Authors: J. Keller, D. Vogel and B. Michel
Affilation: Fraunhofer Institute for Reliability and Microintegration (IZM), Germany
Pages: 57 - 60
Keywords: digital image correlation, deformation measurement, nano sclae
Recent advances in microtechnology and the development of new electronics and micro/nanosystem devices in automotive industry, communication sector and life science have led to a strong need in material characterization on the micro and nano scale. Defects occurring due to thermal or mechanical material mismatches have to be analyzed by suitable methods. If they cannot be avoided completely, e.g. microcracks in materials or at interfaces, evaluation of their effect on reliabilty of the component is inevitable. In addition, the development and evaluation of interface concepts of biological structures to microelectronic materials such as polymers, metals, ceramics and semi-conducting materials will be a fundamental challenge. To fulfil these needs new strategies for reliability assessment on the submicron scale are essential. Under this prerequisite Scanning Probe Microscopy (SPM) serves as the basis for the development of the nanoDAC method (nano Deformation Analysis by Correlation), which allows the determination and evaluation of 2D displacement fields based on SPM data. In-situ SPM scans of the analyzed object are carried out at different thermo-mechanical load states as shown in Fig. 1. In the illustrated case a Scanning Force Microscopy topography signal serves as the imaging technique. It is also possible to use other SPM image sources such as Phase Detection Microscopy or Ultrasonic Force Microscopy. The obtained images are compared utilizing digital image correlation (DIC) based on grayscale cross correlation algorithms. This allows the tracking of local image patterns (compare to Fig. 1) of the analyzed surface structure. The measurement results of the nanoDAC technique are full-field displacement fields. For the images of Fig. 1 the determined vertical (crack opening) displacement field is illustrated in Fig. 2. The nanoDAC method is suited for measurement of mechanical properties such as fracture properties, Young’s modulus, Coefficient of Thermal Expansion, Poisson’s ratio. Furthermore the technique should be used for tracking of structures or particles driven by diffusion processes or nanomanipulators. Future generations of SPM equipment will provide modes for observation of dynamic processes. The nanoDAC method will be a useful tool for evaluation of time-dependent processes observed by in-situ SPM techniques. In addition to the nanoDAC method the fibDAC method will be presented. With the fibDAC (Focused Ion Beam based Deformation Analysis by Correlation) method the classical hole drilling method for stress release measurement has been downscaled to the nanoscale. The ion beam of the FIB station is used as a milling tool which causes the stress release at silicon microstructures of MEMS devices (Fig. 3). The analysis of the stress release is achieved by DIC applied to load state SEM images captured in cross beam equipment (combination of SEM and FIB). The results of the DIC analysis are deformation fields which are transferred to stress solution by application of finite element analysis. In another step the resolution of the method has been improved by the application of trench milling instead of milling of holes. Thereby deformation measurements in the nm range are established. With the presented methods the basis is provided for an experimental reliability analysis of MEMS/NEMS and nanodevices. In combination with numerical methods new strategies for life time evaluation and fatigue can be addressed.