Atomic Force Probing and Focus Exposure Matrix Analysis to Resolve High Leakage Current Failure on SRAM

This paper demonstrates the use of Current Imaging, Atomic Force Probing (AFP) and Focus Exposure Matrix (FEM) analysis to identify the root cause of high leakage current issue in Static Random-Access Memory (SRAM) array in the product. Through current imaging and AFP probing, abnormal current image contrast was observed on the P-Channel Field Effect Transistor (PFET) of bad SRAM bit cells. Further physical failure analysis by delayering and Transmission Electron Microscopy (TEM) found no physical-related defect. This indicates that the high leak path is caused by front-end of line (FEOL) process-related issue. The AFP analysis results indicate a possible implant-related issue. Focus Exposure Matrix (FEM) analysis was carried out on an implant mask and the results correlate well to the SRAM leakage, which suggests counter-doping due to insufficient resist coverage that leads to a new product mask evaluation.