An Alkaline-Developable, Chemically Amplified, Negative-Type Photosensitive Poly(benzoxazole) Resist Based on Poly(o-hydroxy amide), an Active Ester-Type Cross-Linker, and a Photobase Generator

An alkaline-developable, chemically amplified, negative-type, photosensitive poly(benzoxazole) (PSPBO) based on poly(o-hydroxy amide) (PHA), an active ester-type cross-linker bis(p-nitrophenyl) suberoylate (BNPS), and N-{[(4,5-dimethoxy-2-nitrobenzyl)oxy]carbonyl}-2,6-dimethylpiperidine (DNCDP) as a photobase generator (PBG) has been successfully developed to avoid corrosion of copper (Cu) circuits in microchips by a photogenerated acid from photoacid generators (PAGs). This resist film consisting of PHA (80 wt %), BNPS (5 wt %) and DNCDP (15 wt %) showed the high sensitivity (D0.5) of 78 mJ/cm2 and good contrast (γ 0.5) of 4.0 when it was exposed to 365 nm UV light (i-line), postexposure baked (PEB) at 140 °C for 10 s, and developed with 2.38 wt % tetramethylammonium hydroxide aqueous solution (TMAH (aq)) as an alkaline developer at 25 °C. A fine negative image featuring 6 μm resolution patterns was obtained on a film (thickness: 2.5 μm) exposed to i-line by a contact-printed mode, and developed with 2.38 wt % TMAH (aq). The negative image was converted to the corresponding PBO pattern upon heating at 350 °C. Moreover, this resist system formed 9.3 μm thick pattern having 30 μm resolution with 98 mJ/cm2 exposure. The resulting PSPBO showed high thermal stability, low water absorption, low dielectric and excellent mechanical properties. This new image formulation method is the first example of PSPBO using the PBG, and provides a good and versatile process which avoids corrosion of Cu circuits in microchips.