Multiple beam inspection apparatus and method

An optical inspection system for inspecting the surface of a substrate, comprising:

• a light source for emitting a light beam along an optical axis;
• a first set of optical elements arranged for separating the light beam into a plurality of light beams, directing the plurality of light beams to intersection with the surface of the substrate, and focusing the plurality of light beams to a plurality of scanning spots on the surface of the substrate;
• a second set of optical elements adapted for collecting a plurality of transmitted light beams caused by the intersection of the plurality of light beams with the surface of the substrate and by passing the plurality of light beams through the substrate, the second set of optical elements including at least a lens arrangement and a prism;
• a light detector arrangement including individual light detectors that each receive individual ones of the plurality of transmitted light beams, the light detectors being arranged for sensing the light intensity of the transmitted light beams, wherein the lens arrangement focuses the plurality of transmitted light beams onto the prism, and the prism directs the individual ones of the plurality of transmitted light beams towards the individual light detectors of the light detector arrangement;
• and
• a control system for controlling the optical components of the first and second optical elements, and for receiving scan signals from each of the light detectors of the light detector arrangement.