Quantification of local elastic properties using ultrasonic force microscopy

A modified Ultrasonic Force Microscopy (UFM) technique is presented that determines the elasticity (Young's modulus) of a material quantitatively based on the Johnson-Kendall-Roberts model. The periodic oscillation of the sample with MHz frequencies causes a high dynamical stiffness of the cantilever of a scanning probe microscope (SPM). The information about the elasticity of a sample can be extracted from the cantilever response to the amplitude variation. The procedure for the quantitative determination of the reduced Young's modulus is demonstrated for a partially delaminated thin film. For such a sample, no material inhomogeneities exist for the top laver. i. e., surface roughness and sample-tip adhesion are assumed to be constant. Consequently, the UFM signal is not influenced by locally fluctuating material properties and topography. The systematic study shows that film delamination causes a continuous gradient of film stiffness along the delaminated part of the film. The application of this modified UFM technique in physical failure analysis is demonstrated for the nondestructive characterization of buried defects.