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Ion Beam Lithography “Bottoms-up Nanoscale Design” Brian Ellis. Lithography Process. Replication of a master pattern onto a substrate Coat the substrate with a radiation-sensitive polymer film (a resist) Expose specific area of film to radiation, which alters properties (solubility) of film.
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Ion Beam Lithography “Bottoms-up Nanoscale Design” Brian Ellis
Lithography Process • Replication of a master pattern onto a substrate • Coat the substrate with a radiation-sensitive polymer film (a resist) • Expose specific area of film to radiation, which alters properties (solubility) of film
Ion Beam Lithography (IBL) • Ion beams: H+, He+, Ga+ • Several implementations: • Focused IBL (direct writing) • Masked IBL (beam passes through ion-transparent membrane, patterned with absorber material, positioned close to coated substrate) • Resists: Polymethylmethacrylate (PMMA) is most common, Poly(butene-1-sulfone), Poly(2,2,2-trifluoroethyl-α-chloroacrylate) • Penetration of the particle beam is small, compared to electron beam • reduce blurring resulting from beam scattering (reduce proximity effect; increase localization, precision)
Ion Beam (H+, He+) • Ionization region: plasma formed • Potential placed at extraction region removes ions from chamber • J. Melngailis et al. J. Vac. Sci. Tech. 16 (1998), 927.
Gallium Ion Beam • Ion source: tungsten wetted with gallium • Ion extraction is observed by applying 5-7 kV (VEXT) • Aperatures focus beam • Deflector directs the beam onto substrate • <1000 Å spots can be obtained • R. L. Kubena et al. App. Phys. Lett. 34 (1979), 310.
Etching a Gold Substrate • R. L. Kubena et al. J. Vac. Sci. Tech. 16 (1979), 1610.