Ferroelectric properties of undoped HfO2 directly deposited on Si substrates by RF magnetron sputtering

Abstract

In this research, we have investigated the undoped HfO2 formation with a metastable orthorhombic phase on Si substrates and its substrate orientation dependence. A 24-nm-thick HfO2 was deposited by radio-frequency (RF) magnetron sputtering with an Ar/O2 plasma utilizing a Hf target. It was found that metastable orthorhombic phase formation was enhanced at an Ar/O2 flow ratio of 2.0/0.2 sccm followed by post-deposition annealing at 600 °C/30 s in N2 ambient. The memory window (MW) extracted from the capacitance–voltage (C–V) characteristics measured at 100 kHz of Al/HfO2/p-Si(100) was increased from 0.39 to 0.84 V as the Ar/O2 flow ratio during sputtering was increased from Ar/O2 of 2.0/1.0 to 2.0/0.2 sccm. In the case of p-Si(111) substrates, the MW was increased to 0.99 V when the Ar/O2 flow ratio was 2.0/0.2 sccm probably owing to the enhanced crystallization of the metastable orthorhombic phase.