Determination of mechanical properties of PECVD silicon nitride thin films for tunable MEMS Fabry–Pérot optical filters

Abstract

This paper reports an investigation on techniques for determining elastic modulus and intrinsic stress gradient in plasma-enhanced chemical vapor deposition (PECVD) silicon nitride thin films. The elastic property of the silicon nitride thin films was determined using the nanoindentation method on silicon nitride/silicon bilayer systems. A simple empirical formula was developed to deconvolute the film elastic modulus. The intrinsic stress gradient in the films was determined by using micrometric cantilever beams, cross-membrane structures and mechanical simulation. The deflections of the silicon nitride thin film cantilever beams and cross-membranes caused by in-thickness stress gradients were measured using optical interference microscopy. Finite-element beam models were built to compute the deflection induced by the stress gradient. Matching the deflection computed under a given gradient with that measured experimentally on fabricated samples allows the stress gradient of the PECVD silicon nitride thin films introduced from the fabrication process to be evaluated.

Mechanical characteristics of filter structures for MEMS adaptive infrared detectors

“…This approximation is made based on our modeling and experimental results which indicate that the pillar support is sufficiently solid to be represented by the "fixed arm end" boundary condition. A Young's modulus of 97 GPa, which was determined by the 16 , was used for the membrane material, i.e. low temperature silicon nitride (SiN x ) in all the models.…”

“…For the estimation of stress distribution in the membrane, both silicon nitride (SiN x ) L arm structures and cantilever beams of a thickness of 550 nm was fabricated using the following PECVD conditions: deposition temperature of 125 o C, chamber pressure of 875 mtorr, radio frequency power of 75 W and gas flow ratio of 1:10:20 for SiH 4 :NH 3 :N 2 . The method developed in [16] was used to estimate the stress gradient in the SiN x membrane layer. A linear stress gradient was introduced into the FEM beam model.…”

Interfacial energy release rates of SiN/GaAs film/substrate systems determined using a cyclic loading dual-indentation method

“…A Berkovich indenter with an included angle of 142.3° and a tip radius of 100 nm was first used to measure the elastic modulus (E) and hardness (H) of GaAs substrate and SiN films using the Oliver-Pharr method [17]. The E and H of the films were calculated from P-h curves of the film/substrate specimens applying a deconvolution method [18][19][20]. The values of E and H are shown in Table 2.…”

A resonant method for determining the residual stress and elastic modulus of a thin film

“…5 The residual stress can affect the effective stiffness of the film, and hence the accurate characterisation of the film's mechanical properties, as well as the performance and reliability of filmbased devices. [6][7][8] A number of techniques, such as wafer curvature measurement, 9 bulge testing, 10-12 X-ray diffraction, 13,14 and Raman spectroscopy, 15 were developed to measure the residual stress of thin films. Nevertheless, these methods have their limitations.…”

“…The effect of clamping conditions will be investigated in detail in our future work. The other possible errors should mainly come from uncertainties in measurement of the diameter and thickness of diaphragms and the density and Poisson's ratio of the film (although the effect of Poisson's ratio should be insignificant 8 ). The irregularity of the diaphragm edge and non-uniformity in diaphragm thickness would also affect the accuracy.…”