On the effects of thickness on adhesion of TiW diffusion barrier coatings in silicon integrated circuits

In this study, the influence of thickness on adhesion properties of titanium-tungsten (TiW) thin films on silicon substrate has been investigated. The adhesion energy release rate of the coatings in the range of 300 to 1300 nm in thickness has been evaluated via nanoindentation-induced blister technique. Cross-sectional electron microscopy studies proved that thin film coating around the indenter impression has been successfully delaminated. The results also revealed that with increasing the thickness of TiW layer, adhesion toughness of the coating decreases. Accordingly, it was suggested that higher surface energy due to the smaller mean grain size and energy dissipation due to decohesion through the coatings corresponds to higher adhesion in coatings with lower thicknesses. It was found that in thinner films decohesion occurs prior to delamination. As a result, the introduced energy from indentation in thinner films will not merely be spent for delamination and deflection of the crack to the surface of coatings impede interfacial crack to grow further.