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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)
Small Molecule Additives
•Expose specific area of film to radiation, which alters properties
(solubility) of film
Resist
Substrate
Ion Beam
Radiation
Positive
Develop
Pattern
Negative
Strip
Resist
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-1sulfone), 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
Etchinga aGold
GoldSubstrate
Substrate
1400 Å
550 Å
L. Kubena et al. J. Vac. Sci. Tech. 16 (1979), 1610.
R. L. Kubena et al. J. Vac. Sci. Tech. 16 (1979), 1610.
970 Å
400 Å