Three-dimensional memory devices and fabricating methods thereof

1. A method for forming a memory structure, comprising:

forming a bottom conductive layer on a substrate;

forming a bottom isolation layer on the bottom conductive layer;

forming a memory stack on the bottom isolation layer, the memory stack comprising a plurality of dielectric layers alternately arranged with a plurality of conductive layers;

forming an opening penetrating the memory stack and bottom isolation layer to expose the bottom conductive layer;

forming a cap layer on the bottom conductive layer and filling a first portion of the opening;

forming a cylindrical body on the cap layer and filing a second portion of the opening;

forming a top contact on the cylindrical body and filling a third portion of the opening; and

forming a plurality of interconnection structures to electrically couple the bottom conductive layer, the plurality of conductive layers of the memory stack, and the top contact.

2. The method of claim 1 , further comprising:

doping the bottom conductive layer and the cap layer with a first type of dopant.

3. The method of claim 1 , further comprising:

before forming the cylindrical body and the top contact, performing an oxidation process to treat exposed surface of the plurality of conductive layers of the memory stack and the bottom conductive layer to form an oxide layer.

4. The method of claim 3 , further comprising:

before forming the cylindrical body and the top contact, performing a punch etch to remove the oxide layer on the bottom conductive layer to expose a conductive material of the bottom conductive layer.

5. The method of claim 2 , wherein forming the cylindrical body and the top contact comprises:

forming a semiconductor structure on the cap layer to fill the opening;

doping the semiconductor structure with a second type of dopant opposite to the first type of dopant; and

doping a top portion of the semiconductor structure with the first type of dopant, such that the top portion of the semiconductor structure form the top contact, and the remaining portion of the semiconductor structure form the cylindrical body.

6. The method of claim 5 , wherein forming the semiconductor structure comprises:

forming the semiconductor structure in the opening by a patterned epitaxial growth process.

7. The method of claim 5 , wherein forming the semiconductor structure comprises:

forming the semiconductor structure in the opening by a deposition process and a followed recrystallization process.

8. The method of claim 1 , wherein forming the cap layer comprises:

using an cyclic deposition-etch process to form the cap layer, such that a top surface of the cap layer is lower than a bottom surface of a lowest conductive layer of the memory stack.

9. The method of claim 1 , further comprising:

forming a staircase structure in the memory stack;

wherein the plurality of interconnection structures electrically coupled to the plurality of conductive layers of the memory stack are formed on the staircase structure.

10. The method of claim 1 , wherein forming the plurality of interconnection structures comprises:

coupling the top contact to a bit line;

coupling a top conductive layer of the memory stack a word line;

coupling the plurality conductive layers other than the top conductive layer of the memory stack to a plurality of plate lines respectively; and

coupling the bottom conductive layer to a source line.

11. The method of claim 10 , further comprising:

connecting the plurality of plate lines to a common voltage source.

12. The method of claim 10 , further comprising:

coupling the plurality of plate lines to a plurality of independent voltage sources.

13. The method of claim 1 , wherein forming the memory stack comprises:

depositing the plurality of conductive layers, such that each of the plurality of conductive layers of the memory stack has a substantially same first thickness.

14. The method of claim 13 , wherein forming the memory stack further comprises:

depositing the plurality of dielectric layers, such that each of the plurality of dielectric layers of the memory stack has a substantially same second thickness.

15. The method of claim 13 , wherein forming the memory stack further comprises:

depositing the plurality of dielectric layers, such that a top dielectric layer of the memory stack has a third thickness that is different from a second thickness of the other dielectric layers of the memory stack.