Jer-Wei Chang

PMMA microstructure as KrF excimer-laser LIGA material

PMMA (polymethyl methacrylate) has been widely used as x-ray LIGA material for its good features of electrical acid plating of all common metals to industrial applications. Unlike the tough characteristics of polyimide in almost all alkaline and acid solutions, PMMA is easily removed in chemical etchants after electroplating process. For this reason, ablation- etching characteristics of PMMA material for 3D microstructures fabrication using a 248 nm KrF excimer laser were investigated. Moreover, the uses of the laminated dry film were also studied in this work. Experimental results show that PMMA microstructures can produce the near-vertical side- wall profile as the laser fluence up to 2.5 J/cm2. PMMA templates with high aspect ratio of around 25 were demonstrated, and the sequential electroplating processes have realized the metallic microstructures. Moreover, the microstructures fabricated in dry film show the perfect side- wall quality, and no residues of debris were found.

Fabrication of binary microlens array by excimer laser micromachining

A novel technique to fabricate binary microlens on polymer substrates by 248 nm KrF excimer laser micromachining is proposed. A successfully fabricated eight-level binary microlens with diameter 1.25 mm and focal length 43 mm 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 30 nm, which is compatible with those results obtained by other techniques. This technique can fabricate a 2 X 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.