Damascene Naming Subtractive Copper Interconnect
Damascene interconnect is named after an ancient metal-inlay craft, and the analogy is deliberately exact: you carve a trench into a surface first, then fill it with metal, rather than depositing metal everywhere and cutting away what you don't want. Damascening was a decorative technique for inlaying gold or silver wire into a carved groove in steel, and chipmakers borrowed the name directly when copper interconnect replaced aluminum, because copper cannot be patterned by the subtractive etch process aluminum used — copper doesn't form a clean, volatile etch byproduct, so the entire interconnect flow had to be inverted: etch the dielectric first, fill the resulting trench with metal second.
A few things explain why the inlay name fits so precisely, and why single and dual get their own sub-names:
The name captures why copper forced the entire process order to flip, not just a material swap. Aluminum interconnect was subtractive: deposit a blanket aluminum film, pattern photoresist on top, then etch away everything the resist doesn't protect, leaving aluminum lines behind. Copper has no practical dry-etch chemistry that produces a volatile byproduct the way aluminum's chlorine-based etch does, so engineers etch the dielectric into the shape of the desired wire instead, then electroplate copper to overfill that shape, then chemical-mechanical-polish the excess away — the metal is inlaid into a pre-carved cavity exactly as in the original craft, which is why "subtractive" and "damascene" are presented as opposite, not similar, process philosophies.
Single damascene is named for completing one feature type per fill, dual damascene for completing two in the same fill. A single-damascene step fills either a via (the vertical connection between metal layers) or a trench (the horizontal line) in its own separate etch-fill-polish cycle. A dual-damascene step etches both the via hole and the line trench above it before a single copper fill covers both at once — one electroplating step and one CMP step produce a via and its connected line together, which is why dual damascene became the industry-standard copper flow: it cuts the number of metal-fill and polish cycles roughly in half compared to doing vias and lines as separate single-damascene steps.
The copper-specific constraint is also why a barrier layer gets deposited before the copper fill, though that barrier has its own separate name and is not part of what "damascene" itself describes. Damascene names the carve-then-fill order; it says nothing by itself about what thin liner layers coat the trench before the copper goes in, which is a related but distinct naming topic.
Siblings worth distinguishing: this entry covers the damascene-versus-subtractive process-order naming and the single-versus-dual fill-count naming specifically; it does not cover the naming of multi-patterning lithography schemes (LELE, SADP, SAQP), which describe how a pattern reaches the lithography resist before any etch or fill happens, nor CMP defect naming (dishing, erosion), which describes failure modes of the polish step that follows a damascene fill rather than the fill scheme's own name.
Read "damascene" as a direct historical borrowing that tells you the entire process philosophy in one word — carve the insulator, inlay the metal — and read "single" or "dual" in front of it as a count of how many features (via alone, trench alone, or both together) one such inlay cycle completes, which is also a direct count of how many fewer or more fill-and-polish cycles a given interconnect flow requires.