Fabrication of nano-gratings in arsenic sulphide films

Chalcogenide glasses, generally soluble in alkaline solvents, become more resistant to etching in amine-based solvents after exposure to high energy electrons (30 keV). We have used this characteristic for fabricating structures that are suitable for nanolithography. Using a scanning electron microscope equipped with a lithography system, nano-gratings are written digitally with varying point spacing, line pitch, and electron dose. The spot size of the electron beam is ∼1 nm, but the finest structures that have been created in our arsenic sulphide films have lines with widths of 27 nm, separation of 7 nm, and heights from 80 to 250 nm. As the line pitch decreases, the best resolved spacing between the lines decreases until the lines blend into each other, much before the e-beam overlap. A discussion of the optimization of fabrication parameters is included.