Atomic force acoustic microscopy for materials characterization of polysilicon microelectromechanical systems

Roshanak Nilchiani, M.S. Thesis Defense
Department of Engineering Mechanics
University of Nebraska - Lincoln
Advisor:  Dr. Joseph A. Turner

Date: Monday, October 15, 2001
Time: 10:30 a.m.
Place: N205 Walter Scott Engineering Center


Atomic force microscopy (AFM) is the leading method for obtaining surface topographies with nanoscale resolution. Recently, interest has shifted towards obtaining quantitative material stiffness data by modification of the AFM to an Atomic Force Acoustic Microscope (AFAM). The AFAM is achieved through the addition an ultrasonic excitation source that is used to vibrate the sample. The contact with the sample causes shifting of the natural frequencies of the cantilever. Using appropriate contact theories, it is then possible to relate the frequency shifts to changes in surface stiffness. In this talk, the experimental setup of the AFAM and its application to different materials, including polysilicon microelectromechanical systems (MEMS) is discussed. Using this methodology, it is possible to determine the stiffness difference of the individual grains with nanometer resolution, in addition to obtaining the surface characteristics provided by topographical data.