Negative annealing in silicon after the implantation of high-energy sodium ions

Abstract

The implantation of sodium ions with an energy of 300 keV is carried out into high-resistivity p-Si. The annealing of defects at T_ann = 350–450°C and related activation of atoms (the latter occurs at the “tail” of atom distribution) are described by a first-order reaction. At T_ann = 450–525°C and irrespective of the ion dose, negative annealing is observed; this annealing is accompanied by an appreciable increase in the surface resistance ρ_s. According to estimations, the activation energy of this process amounts to ~2 eV. It is our opinion that the annealing is related to the precipitation of sodium donor atoms, which occurs at a depth exceeding by two–three times the projected range R_p of ions. The annealing of defects at T_ann = 525–700°C, which leads to a further decrease in ρ_s, features an activation energy of ~2.1 eV. The hypothesis that the “tail” in the profiles of sodium atoms measured by secondary-ion mass spectroscopy is due to the diffusion of these atoms from the walls of the crater to its center is verified. It is shown that this process is not implemented since the profiles of sodium atoms measured at room temperature do not differ from those measured at–140°C.