Methods for forming three-dimensional memory devices with supporting structure for staircase region

1. A method for forming a three-dimensional (3D) memory device, comprising:

sequentially forming a first semiconductor layer, a first block layer, and a sacrificial layer on a substrate;

forming a block plug extending vertically through the sacrificial layer and the first block layer to divide the sacrificial layer into a supporting portion and a sacrificial portion;

forming a dielectric stack above the sacrificial layer and having a staircase region, such that the supporting portion of the sacrificial layer is below and overlaps the staircase region of the dielectric stack;

forming a channel structure extending vertically through the dielectric stack, the sacrificial portion of the sacrificial layer, and the first block layer, into the first semiconductor layer;

forming an opening extending vertically through the dielectric stack to expose part of the sacrificial portion of the sacrificial layer; and

replacing, through the opening, the sacrificial portion of the sacrificial layer with a second semiconductor layer coplanar with the supporting portion of the sacrificial layer.

2. The method of claim 1 , wherein replacing the sacrificial portion of the sacrificial layer with the second semiconductor layer comprises:

removing, through the opening, the sacrificial portion of the sacrificial layer to form a cavity, stopping at the block plug and the first block layer; and

depositing, through the opening, doped polysilicon into the cavity to form the second semiconductor layer.

3. The method of claim 2 , wherein forming the channel structure comprises:

forming a channel hole extending vertically through the dielectric stack, the sacrificial portion of the sacrificial layer, and the first block layer, into the first semiconductor layer; and

sequentially forming a memory film and a semiconductor channel along a sidewall of the channel hole.

4. The method of claim 3 , wherein replacing the sacrificial portion of the sacrificial layer with the second semiconductor layer further comprises removing, through the opening, part of the memory film to expose part of the semiconductor channel along the sidewall of the channel hole, such that the second semiconductor layer is in contact with the exposed part of the semiconductor channel.

5. The method of claim 1 , wherein forming the block plug comprises:

forming a dent extending vertically through the sacrificial layer and the first block layer; and

depositing silicon oxide to fill the dent and be connected to the first block layer.

6. The method of claim 1 , further comprising:

after forming the sacrificial layer, forming a second block layer on the sacrificial layer, such that the block plug extends vertically through the second block layer as well; and

forming a third semiconductor layer on the second block layer and the block plug.

7. The method of claim 1 , wherein the sacrificial layer comprises polysilicon or silicon nitride.

8. The method of claim 1 , further comprising, after replacing the sacrificial portion of the sacrificial layer with the second semiconductor layer, replacing, through the opening, the dielectric stack with a memory stack.

9. A method for forming a three-dimensional (3D) memory device, comprising:

sequentially forming a first semiconductor layer, a first block layer, and a sacrificial layer on a substrate;

replacing part of the first block layer and the sacrificial layer with a supporting structure;

forming a dielectric stack above the supporting structure and a remainder of the sacrificial layer and having a staircase region, such that the supporting structure overlaps the staircase region of the dielectric stack;

forming a channel structure extending vertically through the dielectric stack, the remainder of the sacrificial layer, and the first block layer, into the first semiconductor layer;

forming an opening extending vertically through the dielectric stack to expose part of the remainder of the sacrificial layer; and

replacing, through the opening, the remainder of the sacrificial layer with a second semiconductor layer coplanar with the supporting structure.

10. The method of claim 9 , wherein replacing the remainder of the sacrificial layer with the second semiconductor layer comprises:

removing, through the opening, the remainder of the sacrificial layer to form a cavity; and

depositing, through the opening, doped polysilicon into the cavity to form the second semiconductor layer.

11. The method of claim 9 , wherein replacing the part of the first block layer and the sacrificial layer with the supporting structure comprises:

removing the part of the first block layer and the sacrificial layer to form a trench; and

depositing silicon oxide to fill the trench.

12. The method of claim 9 , further comprising:

after forming the sacrificial layer, forming a second block layer on the sacrificial layer, such that a top surface of the second block layer is flush with a top surface of the supporting structure; and

forming a third semiconductor layer on the second block layer and the supporting structure.

13. The method of claim 9 , further comprising after replacing the part of the first block layer and the sacrificial layer with the supporting structure, replacing, through the opening, the dielectric stack with a memory stack.

14. A method for forming a three-dimensional (3D) memory device, comprising:

forming a peripheral circuit on a first substrate;

forming a first semiconductor layer on a second substrate;

forming a supporting structure and a second semiconductor layer coplanar with the supporting structure on the first semiconductor layer;

forming a memory stack above the supporting structure and the second semiconductor layer, the memory stack having a staircase region overlapping the supporting structure;

forming a channel structure extending vertically through the memory stack and the second semiconductor layer into the first semiconductor layer; and

bonding the first substrate and the second substrate in a face-to-face manner.

15. The method of claim 14 , wherein forming the supporting structure and the second semiconductor layer comprises:

forming a block layer on the first semiconductor layer and a sacrificial layer on the block layer;

forming a block plug extending vertically through the sacrificial layer and the block layer to divide the sacrificial layer into a supporting portion and a sacrificial portion; and

replacing the sacrificial portion of the sacrificial layer with the second semiconductor layer.

16. The method of claim 14 , wherein forming the supporting structure and the second semiconductor layer comprises:

forming a block layer on the first semiconductor layer and a sacrificial layer on the block layer;

replacing part of the block layer and the sacrificial layer with the supporting structure; and

replacing a remainder of the sacrificial layer with the second semiconductor layer.

17. The method of claim 14 , further comprising, after bonding:

thinning the second substrate to expose the first semiconductor layer; and

forming a source contact above and in contact with the first semiconductor layer.

18. The method of claim 14 , further comprising, prior to bonding, forming a source contact above and in contact with the first semiconductor layer.

19. The method of claim 14 , wherein, after bonding, the memory stack is above the peripheral circuit, the method further comprising:

thinning the second substrate to expose the first semiconductor layer; and

forming a contact through the first semiconductor layer, and a contact pad above the first semiconductor layer and in contact with the contact.

20. The method of claim 14 , wherein after bonding, the memory stack is below the peripheral circuit, the method further comprising:

thinning the first substrate to form a third semiconductor layer; and

forming a contact through the third semiconductor layer, and a contact pad above the third semiconductor layer and in contact with the contact.