Defect inspection method and defect inspection system

A system, comprising:

• an energy source configured to cause an energy beam to be directed to a wafer;
• a plurality of first detectors configured to detect the energy beam scattered from the wafer and to generate a plurality of inspection images in response to the detected energy beam, wherein the plurality of first detectors are positioned at different azimuthal angles;
• and
• a processor electrically coupled to the plurality of first detector and configured to:
• merge the plurality of inspection images to generate a merged image;
• enhance quality of the merged image to generate a processed image;
• determine whether the processed image is qualified using a reference image;
• and
• find defects of a qualified image in response to determining that the processed image is qualified,
• wherein if the processed image comprises a contact-hole pattern,
• the plurality of first detectors are further configured to generate the plurality of inspection images from different azimuthal angles at a same height;
• and
• the processor is further configured to:
• generate the merged image by aligning and merging the plurality of inspection images.

A non-transitory computer-readable storage medium, comprising instructions which, when executed by a processor, perform steps of:

• receiving a plurality of first inspection images comprising a pattern of interest formed on a wafer;
• merging the first inspection images to generate a merged image;
• performing a quality-enhancing operation on the merged image to generate a processed image;
• determining the processed image as a qualified image when a matching ratio that reflects a fraction of correctly aligned features between the processed image and a reference image is above a first predetermined threshold;
• selecting a first feature within the qualified image;
• selecting a second feature within the reference image corresponding to the first feature of the qualified image;
• comparing the qualified image with the reference image to determine a variation in the first feature with respect to the second feature;
• and
• detecting a defect on the wafer based on the comparing of the first and second features.