US20180151588A1

US20180151588A1 - Three-dimensional memory device with discrete self-aligned charge storage elements and method of making thereof

Info

Publication number: US20180151588A1
Application number: US15/361,842
Authority: US
Inventors: Masanori Tsutsumi; Kengo Kajiwara; Raghuveer S. MAKALA
Original assignee: SanDisk Technologies LLC
Current assignee: SanDisk Technologies LLC
Priority date: 2016-11-28
Filing date: 2016-11-28
Publication date: 2018-05-31
Anticipated expiration: 2036-11-28
Also published as: US9991277B1

Abstract

A memory opening can be formed through an alternating stack of insulating layers and sacrificial material layers over a substrate. A material layer stack containing, from outside to inside, an aluminum oxide tunneling dielectric layer, a silicon-containing tunneling dielectric layer, and a vertical semiconductor channel is formed within the memory opening. After forming backside recesses by removing the sacrificial material layers, charge trapping material portions are formed on physically exposed surfaces of the aluminum oxide tunneling dielectric layer by employing a selective silicon nitride deposition process. A backside blocking dielectric layer and electrically conductive layers are formed in the backside recesses. The charge trapping material portions are discrete silicon nitride portions located at levels of the electrically conductive layers and vertically spaced from one another by the insulating layers.

Description

FIELD

The present disclosure relates generally to the field of three-dimensional memory devices and specifically to three-dimensional memory devices employing self-aligned charge storage elements and methods of making thereof.

BACKGROUND

Three-dimensional vertical NAND strings having one bit per cell are disclosed in an article by T. Endoh et al., titled “Novel Ultra High Density Memory With A Stacked-Surrounding Gate Transistor (S-SGT) Structured Cell”, IEDM Proc. (2001) 33-36.
Charge leakage across different levels of control gate electrodes in a charge storage material layer can degrade data retention and data accuracy in a three-dimensional memory device. Methods for improving charge retention and data accuracy in a three-dimensional memory device are thus desired.

SUMMARY

According to an aspect of the present disclosure, a three-dimensional memory device is provided, which comprises: an alternating stack of insulating layers and electrically conductive layers located over a substrate; a vertical semiconductor channel vertically extending through a predominant subset of layers within the alternating stack; a tunneling dielectric layer stack including a silicon-containing tunneling dielectric layer and an aluminum oxide tunneling dielectric layer and laterally surrounding the vertical semiconductor channel; and charge trapping material portions located at each level of the electrically conductive layers that are located at, or above a horizontal plane including a bottom surface of the aluminum oxide tunneling dielectric layer, comprising silicon nitride, contacting portions of an outer sidewall of the aluminum oxide tunneling dielectric layer, and vertically spaced from one another.
According to another aspect of the present disclosure, a method of forming a three-dimensional memory device is provided. 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 material layer stack comprising, from outside to inside, an aluminum oxide tunneling dielectric layer, a silicon-containing tunneling dielectric layer, and a vertical semiconductor channel is formed within the memory opening. Backside recesses are formed by removing the sacrificial material layers selective to the insulating layers. Charge trapping material portions are formed on physically exposed surfaces of the aluminum oxide tunneling dielectric layer by employing a selective silicon nitride deposition process in which silicon nitride grows from the physically exposed surfaces of the aluminum oxide tunneling dielectric layer while not growing from surfaces of the insulating layers. A backside blocking dielectric layer is formed over the charge trapping material portions. Electrically conductive layers are formed in remaining volumes of the backside recesses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic vertical cross-sectional view of a first exemplary structure after formation of at least one peripheral device, a semiconductor material layer, and a gate dielectric layer according to a first embodiment of the present disclosure.

FIG. 2 is a schematic vertical cross-sectional view of the first exemplary structure after formation of an alternating stack of insulating layers and sacrificial material layers according to the first embodiment of the present disclosure.

FIG. 3 is a schematic vertical cross-sectional view of the first exemplary structure after formation of stepped terraces and a retro-stepped dielectric material portion according to the first embodiment of the present disclosure.

FIG. 4A is a schematic vertical cross-sectional view of the first exemplary structure after formation of memory openings and support openings according to the first embodiment of the present disclosure.

FIG. 4B is a top-down view of the first exemplary structure of FIG. 4A. The vertical plane A-A′ is the plane of the cross-section for FIG. 4A.

FIGS. 5A-5H are sequential schematic vertical cross-sectional views of a memory opening during formation of a memory opening fill structure according to the first embodiment of the present disclosure.

FIG. 6 is a schematic vertical cross-sectional view of the first exemplary structure after formation of the memory opening fill structures according to the first embodiment of the present disclosure.

FIG. 7A is a schematic vertical cross-sectional view of the first exemplary structure after formation of backside trenches according to the first embodiment of the present disclosure.

FIG. 7B is a top-down view of the first exemplary structure of FIG. 7A. The vertical plane A-A′ is the plane of the cross-section for FIG. 7A.

FIGS. 8A-8F are sequential vertical cross-sectional views of a memory opening within the first exemplary structure during various processing steps employed to form discrete charge trapping material portions, a backside blocking dielectric layer, and electrically conductive layers according to the first embodiment of the present disclosure.

FIG. 9 is a vertical cross-sectional view of the first exemplary structure after formation of electrically conductive layers according to the first embodiment of the present disclosure.

FIG. 10 is a vertical cross-sectional view of the first exemplary structure after removal of a deposited conductive material from within the backside trenches according to the first embodiment of the present disclosure.

FIG. 11 is a vertical cross-sectional view of the first exemplary structure after formation of an insulating spacer, a source region, and a backside contact trench according to the first embodiment of the present disclosure.

FIG. 12A is a vertical cross-sectional view of the first exemplary structure after formation of additional contact via structures according to the first embodiment of the present disclosure.

FIG. 12B is a top-down view of the first exemplary structure of FIG. 12A. The vertical plane A-A′ is the plane of the cross-section for FIG. 12A.

FIGS. 13A-13D are sequential vertical cross-sectional views of a memory opening within a second exemplary structure during various processing steps employed to form discrete charge trapping material portions, blocking dielectric spacers, a backside blocking dielectric layer, and electrically conductive layers according to a second embodiment of the present disclosure.

DETAILED DESCRIPTION

As discussed above, the present disclosure is directed to three-dimensional memory devices employing discrete self-aligned charge storage elements and methods of making thereof, the various aspects of which are described below. The embodiments of the disclosure can be employed to form various structures including a multilevel memory structure, non-limiting examples of which include semiconductor devices such as three-dimensional monolithic memory array devices comprising a plurality of NAND memory strings. The drawings are not drawn to scale. Multiple instances of an element may be duplicated where a single instance of the element is illustrated, unless absence of duplication of elements is expressly described or clearly indicated otherwise. Ordinals such as “first,” “second,” and “third” are employed merely to identify similar elements, and different ordinals may be employed across the specification and the claims of the instant disclosure. As used herein, a first element located “on” a second element can be located on the exterior side of a surface of the second element or on the interior side of the second element. As used herein, a first element is located “directly on” a second element if there exist a physical contact between a surface of the first element and a surface of the second element.
As used herein, a “layer” refers to a material portion including a region having a thickness. A layer may extend over the entirety of an underlying or overlying structure, or may have an extent less than the extent of an underlying or overlying structure. For example, a layer may be located between any pair of horizontal planes between, or at, a top surface and a bottom surface of the continuous structure. A layer may extend horizontally, vertically, and/or along a tapered surface. A substrate may be a layer, may include one or more layers therein, or may have one or more layer thereupon, thereabove, and/or therebelow.
A monolithic three-dimensional memory array is one in which multiple memory levels are formed above a single substrate, such as a semiconductor wafer, with no intervening substrates. The term “monolithic” means that layers of each level of the array are directly deposited on the layers of each underlying level of the array. In contrast, two dimensional arrays may be formed separately and then packaged together to form a non-monolithic memory device. For example, non-monolithic stacked memories have been constructed by forming memory levels on separate substrates and vertically stacking the memory levels, as described in U.S. Pat. No. 5,915,167 titled “Three-dimensional Structure Memory.” The substrates may be thinned or removed from the memory levels before bonding, but as the memory levels are initially formed over separate substrates, such memories are not true monolithic three-dimensional memory arrays. The various three-dimensional memory devices of the present disclosure include a monolithic three-dimensional NAND string memory device, and can be fabricated employing the various embodiments described herein.
Referring to FIG. 1, a first exemplary structure according to an embodiment of the present disclosure is illustrated, which can be employed, for example, to fabricate a device structure containing vertical NAND memory devices. The first exemplary structure includes a substrate, which can be a semiconductor substrate (9, 10). The substrate can include a substrate semiconductor layer 9. The substrate semiconductor layer 9 maybe a semiconductor wafer or a semiconductor material layer, and can include at least one elemental semiconductor material (e.g., single crystal silicon wafer or layer), at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. The substrate can have a major surface 7, which can be, for example, a topmost surface of the substrate semiconductor layer 9. The major surface 7 can be a semiconductor surface. In one embodiment, the major surface 7 can be a single crystalline semiconductor surface, such as a single crystalline semiconductor surface.
As used herein, a “semiconducting material” refers to a material having electrical conductivity in the range from 1.0×10⁻⁶S/cm to 1.0×10⁵S/cm. As used herein, a “semiconductor material” refers to a material having electrical conductivity in the range from 1.0×10⁻⁶S/cm to 1.0×10⁵S/cm in the absence of electrical dopants therein, and is capable of producing a doped material having electrical conductivity in a range from 1.0 S/cm to 1.0×10⁵S/cm upon suitable doping with an electrical dopant. As used herein, an “electrical dopant” refers to a p-type dopant that adds a hole to a valence band within a band structure, or an n-type dopant that adds an electron to a conduction band within a band structure. As used herein, a “conductive material” refers to a material having electrical conductivity greater than 1.0×10⁵S/cm. As used herein, an “insulator material” or a “dielectric material” refers to a material having electrical conductivity less than 1.0×10⁻⁶S/cm. As used herein, a “heavily doped semiconductor material” refers to a semiconductor material that is doped with electrical dopant at a sufficiently high atomic concentration to become a conductive material, i.e., to have electrical conductivity greater than 1.0×10⁵S/cm. A “doped semiconductor material” may be a heavily doped semiconductor material, or may be a semiconductor material that includes electrical dopants (i.e., p-type dopants and/or n-type dopants) at a concentration that provides electrical conductivity in the range from 1.0×10⁻⁶S/cm to 1.0×10⁵S/cm. An “intrinsic semiconductor material” refers to a semiconductor material that is not doped with electrical dopants. Thus, a semiconductor material may be semiconducting or conductive, and may be an intrinsic semiconductor material or a doped semiconductor material. A doped semiconductor material can be semiconducting or conductive depending on the atomic concentration of electrical dopants therein. As used herein, a “metallic material” refers to a conductive material including at least one metallic element therein. All measurements for electrical conductivities are made at the standard condition.
At least one semiconductor device 700 for a peripheral circuitry can be formed on a portion of the substrate semiconductor layer 9. The at least one semiconductor device can include, for example, field effect transistors. For example, at least one shallow trench isolation structure 120 can be formed by etching portions of the substrate semiconductor layer 9 and depositing a dielectric material therein. A gate dielectric layer, at least one gate conductor layer, and a gate cap dielectric layer can be formed over the substrate semiconductor layer 9, and can be subsequently patterned to form at least one gate structure (150, 152, 154, 158), each of which can include a gate dielectric 150, a gate electrode (152, 154), and a gate cap dielectric 158. The gate electrode (152, 154) may include a stack of a first gate electrode portion 152 and a second gate electrode portion 154. At least one gate spacer 156 can be formed around the at least one gate structure (150, 152, 154, 158) by depositing and anisotropically etching a dielectric liner. Active regions 130 can be formed in upper portions of the substrate semiconductor layer 9, for example, by introducing electrical dopants employing the at least one gate structure (150, 152, 154, 158) as masking structures. Additional masks may be employed as needed. The active region 130 can include source regions and drain regions of field effect transistors. A first dielectric liner 161 and a second dielectric liner 162 can be optionally formed. Each of the first and second dielectric liners (161, 162) can comprise a silicon oxide layer, a silicon nitride layer, and/or a dielectric metal oxide layer. As used herein, silicon oxide includes silicon dioxide as well as non-stoichiometric silicon oxides having more or less than two oxygen atoms for each silicon atoms. Silicon dioxide is preferred. In an illustrative example, the first dielectric liner 161 can be a silicon oxide layer, and the second dielectric liner 162 can be a silicon nitride layer. The least one semiconductor device for the peripheral circuitry can contain a driver circuit for memory devices to be subsequently formed, which can include at least one NAND device.
A dielectric material such as silicon oxide can be deposited over the at least one semiconductor device, and can be subsequently planarized to form a planarization dielectric layer 170. In one embodiment the planarized top surface of the planarization dielectric layer 170 can be coplanar with a top surface of the dielectric liners (161, 162). Subsequently, the planarization dielectric layer 170 and the dielectric liners (161, 162) can be removed from an area to physically expose a top surface of the substrate semiconductor layer 9. As used herein, a surface is “physically exposed” if the surface is in physical contact with vacuum, or a gas phase material (such as air).
An optional semiconductor material layer 10 can be formed on the top surface of the substrate semiconductor layer 9 by deposition of a single crystalline semiconductor material, for example, by selective epitaxy. The deposited semiconductor material can be the same as, or can be different from, the semiconductor material of the substrate semiconductor layer 9. The deposited semiconductor material can be any material that can be employed for the semiconductor substrate layer 9 as described above. The single crystalline semiconductor material of the semiconductor material layer 10 can be in epitaxial alignment with the single crystalline structure of the substrate semiconductor layer 9. Portions of the deposited semiconductor material located above the top surface of the planarization dielectric layer 170 can be removed, for example, by chemical mechanical planarization (CMP). In this case, the semiconductor material layer 10 can have a top surface that is coplanar with the top surface of the planarization dielectric layer 170.
The region (i.e., area) of the at least one semiconductor device 700 is herein referred to as a peripheral device region 200. The region in which a memory array is subsequently formed is herein referred to as a memory array region 100. A contact region 300 for subsequently forming stepped terraces of electrically conductive layers can be provided between the memory array region 100 and the peripheral device region 200. Optionally, a gate dielectric layer 12 can be formed above the semiconductor material layer 10 and the planarization dielectric layer 170. The gate dielectric layer 12 can be, for example, silicon oxide layer. The thickness of the gate dielectric layer 12 can be in a range from 3 nm to 30 nm, although lesser and greater thicknesses can also be employed.
Referring to FIG. 2, a stack of an alternating plurality of first material layers (which can be insulating layers 32) and second material layers (which can be sacrificial material layer 42) is formed over the top surface of the substrate, which can be, for example, on the top surface of the gate dielectric layer 12. As used herein, a “material layer” refers to a layer including a material throughout the entirety thereof. As used herein, an alternating plurality of first elements and second elements refers to a structure in which instances of the first elements and instances of the second elements alternate. Each instance of the first elements that is not an end element of the alternating plurality is adjoined by two instances of the second elements on both sides, and each instance of the second elements that is not an end element of the alternating plurality is adjoined by two instances of the first elements on both ends. The first elements may have the same thickness thereamongst, or may have different thicknesses. The second elements may have the same thickness thereamongst, or may have different thicknesses. The alternating plurality of first material layers and second material layers may begin with an instance of the first material layers or with an instance of the second material layers, and may end with an instance of the first material layers or with an instance of the second material layers. In one embodiment, an instance of the first elements and an instance of the second elements may form a unit that is repeated with periodicity within the alternating plurality.
Each first material layer includes a first material, and each second material layer includes a second material that is different from the first material. In one embodiment, each first material layer can be an insulating layer 32, and each second material layer can be a sacrificial material layer. In this case, the stack can include an alternating plurality of insulating layers 32 and sacrificial material layers 42, and constitutes a prototype stack of alternating layers comprising insulating layers 32 and sacrificial material layers 42. As used herein, a “prototype” structure or an “in-process” structure refers to a transient structure that is subsequently modified in the shape or composition of at least one component therein.
The stack of the alternating plurality is herein referred to as an alternating stack (32, 42). In one embodiment, the alternating stack (32, 42) can include insulating layers 32 composed of the first material, and sacrificial material layers 42 composed of a second material different from that of insulating layers 32. The first material of the insulating layers 32 can be at least one insulating material. As such, each insulating layer 32 can be an insulating material layer. Insulating materials that can be employed for the insulating layers 32 include, but are not limited to, silicon oxide (including doped or undoped silicate glass), silicon nitride, silicon oxynitride, organosilicate glass (OSG), spin-on dielectric materials, dielectric metal oxides that are commonly known as high dielectric constant (high-k) dielectric oxides (e.g., aluminum oxide, hafnium oxide, etc.) and silicates thereof, dielectric metal oxynitrides and silicates thereof, and organic insulating materials. In one embodiment, the first material of the insulating layers 32 can be silicon oxide.
The second material of the sacrificial material layers 42 is a sacrificial material that can be removed selective to the first material of the insulating layers 32. As used herein, a removal of a first material is “selective to” a second material if the removal process removes the first material at a rate that is at least twice the rate of removal of the second material. The ratio of the rate of removal of the first material to the rate of removal of the second material is herein referred to as a “selectivity” of the removal process for the first material with respect to the second material.
The sacrificial material layers 42 may comprise an insulating material, a semiconductor material, or a conductive material. The second material of the sacrificial material layers 42 can be subsequently replaced with electrically conductive electrodes which can function, for example, as control gate electrodes of a vertical NAND device. Non-limiting examples of the second material include silicon nitride, an amorphous semiconductor material (such as amorphous silicon), and a polycrystalline semiconductor material (such as polysilicon). In one embodiment, the sacrificial material layers 42 can be spacer material layers that comprise silicon nitride or a semiconductor material including at least one of silicon and germanium.
In one embodiment, the insulating layers 32 can include silicon oxide, and sacrificial material layers can include silicon nitride sacrificial material layers. The first material of the insulating layers 32 can be deposited, for example, by chemical vapor deposition (CVD). For example, if silicon oxide is employed for the insulating layers 32, tetraethyl orthosilicate (TEOS) can be employed as the precursor material for the CVD process. The second material of the sacrificial material layers 42 can be formed, for example, CVD or atomic layer deposition (ALD).
The sacrificial material layers 42 can be suitably patterned so that conductive material portions to be subsequently formed by replacement of the sacrificial material layers 42 can function as electrically conductive electrodes, such as the control gate electrodes of the monolithic three-dimensional NAND string memory devices to be subsequently formed. The sacrificial material layers 42 may comprise a portion having a strip shape extending substantially parallel to the major surface 7 of the substrate.
The thicknesses of the insulating layers 32 and the sacrificial material layers 42 can be in a range from 20 nm to 50 nm, although lesser and greater thicknesses can be employed for each insulating layer 32 and for each sacrificial material layer 42. The number of repetitions of the pairs of an insulating layer 32 and a sacrificial material layer (e.g., a control gate electrode or a sacrificial material layer) 42 can be in a range from 2 to 1,024, and typically from 8 to 256, although a greater number of repetitions can also be employed. The top and bottom gate electrodes in the stack may function as the select gate electrodes. In one embodiment, each sacrificial material layer 42 in the alternating stack (32, 42) can have a uniform thickness that is substantially invariant within each respective sacrificial material layer 42.
While the present disclosure is described employing an embodiment in which the spacer material layers are sacrificial material layers 42 that are subsequently replaced with electrically conductive layers, embodiments are expressly contemplated herein in which the sacrificial material layers are formed as electrically conductive layers. In this case, steps for replacing the spacer material layers with electrically conductive layers can be omitted.
Optionally, an insulating cap layer 70 can be formed over the alternating stack (32, 42). The insulating cap layer 70 includes a dielectric material that is different from the material of the sacrificial material layers 42. In one embodiment, the insulating cap layer 70 can include a dielectric material that can be employed for the insulating layers 32 as described above. The insulating cap layer 70 can have a greater thickness than each of the insulating layers 32. The insulating cap layer 70 can be deposited, for example, by chemical vapor deposition. In one embodiment, the insulating cap layer 70 can be a silicon oxide layer.
Referring to FIG. 3, a stepped cavity can be formed within the contact region 300 which is located between the memory array region 100 and the peripheral device region 200 containing the at least one semiconductor device for the peripheral circuitry. The stepped cavity can have various stepped surfaces such that the horizontal cross-sectional shape of the stepped cavity changes in steps as a function of the vertical distance from the top surface of the substrate (9, 10). In one embodiment, the stepped cavity can be formed by repetitively performing a set of processing steps. The set of processing steps can include, for example, an etch process of a first type that vertically increases the depth of a cavity by one or more levels, and an etch process of a second type that laterally expands the area to be vertically etched in a subsequent etch process of the first type. As used herein, a “level” of a structure including alternating plurality is defined as the relative position of a pair of a first material layer and a second material layer within the structure.
After formation of the stepped cavity, a peripheral portion of the alternating stack (32, 42) can have stepped surfaces after formation of the stepped cavity. As used herein, “stepped surfaces” refer to a set of surfaces that include at least two horizontal surfaces and at least two vertical surfaces such that each horizontal surface is adjoined to a first vertical surface that extends upward from a first edge of the horizontal surface, and is adjoined to a second vertical surface that extends downward from a second edge of the horizontal surface. A “stepped cavity” refers to a cavity having stepped surfaces.
A terrace region is formed by patterning the alternating stack (32, 42). Each sacrificial material layer 42 other than a topmost sacrificial material layer 42 within the alternating stack (32, 42) laterally extends farther than any overlying sacrificial material layer 42 within the alternating stack (32, 42). The terrace region includes stepped surfaces of the alternating stack (32, 42) that continuously extend from a bottommost layer within the alternating stack (32, 42) to a topmost layer within the alternating stack (32, 42). Each sacrificial material layer 42 other than the topmost sacrificial material layer 42 within the alternating stack (32, 42) laterally extends farther than any overlying sacrificial material layer 42 within the alternating stack (32, 42).
A retro-stepped dielectric material portion 65 (i.e., an insulating fill material portion) can be formed in the stepped cavity by deposition of a dielectric material therein. For example, a dielectric material such as silicon oxide can be deposited in the stepped cavity. Excess portions of the deposited dielectric material can be removed from above the top surface of the insulating cap layer 70, for example, by chemical mechanical planarization (CMP). The remaining portion of the deposited dielectric material filling the stepped cavity constitutes the retro-stepped dielectric material portion 65. As used herein, a “retro-stepped” element refers to an element that has stepped surfaces and a horizontal cross-sectional area that increases monotonically as a function of a vertical distance from a top surface of a substrate on which the element is present. If silicon oxide is employed for the retro-stepped dielectric material portion 65, the silicon oxide of the retro-stepped dielectric material portion 65 may, or may not, be doped with dopants such as B, P, and/or F.
Optionally, drain select level isolation structures 72 (shown in FIG. 12B) can be formed through the insulating cap layer 70 and a subset of the sacrificial material layers 42 located at drain select levels, either at this stage of the process or in a later stage of the process. The drain select level isolation structures 72 can be formed, for example, by forming drain select level isolation trenches and filling the drain select level isolation trenches with a dielectric material such as silicon oxide. Excess portions of the dielectric material can be removed from above the top surface of the insulating cap layer 70.
Referring to FIGS. 4A and 4B, a lithographic material stack (not shown) including at least a photoresist layer can be formed over the insulating cap layer 70 and the retro-stepped dielectric material portion 65, and can be lithographically patterned to form openings therein. The openings include a first set of openings formed over the memory array region 100 and a second set of openings formed over the contact region 300. The pattern in the lithographic material stack can be transferred through the insulating cap layer 70 or the retro-stepped dielectric material portion 65, and through the alternating stack (32, 42) by at least one anisotropic etch that employs the patterned lithographic material stack as an etch mask. Portions of the alternating stack (32, 42) underlying the openings in the patterned lithographic material stack are etched to form memory openings 49 and support openings 19. As used herein, a “memory opening” refers to a structure in which memory elements, such as a memory stack structure, is subsequently formed. As used herein, a “support opening” refers to a structure in which a support structure (such as a support pillar structure) that mechanically supports other elements is subsequently formed. The memory openings 49 are formed through the insulating cap layer 70 and the entirety of the alternating stack (32, 42) in the memory array region 100. The support openings 19 are formed through the retro-stepped dielectric material portion 65 and the portion of the alternating stack (32, 42) that underlie the stepped surfaces in the contact region 300.
The memory openings 49 extend through the entirety of the alternating stack (32, 42). The support openings 19 extend through a subset of layers within the alternating stack (32, 42). The chemistry of the anisotropic etch process employed to etch through the materials of the alternating stack (32, 42) can alternate to optimize etching of the first and second materials in the alternating stack (32, 42). The anisotropic etch can be, for example, a series of reactive ion etches. The sidewalls of the memory openings 49 and the support openings 19 can be substantially vertical, or can be tapered. The patterned lithographic material stack can be subsequently removed, for example, by ashing.
The memory openings 49 and the support openings 19 can be formed through the gate dielectric layer 12 so that the memory openings 49 and the support openings 19 extend from the top surface of the alternating stack (32, 42) to at least the horizontal plane including the topmost surface of the semiconductor material layer 10. In one embodiment, an overetch into the semiconductor material layer 10 may be optionally performed after the top surface of the semiconductor material layer 10 is physically exposed at a bottom of each memory opening 49 and each support opening 19. The overetch may be performed prior to, or after, removal of the lithographic material stack. In other words, the recessed surfaces of the semiconductor material layer 10 may be vertically offset from the undressed top surfaces of the semiconductor material layer 10 by a recess depth. The recess depth can be, for example, in a range from 1 nm to 50 nm, although lesser and greater recess depths can also be employed. The overetch is optional, and may be omitted. If the overetch is not performed, the bottom surfaces of the memory openings 49 and the support openings 19 can be coplanar with the topmost surface of the semiconductor material layer 10.
Each of the memory openings 49 and the support openings 19 may include a sidewall (or a plurality of sidewalls) that extends substantially perpendicular to the topmost surface of the substrate. A two-dimensional array of memory openings 49 can be formed in the memory array region 100. A two-dimensional array of support openings 19 can be formed in the contact region 300. The substrate semiconductor layer 9 and the semiconductor material layer 10 collectively constitutes a substrate (9, 10), which can be a semiconductor substrate. Alternatively, the semiconductor material layer 10 may be omitted, and the memory openings 49 and the support openings 19 can be extend to a top surface of the substrate semiconductor layer 9.
FIGS. 5A-5H illustrate structural changes in a memory opening 49, which is one of the memory openings 49 in the first exemplary structure of FIGS. 4A and 4B. The same structural change occurs simultaneously in each of the other memory openings 49 and in each support opening 19.
Referring to FIG. 5A, a memory opening 49 in the first exemplary structure of FIGS. 4A and 4B is illustrated. The memory opening 49 extends through the insulating cap layer 70, the alternating stack (32, 42), the gate dielectric layer 12, and optionally into an upper portion of the semiconductor material layer 10. At this processing step, each support opening 19 can extend through the retro-stepped dielectric material portion 65, a subset of layers in the alternating stack (32, 42), the gate dielectric layer 12, and optionally through the upper portion of the semiconductor material layer 10. The recess depth of the bottom surface of each memory opening with respect to the top surface of the semiconductor material layer 10 can be in a range from 0 nm to 30 nm, although greater recess depths can also be employed. Optionally, the sacrificial material layers 42 can be laterally recessed partially to form lateral recesses (not shown), for example, by an isotropic etch.
Referring to FIG. 5B, an optional epitaxial channel portion (e.g., an epitaxial channel portion) 11 can be formed at the bottom portion of each memory opening 49 and each support openings 19, for example, by selective epitaxy. Each epitaxial channel portion 11 comprises a single crystalline semiconductor material in epitaxial alignment with the single crystalline semiconductor material of the semiconductor material layer 10. In one embodiment, the epitaxial channel portion 11 can be doped with electrical dopants of the same conductivity type as the semiconductor material layer 10. In one embodiment, the top surface of each epitaxial channel portion 11 can be formed above a horizontal plane including the top surface of a sacrificial material layer 42. In this case, at least one source select gate electrode can be subsequently formed by replacing each sacrificial material layer 42 located below the horizontal plane including the top surfaces of the epitaxial channel portions 11 with a respective conductive material layer. The epitaxial channel portion 11 can be a portion of a transistor channel that extends between a source region to be subsequently formed in the substrate (9, 10) and a drain region to be subsequently formed in an upper portion of the memory opening 49. A cavity 49′ is present in the unfilled portion of the memory opening 49 above the epitaxial channel portion 11. In one embodiment, the epitaxial channel portion 11 can comprise single crystalline silicon. In one embodiment, the epitaxial channel portion 11 can have a doping of the first conductivity type, which is the same as the conductivity type of the semiconductor material layer 10 that the epitaxial channel portion contacts. If a semiconductor material layer 10 is not present, the epitaxial channel portion 11 can be formed directly on the substrate semiconductor layer 9, which can have a doping of the first conductivity type.
Referring to FIG. 5C, a material layer stack including a continuous dielectric liner layer 53, an aluminum oxide tunneling dielectric layer 57, a silicon-containing tunneling dielectric layer 56, and an optional first semiconductor channel layer 601 can be sequentially deposited in the memory openings 49.
The continuous dielectric liner layer 53 includes a dielectric material that is different from the material of the sacrificial material layers 42 and the aluminum oxide tunneling dielectric layer 57. In one embodiment, the continuous dielectric liner layer 53 can include a dielectric semiconductor compound such as silicon oxide or silicon oxynitride. In this case, the continuous dielectric liner layer 53 can be formed by a conformal deposition method such as low pressure chemical vapor deposition, atomic layer deposition, or a combination thereof. The thickness of the continuous dielectric liner layer 53 can be in a range from 1 nm to 20 nm (such as from 2 nm to 6 nm), although lesser and greater thicknesses can also be employed. Alternatively, the continuous dielectric liner layer 53 can be omitted.
Subsequently, the aluminum oxide tunneling dielectric layer 57 can be formed. In one embodiment, the aluminum oxide tunneling dielectric layer 57 can be formed by a conformal deposition process such as atomic layer deposition (ALD). The aluminum oxide tunneling dielectric layer 57 can be deposited as an amorphous material layer, and can be transformed into a polycrystalline material layer in a subsequent annealing step. The thickness of the aluminum oxide tunneling dielectric layer 57 can be in a range from 1 nm to 4 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the sacrificial material layers 42 and the insulating layers 32 can have vertically coincident sidewalls, and the aluminum oxide tunneling dielectric layer 57 can be formed as a single continuous layer.
The silicon-containing tunneling dielectric layer 56 includes a silicon-containing dielectric material. Charge tunneling can be performed through the dielectric material of the silicon-containing tunneling dielectric layer 56 under suitable electrical bias conditions. The charge tunneling may be performed through hot-carrier injection or by Fowler-Nordheim tunneling induced charge transfer depending on the mode of operation of the monolithic three-dimensional NAND string memory device to be formed. The silicon-containing tunneling dielectric layer 56 can include silicon oxide, silicon nitride, silicon oxynitride, and/or combinations thereof. In one embodiment, the silicon-containing tunneling dielectric layer 56 can include a stack of a first silicon oxide layer, a silicon oxynitride layer, and a second silicon oxide layer, which is commonly known as an ONO stack. In one embodiment, the silicon-containing tunneling dielectric layer 56 can include a silicon oxide layer that is substantially free of carbon or a silicon oxynitride layer that is substantially free of carbon. The thickness of the silicon-containing tunneling dielectric layer 56 can be in a range from 2 nm to 20 nm (such as from 3 nm to 10 nm), although lesser and greater thicknesses can also be employed.
The optional first semiconductor channel layer 601 includes a semiconductor material such as at least one elemental semiconductor material, at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. In one embodiment, the first semiconductor channel layer 601 includes amorphous silicon or polysilicon. The first semiconductor channel layer 601 can be formed by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD). The thickness of the first semiconductor channel layer 601 can be in a range from 2 nm to 10 nm, although lesser and greater thicknesses can also be employed. A cavity 49′ is formed in the volume of each memory opening 49 that is not filled with the deposited material layers (53, 57, 56, 601).
Referring to FIG. 5D, the optional first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, the continuous dielectric liner layer 53 are sequentially anisotropically etched employing at least one anisotropic etch process. The portions of the first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, and the continuous dielectric liner layer 53 located above the top surface of the insulating cap layer 70 can be removed by the at least one anisotropic etch process. Further, the horizontal portions of the first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, and the continuous dielectric liner layer 53 at a bottom of each cavity 49′ can be removed to form openings in remaining portions thereof Each of the first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, and the continuous dielectric liner layer 53 can be etched by a respective anisotropic etch process employing a respective etch chemistry, which may, or may not, be the same for the various material layers. Each remaining portion of the first semiconductor channel layer 601 can have a tubular configuration.
A surface of the epitaxial channel portion 11 (or a surface of the semiconductor substrate layer 10 in case the epitaxial channel portions 11 are not employed) can be physically exposed underneath the opening through the first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, and the continuous dielectric liner layer 53. Optionally, the physically exposed semiconductor surface at the bottom of each cavity 49′ can be vertically recessed so that the recessed semiconductor surface underneath the cavity 49′ is vertically offset from the topmost surface of the epitaxial channel portion 11 (or of the semiconductor substrate layer 10 in case epitaxial channel portions 11 are not employed) by a recess distance. A silicon-containing tunneling dielectric layer 56 is located over the aluminum oxide tunneling dielectric layer 57. A set of a continuous dielectric liner layer 53, an aluminum oxide tunneling dielectric layer 57, and a silicon-containing tunneling dielectric layer 56 in a memory opening 49 constitutes a dielectric material layer stack 250. In one embodiment, the first semiconductor channel layer 601, the silicon-containing tunneling dielectric layer 56, the aluminum oxide tunneling dielectric layer 57, and the continuous dielectric liner layer 53 can have vertically coincident sidewalls.
Referring to FIG. 5E, a second semiconductor channel layer 602 can be deposited directly on the semiconductor surface of the epitaxial channel portion 11 or the semiconductor substrate layer 10 if portion 11 is omitted, and directly on the first semiconductor channel layer 601. The second semiconductor channel layer 602 includes a semiconductor material such as at least one elemental semiconductor material, at least one III-V compound semiconductor material, at least one II-VI compound semiconductor material, at least one organic semiconductor material, or other semiconductor materials known in the art. In one embodiment, the second semiconductor channel layer 602 includes amorphous silicon or polysilicon. The second semiconductor channel layer 602 can be formed by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD). The thickness of the second semiconductor channel layer 602 can be in a range from 2 nm to 10 nm, although lesser and greater thicknesses can also be employed. The second semiconductor channel layer 602 may partially fill the cavity 49′ in each memory opening, or may fully fill the cavity in each memory opening.
The materials of the first semiconductor channel layer 601 and the second semiconductor channel layer 602 are collectively referred to as a semiconductor channel material. In other words, the semiconductor channel material is a set of all semiconductor material in the first semiconductor channel layer 601 and the second semiconductor channel layer 602.
Referring to FIG. 5F, in case the cavity 49′ in each memory opening is not completely filled by the second semiconductor channel layer 602, a dielectric core layer 62L can be deposited in the cavity 49′ to fill any remaining portion of the cavity 49′ within each memory opening. The dielectric core layer 62L includes a dielectric material such as silicon oxide or organosilicate glass. The dielectric core layer 62L can be deposited by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD), or by a self-planarizing deposition process such as spin coating.
Referring to FIG. 5G, the horizontal portion of the dielectric core layer 62L can be removed, for example, by a recess etch from above the top surface of the insulating cap layer 70. Each remaining portion of the dielectric core layer 62L constitutes a dielectric core 62. Further, the horizontal portion of the second semiconductor channel layer 602 located above the top surface of the insulating cap layer 70 can be removed by a planarization process, which can employ a recess etch or chemical mechanical planarization (CMP). Each remaining portion of the second semiconductor channel layer 602 can be located entirety within a memory opening 49 or entirely within a support opening 19.
Each adjoining pair of a first semiconductor channel layer 601 and a second semiconductor channel layer 602 can collectively form a vertical semiconductor channel 60 through which electrical current can flow when a vertical NAND device including the vertical semiconductor channel 60 is turned on. A silicon-containing tunneling dielectric layer 56 is surrounded by an aluminum oxide tunneling dielectric layer 57, and laterally surrounds a portion of the vertical semiconductor channel 60. Each adjoining set of a continuous dielectric liner layer 53, an aluminum oxide tunneling dielectric layer 57, and a silicon-containing tunneling dielectric layer 56 collectively constitute a dielectric material layer stack 250, which can store electrical charges with a macroscopic retention time. In some embodiments, a continuous dielectric liner layer 53 may not be present in the dielectric material layer stack 250 at this step. As used herein, a macroscopic retention time refers to a retention time suitable for operation of a memory device as a permanent memory device such as a retention time in excess of 24 hours.
Referring to FIG. 5H, the top surface of each dielectric core 62 can be further recessed within each memory opening, for example, by a recess etch to a depth that is located between the top surface of the insulating cap layer 70 and the bottom surface of the insulating cap layer 70. Drain regions 63 can be formed by depositing a doped semiconductor material within each recessed region above the dielectric cores 62. The drain regions 63 can have a doping of a second conductivity type that is the opposite of the first conductivity type. For example, if the first conductivity type is p-type, the second conductivity type is n-type, and vice versa. The dopant concentration in the drain regions 63 can be in a range from 5.0×10¹⁹/cm³to 2.0×10²¹/cm³, although lesser and greater dopant concentrations can also be employed. The doped semiconductor material can be, for example, doped polysilicon. Excess portions of the deposited semiconductor material can be removed from above the top surface of the insulating cap layer 70, for example, by chemical mechanical planarization (CMP) or a recess etch to form the drain regions 63.
Each combination of an epitaxial channel portion 11 (if present), a dielectric material layer stack 250, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within a memory opening 49 is herein referred to as a memory opening fill structure (11, 250, 60, 62, 63). Each combination of an epitaxial channel portion 11 (if present), a dielectric material layer stack 250, a vertical semiconductor channel 60, a vertical semiconductor channel 60, a dielectric core 62, and a drain region 63 within each support opening 19 fills the respective support openings 19, and constitutes a support pillar structure 20 (shown in FIG. 6). The drain region 63 in the support pillar structure is a dummy drain region because it is not electrically connected to a bit line. Thus, the vertical semiconductor channel 60 and the dielectric material layer stack 250 in the support pillar structure 20 are structural support elements which are not electrically active.
Referring to FIG. 6, the first exemplary structure is illustrated after formation of memory opening fill structures (11, 250, 60, 62, 63) and support pillar structures 20 within the memory openings 49 and the support openings 19, respectively. An instance of a memory opening fill structure (11, 250, 60, 62, 63) can be formed within each memory opening 49 of the structure of FIGS. 4A and 4B. An instance of the support pillar structure 20 can be formed within each support opening 19 of the structure of FIGS. 4A and 4B.
Referring to FIGS. 7A and 7B, a contact level dielectric layer 73 can be formed over the alternating stack (32, 42) of insulating layer 32 and sacrificial material layers 42, and over the memory opening fill structures (11, 250, 60, 62, 63) and the support pillar structures 20. The contact level dielectric layer 73 includes a dielectric material that is different from the dielectric material of the sacrificial material layers 42. For example, the contact level dielectric layer 73 can include silicon oxide. The contact level dielectric layer 73 can have a thickness in a range from 50 nm to 500 nm, although lesser and greater thicknesses can also be employed.
A photoresist layer (not shown) can be applied over the contact level dielectric layer 73, and is lithographically patterned to form openings in areas between clusters of memory opening fill structures (11, 250, 60, 62, 63). The pattern in the photoresist layer can be transferred through the contact level dielectric layer 73, the alternating stack (32, 42) and/or the retro-stepped dielectric material portion 65 employing an anisotropic etch to form backside trenches 79, which vertically extend from the top surface of the contact level dielectric layer 73 at least to the top surface of the substrate (9, 10), and laterally extend through the memory array region 100 and the contact region 300. In one embodiment, the backside trenches 79 can include a source contact opening in which a source contact via structure can be subsequently formed. The photoresist layer can be removed, for example, by ashing.
Referring to FIG. 8A, an etchant that selectively etches the second material of the sacrificial material layers 42 with respect to the first material of the insulating layers 32 can be introduced into the backside trenches 79, for example, employing an etch process. Backside recesses 43 are formed in volumes from which the sacrificial material layers 42 are removed. The removal of the second material of the sacrificial material layers 42 can be selective to the first material of the insulating layers 32, the material of the retro-stepped dielectric material portion 65, the semiconductor material of the semiconductor material layer 10, and the material of the continuous dielectric liner layer 53. In one embodiment, the sacrificial material layers 42 can include silicon nitride, and the materials of the insulating layers 32, the support pillar structure 20, the retro-stepped dielectric material portion 65, and the continuous dielectric liner layer 53 can be selected from silicon oxide and dielectric metal oxides.
The etch process that removes the second material selective to the first material and the continuous dielectric liner layer 53 can be a wet etch process employing a wet etch solution, or can be a gas phase (dry) etch process in which the etchant is introduced in a vapor phase into the backside trenches 79. For example, if the sacrificial material layers 42 include silicon nitride, the etch process can be a wet etch process in which the first exemplary structure is immersed within a wet etch tank including phosphoric acid, which etches silicon nitride selective to silicon oxide, silicon, and various other materials employed in the art. The support pillar structure 20, the retro-stepped dielectric material portion 65, and the memory opening fill structures (11, 250, 60, 62, 63) provide structural support while the backside recesses 43 are present within volumes previously occupied by the sacrificial material layers 42.
Each backside recess 43 can be a laterally extending cavity having a lateral dimension that is greater than the vertical extent of the cavity. In other words, the lateral dimension of each backside recess 43 can be greater than the height of the backside recess 43. A plurality of backside recesses 43 can be formed in the volumes from which the second material of the sacrificial material layers 42 is removed. The memory openings in which the memory opening fill structures (11, 250, 60, 62, 63) are formed are herein referred to as front side openings or front side cavities in contrast with the backside recesses 43. In one embodiment, the memory array region 100 comprises an array of monolithic three-dimensional NAND strings having a plurality of device levels disposed above the substrate (9, 10). In this case, each backside recess 43 can define a space for receiving a respective word line of the array of monolithic three-dimensional NAND strings.
Each of the plurality of backside recesses 43 can extend substantially parallel to the top surface of the substrate (9, 10). A backside recess 43 can be vertically bounded by a top surface of an underlying insulating layer 32 and a bottom surface of an overlying insulating layer 32. In one embodiment, each backside recess 43 can have a uniform height throughout.
Referring to FIG. 8B, physically exposed portions of the continuous dielectric liner layer 53 can be subsequently etched, for example, employing an isotropic etch process that etches the dielectric material of the continuous dielectric liner layer 53 selective to the material of the aluminum oxide tunneling dielectric layer 57. If the continuous dielectric liner layer 53 includes silicon oxide, a wet etch employing hydrofluoric acid can be employed to etch the material of the continuous dielectric liner layer 53 selective to the aluminum oxide tunneling dielectric layer 57. The discrete remaining portions of the continuous dielectric liner layer 53 after the etch process include dielectric liner portions 53′, which are located at each level of the insulating layers 32 that are located at, or above the horizontal plane including the bottom surface of the aluminum oxide tunneling dielectric layer 57. Additional dielectric liner portions 53′ are formed at the level of the insulating cap layer 70.
Portions of the outer sidewalls of the aluminum oxide tunneling dielectric layer 57 are physically exposed to the backside recesses 43 around each dielectric material layer stack 250, which now includes a silicon-containing tunneling dielectric layer 56, an aluminum oxide tunneling dielectric layer 57, and a set of dielectric liner portions 53′ located at each level of the insulating layers 32 and at the level of the insulating cap layer 70.
Referring to FIG. 8C, physically exposed surface portions of the optional epitaxial channel portions 11 and the semiconductor material layer 10 can be optionally converted into dielectric material portions by thermal conversion and/or plasma conversion of the semiconductor materials into dielectric materials. For example, thermal conversion and/or plasma conversion can be employed to convert a surface portion of each epitaxial channel portion 11 into a tubular dielectric spacer 116, and to convert each physically exposed surface portion of the semiconductor material layer 10 into a planar dielectric portion 616. In one embodiment, each tubular dielectric spacer 116 can be topologically homeomorphic to a torus, i.e., generally ring-shaped. As used herein, an element is topologically homeomorphic to a torus if the shape of the element can be continuously stretched without destroying a hole or forming a new hole into the shape of a torus.
The tubular dielectric spacers 116 include a dielectric material that includes the same semiconductor element as the epitaxial channel portions 11 and additionally includes at least one non-metallic element such as oxygen and/or nitrogen such that the material of the tubular dielectric spacers 116 is a dielectric material. In one embodiment, the tubular dielectric spacers 116 can include a dielectric oxide, a dielectric nitride, or a dielectric oxynitride of the semiconductor material of the epitaxial channel portions 11. A planar dielectric portion 616 is formed at the bottom of the backside trenches 79 on the exposed surface of the substrate (9, 10), as shown in FIG. 9, at the same time as the dielectric spacers 116. Each planar dielectric portion 616 includes a dielectric material that includes the same semiconductor element as the semiconductor material layer and additionally includes at least one non-metallic element such as oxygen and/or nitrogen such that the material of the planar dielectric portions 616 is a dielectric material. In one embodiment, the planar dielectric portions 616 can include a dielectric oxide, a dielectric nitride, or a dielectric oxynitride of the semiconductor material of the semiconductor material layer 10. In one embodiment, the tubular dielectric spacers 116 and the planar dielectric portions 616 can include silicon oxide. Formation of the tubular dielectric spacers 116 and the planar dielectric portion 616 is optional.
Referring to FIG. 8D, charge trapping material portions 54 can be formed on physically exposed surfaces of the aluminum oxide tunneling dielectric layer 57 by performing a selective silicon nitride deposition process through the backside trench 79 and the backside recesses 43. In a selective silicon nitride deposition process, silicon nitride grows from the physically exposed surfaces of the aluminum oxide tunneling dielectric layer 57 while not substantially growing from surfaces of the insulating layers 32, the insulating cap layer 70, the contact level dielectric layer 73, or the tubular dielectric spacers 116.
The selective silicon nitride deposition process can include atomic layer deposition (ALD), including plasma enhanced ALD, in which a silicon-containing reactant (such as silicon tetrachloride, dichlorosilane or organosilicon compound) reacts with a nitrogen-containing reactant (such as ammonia or nitrogen plasma) to deposit silicon nitride.
The discrete charge trapping material portions 54 start to grow on the aluminum oxide tunneling dielectric layer 57 exposed in the backside recesses before they grow on the surfaces of the insulating layers 32, the insulating cap layer 70, the contact level dielectric layer 73, or the tubular dielectric spacers 116 (i.e., before they grow on the exposed silicon oxide material). The discrete charge trapping material portions 54 on the aluminum oxide tunneling dielectric layer 57 continue to thicken with each subsequent ALD cycle. In contrast, silicon nitride does not begin to grow on the exposed silicon oxide material until after an incubation period. Thus, the selective growth of the discrete charge trapping material portions 54 on the aluminum oxide tunneling dielectric layer 57 can be terminated before the expiration of the incubation period such that substantially no silicon nitride (i.e., no silicon nitride or trace amounts of silicon nitride) is deposited on the surfaces of the insulating layers 32, the insulating cap layer 70, the contact level dielectric layer 73, or the tubular dielectric spacers 116.
In other words, the selective silicon nitride deposition process can be selective until silicon nitride nucleates on the insulating layers 32. In this case, the silicon nitride deposition process can be terminated before the silicon nitride deposition process becomes non-selective (i.e., deposits silicon nitride material on all surfaces), and the entire deposition process can be a selective silicon nitride deposition process.
In one embodiment, the duration of the selective silicon nitride deposition process can be less than the incubation delay for nucleation of silicon nitride on silicon oxide. In this case, the deposited silicon nitride material can form the discrete charge trapping material portions 54, which are discrete silicon nitride portions having a tubular configuration, i.e., having an annular geometry in which the inner sidewall and the outer sidewall are vertical and spaced from each other by a uniform thickness of the charge trapping material portions 54. In this case, the thickness of the charge trapping material portions 54 can be in a range from 1 nm to 5 nm, such as from 1.5 nm to 4 nm, although lesser and greater thicknesses can also be employed.
Each of the charge trapping material portions 54 laterally surrounds the aluminum oxide tunneling dielectric layer 57. The charge trapping material portions 54 may be formed entirely within the volumes of the memory openings 49 and the support openings 19 (as formed at the processing steps of FIGS. 4A and 4B), or may be formed partially inside the volumes of the memory openings 49 and the support openings 19 and partially outside the volumes of the memory openings 49 and the support openings 19. Thus, at least an inner portion of each of the charge trapping material portions 54 around an aluminum oxide tunneling dielectric layer 57 can be formed within a volume of a memory opening 49 or inside a volume of a support opening 19. A set of the discrete dielectric liner portions 53′ and the charge trapping material portions 54 contacts an entirety of the outer sidewall of the aluminum oxide tunneling dielectric layer 57 within each memory opening 49 or within each support opening 19.
Each silicon nitride material portion on the aluminum oxide tunneling dielectric layers 57 constitutes a charge storage material portion 54. Each contiguous combination of a silicon-containing tunneling dielectric layer 56, an aluminum oxide tunneling dielectric layer 57, dielectric liner portions 53′ located directly on the aluminum oxide tunneling dielectric layer 57, and the charge storage material portions 54 located directly on the aluminum oxide tunneling dielectric layer 57 constitutes a memory film 50. Each combination of a memory film 50 and a vertical semiconductor channel 60 in a memory opening 49 constitutes a memory stack structure 55.
Referring to FIG. 8E, a backside blocking dielectric layer 44 can be optionally formed. The backside blocking dielectric layer 44 includes at least one dielectric material that functions as a control gate dielectric for the control gates to be subsequently formed in the backside recesses 43. The backside blocking dielectric layer 44 can be formed in the backside recesses 43 and on a sidewall of the backside trench 79.
In one embodiment, the backside blocking dielectric layer 44 can include a layer stack of a backside silicon oxide layer 442 and a backside dielectric metal oxide layer 444. The backside silicon oxide layer 442 includes silicon oxide, and can be formed directly on horizontal surfaces of the insulating layers 32 and physically exposed portions of the outer sidewalls of the charge storage material portions 54. The backside silicon oxide layer 442 can be formed by a conformal deposition process such as atomic layer deposition (ALD) or chemical vapor deposition. The thickness of the backside silicon oxide layer 442 can be in a range from 1 nm to 8 nm, such as 2 to 6 nm, although lesser and greater thicknesses can also be employed. The backside silicon oxide layer 442 can be omitted in some embodiments.
The dielectric material of the backside dielectric metal oxide layer 444 can be a dielectric metal oxide such as aluminum oxide, a dielectric oxide of at least one transition metal element, a dielectric oxide of at least one Lanthanide element, a dielectric oxide of a combination of aluminum, at least one transition metal element, and/or at least one Lanthanide element. The backside dielectric metal oxide layer 444 can be deposited by a conformal deposition method such as atomic layer deposition. The thickness of backside dielectric metal oxide layer 444 can be in a range from 1 nm to 10 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the backside dielectric metal oxide layer 444 can consist essentially of aluminum oxide.
The backside blocking dielectric layer 44 is formed on the sidewalls of the backside trenches 79, horizontal surfaces and sidewalls of the insulating layers 32, outer sidewalls of the charge trapping material portions 54, physically exposed surfaces of the insulating cap layer 70 and the contact level dielectric layer 73, and surfaces of the planar dielectric portions 616 (if present) and tubular dielectric spacers 116 (if present). A backside cavity 79′ is present within the portion of each backside trench 79 that is not filled with the backside blocking dielectric layer 44.
Referring to FIGS. 8F and 9, a metallic barrier layer 46A can be deposited on the backside blocking dielectric layer 44. The metallic barrier layer 46A includes an electrically conductive metallic material that can function as a diffusion barrier layer and/or adhesion promotion layer for a metallic fill material to be subsequently deposited. The metallic barrier layer 46A can include a conductive metallic nitride material such as TiN, TaN, WN, or a stack thereof, or can include a conductive metallic carbide material such as TiC, TaC, WC, or a stack thereof. In one embodiment, the metallic barrier layer 46A can be deposited by a conformal deposition process such as chemical vapor deposition (CVD) or atomic layer deposition (ALD). The thickness of the metallic barrier layer 46A can be in a range from 2 nm to 8 nm, such as from 3 nm to 6 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the metallic barrier layer 46A can consist essentially of a conductive metal nitride such as TiN.
A metal fill material is deposited in the plurality of backside recesses 43, on the sidewalls of the at least one the backside trench 79, and over the top surface of the contact level dielectric layer 73 to form a metallic fill material layer 46B. The metallic fill material can be deposited by a conformal deposition method, which can be, for example, chemical vapor deposition (CVD), atomic layer deposition (ALD), electroless plating, electroplating, or a combination thereof. In one embodiment, the metallic fill material layer 46B can consist essentially of at least one elemental metal. The at least one elemental metal of the metallic fill material layer 46B can be selected, for example, from tungsten, cobalt, ruthenium, titanium, and tantalum. In one embodiment, the metallic fill material layer 46B can consist essentially of a single elemental metal. In one embodiment, the metallic fill material layer 46B can be deposited employing a fluorine-containing precursor gas such as WF₆. In one embodiment, the metallic fill material layer 46B can be a tungsten layer including a residual level of fluorine atoms as impurities. The metallic fill material layer 46B is spaced from the insulating layers 32 and the memory stack structures 55 by the metallic barrier layer 46A, which is a metallic barrier layer that blocks diffusion of fluorine atoms therethrough.
A plurality of electrically conductive layers 46 can be formed in the plurality of backside recesses 43, and a continuous metallic material layer 46L can be formed on the sidewalls of each backside trench 79 and over the contact level dielectric layer 73. Each electrically conductive layer 46 includes a portion of the metallic barrier layer 46A and a portion of the metallic fill material layer 46B that are located between a vertically neighboring pair of dielectric material layers, which can be a pair of insulating layers 32, a bottommost insulating layer and a gate dielectric layer 12, or a topmost insulating layer and the insulating cap layer 70. The continuous metallic material layer 46L includes a continuous portion of the metallic barrier layer 46A and a continuous portion of the metallic fill material layer 46B that are located in the backside trenches 79 or above the contact level dielectric layer 73.
Each sacrificial material layer 42 can be replaced with an electrically conductive layer 46. A backside cavity 79′ is present in the portion of each backside trench 79 that is not filled with the backside blocking dielectric layer 44 and the continuous metallic material layer 46L. A tubular dielectric spacer 116 laterally surrounds an epitaxial channel portion 11. A bottommost electrically conductive layer 46 laterally surrounds each tubular dielectric spacer 116 upon formation of the electrically conductive layers 46.
Referring to FIG. 10, the deposited metallic material of the continuous electrically conductive material layer 46L is etched back from the sidewalls of each backside trench 79 and from above the contact level dielectric layer 73, for example, by an isotropic wet etch, an anisotropic dry etch, or a combination thereof. Each remaining portion of the deposited metallic material in the backside recesses 43 constitutes an electrically conductive layer 46. Each electrically conductive layer 46 can be a conductive line structure. Thus, the sacrificial material layers 42 are replaced with the electrically conductive layers 46.
Each electrically conductive layer 46 can function as a combination of a plurality of control gate electrodes located at a same level and a word line electrically interconnecting, i.e., electrically shorting, the plurality of control gate electrodes located at the same level. The plurality of control gate electrodes within each electrically conductive layer 46 are the control gate electrodes for the vertical memory devices including the memory stack structures 55. In other words, each electrically conductive layer 46 can be a word line that functions as a common control gate electrode for the plurality of vertical memory devices.
In one embodiment, the removal of the continuous electrically conductive material layer 46L can be selective to the material of the backside blocking dielectric layer 44. In this case, a horizontal portion of the backside blocking dielectric layer 44 can be present at the bottom of each backside trench 79. The gate dielectric layer 12 can be vertically spaced from the backside trench 79 by the horizontal portion of the backside blocking dielectric layer 44.
In another embodiment, the removal of the continuous electrically conductive material layer 46L may not be selective to the material of the backside blocking dielectric layer 44, or the backside blocking dielectric layer 44 may not be employed. In this case, a top surface and/or sidewall surface, of the gate dielectric layer 12 can be physically exposed at the bottom of the backside trench 79 depending on whether the gate dielectric layer 12 is not removed or partially removed during removal of the continuous electrically conductive material layer 46L. In one embodiment, a top surface of the cap gate dielectric layer 126 can be physically exposed at the bottom of the backside trench 79 after removal of the continuous electrically conductive material layer 46L. A backside cavity 79′ is present within each backside trench 79.
Referring to FIG. 11, an insulating material layer can be formed in the at least one backside trench 79 and over the contact level dielectric layer 73 by a conformal deposition process. Exemplary conformal deposition processes include, but are not limited to, chemical vapor deposition and atomic layer deposition. The insulating material layer includes an insulating material such as silicon oxide, silicon nitride, a dielectric metal oxide, an organosilicate glass, or a combination thereof. In one embodiment, the insulating material layer can include silicon oxide. The insulating material layer can be formed, for example, by low pressure chemical vapor deposition (LPCVD) or atomic layer deposition (ALD). The thickness of the insulating material layer can be in a range from 1.5 nm to 60 nm, although lesser and greater thicknesses can also be employed. The insulating material layer can be formed directly on surfaces of the backside blocking dielectric layer 44 and directly on the sidewalls of the electrically conductive layers 46.
An anisotropic etch is performed to remove horizontal portions of the insulating material layer from above the contact level dielectric layer 73 and at the bottom of each backside trench 79. Each remaining portion of the insulating material layer constitutes an insulating spacer 74. A backside cavity 79′ is present within a volume surrounded by each insulating spacer 74.
The anisotropic etch process can continue with, or without, a change in the etch chemistry to remove portions of the optional backside blocking dielectric layer 44 and the planar dielectric portion 616 that underlies the opening through the insulating spacer 74. An opening is formed though the planar dielectric portion 616 underneath each backside cavity 79′, thereby vertically extending the backside cavity 79′. A top surface of the semiconductor material layer 10 can be physically exposed at the bottom of each backside trench 79. The remaining portion of each planar dielectric portion 616 is herein referred to as an annular dielectric portion 616′, which can include a dielectric oxide of the semiconductor material of the semiconductor material layer 10, have a uniform thickness, and an opening therethrough.
A source region 61 can be formed at a surface portion of the semiconductor material layer 10 under each backside cavity 79′ by implantation of electrical dopants into physically exposed surface portions of the semiconductor material layer 10. Each source region 61 is formed in a surface portion of the substrate (9, 10) that underlies a respective opening through the insulating spacer 74. Due to the straggle of the implanted dopant atoms during the implantation process and lateral diffusion of the implanted dopant atoms during a subsequent activation anneal process, each source region 61 can have a lateral extent greater than the lateral extent of the opening through the insulating spacer 74.
An upper portion of the semiconductor material layer 10 that extends between the source region 61 and the plurality of epitaxial channel portions 11 constitutes a horizontal semiconductor channel 59 for a plurality of field effect transistors. The horizontal semiconductor channel 59 is connected to multiple vertical semiconductor channels 60 through respective epitaxial channel portions 11. The horizontal semiconductor channel 59 contacts the source region 61 and the plurality of epitaxial channel portions 11. A bottommost electrically conductive layer 46 provided upon formation of the electrically conductive layers 46 within the alternating stack (32, 46) can comprise a select gate electrode for the field effect transistors. Each source region 61 is formed in an upper portion of the semiconductor substrate (9, 10). Semiconductor channels (59, 11, 60) extend between each source region 61 and a respective set of drain regions 63. The semiconductor channels (59, 11, 60) include the vertical semiconductor channels 60 of the memory stack structures 55.
A contact via structure 76 can be formed within each backside cavity 79′. Each contact via structure 76 can fill a respective cavity 79′. The contact via structures 76 can be formed by depositing at least one conductive material in the remaining unfilled volume (i.e., the backside cavity 79′) of the backside trench 79. For example, the at least one conductive material can include a conductive liner 76A and a conductive fill material portion 76B. The conductive liner 76A can include a conductive metallic liner such as TiN, TaN, WN, TiC, TaC, WC, an alloy thereof, or a stack thereof. The thickness of the conductive liner 76A can be in a range from 3 nm to 30 nm, although lesser and greater thicknesses can also be employed. The conductive fill material portion 76B can include a metal or a metallic alloy. For example, the conductive fill material portion 76B can include W, Cu, Al, Co, Ru, Ni, an alloy thereof, or a stack thereof.
The at least one conductive material can be planarized employing the contact level dielectric layer 73 overlying the alternating stack (32, 46) as a stopping layer. If chemical mechanical planarization (CMP) process is employed, the contact level dielectric layer 73 can be employed as a CMP stopping layer. Each remaining continuous portion of the at least one conductive material in the backside trenches 79 constitutes a backside contact via structure 76.
The backside contact via structure 76 extends through the alternating stack (32, 46), and contacts a top surface of the source region 61. If a backside blocking dielectric layer 44 is employed, the backside contact via structure 76 can contact a sidewall of the backside blocking dielectric layer 44.
Referring to FIGS. 12A and 12B, additional contact via structures (88, 86, 8P) can be formed through the contact level dielectric layer 73, and optionally through the retro-stepped dielectric material portion 65. For example, drain contact via structures 88 can be formed through the contact level dielectric layer 73 on each drain region 63. Word line contact via structures 86 can be formed on the electrically conductive layers 46 through the contact level dielectric layer 73, and through the retro-stepped dielectric material portion 65. Peripheral device contact via structures 8P can be formed through the retro-stepped dielectric material portion 65 directly on respective nodes of the peripheral devices.
FIGS. 13A-13D illustrate an alternative sequence of processing steps that can be employed to form a second exemplary structure, which is modified from the first exemplary structure or an alternative embodiment thereof by performing the processing steps of FIGS. 13B-13D in lieu of the processing steps of FIGS. 8E and 8F.
Referring to FIG. 13A, the second exemplary structure according to a second embodiment of the present disclosure can be derived from the first exemplary structure illustrated in FIG. 8D. The thickness of the charge storage material regions 54 as provided at the processing step of FIG. 13A may be greater than the target thickness for the charge storage material regions 54 in a final three-dimensional memory device to be formed in order to compensate for subsequent thinning of the charge storage material portions 54. For example, the thickness of the charge storage material portions 54 may be in a range from 3 nm to 15 nm at the processing step of FIG. 13A.
Referring to FIG. 13B, an oxidation process can be performed to convert surface portions of the charge storage material portions 54 exposed in the backside recesses 43 into a silicon-containing dielectric material portions that are employed as a component of blocking dielectrics. A thermal or plasma oxidation method may be used by providing the oxidizing gas through the backside trench 79 and backside recesses 43. The silicon-containing dielectric material portions include silicon oxide or silicon oxynitride, and are herein referred to as blocking dielectric spacers 443. Each of the blocking dielectric spacers 443 can be in a tubular configuration, i.e., can have a vertical inner sidewall and a vertical outer sidewall that are laterally spaced from each other by a uniform thickness. The thickness of each blocking dielectric spacer 443 may be in a range from 1 nm to 12 nm (such as from 2 nm to 8 nm), although lesser and greater thicknesses can also be employed. The charge storage material portions 54 are thinned by oxidation from the outer sidewalls, and can have a thickness in a range from 1 nm to 10 nm after the oxidation process. Each charge storage material portion 54 can have a vertical inner sidewall and a vertical outer sidewall that are laterally spaced from each other by a uniform thickness.
As in the first embodiment, each of the charge trapping material portions 54 laterally surrounds a respective aluminum oxide tunneling dielectric layer 57. At least an inner portion of each of the charge trapping material portions 54 is formed within a volume of a respective memory opening 49 or within a volume of a respective support opening 19.
Referring to FIG. 13C, a backside dielectric metal oxide layer 444 can be formed directly on horizontal surfaces of the insulating layers 32 and outer sidewalls of the blocking dielectric spacers 443. The dielectric material of the backside dielectric metal oxide layer 444 can be a dielectric metal oxide such as aluminum oxide, a dielectric oxide of at least one transition metal element, a dielectric oxide of at least one Lanthanide element, a dielectric oxide of a combination of aluminum, at least one transition metal element, and/or at least one Lanthanide element. The backside dielectric metal oxide layer 444 can be deposited by a conformal deposition method such as atomic layer deposition. The thickness of backside dielectric metal oxide layer 444 can be in a range from 1 nm to 10 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the backside dielectric metal oxide layer 444 can consist essentially of aluminum oxide.
The entire set of blocking dielectric spacers 443 and the backside dielectric metal oxide layer 444 collectively constitutes a backside blocking dielectric layer 44. The backside blocking dielectric layer 44 is formed on the sidewalls of the backside trenches 79, horizontal surfaces and sidewalls of the insulating layers 32, outer sidewalls of the charge trapping material portions 54, physically exposed surfaces of the insulating cap layer 70 and the contact level dielectric layer 73, and surfaces of the planar dielectric portions 616 (if present) and tubular dielectric spacers 116 (if present). A backside cavity 79′ is present within the portion of each backside trench 79 that is not filled with the backside blocking dielectric layer 44.
Referring to FIG. 13D, the processing steps of FIGS. 8F and 9 can be performed to form electrically conductive layers 46 in the remaining volumes of the backside recesses 43. Subsequently, the processing steps of FIGS. 10, 11, and 12A-12B can be sequentially performed to form the second exemplary structure.
Each of the first and second exemplary structures and alternative embodiments can include a three-dimensional memory device. The three-dimensional memory device can include: an alternating stack of insulating layers 32 and electrically conductive layers 46 located over a substrate (9, 10,); a vertical semiconductor channel 60 vertically extending through a predominant subset of layers within the alternating stack (32, 46) (i.e., more than 50% of all layers such as all layers excluding the bottommost electrically conductive layer 46); a tunneling dielectric layer stack (56, 57) including a silicon-containing tunneling dielectric layer 56 and an aluminum oxide tunneling dielectric layer 57 and laterally surrounding the vertical semiconductor channel 60; and charge trapping material portions 54 located at each level of the electrically conductive layers 46 that are located at, or above a horizontal plane including a bottom surface of the aluminum oxide tunneling dielectric layer 57, comprising silicon nitride, contacting portions of an outer sidewall of the aluminum oxide tunneling dielectric layer 57, and vertically spaced from one another.
In one embodiment, discrete dielectric liner portions 53′ can be located at each level of the insulating layers 32 that are located at, or above the horizontal plane including the bottom surface of the aluminum oxide tunneling dielectric layer 57. A set of the discrete dielectric liner portions 53′ and the charge trapping material portions 54 contacts an entirety of the outer sidewall of the aluminum oxide tunneling dielectric layer 57. A dielectric liner portion 53′ can be located between a pair of nearest neighbor charge trapping material portions 54 to vertically separate the pair of nearest neighbor charge trapping material portions 54. In one embodiment, the insulating layers 32 comprise a first silicon oxide material; and the discrete dielectric liner portions 53′ comprise a second silicon oxide material.
In one embodiment, a backside blocking dielectric layer 44 can be located between each vertically neighboring pair of an insulating layer 32 and an electrically conductive layer 46 and contact an outer sidewall of each of the charge trapping material portions 54. In one embodiment, the backside blocking dielectric layer 44 comprises a layer stack of a backside silicon oxide layer 442 and a backside dielectric metal oxide layer 444. The backside silicon oxide layer 442 contacts horizontal surfaces of the insulating layers 32, and the backside dielectric metal oxide layer 444 contacts horizontal surfaces of the electrically conductive layers 46.
In one embodiment, the backside blocking dielectric layer 44 can include backside blocking dielectric spacers 443 laterally surrounding, and contacting an outer sidewall of, a respective one of the charge trapping material portions 54. The backside blocking dielectric spacers 443 comprise a dielectric material comprising silicon and oxygen. A backside dielectric metal oxide layer 444 can contact, and laterally surround, each of the backside blocking dielectric spacers 443. The three-dimensional memory device can further comprise: an epitaxial channel portion 11 underlying, and contacting, the vertical semiconductor channel 60, and a tubular dielectric spacer 116 located at a level of a bottommost electrically conductive layer 46 of the alternating stack (32, 46), laterally surrounding the epitaxial channel portion 11, and comprising a dielectric oxide of a semiconductor material of the epitaxial channel portion 11.
In one embodiment, each of the charge trapping material portions 54 has a tubular shape and has a uniform thickness throughout. The three-dimensional memory device can further comprise: a backside contact trench 79 vertically extending through the alternating stack (32, 46); an insulating spacer 74 located at a periphery of the backside contact trench 79; a backside contact via structure 76 laterally surrounded by the insulating spacer 74; and a source region 61 located in a portion of the substrate (9, 10,) underlying the backside contact trench 79 and contacting the backside contact via structure 76.
In one embodiment, the alternating stack (32, 46) comprises a terrace region in which each electrically conductive layer 46 other than a topmost electrically conductive layer 46 within the alternating stack (32, 46) laterally extends farther than any overlying electrically conductive layers 46 within the alternating stack (32, 46), and the terrace region includes stepped surfaces of the alternating stack (32, 46) that continuously extend from a bottommost layer within the alternating stack (32, 46) to a topmost layer within the alternating stack (32, 46).
Each of the first and second exemplary structures can include a three-dimensional memory device. In one embodiment, the three-dimensional memory device comprises a vertical NAND memory device. The electrically conductive layers 46 can comprise, or can be electrically connected to, a respective word line of the monolithic three-dimensional NAND memory device. The substrate (9, 10,) can comprise a silicon substrate. The vertical NAND memory device can comprise an array of monolithic three-dimensional NAND strings over the silicon substrate. At least one memory cell (as embodied as a portion of a charge storage layer 54 at a level of an electrically conductive layer 46) in a first device level of the array of monolithic three-dimensional NAND strings can be located over another memory cell (as embodied as another portion of the charge storage layer 54 at a level of another electrically conductive layer 46) in a second device level of the array of monolithic three-dimensional NAND strings. The silicon substrate can contain an integrated circuit comprising a driver circuit for the memory device located thereon. The electrically conductive layers 46 can comprise a plurality of control gate electrodes having a strip shape extending substantially parallel to the top surface of the substrate (9, 10,), e.g., between a pair of backside trenches 79. The plurality of control gate electrodes comprises at least a first control gate electrode located in a first device level and a second control gate electrode located in a second device level. The array of monolithic three-dimensional NAND strings can comprise: a plurality of semiconductor channels (59, 11, 60), wherein at least one end portion 60 of each of the plurality of semiconductor channels (59, 11, 60) extends substantially perpendicular to a top surface of the substrate (9, 10,); and a plurality of charge storage elements (as embodied as charge trapping material portions). Each charge storage element can be located adjacent to a respective one of the plurality of semiconductor channels (59, 11, 60).
The discrete charge trapping material portions 54 reduce lateral charge diffusion between adjacent memory cells and improve data retention compared to a continuous charge trapping material layer. The addition of the aluminum oxide tunnel dielectric layer 57 can increase the neutral threshold voltage of the device and further improve data retention.
Although the foregoing refers to particular preferred embodiments, it will be understood that the disclosure is not so limited. It will occur to those of ordinary skill in the art that various modifications may be made to the disclosed embodiments and that such modifications are intended to be within the scope of the disclosure. Where an embodiment employing a particular structure and/or configuration is illustrated in the present disclosure, it is understood that the present disclosure may be practiced with any other compatible structures and/or configurations that are functionally equivalent provided that such substitutions are not explicitly forbidden or otherwise known to be impossible to one of ordinary skill in the art. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.

Claims

1. A three-dimensional memory device comprising:

an alternating stack of insulating layers and electrically conductive layers located over a substrate;

a vertical semiconductor channel vertically extending through the alternating stack;

a tunneling dielectric layer stack including a silicon-containing tunneling dielectric layer and an aluminum oxide tunneling dielectric layer and laterally surrounding the vertical semiconductor channel; and

charge trapping material portions located at each level of the electrically conductive layers that are located at, or above a horizontal plane including a bottom surface of the aluminum oxide tunneling dielectric layer, comprising silicon nitride, directly contacting portions of an outer sidewall of the aluminum oxide tunneling dielectric layer, and vertically spaced from one another, wherein the three-dimensional memory device comprises at least one feature selected from:

a first feature that an entirety of an inner sidewall of the aluminum oxide tunneling dielectric layer directly contacts an outer sidewall of the silicon containing tunneling dielectric layer;

a second feature that an entire inner sidewall of each of the charge trapping material portions directly contacts a respective portion of the outer sidewall of the aluminum oxide tunneling dielectric layer;

a third feature that an entirety of the aluminum oxide tunneling dielectric layer is more proximal to the vertical semiconductor channel than any of the insulating layers is to the vertical semiconductor channel; and

a fourth feature that sidewalls of the insulating layers are not in direct contact with any surface of the charge trapping material portions.

2. The three-dimensional memory device of claim 1, further comprising discrete dielectric liner portions located at each level of the insulating layers that are located at, or above the horizontal plane including the bottom surface of the aluminum oxide tunneling dielectric layer.

3. The three-dimensional memory device of claim 2, wherein:

a set of the discrete dielectric liner portions and the charge trapping material portions contacts an entirety of the outer sidewall of the aluminum oxide tunneling dielectric layer;

one of the set of the dielectric liner portions is be located between a pair of discrete, nearest neighbor charge trapping material portions to vertically separate the pair of nearest neighbor charge trapping material portions;

the insulating layers comprise a first silicon oxide material; and

the discrete dielectric liner portions comprise a second silicon oxide material.

4. The three-dimensional memory device of claim 1, further comprising a backside blocking dielectric layer located between each vertically neighboring pair of an insulating layer and an electrically conductive layer and contacting an outer sidewall of each of the charge trapping material portions.

5. The three-dimensional memory device of claim 4, wherein:

the backside blocking dielectric layer comprises a layer stack of a backside silicon oxide layer and a backside dielectric metal oxide layer;

the backside silicon oxide layer contacts horizontal surfaces of the insulating layers; and

the backside dielectric metal oxide layer contacts horizontal surfaces of the electrically conductive layers.

6. The three-dimensional memory device of claim 4, wherein the backside blocking dielectric layer comprises backside blocking dielectric spacers laterally surrounding, and contacting an outer sidewall of, a respective one of the charge trapping material portions, wherein the backside blocking dielectric spacers comprise a dielectric material comprising silicon and oxygen.

7. The three-dimensional memory device of claim 1, further comprising:

an epitaxial channel portion underlying, and contacting, the vertical semiconductor channel; and

a tubular dielectric spacer located at a level of a bottommost electrically conductive layer of the alternating stack, laterally surrounding the epitaxial channel portion, and comprising a dielectric oxide of a semiconductor material of the epitaxial channel portion.

8. The three-dimensional memory device of claim 1, wherein each of the charge trapping material portions has a tubular shape and has a uniform thickness throughout.

9. The three-dimensional memory device of claim 1, further comprising:

a backside contact trench vertically extending through the alternating stack;

an insulating spacer located at a periphery of the backside contact trench;

a backside contact via structure laterally surrounded by the insulating spacer; and

a source region located in a portion of the substrate underlying the backside contact trench and contacting the backside contact via structure.

10. The three-dimensional memory device of claim 1, wherein the alternating stack comprises a terrace region in which each electrically conductive layer other than a topmost electrically conductive layer within the alternating stack laterally extends farther than any overlying electrically conductive layers within the alternating stack, and the terrace region includes stepped surfaces of the alternating stack that continuously extend from a bottommost layer within the alternating stack to a topmost layer within the alternating stack.

11. The three-dimensional memory device of claim 1, wherein:

the three-dimensional memory device comprises a monolithic three-dimensional NAND memory device;

the electrically conductive layers comprise, or are electrically connected to, a respective word line of the monolithic three-dimensional NAND memory device;

the substrate comprises a silicon substrate;

the monolithic three-dimensional NAND memory device comprises an array of monolithic three-dimensional NAND strings over the silicon substrate;

at least one memory cell in a first device level of the array of monolithic three-dimensional NAND strings is located over another memory cell in a second device level of the array of monolithic three-dimensional NAND strings;

the silicon substrate contains an integrated circuit comprising a driver circuit for the memory device located thereon;

the electrically conductive layers comprise a plurality of control gate electrodes having a strip shape extending substantially parallel to the top surface of the substrate, the plurality of control gate electrodes comprise at least a first control gate electrode located in the first device level and a second control gate electrode located in the second device level; and

the array of monolithic three-dimensional NAND strings comprises:

a plurality of semiconductor channels, wherein at least one end portion of each of the plurality of semiconductor channels extends substantially perpendicular to a top surface of the substrate, and

a plurality of charge storage elements, each charge storage element located adjacent to a respective one of the plurality of semiconductor channels.

12.-22. (canceled)

23. The three-dimensional memory device of claim 1, wherein the tunneling dielectric layer stack is located between the vertical semiconductor channel and the charge trapping material portions.

24. The three-dimensional memory device of claim 1, wherein each of the charge trapping material portions is more distal from the vertical semiconductor channel than the tunneling dielectric layer is from the vertical semiconductor channel.

25. The three-dimensional memory device of claim 1, wherein the three-dimensional memory device comprises the first feature.

26. The three-dimensional memory device of claim 1, wherein the three-dimensional memory device comprises the second feature.

27. The three-dimensional memory device of claim 1, wherein one of the charge trapping material portions includes a topmost surface that is coplanar with a bottom surface of one of the insulating layers and a bottommost surface that is coplanar with a top surface of another of the insulating layers.

28. The three-dimensional memory device of claim 1, wherein the three-dimensional memory device comprises the third feature.

29. The three-dimensional memory device of claim 1, wherein the three-dimensional memory device comprises the fourth feature.

30. The three-dimensional memory device of claim 2, wherein each of the discrete dielectric liner portions has an inner sidewall that directly contacts portions of the outer sidewall of the aluminum oxide tunneling dielectric layer.

31. The three-dimensional memory device of claim 2, wherein each discrete dielectric liner portion that is located between a vertically neighboring pair of charge trapping material portions continuously extends between the vertically neighboring pair of charge trapping material portions as a single continuous structure.

32. A three-dimensional memory device comprising:

a tunneling dielectric layer stack including a silicon-containing tunneling dielectric layer and an aluminum oxide tunneling dielectric layer and laterally surrounding the vertical semiconductor channel;

charge trapping material portions located at each level of the electrically conductive lavers that are located at, or above a horizontal plane including a bottom surface of the aluminum oxide tunneling dielectric layer, comprising silicon nitride, directly contacting portions of an outer sidewall of the aluminum oxide tunneling dielectric layer, and vertically spaced from one another; and

discrete dielectric liner portions located at each level of the insulating layers that are located at, or above the horizontal plane including the bottom surface of the aluminum oxide tunneling dielectric layer,

wherein each charge trapping material portion that is located between a vertically neighboring pair of discrete dielectric liner portions includes an inner sidewall that continuously extends between the vertically neighboring pair of discrete dielectric liner portions such that an entirety of the inner sidewall contacts a respective portion of the outer sidewall of the aluminum oxide tunneling dielectric layer.

33. (canceled)