Micro-Branched Crosslinked Photosensitive Polyimides (PSPIs): Optimizing Dielectric, Thermal, and Lithographic Performance

Abstract

Photosensitive polyimide (PSPI) is critical for advanced packaging but faces limitations in dielectric performance and lithographic resolution. To address these limitations, we adopted a grafting strategy to synthesize high-performance PSPIs through molecular architecture engineering. This approach involved integrating micro-branched crosslinkers-specifically 1,3,5-tris(4-aminophenoxy)benzene (POB) and 1,3,5-tris(4-aminophenyl)benzene (PB) into the 6FDA-TFMB polymer matrix, which allowed for precise control over crosslinking density and topological heterogeneity. The resulting PSPI films exhibit enhanced free volume fractions, leading to reduced dielectric constants (PSPI-2 with 2 mol% POB: Dk = 2.77; PSPI-3 with 3 mol% PB: Dk = 2.62 at 10 GHz) and lower coefficients of thermal expansion (PSPI-2: CTE = 54.3 ppm/°C; PSPI-3: CTE = 59.4 ppm/°C). The micro-branched topology further facilitates efficient grafting kinetics and solubility, enabling enhanced lithographic sensitivity (D0.5 = 37 mJ cm -2 ) and high-resolution patterning with clear imaged patterns of 5 μm (L/S = 1:4) and 10 μm (L/S = 1:1). This work demonstrates micro-branched crosslinked PSPIs as promising materials for microelectronics, balancing low dielectric loss, thermal stability, and mechanical robustness.