Modeling and Fabrication of Timed-Development-and-Thermal- Reflow (TDTR) Process for Microlens

This paper presents modeling and fabrication of timed-development-and-thermal-reflow (TDTR) process for various plano-convex/concave type microlenses on a single substrate. A partial development called a timed development in microlithography determines a remaining amount of uncrosslinked photoresist on the non-UV-exposed photoresist area. The baking process turns the solid uncrosslinked photoresist into the liquid state, to be called as a thermal reflow process, and creates a smooth meniscus to the UV-exposed crosslinked side wall. The proposed TDTR process was modeled on the relationship between a polymer-dissolving rate as a function of development time and a lateral dimension of the chemical contact area. The longer it develops, the deeper trench forms. Given the same development time, trenches with wider lateral dimensions show deeper patterns. This relationship was expressed as the depth and the surface profile of the developing time and the lateral dimension were modeled by the nonlinear regression analysis and verified by the experimental data. To demonstrate the feasibility and usefulness of the proposed fabrication process, various plano-convex microlenses with different heights on a single substrate were successfully fabricated.