Photomask inspection by optical spatial filtering

Details Photomask inspection by optical spatial filtering Photomask inspection by optical spatial filtering

1969-09-15

1977-01-04

Stern, Ronald J.

Optics: measuring and testing

Refraction testing

Prism engaging specimen

350162SF, 356 71, G01B 908, G02B 2700

Patent

active

040009491

ABSTRACT:
An intensity-type optical spatial filtering system is arranged to form a composite visual image of all nonperiodic errors in a photomask or other two-dimensional pattern which contains an array of regularly spaced, normally identical elements. A coherent beam of light is diffracted by the pattern and focused onto a transparency having a second array of discrete opaque regions spaced by a distance inversely proportional to the element spacing on the pattern. The focused light, spatially modulated by the transparency, is reimaged and projected in enlarged form onto a display screen.

REFERENCES:
patent: 3064519 (1962-11-01), Shelton
patent: 3240108 (1966-03-01), Lehan et al.
patent: 3435244 (1969-03-01), Burckhardt et al.
patent: 3614232 (1971-10-01), Mathisen
O'Neill, E. L., "Spatial Filtering in Optics," IRE Transactions on Information Theory, June 1956, pp. 56-64.

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