Measuring shape and deformation of small objects using digital holography

Micro-systems engineering is a fast growing technology with a wide variety of different materials. The task to ensure reliability and precision of the products needs the precise knowledge of the materials' properties, which is too less in dimensions smaller than one millimeter at the moment. Because properties determined at much larger specimen cannot be scaled down without any experimental result, simple and robust methods to analyze the materials' shape and deformation under a given load must be developed. Holographic interferometry and optical contouring techniques are widely used as highly sensitive and contactless methods for deformation and shape analysis. To get a full 3d-information of the objects surface, however, requires a complex optical setup with at least three illumination directions. Especially when small objects like micro-components have to be examined, the ordinary use of conventional halography becomes more and more a problem. In that case digital Holography can be used as a fast, simple and robust method. It replaces the classic holographic recording media by a CCD matrix. The whole reconstruction process of the interference phase is done by computer. Compact and very simple setups can be achieved by use of fiber optics. Several experiments realized in an optimized setup by using four illumination directions are presented to show the advantages of digital holography for the investigation of microsystems. This new technique is applied to components with lateral extensions from 0.1m to 0.001m to examine their shape and their fall three dimensional deformation under a given mechanical load. The results are compared with computer simulations using FEM. For compound Si/Ni microbeams Young's modulus was determined as an example for this technology of measurement.