Achieving low-VT Ni-FUSI CMOS via lanthanide incorporation in the gate stack

This work reports that introducing lanthanide in the gate dielectric or in the gate electrode results, in both cases, in large effective work function (eWF) modulation towards n-type band-edge for Ni-FUSI devices. This is done by: (a) deposition of a Dy2O3 capping layer on the host dielectric (SiON or HfSiON), or (b) simple Yb implantation of nMOS poly gates prior to FUSI. We show that: (1) both cases result in dielectric modification with gate leakage (JG) reduction; (2) adding a cap has no significant impact on Tinv(<1 Å), while up to ∼5 and 2 Å reduction occurs for SiON and HfSiON Yb-implanted devices, respectively, (3) the largest JG reduction (150×) is obtained for capped SiON devices due to dielectric intermixing and formation of a new high-k dielectric (DySiON), comparable to HfSiON in JG and mobility but with 500 mV smaller VT; (4) on the other hand, being less invasive to the host dielectric, the optimized Yb I/I option gives 18% improved mobility compared to capped SiON devices; (5) excellent process control and reliability behavior (VT instability by a.c. pulsed IV, PBTI and TDDB) is reported for both eWF tuning methods. They allow ΔeWF(n−p) values up to ∼800 meV when combined with Ni–silicide FUSI phase engineering, promising for low-VT CMOS.