Investigating the structure–sensitivity relationship of photosensitive polyimide formulated by using a photobase generator

Abstract

Photosensitive polyimides (PSPIs) have been widely used in the buffer coating layer and insulation layer due to their excellent thermal and mechanical stability. In this work, a series of negative-type PSPIs based on poly(amic acid) (PAA) and a photobase generator (PBG) have been developed. Two diamines of 4,4′-oxydianiline (ODA), 3,3′-diaminodiphenyl sulfone (SDA), and four dianhydrides of pyromellitic dianhydride (PMDA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA) and cyclobutene-1,2,3,4-tetracarboxylic dianhydride (CBDA) are copolymerized to PAA through polyaddition, and the PAA is further thermally imidized to polyimide (PI). Through scrutinizing the structure–sensitivity relationship of these PIs, we find that the rigidity and transparency of the PAA/PI backbone play an important role in the sensitivity and contrast of PSPI. Accordingly, PSPI (SDA-ODPA), possessing high optical transparency and a low rigidity represented by the low glass transition point, is capable of providing good photosensitivity of 30 mJ/cm², a high contrast of 2.46, and an excellent pattern resolution of 4 μm after optimizing the prebaking (100°C for 5 min), exposure dose (380 mJ/cm²), post-exposure baking (130°C for 7 min), and development parameters. This work provides the concept of structural design for negative-type PSPI in the microelectronic application.