Electrical characterization of stressed and broken down SiO2 films at a nanometer scale using a conductive atomic force microscope

Abstract

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.

Charge trapping and degradation of HfO/sub 2//SiO/sub 2/ MOS gate stacks observed with enhanced CAFM

“…Moreover, currents from 1 pA up to 1 mA can be measured. Carrier injection has been done from the substrate [6] (deep depletion has been avoided), which corresponds to the SILC generation worst case. (voltages higher than 9 V), the current progressively increases reaching the so called regime C. A second I-V curve measured at the same location ( Fig.…”

Reliability study of ultrathin oxide films subject to irradiation-then-stress treatment using conductive atomic force microscopy

“…Both pre-and post-RVS results, as well as the curve fitting using the FowlerNordheim (FN) tunneling theory [6], are also given in the figure. The current fluctuation observed can be attributed to charge trapping and de-trapping in the oxide [7]. Clearly, the post-RVS curve shifted upward (current is increased at a given voltage).…”

“…3. Porti et al [7] have reported that such a number could be related to the existence of the total defects (defects at the interface and in the bulk) in the oxide film and the trapping/de-trapping of charge at these defects. As shown in Fig.…”

Conductive atomic force microscopy as a tool to reveal high ionising dose effects on ultra thin SiO2/Si structures

“…The most accomplished works can be attributed to Porti et al (2002Porti et al ( , 2003Porti et al ( , 2007 and Wu et al (2007Wu et al ( , 2008Wu and Lin 2006). Both authors have shown that oxide degradation exhibits two aspects.…”

“…C-AFM can simultaneously map topography and current distributions of a sample. Numerous studies have been realised on thin SiO 2 films on Si substrates using this technique (Porti et al 2002(Porti et al , 2003(Porti et al , 2007Wu and Lin 2006;Wu et al 2007Wu et al , 2008Hourani et al 2011). But, at this day, no clear explanation was provided to understand the mechanisms involved at nanoscale in stressed and broken-down thin films.…”