  We report on the transition between two regimes from several-atom clusters to
much larger nanoparticles in Ar magnetron sputter deposition of WSi2, and the
effect of nanoparticles on the properties of amorphous thin films and
multilayers. Sputter deposition of thin films is monitored by in situ x-ray
scattering, including x-ray reflectivity and grazing incidence small angle
x-ray scattering. The results show an abrupt transition at an Ar background
pressure Pc; the transition is associated with the threshold for energetic
particle thermalization, which is known to scale as the product of the Ar
pressure and the working distance between the magnetron source and the
substrate surface. Below Pc smooth films are produced, while above Pc roughness
increases abruptly, consistent with a model in which particles aggregate in the
deposition flux before reaching the growth surface. The results from WSi2 films
are correlated with in situ measurement of stress in WSi2/Si multilayers, which
exhibits a corresponding transition from compressive to tensile stress at Pc.
The tensile stress is attributed to coalescence of nanoparticles and the
elimination of nano-voids.
