NanoDAC - Object Deformation Measurements for Micro and Nanotechnology Applications

摘要

The manufacturing, handling and control of micro and nano scale devices require the quantification of their geometrical and mechanical properties. While the measurement of geometrical and size data is easily accessible by SFM and SEM imaging equipment, mechanical characterization is a general problem for these objects. Different kinds of size effects more often force material property determination directly on micro/nano objects. Therefore, new strategies for material testing have to be developed. Displacements and their derivatives are two basic properties to be measured during testing for many mechanical material properties. The authors make use of SFM and high resolution SEM imaging in order to obtain spatially resolved displacement data over the scan area. Locally applied cross correlation algorithms are utilized to compute displacement fields and the corresponding first order derivatives. Micrographs are captured subsequently for different object load states. The established technique and measurement system (nanoDAC) is reviewed briefly. The authors present different applications of the nanoDAC method establishing the characterization of micro/nano scale material behaviour. Among the application fields are approaches to measure fracture mechanics criteria from crack opening displacement (COD) fields, a method of measuring residual stresses in thin membranes and testing techniques to measure Young's modulus and Poisson's ratios of thin foils and micro wires. The measurement of fracture mechanics bases on linear elastic fracture mechanics. Measured by AFM, COD fields in the very vicinity of crack tips are used to extract fracture toughness values. Stress determination on membranes utilizes the unique capability of focused ion beam (FIB) equipment, which allows concurrent material milling and micrograph capture with high resolution. A Zeiss X-Beam system has been used to mill trenches and holes into membranes of semiconductor structures. Treated that way stress release fields are determined from SEM micrographs. Taking into consideration reasonable stress hypotheses, membrane stresses are calculated from the obtained deformation fields. With the presented methods the basis is provided for an experimental reliability analysis of MEMS/NEMS and nanodevices.