Leveraging Focus Spot Monitoring Data in FEOL to Resolve a High Impact MOL Defect

As feature sizes shrink in 14nm technology and beyond, focus window limited immersion lithography steps like those in the middle of line (MOL) are most susceptible to hotspots caused by small localized variations in wafer topography. Hotspots in MOL are almost always killer, with a near 100% probability of the entire die failing due to the presence of a single hotspot defect. Focus spots are identified by the leveling system in the lithography scanner and the reported as a fault detection and classification (FDC) signal, driving wafer disposition and tool actions. Comprehensive reporting of focus spot signals opens up the possibility of utilizing high volume focus spot data in lieu of defect data where spatially unique hotpsot signals may be lost in the random baseline defectivity. We have analyzed focus spot data collected at a lower impact front end of line (FEOL) step to drive down hotspots at a high impact MOL step, both of which are affected by incoming defectivity due to repeat passes on a common identified tool. This work is an example of the smart resolution of a cross-module contamination issue by innovatively leveraging high volume focus spot monitoring data.