Evaluating microdefect structures by AFM-based deformation measurement

The rapid development of a wide variety of new devises in microelectronics, MEMS, NEMS and nano technology will lead to new challenges for their mechanical characterization and reliability assessment. Measurement of deformations and stresses in microscopic and even nanoscopic regions becomes a key issue. The authors make use of load state images captured by Atomic Force Microscopes (AFM) in order to measure object deformations. Out-of-plane deformation is determined from usual topography scans by computing surface profile differences. NanoDAC, a recently established approach, allows to meet these goals with regard to in-plane deformation. The method bases on cross correlations analysis performed on AFM scans, which are captured from thermally and/or mechanically loaded samples. Finally, local 3D displacement fields and in-plane strain fields are measured. A description of the basic principles and the capability of the technique are given. Furthermore, the authors demonstrate the potential of the mentioned method by its application to microcrack evaluation and the study of sensor and MEMS structure degradation. The first application corresponds to the measurement of crack opening displacement in the very vicinity of crack tips. As a consequence, fracture mechanics parameters are derived and allow to assess the defect with regard to possible crack propagation and component failure. This approach is used to study the influence of nanoscale material structures on crack behavior. The second example illustrates how the impact of thermal loading to the constitution of sensor or MEMS submicron layers is investigated by deformation analysis. The devices had been heated actively under the AFM. Degradation processes due to a severe thermal material mismatch were observed and monitored.