Three-dimensional memory device with self-aligned etch stop rings for a source contact layer and method of making the same
A memory device includes a lower source-level semiconductor layer, a source contact layer, an upper source-level semiconductor layer, and an alternating stack of insulating layers and electrically conductive layers, and a memory opening fill structure vertically extending through the alternating stack and down to an upper portion of the lower source-level semiconductor layer. The memory opening fill structure includes a vertical semiconductor channel, a memory film laterally surrounding the vertical semiconductor channel, and an annular semiconductor cap contacting a bottom surface of the memory film and contacting a top surface segment of the source contact layer. The annular semiconductor cap may be employed as an etch stop structure during a manufacturing process.
1. A memory device, comprising:
a layer stack including a lower source-level semiconductor layer, a source contact layer, and an upper source-level semiconductor layer;
an alternating stack of insulating layers and electrically conductive layers located over the layer stack; and
a memory opening fill structure vertically extending through the alternating stack, the upper source-level semiconductor layer, the source contact layer, and an upper portion of the lower source-level semiconductor layer,
wherein the memory opening fill structure comprises:
a vertical semiconductor channel vertically extending through the alternating stack and into the upper portion of the lower source-level semiconductor layer;
a memory film laterally surrounding the vertical semiconductor channel and vertically extending through the alternating stack and into an upper portion of the upper source-level semiconductor layer; and
a first annular semiconductor cap contacting a bottom surface of the memory film and contacting a top surface segment of the source contact layer.
2. The memory device of claim 1 , wherein the top surface segment of the source contact layer is located within a volume laterally bounded by a cylindrical vertical plane including an interface between the memory film and the insulating layers of the alternating stack.
3. The memory device of claim 1 , wherein the first annular semiconductor cap and the source contact layer comprise silicon having different dopant concentrations from each other.
4. The memory device of claim 1 , wherein the first annular semiconductor cap has an outer cylindrical surface contacting a sidewall of the upper source-level semiconductor layer.
5. The memory device of claim 1 , wherein the memory film comprises:
a charge storage layer that vertically extends through each electrically conductive layer within the alternating stack;
a tunneling dielectric layer that is laterally surrounded by the charge storage layer; and
at least one blocking dielectric layer that laterally surrounds the charge storage layer.
6. The memory device of claim 5 , wherein the first annular semiconductor cap contacts a cylindrical segment of an outer sidewall of the charge storage layer.
7. The memory device of claim 6 , wherein the source contact layer contacts a concave annular bottom surface of the charge storage layer.
8. The memory device of claim 5 , wherein the first annular semiconductor cap contacts a cylindrical segment of an outer sidewall of the tunneling dielectric layer.
9. The memory device of claim 8 , wherein the source contact layer contacts a concave annular bottom surface of the tunneling dielectric layer.
10. The memory device of claim 5 , wherein the at least one blocking dielectric layer comprises:
an inner blocking dielectric layer laterally surrounding the charge storage layer; and
an outer blocking dielectric layer laterally surrounding the inner blocking dielectric layer, wherein the inner blocking dielectric layer has a higher etch rate in dilute hydrofluoric acid than the outer blocking dielectric layer.
11. The memory device of claim 10 , wherein:
the outer blocking dielectric layer comprises a first silicon oxide or oxynitride material; and
the inner blocking dielectric layer comprises a second silicon oxide material including nitrogen atoms at an atomic concentration that is smaller than an atomic concentration of nitrogen atoms within the outer blocking dielectric layer.
12. The memory device of claim 10 , wherein an interface between the inner blocking dielectric layer and the first annular semiconductor cap is located above a horizontal plane including a highest point within an interface between the outer blocking dielectric layer and the first annular semiconductor cap.
13. The memory device of claim 1 , further comprising a second annular semiconductor cap contacting a bottom surface segment of the source contact layer, comprising a same material as the first annular semiconductor cap, and located within a cylindrical vertical plane containing an outer sidewall of the memory film.
14. The memory device of claim 13 , further comprising a dielectric cap structure embedded within the lower source-level semiconductor layer, wherein:
memory film comprises at least one blocking dielectric layer, a charge storage layer, and a tunneling dielectric layer; and
the dielectric cap structure comprises a layer stack including a same set of materials as the memory film.