Insolubilization mechanism and lithographic characteristics of a negative electron beam resist iodinated polystyrene

To elucidate the insolubilization mechanism of iodinated polystyrene (IPS) upon exposure to an electron beam and deep UV, the effects of additives on exposure characteristics of IPS and its parent polymer, polystyrene, are clarified. Results indicate the following mechanism. Iodine atoms produced by homolytic dissociation upon exposure undergo competitive reactions: the radical recombination which is the reverse of dissociation and the formation of other radicals that leads to insolubilization. The proposed reaction mechanism can explain the relationship between the sensitivity and degree of iodination. The G values for crosslinking of IPS, G(X), are also obtained according to Charlesby's theory. The calculated lithographic characteristics on the basis of G(X) are discussed.