A chlorinated resist named ZEP changes from positive- to negative-tone with a high dose of electron beam irradiation. The sensitivities to a 100-kV electron beam as a dual positive- and negative-tone resist are evaluated with various developers. Although the positive-tone sensitivity varies with different developers owing to different solvation strengths, the threshold dose for the positive-negative (P-N) inversion is independent of the developer. According to an analysis using X-ray photoelectron spectroscopy and NMR spectroscopy, the amount of chlorine atoms and terminal double bonds generated by chain scission determines the scission/crosslinking probabilities, i.e., the threshold of the P-N inversion.
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