Structure and method for bonding to copper interconnect structures
An integrated circuit structure and a method for fabricating the structure. The method comprises forming a copper bond pad for attaching the integrated circuit to a package. Copper oxide is removed from the pad by reduction in a hydrogen ion atmosphere. For attaching the integrated circuit to a bump-bonding package an under-bump metallization layer is formed over the reduced copper pad and a solder bump formed thereover. The process can also be employed in a wire bonding process by forming an aluminum layer overlying the cleaned copper pad. The structure of the present invention comprises a copper pad formed in a substrate. A passivation layer defining an opening therein overlies the copper pad. A under-bump metallization layer is disposed in the opening and a solder bump overlies the metallization layer. Alternatively, the structure further comprises an aluminum pad disposed overlying the reduced copper pad.
1. A method for forming a solder bond on a copper pad, comprising:
forming the copper pad;
forming a passivation layer over the copper pad;
forming an opening in the passivation layer to expose a surface of the copper pad;
determining a first surface reflectivity of the copper pad;
subjecting the surface to a reducing agent and an inert carrier gas, subsequent to determining the first surface reflectivity of the copper pad, wherein a proportion of the reducing agent to the inert carrier gas is at least 2:1 to reduce copper oxide on the surface;
determining a second surface reflectivity of the copper pad, subsequent to subjecting the surface to the reducing agent;
controlling the reducing agent according to the first and second surface reflectivity; and
forming the solder bond on the reduced surface.
2. The method of claim 1 wherein the step of forming the solder bond further comprises forming an under-bump metallization layer on the reduced surface.
3. The method of claim 2 further comprising forming a solder bump on the under-bump metallization layer.
4. The method of claim 1 wherein the step of forming the solder bond further comprises forming an aluminum layer on the reduced surface.
5. The method of claim 1 wherein the reducing agent comprises hydrogen ions.
6. The method of claim 5 wherein the step of subjecting the surface is carried out in a radio-frequency back sputter chamber.
7. The method of claim 5 wherein the step of subjecting the surface further comprises subjecting a hydrogen containing species to a plasma for forming the hydrogen ions from the hydrogen containing species.
8. The method of claim 1 wherein the copper pad is formed in a semiconductor substrate.
9. The method of claim 8 wherein the semiconductor substrate comprises interconnect structures, and wherein the copper pad is in conductive communication with at least one of the interconnect structures.
10. The method of claim 1 further comprising sputtering particles on the passivation layer and the surface.
11. The method of claim 10 wherein the step of sputtering particles further comprises sputtering argon ions.
12. The method of claims 1 wherein the copper pad is formed on an integrated circuit.
13. A method for forming a solder bond on a copper surface, comprising
forming the copper surface, wherein unwanted copper oxide forms on the copper surface;
determining a first surface reflectivity of the copper surface;
subjecting the surface to a reducing agent and an inert carrier gas, subsequent to determining the first surface reflectivity of the copper pad, wherein a proportion of the reducing agent to the carrier gas is at least 2:1 to reduce the copper oxide;
determining a second surface reflectivity of the copper surface, subsequent to subjecting the surface to the reducing agent;
controlling the reducing agent in response to the surface reflectivity; and
forming the solder bond on the reduced copper surface.
14. The method of claim 13 wherein the reducing step further comprises exposing the copper surface to hydrogen species ions.
15. The method of claim 14 wherein the exposing step further comprises reducing the copper oxide according to the equation, Cu x O+2H + =Cu+H 2 O.
16. The method of claim 14 wherein the exposing step is carried out in a radio-frequency back sputter chamber.