ABSTRACT:Thermal and photo-induced reactions of radical species generated by y-irradiation of poly(methyl methacrylate) and poly(ethyl methacrylate) have been investigated by means of ESR spectroscopy. The y-irradiation at cryogenic temperature leads to the formation of three major radical species, side chain ---COOC.H 2 • + 1 · -anion radicals and---COOCHC._ 1 H 2 • _ 1 radicals, and main chain -CH-radicals. Cation radicals are immediately converted to the neutral radicals by proton transfer to the polymer molecules. Illumination of the polymer anion radicals with visible light leads to electron detachment or the elimination of ester alkyl groups to form alkyl radicals. Illumination with UV light leads to the conversion of the ---COOCHC. _ 1 H 2• _ 1 radicals to acyl-type-C = 0 radicals. Both the---COOCHC. _ 1 H 2.-1 and the-C = 0 radicals are the precursor of scission-type ·qCH3)(COOC.H2.+ 1)CH 2-radicals.KEY WORDS Poly(methyl methacrylate) / Poly(ethyl methacrylate) /Resist/ Lithography / Radiolysis / Degradation / Chain scission / Radical / ESR / Since poly(alkyl methacrylate)s are typical positive-resist materials in deep UV, electron beam and X-ray lithography, many studies have been carried out for clarifying the mechanism of radiation-induced degradation of poly(alkyl methacrylate)s. It is well known that the irradiation of poly(alkyl methacrylate)s with Ionizing radiations results in the formation of scission-type radicals 1 -3 ·c-(CH3)(COOC.H2.+ 1)CH 2-. The formation of the scission-type radicals strongly suggests that the degradation is induced by the reaction of polymer radicals.Since ionization is the main action of ionizing radiations, radiation-generated positive and negative ion radicals are thought to play important roles in the degradation of the polymers. A considerable amount of spectroscopic studies have been carried out for elucidating the nature and the roles of primary ion rad-* To whom correspondence should be addressed. icals in the degradation of the polymers. 4 -10 However, there have been few consistencies between investigators even for the spectroscopic assignment of the ion radicals. We have recently made the pulse radiolysis studies of poly(alkyl methacrylate) solutions, and determined the optical absorption bands of the polymer anion radicals. 11 We have also made the ESR and electron spin echo studies of yirradiated poly(methyl metacrylate) (PMMA) and found that the y-irradiation at cryogenic temperature leads to the formation of three major radical species, side chain -COOCH 3 ·-anion radials and -COOCH 2 radicals, and main chain -CH-radicals. 12 Upon annealing the polymer to room temperature, the -COOCH 2 radicals were disappeared accompanied by the formation of scission-type ·qcH 3 )(COOCH 3 )CH 2 -radicals, which suggests that the -COOCH2 radicals are respon-835

the case of scrambling, an isotropic label distribution could result even if the monomer residence time were much shorter than the chain residence time. In this case, the majority of the active carbon would be comprised of growing chains. Further evidence against rapid and complete scrambling comes from the iron data in the present work. If the entire product scrambled, then there should be a statistical distribution for the molecular weights, and we show this is not the case.24 V, Concluding RemarksThe estimates of residence times and concentrations ignore the possible contributions of very unreactive intermediates which contribute little to the overall rate. Such material would appear in the long tails in the transient. Because of the long residence time on the surface, this could represent an appreciable amount of carbon, even though it does not contribute appreciably to the rate.The chain growth rates derived here are much faster than previously thought. While in qualitative agreement with earlier conclusions of Biloen,1 23456 7they place an order of magnitude more stringent limit on the rate of chain growth. However, Zhang and Biloen have recently reported measurably slow chain growth on a cobalt catalyst at conditions comparable to those here.8 **The time constants for chain growth which they report are 20-30 times slower than the limit set in Table II. They base their analysis on sequential appearance of 13C in successively longer hydrocarbons (C, through C3). Their data are clearly at odds with our data in Figures 8 and 10, which show simultaneous infusion of 13C into C, and C3 -*• C6 products. The reason for this disagreement is unclear. However, Zhang and Biloen did not use GCMS and the details of how the very complicated reduction of the mass spectrometric data was accomplished have not been published. Alternatively, subtle differences in catalyst properties and/or operating conditions might make a large difference in chain growth rates.

No abstract

No abstract

No abstract