C. Petit

Study of defects induced by high‐electric‐field stress into a thin gate oxide (11 nm) of metal‐oxide‐semiconductor capacitors

The creation of defects into a thin gate oxide (11 nm) of polycrystalline silicon‐oxide‐semiconductor capacitors by electron injection Fowler–Nordheim effect, their electric nature, and their behavior when stressed samples are submitted to a white‐light illumination in the inversion regime are studied. It is shown that low‐electron‐injected fluences cause creation of positive charges and that high fluences generate negative charges in the bulk of the oxide. Current‐voltage characteristics have been performed in the accumulation and the inversion regimes before and after electron injection. These characteristics show a very weak shift and a small distortion which seem to indicate that the negative charges are localized close to the injecting electrode and the positive charges near to the Si/SiO2 interface. These positive charges are annihilated by light illumination without interface‐state generation when stressed samples are biased in the inversion regime. Interface states do not show any saturation and t...

Low voltage stress induced leakage currents and surface states in ultrathin (1.2–2.5 nm) oxides

It has been shown recently that the low voltage gate current in ultrathin oxide metal–oxide–semiconductor devices is very sensitive to electrical stresses. Therefore it can be used as a reliability monitor when the oxide thickness becomes too small for traditional electrical measurements to be used. This paper presents a thorough study of the low voltage gate current variation for different uniformed or localized electrical stress conditions at or above room temperature, and for various oxide thicknesses ranging from 1.2 to 2.5 nm. As it has been proposed recently that this current could be due to electron tunneling through Si/SiO2 interface states, the results obtained in the thicker oxides for the gate current have been compared with the corresponding surface state density variations measured by charge pumping. It is shown that there is no clear relation between low voltage gate current increase after stress and that of surface state density, and that soft or hard oxide breakdown happens when the low vo...

Temperature dependence of the electron affinity difference between Si and SiO2 in polysilicon (n+)–oxide–silicon (p) structures: Effect of the oxide thickness

The variations with temperature of the Fowler–Nordheim (FN) emission in metal–oxide–semiconductor structures when the injecting electrode is the degenerate polysilicon gate (n+) are investigated. The temperature dependence of the electron affinity difference Φ between Si and SiO2 and of the barrier height Φb for three oxide thicknesses (5, 7, and 12 nm) are analyzed. The results are numerically derived from the exact integral expression of the FN current as functions of temperature varying from 25 to 300u2009°C. The variation with temperature of both the obtained Φ and dΦ/dT parameters at the polysilicon (n+)–oxide barrier are discussed with respect to the literature data.

Inelastic electron tunneling spectroscopy: Capabilities and limitations in metal–oxide–semiconductor devices

We report on inelastic electron tunneling spectroscopy of a tunneling metal–oxide–semiconductor (MOS) device over an extended energy range compared to previous results. We have clearly observed the vibrations of the hydrogen-passivated (111)Si Pb center in this extended energy range. The assignment of this mode has been confirmed by a comparison with infrared experiments. Capabilities and limitations of the technique to detect and observe molecular vibrations in tunneling MOS devices are discussed.

Aluminum, oxide, and silicon phonons by inelastic electron tunneling spectroscopy on metal-oxide-semiconductor tunnel junctions: Accurate determination and effect of electrical stress

We do inelastic electrical tunneling spectroscopy (IETS) to provide information concerning the vibrational and excitational modes present in silicon dioxide and phonon modes of the electrodes, and of silicon dioxide in metal-oxide-silicon tunnel junction. We analyze the phonon spectra coming from different parts of the metal-oxide-semiconductor (MOS) junction: the aluminum gate, the SiO2 ultrathin film, and the silicon substrate. We compare the phonon modes for the (100) and (111) silicon orientations. We show that IETS can reveal the modifications of Si-SiO2 interface induced by electrical stresses. After a constant voltage stress, the silicon longitudinal phonon modes are significantly shifted in energy, while the transversal phonon modes stay unaffected. Interface healing after annealing is also observed by IETS. These features make IETS a useful tool for MOS reliability studies.

On the decay of the trapped holes and the slow states in metal–oxide–semiconductor capacitors

We have compared the charge created in p‐metal–oxide–semiconductor capacitors by Fowler–Nordheim injection from the gate and from the substrate. We have shown that an injection from the gate creates a negative charge, trapped holes, and positively charged slow states whereas an injection from the substrate creates a negative charge, slow states, and amphoteric neutral traps; once charged these neutral traps are discharged irreversibly, as are the trapped holes, by an appropriate gate bias. We have observed that the discharge of the trapped holes, and the charge or discharge of the slow states, obey the same general law, but the time response of the trapped holes is always shorter than the time response of the slow states. This general law is equivalent to the so‐called ‘‘universal law,’’ which is the law which describes the time dependence of current observed in any dielectric in response to a step‐function field.

STRESS-INDUCED LEAKAGE CURRENT REDUCTION BY A LOW FIELD OF OPPOSITE POLARITY TO THE STRESS FIELD

Stress-induced leakage currents in 7 and 12 nm thick gate oxides of metal-oxide-semiconductor capacitors, created by negative or positive high field stress, were investigated in details. It is known that stress-induced leakage currents have several components. One of these components, which is observed for both stress and measurement polarities, increases drastically when the oxide thickness decreases. We have observed that this component magnitude is reduced when a low field of opposite polarity to the stress field is applied to the oxide after stress. This effect does not seem to be due to electron trapping in the oxide bulk, during the low field application. We propose therefore, that this current decrease is due to a defect relaxation phenomena induced by the low field. This proposition is compatible with any defect creation process which involves a stress-field-induced motion of atoms.

Inelastic electron tunnelling spectroscopy in N-MOS junctions with ultra-thin gate oxide

Abstract The inelastic electron tunnelling spectroscopy (IETS) technique is performed to provide information concerning the vibrational and excitational modes present in MOS tunnelling junctions (molecular species present in silicon dioxide and phonon modes of both silicon substrate and silicon dioxide). The first relevant structures of silicon substrate phonons are investigated in both (1xa01xa01) and (1xa00xa00) orientations for the first time. The separated peaks obtained after deconvolution are identified and compared with literature data for both silicon orientations. The IET spectrum of ultra-thin silicon dioxide is also obtained though this spectrum is more difficult to detect. Finally, two different technologies of manufacturing MOS tunnelling junctions are compared.

Anode hole injection and stress induced leakage current decay in metal-oxide-semiconductor capacitors

Abstract It is known that stress induced leakage current created by Fowler-Nordheim injection in Si/SiO2 structures has a component which increases drastically as the oxide thickness decreases. In the literature this component is considered to be a reproducible dc component. Nevertheless recent measurements have shown that this component decays continuously when a non-stressing field is applied on the sample. The decay is irreversible as long as the sample undergoes no further stressing. This paper reports complementary information about this phenomenon. The magnitude of the decay is studied as a function of the stress field polarity, the non-stressing field magnitude and polarity, and the measurement field polarity. Our conclusion is that the stress induced leakage current decay is triggered by holes of low energy injected from the anode.

Low voltage and temperature effects on SILC in stressed ultrathin oxide films

Abstract It is generally agreed that stress induced leakage current (SILC), in MOS devices, is due to electrons tunneling through stress-induced neutral traps and that SILC has a steady-state component. However, it was observed that SILC, created by positive or negative Fowler–Nordheim injection in 7 and 5 nm thick oxides, decays slowly but continuously when, after stress, the samples are positively or negatively biased at low voltage. The decay is irreversible as long as the gate voltage is less than 4 V. To explain the SILC decay, it has been proposed that some active traps in the tunneling process might possibly be deactivated. The present communication adds first complementary observations on this subject: it shows that the above phenomenon is observed in 3.8 and 3.5 nm thick oxides after a positive stress; that this phenomenon is stable as long as the temperature remains below the SILC annealing temperature threshold which is equal to 200°C; and that during the SILC decay the interface state density does not diminish and can even increase. This communication shows secondly that after a negative stress two SILC components exist in these thin oxides: one which has all the characteristics of the SILC induced by a positive stress and another which does not exist in thicker oxides, which does not decay when a low voltage is applied after stress and which is not annealed at 300°C.