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In this paper we present results concerning the modeling of oscillations in the I-V g characteristics (V g < 0), of metal/ultra-thin oxide/semiconductor (MOS) structures where the oxide thickness is 45 A. From the theoretical models of the literature we have shown that the modeling of oscillations cannot be made by using the conduction parameters (metal/ultra-thin oxide interface barrier, prefactor K 1 ) at low or high electric fields. However, it requires the determination and a fine analysis at low fields of the excess current which is due to the presence of defects in the oxide layer. The oscillations analysis of this excess current enabled us to show on the one hand a good agreement between the field values corresponding to the theoretical and experimental oscillation extrema, and on the other hand to estimate the defect depth.

In this paper we analyze the interface state of the metal/ ultra thin oxide/ semiconductor structures and their degradation under an electrons injection from the metal or the semiconductor, by Fowler-Nordheim effect, at high electric field (> 10 MV/ cm). The metal used is chromium and the oxide layer thickness is in the range of 60A-130A. Before injection the energy distribution of the interface state in the semiconductor gap present a peak of energy of 0.25eV above the semiconductor valence band edge. The peak density (Nssmax) decreases with the oxide thickness. After injection the degradation of the Nssmax density depends on the oxide thickness, and increases with injected charge independently on the injected field and the polarization mode (V 2 lo-' c/cm2). The injection influence on the interface state density (Nssmid) at mid gap is not important. The Nssmid density is lower than 10" eVcm -for all the injection charges (VO). Also, we showed that the sensitivity to the degradation by electrons injection decreases with the oxide thickness. In comparing with the literature results we deduced a lower interface state density on our structures, and a satisfactory sensitivity to the degradation to high injecting fields. I -2 I-IntroductionThe design and the optimization of the field effect transistors (MOS, MOSFET,. ..)[ 1-41 on the silicon requires a perfect restraint and an excellent reproducibility in time of the threshold voltage and of the transconductance. These two parameters are essentially controlled by the quality of the oxide (Si02)/semiconductor(Si) interface; all defect electrically active (interface state) modifies the static and dynamic behavior of the devices. The carriers of the channel can communicate with the sites of the interface states. Their mobility is then decreased, as well as the transconductance of the transistor. By elsewhere, the interface state degrade the other semiconductor device performances for example the EEPROMmemories,RAM[ 5,6], ... Currently, a lot of studies are devoted to decrease the interface state density as lower possible [ 10-121. So, it is necessary to know their density, their energy distribution in the semiconductor gap and analyze their degradation by carriers or constant current injection [7]. Under these electrical stress influences, we observe the degradation o f the oxide/semiconductor interface [8,9].In the literature, most of the studies concerning the oxide/ semiconductor interface degradation were made on the metall oxide/semiconductor structures having the oxide layer relatively thick (> 150 A).While, few results concern the degradation of the oxide layers thinner than the hundred of Angstroms and in particular at high fields injection (> 10 MV/cm). In this work, in order to have a good understanding of the ultra thin oxide/ semiconductor interface behavior of the metal/ ultra thin oxide/ semiconductor structures where the thickness is lower than the hundred of Angstroms, we analyze from c...

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