Actinic characterization and modeling of the EUV mask stack

Philipsen, Vicky; Hendrickx, Eric; Jonckheere, R.; Davydova, Natalia; Fliervoet, Timon; Neumann, Jens Timo

doi:10.1117/12.2030663

Cited by 23 publications

(15 citation statements)

References 11 publications

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“…The parameters of the mask multilayer are taken from Ref. 24. The options for the mask absorber are summarized in Table 1.…”

Section: Resultsmentioning

confidence: 99%

Attenuated phase shift mask for extreme ultraviolet: can they mitigate three-dimensional mask effects?

2018

J. Micro/Nanolith. MEMS MOEMS

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The understanding, characterization, and mitigation of three-dimensional (3-D) mask effects including telecentricity errors, contrast fading, and best focus shifts become increasingly important for the performance optimization of future extreme ultraviolet (EUV) projection systems and mask designs. We explore the potential of attenuated phase shift mask (attPSM) to mitigate 3-D mask effects and exploit them for future EUV imaging. The scattering of light at the absorber edges results in significant phase deformations, which impact the effective phase and the lithographic performance of attPSM for EUV. Rigorous mask and imaging simulations in combination with multiobjective optimization techniques are employed to identify the most appropriate material properties, mask, and source geometries. The resulting imaging performance is compared to the achievable performance of binary EUV masks.

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“…The parameters of the mask multilayer are taken from Ref. 24. The options for the mask absorber are summarized in Table 1.…”

Section: Resultsmentioning

confidence: 99%

Attenuated phase shift mask for extreme ultraviolet: can they mitigate three-dimensional mask effects?

2018

J. Micro/Nanolith. MEMS MOEMS

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“…The EUV reflective mirror is a calibrated model of an experimentally validated Mo/Si ML mirror capped with Ru [52]. The Ni x Al y absorber models contains two layers: a surface oxide layer with fixed 3 nm thickness and a bulk metal absorber layer.…”

Section: Euv Imaging Simulationsmentioning

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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“…As a result we get a very good match of simulated and measured absorber reflectivity spectra through absorber height. A similar approach to mask stack calibration is also used in other investigations [13] . …”

Section: I I I I Imentioning

confidence: 92%

Experimental approach to EUV imaging enhancement by mask absorber height optimization

et al. 2013

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EUV lithography performance is improved significantly by optimizing and fine-tuning of the EUV mask. The EUV mask is an active element of the scanner optical system influencing main lithographic figure of merits such as image contrast, critical dimension uniformity (CDU), focus and overlay. The mask stack consists of Mo/Si multilayer acting as a bright field and a patterned absorber stack. In this work we will concentrate on investigation of EUV absorber.Absorber topography that is pronounced compared to the imaging wavelength of 13.5 nm, will give rise to various mask 3d effects such as shadowing or dependence of CD on feature orientation, best focus shift of different resolution structures, etc. [1] [2] . Light interference in the absorber layer results in swinging behavior of various lithography metrics as function of the absorber height [5] . Optimization of the mask absorber allows mitigating mask 3d effects and improving imaging performance. In particular, reduction of the absorber height mitigates the shadowing effect and relaxes requirements on Optical Proximity Correction (OPC), but can result in smaller Process Window due to lower imaging contrast and larger best focus shifts.In this work we will show results of an experimental approach to absorber height optimization. A special mask with 27 different absorber heights in the range 40-70 nm is manufactured by Toppan Photomasks. EUV reflectivity spectra are measured for the different absorber heights and an experimental swing curve is constructed.For each absorber height various resolution features are present on the mask. Lines of 27 nm and 22 nm are imaged on the wafer using the ASML EUV scanner NXE:3300B with an NA of 0.33. The experimental CD swing curve is constructed as well as HV change as a function of absorber height. The impact of the absorber height on Exposure Latitude (EL) and Dose to Size (D2S) is investigated. EL improves with increasing absorber height in some cases, however there is no clear EL gain for a 70 nm absorber compared to for example 52 nm absorber. D2S does show a clear trend through absorber height. In particular, D2S can be reduced by absorber height reduction: e.g. for 52 nm absorber D2S is 5% or 1 mJ/cm 2 smaller compared to 70 nm.The experimental results are used for calibration and verification of rigorous mask 3d simulations. This knowledge is crucial for accurate OPC of production masks and allows for accurate litho simulations of EUV user cases as a basis for lithography roadmaps towards High Volume Manufacturing and High NA EUV.EUV absorber behavior is determined by phase shifts Reflectivity Swing Curve X 8% k 6% 4% 2% awrmiim mm 55 6.5 75 85 9.5 10.5 Ab orbe heieht,A /2n Light retardation in the matter 4 phase shift Substrate: LTEM EUV mask n -refraction index of absorber 46, 53, 60, 67.5, 75, 82 (for n = 0.95) 180° phase shift between bright field and dark field: A h 67.5 (for n=0.95) 1. Figure 1 Two types of phase shifts in EUV mask: (a) Interference between reflection at the top of the absorber and from the multil...

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Actinic characterization and modeling of the EUV mask stack

Cited by 23 publications

References 11 publications

Attenuated phase shift mask for extreme ultraviolet: can they mitigate three-dimensional mask effects?

Attenuated phase shift mask for extreme ultraviolet: can they mitigate three-dimensional mask effects?

Ni-Al Alloys as Alternative EUV Mask Absorber

Experimental approach to EUV imaging enhancement by mask absorber height optimization

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