Staircase structure in three-dimensional memory device and method for forming the same

1. A three-dimensional (3D) memory device, comprising:

a memory array structure; and

a staircase structure in an intermediate of the memory array structure and laterally dividing the memory array structure into a first memory array structure and a second memory array structure, the staircase structure comprising a first staircase zone and a bridge structure connecting the first memory array structure and the second memory array structure,

wherein the first staircase zone comprises a first pair of staircases facing each other in a first lateral direction and at different depths, each staircase comprising a plurality of stairs;

at least one stair in the first pair of staircases is electrically connected to at least one of the first memory array structure and the second memory array structure through the bridge structure;

each staircase of the first pair of staircases comprises a plurality of divisions in a second lateral direction perpendicular to the first lateral direction; and

the staircase structure further comprises a second staircase zone, the bridge structure is between the first staircase zone and the second staircase zone in the second lateral direction, the second staircase zone comprises a second pair of staircases facing each other in the first lateral direction and at different depths, and the first staircase zone and the second staircase zone are asymmetric in the second lateral direction.

2. The 3D memory device of claim 1 , wherein

a stair in one of the divisions is vertically between two stairs in another one of the divisions.

3. The 3D memory device of claim 1 , wherein

the memory array structure comprises a plurality of blocks in the second lateral direction; and

the first staircase zone is in one or two of the blocks.

4. The 3D memory device of claim 1 , wherein

the first staircase zone comprises a second pair of staircases facing each other in the first lateral direction and at different depths; and

each staircase of the first and second pairs of staircases are at different depths.

5. The 3D memory device of claim 4 , wherein each stair in the first and second pairs of staircases are at different depths.

6. The 3D memory device of claim 1 , further comprising at least one word line extending laterally in the memory array structure and the bridge structure, such that the at least one stair is electrically connected to the at least one of the first and second memory array structures through the bridge structure by the at least one word line.

7. The 3D memory device of claim 1 , wherein the at least one stair in the first pair of staircases is electrically connected to each one of the first memory array structure and the second memory array structure through the bridge structure.

8. The 3D memory device of claim 1 , wherein the bridge structure comprises vertically interleaved conductive layers and dielectric layers.

9. A three-dimensional (3D) memory device, comprising:

a memory array structure; and

a staircase structure in an intermediate of the memory array structure and laterally dividing the memory array structure into a first memory array structure and a second memory array structure, the staircase structure comprising a first staircase zone and a bridge structure connecting the first memory array structure and the second memory array structure,

wherein the first staircase zone comprises a first staircase comprising a plurality of divisions in a second lateral direction, each division comprising a plurality of stairs in a first lateral direction perpendicular to the second lateral direction;

a stair in one of the divisions is vertically between two stairs in another one of the divisions;

at least one stair in the first staircase is electrically connected to at least one of the first memory array structure and the second memory array structure through the bridge structure; and

the staircase structure further comprises a second staircase zone, the bridge structure is between the first staircase zone and the second staircase zone in the second lateral direction, the second staircase zone comprises a second pair of staircases facing each other in the first lateral direction and at different depths, and the first staircase zone and the second staircase zone are asymmetric in the second lateral direction.

10. A three-dimensional (3D) memory device, comprising:

a memory array structure; and

a staircase structure in an intermediate of the memory array structure and laterally dividing the memory array structure into a first memory array structure and a second memory array structure, the staircase structure comprising a first staircase zone and a bridge structure connecting the first memory array structure and the second memory array structure,

wherein the first staircase zone comprises a first pair of staircases facing each other in a first lateral direction and at different depths, each staircase comprising a plurality of stairs;

at least one stair in the first pair of staircases is electrically connected to at least one of the first memory array structure and the second memory array structure through the bridge structure the first staircase zone comprises a second pair of staircases facing each other in the first lateral direction and at different depths;

each staircase of the first and second pairs of staircases are at different depths; and

the staircase structure further comprises a second staircase zone, the bridge structure is between the first staircase zone and the second staircase zone in a second lateral direction, the second staircase zone comprises a second pair of staircases facing each other in the first lateral direction and at different depths, and the first staircase zone and the second staircase zone are asymmetric in the second lateral direction.

11. The 3D memory device of claim 10 , wherein each stair in the first and second pairs of staircases are at different depths.

12. The 3D memory device of claim 10 , further comprising at least one word line extending laterally in the memory array structure and the bridge structure, such that the at least one stair is electrically connected to the at least one of the first and second memory array structures through the bridge structure by the at least one word line.

13. The 3D memory device of claim 10 , wherein the at least one stair in the first pair of staircases is electrically connected to each one of the first memory array structure and the second memory array structure through the bridge structure.

14. The 3D memory device of claim 10 , wherein the bridge structure comprises vertically interleaved conductive layers and dielectric layers.

15. The 3D memory device of claim 10 , wherein

the memory array structure comprises a plurality of blocks in the second lateral direction; and

the first staircase zone is in one or two of the blocks.

16. The 3D memory device of claim 10 , wherein

each staircase of the first pair of staircases comprises a plurality of divisions in the second lateral direction perpendicular to the first lateral direction,

a stair in one of the divisions is vertically between two stairs in another one of the divisions,

the memory array structure comprises a plurality of blocks in the second lateral direction, and

the first staircase zone is in one or two of the blocks.