Alkaline‐developable positive‐type photosensitive polyimide with high mechanical strength and high resolution based on chain extendable poly(amic acid), thermally degradable cross‐linker and photoacid generator
Yao‐Ming Yeh, Mitsuru Ueda, Chain‐Shu Hsu
Abstract
Abstract A positive‐type photosensitive polyimide ( PSPI ) based on a chain extendable poly(amic acid) ( PAA ), a thermally degradable cross‐linker 1,3,5‐tris[(2‐vinyloxy)ethoxy]benzene ( TVEB ), and a photoacid generator (PAG) (5‐propylsulfonyloxyimino‐5H‐thiophene‐2‐ylidene)‐(2‐methylphenyl)acetonitrile ( PTMA ) has been developed. The chain extendable PAA was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride ( BPDA ) and 4,4′‐oxydianiline ( ODA ) and end‐capped with di‐ tert ‐butyl dicarbonate ( DIBOC ) in N ‐methyl‐2‐pyrrolidone (NMP), which has a controlled molecular weight for developing in a 2.38 wt% tetramethyl ammonium hydroxide aqueous solution ( TMAH aq ) and undergoes a chain extending reaction during curing stage. The photosensitive resist solution was formulated with the polymerization solution (30 wt% in NMP), TVEB (15 wt% for the polymer), and PAG (4.5 wt% for the polymer). The PSPI showed a sensitivity of 47 mJ cm −2 and a contrast of 5.8 when exposed to 365‐nm light, followed by postexposure baking at 90 °C for 10 min and development with the 2.38 wt% TMAH aq at room temperature. A fine‐positive image with 3‐μm line‐and‐space patterns was obtained on a 3‐μm thick film exposed to UV light at 365 nm in the contact‐printed mode. After thermal curing at 350 °C for 1 hr, the resulting PSPI features excellent mechanical strength and elongation.