Inspection method and inspection apparatus

摘要

The field of view of an objective lens is divided into two areas, and a transmission image of a photomask and a composite image obtained by optically synthesizing a transmission image and a reflection image of the photomask are picked up in parallel. A drop image generated at an edge portion of a pattern portion in the composite image is deleted by limiter processing or masking processing, or is deleted by using primary-differentiated signals of a composite image signal and a transmission image signal.

主权项

1. An inspection apparatus that inspects a photomask having a pattern forming surface on which a pattern portion and a light-transmitting portion are formed, and a back surface opposed to the pattern forming surface, the inspection apparatus comprising:
an illumination optical system including: a transmitted illumination optical system that projects a transmitted illumination beam toward a back surface of a photomask to be inspected and illuminates a first area of the photomask; and a reflected illumination optical system that projects a reflected illumination beam toward an element forming surface of the photomask and illuminates a second area of the photomask, the second area being smaller than the first area and overlapping the first area in an optical axis direction; a detection system including: a first image pickup element that receives synthetic light of reflected light and transmitted light output from the second area of the photomask and picks up a composite image obtained by optically synthesizing a transmission image and a reflection image of the photomask; and a second image pickup element that receives transmitted light output from a third area of the photomask and picks up a transmission image of the photomask, the third area being a remaining area of the first area excluding the second area; and a signal processing device that is coupled to the detection system, processes an image signal output from the detection system, and outputs data indicating a defect, wherein the transmitted illumination optical system and the reflected illumination optical system are set so as to satisfy b2a limiter processing unit that performs limiter processing on an image signal output from the first image pickup element to delete a signal portion having a luminance value equal to or smaller than a luminance value b0 that satisfies b2