Hideki Satake

NBTI mechanism in ultra-thin gate dielectric - nitrogen-originated mechanism in SiON

We have investigated the mechanism of negative bias temperature (NBT) degradation of p/sup +/-gate p-MOSFETs having SiON and SiO/sub 2/ films. As a result, it was found that NBT degradation of SiO/sub 2/ is improved by fluorine incorporation, while no effect is observed in that of SiON, and that the activation energy of NBT degradation in SiON is lower than that in SiO/sub 2/. From these experimental results, it is inferred that nitrogen-originated NBT degradation dominates NBT degradation in SiON. It was also found that non-energetic holes existing in the inversion layer contribute to NBT degradation for both SiON and SiO/sub 2/ films, and that the oxide field is indispensable for NBT degradation.

Interfacial properties of single-crystalline CeO2 high-k gate dielectrics directly grown on Si (111)

Interfacial properties of single-crystalline CeO2 high-k dielectrics directly grown on Si (111) were investigated by comparing metal–insulator–semiconductor field-effect transistors (MISFETs) without any interfacial layer [(w/o-IL); direct growth of CeO2 on Si] and those with an interfacial layer (w-IL). FET characteristics, such as the drain current and the S factor, for the w/o-IL MISFET were much worse than those for the w-IL MISFET. The in-gap states attributed to the oxygen defects were detected in the CeO2 directly grown on Si by x-ray photoelectron spectroscopy measurements. The large interface state density induced by the oxygen defects at the CeO2/Si interface may deteriorate the w/o-IL MISFET performances.

Applicability limits of the two-frequency capacitance measurement technique for the thickness extraction of ultrathin gate oxide

Reliable techniques for extracting the gate dielectric layer thickness from capacitance-voltage (C-V) characteristics are essential for manufacturing process quality control. Continued reduction of the dielectric layer thickness has brought about a need for new measurement procedures which can account for the direct tunneling currents through the gate insulator. We present a guideline for performing two-frequency C-V analysis of sub-2 nm gate oxides and show that it is possible to extract the dielectric layer thickness with an error of less than 4%. We show that in order to achieve this level of accuracy, it is necessary to choose the measurement frequencies and the test device size so that the dissipation remains below 1.1 at least at one of the two measurement frequencies.

Correlation between two dielectric breakdown mechanisms in ultra‐thin gate oxides

The origin of stressing polarity dependence of charge‐to‐breakdown, Qbd, in thin SiO2 is discussed based on the temperature dependence of Qbd for both stressing polarities using wet and dry oxides. It was found that the temperature dependence of Qbd, which increases with decreasing temperature in the high temperature region and tends to saturate in the low temperature region, is identical irrespective of the stressing polarity and the oxidation condition. It has been proposed that the strain gradient from Si/SiO2 interface to SiO2/gate electrode interface determines directly both the Si–H bond density which dominates Qbd in high temperature region and the strained Si–O bond density which dominates Qbd in the low temperature region, irrespective of gate polarity and of oxidation condition.

Influence of Nitrogen on Negative Bias Temperature Instability in Ultrathin SiON

Negative bias temperature instability (NBTI) and its recovery phenomenon in ultrathin silicon oxynitride (SiON2) films were investigated. To discuss the influence of nitrogen incorporation into silicon dioxide films, we used NO-nitrided SiON and plasma-nitrided SiON. As a result, it was found that the recovery for plasma-nitrided SiON is less marked than that for NO-nitrided SiON, although NBTI can be suppressed by plasma nitridation. It is also experimentally confirmed that hydrogen plays an important role in these phenomena. On the basis of these results, we proposed nitrogen-originated NBT degradation involving hydrogen at SiON/Si interface and hole trapping/detrapping. Furthermore, NBTI under ac stress was investigated. Not only NBTI was more suppressed under ac stress than under dc stress as already reported, but also, this behavior of dynamic NBTI is independent of nitrogen distribution in SiON.

Improvement of charge-to-breakdown distribution by fluorine incorporation into thin gate oxides

This paper reports on the effect of fluorine incorporation on gate-oxide reliability, especially the spatial distribution of charge-to-breakdown (Q/sub BD/). Fluorine atoms were implanted into gate electrodes and introduced into gate-oxide films by annealing. Excess fluorine incorporation increased the oxide thickness and degraded not only the reliability of Si/SiO/sub 2/ interfaces but also dielectric-breakdown immunity. However, it was found, for the first time, that appropriate fluorine incorporation into gate-oxide films could dramatically improve Q/sub BD/-distribution tails in Weibull plots, while maintaining both Si/SiO/sub 2/ interface characteristics and average Q/sub BD/ values. The experimental result for a depth profile of fluorine atoms indicated that fluorine atoms are located dominantly at the two interfaces of the gate-oxide film. In addition, the results of infrared (IR) absorption analysis indicated that the strain of SiO/sub 2/ structures is reduced with increasing fluorine doses. We proposed that both strain release and restructuring of the SiO/sub 2/ network by fluorine incorporation are responsible for improving the Q/sub BD/ of weaker oxide films.

SiO2 dielectric breakdown mechanism studied by the post-breakdown resistance statistics

The dielectric breakdown mechanism of ultra-thin SiO2 is discussed on the basis of the experimental results of the post-breakdown resistance (Rbd) distribution. We have noticed that the Rbd of SiO2 in MOS devices is strongly related to the SiO2 breakdown characteristics such as the polarity dependence, the oxide field dependence or the oxidation process dependence of Qbd. In this paper, we discuss the dielectric breakdown mechanism of SiO2 from the viewpoint of the statistical correlation between the Rbd distribution, the Qbd distribution and the discharging energy at the SiO2 breakdown, by changing the stress polarity, the stress field, the oxide thickness and the oxidation process. In the case of hard breakdown, it has been clarified that the Rbd distribution for substrate electron injection is clearly different from that for gate electron injection. We have also found that, irrespective of the stress current density, the gate oxide thickness, the stressing polarity and the oxidation process, Rbd can be uniquely correlated to the discharging energy at dielectric breakdown, in the case of hard breakdown. Furthermore, it has been clarified that the Rbd does not depend on the energy dissipation at soft breakdown.

Common origin for stress‐induced leakage current and electron trap generation in SiO2

The origin of stress‐induced leakage current in ultrathin SiO2 has been quantitatively investigated on the basis of the experimental results on temperature dependence of stress‐induced leakage current. We found that stress‐induced leakage current is dependent on stressing temperature, and that it is independent of measurement temperature. It has been quantitatively demonstrated for the first time that the activation energy of the appearance of stress‐induced leakage current agrees well with that of electron trap generation so far reported. It is discussed quantitatively that stress‐induced leakage current and electron trap generation have a common origin.

Study on Zr-silicate interfacial layer of ZrO2 metal-insulator-semiconductor structure

We have investigated the physical and dielectric properties of the Zr-silicate interfacial layer of ZrO2 metal-insulator-semiconductor (MIS) structure fabricated by pulsed-laser ablation deposition. It was found that an ultrathin Zr-silicate interfacial layer is formed on a Si substrate as a result of the reaction between ZrO2 and Si. We showed that MIS capacitors consisting solely of the ultrathin Zr-silicate interfacial layer could be fabricated by selective etching of the ZrO2 layer. The Zr-silicate interfacial layer showed a small equivalent oxide thickness of 0.8 nm, a dielectric constant of 8–9, and low leakage less than 1 A/cm2 at Vg of −1 V.We have investigated the physical and dielectric properties of the Zr-silicate interfacial layer of ZrO2 metal-insulator-semiconductor (MIS) structure fabricated by pulsed-laser ablation deposition. It was found that an ultrathin Zr-silicate interfacial layer is formed on a Si substrate as a result of the reaction between ZrO2 and Si. We showed that MIS capacitors consisting solely of the ultrathin Zr-silicate interfacial layer could be fabricated by selective etching of the ZrO2 layer. The Zr-silicate interfacial layer showed a small equivalent oxide thickness of 0.8 nm, a dielectric constant of 8–9, and low leakage less than 1 A/cm2 at Vg of −1 V.

Band diagram and carrier conduction mechanism in ZrO/sub 2//Zr-silicate/Si MIS structure fabricated by pulsed-laser-ablation deposition

On the basis of the experimental results of XPS analysis and the carrier separation, the band diagram and carrier transport mechanism in ZrO/sub 2/ dielectrics were clarified for the first time. ZrO/sub 2/-MIS structure consists of ZrO/sub 2/ layer and the interfacial Zr-silicate layer. The carrier conduction in ZrO/sub 2/ layer is dominant in the ZrO/sub 2//Zr-silicate/Si MIS structure. It was found that the hole conduction mechanism is different from electron conduction mechanism in ZrO/sub 2/ gate dielectrics.