Alkaline‐developable and negative‐type photosensitive polyimide with high sensitivity and excellent mechanical properties using photo‐base generator

Abstract

An alkaline developable and negative‐type PSPI with a high sensitivity and excellent mechanical properties based on a poly(amic acid) (PAA) and a photo‐base generator has been developed. The PAA was prepared by the polycondensation of p‐phenylenediamine (PDA) with an equimolar of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6‐FDA) and converted thermally to the corresponding polyimide, PI(PDA‐BPDA/6‐FDA). PI(PDA‐BPDA/6‐FDA) showed the high thermal and mechanical properties and the dimensional stability such as the thermal decomposition temperature of 530°C, glass transition temperature of 369°C, linear coefficient of thermal expansion of 28 ppm/K, ultimate tensile strength of 148 MPa, elongation at break of 25% and dielectric constant of 2.8. The PSPI was formulated directly from PAA(PDA‐BPDA/6‐FDA) with a photo‐base generator (PBG), (E)‐3‐(2‐hydroxy‐4‐methoxyphenyl)‐1‐(piperidin‐1‐yl)prop‐2‐en‐1‐one (HMPP) (10 wt% to PAA) and the optimized parameters for photolithographic process were investigated including the PBG content, post‐exposure bake (PEB) temperature, and PEB time. The PSPI based on PAA(PDA‐BPDA/6‐FDA) and HMPP (10 wt% to PAA) showed a sensitivity of 114 mJ/cm2 and contrast of 1.29 when exposed to 365‐nm light (i‐line), post‐exposure baked at 160°C for 5 min, and developed with an aqueous solution of 2.38 wt% tetramethylammonium hydroxide and iso‐propanol. A clear negative 8‐μm features pattern was obtained by contact‐printing and converted into the PI pattern upon heating at 250°C, confirming by scanning electron microscopy and infrared spectroscopy.

Correlating the Molecular Structure of Polyimides with the Dielectric Constant and Dissipation Factor at a High Frequency of 10 GHz

“…Goto et al prepared a series of PIs with low D k s by introducing bulky diphenyl fluorenylidene moieties and concluded that the D k values of PIs were closely related to the imide group content (Imide%) in the repeating unit and fluorine content (F%). Based on their findings, various PIs with low D k have been reported. − Our previous works on low D k PIs also revealed that incorporation of phenylene ether and adamantyl and alicyclic units to dianhydrides and diamines could effectively decrease the D k values of PIs. − Most of the above studies focused on the development of PIs with low D k values at lower frequencies (1 kHz to 10 MHz). , However, few studies investigate the molecular structure of PIs with low D k as well as low D f . − In particular, there is no clear guideline for designing PIs with both low D k and low D f , which is very important for the emerging 5G mobile communications technology. Therefore, it is of great interest and a challenge to establish the design concept of low D k and low D f PIs.…”

Photopolymerization activated by photobase generators and applications: from photolithography to high-quality photoresists

“…As a result, the resulting PI thin film also exhibited high thermal stability, specifically with excellent ductility, high dimensional stability and even low dielectric properties. 100 Nowadays, negative-type PSPIs based on PAA have been widely developed with PBGs. 101 For instance, Chang et al found that the high optical transparency and low rigidity of the polyimide backbone give a significant promotion on the performance of PSPI, especially for the photosensitivity, owing to the designed wide optical bandgap and low rigidity are beneficial for the photochemical reaction and chemical imidization.…”

Microfabrication of functional polyimide films and microstructures for flexible MEMS applications

“…The dissolution rate of PAA in TMAH solution is overly high to obtain a sufficient dissolution contrast between unexposed and exposed areas; thus, photosensitizers are added to the polymer matrix. According to the reaction mechanism, photosensitizers can be divided into two categories: photoacid generators (PAGs) 86 , 89 , 90 and photobase generators (PBGs) 85 , 88 , 91 .…”

“…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 .…”