Systems and methods for optimizing focus for imaging-based overlay metrology

摘要

Methods and systems for focusing and measuring by mean of an interferometer device, having an optical coherence tomography (OCT) focusing system, by separately directing an overlapped measurement and reference wavefront towards a focus sensor and towards an imaging sensor; where a predefined focusing illumination spectrum of the overlapped wavefront is directed towards the focus sensor, and where a predefined measurement illumination spectrum of the overlapped wavefront is directed towards the imaging sensor. Methods and systems for maintaining focus of an interferometer device, having an OCT focusing system, during sample's stage moves.