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Scanning Electron Microscopy

Abstract

First the fundamentals of resist modelling required to implement an analysis of developed resist patterns were studied, which represents the relationship between the energy deposited by incident electrons and the solubility characteristics of a positive or negative resist. Next, two models of single elastic scattering and fast secondary (knock-on) electron production were studied for Monte Carlo simulation of electron scattering in resist film/substrate targets, and the statistical errors of Monte Carlo results were evaluated. Finally, problems in electron beam lithography were investigated with the simulation. The exposure intensity distribution was studied with the two models. A comparison between Monte Carlo calculations and experiments shows that a better agreement is obtained with the knock-on model. An analysis of developed negative resist patterns has been performed by using Monte Carlo results for energy dissipation. A comparison with experimental results revealed that developed resist patterns deform while being stuck to the Si surface by a strong adhesion. Also the time evolution of developed profiles of PMMA (polymethyl methacrylate) resist films was investigated based on the Monte Carlo results for energy dissipation. A quantitative comparison between theory and experiment suggests that some modification is necessary for the empirical constants in the solubility rate due to the electron beam irradiation effect. The spatial resolution was examined for an iso lated PMMA film. Resolutions of 320Å. and 530 Å were found with the single scattering and the knock-on models, respectively. The result with the knock-on model is similar to an experiment value of 600 Å obtained previously. It seems that the knock-on model may be useful for a theoretical study of the ultimate resolution in electron beam lithography.

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