Investigation of the fatigue behavior of Al thin films with different microstructure

Cyclic compressive and tensile stresses occur in metallic films and interconnects applied in sensors and microelectronic devices when exposed to temperature changes. The stresses are induced by differences in the thermal expansion coefficients of the adjacent materials. Repeated cycling leads to damage evolution and, eventually, to failure. In this study we report on a successful strategy how to avoid thermal stress induced fatigue damage. We analysed the deformation structures of 0.2–2 μm thick Al films subjected to thermal cycling between 100 °C and 450 °C up to 10,000 times. The investigations reveal that a reduction in film thickness or controlling the Al texture and the Al/substrate interface structure can be used to prevent thermo-mechanical fatigue damage. The findings are explained by orientation dependent plasticity and differences in dislocation mechanisms for different interface structures, and less accumulated plastic strain for thinner films. The approach is expected to apply in general for metallic films on substrates.

Research highlights▶ Polycrystalline films ≥0.6 μm are subjected to lattice rotations of their grains. ▶ The texture changes from a near (1 1 1) orientation into a (1 1 2) orientation. ▶ Simultaneously, strong surface roughening occurs for the polycrystalline films. ▶ Thermal fatigue damage evolution requires a critical film thickness. ▶ Epitaxial films maintains their initial microstructure after 10,000 thermal cycles.