JPS6473242A - Discrimination of defect and dust on surface to be measured - Google Patents

Abstract

PURPOSE:To enable highly accurate discrimination of a defect and dust on a surface to be measured in a short time, by detecting an image forming position of scattered light from the surface being measured. CONSTITUTION:Incident luminous flux 11 such as laser light is incident on a surface 12 to be measured almost vertically and scattered light thereof forms an image with lenses 13 and 14 on position sensors 15 and 16. When none of a defect 7 and a dust 8 exist on the surface 12 being measured, no scattered light is generated to detect. When they exist, scattered light is generated to forms an image with the lenses 13 and 14 on the position sensors 15 and 16. Here, displacements X1 and X2 on the position sensors 15 and 16 are determined by the position Y and the height Z of the detect 7 or the dust 8. The relationship of the formula of Z=(X1-X2)/2K.sintheta (K is magnification of image) between the height Z and the displacements X1 and X2. When the displacement is X1<X2, the height is given by Z<0 and the presence a defect is judged. When X1>X2, then Z>0 and the presence of a dust is judged.