Interface evolution in a W/Si multilayer after rapid thermal annealing studied by X-ray reflectivity and diffuse scattering

An interface study of the effect of rapid thermal annealing (RTA) in the temperature range 523-1273 K for 5-40 s on a nominally [(50 Angstrom Si/10 Angstrom W) x 9] amorphous multilayer (ML) deposited on an Si(100) wafer was performed by X-ray reflectivity and diffuse-scattering measurements at grazing incidence. The results of the X-ray reflectivity and diffuse-scattering measurements were evaluated by Fresnel optical computational code and within the distorted-wave Born approximation, respectively. Up to the 773 K/5 s annealing step, the r.m.s. interface roughness decreases by 30%, which brings about a reflectivity increase of 20% on the first Bragg maximum. There is a small overall increase of the r.m.s. interface roughness across the ML in the as-deposited state and the interface profiles are highly correlated. From the very beginning of RTA, the fractal interface behaviour is gradually lost and the lateral correlation length increases, this process being accompanied by a decrease of the interface conformality. This tendency continues during the 773 K/20 s annealing; however, the r.m.s. roughness evolution is reversed. During the 1023 K/5 s annealing, the interfaces are no longer 'seen' by the X-rays and during the 1273 K/5 s annealing, a total collapse of-the ML structure takes place.