Foreign particle inspection apparatus

Abstract

A foreign particle inspection apparatus includes a detection optical system (4) for condensing scattered light generated by slant illumination (2) by an optical system (41) with a NA of more than 0.4 from the rear side of a sample using a transparent or semitransparent substrate having an opaque circuit pattern. The circuit pattern, such as a reticle, etc., has a phase shift film for improving the patterning resolution, for shielding diffracted light from the circuit pattern by a spatial filter (44) mounted on the Fourier transform plane, and for forming images on a detector (51). A circuit (113) is also provided for correcting detected values of the detector according to uneven illumination, and a circuit for obtaining the added value of detected values of 2 by 2 pixels. A circuit (114) is provided for obtaining the maximum value of four added values which are shifted pixel by pixel in the four directions around each detector pixel. A circuit (112) is provided for storing the detected result in a memory where the substrate sample is divided into blocks every several hundreds pixels. By this arrangement small foreign particles of the order of submicrons adhered on the substrate can be separated and detected easily and stably from the circuit pattern principally using a simple optical structure.