Effect of residual stress and adhesion on the hardness of copper films deposited on silicon

Continuous indentation testing was used to measure the hardness as a function of indentation depth, of three micron thick copper films deposited on silicon with an intermediate layer of 20 nm thick chromium or titanium. Three different indenters, a nearly perfect Vickers, a Vickers with a 1.2 μm² flat, and a Pyramid with a 25 μm² flat were employed. The hardness data suggest that the titanium interlayer produced significantly greater film/substrate adhesion than the chromium interlayer. A compressive residual stress, which relaxed with time, was detected in the samples with the titanium interlayer.