Effect of Gd and Si co-doping on the band alignment and electrical properties of HfO2 dielectric films prepared by atomic layer deposition

Abstract

Gd and Si co-doped HfO2 gate dielectric thin films were prepared by atomic layer deposition (ALD), while Gd[N(SiMe3)2]3, Hf[NEtMe]4, and H2O are chosen to be precursors. The Gd and Si were successfully co-doped into HfO2 films using only one doping precursor Gd[N(SiMe3)2]3. The doping concentration can be facilely tuned by controlling ALD recipe. The atomic percentages of Si/(Si + Gd + Hf) and Gd/(Si + Gd + Hf) increase from 11.5 to 28.9% and from 6.8 to 28.4% when changing the ALD cycle ratio of GdxSiyO to HfO2 from 1:9 to 1:1. The band gap and band alignment were investigated by X-ray photoelectron spectroscopy. The results imply that the band gap of Gd/Si co-doped HfO2 films has a positive relation with doping concentration. Moreover, the valence band offset decreases with doping concentration first but then increases, while the change of conduction band offset is opposite. The (1:6)-HfxGdySizO films with 11.6 at.% Gd/(Gd + Hf) exhibit the maximum accumulation capacitance and dielectric constant, which are only slightly smaller than those of the HfO2 films. Compared to HfO2 films, the leakage current density of (1:6)-HfxGdySizO films is decreased by at least one order of magnitude. Therefore, Gd and Si co-doping can improve the electrical properties of HfO2 films.