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

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.

Low‐temperature curable, alkaline‐developable, and negative‐type photosensitive polyimide with high resolution and mechanical properties based on chain extendable poly(amic acid) and photo‐base generator

“…DIBOC introduced PAA solution was cooled down to room temperature and kept at −15°C. The molecular weight is found to be 7500 Da which was determined by 1 H‐NMR 23 …”

“…Over and above that, the low molecular weight of PAA employed to achieve high resolution resulted the inferior mechanical properties of the PI film. To facilitate high resolution as well as good mechanical properties, Hsu and coworkers 23 reported the PSPI with a chain‐extending mechanism of PAA s which limited the molecular chain in photolithography stage and extended the molecular chain in curing stage. The PAA with lower molecular weight of (Mn: 7500 Da) showed much higher resolution of 3 μm and moderate mechanical properties meeting the requirement of insulation materials in microelectronics.…”

Advancements in Synthesis Strategies and Optoelectronic Applications of Bio-Based Photosensitive Polyimides

“…Yao et al [51] synthesized polyamic acid by BPDA and ODA, and then used DIBOC for end-capping, obtaining PAA with a controllable molecular weight. Te PAA could undergo chain extension reaction in the curing stage, as shown in Figure 4.…”

Microfabrication of functional polyimide films and microstructures for flexible MEMS applications

“…DAQ is connected with the main chain, and a photochemical transformation of DNQ into indenecarboxylic acid derivative occurs to accelerate dissolution in aqueous alkaline solutions 96 , 104 . The PAG photoreaction produces acid, which deprotects the acid-labile ester group of PAA 94 , 98 .…”

“…Notably, PSPI involves photopatternable PI with photoactive agents and photopatternable PI precursors, such as poly(amic acid) (PAA) or poly(amic ester) (PAE) with photosensitive compounds 85 . The PSPI films are selectively exposed to UV light with a mask, allowing the exposed area to undergo a chemical change, such as cross-linking (negative tone) [86][87][88][89][90][91] and chain scission (positive tone) [92][93][94][95][96][97][98] ; undesired areas are dissolved in the developing solution. Methods for incorporating a wide variety of photochemistries into PI systems has been previously reviewed 84,85,99 .…”