Oxygen‐Doped Molybdenum Films for MOS Gate Application

Ohfuji, Shin ichi; Hashimoto, Chisato; Amazawa, Takao; Murota, Junichi

doi:10.1149/1.2115602

Cited by 11 publications

(10 citation statements)

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“…Although ͑110͒ is the dominant orientation, several crystalline orientations including ͑200͒, ͑211͒, and ͑220͒ are also identified. Therefore, the work function of the MoN-0 sample of 4.6 eV is reasonable and is consistent with other works, [15][16][17] although some recent papers reported that the work function is reduced by implanting nitrogen into Mo͑110͒ film. The nitrogen concentrations are not high enough so that the main phase is Mo 2 N in those works.…”

Section: G198supporting

confidence: 91%

“…Molybdenum ͑Mo͒ films have drawn a lot of attention as a single metal gate electrode of CMOS devices because the work function of Mo on SiO 2 can be adjusted from 4.36 to 4.95 eV. [13][14][15][16][17][18] Moreover, molybdenum has low resistivity, good thermal stability, and high density, which is a benefit for ion-implantation mask. 15,16 The work function of molybdenum varies with the bulk microstructure, which depends on the deposition and annealing conditions.…”

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confidence: 99%

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Investigation of Molybdenum Nitride Gate on SiO[sub 2] and HfO[sub 2] for MOSFET Application

Tsui

Huang

2006

J. Electrochem. Soc.

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It has been reported that the work function of nitrided molybdenum ͑MoN͒ can be modulated by the atomic ratio of N/Mo and is suitable for gate material of complementary metal oxide semiconductor devices. In this work, we investigated the characteristics of MoN x prepared by reactively sputtering deposition from the gate electrode point of view. The main phase of the MoN x films is MoN͑200͒. As the N/Mo ratio increases, the microstructure of MoN x film tends to be amorphous-like and the resistivity increases. After high-temperature annealing, the phase remains stable and grain size increases slightly. The HfO 2 film has better immunity to sputtering damage than SiO 2 film; therefore, the sputtering deposition method could be a choice of metal gate deposition as HfO 2 -based dielectric is used. The work function of MoN x increases with the increase of nitrogen content and tends to saturate at the valence band of Si. No Fermi-pinning effect is observed on HfO 2 film. The work function and thermal stability of MoN x show good thermal stability on both SiO 2 and HfO 2 films up to 800°C at least. All of these results indicate that MoN is a good candidate of gate electrode for p-type metal oxide semiconductor field effect transistors ͑pMOSFETs͒ or fully depleted SOI devices.Metal gates are expected to replace polysilicon gates beyond the 45-nm technology node, according to the ITRS roadmap. 1 Suitable work function ͑⌽ m ͒ and chemical inertia of metal gates are the two main criteria for proper threshold voltage and easy device integration, respectively. The work function of metal gates should be 4.1-4.4 eV for bulk n-type metal oxide semiconductor field effect transistors ͑nMOSFETs͒ and 4.8-5.1 eV for bulk p-type MOSFETs ͑pMOSFETs͒. 2,3 The chemical inert metal gates should be thermally stable enough to avoid chemical reaction with gate dielectric and the surrounding insulators during source/drain dopant activation. With these properties, metal gates could be suitable for the conventional gate process, which is much simpler than the replacement gate process. 4-10 Actually, for the complementary metal oxide semiconductor ͑CMOS͒ fabricated with conventional gate process, dualwork-function metal gates would still be crucial if two different metal gate materials are required. 11,12 The significant challenges are removing the gate materials without damaging the underlying dielectric and simultaneous patterning different gate electrodes.Molybdenum ͑Mo͒ films have drawn a lot of attention as a single metal gate electrode of CMOS devices because the work function of Mo on SiO 2 can be adjusted from 4.36 to 4.95 eV. 13-18 Moreover, molybdenum has low resistivity, good thermal stability, and high density, which is a benefit for ion-implantation mask. 15,16 The work function of molybdenum varies with the bulk microstructure, which depends on the deposition and annealing conditions. 17,18 It can also be modulated by the implantation of nitrogen or argon. 2,18-21 The work function of the ͑110͒-oriented Mo film is 4.95 eV. After nitr...

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Section: G198supporting

confidence: 91%

mentioning

confidence: 99%

Investigation of Molybdenum Nitride Gate on SiO[sub 2] and HfO[sub 2] for MOSFET Application

Tsui

Huang

2006

J. Electrochem. Soc.

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“…Here, the oxygen was doped by reactive sputtering of Mo in a mixture of O~ and Ar gases. After annealing in N~ at 1000~ for 30 min, the oxygen was converted into stable MoO2 in the electrodes (21). With an increase in the oxygen concentration, N• shows a tendency to increase after annealing above 800~ This indicates that the possibility of capturing Na cations in oxygen-doped Mo films is eliminated.…”

Section: Effects Of Nitride On Sodium Diffusion--the Nitriding Ofmentioning

confidence: 99%

Reduction of Sodium Ion Density in Molybdenum‐Gate MOS Devices with the Addition of Tantalum to Gate Electrodes

Ohfuji

Shiono

1985

J. Electrochem. Soc.

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The reduction mechanism of mobile ion contamination in Ta-Mo alloy gate MOS structures has been examined by varying the deposition and annealing conditions of gate metals. Mobile ion density in the gate SiO2 for the Ta-Mo gate structures decreases drastically after forming gas annealing at 1000~ whereas the density increases during nitrogen gas annealing. The structure and composition analysis for the Ta-Mo gate observed by x-ray diffraction, SIMS, and AES indicates that nitriding of Ta-Mo films occurs during the forming gas annealing, and the nitride, MoTaN (tetragonal, CrNbN-type structure), is stable even at 1000~ during annealing. These facts suggest that MoTaN formation at the boundaries of Mo grains, which is similar to the stuffing effect observed in TiN films, is responsible for immobilizing the sodium atoms within the gate electrodes. As a result, the diffusion of sodium from the gate electrode into the SiO2 layers is suppressed.With regard to the development of highly conductive and self-aligned gate electrodes and interconnection lines, molybdenum (Mo) is under active investigation as an alternative to the widely used polycrystalline silicon gate in MOS LSI's (1). In the self-aligned gate process, high temperature annealing above 900~ is necessary to activate implanted ions in the source and drain regions following gate electrode formation. This process causes the impurities sodium (Na) and potassium (K), contained in the Mo electrodes and having a concentration less than 1 ppm (2), to diffuse into the gate SiO2 layers. This alkali ion contamination is known to result in flatband voltage shifts in MOS structures (3). It is essential to prevent this ionic Na and K contamination in the thermally grown SiO2 layers in order to stabilize the Mo-gate MOS characteristics.A phosphosilicate glass stabilization process (4) and an oxidation technique for silicon in the presence of chlorine and chlorine compounds (5) have been developed as methods to obtain passivated oxides. Another possible solution, high temperature annealing of Mo gate electrodes in a forming gas, has been reported to be effective in reducing this contamination (6). We have recently shown that the effect of forming gas annealing is enhanced by hydrogen doping and the addition of tantalum to Mo films (2). The Ta addition is intended to increase the amount of doped hydrogen in the films as a result of the fact that Ta has a higher hydrogen absorption property than Mo (7). It has also been shown that the Na diffusion from these specially designed gate electrodes into the gate oxides is almost entirely prevented when high temperature annealing is performed in a forming gas, although the physical origin of this effect remains unclear.In this work, a reduction mechanism of mobile ion contamination in the Ta-Mo alloy gate MOS structures is examined by varying the deposition and annealing conditions of gate metals. Structural and compositional changes in the Ta-Mo films as a function of process conditions are measured using an x-ray diffractometer, SI...

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“…The key requirements for the new material are chemical inertness, immunity to dopant penetration during source/ drain ion implantation, and thermal stability during the following high temperature processes. 6,7) Metal gates should have a proper work function (È m ) to obtain a suitable threshold voltage for n-or p-type MOSFETs (NMOSFET/ PMOSFET), 8,9) where the work function of the metal should be 4.1-4.4 eV for NMOSFETs and 4.8 -5.1 eV for PMOSFETs. 8,9) To meet these criteria, refractory metals and their nitrides, such as WN, MoN, TaN, and TiN, have been considered as attractive candidates.…”

Section: Introductionmentioning

confidence: 99%

Ta–Pt Alloys as Gate Materials for Metal–Oxide–Semiconductor Field Effect Transistor Application

Huang

Tsui

2009

jjap

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Oxygen‐Doped Molybdenum Films for MOS Gate Application

Cited by 11 publications

References 1 publication

Investigation of Molybdenum Nitride Gate on SiO[sub 2] and HfO[sub 2] for MOSFET Application

Investigation of Molybdenum Nitride Gate on SiO[sub 2] and HfO[sub 2] for MOSFET Application

Reduction of Sodium Ion Density in Molybdenum‐Gate MOS Devices with the Addition of Tantalum to Gate Electrodes

Ta–Pt Alloys as Gate Materials for Metal–Oxide–Semiconductor Field Effect Transistor Application

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