HfO2 gate dielectrics on strained-Si and strained-SiGe layers

Abstract

We report on materials and device characterization of polycrystalline HfO2 gate dielectrics grown by atomic layer deposition (ALD) at 600 °C on strained-Si and strained-SiGe layers. No change in the diffusion profile of Hf into the Si substrate was observed for temperatures in the range 900–1100 °C for 20 min. The strain status in the Si layer remained unaltered after HfO2 deposition and an interface state density of ∼1 × 1011 cm−2 eV−1 was obtained for the thicker HfO2 films. The breakdown fields were in the range 2–5 MV cm−1, which is high compared to HfO2 films grown at higher temperatures. The leakage current was reduced by more than five orders of magnitude for the thin HfO2 with an EOT of 1.25 nm and ultra-thin cap (2.5–3 nm) layers on Si0.77Ge0.23/Si, though high interface state densities (∼1 × 1012 cm−2 eV−1) were observed. The carrier transport through these HfO2 films was found to follow Frenkel–Poole emission over a wide range of applied gate voltages.