Process window discovery, expansion and control of design hotspots susceptible to overlay failures

The latest design nodes have seen development and use of multi-patterning techniques like SAQP and LELELE for density multiplication in semiconductor industry below 28nm processes. Traditional lithography process window studies have centered on focus and dose latitudes and are typically evaluated with inspection and CD measurements on a focus dose modulated wafer. However, on sub 14 nm design nodes, overlay has become an important litho parameter acting as a source of new systematic defects on an otherwise centered process.