Three-dimensional memory device including vertical stack of tubular graded silicon oxynitride portions
A semiconductor structure includes an alternating stack of insulating layers and electrically conductive layers, a memory opening vertically extending through the alternating stack, and a memory opening fill structure located in the memory opening and including a vertical semiconductor channel, a memory film in contact with the vertical semiconductor channel, and a vertical stack of tubular dielectric spacers laterally surrounding the memory film. The tubular dielectric spacers may include tubular graded silicon oxynitride portions having a composition gradient such that an atomic concentration of nitrogen decreases with a lateral distance from an outer sidewall of the memory film, or may include tubular composite dielectric spacers including a respective tubular silicon oxide spacer and a respective tubular dielectric metal oxide spacer. Each of the electrically conductive layers has a hammerhead-shaped vertical cross-sectional profile.
1. A semiconductor structure, comprising:
an alternating stack of insulating layers and electrically conductive layers;
a memory opening vertically extending through the alternating stack; and
a memory opening fill structure located in the memory opening and comprising a vertical semiconductor channel, a memory film in contact with the vertical semiconductor channel, and a vertical stack of tubular graded silicon oxynitride portions laterally surrounding the memory film and having a composition gradient such that an atomic concentration of nitrogen decreases with a lateral distance from an outer sidewall of the memory film,
wherein the memory film comprises a dielectric metal oxide blocking dielectric layer; and
wherein each of the electrically conductive layers has a hammerhead-shaped vertical cross-sectional profile such that a vertical extent of each of the electrically conductive layers has a local minimum within a cylindrical volume laterally bounded by outer sidewall segments of the memory opening fill structure.
2. The semiconductor structure of claim 1 , wherein the local minimum is located between a first cylindrical plane including outer sidewalls of the vertical stack of tubular graded silicon oxynitride portions and a second cylindrical plane including inner sidewalls of the vertical stack of tubular graded silicon oxynitride portions.
3. The semiconductor structure of claim 2 , wherein the local minimum is located along a continuous closed shape that is equidistant from the first cylindrical plane in a plan view along a vertical direction.
4. The semiconductor structure of claim 1 , wherein a tubular graded silicon oxynitride portion within the vertical stack of tubular graded silicon oxynitride portions comprises:
a contoured top surface including an inner concave top surface segment and an outer concave top surface segment that are adjoined to each other; and
a contoured bottom surface including an inner concave bottom surface segment and an outer concave bottom surface segment that are adjoined to each other.
5. The semiconductor structure of claim 1 , wherein the memory film comprises a layer stack including a tunneling dielectric layer and a charge storage layer in contact with the tunneling dielectric layer.
6. The semiconductor structure of claim 5 , wherein the dielectric metal oxide blocking dielectric layer comprises an aluminum oxide layer in contact with the vertical stack of tubular graded silicon oxynitride portions.
7. The semiconductor structure of claim 6 , wherein each of the electrically conductive layers is spaced from the dielectric metal oxide blocking dielectric layer by a respective backside blocking dielectric layer.
8. The semiconductor structure of claim 7 , wherein the respective backside blocking dielectric layer is in contact with a respective pair of tubular graded silicon oxynitride portions and the dielectric metal oxide blocking dielectric layer.
9. The semiconductor structure of claim 7 , wherein:
the memory opening fill structure further comprises a vertical stack of silicon oxide portions located between neighboring pairs of one of the electrically conductive layers and one of the tubular graded silicon oxynitride portions; and
the respective backside blocking dielectric layer is in contact with a respective pair of silicon oxide portions within the vertical stack of silicon oxide portions.
10. The semiconductor structure of claim 6 , wherein the dielectric metal oxide blocking dielectric layer comprises:
a straight inner sidewall that vertically extends straight through each of the electrically conductive layers from a top periphery of the straight inner sidewall to a bottom periphery of the straight inner sidewall; and
a laterally undulating outer sidewall having a first lateral thickness at levels of the insulating layers and having a second lateral thickness at levels of the electrically conductive layers that is less than the first lateral thickness.
11. The semiconductor structure of claim 6 , wherein the dielectric metal oxide blocking dielectric layer has a uniform lateral thickness throughout and comprises a straight inner sidewall that vertically extends straight through each of the electrically conductive layers from a top periphery of the straight inner sidewall to a bottom periphery of the straight inner sidewall.
12. The semiconductor structure of claim 6 , wherein the memory film further comprises a silicon oxide blocking dielectric layer in contact with an inner sidewall of the dielectric metal oxide blocking dielectric layer.
13. The semiconductor structure of claim 1 , wherein each of the electrically conductive layers is in direct contact with a respective pair of insulating layers of the insulating layers of the alternating stack, and is in direct contact with a respective pair of tubular graded silicon oxynitride portions of the vertical stack of tubular graded silicon oxynitride portions.
14. The semiconductor structure of claim 1 , wherein a maximum vertical extent of one of the electrically conductive layers within the cylindrical volume is greater than a vertical extent of a horizontally-extending portion of the one of the electrically conductive layers located outside the cylindrical volume and having a uniform thickness along a vertical direction.