Patent ID: 7041998
Filing Date: 2006-05-09
Classification: G01N

Abstract:
1. In a method for an inspection system for detecting defects in a planar object having periodic structure, a method for providing a modifiable mask to enhance visibility of non-periodic structure in said planar object comprising: projecting, as an input spatial signal, an image of said planar object through a first lens assembly upon a Fourier plane to yield an optical spatial Fourier transform of said spatial signal of said planar object; electrically aligning to said periodic structure an electrically programmable spatial light modulator at the Fourier plane of said first lens assembly in order to block periodic components of said spatial Fourier transform and to yield a filtered optical spatial Fourier transform of predominantly non-periodic components, said spatial light modulator having sufficient resolution, optical energy throughput, and contrast to serve as an effective masking element; and projecting as an output spatial signal an image of said filtered optical spatial Fourier transform through a second lens assembly to an image plane to produce a filtered image to enhance visibility of said non-periodic structure to a spatial optical energy detector; wherein said electrically aligning step employs a converted optical signal from said image plane as a feedback signal.