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Abstract An on-chip fracture mechanics method is extended to characterize subcritical crack growth in submicron freestanding films. The method relies on a self-actuated concept based on MEMS fabrication principles. The configuration consists of a notched specimen attached to actuator beams involving high internal stress. Upon release, a crack initiates at the notch, propagates, and arrests. Several improvements are worked out to limit the mode III component and to avoid crack kinking. The method is applied to subcritical crack growth in 140-nm-thick SiO2 films under different humidity conditions. The data reduction scheme relates crack growth rate to stress intensity factor. The static fracture toughness value is ~ 0.73 MPa $$\sqrt{\mathrm{m}}$$ m , with standard error of 0.01 MPa $$\sqrt{\mathrm{m}}$$ m and standard deviation of 0.17 MPa $$\sqrt{\mathrm{m}}.$$ m . Subcritical crack growth rates are much smaller than in bulk specimens. A major advantage is that many test samples can be simultaneously monitored while avoiding any external equipment. Graphic Abstract

Fracture mechanics has been applied for more than two decades to various configurations of cracks in films on substrate. Fracture toughness data are indeed needed for the design and integrity assessment of many coatings and microelectronics devices. Nevertheless, it is sometimes complicated to deconvolute the constraint exerted by the substrate on the cracking process especially in the presence of viscoelastic or plastic dissipation. Here, a new on chip test method has been developed to determine the fracture toughness of freestanding submicron films. Beside the advantage of avoiding the constraint induced by the substrate, freestanding films allow, if sufficiently thin, direct observation of the fracture mechanisms by transmission electron microscopy. The design of this new nano(micro)-testing consists of two long actuator beams undergoing large internal stress. A specimen is attached to these two actuators, incorporating a notch produced by lithography. Two types of geometries are addressed, one being a double cantilever beam type configuration, while the other is a center cracked panel. Both actuators and specimen are deposited on a sacrificial layer. The etching of the sacrificial layer induces the release of the test structure, with the actuators then contracting and pulling on the test specimen. A crack is initiated from the notch tip, propagates and finally stops when the energy release rate has decreased down to its critical value. This crack arrest measurement avoids the problem of introducing a sufficiently sharp precrack. Analytical equations that describe the stress intensity factor as a function of the geometrical characteristics of the test structures are worked out to guide the dimensional analysis. Extensive finite element analysis provides the full parameter variations necessary to quantify the fracture toughness from experimental data and to capture the process of initiation, unstable cracking and arrest followed by possible further stable propagation. For the sake of a proof of concept, ∼50 and ∼100 nm-thick silicon nitride films produced by low pressure chemical vapor deposition were tested, leading to a mean fracture toughness equal to ∼2 MPa m .