Wafer-to-wafer bonding structure and image sensor including the same

1 . An image sensor comprising:

a first substrate including a pixel array, a first multilayer wiring, a first insulation layer and a first metal pad buried in the first insulation layer; and

a second substrate on and bonded to the first substrate,

wherein the second substrate comprises a logic circuit, a second multilayer wiring, a second insulation layer facing the first insulation layer and a second metal pad buried in the second insulation layer,

wherein the first metal pad comprises a first protrusion surface, a first recessed surface, and a first sloped surface connecting the first protrusion surface with the first recessed surface, each of the first protrusion surface, the first recessed surface, and the first sloped surface being planar surfaces,

wherein the second metal pad comprises a second protrusion surface, a second recessed surface, and a second sloped surface connecting the second protrusion surface with the second recessed surface, each of the second protrusion surface, the second recessed surface, and the second sloped surface being planar surfaces,

wherein the first sloped surface faces the second sloped surface and is parallel with the second sloped surface, and

wherein a first void between bonded portions of the first metal pad and the second metal pad has a parallelogram shape that is defined by the first sloped surface, the second sloped surface, a portion of the first recessed surface, and a portion of the second recessed surface.

2 . The image sensor of claim 1 , wherein a height difference between the first protrusion surface and the first recessed surface is not greater than half of a thickness of the first substrate.

3 . The image sensor of claim 1 , wherein a height difference between the second protrusion surface and the second recessed surface has the same value as a value of the height difference between the first protrusion surface and the first recessed surface.

4 . The image sensor of claim 1 ,

wherein the first protrusion surface of the first metal pad of the first substrate is bonded to the second recessed surface of the second metal pad of the second substrate, and

wherein the second protrusion surface of the second metal pad of the second substrate is bonded to the first recessed surface of the first metal pad of the first substrate.

5 . The image sensor of claim 1 , wherein a slope angle of the first sloped surface or the second sloped surface is less than or equal to about 20 degrees.

6 . The image sensor of claim 1 , wherein a portion of the first insulation layer adjacent to the first recessed surface has a thickness different from a thickness of a portion of the first insulation layer adjacent to the first protrusion surface.

7 . The image sensor of claim 1 , wherein a portion of a surface of the first insulation layer adjacent to the first recessed surface is at the same level as the first recessed surface, and a portion of the surface of the first insulation layer adjacent to the first protrusion surface is at the same level as the first protrusion surface.

8 . The image sensor of claim 1 ,

wherein a selectivity of a material included in the first metal pad differs from a selectivity of a material included in the first insulation layer, and

wherein a selectivity of a material included in the second metal pad differs from a selectivity of a material included in the second insulation layer.

9 . The image sensor of claim 1 , further comprising:

a second void between bonded portions of the first insulation layer and the second insulation layer,

wherein the second void has a mirror symmetrical shape with the first void.

10 . The image sensor of claim 1 , further comprising:

a second void between bonded portions of the first insulation layer and the second insulation layer,

wherein a portion of a surface of the first insulating layer at a first side of the second void is at the same level as the first recessed surface, and a portion of the surface of the first insulating layer at a second side of the second void is at the same level as the first protrusion surface.

11 . The image sensor of claim 1 , wherein the first metal pad and the second metal pad are formed by a damascene process.

12 . The image sensor of claim 1 ,

wherein a material of each of the first metal pad and the second metal pad comprises copper (Cu), and

wherein a material of the first insulation layer and the second insulation layer comprises silicon carbon nitride (SiCN).

13 . An image sensor comprising:

a first substrate including a pixel array, a first multilayer wiring, a first insulation layer and a plurality of first metal pads arranged apart from one another in a horizontal direction to each be buried in the first insulation layer; and

a second substrate on and bonded to the first substrate,

wherein the second substrate comprises a logic circuit, a second multilayer wiring, a second insulation layer facing the first insulation layer and a plurality of second metal pads arranged apart from one another in a horizontal direction to each be buried in the second insulation layer,

wherein each of the plurality of first metal pads comprises a first junction surface comprising a first protrusion surface, a first recessed surface, and a first sloped surface connecting the first protrusion surface with the first recessed surface, each of the first protrusion surface, the first recessed surface, and the first sloped surface being planar surfaces,

wherein each of the plurality of second metal pads comprises a second junction surface comprising a second protrusion surface, a second recessed surface, and a second sloped surface connecting the second protrusion surface with the second recessed surface, each of the second protrusion surface, the second recessed surface, and the second sloped surface being planar surfaces,

wherein the first sloped surface of a first metal pad of the plurality of first metal pads faces and is parallel to the second sloped surface of a corresponding second metal pad of the plurality of second metal pads, and

wherein a first void between bonded portions of the first metal pad of the plurality of first metal pads and the corresponding second metal pad of the plurality of second metal pads has a parallelogram shape that is defined by the first sloped surface of the first metal pad, the second sloped surface of the second metal pad, a portion of the first recessed surface of the first metal pad, and a portion of the second recessed surface of the second metal pad.

14 . The image sensor of claim 13 , wherein the first junction surface of each of the plurality of first metal pads has the same shape and the same height, and the second junction surface of each of the plurality of second metal pads has the same shape and the same height.

15 . The image sensor of claim 13 , wherein a height difference between the second protrusion surface and the second recessed surface of each of the plurality of second metal pads has the same value as a value of the height difference between the first protrusion surface and the first recessed surface of each of the plurality of first metal pads.

16 . The image sensor of claim 13 , wherein the first void is one of a plurality of first voids, each of the plurality of first voids being formed between the first sloped surface of one of the plurality of first metal pads and the second sloped surface of a corresponding one of the plurality of second metal pads.

17 . The image sensor of claim 16 , further comprising:

a plurality of second voids formed between bonded portions of the first insulation layer and the second insulation layer to have the same shape,

wherein the plurality of second voids have a mirror symmetrical shape with the plurality of first voids.

18 . An image sensor comprising:

a lower substrate; and

an upper substrate stacked on and bonded to the lower substrate,

wherein the lower substrate comprises:

a pixel array;

a lower multilayer wiring;

a lower insulation layer formed on an upper surface of the lower substrate;

a lower metal pad buried in the lower insulation layer; and

a lower step formed in the lower metal pad,

wherein the upper substrate comprises:

an upper insulation layer formed on a lower surface of the upper substrate;

a logic circuit;

a multilayer wiring;

an upper metal pad buried in the upper insulation layer; and

an upper step formed in the upper metal pad, and

wherein the lower step comprises a first protrusion surface, a first recessed surface, and a first sloped surface connecting the first protrusion surface with the first recessed surface, each of the first protrusion surface, the first recessed surface, and the first sloped surface being planar surfaces,

wherein the upper step comprises a second protrusion surface, a second recessed surface, and a second sloped surface connecting the second protrusion surface with the second recessed surface,

wherein the upper step engages with the lower step such that the first sloped surface faces and is parallel with the second sloped surface to form direct bonding between the upper substrate and the lower substrate, and

wherein a first void between bonded portions of the lower metal pad and the upper metal pad has a parallelogram shape that is defined by the first sloped surface, the second sloped surface, a portion of the first recessed surface, and a portion of the second recessed surface.

19 . The image sensor of claim 18 ,

wherein a height difference between the first protrusion surface and the first recessed surface of the upper step has the same value as a value of a height difference between the second protrusion surface and the second recessed surface of the lower step,

wherein the first protrusion surface of the upper step is bonded to the second recessed surface of the lower step, and

wherein the second protrusion surface of the lower step is bonded to the first recessed surface of the upper step.