Best focus shift mechanism for thick masks

Burkhardt, Martin; Raghunathan, Ananthan

doi:10.1117/12.2085948

Cited by 14 publications

(10 citation statements)

References 3 publications

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“…These effects are experimentally observable, as feature orientation-dependent shadowing effects [3], best focus variation through pitch [4], feature size-dependent pattern shift through focus [5,6], and pattern asymmetry and contrast loss [7]. Selecting the correct mask absorber material and thickness helps in reducing M3D effects [2,8,9].…”

Section: Figurementioning

confidence: 99%

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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%

“…The introduction of pellicles in EUV lithography will likely reduce the number of cleaning cycles necessary during the lifetime of an EUV mask. In this paper, we have tested cleaning compatibility of Ni x Al y alloy samples by 24 h submersion tests in DIW, and in NH 4 OH.…”

Section: Film Morphologymentioning

confidence: 99%

Ni-Al Alloys as Alternative EUV Mask Absorber

et al. 2018

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“…1 Feature sizes at these nodes require the use of resolution enhancement techniques in EUVL from the start, not leaving much room to further decrease critical dimensions (CD) without using double patterning. 2 The next generation of EUVL at higher NA is under development now and will be required soon after the insertion of EUVL into production in order to keep the technology on track down to smaller feature sizes.…”

Section: Introductionmentioning

confidence: 99%

Emulation of anamorphic imaging on the SHARP extreme ultraviolet mask microscope

Benk

Wojdyla

Chao

et al. 2016

J. Micro/Nanolith. MEMS MOEMS

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Abstract. The SHARP High numerical aperture Actinic Reticle review Project is a synchrotron-based, extreme ultraviolet (EUV) microscope dedicated to photomask research. SHARP emulates the illumination and imaging conditions of current EUV lithography scanners and several generations into the future. An anamorphic imaging optic with increased mask-side numerical aperture (NA) in the horizontal and increased demagnification in the vertical direction has been proposed to overcome limitations of current multilayer coatings and extend EUV lithography beyond 0.33 NA. Zoneplate lenses with an anamorphic 4x/8x NA of 0.55 are fabricated and installed in the SHARP microscope to emulate anamorphic imaging. SHARP's Fourier synthesis illuminator with a range of angles exceeding the collected solid angle of the newly designed elliptical zoneplates can produce arbitrary angular source spectra, matched to anamorphic imaging. A target with anamorphic dense features down to 50-nm critical dimension is fabricated using 40-nm of nickel as the absorber. In a demonstration experiment anamorphic imaging at 0.55 4x/8x NA and 6º central ray angle (CRA) is compared to conventional imaging at 0.5 4x NA and 8º CRA. A significant contrast loss in horizontal features is observed in the conventional images. The anamorphic images show the same image quality in the horizontal and vertical directions.

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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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Best focus shift mechanism for thick masks

Cited by 14 publications

References 3 publications

Ni-Al Alloys as Alternative EUV Mask Absorber

Ni-Al Alloys as Alternative EUV Mask Absorber

Emulation of anamorphic imaging on the SHARP extreme ultraviolet mask microscope

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

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