Multiple beam inspection apparatus and method

An optical inspection system for inspecting a surface of a mask, reticle or semiconductor wafer for defects, comprising:

• a light source for emitting an incident light beam along an optical axis;
• a first set of optical elements arranged for separating the incident light beam into a plurality of individual light beams dedicated to defect inspection, directing the individual light beams to intersect with the surface of the mask, reticle or semiconductor wafer, focusing the individual light beams to a plurality of scanning spots on the surface of the mask, reticle or semiconductor wafer, and scanning the scanning spots over the surface of the mask, reticle or semiconductor wafer when the mask, reticle or semiconductor wafer and the plurality of individual light beams are linearly moved relative to one another in a first direction, wherein the first set of optical components are further arranged to deflect the individual light beams along individual scan paths in a second direction that differs from the first direction, the individual scan paths being offset from each other in the first direction;
• and
• a light detector arrangement including individual light detectors that correspond to individual ones of a plurality of reflected or transmitted light beams caused by the intersection of the individual light beams with the surface of the mask, reticle or semiconductor wafer, the light detectors being arranged for sensing the light intensity of either the reflected or transmitted light.