| abstract |
A method for preparing a copper pad surface for electrical connection that has superior diffusion barrier and adhesion properties is provided. In the method, a copper pad surface is first provided that has been cleaned by an acid solution, a protection layer of a phosphorus or boron-containing metal alloy is then deposited on the copper pad surface, and then an adhesion layer of a noble metal is deposited on top of the protection layer. The protection layer may be a single layer, or two or more layers intimately joined together formed of a phosphorus or boron-containing metal alloy such as Ni-P, Co-P, Co-W-P, Co-Sn-P, Ni-W-P, Co-B, Ni-B, Co-Sn-B, Co-W-B and Ni-W-B. A suitable thickness for the protection layer is between about 1,000 Å and about 10,000 Å, and preferably between about 3,000 Å and about 7,000 Å. The adhesion layer can be formed of a noble metal such as Au, Pt, Pd and Ag to a thickness between about 500 Å and about 4,000 Å, and preferably between about 1,000 Å and about 2,000 Å. Alternatively, a nucleation layer of Pd may be deposited between the copper conductive pad surface and the protection layer prior to the electroless deposition of the protection layer. Alternatively, an additional noble metal layer may be deposited on top of the adhesion layer by an electroless Au deposition process to increase the thickness of the final noble metal layer to about 2,000 Å - 12,000 Å, and preferably between about 4,000 Å and about 6,000 Å. The present invention further discloses a conductive pad for forming an electrical connection thereon which includes a copper pad surface, a protection layer of a phosphorus or boron-containing metal alloy, and an adhesion layer of a noble metal deposited on top of the protection layer. The present invention is further directed to an electrical structure which includes the conductive pad with an electrical connection integrally formed with and on top of the adhesion layer, i.e. either of a wirebond or a solder bump. |