Polymethyl methacrylate sensitivity variation versus the electronic stopping power at ion lithography exposure

Experimental data for the minimum ion dose D0 during exposure and for the contrast parameter γ are presented. A dependence of D0 on the electronic stopping power but no correlation between D0 and nuclear stopping power is found. An analogical dependence on minimum absorbed electronic stopping energy density is also found. The absorbed energy density for H+ ions is comparable with X-ray lithography data but heavier ions are more effective. For the understanding of these relations an electron excitation spike mechanism is suggested. From the non-Rutherford backscattering experiments at 1.7–1.75 MeV the energy losses of protons in polymethyl methacrylate are found to be 25 eV/nm.