High resolution x-ray micromachining using SU-8 resist

Abstract

This paper investigates the feasibility of using SU-8 as a high contrast x-ray resist. The SU-8 resist was irradiated with various x-ray doses and then developed for a fixed time. The developing rate was then measured and plotted versus absorbed x-ray dosage. The results revealed that SU-8 exhibited very high lithographic contrast other than elevated sensitivity. Therefore, a very thin mask absorber is required to switch the negative resist 'ON' or 'OFF'. Preliminary results showed that 1 µm wide, 17 µm thick SU-8 resists could be successfully patterned using an absorber of submicron thickness. Once the absorber thickness is effectively reduced to less than 1 µm, a high-resolution x-ray mask can be patterned simply by conventional UV lithography. An extra soft x-ray beamline was not required to increase the absorber's thickness in certain cases. The process of fabricating the membrane x-ray mask could thus be considerably simplified. X-ray micromachining may be an easy way to pattern high-resolution and high-aspect-ratio microstructures for optical and photonic applications.