Electrical properties and reliability of HfO2 deposited via ALD using Hf(NO3)4 precursor

We have begun an investigation of the electrical properties of thin film HfO₂ deposited via atomic layer deposition (ALD) using Hf(NO₃)₄ and H₂O as precursors. Excellent uniformity was achieved on H-terminated Si with better than 1% variation in C_max over a 6" wafer. Since the most widely used ALD precursor for HfO₂, HfCl₄, requires an initial SiO₂ layer for uniform growth, uniform deposition directly on H-terminated Si is an advantage of using Hf(NO₃)₄. The effective dielectric constant of thin (< 10 nm) films was in the range of κ_eff = 10-12. The "bulk" dielectric constant of the HfO₂ was found to be κ_HfO2 ∼ 15.9 and the effective interfacial layer thickness (assuming κ = 3.9) was calculated to be approximately one to two monolayers. Recent ESR results suggest this interfacial layer is not pure SiO₂. HfO₂ films showed low leakage (10³-10⁶ times less than SiO₂ of equivalent CET) and good equivalent breakdown strength. The relative leakage benefit of HfO₂ over SiO₂ decreased with decreasing effective thickness. Electron trapping was observed under constant voltage stressing.