| 摘要 |
This disclosure describes an optical spatial filtering technique for detecting hole-type defects and excess spot defects in photomasks used in 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 the X-Y direction, this filter advantageously is a cross placed in the transform plane. With rectangular features suppressed, only nonrectangular defect data passes. Spots as small as 0.1 mil are detected and displayed on a TV monitor; or, using a photomultiplier tube, signals are stored on an oscilloscope or by a recorder for analysis, or counted with a pulse counter. Masks or circuits on opaque substrates are also inspected by this method.
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