Interferometry of actuated microcantilevers to determine material properties and test structure nonidealities in MEMS

By integrating interferometric deflection data from electrostatically actuated microcantilevers with a numerical finite difference model, we have developed a step-by-step procedure to determine values of Young´s modulus while simultaneously quantifying nonidealities. The central concept in the methodology is that nonidealities affect the long-range deflections of the beams, which can be determined to near nanometer accuracy. Beam take-off angle, curvature and support post compliance are systematically determined. Young´s modulus is then the only unknown parameter, and is directly found. We find an average value of Young´s modulus for polycrystalline silicon of 164.3 GPa and a standard deviation of 3.2 GPa (±2%), reflecting data from three different support post designs. Systematic errors were assessed and may alter the average value by ±5%. An independent estimate from grain orientation measurements yielded 163.4-164.4 GPa (the Voigt and Reuss bounds), in agreement with the step-by-step procedure. Other features of the test procedure include that it is rapid, nondestructive, verifiable and requires only a small area on the test chip