Metal replacement process for low resistance source contacts in 3D NAND
A fabrication process is provided for a 3D stacked non-volatile memory device which provides a source contact to memory holes at a bottom of a stack. The stack includes alternating control gate layers and dielectric layers on a substrate, and memory holes are etched through the stack. The process avoids the need to etch through films at the bottom of the memory hole. Instead, a path is formed from the bottom of the memory hole to the top of the stack. The path includes a horizontal portion using a voided trench in a substrate dielectric, and a passageway etched in the stack. The memory films, a channel material and a dielectric material are deposited throughout the interior surfaces of the void and the memory holes concurrently. The path is filled with metal to form a continuous, low resistance conductive path.
1. A method for fabricating a 3d stacked non-volatile memory device, comprising:
forming a memory hole in a stack, the stack comprising alternating control gate layers and dielectric layers on a substrate dielectric;
forming a void in the substrate dielectric, a bottom of the memory hole is connected to the void;
forming a passageway in the stack between a top of the stack and the void;
depositing a plurality of materials in the void and the memory hole, the plurality of materials comprise a programmable material, a channel material and a dielectric material;
removing a portion of the dielectric material which is in the void, exposing a portion of the channel material which is in the void;
doping the portion of the channel material which is in the void, the doping comprises introducing a dopant to the void via the passageway; and
depositing a metal in the void and the passageway, the metal extends to the bottom of the memory hole.
2. The method of claim 1 , wherein:
the removing the portion of the dielectric material in the void comprises introducing an etchant into the void via the passageway.
3. The method of claim 1 , wherein:
the forming the void in the substrate dielectric comprises etching away a sacrificial material in the substrate dielectric using an etchant introduced via at least one of the passageway or the memory hole.
4. The method of claim 1 , wherein:
the dielectric material fills the memory hole but does not fill the void.
5. The method of claim 1 , wherein:
the plurality of materials extend continuously throughout the memory hole and the void.
6. The method of claim 1 , further comprising:
applying heat after the doping, the heat causes the dopant to diffuse upwards in a portion of the channel material which is in the memory hole.
7. The method of claim 1 , wherein:
the void comprises a grid which connects a plurality of memory holes.
8. The method of claim 1 , wherein:
the passageway is formed before the plurality of materials are provided in the memory hole and the void; and
the depositing of the plurality of materials occurs via the memory hole and via the passageway.
9. The method of claim 8 , wherein:
the plurality of materials extend continuously throughout the memory hole, the void and the passageway.
10. The method of claim 1 , wherein:
the passageway is formed after the plurality of materials are provided in the memory hole and the void; and
the depositing of the plurality of materials occurs via the memory hole but not via the passageway.
11. The method of claim 10 , wherein:
the forming of the passageway comprises etching though the stack and piercing a portion of the plurality of materials which is in the void.
12. The method of claim 11 , wherein:
an etch stop material is provided on the substrate dielectric within the stack; and
the etching through the stack comprises etching from the top of the stack to the etch stop material, removing a remainder of the etch stop material, depositing a liner and etching through a bottom of the liner before the piercing of the portion of the plurality of materials which is in the void.
13. The method of claim 11 , further comprising:
providing a replacement material for the control gate layers after the etching though the stack and before the piercing the portion of the plurality of materials which is in the void.
14. The method of claim 1 , wherein:
a NAND string is formed in the memory hole;
the NAND string comprises a source-side select gate transistor, a drain-side select gate transistor and a plurality of memory cells between the source-side select gate transistor and the drain-side select gate transistor;
a top control gate layer of the control gate layers is a control gate of the drain-side select gate transistor; and
a bottom control gate layer of the control gate layers is a control gate of the source-side select gate transistor.
15. The method of claim 1 , wherein:
the programmable material comprises a charge trapping film;
the plurality of material comprise a block oxide and a tunnel oxide; and
the charge trapping film is between the block oxide and the tunnel oxide.
16. The method of claim 1 , further comprising:
introducing additional doped material to the void via the passageway, after the doping the portion of the channel material which is in the void.
17. A method for fabricating a 3d stacked non-volatile memory device, comprising:
forming a memory hole in a stack, the stack comprising alternating control gate layers and dielectric layers on a substrate dielectric;
forming a passageway in the stack;
forming a void in the substrate dielectric by etching away a sacrificial material in the substrate dielectric using an etchant introduced via at least one of the passageway or the memory hole, the void connects a bottom of the passageway to a bottom of the memory hole;
depositing a plurality of materials in the passageway, the void and the memory hole, the plurality of materials comprise a programmable material, a channel material and a dielectric material;
removing a portion of the dielectric material which is in the void, exposing a portion of the channel material which is in the void, the removing comprises introducing an etchant into the void via the passageway;
doping the portion of the channel material which is in the void, the doping comprises introducing a dopant to the void via the passageway; and
depositing a metal in the void and the passageway, the metal extends to the bottom of the memory hole.
18. The method of claim 17 , wherein:
a minimum cross-sectional dimension of the passageway and a minimum cross-sectional dimension of the void are larger than a minimum cross-sectional dimension of the memory hole, so that a gap exists in the passageway and in the void but not in the memory hole after the depositing of the dielectric material.
19. A method for fabricating a 3d stacked non-volatile memory device, comprising:
forming a memory hole in a stack, the stack comprising alternating control gate layers and dielectric layers on a substrate dielectric;
forming a void in the substrate dielectric by etching away a sacrificial material in the substrate dielectric using an etchant introduced via the memory hole;
depositing a plurality of materials in the void and the memory hole, the plurality of materials comprise a programmable material, a channel material and a dielectric material;
forming a passageway in the stack which extends from a top of the stack to the void;
removing a portion of the dielectric material which is in the void, exposing a portion of the channel material which is in the void, the removing comprises introducing an etchant into the void via the passageway;
doping the portion of the channel material which is in the void, the doping comprises introducing a dopant to the void via the passageway; and
depositing a metal in the void and the passageway, the metal extends to a bottom of the memory hole.
20. The method of claim 19 , wherein:
an etch stop material is provided on the substrate dielectric within the stack; and
the forming of the passageway comprises etching from the top of the stack to the etch stop material, removing a remainder of the etch stop material, depositing a liner, etching through a bottom of the liner, and etching through a portion of the plurality of materials which is in the void.