Optical inspection method and apparatus

摘要

Apparatus for optically inspecting an object (eg photomask PM) having upper and lower faces for indicating the condition of the object, includes a lighting system (4, 12) periodically reflecting a beam of light from one face of the object (PM) to produce a series of short-duration time-spaced reflected beams, and periodically transmitting a beam of light through both faces of the object (PM) to produce a series of short-duration time-spaced transmitted beams time-interlaced with the reflected beams, a sensor (20) sensing the short-duration time-spaced reflected beams and transmitted beams, and generating electrical outputs corresponding thereto, and processor (32) receiving the electrical outputs and processing them to provide an indication of the condition of the object. A method of optically inspecting an object having upper and lower faces for indicating the condition of the object is also described. <IMAGE>