FIB based measurements for material characterization on MEMS structures

Abstract

The authors present a new approach, fibDAC, which allows to measure and analyze deformation fields on stressed micro and nano components, which can be utilized for mechanical material characterization. The method bases on digital image correlation (DIC) algorithms applied locally to load state images captured from focused ion beam (FIB) equipment. As a result, deformation fields are determined, which occur due to loading of microsystem structures inside the focused ion beam system. A similar tool, called microDAC/nanoDAC, has been reported earlier and applies DIC techniques to SEM or AFM images. The advantages of the new fibDAC approach occur in the incorporation of specimen preparation like ion milling, ion beam surface polishing and DIC patterning as well as specimen loading by ion milling and DIC deformation measurement in a single equipment. Combining measured fields with finite element simulations or analytical solutions of the corresponding mechanical problem, relevant mechanical material properties can be evaluated. Corresponding object loading is accomplished either externally by testing modules designed for application inside the FIB equipment or by ion milling on the test specimen. As an example ion milling on specimens with residual stresses is demonstrated. Released in this way residual stresses cause object deformations nearby the milling area. Measured deformation fields by fibDAC allow to evaluate very local residual stresses. Some principal experiments illustrate the feasibility of the chosen approach. Features and challenges connected with this new method are discussed in some detail.