Morphological evolution of surfaces irradiated by gas cluster ion beams during thin film deposition

Ta2O5 films were deposited with O2 cluster ion beam assisted deposition at various incidence angles θ, between 0° and 80° from surface normal. The surface morphology and cross-sectional images were studied. The film structure was significantly affected by incidence angle. When θ was between 0° and 30°, dense and flat Ta2O5 films were formed. However, in the case of θ between 30° and 60°, ripples were formed on the surface whose wave vector was in the incidence direction and the film surface was rough. On the other hand, when θ was above 70°, the wave vector of the ripple was rotated to perpendicular and surface roughness decreased to the same value at normal incidence. Ripples formed during thin film assisted deposition were similar to surface morphological evolution during the sputtering process.