Fundamental understanding and experimental verification of bright versus dark field imaging

Davydova, Natalia; Finders, Jo; McNamara, John; Setten, Eelco van; Lare, Claire van; Franke, Joern-Holger; Frommhold, Andreas; Capelli, Renzo; Kersteen, Grizelda; Verch, Andreas; Carpaij, Rene; Zekry, Joseph; Fliervoet, Timon

doi:10.1117/12.2573161

Cited by 11 publications

(14 citation statements)

References 5 publications

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“…To address this tradeoff, another metric known as Throughput Criterion (TpT) (Eq. 4) was taken into account [26]. It is an indicator that considers a good balance between NILS and TtS.…”

Section: Simulation Methodsmentioning

confidence: 99%

Evaluation of Ta-Co alloys as novel high-k EUV mask absorber

Thakare¹,

Wu²,

Opsomer

et al. 2022

Optical and EUV Nanolithography XXXV

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An alternate mask absorber is a generally applicable approach as a mitigation strategy for Mask 3-D effects (M3D) observed in EUV lithography. It is also an efficient solution in a production-worthy environment compared to multilayer modification or Source Mask Optimization (SMO) techniques. Absorbers with a high EUV extinction coefficient k allow for lower Best Focus Variation (BFV) through pitch and reduced Telecentricity Errors (TCE). This study evaluates Ta-Co alloys as potential high-k mask absorbers. It includes an experimental study of film morphology, surface composition, and stability of Ta-Co alloys as well as a theoretical investigation of the imaging performance. The optical constants were determined from EUV angle-dependent reflectivity measurements for three selected compositions, viz. TaCo, Ta2Co, and TaCo3. The Ta-Co alloys exhibit a higher EUV extinction coefficient k compared to the currently used TaBN absorber. TaCo and Ta2Co demonstrated smooth surfaces, were stable in a hydrogen environment, and in mask cleaning solutions. These qualified compositions of Ta-Co alloys were selected for aerial image simulations and compared with a TaBN absorber. The optimized absorber thickness for Ta-Co alloy absorbers is based upon NILS enhancement, Threshold to Size (TtS) and balancing of diffraction order amplitudes. A 10 nm alternate line-space pattern with a pitch of 20 nm and 14 nm square contact holes with a pitch of 28 nm were considered for the simulation study using High NA 0.55 EUV lithography process settings. The through pitch imaging performance was evaluated using NILS, TCE and BFV as metrics. Ta-Co alloys allow for a reduction in M3D effects at smaller absorber thickness compared to a 60 nm TaBN absorber.

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“…To address this tradeoff, another metric known as Throughput Criterion (TpT) (Eq. 4) was taken into account [26]. It is an indicator that considers a good balance between NILS and TtS.…”

Section: Simulation Methodsmentioning

confidence: 99%

Evaluation of Ta-Co alloys as novel high-k EUV mask absorber

Thakare¹,

Wu²,

Opsomer

et al. 2022

Optical and EUV Nanolithography XXXV

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“…The M3D-induced overlay error accounts to be 0.175 nm for a focus budget of 35 nm and TCE of 10 mrad (10 mrad x 0.035µm/2), thus consuming ~16% of the overlay budget. TCE restricted to 10 mrad, shouldn't have a significant impact on the overlay budget as per the opinion of Eelco van Setten et al [13]. As a result, we aim to target a TCE of 10 mrad or below for the smallest pitch.…”

Section: Setting Simulation Goals and Defining Target Valuesmentioning

confidence: 99%

“…An additional metric known as Throughput Criterion (TpT) (Eq. 3) was taken into account to address this tradeoff [13]. It is an indicator that considers a good balance between NILS and TtS.…”

Section: 𝑇𝑒𝑙𝑒𝑐𝑒𝑛𝑡𝑟𝑖𝑐 𝜎 𝑓𝑜𝑟 𝐿𝑛𝑆mentioning

confidence: 99%

Optimizing EUV imaging metrics as a function of absorber thickness and illumination source: simulation case study of Ta-Co alloy

Thakare¹,

Delabie

Philipsen

2022

37th European Mask and Lithography Conference

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The imaging performance of a mask in EUV lithography is governed by the optical properties of the absorber material, namely the refractive index n and extinction coefficient k, and by its thickness. The imaging metrics viz. Normalized Intensity Log Slope (NILS), Telecentricity Error (TCE) and Best Focus Variation (BFV) through pitch, exhibit a tradeoff. In addition, the choice of illumination has a significant influence on these imaging metrics. Most of the previous studies have focused on either reflectivity or phase shift induced by the absorber to determine the optimum absorber thickness. The limitation of this approach is that the structure of the patterns on the mask is ignored. This simulation study is intended to facilitate the selection of the optimum absorber thickness with an emphasis on diffraction order analysis and the impact of illumination source shape using a case study of TaCo alloy. The behavior of imaging metrics is investigated as a function of absorber thickness in combination with illumination source shapes recommended in the literature. Maximal NILS, TCE within specified limits, balancing of diffraction order amplitudes with a minimum phase difference, and throughput criterion, are the important parameters that are considered when selecting the optimum absorber thickness. We evaluate and compare the through pitch imaging performance of TaCo alloy with recommended thicknesses, to that of the reference TaBN 60 nm absorber using Leaf shape Dipole (LDP), Inner Half Leaf shape Dipole (IHLDP) and Outer Half Leaf shape Dipole (OHLDP) for Line and Space (LnS) pattern with trench width of 10nm and the smallest pitch of 20 nm. The study confirms that TaCo alloy exhibits improved NILS and lower BFV compared to the reference TaBN 60 nm absorber.

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“…Since SRAF size was not optimized, printability of the SRAF can be seen as a pin hole for BF and transferable SRAF printing for DF case. LCDU can be minimized if NILS is maximized, or increasing in dose where resist is made less sensitive (or more photons contribute to pattern formation) [2] .…”

Section: Flare Impact On Random Logic Clipmentioning

confidence: 99%

EUV single patterning of random logic via using bright field mask

Tan

Gillijns

Lee

et al. 2023

Optical and EUV Nanolithography XXXVI

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Imec logic N2+ design rule defines a minimum via pitch of 36nm. An EUV single patterning solution at 0.33 NA is explored on a random logic via design. From an earlier simulation study [1] , it was shown that Ta-based bright field mask delivers the best resolution enhancement technology (RET) solution. In this paper the simulation results will be validated on wafer. Negative-tone development (NTD) with a metal-oxide resist process using a bright field (BF) mask and positivetone development (PTD) with a chemically amplified resist process using a dark field (DF) mask are compared. In addition, source-mask optimizations (SMO) including sub-resolution assist features (SRAF) were used as a RET, and optical proximity correction (OPC) was carried out on the design clips to achieve optimum lithography performance.We report the best choice among the listed options, and present our recommendation on OPC, RET and process based on the simulation and wafer data in order to improve the resolution, therefore extending the single exposure pitch limit.

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Fundamental understanding and experimental verification of bright versus dark field imaging

Cited by 11 publications

References 5 publications

Evaluation of Ta-Co alloys as novel high-k EUV mask absorber

Evaluation of Ta-Co alloys as novel high-k EUV mask absorber

Optimizing EUV imaging metrics as a function of absorber thickness and illumination source: simulation case study of Ta-Co alloy

EUV single patterning of random logic via using bright field mask

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