Phase, grain structure, stress, and resistivity of sputter-deposited tungsten films

Choi, Dooho; Wang, Bincheng; Chung, Suk Jae; Li, Xuan; Darbal, Amith; Wise, Adam; Nuhfer, Noel T.; Barmak, K.; Warren, Andrew P.; Coffey, Kevin R.; Toney, Michael F.

doi:10.1116/1.3622619

Cited by 98 publications

(57 citation statements)

References 38 publications

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“…Sputtering power was fixed at 250 W. The deposition rate at this power was 1.4 Å/sec. Following deposition, the films were annealed at 850°C for two hours in Ar + 4% H 2 ambient19.…”

Section: Methodsmentioning

confidence: 99%

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Crystallographic anisotropy of the resistivity size effect in single crystal tungsten nanowires

Choi

Moneck

et al. 2013

Sci Rep

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This work demonstrates an anisotropic increase in resistivity with decreasing width in single crystal tungsten (W) nanowires having a height of 21 nm. Nanowire-widths were in the range of 15–451 nm, with the anisotropy observed for widths below 50 nm. The longitudinal directions of the nanowires coincided with the <100>, <110> and <111> orientations of the body centered cubic phase of W. The resistivity increase was observed to be minimized for the <111>-oriented single crystal nanowires, exhibiting a factor of two lower increase in resistivity at a width of ~15 nm, relative to the thin film resistivity (i.e., an infinitely wide wire). The observed anisotropy is attributed to crystallographic anisotropy of the Fermi velocity and the resultant anisotropy of the electron mean free path in W, and underscores the critical role of crystallographic orientation in nanoscale metallic conduction.

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“…Sputtering power was fixed at 250 W. The deposition rate at this power was 1.4 Å/sec. Following deposition, the films were annealed at 850°C for two hours in Ar + 4% H 2 ambient19.…”

Section: Methodsmentioning

confidence: 99%

“…S4] Film thicknesses were measured by X-ray reflectivity. Film resistivities were measured using the van der Pauw method121920.…”

Section: Methodsmentioning

confidence: 99%

Crystallographic anisotropy of the resistivity size effect in single crystal tungsten nanowires

Choi

Moneck

et al. 2013

Sci Rep

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“…1(j)) corresponds to the structural transition 32,33 of W between the amorphous phase and the crystalline bcc phase 9,16 . When the underlayer thickness is larger than d C , the SMR ( Fig.…”

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confidence: 99%

Correlation between the spin Hall angle and the structural phases of early 5d transition metals

Ohkubo

Mitani

et al. 2015

Applied Physics Letters

114

101

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We have studied the relationship between the structure and the spin Hall angle of the early 5d transition metals in X/CoFeB/MgO (X=Hf, Ta, W, Re) heterostructures. Spin Hall magnetoresistance (SMR) is used to characterize the spin Hall angle of the heavy metals.Transmission electron microscopy images show that all underlayers are amorphous-like when their thicknesses are small, however, crystalline phases emerge as the thickness is increased for certain elements. We find that the heavy metal layer thickness dependence of the SMR reflects these changes in structure. The spin Hall angle largest | SH | of Hf, Ta, W and Re (~0.11, 0.10, 0.23 and 0.07, respectively) is found when the dominant phase is amorphous-like. We find that the amorphous-like phase not only possesses large resistivity but also exhibits sizeable spin Hall conductivity, which both contribute to the emergence of the large spin Hall angle.*Email: hayashi.masamitsu@nims.go.jp 2 Heavy metals with strong spin orbit coupling are attracting great interest recently 1-3 as such elements can generate significant amount of spin current via the spin Hall effect 4 . In heterostructures that contain a heavy metal layer and a magnetic layer, the spin current generated within the heavy metal layer can diffuse into the magnetic layer and trigger current induced magnetization switching 2, 5 and domain wall motion [6][7][8][9] . Key to the development of technologies that make use of such current induced effects is the large spin Hall angle of the heavy metal layer 10, 11 .The spin Hall angle, which defines the amount of spin current generated within the layer, is known to be element specific. First principle calculations 12 show that the spin Hall angle of the transition metals depends on the electron filling of the d-orbitals if the mechanism behind it is due to an intrinsic origin (i.e., band structure related) 13 . In addition, the spin Hall effect can originate from spin dependent scattering of electrons, commonly referred to as an extrinsic effect 14,15 . Recently large spin Hall angle has been reported for the heavy transition metals 2,[16][17][18][19] and/or its alloy 20 . The large spin Hall angle for the early 5d transition metals (e.g. Ta and W) has been associated 2,16,21 with the appearance of the distorted tetragonal phase, often known as the A-15 -phase [22][23][24][25] . In order to develop viable devices utilizing the spin Hall effect, it is thus essential to understand how the structure of the heavy metal influences, if any, the size of the spin Hall angle. Identifying the relationship between the structural phase of the heavy metal layer and its spin Hall angle, however, requires thorough and systematic studies.Here we show studies on the spin Hall angle of the early 5d transition metals (Hf, Ta, W, Re) in magnetic heterostructures. Spin Hall magnetoresistance (SMR) 18,[26][27][28] and transmission electron microscopy (TEM) are used to evaluate, respectively, the spin transport properties and the structural phase of the films. We find that t...

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“…However, for the critical dimension lower than tens of nanometer, it is reported that the resistivity of Cu is increased sharply due to the size effect related to the long electron mean free path (EMFP) of 39 nm in addition to the decreased reliability of Cu as the device operating temperatures and current densities are increased . As one of possible replacements of Cu, W, which is widely used as an interconnect layer, a diffusion barrier of semiconductor integrated circuits, a gate material for 3D NAND flash memory, etc is investigated for the next generation interconnection material because of the smaller EMFP of 19 nm and a high melting point (3,695 K compared with Cu of 1,357 K) . Since W has a smaller EMFP than Cu, it is expected to reduce the size effect of surface scattering and grain boundary scattering as it goes to nanometer dimension …”

Section: Introductionmentioning

confidence: 99%

“…As one of possible replacements of Cu, W, which is widely used as an interconnect layer, a diffusion barrier of semiconductor integrated circuits, a gate material for 3D NAND flash memory, etc is investigated for the next generation interconnection material because of the smaller EMFP of 19 nm and a high melting point (3,695 K compared with Cu of 1,357 K) . Since W has a smaller EMFP than Cu, it is expected to reduce the size effect of surface scattering and grain boundary scattering as it goes to nanometer dimension …”

Section: Introductionmentioning

confidence: 99%

Anisotropic atomic layer etching of W using fluorine radicals/oxygen ion beam

Kim

Lee

et al. 2019

Plasma Processes & Polymers

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Atomic layer etching (ALE) has advantages such as precise thickness control, high etch selectivity, and no‐increase in surface roughness which can be applied to sub 10 nm semiconductor device fabrication. In this study, anisotropic ALE of tungsten (W), which is used as an interconnect layer and gate material of semiconductor devices, was investigated by sequentially exposing to F radicals by NF3 plasma to form a WFy layer and following exposure to an oxygen ion beam to remove the WFy layer by forming volatile WOxFy at room temperature. A wide ALE window of F radical adsorption time of ( ≥ 10 s/cycle) and Ox+ ion desorption time of (10 ≤ t ≤ 50 s/cycle at + 44–51 eV of Ox+ ion energy) could be identified, and at the ALE conditions, a precise etch rate of ~2.6 Å/cycle was obtained while increasing the W etch depth linearly with increasing the number of etch cycles. At the optimized W ALE conditions, the W surface roughness after the W ALE was similar to the as‐received W and the etch selectivity over SiO2 was close to infinite. However, after the W ALE, ~ 10% F diffused into W was observed on the etched W surface, and which could be removed by a following process.

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Phase, grain structure, stress, and resistivity of sputter-deposited tungsten films

Cited by 98 publications

References 38 publications

Crystallographic anisotropy of the resistivity size effect in single crystal tungsten nanowires

Crystallographic anisotropy of the resistivity size effect in single crystal tungsten nanowires

Correlation between the spin Hall angle and the structural phases of early 5d transition metals

Anisotropic atomic layer etching of W using fluorine radicals/oxygen ion beam

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