Apparatus with four light detectors for checking surface of mask

Details Apparatus with four light detectors for checking surface of mask Apparatus with four light detectors for checking surface of mask

1988-01-26

1989-12-26

Westin, Edward P.

Radiant energy

Photocells; circuits and apparatus

Optical or pre-photocell system

250572, 356237, G01N 2188, G01N 2132

Patent

active

048899984

ABSTRACT:
An apparatus for detecting foreign particles on a transparent pellicle comprises a first illuminating device having a first optical axis crossing a surface of the pellicle at a predetermined angle for supplying a light beam onto said transparent pellicle along said first optical axis and a second illuminating device having a second optical axis crossing the surface of said pellicle at an angle different from said predetermined angle for supplying a light beam to said transparent pellicle along said second optical axis. The apparatus further includes a detector for comparing quantity of light of a light beam scattered by a foreign particle and directed to a predetermined direction from said first illuminating device with quantity of light of a light beam scattered by the foreign particle and directed to a predetermined direction from said second illuminating device and for determining a surface of the transparent pellicle on which said foreign particle exists.

REFERENCES:
patent: 4172666 (1979-10-01), Clarke
patent: 4468120 (1984-08-01), Tanimoto et al.
patent: 4541715 (1985-09-01), Akiyama et al.
patent: 4610541 (1986-09-01), Tanimoto et al.
patent: 4669875 (1987-06-01), Shiba et al.
patent: 4731855 (1988-03-01), Suda et al.
patent: 4776693 (1988-10-01), Imamura et al.
Akikazu Tanimoto et al, "Proceedings of SPIE", pub. 1984, vol. 470, pp. 242-249.

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