Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1991-06-24
1993-02-02
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
356376, G01N 2186
Patent
active
051840219
ABSTRACT:
A system for inspecting and measuring the dimensions of patterned features on lithographic photomasks includes a confocal scanning microscope beneath which is mounted the photomask to be inspected. The photomask is moved to permit the imaging beam from the microscope to record reflectivity information at closely spaced points along a scan line at the metal-substrate interface within the photomask, and the unpatterned side of the mask is positioned facing the microscope so that the imaging beam passes through the transparent substrate material of the mask to the desired measurement plane. An objective lens specially corrected for imaging through transparent materials is used in the optical system, and compensating glass plates may be selectively placed between the objective lens and the photomask when the substrate of the mask is thinner than the thickness of transparent material for which the objective lens was corrected.
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Allen S.
Kelly Robert S.
Nelms David C.
SiScan Systems, Inc.
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