Bonding structures and methods forming the same

1. A method comprising:

forming a first dielectric layer over a conductive pad;

forming a second dielectric layer over the first dielectric layer;

etching the second dielectric layer to form a first opening, with a top surface of the first dielectric layer exposed to the first opening;

forming a template layer filling the first opening;

applying a patterned photo resist over the template layer;

etching the template layer and the first dielectric layer to form a second opening, wherein the etching is performed using the patterned photo resist as an etching mask, with a top surface of the conductive pad exposed to the second opening; and

plating a conductive pillar in the second opening.

2. The method of claim 1 further comprising forming a conformal dielectric layer extending into the first opening, with the conformal dielectric layer contacting the top surface of the first dielectric layer, wherein the second opening penetrates through the conformal dielectric layer.

3. The method of claim 2 further comprising:

contacting the conductive pillar with a package component, with the conformal dielectric layer spaced apart from the package component; and

separating the conductive pillar from the package component.

4. The method of claim 1 further comprising etching the template layer to reveal the first opening again, wherein sidewalls of the conductive pillar are exposed to the first opening.

5. The method of claim 1 , wherein the conductive pillar has edges contacting edges of the template layer.

6. The method of claim 1 further comprising bonding the conductive pillar to a conductive feature through a solder region, wherein the solder region fills the first opening and contacts a sidewall of the conductive pillar.

7. The method of claim 1 , wherein the plating the conductive pillar is performed without forming a blanket seed layer.

8. A method comprising:

forming a first dielectric layer over a conductive pad, with the first dielectric layer being a planar layer;

forming a second dielectric layer over the first dielectric layer;

etching the second dielectric layer to form a first opening, wherein the etching the second dielectric layer stops when a top surface of the first dielectric layer is exposed;

forming a conformal dielectric layer extending into the first opening;

forming a template layer filling the first opening and over the conformal dielectric layer;

forming a patterned photo resist over the template layer;

etching the template layer, the conformal dielectric layer, and the first dielectric layer to form a second opening;

plating a conductive pillar in the second opening, wherein edges of the conductive pillar are in contact with edges of the template layer, with the conductive pillar connected to the conductive pad; and

removing the template layer.

9. The method of claim 8 , wherein the template layer is formed using tetraethyl orthosilicate (TEOS) as a precursor.

10. The method of claim 8 further comprising:

contacting a top surface of the conductive pillar with a surface of a conductive feature in a package component, with the conformal dielectric layer spaced apart from the package component; and

after the contacting, separating the conductive pillar from the package component.

11. The method of claim 8 , wherein after the template layer is removed, portions of the first opening is revealed again, and sidewalls of the conductive pillar are exposed to the first opening.

12. The method of claim 8 , wherein the conductive pillar comprises:

a first metallic material contacting the top surface of the conductive pad; and

a second metallic material over and contacting the first metallic material.

13. The method of claim 8 further comprising bonding the conductive pillar to a conductive feature through a solder region, wherein the solder region fills the first opening and contacts a sidewall of the conductive pillar.

14. The method of claim 8 , wherein the plating the conductive pillar is performed without forming a blanket seed layer.

15. A method comprising:

depositing a first dielectric layer over a conductive pad;

depositing a second dielectric layer over the first dielectric layer; and

plating a conductive pillar penetrating through the first dielectric layer and the second dielectric layer, wherein the conductive pillar contacts a top surface of the conductive pad, and the conductive pillar is physically spaced apart from the second dielectric layer by a first opening surrounding the conductive pillar;

putting a top surface of the conductive pillar in contact with a surface of a conductive feature in a package component; and

after the contacting, separating the conductive pillar from the package component.

16. The method of claim 15 further comprising forming a conformal dielectric layer extending into the first opening and contacting a top surface of the first dielectric layer, sidewalls of the first dielectric layer and the second dielectric layer, and a top surface of the second dielectric layer.

17. The method of claim 16 further comprising etching the second dielectric layer to form the first opening, wherein the first opening stops on a top surface of the first dielectric layer, and the method further comprises etching the first dielectric layer and the conformal dielectric layer to form a second opening, with the conductive pillar having a bottom portion formed in the second opening.

18. The method of claim 16 , wherein sidewalls of the conductive pillar are further spaced apart from a vertical portion of the conformal dielectric layer.

19. The method of claim 16 , wherein the forming the conductive pillar comprises:

forming a template layer filling the first opening; and

etching the template layer until the conductive pad is revealed, wherein the conductive pillar has a top portion formed in an opening of the template layer.

20. The method of claim 15 , wherein the depositing the second dielectric layer comprises depositing a plurality of dielectric layers, with neighboring layers in the plurality of dielectric layers being formed of different dielectric materials.