Exposure and post-bake thermal treatment in one step for SU8 photoresist

Abstract

This work demonstrates an effect which would allow a reduction in the number of baking steps in a post-development process for a system consisting of the SU8 photoresist with nanoparticles, in which up-conversion luminescence can be excited. Traditionally, writing structures in photoresists involves several steps, e.g. the I-line method requires a UV light source as the writing element, and several bake procedures (post-bake and hard-bake) in the post-development process. Photoresist mixed with nanoparticles (e.g. NaYF4 doped with Tm3+ and Yb3+) makes it possible to use up-conversion luminescence, which opens up new opportunities in photolithography. One opportunity includes recording structures by means of up-conversion luminescence using nanoparticles mixed into the photoresist as a UV light source. However, this work is related to another possibility: the reduction of the number of bake procedures in the post-development process when the structures in the SU8 photoresist are mixed with nanoparticles (NaYF4:Tm3+:Yb3+) that emit visible and ultraviolet light under infrared excitation. It will be shown that NaYF4:Tm3+:Yb3+ nanoparticles act not only as a UV light source, but also as local heaters. Such a double application allows to record structures and thermally fix them simultaneously while retaining the physical properties, which were evaluated using structure hardness measurements and dissolution experiments with two type of solvents (2-propanol and acetone)