Epitaxial growth of tungsten layers on MgO(001)

Abstract

Smooth single crystal W(001) layers were grown on MgO(001) substrates by magnetron sputtering at 900 °C. X-ray diffraction ω–2θ scans, ω-rocking curves, pole figures, and reciprocal space maps indicate a 45°-rotated epitaxial relationship: (001)W‖(001)MgO and [010]W‖[110]MgO, and a relaxed lattice constant of 3.167 ± 0.001 nm. A residual in-plane biaxial compressive strain is primarily attributed to differential thermal contraction after growth and decreases from −0.012 ± 0.001 to −0.001 ± 0.001 with increasing layer thickness d = 4.8–390 nm, suggesting relaxation during cooling by misfit dislocation growth through threading dislocation glide. The in-plane x-ray coherence length increases from 3.4 to 33.6 nm for d = 4.8–390 nm, while the out-of-plane x-ray coherence length is identical to the layer thickness for d ≤ 20 nm, but is smaller than d for d ≥ 49.7 nm, indicating local strain variations along the film growth direction. X-ray reflectivity analyses indicate that the root-mean-square surface roughness increases from 0.50 ± 0.05 to 0.95 ± 0.05 nm for d = 4.8–19.9 nm, suggesting a roughness exponent of 0.38, but remains relatively constant for d > 20 nm with a roughness of 1.00 ± 0.05 nm at d = 47.9 nm.

The electrical resistivity of rough thin films: A model based on electron reflection at discrete step edges

“…62,64, and 65 for epitaxial ScN(001), Sc 1-x Al x N(001), and W(001) layers, confirming that there is no significant change in the structural quality of the samples during annealing for d 20 nm, as previously reported in Ref. 62. The surface morphology is quantitatively analyzed by extracting the height-height correlation function H(r) from atomic force micrographs (AFM) following the procedure described in Refs.…”

“…(14) for the thin film resistivity as a function of the root mean square surface roughness x and the lateral correlation length n of the surface morphology. We have chosen as an experimental model system epitaxial W(001) films, primarily because the high melting point facilitates epitaxial (single-crystal) growth of thin continuous layers on insulating substrates down to thicknesses of 4 nm, 62,63 and we have previously developed in situ annealing procedures that allow variations in the surface roughness with negligible changes in the crystalline quality. 39 4.5-52 nm thick W(001) films were deposited on MgO(001) substrates in a three chamber ultrahigh vacuum DC magnetron sputter deposition system with a base pressure <10 À9 Torr following the procedure in Ref.…”

“…39 4.5-52 nm thick W(001) films were deposited on MgO(001) substrates in a three chamber ultrahigh vacuum DC magnetron sputter deposition system with a base pressure <10 À9 Torr following the procedure in Ref. 62. After deposition, they were transported without breaking vacuum to the analysis chamber maintained at a base pressure of 10 À9 Torr for in situ resistivity measurements by a linear 4-point probe, as described in Ref.…”

Surface roughness dependence of the electrical resistivity of W(001) layers

“…The 4-390 nm thick W films were deposited on MgO(001) substrates in a three chamber ultrahigh vacuum DC magnetron sputter deposition system with a base pressure <10 À9 Torr following the procedure in Ref. 49. After deposition, they were transported without breaking vacuum to the analysis chamber maintained at a base pressure of 10 À9 Torr for in situ resistivity measurements using a linear 4-point probe, as described in Ref.…”

“…The layer thickness and surface roughness were determined from x-ray reflectivity (XRR) analyses for samples thinner than 50 nm according to the procedure described in Ref. 49. The surface morphology of 4-50 nm thick samples was also examined using a Digital Instruments Multimode III-a atomic force microscope (AFM).…”