The crystal field splittings and Jahn–Teller (J-T) distortions in Hf-based high-κ dielectric oxides on n-type Ge (100) substrates were investigated through the examination of O K1 edge spectra, obtained via x-ray absorption spectroscopy. Second derivative analysis of these O K1 edge spectra provided unambiguous evidence of J-T d-state degeneracy removal, resulting from the symmetry of the local atomic bonding environment. Additionally, two distinct defect states were found below the conduction band edge. The conduction band’s molecular orbital energy structure, including defect states, was determined based on the results of these investigations. Moreover, the thermal evolution of the defect states was found to be dependent on both postdeposition annealing temperature and Hf-based high-κ dielectric oxides. These subband-edge defect states were determined to be electrically active, and their density and the local atomic bonding symmetry were found to be correlated with the effective electron charge trapping measured in related device structures.
The native oxide and carbon-contaminant-minimized Ge surface with ammonium hydroxide ͑NH 4 OH͒-based cleaning for high-k/Ge metal-oxide-semiconductor ͑MOS͒ gate stack application is reported. Furthermore, the carbon-free interfacial Ge-oxide layer preparation on the cleaned Ge surfaces was also studied. The thickness of GeO 2 on Ge surface before, during, and after different cleaning processes was evaluated by the spectroscopic ellipsometry measurements. The HF rinsing step in the cyclic HF/deionized water cleaning was not effective for a removal of native GeO 2 because it cannot form the soluble species by a chemical reaction in the low pH HF solution. A cyclic NH 4 OH-based cleaning results in a minimum residual GeO 2 at 3 and 8 Å on Ge͑111͒ and ͑100͒, respectively. The fast regrowth of GeO 2 on cleaned Ge surfaces under air exposure was observed, regardless of the cleaning methods. However, Auger electron spectroscopy spectra showed less amount of carbon on Ge surfaces with NH 4 OH-based cleaning than HF-based cleaning. The small amount of residual carbon after NH 4 OH-based wet cleaning was completely removed by O 2 plasma for a very thin ͑ ϳ10 Å͒ surface oxidation in the remote plasma-enhanced chemical vapor deposition chamber.
Defect states in HfO2 and HfSiON films deposited on Ge(100) substrates were studied by spectroscopic ellipsometry (SE) and x-ray absorption spectroscopy (XAS). In addition, structural and compositional changes in these films were examined via medium energy ion scattering (MEIS). SE and XAS experiments revealed two distinct band edge defect states, located at 1.7±0.1eV and at 2.7±0.1 below the conduction band edges of these films. The number of defect states in HfO2 increased noticeably following postdeposition annealing (PDA), whereas in HfSiON, it showed only small increases following the same treatment. MEIS measurements showed that Ge diffusion into HfO2 films was enhanced significantly by PDA as well; however, this effect was less pronounced in the HfSiON films. The suppression of defect state enhancement in HfSiON films was correlated with lower levels of Ge diffusion and increased structural stability with respect to HfO2.
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