Lithography exposure characteristics of poly(methyl methacrylate) (PMMA) for carbon, helium and hydrogen ions

Why are hydrogen ions best for MeV ion beam lithography?

“…The detailed cleaning procedure was described previously in Ref. [15]. The ion exposures were performed by using the PPAL system at the 1.7 MeV Pelletron in Jyväskylä [3,4], with various fluences using 2 MeV 1 H þ , 3 MeV 4 He 2þ and 6 MeV 12 C 3þ ions (Table 1) Confocal Raman measurements for the different ions irradiations were conducted at Nanoscience Center, University of Jyväs-kylä using backscattering geometry, with 532.0 nm excitation [16].…”

“…L represents a tolerance to a change in exposure from experimental variations and stitching [15]. L is 10.6, 2.25 and 1.9 for 1 H, 4 He and 12 C. This implies PMMA is most tolerant toward differences in exposure for proton irradiation.…”

Development of economic MeV-ion microbeam technology at Chiang Mai University

“…Exposure characteristics of the materials to the microbeam were studied for fluence conditions satisfying production of good quality microstructures. In order to produce microstructures in "positive" resist tone of PMMA, the ion fluence Φ should satisfy the [14] so that an applied ion fluence for a certain material could be determined from the database. In using apertures for microbeams, concerns are normally on the beam scattering caused divergence behind the aperture.…”