Behavior of Local Current Leakage in Stressed Gate SiO₂ Films Analyzed by Conductive Atomic Force Microscopy

Abstract

We studied local leakage currents induced in stressed gate SiO2 films and their time dependence by conductive atomic force microscopy (C-AFM). The current-voltage characteristics of the leakage currents detected in the C-AFM observations indicate Fowler-Nordheim tunneling currents enhanced by holes trapped in the stressed SiO2 films. By repeated C-AFM observations at the same area, it was found that individual spot currents decrease at different rates. This result indicates hole detrapping with different time constants from the stress-induced defects that have different features.

Analysis of Local Breakdown Process in Stressed Gate SiO2 Films by Conductive Atomic Force Microscopy

“…Using this technique, we have studied the degradation phenomena of gate SiO 2 films and observed that local leakage current spots appearing in current images are caused by stress-induced defects with trapped holes. 18,19) Furthermore, the detrapping phenomena of these trapped holes with different detrapping rates 20) and the stability of stress-induced defects 21) have been verified.…”

Characterization of Local Current Leakage in La2O3–Al2O3 Composite Films by Conductive Atomic Force Microscopy

“…The alternate long and short dashed line shown at higher voltages in Fig. 1 is an I-V curve calculated from the equation of F-N tunneling conduction, 9) assuming that the average barrier height and effective mass for electrons is 1.75 eV and 0:5m 0 , respectively. Here, m 0 is the rest mass of an electron.…”

“…4(b), I-V characteristics at higher voltages can be fit to an F-N tunneling conduction curve with a shift to low voltage. According to the F-N tunneling conduction mechanism, 9,15) at least three possibilities can explain this voltage shift: the thinning of the films, electric field enhancement due to positive charges in the film, and lowering the barrier height for electrons in the film. As mentioned earlier, it seems unlikely that these leakage spots come from the variation in film thickness.…”

“…Recently, we developed a C-AFM observation technique for degradation phenomena in gate SiO 2 films in which constant current stress was applied in the form of a MOS capacitor, 8) and we demonstrated quantitative agreement of the trapped hole density measured by C-AFM and the MOS capacitors. 9) However, for high-k films, such quantitative comparison between local and macroscopic characteristics has rarely been performed to date.…”

Behavior of Local Charge-Trapping Sites in La2O3–Al2O3 Composite Films under Constant Voltage Stress

“…10) The distribution of trapped holes and their trapping and detrapping phenomena have been revealed by observing the time dependence of local leakage current of the gate SiO 2 films by C-AFM. [11][12][13] The influence of trapped holes on the breakdown processes has been also clarified. 14) La 2 O 3 -Al 2 O 3 composite films are one of the promising candidates for next-generation gate high-k films because of their comparatively large dielectric constants and electron barrier height for Si.…”