A novel dark field in-process optical inspection method for micro-openings on mirrored surfaces beyond the diffraction limit using active phase control

We propose a novel in-process optical inspection method for micro-openings on a mirrored surface, such as mechanical functional gaps in micro-electro-mechanical systems (MEMS) and microchannels in microfluidics systems. The proposed method has not only highly sensitive detection characteristics based on dark field observations but also super-resolution observation characteristics based on the light scattering dependence of the edges of the micro-opening on the orientation of incident light under coherent imaging. Both theoretical and experimental analyses suggest that we can confirm the existence of proper micro-openings beyond the diffraction limit of imaging optics by shifting the relative phase of the counter-propagating incident beams.