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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.
Date of Conference: 15-17 May 2012