Using AFM Measurements for Failure Indication During High-Cycle Fatigue Testing of thin Metal Films on MEMS Cantilevers

Abstract

We use Si MEMS cantilevers as sample carriers to gain high cycle fatigue data for thin metal films by accelerated stress testing. A typical number of 107 cycles can thus be achieved in a couple of hours. A closed loop control using laser beam deflection allows to keep the load on the thin film constant while in parallel its degradation is monitored continuously by recording resonance frequency, thin layer electrical resistance and surface roughness, the latter ex situ by AFM. We show a correlation between those three failure indicators and motivate a relationship with the failure parameter within a physics-of-failure based reliability paradigm. The proposed method opens an introspect view on the degradation behaviour of thin metal films as well as a rapid statement on their reliability under vibration loading at different temperatures. In this paper, the method is exemplified on the disruption of $1.2 \mu \mathrm{m}$ thin sputtered Aluminium layers.