A Contact Point Detection for Indentation Test of Low-k Film

− In the instrumented indentation test including nanoindentation, the mechanical parameters are calculated by test force and indenter contact/surface area. The area is determined as a function of depth, which is measured as the displacement from surface of sample. Therefore how to determine the surface is important, however, it is not easy to determine sample surface exactly during the test. Because nanoindentation machines detect the surface as a velocity decreasing point or stiffness increasing point with monitoring the indenter motion at the surface finding process. The detected surface point much deeper than the original sample surface and varies with depending on the mechanical properties of the sample. In this report, we observed the surface contact behaviour of sapphire and low-k film using commercial indentation tester ENT-1100a (Elionix Co.). In the small penetration depth, observed results show the good agreement with Hertz’s contact theory for both hard and very soft material. Then the first portion of the loading curve is fitted to the elastic theory, and surface point is determined as zero-force point of the fitted curve. We applied the proposed surface correction method for the elastic modulus measurement of low-k films, which have 150, 200, 300, 500 and 700 nm thickness on silicon substrate. The variation of estimated film modulus for each thickness sample was obtained as 611 GPa without correction and as 5-7 GPa after the proposed correction.