Novel at-design-rule via-to-metal overlay metrology for 193-nm lithography

The effect of scanner aberrations on pattern placement errors (PPE) in the copper interconnect lithography process is studied both in simulations and experimentally. A new grating-based overlay mark, advanced imaging metrology, enables measuring device feature overlay. It is shown that the grating mark exhibits superior performance over conventional box-in-box marks. A comparison between grating-based optical and direct CD scanning electron microscopic (SEM) device overlay measurements was done. Both CD SEM and grating mark optical measurements show sensitivity to PPE. Good matching between the new grating target and device overlays was demonstrated.