Modeling the breakdown spots in silicon dioxide films as point contacts

Experiments and simulations are combined to demonstrate that the hard dielectric breakdown of thin SiO2 films in polycrystaline silicon/oxide/semiconductor structures leads to the formation of conduction paths with atomic-size dimensions which behave as point contacts between the silicon electrodes. Depending on the area of the breakdown spots, the conduction properties of the breakdown paths are shown to be those of a classical Sharvin point contact or of a quantum point contact

Soft breakdown fluctuation events in ultrathin SiO2 layers

When an ultrathin (<5 nm) oxide is subjected to electrical stress, several soft-breakdown events can occur prior to the final dielectric breakdown. After the occurrence of such failure events, the current-voltage (I-V)characteristic corresponds to the superposition of highly conductive spots and background conduction through the undegraded capacitor area. In this conduction regime, the application of a low constant voltage gives rise to large leakage current fluctuations in the form of random telegraph signal. Some of these fluctuations have been identified with ON/OFF switching events of one or more local conduction spots, and not with a modulation of their conductance. The experimental soft-breakdown I-Vcharacteristics are shown to be better understood if the spot conduction is considered to be locally limited by the siliconelectrodes and not by the oxide

Nanometer-scale electrical characterization of stressed ultrathin SiO2 films using conducting atomic force microscopy

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

Breakdown-induced negative charge in ultrathin SiO2 films measured by atomic force microscopy

Atomic-force-microscopy-based techniques have been used to investigate at a nanometer scale the dielectric breakdown (BD) of ultrathin (<6 nm) SiO2films of metal-oxide-semiconductordevices. The results show that BD leads to negative charge at the BD location and the amount of created charge has been estimated. Moreover, the comparison of the charge magnitude generated during current-limited stresses and stresses without current limit demonstrates that the observed BD induced negative charge is related to the structural damage created by the oxide BD

Recovery of the MOSFET and circuit functionality after the dielectric breakdown of ultra-thin high-k gate stacks

The reversibility of the gate dielectric breakdown in ultra-thin high-k dielectric stacks is reported and analyzed. The electrical performance of MOSFETs after the dielectric recovery is modeled and introduced in a circuit simulator. The simulation of several digital circuits shows that their functionality can be restored after the BD recovery

Nanometer-scale oxidation of Si(100) surfaces by tapping mode atomic force microscopy

The nanometer¿scale oxidation of Si(100) surfaces in air is performed with an atomic force microscope working in tapping mode. Applying a positive voltage to the sample with respect to the tip, two kinds of modifications are induced on the sample: grown silicon oxide mounds less than 5 nm high and mounds higher than 10 nm (which are assumed to be gold depositions). The threshold voltage necessary to produce the modification is studied as a function of the average tip¿to¿sample distance

Nondestructive multlple breakdown events in very thin SI02 films

Several breakdown events and multilevel current fluctuations have been observed when ultrathin SiO2 films are subjected to constant-voltage stresses. These breakdown events are sometimes reversible, and consist in a local change of conduction mechanism. This reversibility shows that no catastrophic thermal effects occur, and that the breakdown is only a local switching between two oxide conduction states of very different conductivities

Reversible dielectric breakdown in ultra Hf based high-k stacks under current limited stresses

The effects of a current-limited breakdown (BD) on the post-BD current of MOS capacitors with a thin high-k dielectric stack have been analysed. A strong current reduction after BD and, consequently, a partial recovery of the insulating properties of the dielectric stack is observed. The similarities with the Resistive Switching phenomenon observed in MIM structures for memory applications are discussed

Temperature dependence of the resistive switching-related currents in ultra-thin high-k based MOSFETs

In this work, the temperature dependence of the resistive switching phenomenon in metal-oxide-semiconductor field-effect-transistor (MOSFETs) with an ultra-thin Hf-based high-k dielectric is studied through analysis of the gate and drain currents for the two dielectric conductivity states. These two different conductive states of the resistive switching have been associated with the dielectric breakdown (BD) and dielectric BD reversibility (R), respectively, and are related to the creation of a BD path through the dielectric that can be understood as a conductive filament. The results of the temperature dependence of the post-BD gate current are in agreement with those obtained from the study of the injected charge to recovery, which is a useful parameter with which to analyze the switch from the high to low conductivity state. The drain current in the MOSFETs for the two conductivity states, for different locations of the BD path along the channel (close to the source and close to the drain), and at several temperatures has also been studied. The results contribute to a better understanding of the resistive switching phenomenon in ultra-thin gate dielectrics. This contribution could be useful for the developing of models to describe BD reversibility