Focus considerations of design pitches and absorber choice for EUV random logic

Burkhardt, Martin; Chen, Zheng G.; Halle, Scott; Lallement, Romain J.; Sieg, Stuart; Meli, Luciana

doi:10.1117/12.2614296

Cited by 10 publications

(10 citation statements)

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“…1, we observe that the BF/DOF/EL are well predicted by simulations. BF shifts through pitch due to the mask 3D effects, 1 where the shift directions and ranges are also the function of the illumination. In general, the BF is more positive at the illumination optimized pitches and shifts toward negative direction while pitches are away from the illumination optimized pitch.…”

Section: Experiments and Simulation Validationmentioning

confidence: 99%

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EUV sub-resolution assist feature impact: experimental and simulation evaluation

Chen

Burkhardt

Sieg

et al. 2023

Optical and EUV Nanolithography XXXVI

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Aggressive off-axis illumination must be used to resolve line space pitches of 28nm and below. The consequence is that the best focus (BF) shifts a lot and depth of focus shrinks rapidly through pitch. This is mainly due to the mask 3D effects. To reduce the impact the best-known method is to introduce sub-resolution assist features (SRAF). We explored wafer printing with SARF size of 6-8 nm and analyzed BF and DOF impact. Clear SRAF sizes of 6-8 nm do not print with PCAR but some 7-8 nm clear SRAF printed with NTD MOR due to the higher resolution and over exposure preference. Then we validated the experiments with SLITHO simulation tool, and we found a good experiment-simulation match of BF/DOF/EL/MEF w and w/o SRAF through pitch with the three P28 illumination candidates. Overall SRAF can improve the DOF and exposure latitude (EL) for the given pitches with SRAF capable and help shift the BF to the favored focus direction. With the validated model we further study BF/DOF/EL/MEF w and w/o SRAF through pitch with the small/medium/large sigma illuminations designed for 28nm pitch, with traditional TaBN and other three candidate absorbers. We will also discuss the SRAF size and placement sensitivities. Through this work we are confident to implement SRAF to enlarge the common process window for a large range of pitches.

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Section: Experiments and Simulation Validationmentioning

confidence: 99%

“…This is mainly due to the mask 3D effects. 1 There are several ways to mitigate the impacts. One of the best-known methods is to apply sub-resolution assist features (SRAF), which is popularly used in DUV.…”

Section: Introductionmentioning

confidence: 99%

EUV sub-resolution assist feature impact: experimental and simulation evaluation

Chen

Burkhardt

Sieg

et al. 2023

Optical and EUV Nanolithography XXXVI

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“…Mask structure details are reported at the bottom-left of each table: these values are at wafer level, for mask dimensions they must be multiplied by 8 in case of horizontal structures, by 4 if vertical. It should be noted how the SMO naturally leads to having strong asymmetry along the vertical axis of both illumination and mask SRAF CD and SRAF Spacing to counterbalance mask shadowing effects which naturally distort positive and negative diffraction orders 5,6,7 .…”

Section: Organic Ptd Carmentioning

confidence: 99%

“…This comes after almost 20 years of steady ~ 100 nm DoF, from the last nodes printed with ArFi lithography to current nodes where EUV has been implemented. Unfortunately, due to the reflective nature of EUV optical systems, several across-focus effects such as best focus shift 5,6 and Pattern Placement Errors (PPE) 7,8 further limit the Process Window (PW) when different structures must be combined.…”

Section: Introductionmentioning

confidence: 99%

Depth of focus in high-NA EUV lithography: a simulation study

Burov¹,

Pret²,

Gronheid

2022

Photomask Technology 2022

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High-NA EUV lithography tools are projected to be deployed in HVM by 2025/2026, with the introduction of the N1.4 node. This should allow single-exposure EUVL at 30 nm pitch and below and reduce cost and complexity. One of the main challenges in process control will be the budgeting of depth of focus. With Rayleigh’s equations in mind and considering a relatively thick photoresist needed for etching purposes, an overall focus window of less than 40 nm is expected for high-NA EUV exposures. This is concerning, considering that after almost two decades at roughly constant depth of focus (~100 nm for 1.35 NA ArF immersion and 0.33 NA EUV), we may potentially be dealing with 2-3X lower usable focus range. On top of that - and differently from the DUV case - increasing NA in EUVL exacerbates the impact of complex 3D mask effects which, in a non-telecentric tool with an oblique incidence at the mask, negatively impact best focus shifts across mask pitch and feature CD. In this paper, we look at how to mitigate lines/spaces depth of focus loss across pitch by exploring source, mask pattern and mask stack optimization. Moreover, we compare the best strategy between bright/dark exposures, mask transmissivity, and phase-shifting combined with assist features, resist thickness, and feature orientation. Finally, we compare the optical performance with defect-aware process windows at 0.33 vs. 0.55 NA based upon stochastic resist calibration for generic positive-tone organic CAR, and negative-tone inorganic platforms.

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“…When simulation studies demonstrated the significant impact of mask absorbers on image quality at the wafer level for EUV imaging, a resurgence of interest in studies related to materials for EUV mask absorbers is observed in recent times [1]. 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.…”

Section: Introductionmentioning

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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Focus considerations of design pitches and absorber choice for EUV random logic

Cited by 10 publications

References 0 publications

EUV sub-resolution assist feature impact: experimental and simulation evaluation

EUV sub-resolution assist feature impact: experimental and simulation evaluation

Depth of focus in high-NA EUV lithography: a simulation study

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

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