Low-energy Electron-beam Lithography of ZEP-520 Positive Resist

Low-energy electron-beam (e-beam) lithography using ZEP-520 as a positive resist has been investigated in the energy range between 0.5 and 20 keV. The interaction between electrons and ZEP-520 resist, and its effect on the exposure dose and the penetration depth of the electrons have been studied as a function of electron energy. At 10 keV ~ 20 keV energy, we were able to achieve line gratings of about 25 nm width and 80 nm pitch in ZEP-520 films of 180 nm-thickness on silicon substrate. It is found that the main limitation in achieving high resolution and dense pattern exposure at low energy is the electron forward scattering effect for thicker resist film. Using 60nm thickness of ZEP-520 resist, we have achieved 15 nm line width with 60 nm pitch grating structures