Patent Publication Number: US-2023140959-A1

Title: Memory devices having cell over periphery structure, memory packages including the same, and methods of manufacturing the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. application Ser. No. 17/026,637, filed on Sep. 21, 2020, which claims priority to and the benefit of, under 35 U.S.C. § 119, Korean Patent Application No. 10-2019-0175917, filed on Dec. 27, 2019 in the Korean Intellectual Property Office (KIPO), the contents of each of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     Example embodiments relate generally to semiconductor integrated circuits, and more particularly to memory devices having cell over periphery (COP) structure, memory packages including the memory devices, and methods of manufacturing the memory devices. 
     2. Description of the Related Art 
     Vertical memory devices, also known as three-dimensional (3D) memory devices, are memory devices that include a plurality of memory cells stacked repeatedly on a surface of a substrate. These memory devices are able to have a very high storage capacity within a very small structure. In some example embodiments, in a vertical memory device, a channel may protrude or may be extended vertically from the surface of the substrate, and gate lines and insulation layers surrounding the vertical channel may be repeatedly stacked. 
     However, the reduction of the size of the vertical memory device is limited because the memory device should still include a peripheral circuit for driving a memory cell array and a wiring structure to electrically connect the memory cell array with the peripheral circuit. 
     SUMMARY 
     Some example embodiments of the present disclosure provide memory devices configured to reduce manufacturing cost and preventing performance degradation while reducing size. Such memory devices may have a high degree of integration and excellent electrical characteristics. 
     Some example embodiments of the present disclosure provide memory packages including memory devices configured to reduce manufacturing cost and preventing performance degradation while reducing size. 
     Some example embodiments of the present disclosure provide methods of manufacturing memory devices configured to reduce manufacturing cost and preventing performance degradation while reducing size. 
     According to some example embodiments, a memory device may include a first semiconductor layer and a second semiconductor layer. The first semiconductor layer may include a plurality of wordlines extending in a first direction and a plurality of bitlines extending in a second direction that is perpendicular to the first direction. The first semiconductor layer may further include an upper substrate, and a memory cell array on the upper substrate. The memory cell array may include a plurality of memory blocks extending sequentially in a serial pattern along the second direction. The second semiconductor layer may be beneath the first semiconductor layer in a third direction. The third direction may be perpendicular to both the first direction and the second direction. The second semiconductor layer may include a lower substrate, and an address decoder on the lower substrate and configured to control the memory cell array. Each memory block of the plurality of memory blocks may include a core region including a plurality of memory cells, a first extension region adjacent to a first side of the core region and a second extension region adjacent to a second side of the core region opposite the first side. The first extension region may include a plurality of wordline contacts configured to establish an electrical connection with the plurality of wordlines. The second extension region may include an insulating mold structure. The second extension region may include a plurality of step zones having a step shape in a cross-sectional view, and at least one flat zone having a flat shape in the cross-sectional view. The memory device may further include a plurality of through-hole vias penetrating the insulating mold structure in the at least one flat zone. The plurality of wordlines and the address decoder may be electrically connected to each other by at least the plurality of through-hole vias. 
     According to some example embodiments, a memory package may include a base substrate, and a plurality of memory chips stacked on the base substrate. Each memory chip of the plurality of memory chips may include a first semiconductor layer and a second semiconductor layer under the first semiconductor layer in a third direction, the third direction perpendicular to both the first direction and the second direction. The first semiconductor layer may include a plurality of wordlines extending in a first direction and a plurality of bitlines extending in a second direction crossing the first direction. The first semiconductor layer may further include an upper substrate, and a memory cell array on the upper substrate. The memory cell array may include a plurality of memory blocks extending sequentially in a serial pattern along the second direction. The second semiconductor layer may include a lower substrate, and an address decoder on the lower substrate and configured to control the memory cell array. Each memory block of the plurality of memory blocks may include a core region including a plurality of memory cells; a first extension region adjacent to a first side of the core region and a second extension region adjacent to a second side of the core region opposite the first side. The first extension region may include a plurality of wordline contacts configured to establish an electrical connection with the plurality of wordlines. The second extension region may include an insulating mold structure. The second extension region may include a plurality of step zones having a step shape in a cross-sectional view, and at least one flat zone having a flat shape in the cross-sectional view. The memory package may further include a plurality of through-hole vias penetrating the insulating mold structure in the at least one flat zone. The plurality of wordlines and the address decoder may be electrically connected to each other by at least the plurality of through-hole vias. 
     According to some example embodiments, a method of manufacturing a memory device including a first semiconductor layer and a second semiconductor layer that are stacked in a third direction perpendicular to first and second directions crossing each other, may include forming the second semiconductor layer that includes a lower substrate and an address decoder on the lower substrate, the address decoder configured to control a memory cell array. The method may include forming the first semiconductor layer stacked on the second semiconductor layer in the third direction, the first semiconductor layer including an upper substrate and the memory cell array on the upper substrate, the memory cell array including a plurality of memory blocks extending sequentially in a serial pattern, a plurality of wordlines extending in a first direction, and a plurality of bitlines extending in a second direction crossing the first direction. Each memory block of the plurality of memory blocks may include a core region including a plurality of memory cells, a first extension region formed adjacent to a first side of the core region, and a second extension region formed adjacent to a second side of the core region opposite the first side. Forming the first semiconductor layer may include forming a mold structure based on repeatedly stacking insulating interlayers and sacrificial layers on the upper substrate alternately along the third direction, forming the first extension region and the second extension region based on partially removing the mold structure, forming wordline cut regions, the wordline cut regions being formed along a boundary of the core region and a boundary of the first extension region, the wordline cut regions being formed to cross an inner portion of the core region and an inner portion of the first extension region, the wordline cut regions being not formed in the second extension region, removing the sacrificial layers in the core region and in the first extension region using the wordline cut regions to form one or more spaces, forming the plurality of wordlines in the one or more spaces, forming a plurality of wordline contacts configured to establish an electrical connection with the plurality of wordlines in the first extension region, forming a plurality of through-hole vias in the second extension region, and electrically connecting the plurality of wordline contacts with separate, respective through-hole vias of the plurality of through-hole vias. The sacrificial layers in the second extension region may be maintained, such that the second extension region includes an insulating mold structure in which the insulating interlayers and the sacrificial layers are alternately and repeatedly stacked. The second extension region may include a plurality of step zones having a step shape in a cross-sectional view, and at least one flat zone having a flat shape in the cross-sectional view. The plurality of through-hole vias penetrating the insulating mold structure may be formed in the flat zone. The plurality of wordlines and the address decoder may be electrically connected with each other by at least the plurality of through-hole vias. 
     According to some example embodiments, a memory device may include a first semiconductor layer and a second semiconductor layer. The first semiconductor layer may include a plurality of wordlines extending in a first direction and a plurality of bitlines extending in a second direction that is perpendicular to the first direction. The first semiconductor layer may further include an upper substrate, and a memory cell array on the upper substrate. The memory cell array may include a plurality of memory blocks extending sequentially in a serial pattern along the second direction. The second semiconductor layer may be beneath the first semiconductor layer in a third direction. The third direction may be perpendicular to both the first direction and the second direction. The second semiconductor layer may include a lower substrate, and an address decoder on the lower substrate and configured to control the memory cell array. Each memory block of the plurality of memory blocks may include a core region including a plurality of memory cells, a first extension region adjacent to a first side of the core region and a second extension region adjacent to a second side of the core region opposite the first side. The first extension region may include a plurality of wordline contacts configured to establish an electrical connection with the plurality of wordlines. The second extension region may include an insulating mold structure. The second extension region may include a plurality of step zones having a step shape in a cross-sectional view, and at least one flat zone having a flat shape in the cross-sectional view. The memory device may further include a plurality of through-hole vias penetrating the insulating mold structure in the at least one flat zone. The plurality of wordlines and the address decoder may be electrically connected to each other by at least the plurality of through-hole vias. The memory cell array may be included in a memory cell region that includes a first metal pad. The address decoder may be included in a peripheral circuit region that includes a second metal pad and is vertically connected to the memory cell region by the first metal pad and the second metal pad. 
     The memory device according to some example embodiments may have a relatively small size by adopting the cell over periphery (COP) structure in which the peripheral circuit is formed on the semiconductor substrate and the memory cell array is stacked on the peripheral circuit. 
     In addition, in the memory device, the memory package and the method of manufacturing the memory device according to some example embodiments, the through-hole vias for electrically connecting the wordlines with the peripheral circuit may be formed in the flat zoned of the second extension regions including the insulating mold structures, and may be formed to penetrate the insulating mold structures. Accordingly, all wordlines may be efficiently connected to the peripheral circuit without additional wiring, and the manufacturing cost may be reduced and the performance degradation may be prevented while the size of the memory device is reduced. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative, non-limiting example embodiments will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings. 
         FIG.  1    is a perspective view of a memory device according to some example embodiments. 
         FIG.  2    is a block diagram illustrating a memory device according to some example embodiments. 
         FIG.  3    is a perspective view illustrating an example of a memory block included in a memory cell array of a memory device of  FIG.  2   . 
         FIG.  4    is a circuit diagram illustrating an equivalent circuit of a memory block described with reference to  FIG.  3   . 
         FIG.  5    is a plan view of an example of a memory cell array included in a memory device according to some example embodiments. 
         FIG.  6    is an enlarged view of a portion “A” in a memory cell array of  FIG.  5   . 
         FIG.  7 A  is a cross-sectional view of an example of a memory cell array taken along a line IT of  FIG.  6   . 
         FIG.  7 B  is a cross-sectional view of an example of a memory cell array taken along a line II-II′ of  FIG.  6   . 
         FIGS.  8 A,  8 B,  8 C,  8 D,  8 E and  8 F  are cross-sectional views for describing a method of manufacturing a memory device according to some example embodiments. 
         FIG.  9    is a plan view of an example of a core region included in a memory cell array of  FIG.  5   . 
         FIGS.  10 ,  11 ,  12  and  13    are plan views of examples of a memory cell array included in a memory device according to some example embodiments. 
         FIG.  14    is a block diagram illustrating an example of an address decoder included in a memory device according to some example embodiments. 
         FIG.  15    is a cross-sectional view of a memory package according to some example embodiments. 
         FIG.  16    is a block diagram illustrating a storage device including a memory device according to some example embodiments. 
         FIG.  17    is a cross-sectional view of a nonvolatile memory device according to example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Various example embodiments will be described more fully with reference to the accompanying drawings, in which some example embodiments are shown. The present disclosure may, however, be embodied in many different forms and should not be construed as limited to the example embodiments set forth herein. Like reference numerals refer to like elements throughout this application. 
     It will be understood that an element that is “on” another element may be “above” or “beneath” the other element. Additionally, an element that is on another element may be “directly” on the other element, such that the element is in direct contact with at least a portion of the other elements, or “indirectly” on the other element, such that the element is isolated from direct contact with the other element by one or more interposing spaces or structures. 
     It will be understood that elements and/or properties thereof may be recited herein as being “the same” or “equal” as other elements, and it will be further understood that elements and/or properties thereof recited herein as being “the same” as or “equal” to other elements may be “the same” as or “equal” to or “substantially the same” as or “substantially equal” to the other elements and/or properties thereof. Elements and/or properties thereof that are “substantially the same” as or “substantially equal” to other elements and/or properties thereof will be understood to include elements and/or properties thereof that are the same as or equal to the other elements and/or properties thereof within manufacturing tolerances and/or material tolerances. Elements and/or properties thereof that are the same or substantially the same as other elements and/or properties thereof may be structurally the same or substantially the same, functionally the same or substantially the same, and/or compositionally the same or substantially the same. 
     It will be understood that elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, distances, parallel or perpendicular arrangement or the like) described herein as being “substantially” the same encompasses elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, distances, parallel or perpendicular arrangement, or the like) that are the same within manufacturing tolerances and/or material tolerances and/or elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, distances, parallel or perpendicular arrangement or the like) that have a relative difference in magnitude that is equal to or less than 10%. Further, regardless of whether elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, distances, parallel or perpendicular arrangement, or the like) are modified as “substantially,” it will be understood that these elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, parallel or perpendicular arrangement, or the like) should be construed as including a manufacturing or operational tolerance (e.g., ±10%) around the stated elements and/or properties thereof (e.g., structures, properties of one or more elements, lengths, distances, parallel or perpendicular arrangement, or the like). 
     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 include a tolerance of ±10% around the stated numerical value. When ranges are specified, the range includes all values therebetween such as increments of 0.1%. 
     Where directions, arrangements, orientations, any combination thereof, or the like with regard to one or more elements are described herein to be “substantially” a certain direction, orientation, arrangement, any combination thereof, or the like (e.g., “substantially perpendicular,” “substantially parallel,” “substantially vertical,” etc.), it will be understood that said directions, arrangements, orientations, any combination thereof, or the like with regard to the one or more elements may have a value that includes a tolerance of ±10% around the value of the certain direction, orientation, arrangement, any combination thereof, or the like (e.g., a tolerance of ±10% around exactly perpendicular). 
     It will be understood that some or all of any of the devices, controllers, generators, decoders, units, modules, or the like according to any of the example embodiments as described herein, including some or all of any of the elements of the address decoder  600  shown in  FIG.  14   , the storage device  1000  shown in  FIG.  16   , memory device  500  shown in  FIG.  2   , any combination thereof, or the like may be included in, may include, and/or may be implemented by one or more instances of processing circuitry such as hardware including logic circuits, a hardware/software combination such as a processor executing software; or a combination thereof. In some example embodiments, said one or more instances of processing circuitry may include, but are not limited to, a central processing unit (CPU), an application processor (AP), an arithmetic logic unit (ALU), a graphic processing unit (GPU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC) a programmable logic unit, a microprocessor, or an application-specific integrated circuit (ASIC), etc. In some example embodiments, any of the memories, memory units, or the like as described herein may include a non-transitory computer readable storage device, for example a solid state drive (SSD), storing a program of instructions, and the one or more instances of processing circuitry may be configured to execute the program of instructions to implement the functionality of some or all of any of the devices, controllers, decoders, units, modules, or the like according to any of the example embodiments as described herein, including any of the methods of operating any of same as described herein. 
       FIG.  1    is a perspective view of a memory device according to some example embodiments. 
     In  FIG.  1   , two directions that are each parallel or substantially parallel to a first surface (e.g., a top surface) of a substrate and crossing each other (e.g., perpendicular or substantially perpendicular to each other) are referred to as a first direction D 1  (e.g., a X-axis direction) and a second direction D 2  (e.g., a Y-axis direction). Restated, the second direction D 2  may be perpendicular or substantially perpendicular to the first direction D 1 . In addition, a direction vertical or substantially vertical to the first surface of the substrate is referred to as a third direction D 3  (e.g., a Z-axis direction). In some example embodiments, the first and second directions D 1  and D 2  may be perpendicular or substantially perpendicular to each other. In addition, the third direction D 3  may be perpendicular or substantially perpendicular to both the first and second directions D 1  and D 2 . Further, a direction indicated by an arrow in the figures and a reverse direction thereof are considered as the same direction. The definition of the first, second and third directions D 1 , D 2  and D 3  are same in the subsequent figures. 
     Referring to  FIG.  1   , a memory device  10  includes a first semiconductor layer L 1  and a second semiconductor layer L 2 . The first semiconductor layer L 1  is stacked on the second semiconductor layer L 2  in the third direction D 3 , and the second semiconductor layer L 2  is disposed under (e.g., directly beneath or indirectly beneath) the first semiconductor layer L 1  in the third direction D 3 . 
     The first semiconductor layer L 1  may include a memory cell array MCA, and the second semiconductor layer L 2  may include a peripheral circuit. Thus, the first semiconductor layer L 1  may be referred to as a memory cell region (MCR), and the second semiconductor layer L 2  may be referred to as a peripheral circuit region (PCR). 
     In some example embodiments, the peripheral circuit may include an address decoder ADEC, which may be on (e.g., directly on) the lower substrate LSUB. However, some example embodiments are not limited thereto, and the peripheral circuit may further include a control circuit, a page buffer circuit, and the like as will be described with reference to  FIG.  2   . 
     In some example embodiments, as will be described with reference to  FIG.  7 A , the second semiconductor layer L 2  may include a lower substrate LSUB, and the peripheral circuit and various circuits may be formed on the second semiconductor layer L 2  by forming semiconductor elements (e.g., transistors) and patterns for wiring the semiconductor elements on the lower substrate. 
     After the circuits are formed on the second semiconductor layer L 2 , the first semiconductor layer L 1  including the memory cell array MCA, a plurality of wordlines WL and a plurality of bitlines BL may be formed. Restated, and as described herein and as shown in at least  FIGS.  1 ,  3 - 4 ,  7 A, and  7 B , the first semiconductor layer L 1  may include a plurality of wordlines WL extending (e.g., extending in parallel) in a first direction D 1  and a plurality of bitlines BL extending (e.g., extending in parallel) in a second direction D 2  that is perpendicular to the first direction D 1 . 
     In some example embodiments, as will be described with reference to  FIG.  7 A , the first semiconductor layer L 1  may include an upper substrate USUB, and the memory cell array MCA may be formed on the first semiconductor layer L 1 , such that the memory cell array MCA is on (e.g., directly on) the upper substrate USUB, by forming a plurality of gate conductive layers stacked on the upper substrate and a plurality of pillars that pass through the plurality of gate conductive layers and extend in a vertical direction (e.g., the third direction D 3 ) perpendicular to a top surface of the upper substrate. In some example embodiments, each of the plurality of wordlines WL may extend in the first direction D 1 , and the plurality of wordlines WL may be arranged along the second direction D 2 . In addition, each of the plurality of bitlines BL may extend in the second direction D 2 , and the plurality of bitlines BL may be arranged along the first direction D 1 . 
     Further, the first semiconductor layer L 1  may include patterns for electrically connecting the memory cell array MCA (e.g., the plurality of wordlines WL and the plurality of bitlines BL) with the circuits formed in the second semiconductor layer L 2 . In some example embodiments, as will be described with reference to  FIGS.  5 ,  6 ,  7 A and  7 B , the plurality of word lines WL and the address decoder ADEC may be electrically connected with each other by a plurality of through-hole vias THV formed in a flat zone of an extension region that is formed adjacent to one side of the memory cell array MCA and includes an insulating mold structure. 
     The memory device  10  according to some example embodiments may have or adopt a structure in which the peripheral circuit is formed below and the memory cell array MCA is stacked on the peripheral circuit, e.g., a cell over periphery (COP) structure in which the peripheral circuit and the memory cell array MCA are disposed or arranged in the third direction D 3 . Accordingly, the memory device  10  may have a relatively small size. 
       FIG.  2    is a block diagram illustrating a memory device according to some example embodiments. 
     Referring to  FIG.  2   , a memory device  500  includes a memory cell array  510 , an address decoder  520  (e.g., address decoder circuit), a page buffer circuit  530 , a data input/output (I/O) circuit  540 , a voltage generator  550  and a control circuit  560 . 
     In some example embodiments, the memory device  500  may be a nonvolatile memory device. The memory device  500  may have the above-described COP structure. In some example embodiments, the memory cell array  510  may be formed in the first semiconductor layer L 1 , and the address decoder  520 , the page buffer circuit  530 , the data I/O circuit  540 , the voltage generator  550  and the control circuit  560  may be formed in the second semiconductor layer L 2 . 
     The memory cell array  510  is connected to the address decoder  520  via a plurality of string selection lines SSL, a plurality of wordlines WL and a plurality of ground selection lines GSL. The memory cell array  510  is further connected to the page buffer circuit  530  via a plurality of bitlines BL. The memory cell array  510  may include a plurality of memory cells (e.g., a plurality of nonvolatile memory cells) that are connected to the plurality of wordlines WL and the plurality of bitlines BL. The memory cell array  510  may be divided into a plurality of memory blocks BLK 1 , BLK 2 , . . . , BLKz (z being any positive integer) each of which includes memory cells. In addition, each of the plurality of memory blocks BLK 1 , BLK 2 , . . . , BLKz may be divided into a plurality of pages. 
     In some example embodiments, as will be described with reference to  FIGS.  3  and  4   , the memory cell array  510  may be a three-dimensional memory cell array, which is formed on a substrate in a three-dimensional structure (or a vertical structure). In this example, the memory cell array  510  may include a plurality of cell strings (e.g., a plurality of vertical NAND strings) that are vertically oriented such that at least one memory cell is located over another memory cell. 
     The control circuit  560  receives a command CMD and an address ADDR from an outside (e.g., from a host device and/or a memory controller), and control erasure, programming and read operations of the memory device  500  based on the command CMD and the address ADDR. An erasure operation may include performing a sequence of erase loops, and a program operation may include performing a sequence of program loops. Each program loop may include a program operation and a program verification operation. Each erase loop may include an erase operation and an erase verification operation. The read operation may include a normal read operation and data recover read operation. 
     In some example embodiments, the control circuit  560  may generate control signals CON, which are used for controlling the voltage generator  550 , and may generate control signal PBC for controlling the page buffer circuit  530 , based on the command CMD, and may generate a row address R_ADDR and a column address C_ADDR based on the address ADDR. The control circuit  560  may provide the row address R ADDR to the address decoder  520  and may provide the column address C_ADDR to the data I/O circuit  540 . 
     The address decoder  520  may be connected to the memory cell array  510  via the plurality of string selection lines SSL, the plurality of wordlines WL and the plurality of ground selection lines GSL. 
     In some example embodiments, in the data erase/write/read operations, the address decoder  520  may determine at least one of the plurality of wordlines WL as a selected wordline, and may determine the rest or remainder of the plurality of wordlines WL other than the selected wordline as unselected wordlines, based on the row address R_ADDR. 
     In addition, in the data erase/write/read operations, the address decoder  520  may determine at least one of the plurality of string selection lines SSL as a selected string selection line, and may determine the rest or remainder of the plurality of string selection lines SSL other than the selected string selection line as unselected string selection lines, based on the row address R_ADDR. 
     Further, in the data erase/write/read operations, the address decoder  520  may determine at least one of the plurality of ground selection lines GSL as a selected ground selection line, and may determine the rest or remainder of the plurality of ground selection lines GSL other than the selected ground selection line as unselected ground selection lines, based on the row address R_ADDR. 
     The voltage generator  550  may generate voltages VS that are used for an operation of the memory device  500  based on a power PWR and the control signals CON. The voltages VS may be applied to the plurality of string selection lines SSL, the plurality of wordlines WL and the plurality of ground selection lines GSL via the address decoder  520 . In addition, the voltage generator  550  may generate an erase voltage VERS that is required for the data erase operation based on the power PWR and the control signals CON. The erase voltage VERS may be applied to the memory cell array  510  directly or via the bitline BL. 
     In some example embodiments, during the erase operation, the voltage generator  550  may apply the erase voltage VERS to a common source line and/or the bitline BL of a memory block (e.g., a selected memory block) and may apply an erase permission voltage (e.g., a ground voltage) to all wordlines of the memory block or a portion of the wordlines via the address decoder  520 . In addition, during the erase verification operation, the voltage generator  550  may apply an erase verification voltage simultaneously to all wordlines of the memory block or sequentially to the wordlines one by one. 
     In some example embodiments, during the program operation, the voltage generator  550  may apply a program voltage to the selected wordline and may apply a program pass voltage to the unselected wordlines via the address decoder  520 . In addition, during the program verification operation, the voltage generator  550  may apply a program verification voltage to the selected wordline and may apply a verification pass voltage to the unselected wordlines via the address decoder  520 . 
     In addition, during the normal read operation, the voltage generator  550  may apply a read voltage to the selected wordline and may apply a read pass voltage to the unselected wordlines via the address decoder  520 . During the data recover read operation, the voltage generator  550  may apply the read voltage to a wordline adjacent to the selected wordline and may apply a recover read voltage to the selected wordline via the address decoder  520 . 
     In view of at least the above, it will be understood that the address decoder  520  may be configured to control the memory cell array  510 . 
     The page buffer circuit  530  may be connected to the memory cell array  510  via the plurality of bitlines BL. The page buffer circuit  530  may include a plurality of page buffers. In some example embodiments, each page buffer may be connected to one bitline. In other example embodiments, each page buffer may be connected to two or more bitlines. 
     The page buffer circuit  530  may store data DAT to be programmed into the memory cell array  510  or may read data DAT sensed from the memory cell array  510 . In other words, the page buffer circuit  530  may operate as a write driver or a sensing amplifier according to an operation mode of the memory device  500 . 
     The data I/O circuit  540  may be connected to the page buffer circuit  530  via data lines DL. The data I/O circuit  540  may provide the data DAT from an outside of the memory device  500  to the memory cell array  510  via the page buffer circuit  530  or may provide the data DAT from the memory cell array  510  to the outside of the memory device  500 , based on the column address C_ADDR. 
       FIG.  3    is a perspective view illustrating an example of a memory block included in a memory cell array of a memory device of  FIG.  2   . 
     Referring to  FIG.  3   , a memory block BLKi includes a plurality of cell strings (e.g., a plurality of vertical NAND strings) which are formed on a substrate in a three-dimensional structure (or a vertical structure). The memory block BLKi includes structures extending along the first, second and third directions D 1 , D 2  and D 3 . 
     A substrate  111  (e.g., upper substrate USUB of the first semiconductor layer L 1 ) is provided. In some example embodiments, the substrate  111  may have a well of a first type of charge carrier impurity (e.g., a first conductivity type) therein. In some example embodiments, the substrate  111  may have a p-well formed by implanting a group 3 element such as boron (B). In particular, the substrate  111  may have a pocket p-well provided within an n-well. In some example embodiments, the substrate  111  has a p-type well (or a p-type pocket well). However, the conductive type of the substrate  111  is not limited to p-type. 
     A plurality of doping regions  311 ,  312 ,  313  and  314  arranged along the second direction D 2  are provided in/on the substrate  111 . These plurality of doping regions  311  to  314  may have a second type of charge carrier impurity (e.g., a second conductivity type) different from the first type of the substrate  111 . In some example embodiments of the inventive concepts, the first to fourth doping regions  311  to  314  may have n-type. However, the conductive type of the first to fourth doping regions  311  to  314  is not limited to n-type. 
     A plurality of insulation materials  112  extending along the first direction D 1  are sequentially provided along the third direction D 3  on a region of the substrate  111  between the first and second doping regions  311  and  312 . In some example embodiments, the plurality of insulation materials  112  are provided along the third direction D 3 , being spaced by a specific distance. In some example embodiments, the insulation materials  112  may include an insulation material such as an oxide layer. 
     A plurality of pillars  113  penetrating the insulation materials along the third direction D 3  are sequentially disposed along the first direction D 1  on a region of the substrate  111  between the first and second doping regions  311  and  312 . In some example embodiments, the plurality of pillars  113  penetrate the insulation materials  112  to contact the substrate  111 . 
     In some example embodiments, each pillar  113  may include a plurality of materials. In some example embodiments, a channel layer  114  of each pillar  113  may include a silicon material having a first conductivity type. In some example embodiments, the channel layer  114  of each pillar  113  may include a silicon material having the same conductivity type as the substrate  111 . In some example embodiments of the inventive concepts, the channel layer  114  of each pillar  113  includes p-type silicon. However, the channel layer  114  of each pillar  113  is not limited to the p-type silicon. 
     An internal material  115  of each pillar  113  includes an insulation material. In some example embodiments, the internal material  115  of each pillar  113  may include an insulation material such as a silicon oxide. In some examples, the internal material  115  of each pillar  113  may include an air gap. The term “air” as discussed herein, may refer to atmospheric air, or other gases that may be present during the manufacturing process. 
     An insulation layer  116  is provided along the exposed surfaces of the insulation materials  112 , the pillars  113 , and the substrate  111 , on a region between the first and second doping regions  311  and  312 . In some example embodiments, the insulation layer  116  provided on surfaces of the insulation material  112  may be interposed between pillars  113  and a plurality of stacked first conductive materials  211 ,  221 ,  231 ,  241 ,  251 ,  261 ,  271 ,  281  and  291 , as illustrated. In some examples, the insulation layer  116  need not be provided between the first conductive materials  211  to  291  corresponding to ground selection lines GSL (e.g.,  211 ) and string selection lines SSL (e.g.,  291 ). In this example, the ground selection lines GSL are the lowermost ones of the stack of first conductive materials  211  to  291  and the string selection lines SSL are the uppermost ones of the stack of first conductive materials  211  to  291 . 
     The plurality of first conductive materials  211  to  291  are provided on surfaces of the insulation layer  116 , in a region between the first and second doping regions  311  and  312 . In some example embodiments, the first conductive material  211  extending along the first direction D 1  is provided between the insulation material  112  adjacent to the substrate  111  and the substrate  111 . In more detail, the first conductive material  211  extending along the first direction D 1  is provided between the insulation layer  116  at the bottom of the insulation material  112  adjacent to the substrate  111  and the substrate  111 . 
     A first conductive material extending along the first direction D 1  is provided between the insulation layer  116  at the top of the specific insulation material among the insulation materials  112  and the insulation layer  116  at the bottom of a specific insulation material among the insulation materials  112 . In some example embodiments, a plurality of first conductive materials  221  to  281  extending along the first direction D 1  are provided between the insulation materials  112  and it may be understood that the insulation layer  116  is provided between the insulation materials  112  and the first conductive materials  221  to  281 . The first conductive materials  211  to  291  may be formed of a conductive metal, but in other embodiments of the inventive concepts the first conductive materials  211  to  291  may include a conductive material such as a polysilicon. 
     The same structures as those on the first and second doping regions  311  and  312  may be provided in a region between the second and third doping regions  312  and  313 . In the region between the second and third doping regions  312  and  313 , a plurality of insulation materials  112  are provided, which extend along the first direction D 1 . And, a plurality of pillars  113  are provided that are disposed sequentially along the first direction D 1  and penetrate the plurality of insulation materials  112  along the third direction D 3 . An insulation layer  116  is provided on the exposed surfaces of the plurality of insulation materials  112  and the plurality of pillars  113 , and a plurality of first conductive materials  211  to  291  extend along the first direction D 1 . Similarly, the same structures as those on the first and second doping regions  311  and  312  may be provided in a region between the third and fourth doping regions  313  and  314 . 
     A plurality of drain regions  320  are provided on the plurality of pillars  113 , respectively. The drain regions  320  may include silicon materials doped with a second type of charge carrier impurity. In some example embodiments, the drain regions  320  may include silicon materials doped with an n-type dopant. In some example embodiments of the inventive concepts, the drain regions  320  include n-type silicon materials. However, the drain regions  320  are not limited to n-type silicon materials. 
     On the drain regions, a plurality of second conductive materials  331 ,  332  and  333  are provided, which extend along the second direction D 2 . The second conductive materials  331  to  333  are disposed along the first direction D 1 , being spaced apart from each other by a specific distance. The second conductive materials  331  to  333  are respectively connected to the drain regions  320  in a corresponding region. The drain regions  320  and the second conductive material  333  extending along the second direction D 2  may be connected through each contact plug. Each contact plug may be, in some example embodiments, a conductive plug formed of a conductive material such as a metal. The second conductive materials  331  to  333  may include metal materials. The second conductive materials  331  to  333  may include conductive materials such as a polysilicon. 
     In the example of  FIG.  3   , the first conductive materials  211  to  291  may be used to form the wordlines WL, the string selection lines SSL and the ground selection lines GSL. In some example embodiments, the first conductive materials  221  to  281  may be used to form the wordlines WL, where conductive materials belonging to the same layer may be interconnected. The second conductive materials  331  to  333  may be used to form the bitlines BL. The number of layers of the first conductive materials  211  to  291  may be changed variously according to process and control techniques. 
       FIG.  4    is a circuit diagram illustrating an equivalent circuit of a memory block described with reference to  FIG.  3   . 
     A memory block BLKi of  FIG.  4    may be formed on a substrate in a three-dimensional structure (or a vertical structure). In some example embodiments, a plurality of NAND strings included in the memory block BLKi may be formed in a direction perpendicular to the substrate. 
     Referring to  FIG.  4   , the memory block BLKi may include a plurality of NAND strings NS 11 , NS 12 , NS 13 , NS 21 , NS 22 , NS 23 , NS 31 , NS 32  and NS 33  connected between bitlines BL 1 , BL 2  and BL 3  and a common source line CSL. Each of the NAND strings NS 11  to NS 33  may include a string selection transistor SST, a plurality of memory cells MC 1 , MC 2 , MC 3 , MC 4 , MC 5 , MC 6 , MC 7  and MC 8 , and a ground selection transistor GST. In some example embodiments, the bitlines BL 1  to BL 3  may correspond to the second conductive materials  331  to  333  in  FIG.  3   , and the common source line CSL may be formed by interconnecting the first to fourth doping regions  311  to  314  in  FIG.  3   . 
     Each string selection transistor SST may be connected to a corresponding string selection line (one of SSL 1 , SSL 2  and SSL 3 ). The plurality of memory cells MCI to MC 8  may be connected to corresponding wordlines WL 1 , WL 2 , WL 3 , WL 4 , WL 5 , WL 6 , WL 7  and WL 8 , respectively. Each ground selection transistor GST may be connected to a corresponding ground selection line (one of GSL 1 , GSL 2  and GSL 3 ). Each string selection transistor SST may be connected to a corresponding bitline (e.g., one of BL 1  to BL 3 ), and each ground selection transistor GST may be connected to the common source line CSL. In the example of  FIG.  4   , some of the string selection transistors SST are connected to the same bitline (e.g., one of BL 1  to BL 3 ) to connect corresponding NAND strings to the same bitline up appropriate selection via selection voltages applied to the appropriate sting selection lines SSL 1  to SSL 3  and ground selection lines GSL 1  to GSL 3 . 
     The cell strings connected in common to one bitline may form one column, and the cell strings connected to one string selection line may form one row. In some example embodiments, the cell strings NS 11 , NS 21  and NS 31  connected to the first bitline BL 1  may correspond to a first column, and the cell strings NS 11 , NS 12  and NS 13  connected to the first string selection line SSL 1  may form a first row. 
     Wordlines (e.g., WL 1 ) having the same height may be commonly connected, and the ground selection lines GSL 1  to GSL 3  and the string selection lines SSL 1  to SSL 3  may be separated. Memory cells located at the same semiconductor layer share a wordline. Cell strings in the same row share a string selection line. The common source line CSL is connected in common to all of cell strings. 
     In  FIG.  4   , the memory block BLKi is illustrated to be connected to eight wordlines WL 1  to WL 8  and three bitlines BL 1  to BL 3 , and each of the NAND strings NS 11  to NS 33  is illustrated to include eight memory cells MCI to MC 8 . However, some example embodiments are not limited thereto. In some example embodiments, each memory block may be connected to any number of wordlines and bitlines, and each NAND string may include any number of memory cells. 
     A three-dimensional vertical array structure may include vertical NAND strings that are vertically oriented such that at least one memory cell is located over another memory cell. The at least one memory cell may comprise a charge trap layer. The following patent documents, which are hereby incorporated by reference in their entirety, describe suitable configurations for a memory cell array including a 3D vertical array structure, in which the three-dimensional memory array is configured as a plurality of levels, with wordlines and/or bitlines shared between levels: U.S. Pat. Nos. 7,679,133; 8,553,466; 8,654,587; 8,559,235; and US Pat. Pub. No. 2011/0233648. 
     Although the memory cell array included in the nonvolatile memory device according to some example embodiments is described based on a NAND flash memory device, the nonvolatile memory device according to some example embodiments may be any nonvolatile memory device, e.g., a phase random access memory (PRAM), a resistive random access memory (RRAM), a nano floating gate memory (NFGM), a polymer random access memory (PoRAM), a magnetic random access memory (MRAM), a ferroelectric random access memory (FRAM), a thyristor random access memory (TRAM), etc. 
       FIG.  5    is a plan view of an example of a memory cell array included in a memory device according to some example embodiments. 
     Referring to  FIG.  5   , a memory cell array  100  includes a plurality of memory blocks BLK 1 , BLK 2 , BLK 3  and BLK 4 . 
     The plurality of memory blocks BLK 1  to BLK 4  are arranged along the second direction D 2 . Restated, the plurality of memory blocks BLK 1  to BLK 4  extend sequentially in a serial pattern along the second direction D 2 . In some example embodiments, the plurality of memory blocks BLK 1  to BLK 4  may include the first memory block BLK 1 , the second memory block BLK 2 , the third memory block BLK 3  and the fourth memory block BLK 4  that are sequentially arranged (e.g., extending sequentially in a serial pattern) along the second direction D 2 , for example such that the third memory block BLK 3  and the fourth memory block BLK 4  are adjacent to each other in the second direction D 2 . However, some example embodiments are not limited thereto, and the number of memory blocks may be changed variously according to some example embodiments. 
     Each of the plurality of memory blocks BLK 1  to BLK 4  includes a respective one of core regions COR 1 , COR 2 , COR 3  and COR 4 , a respective one of first extension regions EXR 1 - 1 , EXR 2 - 1 , EXR 3 - 1  and EXR 4 - 1 , and a respective one of second extension regions EXR 1 - 2 , EXR 2 - 2 , EXR 3 - 2  and EXR 4 - 2 . 
     Each of the core regions COR 1  to COR 4  may include a plurality of memory cells, and may include a plurality of channels extending along the third direction D 3 . A channel structure in the core regions COR 1  to COR 4  will be described with reference to  FIG.  9   . Each of the first extension regions EXR 1 - 1  to EXR 4 - 1  may be formed adjacent to a first side of a corresponding core region among the core regions COR 1  to COR 4 , while each of the second extension regions EXR 1 - 2  to EXR 4 - 2  may be formed adjacent to a second side opposite to the first side of the corresponding core region among the core regions COR 1  to COR 4 . As will be described with reference to  FIG.  6   , each of the first extension regions EXR 1 - 1  to EXR 4 - 1  may include a plurality of wordlines WL and a plurality of wordline contacts WC configured to establish an electrical connection with (e.g., to directly contact one or more of) the plurality of wordlines WL. Each of the second extension regions EXR 1 - 2  to EXR 4 - 2  may include a respective one of insulating mold structures IMD 1 , IMD 2 , IMD 3  and IMD 4 . In other words, the first extension regions EXR 1 - 1  to EXR 4 - 1  may be regions in which conductive materials for forming the plurality of wordlines WL are stacked, and the second extension regions EXR 1 - 2  to EXR 4 - 2  may be regions in which only insulating materials are stacked without including conductive materials. 
     In some example embodiments, as shown in  FIG.  5   , the first memory block BLK 1  may include the core region COR 1 , the first extension region EXR 1 - 1  that is formed adjacent to a first side (e.g., the right side shown in  FIG.  5   ) of the core region COR 1  and includes the plurality of wordline contacts WC, and the second extension region EXR 1 - 2  that is formed adjacent to a second side (e.g., the left side shown in  FIG.  5   ) of the core region COR 1  that is opposite to the first side of the core region COR 1  and includes the insulating mold structure IMD 1 . 
     In some example embodiments, and as shown in at least  FIG.  5   , the first extension regions EXR 1 - 1  to EXR 4 - 1  and the second extension regions EXR 1 - 2  to EXR 4 - 2  may be aligned along the second direction D 2  and may be alternately arranged along the second direction D 2 . Restated, and as shown in at least  FIG.  5   , a first extension region EXR 1 - 1  of the first memory block BLK 1 , a second extension region EXR 2 - 2  of the second memory block BLK 2 , a first extension region EXR 3 - 1  of the third memory block BLK 3 , and a second extension region EXR 4 - 2  of the fourth memory block BLK 4  may be aligned along the second direction D 2 . In some example embodiments, on the right side of the memory cell array  100 , the first extension region EXR 1 - 1  of the first memory block BLK 1 , the second extension region EXR 2 - 2  of the second memory block BLK 2 , the first extension region EXR 3 - 1  of the third memory block BLK 3  and the second extension region EXR 4 - 2  of the fourth memory block BLK 4  may be aligned along the second direction D 2 , and thus the second extension region EXR 2 - 2  may be disposed between the first extension regions EXR 1 - 1  and EXR 3 - 1 . Similarly, on the left side of the memory cell array  100 , the second extension region EXR 1 - 2  of the first memory block BLK 1 , the first extension region EXR 2 - 1  of the second memory block BLK 2 , the second extension region EXR 3 - 2  of the third memory block BLK 3  and the first extension region EXR 4 - 1  of the fourth memory block BLK 4  may be aligned along the second direction D 2 . 
     Each of the first extension regions EXR 1 - 1  to EXR 4 - 1  may include two or more of wordline step zones WSZ 1 - 1 , WSZ 1 - 2 , WSZ 2 - 1 , WSZ 2 - 2 , WSZ 3 - 1 , WSZ 3 - 2 , WSZ 4 - 1  and WSZ 4 - 2  having a step (or stair) shape in a cross-sectional view, and at least one of wordline flat zones WFZ 1 - 1 , WFZ 2 - 1 , WFZ 3 - 1  and WFZ 4 - 1  having a flat (or plane) shape in a cross-sectional view. In some example embodiments, the first extension region EXR 1 - 1  may include two wordline step zones WSZ 1 - 1  and WSZ 1 - 2 , and one wordline flat zone WFZ 1 - 1  disposed between the wordline step zones WSZ 1 - 1  and WSZ 1 - 2 . As will be described and shown with reference to  FIG.  6   , the plurality of wordline contacts WC may be formed in the wordline step zones WSZ 1 - 1  to WSZ 4 - 2 . 
     Each of the second extension regions EXR 1 - 2  to EXR 4 - 2  may include two or more of step zones SZ 1 - 1 , SZ 1 - 2 , SZ 2 - 1 , SZ 2 - 2 , SZ 3 - 1 , SZ 3 - 2 , SZ 4 - 1  and SZ 4 - 2  having a step shape in a cross-sectional view, and at least one of flat zones FZ 1 - 1 , FZ 2 - 1 , FZ 3 - 1  and FZ 4 - 1  having a flat shape in a cross-sectional view. In some example embodiments, and as shown in at least  FIGS.  7 A- 7 B , the second extension region EXR 2 - 2  may include two step zones SZ 2 - 1  and SZ 2 - 2  that each have a step shape in a cross-sectional view, and one flat zone FZ 2 - 1  disposed between the step zones SZ 2 - 1  and SZ 2 - 2  and having a flat shape in a cross-sectional view. 
     The plurality of through-hole vias THV penetrating the insulating mold structures IMD 1  to IMD 4  may be formed in the flat zones FZ 1 - 1  to FZ 4 - 1  of the second extension regions EXR 1 - 2  to EXR 4 - 2 , such that a given second extension region of each memory block of a memory cell array includes a plurality of through-hole vias THV penetrating the insulating mold structure IMD (e.g., extending in the third direction D 3 ) in the at least one flat zone FZ of the given second extension region. It will be understood, as shown in at least  FIGS.  6 - 7 B , that the through-hole vias THV are “in” one or more flat zones FZ of one or more particular second extension regions of one or more memory blocks. As will be described with reference to  FIGS.  6  and  7 A , the wordlines WL may be electrically connected to an address decoder  522  through the wordline contacts WC, upper conductive lines UPM and the through-hole vias THV. Restated, the plurality of wordlines WL of the first semiconductor layer L 1  and the address decoder  522  may be electrically connected to each other by at least the plurality of through-hole vias THY. 
     In some example embodiments, and as shown in at least  FIG.  5   , the wordline step zones WSZ 1 - 1  to WSZ 4 - 2  in the first extension regions EXR 1 - 1  to EXR 4 - 1  and the step zones SZ 1 - 1  to SZ 4 - 2  in the second extension regions EXR 1 - 2  to EXR 4 - 2  may be aligned along the second direction D 2 , and the wordline flat zones WFZ 1 - 1  to WFZ 4 - 1  in the first extension regions EXR 1 - 1  to EXR 4 - 1  and the flat zones FZ 1 - 1  to FZ 4 - 1  in the second extension regions EXR 1 - 2  to EXR 4 - 2  may also be aligned along the second direction D 2 . 
       FIG.  6    is an enlarged view of a portion “A” in a memory cell array of  FIG.  5   . 
     Referring to  FIGS.  5  and  6   , the first extension region EXR 1 - 1  of the first memory block BLK 1  may include the wordline step zone WSZ 1 - 1 , the wordline flat zone WFZ 1 - 1 , and the wordline step zone WSZ 1 - 2  that are alternately arranged along the first direction D 1 . Similarly, the second extension region EXR 2 - 2  of the second memory block BLK 2  may include the step zone SZ 2 - 1 , the flat zone FZ 2 - 1  and the step zone SZ 2 - 1  that are alternately arranged along the first direction D 1 , the first extension region EXR 3 - 1  of the third memory block BLK 3  may include the wordline step zone WSZ 3 - 1 , the wordline flat zone WFZ 3 - 1  and the wordline step zone WSZ 3 - 2  that are alternately arranged along the first direction D 1 , and the second extension region EXR 4 - 2  of the fourth memory block BLK 4  may include the step zone SZ 4 - 1 , the flat zone FZ 4 - 1  and the step zone SZ 4 - 1  that are alternately arranged along the first direction D 1 . Accordingly, in each extension region, the flat zone included in the extension region is between two step zones of a plurality of step zones of the extension region to establish an alternating pattern of step zones that extends along the first direction D 1 .  FIGS.  5  and  6    illustrate an example where the number (“quantity”) of step zones and the number of wordline step zones are greater than the number of flat zones and the number of wordline flat zones, respectively. The quantity of step zones in each extension region may be greater than the quantity of flat zones in each extension region. The quantity of step zones in the memory cell array may be greater than the quantity of flat zones in the memory cell array. For example, in a second extension region EXR 2 - 2 , the quantity of step zones (e.g., SZ 2 - 1 , SZ 2 - 2 ) is greater than the quantity of flat zones (e.g., FZ 2 - 1 ) in the second extension region EXR 2 - 2 . 
     Since the first extension region EXR 1 - 1 , the second extension region EXR 2 - 2 , the first extension region EXR 3 - 1  and the second extension region EXR 4 - 2  are aligned along the second direction D 2 , the wordline step zone WSZ 1 - 1 , the step zone SZ 2 - 1 , the wordline step zone WSZ 3 - 1  and the step zone SZ 4 - 1  may also be aligned along the second direction D 2 . Similarly, the wordline flat zone WFZ 1 - 1 , the flat zone FZ 2 - 1 , the wordline flat zone WFZ 3 - 1  and the flat zone FZ 4 - 1  may be aligned along the second direction D 2 , and the wordline step zone WSZ 1 - 2 , the step zone SZ 2 - 1 , the wordline step zone WSZ 3 - 2  and the step zone SZ 4 - 1  may be aligned along the second direction D 2 . 
     The first extension regions EXR 1 - 1  and EXR 3 - 1  may include gate conductive layers GL 11 , GL 12 , GL 13 , GL 14 , GL 31 , GL 32 , GL 33  and GL 34  forming string selection lines SSL, wordlines WL and ground selection lines GSL. The plurality of wordline contacts (or gate contacts) WC for an electrical connection with the string selection lines SSL, the wordlines WL and the ground selection lines GSL may be formed in the wordline step zones WSZ 1 - 1  and WSZ 3 - 1  of the first extension regions EXR 1 - 1  and EXR 3 - 1 . 
     The second extension regions EXR 2 - 2  and EXR 4 - 2  may include the insulating mold structures IMD 2  and IMD 4 . The plurality of through-hole vias THV may be formed in the flat zones FZ 2 - 1  and FZ 4 - 1  of the second extension regions EXR 2 - 2  and EXR 4 - 2  such that the plurality of through-hole vias THV penetrate the insulating mold structures IMD 2  and IMD 4 . The plurality of wordline contacts WC and the plurality of through-hole vias THV may be electrically connected with each other by at least the upper conductive lines UPM. 
     In some example embodiments, among the plurality of wordlines WL, some of wordlines connected to the first memory block BLK 1  (e.g., first wordlines included in the gate conductive layer GL 14 ) and some of wordlines connected to the third memory block BLK 3  (e.g., second wordlines included in the gate conductive layer GL 31 ) may be electrically coupled to the address decoder  522  by at least through-hole vias THV formed in the flat zone FZ 2 - 1  of the second extension region EXR 2 - 2  of the second memory block BLK 2  between the first and third memory blocks BLK 1  and BLK 3 . For example, as shown in  FIGS.  6 - 7 B , first wordlines connected to the first memory block BLK (e.g., the wordlines WL 1 _ 2  to WL 4 _ 2  shown in  FIG.  7 B ) and second wordlines connected to the third memory block (e.g., the wordlines WL 1 _ 1  to WL 4 _ 1  shown in  FIG.  7 A ), may be electrically connected to the address decoder  522  (e.g., as shown in  FIGS.  7 A- 7 B ) by at least through-hole vias THV in a flat zone FZ 2 - 1  of the second extension region EXR 2 - 2  of the second memory block BLK (e.g., via wordline contacts WC, upper conductive lines UPM, and through-hole vias THV shown in  FIGS.  6  and  7 B  with regard to the “first wordlines” and shown in  FIGS.  6  and  7 A  with regard to the “second wordlines”). 
     In some example embodiments, and as shown in at least  FIG.  6   , among the wordlines connected to the third memory block BLK 3 , remaining wordlines (e.g., third wordlines included in the gate conductive layer GL 34 ) other than (e.g., separate from) the some of the wordlines electrically connected to the address decoder  522  by at least the through-hole vias THY formed in the flat zone FZ 2 - 1  of the second extension region EXR 2 - 2  of the second memory block BLK 2  may be electrically connected to the address decoder  522  by at least through-hole vias THV in the flat zone FZ 4 - 1  of the second extension region EXR 4 - 2  of the fourth memory block BLK 4  (e.g., by at least word contacts WC, upper conductive lines UPM, and through-hole vias THV as shown at the top of  FIG.  6   ). For example, the plurality of wordlines WL may include third wordlines connected to the third memory block BLK 3  (e.g., third wordlines included in the gate conductive layer GL 34 ), the third wordlines separate from the second wordlines (e.g., second wordlines included in the gate conductive layer GL 31 ), the third wordlines electrically connected to the address decoder  522  by at least through-hole vias THY in the flat zone FZ 4 - 1  of the second extension region EXR 4 - 2  of the fourth memory block BLK 4 . 
     In some example embodiments, and as shown for example in at least  FIG.  5   , the first memory block BLK 1  may be disposed adjacent to an edge El of the memory cell array  100 . Among the wordlines connected to the first memory block BLK 1 , remaining wordlines (e.g., fourth wordlines DWL included in the gate conductive layer GL 11 ) other than the some of the wordlines electrically connected to the address decoder  522  by at least the through-hole vias THY formed in the flat zone FZ 2 - 1  of the second extension region EXR 2 - 2  of the second memory block BLK 2  may be dummy wordlines that are not electrically connected to the address decoder  522 . For example, and as shown in at least  FIG.  6   , the plurality of wordlines may include wordlines DWL connected to the first memory block BLK 1 , where the wordlines are separate from the wordlines electrically connected to the address decoder  522  by at least the through-hole vias THV formed in the flat zone FZ 2 - 1  of the second extension region EXR 2 - 2  of the second memory block BLK 2 , wherein the wordlines DWL are dummy wordlines that are not electrically connected to the address decoder  522 . 
     Although  FIG.  6    illustrates that the wordline contacts WC are formed only on some gate conductive layers for convenience of illustration, the wordline contacts WC may be formed on all gate conductive layers requiring the electrical connection. According to some example embodiments, the gate conductive layers included in the wordline step zones WSZ 1 - 2  and WSZ 3 - 2  may be connected to the address decoder  522  in a manner which will be described with reference to  FIGS.  10  and  11   , or may be connected to the address decoder  522  in a different manner, or may not be connected to the address decoder  522 . 
       FIG.  7 A  is a cross-sectional view of an example of a memory cell array taken along a line I-I′ of  FIG.  6   .  FIG.  7 B  is a cross-sectional view of an example of a memory cell array taken along a line II-II′ of  FIG.  6   . 
     Referring to  FIGS.  5 ,  6 ,  7 A, and  7 B , the second semiconductor layer L 2  may include a lower substrate LSUB and the address decoder  522  formed on the lower substrate LSUB. In addition, the second semiconductor layer L 2  may include lower contacts LMC electrically connected to the address decoder  522 , lower conductive lines LPM electrically connected to the lower contacts LMC, and a lower insulating layer IL 1  covering the lower contacts LMC and the lower conductive lines LPM. 
     The address decoder  522  may be formed on a portion of the lower substrate LSUB. In other words, the address decoder  522  may be formed by forming a plurality of transistors TR on the lower substrate LSUB. 
     The first semiconductor layer L 1  may include an upper substrate USUB, and a vertical structure VS and the insulating mold structure IMD 2  that are formed on the upper substrate USUB. In addition, the first semiconductor layer L 1  may include upper contacts UMC, bitlines BL_ 1  and BL_ 2 , the wordline contacts WC and the upper conductive lines UPM that are electrically connected to the vertical structure VS. Additionally, the first semiconductor layer L 1  may include the through-hole vias THV formed in the insulating mold structure IMD 2  and electrically connected to the wordline contacts WC. The first semiconductor layer L 1  may further include an upper insulating layer IL 2  covering the vertical structure VS, the insulating mold structure IMD 2  and various conductive lines. 
     The upper substrate USUB may be a support layer that supports the gate conductive layers GL 31  and GL 14 . In some example embodiments, the upper substrate USUB may be referred to as a base substrate. 
     The vertical structure VS may include the gate conductive layers GL 31  and GL 14  located on the upper substrate USUB, and pillars P 1  and P 2  that penetrate or pass through the gate conductive layers GL 31  and GL 14  and extend in the third direction D 3  on a top surface of the upper substrate USUB. The gate conductive layers GL 31  and GL 14  may include ground selection lines GSL_ 1  and GSL_ 2 , wordlines WL 1 _ 1 , WL 2 _ 1 , WL 3 _ 1 , WL 4 _ 1 , WL 1 _ 2 , WL 2 _ 2 , WL 3 _ 2  and WL 4 _ 2 , and string selection lines SSL_ 1  and SSL_ 2 . The ground selection lines GSL_ 1  and GSL_ 2 , the wordlines WL 1 _ 1  to WL 4 _ 2 , and the string selection lines SSL_ 1  and SSL_ 2  may be sequentially formed on the upper substrate USUB, and insulating interlayers  52  may be located under or over each of the gate conductive layers GL 31  and GL 14 . In other words, the conductive layers (e.g., the ground selection lines GSL_ 1  and GSL_ 2 , the wordlines WL 1 _ 1  to WL 4 _ 2 , and the string selection lines SSL_ 1  and SSL_ 2 ) including a conductive material (e.g., a metal material and/or a polysilicon) and the insulating interlayers  52  including an insulating material (e.g., a silicon oxide based material) may be alternately stacked in the third direction D 3 . As shown, the wordlines WL 1 _ 1  to WL 4 _ 2  and at least a portion of the insulating interlayers  52  extend in parallel to each other in an alternating pattern (e.g., are alternately stacked) in the third direction D 3 . The vertical structure VS may correspond to the core region and the first extension region. 
     The pillars P 1  and P 2  may include surface layers S 1  and S 2 , and insides I 1  and I 2 , respectively. In some example embodiments, the surface layers S 1  and S 2  of the pillars P 1  and P 2  may include a silicon material doped with an impurity, or a silicon material not doped with an impurity. 
     In some example embodiments, the ground selection lines GSL_ 1  and GSL_ 2  and a portion of the surface layers S 1  and S 2  adjacent to the ground selection lines GSL_ 1  and GSL_ 2  may form ground selection transistors (e.g., the ground selection transistor GST in  FIG.  4   ). In addition, the wordlines WL 1 _ 1  to WL 4 _ 2  and a portion of the surface layers S 1  and S 2  adjacent to the wordlines WL 1 _ 1  to WL 4 _ 2  may form memory cells (e.g., the memory cells MC 1  to MC 8  in  FIG.  4   ). Further, the string selection lines SSL_ 1  and SSL_ 2  and a portion of the surface layers S 1  and S 2  adjacent to the string selection lines SSL_ 1  and SSL_ 2  may form string selection transistors (e.g., the string selection transistor SST in  FIG.  4   ). 
     Drain regions DR may be formed on the pillars P 1  and P 2 . The drain regions DR may be electrically connected to the bitlines BL_ 1  and BL_ 2  by at least the upper contacts UMC. In some example embodiments, the drain regions DR may include a silicon material doped with an impurity. An etch-stop layer  53  may be formed on a side wall of the drain regions DR. A top surface of the etch-stop layer  53  may be formed on the same level as a top surface of the drain regions DR. 
     As illustrated in  FIGS.  7 A and  7 B , a cross-section of a portion disposed in the first extension region EXR 3 - 1  among the vertical structures VS may form a stepped structure. The stepped structure (or stepped pad structure) may be referred to as a “wordline pad.” In addition, a flat zone may exist in the middle of the stepped structure. 
     As shown in  FIGS.  7 A- 7 B , in a second extension region (e.g., EXR 2 - 2 ), the insulating mold structure IMD 2  may include sacrificial layers  51  and the insulating interlayers  52  that are alternately stacked (e.g., extend in parallel to each other in an alternating pattern) in the third direction D 3  on the upper substrate USUB. The sacrificial layers  51  and the insulating interlayers  52  may both include insulating materials, and may each include insulating materials having different properties. For example, the insulating interlayers  52  may include a silicon oxide based material, and the sacrificial layers  51  may include a silicon nitride based material. The insulating mold structure IMD 2  may also form a stepped structure with a flat zone. The through-hole vias THV may be formed in the flat zone and may be formed by penetrating the insulating mold structure IMD 2 . Thus, there may be no need to further form an insulating material surrounding the through-hole vias THV, which is advantageous in the manufacturing process. 
       FIGS.  8 A,  8 B,  8 C,  8 D,  8 E and  8 F  are cross-sectional views for describing a method of manufacturing a memory device according to some example embodiments. For clear and concise description, manufacturing processes of some elements in  FIGS.  5 ,  6 ,  7 A and  7 B  may be omitted. 
     Referring to  FIG.  8 A , gate structures and source/drain regions may be formed on the lower substrate LSUB, and the lower contacts LMC, the lower conductive lines LPM and the lower insulating layer IL 1  may be formed, such that the second semiconductor layer L 2  that includes a lower substrate LSUB and an address decoder  522  on the lower substrate LSUB is formed as shown in at least  FIG.  8 A , the address decoder  522  configured to control a memory cell array MCA. 
     A semiconductor substrate including crystalline silicon formed of a single crystal and/or crystalline germanium formed of a single crystal may be used as the lower substrate LSUB. In some example embodiments, the lower substrate LSUB may be obtained from a silicon wafer. 
     A gate insulation layer and a gate electrode layer may be formed on the lower substrate LSUB, and then may be etched to form gate insulation layer patterns and gate electrodes. Thus, the gate structures including the gate insulation layer patterns and the gate electrodes sequentially stacked on the lower substrate LSUB may be formed. 
     An ion-implantation process may be performed using the gate structures as an implantation mask to form the source/drain regions at upper portions of the lower substrate LSUB (e.g., the upper surface of the lower substrate LSUB) adjacent to the gate structures. Accordingly, a plurality of transistors TR may be defined and formed on the lower substrate LSUB by at least the gate structures and the source/drain regions. 
     The gate insulation layer may be formed of silicon oxide or a metal oxide by, in some example embodiments, a chemical vapor deposition (CVD) process, a plasma enhanced chemical vapor deposition (PECVD) process, a spin coating process, an atomic layer deposition (ALD) process, etc. In addition, the gate insulation layer may be formed by a thermal oxidation process on a top surface of the lower substrate LSUB. The gate electrode layer may include a metal, a metal nitride or doped polysilicon by, e.g., an ALD process or a sputtering process. 
     After that, the lower contacts LMC, the lower conductive lines LPM and the lower insulating layer IL 1  may be formed on the lower substrate LSUB. 
     In some example embodiments, a first lower insulating layer (e.g., lower insulating layer IL 1 ) covering the gate structures may be formed on the lower substrate LSUB. The lower contacts LMC may be formed through the first lower insulating layer to be in contact with the source/drain regions. The lower conductive lines LPM electrically connected to the lower contacts LMC may be formed on the first lower insulating layer. A second lower insulating layer covering the lower conductive lines LPM may be formed on the first lower insulating. Although one lower insulating layer IL 1  is illustrated in  FIG.  8 A , a plurality of (e.g., two or more of) lower insulating layers may be formed. 
     The lower insulating layer IL 1  may be formed of an insulating material, e.g., silicon oxide by, e.g., a CVD process or a spin coating process. The lower contacts LMC and the lower conductive lines LPM may be formed of a metal or a metal nitride by, e.g., an ALD process or a sputtering process. 
     Referring to  FIG.  8 B , the upper substrate (or a base layer) USUB may be formed on the lower insulating layer IL 1 , and the insulating interlayers  52  and the sacrificial layers  51  may be formed alternately and repeatedly on the upper substrate USUB to form a mold structure. Restated, as shown in  FIG.  8 B , a mold structure may be formed based on repeatedly stacking insulating interlayers  52  and sacrificial layers  51  on the upper substrate USUB alternately along the third direction D 3 . 
     In some example embodiments, the upper substrate USUB may be formed of polysilicon by a sputtering process, a CVD process, an ALD process, a physical vapor deposition (PVD) process, etc. The upper substrate USUB may be formed of polysilicon doped with, e.g., p-type impurities such as boron (B). Here, the upper substrate USUB may serve as a p-type well. 
     In some example embodiments, an amorphous silicon layer may be formed on the lower insulating layer IL 1 , and then a thermal treatment or a laser irradiation may be performed to transform the amorphous silicon layer into the upper substrate USUB including a crystalline silicon of a single crystal. Here, defects in the upper substrate USUB may be cured or substantially cured so that a functional characteristic of the upper substrate USUB as the p-type well may be enhanced. 
     In some example embodiments, the upper substrate USUB may be formed by a wafer bonding process. Here, a wafer (e.g., a crystalline silicon formed of a single crystal wafer) may be attached on the lower insulating layer IL 1 , An upper portion of the wafer may be removed or planarized to form the upper substrate USUB. 
     In some example embodiments, the insulating interlayers  52  may be formed of a silicon oxide based material, e.g., silicon dioxide, silicon oxycarbide and/or silicon oxyfluoride. The sacrificial layers  51  may be formed of a material that may have an etching selectivity with respect to the insulating interlayers  52  and may be easily removed by a wet etching process. In some example embodiments, the sacrificial layers  51  may be formed of a silicon nitride based material, e.g., silicon nitride (SiN) and/or silicon boronitride (SiBN). 
     The insulating interlayers  52  and the sacrificial layers  51  may be formed by a CVD process, a PECVD process, a spin coating process, an ALD process, etc. 
     The sacrificial layers  51  may be removed in a subsequent process to provide spaces for a GSL, wordlines and an SSL. In some example embodiments, each of the GSL and the SSL may be formed in a single level, and the wordlines may be formed in 4 levels. Here, the sacrificial layers  51  may be formed in 6 levels, and the insulating interlayers  52  may be formed in 7 levels as illustrated in  FIG.  6   . However, the stacked number of the GSL, the SSL and the wordlines might not be limited to the examples provided herein. 
     Referring to  FIG.  8 C , among a lateral portion of the mold structure, portions corresponding to the first extension regions EXR 1 - 1  to EXR 4 - 1  and the second extension regions EXR 1 - 2  to EXR 4 - 2  are selectively and partially removed, such that the first and second extension regions EXR 1 - 1  to EXR 4 - 2  are at least partially formed. Thus, the step zones and the flat zones described with reference to  FIGS.  5 ,  6 ,  7 A and  7 B  may be formed. 
     Referring to  FIG.  8 D , wordline cut regions (or gate line cut regions) may be formed to remove portions of the sacrificial layers  51  included in the core regions COR 1  to COR 4  and the first extension regions EXR 1 - 1  to EXR 4 - 1 . In  FIG.  8 D , portions indicated by bold dotted lines may represent the wordline cut regions. 
     In some example embodiments, the wordline cut regions may be formed along boundaries of the core regions COR 1  to COR 4  and boundaries of the first extension regions EXR 1 - 1  to EXR 4 - 1 , may be formed to cross inner portions or interiors (e.g., center portions) of the core regions COR 1  to COR 4  and inner portions or interiors of the first extension regions EXR 1 - 1  to EXR 4 - 1 , and may not be formed in the second extension regions EXR 1 - 2  to EXR 4 - 2  (it may be referred to as WL-Cut skip). Accordingly, the sacrificial layers  51  included in the second extension regions EXR 1 - 2  to EXR 4 - 2  may be maintained without being removed (In other words, W-replacement may not occur), such that the second extension regions EXR 1 - 2  to EXR 4 - 2  each include an insulating mold structure (e.g., IMD 2 ) in which the insulating interlayers  52  and the sacrificial layers  51  are alternately and repeatedly stacked. 
     Referring to  FIG.  8 E , channel holes (not illustrated) may be formed through the mold structure, the pillars P 1  and P 2  including the surface layers S 1  and S 2  and the insides I 1  and  12  may be formed in the channel holes. The drain regions DR capping the channel hole may be formed on the pillars P 1  and P 2 . 
     After that, the sacrificial layers  51  in the core regions COR 1  to COR 4  and the first extension regions EXR 1 - 1  to EXR 4 - 1  may be removed by using the wordline cut regions, thereby forming spaces, and the ground selection lines GSL_ 1  and GSL_ 2 , the wordlines WL 1 _ 1  to WL 4 _ 2  and the string selection lines SSL_ 1  and SSL_ 2  may be formed at the spaces from which the sacrificial layers  51  are removed, for example as shown in at least  FIG.  8 E . 
     Referring to  FIGS.  7 A and  8 F , the upper contacts UMC, the bitlines BL_ 1  and BL_ 2 , the wordline contacts WC, the through-hole vias THV, the upper conductive lines UPM and the upper insulating layer IL 2  may be formed, such that a first semiconductor layer L 1  is formed stacked on the second semiconductor layer L 2  in the third direction D 3 , where the first semiconductor layer L 1  includes the upper substrate USUB and the memory cell array MCA according to any of the example embodiments on the upper substrate USUB. As shown in  FIGS.  8 B- 8 F , forming the first semiconductor layer L 1  may include performing the operations shown and described with reference to some or all of  FIGS.  8 B- 8 F . 
     In some example embodiments, a first upper insulating layer covering the vertical structure VS and the insulating mold structure IMD 2  may be formed on the upper substrate USUB. The upper contacts UMC, the wordline contacts WC and the through-hole vias THV may be formed, in first and second extension regions, respectively, through the first upper insulating layer. The bitlines BL_ 1  and BL_ 2  and the upper conductive lines UPM electrically connected to the upper contacts UMC, the wordline contacts WC and the through-hole vias THV may be formed on the first upper insulating layer. A second upper insulating layer covering the bitlines BL_ 1  and BL_ 2  and the upper conductive lines UPM may be formed on the first upper insulating layer. Forming the upper conductive lines UPM may thus electrically connect the wordlines contacts WC with separate, respective through-hole vias THV. Although one upper insulating layer IL 2  is illustrated in  FIG.  7 A , a plurality of (e.g., two or more of) upper insulating layers may be formed. 
     In the memory device  10  according to some example embodiments that has the memory cell array  100  of the vertical structure and has the COP structure, the through-hole vias THV for electrically connecting the string selection lines SSL, the wordlines WL and the ground selection lines GSL with the peripheral circuit may be formed in the flat zoned FZ 1 - 1  to FZ 4 - 1  of the second extension regions EXR 1 - 2  to EXR 4 - 2 , and may be formed to penetrate the insulating mold structures IMD 1  to IMD 4 . Accordingly, all wordlines may be efficiently connected to the peripheral circuit without additional wiring even if the level (e.g., the number in the third direction D 3 ) of wordlines in the memory cell array increases, and the manufacturing cost may be reduced and the performance degradation may be prevented while the size of the memory device  10  is reduced. 
       FIG.  9    is a plan view of an example of a core region included in a memory cell array of  FIG.  5   . 
     Referring to  FIG.  9   , a core region CR may include a plurality of channel holes CH. 
     A channel hole size, in some example embodiments, a channel hole diameter, may be varied according to positions within the core region CR. In some example embodiments, portions adjacent to first and second edges EDG 1  and EDG 2  may have a relatively low peripheral density, and thus channel holes CHa adjacent to the first and second edges EDG 1  and EDG 2  may have different diameters from those of the other channel holes CH. Channel holes CHb located in a center of the core region CR may have diameters larger than those of the channel holes CHa adjacent to the first and second edges EDG 1  and EDG 2 . A memory block BLKa may be adjacent to the second edge EDG 2 , and may be spaced apart from the second edge EDG 2  by a first distance d 1 . A memory block BLKb may not be adjacent to the first and second edges EDG 1  and EDG 2 , may be in the center of the core region CR, and may be spaced apart from the second edge EDG 2  by a second distance d 2 . The second distance d 2  may be greater than the first distance d 1 . A first diameter of the channel hole CHa included in the memory block BLKa may be smaller than a second diameter of the channel hole CHb included in the memory block BLKb. 
       FIGS.  10 ,  11 ,  12  and  13    are plan views of examples of a memory cell array included in a memory device according to some example embodiments. The descriptions repeated with  FIGS.  5 ,  6 ,  7 A and  7 B  will be omitted. 
     As with the example of  FIG.  6   ,  FIGS.  10 ,  11 ,  12  and  13    are enlarged plan views showing a portion of the memory cell array. For convenience, the upper conductive lines UPM are illustrated as bold lines in  FIGS.  10 ,  11 ,  12  and  13   . 
     Referring to  FIG.  10   , an example of  FIG.  10    may be the same or substantially the same as the example of  FIG.  6   , except that a memory cell array  100   a  of  FIG.  10    further includes wordline flat zones WFZ 1 - 2  and WFZ 3 - 2  and a flat zone FZ 2 - 2 .  FIG.  10    illustrates an example where the number (“quantity”) of step zones and the number of wordline step zones are equal or substantially equal to the number of flat zones and the number of wordline flat zones, respectively. As shown in  FIG.  10   , for example, the second extension region EXR 2 - 2  of the second memory block BLK 2 , the step zones of the second extension region EXR 2 - 2  includes a first step zone SZ 2 - 1  and a second step zone SZ 2 - 2  that extend sequentially in a first series pattern along the first direction D 1 , the flat zones of the second extension region EXR 2 - 2  include a first flat zone FZ 2 - 1  and a second flat zone FZ 2 - 2  that extend sequentially in a second series pattern along the first direction D 1 , and the first flat zone FZ 2 - 1  is between the first step zone SZ 2 - 1  and the second step zone SZ 2 - 2  in the first direction D 1 , and the second step zone SZ 2 - 2  is between the first flat zone FZ 2 - 1  and the second flat zone FZ 2 - 2  in the first direction D 1 . 
     As shown in  FIG.  10   , a quantity of step zones in each extension region may be equal to the quantity of flat zones in each extension region. The quantity of step zones in the memory cell array may be equal to the quantity of flat zones in the memory cell array. 
     The plurality of through-hole vias THY may be formed to penetrate the insulating mold structure IMD 2  in the flat zones FZ 2 - 1  and FZ 2 - 2  of the second extension region EXR 2 - 2 . In the example of  FIG.  10   , the sizes (or areas) of the flat zones FZ 2 - 1  and FZ 2 - 2  may be the same or substantially the same as each other, and the number (e.g., quantity) (or density) of the through-hole vias THV formed in the flat zones FZ 2 - 1  and FZ 2 - 2  may be equal or substantially equal to each other. The wordline contacts WC formed in the wordline step zones WSZ 1 - 1  and WSZ 3 - 1  may be connected to the through-hole vias THV in the flat zone FZ 2 - 1 , and the wordline contacts WC formed in the wordline step zones WSZ 1 - 2  and WSZ 3 - 2  may be connected to the through-hole vias THY in the flat zone FZ 2 - 2 . As shown in  FIG.  10   , the first quantity of through-hole vias THV 1  in the first flat zone FZ 2 - 1  may be equal to a second quantity of through-hole vias THV 2  in the second flat zone FZ 2 - 2 . 
     Referring to  FIG.  11   , an example of  FIG.  11    may be the same or substantially the same as the example of  FIG.  6   , except that wordline flat zones WFZ 1 - 1   b  and WFZ 3 - 1   b  and a flat zone FZ 2 - 1   b  in a memory cell array  100   b  of  FIG.  11    are changed. 
     In the example of  FIG.  11   , the sizes of the wordline flat zones WFZ 1 - 1   b  and WFZ 3 - 1   b  and the flat zone FZ 2 - 1   b  may be larger than the sizes of the wordline flat zones WFZ 1 - 1  and WFZ 3 - 1  and the flat zone FZ 2 - 1  in  FIG.  6   , and the number of the through-hole vias THV formed in the flat zone FZ 2 - 1   b  may be greater than the number of the through-hole vias THV formed in the flat zone FZ 2 - 1  in  FIG.  6   . The wordline contacts WC formed in the wordline step zones WSZ 1 - 1 , WSZ 1 - 2 , WSZ 3 - 1  and WSZ 3 - 2  may be connected to the through-hole vias THV in the flat zone FZ 2 - 1   b.    
     Referring to  FIG.  12   , an example of  FIG.  12    may be the same or substantially the same as the example of  FIG.  10   , except that wordline flat zones WFZ 1 - 1   c,  WFZ 1 - 2   c,  WFZ 3 - 1   c  and WFZ 3 - 2   c  and flat zones FZ 2 - 1   c  and FZ 2 - 2   c  in a memory cell array  100   c  of  FIG.  12    are changed. 
     A plurality of through-hole vias THV 1  and THV 2  may be formed to penetrate the insulating mold structure IMD 2  in the flat zones FZ 2 - 1   c  and FZ 2 - 2   c  of the second extension region EXR 2 - 2 . In the example of  FIG.  12   , the number of through-hole vias THV 1  formed in the flat zone FZ 2 - 1   c  and the number of through-hole vias THV 2  formed in the flat zone FZ 2 - 2   c  may be different from each other. In some example embodiments, the sizes of the wordline flat zones WFZ 1 - 1   c  and WFZ 3 - 1   c  and the flat zone FZ 2 - 1   c  may be larger than the sizes of the wordline flat zones WFZ 1 - 2   c  and WFZ 3 - 2   c  and the flat zone FZ 2 - 2   c,  and thus the number of through-hole vias THV 1  formed in the flat zone FZ 2 - 1   c  may be greater than the number of through-hole vias THV 2  formed in the flat zone FZ 2 - 2   c.  The wordline contacts WC formed in the wordline step zones WSZ 1 - 1  and WSZ 3 - 1  and some of the wordline contacts WC formed in the wordline step zones WSZ 1 - 2  and WSZ 3 - 2  may be connected to the through-hole vias THV 1  in the flat zone FZ 2 - 1   c,  and the rest or remainder of the wordline contacts WC formed in the wordline step zones WSZ 1 - 2  and WSZ 3 - 2  may be connected to the through-hole vias THV 2  in the flat zone FZ 2 - 2   c.  Accordingly, and as shown in  FIG.  12   , among the plurality of through-hole vias THV in the flat zones of the second extension region EXR 2 - 2 , a first quantity of through-hole vias THV 1  in the first flat zone FZ 2 - 1   c  is different from (e.g., greater than) a second quantity of through-hole vias THV 2  in the second flat zone FZ 2 - 2   c.  As further shown in  FIG.  12   , a size (e.g., area A 1  and/or volume) of the first flat zone FZ 2 - 1   c  may be different from (e.g., greater than) a size (e.g., area A 2  and/or volume) of the second flat zone FZ 2 - 2   c.    
     Referring to  FIG.  13   , an example of  FIG.  13    may be the same or substantially the same as the example of  FIG.  10   , except that wordline step zones WSZ 1 - 1   d,  WSZ 1 - 2   d,  WSZ 3 - 1   d  and WSZ 3 - 2   d,  step zones SZ 2 - 1   d  and SZ 2 - 2   d  and flat zones FZ 2 - 1   d  and FZ 2 - 2   d  in a memory cell array  100   d  of  FIG.  13    are changed. As further shown in  FIG.  13   , a size (e.g., area A 3  and/or volume) of the first step zone SZ 2 - 1   d  may be different from (e.g., greater than) a size (e.g., area A 4  and/or volume) of the second step zone SZ 2 - 2   d,  and the first quantity of through-hole vias THY in the first flat zone FZ 2 - 1   d  may be different from (e.g., greater than) a second quantity of through-hole vias THV 2  in the second flat zone FZ 2 - 2   d.    
     The plurality of through-hole vias THV 1  and THV 2  may be formed to penetrate the insulating mold structure IMD 2  in the flat zones FZ 2 - 1   d  and FZ 2 - 2   d  in the second extension region EXR 2 - 2 . In the example of  FIG.  13   , the number of through-hole vias THV 1  formed in the flat zone FZ 2 - 1   d  and the number of through-hole vias THV 2  formed in the flat zone FZ 2 - 2   d  may be different from each other. In some example embodiments, the sizes of the wordline flat zones WFZ 1 - 1   d  and WFZ 3 - 1   d  and the flat zone FZ 2 - 1   d  may be larger than the sizes of the wordline flat zones WFZ 1 - 2   d  and WFZ 3 - 2   d  and the flat zone FZ 2 - 2   d,  and thus the number of through-hole vias THV 1  formed in the flat zone FZ 2 - 1   d  may be greater than the number of through-hole vias THV 2  formed in the flat zone FZ 2 - 2   d.  The wordline contacts WC formed in the wordline step zones WSZ 1 - 1   d  and WSZ 3 - 1   d  may be connected to the through-hole vias THV 1  in the flat zone FZ 2 - 1   d,  and the wordline contacts WC formed in the wordline step zones WSZ 1 - 2   d  and WSZ 3 - 2   d  may be connected to the through-hole vias THV 2  in the flat zone FZ 2 - 2   d.    
     In some example embodiments, two or more of the examples described above may be combined to implement the memory device according to some example embodiments. Although example embodiments are described based on specific numbers of memory blocks, step zones, flat zones and through-hole vias, some example embodiments are not limited thereto. 
       FIG.  14    is a block diagram illustrating an example of an address decoder included in a memory device according to some example embodiments. 
     Referring to  FIG.  14   , an address decoder  600  may include a decoder  610  (e.g., decoder circuit) and a switch circuit  620 . 
     The decoder  610  may receive an address ADDR (e.g., address signal), and may generate a selection signal SS that selects at least a portion of a memory cell array MCA as indicated by at least the address ADDR. The decoder  610  may provide the selection signal SS to the switch circuit  620 . 
     The switch circuit  620  may be connected to separate, respective selection lines SL connected to a voltage generator  650 . The switch circuit  620  may be connected to the memory cell array MCA through at least one string selection line SSL, a plurality of wordlines WL 1  to WLn and at least one ground selection line GSL. 
     The switch circuit  620  may include a plurality of pass transistors PT 11 , PT 12 , PT 13  and PT 14  and a switch controller  621  (e.g., switch control circuit). The plurality of pass transistors PT 11  to PT 14  may be connected to the voltage generator  650  through separate, respective selection lines SL, and may be connected to the string selection line SSL, the plurality of wordlines WL 1  to WLn and the ground selection line GSL of the memory cell array MCA, respectively. The switch controller  621  (also referred to herein as a switch control circuit) may generate a switching control signal SCS based on the selection signal SS to control turn-on and turn-off of the plurality of pass transistors PT 11  to PT 14  and turn-on timing of the plurality of pass transistors PT 11  to PT 14 . 
     The string selection line SSL, the plurality of wordlines WL 1  to WLn and the ground selection line GSL may be electrically connected to separate, respective pass transistors of the plurality of pass transistors PT 11  to PT 14  by at least the through-hole vias THV described with reference to  FIG.  5    and the like. 
       FIG.  15    is a cross-sectional view of a memory package according to some example embodiments. 
     Referring to  FIG.  15   , a memory package  700  includes a base substrate  710  and a plurality of memory chips CHP 1 , CHP 2  and CHP 3  stacked on the base substrate  710 . 
     Each of the memory chips CHP 1 , CHP 2 , and CHP 3  may include a peripheral circuit region PCR and a memory cell region MCR, and may further include a plurality of I/O pads IOPAD. The peripheral circuit region PCR and the memory cell region MCR in  FIG.  15    may correspond to the second semiconductor layer L 2  and the first semiconductor layer L 1  described with reference to  FIG.  1   , respectively, and further may include said elements described herein to be included in the second semiconductor layer L 2  and the first semiconductor layer L 1 , respectively, according to any of the example embodiments. For example, the memory cell region MCR may include an upper substrate USUB and a memory cell array MCA thereon and including memory blocks extending along the second direction D 2 , and the peripheral circuit region PCR may include a lower substrate LSUB and an address decoder ADEC configured to control the memory cell array, where the memory blocks may have a same structure according to any of the example embodiments of memory blocks. The plurality of I/O pads IOPAD may be formed on the memory cell area MCR. The plurality of memory chips CHP 1 , CHP 2 , and CHP 3  may include the memory device according to some example embodiments. 
     In some example embodiments, the plurality of memory chips CHP 1 , CHP 2 , and CHP 3  may be stacked on the base substrate  710  such that a surface on which the plurality of I/O pads IOPAD are formed faces upwards. In some example embodiments, the plurality of memory chips CHP 1 , CHP 2 , and CHP 3  may be stacked in a downside-down state such that a second surface (e.g., a bottom surface) of the semiconductor substrate of each memory chip faces downwards. In other words, with respect to each of the plurality of memory chips CHP 1 , CHP 2 , and CHP 3 , the memory cell region MCR may be located on the peripheral circuit region PCR. 
     In some example embodiments, with respect to each of the plurality of memory chips CHP 1 , CHP 2 , and CHP 3 , the plurality of I/O pads IOPAD may be arranged near one side of the semiconductor substrate. As such, the plurality of memory chips CHP 1 , CHP 2 , and CHP 3  may be stacked scalariformly, that is, in a step shape, such that the plurality of I/O pads IOPAD of each memory chip may be exposed. In such stacked state, the plurality of memory chips CHP 1 , CHP 2 , and CHP 3  may be electrically connected to the base substrate  710  through a plurality of bonding wires BW. 
     The plurality of stacked memory chips CHP 1 , CHP 2 , and CHP 3  and the plurality of bonding wires BW may be fixed by a sealing member  740 , and adhesive members  730  may intervene between the base substrate  710  and the plurality of memory chips CHP 1 , CHP 2 , and CHP 3 . Conductive bumps  720  may be formed on a bottom surface of the base substrate  710  for electrical connections to the external device. 
       FIG.  16    is a block diagram illustrating a storage device including a memory device (also referred to herein as a storage device) according to some example embodiments. 
     Referring to  FIG.  16   , a storage device  1000  includes a plurality of nonvolatile memory devices  1100  and a controller  1200  (e.g., control circuit). In some example embodiments, the storage device  1000  may be any storage device such as an embedded multimedia card (eMMC), a universal flash storage (UFS), a solid state disc or solid state drive (SSD), etc. 
     The controller  1200  may be connected to the nonvolatile memory devices  1100  via a plurality of channels CH 1 , CH 2 , CH 3 , . . . , CHi. The controller  1200  may include one or more processors  1210 , a buffer memory  1220 , an error correction code (ECC) circuit  1230 , a host interface  1250  and a nonvolatile memory interface  1260 , connected via at least one bus  1205 . 
     The buffer memory  1220  may store data used to drive the controller  1200 . The ECC circuit  1230  may calculate error correction code values of data to be programmed during a program operation, and may correct an error of read data using an error correction code value during a read operation. In a data recovery operation, the ECC circuit  1230  may correct an error of data recovered from the nonvolatile memory devices  1100 . The host interface  1250  may provide an interface with an external device. The nonvolatile memory interface  1260  may provide an interface with the nonvolatile memory devices  1100 . 
     Each of the nonvolatile memory devices  1100  may correspond to the memory device according to some example embodiments, and may be optionally supplied with an external high voltage VPP. 
       FIG.  17    is a cross-sectional view of a nonvolatile memory device according to example embodiments. 
     Referring to  FIG.  17   , a nonvolatile memory device or a memory device  2000  may have a chip-to-chip (C2C) structure. The C2C structure may refer to a structure formed by manufacturing an upper chip including a memory cell region or a cell region CELL on a first wafer, manufacturing a lower chip including a peripheral circuit region PERI on a second wafer, different from the first wafer, and then connecting the upper chip and the lower chip in a bonding manner. For example, the bonding manner may include a method of electrically connecting a bonding metal formed on an uppermost metal layer of the upper chip and a bonding metal formed on an uppermost metal layer of the lower chip. For example, when the bonding metals may be formed of copper (Cu), the bonding manner may be a Cu-Cu bonding, and the bonding metals may also be formed of aluminum or tungsten. 
     Each of the peripheral circuit region PERI and the cell region CELL of the memory device  2000  may include an external pad bonding area PA, a wordline bonding area WLBA, and a bitline bonding area BLBA. 
     The peripheral circuit region PERI may include a first substrate  2210 , an interlayer insulating layer  2215 , a plurality of circuit elements  2220   a,    2220   b,  and  2220   c  formed on the first substrate  2210 , first metal layers  2230   a,    2230   b,  and  2230   c  respectively connected to the plurality of circuit elements  2220   a,    2220   b,  and  2220   c,  and second metal layers  2240   a,    2240   b , and  2240   c  formed on the first metal layers  2230   a,    2230   b,  and  2230   c.  In an example embodiment, the first metal layers  2230   a,    2230   b,  and  2230   c  may be formed of tungsten having relatively high resistance, and the second metal layers  2240   a,    2240   b,  and  2240   c  may be formed of copper having relatively low resistance. 
     In an example embodiment illustrate in  FIG.  17   , although the first metal layers  2230   a ,  2230   b,  and  2230   c  and the second metal layers  2240   a,    2240   b,  and  2240   c  are shown and described, they are not limited thereto, and one or more metal layers may be further formed on the second metal layers  2240   a,    2240   b,  and  2240   c.  At least a portion of the one or more metal layers formed on the second metal layers  2240   a,    2240   b,  and  2240   c  may be formed of aluminum or the like having a lower resistance than those of copper forming the second metal layers  2240   a,    2240   b,  and  2240   c.    
     The interlayer insulating layer  2215  may be disposed on the first substrate  2210  and cover the plurality of circuit elements  2220   a,    2220   b,  and  2220   c,  the first metal layers  2230   a ,  2230   b,  and  2230   c,  and the second metal layers  2240   a,    2240   b,  and  2240   c.  The interlayer insulating layer  2215  may include an insulating material such as silicon oxide, silicon nitride, or the like. 
     Lower bonding metals  2271   b  and  2272   b  may be formed on the second metal layer  2240   b  in the wordline bonding area WLBA. In the wordline bonding area WLBA, the lower bonding metals  2271   b  and  2272   b  in the peripheral circuit region PERI may be electrically connected to upper bonding metals  2371   b  and  2372   b  in the cell region CELL in a bonding manner, and the lower bonding metals  2271   b  and  2272   b  and the upper bonding metals  2371   b  and  2372   b  may be formed of aluminum, copper, tungsten, or the like. Further, the upper bonding metals  2371   b  and  2372   b  in the cell region CELL may be referred as first metal pads and the lower bonding metals  2271   b  and  2272   b  in the peripheral circuit region PERI may be referred as second metal pads. 
     The cell region CELL may include at least one memory block. The cell region CELL may include a second substrate  2310  and a common source line  2320 . On the second substrate  2310 , a plurality of wordlines  2331 ,  2332 ,  2333 ,  2334 ,  2335 ,  2336 ,  2337 , and  2338  (i.e.,  2330 ) may be stacked in a third direction D 3 , perpendicular to an upper surface of the second substrate  2310 . At least one string selection line and at least one ground selection line may be arranged on and below the plurality of wordlines  2330 , respectively, and the plurality of wordlines  2330  may be disposed between the at least one string selection line and the at least one ground selection line. 
     In the bitline bonding area BLBA, a channel structure CH may extend in the third direction D 3 , perpendicular to the upper surface of the second substrate  2310 , and pass through the plurality of wordlines  2330 , the at least one string selection line, and the at least one ground selection line. The channel structure CH may include a data storage layer, a channel layer, a buried insulating layer, and the like, and the channel layer may be electrically connected to a first metal layer  2350   c  and a second metal layer  2360   c.  For example, the first metal layer  2350   c  may be a bitline contact, and the second metal layer  2360   c  may be a bitline. In an example embodiment, the bitline  2360   c  may extend in a second direction D 2 , parallel to the upper surface of the second substrate  2310 . 
     In an example embodiment illustrated in  FIG.  32   , an area in which the channel structure CH, the bitline  2360   c,  and the like are disposed may be defined as the bitline bonding area BLBA. In the bitline bonding area BLBA, the bitline  2360   c  may be electrically connected to the circuit elements  2220   c  providing a page buffer  2393  in the peripheral circuit region PERI. For example, the bitline  2360   c  may be connected to upper bonding metals  2371   c  and  2372   c  in the cell region CELL, and the upper bonding metals  2371   c  and  2372   c  may be connected to lower bonding metals  2271   c  and  2272   c  connected to the circuit elements  2220   c  of the page buffer  2393 . 
     In the wordline bonding area WLBA, the plurality of wordlines  2330  may extend in a first direction D 1 , parallel to the upper surface of the second substrate  2310 , and may be connected to a plurality of cell contact plugs  2341 ,  2342 ,  2343 ,  2344 ,  2345 ,  2346 , and  2347  (i.e.,  2340 ). The plurality of wordlines  2330  and the plurality of cell contact plugs  2340  may be connected to each other in pads provided by at least a portion of the plurality of wordlines  2330  extending in different lengths in the first direction D 1 . A first metal layer  2350   b  and a second metal layer  2360   b  may be connected to an upper portion of the plurality of cell contact plugs  2340  connected to the plurality of wordlines  2330 , sequentially. The plurality of cell contact plugs  2340  may be connected to the circuit region PERI by the upper bonding metals  2371   b  and  2372   b  of the cell region CELL and the lower bonding metals  2271   b  and  2272   b  of the peripheral circuit region PERI in the wordline bonding area WLBA. 
     The plurality of cell contact plugs  2340  may be electrically connected to the circuit elements  2220   b  providing a row decoder  2394  in the peripheral circuit region PERI. In an example embodiment, operating voltages of the circuit elements  2220   b  providing the row decoder  2394  may be different than operating voltages of the circuit elements  2220   c  providing the page buffer  2393 . For example, operating voltages of the circuit elements  2220   c  providing the page buffer  2393  may be greater than operating voltages of the circuit elements  2220   b  providing the row decoder  2394 . 
     A common source line contact plug  2380  may be disposed in the external pad bonding area PA. The common source line contact plug  2380  may be formed of a conductive material such as a metal, a metal compound, polysilicon, or the like, and may be electrically connected to the common source line  2320 . A first metal layer  2350   a  and a second metal layer  2360   a  may be stacked on an upper portion of the common source line contact plug  2380 , sequentially. For example, an area in which the common source line contact plug  2380 , the first metal layer  2350   a,  and the second metal layer  2360   a  are disposed may be defined as the external pad bonding area PA. 
     Input/output pads  2205  and  2305  may be disposed in the external pad bonding area PA. A lower insulating film  2201  covering a lower surface of the first substrate  2210  may be formed below the first substrate  2210 , and a first input/output pad  2205  may be formed on the lower insulating film  2201 . The first input/output pad  2205  may be connected to at least one of the plurality of circuit elements  2220   a,    2220   b,  and  2220   c  disposed in the peripheral circuit region PERI through a first input/output contact plug  2203 , and may be separated from the first substrate  2210  by the lower insulating film  2201 . In addition, a side insulating film may be disposed between the first input/output contact plug  2203  and the first substrate  2210  to electrically separate the first input/output contact plug  2203  and the first substrate  2210 . 
     An upper insulating film  2301  covering the upper surface of the second substrate  2310  may be formed on the second substrate  2310 , and a second input/output pad  2305  may be disposed on the upper insulating layer  2301 . The second input/output pad  2305  may be connected to at least one of the plurality of circuit elements  2220   a,    2220   b,  and  2220   c  disposed in the peripheral circuit region PERI through a second input/output contact plug  2303 . 
     According to embodiments, the second substrate  2310  and the common source line  2320  may not be disposed in an area in which the second input/output contact plug  2303  is disposed. Also, the second input/output pad  2305  may not overlap the wordlines  2330  in the third direction D 3 . The second input/output contact plug  2303  may be separated from the second substrate  2310  in the direction, parallel to the upper surface of the second substrate  310 , and may pass through the interlayer insulating layer  2315  of the cell region CELL to be connected to the second input/output pad  2305 . 
     According to embodiments, the first input/output pad  2205  and the second input/output pad  2305  may be selectively formed. For example, the memory device  2000  may include only the first input/output pad  2205  disposed on the first substrate  2210  or the second input/output pad  2305  disposed on the second substrate  2310 . Alternatively, the memory device  200  may include both the first input/output pad  2205  and the second input/output pad  2305 . 
     A metal pattern in an uppermost metal layer may be provided as a dummy pattern or the uppermost metal layer may be absent, in each of the external pad bonding area PA and the bitline bonding area BLBA, respectively included in the cell region CELL and the peripheral circuit region PERI. 
     In the external pad bonding area PA, the memory device  2000  may include a lower metal pattern  2273   a,  corresponding to an upper metal pattern  2372   a  formed in an uppermost metal layer of the cell region CELL, and having the same shape as the upper metal pattern  2372   a  of the cell region CELL, in an uppermost metal layer of the peripheral circuit region PERI. In the peripheral circuit region PERI, the lower metal pattern  2273   a  formed in the uppermost metal layer of the peripheral circuit region PERI may not be connected to a contact. Similarly, in the external pad bonding area PA, an upper metal pattern, corresponding to the lower metal pattern formed in an uppermost metal layer of the peripheral circuit region PERI, and having the same shape as a lower metal pattern of the peripheral circuit region PERI, may be formed in an uppermost metal layer of the cell region CELL. 
     The lower bonding metals  2271   b  and  2272   b  may be formed on the second metal layer  2240   b  in the wordline bonding area WLBA. In the wordline bonding area WLBA, the lower bonding metals  2271   b  and  2272   b  of the peripheral circuit region PERI may be electrically connected to the upper bonding metals  2371   b  and  2372   b  of the cell region CELL by a Cu—Cu bonding. 
     Further, the bitline bonding area BLBA, an upper metal pattern  2392 , corresponding to a lower metal pattern  2252  formed in the uppermost metal layer of the peripheral circuit region PERI, and having the same shape as the lower metal pattern  2252  of the peripheral circuit region PERI, may be formed in an uppermost metal layer of the cell region CELL. A contact may not be formed on the upper metal pattern  2392  formed in the uppermost metal layer of the cell region CELL. 
     In an example embodiment, corresponding to a metal pattern formed in an uppermost metal layer in one of the cell region CELL and the peripheral circuit region PERI, a reinforcement metal pattern having the same shape as the metal pattern may be formed in an uppermost metal layer in another one of the cell region CELL and the peripheral circuit region PERI, and a contact may not be formed on the reinforcement metal pattern. 
     The memory device  2000  may be the memory device according to example embodiments. 
     The inventive concept may be applied to various electronic devices and/or systems including the memory devices and the memory packages. In some example embodiments, the inventive concept may be applied to systems such as a personal computer (PC), a server computer, a data center, a workstation, a mobile phone, a smart phone, a tablet computer, a laptop computer, a personal digital assistant (PDA), a portable multimedia player (PMP), a digital camera, a portable game console, a music player, a camcorder, a video player, a navigation device, a wearable device, an internet of things (IoT) device, an internet of everything (IoE) device, an e-book reader, a virtual reality (VR) device, an augmented reality (AR) device, a robotic device, a drone, etc. 
     The foregoing is illustrative of example embodiments and is not to be construed as limiting thereof. Although some example embodiments have been described, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from the novel teachings and advantages of the example embodiments. Accordingly, all such modifications are intended to be included within the scope of the example embodiments as defined in the claims. Therefore, it is to be understood that the foregoing is illustrative of various example embodiments and is not to be construed as limited to the specific example embodiments disclosed, and that modifications to the disclosed example embodiments, as well as other example embodiments, are intended to be included within the scope of the appended claims.