Researchers at the National Institute of Standards and Technology (NIST), in collaboration with Intel, have used an extension of contact resonance AFM (CR-AFM) to map the mechanical properties of nanoscale structures. CR-AFM measures the change in vibration of an AFM cantilever probe as it is brought into contact with the material or structure to be studied.

Measurement of the change in vibrational resonance frequency enables the elastic, conservative properties of materials to be determined. Additional measurements of the vibrational resonance amplitude along with the resonant frequency enable contact damping, dissipative properties of materials to be determined as well.

Real-time monitoring

The researchers used a feedback technique to rapidly determine the resonance frequency and amplitude during scanning of the probe over a surface in contact mode imaging. In this way, maps of resonance frequency and amplitude were obtained in addition to the usual topography, with about 2 nm pixel size.

The technique was demonstrated on an advanced semiconductor interconnection structure, revealing clear differences in contact stiffness and damping between the Cu lines and the surrounding dielectric material and the intervening Ta/TaN barrier layer. By varying the load applied to the probe, the team was able to probe the decay of damping with depth beneath the surfaces of the Cu and the dielectric.

The method could be used to detect sub-surface defects that limit device performance and reliability.

Full details can be found in the journal Nanotechnology.