Atomic Force Acoustic Microscopy for Materials Characterization of Microelectromechanical Systems

Atomic force acoustic microscopy (AFAM) can be used to make quantitative images of surface stiffness with high resolution. The technique utilizes the dynamic response of the atomic force microscope (AFM) cantilever, specifically in terms of the higher-order cantilever modes. Motion of the specimen while in contact with the AFM tip induces vibrations in the cantilever. The dynamical properties of the cantilever change during scanning due to the variations of surface stiffness. Both stiff and compliant cantilevers may be used for stiffness imaging if the appropriate vibration mode is chosen. Experimental AFAM results on polysilicon for microelectromechanical systems (MEMS) are presented. The AFAM results provide stiffness information about the material microstructure that is not available from topography information alone. The technique provides in-situ stiffness information without damaging the MEMS.