Methods and architectures for IC interconnect trenches, and trench plugs that define separations between two adjacent trench ends. Plugs and trenches may be defined through a multiple patterning process. An upper grating pattern may be summed with a plug keep pattern into a pattern accumulation layer. The pattern accumulation layer may be employed to define plug masks. A lower grating pattern may then be summed with the plug masks to define a pattern in trench ILD material, which can then be backfilled with interconnect metallization. As such, a complex damascene interconnect structure can be fabricated at the scaled-down geometries achievable with pitch-splitting techniques. In some embodiments, the trenches are located at spaces between first spacer masks defined in a patterning process associated with the first grating pattern while the plug masks are located based on a tone-inversion of second spacer masks associated with the second grating pattern.