The carbon (C) co-implantation and advanced flash anneal were employed to form the ultra shallow junction (USJ) for future nano CMOS technology applications. The effects of the C co-implantation process on dopant transient enhanced diffusion (TED) of the phosphorus (P) doped nano USJ NMOSFETs were investigated in details. The USJ NMOSFETs were prepared by a foundry’s 55 nano CMOS technology. Various implantation energies and doses for both C and P ions were employed. Results show the suppression of the TED is strongly dependent on both C and P implantation conditions. Besides, the mechanisms of P TED and suppression by C ion co-implantation were illustrated comprehensively with schematic models.