Radiation‐Induced Cross‐linking and Chain Scission Reactions in Chlorinated Polymethylstyrene Electron‐Beam Resists

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Abstract
Structurally characterized polymers of o‐, m‐, and p‐methylstyrene, 2,4‐ and 2,5‐dimethylstyrene, and 2,4, 6‐trimethylstyrene prepared by anionic mechanisms and chlorinated selectively at substituent methyl positions, have been assessed as negative‐working electron‐beam resists. Copolymers of vinyl benzyl chloride and o‐, m‐, and p‐methylstyrene prepared by a radical mechanism are similarly assessed. The lithographic data have been correlated in accordance with Inokuti's theory for the radiation‐induced simultaneous cross‐linking and scission of polymers with generalized Poisson distributions. All the polymers substantially substituted with methyl groups in the ortho position are shown not to undergo radiation‐induced chain scission and accordingly display the highest lithographic contrasts. Lithographic reactivities and the radiation chemical yields are further correlated in accordance with the Charlesby‐Pinner relationship and are shown to be independent of both molecular weight and polydispersity and therefore characteristic of chain microstructure. Lithographic contrast is shown to arise from variations in gel dose.

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