Interactions between silica xerogel and tantalum

Abstract

Thin films of tantalum, a potential diffusion barrier, were deposited on xerogel films. The structures were annealed at different temperatures and in different ambient environments and analyzed using Rutherford backscattering spectrometry (RBS), optical microscopy, and the Scotch™ tape test, in order to assess the extent of interaction with the xerogel film. When annealed in nitrogen with at most trace amounts of oxygen (equivalent to 10−7–10−6 Torr vacuum), RBS analysis for Ta does not show diffusion of this metal through the xerogel when annealed up to 450 °C. However, the presence of larger concentrations of oxygen in the annealing environment was found to cause oxidation of Ta thin films, and this leads to Ta film buckling and diffusion-like RBS spectra. Ta does not buckle nor diffuse into the xerogel film at temperatures up to 640 °C when the metal is capped with a Si3N4 layer. Analysis of the samples by RBS microbeam shows that the low energy Ta tail originates from only a portion of the sample surface, the shape of which resembles Ta buckles. RBS spectra collected from other parts of the samples show no Ta diffusion into xerogel. Adhesion of Ta to porous xerogel is reduced compared to SiO2, due to the reduced contact area at the interface between the materials.