Thin film optical interference causes a sinusoidal variation in lithographic properties with film thickness known as the swing effect. The most well known manifestations are the threshold clearing energy (E$-0$/) and critical dimension (CD) swings which arise due to variations in the in-coupling efficiency of light. The E$-0$/ swing is conceptually simple, requiring only that the amount of photo-active compound (PAC) conversion is constant within a swing film thickness cycle. The present work verifies that E$-0$/ swing is a purely optical effect and is independent of bulk dissolution curve details. For resists of identical optical properties, the faster one will have the lower E$-0$/ swing. `Secondary' swing effects, defined here as lithographic changes arising due to remnant standing wave phase at the film surface, include variations in gamma, resolution, focus latitude, and profile. Some i-line photoresists, particularly those which give significant surface induction in development, show large oscillations in these performance measures depending on swing phase.
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