Electrical properties of nanometer-scale Si p+-n junctions fabricated by low energy Ga+ focused ion beam implantation

Abstract

Diodes have been fabricated by on-axis Ga+ focused ion beam (FIB) implantation at 4–25 keV into n-Si 〈100〉 wafers doped to 2×1015/cm3. Post-implantation anneal was performed at 600 °C for 30 s to electrically activate the Ga and to regrow the implanted layer. SIMS measurements performed to obtain the Ga concentration depth profile indicate good agreement with trim simulation even at low energies. At 4 keV an electrical junction depth of 15 nm is obtained from spreading resistance profiling (SRP). The junction depth was found to vary linearly with energy over the range explored. The electrical properties of the diodes were obtained from I-V characteristics. The leakage current density of the 5 keV diode was measured to be 1 and 20 nA/cm2 at a reverse bias of 1 and 5 V, respectively. The corresponding leakage current density values for the 10 and 15 keV diodes were between 25% and 50% lower than those reported for 5 keV. The reverse bias breakdown voltage was between 105 and 110 V for all diodes. The combination of nanometer-scale junction depth, low leakage current density, and high breakdown voltage indicate that low energy Ga FIB implantation is a promising technology for ultrashallow p+ -n junction fabrication.