The effect from the substrate reflection to the inclined UV lithography of SU-8 photoresist

Abstract

Recently, the inclined UV lithography technology based on SU-8 negative thick photoresists has been mature and attractive due to the in-depth research of SU-8. With the increasing demand for the high-fidelity oblique structures of SU-8, the simulation of inclined UV lithography becomes more important. Based on the Fresnel-Kirchhoff diffraction theory, a simple light intensity distribution model is established in this paper by the Fresnel approximation and paraxial approximation solutions to simulate the 2D inclined UV lithography. The refraction and reflection at the air/photoresist interface and the reflection at the substrate surface are integrally considered in the modeling. The oblique SU-8 structures were fabricated on both glass wafers and silicon wafers, which show different reflection-induced profiles after development. According to the comparison of the simulation and experimental results, it is demonstrated that the substrate reflection has significant influence to the inclined UV lithography, and the validity of the model is also verified.