Three-dimensional integrated circuits with protection layers

1. A semiconductor structure comprising:

a first die comprising:

a first substrate; and

a first bonding pad over the first substrate;

a second die having a first surface and a second surface opposite the first surface, wherein the second die comprises a second bonding pad on the first surface and bonded to the first bonding pad of the first die through flip-chip bonding, and wherein the first die and the second die have a gap therebetween; and

a protection layer having a vertical portion on a sidewall of the second die, and a horizontal portion extending over the first die, wherein the protection layer seals the gap between the first die and the second die.

2. The semiconductor structure of claim 1 further comprising a coating on the horizontal portion of the protection layer and in a region defined by the vertical portion and the horizontal portion of the protection layer.

3. The semiconductor structure of claim 2 , wherein a top edge of the vertical portion of the protection layer is substantially level with a top surface of the coating.

4. The semiconductor structure of claim 1 , wherein the protection layer comprises a material selected from the group consisting essentially of diamond film, amorphous carbon, silicon oxide, silicon nitride, silicon carbide, silicon oxynitride, silicon oxycarbide, and combinations thereof.

5. The semiconductor structure of claim 1 , wherein the protection layer is formed on all sidewalls of the second die, and encircles the second die.

6. The semiconductor structure of claim 1 , wherein the protection layer has a thickness of between about 50 Å and about 2000 Å.

7. The semiconductor structure of claim 1 , wherein the first die further comprises an active device in the first substrate and an interconnect structure over the first substrate, wherein the interconnect structure is connected to the first bonding pad.

8. The semiconductor structure of claim 1 , wherein the first die is free from active devices.

9. The semiconductor structure of claim 1 further comprising a third die stacked on the second die, and an additional protection layer on a sidewall of the third die and extending over the second die.

10. The semiconductor structure of claim 1 further comprising a third die stacked on the first die, wherein the protection layer is on a sidewall of the third die and extending over the first die.

11. The semiconductor structure of claim 1 , wherein the second die comprises:

a second substrate;

an active device in the second substrate;

an interconnect structure over the second substrate, wherein the second bonding pad is electrically coupled to the interconnect structure;

and

a contact pad on the second surface and electrically connected to the second bonding pad.

12. The semiconductor structure of claim 11 further comprising a through-silicon via in the second substrate and electrically interconnecting the second bonding pad and the contact pad of the second die.