Hybrid bonding with air-gap structure

1. A method comprising:

performing a first Chemical Mechanical Polish (CMP) on surface features of a first package component, wherein the surface features comprise a first metal pad encircled by a first surface dielectric layer, and the first CMP is performed using a first slurry;

performing a second CMP on the surface features of the first package component using a second slurry different from the first slurry, wherein the second CMP is started when the first surface dielectric layer is exposed, wherein in the second CMP, a first trench is formed in a peripheral region of the first metal pad; and

bonding the first package component to a second package component, wherein the first metal pad is bonded to a second metal pad of the second package component, and the first surface dielectric layer is bonded to a second surface dielectric layer of the second package component.

2. The method of claim 1 , wherein the first metal pad comprises a barrier layer, and a metallic material encircled by the barrier layer, wherein a sidewall of the barrier layer is exposed to the first trench.

3. The method of claim 2 , wherein the second metal pad comprises a second trench, and the first trench is joined to the second trench.

4. The method of claim 2 , wherein after the first CMP and before the second CMP, substantially no trench is generated in the metallic material.

5. The method of claim 2 , wherein in the second CMP, a galvanic potential difference between the metallic material and the barrier layer is greater than about 0.3V.

6. The method of claim 2 , wherein the metallic material comprises copper, the first surface dielectric layer comprises silicon oxynitride, and the second CMP is performed using a slurry comprising K 2 SO 4 , citric acid, or benzotriazole.

7. The method of claim 1 , wherein the first trench has a depth greater than about 0.3 μm.

8. The method of claim 2 , wherein at a stopping time point of the first CMP, the first surface dielectric layer is covered by horizontal portions of the barrier layer, and the barrier layer is conductive.

9. A method comprising:

forming an opening in a dielectric layer;

depositing a barrier layer, wherein the barrier layer extends into the opening;

filling the opening with a metallic material, with the metallic material being over the barrier layer;

performing a first Chemical Mechanical Polish (CMP) to remove excess portions of the metallic material and the barrier layer until the dielectric layer is revealed, wherein the first CMP is performed using a first slurry, and wherein remaining portions of the metallic material and the barrier layer in the opening form a first metal pad; and

performing a second CMP on the first metal pad using a second slurry different from the first slurry to form trench in a peripheral region of the first metal pad, wherein at a starting time point of the second CMP, the dielectric layer is exposed.

10. The method of claim 9 , wherein after the first CMP and before the second CMP, substantially no trench is generated to extend into the first metal pad.

11. The method of claim 9 , wherein the first metal pad is recessed more in the peripheral region than in a center region encircled by the peripheral region.

12. The method of claim 9 , wherein the trench is in the metallic material, and a sidewall of the barrier layer is exposed to the trench.

13. The method of claim 9 , wherein the trench forms a trench ring.

14. The method of claim 9 , wherein in the second CMP, a galvanic potential difference between the metallic material and the barrier layer is greater than about 0.3V.

15. The method of claim 9 , wherein the metallic material comprises copper, the dielectric layer comprises silicon oxynitride, and the second CMP is performed using a slurry comprising K 2 SO 4 , citric acid, or benzotriazole.

16. The method of claim 9 further comprising bonding the first metal pad with a second metal pad.

17. A method comprising:

performing a first Chemical Mechanical Polish (CMP) on a first metal pad of a first package component, wherein the first metal pad is encircled by a first surface dielectric layer, and substantially no recess is generated to extend from a top surface of the first metal pad into the first metal pad;

performing a second CMP on the first metal pad of the first package component, wherein the second CMP is performed using a second CMP condition different from a first CMP condition for performing the first CMP, with a trench generated to extend into the first metal pad; and

bonding the first package component to a second package component, wherein the first metal pad is bonded to a second metal pad of the second package component, and wherein the first surface dielectric layer is bonded to a second surface dielectric layer of the second package component.

18. The method of claim 17 , wherein the first CMP condition comprises a first slurry, and the second CMP condition comprises a second slurry different from the first slurry.

19. The method of claim 17 , wherein the trench forms a ring, with the trench separated from the first surface dielectric layer by a thin layer of conductive material.

20. The method of claim 19 , wherein the thin layer of conductive material is formed of a material different from a material of a portion of the first metal pad encircled by the trench.