A Study on Three Dimensional Mask Effect of Attenuated Phase-Shift Mask in Advanced Optical Lithography

Along with the extension of optical lithography to 28nm node and beyond, several effects that can be neglected in previous technology nodes become more and more prominent. One of the most striking effects is the 3D mask effect where the mask transmittance and phase are influenced by the mask topography. This study started with Kirchhoff mask model based experiment of 28nm node SRAM cell features based on Attenuated Phase-shift mask (Att. PSM), which were calibrated into Optical proximity correction (OPC) process models. A 28nm test model was constructed with Kirchhoff mask modeling approach. Once the standard Kirchhoff effects were working on the test wafer, the 3D mask effects were included for the same data. Then the interactive relations among these mask data were investigated and found to generate as much as 15nm edge shift differences. The mask model was then refit including the 3D mask effect and compared with the Kirchhoff mask model in the simulator to better understand the impact of 3D mask effect on patterns.