Properties Of High-k Dielectrics Research Articles

DFT analysis of the electronic, optical, phonon, elastic, and mechanical features of ternary Rb2XS3 (X = Si, Ge, Sn) chalcogenides

Density functional theory (DFT) calculations were executed for the titled features of hitherto unreported Rb2XS3 (X = Si, Ge, Sn) chalcogen compounds. All compounds were found to be in semiconducting character where they demonstrate high-k dielectric properties, high optical conductivity, high refractivity and reasonable absorbance. In addition, obtained phonon dispersion curves of all compounds with positive phonon frequencies stipulate the dynamical stability. Also, computed elastic stiffness constants prove mechanical stability and bilateral agreement between Pugh ratio analyses with Poisson ratio results confirms the ductile mechanical feature of all addressed compounds. Overall, with satisfactory optical, elastic and mechanical aspects, Rb2XS3 (X = Si, Ge, Sn) chalcogenides can be promising materials for recent optoelectronics and microelectronics with diverse applications.

Selective hydrogenation improves interface properties of high-k dielectrics on 2D semiconductors

The integration of high-k dielectrics with two-dimensional (2D) semiconductors is a critical step towards high-performance nanoelectronics, which however remains challenging due to the high density of interface states and the damage to the monolayer 2D semiconductors. In this study, we propose a selective hydrogenation strategy to improve the interface properties while the 2D semiconductors are not affected. Using the interface of monolayer molybdenum disulfide (MoS2) and silicon nitride as an example, we show substantially improved interface properties for electronic applications after the interfacial hydrogenation, as evidenced by reduced inhomogeneous charge redistribution, increased band offset, and nearly intact electronic properties of MoS2. Importantly, this hydrogenation process selectively occurs only at the silicon nitride surface and is compatible with the current semiconductor fabrication process. We further show that this strategy is general and applicable to other interfaces between high-k dielectrics and 2D semiconductors such as hafnium dioxide (HfO2) on the monolayer MoS2. Our results demonstrate a simple yet viable way to improve the integration of high-k dielectrics on a broad range of 2D transition metal disulfide semiconductors, shedding light on practical electronic and optoelectronic applications.

Optical band gap analysis and modeling for ultra-thin high-k dielectrics in high-k/metal gate transistors

A highly precise band gap measurement based on deep UV spectroscopic ellipsometry along with Bruggeman effective model approximation was developed for high-k/metal gate CMOS with ultrathin EOT (<1.5 nm). By applying and comparing the measurement for HfO2 on SiO2 and SiON interfacial layers with different thicknesses, N%, and annealing conditions, two new sub band gap states corresponding to nitrogen in the film are observed. Together with X-ray photoelectron spectroscopy and electrical measurements, it is found that the band gap energies can be correlated to N% and the leakage current of the high-k films by linear regression (R2 = 0.95). This indicates that the method is capable of quantifying physical and electrical properties of high-k dielectrics, and therefore a time consuming physical analysis or expensive electrical test on fully built devices for gate dielectrics can be avoided.

Electrical characterization of top-gated molybdenum disulfide metal–oxide–semiconductor capacitors with high-k dielectrics

Top-gated metal–oxide–semiconductor (MOS) capacitor test structures were fabricated with 30nm HfO2 and Al2O3 thin films by atomic layer deposition (ALD) on surface-functionalized, bulk molybdenum disulfide (MoS2), and characterized with C–V and I–V measurements. The C–V results showed significantly different behavior for MoS2 samples compared to conventional Si MOS capacitors, where the area dependence, frequency dependence, and hysteresis results demonstrate the possibility of different properties of high-k dielectrics on MoS2. The C–V frequency dispersion suggests the existence of defects in the interfacial region of the high-k/MoS2.

Polycrystallization effects on the nanoscale electrical properties of high-k dielectrics

In this study, atomic force microscopy-related techniques have been used to investigate, at the nanoscale, how the polycrystallization of an Al2O3-based gate stack, after a thermal annealing process, affects the variability of its electrical properties. The impact of an electrical stress on the electrical conduction and the charge trapping of amorphous and polycrystalline Al2O3 layers have been also analyzed.

The Influence of Defects and Impurities on Electrical Properties of High-k Dielectrics

Electrical properties of thin high-k dielectric films are influenced (or even governed) by the presence of macroscopic, microscopic and atomic-size defects. For most applications, a structurally perfect dielectric material with moderate parameters would have sufficiently low leakage and sufficiently long lifetime. But defects open new paths for carrier transport, increasing the currents by orders of magnitude, causing instabilities due to charge trapping, and promoting the formation of defects responsible for electrical breakdown events and for the failure of the film. We discuss how currents flow across the gate stack and how damage is created in the material. We also illustrate the contemporary basic knowledge on hazardous defects (including certain impurities) in high-k dielectrics using the example of a family of materials based on Pr oxides. As an example of the influence of stoichiometry on the electrical pa-rameters of the dielectric, we analyze the effect of nitrogen incorporation into ultrathin Hf silicate films.

Investigation on Structural and Electrical Properties of High-k Dielectrics Prepared by Furnace Atomic Layer Deposition with Precursor Cross-flow

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Non-contact Corona-Kelvin based Metrology for High-k Dielectric Characterization with an Extension to Micro-Scale Measurement

AbstractIn-line monitoring of the electrical properties of high-k dielectrics in logic or memory fab-lines has become increasingly important in the semiconductor industry. Non-contact corona-Kelvin based metrology can be used to affectively monitor in-line key dielectric properties. Furthermore, we present an important extension of this metrology to the micro-scale that allows measurement of dielectric properties on test sites as small as 40μm × 70μm. This is achieved through miniaturization of the corona charging apparatus and of the Kelvin probe without a sacrifice in precision or repeatability. Corona-Kelvin micro-metrology allows for the monitoring of the critical dielectric properties directly on product wafers that can then be returned to the fab-line for continued processing. Application examples are given for dielectric capacitance of advanced dielectrics and for the properties of an oxide-nitride-oxide (ONO) memory structure. In the latter case we demonstrate programming and erasing of the ONO structure realized by corona charging. We also use the measured flatband voltage and total charge to identify the location of the programmed charge at the first SiO2/Si3N4 interface in the ONO structure.

Leakage current and breakdown electric-field studies on ultrathin atomic-layer-deposited Al2O3 on GaAs

Atomic-layer deposition (ALD) provides a unique opportunity to integrate high-quality gate dielectrics on III-V compound semiconductors. We report detailed leakage current and breakdown electric-field characteristics of ultrathin Al2O3 dielectrics on GaAs grown by ALD. The leakage current in ultrathin Al2O3 on GaAs is comparable to or even lower than that of state-of-the-art SiO2 on Si, not counting the high-k dielectric properties for Al2O3. A Fowler-Nordheim tunneling analysis on the GaAs∕Al2O3 barrier height is also presented. The breakdown electric field of Al2O3 is measured as high as 10MV∕cm as a bulk property. A significant enhancement on breakdown electric field up to 30MV∕cm is observed as the film thickness approaches to 1nm.

Engineering the nm-thick Interface Layer Formed Between a High-k Film and Silicon

ABSTRACTThe interface layer between thin sputter-deposited tantalum oxide (TaOx) high-k film and silicon substrate was engineered with the Hf doping method and the insertion of a thin 5Å TaNx interface. The following results have been obtained: 1) the Hf dopant in the TaOx film was involved in the interface formation process, e.g., forming a new, thinner high-k HfSixOy interface layer rather than the SiOx layer, 2) when the TaNx interface was inserted, the interface layer composition was even more complicated, e.g., including TaOxNy and HfSixOy structures. No hafnium nitride or oxynitride was detected, 3) the interface layer structure was changed, e.g., from single-zone to multi-zone with different compositions, 4) when a low concentration of Hf existed in the TaOx film, the high-k dielectric properties, such as the k value, fixed charge density, dielectric strength, were improved, and 5) when the thin TaNx interface layer was inserted, the above electric properties were further improved. However, the fixed charge density and interface states were increased due to the insertion of the TaNx interface layer. These results were contributed by factors such as the charge-trapping characteristics in the interface layer and the some damage repairing mechanisms. In summary, this research proved that the high-k film's interface layer and bulk properties could be were improved with the doping process as well as the insertion of an ultra-thin TaNx interface film.

Photoemission and ab initio theoretical study of interface and film formation during epitaxial growth and annealing of praseodymium oxide on Si(001)

X-ray photoelectron spectroscopy (XPS) was performed to study the formation process of Pr2O3/Si(001) interfaces and films during epitaxial growth and postgrowth annealing. A significant shift in the Pr and O core-level binding energy was found accompanied by an analogous shift in the Pr2O3 valence band maximum. This shift depends on the oxide layer thickness and interface structure, as indicated by ab initio pseudopotential calculations. It is caused by interface dipoles in the Si/Pr2O3 interface region due to the accumulation of oxygen. Besides providing a insight into the growth mechanism and interface properties of high-K dielectrics on Si, our results also demonstrate the usefulness of in vacuoXPS for investigating epitaxial growth processes.