Electron-beam lithography with aromatic self-assembled monolayers on silicon surfaces

Aromatic self-assembled monolayers are formed via the coupling of hydroxy head groups to hydrogen-terminated silicon surfaces. We first investigate the application of 4-hydroxy-1,1′-biphenyl as an ultrathin negative tone electron-beam (e-beam) resist using conventional e-beam lithography with a beam energy of 3 keV. We demonstrate the fabrication of nanometer silicon patterns that are transferred using the modified monolayer as a resist mask for a wet chemical etching process in potassium hydroxide. The necessary dose for complete cross linking was determined to be 20 mC/cm2. Using this approach, isolated silicon structures with lateral dimensions down to ∼10 nm and periodic structures with a resolution of ∼20 nm were fabricated. On the other hand, 4′-nitro-4-hydroxy-1,1′-biphenyl has been found not to form monolayers suitable for chemical lithography on hydrogenated silicon surfaces. Upon adsorption, the nitro groups are partially reduced to amino groups by the hydrogenated surface and some of the molecules bind to the surface via the nitrogen terminus.