Tantalum and copper layers were deposited on a thermally oxidized Si substrate in a magnetron sputtering process.Nanoindentation was adopted to investigate the hardness and elastic modulus of the Cu/Ta/SiO_2/Si multilayer system.The hardness shows an apparent dependence on the film thickness,and decreases with the increase of film thickness,whereas the elastic modulus does not.To reveal the structural change,a trench through the center of a residual indent was cut by a focused ion beam,and then examined using an ion-microscope.TEM analysis showed that delamination occurs at the interface between the Ta and the SiO_2 layer of the residual indent, suggesting that the destruction under a relatively large load is due to weak bonding. Tantalum and copper layers were deposited on a thermally oxidized Si substrate in a magnetron sputtering process. Nanoindentation was adopted to investigate the hardness and elastic modulus of the Cu / Ta / SiO 2 / Si multilayer system. The hardness shows an apparent dependence on the film thickness , and decreases with the increase of film thickness, whereas the elastic modulus does not.To reveal the structural change, a trench through the center of a residual indent was cut by a focused ion beam, and then examined using an ion-microscope. TEM analysis showed that delamination occurs at the interface between the Ta and the SiO_2 layer of the residual indent, suggesting that the destruction under a relatively large load is due to weak bonding.