Thermal response of Ru electrodes in contact with SiO2 and Hf-based high-k gate dielectrics.

A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with SiO2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the Ru/SiO2, Ru/HfO2, and Ru/HfSiOx film systems were observed through cross-sectional high-resolution transmission electron microscopy, high angle annular dark field scanning transmission electron microscopy with electron-energy-loss spectra, and energy dispersive x-ray spectra analysis. Ru interacted with SiO2, but remained stable on HfO2 at 1000 °C. The onset of Ru/SiO2 interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a 900 °C/10-s anneal. The dependence of capacitor device degradation with decreasing SiO2 thickness suggests Ru diffuses through SiO2, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on Ru/HfSiOx samples may be due to phase separation of HfSiOx into HfO2 grains within a SiO2 matrix, suggesting that SiO2 provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the Ru/SiO2 system at 1000 °C is presented. [ABSTRACT FROM AUTHOR]