Low-voltage electron beam lithography with a scanning tunneling microscope

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Abstract
Studies of a polydiacetylene negative electron beam resist have been made in a scanning tunneling microscope operated in vacuum at pressures in the 10−8 Torr range. The resist can be imaged if it is applied as a thin film to a conductive flat substrate and the tip bias voltage is chosen appropriately. An exposure threshold energy close to 8 eV has been observed for the formation of raised features in the resist. A minimum feature size of about 20 nm has been measured when written at an energy just above the exposure threshold. Details of the necessary substrate preparation are described together with the operation of the scanning tunneling microscope during imaging and exposure. The exposure dose is applied by raising the bias voltage for a specific time while keeping the tip‐sample current constant which has permitted insights into the mechanisms of the resist exposure.