Adding cap to copper passivation flow for electroless plating
An integrated circuit includes a metal seed layer contacting a metal element of a top interconnect layer, a plated copper pad over the seed layer, a plated metal cap layer on the top surface of the copper pad, an upper protective overcoat covering a lateral surface of the copper pad and overlapping a top surface of the cap layer with a bond pad opening exposing the cap layer, and a bond pad of electroless plated metal in the bond pad opening.
1. A process of forming an integrated circuit, comprising the steps of:
forming an interconnect region, said interconnect region including a top interconnect level and a metal element of said top interconnect level, said metal element being exposed in an area for a bond pad;
forming a metal seed layer over said integrated circuit, so that said seed layer makes electrical contact to said metal element;
forming a plating mask over said seed layer so as to expose an area over said metal element;
performing a first plating operation to form a copper pad over said metal element in said exposed area of said plating mask, so that said copper pad makes electrical connection to said seed layer;
performing a second plating operation to form a metal cap layer free of copper on a top surface of said copper pad;
removing said plating mask;
performing a seed layer etch to remove a portion of said seed layer outside said copper pad;
forming an upper protective overcoat over said integrated circuit, said upper protective overcoat overlapping a top surface of said metal cap layer and covering said lateral surface of said copper pad, said upper protective overcoat having a bond pad opening which exposes a portion of said top surface of said metal cap layer; and
forming a bond pad of electroless plated metal in said bond pad opening, said bond pad making electrical connection to said metal cap layer.
2. The process of claim 1 , in which said metal cap layer includes nickel between 1 to 3 microns thick.
3. The process of claim 1 , in which said metal cap layer includes a metal selected from the group consisting of: nickel, palladium, gold and any combination thereof.
4. The process of claim 1 , in which said step of forming said metal cap layer includes an electroplating process.
5. The process of claim 1 , in which said step of forming said metal cap layer includes an electroless plating process.
6. The process of claim 1 , in which said upper protective overcoat includes polyimide.
7. The process of claim 1 , in which step of forming said seed layer includes:
sputtering layer of titanium tungsten alloy so that said layer of titanium tungsten alloy contacts said metal element; and
sputtering a layer of copper on said layer of titanium tungsten alloy.
8. The process of claim 1 , in which said bond pad provides a wirebond pad.
9. The process of claim 1 , in which said step of forming said bond pad is performed so that a top surface of said bond pad is coplanar with a top surface of said upper protective overcoat within 100 nanometers.
10. The process of claim 1 , in which said step of forming said bond pad includes plating a layer of nickel.