Optimization of exposure parameters for lift-off process of sub-100 features using a negative tone electron beam resist

A thorough study of exposure parameters for electron beam lithography using AR7520 negative tone electron beam resist is here presented. We optimized the beam voltage, apertures diameter and resist thickness in order to achieve the smaller dimensions possible for each resist thicknesses. Monte Carlo simulations of the electrons scattering process correlated the experimental results indicating a less efficient energy deposition into the resist layer for larger beam energies and resist thicknesses, thus resulting in larger doses required to expose a selected dot size. Furthermore, for the particular exposure conditions used we determined a forward scattered electrons range between 50 nm and 170 nm, depending on the dot nominal size. On the other hand, a reduced backscattering electrons range was observed showing a constant value of 560 nm, being therefore more significant when larger dimensions are exposed in a point-by-point exposure, and thus supporting the smaller doses observed for larger sizes. Finally, a baking step is used to further improve the etch resistance of the resist, which allied to the optimized exposure parameters, opens a pathway to achieve sub-100nm critical dimensions for the reproducible fabrication of nanometric devices using a simple lift-off method.