Fast and blister-free irradiation conditions for cross-linking of PMMA induced by 2MeV protons
For soft lithography, the conventional negative tone resists, such as SU-8, that are used to create the mold have a number of drawbacks. PMMA, which is normally used as a positive tone resist, can be used as a negative resist by using high-fluence irradiation conditions. In this report, we outline optimization of the irradiation conditions for PMMA thin films using 2MeV H+ ions to exploit their ability to work as a negative tone resist at ion fluences above 1.01015ionscm?2. The main aim was to induce cross-linking while maintaining the exposed regions free of blisters and maintaining short irradiation times. We found that by using a two-step process with a low-flux irradiation, followed by a high-flux irradiation, the exposure time could be shortened by ?50%. We also found that ion fluences greater than 5.01015ionscm?2 minimized the distortion in stitched regions.
blisters cross-linking pmma negative resists contraction h+ ion irradiation