Fourier filters and wafer inspection systems are provided. One embodiment
relates to a one-dimensional Fourier filter configured to be included in
a bright field inspection system such that the bright field inspection
system can be used for broadband dark field inspection of a wafer. The
Fourier filter includes an asymmetric illumination aperture configured to
be positioned in an illumination path of the inspection system. The
Fourier filter also includes an asymmetric imaging aperture complementary
to the illumination aperture. The imaging aperture is configured to be
positioned in a light collection path of the inspection system such that
the imaging aperture blocks light reflected and diffracted from
structures on the wafer and allows light scattered from defects on the
wafer to pass through the imaging aperture.