A Technique for Estimation of Residual Stress and Young’s Modulus of Compressively Stressed Thin Films Using Microfabricated Beams

Predictive design of MEMS devices and their performance evaluation require post-fabrication measurement of essential material properties, such as Young's modulus and residual stress, as these are usually affected by fabrication process conditions. To our knowledge, few techniques exist for the measurement of residual stress in micromechanical structures fabricated from compressively-stressed amorphous dielectric thin films. Here, we propose a method for estimating residual stress and Young's modulus from the post-buckling dynamic response of fixed-fixed microbeams and frequency response of cantilevers, respectively. Static deflection profiles and first natural frequencies of buckled beams are used in this analysis. Further, the proposed method uses the length of the beams as an unknown to account for the variation in the actual length of a fabricated beam due to the presence of undercut. The effective length is simultaneously determined from the analysis of the measured data using multi-parameter curve fitting. 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 applicable for dielectric thin films in addition to crystalline and conducting films. Using the proposed method, residual stress is estimated in amorphous silicon carbide thin films deposited by PECVD and reactive-sputtering. In addition, the modulus values of three materials (PECVD SiNx, PECVD SiC, and sputtered SiC) are estimated and compared with reported results. [2019-0090]