Electrical active defects in the band-gap induced by Ge-preamorphization of Si-substrates

摘要

Ultra-shallow p~+-n junctions have been obtained from Ge~+-preamorphized and crystalline <100> silicon substrates. B~+ and BF_2~+ dopants have been used. Boron was implanted at low energy 3 keV/10~(15) cm~(-2) while an equivalent energy of 15 keV /10~(15) cm~(-2) was chosen for BF_2~+. Rapid Thermal Annealing (RTA) for 15 s at 950 deg C was then used for dopant electrical activation and implantation damage removal. Electrically active defects in these samples were characterized using Deep Level Transient Spectroscopy (DLTS) and isothermal transient capacitance (triangle open(t,T)). Two electron traps were detected in the upper half of the band gap at E_c - 0.20 eV and E_c - 0.45 eV, respectively. These traps are shown to be induced by the Ge~+ preamorphization stage. Dopant implantation along with RTA result in the formation of a depth distributed energy continuum for B~+ and BF_2~+ implants. Each continuum has been ascribed to annealing residual defects. Low energy B~+ implantation is seen to induce twice as many defects as BF_2~+ implantation. From isothermal transient capacitance (triangle openC(T,T)), reliable damage concentration profiles have been obtained, revealing that preamorphization induces not only defects in the regrown silicon layer but also a relatively high concentration of electrically active defects up to 3.5 #mu#m into the bulk.