Bilayer metal gate electrodes with tunable work function: Mechanism and proposed model

Lu, Ching-Huang; Wong, Geoffrey B.; Birringer, Ryan P.; Dauskardt, Reinhold H.; Deal, Michael D.; Clemens, Bruce M.; Nishi, Yoshio

doi:10.1063/1.3326237

Cited by 19 publications

(15 citation statements)

References 10 publications

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“…When a polar dipole 18 forms at the TaN/n-Ge interface, the potential of the polar dipole di pole at the TaN/n-Ge interface must be considered in Eq. (3) 19,20 Carrier redistribution 19 and metal interdiffusion 20 have been proposed to explain the EWF modulation of the bi-layer metal stacks.…”

Section: Resultsmentioning

confidence: 99%

Ohmic Contact Formation of Sputtered TaN on n-Type Ge with Lower Specific Contact Resistivity

Zheng

Wang

Huang

et al. 2012

ECS J. Solid State Sci. Technol.

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Modulation of the effective Schottky barrier height of Al/TaN/n-Ge Schottky junctions by varying TaN thickness and ohmic contact formation on n-type Ge substrates is reported. A specific contact resistivity of 2.7×10 −5 · cm 2 is achieved for a Al/TaN(400/15 nm) layer on moderately doped n-type Ge, which is smaller by two orders of magnitude compared with that of an Al layer (1.2×10 −3 · cm 2 ) in direct contact with the same wafer. Sputtering a thin TaN layer on n-Ge effectively improves the contact resistivity of a metal/n-Ge contact by significantly reducing the effective Schottky barrier height, facilitating the fabrication of high-performance Ge devices. Germanium (Ge) is considered as one of the most promising materials due to its high electron and hole mobilities in electronic and photonic device applications. The metal-oxide-semiconductor fieldeffect transistor (MOSFET) with Ge channel facilitates the fabrication of next generation high-mobility devices. 1,2 Despite significant progress in the p-channel Ge MOSFET, the n-channel Ge MOSFET still suffers from serious challenges. 3,4 Non-ohmic or high-resistivity contacts for metal/n-Ge are roadblocks for Ge-based complementary metal-oxide semiconductor technology. 5 Low-resistivity contacts of metal/n-Ge are difficult to achieve due to the high Schottky barrier height (SBH) caused by the strong Fermi-level pinning (FLP) and low activation limits as well as the concentration-enhanced diffusion of n-type dopants in Ge. 6 Strong FLP at the charge neutrality level close to the valence band edge of Ge results in a high electron SBH on n-type Ge, independent on the work function of the metal and presents a high contact resistance. [6][7][8] Several methods have been proposed to alleviate the FLP effect and obtain the ohmic contact for n-Ge such as using sulfur-passivated metal germanide 9 or germanium nitridation 10 or inserting an ultrathin insulator interlayer (e.g., Al 2 O 3 , 11 SiN, 12 GeO x or AlO x , 13 and TiO 2 , 14 among others). Although an ultra-thin insulator interlayer can decrease the effective SBH for metal/insulator/n-Ge, the thickness of the insulator must be strictly maintained in the range of 0 ∼ 8 nm for TiO 2 , 14 and in the range of 0 ∼ 1 nm for the other insulators such as Al 2 O 3 , etc. 11 However, a specific contact resistivity (ρ c ) of 1×10 −2 · cm 2 is too high 15 for n+ source/drain contacts in Ge nMOSFET. Recently, an ohmic contact formation was obtained by directly depositing TiN on an n-Ge wafer, but no ρ c was reported. 16 In the present paper, we prepared Al/TaN/n-Ge Schottky junctions to investigate SBH modulation by varying the TaN thickness. Given that the metallic property of TaN does not introduce a significant tunneling resistance, TaN thickness can be varied in a wide range without increasing the tunneling resistance. Thus, a low ρ c of TaN directly sputtered on n-type Ge is achieved. ExperimentalTo study SBH modulations by varying TaN thickness, Schottky diodes were fabricated using n-type Ge(100) substrates with resisti...

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Section: Resultsmentioning

confidence: 99%

Ohmic Contact Formation of Sputtered TaN on n-Type Ge with Lower Specific Contact Resistivity

Zheng

Wang

Huang

et al. 2012

ECS J. Solid State Sci. Technol.

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show abstract

“…[14][15][16][17] or on Hf-based dielectrics (Refs. [18][19][20][21]. Due to significant thermal stability concerns, 22 metal alloys are usually not considered as candidates for high-temperature (∼1000 • C) process flows (the gate-first approach), where alternatives such as ultrathin dielectric capping layers 23,24 and/or refractory metal nitrides 25,26 are employed for EWF tuning.…”

Section: Introductionmentioning

confidence: 99%

Composition and crystallography dependence of the work function: Experiment and calculations of Pt-Al alloys

et al. 2012

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The work function (WF) of several phases of Pt-Al alloys is investigated. A first-principles study is performed to determine the dependence of the vacuum WF (VWF) on the phase, crystallographic orientation, and atomic termination. In parallel, the effective WF (EWF) of these alloys is experimentally measured using metal-oxide semiconductor devices. A detailed microstructural characterization based on x-ray diffraction and transmission electron microscopy allows the comparison between experiment and calculations. It is found that despite the formation of a complex microstructure, the calculated VWF values are in good agreement with the experimental EWF values. The possible VWF range for each phase has a relatively small (∼0.5 eV) span for different orientations and atomic terminations, and it is found that Pt atoms in the terminating plane are more dominant than Al atoms. The results demonstrate that first-principles calculations of the WF of alloys can be used to successfully predict the experimental WF and that knowledge of the microstructure is important for the accuracy of these calculations.

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“…Reliability issues related to fracture in thin-film structures have complicated integration of new materials, such as low-k dielectric films, into complimentary metal-oxide semiconductor ͑CMOS͒ devices at previous technology nodes. 5 In a previous publication, work function tuning behavior was demonstrated for Ti/Pt and Pt/Ti bilayers on both SiO 2 and HfO 2 dielectrics. 9 A variety of different metal bilayer systems have been investigated for their work function tuning characteristics, and one proposed mechanism for this tuning behavior is metal interdiffusion between the two layers.…”

Section: Introductionmentioning

confidence: 97%

Bilayer metal gate electrodes with tunable work function: Adhesion and interface characterization

Birringer

Deal

et al. 2010

Journal of Applied Physics

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Fabrication of advanced La-incorporated Hf-silicate gate dielectrics using physical-vapor-deposition-based in situ method and its effective work function modulation of metal/high-k stacks Effective work function modulation of TaN metal gate on Hf O 2 after postmetallization annealing Appl. Phys. Lett. 91, 112105 (2007); 10.1063/1.2783472 Measurements of metal gate effective work function by x-ray photoelectron spectroscopyThe dependence of Pt film thickness and forming gas annealing on the interface fracture properties and interface composition of Ti/Pt bilayer gate electrode films on a HfO 2 gate dielectric are reported. These fracture properties and composition results are directly compared to work function tuning behavior witnessed in metal-oxide semiconductor ͑MOS͒ capacitors fabricated from the same films. The interface fracture energy of the metal bilayer/gate dielectric interface is strongly dependent on thickness after a forming gas anneal but shows no thickness dependence in the as-deposited case. The flat-band voltage increases abruptly and then remains constant as the thickness of the Pt film is increased in the as-deposited case but varies gradually with increasing Pt thickness after a forming gas anneal. Angle-resolved x-ray photoelectron spectroscopy characterization of the resulting fracture surfaces confirms that Ti diffusion to the metal bilayer/gate dielectric interface is responsible for these effects.

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Bilayer metal gate electrodes with tunable work function: Mechanism and proposed model

Cited by 19 publications

References 10 publications

Ohmic Contact Formation of Sputtered TaN on n-Type Ge with Lower Specific Contact Resistivity

Ohmic Contact Formation of Sputtered TaN on n-Type Ge with Lower Specific Contact Resistivity

Composition and crystallography dependence of the work function: Experiment and calculations of Pt-Al alloys

Bilayer metal gate electrodes with tunable work function: Adhesion and interface characterization

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