Thin-layer p–n junction fabrication using Ga and In focused ion beam implantation

Abstract

The fabrication of shallow p–n junction impurity profiles using Ga and In focused ion beam (FIB) implantation in conjunction with rapid thermal annealing is reported. A 75-keV focused ion beam with 80 mA/cm2 current density and 0.5-μm beam diameter was used to implant Ga+ and In+ into (100) Si substrates at doses ranging from 1×1013 to 5×1015/cm2. The annealing temperature was varied from 600 to 1000 °C for various times, 10–30 s. Secondary ion mass spectrometry and spreading resistance profiling were used to measure the implanted species atomic and carrier concentration depth profiles. As compared to the conventional broad beam implantation, the FIB implanted Ga concentration depth profiles exhibit higher activation percentage in the end-of-range and tail region. This results in thicker layers and deeper p+–n junctions, but with lower sheet resistance and leakage current. A similar phenomenon is also observed in In FIB-implanted samples. The damage generated by the high dose rate implantation is possibly responsible for this phenomenon. p+–n diodes fabricated using Ga FIB doping exhibit very good diode electrical characteristics: ideality factor as low as 1.01, leakage current density below 1 nA/cm2 at −1 V reverse bias, and breakdown voltage of ∼35 V. Diodes fabrication with In generally exhibit shallower junctions, but higher leakage current. Bipolar transistors have been fabricated using FIB-implanted Ga and In thin base layers. Common emitter current gain of 70 and 10 were obtained for Ga and In FIB-implanted bipolar transistors, respectively.