PHOTOLYSIS OF UNSUBSTITUTED AND P-METHOXYCARBONYL SUBSTITUTED 2-METHYL-1-PHENYLPROP-2-EN-1-ONE COPOLYMERS IN SOLUTION

A new monomer, methyl 4-(2-methyl-1-oxoprop-2-en-1-yl)benzoate (p-(met hoxycarbonyl)phenyl isopropenyl ketone, MeOCO-PIPK), was synthesized a nd copolymerized with styrene and methyl methacrylate (MMA). The copol ymers of MeOCO-PIPK and 2-methyl-1-phenylprop-2-en-1-one (phenyl isopr openyl ketone, PIPK) with styrene and MMA were photolyzed by deep-, mi d- and near-UV light in dilute solution; and the quantum yields of sci ssion, phi(s), and the UV absorption spectra were measured. The p-meth oxycarbonyl substitution increased the molar extinction coefficients o f the ketone monomer units extensively, but slightly lowered the phi(s ) values in styrene and MMA copolymers. This is expected to increase t he net sensitivity of solid alms of the polymers. The phi(s) was found independent of the wavelength, despite the concurrent absorption by s tyrene units in the styrene copolymers. Larger phi(s) values were obta ined for the MMA copolymers than the corresponding styrene copolymers. Solvents with larger dielectric constants gave larger phi(s) for the copolymer of MMA with PIPK; but when the dielectric constants were sim ilar, lower phi(s) values were observed in the solvents with more easi ly abstractable hydrogens. A large bleaching effect was seen in MMA co polymers, which should make possible the formation of resist patterns with steep profiles when used in photolithography. (C) 1996 John Wiley & Sons, Inc.