Work function tunability of refractory metal nitrides by lanthanum or aluminum doping for advanced CMOS devices

Abstract

A lanthanum (La)-doped HfN is investigated as an n-type metal gate electrode on SiO2 with tunable work function. The variation of La concentration in (HfxLa1-x) Ny modulates the gate work function from 4.6 to 3.9 eV and remains stable after high-temperature annealing (900 °C to 1000 °C), which makes it suitable for n-channel MOSFET application. An ultrathin high-k dielectric layer was formed at the metal/SiO2 interface due to the (HfxLa1-x) Ny and SiO2 interaction during annealing. This causes a slight reduction in the effective oxide thickness and improves the tunneling current of the gate dielectric by two to three orders. We also report the tunability of TaN with Al doping, which is suitable for a p-type metal gate work function. Based on our results, several dual-gate integration processes by incorporating lanthanum or aluminum into a refractory metal nitride for CMOS technology are proposed. © 2007 IEEE.