A single electron tunneling force spectroscopy study of dielectric materials

Single electron tunneling force microscopy has been developed over the last decade as a tool to manipulate the occupation and probe the properties of trap states in completely non conducting materials. The technique has been advanced through the efforts of several generations of graduate students in the Clayton Williams research group. Previous graduate students have demonstrated that the single electron tunneling force microscopy technique can repeatably facilitate single electron tunneling between a metallic tip and an electron trap state in a completely non conducting, dielectric material. Also the single electron tunneling force spectroscopy technique has been shown to make these measurements with atomic scale resolution. As solid state device technology rushes toward higher power and increasingly smaller devices single electron tunneling force microscopy is uniquely positioned to identify the properties of trap states in dielectric materials with atomic scale resolution. The main thrust of this work has been concerned with demonstrating a repeatable spectroscopic method which can be used to reliably measure the energy of electron and hole traps due to defect states in dielectric materials. The single electron tunneling force spectroscopy technique was used to make spectroscopic measurements at several places on the surface of SiO2, Si3N4 and HfO2 films. The spectra measured were compared to known trap states in both the theoretical and experimental literature. The data show that the density of trap states is not spatially homogeneous, but varies from measurement to measurement. Most of the defect states identified by the single electron tunneling force spectroscopy technique correspond nicely with trap state energies found in either the experimental or theoretical literature. However, several states, not found in the literature, have also been identified by the scanning electron tunneling force spectroscopy technique. Additionally single electron tunneling force spectroscopy has provided evidence of irreversible and reversible tunneling events with irreversible tunneling predominantly near the conduction and valence bands. A noted asymmetry in the amount of irreversible tunneling in favor of trap states near the valence band edge has also been identified. Finally a first demonstration of state creation and characterization by SETFS in SiO2 is discussed.