Cresol-substituted benzaldehyde Novolak resins

Table II. Glass Transition Temperatures of m-Cresol-Substituted Benzaldehyde Novolak Resins...

The glass transition temperatures of these Novolaks are given in Table II. Except for the methoxy group substituted benzaldehyde Novolak resins, their glass transition temperatures are reasonably high, and the elemental analysis shows one-to-one condensation of m-cresol and substituted benzaldehyde under acidic polymerization conditions (27). 

The preparation method is similar to that for the cresol-formaldehyde Novolak resin with a molar ratio of cresol/benzaldehyde = 1.1 in acidic conditions. We have prepared varieties of substituted m-cresol-benzaldehyde Novolak resins, and 1-, and 2-naphthol-4-hydroxybenzaldehyde Novolak resins in the same manner. Almost all of these benzaldehyde Novolak resins give excellent resist films when spin-coated onto silicon or silicon dioxide substrates after being dissolved, together with a photoactive compound, in a solvent like 2-... 

The UV-absorption spectra of these Novolak resins vary widely depending upon substitution. However, the m-cresol-benzaldehyde Novolak resin is characteristic in its transparency within 300-320 nm in comparison with the cresol-formaldehyde resin. The chlorinated Novolak resin made of 2-chloro-5-methylphenol and formaldehyde has a slightly stronger UV absorption in this wavelength range, but weaker absorption in the range of 250 and 300 nm in comparison with a commercially available cresol-formaldehyde Novolak resin, as shown in Figure 4. 

---