Three dimensional NAND device containing dielectric pillars for a buried source line and method of making thereof

A three-dimensional memory device includes an alternating stack of electrically conductive layers and insulating layers located over a substrate, an array of memory stack structures, each memory stack structure extending through the alternating stack and including a memory film and a semiconductor channel laterally surrounded by the memory film, and an array of dielectric pillars located between the alternating stack and the substrate.

FIELD

The present disclosure relates generally to the field of semiconductor devices and specifically to three-dimensional memory structures, such as vertical NAND strings and other three-dimensional devices, and methods of making thereof.

BACKGROUND

SUMMARY

According to an aspect of the present disclosure, a three-dimensional memory device is provided, which comprises an alternating stack of electrically conductive layers and insulating layers located over a substrate; an array of memory stack structures, each memory stack structure extending through the alternating stack and including a memory film and a semiconductor channel laterally surrounded by the memory film; and an array of dielectric pillars located between the alternating stack and the substrate.

According to another aspect of the present disclosure, a method of manufacturing a three-dimensional memory device is provided. A sacrificial matrix layer is formed over a substrate. The sacrificial matrix layer is patterned to form an array of cavities. An array of dielectric pillars is formed by filling the array of cavities with a dielectric fill material. An alternating stack of insulator layers and spacer material layers is formed over the array of dielectric pillars and the sacrificial matrix layer. An array of memory stack structures is formed through the alternating stack and the sacrificial matrix layer. The sacrificial matrix layer is replaced with a source conductive layer.

DETAILED DESCRIPTION

As discussed above, the present disclosure is directed to three-dimensional memory structures, such as vertical NAND strings and other three-dimensional devices, 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 “field effect transistor” refers to any semiconductor device having a semiconductor channel through which electrical current flows with a current density modulated by an external electrical field. As used herein, an “active region” refers to a source region of a field effect transistor or a drain region of a field effect transistor. A “top active region” refers to an active region of a field effect transistor that is located above another active region of the field effect transistor. A “bottom active region” refers to an active region of a field effect transistor that is located below another active region of the field effect transistor. A monolithic three-dimensional memory array is a memory array 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 toFIG. 1, an 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 exemplary structure includes a substrate, which can be a semiconductor substrate (e.g., a semiconductor substrate, such as a single crystalline silicon wafer). The substrate can include a substrate semiconductor layer10. The substrate semiconductor layer10is a semiconductor material layer, and can include at least one elemental semiconductor material (e.g., silicon, such as single crystalline silicon), 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.

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, 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 “insulating material” or a “dielectric material” refers to a material having electrical conductivity less than 1.0×10−6S/cm. All measurements for electrical conductivities are made at the standard condition. The substrate semiconductor layer10can include at least one doped well (not expressly shown) having a substantially uniform dopant concentration therein.

The exemplary structure can have multiple regions for building different types of devices. Such areas can include, for example, a device region100, a contact region300, and a peripheral device region200. In one embodiment, the substrate semiconductor layer10can include at least one a doped well in the device region100. As used herein, a “doped well” refers to a portion of a semiconductor material having a doping of a same conductivity type (which can be p-type or n-type) and a substantially same level of dopant concentration throughout. The doped well can be the same as the substrate semiconductor layer10or can be a portion of the substrate semiconductor layer10. The conductivity type of the doped well is herein referred to as a first conductivity type, which can be p-type or n-type. The dopant concentration level of the doped well is herein referred to as a first dopant concentration level. In one embodiment, the first dopant concentration level can be in a range from 1.0×1015/cm3to 1.0×1018/cm3, although lesser and greater dopant concentration levels can also be employed. As used herein, a dopant concentration level refers to average dopant concentration for a given region.

Peripheral devices210can be formed in, or on, a portion of the substrate semiconductor layer10located within the peripheral device region200. The peripheral devices can include various devices employed to operate the memory devices to be formed in the device region100, and can include, for example, driver circuits for the various components of the memory devices. The peripheral devices210can include, for example, field effect transistors and/or passive components such as resistors, capacitors, inductors, diodes, etc.

A lower source insulating layer12can be formed above the substrate semiconductor layer10. The lower source insulating layer12provides electrical isolation of a continuous source structure to be subsequently formed from the substrate semiconductor layer10. The lower source insulating layer12can include, for example, silicon oxide and/or a dielectric metal oxide (such as HfO2, ZrO2, LaO2, etc.). The thickness of the lower source insulating layer12can be in a range from 3 nm to 30 nm, although lesser and greater thicknesses can also be employed.

A sacrificial matrix layer14can be formed over the lower source insulating layer14. The sacrificial matrix layer14includes a material that can be removed selective to the material of the lower source insulating layer12, and selective to the materials of an upper source insulating layer and an insulating spacer to be subsequently formed. For example, the sacrificial matrix layer14can include a semiconductor material such as polysilicon or a silicon-germanium alloy, or can include amorphous carbon, an organic polymer, or an inorganic polymer. The sacrificial matrix layer14can be deposited by chemical vapor deposition, physical vapor deposition, or spin coating. The thickness of the sacrificial matrix layer14can be in a range from 10 nm to 60 nm, although lesser and greater thicknesses can also be employed.

An optional upper source insulating layer16can be formed above the sacrificial matrix layer14. The upper source insulating layer16provides electrical isolation of the continuous source structure to be subsequently formed from electrically conductive layers to be subsequently formed. The upper source insulating layer16can include, for example, silicon oxide and/or a dielectric metal oxide (such as HfO2, ZrO2, LaO2, etc.). The thickness of the upper source insulating layer16can be in a range from 3 nm to 30 nm, although lesser and greater thicknesses can also be employed. If a subsequent alternating stack to be formed over the upper source insulating layer16starts with a sacrificial material layer, the upper source insulating layer16is preferably included. If a subsequent alternating stack to be formed over the upper source insulating layer16starts with an insulating layer, the upper source insulating layer16is optional, and the first insulating material of the alternating stack can function as, i.e., can be identified as, an upper source insulating layer16. While the present disclosure is described employing an embodiment in which the upper source insulating layer16is a distinct from a bottommost insulating layer of an alternating stack to be subsequently formed, embodiments are expressly contemplated in which the upper source insulating layer16is the same as the bottommost insulating layer.

Referring toFIG. 2, a photoresist layer (not shown) can be applied over the upper source insulating layer16and can be lithographically patterned to form an array of opening therein. The pattern of the array of openings in the photoresist layer can be transferred through the upper source insulating layer16and the sacrificial matrix layer14by an anisotropic etch such as a reactive ion etch. The lower source insulating layer12can be employed as an etch stop layer. If desired, the etch may be continued through the lower source insulating layer12to or into the top surface of the substrate semiconductor layer10. An array of via cavities19can be formed in the sacrificial matrix layer14. The cavities19may extend to the lower source insulating layer12, through the lower source insulating layer12to the top surface of the substrate semiconductor layer10or into the substrate semiconductor layer10. The array of via cavities19may have a periodic pattern. In one embodiment, each via cavity19can have substantially vertical sidewalls and/or can have a substantially circular horizontal cross-sectional shape. In one embodiment, each via cavity19can have a substantially cylindrical shape. In one embodiment, the array of via cavities19can be a two-dimensional periodic array of instances of a unit cell structure. The photoresist layer can be subsequently removed, for example, by ashing.

Referring toFIG. 3, a dielectric fill material is deposited in the array of via cavities19, for example, by chemical vapor deposition or spin coating. The dielectric fill material can include, for example, silicon oxide (such as doped silicate glass or undoped silicate glass), a dielectric metal oxide, silicon nitride, organosilicate glass, or a combination thereof. For example, the dielectric fill material can include silicon oxide. Excess portions of the deposited dielectric fill material can be removed from above the horizontal plane including the top surface of the upper source insulating layer16by a planarization process, which can employ a recess etch and/or chemical mechanical planarization.

The remaining portions of the dielectric fill material that fill the via cavities19constitute an array of dielectric pillars20. The array of dielectric pillars20may have a periodic pattern. In one embodiment, each dielectric pillar20can have substantially vertical sidewalls and/or can have a substantially circular horizontal cross-sectional shape. In one embodiment, each dielectric pillar20can have a substantially cylindrical shape. In one embodiment, the array of dielectric pillars20can be a two-dimensional periodic array of instances of a unit cell structure. The top surfaces of the dielectric pillars20and the top surface of the upper source insulating layer16can be coplanar, i.e., can be located within a same Euclidean plane.

FIGS. 4A-4Cillustrate various exemplary patterns that can be employed for the array of dielectric pillars20. Specifically,FIGS. 4A-4Cillustrate the array of dielectric pillars20for first, second, and third exemplary configurations, respectively. The pattern illustrated inFIG. 4Ais herein referred to as a zigzag pattern, the pattern illustrated inFIG. 4Bis herein referred to as a lattice pattern, and the pattern illustrated inFIG. 4Cis herein referred to as a diagonal pattern. The zigzag pattern may comprise zigzag rows (i.e., saw tooth shaped rows) of dielectric pillars20. The rows may extend parallel to the word line direction or parallel to the bit line direction. The lattice pattern may comprise a plurality of linear rows and columns of pillars20which form rectangular or square unit cells of pillars20. The diagonal pattern may comprise a plurality of parallel diagonal rows of pillars20which extend at an angle of 30 to 60 degrees, such as about 45 degrees, with respect to the bit line and word line directions. The rows form parallelogram shaped unit cells which lack a right angle. The periodicity of each pattern may be selected to be commensurate with the pattern of memory openings to be subsequently formed. In one embodiment, the periodicity of each pattern of the dielectric pillars20can be the same as, or can be an integer multiple of, the periodicity of the memory openings to be subsequently formed along the same direction.

Referring toFIG. 5, an alternating stack of first material layers (which can be insulating layers32) and second material layers (which are referred to spacer material layers) is formed over the upper source insulating layer16. As used herein, a “material layer” refers to a layer including a material throughout the entirety thereof. In one embodiment, the alternating stack may include the insulating layers32and spacer material layers that are located between each vertically neighboring pair of insulating layers32. As used herein, a “spacer material layer” refers to a material layer that is located between two other material layers, i.e., between an overlying material layer and an underlying material layer. The spacer material layers can be formed as electrically conductive layers, or can be replaced with electrically conductive layers in a subsequent processing step.

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 layer32, and each second material layer (i.e., the spacer material layers) can be a sacrificial material layer42. In this case, the stack can include an alternating plurality of insulating layers32and sacrificial material layers42, and constitutes an in-process alternating stack comprising insulating layers32and sacrificial material layers42. As used herein, an “alternating stack” of first elements and second elements is a structure in which instances of a first element and instances of a second element alternate along a same direction, such as a vertical direction. 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. Thus, the in-process alternating stack (32,42) can be formed over the layer stack of the lower source insulator layer12, the sacrificial matrix layer14, and the upper source insulator layer16.

In an illustrative example, the insulating layers32can include silicon oxide, and sacrificial material layers can include silicon nitride. As used herein, silicon nitride, or a silicon nitride material, refers to a dielectric compound of at least one Group IV element and at least one non-metallic element such that silicon accounts more than 50 atomic percent of the at least one Group IV element and nitrogen accounts for more than 50 atomic percent of the non-metallic element. As such, silicon nitrides include Si3N4and a silicon oxynitride in which the atomic concentration of nitrogen is greater than the atomic concentration of oxygen. As used herein, silicon oxide, or a silicon oxide material, refers to a dielectric compound of at least one Group IV element and at least one non-metallic element such that silicon accounts more than 50 atomic percent of the at least one Group IV element and oxygen accounts for more than 50 atomic percent of the non-metallic element. Silicon oxides include silicon dioxide, an oxide of a silicon-germanium alloy in which the atomic concentration of silicon is greater than the atomic concentration of germanium, a silicon oxynitride in which the atomic concentration of oxygen is greater than the atomic concentration of nitrogen, and doped derivatives thereof (such as phosphosilicate glass, fluorosilicate glass, borophosphosilicate glass, organosilicate glass, etc.). The first material of the insulating layers32can be deposited, for example, by chemical vapor deposition (CVD). For example, if silicon oxide is employed for the insulating layers32, tetraethyl orthosilicate (TEOS) can be employed as the precursor material for the CVD process. The second material of the sacrificial material layers42can be formed, for example, CVD or atomic layer deposition (ALD).

Optionally, an insulating cap layer70can be formed over the alternating stack (32,42). The insulating cap layer70includes a dielectric material that is different from the material of the sacrificial material layers42. In one embodiment, the insulating cap layer70can include a dielectric material that can be employed for the insulating layers32as described above. The insulating cap layer70can have a greater thickness than each of the insulating layers32. The insulating cap layer70can be deposited, for example, by chemical vapor deposition. In one embodiment, the insulating cap layer70can be a silicon oxide layer.

Referring toFIG. 6, a lithographic material stack (not shown) including at least a photoresist layer can be formed over the insulating cap layer70and the alternating stack (32,42), and can be lithographically patterned to form openings therein. The pattern in the lithographic material stack can be transferred through the optional insulating cap layer70, through entirety of the alternating stack (32,42), and through the upper source insulating layer16, the sacrificial matrix layer14, and the lower source insulating layer12by at least one anisotropic etch that employs the patterned lithographic material stack as an etch mask. Portions of the insulating cap layer70, the alternating stack (32,42), the upper source insulating layer16, the sacrificial matrix layer14, and the lower source insulating layer12underlying the openings in the patterned lithographic material stack are etched to form memory openings49. In other words, the transfer of the pattern in the patterned lithographic material stack through the optional insulating cap layer70, through entirety of the alternating stack (32,42), and through the upper source insulating layer16, the sacrificial matrix layer14, and the lower source insulating layer12and optionally partially through the substrate semiconductor layer10forms the memory openings49. 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. Optionally, the lower source insulating layer12may be used as an etch stop layer. The sidewalls of the memory openings49can be substantially vertical, or can be tapered. The patterned lithographic material stack can be subsequently removed, for example, by ashing.

FIG. 7A-7Cillustrate the first, second, and third exemplary configurations, respectively, for the sacrificial material layer14, the array of dielectric pillars20, and the array of memory openings49in horizontal cross-sectional views along a horizontal plane that passes through the sacrificial material layer14. In one embodiment, the array of dielectric pillars20and the array of memory openings49collectively constitute a two-dimensional periodic array of multiple instances of a unit cell structure “U”. The unit cell structure U can include multiple memory openings49(such as four memory opening as illustrated inFIGS. 7A-7C) and at least one dielectric pillar20(which may be two dielectric pillars20composed of one whole pillar inside the unit cell and quarters of the four pillars at the vertices of the unit cell as illustrated inFIG. 7A, or a single dielectric pillar20composed of quarters of the four pillars at the vertices of the unit cell as illustrated inFIGS. 7B and 7C). In one embodiment, the array of memory openings49can comprise a hexagonal array of memory openings49. In one embodiment, the ratio of the total number of the multiple memory openings49in the unit cell structure U to the total number of the at least one dielectric pillar20in the unit cell structure U can be in a range from 2 to 4. For example, the ratio can be 2 as illustrated inFIG. 7A, or 4 as illustrated inFIG. 7B, or 3 as illustrated inFIG. 7C.

A memory stack structure can be formed in each memory opening49in subsequent processing steps.FIGS. 8A-8Dillustrate the process of forming a memory stack structure in a memory opening49. While a particular embodiment is illustrated herein for formation of memory stack structures, embodiments are expressly contemplated herein in which different types of memory stack structures are formed.

Referring toFIG. 8A, a memory opening49is illustrated. The memory opening49extends through the insulating cap layer70, the alternating stack (32,42) and the layer stack of the upper source insulating layer16, the sacrificial matrix layer14, and the lower source insulating layer12, and optionally into an upper portion of the substrate semiconductor layer10. The recess depth of the bottom surface of each memory opening49with respect to the top surface of the substrate semiconductor layer10can be in a range from 0 nm to 30 nm, although greater recess depths can also be employed. Optionally, the sacrificial material layers42can be laterally recessed partially to form lateral recesses (not shown), for example, by an isotropic etch.

Referring toFIG. 8B, a set of layers for formation of a memory film is deposited within each memory opening. The set of layers may include, for example, an optional outer blocking dielectric layer502L, an optional inner blocking dielectric layer503L, a charge storage element layer504L, and a tunneling dielectric layer506L.

Specifically, each of the outer and inner blocking dielectric layers (502L,503L) can includes at least one dielectric material, which can be silicon oxide, a dielectric metal oxide, or a combination thereof. As used herein, a dielectric metal oxide refers to a dielectric material that includes at least one metallic element and at least oxygen. The dielectric metal oxide may consist essentially of the at least one metallic element and oxygen, or may consist essentially of the at least one metallic element, oxygen, and at least one non-metallic element such as nitrogen. In one embodiment, at least one of the outer and inner blocking dielectric layers (502L,503L) can include a dielectric metal oxide having a dielectric constant greater than 7.9, i.e., having a dielectric constant greater than the dielectric constant of silicon nitride. Non-limiting examples of dielectric metal oxides include aluminum oxide (Al2O3), hafnium oxide (HfO2), lanthanum oxide (LaO2), yttrium oxide (Y2O3), tantalum oxide (Ta2O5), silicates thereof, nitrogen-doped compounds thereof, alloys thereof, and stacks thereof. The dielectric metal oxide can be deposited, for example, by chemical vapor deposition (CVD), atomic layer deposition (ALD), pulsed laser deposition (PLD), liquid source misted chemical deposition, or a combination thereof. Additionally or alternately, at least one of the outer and inner blocking dielectric layers (502L,503L) can include silicon oxide, silicon oxynitride, silicon nitride, or a combination thereof. In one embodiment, the blocking dielectric layers (502L,503L) can include a stack of aluminum oxide and silicon oxide. Each of the outer and inner blocking dielectric layers (502L,503L) 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 blocking dielectric layers (502L,503L) can be in a range from 1 nm to 30 nm, although lesser and greater thicknesses can also be employed.

The charge storage element layer504L can include a single layer of a charge trapping material including a dielectric charge trapping material, which can be, for example, silicon nitride. Alternatively, the charge storage element layer504L can include a conductive material such as doped polysilicon or a metallic material that is patterned into multiple electrically isolated portions (e.g., floating gates), for example, by being formed within lateral recesses into sacrificial material layers42. In one embodiment, the charge storage element layer504L includes a silicon nitride layer.

The charge storage element layer504L can be formed as a single memory material layer of homogeneous composition, or can include a stack of multiple memory material layers. The multiple memory material layers, if employed, can comprise a plurality of spaced-apart floating gate material layers that contain conductive materials (e.g., metal such as tungsten, molybdenum, tantalum, titanium, platinum, ruthenium, and alloys thereof, or a metal silicide such as tungsten silicide, molybdenum silicide, tantalum silicide, titanium silicide, nickel silicide, cobalt silicide, or a combination thereof) and/or semiconductor materials (e.g., polycrystalline or amorphous semiconductor material including at least one elemental semiconductor element or at least one compound semiconductor material). Alternatively or additionally, the charge storage element layer504L may comprise an insulating charge trapping material, such as one or more silicon nitride segments. Alternatively, the charge storage element layer504L may comprise conductive nanoparticles such as metal nanoparticles, which can be, for example, ruthenium nanoparticles. The charge storage element layer504L can be formed, for example, by chemical vapor deposition (CVD), atomic layer deposition (ALD), physical vapor deposition (PVD), or any suitable deposition technique for storing electrical charges therein. The thickness of the charge storage element layer504L can be in a range from 2 nm to 20 nm, although lesser and greater thicknesses can also be employed.

In an illustrative example, the optional outer blocking dielectric layer502L can include a dielectric metal oxide such as aluminum oxide, and the inner blocking dielectric layer503L can include a dielectric oxide of a semiconductor material such as silicon oxide. The charge storage element layer504L can include any type of charge storage material, and may be formed as a continuous material layer including a charge trapping material, or may be formed as a plurality of vertically isolated charge trapping material portions that are located at each level of the sacrificial material layers42, for example, by being deposited in recessed regions by a combination of a conformal deposition process and an anisotropic etch. The tunneling dielectric layer506L includes a material that can be employed as a tunneling dielectric material, which can be, for example, silicon oxide or an ONO stack.

A semiconductor channel layer60L can be deposited over the tunneling dielectric layer506L. The semiconductor channel layer60L 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 semiconductor channel layer60L includes amorphous silicon or polysilicon. The semiconductor channel layer60L can be formed by a conformal deposition method such as low pressure chemical vapor deposition (LPCVD). The thickness of the semiconductor channel layer60L can be in a range from 2 nm to 10 nm, although lesser and greater thicknesses can also be employed. A cavity49′ is formed in the volume of each memory opening49that is not filled with the deposited material layers (502L,503L,504L,506L,60L).

Referring toFIG. 8C, a dielectric material can be deposited to fill the cavity49′ within each memory opening49. The dielectric material 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. Exemplary dielectric materials that can be employed to fill the cavities49′ include silicon oxide (undoped silicate glass or doped silicate glass) and organosilicate glass.

A planarization process can be performed to remove excess portions of the dielectric material, the semiconductor channel layer60L, the tunneling dielectric layer506L, the charge storage element layer504L, and the blocking dielectric layers (502L,503L) from above the horizontal plane including the top surface of the insulating cap layer70. A recess etch and/or chemical mechanical planarization process can be employed. Each remaining portion of the outer blocking dielectric layer502L in a memory opening constitutes an outer blocking dielectric502. Each remaining portion of the inner blocking dielectric layer503L in a memory opening constitutes an inner blocking dielectric503. Each remaining portion of the charge storage element layer504L in a memory opening includes charge storage elements504(which may be embodied as a single continuous memory material layer (charge storage layer) or as discrete charge storage material portions located at each level of the sacrificial material layers42). In one embodiment, portions of a single continuous memory material layer including a charge trapping dielectric material (such as silicon nitride) that are located at levels of the sacrificial material layers42constitute the charge storage elements, while portions of the same single continuous memory material layer located at each level of the insulating layers32provide electrical isolation among vertically neighboring charge storage elements. Each remaining portion of the tunneling dielectric layer506L in a memory opening constitutes a tunneling dielectric506. Each remaining portion of the semiconductor channel layer60L in a memory opening constitutes a semiconductor channel60, which includes a vertical semiconductor channel that extend along the vertical direction. Each remaining portion of the dielectric material constitutes a dielectric core62. Each adjoining set of an optional outer blocking dielectric502, an inner blocking dielectric503, a set of charge storage elements504, and a tunneling dielectric506collectively constitute a memory film50.

Referring toFIG. 8D, each dielectric core62can be vertically recessed, for example, by a recess etch with respect to the memory film50. The recess etch of the dielectric core62may, or may not, be selective to the semiconductor channel60. Drain regions63can be formed by depositing a doped semiconductor material within each recessed region above the dielectric cores62. 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 layer70, for example, by chemical mechanical planarization (CMP) or a recess etch to form the drain regions63. Each set of a memory film50and a semiconductor channel60located within a same memory opening constitutes a memory stack structure55.

FIG. 9illustrates the exemplary structure that incorporates multiple instances of the exemplary memory stack structure55ofFIG. 8D. Each memory stack structure55includes from outside to inside, at least one optional blocking dielectric (502,503) (which may include an outer blocking dielectric502and an inner blocking dielectric503), charge storage elements504that may be memory elements (as embodied vertically spaced portions of a memory material layer located at levels of each sacrificial material layers42), a tunneling dielectric506, and a semiconductor channel60. While the present disclosure is described employing the illustrated configuration for the memory stack structure, the methods of the present disclosure can be applied to alternative memory stack structures including a polycrystalline semiconductor channel.

Referring toFIG. 10, an optional first contact level dielectric layer71can be formed over the substrate semiconductor layer10. As an optional structure, the first contact level dielectric layer71may, or may not, be formed. In case the first contact level dielectric layer71is formed, the first contact level dielectric layer71includes a dielectric material such as silicon oxide, silicon nitride, silicon oxynitride, porous or non-porous organosilicate glass (OSG), or a combination thereof. If an organosilicate glass is employed, the organosilicate glass may, or may not, be doped with nitrogen. The first contact level dielectric layer71can be formed over a horizontal plane including the top surface of the insulating cap layer70and the top surfaces of the drain regions63. The first contact level dielectric layer71can be deposited by chemical vapor deposition, atomic layer deposition (ALD), spin-coating, or a combination thereof. The thickness of the first contact level dielectric layer71can be in a range from 10 nm to 300 nm, although lesser and greater thicknesses can also be employed.

In one embodiment, the first contact level dielectric layer71can be formed as a dielectric material layer having a uniform thickness throughout. The first contact level dielectric layer71may be formed as a single dielectric material layer, or can be formed as a stack of a plurality of dielectric material layers. Alternatively, formation of the first contact level dielectric layer71may be merged with formation of at least one line level dielectric layer (not shown). While the present disclosure is described employing an embodiment in which the first contact level dielectric layer71is a structure separate from an optional second contact level dielectric layer or at least one line level dielectric layer to be subsequently deposited, embodiments in which the first contact level dielectric layer71and at least one line level dielectric layer are formed at a same processing step, and/or as a same material layer, are expressly contemplated herein.

In one embodiment, the first contact level dielectric layer71, the insulating cap layer70, the alternating stack (32,42), and the layer stack of the upper source insulating layer16, the sacrificial matrix layer14, and the lower source insulating layer12can be removed from the peripheral device region200, for example, by a masked etch process. In addition, a stepped cavity can be formed within the contact region300by patterning a portion of the alternating stack (32,42). As used herein, a “stepped cavity” refers to a cavity having stepped surfaces. 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 “step” refers to a vertical shift in the height of a set of adjoined surfaces.

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 semiconductor layer10. 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 stack 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 all stepped surfaces, mask material layers employed to form the stepped surfaces can be removed, for example, by ashing. Multiple photoresist layers and/or multiple etch processes can be employed to form the stepped surfaces.

A dielectric material such as silicon oxide is deposited in the stepped cavity and over the peripheral devices210in the peripheral device region200. Excess portions of the deposited dielectric material can be removed from above the top surface of the first contact level dielectric layer71, for example, by chemical mechanical planarization (CMP). The remaining portion of the deposited dielectric material filling the stepped cavity in the contact region300and overlying the substrate semiconductor layer10in the peripheral device region200constitutes a retro-stepped dielectric material portion65. 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 as the dielectric material, the silicon oxide of the retro-stepped dielectric material portion65may, or may not, be doped with dopants such as B, P, and/or F. The top surface of the retro-stepped dielectric material portion65can be coplanar with the top surface of the first contact level dielectric layer71.

The region over the peripheral devices210and the region over the stepped cavities can be filled simultaneously with the same dielectric material, or can be filled in different processing steps with the same dielectric material or with different dielectric materials. The cavity over the peripheral devices210can be filled with a dielectric material prior to, simultaneously with, or after, filling of the cavity over the stepped surface of the contact region300with a dielectric material. While the present disclosure is described employing an embodiment in which the cavity in the peripheral device region200and the stepped cavity in the contact region300are filled simultaneously, embodiments are expressly contemplated herein in which the cavity in the peripheral device region200and the stepped cavity in the contact region300are filled in different processing steps.

Referring toFIG. 11, through-stack dielectric support pillars7P may be optionally formed through the retro-stepped dielectric material portion65and/or through the first contact level dielectric layer71and/or through the alternating stack (32,42). In one embodiment, the through-stack dielectric support pillars7P can be formed in the contact region300, which is located adjacent to the device region100. The through-stack dielectric support pillars7P can be formed, for example, by forming an opening extending through the retro-stepped dielectric material portion65and/or through the alternating stack (32,42) and at least to the top surface of the substrate semiconductor layer10, and by filling the opening with a dielectric material that is resistant to the etch chemistry to be employed to remove the sacrificial material layers42.

In one embodiment, the through-stack dielectric support pillars7P can include silicon oxide and/or a dielectric metal oxide such as aluminum oxide. In one embodiment, the portion of the dielectric material that is deposited over the first contact level dielectric layer71concurrently with deposition of the through-stack dielectric support pillars7P can be present over the first contact level dielectric layer71as a second contact level dielectric layer73. Each of the through-stack dielectric support pillars7P and the second contact level dielectric layer73is an optional structure. As such, the second contact level dielectric layer73may, or may not, be present over the insulating cap layer70and the retro-stepped dielectric material portion65. The first contact level dielectric layer71and the second contact level dielectric layer73are herein collectively referred to as at least one contact level dielectric layer (71,73). In one embodiment, the at least one contact level dielectric layer (71,73) can include both the first and second contact level dielectric layers (71,73), and optionally include any additional via level dielectric layer that can be subsequently formed. In another embodiment, the at least one contact level dielectric layer (71,73) can include only the first contact level dielectric layer71or the second contact level dielectric layer73, and optionally include any additional via level dielectric layer that can be subsequently formed. Alternatively, formation of the first and second contact level dielectric layers (71,73) may be omitted, and at least one via level dielectric layer may be subsequently formed, i.e., after formation of a first source contact via structure.

The second contact level dielectric layer73and the through-stack dielectric support pillars7P can be formed as a single continuous structure of integral construction, i.e., without any material interface therebetween. In another embodiment, the portion of the dielectric material that is deposited over the first contact level dielectric layer71concurrently with deposition of the through-stack dielectric support pillars7P can be removed, for example, by chemical mechanical planarization or a recess etch. In this case, the second contact level dielectric layer73is not present, and the top surface of the first contact level dielectric layer71can be physically exposed.

Referring toFIGS. 12A and 12B, a photoresist layer (not shown) can be applied over the at least one contact level dielectric layer (71,73), and can be lithographically patterned to form openings within areas between the memory blocks. In one embodiment, each opening in the photoresist layer can have a rectangular shape such that a pair of sidewalls of an opening laterally extends along a first horizontal direction.

Backside trenches79can be formed between each neighboring pair of clusters of the memory stack structures55by transferring the pattern of the openings in the photoresist layer through the at least one contact level dielectric layer (71,73), the retro-stepped dielectric material portion65, the alternating stack (32,42), and the optional upper source insulator layer16(if present). The sacrificial matrix layer14can be physically exposed at the bottom of each backside trench79. Clusters of the memory stack structures55can be laterally spaced by the backside trenches79. Each cluster of memory stack structures55in conjunction with the portions of the alternating stack (32,42) that surround the cluster constitutes a memory block. A memory block can be laterally bounded by a pair of backside trenches79.FIG. 12Ais a vertical cross-sectional view along the zigzag vertical plane X-X′ inFIG. 12B.FIG. 12Bis a see-through top-down view in which underlying elements are shown in dotted lines.

FIG. 13Aillustrates a horizontal cross-sectional view of a dotted rectangular region “M” of the exemplary structure ofFIG. 12Balong a horizontal plane including the sacrificial matrix layer14shown inFIG. 12A. The view inFIG. 13Acorrespond to the first (i.e., zigzag) configuration for the array of dielectric pillars20and the array of memory stack structures55.FIGS. 13B and 13Cshow the corresponding horizontal cross-sectional views for the second and third configurations. The direction of the zigzag rows of pillars20inFIGS. 12B and 13Aextend in the bit line direction perpendicular to the trench79elongation direction and the word line direction. However, in another embodiment, the direction of the zigzag rows of pillars20inFIGS. 12B and 13Amay be rotated by 90 degreed to extend perpendicular to the bit line direction, and parallel to the trench79elongation direction and the word line direction.

The array of dielectric pillars20and the array of memory stack structures55collectively constitute a two-dimensional periodic array of multiple instances of a unit cell structure U1that includes multiple memory stack structures55and at least one dielectric pillar20. The array of memory stack structures55can comprise an hexagonal array of memory stack structures55. The ratio of the total number of the multiple memory stack structures55in the unit cell structure U1to the total number of the at least one dielectric pillar20in the unit cell structure U1can be in a range from 2 to 4.

Referring toFIG. 14, backside recesses43can be formed by removing the sacrificial material layers42selective to the insulating layers32and the sacrificial matrix layer14. Specifically, an etchant that selectively etches the second material of the sacrificial material layers42with respect to the first material of the insulating layers32and the sacrificial matrix layer14can be introduced into the backside trenches79, for example, employing an etch process. The backside recesses43are formed in volumes from which the sacrificial material layers42are removed. The removal of the second material of the sacrificial material layers42can be selective to the first material of the insulating layers32, the material of the through-stack dielectric support pillars7P, the material of the retro-stepped dielectric material portion65, the semiconductor material of the substrate semiconductor layer10, the material of the sacrificial matrix layer14, and the material of the outermost layer (such as the outer blocking dielectrics502) of the memory stack structures55. In one embodiment, the sacrificial material layers42can include silicon nitride, the sacrificial matrix layer14can include polysilicon or amorphous silicon, and the materials of the insulating layers32, the through-stack dielectric support pillars7P, and the retro-stepped dielectric material portion65can be selected from silicon oxide and dielectric metal oxides.

Each backside recess43can 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 recess43can be greater than the height of the backside recess43. A plurality of backside recesses43can be formed in the volumes from which the second material of the sacrificial material layers42, the material of the silicon oxide layer501, and the material of the silicon nitride layer502are removed. The memory openings in which the memory stack structures (50,60) are formed are herein referred to as front side recesses or front side cavities in contrast with the backside recesses43. In one embodiment, the device region100comprises an array of monolithic three-dimensional NAND strings having a plurality of device levels disposed above the substrate (e.g., above the substrate semiconductor layer10). In this case, each backside recess43can define a space for receiving a respective word line of the array of monolithic three-dimensional NAND strings.

Each of the plurality of backside recesses43can extend substantially parallel to the top surface of the substrate semiconductor layer10. A backside recess43can be vertically bounded by a top surface of an underlying insulating layer32and a bottom surface of an overlying insulating layer32. In one embodiment, each backside recess43can have a uniform height throughout. In one embodiment, an optional backside blocking dielectric, such as an aluminum oxide dielectric, may be deposited into the backside recesses43in contact with the exposed portions of the memory film50in the backside recesses43. In this embodiment, one or both of the front side blocking dielectric layers502and/or503may be omitted.

Referring toFIG. 15, at least one metallic material can be deposited in the backside recesses to form electrically conductive layers46. Optionally, a backside blocking dielectric layer (not shown) can be formed on the physically exposed surfaces of the memory stack structures55and the insulating layers32prior to deposition of the at least one metallic material. In one embodiment, the at least one metallic material can include a conductive metallic compound layer (such as a conductive metal nitride layer including a conductive metal nitride such as TiN, TaN, or WN, or a conductive metal carbide layer including a conductive metal carbide such as TiC, TaC, or WC). The conductive metallic compound layer can include a metallic material that functions as a barrier material layer, i.e., a material layer that functions as a diffusion barrier for impurity atoms or gases, and/or as an adhesion promoter layer, i.e., a material layer that promotes adhesion of subsequent layers to the insulating layers32(in case a backside blocking dielectric layer is not employed) or to a backside blocking dielectric layer (in case a backside blocking dielectric layer is employed). The conductive metallic compound layer can be deposited by a conformal deposition process such as chemical vapor deposition (CVD) or atomic layer deposition (ALD). The thickness of the conductive metallic compound layer can be in a range from 1 nm to 6 nm, although lesser and greater thicknesses can also be employed.

In one embodiment, the at least one metallic material can further include a metal layer. The metal layer can include an elemental metal or an intermetallic alloy, which can be deposited in the remaining portions of the backside recesses43, over the sidewalls of the backside trench79, and over the top surface of the at least one contact level dielectric layer (71,73). The metal layer can be deposited as a continuous metal layer directly on the surfaces of the conductive metallic compound layer. The metal layer can be deposited by a conformal deposition method such as chemical vapor deposition (CVD) or atomic layer deposition (ALD). Remaining portions of the backside recesses43can be filled with the metal layer. The thickness of the deposited metal, as measured on a sidewall of the backside trench79, can be greater than one half of the maximum height of the remaining portions of the backside recesses43so that the entire volume of each backside recess43is filled with the combination of the optional backside blocking dielectric layer58, the metallic compound layer, and the metal layer.

The metal layer can include a metal such as W, Co, Al, Cu, Ru, Au, Pt, or a combination thereof. The metal layer can be deposited by a chemical vapor deposition (CVD) process or an atomic layer deposition (ALD) process that employs a metal-containing precursor gas. In one embodiment, the metal-containing precursor gas can be free of fluorine, i.e., does not contain fluorine. Chemical vapor deposition or atomic layer deposition of metal employs a metal precursor that can be easily vaporized to leave high-purity metal on a surface without causing surface damage. In one embodiment, an organometallic compound with relatively high vapor pressures and good thermal stability can be employed as the metal precursor gas to deposit metal without requiring hydrogen.

Vertically-extending portions of the deposited metallic material(s) can cover the entirety of the sidewall of the backside trench79. As deposited, a vertically-extending portion of the deposited metallic material(s) can be continuously adjoined to metal portions located within each vertically neighboring pair of backside recesses43, and can be adjoined to a horizontal portion of the metal layer that overlies the at least one contact level dielectric layer (71,73).

An etch process can be performed to remove the at least one metallic material from above the at least one contact level dielectric layer (71,73) and from the sidewalls of the backside trenches79. The etch process can include an isotropic etch step, an anisotropic etch step, or a combination thereof. In an illustrative example, a reactive ion etch employing at least one halide-containing gas such as CHF3, CClF3, CF4, SF6, SiF4, Cl2, NF3can be employed for the etch process. Optionally, oxidants such as O2or O3can be employed in combination with the at least one halide-containing gas. The electrically conductive layers46remain around each backside trench79as discrete layers that are electrically isolated from one another.

Referring toFIG. 16, an insulating spacer74can be formed on the sidewalls of each backside trench79by deposition of a continuous dielectric material layer and an anisotropic etch that removes horizontal portions of the continuous dielectric material layer. Each insulating spacer74includes a dielectric material, which can comprise, for example, silicon oxide, silicon nitride, a dielectric metal oxide, a dielectric metal oxynitride, or a combination thereof. The thickness of each insulating spacer74, as measured at a bottom portion thereof, can be in a range from 1 nm to 50 nm, although lesser and greater thicknesses can also be employed. In one embodiment, the thickness of the insulating spacer74can be in a range from 3 nm to 10 nm.

Each insulating spacer74has an outer sidewall that contacts the sidewalls of the insulating layers32and the electrically conductive layers46, and the sidewalls of the upper source insulating layer16. Further, each insulating spacer74can contact a surface of the sacrificial matrix layer14. Thus, each insulating spacer74can be formed at a periphery of a respective backside trench79and over a portion of the sacrificial matrix layer14and on sidewalls of the upper source insulator layer16.

Referring toFIG. 17, the sacrificial matrix layer14can be removed selective to the array of dielectric pillars20, the lower source insulating layer12, the upper source insulating layer16, the through-stack dielectric pillar structures7P, and the insulating spacers74to form a source line cavity15. The sacrificial matrix layer14is preferably removed after formation of the electrically conductive layers46. In one embodiment, the array of dielectric pillars20, the lower source insulating layer12, the upper source insulating layer16, the through-stack dielectric pillar structures7P, and the insulating spacers74can include various types of silicon oxide, and the sacrificial matrix layer14can include a semiconductor material (such as amorphous silicon, polysilicon or a silicon-germanium alloy), amorphous carbon, or an organic or inorganic polymer. For example, if the sacrificial matrix layer14includes polysilicon, a wet etch employing potassium hydroxide (KOH) may be employed to remove the sacrificial material layer14selective to the array of dielectric pillars20, the lower source insulating layer12, the upper source insulating layer16, the through-stack dielectric pillar structures7P, and the insulating spacers74. Sidewalls of the memory stack structures55can be physically exposed to the source line cavity15. Further, the sidewalls of the dielectric pillars20can be physically exposed to the source line cavity15.

A physically exposed portion of each memory film50can be removed after removal of the sacrificial matrix layer14. The physically exposed portions of the memory films50can be removed, for example, by an isotropic etch such as a wet etch. Thus, sidewalls of the semiconductor channels60become physically exposed at the level of the source line cavity15. A remaining portion of each memory film50that underlies a physically exposed sidewall of a respective semiconductor channel60constitutes a dielectric cap plate58, which underlies the semiconductor channel60and comprises a same set of dielectric materials as the remaining portion of the memory film50located above the source line cavity15. Optionally, an annular source region61may be formed by introducing electrical dopants to a lower portion of each semiconductor channel60by plasma doping or gas phase doping.

In general, a polycrystalline silicon structure (embodied as a source region61) can be provided at a lower end of each semiconductor channel60by deposition of a polysilicon material portion on the annular exposed portion of each semiconductor channel60and/or doping of an annular exposed portion of each semiconductor channel60located at the level of the source line cavity15. Three types of polysilicon (including p+ type polysilicon, undoped polysilicon, and n+ type polysilicon) can be selected for the polycrystalline silicon structure, which can function as a polysilicon source region61. Table 1 provides a summary of erase and read mechanisms for each type of polysilicon that is employed for a source region61.

The p+ polysilicon source region can employ coupling erase while other types of source regions can employ GIDL erase. The benefits of embodiments of the present disclosure include, but are not limited to, prevention of stack collapse employing a marginal device area increase (due to formation of the dielectric pillars20). Removal of the sacrificial matrix layer14does not require use of a reactive ion etch, but an isotropic etch process may be employed to remove the sacrificial matrix layer14.

Referring toFIG. 18, at least one conductive material is deposited to form the source line cavity15by at least one conformal deposition method such as chemical vapor deposition (CVD), atomic layer deposition (ALD), electroplating, and/or electroless plating. In one embodiment, the at least one conductive material can include a metallic liner material such as a conductive metallic nitride or a conductive metallic carbide, and a metallic fill material such as W, Cu, Al, Co, Ru, and alloys thereof. For example, a metallic liner material layer76A including the metallic liner material and a metallic fill material layer76B including the metallic fill material can be deposited to fill the source line trench15and the backside trench79during a same set of deposition processes. Portions of the at least one conductive material above the horizontal plane including the top surface of the at least one contact level dielectric layer (71,73) can be removed by a planarization process. In one embodiment, the planarization process can be a chemical mechanical planarization (CMP) process that employs one of the at least one contact level dielectric layer (71,73) as a stopping layer. A continuous source structure76can be formed within each continuous volume of a source line trench15and at least one backside trench79connected to the source line trench15. In one embodiment, a source line trench15can be connected to a plurality of backside trenches79, and the continuous source structure76can fill the entirety of the continuous volume including the source line trench15and the plurality of backside trenches79. The continuous source structures76can function as a source contact structure, or a combination of a source structure and a source contact structure.

The portion of each continuous source structure76that fills a source line cavity15is herein referred to as a source conductive layer76L. Thus, the source matrix layer14is replaced with the source conductive layer76L which extends in a horizontal direction parallel to the top surface of the substrate (i.e., the substrate semiconductor layer10). The source conductive layer76L can contact sidewalls of each dielectric pillar20in the array of dielectric pillars20. Each portion of the continuous source structure76that fills a backside trench79constitutes a source conductive via structure76V. Each source conductive via structure76Vt extends vertically through the alternating stack (32,46) perpendicular to the top surface of the substrate10. The continuous source structure76is an integral structure without an interface between any of the source conductive via structures76V and the source conductive layer76L. As used herein, an “integral structure” refers to a single continuous structure that is not divided into multiple physically disjoined portions. As used herein, an “interface” refers to a microscopic interface between two elements that is characterized by differences in material composition, presence of a void, or presence of an interfacial material that can be detected by analytic means (such as transmission electron microscopy, scanning electron microscopy, and/or secondary ion mass spectroscopy).

Thus, the continuous source structure76can be formed by simultaneously filling the source line cavity15and the at least one backside trench79with at least one conductive material. Each source conductive via structure76V is formed on an inner sidewall of a respective insulating spacer74. The source line structure76L can be formed directly on the source region61which comprises a deposited polysilicon layer on or a doped region in the exposed sidewall of each semiconductor channel60.

Referring toFIG. 19, a photoresist layer (not shown) can be applied over the topmost layer of the exemplary structure (which can be, for example, the second contact level dielectric layer73), and can be lithographically patterned to form various openings in the device region100, the peripheral device region200, and the contact region300. The locations and the shapes of the various openings are selected to correspond to electrical nodes of the various devices to be electrically contacted by contact via structures. In one embodiment, a single photoresist layer may be employed to pattern all openings that correspond to the contact via cavities to be formed, and all contact via cavities can be simultaneously formed by at least one anisotropic etch process that employs the patterned photoresist layer as an etch mask. In another embodiment, a plurality of photoresist layers may be employed in combination with a plurality of anisotropic etch processes to form different sets of contact via cavities with different patterns of openings in the photoresist layers. The photoresist layer(s) can be removed after a respective anisotropic etch process that transfers the pattern of the openings in the respective photoresist layer through the underlying dielectric material layers and to a top surface of a respective electrically conductive structure.

In an illustrative example, drain contact via cavities can be formed over each memory stack structure55in the device region100such that a top surface of a drain region63is physically exposed at the bottom of each drain contact via cavity. Word line contact via cavities can be formed to the stepped surfaces of the alternating stack (32,46) such that a top surface of an electrically conductive layer46is physically exposed at the bottom of each word line contact via cavity in the contact region300. A device contact via cavity can be formed to each electrical node of the peripheral devices210to be contacted by a contact via structure in the peripheral device region200.

The various via cavities can be filled with at least one conductive material, which can be a combination of an electrically conductive metallic liner material (such as TiN, TaN, or WN) and a metallic fill material (such as W, Cu, or Al). Excess portions of the at least one conductive material can be removed from above the at least one contact level dielectric layer (71,73) by a planarization process, which can include, for example, chemical mechanical planarization (CMP) and/or a recess etch. Drain contact via structures88can be formed on the respective drain regions63. Word line contact via structures84can be formed on the respective electrically conductive layers46. Peripheral device contact via structures8P can be formed on the respective nodes of the peripheral devices210. Additional metal interconnect structures (not shown) and interlayer dielectric material layers (not) shown can be formed over the exemplary structure to provide electrical wiring among the various contact via structures.

The exemplary structure according to embodiments of the present disclosure can include a three-dimensional memory device. The three-dimensional memory device comprises an alternating stack of electrically conductive layers46and insulating layers32located over a substrate10, and an array of memory stack structures55. Each memory stack structure55extends through the alternating stack (32,46), and includes a memory film50and a semiconductor channel60laterally surrounded by the memory film50. The three-dimensional memory device can further include an array of dielectric pillars20located between the alternating stack (32,46) and the substrate10. A continuous source structure76can be provided, which includes a source conductive layer76L that extends horizontally and laterally surrounds each dielectric pillar20in the array of dielectric pillars20. The continuous source structure76can further include a source conductive via structure76V that extends vertically through the alternating stack (32,46). The continuous source structure76can be an integral structure without an interface between the source conductive via structure76V and the source conductive layer76L. The source conductive layer76L may comprise a buried source line or electrode, while the source conductive via structure76V may comprise a source local interconnect.

The three-dimensional memory device can include a lower source insulator layer12located between the substrate10and the source conductive layer76L, an upper source insulator layer16located between the source conductive layer76L and the alternating stack (32,46), and an insulating spacer74laterally surrounding the source conductive via structure76V. In one embodiment, the continuous source structure76can comprise a metallic dielectric liner76A contacting sidewalls of the array of dielectric pillars20and extending above a topmost surface of the alternating stack (32,46), and a conductive fill material portion76B surrounded by the metallic dielectric liner76A.

A stepped surface region can be provided in the contact region300. End portions of the electrically conductive layers46form stepped surfaces in the stepped surface region. The source conductive layer76L can laterally extend farther than any of the electrically conductive layers46. In one embodiment, the continuous source structure76can contact at least one of outer sidewall of each source region61and an annular bottom surface of the memory film50.

In one embodiment, each dielectric pillar20in the array of dielectric pillars20can have a topmost surface located at, or underneath, a first horizontal plane including a bottommost surface of the alternating attack (32,46), and can have a bottommost surface located at, or above, a second horizontal plane including a top surface of the substrate10. In one embodiment, the array of dielectric pillars20can comprise silicon oxide. The dielectric pillars20which terminate below the alternating stack (32,46) are different from the through-stack dielectric support pillars7P which extend through the entire alternating stack (32,46).

In one embodiment, the monolithic three-dimensional memory device comprises a vertical NAND device located over the substrate, and the electrically conductive layers46comprise, or are electrically connected to, a respective word line of the NAND device. In one embodiment, the substrate10comprises a silicon substrate, the vertical NAND device comprises an array of monolithic three-dimensional NAND strings located 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 can contain an integrated circuit comprising a driver circuit for the memory device located thereon.

The array of monolithic three-dimensional NAND strings can comprise a plurality of semiconductor channels60. At least one end portion of each of the plurality of semiconductor channels60extends substantially perpendicular to a top surface of the substrate. The array of monolithic three-dimensional NAND strings can comprise a plurality of charge storage elements. Each charge storage element can be located adjacent to a respective one of the plurality of semiconductor channels60. The array of monolithic three-dimensional NAND strings can 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 comprises 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.

Referring toFIG. 20, a graph illustrating magnitude of stress on memory stack structures55for various configurations of dielectric pillars according to embodiments of the present disclosure. The unit of the vertical axis (for the magnitude of stress) is arbitrary. The case labeled “Ref” refers to a configuration in which the array of dielectric pillars20is not present. The case labeled “Diagonal layout” refers to the third configuration for the array of dielectric pillars20. The case labeled “Zigzag layout” refers to the first configuration for the array of dietetic pillars20.

The array of dielectric pillars20reduces mechanical stress to provide stable structures during the manufacturing process. The simulation data ofFIG. 20was obtained with the assumption of100layers within the alternating stack (32,46) employing a linear repeating boundary condition. Based on a computer simulation of finger tilting and stresses on the dielectric pillars20under imbalanced capillary force, the amplitude of finger tilting, or the risk of finger collapse, can be reduced by 25% with the zigzag layout.

The exemplary structure of the present disclosure employs the continuous source structure76as a bottom connection for the semiconductor channels60in the memory openings49. The array of dielectric pillars20provides structural protection against mechanical stress on the memory stack structures55during formation of the source conductive layer76L.

The array of dielectric pillars20can be employed to prevent collapse of the source line cavity15, and to enable formation of the continuous source structure76that includes the source conductive layer76L. While the presence of the dielectric pillars20may adversely affect the source-side contact resistance, the degradation of the source-side contact resistance is manageable at the densities illustrated inFIGS. 13A-13C.

Although the foregoing refers to particular preferred embodiments, it will be understood that the invention 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 invention. All of the publications, patent applications and patents cited herein are incorporated herein by reference in their entirety.