Sub-30 nm lithography in a negative electron beam resist with a vacuum scanning tunneling microscope

We report studies of minimum feature sizes in 50 nm films of the high-resolution negative electron beam resist, SAL-601-ER7 from the Shipley Corporation. Developed linewidths of 27 nm and line spacing of 55 nm, from center to center, were produced by lithography with a vacuum scanning tunneling microscope (STM). In contrast, a minimum linewidth of 95 nm was obtained from exposure with a 17 nm (1/e diameter) 50 kV electron beam. Patterns written in the STM at electron energies down to 15 eV were visible in the developed resist. The limit at 15 eV is related to the operation of the STM and does not represent an exposure threshold energy for the resist.