Enhancement of copper-sapphire adhesion induced by ion beam mixing

The phenomenon of irradiation enhanced adhesion of thin copper films deposited on sapphire has been studied. After irradiation of copper-sapphire interfaces with 1.5 MeV energy xenon ions. the bonding between metal and clean ceramic has been dramatically improved. This continuous adhesion enhancement has been measured as a function of ion dose from 5 × 1015 up to 3 × 1016 ions/cm2 by pin pull test experiments. The adhesion force measured after mixing with 3 × 1016 ions/cm2 is six times larger than for the unmixed sample. According to alpha particle Rutherford backscattering analysis, the copper-sapphire interface remains abrupt, even after 3 × 1015 ions/cm2. So, in order to clarify the mechanism responsible for such enhancement of adhesion, microstructural characterization of the interfaces has been performed at an atomic scale using high resolution transmission electron microscopy (HRTEM). These observations have shown that the copper-sapphire interface has been modified within a thin region (a few atomic planes) in which the interface roughness has clearly increased. The width of this interfacial region corresponds rather well to that deduced form the calculation of the recoil atom distributions induced during the ballistic stage of the incident ion interaction. Thus, no long range diffusion seems to occur after this primary stage in this metal-ceramic system. In the absence of any interfacial compound induced by irradiation between copper and sapphire, the increase in roughness of the interface has been assumed to be one of the parameters promoting the copper-sapphire adhesion enhancement. One of the most interesting results in ion beam mixing applied to metal-ceramic systems arises from the experimental result that ion beam irradiation often induces an enhancement of adhesion between the metallic film and the substrate. This effect has been clearly shown [3–5] on different combinations of metal and ceramic materials with a wide range of mixing conditions, i.e. by varying the nature and the energy of the incoming particle.