Kenji Itaka

Suppression of Fermi Level Pinning and Flat Band Voltage Shift by Inserting Diamond-Like Carbon at a High-k/SiO2 Interface in a Gate Stack Structure

Fermi level pinning (FLP) has been a major impediment to limiting flat band voltage (Vfb) shift in the metal/high-k gate stacks. This phenomenon occurs due to dipole formation at the high-k/SiO2 interface, caused by oxygen diffusion from the high-k oxide to the underlying SiO2. One method of eliminating FLP is to suppress oxygen diffusion through the high-k/SiO2 interface. Diamond-like carbon (DLC) has potential as an oxygen diffusion barrier, since it has an appropriate optical band gap and dielectric constant. After inserting DLC into a high-k/SiO2 interface, we found that FLP was suppressed, since we observed a less flat band shift before and after rapid thermal annealing in an oxygen atmosphere. We could also see a clear work function dependence, giving direct evidence of FLP elimination when using Pt and W in an HfO2/DLC/SiO2 gate stack.