engleski

Surface features of the sputter-deposited tungsten films

Different phases of tungsten were produced by magnetron sputtering either as a single layer or the multilayers. A stable alpha-W phase (b.c.c. structure) is predominantly obtained at low working gas pressure, metastable beta-W phase (A15 structure) is obtained at increased working gas pressure, and amorphous-like tungsten (a-W) is obtained at even higher pressure. The occurence of various phases is related to the oxygen content and built-in stresses in the prepared thin films. We varied the pressure during the preparation to produce tungsten films composed of stacked layers of different tungsten phases. The surface roughness/ topography of such films was examined by the AFM, and subsurface layer structure by the SAXS and X-ray reflectivity measurements. Tungsten multilayers were prepared by sequential deposition of tungsten sputtered under different conditions in a cylindrical magnetron device. Working gas pressure was varied in the range of 0, 7 - 3, 5 Pa, and circular substrates (monocrystalline silicon, borosilicate glass) were cooled in contact with the LN2 container. The deposition rate was about 0, 17 nm/s, and the total film thickness range was 50-200 nm. AFM study revealed complex dependence of surface features on the preparation conditions. SAXS data show presence of surface/ subsurface nanoparticles whose size depends on the top layer phase. Finally, the X-ray reflectivity suggests that the surface roughness is increasing with overall thickness, with Bragg peaks missing in most of the multilayered samples.

tungsten films; surface features; magnetron sputtering

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