Insight into unusual impurity absorbability of GeO2 in GeO2/Ge stacks

Abstract

Adsorbed species and its diffusion behaviors in GeO2/Ge stacks, which are future alternative metal-oxide-semiconductor (MOS) materials, have been investigated using various physical analyses. We clarified that GeO2 rapidly absorbs moisture in air just after its exposure. After the absorbed moisture in GeO2 reaches a certain limit, the GeO2 starts to absorb some organic molecules, which is accompanied by a structural change in GeO2 to form a partial carbonate or hydroxide. We also found that the hydrogen distribution in GeO2 shows intrinsic characteristics, indicative of different diffusion behaviors at the surface and at the GeO2/Ge interface. Because the impurity absorbability of GeO2 has a great influence on the electrical properties in Ge-MOS devices, these results provide valuable information in realizing high quality GeO2/Ge stacks for the actual use of Ge-MOS technologies.

Comparative study of GeO2/Ge and SiO2/Si structures on anomalous charging of oxide films upon water adsorption revealed by ambient-pressure X-ray photoelectron spectroscopy

“…The thermal desorption spectra of molecules desorbed from the thermally grown GeO 2 and SiO 2 films indicated that GeO 2 has an unusual characteristic in terms of its absorbability of water molecules in air. 14,15 This strongly implies that the absorbance of moisture is the origin of the change in DE GeO 2 upon air exposure as shown in Figs. 2(a) and 2(b).…”

“…This agrees with the result of a dynamic SIMS analysis of an air-exposed GeO 2 /Ge sample, in which a certain amount of hydrogen was detected near the GeO 2 /Ge interface. 15 It is likely that infiltrated water molecules promote hydroxylation to generate hole-trap states in the GeO 2 films, especially near the GeO 2 /Ge interface or in the suboxide layer. These traps above the Ge Fermi level in the suboxide layer are positively charged by the electrons emitted to the Ge bulk, as suggested by Oniki and Ueno.…”

“…The contamination level on GeO 2 tended to be higher than that on SiO 2 , probably because a GeO 2 film absorbs organic molecules unlike SiO 2 . 15 An O 1s spectrum together with a Ge 3d spectrum and a Si 2p spectrum were used to estimate the water layer thickness under an equilibrium condition on GeO 2 and SiO 2 surfaces, respectively. In the presence of water vapor, the O 1s spectrum after Shirley background subtraction included contributions from oxygen in the oxide film, in the adsorbed water species, and in the gas phase.…”

“…Diverse physical analyses such as by thermal desorption spectroscopy, infrared spectroscopy, and secondary ion mass spectrometry revealed the origin to be infiltration of adsorbed water or organic molecules into the GeO 2 film. [12][13][14][15] X-ray photoelectron spectroscopy (XPS) is a powerful tool for identifying various properties of oxide/semiconductor structures. Analysis of the chemical shift of oxidation states is especially important for determining the oxide thickness, suboxide structure, and band offset.…”

GeO2/Ge structure submitted to annealing in deuterium: Incorporation pathways and associated oxide modifications

“…[17][18][19] All these results point to a different effect of FGA on dielectric stacks prepared on Ge in comparison with SiO 2 /Si. Hints of the mechanisms underlying H incorporation in GeO 2 were provided by Ogawa and coworkers, 20 who investigated the depth distribution of H within GeO 2 films. They observed high amounts of H incorporated at the GeO 2 /Ge interfacial region, as result of thermal treatments under a humid atmosphere.…”