Infrared scanning white light interferometry using a solid state light source

Scanning White Light Interferometry (SWLI) allows surface characterization of MEMS components. With transparent samples SWLI can image multiple stacked layers. However, since silicon is opaque to visible wavelengths, only the top layer can be measured using visible light. We combined multiple infrared light emitting diodes (IR-LEDs) to achieve adjustable IR illumination. This allows simultaneous measurement of top and bottom surface topographies of silicon samples - such as MEMS membranes- using a SWLI equipped with an IR camera. This advances the state of the art of the field of MEMS characterization by allowing looking under membranes of these devices during operation.