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

Abstract

A systematic experimental evaluation of the thermal stability of Ru metal gate electrodes in direct contact with SiO 2 and Hf-based dielectric layers was performed and correlated with electrical device measurements. The distinctly different interfacial reactions in the Ru/ SiO 2 , Ru/ HfO 2 , and Ru/ HfSiO x 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 SiO 2 , but remained stable on HfO 2 at 1000°C. The onset of Ru/ SiO 2 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 SiO 2 thickness suggests Ru diffuses through SiO 2 , followed by an abrupt, rapid, nonuniform interaction of ruthenium silicide as Ru contacts the Si substrate. Local interdiffusion detected on Ru/ HfSiO x samples may be due to phase separation of HfSiO x into HfO 2 grains within a SiO 2 matrix, suggesting that SiO 2 provides a diffusion pathway for Ru. Detailed evidence consistent with a dual reaction mechanism for the Ru/ SiO 2 system at 1000°C is presented.

Temperature dependence of the work function of ruthenium-based gate electrodes

“…8. The fact that a distinct layer is observed as the temperature is increased from 700 to 900°C only on SiO 2 is consistent with recent data showing the Ru metal to be much less stable on SiO 2 than Hf O 2 [16]. In Fig.…”

Partial Oxidation of Thin Film Ruthenium in MOS Structure-Chemical, Compositional and Electrical Properties

“…The interface states appear to be gate oxide thickness dependant. Wen et al 12 also found a similar trend but could not provide an explanation for it.…”

In Situ Auger Electron Spectroscopy Study of Atomic Layer Deposition: Growth Initiation and Interface Formation Reactions during Ruthenium ALD on Si−H, SiO2, and HfO2 Surfaces

“…Ruthenium metal has a relatively high metal work function (4.7-5.2 eV), good thermal stability, and low resistivity in both reduced and oxidized states. These properties make it valuable for many possible applications in metal oxide semiconductor (MOS) device fabrication, including metal gate electrodes to replace common polycrystalline silicon gates, [1][2][3] and nucleation seed layers for copper interconnect formation. 4 Ruthenium is also considered for capacitor electrodes in dynamic and ferroelectric random access memories.…”