Study on damage and fracture of thin-film stacked structures through indentation test with acoustic emission sensing

Abstract

An indentation damage test comprises a micro-mechanical tester and an acoustic emission sensor is employed to evaluate the critical force or displacement required to crack the bulk Si die specimen and thin-film stacked specimens. The associated works before and after the indentation damage test are examined from the force-displacement F-d curve. The pseudo-work of indentation damage Wd describes the work done by the indenter on the damaged specimen after the crack initiation and propagation, which can be determined by multipling the onset crack force Fc with the ‘pop-in’ or plateau length l obtained from the F-d curve. A simple energy-based approach is then proposed to determine the work of indentation fracture Wf based on the difference in the elastic strain recovery between a damaged and a non-damaged specimen during the unloading stage from the onset crack force Fc. It is found that the energy involved in cracking the specimen is much higher than the work done by the indenter at Fc onto those damaged specimens, i.e. Wd<Wf. It is observed that Wf varies proportionally with the acoustic emission energy EAE when cracking occurs. Generally, a lower and a higher value of EAE obtained from the indentation damage test are related to the through-thickness crack in the intermediate dielectric layer and the sub-surface cone crack in Si substrate, respectively.