Salty development of an optical photoresist

Abstract

In this series of experiments, we add salt to a photoresist developer and observe the effect on photoresist contrast. In order to measure contrast, we designed an anti-reflection coating stack to reduce reflections between the photomask and the photoresist. After development, we observe that for 400 nm exposures of photoresist PS4 that there is no significant change in contrast with salty development, however, for samples exposed at 220 nm, there is contrast enhancement. However, it is not clear how much of the contrast enhancement for the 220 nm samples was due to the shorter wavelength, and how much was due to a different developer concentration versus the 400 nm samples. That being said, we hypothesize that the observed contrast enhancement is due to differences in photoresist cross-linking due to the different wavelength exposures.