Spatial filter for optically based defect inspection system

Details Spatial filter for optically based defect inspection system Spatial filter for optically based defect inspection system

1990-11-02

1992-12-15

Nelms, David C.

Radiant energy

Photocells; circuits and apparatus

Interference pattern analysis

356237, 382 31, G02B 2742

Patent

active

051720000

ABSTRACT:
In an imaging system (10) for detecting defects in a specimen (14) having a repetitive pattern (16), a spatial filter (50) receives a spatial frequency spectrum produced by a Fourier transform lens (34) and blocks preselected spatial frequency components thereof. The spatial filter includes an array of substantially parallel opaque stripes (70a-70c) that are positioned on a substantially transparent substrate (72). In one embodiment, the stripes are spaced apart by equal distances (78) and are of increasing widths (76a-76c) that correspond to the orders of diffraction of the Fourier transform pattern (45) produced by the Fourier transform lens. The spatial filter can be used to filter light spots forming a Fourier transform pattern for specimens having repetitive pattern sizes included within a specified range of sizes.

REFERENCES:
patent: 4330775 (1982-05-01), Iwamoto et al.
patent: 4806774 (1989-02-01), Lin et al.
patent: 4871257 (1989-10-01), Suzuki et al.

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