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SMART InspEction system for High Speed and multifunctional testing of MEMS and MOEMS

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Interferometer design

The micro-optical interferometers are the heart of the SMARTIEHS instrument. The first preliminary design is shown on this page. The design process is still proceeding. Updates of the design will be introduced here.

The proposed laser interferometer architecture is a DOE based Twymann-Green interferometer setup (figure below). TG configuration is very frequently used for non-contact, field covering measurement of MEMS/MOEMS with reflective (not scattering) surfaces and it was proven the very efficient configuration for active MEMS testing.

The interferometer is formed from a two substrates. The top substrate is a glass plate with a diffraction grating DOE1 etched on the surface. This grating allows changing the direction of the incident, collimated beam in order to illuminate the splitting diffraction grating DOE2. Second substrate is also made from glass and contains DOE2, DOE3 and a mirror surface. The part of light transmitted by DOE2 forms a reference beam. This beam is reflected from mirror on upper side of waver and impinge DEO3 which is a reference mirror. The beam diffracted by DOE2 in direction of object is an object bean and impinges on object surface. Both beams after reflection are recombined by DOE2 and interference patters is imaged (through imaging lens integrated with wafer) at a camera.  

 laser interferometer design


White light interferometer has Mirau configuration. The configuration is shown in figure below. Interferometer consists from 2 glass substrates. Upper – lens wafer carries imaging lenses and reference mirrors. Second wafer has a coating on upper side which is partly reflective. It serves as a beam splitter which divide beam into an object and a reference beam. The reference beam is reflected from mirror in upper wafer. The object beam is reflected from the object. Both beams are recombined on beam splitter wafer and imaged through imaging lens onto the camera.


 LC interferometer design

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