Copper-encapsulated silicon micromachined structures

Selective copper encapsulation on silicon has been used to fabricate micromachined devices such as inductors with quality factors over 30 at frequencies above 5 GHz. The devices are fabricated using either polysilicon surface micromachining, or integrated polysilicon and deep reactive ion etching bulk silicon micromachining. Their exposed silicon surfaces are selectively activated by palladium activation, which allows the subsequent copper deposition on the activated silicon surfaces only. This silicon encapsulated-with-copper technique takes advantage of both the excellent mechanical properties of silicon (to maintain structural integrity), and the high conductivity of copper (for electrical signal transmission). Furthermore, the process not only minimizes interfacial forces typical of physical metal deposition on silicon, but also balances the forces by metal encapsulation on all sides of the silicon structures.