Monitoring changes in photomask defectivity

An inspection system for inspecting a photolithographic reticle, the system comprising at least one memory and at least one processor that are configured to perform the following operations:

• in a first single-die inspection of a reticle that is has been identified as being within specifications, generating a plurality of baseline events corresponding to a plurality of unusual baseline features of the reticle, wherein each baseline event indicates a location and a size value for a corresponding unusual baseline feature;
• after using the reticle in one or more photolithography processes, performing a second single-die inspection of the reticle so as to generate a plurality of current events corresponding to a plurality of current unusual features of the reticle, wherein each current event indicates a location and a size value for a corresponding current unusual feature;
• and
• generating an inspection report of a plurality of candidate reticle defects and their images, wherein the candidate defects include a first subset of the current events and their corresponding plurality of candidate defect images and exclude a second subset of the current events and their corresponding plurality of excluded images, wherein each of the first subset of events included in the inspection report has a location and size value that fails to match any baseline event's location and size value by a predefined amount, and each of the second subset of events excluded from the inspection report has a location and size value that matches any baseline event's location and size value by the predefined amount.

A computer readable medium having instruction stored thereon for performing the following operations:

• performing a first single-die inspection of a reticle that is has been identified as being within specifications so as to generate a plurality of baseline events corresponding to a plurality of unusual baseline features of the reticle, wherein each baseline event indicates a location and a size value for a corresponding unusual baseline feature;
• after using the reticle in one or more photolithography processes, performing via an optical reticle inspection tool a second single-die inspection of the reticle so as to generate a plurality of current events corresponding to a plurality of current unusual features of the reticle, wherein each current event indicates a location and a size value for a corresponding current unusual feature;
• and
• generating an inspection report of a plurality of candidate reticle defects and their images, wherein the candidate defects include a first subset of the current events and their corresponding plurality of candidate defect images and exclude a second subset of the current events and their corresponding plurality of excluded images, wherein each of the first subset of events included in the inspection report has a location and size value that fails to match any baseline event's location and size value by a predefined amount, and each of the second subset of events excluded from the inspection report has a location and size value that matches any baseline event's location and size value by the predefined amount.