System for Detecting Anomalies and/or Features of a Surface

Abstract

A cylindrical mirror or lens is used to focus an input collimated beam of light onto a line on the surface to be inspected, where the line is substantially in the plane of incidence of the focused beam. An image of the beam is projected onto an array of charge-coupled devices parallel to the line for detecting anomalies and/or features of the surface, where the array is outside the plane of incidence of the focused beam. For inspecting surface with a pattern thereon, the light from the surface is first passed through a spatial filter before it is imaged onto the charge-coupled devices. The spatial filter includes stripes of scattering regions that shift in synchronism with relative motion between the beam and the surface to block Fourier components from the pattern. The spatial filter may be replaced by reflective strips that selectively reflects scattered radiation to the detector, where the reflective strips also shifts in synchronism with the relative motion.

1 . A method for detecting anomalies associated with a surface with a diffracting pattern, comprising: 
 focusing a beam of electromagnetic radiation to a line on the surface;    causing relative rotational motion between the surface and the beam;    causing scattered radiation from the line to interact with an array of elongated strips that shift substantially in synchronism with the rotational motion, so that diffraction from the pattern will not reach a detector as the pattern rotates; and    detecting scattered radiation from the line by means of the detector.    
   
   
       2 . An apparatus for detecting anomalies associated with a surface with a diffracting pattern, comprising: 
 optics focusing a beam of electromagnetic radiation to a line on the surface;    an instrument causing relative rotational motion between the surface and the beam;    a detector; and    an array of elongated strips that interact with scattered radiation from the line, wherein said strips shift substantially in synchronism with the rotational motion so that diffraction from the pattern does not reach the detector as the pattern rotates;    wherein the detector detects radiation from the surface reaching the filter and provides a signal indicative of said anomalies.