Design of a micro-optical low coherent interferometer array for the characterisation of MEMS and MOEMS

Abstract

The EU-project SMARTIEHS (SMART InspEction system for High Speed and multi-functional testing of MEMS and MOEMS) develops a new inspection concept for MEMS and MOEMS (M(O)EMS) testing on the wafer level. The inspection systems on market today are based on a serial approach inspecting one M(O)EMS structure at the time. The SMARTIEHS concept is based on a parallel approach. A wafer-to-wafer inspection concept is adopted from the electronic probing cards in the micro electronics industry. In SMARTIEHS a micro-optical probing wafer is aligned on top of the M(O)EMS wafer under investigation.The 4-inch probing wafer contains a 5x5 array of micro-optical interferometers, allowing the inspection of 25 MEMS structures within one measurement cycle. The measurement time can thus be reduced by a factor of 25. This factor can be easily increased by extending the size of the probing wafer. In the project two different types of interferometers are developed to demonstrate the multifunctional approach of the system. A laser interferometer is applied for the detection of the resonance frequency and the amplitude distribution, while a low coherent interferometer is applied for the measurement of shape and deformation. A 5x5 channel Smart Pixel camera array detects the interference signals.This paper presents the design of the micro-optical low coherent interferometer array. The configuration is based on the well known Mirau-interferometer. The main challenge is the realisation of the array concept based on micro-optical components produced with standard micro-fabrication processes on the wafer level.This results in special requirements both for the optical design of the interferometer, the micro- fabrication processes, and for the scanning system. The interferometer array consists of several wafers, mounted in a wafer stack. The essential parts are: a microlens array, a beam splitter wafer and a reference mirror array. The paper will present different designs of micro-optical Mirau in

Design of a micro-optical low coherent interferometer array for the characterisation of MEMS and MOEMS