Optimization of process window simulations for litho-friendly design framework

Abstract

Cutting edge technology node manufacturers are always researching how to increase yield while still optimally using silicon wafer area, this way these technologies will appeal more to designers. Many problems arise with such requirements, most important is the failure of plain layout geometric checks to capture yield limiting features in designs, if these features are recognized at an early stage of design, it can save a lot of efforts at the fabrication end. A new trend of verification is to couple geometric checks with lithography simulations at the designer space. A lithography process has critical parameters that control the quality of its resulting output. Unfortunately some of these parameters can not be kept constant during the exposure process, and the variability of these parameters should be taken into consideration during the lithography simulations, and the lithography simulations are performed multiple times with these variables set at the different values they can have during the actual process. This significantly affects the runtime for verification. In this paper the authors are presenting a methodology to carefully select only needed values for varying lithography parameters; that would capture the process variations and improve runtime due to reduced simulations. The selected values depend on the desired variation for each parameter considered in the simulations. The method is implemented as a tool for qualification of different design techniques.