Correcting deviations in the shape of projected images in the electron beam block exposure column

摘要

The block exposure column has a mask with one hundred stencils in a deflection area. Each mask pattern projected by electron beams is reduced in size to 1/60th and imaged onto a wafer. Deviations in image shapes are dependent on deflected beam trajectories and imaging beam currents. We show techniques to measure the image shapes using reflected electron signals. Correction methods are proposed to reduce the deviations. After the corrections, the block exposure can expose images of every mask pattern of the size 5x5 μm with the image size deviation less than 11 nm, which includes 5.8 nm of an isotropic expansion and 9.6 nm of distortions.