Abstract
A technique to deposit 5-20 nm thick β-phase W using a 2-second periodic pulse of 1 sccm-N2 gas on Si(001) and SiN(5 nm)/Si(001) substrates is reported. Resistivity, X-ray photoelectron spectroscopy and X-ray reflectivity were utilized to determine phase, bonding and thickness, respectively. X-ray diffraction patterns were utilized to determine the crystal structure, lattice constant and crystal size using the LeBail method. The flow rate of Nitrogen gas (continuous vs. pulsing) had significant impact upon the crystallinity and formation of β-phase W.
Highlights
Thin β phase W films exhibit a giant spin Hall effect which can be integrated into a non-volatile spin logic device to interact with an adjacent magnetic layer.[1,2]
Introducing O2 during the deposition has been shown to stabilize β tungsten enabling the growth of thicker films, but high concentrations of it forms an amorphous-like phase.[6,7,8,9,10,11,12]
The lattice constants of the β-phase W films are in agreement with previous β phase films grown with and without O2.15–19 the films are less resistive than previous β-W films which are typically around ∼200 μΩ cm, which maybe beneficial for producing devices with lower resistances than films grown with O2.5,6 The α phase-W films have two peaks around W(110) these peaks were not commented for in earlier studies and fit well with a W5Si3
Summary
Thin β phase W films exhibit a giant spin Hall effect which can be integrated into a non-volatile spin logic device to interact with an adjacent magnetic layer.[1,2] Tungsten films thicker than 5 nm naturally transform to bulk α phase, making it challenging to produce β-W thick enough for device fabrication under large scale manufacturing conditions.[3,4] For example, the W film must be thick enough to survive the etch of the magnetic films and be under the spin diffusion length for effective device functioning which puts the desirable thickness in the 10-20 nm range.[5]. This creates a need to form 10-20 nm thick β-W films without the assistance of O2 gas flow and find the optimum conditions for N2 flow during tungsten deposition
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