Improving chip performance by photomask tuning: ultimate intra-field CD control as a major part of an overall excursion prevention strategy

Excursion prevention is one of the key points in the mission of leading edge foundries. In this paper, we concentrate on patterning excursions and how to prevent them. This strategy concentrates pro-actively on the task to minimize the distributions of critical input parameters as much as possible, independently upon a certain pre-defined specification is met or not. In our paper, we will describe this concept by improving intra-field CDU using CD Correction (CDC) by mask tuning. Mask Tuning by the ForTune system uses ultra-short pulse laser technology to locally change the mask transmission, based on the wafer intra-field CDU, and hence improves CDU on wafer (CDC). To ensure a save patterning with a large enough process window without any negative yield or reliability impact, our concept looks for the tail of the final CD distribution instead of traditional 3-sigma numbers. By using a calibrated 3D resist model, we simulate the wafer CD distribution under all combinations of the Litho input parameter distributions dose, focus and mask CDU. As a result of the simulation, we get thousands of CD-results. The tail of that CD distribution still needs to be larger than the minimum CD needed for a safe etch transfer. Based on our simulation data we can calculate patterning failure probabilities and thus expected yield loss for the different patterning cases, including systematic process deviations (mask, dose, focus). At the final step, we will show in detail how the pro-active optimization of intra-field CDU by Mask Tuning using the ForTune CDC process will give us more patterning margin and thus will reduce the failure probability dramatically. The calculated yield loss for the worst scenario (focus and dose offset additionally to the mask signature) will be reduced from several percentages close to zero.