Mechanical characterization of silicon nitride thin-films using microtensile specimens with integrated 2D diffraction gratings

This paper reports on the mechanical characterization of microtensile specimens made of silicon nitride (SiNx) thin-films with integrated 2D reflective gratings. By applying an axial force, the structures respond mechanically with an elongation and contraction in the longitudinal and transversal directions, respectively. The corresponding variations of both periods of the grating are monitored in real time by measuring the diffraction pattern resulting from the illumination of the grating with monochromatic light. The strain components are thus evaluated locally in the structure. By integrating such an optical technique with an efficient test structure previously developed, the extraction of materials' Young's modulus E, Poisson's ratio nu, residual strain epsivres and stress sigmares and fracture strength sigma0 is in principle made possible from the measurement of a single test structure. Here we demonstrate the extraction of E, epsivres, sigmares and sigma0 of the nitride films.