Electrical Defect Density Test Structures for DFM in the Sub-wavelength Lithography Regime with Copper Metallization

Serpent/comb test structures are standard electrical defect monitors for semiconductor interconnect processes. Traditionally, these test structures are drawn as straight lines, based on the assumption that defects are random and independent of geometry. However, with lithography now performed in the sub-wavelength regime, critical dimensions are not always printed as drawn, depending on the surrounding geometries. Therefore, defect density is not random but has a systematic component. Effective design for yield depends on understanding systematic process/layout interactions. This paper describes test structures to characterize defect density sensitivity to layout, followed by experimental results on copper metallization.