Indium channel implants for improved MOSFET behavior at the 100-nm channel length regime

The authors report on the use of indium as an alternative channel implant in MOSFETs. Indium has an atomic weight of 115, and the implant peak can be placed with tens of nanometers of the surface. The profile is skewed toward the bulk, resulting in a very low surface concentration. Deep-submicrometer-channel-length devices with oxide thickness of 2.5 nm were fabricated using X-ray lithography and indium channel implants from 100 keV to 300 keV, keeping the dose constant at 10/sup 13/ cm/sup -2/. Activation of the indium implant was achieved by rapid thermal annealing (5 s at 1050 degrees C). As expected, low indium implant energies result in high device threshold voltage (up to 0.33 V for L=0.15 mu m and up to 0.24 V for L=0.1 mu m). Turn-off characteristics were excellent (subthreshold slope=80 mV/dec for L=0.15 mu m and 100 mV/dec for L=0.1 mu m, at V/sub DS/=1 V). Low-field mobility for indium-doped channels was about 380 cm/sup 2//V-s (as compared to 420 for boron doped channels), and no degradation in mobility was observed as implant energy was reduced. A reduction in normalized substrate current is observed in indium-implanted channels for very short channel lengths.