Polymer 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. 

Lastly, the polyimide has some inherent photosensitivity. The use of a photosensitive polymer requires fewer processing steps, which also implies an increased yield for the circuit. Ciba-Geigy announced the formulation of inherently photosensitive polyimides in 1985.(5) The use of an inherently photosensitive polyimide is attractive because no sensitizers are added to contaminate the final resin, no functionality is added which degrades the thermal and chemical resistance, and fewer volatiles are present to contaminate the resin or equipment than in some other approaches to photosensitive polyimides. Recent work has shown that these polyimides crosslink on irradiation through hydrogen abstraction by triplet benzophenone and subsequent coupling of the resultant radicals. ... 

Unlike other photosensitive polyimides (2), the use of N-phenylmaleImide (10% to polymer weight) as crosslinking agent did not improve the photopolymerization of PSiPI. 

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. 

Alkali-Developable Base Polymers. Since the dissolution rate of PAAs is too fast in 2.38% TMAH solution, the photosensitive system composed of PAA and a DNQ compound suffers from low contrast of the difference in dissolution rate between exposed and unexposed area. It implies that the optimization of the dissolution rate of base polyimide precursor in the developer is needed. PAA/PAE blends, PAA/PAE copolymer, and PAE with pendant carboxylic acid (PAE-COOH) were evaluated as base polymers for photosensitive polyimides. 

In an attempt to improve thermal stability even further a series of poly-anhydride-imides have been prepared containing phosphorus. While such polymers had good hydrolytic stability, they had little heat resistance and poor flame retardency. Several papers have appeared on the synthesis of polyesteri-mides. Photosensitive polyimides have also been prepared. " ... 

Ogura T, Higashihara T, Ueda M. Low-CTE photosensitive polyimide based on semialicyclic poly(amic acid) and photobase generator. J. Polym. Sd. Part A 2010 481317-1323. 

Jin XZ, Ishii H (2005) Novel positive-type photosensitive polyimide with low dielectric constant. J. Appl. Polym. Sci. 98 15-21. 

Srisuwan S, Thongyai S, Praserthdam P (2010) Synthesis and characterizatirai of low-dielectric photosensitive polyimide/silica hybrid materials. J Appl Polym Sci 117 2422-2427 Tagam N, Okada M, Hira N, Ohki Y, Tanaka T, finai T, Harada M, Ochi M (2008) Dielectric properties of epoxy/clay nanocomposites—effects of curing agent and clay dispersion method. IEEE Trans Diel Electr Insul 15 24—32... 

Design of the reactions via long-lived active intermediate was found to be important for developing photosensitive polyimide tystems, and this concept is especially effective for the reactions in solid state 11), because the solid-state reactions are controlled by the molecular motions 12). In addition, change in the electronic state in polymer solid was found to affect the efficient of their photoreactions. Charge-transfer structure is one of the characteristic nature of aromatic polyimides, which is affected by the change in their physical properties, and which in turn controls their photoreactivities. 

The polymer-dispersed liquid crystal was used as a modulating medium in optically controlled modulators instead of the liquid crystal [261-264], The sandwiched structure from polyimide photosensitive film and the polymer dispersed liquid crystal film - i.e. the optically controlled solid state modulator -had the characteristics presented in Fig. 36 [261]. Contrast ratio 35 1, response time > 400 ps, decay time 80 ms and sensitivity 5 x 10 sJcm 2 were obtained. 

Besides polyimides, photoconductive polymers with conjugated bonds also can be successfully used in liquid crystal spatial light modulators [262-264], The high resolution, mechanical and electrical stability and possibility for sensitization of the photosensitivity make the use of organic polymer photoconductors in spatial light modulators very attractive. Devices such as phase... 

Polyimides based on 2,6-diamino-p-cresol were acylated with acryloylchloride [71, 72] to impart photosensitivity to these polymers. The acylation was carried out in accordance with Scheme 5.12. The extent of esterification of hydroxyl groups, as determined by H-NMR spectroscopy, ranged from 60 to 40% for various polyimides (Table 5.14). 

Some new electronic applications of polyimide-siloxane adhesives have been already partially reviewed. In addition, the development of photo-crosslinkable copolymers has been of great interest for the development of components of electronic devices [126]. The general field of photosensitive polymers was reviewed by Horie and Hamishita in 1995 [127]. A number of papers have investi-... 

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. 

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