Photomask inspection by spatial filtering

作者: Norman N Axelrod

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摘要: This disclosure describes an optical spatial filtering technique for detecting hole-type defects and excess spot in photomasks used making microcircuits. An approximate form factor intensity filter provides suppression of the regularly shaped mask features. For masks with features whose boundaries are along only X-Y direction, this advantageously is a cross placed transform plane. With rectangular suppressed, nonrectangular defect data passes. Spots as small 0.1 mil detected displayed on TV monitor; or, using photomultiplier tube, signals stored oscilloscope or by recorder analysis, counted pulse counter. Masks circuits opaque substrates also inspected method.

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