Sub-resolution defect detection

An optical metrology apparatus configured to detect a sub-resolution defect, the optical metrology apparatus comprising:

• a light source that produces an illumination beam;
• an objective lens that directs the illumination beam to be incident on a sample and to receive light reflected by the sample,
• at least one detector array that receives the light after it is reflected by the sample and acquires optical metrology data from the light, wherein the optical metrology data comprises an intensity value at each pixel in the at least one detector array;
• and
• at least one processor coupled to the at least one detector array, the at least one processor obtains the optical metrology data, determines parameter values for a signal model for a pixel of interest in the at least one detector array based on the optical metrology data received by a plurality of pixels neighboring the pixel of interest, determines a residual for the pixel of interest using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest, and detects a defect, which is smaller than the pixel of interest, at a location on the sample corresponding to the pixel of interest using the residual for the pixel of interest.

An apparatus configured to detect a sub-resolution defect, the apparatus comprising:

• means for obtaining optical metrology data from a sample, the optical metrology data comprising an intensity value at each pixel in at least one detector array;
• means for determining parameter values for a signal model for a pixel of interest in the at least one detector array based on the optical metrology data received by a plurality of pixels neighboring the pixel of interest;
• means for determining a residual for the pixel of interest using the optical metrology data received by the pixel of interest and determined parameter values for the signal model for the pixel of interest;
• and
• means for detecting a defect, which is smaller than the pixel of interest, at a location on the sample corresponding to the pixel of interest using the residual for the pixel of interest.