Polyamic acid esters with pendant

We report on the positive alkali-developable photosensitive polyimides based on an alkali-soluble polyimide precursor as a base polymer and diazonaphthoquinone (DNQ) sensitizer to improve process stability and sensitivity. Polyamic acid ester with pendant carboxylic acid (PAE-COOH) showed good dissolution behavior in aqueous alkali developer. The dissolution rate of PAE-COOH was controlled by the content of pendant carboxylic acid. It was found that a photosensitive system composed of butyl ester of PAE-COOH and a DNQ compound can avoid the residue at the edge of hole patterns (footing) after development, while that of methyl ester of PAE-COOH showed the residue. A DNQ compound containing sulfonamide derived from diaminodiphenylether renders improved sensitivity compared with DNQ compounds derived from phenol derivatives. 

Polymer Synthesis. Basic structures of polyamic acids (PAA), polyamic acid esters (PAE), copolymers of PAA and PAE, and polyamic acid esters with pendant carboxylic acid (PAE-COOH) used for this study are described in Figure 1. After dissolving a diamine into N-methylpyrrolidone, polyamic acids (PAA) were synthesized by adding tetracarboxylic dianhydrides slowly for about Ihr into the ice-cooled diamine solution as described in the literarure [7]. 

Figure 1 Polymer structure of polyamic acid (PAA), polyamic acid ester (PAE) and polyamic acid ester with pendant carboxylic acid.

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