ZEP520A — A resist for electron-beam grayscale lithography and thermal reflow

Abstract

The usability of ZEP520A as resist for thermally activated selective topography equilibration (TASTE) was investigated. It was found that (i) a high-contrast resist such as ZEP520A is well suitable for grayscale electron-beam lithography, (ii) a selective thermal reflow is possible with ZEP520A and (iii) reflow is governed by the same energy minimization principle as known from poly (methyl methacrylate) (PMMA), another linear thermoplastic resist. The high contrast of ZEP520A does not play a role for the step-to-step sidewall angle as this is only governed by the design of the step. ZEP520A and similar positive tone resists on the market provide the same reflow-feature variety as PMMA including stable and unstable, concave and convex, arbitrary stepped and sloped features as well as combinations of all these features. The advantage of ZEP520A is a reduced writing time due to its high sensitivity. Finally, the transfer of the reflow process to structures being much smaller than typical TASTE structures so far was demonstrated.