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EUV Maskless Lithography

EUV Maskless Lithography J. Vac. Sci. Technol. B 30, 051606 (2012); http://dx.doi.org/10.1116/1.4752112. EUV Maskless Lithography. Concept: -Scanned-spot array (e.g., 4000-by-4000 array over 10 mm square image field, 2.5 μ m spacing)

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EUV Maskless Lithography

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  1. EUV MasklessLithographyJ. Vac. Sci. Technol. B 30, 051606 (2012); http://dx.doi.org/10.1116/1.4752112 K. Johnson kjinnovation@earthlink.net

  2. EUV Maskless Lithography Concept: • -Scanned-spot array (e.g., 4000-by-4000 array over 10 mm square image field, 2.5 μm spacing) • Spots can be either individually modulated (with an SLM) or source-modulated (for printing periodic patterns). Performance capability (based on JVST-B paper): • ~20 nm print resolution (13.5-nm wavelength, 0.3 NA, EUV source ~40 μm diameter with 1 steradian collection per image field) • ~30 (300-mm) wafers per hour, with 500 kHz EUV source (“… Using a 10 μm nozzle tin droplets as small as 17 μm in diameter at a 550 kHz repetition rate have been demonstrated. …” Brandt et al., Ref. 25) Advantages: • Maskless • Eliminates coherent proximity effects • Comparatively simple optics (e.g., only 2 projection mirrors) • Comparatively moderate EUV power requirement K. Johnson kjinnovation@earthlink.net

  3. Schematic: object surface object spot array detail view 1 M2 M1 Projection Optics • Two-mirror, flat-image Schwarzschild system • 10-mm square image field • 10-X reduction • 0.3 NA (obscuration: 0.12-NA) Effect of central obscuration on focused image spot: unobscured obscured side lobe (Side lobe has relatively minimal effect because image spots do not overlap.) K. Johnson kjinnovation@earthlink.net

  4. Schematic (detail view 1) EUV illumination L0 L1 intermediate focus aperture object surface virtual object spot microchannel array L2 Spot-Generation Optics • Phase-Fresnel microlens arrays (L1 & L2) in achromatic configuration (L0 beam shaper optional) • Transmittance (including lenses, substrates, fill factor losses) about 20%; no spectral narrowing. • Can accommodate SLM shutters at intermediate foci. Microlens Fresnel zone structure at edge of object field detailview 2 mm K. Johnson kjinnovation@earthlink.net

  5. Microlens profile(detail view 2) Microlens Structure • Stepped Fresnel profile: 8 bilayers of Mo (20 nm) / Ru (2 nm etch stop) on thin Si substrate • Minimum Fresnel zone width: 0.9 μm • Deposition tolerances: about 26X less stringent than EUV reflection optics • Axial lens positioning tolerance (focus): about 100X less stringent than EUV reflection optics • Patterning/alignment tolerances: about 10 nm (comparable to EUV photomasks) K. Johnson kjinnovation@earthlink.net

  6. Aberration Compensation • Microlens design completely eliminates geometric aberration (including image distortion and image field curvature). • Microlens doublet configuration substantially eliminates chromatic aberration. Image of object point (at field edge), no aberration correction: With aberration correction (at 3 wavelengths: 13.4, 13.5, 13.6 nm): nm nm K. Johnson kjinnovation@earthlink.net

  7. EUV Source and Collection Optics • Power requirement: modest due to comparatively low throughput (e.g., 30 wph) and few near-normal-incidence mirrors. • Source size requirement: The scan spots are demagnified images of the source; should be within the diffraction limit. (1 steradian collected from a 40-μm source could be partitioned, e.g., into a 4000-by-4000 array of spots with 1-steradian convergence cones and 10-nm geometric spot size). • Rep rate requirement: Printing throughput is proportional to the rep rate and number of spots (e.g., with a 500 kHz rep rate, 16 million spots, and 10-nm grid step, the scan rate would be 8 cm2/sec). • Source power sharing: The source size (area) can be N times larger, and the rep rate N times smaller, if N print units are supplied from a single source. (Throughput per source will be the same as N=1.) • The microlens design can correct moderate imperfections in the collection optics : • Non-ideal beam shape. • Nonuniform source magnification across microlens array. • Nonuniformradiant intensity across microlens array. K. Johnson kjinnovation@earthlink.net

  8. EUV Maskless Lithography Development Tasks • Develop system design outline based on realistic, practical source characteristics: • Source size? (limits print resolution) • Rep rate? (limits printing throughput) • Power? (comparatively moderate power requirement) • Develop detailed, full-system optical design; simulate lithography performance. • Evaluate microlens/microchannel fabrication methods. • Evaluate SLM feasibility. • Economic modeling. • Proof-of-concept prototype (e.g., using the CXRO’s MET tool) • Productization options: • Source-modulated (alternative to interference lithography, GRATE for HVM) • Full image modulation with SLM (alternative to maskless e-beam, e.g., REBL, MAPPER) • BEUV (Maskless capability and simplified projection optics could facilitate accelerated development of 6.x-nm lithography.) K. Johnson kjinnovation@earthlink.net

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