Surface defect tester

A surface defect tester for detecting a defect in a surface of a faceplate by scanning the surface with light beam and receiving light reflected by the surface by a light receiver, comprising:

• a light illuminating system for relatively scanning the surface of the faceplate by irradiating the surface with a light beam having width in a direction perpendicular to a main scanning direction;
• a first light receiver composed of an arrangement of n light receiving elements, where n is an integer equal to or larger than 2;
• an optical system for focusing an image of a scanning position on the faceplate on a light receiving region defined by said arrangement of said n light receiving elements such that an amount of light received by said light receiving region becomes a peak at a center of said light receiving region in an arranging direction of said light receiving elements and is gradually reduced substantially symmetrically toward both ends thereof in the same direction, at least two of said n light receiving elements being arranged in symmetrical positions in the light receiving region about said center of said light receiving region as a reference;
• and
• a defect detector for detecting the defect by using a difference in level between light signals received from said symmetrically arranged two light receiving elements as a defect detection signal, said focused image being moved in said arranging direction when said light receiver receives light reflected by a recessed or protruded defect by the scanning in said main scan direction.