Interface state degradation of metal/ultra-thin oxide/semiconductor structures under electron injections at high field

Abstract

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<O, W O ) of the structure for the high injected charge (Qinj > 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 (V<O, V>O). 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...

Ageing of metal/ultra-thin oxide/semiconductor structures under Fowler–Nordheim current injection

“…Figure 2 shows the densities of the mid-gap interface states and maximum interface states (the distribution peak of interface states [24]) according to oxide thickness. We can see that these densities decrease with oxide thickness.…”

“…This also enabled us to study the influence of these positive charges on carriers injected during the acquisition of I (V g ) characteristics in the inversion mode (V g > 0). 6(A) shows the typical maximum density value of interface states (N ss max ) [24] according to injected charges, current and mode of injection. These behaviours are observed for an oxide thickness varying from 6 to 12.5 nm.…”

“…Like the creation of charges in the oxide layer, new interface states [9,[18][19][20][21][22][23] can be observed after carrier injection. The maximum density of these interface states is a function of the injected charge and may be expressed as follows [9,23,24]:…”

Modelling of the influence of charges trapped in the oxide on theI(Vg) characteristics of metal–ultra-thin oxide–semiconductor structures

“…The degradation of metal-ultra-thin oxide-semiconductor structures (MOS), due to carrier injection, is evidenced by the creation of interface states and the formation of negative and positive charges in the oxide [1][2][3][4][5][6][7][8][9]. These interfacial and bulk charges cause instability of MOS devices and oxide breakdown [10][11][12][13].…”