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

Abstract

Thispaper reports on the mechanical characterization of microtensile specimens made of silicon nitride (SiN x ) 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 , residual strain res and stress res and fracture strength 0 is in principle made possible from the measurement of a single test structure. Here we demonstrate the extraction of E, res , res and 0 of the nitride films.

Fracture properties of PECVD silicon nitride thin films by long rectangular memrane bulge test

“…Assuming a Poisson's ratio of 0.25 for PECVD SiN x thin film, the calculated Young's moduli for wafers A and B are 125 ± 18 GPa and 131 ± 24 GPa, respectively. These values are in agreement with the reported ones characterized by bulge testing and microtensile testing [8], [11].…”

“…The prestress of PECVD SiN x thin films can be controlled by adjusting the ratio of low frequency power to the total deposition power in dual frequency PECVD technique [11]. In this study, high frequency (13.56 MHz) was adopted, resulting in tensile stress for SiN x thin films, 178 ± 22 MPa for wafer A and 194 ± 34 MPa for wafer B, consistent with the reported values of similar SiN x thin film [2].…”

Fracture Properties of LPCVD Silicon Nitride and Thermally Grown Silicon Oxide Thin Films From the Load-Deflection of Long $\hbox{Si}_{3}\hbox{N}_{4}$ and $\hbox{SiO}_{2}/\hbox{Si}_{3}\hbox{N}_{4}$ Diaphragms

“…, J. The goal is then to compare these data, to compute their fracture probability using (8) or (10), and to extract the Weibull modulus m and mean fracture strength μ from these data. One method to achieve this is to translate the samples into an equivalent set of J uniformly stressed samples with identical reference volume V E .…”

“…The issue of fixing the sample onto the loading mechanism has been circumvented by appropriate design and fabrication of the samples permitting a perpendicular force to be translated into an essentially uniaxial load of the tensile sample [6] or bulk-micromachined silicon frames comprising in-plane fixed and movable parts whose configuration allows the uniaxial elongation of bridging microtensile specimens [7]. Such techniques have been improved in terms of fabrication yield, and sensing and actuation methods, reaching a point where the reliable wafer-scale microtensile testing of thin films is possible via involved experimental setups [8]- [10]. In addition, round-robin tests have been performed in order to compare various experimental approaches using the very same thin-film materials, like single-crystal silicon, polysilicon, nickel, and titanium, in the form of different test structures [11].…”

AlCuMgMn micro-tensile samples

“…We used the most direct way of measuring mechanical properties of AlCuMgMn films: tensile testing which was adapted to the micro-scale [4,12,13]. Especially designed micro-tensile samples were fabricated and measured using a dedicated system.…”