Phenol carboxylic acid formaldehyde condensation

Reaction XXXIH. (a) Condensation of an Aromatic Carboxylic Acid with Formaldehyde. (Lederer-Manasse).—In the presence of mineral acids formaldehyde condenses to di-phenyl derivatives with aromatic acids in much the same way as with phenols (Reaction XIII.), except that in this case it is in the meta position the condensation takes place. 

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. 

Positive-Tone Photoresists based on Dissolution Inhibition by Diazonaphthoquinones. The intrinsic limitations of bis-azide—cyclized rubber 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 phenolic structure 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 carboxylic 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 solubility is controlled by chemical and polarity differences rather than molecular size. 

As just mentioned, strong or weak acidic ion exchangers contain sulfonic acid or carboxylic acid groups in the H or alkali metal salt form and consist of 1,4-divinylbenzene cross-linked polyst3Tene or poly(acrylic acid) as shown in formulae 7a and 7b. Another example is the sulfonated phenol-formaldehyde condensation polymer 8. The preparation of ion-exchange resins and the determination of their capacities are described in Section 5.4, Experiments 5-1 and 5-2. 

Both organic and inorganic solid acids are used. As organic acids, Bronsted acids such as condensed compounds of /Mira-substituted phenol with formaldehyde,and Lewis acids such as zinc salts of the above compounds and those of aromatic carboxyl acids are used. As inorganic acids, montmorillonite clays such as bentonite, fuller s earth, kaoline, chinaclay, and their chemically modified materials are used. 

Figure 9 Overview of the structure and chemistry of two-component DNQ-novolac resists. The polymer resins in these resists are novolacs (which are soluble in both organic solvents used for film casting and aqueous alkaline solutions used for development) that are made by co-condensation of phenols (i.e., typically m- and p-cresol) and formaldehyde. The sensitizer in these resists are substituted DNQs which inhibit the dissolution of novolac and which upon exposure to UV light transform into carboxylic acids that generally increase the dissolution of novolacs in aqueous alkaline solutions.

The sulfonation products of phenol can be condensed without separation, and a highly cross-linked material can be obtained in appropriate conditions. Other resins can be prepared similarly to sulfonic resins. For example starting with salicylic acid and formaldehyde, a resin with carboxylic groups is obtained. 

The use of these intermediates to produce shikimates is shown in Figure 6.32. In principle, anethole (53) and estragole (methyl chavicol) (52) are available from phenol, but in practice, the demand is met by extraction from turpentine. Carboxylation of phenol gives salicylic acid (38) and hence serves as a source for the various salicylate esters. Formylation of phenol by formaldehyde, in the presence of a suitable catalyst, has now replaced the Reimer-Tiemann reaction as a route to hydroxybenzaldehydes. The initial products are saligenin (189) and p-hydroxybenzyl alcohol (190), which can be oxidized to salicylaldehyde (191) and p-hydroxybenzaldehyde (192), respectively. Condensation of salicylaldehyde with acetic acid/acetic anhydride gives coumarin (50) and 0-alkylation ofp-hydroxybenzaldehyde gives anisaldehyde (44). As mentioned earlier, oxidation of phenol provides a route to catechol (184) and guaiacol (188). The latter is a precursor for vanillin, and catechol also provides a route to heliotropin (61) via methylenedioxybenzene (193). 

---