Direct visualization of anomalous-phosphorus diffusion in failure-bit gates of SRAM-load pMOSFETs with high-resolution scanning spreading resistance microscopy

In this study, we directly observed fail bits of pMOS with V
_th
variations in SRAM by both SSRM and a nanoprober, clarified that the failure is originated from the phosphorus anomalous diffusion into the pMOS gate bottom. We succeeded in observing the pn-junction boundary within a thin SRAM poly-Si gate with the size of less than 60 nm. The gate-phosphorus doping and STI geometry influence on pn boundary is investigated systematically. A significant improvement in process margin is achieved with controlling of the phosphorous-anomalous diffusion.