Effect of sidewall morphology on the fracture and fatigue properties of polysilicon structural films

This study highlights the difference in the sidewall morphology of n+-type polysilicon films from two popular microelectromechanical systems (MEMS) processes and its effect on fracture and fatigue properties. Atomic force and transmission electron microscopy show that thick silicon oxides (20 ± 5 nm) are found in PolyMUMPs films, caused by galvanic corrosion from the presence of gold on the chip, whereas in SUMMiT films a much thinner (3.5 ± 1.0 nm) native oxide was observed. These thicker oxide layers, in combination with differences in sidewall roughness (14 ± 5 nm for PolyMUMPs and 10 ± 2 nm for SUMMiT), have a significant effect on the fracture and fatigue properties of polysilicon structures; this is shown by measuring fracture strength (3.8 ± 0.3 GPa for PolyMUMPs and 4.8 ± 0.2 GPa for SUMMiT) and stress-lifetime high-cyclic fatigue curves.