Hexagonal microlens array modeling and fabrication using a thermal reflow process

A mathematical model for designing and fabricating a hexagonal microlens array using a thermal reflow process was developed in this study. The experimental results proved that a hexagonal microlens array could be produced without a gap at each microlens periphery. A hexagonal microlens array with a higher fill factor was successfully produced. In this experiment, hexagonal photoresist columns were formed onto a silicon substrate made using a lithographic process. The hexagonal pattern was laid out in an ortho-triangle on a PET (polyethylene terephthalate)-based mask. Using precise temperature and time control during the thermal reflow process, a hexagonal microlens array with lateral honeycomb geometry was formed from the melted photoresist flowing outward simultaneously and uniformly. The surface tension effect transformed the photoresist column surface into a spherical profile. The error in the fabricated microlens characteristics was within ±3% between two theoretical models used to predict the photoresist column thickness and actual thickness. This model is feasible for fabricating various sized hexagonal microlens arrays.