Three-dimensional memory device including discrete charge storage elements with laterally-protruding profiles and methods of making thereof
A three-dimensional memory device includes an alternating stack of insulating layers and electrically conductive layers located over a substrate, memory openings vertically extending through the alternating stack and having lateral protrusions at levels of the electrically conductive layers, and memory opening fill structures located in the memory openings. Each of the memory opening fill structures includes a vertical semiconductor channel, a dielectric material liner laterally surrounding the vertical semiconductor channel, and a vertical stack of discrete memory elements laterally surrounding the dielectric material liner and located within volumes of the lateral protrusions. Each discrete memory element includes a vertical inner sidewall and a convex or stepped outer sidewall.
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 having lateral protrusions at levels of the electrically conductive layers;
memory opening fill structures located in the memory openings, wherein each of the memory opening fill structures comprises a vertical semiconductor channel, a dielectric material liner laterally surrounding the vertical semiconductor channel, and a vertical stack of discrete memory elements laterally surrounding the dielectric material liner and located within volumes of the lateral protrusions, wherein each discrete memory element within the vertical stack of discrete memory elements comprises a vertical inner sidewall and a stepped outer sidewall that is located entirely within a respective volume of a single lateral protrusion of the volumes of the lateral protrusions, is laterally offset outward from the vertical inner sidewall by a greater lateral offset distance at a central segment thereof than at a top segment thereof and than at a bottom segment thereof, and comprises a plurality of vertical outer sidewall segments and a plurality of horizontal outer sidewall segments that are adjoined to each other; and
wherein:
the plurality of vertical outer sidewall segments of each stepped outer sidewall comprise at least five vertical outer sidewall segments that are laterally offset from the vertical semiconductor channel by at least three different lateral offset distances; and
the plurality of horizontal outer sidewall segments of each stepped outer sidewall comprise at least six horizontal outer sidewall segments that are vertically spaced from the substrate by different vertical distances.
2. The three-dimensional memory device of claim 1 , wherein:
the top segment of the stepped outer sidewall of each discrete memory element comprises a first one of the plurality of vertical outer sidewall segments of a respective one of the stepped outer sidewalls;
the bottom segment of the stepped outer sidewall of each discrete memory element comprises a second one of the plurality of vertical outer sidewall segments of the respective one of the stepped outer sidewalls; and
the central segment of the stepped outer sidewall of each discrete memory element comprises a third one of the plurality of vertical outer sidewall segments of the respective one of the stepped outer sidewalls.
3. The three-dimensional memory device of claim 2 , wherein the first one and the second one of the plurality of vertical outer sidewall segments are equidistant from the vertical semiconductor channel.
4. 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 having lateral protrusions at levels of the electrically conductive layers; and
memory opening fill structures located in the memory openings,
wherein each of the memory opening fill structures comprises a vertical semiconductor channel, a dielectric material liner laterally surrounding the vertical semiconductor channel, and a vertical stack of discrete memory elements laterally surrounding the dielectric material liner and located within volumes of the lateral protrusions,
wherein each discrete memory element within the vertical stack of discrete memory elements comprises a vertical inner sidewall and a convex outer sidewall that is laterally offset outward from the vertical inner sidewall by a greater lateral offset distance at a central segment thereof than at a top segment thereof and than at a bottom segment thereof,
wherein the convex outer sidewall of each discrete memory element is adjoined to the vertical inner sidewall of a respective discrete memory element,
wherein an entirety of the convex outer sidewall of each discrete memory element is convex; and
wherein:
the plurality of vertical outer sidewall segments of each stepped outer sidewall comprise at least five vertical outer sidewall segments that are laterally offset from the vertical semiconductor channel by at least three different lateral offset distances; and
the plurality of horizontal outer sidewall segments of each stepped outer sidewall comprise at least six horizontal outer sidewall segments that are vertically spaced from the substrate by different vertical distances.
5. The three-dimensional memory device of claim 1 , wherein each of the memory opening fill structures further comprises a blocking dielectric layer in contact with an entirety of the stepped outer sidewalls of the vertical stack of discrete memory elements.
6. The three-dimensional memory device of claim 5 , wherein all surfaces of the vertical stack of discrete memory elements within each memory opening fill structure are in direct contact with a respective surface of the blocking dielectric layer and the dielectric material liner.
7. The three-dimensional memory device of claim 1 , wherein each electrically conductive layer of the electrically conductive layers that laterally surrounds a respective discrete memory element of the vertical stack of discrete memory elements comprises a stepped sidewall that faces the stepped sidewall of the respective discrete memory element.
8. The three-dimensional memory device of claim 1 , wherein:
the discrete memory elements comprise charge storage elements;
the dielectric material liner comprises a tunneling dielectric layer; and
the three-dimensional memory device comprises an array of vertical NAND strings.
9. The three dimensional memory device of claim 1 , wherein:
the plurality of vertical outer sidewall segments comprises at least three vertical outer sidewall segments; and
the plurality of horizontal outer sidewall segments comprises at least four horizontal outer sidewall segments.
10. The three-dimensional memory device of claim 1 , wherein:
the plurality of vertical outer sidewall segments comprises five vertical outer sidewall segments; and
the plurality of horizontal outer sidewall segments comprises six horizontal outer sidewall segments.
11. The three-dimensional memory device of claim 1 , wherein each discrete memory element within the vertical stack of discrete memory elements is located at a same level of a respective electrically conductive layer of the electrically conductive layers, and has a vertical extent that is less than a thickness of a vertical extent of the respective electrically conductive layer.
12. The three-dimensional memory device of claim 5 , wherein each discrete memory element is located between a respective vertically neighboring pair of insulating layers of the insulating layers which includes a respective overlying insulating layer and a respective underlying insulating layer.
13. The three-dimensional memory device of claim 12 , wherein:
each discrete memory element is located entirely below a respective first horizontal plane including a bottom surface of the respective overlying insulating layer; and
each discrete memory element is located entirely above a respective second horizontal plane including a top surface of the respective underlying insulating layer.
14. The three-dimensional memory device of claim 13 , wherein:
a topmost one of the plurality of horizontal outer sidewall segments of each discrete memory element is vertically spaced from the respective first horizontal plane by a thickness of the blocking dielectric layer; and
a bottommost one of the plurality of horizontal outer sidewall segments of each discrete memory element is vertically spaced from the respective second horizontal plane by the thickness of the blocking dielectric layer.
15. The three-dimensional memory device of claim 5 , wherein the stepped outer sidewall of each discrete memory element is contacted by a respective set of at least four horizontally-extending surface segments of the blocking dielectric layer.
16. The three-dimensional memory device of claim 5 , wherein:
an electrically conductive layer of the electrically conductive layers comprises a stepped inner sidewall that faces one of the discrete memory elements; and
the stepped inner sidewall of the electrically conductive layer comprises three vertically-extending surface segments that are adjoined by two horizontally-extending surface segments.
17. The three-dimensional memory device of claim 16 , wherein:
said one of the discrete memory elements is located between a neighboring pair of insulating layers of the insulating layers;
the electrically conductive layer is vertically spaced from the neighboring pair of insulating layers by a backside blocking dielectric layer; and
the electrically conductive layer is laterally spaced from said one of the discrete memory elements by a contoured portion of the backside blocking dielectric layer and a contoured portion of the blocking dielectric layer.
18. The three-dimensional memory device of claim 17 , wherein the contoured portion of the backside blocking dielectric layer contacts the contoured portion of the blocking dielectric layer at a stepped interface including at least three vertical interface segments and at least two horizontal interface segments.
19. The three-dimensional memory device of claim 4 , wherein:
each of the memory opening fill structures further comprises a blocking dielectric layer in contact with an entirety of the convex outer sidewalls of the vertical stack of discrete memory elements;
the blocking dielectric layer comprises an inner sidewall that comprises vertically-extending surface segments that contact surface segments of the dielectric material liner and concave surface segments that contact the convex outer sidewalls of the vertical stack of discrete memory elements;
a first subset of the electrically conductive layers comprises a respective concave surface that faces a respective discrete memory element within the vertical stack of memory elements; and
a second subset of the electrically conductive layers comprises a vertical sidewall that faces a respective one of the memory opening fill structures and is located at a level at which no discrete memory element is present.