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

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.

Automated summary

Gadolinium (Gd) and Silicon (Si) co-doped HfO2 gate dielectric thin films were successfully prepared by atomic layer deposition (ALD) with precise control over the doping concentration. The band gap of the films was found to have a positive correlation with the doping concentration, while the valence band offset initially decreased and then increased with doping concentration. The electrical properties of the films were significantly improved compared to pure HfO2 films, with a decreased leakage current density by at least one order of magnitude.