Three-dimensional memory device containing annular etch-stop spacer and method of making thereof
A method of forming a monolithic three-dimensional memory device includes forming a first alternating stack over a substrate, forming an insulating cap layer, forming a first memory opening through the insulating cap layer and the first alternating stack, forming a sacrificial pillar structure in the first memory opening, forming a second alternating stack, forming a second memory opening, forming an inter-stack memory opening, forming a memory film and a first semiconductor channel layer in the inter-stack memory opening, anisotropically etching a horizontal bottom portion of the memory film and the first semiconductor channel layer to expose the substrate at the bottom of the inter-stack memory opening such that damage to portions of the first semiconductor channel layer and the memory film located adjacent to the insulating cap layer is reduced or avoided, and forming a second semiconductor channel layer in contact with the exposed substrate in the inter-stack memory opening.
1. A monolithic three-dimensional memory device, comprising:
a first alternating stack of first insulating layers and first electrically conductive layers located over a top surface of a substrate;
an insulating cap layer overlying the first alternating stack;
a second alternating stack of second insulating layers and second electrically conductive layers overlying the insulating cap layer; and
a memory stack structure extending through the second alternating stack, the insulating cap layer, and the first alternating stack and comprising a semiconductor channel and a memory film including a plurality of charge storage regions,
wherein:
the insulating cap layer comprises a first concave surface having a first radius of curvature, laterally surrounding the memory stack structure, and adjoined to an upper periphery of a substantially vertical sidewall of the memory stack structure; and
the insulating cap layer comprises a second concave surface having a second radius of curvature that is greater than the first radius of curvature, laterally surrounding the memory stack structure, and adjoined to an upper periphery of the first concave surface.
2. The monolithic three-dimensional memory device of claim 1 , wherein the memory stacks structure contains a tapered portion adjacent to the insulating cap layer.
3. The monolithic three-dimensional memory device of claim 1 , wherein:
an upper periphery of the second concave surface is adjoined to a lower periphery of a substantially vertical sidewall of the insulating cap layer;
a first convex sidewall of the memory stack structure contacts the first concave sidewall of the insulating cap layer; and
a second convex sidewall of the memory stack structure contacts the second concave sidewall of the insulating cap layer.
4. The monolithic three-dimensional memory device of claim 1 , further comprising an annular spacer that laterally surrounds the memory stack structure, wherein:
a first convex sidewall of the annular spacer contacts the first concave sidewall of the insulating cap layer; and
a second convex sidewall of the annular spacer contacts the second concave sidewall of the insulating cap layer.