Jun 6, 2012
CR-AFM maps stiffness and damping with nanoscale resolution
Measurements of mechanical properties at the nanoscale are critical in optimizing the performance and reliability of advanced devices containing tiny features, such as those in modern microelectronics components. A new atomic force microscopy (AFM) technique has been developed that enables both conservative and dissipative mechanical properties of materials to be mapped with nanoscale spatial resolution.
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.
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.
About the author
Dr Gheorghe Stan is a member of the Nanomechanical Properties Group at NIST, Gaithersburg, MD. He is developing CR-AFM and other AFM techniques to measure the nanoscale mechanical properties of materials and structures. Dr Sean King is a Senior Technical Contributor within Portland Technology Development of Intel Corporation, Hillsboro, OR. He is investigating new materials, processes and metrologies to enable the fabrication of advanced (<10 nm) microelectronic interconnect structures. Dr Robert Cook is a NIST Fellow and Leader of the Nanomechanical Properties Group at NIST. He is leading research to develop measurements and standards for nanoscale measurements of elastic, plastic, fracture and viscous properties of materials.