Physical and electrical properties of lanthanide-incorporated tantalum nitride for n-channel metal-oxide-semiconductor field-effect transistors
TL;DR: In this article, the work function of lanthanide-incorporated tantalum nitride (TaN) was studied as a potential metal gate candidate for n-channel metal-oxide-semiconductor field effect transistors (n-MOSFETs).
Abstract: Lanthanide-incorporated tantalum nitride (TaN) is studied as a potential metal gate candidate for n-channel metal-oxide-semiconductor field-effect transistors (n-MOSFETs). Lanthanides such as terbium (Tb), erbium (Er), and ytterbium (Yb) are introduced into TaN to form Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy metal gates, respectively, on SiO2 dielectric. The resistivity, crystallinity, film composition, and work function of Ta1−xTbxNy, Ta1−xErxNy, and Ta1−xYbxNy films were investigated at different post-metal-anneal temperatures and for different lanthanide concentrations. It was found that the work function of lanthanide-incorporated TaN can be effectively tuned by increasing the concentration of lanthanide. Work functions of about 4.2–4.3eV can be achieved even after a 1000°C rapid thermal anneal, making lanthanide-incorporated TaN a promising metal gate candidate for n-MOSFETs. The enhanced nitrogen concentration and the possible presence of lanthanide-N or Ta-N-lanthanide compounds in lanthanide-incorp...
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TL;DR: The photocatalytic activities of R3MO7 and R2Ti2O7 (R=Y, Gd, La; M=Nb, Ta) strongly depended on the crystal structure, and the octahedral network certainly increased the mobility of electrons and holes, thereby enhancing photoc atalytic activity.
Abstract: The photocatalytic activities of R3MO7 and R2Ti2O7 (R = Y, Gd, La; M = Nb, Ta) strongly depended on the crystal structure. Overall, photocatalytic water splitting into H2 and O2 proceeded over La3TaO7 and La3NbO7, which have an orthorhombic weberite structure, Y2Ti2O7 and Gd2Ti2O7, which have a cubic pyrochlore structure, and La2Ti2O7, which has a monoclinic perovskite structure. All of these materials are composed of a network of corner-shared octahedral units of metal cations (TaO6, NbO6, or TiO6); materials without such a network were inactive. The octahedral network certainly increased the mobility of electrons and holes, thereby enhancing photocatalytic activity.
265 citations
TL;DR: In this article, the authors review the current status and challenges in novel high-k dielectrics and metal gates research for planar CMOS devices and alternative device technologies to provide insights for future research.
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TL;DR: Work functions of sub-and monolayers Mo on metal Ta of various orientations were investigated using first-principles methods based on density functional theory in this article, which revealed that the work function has strongly orientation dependence.
Abstract: Work functions of sub- and monolayers Mo on metal Ta of various orientations are investigated using first-principles methods based on density functional theory. The calculated results reveal that the work function has strongly orientation dependence. However, for a given surface orientation, the work function is insensitive to distributions of Ta/Mo atoms in the surface layer. Moreover, it is found that work functions of the (100) and (111) surfaces increase with increasing Mo composition in the surface layer but those of the (110) decrease. By analysis of surface dipole density, it is found that the metal work function is mainly determined by surface orientation and surface charge redistribution.
29 citations
TL;DR: In this article, the plane-wave pseudopotential method within the generalized gradient approximation was used to study the structural stability and electronic structures for several TaN phases, and the ground-state structure of TaN among the five crystallographic structures that have been studied.
Abstract: Using the plane-wave pseudopotential method within the generalized gradient approximation, we have studied the structural stability and electronic structures for several TaN phases. Our results show CoSn is the calculated ground-state structure of TaN among the five crystallographic structures that have been studied. The order of energetic stability of phase structures of TaN from low to high is: CsCl < ZnS-B3 < NaCl < WC < CoSn. The higher stability of TaN in the CoSn and WC structures is due to the formation of pseudogap around the Fermi level and the stronger hybridization between N-2p states and Ta-5d states. TaN in all structures studied has a metallic nature. The calculated bulk modulus indicates that TaN in the WC structure may be a less compressible material. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
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TL;DR: In this article, the relative effective mass in the forbidden energy gap was found to be about 0.4, which is lower by a factor of five to ten than the expected values, probably due to trapping effects.
Abstract: Electronic conduction in thermally grown SiO2 has been shown to be limited by Fowler‐Nordheim emission, i.e., tunneling of electrons from the vicinity of the electrode Fermi level through the forbidden energy gap into the conduction band of the oxide. Fowler‐Nordheim characteristics have been observed over more than five decades of current for emission from Si, Al, and Mg. If previously measured values of the barrier heights are used, the slopes of the Fowler‐Nordheim characteristics (log J/E2 vs 1/E) imply values of the relative effective mass in the forbidden band of about 0.4. These values take into account corrections for image‐force barrier lowering and for temperature effects. The absolute values of the currents are lower by a factor of five to ten than the theoretically expected values, probably due to trapping effects. The temperature dependence of the current was found to follow the theoretical curve from 80°–420°K. However, an inconsistent relative effective mass of about 0.95 had to be assumed....
1,640 citations
TL;DR: In this paper, the optimal gate electrode work function was determined for the 50 nm technology node using a simulation strategy that takes into account the impact of short-channel effects on device performance in uniformly doped and super-steep-retrograde doped channels in conventional and dynamic threshold operation.
Abstract: The optimal gate electrode workfunction was determined for the 50 nm technology node using a simulation strategy that takes into account the impact of short-channel effects on device performance in uniformly doped and super-steep-retrograde doped channels in conventional and dynamic threshold operation. Classical device simulations suggest that the optimal workfunction is such that the gate Fermi level is 0.2 eV below (above) the conduction (valence) band edge of silicon for NMOS (PMOS) devices. However, when quantum mechanical effects are taken into account, the optimal workfunction is such that the gate Fermi level coincides with the conduction (valence) band edge. Midgap gates are not viable because the resulting short-channel effects are too severe. In a surrounding-gate transistor the optimal workfunction is attained when the gate Fermi level is 0.35 eV below (above) the conduction (valence) band edge in NMOS (PMOS) device. Midgap gates are not viable because the resulting threshold voltage is too high and cannot be reduced by lowering the substrate doping.
194 citations
TL;DR: In this article, the characteristics of the binary alloys Ta-Pt and Ta-Ti for gate electrode application were explored and the work function of the metal alloys can be modulated from 4.16 eV to 5.05 eV continuously with a proper composition of high and low work function metals.
Abstract: This paper explores the characteristics of the binary alloys Ta-Pt and Ta-Ti for gate electrode application. With a proper composition of high and low work function metals, the work function of the metal alloys can be modulated from 4.16 eV to 5.05 eV continuously. The alloys show good thermal stability and inner chemical activity on both silicon dioxide and hafnium dioxide. Thermal stress generated from the alloy film increases interface state density and hence effective oxide charges. This problem can be greatly reduced with a W/Ta-Pt stack structure, where W acts as the main conducting metal and Ta-Pt acts as work function control metal. All of these properties make them suitable for use in all device applications.
107 citations
TL;DR: In this article, the resistivity, crystallinity, and work function of Tantalum nitride (TaN) films were investigated as a function of nitrogen flow rate, and the work function increased to 4.5-4.7 eV with less dependency on the nitrogen flow rates.
Abstract: Tantalum nitride (TaN) films were prepared by reactive sputtering in a gas Ar and N2 for gate electrode applications. Resistivity, crystallinity, and work function of the films were investigated as a function of nitrogen flow rate. As the nitrogen flow rate increased from 0 to 20 sccm, the resistivity of as-deposited TaN films increased from 132 to 1.4×105 μΩ cm. With a nitrogen flow rate of 8 and 10 sccm, the fcc TaN phase was obtained. The work function of the TaN films was investigated using TaN-gated nmetal–oxide–semiconductor capacitors with SiO2 gate dielectrics of various thicknesses. As the nitrogen flow rate increased from 4 to 12 sccm, the work function decreased from 4.1 to 3.4 eV for as-deposited films. After annealing at 950 °C for 1 min, the work function increased to 4.5–4.7 eV, with less dependency on the nitrogen flow rate.
96 citations
TL;DR: Work function and thermal stability of reactive sputtered Ti1−xAlxNy films were investigated for a metal gate electrode using a metaloxide-semiconductor (MOS) structure as mentioned in this paper.
Abstract: Work function and thermal stability of reactive sputtered Ti1−xAlxNy films were investigated for a metal gate electrode using a metal–oxide–semiconductor (MOS) structure. It is found that the work function (ΦM) values of Ti1−xAlxNy are ranged from 4.36 to 5.13 eV with a nitrogen partial flow rate (fN2). The ΦM values of Ti1−xAlxNy films, 4.36 eV for nMOS (n-Ti1−xAlxNy) and 5.10–5.13 eV for pMOS (p-Ti1−xAlxNy), may be applicable to dual metal gate electrodes. Excellent thermal stability up to 1000 °C was obtained on SiO2 as observed by the negligible change of capacitance equivalent thickness and Al 2p core level spectra for p-Ti1−xAlxNy (y∼1.0,fN2=50%), whereas a limited stability was attained in case of n-Ti1−xAlxNy (fN2⩽40%). The p-Ti1−xAlxNy can be a good candidate for pMOS device feasibility because of good thermal stability, while the n-Ti1−xAlxNy may be applicable for nMOS gate electrode in low thermal devices using damascene gate process.
43 citations