The aerial images of modern photomasks are highly susceptible to CD errors, owing to the high MEEF values
characteristic of the low-k1 regime. The requirement for tight wafer CD control thus places stringent constraints on mask
errors. Nevertheless, multiple physical variations of the mask parameters can lead to the same aerial CD error.
We introduce IntenCDTM, a novel, fast and precise CD variation mapping application running on Applied Materials'
aerial image inspection tools. The IntenCD application generates a high-precision map of the CD variation, and allows
tighter control of mask manufacturing process and qualification, without loss of precision compared to slow, discrete
measurement tools such as CD SEM, but with a higher throughput, while offering complete mask coverage and higher
We study and provide the theoretical basis to the IntenCD application. We analyze image formation of dense, repetitive
mask patterns under aerial imaging conditions and show, analytically and numerically (through a series of simulations),
that for a small perturbation of the nominal physical mask parameters, the relative variation of the average aerial
intensity scales linearly with the relative aerial CD error. This linear relation, unique to aerial imaging mask inspection,
is independent of the physical source of the variation and of the mask design pitch. Our results imply that a robust aerial
intensity measurement can detect sub-nm aerial CD variations. We discuss some practical problems that have to be
addressed to obtain this challenging resolution, and describe in some detail the technological solutions.