Automatic dose optimization system for resist cross-sectional profile in a electron beam lithography

A computer-aided dose optimization system to obtain a modified resist cross-sectional profile is demonstrated based on resist development simulation and an iteration procedure of the exposure dose profile for a positive electron beam resist. The absorbed energy in the resist by the electron beam exposure is evaluated by conventional Monte-Carlo simulation and the resist cross-sectional profile after development is predicted by a cell removal model. The exposure dose profile is optimized by an iteration procedure based on the predicted resist development profile. The exposure dosages at each point are corrected based on the difference of the average absorbed energy density between the desired developed surface and the predicted profile by the resist development simulation. The system is applied for blaze pattern fabrication for diffractive optical elements and a fine blaze pattern is successfully obtained.