Three-dimensional structures increasingly find applications in various devices such as diffractive optical elements, photonic element, microelectromechanical systems, etc., and are often fabricated by e-beam lithography. Their performance is known to be highly sensitive to their dimensions. Therefore, it is critical to achieve high dimensional accuracy for the desired characteristics. However, as the feature size in three-dimensional structures decreases down to nanoscale, the lateral development of the resist and the proximity effect due to electron scattering can make dimensions of the written features in a device substantially different from the target dimensions. In this study, this issue is addressed for staircase structures; specifically, minimizing the difference between the target and the actual widths of each step. Through computer simulation and experiments, it has been shown that significant improvement in dimensional accuracy, especially the step widths of the staircase structures, can be achieved by the proposed practical width-adjustment scheme.