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, from a first side of a stack of layers, a first hole that extends vertically from the first side towards a first substrate;
bonding a second substrate to the stack of layers;
removing the first substrate; and
forming, from a second side of the stack of layers, a second hole that extends vertically from the second side to align and connect with the first hole.
2. The method of claim 1 , wherein the second substrate comprises a logic layer.
3. The method of claim 1 , wherein the second substrate is directly bonded to a top layer of the stack of layers without using an adhesive.
4. The method of claim 3 , wherein one or both of the first and second substrates are formed from glass or quartz.
5. The method of claim 1 , further comprising:
at least partially filling the aligned first and second holes with a conductive material.
6. The method of claim 1 , wherein the stack of layers comprises a plurality of alternating layers and the method further comprises:
sequentially depositing a plurality of conformal layers in the aligned first and second holes; and
forming memory cells at intersections of the plurality of conformal layers and one of the alternating layers.
7. The method of claim 6 , wherein forming the memory cells comprises replacing one of the alternating layers with a conductive material.
8. The method of claim 1 , further comprising:
at least partially filling the aligned first and second holes with a dielectric material.
9. The method of claim 1 , further comprising:
depositing a conductive material in the first hole before removing the first substrate.
10. The method of claim 1 , further comprising:
depositing a dielectric material in the first hole before removing the first substrate.