Patent Publication Number: US-2022238672-A1

Title: Vertical nand flash memory device and method of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2021-0010265, filed on Jan. 25, 2021, and 10-2021-0191651, filed on Dec. 29, 2021, in the Korean Intellectual Property Office. The entire disclosure of each application is incorporated by reference herein. 
     BACKGROUND 
     1. Field 
     The present disclosure relates to a vertical NAND flash memory device and/or a method of manufacturing the same. 
     2. Description of the Related Art 
     As the hard disk has been replaced by a solid state drive (SSD), a NAND flash memory device, which is a nonvolatile memory device, has been widely commercialized. Recently, based on miniaturization and high integration, a vertical NAND flash memory device, in which a plurality of memory cells are stacked in a direction vertical to a substrate, has been developed. 
     In the vertical NAND flash memory device, due to an increase in the number of stacked memory cells and a decrease in the heights of the stacked memory cells, a charge mobility between the memory cells may occur, and thus, the charge retention characteristics of the memory cells may deteriorate. 
     SUMMARY 
     Provided are a vertical NAND flash memory device and/or a method of manufacturing the same. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments of the disclosure. 
     According to an embodiment, a vertical NAND flash memory device may include a substrate; a structure on substrate including a plurality of conductive layers arranged in parallel to an upper surface of the substrate, the structure including a channel hole formed vertical to the substrate and penetrating the plurality of conductive layers; a charge trap layer on an inner wall of the channel hole, the charge trap layer including a base and nanostructures distributed in the base; and a channel layer on the charge trap layer. The nanostructures may include a material having a trap density of about 1×10 19  cm −3  to about 10×10 19  cm −3 , and the base may include a material having a conduction band offset (CBO) of about 0.5 eV to about 3.5 eV with respect to the material included in the nanostructures. 
     In some embodiments, the trap density of the material included in the nanostructures may be about 2×10 19  cm −3  to about 5×10 19  cm −3 . 
     In some embodiments, the material included in the base may have a higher band gap than the material included in the nanostructures. 
     In some embodiments, the CBO of the material included in the base may be about 1.0 eV to about 2.0 eV with respect to the material included in the nanostructures. 
     In some embodiments, the nanostructures may include at least one of SiN, GaN, GaO, HfO, ScO, SrO, ZrO, YO, TaO, BaO, and ZnS. 
     In some embodiments, the base may include at least one of SiO, AlO, MgO, AlN, BN, and GaN. 
     In some embodiments, a combination of the material included in the nanostructures and the material included in the base may include a combination of HfO and SiO, a combination of HfO and AlO, a combination of SiN and AlO, or a combination of ZrO and AlO. 
     A size of the nanostructures may be about 1 nm to about 20 nm. The size of the nanostructures may be about 3 nm to about 5 nm. 
     In some embodiments, a gap between the nanostructures may be about 2 nm to about 25 nm. The gap between the nanostructures may be about 2 nm to about 10 nm. 
     In some embodiments, a ratio of a volume of the nanostructures in the charge trap layer to a volume of the charge trap layer may be about 15% to about 75%. The ratio of the volume of the nanostructures in the charge trap layer to the volume of the charge trap layer may be about 25% to about 60%. 
     In some embodiments, the base may have an amorphous structure, and the nanostructures have a crystalline structure or an amorphous structure. 
     In some embodiments, the charge trap layer may be formed by inducing spinodal decomposition through a heat treatment process on a mixture of the material included in the base and the material included in the nanostructures. 
     In some embodiments, the charge trap layer may have a surface roughness that is equal to or less than about 2 nm root-mean-square (RMS). 
     In some embodiments, the nanostructures may be buried in the base. At least one of the nanostructures may be exposed from the base. 
     In some embodiments, a gap between the conductive layers may be equal to or less than about 30 nm. 
     In some embodiments, the structure on the substrate may include an insulating layer between the conductive layers and the insulating layer may extend in parallel to the substrate. 
     In some embodiments, the vertical NAND flash memory device may further include a barrier dielectric layer between the charge trap layer and the plurality of conductive layers. 
     In some embodiments, the vertical NAND flash memory device may further include a tunneling dielectric layer between the charge trap layer and the plurality of channel layers. 
     In some embodiments, the vertical NAND flash memory device may further include a filling dielectric layer on an inner side of the channel layer and the filling dielectric layer may fill the channel hole. 
     According to an embodiment, a method of manufacturing a vertical NAND flash memory device may include alternately stacking a first layer and a second layer on a substrate; forming a channel hole in the first layer and the second layer, the channel hole penetrating the layer and the second layer in a direction vertical to the substrate; and forming a charge trap layer on an inner wall of the channel hole. The charge trap layer may include a base and nanostructures distributed in the base. The forming the charge trap layer may include forming a mixture material layer on the inner wall of the channel hole and inducing spinodal decomposition by performing a heat treatment process on the mixture material layer. The mixture material layer may include a material included in the base and a material included in the nanostructures. 
     In some embodiments, the material included in the nanostructures may have a trap density of about 1×10 19  cm −3  to about 10×10 19  cm −3  and the material included in the base may have a conduction band offset (CBO) of about 0.5 eV to about 3.5 eV with respect to the material included in the nanostructures. 
     In some embodiments, the trap density of the material included in the nanostructures may be about 2×10 19  cm −3  to about 5×10 19  cm −3 . 
     In some embodiments, the material included in the nanostructures may include at least one of SiN, GaN, GaO, HfO, ScO, SrO, ZrO, YO, TaO, BaO, and ZnS. 
     In some embodiments, the CBO of the material included in the base may be about 1.0 eV to about 2.0 eV with respect to the material included in the nanostructures. 
     In some embodiments, the material included in the base may include at least one of SiO, AlO, MgO, AlN, BN, and GaN. 
     In some embodiments, a combination of the material included in the nanostructures and the material included in the base may include a combination of HfO and SiO, a combination of HfO and AlO, a combination of SiN and AlO, or a combination of ZrO and AlO. 
     In some embodiments, the forming the mixture material layer on the inner wall of the channel hole may be performed by atomic layer deposition (ALD). 
     In some embodiments, the charge trap layer may be formed to have a surface roughness that is equal to or less than about 2 nm root-mean-square (RMS). 
     In some embodiments, a size of the nanostructures may be about 1 nm to about 20 nm. 
     In some embodiments, a gap between the nanostructures may be about 2 nm to about 25 nm. 
     In some embodiments, the ratio of a volume of the nanostructures in the charge trap layer to a volume of the charge trap layer may be about 15% to about 75%. 
     In some embodiments, the nanostructures may be buried in the base, or at least one of the nanostructures may be exposed from the base. 
     In some embodiments, the first layer may include a first insulating material, and the second layer may include a conductive material. 
     In some embodiments, the first layer may include a first insulating material, and the second layer may include a second insulating material. In this case, the method may further include forming a conductive layer on the substrate after removing the second layer. 
     According to an example embodiment, a vertical NAND flash memory device may include a substrate; a plurality of conductive layers and a plurality of insulating layers alternately stacked on an upper surface of the substrate; and a channel structure. The plurality of conductive layers and the plurality of insulating layers may define a channel hole extending in a vertical direction through the plurality of conductive layers and the plurality of insulating layers. The channel structure may be in the channel hole. The channel structure may include a channel layer extending the vertical direction. The channel structure may include a plurality of nanostructures distributed in a base between the channel layer and a sidewall of the channel hole. A material included in the plurality of nanostructures may have a lower band gap compared to a material included in the base. The material included in the nanostructures may have a trap density of about 1×10 19  cm −3  to about 10×10 19  cm −3 . A conduction band offset (CBO) of the material included in the base with respect to the material included in the nanostructures may be about 0.5 eV to about 3.5 eV. 
     In some embodiments, the base may have an amorphous structure and the plurality of nanostructures may have a crystalline structure or an amorphous structure. The plurality of nanostructures may have at least one of a spherical shape, an oval shape, and a rod shape. 
     In some embodiments, the material included in the plurality of nanostructures may include at least one of SiN, GaN, GaO, HfO, ScO, SrO, ZrO, YO, TaO, BaO, and ZnS, and the material included in the base may include at least one of SiO, AlO, MgO, AlN, BN, and GaN. 
     In some embodiments, the channel structure may include at least one of: a barrier dielectric layer between the channel layer and plurality of nanostructures distributed in the base; and a tunneling dielectric layer between the channel layer and plurality of nanostructures distributed in the base. 
     In some embodiments, the channel structure may include a charge trap layer containing the plurality of nanostructures distributed in the base. A surface roughness of the charge trap layer may be equal to or less than about 2 nm RMS. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  schematically illustrates a vertical NAND flash memory device according to an example embodiment; 
         FIG. 2  is a cross-sectional view of the vertical NAND flash memory device taken along line II-II′ of  FIG. 1 ; 
         FIGS. 3 through 10  are views for describing a method of manufacturing a vertical NAND flash memory device, according to an example embodiment; 
         FIG. 11  is a cross-sectional view of a vertical NAND flash memory device according to another example embodiment; 
         FIG. 12  is a cross-sectional view of a vertical NAND flash memory device according to another example embodiment; 
         FIG. 13  is a cross-sectional view of a vertical NAND flash memory device according to another example embodiment; and 
         FIG. 14  is a block diagram of an electronic device according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. In this regard, the present embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain aspects. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. For example, “at least one of A, B, and C,” “at least one of A, B, or C,” “one of A, B, C, or a combination thereof,” and “one of A, B, C, and a combination thereof,” respectively, may be construed as covering any one of the following combinations: A; B; C; A and B; A and C; B and C; and A, B, and C.” 
     Hereinafter, example embodiments will be described in detail by referring to the accompanying drawings. In the drawings, the same reference numerals denote the same elements and sizes of elements may be exaggerated for clarity and convenience of explanation. Also, the embodiments described hereinafter are only examples, and various modifications may be made based on the embodiments. 
     Hereinafter, it will be understood that when an element is referred to as being “on” or “above” another element, the element can be directly over or under the other element and directly on the left or on the right of the other element, or intervening elements may also be present therebetween. As used herein, the singular terms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that when a part “includes” or “comprises” an element, unless otherwise defined, the part may further include other elements, not excluding the other elements. 
     The term “the” and other equivalent determiners may correspond to a singular referent or a plural referent. Operations included in a method may be performed in an appropriate order, unless the operations included in the method are described to be performed in an apparent order, or unless the operations included in the method are described to be performed otherwise. 
     Also, the terms such as “. . . unit,” “module,” or the like used in the specification indicate a unit, which processes at least one function or motion, and the unit may be implemented by hardware or software, or by a combination of hardware and software. 
     When the terms “about” or “substantially” are used in this specification in connection with a numerical value, it is intended that the associated numerical value includes a manufacturing or operational tolerance (e.g., ±10%) around the stated numerical value. Moreover, when the words “generally” and “substantially” are used in connection with geometric shapes, it is intended that precision of the geometric shape is not required but that latitude for the shape is within the scope of the disclosure. Further, regardless of whether numerical values or shapes are modified as “about” or “substantially,” it will be understood that these values and shapes should be construed as including a manufacturing or operational tolerance (e.g., ±10%) around the stated numerical values or shapes. 
     The connecting lines, or connectors shown in the various figures presented are intended to represent example functional relationships and/or physical or logical couplings between the various elements. It should be noted that many alternative or additional functional relationships, physical connections or logical connections may be present in a practical device. 
     All examples and example expressions are only used to describe the disclosure in detail, and unless it is defined by the scope of the claims, these examples and example expressions do not limit the scope of the disclosure. 
       FIG. 1  schematically illustrates a vertical NAND flash memory device  100  according to an example embodiment. 
     Referring to  FIG. 1 , the vertical NAND flash memory device  100  may include a substrate  110  and a plurality of memory cells MCs stacked in a direction vertical to a surface of the substrate  110  (that is, a z-axis direction in  FIG. 1 ). The plurality of memory cells MCs may include insulating layers  121  and conductive layers  130  alternately stacked in the direction vertical to the surface of the substrate  110 . Also, a plurality of channel holes  190  may be formed through the insulating layers  121  and the conductive layers  130  in a direction vertical to the substrate  110 . The insulating layer  121  and conductive layer  130  alternately stacked may be referred to as a stacked structure and the stacked structure may define the channel holes  190 .  FIG. 1  illustrates an example in which the channel holes  190  are arranged to have a shape of a one-dimensional (1D) array. However, the channel holes  190  are not limited thereto and may be arranged to have a shape of a two-dimensional (2D) array. 
       FIG. 2  is a cross-sectional view of the vertical NAND flash memory device  100  of  FIG. 1 , taken along line II-II′ of  FIG. 1 . For convenience,  FIG. 2  illustrates a cross-section of one of the plurality of memory cells MCs of the vertical NAND flash memory device  100 , which will be likewise applied to the drawings to be described hereinafter. 
     Referring to  FIG. 2 , the insulating layer  121  and the conductive layer  130  may be alternately stacked on the substrate  110  in a direction vertical to a surface (that is, an x-y plane of  FIG. 2 ) of the substrate  110 . Here, each of the insulating layer  121  and the conductive layer  130  may be provided to extend in a direction parallel to the surface of the substrate. 
     The substrate  110  may include various materials. For example, the substrate  110  may include a monocrystalline silicon substrate, a compound semiconductor substrate, or a silicon on insulator (SOI) substrate, but is not limited thereto. Also, the substrate  110  may further include, for example, an impurity area that is doped with impurities, an electronic device such as a transistor, etc., or a peripheral circuit, etc. configured to select and control memory cells for storing data. 
     The conductive layer  130  may be a control gate, and a word line (not shown) may be electrically connected to the conductive layer  130 . The conductive layer  130  may include, for example, a metal material having excellent electrical conductivity such as Au, silicon doped with impurities, or the like. However, it is only an example, and the conductive layer  130  may include other various materials. 
     The insulating layer  121  may function as a spacer layer for the insulations between the conductive layers  130 . The insulating layer  121  may include, for example, silicon oxide (SiO), silicon nitride (SiN), etc., but is not limited thereto. 
     The channel hole  190  may be formed through the insulating layer  121  and the conductive layer  130 . Here, the channel hole  190  may be formed to extend in a direction vertical to the surface of the substrate  110  (that is, a z-axis direction of  FIG. 2 ). The channel hole  190  may be formed to have a circular cross-section. 
     A barrier dielectric layer  140 , a charge trap layer  150 , and a tunneling dielectric layer  160  may be sequentially provided on an inner wall of the channel hole  190 . Here, when a certain voltage is applied to the conductive layer  130 , which is a control gate, a charge flowing between a source and a drain of a channel layer  170 , which is to be described below, may pass through the tunneling dielectric layer  160  so as to be trapped in the charge trap layer  150 , and thus, information may be stored. 
     Each of the barrier dielectric layer  140 , the charge trap layer  150 , and the tunneling dielectric layer  160  may be provided to extend in the direction vertical to the surface of the substrate  110 . Each of the barrier dielectric layer  140 , the charge trap layer  150 , and the tunneling dielectric layer  160  may be provided to have a cylindrical shape. 
     The barrier dielectric layer  140  may be provided at the inner wall of the channel hole  190  to contact the insulating layer  121  and the conductive layer  130 . The barrier dielectric layer  140  may include, for example, SiO or metal oxide, but is not limited thereto. 
     The charge trap layer  150  may be provided on an inner side of the barrier dielectric layer  140 . The charge trap layer  150  may include a base  151  and nanostructures  152  distributed in the base  151 . 
     Here, the nanostructures  152  may include a material having the excellent charge trap characteristics, and the base  151  may include a material having the excellent blocking characteristics with respect to a charge mobility. The nanostructures  152  may have a crystalline structure or an amorphous structure, and the base  151  may have an amorphous structure. 
     The material included in the nanostructures  152  may have a greater trap density than the material included in the base  151 . In detail, the material included in the nanostructures  152  may have a trap density of 1×10 19  cm −3  to 10×10 19  cm −3 . For example, the material included in the nanostructures  152  may have a trap density of 1×10 19  cm −3  to 6×10 19  cm −3 . For example, the material included in the nanostructures  152  may have a trap density of 2×10 19  cm −3  to 5×110 19  cm −3 . 
     The material included in the base  151  may have a greater band gap than the material included in the nanostructures  152 . Also, the material included in the base  151  may have a conduction band offset (CBO) having a value that is equal to or greater than a desired and/or alternatively predetermined value with respect to the material included in the nanostructures  152 . Here, the CBO denotes a difference between an energy level of a conduction band of the material included in the nanostructures  152  and an energy level of a conduction band of the material included in the base  151 . 
     The material included in the base  151  may have a CBO of 0.5 eV to 3.5 eV with respect to the material included in the nanostructures  152 . For example, the material included in the base  151  may have a CBO of 1.0 eV to 2.0 eV with respect to the material included in the nanostructures  152 . For example, the material included in the base  151  may have a CBO of 1.0 eV to 1.5 eV with respect to the material included in the nanostructures  152 . 
     The nanostructures  152  may include or be formed of, for example, at least one of SiN, GaN, GaO, HfO, ScO, SrO, ZrO, YO, TaO, BaO, and ZnS. However, it is not limited thereto. 
     The base  151  may include, for example, at least one of SiO, AlO, MgO, AlN, BN, and GaN. However, it is not limited thereto. 
     A combination of the materials of the nanostructures  152  and the base  151  may include, for example, a combination of HfO and SiO, a combination of HfO and AlO, a combination of SiN and AlO, or a combination of ZrO and AlO. However, it is only an example. 
     The nanostructures  152  may have, for example, a spherical shape, an oval shape, a disk shape, or a rod shape. The nanostructures  152  may have a desired and/or alternatively predetermined nano-level size. Here, the size of the nanostructures  152  may be defined to have the following meaning according to a shape of the nanostructures  152 . When the nanostructures  152  have a spherical shape or an oval shape, the size of the nanostructures  152  may denote an average diameter of the nanostructures  152 . When the nanostructures  152  have a disk shape, the size of the nanostructures  152  may denote a thickness of the nanostructures  152 . Also, when the nanostructures  152  have a rod shape, the size of the nanostructures  152  may denote a sectional diameter of the nanostructures  152 . 
     According to the present embodiment, the nanostructures  152  may have a size of about 1 nm to about 20 nm. For example, the nanostructures  152  may have a size of 2 nm to 10 nm. For example, the nanostructures  152  may have a size of 3 nm to 5 nm. 
     The nanostructures  152  may be arranged in the base  151  to have a desired and/or alternatively predetermined gap between each other. Here, the gap between the nanostructures  152  may be defined to be a distance between centers of adjacent nanostructures  152 . According to the present embodiment, the gap between the nanostructures  152  may be 2 nm to 25 nm. For example, the gap between the nanostructures  152  may be 2 nm to 15 nm. For example, the gap between the nanostructures  152  may be 2 nm to 10 nm. A thickness of a base material between the nanostructures  152  may be about 1 nm to about 5 nm. 
     A ratio (that is, a volume ratio) of the nanostructures  152  in the charge trap layer  150  may be about 15% to about 75%. For example, the ratio of the nanostructures  152  in the charge trap layer  150  may be about 25% to about 65%. 
     The size, the distribution, etc. of the nanostructures  152  described above may be measured, for example, by a transmission electron microscopy (TEM) analysis. In addition, the size of the nanostructures  152  may be measured, for example, by an X-ray diffraction (XRD) analysis or a photoluminescence (PL) analysis. 
     The charge trap layer  150  including the base  151  and the nanostructures  152  distributed in the base  151  may be formed by forming a mixture of the material included in the base  151  and the material included in the nanostructures  152  via atomic layer deposition (ALD) and inducing spinodal decomposition by performing heat treatment on the mixture, as described below. Here, the spinodal decomposition may occur when formation energy according to the mixing of the material included in the base  151  and the material included in the nanostructures  152  at a desired and/or alternatively predetermined temperature, that is, a Gibbs free-energy change (ΔG), is greater than 0. The shape and the size of the nanostructures  152  may be adjusted according to a temperature of the heat treatment on the mixture of the material included in the base  151  and the material included in the nanostructures  152 . 
     As described above, the charge trap layer  150  may be formed via the ALD and the spinodal decomposition, and thus, the charge trap layer  150  may have a relatively more uniform surface. For example, the charge trap layer  150  may be formed to have a surface roughness that is equal to or less than about 2 nm root-mean-square (RMS). As a specific example, the charge trap layer  150  may be formed to have a surface roughness that is equal to or less than about 1 nm RMS. 
     Each nanostructure  152  may be formed to be entirely buried in the base  151 . However, it is not limited thereto, and at least one of the nanostructures  152  may be exposed from the base  151 . In this case, the exposed one of the nanostructures  152  may form an interface between the charge trap layer  150  and the barrier dielectric layer  140  or an interface between the charge trap layer  150  and the tunneling dielectric layer  160 . 
     The tunneling dielectric layer  160  may be provided on the charge trap layer  150 . The tunneling dielectric layer  160  may indicate a layer in which charge tunneling occurs and may include, for example, SiO or metal oxide, but is not limited thereto. 
     The channel layer  170 , which includes a semiconductor material, may be provided on the tunneling dielectric layer  160 . The channel layer  170  may be provided to have a cylindrical shape. Also, on the channel layer  170 , a filling dielectric layer  180  may be provided to fill the channel hole  190 . The filling dielectric layer  180  may include, for example, SiO or air, but is not limited thereto. 
     In the vertical NAND flash memory device  100  according to the present embodiment, the charge trap layer  150  vertically formed on the substrate  110  may include the base  151  including the material having the excellent blocking characteristics for the charge mobility and the nanostructures  152  distributed in the base  151  and including the material having the excellent charge trap characteristics, and thus, spreading of charges may be prevented to improve the charge retention characteristics. Because the charge retention characteristics are improved as described above, a gap between the conductive layers  130  may be reduced, and thus, the vertical NAND flash memory device  100  may have high integration. For example, the gap between the conductive layers  130  may be equal to or less than about 30 nm. For example, the gap between the conductive layers  130  may be 1 nm to 20 nm. However, it is not limited thereto. 
     Also, the charge trap layer  150  may be formed by ALD and spinodal decomposition, and thus, the surface of the charge trap layer  150  may be formed to be relatively more uniform to improve the device uniformity. 
     When nanoparticles and a base material included in a charge trap layer are separately formed according to a previous nucleation and growth method, the charge trap layer may have a relatively great surface roughness corresponding to about a half of the size of the nanoparticles, for example, about 2 nm to 3 nm RMS. In this case, a tunneling dielectric layer and a channel layer formed on the charge trap layer may have increased non-uniformity, and thus, the device uniformity may deteriorate. However, according to the present embodiment, because the charge trap layer  150  may be formed via ALD and spinodal decomposition, the charge trap layer  150  may have a relatively more uniform surface compared to the related art, thereby improving the device uniformity. For example, the charge trap layer  150  may be formed to have a surface roughness that is equal to or less than about 2 nm RMS. As a specific example, the charge trap layer  150  may be formed to have a surface roughness that is equal to or less than about 1 nm RMS. 
       FIGS. 3 through 10  are views for describing a method of manufacturing a vertical NAND flash memory device, according to an example embodiment. 
     Referring to  FIG. 3 , a substrate  210  may be prepared. The substrate  210  may include various materials. For example, the substrate  210  may include a monocrystalline silicon substrate, a compound semiconductor substrate, or an SOI substrate, but is not limited thereto. Also, the substrate  210  may further include an impurity area doped with impurities, an electronic device such as a transistor, etc., or a peripheral circuit, etc. configured to select and control memory cells for storing data. 
     Next, a first layer  221  and a second layer  231  may be alternately stacked on the substrate  210 . The first layer  221  and the second layer  231  may be alternately stacked in a direction vertical to a surface of the substrate  210 . Also, each of the first layer  221  and the second layer  231  may be formed to extend in a direction parallel to the surface of the substrate  210 . 
     The first layer  221  may be an insulating layer. The first layer  221  may include, for example, SiO, SiN, etc., but is not limited thereto. Also, the second layer  231  may be, for example, a conductive layer. In this case, the second layer  231  may include, for example, a metal material having excellent electrical conductivity such as Au, silicon doped with impurities, or the like, but is not limited thereto. As described below, the second layer  231  may not be a conductive layer. Rather, the second layer  231  may be an insulating layer including a different insulating material from the insulating layer corresponding to the first layer  221 . 
     The first layer  221  and the second layer  231  may be formed by various deposition methods, for example, chemical vapor deposition (CVD), ALD, physical vapor deposition (PVD), etc. 
     Referring to  FIG. 4 , a channel hole  290  may be formed through the first layer  221  and the second layer  231 . Here, the channel hole  290  may be formed to extend in a direction vertical to the surface of the substrate  210 . The channel hole  290  may be formed to have a circular cross-section. The channel hole  290  may be formed by anisotropic-etching the first layer  221  and the second layer  231 . 
     Referring to  FIG. 5 , a barrier dielectric layer  240  may be formed on an inner wall of the channel hole  290 . The barrier dielectric layer  240  may be formed to extend in the direction vertical to the surface of the substrate  210 . Here, the barrier dielectric layer  240  may be formed on the inner wall of the channel hole  290  to contact the first layer  221  and the second layer  231 . The barrier dielectric layer  240  may be formed to have a cylindrical shape. The barrier dielectric layer  240  may be formed by depositing, for example, SiO, metal oxide, etc. on the inner wall of the channel layer  290  via ALD. 
     Next, a mixture material layer  250 ′ may be formed on the barrier dielectric layer  240 . Here, the mixture material layer  250 ′ may indicate a layer including a mixture of a material included in a base ( 251  of  FIG. 8 ) and a material included in nanostructures ( 252  of  FIG. 8 ) of a charge trap layer ( 250  of  FIG. 8 ). 
     The material included in the nanostructures  252  may have a trap density of 1×10 19  cm −3  to 10×10 19  cm −3 . For example, the material included in the nanostructures  252  may have a trap density of 2×10 19  cm −3  to 5×10 19  cm −3 . The nanostructures  252  may include, for example, at least one of SiN, GaN, GaO, HfO, ScO, SrO, ZrO, YO, TaO, BaO, and ZnS. However, it is not limited thereto. 
     The material included in the base  251  may have a CBO of 0.5 eV to 3.5 eV with respect to the material included in the nanostructures  252 . For example, the material included in the base  251  may have a CBO of 1.0 eV to 2.0 eV with respect to the material included in the nanostructures  252 . For example, the material included in the base  251  may have a CBO of 1.0 eV to 1.5 eV with respect to the material included in the nanostructures  252 . The base  251  may include, for example, at least one of SiO, AlO, MgO, AlN, BN, and GaN. However, it is not limited thereto. 
     To make spinal decomposition occur as described below, formation energy according to the mixing of the material included in the base  151  and the material included in the nanostructures  152 , that is, a Gibbs free-energy change (ΔG), may have to be greater than 0. A combination of the materials of the nanostructures  252  and the base  251  that satisfies this condition may include, for example, a combination of HfO and SiO, a combination of HfO and AlO, a combination of SiN and AlO, or a combination of ZrO and AlO. However, it is only an example. 
     For example, when the nanostructures  252  include SiN, and the base  251  includes AlO, a mixture of the material included in the base  251  and the material included in the nanostructures  252  may include Al x Si y O. 
     The mixture material layer  250 ′ may be formed by depositing the mixture of the material included in the base  251  and the material included in the nanostructures  252  on the barrier dielectric layer  240  via ALD. Here, the mixture material layer  250 ′ may have a metal-stable mixed phase. 
     The mixture material layer  250 ′ may be formed on the barrier dielectric layer  240  by ALD, and thus, the mixture material layer  250 ′ may have a uniform surface. For example, the mixture material layer  250 ′ may be formed to have a surface roughness that is equal to or less than about 2 nm RMS. As a more specific example, the mixture material layer  250 ′ may be formed to have a surface roughness that is equal to or less than 1 nm RMS. 
     Referring to  FIG. 6 , a tunneling dielectric layer  260  may be formed on the mixture material layer  250 ′. The tunneling dielectric layer  260  may be formed by depositing, for example, SiO, metal oxide, etc., on the mixture material layer  250 ′ via ALD. Next, a channel layer  270  may be formed on the tunneling dielectric layer  260 . The channel layer  270  may be formed by depositing a semiconductor material on the tunneling dielectric layer  260  via ALD. Also, a filling dielectric layer  280  may be formed on the channel layer  270 . The filling dielectric layer  280  may be formed by depositing, for example, SiO, to fill the channel layer  290 , via ALD. Alternatively, the filling dielectric layer  280  may include air. 
     Referring to  FIG. 7 , a heat treatment process may be performed on a structure illustrated in  FIG. 6  at desired and/or alternatively predetermined temperature. Via the heat treatment process, the spinodal decomposition may occur in the mixture material layer  250 ′, to form the base  251  and the nanostructures  252 . Here, the nanostructures  252  may be formed to be distributed in the base  251 . Accordingly, as illustrated in  FIG. 8 , the mixture material layer  250 ′ may be transformed into the charge trap layer  250  including the base  251  and the nanostructures  252  distributed in the base  251 . 
     For example, the mixture material layer  250 ′ including Al x Si y O may be formed on the barrier dielectric layer  240  via ALD at a temperature of about 400° C., and then, a heat treatment process may be performed on the mixture material layer  250 ′ at a temperature of about 700° C. Then, the spinodal decomposition may occur, and thus, the base  251  including AlO and the nanostructures  252  including SiN and distributed in the base  251  may be formed. However, it is only an example. 
     The nanostructures  252  distributed in the base  251  may have, for example, a spherical shape, an oval shape, a disk shape, or a rod shape. As described above, a size of the nanostructures  252  may be defined to have the following meaning according to a shape of the nanostructures  252 . When the nanostructures  252  have a spherical shape or an oval shape, the size of the nanostructures  252  may denote an average diameter of the nanostructures  252 , when the nanostructures  252  have a disk shape, the size of the nanostructures  252  may denote a thickness of the nanostructures  252 , and when the nanostructures  252  have a rod shape, the size of the nanostructures  252  may denote a sectional diameter of the nanostructures  252 . The nanostructures  252  may have a size of 1 nm to 20 nm. For example, the nanostructures  252  may have a size of 3 nm to 5 nm. The shape and the size of the nanostructures  252  may be adjusted according to a temperature of heat treatment on the mixture of the material included in the base  251  and the material included in the nanostructures  252 . 
     The nanostructures  252  may be arranged in the base  251  to have a desired and/or alternatively predetermined gap between each other. Here, the gap between the nanostructures  252  may be defined to be a distance between centers of adjacent nanostructures  252 . The gap between the nanostructures  252  may be 2 nm to 25 nm. For example, the gap between the nanostructures  252  may be 2 nm to 10 nm. A thickness of a base material between the nanostructures  252  may be about 1 nm to about 5 nm. 
     A ratio of the nanostructures  252  in the charge trap layer  250  may be about 15% to about 75%. For example, the ratio of the nanostructures  252  in the charge trap layer  250  may be about 25% to about 65%. As described above, the size and the distribution, etc. of the nanostructures  252  may be measured, for example, by a TEM analysis, an XRD analysis, or a PL analysis. However, it is not limited thereto. 
     In the charge trap layer  250 , all of the nanostructures  252  may be formed to be buried in the base  251 , or at least one of the nanostructures  252  may be exposed from the base  251 . The base  251  may have an amorphous structure, and the nanostructures  252  may have a crystalline structure or an amorphous structure. 
     Because the charge trap layer  250  may be formed by letting the spinodal decomposition occur in the mixture material layer  250 ′ formed by ALD, the charge trap layer  250  may have approximately the same surface roughness as the mixture material layer  250 ′. Accordingly, the charge trap layer  250  may have a uniform surface. For example, the charge trap layer  250  may have a surface roughness that is equal to or less than about 2 nm RMS (more specifically, equal to or less than 1 m RMS). 
     Above, a case in which the heat treatment process for the spinodal decomposition is performed on the structure illustrated in  FIG. 6  is described. However, the disclosure is not limited thereto. The heat treatment process for the spinodal decomposition may be performed in any order of operations after the mixture material layer  250 ′ is formed on the barrier dielectric layer  240  via ALD. 
     Above, a case in which the second layer  231  illustrated in  FIG. 3  is a conductive layer is described. Alternatively, the second layer  231  in  FIG. 3  may not be a conductive layer and may be an insulating layer including a different insulating material from an insulating material of the first layer  221 . In this case, after selectively removing the second layer  231  as illustrated in  FIG. 9 , a conductive layer  232  may be formed at an area from which the second layer  231  is removed as illustrated in  FIG. 10 . 
       FIG. 11  is a cross-sectional view of a vertical NAND flash memory device  300  according to another example embodiment. Hereinafter, aspects that are different from the aspects of the embodiments described above are mainly described. 
     Referring to  FIG. 11 , a charge trap layer  350  may include a base  351  and nanostructures  352  having a rod shape and distributed in the base  351 . The base  351  and the nanostructures  352  may be formed by letting the spinodal decomposition occur in a mixture of a material included in the base  351  and a material included in the nanostructures  352  as described above. 
     Both ends of the nanostructures  352  may be exposed from the base  351 . In this case, one exposed end of the nanostructures  352  may form an interface between the charge trap layer  350  and the barrier dielectric layer  140 , and the other exposed end of the nanostructures  352  may form an interface between the charge trap layer  350  and the tunneling dielectric layer  160 . 
     In  FIG. 6 , when a nucleation promotor, etc. are formed on a surface of the barrier dielectric layer  140  and a surface of the tunneling dielectric layer  160 , the surfaces contacting the mixture material layer  250 ′, nucleation and growth may begin on the surface of the barrier dielectric layer  140  and the surface of the tunneling dielectric layer  160  during the spinodal decomposition, and thus, the nanostructures  352  having the rod shape as illustrated in  FIG. 11  may be formed. 
       FIG. 12  is a cross-sectional view of a vertical NAND flash memory device  400  according to another example embodiment. 
     Referring to  FIG. 12 , a charge trap layer  450  may include a base  451  and nanostructures  452  having a rod shape and distributed in the base  451 . Here, an end of the nanostructures  452  may be exposed from the base  451 , and the other end of the nanostructures  452  may be buried in the base  451 . In this case, the exposed end of the nanostructures  452  may form an interface between the charge trap layer  450  and the barrier dielectric layer  140 . 
     In  FIG. 6 , when a nucleation promotor, etc. are formed on a surface of the barrier dielectric layer  140 , the surfaces contacting the mixture material layer  250 ′, nucleation and growth may begin on the surface of the barrier dielectric layer  140  during the spinodal decomposition, and thus, the nanostructures  452  having the rod shape as illustrated in  FIG. 12  may be formed. 
       FIG. 13  is a cross-sectional view of a vertical NAND flash memory device  500  according to another example embodiment. 
     Referring to  FIG. 13 , a charge trap layer  550  may include a base  551  and nanostructures  552  having a rod shape and distributed in the base  551 . Here, an end of the nanostructures  552  may be exposed from the base  551 , and the other end of the nanostructures  552  may be buried in the base  551 . In this case, the exposed end of the nanostructures  552  may form an interface between the charge trap layer  550  and the tunneling dielectric layer  160 . 
     In  FIG. 6 , when a nucleation promotor, etc. are formed on a surface of the tunneling dielectric layer  160 , the surface contacting the mixture material layer  250 ′, nucleation and growth may begin on the surface of the tunneling dielectric layer  160  during the spinodal decomposition, and thus, the nanostructures  552  having the rod shape as illustrated in  FIG. 13  may be formed. 
     Above, the cases are described in which at least one of both ends of the nanostructures  352 ,  452 , and  552  having the rod shape is exposed from the bases  351 ,  451 , and  551 , respectively. However, the disclosure is not limited thereto, and the nanostructures  352 ,  452 , and  552  having the rod shape may be buried in the bases  351 ,  451 , and  551 , respectively. 
       FIG. 14  is a block diagram of an electronic device according to an embodiment. 
     Referring to  FIG. 14 , an electronic device  600  may include a processor  620 , a memory  630 , and a device  640  (e.g., image sensor and/or display device) that are electrically coupled together via a bus  610 . The device  640  may be an image sensor (e.g., a device including CMOS image sensor circuit) and/or a display device (e.g., a LED display, a holographic display). The memory  630 , which may be a non-transitory computer readable medium, may store a program of instructions and/or other information. The memory  630  may be a nonvolatile memory, such as a vertical NAND flash memory device according to one of the embodiments discussed above. The processor  620  may execute the stored program of instructions to perform one or more functions. For example, when the device  640  includes a sensor such as an image sensor, the processor  620  may be configured to process electrical signals generated by the device  640 . Additionally, when the device includes a display device, the processor  620  may be configured to generate an output (e.g., an image to be displayed on a display) based on such processing and/or information received from an external host (not shown). 
     As described above, in the vertical NAND flash memory device according to an example embodiment, the charge trap layer vertically formed on the substrate may include the base including the material having the excellent blocking characteristics for a charge mobility and the nanostructures distributed in the base and including the material having the excellent charge trap characteristics, and thus, spreading of charges may be limited and/or prevented to improve the charge retention characteristics. Also, the charge trap layer may be formed by ALD and spinodal decomposition, and thus, the surface of the charge trap layer may be formed to be relatively more uniform to improve the device uniformity. The NAND flash memory device may be applied in an electronic device including a processor and/or other components. Embodiments are described above. However, these are examples, and one of ordinary skill in the art may achieve various modifications based on the embodiments. 
     One or more of the elements disclosed above may include or be implemented in processing circuitry such as hardware including logic circuits; a hardware/software combination such as a processor executing software; or a combination thereof. For example, the processing circuitry more specifically may include, but is not limited to, a central processing unit (CPU) , an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, application-specific integrated circuit (ASIC), etc. 
     It should be understood that embodiments described herein should be considered in a descriptive sense only and not for purposes of limitation. Descriptions of features or aspects within each embodiment should typically be considered as available for other similar features or aspects in other embodiments. While one or more embodiments have been described with reference to the figures, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope as defined by the following claims.