Time-varying intensity map generation for reticles

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:

• defining a plurality of patch areas of a reticle;
• prior to using a reticle in any photolithography process, using an optical reticle inspection tool during a first inspection to obtain, for each of a plurality of sets of one or more patch areas, a reference average of multiple reference intensity values corresponding to light measured from a plurality of sub-areas of each patch area of the reticle;
• after using the reticle in a plurality of photolithography processes, using the optical reticle inspection tool during a second inspection to obtain, for each of the sets of one or more patch areas, an average of multiple test intensity values corresponding to light measured from the plurality of sub-areas of each patch area of the reticle, wherein a same setup recipe for the optical reticle inspection tool is used for both the first and second inspections;
• and
• generating a difference intensity map comprising a plurality of map values that each corresponds to a difference between each average of the test intensity values and average of the reference intensity values for each of the sets of one or more patches, wherein the difference intensity map indicates whether the reticle has degraded over time more than a predefined level.

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

• defining a plurality of patch areas of a reticle;
• prior to using a reticle in any photolithography process, using an optical reticle inspection tool during a first inspection to obtain, for each of a plurality of sets of one or more patch areas, a reference average of multiple reference intensity values corresponding to light measured from a plurality of sub-areas of each patch area of the reticle;
• after using the reticle in a plurality of photolithography processes, using the optical reticle inspection tool during a second inspection to obtain, for each of the sets of one or more patch areas, an average of multiple test intensity values corresponding to light measured from the plurality of sub-areas of each patch area of the reticle, wherein a same setup recipe for the optical reticle inspection tool is used for both the first and second inspections;
• and
• generating a difference intensity map comprising a plurality of map values that each corresponds to a difference between each average of the test intensity values and average of the reference intensity values for each of the sets of one or more patches, wherein the difference intensity map indicates whether the reticle has degraded over time more than a predefined level.