Effect of fused silica surface wettability on thermal reflow of polymer microlens arrays

The objective of this study is to analyze the influence of substrate wettability and reflow conditions on the shape, lateral dimensions and optical properties of plano-convex lenses with nominal diameter of 16–28 µm fabricated by photolithographically patterning 7.5 µm thick layer of positive ma-P 1275 resist and subsequent thermal reflow. Five types of fused silica substrates modified by different plasma treatments and ion beam deposition of diamond like carbon (DLC) films were selected for the fabrication of microlens arrays in such a way that complete set of them could cover a wide range of wettability. At the same conditions of thermal reflow, defectivity of fabricated microlens arrays and resulting shape of the microlenses depended on the substrate treatment. Differences were especially marked for the lenses with smaller diameter. The best results were obtained for microlens arrays on DLC and SiOx doped DLC coated substrates. Minimal temperature required for complete reflow of the lenses with nominal diameter of 16–28 µm on SiOx doped DLC coated fused silica substrates depended on the lateral dimensions of the lenses and varied from 130 to 140 °C. Radius of curvature for the fabricated lenses could be somewhat tailored by the further increase of reflow temperature.