AVS 60th International Symposium and Exhibition
    Nanometer-scale Science and Technology Wednesday Sessions
       Session NS+AS+BI+SP-WeM

Paper NS+AS+BI+SP-WeM5
AFM-based Chemical and Mechanical Property Characterization of Low-k/Cu Interconnects

Wednesday, October 30, 2013, 9:20 am, Room 203 B

Session: Nanoscale Imaging and Microscopy
Presenter: M. Lo, Anasys Instruments
Authors: M. Lo, Anasys Instruments
S.W. King, Intel Corporation
E. Dillon, Anasys Instruments
Q. Hu, Anasys Instruments
R. Shetty, Anasys Instruments
C. Prater, Anasys Instruments
Correspondent: Click to Email
Infrared (IR) spectroscopy is a powerful technique for characterizing the chemical bonding in low dielectric constant (i.e. low-k) materials utilized in nano-electronic Cu interconnect structures. Combined with nanoindentation and other techniques, IR spectroscopy has enabled the structure-property relationships in these materials to be determined. However, such property analysis have been primarily limited to characterizing blanket films due to the spatial resolution of a typical IR measurements being diffraction limited to ca. 3 - 10 μm. Further advances in low-k materials and failure analysis would be greatly enhanced by the ability to perform IR spectroscopy and other material property characterization on actual nanometer scale low-k/Cu interconnects. In this report, we demonstrate both AFM based IR chemical analysis and contact resonance mechanical analysis of a single layer 90 nm low-k/Cu interconnect structure.

To achieve better spatial resolution in IR spectroscopy measurements, a broadly tunable infrared laser was coupled to an atomic force microscope (AFM-IR). IR laser pulses at the wavelengths of the low-k materials characteristics absorption bands was utilized to create rapid thermal expansion that invoked vibrations in the AFM tip directly in contact with the sample. Amplitudes of the ringing motion of the AFM tip were recorded as the same tip scanned over the areas of interest. By detecting only the perturbations directly underneath the AFM tip, spatial resolution below the diffraction limits of IR radiation could therefore be achieved. In this manner, IR spectra and 2D images of a < 1.5 μm wide interlayer dielectric (ILD) in a low-k/Cu interconnect were achieved.

To complement the AFM-IR technique and achieve nanometer scale structure property measurements, AFM-based contact resonance (CR-AFM) measurements were performed in parallel. The CR-AFM technique probes the relative mechanical property of different materials and has been previously demonstrated useful for characterizing the elastic properties of low-k material in similar Cu interconnect structures. For the current CR-AFM measurements, the resonant frequency of the AFM tip was controlled by modulating the alternating current going through a specialized ThermaLever™, which interacts with the magnetic field of a magnet nearby. As this tip scans from ILD to other metallic layers, the frequency of the AFM tip vibration changes due to the variations in the mechanical stiffness from one material to another. By combining the AFM-IR and CR-AFM techniques, both chemical and mechanical analysis of a low-k/Cu nano-electronic structure were achieved using an AFM at high spatial resolution.