MEV ION-BEAM LITHOGRAPHY OF PMMA

X-ray lithography mask contrast is limited by the thickness of the patterned absorber layer. This is limited by the need to use thin resist layers to maintain the high spatial resolution when fabricated using electron beam lithography (EBL) because electron scattering severely limits the minimum achievable linewidth in thick samples. A MeV proton beam suffers much less lateral scattering than a keV electron beam so higher resolutions should be possible in thick resist layers. This paper presents experimental results showing a 2.0 mum wide channel etched through approximately 10 mum of PMMA (polymethyl methacrylate) using a focused 3 MeV proton beam. Simulations demonstrating that the minimum attainable linewidths for 3 MeV protons are approximately 120 nm through 10 mum of PMMA are also presented.