183 TOWARD MEASUREMENT OF THIN FILM PROPERTIES BY ENHANCED MOIRE INTERFEROMETRY Arkady S. Voloshin, Fazil Erdogan and Leng-Tsun Tsai Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, PA 18015 ABSTRACT Growing use of thin films in encapsulated integrated circuits(IC's) necessitated new developments in measurement of their mechanical properties in-situ. This can be done by a hybrid analytical experimental approach. The films are approximated by orthotropic membranes and the substrate is assumed to be an elastic continuum. It can be shown that power of stress singularity is a function of geometry and film/substrate material properties. By loading the sample and measuring actual displacement field in the close proximity to the crack or edge, one can evaluate the needed properties. The technique used to measure full field displacements is enhanced moire' interferometry. It is based on the formation of fringes by the coexistence of light wave fronts diffracted from a specimen grating of high frequency. These specimen gratings are created on the specimen surface using a replication technique from a specially prepared mold. Two beams of coherent laser light illuminate the specimen grating obliquely to create a virtual reference grating in front of the specimen. The frequency f of this grating is chosen to be 2400 lines/ mm, this corresponds to a sensitivity of 0.417 plk per fringe order. When the specimen is deformed the interference pattern (moire' fringes) is formed and collected by a video camera connected to a PC-based digital image processor. Analysis of the moire pattern results in full field displacement. INTRODUCTION Dielectric and metallic thin films continue to be one of the common features of the integrated circuits (IC's). The residual stresses may be developed during film processing and cooling or as a result of the coefficient of thermal expansion (CTE) mismatch between the film and substrate. Since residual stresses are often responsible for cracking and/or delamination many efforts were contributed to evaluation of those stresses [1,2,3]. However, in all those and similar works one quietly assumes that all necessary material properties of the films involved are known or easily available form the literature. It is true that one can get some numbers from the reference books, however the main problem is that those numbers were obtained either from a bulk material or from films removed from substrate and subjected to mechanical loading. While those results provide correct mechanical properties, they are characteristic only of the bulk material or the sample removed from the substrate. Mat. Res. Soc. Symp. Proc. Vol. 203. ©1991 Materials Research Society