Semiconductor device having a copper pillar interconnect structure

1. A method of manufacturing a semiconductor device, the method comprising:

depositing a photoresist layer over a semiconductor substrate;

patterning the photoresist layer to form an opening in the photoresist layer;

forming a copper pillar in the opening;

forming a diffusion barrier layer over the copper pillar and over a photoresist portion of the photoresist layer directly adjoining the opening; and

depositing a solder structure over the diffusion barrier layer,

wherein forming the diffusion barrier layer comprises:

plating a base portion of the diffusion barrier layer in the opening; and

plating an overhang portion of the diffusion barrier layer over the base portion and over the photoresist portion.

2. The method of claim 1 , wherein the overhang portion of the diffusion barrier layer is formed by mushroom plating.

3. The method of claim 1 , wherein depositing the solder structure comprises:

depositing an additional photoresist layer over the diffusion barrier layer;

patterning the additional photoresist layer to form a solder opening in the additional photoresist layer; and

depositing the solder structure in the solder opening.

4. A method of manufacturing a semiconductor device, the method comprising:

depositing a first photoresist layer over a semiconductor substrate;

patterning the first photoresist layer to form an opening in the first photoresist layer;

forming a copper pillar in the opening;

depositing a second photoresist layer over the semiconductor substrate;

patterning the second photoresist layer to form an overhang opening in the second photoresist layer, the overhang opening being aligned with the opening and having a width which is greater than a width of the opening;

forming a diffusion barrier layer over the copper pillar and in the overhang opening; and

depositing a solder structure over the diffusion barrier layer.

5. The method of claim 4 , wherein depositing the second photoresist layer over the semiconductor substrate and patterning the second photoresist layer to form the overhang opening in the second photoresist layer is performed before forming the copper pillar in the opening.

6. The method of claim 4 , wherein the second photoresist layer is deposited over the first photoresist layer.

7. The method of claim 6 , wherein the second photoresist layer is deposited after forming the copper pillar in the opening.

8. The method of claim 4 , wherein forming the diffusion barrier layer comprises:

plating a base portion of the diffusion barrier layer in the opening; and

plating an overhang portion of the diffusion barrier layer in the overhang opening.

9. The method of claim 4 , wherein depositing the solder structure comprises:

depositing the solder structure in the overhang opening.

10. A method of manufacturing a semiconductor device, the method comprising:

depositing a photoresist layer over a semiconductor substrate;

patterning the photoresist layer to form an opening in the photoresist layer;

forming a copper pillar in the opening;

forming a diffusion barrier layer over the copper pillar and over a photoresist portion of the photoresist layer directly adjoining the opening; and

depositing a solder structure over the diffusion barrier layer,

wherein depositing the solder structure comprises:

depositing an additional photoresist layer over the diffusion barrier layer;

patterning the additional photoresist layer to form a solder opening in the additional photoresist layer; and

depositing the solder structure in the solder opening.

11. A method of manufacturing a semiconductor device, the method comprising:

coating a surface of a semiconductor substrate by a seed layer, the seed layer covering a die pad exposed at the surface of the semiconductor substrate;

depositing a photoresist layer on the seed layer;

patterning the photoresist layer to form an opening in the photoresist layer, the opening exposing a part of the seed layer that covers the die pad;

forming a copper pillar in the opening;

forming a diffusion barrier layer over the copper pillar and over a photoresist portion of the photoresist layer directly adjoining the opening; and

depositing a solder structure over the diffusion barrier layer,

wherein the diffusion barrier layer prevents direct contact of the solder structure and the copper pillar.

12. The method of claim 11 , further comprising:

after depositing the solder structure over the diffusion barrier layer, removing the photoresist layer and all of the seed layer except for a section of the seed layer that is interposed between the die pad and the copper pillar.

13. The method of claim 12 , further comprising:

after the removing, reflowing the solder structure.

14. The method of claim 11 , wherein forming the diffusion barrier layer comprises:

plating a base portion of the diffusion barrier layer in the opening; and

plating an overhang portion of the diffusion barrier layer over the base portion and over the photoresist portion.

15. The method of claim 14 , wherein the overhang portion of the diffusion barrier layer is formed by mushroom plating.

16. The method of claim 11 , wherein depositing the solder structure comprises:

depositing an additional photoresist layer over the diffusion barrier layer;

patterning the additional photoresist layer to form a solder opening in the additional photoresist layer; and

depositing the solder structure in the solder opening.

17. The method of claim 11 , wherein copper metal of the copper pillar is deposited by electroplating on the part of the seed layer exposed by the opening in the photoresist layer.