Diazonaphthoquinone isomers

Figure 19 shows the ultraviolet absorption spectrum of a typical diazonaphthoquinone and a common novolac resin. The naphthoquinone sensitizer has a strong absorbance at the 365 nm., 405 nm., and to a lesser extent the 436 nm. mercury emission lines. There are two diazonaphthoquinone isomers that are used in commercial photoresist formulations that are available at this time. The 5-arylsulfonates are by far the most commonly used. A spectrum of a representative of this class of materials is depicted in Figure 20. The 5-arylsulfonate materials are characterized by an absorbance maximum at approximately 400 nm. and a second, slightly stronger maximum at approximately 340 nm.

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cycHzed mbber resist systems led the semiconductor industry to shift to a class of imaging materials based on diazonaphthoquinone (DNQ) photosensitizers. Both the chemistry and the imaging mechanism of these resists (Fig. 10) differ in fundamental ways from those described thus far (23). The DNQ acts as a dissolution inhibitor for the matrix resin, a low molecular weight condensation product of formaldehyde and cresol isomers known as novolac (24). The phenoHc stmcture renders the novolac polymer weakly acidic, and readily soluble in aqueous alkaline solutions. In admixture with an appropriate DNQ the polymer s dissolution rate is sharply decreased. Photolysis causes the DNQ to undergo a multistep reaction sequence, ultimately forming a base-soluble carboxyHc acid which does not inhibit film dissolution. Immersion of a pattemwise-exposed film of the resist in an aqueous solution of hydroxide ion leads to rapid dissolution of the exposed areas and only very slow dissolution of unexposed regions. In contrast with crosslinking resists, the film solubiHty is controUed by chemical and polarity differences rather than molecular size. 

In his pioneering work, Sus (1944) assumed that the final product of photodediazoniation of 2,1-diazonaphthoquinone (10.75) is indene-l-carboxylic acid (10.79, not the 3-isomer 10.78). He came to this conclusion on the basis of some analogies (in addition to an elemental analysis). Cope et al. (1956) as well as Yates and Robb (1957) found that the infrared spectrum of the product was consistent with an a,P-unsaturated acid. Later, Melera et al. (1974) verified the structure 10.78 by H NMR spectroscopy. Friedrich and Taggart (1975) showed that the equilibrium between 10.78 and 10.79 at 233 K lies on the side of the latter, but 10.78 clearly predominates at or above 0°C. Ponomareva et al. (1980) showed that not only 2,1-, but also 1,2-diazo-naphthoquinone yields indene-3- and not -1-carboxylic acid. 

HPR-206 Positive Photoresist (Olin-Hunt) Mixed Isomer Novolac + Diazonaphthoquinone Photoactive Compounds 120-140... 

Figure 21. Absorbance spectrum of a l-oxo 2 diazonaphthoquinone-4-arylsulfonate. These materials differ spectrally from the 5 isomers shown in Figure 20 and are used in certain commercial resist formulations.

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