Modeling laser bandwidth for OPC applications

Abstract

With the push toward 32 nm half-pitch, OPC models will need to account for a wider range of sources of imaging variability in order to meet the CD budget requirements. The effects of chromatic aberration on imaging have been a recent area of interest but little work has been done to include this effect in OPC models. Chromatic aberrations in the optical system give rise to a blurring of the intensity distribution in the imaging plane even for highly line-narrowed immersion laser sources. The resulting focus blur can introduce a feature-dependent CD bias of several nanometers. Usually, the empirical components of the resist model can reduce or completely compensate for this imaging effect. However, it is not well known if including a more physical image model over a large range of laser bandwidth conditions will improve the OPC accuracy or process-variability robustness.This study demonstrates the correlation of physical laser bandwidth perturbations with perturbations of the optical model in Calibre. The laser bandwidth is experimentally perturbed to obtain several sets of CD measurements for different bandwidths. These are then used in model calibration with the corresponding perturbation in the optical model. Finally, we quantify the improvement in model accuracy obtained when including an input of laser bandwidth.