Cross-linking photosensitive polyimide

Direct Patterning of Photosensitive Polyimides. Photosensitive polyi-mides (PSPIs) are recently developed materials that can be directly photo-patterned like a negative photoresist (80,85,88,146-148). The most common PSPIs are polyamic acids that have been esterified with photoreactive alcohols and combined with photoinitiators to form a polymer that will crosslink under exposure to UV radiation and become insoluble. The unexposed material is selectively dissolved in a developer solution, and the patterned film is then cured to convert the cross-linked polyamic acid to a polyimide and drive off the cross-linking groups. 

Thermal tempering of the photosensitive or cross-linked polymer gives the polyimide siloxane which has been previously shown to be an excellent candidate as an insulating polymer in electronics. The use of such a directly patternable polyimide for dielectric and passivation applications, particularly in microelectronics, should become increasingly important as polyimides become more widely accepted in the industry. 

Preparation of photocross-linkable furan-containing polyimides was also reported [165]. It was also found that the polymer cross-links with the aid of singlet oxygen. Formations of fine pattern images can be formed. This was taken as clear evidence of the successful photolithography in this photo-curable system that uses Ceo as the photosensitizer [165]. 

Fig. 13. Photochemical cross-linking of a covalent-tsrpe photosensitive polyimide precursor.

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