Effects of the TaNx interface layer on doped tantalum oxide high-k films

Electrical properties of zirconium-doped tantalum oxide ͑Zr-doped TaO x ͒ high-k gate dielectric films integrated with Mo, MoN, and WN gate electrodes were studied. The Zr-doped TaO x film with the Zr/͑Ta + Zr͒ ratio of 0.33, which showed good dielectric properties in previous studies, was used as the high-k film in this study. A single metallic Zr/Ta alloy target was used for the sputter deposition. The resistivities of the MoN and WN films were minimized by adjusting the N 2 concentration in the sputtering gas, i.e., 10% N 2 ͑90% Ar͒ for MoN and 2.5% N 2 for WN, respectively. Microstructures of the gate electrodes were investigated with X-ray diffraction. Current density, equivalent oxide thickness, breakdown strength, flatband voltage, hysteresis, interface state density, and frequency dispersion of capacitors with different gate electrode materials were analyzed and compared. Device characteristics changed drastically with the gate electrode material, mainly due to the difference in work functions.Continuous shrinkage of channel length and gate oxide thickness of metal oxide semiconductor ͑MOS͒ transistors contributes to improved device performance and high circuit density. However, a number of obstacles have emerged from this strategy, for example, a high gate tunneling leakage current, polycrystalline silicon ͑poly-Si͒ gate depletion, high gate resistance, boron penetration into the gate dielectric, and reliability. 1-5 When the silicon oxide gate dielectric layer is replaced by a high dielectric constant ͑high-k͒ film, the leakage current problem can be solved because a thick gate dielectric layer can be used. 1,2 In principle, some of these problems may be solved by replacing the poly-Si gate with a metal gate. 2 For example, with a poly-Si gate electrode, the capacitance equivalent thickness ͑CET͒ of an MOS capacitor is influenced by three factors: ͑a͒ the contribution from the silicon substrate, i.e., the quantum mechanical effect, ͑b͒ the dielectric layer itself, and ͑c͒ the carrier depletion layer in the poly-Si gate. 6 The replacement of the poly-Si gate with a metal gate could eliminate the polydepletion, thus reducing the CET by 3-5Å without a substantial increase in leakage current. 2 In addition, the gate resistivity can be reduced. Without the boron-doped poly-Si gate, the boron penetration problem does not exist.It was reported that the electrical characteristics of the high-k gate dielectric film actually depend on the properties of the gate electrode material, such as work function and interface thermal stability. 7,8 Therefore, there are many requirements for the gate electrode material. For an n-MOSFET, the metal gate needs a work function of 4.1-4.3 eV; for a p-MOSFET, it needs to be 5.0-5.2 eV. 9 Other requirements include thermal stability in contact with the gate dielectric film, ease of hydrogen diffusion for the dielectric interface passivation, and a simple deposition method. 10,11 Theoretical studies showed that the gate work function could vary significantly with the metal's micros...

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“…[20][21][22][23][24][25] In addition to the physical properties, the influences of these electrodes to dielectric characteristics were studied.…”

mentioning

confidence: 99%

Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes

Tewg

Kuo

Lü

2005

J. Electrochem. Soc.

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“…The ESCA result shows that for both un-doped and Hf-doped TaO x /TaN x structures, the bulk film contains Ta in the Ta 2 O 5 form [4]. When the bulk film is sputtered off, the low energy Ta peaks, e.g., Ta-N and Ta-O (N), appear.…”

Section: Hf Doping and Tan X Interface Layer Effects On Interface Chementioning

confidence: 98%

“…The N ion signals could be used as an indication of the profile of TaO x N y interfacial layer [4]. Therefore, the interface layer formation process is selflimited.…”

Section: Hf Doping Effects On Interface Layer Thicknessmentioning

confidence: 99%

“…However, Ta 2 O 5 forms a SiO xlike interface layer when it is in direct contact with silicon after a high temperature process step [1]. When a 5Å tantalum nitride (TaN x ) is inserted between the Hf-doped TaO x and silicon, many the film's dielectric properties can be further improved due to the change of the interfacial layer composition [3,4]. Nevertheless, if the interface is like the thermally grown SiO 2 , this can result in the improvement of device performance, such as the low interface state density and high mobility.…”

Section: Introductionmentioning

confidence: 99%

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

2004

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The interface layer between thin sputter-deposited tantalum oxide (TaO x ) high-k film and silicon substrate was engineered with the Hf doping method and the insertion of a thin 5Å TaN x interface. The following results have been obtained: 1) the Hf dopant in the TaO x film was involved in the interface formation process, e.g., forming a new, thinner high-k HfSi x O y interface layer rather than the SiO x layer, 2) when the TaN x interface was inserted, the interface layer composition was even more complicated, e.g., including TaO x N y and HfSi x O y 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 TaO x film, the high-k dielectric properties, such as the k value, fixed charge density, dielectric strength, were improved, and 5) when the thin TaN x 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 TaN x 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 TaN x interface film.

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“…However, its lower k value limits the scalability of Ge MOS devices, even as an interlayer. More recently, Lu et al 7 reported that an ultrathin tantalum nitride film deposited between high-k dielectric and Si substrate could suppress the formation of the SiO x interlayer during subsequent high-temperature annealing. This is because tantalum nitride can function as a diffusion barrier and can be oxidized to form nonconductive TaO x N y after annealing in O 2 .…”

Section: Improved Electrical Properties Of Ge Metal-oxide-semiconductmentioning

confidence: 99%

Improved electrical properties of Ge metal-oxide-semiconductor capacitor with HfTa-based gate dielectric by using TaOxNy interlayer

Zhang

Li³

et al. 2008

Applied Physics Letters

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HfTa-based oxide and oxynitride with or without TaOxNy interlayer are fabricated on Ge substrate to form metal-oxide-semiconductor (MOS) capacitors. Their electrical properties and reliabilities are measured and compared. The results show that the MOS capacitor with a gate stack of HfTa-based oxynitride and thin TaOxNy interlayer exhibits low interface-state/oxide-charge densities, low gate leakage, small hysteresis, small capacitance equivalent thickness (∼0.94nm), and high dielectric constant (∼24). All these should be attributed to the blocking role of the TaOxNy interlayer against penetration of O into the Ge substrate and interdiffusions of Hf, Ge, and Ta, thus effectively suppressing the formation of unstable low-k GeOx and giving a superior TaOxNy∕Ge interface. Moreover, incorporation of N into both the interlayer and high-k dielectric greatly improves device reliability through the formation of strong N-related bonds.

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Effects of the TaNx interface layer on doped tantalum oxide high-k films

Cited by 13 publications

References 15 publications

Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes

Zirconium-Doped Tantalum Oxide Gate Dielectric Films Integrated with Molybdenum, Molybdenum Nitride, and Tungsten Nitride Gate Electrodes

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

Improved electrical properties of Ge metal-oxide-semiconductor capacitor with HfTa-based gate dielectric by using TaOxNy interlayer

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