Methods that include acquiring aerial images of a reticle for different
values of a member of a set of lithographic variables are provided. One
method also includes determining a presence of an anomaly in a design
pattern of the reticle by comparing at least one pair of the aerial
images corresponding to at least two of the different values. A different
method includes comparing at least one pair of the aerial images
corresponding to at least two of the different values and determining an
area on the reticle where a lithography process using the reticle is most
susceptible to failure based on the results of the comparison. Another
embodiment includes determining a presence of transient repeating defects
on the reticle by subtracting non-transient defects from the aerial
images and comparing at least one pair of the aerial images corresponding
to at least two of the different values.