Inspecting high-resolution photolithography masks

摘要

Optical inspection methods and apparatus for high-resolution photomasks using only a test image. A filter is applied to an image signal received from radiation that is transmitted by or reflected from a photomask having a test image. The filter may be implemented using programmed control to adjust and control filter conditions, illumination conditions, and magnification conditions.

主权项

1. A method comprising:
illuminating a portion of a lithographic mask having a high-resolution mask pattern with an incident light beam having a characteristic optical bandwidth and focused through an optical element; capturing light that is transmitted through the mask or reflected by the mask, the captured light forming a sensed image file; and using a processor to:
apply a filter function to the sensed image file to obtain a filtered image file having the high-resolution mask pattern removed and having desired frequency characteristics;perform a mathematical operation in the frequency domain using the sensed image file and the filtered image file to obtain a resultant image in accord with an image processing scheme; andevaluate the resultant image for indications of defects in the lithographic mask.