CHARACTERIZATION AND APPLICATION OF PAG DILUTED SU-8

Abstract

The concentration of photoacidgenerator (PAG) in SU-8 determines the UV absorption and, therefore, is a limiting factor of the applicable SU-8 thickness. The motivation of this work is to improve SU-8 process control and expand the application scope of SU-8 by modifying its PAG concentration. In this paper we present the experimental results on lithographic properties of SU-8 as the function of PAG concentration (varying up to 2 orders of magnitude). It includes determining the minimum bottom dose and minimum effective energy density for x-ray and UV lithography of SU-8, respectively, and the UV absorption spectra of SU-8. It is fund that as the PAG concentration reduced, SU-8 has lower sensitivities in UV and x-ray lithography, and lower UV absorption coefficients. By using PAG diluted SU-8 taller microstructures with vertical sidewall can be obtained with UV lithography. Based on the large difference in lithographic sensitivities between normal and PAG diluted SU-8, we have developed a new process concept for making 3D microstructures. The 3D microstructures fabricated based on this new process, including microcantilever and microchannel, will be presented.