Characterizing an implanted Si/Si p-n junction with lower doping level by combined electron holography and focused-ion-beam milling

A Si/Si p-n junction with very low doping level was made via a standard device fabrication process by implanting As ions at 25 keV into a p-type Si substrate with a boron concentration of 10(15) cm(-3), followed by heat annealing at 1035 degreesC for 33 s. To characterize this junction, a pair of 45degrees wedge-shape cross sections was prepared simultaneously by focused-ion-beam milling and examined using off-axis electron holography. The reconstructed phase images clearly show the phase shift induced by the electrostatic potential drop across the p-n junction, indicating that the junction has been mapped successfully. Quantitative measurements from the phase images give the potential values of 12.21+/-0.40 and 11.50+/-0.27 V, respectively, for the n- and p-type sides of the junction, 0.71+/-0.05 V for the potential drop across the junction and 50.10+/-3.88 nm for the total electric dead layer thickness. This work demonstrates that electron holography is a powerful technique for characterizing low dopant level p-n junctions in practical devices. (C) 2002 American Institute of Physics.