An electric contact structure includes a first structural layer; a second structural layer made of dielectric material extending over the first structural layer; and an intermediate layer made of conductive material extending between the first structural layer and the second structural layer. A trench extends in the second structural layer delimited laterally by a wall of the second structural layer and at the bottom by a surface region of the intermediate layer. A diffusion barrier extends in the trench covering the surface region of the intermediate layer and the wall of the second structural layer. The diffusion barrier is a TiW—TiN—TiW tri-layer.