Photoresist, film formation

Ichimura et al. [76] have described photoresists based on soluble polymers bearing methacrylated side-chain groups which are photocross-linked by a free radical mechanism using a diphenyliodonium salt as initiator, with a p-dimethylaminobenzylidine sensitizer. These investigators found spectroscopic evidence for in situ ground state charge transfer complex formation between the sensitizer and initiator, and that such complexes are involved both in the photocross-linking process as well as in the thermal instability of the photoresist films. 

Sato, H. Katsuma, K. Tsujimoto, A. Photosensitive polymer compositions, photoresist films, and formation of resist patterns. Jpn. Kokai Tokkyo Koho JP 2005321587, 2005 Chem. Abstr. 2005,143, 469619. 

Manufacture of Printed Wiring Boards. Printed wiring boards, or printed circuit boards, are usually thin flat panels than contain one or multiple layers of thin copper patterns that interconnect the various electronic components (e.g. integrated circuit chips, connectors, resistors) that are attached to the boards. These panels are present in almost every consumer electronic product and automobile sold today. The various photopolymer products used to manufacture the printed wiring boards include film resists, electroless plating resists (23), liquid resists, electrodeposited resists (24), solder masks (25), laser exposed photoresists (26), flexible photoimageable permanent coatings (27) and polyimide interlayer insulator films (28). Another new use of photopolymer chemistry is the selective formation of conductive patterns in polymers (29). 

The workhorse of the VLSI industry today is a composite novolac-diazonaphthoquinone photoresist that evolved from similar materials developed for the manufacture of photoplates used in the printing industry in the early 1900 s (23). The novolac matrix resin is a condensation polymer of a substituted phenol and formaldehyde that is rendered insoluble in aqueous base through addition of 10-20 wt% of a diazonaphthoquinone photoactive dissolution inhibitor (PAC). Upon irradiation, the PAC undergoes a Wolff rearrangement followed by hydrolysis to afford a base-soluble indene carboxylic acid. This reaction renders the exposed regions of the composite films soluble in aqueous base, and allows image formation. A schematic representation of the chemistry of this solution inhibition resist is shown in Figure 6. 

Figure 11 depicts the dose effect on the gel formation of hb-PAA films (If = 1-2 xm) after they have been exposed to a weak UV light with a power of about 1 mW/cm2. Although the photo-cross-linking conditions had not been optimized, all the four hb-VAAs already exhibited much higher sensitivities (Do.5 = 43-180 mj/cm2) than those of commercial polyfamic ester)-based photoresists (Dq.s = 650-700 mj/cm2) [137]. 

Figure 1.31 Model for the texture dependent oxide growth on Zr surfaces. The crystallographic orientation angles of substrate Zr and oxide film Zr02 are given in addition to the electrochemically (photoresist method) determined formation factors [17].

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