Optics: measuring and testing – Inspection of flaws or impurities – Having predetermined light transmission regions
Patent
1996-04-19
1998-11-17
Nelms, David C.
Optics: measuring and testing
Inspection of flaws or impurities
Having predetermined light transmission regions
356339, 356364, 356367, G01N 2100
Patent
active
058384332
ABSTRACT:
The present invention discloses a mask defect inspection apparatus for optically detecting a defect on a mask having a circuit pattern, which comprises an illumination system for illuminating the mask with inspection light; a first light receiving optical system for receiving the inspection light reflected by the mask; a second light receiving optical system for receiving the inspection light transmitted by the mask; a first spatial filter for shielding the inspection light passing through a central region including the optical axis of the first light receiving optical system in an optical Fourier transform plane for the circuit pattern in the first light receiving optical system; a second spatial filter for shielding the inspection light passing through a central region including the optical axis of the second light receiving optical system in an optical Fourier transform plane for the circuit pattern in the second light receiving optical system; a first detector for photoelectrically converting the inspection light having passed through the first spatial filter; a second detector for photoelectrically converting the inspection light having passed through the second spatial filter; and a gain adjusting circuit for adjusting a gain of a first output signal from the first detector to output a third output signal and adjusting a gain of a second output signal from the second detector to output a fourth output signal, wherein the defect is detected based on either a relative intensity difference or intensity ratio between the third output signal and the fourth output signal gain-adjusted by the gain adjusting circuit.
REFERENCES:
patent: 3790287 (1974-02-01), Cuthbert et al.
patent: 4468120 (1984-08-01), Tanimoto et al.
patent: 4610541 (1986-09-01), Tanimoto et al.
patent: 4681442 (1987-07-01), Wagner
Nelms David C.
Nikon Corporation
Ratiff Reginald A.
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