Characterization of nano-thin films and membranes by use of atomic force acoustic microscopy methods

The atomic force acoustic microscopy (AFAM) technique combines the principle of atomic force microscopy (AFM) for nanoscale imaging with the ability to detect changes in elastic modulus on a tested sample. Depending on the mode of operation, AFAM provides qualitative and quantitative information on the effective stiffness of the probed sample either in the form of images or point measurements. AFAM is a contact based method and as such provides information on the sample indentation modulus from a volume that is compressed under the AFM tip. The size of the compressed volume depends on the static load applied to the tip, tip radius, and the elastic properties of the tip and the probed sample and thus it can be controlled. The AFAM technique can be a powerful tool for characterization of thinfilm systems and detection of defects that are buried at a depth of about 30 nm - 150 nm. We used the AFAM method to study various nano-thin systems. A set of nine square membranes 3.7 µm x 3.7 µm large, with thickness increasing in 30 nm steps from 30 nm to 270 nm was dry etched in silicon. AFAM qualitative images obtained on the surface of this sample showed all the membranes allowing for their localization. In addition, we used AFAM to determine indentation modulus of silicon oxide films Mf with the thickness varying from 7 nm to 28 nm. The values obtained for Mf varied from 80 GPa to 90 GPa and were in good agreement with the literature values