Due to the low k1-factor which leads to reduced process latitude, it is becoming increasingly important that OPC and lithography verification take into account process variations. An essential element to the successful implementation of full-chip, process window aware RET/OPC design and verification is a lithography model that is able to accurately describe the lithography process across the entire focus-exposure window. Moreover, a straightforward calibration without requiring excessive amount of through process window measurements is also critical to ensure quick turnaround-time.
In this paper, we introduce a new Focus Exposure Matrix (FEM) model based on Brion's Tachyon platform. The FEM model has two adjustable parameters: focus and exposure. By adjusting these parameters, new models at arbitrary process conditions within the process window can be quickly derived, with which large number of simulation results can be obtained at different exposure and focus for detailed process window analysis. The fitting of FEM model is through a single calibration process using wafer measurements at limited number of sampling locations within the process window. The resulting calibrated FEM model is shown to have superior fitting as well as prediction accuracy, without requiring massive additional focus-exposure measurements.
Accurate FEM modeling enables two important applications in the deep sub-wavelength regime: lithography manufacturability check (LMC) and optical proximity correction (OPC). FEM-enabled LMC proves to be a substantial advance in model-based verification by providing through process window analysis capability. Furthermore, FEM models can be employed in OPC practically to prevent catastrophic failures due to process variation while still maintaining satisfactory OPC quality in terms of matching the modeled wafer image to design intent.
In this paper, we use real data and simulation results to demonstrate the quality of the FEM-model and its effectiveness in the LMC and OPC applications.