Inspection method and inspection apparatus

An inspection apparatus comprising:

• an illumination optical system including:
• a light source that emits linearly-polarized light having a predetermined wavelength,
• a polarizing beam splitter directing the linearly-polarized light emitted from the light source, and
• a half-wave plate and a quarter-wave plate forming the linearly-polarized light directed by the polarizing beam splitter into elliptically-polarized light having a major axis in a direction except an angle in the ranges of −5 degrees to 5 degrees and 85 degrees to 95 degrees with respect to the length direction of a line of a repetitive pattern formed on a target to illuminate the target;
• an imaging optical system using the quarter-wave plate, the half-wave plate, and the polarizing beam splitter to transmit the light reflected by the target and further including an image capturing sensor that obtains an optical image of the pattern formed on the target based on the light reflected by the target and transmitted from the polarizing beam splitter to form an optical image of the reflected light of the target on the image capturing sensor;
• an image processor that obtains an average gray level A and a standard deviation of a gray level a of the optical image with respect to each of a plurality of optical images acquired by changing the angle of the polarization of the reflected light incident on the image capturing sensor and detects a defect of the target using a specific optical image obtained at a selected angle of polarization of the reflected light which provides a value of (σ/√A) obtained from the standard deviation a and the average gray level A that becomes a minimum.