Advanced electron beam photomask writers operate at an acceleration voltage of 50 kV. Electrons hitting the photoresist at that energy suffer significant forward scattering in the resist and backscattering from the mask stack, back into the resist material. On a typical photomask, 40% or more of the electrons contribute to backscattering in a one sigma range of about 10 μm.Due to the large amount of backscattering, the resist image contrast on a mask degrades significantly with increasing exposed pattern density. While PEC (Proximity Effect Correction) can keep the CD (Critical Dimension) on target in a wide range of pattern densities, the PW (Process Window) degrades with increasing density.This degradation in process window can partially be compensated by reducing the exposure dose in areas of mask patterns which do not define an edge directly (the inner region of a pattern) while keeping the dose at the edges of the patterns high. For example, when exposing an inverse curvilinear pattern with large exposed areas, the large inner area, here called bulk area, can be exposed at a low dose, while the sleeve, defining the edge of the shape, can be exposed at nominal dose or above. In this case, the bulk area does not contribute to scattering as much as in a standard exposure and the image edge slope increases, which then increases the process window.Applying such a dose splitting scheme on VSB (Variable Shaped Beam) writers is relatively expensive in terms of mask write times since it increases the number of VSB shots needed to write a mask. However, on MBMWs (Multi-Beam Mask Writers), such a dose split can easily be accomplished and doesn't impact mask write time.Since curvilinear masks become more important at the leading edge, we investigate the effect of bulk-sleeve dose splitting on curvilinear mask shapes of various pattern densities. We investigate systematically the effect of bulk and sleeve dose levels as well as sleeve width on process window using a calibrated mask model.