Role of nitrogen partial pressure, deposition rate and annealing on stability of β-W phase

The discovery of a large Spin Hall angle in β-W makes it a potential spin–orbit torque (SOT) material for its incorporation in SOT-MRAM devices. The β-W is a metastable phase that transforms to a stable α-W phase above a certain film thickness and temperature. In this study, we report the growth of...

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Bibliographic Details
Published in:Applied physics. A, Materials science & processing Materials science & processing, 2023-05, Vol.129 (5), Article 312
Main Authors: Singh, Hardepinder, Gupta, Mukul, Gupta, Pooja, Penacchio, Rafaela F. S., Morelhao, Sergio L., Kumar, Hardeep
Format: Article
Language:English
Subjects:
Annealing
Applied physics
Characterization and Evaluation of Materials
Condensed Matter Physics
Deposition
Film thickness
Machines
Manufacturing
Materials science
Metastable phases
Nanotechnology
Nitrogen
Optical and Electronic Materials
Partial pressure
Physics
Physics and Astronomy
Processes
Sputtering
Surface roughness
Surfaces and Interfaces
Thermal stability
Thick films
Thin Films
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Summary:The discovery of a large Spin Hall angle in β-W makes it a potential spin–orbit torque (SOT) material for its incorporation in SOT-MRAM devices. The β-W is a metastable phase that transforms to a stable α-W phase above a certain film thickness and temperature. In this study, we report the growth of 50–70 nm thick W films prepared by nitrogen reactive sputtering at various nitrogen partial pressures in the range of 0–10% and two sputtering powers (P W ) of 30  W and 100  W . To study the thermal stability of thin films, some of the films are vacuum annealed at 200–400 °C. W films are characterized by X-ray diffraction, X-ray reflectivity and electrical resistivity measurements. The deposition rate, W film density and surface roughness tends to decrease at both the powers with an increase in nitrogen partial pressure ( R N 2 ) from 0 to 10%. XRD measurements show that at R N 2  = 0% the tungsten film contains mixed/pure α-W phase at 30  W /100  W , indicating the dependence of W-phase formation on the deposition power (rate). The R N 2  = 2% stabilizes the β-W phase at P W  = 30  W , however, higher R N 2 of 3% is required to stabilize β-W at P W  = 100  W . The α-W films deposited at R N 2  = 0% and 100 W are found to be stable upto 400 °C indicating the thermal stability of α-W phase. The 70 nm thick β-W films deposited at R N 2  = 3% and P W  = 100  W are thermally stable upto 300 °C as a majority phase with volume fraction (f β ) ~ 80%, and even at 400 °C a complete transformation to pure α-W phase is not observed.
ISSN:0947-8396
1432-0630
DOI:10.1007/s00339-023-06552-x