Microlens fabrication by 3D electron beam lithography combined with thermal reflow technique

• Microlens pixel height array was designed assigning gray scale level to each pixel.
• Microlens arrays were fabricated by 3D EBL followed by thermal reflow process.
• The shape and RMS surface roughness of microlens vary with e-beam exposure dose.

Microlenses are widely used in mobile phones, digital projectors, light emitting diodes, etc. In this work, the microlenses were fabricated on fused silica substrates using dose modulated 3D electron beam lithography combined with thermal reflow technique. The focused spot size of microlenses after thermal reflow was measured by optical microscopy at a fixed focal distance and the geometry of microlenses was evaluated by atomic force microscope. It was shown that the shape of a profile of the “step-wise” patterned and reflowed microlens is strongly dependent on exposure dose. In the case of exposure dose variation from 80μC/cm2 to 140 μC/cm2, the microlens with a diameter of 16 μm and a height of 1.6 μm deviates by its profile from a design target curve by 237 nm to 127 nm. At the same time the root mean square surface roughness parameter increases from 520.7 nm to 564.6 nm. We found that a greater nominal 3D exposure dose is providing more precise reproduction of the microlens shape.

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