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Electron-beam lithography’s resolution limit is greater than the beam diameter due to resist limitations as well as electron interaction with solids. We examine the effect of molecular weight on the resolution of poly(methyl methacrylate) (PMMA). The experimental procedure uses thin Si3N4 in order to reduce the backscattered electron contribution to the exposure, and the resist contrast standard deviation σ was determined. Molecular weights of 950×103, 120×103, and 15×103 amu were used. It is found that relatively equivalent exposure and resolution are found in each case, and that the entanglement threshold is either lower than thought, or is not a factor in the resolution of PMMA. Lines as small as 7 nm are found in the highest molecular weight.
Khoury et al. (Mon,) studied this question.