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X-ray study of structure and morphology of magnetron sputtered W thin films

Tungsten (W) thin films were prepared by magnetron sputtering on Si substrates kept at room temperature. The film structure and morphology as a function of two magnetron deposition parameters - Ar pressure and W sputtering power - were investigated by using graz ing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR) and grazing incidence small angle X-ray scattering (GISAXS). The film thickness, density and surface roughness values have been obtained from the XRR measurements, while GISAXS revealed the nano-scale density variation in the films. We found that depositions at low Ar pressure (< 5 mtorr) and with high sputtering power (> 20 watt) result in compact and stable alpha-phase tungsten films with a relatively smooth surface. On the other hand, deposition at high Ar pressure and/or with low sputter power results in nanostructured metastable beta-phase tungsten films, which might exhibit up to 50% reduced density compared to the tungsten bulk density. The density reduction is attributed to the columnar morphology which consists ofparallel rod-like regions of p-W which are surrounded by voids and directed toward the surface. These results are useful in optimizing the process parameters for the production of multilayer X-ray mirrors based on W as material for the diffracting layers.

Tungsten (W) thin films; magnetron sputtering; GIXRD; XRR; GISAXS; X-ray

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