Leakage current study of Si1−xCx embedded source/drain junctions

This work investigates the impact of various processing parameters on the leakage current of in situ P-doped Si1−xCx embedded source/drain (S/D) junctions, i.e., the carbon content x (%) and the thermal budget used either before or after the selective epitaxial deposition. It is shown that while the area leakage current density, generated by defects in the depletion region is not affected by the epitaxial process or the strain in the substrate, the perimeter leakage current density (JP) increases with x. From the stronger reverse bias dependence of JP, it is derived that a higher electric field exists along the junction periphery. This is confirmed by capacitance-voltage (C-V) measurements, demonstrating a higher p-well B doping density for increasing x. It is believed that this originates from the strain dependence of the B diffusivity in the p-well region. No evidence of electrically active extended defect formation was found, so it is expected that the off-state current of embedded Si1−xCx S/D nMOSFETs will not be adversely affected by the selective epitaxial deposition.