Abstract
In this paper, the conduction properties of dielectric ultra-thin layers are studied using atomic force microscopy. Especially, the conductive-atomic force microscope allows to measure the leakage current at the nanoscale and to study the degradation mechanisms locally. Nonetheless, the dielectric layer seems to be damaged by a technique's specific phenomenon: hillocks appear when a positive tip bias is applied on different dielectrics. In this paper, the formation of these hillocks is studied. Contrary to what is observed during the dielectric breakdown, the conductivity is reduced after hillocks formation which occurs after the dielectric breakdown. Moreover, we have observed the formation of cavities in the silicon substrate linked to the formation of hillocks, which is not compatible with a swelling process (as dielectric breakdown induced epitaxy). We propose that these results may be explained by an electro-thermal effect due to the large dissipated energy, maybe combined with the oxidation of the substrate. Finally, the interdependence of measurements is demonstrated during serial acquisition.
Highlights
Thin dielectric layers are essential components in microelectronic devices and the study of the mechanisms which govern dielectric breakdown provides crucial information about their reliability and life-time
Contrary to what is observed during the dielectric breakdown, the conductivity is reduced after hillocks formation which occurs after the dielectric breakdown
We have observed the formation of cavities in the silicon substrate linked to the formation of hillocks, which is not compatible with a swelling process
Summary
Thin dielectric layers are essential components in microelectronic devices and the study of the mechanisms which govern dielectric breakdown provides crucial information about their reliability and life-time. The leakage current and the oxide degradation (and breakdown) are studied at the device scale. A lot of results available in the literature were obtained in ambient atmosphere In this case, a water layer exists on the sample surface and a meniscus appears at the tip-sample contact.. When a negative bias is applied to the AFM tip relatively to the substrate, some OHÀ ions may be injected through the oxide layer, inducing silicon substrate oxidation. The first proposed explanation is that the observation of a sample surface inflation is only due to injection of electric charges in the dielectric which influences the topographical mapping.. We propose a theory that allows a better understanding of mechanisms that induce the apparition of hillocks under positive AFM bias relatively to the substrate
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