A tensile test for freestanding low-k thin films using a lift-off technique

Abstract

Since decreasing dielectric constants of insulators greatly alleviates the RC-delay, the materials with low/ultra-low-k dielectric (LK/ULK) constant have been integrated into the back end of line (BEOL) of advanced chips. However, the mechanical performance of LK/ULK is weak compared with that of traditional dielectrics, e.g. SiO2, which poses a serious risk to the reliability during fabrication or packaging. To improve the reliability design in state-of-the-art devices, determining the mechanical properties of LK/ULK accurately is critical. In this study, we proposed a lift-off technique to obtain freestanding test samples of low-k thin films, which involves lithography and micromachining techniques to pattern the samples in designed shapes and release them from the substrate. The samples of low-k film consistent with the actual manufacturing process were subjected to uniaxial tensile tests to measure their modulus and strength using an in-situ tensiometer apparatus. The test results showed that the low-k film's elastic modulus is ~2.5 GPa and its tensile strength is about 18.3 MPa. When the low-k film experienced different moisture absorptions, the modulus is decreased with the increase of moisture content