An Alkaline-Developable, Negative-Working Photosensitive Polybenzoxazole Based on Poly(o-hydroxyamide), a Vinyl Sulfone-Type Cross-Linker, and a Novel Photobase Generator

Abstract

An alkaline-developable, negative-working, photosensitive polybenzoxazole (PSPBO) based on poly(o-hydroxyamide) (PHA), a cross-linker 1,6-bis(vinyl sulfone)hexane (HBVS) having a flexible aliphatic chain, and N-{[(4,5-methylenedioxy-2-α-methylnitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine (MNCDP) as a novel photobase generator (PBG) has been developed to avoid the corrosion of copper (Cu) circuits in microchips by photogenerated acid from photoacid generators (PAGs). The resist consisting of PHA (75 wt %), HBVS (10 wt %), and MNCDP (15 wt %) showed excellent sensitivity (D0.5) of 62 mJ/cm2 and a high contrast (γ0.5) of 4.1 when it was exposed to 365 nm wavelength light (i-line), postexposure baked (PEB) at 170 °C for 2 min, and developed with tetramethylammonium hydroxide aqueous solution (TMAH(aq)) at 25 °C. A fine negative pattern having 8 μm resolution on the 2.1 μm-thick film was obtained by exposure to 150 mJ/cm2 of i-line by using a contact-printed mode. The resulting polymer film cured at 350 °C in an air atmosphere had a low dielectric constant (ε: 2.78), high thermal stability, good mechanical properties, and low water absorption, all of which properties were comparable to those of PBO film. This novel patterning system with both a new PBG and cross-linker can be one of the candidates for the next generation microchips fabrication process which avoids corrosion of Cu circuits in semiconductor devices.