Micro-branched crosslinked photosensitive polyimides (PSPIs): optimizing dielectric, thermal, and lithographic performance

Abstract

Photosensitive polyimides (PSPIs) are critical for advanced packaging but face limitations due to their 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 exhibited enhanced free volume fractions, leading to reduced dielectric constants (PSPI-2 with 2 mol% POB: D_k = 2.77; PSPI-3 with 3 mol% PB: D_k = 2.62 at 10 GHz) and lower coefficients of thermal expansion (PSPI-2: CTE = 54.3 ppm °C⁻¹; PSPI-3: CTE = 59.4 ppm °C⁻¹). The micro-branched topology further facilitated efficient grafting kinetics and solubility, enabling enhanced lithographic sensitivity (D_0.5 = 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.