All water based nanoscale electron beam lithography using polyacrylic acid hydrogel as a resist

This work investigates improving pattern resolution and contrast in polyacrylic acid (PAA) hydrogel films as a resist to below 100 nm lateral dimensions using electron beam lithography. Hydrogels readily absorb water and swell to many times their original size. Additionally, they are biodegradable, biocompatible, and sensitive to many environmental parameters with a broad range of applications. The ability to create arbitrary patterns with precise dimensions and placement further improves the usefulness of PAA. Previous work by the author achieved 1.8 μm linewidths and dot diameters in 50k molecular weight (MW) PAA. Using PAA as a resist is unique in that its carrier solvent, developer, and remover are all water compared to other resists, which use harsh chemicals. In this new work, 50k MW PAA was further investigated and the resolution was improved to 147 nm linewidths and 167 dot diameters by using 25 nm thick films. The effect of MW on dose sensitivity curves was investigated, and it was found that resolution was substantially improved to 30 nm linewidths and 46 nm dot diameters by switching to 5k MW PAA.