Development of a multifunctional nanoindenter integrated in-situ Scanning Electron Microscope - application to the monitoring of piezoresponse and electro-mechanical failures

Abstract

The rising complexity of multi-material structures integrated into multi-functional devices requires the development of dedicated characterization tools capable of simultaneously monitoring different physical magnitudes with a relevant spatial resolution. This paper reports the development and the application of an original instrument based on a nanoindenter coupled with fine electrical measurements and integrated in-situ a Scanning Electron Microscope (SEM). The performances and capabilities of this home-developed instrument are illustrated through two different case studies.First, a micrometer-scale piezoelectric structure made up of wurtzite-single crystalline AlN islands grown on top of conductive Si pillars is tested. In-situ SEM imaging is used to precisely position the indenting probe on these individual islands, while the instrument sensitivity and repeatability are used to monitor their low-signal piezoresponse. Effective piezoelectric coefficients are also extracted for different loading/unloading conditions.Secondly a Si3N4/AlSiCu/SiO2 stack, which is standardly integrated as a passivation structure on top of microelectronic chips, is electrically and mechanically stressed and monitored up to its failure. The mechanical failure mechanisms (buried or emerging cracks) are discriminated thanks to the real-time SEM imaging of the indentation test. The instrument high sensitivity is used to monitor early current leakages that are attributed to conduction paths induced by mechanical failures.Combining high electro-mechanical sensitivity and precise probe positioning appears as an efficient way to monitor and analyze low-level electrical responses of small-scale structures. This approach paves the way to the fine characterization of micro/nano-systems displaying mechanically-driven electrical properties (conduction mechanism, leakage, breakdown,) like 2D-materials, dielectrics in microelectronic devices, strain-sensors, enamelled Litz wires,…