Fabrication of binary microlens array by excimer laser micromachining

A novel technique to fabricate binary microlens on polymer substrates by 248nm KrF excimer laser micromachining is proposed. A successfully fabricated eight-level binary microlens with diameter 1.25mm and focal length 43mm on polycarbonate (PC) sheet is also reported. Using this technique, microlens patterns are mask-projected on the polymer materials via the laser ablation effect instead of complicated multi-stepped lithography and etching processes. Moreover, the precise ablated depth of microlens can be achieved by adequately controlling the number of laser pulses. In order to reduce alignment complexity and offset, multiple mask patterns are produced in one quartz plate and the mask holder is loaded by a servo-controlled x-y stage. SEM pictures and optical interference inspections show that the etched surface and sidewall have roughness deviation less than 30nm, which is compatible with those results obtained by other techniques. This technique can fabricate a 2×2 array of eight-level binary microlens in about several seconds. He-Ne laser and proper optics arrangements are used to measure the diffraction efficiency of the fabricated devices. Experimental results show that the unique technique can produce the multi-level microlens with submicrometer feature size, high-quality surface morphology, and satisfactory optical characteristics.