A novel approach to optical wafer pre-alignment using innovative ranging edge detectors

This work describes a novel approach to improving accuracy of optical wafer pre-align systems especially for thin, warped, bonded or carrierless-ultrathin wafers. Using 3D wafer modeling, provided by innovative Ranging Edge Detectors (RED, RE-Detector), the proposed signal processing enables maximum likelihood parameter estimation for best wafer alignment results. Additionally the sensor principle of an RE-Detector enables accurate detection of transparent substrates like sapphire (Al₂O₃), silicon carbide (SiC) or evec glass wafers. This paper describes how wafer pre-alignment has been modified for thin wafer handling with RED pee-alignment resulting in significantly better position accuracy, less wafer damage and cost reduction.