Metal-gate-induced reduction of the interfacial layer in Hf oxide gate stacks

The properties of high-κ metal oxide gate stacks are often determined in the final processing steps following dielectric deposition. We report here results from medium energy ion scattering and x-ray photoelectron spectroscopy studies of oxygen and silicon diffusion and interfacial layer reactions in multilayer gate stacks. Our results show that Ti metallization of HfO2∕SiO2∕Si stacks reduces the SiO2 interlayer and (to a more limited extent) the HfO2 layer. We find that Si atoms initially present in the interfacial SiO2 layer incorporate into the bottom of the high-κ layer. Some evidence for Ti–Si interdiffusion through the high-κ film in the presence of a Ti gate in the crystalline HfO2 films is also reported. This diffusion is likely to be related to defects in crystalline HfO2 films, such as grain boundaries. High-resolution transmission electron microscopy and corresponding electron energy loss spectroscopy scans show aggressive Ti–Si intermixing and oxygen diffusion to the outermost Ti layer, given ...