Three-dimensional memory device containing a silicon nitride ring in an opening in a memory film and method of making the same
An alternating stack of insulating layers and sacrificial material layers is formed over a substrate. A memory opening is formed through the alternating stack. A memory film including a silicon nitride layer and a tunneling dielectric layer is formed in the memory opening, and an opening is formed through the memory film. A chemical oxide layer is formed on a physically exposed surface of an underlying semiconductor material portion. A silicon nitride ring can be formed by selectively growing a silicon nitride material from an annular silicon nitride layer portion of the silicon nitride layer while suppressing deposition of the silicon nitride material on the tunneling dielectric layer and on the chemical oxide layer. A vertical semiconductor channel can be formed by depositing a continuous semiconductor material layer on the underlying semiconductor material portion and the tunneling dielectric layer and on the silicon nitride ring.
1. A three-dimensional memory device, comprising:
an alternating stack of insulating layers and electrically conductive layers located over a substrate;
memory openings vertically extending through the alternating stack; and
memory opening fill structures located within a respective one of the memory openings, wherein each of the memory opening fill structures comprises:
a memory film contacting a sidewall of a respective memory opening, comprising a layer stack including at least a tunneling dielectric layer and a silicon nitride layer, and including an opening at a bottom portion thereof;
a silicon nitride ring contacting a sidewall of the opening in the memory film; and
a vertical semiconductor channel contacting an inner sidewall of a vertically-extending portion of the memory film and extending through the silicon nitride ring and contacting a semiconductor material portion that underlies the memory film and the silicon nitride ring,
wherein the silicon nitride ring vertically extends from a top surface of the semiconductor material portion to a periphery of an interface between the tunneling dielectric layer and the vertical semiconductor channel.
2. The three-dimensional memory device of claim 1 , wherein:
the silicon nitride layer comprises an annular silicon nitride layer portion through which the opening at the bottom portion of the memory film extends; and
the tunneling dielectric layer comprises an annular tunneling dielectric layer portion through which the opening at the bottom portion of the memory film extends.
3. The three-dimensional memory device of claim 2 , wherein the silicon nitride ring contacts a sidewall of the annular silicon nitride layer portion, an upper surface of the annular silicon nitride layer portion, and a lower surface of the annular silicon nitride layer portion.
4. The three-dimensional memory device of claim 2 , wherein the silicon nitride ring contacts a sidewall of the annular tunneling dielectric layer portion.
5. The three-dimensional memory device of claim 2 , wherein:
the layer stack includes a blocking dielectric layer that contacts the silicon nitride layer and sidewalls of the insulating layers of the alternating stack;
the blocking dielectric layer comprises an annular blocking dielectric layer portion through which the opening at the bottom portion of the memory film extends; and
the silicon nitride ring contacts a sidewall of the annular blocking dielectric layer portion.
6. The three-dimensional memory device of claim 5 , wherein:
the sidewall of the annular blocking dielectric layer portion is laterally recessed outward relative to an interface between a sidewall of the annular silicon nitride layer portion and the silicon nitride ring; and
the sidewall of the annular tunneling dielectric layer portion is laterally recessed outward relative to the interface between the sidewall of the annular silicon nitride layer portion and the silicon nitride ring.
7. The three-dimensional memory device of claim 1 , wherein a portion of the vertical semiconductor channel contacting the silicon nitride ring has a greater thickness than a portion of the vertical semiconductor channel contacting the tunneling dielectric layer.
8. The three-dimensional memory device of claim 1 , wherein:
the vertical semiconductor channel comprises polysilicon;
the substrate comprises single crystalline silicon; and
the semiconductor material portion comprises a single crystal silicon epitaxial pedestal structure that is in epitaxial alignment with the substrate.
9. The three-dimensional memory device of claim 8 , wherein an entirety of a periphery between the vertical semiconductor channel and the epitaxial pedestal structure is located on a surface of the silicon nitride ring.
10. The three-dimensional memory device of claim 1 , wherein each of the memory opening fill structures comprises:
a dielectric core contacting an inner sidewall of the vertical semiconductor channel; and
a drain region including a doped semiconductor material and contacting a top end of the vertical semiconductor channel.
11. The three-dimensional memory device of claim 1 , wherein each vertically neighboring pair of an insulating layer and an electrically conductive layer of the alternating stack is spaced from each other by a backside blocking dielectric layer that contacts outer sidewalls of the memory opening fill structures.
12. The three-dimensional memory device of claim 1 , wherein:
the alternating stacks comprise stepped surfaces in a staircase region, wherein each electrically conductive layer other than a topmost one of the electrically conductive layers laterally extends farther than an overlying electrically conductive layer;
layer contact via structures contact a top surface of a respective one of the electrically conductive layers in the staircase region;
a retro-stepped dielectric material portion overlies the stepped surfaces; and
support pillar structures extend through the retro-stepped dielectric material portion and the stepped surfaces in the staircase region.