Abstract

In this work, a low-cost and high-resolution x-ray micromask is developed by sputtered lead film on a Mylar sheet substrate with the lift-off process and the x-ray mask is experimented for patterning SU-8 negative photoresist on a glass substrate. Sputtering is selected for Pb thick film deposition due to its high sputtering yield. The Pb mask is used for x-ray lithography of SU-8 photoresist with 5 µm closely spaced square array patterns, designed for electrowetting electrodes on a microfluidic chip. For 140 µm thick SU-8 photoresist, a Pb film thickness of around 10 µm was used to block x-rays with 95% x-ray image contrast at a critical dose of 4200 mJ cm−3. A high aspect ratio of 26.5 of SU8 microstructure with 5 µm lateral resolution has been demonstrated by the developed low-cost Pb-based x-ray mask. In addition, a steep sidewall angle of nearly 90° for SU-8 structure is confirmed. The results demonstrate that the Pb-based x-ray mask offers high-resolution x-ray lithography at a very low cost. Therefore, it is highly promising for commercial applications.

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