Method for manufacturing semiconductor device having electrode for external connection

1. A method for manufacturing a semiconductor device, comprising:

forming a first metal film over an electrode pad disposed on a substrate;

forming a second metal film on the first metal film;

forming a first oxide film on a surface of the first metal film and a second oxide film on a surface of the second metal film by oxidizing the surfaces of the first metal film and the second metal film;

removing the first oxide film; and

melting the second metal film after removing the first oxide film.

2. The method according to claim 1 , wherein a metal surface of the first metal film is exposed by removing the first oxide film.

3. The method according to claim 2 , wherein part of the first metal film is removed along with the first oxide film in removing the first oxide film.

4. The method according to claim 3 , wherein, as a result of removing the part of the first metal film along with the first oxide film, a side surface of the first metal film is receded inward with respect to a side surface of the second metal film.

5. The method according to claim 1 , wherein, after the surfaces of the first metal film and the second metal film are oxidized, the first oxide film is removed by being exposed to a solution having a higher etching rate for the first oxide film than for the second oxide film.

6. The method according to claim 5 , wherein the first metal film contains Ni, the second metal film contains Sn and Ag, and the solution contains hydrogen peroxide and sulfuric acid.

7. The method according to claim 1 , further comprising, before forming the first metal film, forming a third metal film that covers a region including a surface of the electrode pad, the third metal film having a single layer structure or a multilayer structure,

wherein the first metal film is formed above the electrode pad by electroplating using the third metal film so that the first metal film is separated from the electrode pad with the third metal film in between, and the second metal film is formed on the first metal film.

8. The method according to claim 7 , further comprising, after formation of the first and second metal films, removing portions of the third metal film exposed from the first metal film,

wherein after the portions of the third metal film are removed, the surfaces of the first and second metal films are oxidized.

9. The method according to claim 7 , wherein

after formation of the first and second metal films, portions of the third metal film are exposed, and the surfaces of the first and second metal films and the surface of the portions of the third metal film are oxidized, and

after the surfaces of the first and second metal films, and portions of the third metal film are oxidized, the first oxide film is removed together with a third oxide film formed on the surface of the portions of the third metal film.

10. The method according to claim 9 , further comprising, after the third oxide film is removed, a step of removing the portions of the third metal film.

11. The method according to claim 1 , wherein melting the second metal film is conducted in a reducing gas atmosphere.

12. The method according to claim 1 , wherein in oxidizing the surfaces of the first and second metal films, the first and second metal films are exposed to an oxidizing gas atmosphere.

13. The method according to claim 12 , wherein the first and second metal films are exposed to an oxidizing gas atmosphere having a temperature lower than the melting point of the second metal film.