Assist features: placement, impact, and relevance for EUV imaging

Mochi, Iacopo; Philipsen, Vicky; Gallagher, Emily; Hendrickx, Eric; Lyakhova, Kateryna; Wittebrood, Friso; Schiffelers, Guido; Fliervoet, Timon; Wang, Shibing; Hsu, Stephen; Plachecki, Vince; Baron, Stan; Laenens, Bart

doi:10.1117/12.2220025

Cited by 11 publications

(7 citation statements)

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“…Selecting the correct mask absorber material and thickness helps in reducing M3D effects [2,8,9]. This approach is complementary to other M3D mitigation strategies, such as source optimization [10], sub-resolution assist feature placement [11], and transition to anamorphic high-NA EUV lithography [12]. This paper will focus on absorber material as a mitigation strategy for M3D effects, and we verify whether mask absorber materials with high extinction coefficient κ and refractive coefficient n close to unity can be generated by combining Al and Ni in an alloy.…”

Section: Figurementioning

confidence: 99%

Ni-Al Alloys as Alternative EUV Mask Absorber

et al. 2018

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Extreme ultraviolet (EUV) lithography is being industrialized as the next candidate printing technique for high-volume manufacturing of scaled down integrated circuits. At mask level, the combination of EUV light at oblique incidence, absorber thickness, and non-uniform mirror reflectance through incidence angle, creates photomask-induced imaging aberrations, known as mask 3D (M3D) effects. A possible mitigation for the M3D effects in the EUV binary intensity mask (BIM), is to use mask absorber materials with high extinction coefficient κ and refractive coefficient n close to unity. We propose nickel aluminide alloys as a candidate BIM absorber material, and characterize them versus a set of specifications that a novel EUV mask absorber must meet. The nickel aluminide samples have reduced crystallinity as compared to metallic nickel, and form a passivating surface oxide layer in neutral solutions. Composition and density profile are investigated to estimate the optical constants, which are then validated with EUV reflectometry. An oxidation-induced Al L2 absorption edge shift is observed, which significantly impacts the value of n at 13.5 nm wavelength and moves it closer to unity. The measured optical constants are incorporated in an accurate mask model for rigorous simulations. The M3D imaging impact of the nickel aluminide alloy mask absorbers, which predict significant M3D reduction in comparison to reference absorber materials. In this paper, we present an extensive experimental methodology flow to evaluate candidate mask absorber materials.

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Section: Figurementioning

confidence: 99%

Ni-Al Alloys as Alternative EUV Mask Absorber

et al. 2018

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“…Foundries started to apply SRAF in EUV and lithographers reported EUV SRAF study and evaluation. 2,3,4,5 The early published works are mostly based on the simulation and experiments with larger assist sizes, i.e., 10-14 nm, for the larger insert pitches of 72 nm above for the minimum pitch of 36 nm application.…”

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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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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“…It has been shown that they can be also used to reduce the differences between the BF position of dense and isolated features [40][41][42]. The impact of assist features on the phase of the near field and on the BF vs. pitch is demonstrated in Figure 17.…”

Section: Sub-resolution Assist Featuresmentioning

confidence: 99%

Characterization and mitigation of 3D mask effects in extreme ultraviolet lithography

Erdmann

Evanschitzky

et al. 2017

Advanced Optical Technologies

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Abstract:The reflection and diffraction of extreme ultraviolet (EUV) light from lithographic masks and the projection imaging of these masks by all-reflective systems introduce several significant imaging artifacts. The off-axis illumination of the mask causes asymmetric shadowing, a size bias between features with different orientations and telecentricity errors. The image contrast varies with the feature orientation and can easily drop far below intuitively expected values. The deformation of the wavefront or phase of the incident light by thick absorbers generates aberration-like effects, especially variations of the best-focus (BF) position vs. the pitch and size of the imaged patterns. Partial reflection of light from the top of the absorber generates a weak secondary image, which superposes with the main image. Based on a discussion of the root causes of these phenomena, we employ mask diffraction and imaging analysis for a quantitative analysis of these effects for standard EUV masks. Simulations for various non-standard types of mask stacks (e.g. etched multilayers, buried shifters, etc.) and for various non-standard absorber materials are used to explore the imaging capabilities of alternative masks for EUV lithography. Finally, an outlook at anamorphic systems for larger numerical apertures is given.

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Assist features: placement, impact, and relevance for EUV imaging

Cited by 11 publications

References 0 publications

Ni-Al Alloys as Alternative EUV Mask Absorber

Ni-Al Alloys as Alternative EUV Mask Absorber

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

Characterization and mitigation of 3D mask effects in extreme ultraviolet lithography

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