Towards barrier height modulation in HfO2/TiN by oxygen scavenging – Dielectric defects or metal induced gap states?

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 SiO2 (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 (HfO2) by using internal photoemission. It will be shown that defects in the dielectric rather than MIGS control the barrier height.

Graphical abstractModulation of barrier height up to 0.8 eV for the same TiN/HfO2 injected interface.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Modulation of defects in HfO2 by using an oxygen scavenger (i.e., Hf). ► Modulation of barrier height up to 0.9eV for the same HfO2/TiN deposition chemistry and interface. ► Defect spectroscopy reveals the energy position of these defects at 0.6–0.7eV below the HfO2 conduction band.