Crosslinking Reactions in Negative Electron Resists Composed of Halogenated Aromatic Polymers

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Abstract
Crosslinking reactions in halogenated aromatic polymers which provide useful negative electron resists with high dry etching durability and high contrast were studied. Halogenated aromatic polymers show characteristic features, such as the saturation of crosslinking reactivity with an increase of halogen content and little postirradiation polymerization effect. The reactivity saturation is dependent not on the ring size or main chain structure of the aromatic polymer, but on the kind of halogen atom. The larger halogen atoms tend to exhibit more rapid saturation with halogen content, suggesting a steric effect. The strong participation of radical species formed by the dissociation of the carbon‐halogen bond in the crosslinking reaction was verified from studies of radical scavenger effect and electron spin resonance spectroscopy. Considerable amounts of radical species remain after the crosslinking reaction has finished in vacuum, but remain in polymer films without crosslinking because of the high glass‐transition temperatures of aromatic polymers and decreasing chain reactivity by halogen atoms, resulting in negligible postirradiation polymerization.

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