Protective layer for contact pads in fan-out interconnect structure and method of forming same

1. A method for integrated circuit packaging comprising:

providing a die having a contact pad on a top surface;

forming a passivation layer over and in physical contact with the contact pad;

forming a conductive protective layer over and covering the contact pad, the conductive protective layer comprising a first conductive material and a second conductive material over the first conductive material, the first conductive material being different from the second conductive material, the first conductive material extending through the passivation layer and physically contacting the contact pad, the second conductive material extending over and physically contacting a top surface of the passivation layer;

attaching the die to a carrier, the contact pad being interposed between the carrier and the conductive protective layer;

forming a molding compound over the die and the conductive protective layer;

planarizing the molding compound to expose an insulating layer disposed on a top surface of the conductive protective layer, wherein the insulating layer comprises a sidewall substantially aligned with or contacting a sidewall of the die, wherein a topmost surface of the insulating layer is level with a topmost surface of the molding compound, and wherein the insulating layer physically contacts a sidewall of the second conductive material of the conductive protective layer;

after planarizing the molding compound, while the die is attached to the carrier, exposing the conductive protective layer by laser drilling the insulating layer; and

forming a redistribution layer (RDL) over the die, wherein the RDL is electrically connected to the contact pad through the conductive protective layer.

2. The method of claim 1 , wherein the forming the conductive protective layer comprises an electroless plating process.

3. The method of claim 2 , wherein the electroless plating process comprises pretreating the die by applying one or more chemical washes to the contact pad and submerging the die in an electroless bath solution at a temperature of about 60 degrees Celsius (C) to about 80 degrees C.

4. The method of claim 1 , wherein the conductive protective layer comprises nickel (Ni), copper (Cu), silver (Ag), gold (Au), palladium (Pd), platinum (Pt), tin (Sn), zinc (Zn), ruthenium (Ru), a noble metal, or a combination thereof.

5. The method of claim 1 , wherein laser drilling the insulating layer comprises laser drilling an opening exposing the conductive protective layer using an ultraviolet laser or a carbon dioxide laser.

6. The method of claim 1 , wherein the insulating layer comprises a first polymer layer.

7. The method of claim 6 , wherein planarizing the molding compound comprises grinding the molding compound to expose the first polymer layer.

8. The method of claim 6 , wherein the first polymer layer comprises polyimide (PI), polybenzoxazole (PBO), benzocyclobuten (BCB), epoxy, silicone, acrylates, nano-filled pheno resin, siloxane, a fluorinated polymer, polynorbornene, or a combination thereof.

9. The method of claim 6 , further comprising:

forming a second polymer layer over the RDL;

forming an under bump metallurgy (UBM) in the second polymer layer, wherein the UBM is electrically connected to the RDL; and

forming a conductive bump on the UBM.

10. The method of claim 1 , wherein the insulating layer and the molding compound are formed of a same material.

11. The method of claim 1 , wherein forming the molding compound comprises forming the molding compound to extend along sidewalls of the passivation layer.

12. A method for integrated circuit packaging comprising:

providing a die having one or more contact pads on a top surface;

forming a conductive protective layer over the die by electroless plating each of the one or more contact pads with a metallic material;

after forming the conductive protective layer over the die, attaching a bottom surface of the die to a carrier;

after attaching the bottom surface of the die to the carrier, forming a molding compound over the die and the conductive protective layer, wherein the molding compound further extends along sidewalls of the die;

reducing a thickness of the molding compound;

after reducing the thickness of the molding compound and while the bottom surface of the die is attached to the carrier, exposing the conductive protective layer by laser drilling; and

forming a redistribution layer (RDL) over the die, wherein the RDL extends through a first polymer layer over the die, and wherein the RDL is electrically connected to the one or more contact pads through the conductive protective layer.

13. The method of claim 12 , wherein the exposing the conductive protective layer comprises laser drilling one or more openings in the molding compound.

14. The method of claim 12 , wherein the exposing the conductive protective layer comprises laser drilling one or more openings in a second polymer layer, wherein the second polymer layer is disposed over and contacting the conductive protective layer.

15. The method of claim 12 , where the metallic material comprises nickel (Ni), copper (Cu), silver (Ag), gold (Au), palladium (Pd), platinum (Pt), tin (Sn), zinc (Zn), ruthenium (Ru), a noble metal, or a combination thereof.

16. An integrated circuit (IC) structure comprising:

a die comprising a contact pad on a top surface, wherein the contact pad physically contacts the top surface of the die;

a passivation layer over and covering edges of the contact pad, wherein the passivation layer physically contacts the top surface of the die;

a metallic protective layer over the contact pad, the metallic protective layer comprising a first portion and a second portion over the first portion, the first portion comprising a first metallic material, the second portion comprising a second metallic material different from the first metallic material, wherein the first metallic material physically contacts the contact pad, and wherein the second metallic material extends over and physically contacts a top surface of the passivation layer;

a polymer layer over the metallic protective layer and the passivation layer, the polymer layer physically contacting the passivation layer, wherein a width of the second portion of the metallic protective layer narrows as the second portion of the metallic protective layer extends away from the top surface of the passivation layer and into the polymer layer;

a molding compound extending along sidewalls of the die and the passivation layer, a topmost surface of the molding compound being level with a topmost surface of the polymer layer; and

a redistribution layer (RDL) over the die and the molding compound, wherein a portion of the RDL extends through the polymer layer, physically contacts the metallic protective layer and is electrically connected to the contact pad through the metallic protective layer.

17. The IC structure of claim 16 , wherein the metallic protective layer comprises nickel (Ni), copper (Cu), silver (Ag), gold (Au), palladium (Pd), platinum (Pt), tin (Sn), zinc (Zn), ruthenium (Ru), a noble metal, or a combination thereof.

18. The IC structure of claim 16 , wherein the metallic protective layer has a thickness between 2 μm to 5 μm.

19. The IC structure of claim 16 , wherein the molding compound extends along sidewalls of the polymer layer.

20. The IC structure of claim 16 , wherein the polymer layer comprises polyimide (PI), polybenzoxazole (PBO), benzocyclobuten (BCB), epoxy, silicone, acrylates, nano-filled pheno resin, siloxane, a fluorinated polymer, polynorbornene, or a combination thereof.

21. The IC structure of claim 16 , wherein a sidewall of the second portion of the metallic protective layer has an angle defined by a first line tangent to the sidewall of the second portion of the metallic protective layer and a second line parallel to a top surface of the passivation layer, and wherein the angle is between 45° and 90°.

22. The IC structure of claim 16 , wherein the second portion of the metallic protective layer has a horizontal dimension and a vertical dimension, wherein the horizontal dimension is substantially equal to the vertical dimension.

23. The IC structure of claim 16 , wherein the polymer layer contacts a sidewall of the metallic protective layer.

24. The IC structure of claim 16 , wherein the first metallic material is nickel (Ni), and wherein the second metallic material is copper (Cu).