Although some form of volatile copper compound has been known to exist since 1947, with more discovered as the century progressed, none were in industrial use, so copper could not be patterned by the previous techniques of photoresist masking and plasma etching that had been used with great success with aluminium. The inability to plasma etch copper called for a drastic rethinking of the metal patterning process and the result of this rethinking was a process referred to as an "additive patterning", also known as a "Damascene" or "dual-Damascene" process by analogy to a traditional technique of metal inlaying.