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

Thakare, Devesh; Delabie, Annelies; Philipsen, Vicky

doi:10.1117/12.2640098

Cited by 2 publications

(2 citation statements)

References 20 publications

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“…The results of our preliminary simulations also support the idea of improving EUV imaging metrics as a function of optical properties and thickness of the absorber with the inclusion of an illumination source. A separate paper will discuss the detailed reasoning and methods employed for determining the optimized absorber thickness 38 Telecentric σ for LnS=λ2NAP,Telecentric σ for CH=λ2NAP,where λ denotes the wavelength of the illumination, NA is the numerical aperture, and P is the pattern pitch.…”

Section: Methodsmentioning

confidence: 99%

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

Thakare

Opsomer

et al. 2023

J. Micro/Nanopattern. Mats. Metro.

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Background: A plausible approach for mitigating the mask 3-D (M3D) effects observed in extreme ultraviolet (EUV) lithography is to replace the existing mask absorber with alternative materials. Absorbers with a high EUV extinction coefficient k allow for lower best focus variation (BFV) through pitch and reduced telecentricity errors (TCEs).Aim: We aim to evaluate Ta-Co alloys as potential high-k mask absorbers from material suitability and imaging standpoints.Approach: We study the film morphology, surface composition, and stability of Ta-Co alloys in mask cleaning solutions and a hydrogen environment as present in the EUV scanner to assess the material suitability from an experimental aspect. Optical constants for three selected compositions, viz., TaCo, Ta 2 Co, and TaCo 3 , were determined from EUV angle-dependent reflectivity measurements. Next, utilizing rigorous simulation software, the imaging performance of Ta-Co alloys is evaluated and compared with the reference absorber. The recommended absorber thickness for Ta-Co alloy absorbers is based upon normalized image log slope (NILS) enhancement, threshold to size, and balancing of diffraction order amplitudes. A 10 nm line and space pattern with a pitch of 20 nm and 14 nm square contact holes with a pitch of 28 nm are used for the simulation study using high numerical aperture 0.55 EUV lithography process settings. The primary imaging metrics for through pitch evaluation include NILS, TCE, and BFV. Results:The Ta-Co alloys exhibit a higher EUV extinction coefficient k compared with the currently used Ta-based absorber. TaCo and Ta 2 Co demonstrate smooth surfaces and are stable in a hydrogen environment and in mask-cleaning solutions. Conclusion:Ta-Co alloys allow for a reduction in M3D effects at a lower absorber thickness compared with a 60 nm Ta-based reference absorber.

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Section: Methodsmentioning

confidence: 99%

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

Thakare

Opsomer

et al. 2023

J. Micro/Nanopattern. Mats. Metro.

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“…To understand the preferred EUV n & k regions for mask absorber in terms of best focus variation and MEEF through pitch, we plot for the selected illumination source (C) the multiple graphs through absorber thickness as shown in Figure 12. Typically, the absorber thickness optimization methodology is depicted by best trade-off between imaging properties, NILS, dose which indicates throughput, telecentricity error and best focus shift 19 . In this paper, the desirable thickness region (purple area in Fig.…”

Section: Impact Of Mask Absorber Optical Properties At 033-na Euv Ima...mentioning

confidence: 99%

Study of MEEF improvement with low-n absorber EUVL mask

Takahata,

Kovalevich,

Simone

et al. 2024

Optical and EUV Nanolithography XXXVII

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Extreme ultraviolet lithography (EUVL) system at 0.33 numerical aperture (NA) has been used for high volume manufacturing of advanced technology node devices. As pattern pitch shrinks, low-k1 imaging becomes necessary but it typically suffers from reduced imaging contrast. In the case of low-k1 imaging, critical dimension (CD) variation on EUV mask enhances on wafer, which is called Mask Error Enhancement Factor (MEEF). CD variation for tighter line and space (L/S) features on the photomask has taken up a large fraction of wafer CD variation. Therefore, it is important to balance improvement of Normalized Image Log Slope (NILS) and MEEF. Understanding the mask contribution to EUVL is one of the important initiatives to further optimize 0.33-NA EUVL employability towards pushing down pitch scaling. The optical properties of the EUV mask absorber, which are the refraction index n and extinction coefficient k, have potential to improve NILS and MEEF. Low-n attenuated phase-shift mask (attPSM) is expected to mitigate mask three dimensional (M3D) effects and to enhance the image contrast compared to traditional Ta-based absorber mask. In this study we experimentally evaluated the MEEF on the drawn feature size, illumination, and mask absorber properties to characterize the impact of these optical factors on MEEF for the appropriate condition using the NXE:3400B EUV scanner. This paper covers two types of mask absorber materials which are Ta-based and low-n attPSM. We experimentally demonstrated that low-n absorber EUVL mask is expected to improve the balance of MEEF at vertical L/S through pitch due to suppression of best focus variation. We also tried to identify the suitable absorber optical properties in terms of MEEF and NILS on both 0.33-NA and 0.55-NA EUVL through rigorous lithographic simulations.

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

Cited by 2 publications

References 20 publications

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

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

Study of MEEF improvement with low-n absorber EUVL mask

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