Understanding illumination effects for control of optical proximity effects (OPE)

Optical lithography has had great success in recent history in utilizing the most advanced optical technology to create NA=1.35 immersion lenses. These lenses have aberration levels at or below the 5m level. Much of this is due to advancements in lens design, materials, and aspheric polishing techniques. Now that the lenses are nearly "perfect", more attention is being given to the illuminator and its performance. This paper examines the fundamental metrics that are used to analyze the illumination source shape as it pertains to the optical proximity effect (OPE). It is found that the more traditional metric of partial coherence, σ, is often not sufficient to explain through pitch CD performance. Metrics are introduced to compare multiple sources and compared to their correlation to OPE with respect to a reference. A new parametric model for annular illumination is introduced and shown to correlate within an RMS=0.03nm of the OPE data.