Thermal and Photo-Induced Reactions of Polymer Radicals in γ-Irradiated Poly(alkyl methacrylate)

Abstract

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

Spin-Correlated Radical Ion Pairs Generated in Liquid Haloalkanes Using High-Energy Radiation

“…In irradiated PEMA, 63 the EPR line of the RA is similar to that mentioned above. No EPR signal was observed that could be assigned to the primary RC, even at 4.2 K. 63 This particle seems to decay rapidly via proton transfer. 62,63 Thus, it seems likely that the observed fluorescence from the PEMA + pTP solution appeared due to the recombination of pTP +• /PEMA −• RIPs.…”

Electron spin echo studies of free radicals in irradiated polymers

“…The similar photo-induced radical conversion has been confirmed also for methyl pivalate, C ( C H 3 )3COOCH3, as a model compound of PMMA [43].…”

“…Figure 10 shows the photo-induced transformation of radical species in irradiated PMMA [43]. Figure 10 shows the photo-induced transformation of radical species in irradiated PMMA [43].…”

Theoretical Study of Ionization of Polymers for EUV Resist

“…From Figs. 7-8, we found poly(4-hydroxy styrene) has less energy barrier of ionization than poly(acrylic acid) , which coincides with more unstable radical cations of poly(acrylic acid) [14,15]. Figures 9 and 10 shows the decrease of electrons on substituent before and after ionization of poly(4-hydroxy-2,3,5,6-tetra substituted styrene) and poly(α-substituted acrylic acid), respectively.…”