Patent ID: 6052478
Filing Date: 2000-04-18
Classification: G01N,G03F

Abstract:
An optical inspection system for inspecting objects formed on substrates, comprising:a stage for carrying a substrate to be inspected such that a surface of said substrate moves in at least two directions within an inspection plane;laser means for providing an illuminating beam of light;optical elements defining a first optical axis intersecting said inspection plane and along which said illuminating beam of light is initially passed, said optical elements including a variable magnification subsystem for focusing said beam of light to a spot on the substrate to be inspected;a beam deflector disposed along said first optical axis and operative to deflect said beam of light in oscillatory fashion whereby said spot is caused to sweep across the surface of said substrate from one side to another of the path traced by the intersection of said optical axis with said substrate as said substrate is moved in said particular manner, and in a direction transverse to said path, as the substrate is carried along said path, the limits of deflection of said beam of light from one side of said path to the other defining the width of a scanning swath over a care area of the substrate including at least a portion of one of said objects;a light detector for detecting changes in the intensity of said beam of light caused by its intersection with the inspected substrate as said beam of light is either transmitted or reflected by said substrate, said light detecting means being responsive to the detected changes in intensity and operative to develop scan signals corresponding thereby, said light detecting means including sampling means for sampling said scan signals to produce sample signals; andan electronic comparator for comparing said pixel sample signals to corresponding reference signals whereby differences therebetween are identified.