that contribute to initial pulling strains that impact stress and deformation in the local feature regions. Mask optimization at block 1040 can prevent or reduce exposure at such unnecessary areas in the bulk regions to mitigate defectivity in the local feature regions of the resist.

[0133] Figure 12 A shows a top plan view of an example photoresist film comprising bulk regions and local feature regions, where stress in the photoresist film varies depending on the region of the photoresist film, according to some implementations. The photoresist film 1200 may be patterned with a line- and- separator geometry, where the grey regions represent the photoresist material and the white regions represent empty space or lines. The photoresist film 1200 may include bulk regions 1210 and local feature regions 1220. The local feature regions 1220 correspond to areas of the photoresist film 1200 along or proximate to localized features such as lines or spaces. The bulk regions 1210 correspond to areas of the photoresist film 1200 separate from the local feature regions 1220 and not proximate to any localized features such as lines or spaces. As shown in Figure 12A, the bulk regions 1210 include an area of photoresist material (i.e., separator) connecting a first portion having a plurality of lines and a second portion having a plurality of lines.

[0134] Elevated stress and deformation may occur in the photoresist film 1200 after development at certain locations in the photoresist film 1200. For instance, elevated stress and deformation may occur in locations at or proximate a conjunction of the bulk regions 1210 and the local feature regions 1220. In Figure 12A, a stress value is greater at spot 1240 than at a spot 1230 of the photoresist film 1200. The relative additional stress at the spot 1240 can be reduced by reducing an exposure dose. Instead of reducing the exposure dose in the local feature regions 1220, the mask optimization strategy reduces the exposure dose in the bulk regions 1210. This leads to reduced strain and reduced relative stress of local feature regions 1240 of the photoresist film 1200. Ultimately, this can reduce mechanically-induced defects in the photoresist film 1200.

[0135] Figure 12B shows a lateral deformation distribution in a magnified top plan view of a portion of an example photoresist film. The upper section of Figure 12B shows local feature regions with a line formed in the local feature regions, and the lower section of Figure 12B shows bulk regions without any line formed in the bulk regions. Areas proximate the line in the local feature regions exhibit relatively high initial strain that leads to increased amounts of lateral deformation. Specifically, an area 1250 enclosed by dashed lines shows high amounts of lateral deformation near the line formed in the local feature regions.

[0136] Figure 12C shows a lateral deformation distribution in a magnified top plan view of a portion of an example photoresist film formed with an assist feature in the bulk regions according to some implementations. The upper section of Figure 12C shows local feature regions with a line formed in the local feature regions, and the lower section of Figure 12C shows bulk regions without any line formed in the bulk regions. However, unlike Figure 12B, a recessed feature 1260 is formed in the bulk regions. The recessed feature 1260 is formed by adding one or more assist features to the photomask for patterning the photoresist film 1200, where the one or more assist features prevent or reduce exposure to one or more areas in the bulk regions. After development, the one or more areas in the bulk regions are removed to form the recessed feature 1260, where a volume of the photoresist film 1200 is reduced by application of the one or more assist features in the photomask. As shown in Figure 12C, areas proximate the line in the local feature regions have reduced lateral deformation as a result of the recessed feature 1260 compared to bulk regions without a recessed feature in Figure 12B. The same area 1250 enclosed by dashed lines show reduced amounts of lateral deformation near the line formed in the local feature regions.

[0137] Returning to Figure 10, at blocks 1050 and 1055 of the process 1000, application of the defect-reduction strategy may include identifying one or more areas with high stress in local feature regions of a resist, and performing an optical proximity correction operation on a photomask to reduce defectivity in the local feature regions. In some implementations, performing the optical proximity correction is based at least in part on the stress and deformation in the resist. Using the mechanical learnings from the mechanical simulation, the final stress in the resist may be tied to mechanically-induced defects. The optical proximity correction operation at block 1055 may correct the photomask in a manner to reduce the high strain or high stress in the local feature regions of the resist, where reducing the high strain or high stress in the local feature regions is correlated with reduced defectivity in the resist after development.

[0138] Standard optical proximity correction is a technique that modifies a photomask to compensate for image distortions caused by diffraction or process effects. Standard optical proximity correction relies on simulations that model the lithography process and predict how the photomask will be imaged onto the substrate. Based on the simulations, modifications are made to the photomask pattern, where such modifications can include edge adjustments and subresolution assist features. Enhanced optical proximity correction at blocks 1050 and 1055 relies on information ascertained from the mechanical simulation at block 1010 to identify mechanically- induced defects in the resist from the lithography process. Information ascertained from the mechanical simulation is used to identify areas of high strain at block 1050 that may contribute to stress and deformation in the local feature regions of the resist. Based on the mechanical simulation at block 1010 and the identification of areas of high strain in the resist at block 1050, modifications are made to the photomask pattern at block 1055. Example modifications to the photomask can include edge adjustments or feature additions such as sub-resolution assist features that are made in the local feature regions of the resist. Other example modifications to the photomask can include mask bias that adjusts the size or shape of features on the mask.

[0139] Enhanced optical proximity correction may apply optical models and/or rules to make modifications to the photomask, such as adding auxiliary components (e.g., sub-resolution assist features), edge adjustments, or mask bias, so that the final pattern on the resist has reduced mechanical defects. In some implementations, performing the optical proximity correction operation at block 1055 makes corrections to the photomask according to geometric characteristics of a target pattern and reduction of mechanical defects in the resist that are associated with the initial strain. In some implementations, the optical proximity correction operation employs a rules- based correction. Rules, which may include mathematical relationships that convey how features are printed, may be added to correct the photomask to mitigate mechanically-induced defects. In some implementations, the optical proximity correction employs a model-based correction. Models and simulations may drive the mask modifications to mitigate mechanically-induced defects.

[0140] Mask optimization at block 1040 modifies the photomask to impact exposure in the bulk regions of the resist. Enhanced optical proximity correction at blocks 1050 and 1055 modifies the photomask to impact the local feature regions of the resist. Accordingly, mask optimization may work in conjunction with enhanced optical proximity correction. Enhanced optical proximity correction modifies the photomask based on mechanical learnings that identify structurally problematic locations in the resist. Standard optical proximity correction modifies the photomask based on optical learnings that identify image distortions caused by interference or diffraction effects. Thus, standard optical proximity correction may work in conjunction with enhanced optical proximity correction. In some implementations of the present disclosure, standard optical proximity correction may work in conjunction with mask optimization and enhanced optical proximity correction.

[0141] Figure 13 A shows a stress distribution in a magnified top plan view of a portion of an example photoresist film prior to an enhanced optical proximity correction operation. A photoresist film 1300 is shown in a general inverse tip geometry. A first line 1310 extends from a lower section of the photoresist film 1300 and a second line 1320 extends from an upper section of the photoresist film 1300. A first tip of the first line 1310 and a second tip of the second line 1320 form an overlapping junction region 1330, where the overlapping junction region 1330 is between the first line 1310 and the second line 1320. Stress in the overlapping junction region 1330 may be high relative to other areas of the photoresist film 1300. The stress distribution in the photoresist film 1300 can be calculated from a mechanical simulation as described above. The stress distribution from the mechanical simulation can identify structurally problematic locations, such as the overlapping junction region 1330, in the photoresist film 1300.

[0142] Figure 13B shows a stress distribution in a magnified top plan view of the portion of the example photoresist film after an enhanced optical proximity correction operation to address mechanical defects according to some implementations. The enhanced optical proximity correction uses the mechanical learning from the mechanical simulation to identify the high relative stress at the overlapping junction region 1330 in the photoresist film 1300. An enhanced optical proximity correction modifies a photomask for patterning a modified photoresist film 1350. Based on the modified photomask, the modified photoresist film 1350 has a feature critical dimension (CD) change at the overlapping junction region 1330. Here, the feature CD of the overlapping junction region 1330 has increased in Figure 13B relative to Figure 13 A, where the increased feature CD results in a reduced stress at the overlapping junction region 1330. The enhanced optical proximity correction can modify a photoresist film to adjust local CD in a local feature region and reduce stress. In doing so, the enhanced optical proximity correction reduces defectivity in the photoresist film.

[0143] Certain embodiments disclosed herein relate to computational systems for generating and/or using various computational models. Certain embodiments disclosed herein relate to methods for generating and/or using a computational model implemented on such systems. A system for generating a computational model may also be configured to receive data and instructions such as program code representing physical processes occurring during the semiconductor device fabrication operation. In this manner, a computational model is generated or programmed on such system.

[0144] Many types of computing systems having any of various computer architectures may be employed as the disclosed systems for implementing computational models and algorithms for generating and/or optimizing such models. For example, the systems may include software components executing on one or more general purpose processors or specially designed processors such as Application Specific Integrated Circuits (ASICs) or programmable logic devices (e.g., Field Programmable Gate Arrays (FPGAs)). Further, the systems may be implemented on a single device or distributed across multiple devices. The functions of the computational elements may be merged into one another or further split into multiple sub-modules.

[0145] In some embodiments, code executed during generation or execution of a computational model on an appropriately programmed system can be embodied in the form of software elements which can be stored in a nonvolatile storage medium (such as optical disk, flash storage device, mobile hard disk, etc.), including a number of instructions for making a computer device (such as personal computers, servers, network equipment, etc.).

[0146] At one level a software element is implemented as a set of commands prepared by the programmer/developer. However, the module software that can be executed by the computer hardware is executable code committed to memory using “machine codes” selected from the specific machine language instruction set, or “native instructions,” designed into the hardware processor. The machine language instruction set, or native instruction set, is known to, and essentially built into, the hardware processor(s). This is the “language” by which the system and application software communicates with the hardware processors. Each native instruction is a discrete code that is recognized by the processing architecture and that can specify particular registers for arithmetic, addressing, or control functions; particular memory locations or offsets; and particular addressing modes used to interpret operands. More complex operations are built up by combining these simple native instructions, which are executed sequentially, or as otherwise directed by control flow instructions.

[0147] The inter-relationship between the executable software instructions and the hardware processor is structural. In other words, the instructions per se are a series of symbols or numeric values. They do not intrinsically convey any information. It is the processor, which by design was preconfigured to interpret the symbols/numeric values, which imparts meaning to the instructions.

[0148] The models used herein may be configured to execute on a single machine at a single location, on multiple machines at a single location, or on multiple machines at multiple locations. When multiple machines are employed, the individual machines may be tailored for their particular tasks. For example, operations requiring large blocks of code and/or significant processing capacity may be implemented on large and/or stationary machines.

[0149] In addition, certain embodiments relate to tangible and/or non-transitory computer readable media or computer program products that include program instructions and/or data (including data structures) for performing various computer-implemented operations. Examples of computer-readable media include, but are not limited to, semiconductor memory devices, phasechange devices, magnetic media such as disk drives, magnetic tape, optical media such as CDs, magneto-optical media, and hardware devices that are specially configured to store and perform program instructions, such as read-only memory devices (ROM) and random access memory (RAM). The computer readable media may be directly controlled by an end user or the media may be indirectly controlled by the end user. Examples of directly controlled media include the media located at a user facility and/or media that are not shared with other entities. Examples of indirectly controlled media include media that is indirectly accessible to the user via an external network and/or via a service providing shared resources such as the “cloud.” Examples of program instructions include both machine code, such as produced by a compiler, and files containing higher level code that may be executed by the computer using an interpreter.

[0150] In various embodiments, the data or information employed in the disclosed methods and apparatus is provided in an electronic format. Such data or information may include design layouts, simulation values, sensor values, and the like. As used herein, data or other information provided in electronic format is available for storage on a machine and transmission between machines. Conventionally, data in electronic format is provided digitally and may be stored as bits and/or bytes in various data structures, lists, databases, etc. The data may be embodied electronically, optically, etc.

[0151] In some embodiments, a computational model can be viewed as a form of application software that interfaces with a user and with system software. System software typically interfaces with computer hardware and associated memory. In some embodiments, the system software includes operating system software and/or firmware, as well as any middleware and drivers installed in the system. The system software provides basic non-task-specific functions of the computer. In contrast, the modules and other application software are used to accomplish specific tasks. Each native instruction for a module is stored in a memory device and is represented by a numeric value.

[0152] An example computer system 1400 is depicted in Figure 14. As shown, computer system 1400 includes an input/output subsystem 1402, which may implement an interface for interacting with human users and/or other computer systems depending upon the application. Embodiments of the disclosure may be implemented in program code on system 1400 with I/O subsystem 1402 used to receive input program statements and/or data from a human user (e.g., via a GUI or keyboard) and to display them back to the user. The I/O subsystem 1402 may include, e.g., a keyboard, mouse, graphical user interface, touchscreen, or other interfaces for input, and, e.g., an LED or other flat screen display, or other interfaces for output.

[0153] Communication interfaces 1407 can include any suitable components or circuitry used for communication using any suitable communication network (e.g., the Internet, an intranet, a wide-area network (WAN), a local-area network (LAN), a wireless network, a virtual private network (VPN), and/or any other suitable type of communication network). For example, communication interfaces 1407 can include network interface card circuitry, wireless communication circuitry, etc.

[0154] Program code may be stored in non-transitory media such as secondary memory 1410 or memory 1408 or both. In some embodiments, secondary memory 1410 can be persistent storage. One or more processors 1404 reads program code from one or more non-transitory media and executes the code to enable the computer system to accomplish the methods performed by the embodiments herein, such as those involved with generating or using a model as described herein. Those skilled in the art will understand that the processor may accept source code, such as statements for executing training and/or modelling operations, and interpret or compile the source code into machine code that is understandable at the hardware gate level of the processor. A bus 1405 couples the I/O subsystem 1402, the processor 1404, peripheral devices 1406, communication interfaces 1407, memory 1408, and secondary memory 1410.

Conclusion

[0155] It is understood that the examples and implementations described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art. Although various details have been omitted for clarity’s sake, various design alternatives may be implemented. Therefore, the present examples are to be considered as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein, but may be modified within the scope of the disclosure.

Claims

1. A method of determining stress and deformation in a resist after development, the method comprising: receiving, in a mechanical simulation, experimental data sets regarding exposure and post-exposure bake performed on the resist as inputs; determining, using the mechanical simulation, an initial strain in the resist based at least in part on the experimental data sets; and determining, using the mechanical simulation, stress and deformation in the resist after development based at least in part on the initial strain and pattern geometry of the resist.

2. The method of claim 1 , wherein the resist is a negative tone resist.

3. The method of claim 1, wherein the resist comprises a metal-oxide-containing EUV resist.

4. The method of claim 1 , wherein determining the stress and deformation in the resist after development comprises: constructing a geometric representation of the resist after development; meshing the geometric representation of the resist to form one or more meshes; applying the initial strain in the resist to the geometric representation of the resist; and performing calculations with governing equations in each of the meshes iteratively to obtain the stress and deformation in the resist after development.

5. The method of claim 1, further comprising: correlating the stress and deformation in the resist to one or more defects in the resist after development.

6. The method of claim 1 , wherein the experimental data sets comprise an aerial image of the resist after exposure, wherein the aerial image comprises a planar intensity distribution of incoming EUV light observed by the resist.

7. The method of claim 1, wherein the experimental data sets comprise volume losses of the resist after post-exposure bake associated with conditions of the post-exposure bake.

8. The method of claim 7, further comprising: determining a relationship between the volume losses of the resist after post-exposure bake and lateral shrinkage, stress accumulation, and thickness loss after development.

9. The method of claim 1, wherein determining the initial strain in the resist comprises calculating strain in the resist using an aerial image of the resist after exposure and using volume losses of the resist after post-exposure bake associated with conditions of the post-exposure.

10. The method of claim 1, wherein determining the stress and deformation in the resist after development comprises quantifying the stress and deformation in the resist using a multi- step static mechanical simulation.

11. The method of claim 1 , further comprising: training the mechanical simulation using experimental defectivity data compared against the stress and deformation in the resist determined from the mechanical simulation.

12. A mechanical simulation for determining stress and deformation in a resist after development comprising one or more non-transitory machine readable media comprising logic configured to implement: a static mechanical simulation configured to receive experimental data sets associated with exposure and post-exposure bake as inputs, configured to determine an initial strain in the resist based at least in part on the experimental data sets, and configured to determine the stress and deformation in the resist after development based at least in part on the initial strain in the resist.

13. The mechanical simulation of claim 12, wherein the resist is a negative tone resist.

14. The mechanical simulation of claim 12, wherein the resist comprises a metal-oxide- containing EUV resist.

15. The mechanical simulation of claim 12, wherein the static mechanical simulation configured to determine the stress and deformation in the resist is configured to construct a geometric representation of the resist after development, mesh the geometric representation of the resist to form one or more meshes, apply the initial strain in the resist to the geometric representation of the resist, and perform calculations with governing equations in each of the one or more meshes iteratively to obtain the stress and deformation in the resist after development.

16. The mechanical simulation of claim 12, wherein the static mechanical simulation is further configured to correlate the stress and deformation in the resist to one or more defects in the resist after development.

17. A method of reducing defectivity in a resist, the method comprising: identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist comprises bulk regions and local feature regions; and generating a photomask with one or more assist features to reduce patterning radiation exposure in the bulk regions of the resist, wherein the one or more assist features to the photomask reduce the mechanically-induced defects in the resist in the local feature region.

18. The method of claim 17, wherein the one or more assist features to the photomask reduce a volume of the resist in the bulk regions and reduce an exposure dose to the resist.

19. The method of claim 17, wherein reducing patterning radiation exposure in the bulk regions is correlated with reducing an initial strain in the resist.

20. The method of claim 17, further comprising: identifying one or more areas in the bulk region for removal that are not necessary to a patterned resist after development; and correlating the one or more areas in the bulk region for removal to the one or more assist features of the photomask.

21. The method of claim 20, further comprising: determining, using the mechanical simulation, that the one or more areas in the bulk region for removal will reduce the initial strain in the resist in the local feature region.

22. A method of reducing initial strain in a resist, the method comprising; identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist comprises bulk regions and local feature regions; and selecting a pre-exposure operation that reduces the initial strain in the resist, wherein the pre-exposure operation comprises blanket resist exposure to DUV, post-application bake, or deposition of a blended resist fdm for the resist.

23. The method of claim 22, wherein the pre-exposure operation comprises blanket resist exposure to DUV.

24. The method of claim 23, wherein the blanket resist exposure to DUV reduces a dose for the EUV exposure.

25. The method of claim 23, wherein the blanket resist exposure to DUV reduces a shrinkage contrast between exposed regions and unexposed regions of the resist after EUV exposure.

26. The method of claim 22, wherein the pre-exposure operation reduces a dose for the EUV exposure and reduces a shrinkage contrast between exposed regions and unexposed regions of the resist after the EUV exposure.

27. A method of reducing detectivity in a resist, the method comprising: identifying, using a mechanical simulation, mechanically-induced defects in the resist based at least in part on an initial strain and pattern geometry of the resist, where the resist comprises bulk regions and local feature regions; identifying one or more areas with high stress in the local feature regions of the resist; and performing an optical proximity correction (OPC) operation on a photomask to reduce defectivity in the local feature regions.

28. The method of claim 27, wherein performing the OPC operation is based at least in part on the initial strain in the resist.

29. The method of claim 27, wherein performing the OPC operation on the photomask makes corrections to the photomask according to geometric characteristics of a target pattern and reduction of mechanical defects in the resist that are associated with the initial strain.

30. The method of claim 27, wherein performing the OPC operation on the photomask to reduce the defectivity in the local feature regions is correlated with the initial strain in the resist.