Study Of Contact Properties Of Metal Nitrides On N-Ge

Germanium (Ge) is renewed as one of the promising candidate channel materials for next generation high performance integrated circuits due to its high carrier mobility. And Furthermore, since Ge is a group IV element like Si, it is completely compatible with current manufacturing facilities as it does not act as a dopant impurity. However, the Fermi-level pinning effect (FLP) at metal/Ge interfaces lead to a large barrier to n-type Ge and a high contact resistance. Therefore, the research on alleviation of FLP and reduction of the specific contact resistivity of metal/n+-Ge becomes a critical issue in fabrication of Ge devices.This thesis addresses the mechanism of modulation of Schottky barrier height in the metal nitrides/n-Ge contacts. Compositional titanium nitride and tungsten nitride films were deposited on the n-Ge substrates by reactive sputtering in a magnetron sputtering system with mixed N2-Ar atmosphere.1. Compositional titanium nitride and tungsten nitride films were deposited on n-type Ge substrates by reaction sputtering in a magnetron system with various Ar/N2flow ratio.2. We demonstrated the modulation of the Schottky barrier height in metal nitride/n-Ge contact. It is found that Schottky barrier heights gradually decreased with the increasing of N content in metal nitride films. As the N content reached a certain percentage, the metal nitride/n-Ge eventually shows ohmic property. And the specific contact resistance in the WNx/n-Ge contact is extracted from circular transmission line method. The results show that the specific contact resistance of WNx/n-Ge si about3.1x10-4μΩcm.3. The mechanism of modulation of Schottky barrier height in the metal nitrides/n-Ge contacts was discussed:both N and Ti formed bonds with Ge at the metal nitride/Ge contact interface. But the difference in the pauling electronegativity of Ge and N is large which means the N-Ge bond is not pure covalent but partially ionic. So the many N-Ge bonds can be dealt as interfacial dipoles with the direction from the nitride side to Ge side. As a result, the N-Ge dipoles largely modulate the Fermi-level pinning effect. And the modulation effect depends on the N content in the metal nitride films.