Three-dimensional memory devices having through array contacts and methods for forming the same

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

forming a dielectric stack comprising a plurality of dielectric/sacrificial layer pairs on a substrate;

forming a channel structure extending vertically through the dielectric stack;

forming a first opening extending vertically through the dielectric stack;

forming a spacer on a sidewall of the first opening;

forming a through array contact (TAC) extending vertically through the dielectric stack by depositing a conductor layer in contact with the spacer in the first opening;

after forming the TAC, forming a slit extending vertically through the dielectric stack; and

forming a memory stack comprising a plurality of conductor/dielectric layer pairs on the substrate by replacing, through the slit, the sacrificial layers in the dielectric/sacrificial layer pairs with a plurality of conductor layers.

2. The method of claim 1 , further comprising prior to forming the first opening, forming a staircase structure at one side of the dielectric stack.

3. The method of claim 2 , further comprising forming a plurality of word line contacts each in contact with a respective one of the conductor layers of the conductor/dielectric layer pairs in the staircase structure.

4. The method of claim 1 , further comprising forming a slit structure by depositing a conductor layer in the slit.

5. The method of claim 1 , further comprising prior to forming the first opening, forming a dummy channel structure extending vertically through the dielectric stack.

6. The method of claim 1 , wherein forming the first opening comprises simultaneously etching the first opening through the dielectric stack and a second opening outside of the dielectric stack.

7. The method of claim 6 , wherein forming the TAC comprises depositing the conductor layer in the first opening to form the TAC and in the second opening to form a peripheral contact.

8. The method of claim 1 , wherein forming the spacer on the sidewall of the first opening comprises:

depositing a dielectric layer on the sidewall and a bottom surface of the first opening; and

removing part of the dielectric layer that is deposited on the bottom surface of the first opening.

9. The method of claim 8 , wherein the deposition of the dielectric layer comprises atomic layer deposition (ALD), and the removal of the part of the dielectric layer comprises anisotropic etching on the bottom surface of the first opening.

10. The method of claim 1 , wherein forming the spacer on the sidewall of the first opening comprises:

forming a plurality of shallow recesses by removing parts of the sacrificial layers abutting the sidewall of the first opening;

depositing a dielectric layer filling in the shallow recesses and on the sidewall and a bottom surface of the first opening; and

removing part of the dielectric layer that is deposited on the bottom surface of the first opening.

11. The method of claim 10 , wherein the removal of the part of the dielectric layer comprises isotropic etching on the sidewall and the bottom surface of the first opening.

12. The method of claim 1 , wherein forming the first opening comprises:

simultaneously etching the first opening through the dielectric stack, a second opening outside of the dielectric stack, and a third opening through the dielectric stack,

wherein a lateral dimension of the third opening is smaller than lateral dimensions of the first and second openings.

13. The method of claim 12 , wherein forming the spacer on the sidewall of the first opening comprises:

depositing a dielectric layer (i) fully filling in the third opening to form a dummy channel structure and (ii) partially filling in the first opening and the second opening; and

removing parts of the dielectric layer that are deposited on a bottom surface of the first opening and on a bottom surface of the second opening.

14. The method of claim 12 , wherein each of the first, second, and third openings has a nominally circular shape in the plan view.

15. The method of claim 1 , wherein the dielectric layers in the dielectric/sacrificial layer pairs comprise silicon oxide, the sacrificial layers in the dielectric/sacrificial layer pairs comprise silicon nitride, and the spacer comprises silicon oxide.

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

forming a dielectric stack comprising a plurality of dielectric/sacrificial layer pairs on a substrate;

forming a channel structure extending vertically through the dielectric stack;

simultaneously etching a first opening through the dielectric stack, a second opening outside of the dielectric stack, and a third opening through the dielectric stack, wherein a lateral dimension of the third opening is smaller than lateral dimensions of the first and second openings;

depositing a dielectric layer (i) fully filling in the third opening to form a dummy channel structure and (ii) partially filling in the first opening and the second opening;

removing parts of the dielectric layer that are deposited on a bottom surface of the first opening and on a bottom surface of the second opening;

depositing a conductor layer (i) filling in the first opening to form a through array contact (TAC) and (ii) filling in the second opening to form a peripheral contact;

after forming the TAC and peripheral contact, forming a slit extending vertically through the dielectric stack; and

forming a memory stack comprising a plurality of conductor/dielectric layer pairs on the substrate by replacing, through the slit, the sacrificial layers in the dielectric/sacrificial layer pairs with a plurality of conductor layers.

17. The method of claim 16 , wherein each of the first, second and third openings has a nominally circular shape in the plan view.