THREE-DIMENSIONAL MEMORY DEVICE WITH TOP-CONTACT THROUGH-STACK CONTACT VIA STRUCTURES AND METHODS FOR FORMING THE SAME
A device structure includes an alternating stack of insulating layers and electrically conductive layers, a retro-stepped dielectric material portion, a memory stack structure vertically extending through the alternating stack and including a vertical semiconductor channel vertical stack of memory elements, and a layer contact via structure. The layer contact via structure may be a tubular layer contact via structure contacting an annular top surface segment of a first electrically conductive layer of the electrically conductive layers. Alternatively, a first electrically conductive layer may include a horizontally-extending portion that is located outside a volume of the contact via opening and a vertically-extending tubular portion located in a peripheral region of the contact via opening, and the layer contact via structure may contact an inner sidewall of the vertically-extending tubular portion.
1 . A device structure, comprising:
an alternating stack of insulating layers and electrically conductive layers;
a memory stack structure vertically extending through the alternating stack and comprising a vertical semiconductor channel and a vertical stack of memory elements;
a contact via opening vertically extending through a subset of the electrically conductive layers and a subset of the insulating layers, wherein a topmost layer within the subset of the electrically conductive layers comprises a first electrically conductive layer, and the first electrically conductive layer comprises a horizontally-extending portion that is located outside a volume of the contact via opening and further comprises a vertically-extending tubular portion located in a peripheral region of the contact via opening and adjoined to the horizontally-extending portion; and
a layer contact via structure located in a center region of the contact via opening and contacting an inner sidewall of the vertically-extending tubular portion.
2 . The device structure of claim 1 , further comprising a retro-stepped dielectric material portion having a stepped bottom surface and overlying a region of the alternating stack in which the electrically conductive layers have variable lateral extents, wherein the contact via opening vertically also extends through the retro-stepped dielectric material portion.
3 . The device structure of claim 2 , further comprising a contact-level dielectric layer overlying the alternating stack and the retro-stepped dielectric material portion, wherein a topmost surface of the vertically-extending tubular portion is located below a horizontal plane including a top surface of the contact-level dielectric layer.
4 . The device structure of claim 2 , wherein a topmost surface of the vertically-extending tubular portion is located above a horizontal plane including a top surface of the retro-stepped dielectric material portion.
5 . The device structure of claim 2 , wherein each of the electrically conductive layers is spaced from a most proximal one of the insulating layers by a respective outer blocking dielectric layer.
6 . The device structure of claim 5 , wherein the vertically-extending tubular portion of the first electrically conductive layer is laterally spaced from the retro-stepped dielectric material portion by a tubular portion of a first outer blocking dielectric layer of the outer blocking dielectric layers.
7 . The device structure of claim 1 , wherein the layer contact via structure comprises:
an upper portion that overlies the vertically-extending tubular portion and having a first lateral extent; and
a lower portion that is laterally surrounded by the vertically-extending tubular portion and having a second lateral extent that is less than the first lateral extent.
8 . The device structure of claim 7 , wherein:
the vertically-extending tubular portion comprises a straight outer cylindrical sidewall and a contoured inner cylindrical sidewall; and
a lateral distance between the straight outer cylindrical sidewall and the contoured inner cylindrical sidewall decreases as a function of a vertical distance from a horizontal plane including a bottommost surface of the alternating stack.
9 . The device structure of claim 7 , wherein the layer contact via structure comprises a tapered portion located between the upper portion and the lower portion and having a variable lateral extent that increases with a vertical distance from a horizontal plane including a bottommost surface of the alternating stack.
10 . The device structure of claim 1 , wherein the layer contact via structure comprises a contoured bottom surface having an inverted concave conical profile.
11 . The device structure of claim 1 , further comprising a finned dielectric material portion located within a lower region of the contact via opening and including a vertical stack of annular dielectric fin portions at levels of the subset of the insulating layers.
12 . The device structure of claim 11 , further comprising a vertical stack of silicon oxide liners located at levels of the subset of the electrically conductive layers and laterally surrounding the finned dielectric material portion, wherein the subset of the electrically conductive layers is laterally spaced from the finned dielectric material portion by the vertical stack of silicon oxide liners.
13 . The device structure of claim 11 , further comprising a vertical stack of tubular silicon portions located at the levels of the subset of the insulating layers and interposed between the finned dielectric material portion and the subset of the insulating layers.
14 . The device structure of claim 11 , wherein:
the finned dielectric material portion comprises a contoured top surface;
a center point of the contoured top surface is a lowest point of the contoured top surface; and
a vertical distance between any arbitrarily selected point on the contoured top surface and a horizontal plane including a bottommost surface of the alternating stack increases with a radial distance from the center point to the arbitrarily selected point.
15 . A method of forming a device structure, 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 memory stack structures through the alternating stack, wherein each of the memory stack structures comprises a respective vertical semiconductor channel and a vertical stack of memory elements;
forming a contact via opening through the retro-stepped dielectric material portion, a subset of the sacrificial material layers within the alternating stack, and a subset of the insulating layers within the alternating stack, wherein a topmost layer within the subset of the sacrificial material layers comprises a first sacrificial material layer;
laterally recessing a sidewall of the retro-stepped dielectric material portion around the contact via opening by performing an etch back process;
forming a sacrificial tubular structure in a peripheral region of the contact via opening on the laterally recessed sidewall of the retro-stepped dielectric material portion;
replacing the sacrificial material layers and the sacrificial tubular structure with at least electrically conductive layers, wherein a combination of the first sacrificial material layer and the sacrificial tubular structure is replaced with at least a first electrically conductive layer; and
forming a layer contact via structure on an inner-sidewall of a vertically-extending tubular portion of the first electrically conductive layer.
16 . The method of claim 15 , wherein:
the etch back process also laterally recesses sidewalls of the subset of the insulating layers to form lateral annular cavities; and
the method further comprises forming a finned dielectric material portion in a lower region of the contact via opening, wherein the finned dielectric material portion comprises a vertical stack of annular dielectric fin portions that fill the lateral annular cavities.
17 . The method of claim 16 , further comprising:
depositing a conformal silicon liner in a peripheral region of the contact via opening; and
depositing a dielectric fill material layer over the conformal silicon liner, wherein a lower portion of the dielectric fill material layer fills the lower region of the contact via opening, and an upper portion of the dielectric fill material layer is formed in a peripheral portion of an upper region of the contact via opening with a void in a center portion of the upper region of the contact via opening.
18 . The method of claim 17 , further comprising recessing the dielectric fill material layer, wherein:
a remaining portion of the dielectric fill material layer that remains in the lower region of the contact via opening comprises the finned dielectric material portion; and
a vertically-extending portion of the conformal silicon liner is physically exposed in the upper region of the contact via opening.
19 . The method of claim 17 , further comprising:
etching materials of the sacrificial material layers and the sacrificial tubular structure selectively to materials of the insulating layers and the conformal silicon liner during a same etching step to form voids in volumes from which the sacrificial material layers and the sacrificial tubular structure are removed;
converting segments of the conformal silicon liner into silicon oxide liners; and
depositing a combination of an outer blocking dielectric layer and a respective one of the electrically conductive layers in each of the voids.
20 . The method of claim 15 , wherein the sacrificial tubular structure is formed by conformally depositing a sacrificial fill material in a peripheral region of the contact via opening and by anisotropically etching horizontally-extending portions of the sacrificial fill material, wherein a remaining vertically-extending portion of the sacrificial fill material comprises the sacrificial tubular structure.