Point spread function and total process function measured for a variable-shaped electron beam system

Abstract

In the field of electron beam lithography, accurate exposure requires a precise proximity effect correction (PEC). The most common approaches for PEC such as dose modification, shape modification, and hybrid models require the evaluation of the point spread function (PSF) and, in view of real applications, the measurement of the total process function (TPF) considering both tool behavior and process effects. In contrast to research tools equipped with a Gaussian beam column, variable-shaped beam (VSB) systems are established in the commercial field, e.g., for mask fabrication. In this paper, the authors present an approach to measure PSF and TPF on a VSB lithography tool. This method is based on the well known point exposure distribution measurement technique early introduced for Gaussian beam systems by Rishton and Kern [J. Vac. Sci. Technol., B 5, 135 (1987)]. The approach is enhanced by application of specific features provided on a VSB system. The interpretation of the experiment was enabled by a comparison of the measured data with calculations of the energy deposition in the resist using Monte Carlo simulations. Results are presented for hydrogen silsesquioxane and Novolac negative tone resists that are used on standard i-line photomasks.