Hafnium oxynitride (HfOxNy) gate dielectric was prepared using reactive sputtering followed by postdeposition annealing at 650 °C in a N2 ambient. Nitrogen incorporation in the dielectric was confirmed by x-ray photoelectron spectroscopy analysis. In comparison to HfO2 of the same physical thickness, HfOxNy gate dielectric showed lower equivalent oxide thickness (EOT) and lower leakage density (J). Even after a high-temperature postmetal anneal at 950 °C, an EOT of 9.6 Å with J of 0.8 mA/cm2 @−1.5 V was obtained. In contrast, J of ∼20 mA/cm2 @−1.5 V for HfO2 with an EOT of 10 Å was observed. The lower leakage current and superior thermal stability of HfOxNy can be attributed to the formation of silicon–nitrogen bonds at the gate dielectric/Si interface and strengthened immunity to oxygen diffusion by the incorporated nitrogen.

The effects of high temperature forming gas (N2:H2=96:4) anneal (600 °C) prior to metallization have been evaluated in terms of the improvement in the carrier mobility of HfO2/nitride layer gate stack metal-oxide-semiconductor field-effect transistors with TaN gate electrode. The high-temperature forming gas anneal has been found to be effective in improving the interface quality by lowering both interface state density and interface charges. The improvements resulting in decreased Coulombic scattering centers can be attributed to hydrogen atoms that were concentrated near the interface.

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A surface nitridation technique using NH3 anneal has been investigated to reduce interface reaction and consequently the equivalent oxide thickness (EOT) of TaN/HfO2/Si metal–oxide–semiconductor capacitor. For the same EOT, the nitrided samples showed 1–2 order of magnitude lower leakage current density compared to the non-nitrided ones. Furthermore, the nitrided samples showed better thermal stability. However, nitridation induced higher interface state density and larger hysteresis. The degraded interface quality due to the nitridation was improved by post-metal annealing (PMA). Using the optimized nitridation and PMA, EOT of the capacitor was scaled down to ∼10 Å with keeping leakage current below 0.1 mA/cm2 at −1.5 V. Interface state density and hysteresis were ∼8.4×1010 eV−1/cm2, and 45 mV, respectively.

This letter presents the effects of surface preparation for hafnium-based dielectrics on the bulk carrier generation rates and the carrier mobility. Different surface preparations result in different interfacial layers. Nitrogen-incorporated layers effectively block impurity penetration from hafnium oxide, and lead to the increase of bulk carrier generation lifetime. However, nitrogen-incorporated interface layers increase interface state density and degrade channel mobility, even though bulk carrier generation lifetime is increased. Thus, mobility degradation is preliminarily caused by fixed charge and interface states of the high-k dielectrics.