Validation of inverse lithography technology (ILT) and its adaptive SRAF at advanced technology nodes

Abstract

In this paper, an overview of Inverse Lithography Technology (ILT) based on Level Set Methods (LSM) is provided. Applications of ILT in the advanced lithography process are then shown for several different devices, including DRAM, SRAM, FLASH, random logic, and imaging devices. ILT is used to correct the main patterns, as well as automatically insert SRAFs using model-based mathematical methods. The process of SRAF generation in ILT is unified with the process of inversion. With the help of ILT, SRAFs can be inserted where physically needed, independent of source parameters or target patterns. Results that demonstrate the adaptive nature of ILT SRAF insertion capability are presented. Wafer verification results were collected by multiple advanced semiconductor manufacturing companies at advanced technology nodes, including 45nm and 32nm nodes, and compared with their current OPC solution. Final wafer results presented here demonstrate that ILT improves pattern fidelity, enlarges process window, and provides remarkable control for line-end shortening.