Investigation of strain in microstructures by a novel moire method

A focused ion beam (FIB) moire method is proposed and demonstrated to measure the strain in microstructures. This technique is based on the advantages of the FIB system in nanofabrication, imaging, selective deposition, and fine adjustment. A nanograting is directly written on the top of the microstructures by ion milling without the requirement of an etch mask. The FIB moire pattern is formed by the interference between a prepared specimen grating and FIB raster scan lines. The strain of the microstructures is derived by calculating the average spacing of moire fringes. The sensitivity and accuracy of FIB moire in strain measurement is subsequently discussed. Since the local strain of a microstructure itself can be monitored during the process, the FIB moire technique has many potential applications in the mechanical metrology of microelectromechanical systems (MEMS). As an example, the strain distribution along the sticking microstructures and the contribution of surface oxidization and mass loading to the cantilever strain is determined by this FIB moire technique.