In this work, we demonstrate the applicability of conducting atomic force microscopy (AFM) for the quantitative electrical characterization of thin (3–40 nm) SiO2 films on a nanometer scale length. Fowler–Nordheim (F–N) tunneling currents on the order of 0.02–1 pA are measured simultaneously with the oxide surface topography by applying a voltage between the AFM tip and the silicon substrate. Current variations in the F–N current images are correlated to local variations of the oxide thickness on the order of several angströms to nanometers. From the microscopic current–voltage characteristics the local oxide thickness can be obtained with an accuracy of ±0.3 nm. Local oxide thinning of up to 3.3 nm was found at the edge between gate oxide and field oxide of a metal-oxide-semiconductor capacitor with a 20-nm-thick gate oxide.

A conductive atomic force microscope (C-AFM) has been used to investigate the degradation and breakdown of ultrathin (<6 nm) films of SiO2 at a nanometric scale. Working on bare gate oxides, the conductive tip of the C-AFM allows the electrical characterization of nanometric areas. Due to the extremely small size of the analyzed areas, several features, which are not registered during macroscopic tests, are observed. In particular, before the oxide breakdown, switchings between different conduction states and sudden changes of conductivity have been measured, which have been related to the prebreakdown noise observed in conventional metal–oxide–semiconductor structures. Moreover, similar switchings have been also measured after the oxide breakdown, which have been related to the opening or closure of conduction channels between the electrodes. The C-AFM has also allowed the determination of the areas in which the degradation and breakdown take place. The results have shown that, although degradation takes place in areas of few hundreds of nm2, breakdown is laterally propagated to neighbor spots, affecting areas of thousands of nm2. The size of the affected area has been found to be strongly related to the hardness of the breakdown event. The phenomenology observed with the C-AFM provides experimental evidence of the local nature of the degradation and breakdown processes in ultrathin SiO2 films. Therefore, the C-AFM is a powerful tool to analyze the microscopic physics of these phenomena at the same dimensional scale at which they take place.

In this work ballistic electron emission microscopy was used to probe on nanometer scale the local Schottky barrier height in metal-semiconductor (MS) contacts with an intentionally inhomogeneously prepared metallization. Schottky barrier maps of heterogeneous Au/Co/GaAs67P33(100)-Schottky contacts show areas with different barrier heights which can be correlated to different metallizations (Au or Co) at the interface. The local Schottky barrier height of the Co patches depends on their lateral extension. This result can be explained by the theory of the potential pinch-off effect in inhomogeneous MS contacts.

No abstract

A conductive atomic force microscope has been used to electrically stress and to investigate the effects of degradation in the conduction properties of ultrathin (<6 nm) SiO2 films on a nanometer scale (areas of ≈100 nm2). Before oxide breakdown, switching between two states of well-defined conductivity and sudden changes of conductivity were observed, which are attributed to the capture/release of single charges in the defects generated during stress.

In this work, a conductive atomic force microscope (C-AFM) has been used to study the post-breakdown (BD) behaviour of ultrathin SiO2 films at the nanometre scale. In particular, the post-BD conduction and BD propagation have been analysed. Although the post-BD switchings in the current-voltage curves measured with C-AFM demonstrate the localized nature of the phenomenon, it has been observed that it is electrically propagated to neighbouring areas.

In this work we investigated the relationship between the integral Schottky barrier height (SBH) obtained from conventional current–voltage (I–V) measurement and the distribution of the local SBH measured by ballistic electron emission microscopy (BEEM) on a nanometer scale length. For this purpose, we investigated inhomogeneous Au/Co/GaAs67P33-Schottky contacts. The samples were prepared by the deposition of a discontinuous Co film on the semiconductor followed by the deposition of a continuous Au film. This provided regions with local presence of one or the other metal (Au or Co) at the metal-semiconductor interface, resulting in mesoscopically extended SBH inhomogeneities. The local SBH distribution as well as the integral SBH depended on the preparation parameter of the Co layer, i.e., on the combination of the substrate temperature (300 or 500 K) and the nominal Co thickness (0, 0.25, 0.5, 0.8, 1.0 nm). For the different preparation parameters, statistical distributions of the local SBH were measured by BEEM. Treating these SBH distributions in terms of a parallel conduction model for the electron transport across the MS interface, we calculated for each preparation parameter an integral SBH and compared it with the measured integral SBH obtained from conventional I–V measurement. The calculated and measured integral SBH’s were in very good agreement, demonstrating clearly the strong influence of the low SBH regions on the electron transport across the interface and therefore on the integral SBH. The SBH values for homogeneous Au/GaAs67P33- and Co/GaAs67P33-Schottky contacts, i.e., with only one sort of metal at the interface, were determined to be ΦSBAu=1180±10 meV and ΦSBCo=1030±10 meV. As with regard to the inhomogeneous Schottky contacts the fraction of area of the MS interface covered by Co increased, the local SBH distributions as well as the integral SBH’s decreased gradually from the value of ΦSBAu to ΦSBCo.

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