Dark field imaging defect inspection system for repetitive pattern integrated circuits

Apparatus which may be used to locate defects on a surface having a repetitive pattern comprising:

• a) illuminating means for illuminating the surface with at least one beam of monochrome light at a desired angle with respect to the surface of the wafer of between 8 degrees and a predetermined maximum angle;
• b) lens means positioned with an optical axis normal to the surface for capturing light which is scattered from the surface at angles within the numerical aperture of the lens means, wherein the numerical aperture of the lens means defines said predetermined maximum angle;
• c) filtering means for spatially filtering the captured light to attenuate spatial frequencies corresponding to the repetitive pattern relative to spatial frequencies corresponding to the defects;
• and
• d) imaging means for focusing the spatially filtered light into an image, wherein images of the defects are accentuated relative to the image of the repetitive pattern.

A method of locating defects on a surface having a repetitive pattern comprising the steps of:

• a) illuminating the surface with a beam of monochrome light at an angle of between 8 and 45 degrees with respect to the surface;
• b) capturing any light which is scattered from the surface at angles between 45 degrees and 90 degrees;
• c) spatially filtering the captured light to attenuate spatial frequencies corresponding to the repetitive pattern relative to spatial frequencies corresponding to the defects;
• d) focusing the spatially filtered light into an image, wherein components of the image representing the defects on the surface are accentuated relative to components of the image representing the repetitive pattern.