HIGH-RESOLUTION LITHOGRAPHY WITH A VACUUM STM

The scanning tunneling microscope (STM) is demonstrated to be a useful low-energy e-beam lithographic tool and a valuable probe of resist materials. Lithography with a vacuum STM and a 10 nm 50 kV e-beam has been performed on identically prepared and processed films of a state-of-the-art high-resolution negative resist (SAL-601 from Shipley). On bulk substrates (Si and GaAs), resist films up to 50 nm thick have been patterned, developed and observed in a scanning electron microscope. A resist thickness of 50 nm is sufficient to withstand a reactive ion etch. On Si, the minimum feature size observed with the 50 kV e-beam was 95 nm. In contrast, the STM lithography defined features observed in the developed resist to have linewidths down to 23 nm. The variation of feature size with exposure dose, exposure voltage and resist thickness has been studied. The STM lithography has shown that SAL-601 is inherently capable of sub 25 nm resolution and that low voltage e-beam lithography can produce smaller minimum feature sizes than lithography with a 10 nm 50 kV e-beam.