Photomask inspection method

1. A photomask inspection method, comprising:

acquiring reflected image data and transmitted image data of a photomask having a glass region and a film region formed on the glass on a surface thereof;

creating inverted reflected image data by subtracting the reflected image data from pixel value data of the glass region and the film region;

creating offset inverted reflected image data by raising pixel values of the inverted reflected image data by a fixed amount;

creating normalized correlation reflected image data by computing a normalized correlation of the offset inverted reflected image data and an offset Gaussian distribution-type kernel;

identifying foreign particle candidates by comparing the normalized correlation reflected image data and a predetermined threshold;

creating offset transmitted image data by subtracting the pixel value data of the film region from the transmitted image data and then raising the pixels values by the fixed amount;

creating normalized correlation transmitted image data by computing a normalized correlation of the offset transmitted image data and the offset Gaussian distribution-type kernel;

identifying holes by comparing the normalized correlation transmitted image data and the predetermined threshold; and

determining, among the foreign particle candidates, those foreign particles that are not located at the same position as the holes as true foreign particles.

2. The method according to claim 1 , wherein the photomask has two regions, a glass region and a film region where a transmittance to inspection light is lower than in the glass region, on the surface thereof.