MacroCD contact ellipticity measurement for lithography tool qualification

Contact hole integrity is an important metric for IC manufacturers, which is reflected in tight ellipticity control as part of the lithography tool qualifications. The current ellipticity measurement methodology is very sensitive to random process variations of the contact hole shape. Determining ellipticity in a systematic manner poses a challenge on qualification productivity, as acquiring more data for statistical validity leads to unacceptably long measurement times. The introduction of the so-called MacroCD Vector measurement enables a single shot large sampling of contact holes, including vector calculation and averaging of all individual contact ellipticity results within the MacroCD measurement array. Based on these enhanced measurement features, it is shown that contact hole ellipticity can be determined with much higher accuracy while local, mostly process induced variations can be characterized simultaneously. This opens possibilities to study correlation between ellipticity and possible root causes in the litho process module.