Thickness dependency of adhesion properties of TiW thin films

The interfacial adhesion properties of Titanium-Tungsten (TiW) thin films with thickness in the range of 300 to 1300 nm to single crystal silicon have been studied by means of nano-indentation technique. The adhesion energy release rate of the coatings has been evaluated by using nanoindentation-induced blister technique. The radius of the blister around the indenter impression which was related to the delaminated film increased significantly with increasing the thickness of coatings, which indicates better adhesion of thinner TiW coatings on silicon substrate by a direct geometrical and qualitative comparison. The obtained steady-state strain energy (G_s) values decreased with increasing the thickness of TiW films. Furthermore at the same indentation load radial cracking at the corners of the indenter (de-cohesion) was observed in the thinner films, while thicker films did not show de-cohesion behavior but a more pronounced delaminated area around the indenter impression. It is suggested that the higher adhesion strength of the thinner films is related to the higher surface energy due to the smaller mean grain size and energy dissipation due to decohesion of the films.