US Patent 7433034 Darkfield defect inspection with spectral contents

A metrology device produces broadband illumination, e.g., an illumination line, that is incident on a substrate at an oblique angle of incidence and which is scanned across the substrate. A first detector collects a darkfield image, while a second detector collects the spectrally reflected light. The angle of incidence of the illumination is variable so that the darkfield image is received by the first detector without interference from diffracting structures on the substrate. Alternatively, the position of the first detector may be varied to receive the darkfield image, or a filter may be used to filter out light from any non-defect diffracting structures on the substrate. A processor uses the darkfield data from the first detector to determine if a defect is present on the substrate and uses the spectral data from the second detector to identify the material composition of the defect.