Multi-tier three-dimensional memory device with nested contact via structures and methods for forming the same
A semiconductor structure includes a first alternating stack of first insulating layers and first electrically conductive layers having first stepped surfaces and located over a substrate, a second alternating stack of second insulating layers and second electrically conductive layers having second stepped surfaces, and memory opening fill structures extending through the alternating stacks. A contact via assembly is provided, which includes a first conductive via structure vertically extending from a top surface of one of the first electrically conductive layers through a subset of layers within the second alternating stack and through the second retro-stepped dielectric material portion, an insulating spacer located within an opening through the subset of layers, and a second conductive via structure laterally surrounding the insulating spacer and contacting a second electrically conductive layer.
1. A semiconductor structure comprising:
a first alternating stack of first insulating layers and first electrically conductive layers having first stepped surfaces and located over a substrate;
a first retro-stepped dielectric material portion overlying the first stepped surfaces;
a second alternating stack of second insulating layers and second electrically conductive layers having second stepped surfaces;
a second retro-stepped dielectric material portion overlying the second stepped surfaces;
memory openings vertically extending through the first alternating stack and the second alternating stack;
memory opening fill structures located in the memory openings and comprising a respective vertical semiconductor channel and a respective memory film; and
a contact via assembly comprising a first conductive via structure vertically extending from a top surface of one of the first electrically conductive layers through a subset of layers within the second alternating stack and through the second retro-stepped dielectric material portion, an insulating spacer located within an opening through the subset of layers within the second alternating stack, and a second conductive via structure laterally surrounding the insulating spacer and contacting a top surface of a topmost second electrically conductive layer of the subset of layers within the second alternating stack.
2. The semiconductor structure of claim 1 , wherein the first conductive via structure comprises:
a first-tier conductive pillar structure contacting and vertically extending through the first retro-stepped dielectric material portion; and
a second-tier conductive pillar structure contacting and laterally surrounded by the insulating spacer.
3. The semiconductor structure of claim 2 , wherein the second-tier conductive pillar structure comprises a different conductive material than the first-tier conductive pillar structure.
4. The semiconductor structure of claim 3 , wherein:
the first-tier conductive pillar structure comprises a doped semiconductor material; and
the second-tier conductive pillar structure comprises a metallic material.
5. The semiconductor structure of claim 2 , wherein a top surface of the first-tier conductive pillar structure has a greater area than a bottom surface of the second-tier conductive pillar structure.
6. The semiconductor structure of claim 2 , wherein an annular bottom surface of the insulating spacer contacts a top surface of the first-tier conductive pillar structure.
7. The semiconductor structure of claim 2 , wherein an annular top surface of the insulating spacer is located within a horizontal plane including a top surface of the first-tier conductive pillar structure.
8. The semiconductor structure of claim 7 , wherein an annular top surface of the second conductive via structure is located within the horizontal plane including the top surface of the second-tier conductive pillar structure.
9. The semiconductor structure of claim 2 , wherein a top surface of the first-tier conductive pillar structure contacts a bottom surface of a bottommost second insulating layer within the second alternating stack.
10. The semiconductor structure of claim 2 , wherein an entirety of a cylindrical surface of the second-tier conductive pillar structure contacts an inner cylindrical sidewall of the insulating spacer.
11. The semiconductor structure of claim 10 , wherein an outer cylindrical sidewall of the insulating spacer contacts sidewalls of the subset of layers within the second alternating stack and an inner cylindrical sidewall of the second conductive via structure.
12. The semiconductor structure of claim 1 , wherein the second conductive via structure has a same material composition as the second electrically conductive layers.
13. The semiconductor structure of claim 1 , wherein the second conductive via structure comprises:
an inner cylindrical sidewall contacting the insulating spacer; and
an outer cylindrical sidewall contacting the second retro-stepped dielectric material portion,
wherein a lateral distance between the inner cylindrical sidewall and the outer cylindrical sidewall is not uniform in a horizontal cross-sectional view.
14. The semiconductor structure of claim 1 , wherein each of the memory films comprises a tunneling dielectric layer, a blocking dielectric layer and a charge storage layer located between the tunneling dielectric layer and the blocking dielectric layer.