<title>Inspection system for MEMS characterization on wafer level using ESPI</title>

Abstract

Characterizing the mechanical properties of MEMS structures at a very early stage of manufacturing is a challenging task for quality assurance in this field. The paper describes a new solution that is based upon the vibration analysis of the microparts. The microvibrations have nm amplitudes and are detected by electronic speckle pattern interferometry (ESPI). A specific signal processing technique (moving phase reversal reference) has been applied to make the solution robust.Comprehensive numerical simulations provide the theoretical base for estimating the frequencies and mode shapes expected for perfect MEMS as well as for typical faults. The complete wafer ensemble was modeled to gain knowledge about best suited wafer clamping and about interactions between the microparts vibrating. A laboratory system for 4" wafer has been built, and extensive tests show that such key properties as e.g. the thickness of springs or membranes can be determined exactly by means of the hybride approach. Automated frequency scanning and corresponding digital image processing open the way to reliable and fast industrial systems for MEMS testing on wafer level.

Micro-motion analyzer used for dynamic MEMS characterization

“…For example, a fully automated measurement system is designed to evaluate the dynamic characteristics of micromechanical structures with laser Doppler vibrometers in the University of Newcastle by Burdess et al [2,3]; a computercontrolled stroboscopic interferometer system for measuring outof-plane motions and deformations of MEMS structures with nanometer accuracy was described by Hart [9,10]; Georges et al study on the vibrating mode shape analysis in a large field using strobed illumination, digital holography and phase-shifting interferometry in Liege University of Belgium [11].…”