Work Function Tuning of Fully Silicided NiSi Metal Gates Using a TiN Capping Layer

Sim, J.H.; Wen, Huang-Chun; Lu, Jiong-Ping; Kwong, Dim‐Lee

doi:10.1109/led.2004.833840

Cited by 16 publications

(7 citation statements)

References 14 publications

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“…10,11 In addition, NiSi electrodes have been shown to be thermally and chemically stable on epitaxial Gd 2 O 3 during silicidation. 12 In this letter, we investigate the gate leakage current mechanisms in MOS capacitors with the material combination of epitaxial Gd 2 O 3 high-k dielectrics and FUSI NiSi metal gate electrodes.…”

mentioning

confidence: 99%

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Gottlob

Echtermeyer

Schmidt

et al. 2008

Electrochem. Solid-State Lett.

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We report on leakage current mechanisms in epitaxial gadolinium oxide ͑Gd 2 O 3 ͒ high-k gate dielectrics suitable for low standby power logic applications. The investigated p-type metal-oxide-semiconductor capacitors are gated with complementary-metaloxide-semiconductor-compatible fully silicided nickel silicide electrodes. The Gd 2 O 3 thickness is 5.9 nm corresponding to a capacitance equivalent oxide thickness of 1.8 nm. Poole-Frenkel conduction is identified as the main leakage mechanism with the high-frequency permittivity describing the dielectric response on the carriers. A trap level of ⌽ T = 1.2 eV is extracted. The resulting band diagram strongly suggests hole conduction to be dominant over electron conduction.The semiconductor industry has been driven for the past four decades by a continuous downscaling of transistor dimensions. Today, however, further scaling of the traditional silicon oxide-based gate dielectrics is questionable due to intolerable gate leakage current levels. 1 An era of "material limited device scaling" has therefore been proclaimed in the latest edition of the International Technology Roadmap for Semiconductors ͑ITRS͒. 2 A key task, according to the ITRS, is the identification of transistor gate stacks with high dielectric constant ͑high-k͒ insulators and metal electrodes.Hafnium-based high-k oxides are widely considered as the nextgeneration gate dielectrics. Even though they will be introduced into manufacturing in the near future, it seems likely that another group of high-k materials will be needed to scale complementary-metaloxide-semiconductor ͑CMOS͒ technology to its final limit. The group of rare-earth or lanthanide oxides is rated as the top contender for this "final" high-k material. 3,4 Among them, epitaxially grown oxides have shown high potential. 5-7 A distinct advantage is associated with their deposition method: molecular beam epitaxy ͑MBE͒ potentially allows interface engineering, with abrupt interfaces to the silicon substrate and perfect lattice matching.The large bandgap of gadolinium oxide 5 ͑Gd 2 O 3 ͒ of E g = 5.9 eV is favorable for low leakage currents. A considerable asymmetry of the band offsets to silicon, however, might compromise this advantage, resulting in a clear imbalance toward hole conduction ͓valence band ͑VB͒ offset 4,8,9 of ⌬VB = 2.0-2.2 eV and conduction band ͑CB͒ offset of ⌬CB = 2.6-2.8 eV͔.Fully silicided ͑FUSI͒ nickel silicide ͑NiSi͒ metal gates are receiving increased interest due to their general CMOS process compatibility and their potential for work function tuning. 10,11 In addition, NiSi electrodes have been shown to be thermally and chemically stable on epitaxial Gd 2 O 3 during silicidation. 12 In this letter, we investigate the gate leakage current mechanisms in MOS capacitors with the material combination of epitaxial Gd 2 O 3 high-k dielectrics and FUSI NiSi metal gate electrodes. While ultra thin layers with a capacitance equivalent thickness ͑CET͒ of 0.86 nm and potential for high-performance logic applications have been pre...

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mentioning

confidence: 99%

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Gottlob

Echtermeyer

Schmidt

et al. 2008

Electrochem. Solid-State Lett.

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“…We have reported that the TiN capping layer has small impact on the work function of As-doped FUSI devices in NiSi, but has significant impact on B-doped FUSI devices due to the TiN interface acting as a sink for dopants, resulting in a 0.13 eV reduction of the effective work function. 12 The fixed oxide charges and interface states density are not affected as a result of …”

Section: Resultsmentioning

confidence: 99%

“…The role of the TiN-capping layer on dopant distribution on As-doped samples is also different from that observed in B-doped samples, and the trend in NiSi FUSI gates. 12 Explanation of the mechanism for dopant tuning effect is still uncertain; however, this observation suggests that dopants still play a factor in the work function change of CoSi 2 , and the differences in effective work function modulation is highly dependent on the bulk silicide material.…”

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confidence: 99%

Investigation of Dopant Effects in CoSi2 and NiSi Fully Silicided Metal Gates

Wen

Liu

Sim

et al. 2005

Electrochemical and Solid-State Letters

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CoSi 2 full silicidation ͑FUSI͒ of doped poly-Si metal gates was investigated to further the understanding of the modulation of effective work function from dopants in CoSi 2 and NiSi FUSI gated metal oxide semiconductor devices. By using a TiN-capping layer to manipulate the dopant distribution, dopants have been confirmed to be effective in tuning the work function for both CoSi 2 and NiSi. However, from the drastic reduction of the As tuning effect in CoSi 2 , we understand that the amount of effective work function tuning is not only directly dependent on the interfacial dopant concentration, but the mechanism of dopant tuning the work function is strongly dependent of the bulk material type.Full silicidation ͑FUSI͒ of doped polysilicon gate has recently been proposed with a process compatible with present complementary metal oxide semiconductor ͑CMOS͒ technology to form tunable work function metal gates. NiSi, TiSi, and HfSi FUSI gates have been shown with tunable effective work function from variation of the type and concentration of dopants in poly-Si. As, B, P, and Sb dopants were found to be capable of setting threshold voltages suitable for n-and p-channel metal oxide semiconductor ͑NMOS and PMOS͒ transistors. 1-10 The mechanism of dopant incorporation on tuning the effective work function has not been thoroughly understood; possibilities of this change include metal/dielectric interface dipole formation, or interfacial grain structure change, etc. To enhance our understanding on this issue, CoSi 2 FUSI gates has been formed in comparison to the commonly researched NiSi FUSI gates with identical dopant incorporation processes. Undoped CoSi 2 FUSI gates also exhibits an effective work function near midgap. 2 Due to agglomeration effects and the reaction kinetics of CoSi 2 , some concerns need to be addressed for integration in the gate-last process when fully siliciding small poly-Si gate dimensions. 10 Other reports have suggested that high-temperature processes cause metal diffusion of Co toward the gate dielectric. 11 However, CoSi 2 is an attractive candidate for the FUSI gate due to its low resistivity and excellent thermal stability which is capable of withstanding the high S/D annealing temperature. In this work, a TiN-capping layer has also been added on the gate material to help identify the relationship between the distribution of As and B dopants and the work function. A distinct difference in the effect of dopant on work function tuning in CoSi 2 compared to that in NiSi has been observed. The role of the TiN-capping layer on dopant distribution on As-doped samples is also different from that observed in B-doped samples, and the trend in NiSi FUSI gates. 12 Explanation of the mechanism for dopant tuning effect is still uncertain; however, this observation suggests that dopants still play a factor in the work function change of CoSi 2 , and the differences in effective work function modulation is highly dependent on the bulk silicide material. ExperimentalCapacitors with 2.5 nm thick gate oxid...

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“…Thus it is presumed that under the BTS conditions of 200 C and AE2 V the SiO 2 grown in dry oxygen ambient is a good diffusion barrier to Ni atoms. [33][34][35][36] The Si interface quality of the NiSi gate was analyzed from the interface state densities. As shown in Fig.…”

Section: Electrical Behaviormentioning

confidence: 99%

Investigation of NiSi Fully-Silicided Gate on SiO₂ and HfO₂ for Applications in Metal–Oxide–Semiconductor Field-Effect Transistors

Huang¹,

Tsui²

2006

Jpn. J. Appl. Phys.

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Effective work function modulation (È m,eff ) and the thermal/electrical stability of NiSi fully-silicided (FUSI) gates on SiO 2 and HfO 2 are investigated. A new method, implant-to-silicide, differing from the pre-doped method, is used to realize È m,eff adjustments. The È m,eff of NiSi FUSI gates on SiO 2 can be tuned by incorporating BF 2 þ or P þ dopants after silicidation. Nevertheless, the Fermi-pinning effect was observed in the NiSi/HfO 2 gate which limits the È m,eff adjustment. A thin SiO 2 interfacial layer can reduce the Fermi-pinning effect. A NiSi FUSI gate on SiO 2 is thermally stable up to 600 C. The thermal stress and impurity diffusion after a prolonged 600 C annealing degraded the oxide integration. The temperature of the post-silicidation process should be as low as possible to lessen the thermal stress and impurity diffusion.

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Work Function Tuning of Fully Silicided NiSi Metal Gates Using a TiN Capping Layer

Cited by 16 publications

References 14 publications

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Investigation of Dopant Effects in CoSi2 and NiSi Fully Silicided Metal Gates

Investigation of NiSi Fully-Silicided Gate on SiO₂ and HfO₂ for Applications in Metal–Oxide–Semiconductor Field-Effect Transistors

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Work Function Tuning of Fully Silicided NiSi Metal Gates Using a TiN Capping Layer

Cited by 16 publications

References 14 publications

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Leakage Current Mechanisms in Epitaxial Gd[sub 2]O[sub 3] High-k Gate Dielectrics

Investigation of Dopant Effects in CoSi2 and NiSi Fully Silicided Metal Gates

Investigation of NiSi Fully-Silicided Gate on SiO2 and HfO2 for Applications in Metal–Oxide–Semiconductor Field-Effect Transistors

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Investigation of NiSi Fully-Silicided Gate on SiO₂ and HfO₂ for Applications in Metal–Oxide–Semiconductor Field-Effect Transistors