Effect of process parameters and packing density on dimensional errors for densely packed high-aspect-ratio SU-8 microstructures in x-ray lithography

Abstract

X-ray lithographic conditions for high-aspect-ratio SU-8 resist structures are characterized for potential application in x-ray optics and bioMEMS. The effects of the main process parameters, such as exposure dose, postexposure bake, development time, and the packing density of the microfabricated features, on the increase in feature size at the top portion of the resist (as compared to that in masks) are investigated. We find that lower postexposure bake and exposure dose leads toward minimizing dimensional errors. Further improvements in reducing the dimensional errors can be achieved by overdeveloping the structures. Using overdevelopment, we demonstrate an improvement in dimensional error for a given structure from 5 to 3.3%.