Three-dimensional memory device including a dummy word line with tapered corner and method of making the same
A memory device includes at least one alternating stack of insulating layers and electrically conductive layers, a memory opening vertically extending through the at least one alternating stack, and a memory opening fill structure located in the memory opening and containing a vertical stack of memory elements and a vertical semiconductor channel. The memory opening fill structure includes a lateral protrusion having a tapered sidewall surface; and one of the electrically conductive layers is a taper-containing electrically conductive layer that is located at a level of the lateral protrusion of the memory opening fill structure.
1. A memory device, comprising:
at least one alternating stack of insulating layers and electrically conductive layers;
a memory opening vertically extending through the at least one alternating stack; and
a memory opening fill structure located in the memory opening and comprising a vertical stack of memory elements and a vertical semiconductor channel,
wherein:
the memory opening fill structure comprises a lateral protrusion having a tapered sidewall surface; and
one of the electrically conductive layers of the at least one alternating stack comprises a taper-containing electrically conductive layer that is located at a level of the lateral protrusion of the memory opening fill structure;
wherein the taper-containing electrically conductive layer comprises a contoured sidewall having a tapered sidewall segment that is parallel to the tapered sidewall surface of the lateral protrusion;
wherein the tapered sidewall segment is an annular tapered sidewall segment having an inner periphery that is vertically offset from an outer periphery by a vertical offset distance;
wherein the contoured sidewall comprises a first vertical straight cylindrical sidewall segment that is adjoined to the outer periphery of the annular tapered sidewall segment; and
wherein the contoured sidewall further comprises a second vertical straight cylindrical sidewall segment that is adjoined to the inner periphery of the annular tapered sidewall segment.
2. A method of forming a memory device, comprising:
forming at least one alternating stack comprising insulating layers and sacrificial material layers, wherein one of the sacrificial material layers comprises a composite sacrificial material layer including a primary sacrificial material sublayer including a first sacrificial material and a secondary sacrificial material sublayer including a second sacrificial material that is different from the first sacrificial material;
forming a memory opening through the at least one alternating stack such that the composite sacrificial material layer comprises a recessed sidewall that is laterally recessed outward from a vertical axis passing through a geometrical center of a volume of the memory opening and has a tapered recessed surface segment;
forming a memory opening fill structure within the memory opening, wherein the memory opening fill structure comprises a vertical stack of memory elements and a vertical semiconductor channel, and comprises a lateral protrusion having a tapered sidewall surface that is parallel to the tapered recessed surface segment; and
replacing the sacrificial material layers with electrically conductive layers,
wherein one of the electrically conductive layers comprises a taper-containing electrically conductive layer that is formed in a volume from which the composite sacrificial material layer is removed; and
wherein the taper-containing electrically conductive layer comprises a dummy word line having a contoured sidewall having a tapered sidewall segment that is parallel to the tapered sidewall surface of the lateral protrusion.