Damascene process
Beginner
Making copper wires by cutting grooves in an insulating layer, filling them with copper and polishing off the excess, like inlaying metal in wood.
Novice
Copper can’t be patterned by plasma etching, so the pattern is etched as trenches in the insulator instead. A barrier layer, copper electroplating and chemical-mechanical polishing leave copper only in the trenches.
Expert
Dual damascene etches the via holes and the line trenches, then fills both in one plating step. Ta/TaN barriers keep copper out of the dielectric; CMP dishing and erosion in wide or dense regions are why metal density rules exist.
Explained in Making them (Transistors).
See also: Chemical-mechanical polishing (CMP), Metal stack.