Three-dimensional memory device with finned support pillar structures and methods for forming the same
A three-dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers located over a substrate, memory openings vertically extending through a first region of the alternating stack, memory opening fill structures located in the memory openings, and support pillar structures vertically extending through a second region of the alternating stack. Each of the support pillar structures includes a central columnar structure and a set of fins laterally protruding from the central columnar structure at levels of a subset of the electrically conductive layers.
1. A three-dimensional memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers;
memory openings vertically extending through a first region of the alternating stack;
memory opening fill structures located in the memory openings and comprising a respective vertical stack of memory elements located at levels of the electrically conductive layers;
a support pillar structure vertically extending through a second region of the alternating stack and comprising a central columnar structure and a set of fins laterally protruding from the central columnar structure at levels of a subset of the electrically conductive layers, wherein the second region comprises a staircase region in which the alternating stack comprises stepped surfaces; and
a retro-stepped dielectric material portion that overlies the stepped surfaces,
wherein:
the support pillar structure vertically extends through the retro-stepped dielectric material portion;
a first subset of the electrically conductive layers overlies a horizontal plane including a horizontal interface between a topmost fin of the set of fins and a horizontal surface segment of a stepped bottom surface of the retro-stepped dielectric material portion; and
a second subset of the electrically conductive layers underlies the horizontal plane.
2. The three-dimensional memory device of claim 1 , wherein a bottom lateral protrusion distance between the central columnar structure and a cylindrical sidewall of a bottommost fin within the set of fins is smaller than a top lateral protrusion distance between the central columnar structure and a cylindrical sidewall of a topmost fin within the set of fins.
3. The three-dimensional memory device of claim 1 , wherein:
the set of fins has a variable lateral protrusion distance as measured between the central columnar structure and a cylindrical sidewall of a respective fin; and
the variable lateral protrusion distance increases gradually with a vertical distance from the substrate.
4. The three-dimensional memory device of claim 1 , wherein:
the set of fins has a variable lateral protrusion distance as measured between the central columnar structure and a cylindrical sidewall of a respective fin; and
the variable lateral protrusion distance increases stepwise with a vertical distance from the substrate.
5. The three-dimensional memory device of claim 1 , wherein:
a bottommost fin within the set of fins has a bottom fin lateral extent that is a maximum lateral dimension within the bottommost fin;
a topmost fin within the set of fins has a top fin lateral extent that is a maximum lateral dimension within the topmost fin; and
the bottommost fin lateral extent is smaller than the topmost fin lateral extent.
6. The three-dimensional memory device of claim 1 , wherein the central columnar structure has a variable lateral extent such that a topmost portion of the central columnar structure that is not adjoined to any fin within the set of fins has a greater width than a bottommost portion of the central columnar structure that is not adjoined to any fin within the set of fins.
7. The three-dimensional memory device of claim 1 , wherein the set of fins has a same lateral protrusion distance as measured between the central columnar structure and a cylindrical sidewall of a respective fin, and all fins within the set of fins have a same lateral extent.
8. The three-dimensional memory device of claim 1 , wherein each layer within the alternating stack is present within the first region.
9. The three-dimensional memory device of claim 1 , wherein the support pillar structure comprises a dielectric pillar structure that consists essentially of a dielectric material selected from:
(i) silicon oxide; or
(ii) a stack comprising at least one silicon oxide layer and a metal oxide dielectric material layer.
10. The three-dimensional memory device of claim 1 , wherein the support pillar structure is free of any fin above the horizontal plane and the entire set of the fins is located below the horizontal plane, and the support pillar structure comprises a straight sidewall that vertically extends from a top surface of the retro-stepped dielectric material portion to the horizontal plane.
11. The three-dimensional memory device of claim 10 , further comprising additional support pillar structures vertically extending through the second region of the alternating stack and comprising a respective central columnar structure and a respective set of fins laterally protruding from the respective central columnar structure at levels of a respective subset of the electrically conductive layers, wherein a total number of fins per support pillar structure differs for at least one pair of additional support pillar structures of the additional support pillar structures.
12. The three-dimensional memory device of claim 1 , further comprising layer contact via structures located over the second region of the alternating stack and vertically extending through the retro-stepped dielectric material portion and contacting a top surface of a respective one of the electrically conductive layers.
13. The three-dimensional memory device of claim 1 , wherein:
the vertical stack of memory elements comprises portions of a memory material layer;
each of the memory opening fill structures lacks the fins; and
each of the memory opening fill structures further comprises a respective vertical semiconductor channel.
14. A method of forming a three-dimensional memory device, comprising:
forming an alternating stack of insulating layers and sacrificial material layers over a substrate;
forming stepped surfaces by patterning the alternating stack in a staircase region;
forming a retro-stepped dielectric material portion over the stepped surfaces;
forming support openings through the alternating stack and through the retro-stepped dielectric material portion;
laterally recessing the sacrificial material layers selective to the insulating layers around the support openings by introducing into the support openings an isotropic etchant that etches the sacrificial material layers selective to the insulating layers and selective to the retro-stepped dielectric material portion, wherein fin cavities are formed in volumes from the sacrificial material layers are etched, and wherein a first support opening of the support openings comprises a first subset of the fin cavities such that a first subset of the sacrificial material layers overlies a horizontal plane including a horizontal interface between the retro-stepped dielectric material portion and a topmost fin cavity within the first subset of the fin cavities, and a second subset of the sacrificial material layers underlies the horizontal plane;
forming support pillar structures in volumes of the support openings and the fin cavities by depositing at least one fill material in the support openings and the fin cavities, wherein each of the support pillar structures comprises a central columnar structure and a set of fins laterally protruding from the central columnar structure at levels of a subset of the sacrificial material layers;
forming memory openings through a region of the alternating stack that is laterally spaced from the support pillar structures;
forming memory opening fill structures in the memory openings, wherein each of the memory opening fill structures comprises a respective vertical stack of memory elements located at levels of the sacrificial material layers; and
replacing the sacrificial material layers with electrically conductive layers.
15. The method of claim 14 , wherein the sacrificial material layers comprise:
a first sacrificial material layer having a first etch rate in the isotropic etchant; and
a second sacrificial material layer having a second etch rate in the isotropic etchant that is greater than the first etch rate, and overlying the first sacrificial material layer.
16. The method of claim 15 , wherein the sacrificial material layers further comprise a third sacrificial material layer having a third etch rate in the isotropic etchant that is greater than the second etch rate, and overlying the second sacrificial material layer.
17. The method of claim 15 , wherein:
the first sacrificial material layer comprises a first silicon nitride material having a first density; and
the second sacrificial material layer comprises a second silicon nitride material having a second density lower than the first density.
18. The method of claim 14 , wherein:
the support openings are formed through the stepped surfaces;
the first support opening is free of any fin cavity above the horizontal plane; and
a first support pillar structure of the support pillar structures is formed within the first support opening and comprises a straight sidewall that vertically extends from a top surface of the retro-stepped dielectric material portion to the horizontal plane.
19. The method of claim 14 , wherein:
the support pillar structure comprises a dielectric pillar structure that consists essentially of a dielectric material;
the vertical stack of memory elements comprises portions of a memory material layer;
each of the memory opening fill structures lacks the fins; and
each of the memory opening fill structures further comprises a respective vertical semiconductor channel.
20. The method of claim 14 , further comprising:
forming backside trenches through the alternating stack;
forming backside recesses by removing the sacrificial material layers selective to the insulating layers, the support pillar structures, and the memory opening fill structures by introducing another isotropic etchant into the backside trenches, wherein cylindrical surfaces of the fins of the support pillar structures are physically exposed to the backside recesses; and
forming the electrically conductive layers in the backside recesses by depositing at least one conductive material in the backside recesses.