A nanometer scale surface morphology study of W thin films

Microstructure of tungsten thin films deposited by RF-sputtering is studied as a function of their thicknesses. These films have been deposited on (100) oriented single crystal Si substrate and Si substrate covered by a 100-nm-thick Ti layer. The crystalline structure is studied by X-ray Diffraction (XRD) and Grazing Incidence XRD (GIXRD). The surface and the cross-section morphology are observed by high resolution Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). XRD patterns exhibit peaks corresponding to pure W phase. GIXRD analysis shows that the more the thickness increases, the more the film is oriented along the [110] direction. AFM observations show that films exhibit a particular morphology constituted of “piles of platelets” oriented perpendicularly to the wafer surface. These “piles of platelets” are in plane randomly oriented and are sometime observed upon all the thicknesses of the layer. This particular morphology is observed whatever the substrate is, and is explained by thin layer growth theories.