Micron-sized fracture experiments on amorphous SiOx films and SiOx/SiNx multi-layers

In this study miniaturized monolithic cantilevers of thermally grown silicon oxide and multi-layer cantilevers of plasma enhanced chemical vapor deposited silicon oxide and nitride were mechanically characterized. In order to determine the fracture stress as well as the fracture toughness, un-notched and focused ion beam pre-notched cantilevers were tested. While the thickness of the monolithic cantilevers was varied from 280 nm to 2380 nm, the individual sub-layer thickness of the multi-layer cantilevers was adjusted to 50 nm. Bending experiments reveal a small increase of the fracture stresses with decreasing cantilever thicknesses. For the multi-layer stacks the tensile stress at fracture slightly exceeds the strength values of the corresponding monolithic materials. Furthermore, it is demonstrated that the specimens pre-notched by focused ion beam do not show significant changes in fracture toughness with varying pre-notch size. This makes the applied test a reproducible technique to determine fracture toughness of brittle films.