Electroless copper plating applicable for bulk-silicon micromachined radio frequency inductor

An electroless copper plating process has been developed for bulk-silicon micromachined radio frequency (RF) inductor. In the process, isotropic oxygen plasma bombardment is used for silicon surface pretreatment and activation time is optimized. High quality copper film with thickness up to 890 nm is plated on single-crystal silicon surface, resulting in low sheet resistivity of 0.04 Omega/square. The electroless copper plating technology is combined with bulk-silicon micromachining to fabricate a new kind of RF inductor consisting of suspended single-crystal silicon spiral with copper coated as conducting surface. A highly conformal copper coating layer is formed on every side of the suspended silicon spiral inductor using the plating process. Quality factor over 30 at 11 GHz and self-resonant frequency higher than 15 GHz are achieved for an inductance of 4 nH. Further inductor RF performance improvement by means of thicker copper coating is conceivable. (c) 2006 Elsevier B.V. All rights reserved.Materials Science, MultidisciplinaryMaterials Science, Coatings & FilmsPhysics, AppliedPhysics, Condensed MatterSCI(E)EI3ARTICLE42607-261151