Illumination optimization effects on OPC and MDP

Illumination optimization has always been an important part of the process characterization and setup for new technology nodes. As we move to the 130nm node and beyond, this phase becomes even more critical due to the limited amount of available process window and the application of advanced model based optical proximity corrections (OPC). Illumination optimization has some obvious benefits in that it maximizes process latitude and therefore makes a process more robust to dose and focus variations that naturally occur during the manufacturing process. By mitigating the effect of process excursions, there are fewer numbers of reworks, faster cycle times and ultimately higher yield. Although these are the typical benefits associated with illumination optimization, there are also other potential benefits realized from an OPC modeling and mask data preparation (MDP) perspective as well. This paper will look into the not so obvious effects illumination optimization has on OPC and MDP. A fundamental process model built with suboptimal optical settings is compared against a model based on the optimal optical conditions. The optimal optical conditions will be determined based on simulations of the process window for several structures in a design using a metric of maximum common depth of focus (DOF) for a given minimum exposure latitude (EL). The amount of OPC correction will be quantified for both models and a comparison of OPC aggressiveness will be made. OPC runtimes will also be compared as well as output file size, amount of fragmentation, and the number of shot counts required in the mask making process. In conclusion, a summary is provided highlighting where OPC and MDP can benefit from proper illumination optimization.