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),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 (D 0.5 ) of 78 mJ/cm 2 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/cm 2 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.
IntroductionPhotosensitive poly(benzoxazole)s (PSPBOs) are widely utilized as protection and insulating layers in manufacturing semiconductors because of their good mechanical properties, low water absorption, and low dielectric constant. 1-3 Moreover, an outstanding advantage of the PSPBO resist system is to simplify the pattern-formation processes, where phenolic hydroxyl groups in PHA as a precursor of PBO provide adequate solubility to an aqueous alkaline developer. Also, capability of development in an aqueous alkaline solution is beneficial for an environmentally benign process. In general, PSPBOs are formulated from PHA with 20 -30 wt % o-diazonaphthoquinone (DNQ) as a photoactive dissolution inhibitor, which is converted into an alkaline-developable indene carboxylic acid as a dissolution promoter to provide a positive image. Meanwhile, the drawback of the PSPBO system using DNQ is photosensitivity, which is low (in the range of 200-400 mJ/ cm 2 ) to obtain a patterned film. 1,4-6 Recently, chemically amplified-type PSPBOs have been reported to improve the photosensitivity, where PHA is combined with a cross-linker or a dissolution inhibitor, and PAG, which generates the sulfonic acid derivatives. 7-12 However, a photogenerated acid from PAG induces corrosion of Cu circuits in microchips. To overcome this problem, a novel photoimage formation system is strongly required for the next generation PSPBO resist systems. The most straightforward approach is to use PBG instead of PAG, and a base-catalyzed esterification of phenol with an active...