Facile formulation of alkaline-developable positive-type photosensitive polyimide based on fluorinated poly(amic acid), poly(amic acid), and fluorinated diazonaphthoquinone

Abstract

An alkaline-developable, positive-type, and photosensitive polyimide (PSPI) based on fluorinated poly(amic acid) (FPAA), poly(amic acid) (PAA), and fluorinated diazonaphthoquinone (FDNQ-1) as a photoactive compound has been successfully developed. The solution of FPAA, PAA, and FDNQ-1 was spin-coated on a silicon wafer and prebaked. The two phase-separated layers, a thin top layer of FPAA containing FDNQ-1 and a thick bottom layer of PAA, were formed due to the high polarity difference between PAA and FPAA containing FDNQ-1. This phase separation was directly observed in an SEM image. The upper thin layer acted as a photosensitive layer, and a fine pattern was formed in the bottom layer. The PSPI containing PAA (85 wt%), FPAA (15 wt%), and FDNQ-1 (25 wt% to polymers) showed an excellent sensitivity of 60 mJ cm⁻² and a high contrast of 3.3 when it was exposed to 365 nm wavelength light (i-line) and developed with a 0.238 wt% tetramethylammonium hydroxide aqueous solution (TMAHaq) at 25 °C. A fine positive pattern having a 6 μm resolution on the 1.0 μm film was obtained by exposure to 100 mJ cm⁻²i-line in the contact-printed mode. The resulting polymer film was converted to the corresponding PI cured at 300 °C. This novel positive patterning PI system can be one of the candidates for the next generation microchip fabrication process which provides a facile formulation of PSPI.