Strain analysis in MEMS/NEMS structures and devices by using focused ion beam system

Abstract

Measurement of residual strain/stress in microstructures using a focused ion beam (FIB) moiré technique is demonstrated in this paper. This technique is selected based on advantages of the FIB system in nano-machining, in situ deposition, imaging, and fine adjustment. A nano-grating is directly written on the top of the microstructures by ion milling without any etch mask; the FIB moiré pattern is formed by the interference between a prepared specimen grating and raster scan lines. Effects of milling sequence, grating spacing and trench depth on the nano-grating structures and moiré fringes have been investigated. Strain evolution in microstructures during underlying sacrificial layer etching was studied. The sign of strain was derived from a rotation moiré technique. Moreover, a mass loading gauge with nano-gram resolution has been built. Since the local strain of a microstructure itself can be monitored during the process, the FIB moiré technique has many potential applications in the mechanical metrology of micro/nano-electro-mechanical-systems (MEMS/NEMS).