A comprehensive Monte Carlo program (piber) has been developed for the simulation of ion beam exposure of resists. piber has been used to study ion ranges, backscattering coefficients, and energy-loss distribution data for various combinations of incident ions and multilayered targets. For lithographic applications, the spatial ion energy-loss distribution in polymethyl methacrylate (PMMA) generated with piber for a δ-function exposure is convoluted with realistic incident ion beam shape (Gaussian, square, etc.) to produce latent images. A string development model is then used to generate developed ion beam exposure profiles in PMMA. The developed profiles for isolated lines have been studied as a function of parameters such as ion energy, resist thickness, and exposure dosage. Closely spaced lines have also been simulated in order to study proximity effects. It is demonstrated that proximity problems are greatly reduced in comparison with electron beam exposed patterns.
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Karapiperis et al. (1981) studied this question.