(486g) Modeling Of HfO2/Ru Interfaces

Continued scaling of metal oxide semiconductor field effect transistors (MOSFETs) into the ?nano? regime requires not only the replacement of the silicon dioxide gate dielectric by high-k materials, but also polycrystalline Si (poly-Si) gate electrodes by metal gates. Hafnium dioxide (HfO2) has emerged as a leading candidate for the gate dielectric due to its relatively high dielectric constant, wide band gap and stability on Si. Ruthenium has been studied as a potential gate electrode material for p-type channel MOSFETs due the compatibility of its workfunction with PMOS and its predicted bulk stability. The electronic properties of metal oxide semiconductor gate electrodes are strong functions of the structure of the metal-dielectric interface. We use density functional theory to investigate the structures and electronic properties of Ru/HfO2 interfaces. We find that atom?by-atom deposited Ru films have significantly different interfacial structures than epitaxially connected Ru films on m-HfO2 (001) surface. Atom-by-atom deposited films are rougher than epitaxially connected films, even when forced to form two-dimensional films. These interfacial structural differences lead to differences in the electronic properties of the films and therefore affect electrical properties, such as the work function of the gate-electrode. We found that for both types of films the partial density of states of interfacial layers are significantly different from that of the bulk region. Each shows charge transfer from the interfacial Ru layer to the interfacial dielectric layer, although the magnitude of charge transfer varies. Thus both films exhibit metal induced gap states in the band gap region of the interface localized on atoms of the HfO2 interfacial layer.