Modeling of Projection Electron Lithography

Projection Electron Lithography (PEL) has recently become a leading candidate for the next generation of lithography systems after the successful demonstration of SCAPEL by Lucent Technologies and PREVAIL by IBM. These systems use a scattering membrane mask followed by a lens with limited angular acceptance range to form an image of the mask when illuminated by high energy electrons. This paper presents an initial modeling system for such types of projection electron lithography systems. Monte Carlo modeling of electron scattering within the mask structure creates an effective mask "diffraction" pattern, to borrow the standard optical terminology. A cutoff of this scattered pattern by the imaging "lens" provides an electron energy distribution striking the wafer. This distribution is then convolved with a "point spread function", the results of a Monte Carlo scattering calculation of a point beam of electrons striking the resist coated substrate and including the effects of beam blur. Resist exposure and development models fi-om standard electron beam lithography simulation are used to simulate the final three-dimensional resist profile.