TUNNELING SPECTROSCOPY ON METAL-INSULATOR-SILICON STRUCTURES WITH VERY THIN INSULATING LAYERS

Tunneling measurements were performed at 4.2 K to investigate metal-insulator-silicon junctions with very thin silicon oxide or silicon nitride layers (2-5 nm) as tunneling barriers. For the measurements at 4.2 K highly degenerate P- or B-doped Si samples were used. Silicon oxide layers were produced by oxidation of Si in dry oxygen at 600-degrees-C or by plasma deposition in an oxygen glow discharge. Silicon nitride films were prepared by nitridation in a NH3 discharge. The effects of interface states, the Si doping density, the metal of the gate electrode and the tunneling barrier material on the tunneling conductivity were studied systematically. Changes in the conductivity were found to be related to changes in the density of interface states, caused by annealing processes or by high-field stress. Vibrational modes of phonons and impurities in the structures were detected by inelastic electron tunneling spectroscopy. Using this approach a direct correlation between the increase in the density of interface states and the decrease of the density of Si-H groups was established.