A Structural Design Approach for Aqueous Developing Negative Photosensitive Polyimide Based on Hybrid Side Chains

Abstract

Negative-type photosensitive polyimides (n-PSPI) for advanced packaging currently suffer from low resolution, high processing costs, and environmental issues due to organic solvent development, while water-developable alternatives often compromise performance by introducing polar groups or additives into the main chain. Here, we report a side-chain engineering approach for polyamide ester (PAE) precursors that simultaneously incorporates photosensitive methacrylate groups and water-soluble tertiary amine salts. Optimizing the side-chain ratio (DMEA/HEMA = 7:3) yields a dissolution rate contrast of 3.42 μm/min and enables 5 μm line/space patterning using 2.38 wt % TMAH aqueous developer. The hybrid side chains are completely eliminated during thermal imidization (confirmed by FT-IR), preserving the pristine polyimide backbone properties: Td5% > 530 °C, Tg ≈ 265 °C, tensile strength >120 MPa, and low dielectric constant (Dk ≈ 3.32 at 1 MHz, 3.25 at 10 GHz) with dissipation factor <0.006. This strategy overcomes the trade-off between water developability and performance, offering a practical route to high-resolution, high-performance photosensitive polyimides for next-generation semiconductor packaging.