3D NAND-high aspect ratio strings and channels
Aspects of the disclosure relate to forming a completed stack of layers. Forming the completed stack of layers may include forming a first stack of layers on a first substrate and forming a second stack of layers on a second substrate. The first stack of layers may be bonded to the second stack of layers. The first or second substrate may be removed. Prior to bonding the first stack of layers and the second stack of layer, one or more holes may be etched in the first stack of layers. After removing the second substrate, one or more holes may be etched in the second stack of layers, wherein each of the one or more holes in the second stack of layers extend into a corresponding hole in the one or more holes in the first stack of layers.
1 . A method of forming a memory cell stack in 3D NAND memory, the method comprising:
forming a first stack of layers on a first substrate;
forming a second stack of layers on a second substrate;
depositing a buffer layer on the first stack of layers;
directly bonding the second stack of layers to the buffer layer on the first stack of layers to form the memory cell stack, wherein the second stack of layers is directly bonded to the buffer layer on the first stack of layers without using an intervening adhesive; and
after bonding the second stack of layers to the buffer layer on the first stack of layers, removing at least a portion of the second substrate.
2 . The method of claim 1 , wherein removing at least the portion of the second substrate comprises using a backgrind process, a CMP process, or an etch process.
3 . The method of claim 1 , further comprising forming a hole in the second stack after bonding the second stack to the buffer layer on the first stack.
4 . The method of claim 3 , further comprising depositing a conductive material in the hole to form a contact.
5 . The method of claim 3 , further comprising depositing a plurality of conformal layers in the hole to at least partially form one or more memory cells of the memory cell stack.
6 . The method of claim 1 , further comprising:
prior to bonding the second stack, forming a first hole in the first stack; and
sequentially depositing a plurality of conformal layers in the first hole to at least partially form memory cells of the memory cell stack.
7 . The method of claim 6 , further comprising after bonding the second stack, forming a second hole in the second stack, the second hole being aligned with the first hole.
8 . The method of claim 6 , wherein at least partially forming memory cells further comprises: after sequentially depositing the plurality of conformal layers and prior to bonding the second stack, depositing silicon oxide in the first hole to form a dielectric core.
9 . The method of claim 1 , wherein the first stack and the second stack each comprise alternating layers of silicon nitride and silicon oxide.
10 . The method of claim 9 , wherein the first stack and the second stack each comprise at least 16 sets of the alternating layers.
11 . The method of claim 1 , wherein the first stack and the second stack each comprise alternating layers of silicon oxide and polysilicon.
12 . The method of claim 1 , wherein:
the first stack and second stack each comprise a repeating sequence of layers, and
the repeating sequence comprises a silicon oxide layer, a silicon nitride layer, a silicon oxynitride layer, a silicon carbonitride layer, or a combination thereof.
13 . The method of claim 1 , further comprising, prior to bonding the second stack to the buffer layer on the first stack, forming a first hole in the first stack.
14 . The method of claim 13 , further comprising forming a second hole in the second stack, wherein the second hole connects with the first hole to define an extended hole that extends vertically through the first and second stacks.
15 . The method of claim 13 , further comprising:
forming a second hole in the second stack, wherein the second hole is aligned with the first hole; and
depositing a conductive material in the aligned first and second holes to form a contact.
16 . The method of claim 13 , further comprising:
forming a second hole in the second stack, wherein the second hole is aligned with the first hole; and
depositing a dielectric material in the aligned first and second holes to form a support pillar.
17 . The method of claim 13 , further comprising, prior to bonding the second stack, forming a second hole in the second stack.
18 . The method of claim 17 , further comprising, prior to bonding the second stack to the buffer layer on the first stack, depositing a conductive material to at least partially fill each of the first and second holes.
19 . A method of forming a memory cell stack in 3D NAND memory, the method comprising:
forming a first stack of layers on a first substrate;
forming a second stack of layers on a second substrate;
prior to bonding the second stack of layers, forming a first hole in the first stack of layers;
depositing a first plurality of conformal layers in the first hole to at least partially form the memory cell stack;
bonding the second stack to the first stack to form the memory cell stack; and
after bonding the second stack to the first stack:
removing at least a portion of the second substrate;
forming a second hole in the second stack, the second hole being aligned with the first hole; and
depositing a second plurality of conformal layers in the second hole to at least partially form the memory cell stack.
20 . A method of forming a memory cell stack in 3D NAND memory, the method comprising:
forming a first stack of layers on a first substrate;
forming a second stack of layers on a second substrate;
prior to bonding the second stack of layers, forming a first hole in the first stack of layers;
bonding the second stack to the first stack to form the memory cell stack;
after bonding the second stack to the first stack, removing at least a portion of the second substrate;
forming a second hole in the second stack, wherein the second hole is aligned with the first hole; and
depositing a dielectric material in the aligned first and second holes to form a support pillar.