An evaluation of photoresist thickness for semiellipsoid microlens fabrication before thermal reflow using the prolate spheroid approximation

We present a new semiellipsoid microlens fabrication method using the lift-off and alignment exposure processes. The lift-off method is used to create an elliptical copper base before the thermal reflow process. During the photoresist thermal reflow process, the elliptical base can precisely define the bottom shape of the liquid photoresist. The prolate spheroid approximation method is developed to estimate the thickness of elliptic photoresist column required by the semiellipsoid microlens of a certain height, with the error being controlled within ±3%.