Towards barrier height modulation in HfO 2/TiN by oxygen scavenging – Dielectric defects or metal induced gap states?

Abstract

The band alignment between a dielectric and a metal gate is crucial as it controls the MOSFET threshold voltage as well as the leakage in metal–insulator–metal (MIM) structure. In the ideal Schottky–Mott model the barrier height should be controlled only by the workfunction and the electron affinity of the materials considered. However, this seems the case only for few insulating materials other than SiO 2 (i.e., Fermi level pinning). The most popular explanation invokes metal-induced gap states (MIGS), where electron states from the bulk of a metal tails into the insulator. The MIGS hypothesis explains a rather large series of experimental results and, importantly, predicts that the MI barrier height will mostly be controlled by the energy distribution of electron states in the bulk of the contacting metal and dielectric. In this paper, we analyze the band alignment of contacting metal (TiN) and dielectric (HfO 2) by using internal photoemission. It will be shown that defects in the dielectric rather than MIGS control the barrier height.