High NA swing curve effects

The periodic variations of dose-to-clear, reflection and CD with resist thickness are well known phenomena commonly known as swing curves. Proper process control dictates that the resist thickness is chosen at a swing extreme, so as to reduce dose variation. Swing curves are commonly calculated for normal incidence waves. The recent trends toward high NA optics and use of off-axis illumination introduce oblique waves into the swing curve problem. Significant shifts in the magnitude and the phase of the different swing curves are now possible, and these shifts depend on exposure illumination configuration. This paper will discuss the impact of oblique waves on the swing curve. Experimental swing curves for both 248 and 193nm resist processes will be compared with expectations from simulations.