Near neighbor averaging: A technique for improving image uniformity in aperture array lithography

Ion beam aperture array lithography was developed to rapidly form large arrays of periodic patterns whose shape is defined at the printing step. This is accomplished with a massive array of ion beamlets formed by exposing a stencil mask with a dense array of openings to a broad ion beam; these can be moved across the wafer surface to write the shape of the unit element with each beamlet. In this work, the authors demonstrate that the uniformity of the aperture array mask image can be significantly improved by averaging the exposure with images formed by the neighboring apertures. This reduces the tolerances for patterns in the stencil mask and allows for the correction of random defects that may occur during the mask fabrication process. To achieve this, each aperture image is formed as the sum of the images of itself and its neighbors. They demonstrate, through modeling and experiment, that this process can form images where the standard deviation of the openings has been reduced by a factor of 3 when averaging the exposure over nine neighboring apertures. They show that the size distribution scales inversely with the square root of the number of near neighbor exposures.