Abstract: A SRAM single bit failure at write mode was carefully analyzed.By nano-probing the failed bit,it was found that a weak access-NMOS disabled the write-operation of that particular bit.ATEM check showed that the failed bit has large poly grain size as compared to a normal bit,which causes the gate work function to change and lower the local arsenic concentration.It is then verified by SPICE simulation that the local poly depletion is the origin of the access-NMOS conductibility degradation.