Bonded assembly containing oxidation barriers, hybrid bonding, or air gap, and methods of forming the same

1. A bonded assembly, comprising:

a first semiconductor die comprising a first substrate, first semiconductor devices, and first bonding pads that are electrically connected to a respective node of the first semiconductor devices and laterally surrounded by a first pad-level dielectric layer, wherein the first pad-level dielectric layer comprises a first polymer material layer and first polymer hairs extending from a horizontal surface of the first polymer material layer, having a diameter or maximum width from 0.1 microns to 10 microns, a height from 0.1 microns to 5 microns, and a periodicity from 0.2 microns to 10 microns; and

a second semiconductor die comprising a second substrate, second semiconductor devices, and second bonding pads that are electrically connected to a respective node of the second semiconductor devices and laterally surrounded by a second pad-level dielectric layer, wherein each of the second bonding pads is bonded to a respective one of the first bonding pads, and the first polymer hairs contact the second pad-level dielectric layer.

2. The bonded assembly of claim 1 , wherein the first polymer hairs have the diameter or maximum width from 0.2 microns to 4 microns, the height from 0.15 microns to 2 microns, and the periodicity from 0.4 microns to 4.5 microns.

3. The bonded assembly of claim 1 , wherein the first pad-level dielectric layer comprises a first pad-level silicon-containing dielectric layer laterally surrounding portions of the first bonding pads that are proximal to the first substrate, and contacting the first polymer hairs.

4. The bonded assembly of claim 1 , wherein the second pad-level dielectric layer comprises a second polymer material layer.

5. A method of forming a bonded assembly, comprising:

providing a first semiconductor die comprising a first substrate, first semiconductor devices, and first bonding pads that are electrically connected to a respective node of the first semiconductor devices and laterally surrounded by a first pad-level dielectric layer, wherein the first pad-level dielectric layer comprises a stack of a first pad-level silicon-containing dielectric layer and a first polymer material layer including a first polymer material;

providing a second semiconductor die comprising a second substrate, second semiconductor devices, and second bonding pads that are electrically connected to a respective node of the second semiconductor devices and laterally surrounded by a second pad-level dielectric layer; and

bonding the first bonding pads to the second bonding pads while the first polymer material contacts the second pad-level dielectric layer.

6. The method of claim 5 , further comprising treating a surface portion of the first polymer material layer with a first plasma, wherein:

an underlying portion of the first polymer material layer that is not treated with the first plasma comprises a first proximal polymer material layer; and

the surface portion of the first polymer material layer is converted into a first distal polymer material layer having at least one of a greater hydrophilicity or greater cross-linking density than the first proximal polymer material layer.

7. The method of claim 6 , wherein:

the first distal polymer material layer has the greater hydrophilicity than the first proximal polymer material layer;

the first distal polymer material layer has higher surface energy than the first proximal polymer material layer; and

the first distal polymer material layer has a smaller contact angle than the first proximal polymer material layer.

8. The method of claim 6 , wherein:

the first plasma increases density of polar functional groups in the first polymer material; and

the first proximal polymer material layer is essentially free of the polar function groups or includes the polar functional groups at a density that is lower than a density of the polar functional groups within the first distal polymer material layer.

9. The method of claim 6 , wherein:

the first plasma increases a cross-linking density of the first polymer material in the first distal polymer material layer; and

the first distal polymer material layer has the greater cross-linking density than the first proximal polymer material layer.

10. The method of claim 6 , further comprising treating a surface portion of the second polymer material layer with a second plasma, wherein:

an underlying portion of the second polymer material layer that is not treated with the second plasma comprises a second proximal polymer material layer;

the surface portion of the second polymer material layer is converted into a second distal polymer material layer having at least one of a greater hydrophilicity or greater cross-linking density than the second proximal polymer material layer; and

the second distal polymer material layer bonds with the first distal polymer material layer while the second bonding pads bond with the first bonding pads.

11. The method of claim 5 , further comprising forming first polymer hairs by patterning a surface portion of the first polymer material layer, wherein the first polymer hairs extend from a horizontal surface of the first polymer material layer, and provide enhanced adhesion to the second pad-level dielectric layer through at least one of Van der Waals force or through capillary interaction.

12. The method of claim 11 , wherein the first polymer hairs have a diameter or maximum width from 0.1 microns to 10 microns, a height from 0.1 microns to 5 microns, and a periodicity from 0.2 microns to 10 microns.

13. The method of claim 12 , wherein the first polymer hairs have the diameter or maximum width from 0.2 microns to 4 microns, the height from 0.15 microns to 2 microns, and the periodicity from 0.4 microns to 4.5 microns.

14. The method of claim 11 , wherein the second pad-level dielectric layer comprises a second polymer material layer or a silicon-containing dielectric layer.

15. The method of claim 5 , further comprising:

vertically recessing the first pad-level dielectric layer which initially comprises the first pad-level silicon-containing dielectric layer relative to the first bonding pads, and forming the first polymer material layer on the first pad-level silicon-containing dielectric layer around the first bonding pads, such that the first pad-level dielectric layer comprises the first polymer material layer and the first pad-level silicon-containing dielectric layer; and

vertically recessing the second pad-level dielectric layer which initially comprises a second pad-level silicon-containing dielectric layer relative to the second bonding pads, and forming a second polymer material layer on the second pad-level silicon-containing dielectric layer around the second bonding pads, such that the second pad-level dielectric layer comprises the second polymer material layer and the second pad-level silicon-containing dielectric layer.

16. The method of claim 15 , further comprising forming an air gap between the first pad-level silicon-containing dielectric layer and the second pad-level silicon-containing dielectric layer by removing the first polymer material layer and the second polymer material layer after bonding the second bonding pads to the first bonding pads.

17. The method of claim 16 , wherein:

thermal decomposition temperatures of the first polymer material layer and the second polymer material layer are lower than an elevated temperature of an anneal process during which the second bonding pads are bonded to the first bonding pads; and

removal of the first polymer material layer and the second polymer material layer is performed during the anneal process.

18. The method of claim 5 , further comprising:

selectively forming a first self-assembled monolayer (SAM) material having a first tail group on physically exposed surfaces of the first bonding pads while suppressing deposition of the first SAM material on the first polymer material layer; and

selectively forming a second SAM material having a second tail group on physically exposed surfaces of the second bonding pads while suppressing deposition of the second SAM material on the second polymer material layer, wherein the second tail group has affinity to the first tail group,

wherein the first SAM material and the second SAM material are decomposed during the bonding.

19. A bonded assembly, comprising:

a first semiconductor die comprising a first substrate, first semiconductor devices, and first bonding pads that are electrically connected to a respective node of the first semiconductor devices and laterally surrounded by a first pad-level dielectric layer, wherein the first pad-level dielectric layer comprises a first distal surface that is more proximal to the first substrate than distal surfaces of the first bonding pads are to the first substrate; and

a second semiconductor die comprising a second substrate, second semiconductor devices, and second bonding pads that are electrically connected to a respective node of the second semiconductor devices and laterally surrounded by a second pad-level dielectric layer, wherein each of the second bonding pads is bonded to a respective one of the first bonding pads, the second pad-level dielectric layer comprises a second distal surface that is more proximal to the second substrate than distal surfaces of the second bonding pads are to the second substrate,

wherein an air gap is present between the first pad-level dielectric material layer and the second pad-level dielectric layer, and the air gap laterally surrounds each bonded pair of the first bonding pad and second bonding pad.

20. The bonded assembly of claim 19 , wherein:

each of the first bonding pads and the second bonding pads comprises a respective metallic barrier liner including a respective metallic nitride material and a respective metallic fill material portion laterally surrounded by the respective metallic barrier liner; and

each of the metallic barrier liners comprises a respective outer sidewall that includes a distal segment that is physically exposed to the air gap and a proximal segment that contacts one of the first pad-level dielectric layer and the second pad-level dielectric layer.