Measurement of Micromechanical Properties with the FIBDAC Method

© Fraunhofer IKTS
Fig. 1: (A-C) Different FIB patterns on a microelectronic sample in order to relieve in-plane stress (left-to-right: single slot, double slot, pillar).
© Fraunhofer IKTS
Fig. 2: SEM image of the high contrast pattern on top of the ROI.
© Fraunhofer IKTS
Fig. 3: SEM image of the ROI after FIB milling.

The determination of micro-mechanical properties is an important field in material science as well as microelectronics research and development. Beside basic material parameters like Young’s modulus or Poisson’s ratio, the stress-strain state of a material is one of the key parameters to describe its overall mechanical behavior. Beside well-established methods for micro-mechanical parameter determination like nanoindentation, also methods for the characterization of the microscopic stress-strain state exist at Fraunhofer IKTS. One of these methods is the FIBDAC method which is here described stepwise:

    (c) Fraunhofer IKTS
  • - Creating a stable, unique, high contrast pattern on top of the Region Of Interest (ROI) by gold sputtering and successive focused ion beam (FIB) milling
  • - Taking a high quality image of the ROI with a Scanning Electron Microscope (SEM)
  • - Milling a slit into the region of interest with the FIB, slit dimensions: width 1–2 µm, length approx. 10 µm, relaxing in-plane stress results in stress-strain relief
  • - Taking a second high quality image of the ROI  
  • - Calculation of the resulting strain field with the help of image processing software (Digital Auto Correlation – DAC) x-shift in pixel
  • - Feeding the strain data into a finite-element model or into a semianalytical model in order to calculate the stress on the basis of pre-determined elastical properties (Young’s modulus)