PEALD of HfO₂ Thin Films: Precursor Tuning and a New Near-Ambient-Pressure XPS Approach to in Situ Examination of Thin-Film Surfaces Exposed to Reactive Gases

Abstract

A bottom-up approach starting with the development of new Hf precursors for plasma-enhanced atomic layer deposition (PEALD) processes for HfO2 followed by in situ thin-film surface characterization of HfO2 upon exposure to reactive gases via near-ambient-pressure X-ray photoelectron spectroscopy (NAP-XPS) is reported. The stability of thin films under simulated operational conditions is assessed, and the successful implementation of HfO2 dielectric layers in metal–insulator–semiconductor (MIS) capacitors is demonstrated. Among the series of newly synthesized mono-guanidinato-tris-dialkyl-amido class of Hf precursors, one of them, namely, [Hf­{η2-( i PrN)2CNEtMe}­(NEtMe)3], was representatively utilized with oxygen plasma, resulting in a highly promising low-temperature PEALD process at 60 °C. The new precursors were synthesized in the multigram scale and thoroughly characterized by thermogravimetric analyses, revealing high and tunable volatility reflected by appreciable vapor pressures and accompanied by thermal stability. Typical ALD growth characteristics in terms of linearity, saturation, and a broad ALD window with constant growth of 1.06 Å cycle–1 in the temperature range of 60–240 °C render this process very promising for fabricating high-purity smooth HfO2 layers. For the first time, NAP-XPS surface studies on selected HfO2 layers are reported upon exposure to reactive H2, O2, and H2O atmospheres at temperatures of up to 500 °C revealing remarkable stability against degradation. This can be attributed to the absence of surface defects and vacancies. On the basis of these promising results, PEALD-grown HfO2 films were used as dielectric layers in the MIS capacitor device fabrication exhibiting leakage current densities less than 10–7 A cm–2 at 2 MV cm–1 and permittivities of up to 13.9 without postannealing.

The synergistic effect of Hf-O-Ru bonds and oxygen vacancies in Ru/HfO2 for enhanced hydrogen evolution

“…The binding energies of Hf 4f 5/2 and Hf 4f 7/2 core levels for V O -Ru/HfO 2 -OP are 18.4 and 16.7 eV (Supplementary Fig. 9a), respectively, which are in good agreement with the values of Hf 4f 5/2 and Hf 4f 7/2 doublet peaks for HfO 2 30 . No obvious shift in the O 1 s and Hf 4 f peaks of V O -Ru/HfO 2 -OP relative to that of pristine HfO 2 that could be attributed to the ultralow Ru loading on the HfO 2 support was observed.…”

Formation of mononuclear N,O-chelate zirconium complexes by direct insertion of epoxide into tetrakis(dimethylamido)zirconium: highly promising approach for developing an ALD precursor of ZrO2 thin films

“…Notably, the minor decomposition of complex 1 cannot be ignored, due to the short-term air exposure of the sample during the TGA-DSC measurement. 31 From the DSC curve, we can see that the melting point of complex 1 is approximately 105 °C, due to one endothermic peak at this temperature. The other endothermic peak at 377 °C may be attributed to the vaporization of the decomposed product.…”

Oxygen vacancies engineering by coordinating oxygen-buffering CeO2 with CoO nanorods as efficient bifunctional oxygen electrode electrocatalyst

“…Adventitious C1s (284.4 eV) was employed for the spectra calibration. The atomic percentage compositions were obtained by deconvoluting all the signals using Lor- entz-Gauss functions, 20% Lorentzian-80% Gaussian, with XPSPEAK41 program [29][30][31].…”