E-beam proximity correction for negative tone chemically amplified resists taking into account post-bake effects
Glezos N., Patsis GP., Rosenbusch A., Cui Z.
The use of chemically amplified resists (CARs) in electron beam lithography required an additional processing lithography step i.e. post exposure bake (PEB). During this step the acid produced during exposure diffuses and chain reactions occur. In this paper, the method of single pixel exposures is used in order to evaluate the diffusion coefficient. This approach is applied in the case of three resists, namely AZPN114 (Hoechst), SAL601 (Shipley) and the experimental EPR. In the case of AZPN114 diffusion is limited for the higher Θ values in the center of the pattern but is considerably larger at the edge. EPR represents an extreme case where diffusion is limited by a strong cage effect due to a fast completion of the reaction while SAL601 represents an intermediate case. The diffusion coefficient is used in combination with the e-beam simulator SELID to provide data for proximity correction. The reaction-diffusion system for the specific values of the thermal processing parameters is used to modify the point spread function I. The resulting actual acid concentration for a point exposure is convoluted for a given layout. Subsequently, proximity correction is performed as in the case of conventional resists.