Top-edge profile control for SU-8 structural photoresist

Profile control for SU-8 ultrathick photoresist has been examined specifically with respect to a "T-topping" phenomenon observed at the top edge. It has been confirmed that filtering ultraviolet (UV) radiation below 350 nm is successful in correcting this type of geometric defect. The effectiveness of a doped glass filter (Hoya UV-34) has been verified, and an alternative approach using a vapor-deposited thin-film coating has been presented. The thin-film filter demonstrates equal success in reducing the T-topping defect. This alternative approach furthermore offers advantages related to cost, design flexibility, robustness, and environmental impact. Modifying exposure dose and pre-bake temperature without any filter was observed to have minimal impact.