Angled implant fully overlapped LDD (AI-FOLD) NFETs for performance and reliability

Fully overlapped lightly doped drain FOLD n-channel MOSFETs built for the purpose of improving the tradeoff between performance and reliability are discussed. Full gate overlap was achieved by using angled implants to extend LDD (lightly-doped drain) regions beneath the gate edge of devices. The dose and energy of the angled implants were varied. The parasitic overlap capacitance and series resistance as well as the reliability enhancement introduced by the FOLD structure are investigated in detail. The series resistance is shown to be strongly dependent on gate voltage, while the overlap capacitance is found to be reduced significantly by depletion of the FOLD drain regions. The corresponding reduction in hot-carrier-limited channel length more than compensates for the increase in parasitics, indicating substantial enhancement in net drive performance