The strip and cleaning step follows MET6 trench ashing to prepare the low-k dielectric trench for Ta-based liner and Cu seed deposition P3.Ashing primarily removes the bulk organic photoresist, but it often leaves behind highly crosslinked fluorocarbon polymer residues generated during the preceding fluorocarbon-based dielectric etch P1.If these post-etch residues remain on the trench sidewalls, they severely degrade the adhesion of the subsequent Ta barrier layer and increase contact resistance