Patent ID: 8766192

Claim:
A method of inspecting a substrate having intrinsic heterogeneous patterns, the method comprising the steps of: providing an optical device and front-side lighting on a first side of the substrate; providing near-infrared lighting on a second side of the substrate opposite to the first side, the near-infrared lighting comprising a plurality of near-infrared light sources and operable to penetrate the substrate so as to be detectable by the optical device through the substrate; obtaining at least one first image of the substrate illuminated by the front-side lighting; obtaining a plurality of second images of the substrate illuminated by the near-infrared lighting from the second side, wherein each image of the substrate is obtained while the substrate is illuminated by a respective one of the plurality of near-infrared light sources; and thereafter processing the first and second images to distinguish between the heterogeneous patterns on the substrate and any cracks present on the substrate.