XRD line profile analysis of tungsten thin films

Thin tungsten films were deposited onto glass substrates by DC magnetron sputtering at different substrate temperatures (77, 293, 523 K) and at different working-gas pressures in the range 0.7-2.8 Pa. Samples were characterized by X-ray diffraction (XRD) and subsequently refined with the Rietveld method. Using this method the diffracting domain size and the root mean square (r.m.s.) microstrain have been determined. The dependence of structural parameters on deposition conditions was investigated as well. It was found that residual stress and lattice parameter are correlated. We suggest that the observed increase of lattice parameters in comparison to the bulk values occurred due to the substitutional incorporation of Ar atoms, and W atoms residing in auto-interstitial positions. The high values of r.m.s. microstrain, 0.251% for β-W and 0.345% for α-W, on average, confirmed this feature. The α phase is predominantly found at low Ar pressure, while an increase in the latter causes the increase of the fraction of the β phase. The substrate temperature also exhibits an impact on the phase composition. The size-microstrain analysis showed larger domain sizes and smaller r.m.s. microstrain of the β phase compared to the α phase. The ratio of average volume-weighted domain sizes of α and β tungsten, Dα-211/Dβ-200, is correlated with the ratio of relative fractions of α and β, Wα/Wβ.