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We found novel quantitative esterification in poly(amic acid) (PAA) by reacting with N,N-dimethylformamide dialkyl acetals (DFAs). Different alkyl ester was obtained by changing the alkyl group in DFAs. The esterification ratio was determined by amount of DFAs. The reaction proceeds under mild condition without any catalysis. It has not been reported such a kind of quantitative partial esterification before. The partial esterification allowed us to control the solubility of PAA to alkaline solutions. The strict solubility rate control to alkaline solution of PAA was quite important for positive tone photosensitive polyimide (posi PSPI). The partial esterification of PAA gave us a way to strict dissolution control. By using it, we could obtain posi PSPI just mixing with diazonaphthoquinone compound. Polyimides are widely used for semiconductor applications such as inter-layer dielectrics, protection layers (buffer coatings), and re-distribution layers for wafer level package.1 For these applications, polyimide is required to make a fine pattern by photo-lithographic technique. In early times polyimide was patterned by chemical etching through photo-resist pattern. In order to simplify the polyimide pattering process, several groups developed the addition of photosensitivity to polyimide precursor namely PSPI.2,3 Most of the PSPIs were negative tone type, which made exposed area insoluble by photoreaction. In order to progress semiconductor, polyimide is required fine pattern such as 5 mm or less. To realize such a fine pattern, posi PSPI was desired. First posi PSPI was reported by Loprest et al. 4 The posi PSPI was composed of PAA and naphthoquinone diazide compound which is popular for novolak photo resist system. But it was not realized due to high solubility of PAA to alkaline solution. In order to obtain suitable solubility of PAA, Simmons reported partial protection by reaction with 1,4-dihydropyrane.5 There were few drawbacks for this reaction. One was that the reaction did not proceed quantitatively. Another was that reaction condition needs acidic catalyst. Excess amount of 1,4-dihydropyrane with acidic catalyst and long reaction time were required. Posi PSPI from special PAA structure was reported by Sakayori et al. 6On the other hand, Rubner reported positive tone photosensitive polybenzoxazole precursor.7 Polybenzoxazole precursor was poly(hydroxyamide) which has phenolic groups in the polymer chain. The acidity of phenol group was much weaker than that of aromatic carboxylic acid. The positive tone photosensitive polybenzoxazole precursor was applied for buffer coating of semiconductor devices. 8 Recently Watanabe et al. reported the negative tone photosensitive polybenzoxazole precursor by using acid catalysis cross linking. 9From the point of polyimide base development, Kubota reported a different posi PSPI by introduction of o-nitirobenzyl group to carboxylic acid in PAA.10 Omote reported chemical amplification system by mixing with t-butyl protected PAA and photo-acid-generators.11 Okabe invented...

We have investigated molecular motion and polarity of polyimide chain to developed novel low dielectric constant (Dk) and dissipation factor (Df) polyimides. We found that Df at 10-100 GHz corresponds molecular mobility at-150 to-50 ℃. To reduce the dielectric loss (=Df) at high frequency, restriction of molecular motion at low temperature was important. In addition, to reduce polar and flexible unit in the polyimide chain is also important to obtain low Dk and Df polyimide. We exploited these knowledge for development of low dielectric loss polyimide for RDL. As the result, we achieved 0.002 of loss tangent and 2.7 of dielectric constant respectively about novel polyimide. Those polyimides are patternable by alkaline wet etching with positive photo-resist development and by UV laser ablation method. We also have developed photo-definable low loss tangent polyimide by blending of photo active reagent. Lower insertion loss of microstrip line was observed by the novel low Df polyimide than by conventional photosensitive polyimide. Those low dielectric loss polyimides are suitable for insulator of FO-WLP, interposer and other RF applications for microelectronics.

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