A 3D profile simulator for inclined/multi-directional UV lithography process of negative-tone thick photoresists

A three-dimensional (3D) profile simulator that integrates aerial image module, exposure module, post-exposure bake (PEB) module and development module is presented in this paper for the inclined/multi-directional ultraviolet (UV) lithography of negative thick photoresist such as SU-8. Based on the scalar diffraction theory, the improved paraxial approximation and Fresnel approximation solutions are developed to simulate the inclined UV light intensity distribution into photoresist with the refraction, the absorption of SU-8 and the reflection at substrate surface incorporated effectively. A 3D dynamic cellular automate method for photoresist etching simulation is improved to calculate the final development patterns efficiently and accurately. The 3D profiles of oblique developed photoresist with or without reflection-induced structures as well as multi-directional-exposure structures are successfully predicted by this simulator, which demonstrate good agreement with the experimental results.