Development of a multifunctional nanoindenter integrated in-situ Scanning Electron Microscope - application to the monitoring of piezoresponse and electro-mechanical failures
Résumé
The rising complexity of multi-material structures integrated into multi-functional devices requires the devel
opment 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 in
strument 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 Si 3N4/AlSiCu/SiO2 stack, which is standardly integrated as a passivation structure on top of mi
croelectronic 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,...
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