Expanded head pillar for bump bonds

1. A microelectronic device, comprising:

a substrate having an input/output (I/O) surface;

an I/O pad on the I/O surface; and

a bump bond structure on the I/O pad, the bump bond structure including:

an electrically conductive pillar, including:

a column on the I/O pad;

an expanded head on the column, wherein:

the expanded head extends past the column on all lateral sides of the column by a lateral distance that is approximately equal to a vertical thickness of the expanded head;

the expanded head has a rounded side profile with a radius that is approximately equal to the thickness of the expanded head; and

the expanded head has a contact surface which is flat, the contact surface being located opposite from the column; and

solder on the contact surface of the expanded head.

2. The microelectronic device of claim 1 , further comprising a seed layer between the column and the I/O pad.

3. The microelectronic device of claim 1 , wherein the column and the expanded head include primarily copper.

4. A method of forming a microelectronic device, comprising:

providing a substrate having an input/output (I/O) surface, with an I/O pad on the I/O surface;

forming a seed layer over the I/O surface, so that the seed layer contacts the I/O pad, the seed layer providing an electrically conductive layer;

forming a plating mask over the seed layer, so that the plating mask exposes the seed layer over the I/O pad;

electroplating metal on the seed layer where exposed by the plating mask, so that the metal extends through the plating mask to form an electrically conductive pillar, the electrically conductive pillar including

a column on the I/O pad extending from the seed layer to a top surface of the plating mask, the top surface of the plating mask being located opposite from the seed layer; and

an expanded head on the column, wherein:

the expanded head extends past the column on all lateral sides of the column by a lateral distance that is approximately equal to a vertical thickness of the expanded head;

the expanded head has a rounded side profile with a radius that is approximately equal to the thickness of the expanded head; and

the expanded head has a contact surface which is flat, the contact surface being located opposite from the column;

forming solder on the contact surface of the expanded head;

removing the plating mask; and

removing the seed layer where exposed by the column.

5. The method of claim 4 , wherein forming the plating mask includes a photolithographic process using photoresist.

6. The method of claim 4 , wherein the column and the expanded head include primarily copper.

7. A microelectronic device, comprising:

a substrate having an input/output (I/O) surface;

an I/O pad on the I/O surface; and

a bump bond structure on the I/O pad, the bump bond structure including:

an electrically conductive pillar, including:

a column on the I/O pad;

an expanded head on the column, wherein:

the expanded head has a contact surface which is flat, the contact surface being located opposite from the column;

the expanded head extends laterally past the column by a first lateral distance in a first lateral direction and by a second lateral distance in a second lateral direction; and

the first lateral distance is greater than the second lateral distance; and

solder on the contact surface of the expanded head.

8. The microelectronic device of claim 7 , wherein the column and the expanded head include primarily copper.

9. The microelectronic device of claim 7 , wherein the flat contact surface extends to a lateral perimeter of the expanded head.

10. A method of forming a microelectronic device, comprising:

providing a substrate having an input/output (I/O) surface, with an I/O pad on the I/O surface;

forming an electrically conductive pillar on the I/O pad, the electrically conductive pillar including

a column on the I/O pad; and

an expanded head on the column, wherein:

the expanded head has a contact surface which is flat, the contact surface being located opposite from the column;

the expanded head extends laterally past the column by a first lateral distance in a first lateral direction and by a second lateral distance in a second lateral direction; and

the first lateral distance is greater than the second lateral distance; and

forming solder on the contact surface of the expanded head.

11. The method of claim 10 , wherein forming the electrically conductive pillar includes:

forming a seed layer over the I/O surface, so that the seed layer contacts the I/O pad, the seed layer providing an electrically conductive layer;

forming a column plating mask over the seed layer, so that the column plating mask has a column opening that exposes the seed layer over the I/O pad;

forming a head plating mask over the column plating mask, so that the head plating mask has a head opening that exposes the column opening in the column plating mask;

electroplating copper on the seed layer where exposed by the column plating mask, so that the copper extends through the column opening to form the column and into the head opening to form the expanded head;

removing the head plating mask;

removing the column plating mask; and

removing the seed layer where exposed by the column.

12. The method of claim 10 , wherein forming the electrically conductive pillar includes:

forming a seed layer over the I/O surface, so that the seed layer contacts the I/O pad, the seed layer providing an electrically conductive layer;

forming a pillar plating mask over the seed layer, so that the pillar plating mask has a column opening that exposes the seed layer over the I/O pad and a head opening that exposes the column opening;

electroplating metal on the seed layer where exposed by the pillar plating mask, so that the metal extends through the column opening to form the column and into the head opening to form the expanded head;

removing the pillar plating mask; and

removing the seed layer where exposed by the column.

13. The method of claim 10 , wherein forming the electrically conductive pillar includes forming the column by a first additive process, and forming the expanded head by a second additive process.

14. A microelectronic device, comprising:

a substrate having an input/output (I/O) surface;

a first I/O pad on the I/O surface; and

a bump bond structure on the first I/O pad, the bump bond structure including:

an electrically conductive pillar, including:

a first column on the I/O pad;

an expanded head on the first column, wherein:

the expanded head has a contact surface, the contact surface being located opposite from the first column;

the expanded head extends laterally past the first column in at least one lateral direction;

the bump bond structure has a first connection area on the contact surface; and

the bump bond structure has a second connection area on the expanded head; and

solder on the contact surface of the expanded head.

15. The microelectronic device of claim 14 , wherein the second connection area is on the contact surface of the expanded head.

16. The microelectronic device of claim 14 , wherein:

the microelectronic device includes a second I/O pad on the I/O surface;

the electrically conductive pillar includes a second column on the second I/O pad; and

the second column contacts the expanded head at the second connection area.

17. A method of forming a microelectronic device, comprising:

providing a substrate having an input/output (I/O) surface, with an I/O pad on the I/O surface;

forming an electrically conductive pillar on the I/O pad, the electrically conductive pillar including

a column on the I/O pad; and

an expanded head on the column, wherein:

the expanded head has a contact surface, the contact surface being located opposite from the first column;

the expanded head extends laterally past the first column in at least one lateral direction;

the bump bond structure has a first connection area on the contact surface; and

the bump bond structure has a second connection area on the expanded head; and

forming solder on the contact surface of the expanded head.

18. The method of claim 17 , wherein forming the electrically conductive pillar includes:

forming a first seed layer over the I/O surface, so that the first seed layer contacts the I/O pad, the first seed layer providing an electrically conductive layer;

forming a column plating mask over the first seed layer, so that the column plating mask has a column opening that exposes the first seed layer over the I/O pad;

electroplating metal on the first seed layer to form the column in the column opening;

forming a second seed layer over the column plating mask so that the second seed layer contacts the column;

forming a head plating mask over the second seed layer, so that the head plating mask has a head opening that exposes the second seed layer over the column;

electroplating metal on the second seed layer where exposed by the head plating mask, to form the expanded head;

removing the head plating mask;

removing the second seed layer where exposed by the expanded head;

removing the column plating mask; and

removing the first seed layer where exposed by the column.

19. The method of claim 17 , wherein forming the electrically conductive pillar includes:

forming a first seed layer over the I/O surface, so that the first seed layer contacts the I/O pad, the first seed layer providing an electrically conductive layer;

forming a column plating mask over the first seed layer, so that the column plating mask has a column opening that exposes the first seed layer over the I/O pad;

electroplating copper on the first seed layer to form the column in the column opening;

forming a head trench layer over the column plating mask, so that the head trench layer has a head trench which exposes the column;

forming a second seed layer over the head trench layer so that the second seed layer contacts the column;

electroplating copper on the second seed layer to form a copper head layer in the head trench;

removing the copper head layer and the second seed layer from over the head trench layer adjacent to the head trench, leaving the copper head layer in the head trench to provide the expanded head;

removing the head trench layer;

removing the column plating mask; and

removing the first seed layer where exposed by the column.

20. The method of claim 19 , wherein removing the copper head layer and the second seed layer from over the head trench layer adjacent to the head trench is performed by a copper chemical mechanical polishing (CMP) process.