Characteristics of HfO2 thin films deposited by plasma-enhanced atomic layer deposition using O2 plasma and N2O plasma

Abstract

The characteristics of HfO2 dielectrics deposited by the plasma-enhanced atomic layer deposition (PEALD) method using O2 and N2O plasmas were investigated. The deposited HfO2 films had a randomly oriented polycrystalline phase while the interfacial layers of the films were amorphous. During the PEALD process with N2O plasma, nitrogen was mainly incorporated into the interfacial region between the HfO2 film and the Si substrate. The nitrogen content of 2–3at.% in the interface was analyzed by Auger electron spectroscopy. The incorporated nitrogen at the interface effectively suppressed residual oxygen diffusion during subsequent annealing at 800°C in a N2 atmosphere. A thicker interfacial layer was observed in the as-deposited and annealed HfO2 film with O2 plasma than with N2O plasma. For HfO2 films prepared with the N2O plasma, where equivalent oxide thickness (EOT) increased from 1.43to1.56nm after annealing, the leakage current densities, measured at a gate bias voltage of ∣VG−VFB∣=2, increased from 3.5×10−8to4.8×10−8A∕cm2. For HfO2 films prepared with the O2 plasma, where EOT increased from 1.60to2.01nm after annealing, the leakage current densities decreased from 1.1×10−6to1.3×10−7A∕cm2. The film with O2 plasma had a higher amount of negative fixed oxide charges than the film with N2O plasma. N2O plasma improved the leakage current properties by allowing nitrogen incorporation at the interfacial region and less crystallization of HfO2 film.