ELECTRON-BEAM LITHOGRAPHY WITH THE SCANNING TUNNELING MICROSCOPE

The scanning tunneling microscope (STM), operated in vacuum in the field emission mode, has been used in lithographic studies of the resist SAL-601 from Shipley. Patterns have been written by raising the tip-sample voltage above -12 V while operating the STM in the constant current mode. Resist films, 50 nm thick, have been patterned and the pattern transferred into the GaAs substrate by reactive ion etching. The variation of feature size with applied dose and tip-sample bias voltage has been studied. Comparisons have been made to lithography with a 10 nm, 50 kV electron e-beam in a JEOL JBX-5DII in the same resist thickness films. In all cases the resist films were processed in the standard fashion before and after exposure. The STM can write smaller minimum features sizes and has a greater process latitude. Proximity effects are absent due to the reduced scattering range of the low energy primary electrons. However, the writing speed is slower, being limited by the response of the piezoelectric scanner. Advances have been made recently in the construction of fast STMs which scan at video rates making the STM comparable in speed to the JEOL for nanolithography. The development of ultralow voltage e-beam lithography based on STM technology is discussed.