Ge interface engineering using ultra-thin La2O3 and Y2O3 films: A study into the effect of deposition temperature

Abstract

A study into the optimal deposition temperature for ultra-thin La2O3/Ge and Y2O3/Ge gate stacks has been conducted in this paper with the aim to tailor the interfacial layer for effective passivation of the Ge interface. A detailed comparison between the two lanthanide oxides (La2O3 and Y2O3) in terms of band line-up, interfacial features, and reactivity to Ge using medium energy ion scattering, vacuum ultra-violet variable angle spectroscopic ellipsometry (VUV-VASE), X-ray photoelectron spectroscopy, and X-ray diffraction is shown. La2O3 has been found to be more reactive to Ge than Y2O3, forming LaGeOx and a Ge sub-oxide at the interface for all deposition temperature studied, in the range from 44 °C to 400 °C. In contrast, Y2O3/Ge deposited at 400 °C allows for an ultra-thin GeO2 layer at the interface, which can be eliminated during annealing at temperatures higher than 525 °C leaving a pristine YGeOx/Ge interface. The Y2O3/Ge gate stack deposited at lower temperature shows a sub-band gap absorption feature fitted to an Urbach tail of energy 1.1 eV. The latter correlates to a sub-stoichiometric germanium oxide layer at the interface. The optical band gap for the Y2O3/Ge stacks has been estimated to be 5.7 ± 0.1 eV from Tauc-Lorentz modelling of VUV-VASE experimental data. For the optimal deposition temperature (400 °C), the Y2O3/Ge stack exhibits a higher conduction band offset (>2.3 eV) than the La2O3/Ge (∼2 eV), has a larger band gap (by about 0.3 eV), a germanium sub-oxide free interface, and leakage current (∼10−7 A/cm2 at 1 V) five orders of magnitude lower than the respective La2O3/Ge stack. Our study strongly points to the superiority of the Y2O3/Ge system for germanium interface engineering to achieve high performance Ge Complementary Metal Oxide Semiconductor technology.

Trap Reduction through O3 Post‐Deposition Treatment of Y2O3 Thin Films Grown by Atomic Layer Deposition on Ge Substrates

“…This is consistent with the YGeO x peak position of the previous reports. [ 20 ] However, there was no peak near ≈32.5 eV, which corresponded to the GeO 2 . This indicates that the interfacial layer formed through IOF and OPA was mostly the YGeO x layer with the minimal involvement of the GeO 2 formation, which is different from the previous report.…”

Electrical Properties and Interfacial Issues of HfO2/Ge MIS Capacitors Characterized by the Thickness of La2O3 Interlayer

“…A substrate peak (Ge 3d 0 ) located at ~28.6 eV with additional peaks at higher binding energies in relation to the IL (consisting of Ge oxides and germanate) could be observed in all spectra. The Ge 3d 0 substrate peak is fitted with a doublet of Ge 3d 5/2 and Ge 3d 3/2 with spin-orbit splitting of 0.6 eV and intensity ratio of 3:2, respectively [18]. The Ge oxides (GeO x ) consist of four peaks (Ge 1+ , Ge 2+ , Ge 3+ , Ge 4+ ), which are at higher binding energy respect to the Ge 3d 0 with energy shifts of 0.8, 1.8, 2.6, and 3.4 eV, respectively [19].…”

Effective reduction of trap density at the Y2O3/Ge interface by rigorous high-temperature oxygen annealing

“…The resulting oxygen-densification may suppresses GeO volatilization and maintains GeO 2 integrity and interface quality. 48 Mitrovic et al 51 reported on neutral oxygen vacancy coordinated with two Ge ions and Ge 2þ coordinated with two oxygen defects in sub-stoichiometric GeO x layer at the Y 2 O 3 /Ge interface which are disappearing when higher temperatures of 400 C are used for the growth of Y 2 O 3 by MBE. Similar mechanisms have to be taken into account for the annealed samples treated in this survey, which finally means that the chosen annealing parameters (high PDA temperature, longer annealing times) may effectively decrease the density of DB and OD at the oxide/Ge interface.…”