Smart pixel camera based signal processing in an interferometric test station for massive parallel inspection of MEMS and MOEMS

Abstract

The paper presents the electro-optical design of an interferometric inspection system for massive parallel inspection of Micro(Opto)ElectroMechanicalSystems (M(O)EMS). The basic idea is to adapt a micro-optical probing wafer to the M(O)EMS wafer under test. The probing wafer is exchangeable and contains a micro-optical interferometer array: a low coherent interferometer (LCI) array based on a Mirau configuration and a laser interferometer (LI) array based on a Twyman-Green configuration. The interference signals are generated in the micro-optical interferometers and are applied for M(O)EMS shape and deformation measurements by means of LCI and for M(O)EMS vibration analysis (the resonance frequency and spatial mode distribution) by means of LI. Distributed array of 5x5 smart pixel imagers detects the interferometric signals. The signal processing is based on the "on pixel" processing capacity of the smart pixel camera array, which can be utilised for phase shifting, signal demodulation or envelope maximum determination. Each micro-interferometer image is detected by the 140 x 146 pixels sub-array distributed in the imaging plane. In the paper the architecture of cameras with smart-pixel approach are described and their application for massive parallel electrooptical detection and data reduction is discussed. The full data processing paths for laser interferometer and low coherent interferometer are presented.

Micro-optics in advanced optical metrology

“…Interferometric signals obtained in each interferometer channel are analyzed by the specially designed Smart-Pixel Camera [12,13] consisting of the matrix of 5x5 imager modules. Each module consists of 140x140 smart-pixels that allows for the direct demodulation of the time dependent interferometric signal [14,15]. To implement excitation for an objects, a glass wafer structured with transparent Indium Tin Oxide (ITO) electrodes, is placed between the LI optical wafer and object.…”

Parallel approach to MEMS and micro-optics interferometric testing

“…Figure 9 presents the evaluated wrapped phase (mod 2π) proportional to the topography of the investigated device in 10 channels measured parallel (at single measurement cycle). The dynamic properties of the objects were measured with proposed quasi heterodyned method in the laser interferometer subsystem 7,8 . As an object the special calibrated piezoelectric transducer with the silicon mirror glued at the top was used.…”

Comparison of full-field interferometric measurement techniques applied to small vibration amplitudes determination

“…There have been many attempts to extend measurement capabilities to 2D case. The most successful ones include additional scanning system [5], special beam steering with spatial light modulators [6] and multiple sensors head [7]. In this paper we wish to present an alternative methods that may also be used for characterization of dynamic properties of microstructures.…”