High-Performance and Safer Wet Stripper for 50 to 400 µm-Thick Negative Photoresists and Laminated Films in Wafer Level Packaging

Thick negative-tone photoresists are increasingly used to fabricate high-aspect-ratio structures such as copper pillars, which are critical in advanced packaging technologies. However, their high film thicknesses and strong crosslinking make complete removal particularly challenging. This study presents the development of a new photoresist stripper formulation, free of N-methyl-2-pyrrolidone (NMP) and tetramethylammonium hydroxide (TMAH), designed to address both efficiency and material compatibility requirements in advanced packaging environments. Through a systematic formulation approach, including each formulation components screening, an optimized stripper was developped. Compared to conventional TMAH-based strippers, this new formulation enables significantly faster stripping of thick resists, up to 400 µm, and laminated films, while maintaining excellent compatibility with sensitive materials. The results validate its performance across a range of advanced applications, while offering substantial safety and environmental benefits.