Fabrication of nickel dots using selective electroless deposition on silicon wafer

The selective deposition of nickel on n-Si(100) wafer in aqueous solution was investigated. It was confirmed by cross-sectional FE-TEM examination that the deposition of nickel occurred from a solution of nickel ions prepared by excluding the hypophosphitc reducing agent from the conventional electroless nickel plating bath, and that this deposition reaction accompanied the formation of SiO₂. This finding shows that the electrons needed to reduce the nickel ions to the metal are supplied directly from the Si wafer. By utilizing this galvanic displacement reaction, nickel metal in the form of minute dots measuring 1 μm in diameter was selectively deposited using a silicon oxide layer as the resist in combination with a two-step process, which consisted of the first step of immersing a Si water into a solution containing nickel ions but no reducing agent to form nuclei of nickel metal, and the second step of immersing the wafer with the nuclei into a conventional electroless nickel plating bath to cause the growth of the nuclei to the desired size.