Thermal response of Ru electrodes in contact with SiO ₂ and Hf-based high-k gate dielectrics

A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with Si O2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the RuSi O2, RuHf O2, and RuHfSi Ox 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 Si O2, but remained stable on Hf O2 at 1000°C. The onset of RuSi O2 interfacial interactions is identified via silicon substrate pitting possibly from Ru diffusion into the dielectric in samples exposed to a 900°C10-s anneal. The dependence of capacitor device degradation with decreasing Si O2 thickness suggests Ru diffuses through Si O2, followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on RuHfSi Ox samples may be due to phase separation of HfSi Ox into Hf O2 grains within a Si O2 matrix, suggesting that Si O2 provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the RuSi O2 system at 1000°C is presented.