Two-dimensional electrostatic potential of 45 nm technology semiconductor devices was mapped by electron holography with 2 nm resolution. The 2-D active dopant distribution was reconstructed by the inverse modeling of the electrostatic potential. Identically manufactured devices with and without a carbon co-implant were compared. The authors show that in the presence of the carbon co-implant, the two-dimensional diffusion of the boron halo implant during thermal processing is reduced. It is demonstrated that the carbon co-implant improves the control of the device short channel effects. © 2011 American Vacuum Society.