Molecular weight distribution effects of novolak resin-based chemical amplification negative resist systems are investigated for electron-beam lithography. The resist systems investigated consist of onium salts as an acid generator, a methoxymethyl melamine crosslinker, and a conventional/fractionated novolak resin matrix. Delineated patterns of both types of resist systems are compared to evaluate submicron-scale resolution. The conventional novolak resin-based system shows higher contrast than the fractionated one. High aspect ratio patterns are resolved for the conventional novolak-based resist, whereas poor results are obtained for the fractionated resin-based one on the submicron scale. Very thin films (30 nm) of both resist systems are delineated with a finely focused electron beam (diameter: approximately 2 nm at 5 kV) from a scanning electron microscope. Nanometer-scale edge roughness (nanoedge roughness) is observed for the conventional novolak resin-based resist. On the contrary, the degree of nanoedge roughness is greatly reduced for the fractionated one.
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Shiraishi et al. (1994) studied this question.