Ge/GeO₂Interface Control with High-Pressure Oxidation for Improving Electrical Characteristics

Abstract

High-pressure oxidation (HPO) of germanium (Ge) for improving electrical properties of Ge/GeO 2 stacks was investigated. The capacitance-voltage (C-V ) characteristics of metal/GeO 2 /Ge capacitors fabricated with HPO revealed improved electrical properties without any post-deposition annealing, and the interface states density (D it ) was reduced to 2 Â 10 11 eV À1 cm À2 near the midgap. Moreover, the refractive index of thermally oxidized GeO 2 was increased by HPO. It is also discussed from a thermodynamic viewpoint of the Ge/GeO 2 system that the GeO desorption from Ge/GeO 2 stacks could be efficiently suppressed by HPO.

In situ synchrotron radiation photoelectron spectroscopy study of the oxidation of the Ge(100)-2 × 1 surface by supersonic molecular oxygen beams

“…25,27,43,44 This result clearly indicates that the Ge(100)-2 × 1 surface is quite inert toward oxidation by pure oxygen gas unlike the case of Si oxides. The results obtained in this study seem to be considerably different from the reported results for high pressure 11 and atmospheric oxidation, 14 where the Ge 4+ state was clearly identified. Since the present results suggest that Ge 4+ cannot be formed by the reaction of pure oxygen gas at room temperature, it is likely that several processes play a role in progressing oxidation in the other methods.…”

“…Since the present results suggest that Ge 4+ cannot be formed by the reaction of pure oxygen gas at room temperature, it is likely that several processes play a role in progressing oxidation in the other methods. 11,14 One possible reason for the production of Ge oxides with high oxidation states is that oxygen diffusion into oxides is dominant at high temperature. 46 This oxygen transport mechanism involved in the thermal Ge oxidation may facilitate oxidation and prevent GeO desorption relevant to GeO 2 decomposition.…”

“…We showed that the Ge(100) surface is so inert that it cannot be completely covered with monolayer-thickness GeO 2 by oxidation with pure O 2 gas at room temperature, indicating a pressure and temperature gap between our oxidation and other methods. 11,14 Further experimental studies using ambient pressure XPS 47 may be able to fill the pressure gap observed in Ge(100) oxidation. In addition, we are confident that our research will serve as a basis for future studies on thermal oxidation using molecular beams.…”

“…1 In the development of Gebased MISFET devices, controlled formation of the surface oxide in a wide variety of ways is important for precise fabrication of dielectric/Ge interfaces. [2][3][4][5][6][7][8][9][10][11][12][13] Therefore, atomic-level understanding of the oxidation of Ge surfaces, especially in the monolayer or sub-monolayer region, is a key research issue. However, the fundamental aspects of the oxidation reaction of Ge surfaces are not well understood, which is in strong contrast to Si surfaces.…”

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

“…Recently, theoretical studies showed that a low interface defect (Ge dangling bond) was obtained for the GeO 2 /Ge interface due to its viscoelastic properties, 5,6 and some experimental studies demonstrated good electrical properties of the Ge-MOS. [7][8][9][10] For example, Hosoi et al reported that the electrical properties of Ge-MOS capacitors could be improved by in situ vacuum annealing at 300 C prior to metal gate electrode deposition, and an increase in the inversion capacitance, depending on its air exposure time, could be suppressed by an Al 2 O 3 layer capped on the GeO 2 surface. 8 Meanwhile, Kutsuki et al reported that surface nitridation on ultrathin GeO 2 was an effective way to improve the electrical properties (drastic suppression of leakage current, etc.)…”