Abstract
The very tight critical dimension(CD) specification as well as the very small energy latitude(EL) of the 65-nm node and beyond, planned to be accomplished by ArF lithography, require that the control of the employed thin-film stack should also be very tight. In such cases, there are generally several optical parameters of the thin-film stack that have appreciable effects on CD variation. So, we can not just focus on minimizing the swing effect by minimizing substrate reflectivity, as we did conventionally. Here, we propose a systematic methodology for doing optimization of the thin-film stack when several optical parameters of the thin-film stack come into play simultaneously. By adopting a proper figure of merit, the optimization can be done automatically. The specially designed algorithm ensures that global optimization can be achieved.