Simultaneous Determination of Young’s Modulus and Residual Stress in PECVD a-SiC from Postbuckling Vibration of MEMS Beams

For design of MEMS structures, an accurate measurement of material properties of thin films is necessary, which vary considerably due to process variations. In addition, performance of MEMS devices are often affected due to process induced residual stresses and even dimensional variations. Thus, it is essential that we develop techniques to determine these important material and structural properties from each complete fabrication process. In this work, we exploit the invariance of even modes of buckled beams w.r.t. change in stress for decoupling effects of modulus and stress on dynamic characteristics of MEMS beams. This enables simultaneous estimation of Young's modulus and residual stress. The technique is demonstrated by estimating modulus and stress in amorphous silicon carbide thin films deposited by PECVD. Use of post-buckling analysis makes this technique useful for thin films with high compressive stresses. Since the proposed method does not involve electrostatic actuation, it is equally applicable to dielectric thin films.