Summary Abstract: High resolution ion beam lithography

A new type of high resolution mask for ion beam lithography is described. The mask employs a thin membrane with regions of two different thicknesses to provide contrast for proton exposure of resist. A conventional ion implantation system is used to generate a collimated beam of protons for flood exposure of the sample. Beam energy is chosen so the the protons pass through the thin areas of the mask and emerge with sufficient energy to expose the resist, but are stopped in the thick areas. Experiments using polyimide membrane masks have yielded promising results. The ability to reactive ion etch structures with nearly vertical sidewalls in polyimide allows the fabrication of masks having both high contrast and high resolution. The stopping power of polyimide was determined by measuring the transmission of protons through membranes of known thickness, as a function of incident beam energy. In the energy range from 50–200 keV, the stopping power of polyimide for protons was measured to be ∠100 keV/μm. Mask fabrication procedures and exposure experiments to determine the resolution of this technique are reported. Patterns with linewidths of 〈0.1μm have been successfully replicated.