An ultra heat-resistant polyimide formulated with photo-base generator for alkaline-developable, negative-type photoresist

Abstract

An alkaline-developable and negative-type photosensitive polyimide (PSPI) based on poly(amic acid) (PAA) and a photo-base generator (PBG) has been developed by using chemical amplification method. The PAA(PDA-BPDA) is composed of p-phenylenediamine (PDA) and 4,4′-biphtalic dianhydride (BPDA), and the derived PI possesses excellent thermal and thermo mechanical stability due to the highly rigid and linear backbone. The photolithographic parameters for the PSPI including the PBG content, post-exposure baking (PEB) temperature, PEB time and the molecular weight of the PAA was investigated with the adoption of (E)-3-(2-hydroxy-4-methoxyphenyl)-1-(piperidin-1-yl)prop-2-en-1-one (HMPP) as the PBG. The PSPI based on PAA(PDA-BPDA) with a molar ratio of 0.9/1.0 between PDA and BPDA, and HMPP (15 wt% to PAA) showed a sensitivity of 142 mJ/cm2 and contrast of 0.58 when exposed to 365-nm light (i-line), PEB at 170 °C for 5 min, and developed with an aqueous solution of 2.38 wt% tetramethylammonium hydroxide and isopropanol. A clear negative 4-μm feature pattern was obtained and imidized into the PI pattern upon heating at 250 °C, confirming by scanning electron microscopy. This is the first work to utilize a highly rigid backbone with high thermal stability for PSPIs. The outstanding thermal and thermo mechanical stability manifests that developed PSPIs is highly potential in the microelectronics.