Patent Publication Number: US-2023146041-A1

Title: Non-volatile memory device including multi-stack memory block and operating method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application Nos. 10-2021-0154260, filed on Nov. 10, 2021, in the Korean Intellectual Property Office, and 10-2022-0039874, filed on Mar. 30, 2022, in the Korean Intellectual Property Office, the disclosures of each of which are incorporated by reference herein in their entireties. 
     BACKGROUND 
     The inventive concepts relate to a non-volatile memory device including a multi-stack memory block, and/or an operating method thereof. 
     A system using semiconductor chips uses dynamic random access memory (DRAM) as an operating memory or main memory to store data or instructions used by a host or to perform a computational operation, and uses a storage device including a non-volatile memory as a storage medium. As demands for storage devices having a large capacity have increased, the number of memory cells and word lines stacked on a substrate of a non-volatile memory has increased. 
     SUMMARY 
     One or more example embodiments relates to a highly-reliable non-volatile memory device in which a threshold voltage of dummy word lines is monitored and a block reset operation is performed based on a result of the monitoring. 
     According to an example embodiment of the inventive concepts, an operating method of a memory system including a memory controller and a non-volatile memory device, the non-volatile memory device being operated under a control of the memory controller and the non-volatile memory device including a first memory block and a second memory block, the method includes determining, by the memory controller, whether the first memory block satisfies a block reset condition, in response to the first memory block satisfying the block reset condition, applying a turn-on voltage to word lines of dummy cells included in the first memory block, transferring data pre-programmed in the first memory block to the second memory block, erasing the first memory block, and re-programming the dummy cells of the first memory block. 
     According to an example embodiment of the inventive concepts, an operating method of a non-volatile memory device, the non-volatile memory device including first to third memory blocks, each of the first to third memory blocks including a first sub-block, a second sub-block, and a dummy block, wherein the first sub-block includes a first plurality of memory cells, the second sub-block includes a second plurality of memory cells, and the dummy block includes a plurality of dummy cells, the second sub-block being arranged on the first sub-block, and the dummy block is arranged between the first sub-block and the second sub-block. The method includes receiving a command for the first memory block to perform an operation, in response to the first memory block satisfying the block reset condition, performing a block reset operation by the first memory block, wherein the performing of the block reset operation includes applying a turn-on voltage to dummy word lines included in the dummy block of the first memory block, transferring, to the second memory block, data previously programmed in the first sub-block or the second sub-block of the first memory block, performing an erase operation entirely on the first memory block, and re-programming the dummy cells of the first memory block. 
     According to an example embodiment of the inventive concepts, a semiconductor apparatus includes a memory controller configured to generate any one of a program command, a read command, or an erase command, and a non-volatile memory device which is operated under a control of the memory controller, the non-volatile memory device includes a first memory block and a second memory block, wherein the memory controller is configured to determine whether the first memory block satisfies a block reset condition, and the non-volatile memory device is configured to, in response to the first memory block satisfying the block reset condition, apply a turn-on voltage to word lines of dummy cells included in the first memory block, transfer data previously programmed in the first memory block to the second memory block, then erase the first memory block, and re-program the dummy cells of the first memory block. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Example embodiments of the inventive concepts will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a flowchart of a block reset method of a non-volatile memory device, according to some example embodiments of the inventive concepts; 
         FIG.  2    is a conceptual block diagram of a memory system according to some example embodiments of the inventive concepts; 
         FIG.  3    is a block diagram of a non-volatile memory device according to some example embodiments of the inventive concepts; 
         FIG.  4    is a perspective view illustrating a memory block according to some example embodiments of the inventive concepts; 
         FIG.  5    is an equivalent circuit diagram of a non-volatile memory device according to some example embodiments of the inventive concepts; 
         FIG.  6    is a flowchart of an erase method of a non-volatile memory device, according to some example embodiments of the inventive concepts; 
         FIG.  7    is a flowchart of a program method of a non-volatile memory device, according to some example embodiments of the inventive concepts; 
         FIG.  8    is a flowchart of a program method of a non-volatile memory device, according to some example embodiments of the inventive concepts; 
         FIG.  9    is a diagram illustrating a distribution of threshold voltages of memory cells that are programmed, according to some example embodiments of the inventive concepts; 
         FIG.  10    is a flowchart of a data recovery method of a non-volatile memory device when a read error occurs, according to some example embodiments of the inventive concepts; 
         FIG.  11    is a cross-sectional view illustrating a structure of a non-volatile memory device according to some example embodiments of the inventive concepts; 
         FIG.  12    is a block diagram of a computing system according to some example embodiments of the inventive concepts; and 
         FIG.  13    is a block diagram of a solid-state drive (SSD) system according to some example embodiments of the inventive concepts. 
     
    
    
     DETAILED DESCRIPTION OF THE EXAMPLE EMBODIMENTS 
     Hereinafter, example embodiments will be described in detail with reference to the accompanying drawings. 
     When describing with reference to the drawings, the same or corresponding elements are given the same reference characters, and redundant descriptions thereof are omitted. 
       FIG.  1    is a flowchart of a block reset method S 100  of a non-volatile memory device, according to some example embodiments of the inventive concepts. 
     Referring to  FIG.  1   , the block reset method S 100  of the non-volatile memory device may include a plurality of operations S 110  to S 150 . A plurality of cell strings may be divided into two sub-blocks, as described later with reference to  FIG.  5   , or may be divided into three or more sub-blocks. The plurality of cell strings may include a dummy block between the sub-blocks, as described later with reference to  FIG.  5   . 
     In operation S 110 , it may be determined whether a first memory block (BLK 1  in  FIG.  3   ) satisfies a block reset condition. To determine whether the block reset condition is satisfied, a threshold voltage (Vth, DC ) of dummy cells included in a dummy block (DB in  FIGS.  4  and  5   ) may be monitored. The threshold voltage (Vth, DC ) of the dummy cells may be compared to a first reference voltage V 1 . When a voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than a voltage level of the first reference voltage V 1 , an error may occur during a read operation. In other words, the voltage level of the first reference voltage V 1  may have a threshold value at which the first memory block (BLK 1  in  FIG.  3   ) may normally perform a read operation. Normally performing a read operation or other operation means performing a read operation under the designed conditions for the read operation. A read operation performed under conditions other than the designed conditions (for example if the voltage level of the first voltage V 1  is below a threshold voltage) may cause the read operation to be unsuccessful. Accordingly, the voltage level of the first reference voltage V 1  may have a reference value for determining whether a block reset operation is necessary or desired. The voltage level of the first reference voltage V 1  may have a preset value or may have a value input by a user. The voltage level of the first reference voltage V 1  is described in greater detail later with reference to  FIG.  9   . 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the first memory block (BLK 1  in  FIG.  3   ) may not satisfy the block reset condition. Accordingly, operation S 110  may be terminated. In other words, when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , it may be determined that the block reset operation is unnecessary or undesired. 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the first memory block (BLK 1  in  FIG.  3   ) may satisfy the block reset condition. Accordingly, operation S 120  may be performed. In other words, when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , it may be determined that the block reset operation is necessary or desired. Consequently, it may also be determined to perform the block reset operation. 
     In operation S 120 , a turn-on voltage may be applied to word lines of the dummy cells. A voltage level of the turn-on voltage may be greater than the voltage level of the threshold voltage (Vth, DC ) of the dummy cells. When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the voltage level of the turn-on voltage may be greater than a voltage level of a voltage applied to the word lines of the dummy cells to turn on the dummy cells. For example, the voltage level of the turn-on voltage may be greater than a maximum voltage level (e.g., first voltage level) that may be achieved by a read voltage or that the read voltage is configured to obtain. The read voltage may include a voltage applied to word lines of memory cells included in a sub-block during a read operation. For example, the voltage level of the turn-on voltage may be greater than the voltage level of the first reference voltage V 1 . Accordingly, a channel may be provided in the dummy cell. 
     In operation S 130 , data pre-programmed in a sub-block included in the first memory block (BLK 1  in  FIG.  3   ) may be transferred to a second memory block (BLK 2  in  FIG.  3   ). For example, when a first sub-block (SB 1  in  FIG.  5   ) and a second sub-block (SB 2  in  FIG.  5   ) arranged at an upper end (e.g., above) of the first sub-block (SB 1  in  FIG.  5   ) are included in the first memory block (BLK 1  in  FIG.  5   ) and the first sub-block (SB 1  in  FIG.  5   ) is pre-programmed, data pre-programmed in the first sub-block (SB 1  in  FIG.  5   ) may be transferred to the second memory block (BLK 2  in  FIG.  3   ). The second memory block (BLK 2  in  FIG.  3   ) may include a normal memory block. The normal memory block may denote a memory block in which a voltage level of a threshold voltage (Vth, DC ) of dummy cells included in the memory block is greater than 0 V and less than a voltage level of the first reference voltage V 1 . 
     In operation S 140 , an erase operation may be performed on the entire first memory block (BLK 1  in  FIG.  5   ). Accordingly, data programmed in the first sub-block (SB 1  in  FIG.  5   ), the second sub-block (SB 2  in  FIG.  5   ), and the dummy block (DB in  FIGS.  4  and  5   ) included in the first memory block (BLK 1  in  FIG.  5   ) may all be erased. In other words, the first memory block may be reset by erasing the data programmed in the first sub-block SB 1 , the second sub-block SB 2 , and the dummy block DB. 
     In operation S 150 , dummy cells included in the dummy block (DB in  FIGS.  4  and  5   ) may be re-programmed A voltage level of a threshold voltage (Vth, DC ) of the re-programmed dummy cells may be less than the voltage level of the first reference voltage V 1 . By re-programming the dummy cells, it may be controlled that the voltage level of the threshold voltage (Vth,DC) of the dummy cells is kept in a certain range. 
     According to the inventive concepts, even when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than the voltage level of the first reference voltage V 1 , and thus, the memory block is not capable of performing a normal read operation, the pre-programmed data may be transferred to another memory block via the dummy cells which is turned on in operation S 120 , so that data loss may be prevented. Furthermore, an erase operation may be performed on an entire memory block not capable of performing a normal read operation, to recover a defective memory block, and thus, the productivity of the non-volatile memory device may be improved. In addition, the voltage level of the threshold voltage (Vth, DC ) of the dummy cells may be kept in a certain range, and thus, the reliability of operations of the non-volatile memory device may be improved. 
     The block reset method S 100  including the plurality of operations S 110  to S 150  may be applicable to each of program operation, erase operation, and read operation of the non-volatile memory device. Detailed operations of the non-volatile memory device are described in greater detail later with reference to  FIGS.  7  to  10   . 
       FIG.  2    is a conceptual block diagram of a memory system  100  according to some example embodiments of the inventive concepts. 
     Referring to  FIG.  2   , the memory system  100  may include a memory controller  110  and at least one non-volatile memory device (NVM)  120 . In  FIG.  2   , the memory system  100  includes one non-volatile memory device  120 . However, the inventive concepts are not limited thereto, and the memory system  100  may include a plurality of non-volatile memory devices. The non-volatile memory device  120  may include negative-AND (NAND) flash memory. 
     In some example embodiments, the memory system  100  may include an internal memory embedded in an electronic apparatus. For example, the memory system  100  may include an embedded universal flash storage (UFS) memory device, an embedded multi-media card (eMMC), or a solid-state drive (SSD). In some example embodiments, the memory system  100  may include an external memory that is detachable from the electronic apparatus. For example, the memory system  100  may include at least one of a UFS memory card, a compact flash (CF) card, a secure digital (SD) card, a micro secure digital (Micro-SD) card, a mini secure digital (Mini-SD) card, an extreme digital (xD) card, and a memory stick. 
     The memory controller  110  may process a request from a host. The memory controller  110  may control operations of the non-volatile memory device  120  according to the request from the host. The memory controller  110  may control the non-volatile memory device  120  such that the non-volatile memory device  120  performs any of a program operation, a read operation, and an erase operation. In addition, the memory controller  110  may also control the non-volatile memory device  120  such that an internal management operation or background operation of the non-volatile memory device  120  is performed, regardless of the request from the host. 
     The memory controller  110  may execute firmware. For example, when the non-volatile memory device  120  is a NAND flash memory device, the memory controller  110  may execute firmware, such as a flash translation layer, to control communication between the host and the non-volatile memory device  120 . The memory controller  110  may be implemented by using a system-on-chip (SoC), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or the like. 
     Although not shown, the memory controller  110  may further include an error correction code (ECC) unit. The ECC unit may provide accurate data by detecting and correcting an error in data input from the host or data output from the non-volatile memory device  120 . 
     The non-volatile memory device  120  may perform a program operation, a read operation, and an erase operation, under control by the memory controller  110 . The non-volatile memory device  120  may receive, from the memory controller  110 , a write command CMD, an address ADDR, a control signal CTRL, and data DATA, and write data to memory cells corresponding to the address ADDR. The non-volatile memory device  120  may receive a read command CMD and an address ADDR from the memory controller  110  and output, to the memory controller  110 , data DATA read from the memory cells corresponding to the address ADDR. The non-volatile memory device  120  may receive an erase command CMD and an address ADDR from the memory controller  110  and erase data from memory cells corresponding to the address ADDR. 
     The non-volatile memory device  120  may include a memory cell array  121  and a control circuit  122 . The memory cell array  121  may include a plurality of memory blocks BLK 1  to BLKn. Each of the plurality of memory blocks BLK 1  to BLKn may be implemented in a memory cell array in which a plurality of memory cells have a two-dimensional array structure or a three-dimensional array structure. The memory cells may include a NAND flash memory cell, but are not limited thereto, and the memory cells may include resistive memory cells, such as resistive random-access memory (RAM; ReRAM) memory cells, phase-change RAM (PRAM) memory cells, and magnetoresistive RAM (MRAM) memory cells. Each of the plurality of memory blocks BLK 1  to BLKn may be a unit for an erase operation, and according to some example embodiments, the erase operation may be performed in units of sub-blocks included in each of the plurality of memory blocks. 
     As described later with reference to  FIG.  4   , each of the plurality of memory blocks BLK 1  to BLKn may include the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ), which are stacked in a vertical direction with respect to a substrate. In addition, each of the plurality of memory blocks BLK 1  to BLKn may include the dummy block (DB in  FIG.  4   ) between the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ). The dummy block (DB in  FIG.  4   ) may include a boundary surface (or a junction portion) of a first stack and a second stack defined in a process, and dummy cells adjacent to the boundary surface. However, the inventive concepts are not limited thereto, and according to some example embodiments, each of the plurality of memory blocks BLK 1  to BLKn may include n sub-blocks, where n is a natural number greater than or equal to 3, and (n−1) dummy blocks arranged at a boundary of the sub-blocks. 
     The control circuit  122  may perform a program operation so that the threshold voltages of the memory cells of the memory cell array  121  have target states, based on a program command received from the memory controller  110 . The program operation may be performed by program loops based on a voltage increase of a program voltage, and each of the program loops may include a program period and a verification period. The control circuit  122  may perform a read operation on a memory cell selected from among the memory cells included in the memory cell array  121 , based on a read command received from the memory controller  110 . The control circuit  122  may perform an erase operation on a memory cell selected from among the memory cells included in the memory cell array  121 , based on an erase command received from the memory controller  110 . 
     The control circuit  122  may monitor a threshold voltage of dummy cells at the boundary of the sub-blocks from among the memory cells included in the memory cell array  121 . The control circuit  122  may transmit a result of the monitoring of the threshold voltage of the dummy cells to the memory controller  110 . The memory controller  110  may determine whether to perform the block reset operation S 100  described above with reference to  FIG.  1   , based on the monitoring result of the threshold voltage of the dummy cells. 
     For example, when the voltage level of the threshold voltage of the dummy cells is greater than the voltage level of the first reference voltage V 1 , the memory controller  110  may generate a block reset command CMD and transmit the generated block reset command CMD to the control circuit  122 . The control circuit  122  may perform a block reset operation on a memory block selected from among the memory blocks included in the memory cell array  121 , based on the received block reset command CMD. A configuration of the non-volatile memory device  120  is described in greater detail below. 
       FIG.  3    is a block diagram of a non-volatile memory device  120  according to some example embodiments of the inventive concepts. In detail,  FIG.  3    is a block diagram for describing the non-volatile memory device  120  in  FIG.  2   , as an example. 
     Referring to  FIG.  3   , the non-volatile memory device  120  may include the memory cell array  121 , the control circuit  122 , a voltage generator  123 , a row decoder  124 , a page buffer unit  125 , and input/output (I/O) circuit unit  126 . Although not shown, the non-volatile memory device  120  may further include an input/output interface. 
     The memory cell array  121  may be connected to word lines WL, string select lines SSL, ground select lines GSL, and bit lines BL. The memory cell array  121  may be connected to the row decoder  124  via the word lines WL, the string select lines SSL, and the ground select lines GSL, and may be connected to the page buffer unit  125  via the bit lines BL. 
     The memory cell array  121  may include a three-dimensional (3D) memory cell array. The 3D memory cell array may be monolithically provided at least one physical level of memory cell arrays having an active area and circuitry, wherein the active area is disposed on a silicon substrate, and the circuitry is associated with an operation of the memory cells and is provided on or in the substrate. The term “monolithic” may mean that layers of each level constituting the array are stacked directly above layers of each lower level of the array. The 3D memory cell array may include NAND strings that are vertically arranged such that at least one memory cell is on another memory cell. The at least one memory cell may include a charge trap layer. However, the inventive concepts are not limited thereto, and in another example embodiment, the memory cell array  121  may include a two-dimensional memory cell array. 
     The memory cell array  121  may include the plurality of memory blocks BLK 1  to BLKn. Each of the plurality of memory blocks BLK 1  to BLKn may include a plurality of memory cells and a plurality of select transistors. The plurality of memory cells may be connected to the word lines WL, and the plurality of select transistors may be connected to the string select lines SSL or the ground select lines GSL. The plurality of memory cells may include NAND flash memory cells, but are not limited thereto. 
     Each of the plurality of memory blocks BLK 1  to BLKn may have a 3D structure (or a vertical structure). For example, each of the plurality of memory blocks BLK 1  to BLKn may include a plurality of NAND strings extending in a direction perpendicular to the substrate. However, the inventive concepts are not limited thereto, and each of the plurality of memory blocks BLK 1  to BLKn may have a two-dimensional structure. Each of the plurality of memory blocks BLK 1  to BLKn may include a plurality of sub-blocks. For example, each of the plurality of memory blocks BLK 1  to BLKn may include two or more sub-blocks. 
     Each of the memory cells included in the memory cell array  121  may include a multi-level cell (MLC) storing  2  or more bits of data, a triple-level cell (TLC) storing three bits of data, or a quad-level cell (QLC) storing four bits of data. Accordingly, the plurality of memory blocks BLK 1  to BLKn may include at least one of a multi-level cell block including MLCs, a triple-level cell block including TLCs, and a quad-level cell block including QLCs. 
     When a program voltage is applied to the memory cell array  121 , the plurality of memory cells may be in a program state, and when an erase voltage is applied to the memory cell array  121 , the plurality of memory cells may be in an erase state. Each of the memory cells may have an erase state or at least one program state, which are differentiated according to a threshold voltage V th . For example, when a memory cell is an MLC, the memory cell may have an erase state or at least three program states. 
     The control circuit  122  may output various internal control signals for performing a program operation, read operation, erase operation, and block reset operation on the memory cell array  121 , based on the command CMD, the address ADDR, and the control signal CTRL received from the memory controller ( 110  in  FIG.  2   ). The control circuit  122  may provide a row address R_ADDR to the row decoder  124 , provide a column address to the input/output circuit unit  126 , and provide a voltage control signal CTRL_VOL to the voltage generator  123 . The control circuit  122  may monitor a threshold voltage of dummy cells included in the memory cell array  121  and transmit a result of the monitoring to the memory controller ( 110  in  FIG.  2   ). 
     The voltage generator  123  may generate voltages of various types to ensure that the memory cell array  121  performs a program operation, block program operation, read operation, and erase operation, based on the voltage control signal CTRL_VOL received from the control circuit  122 . For example, the voltage generator  123  may generate a word line voltage VWL, such as a program voltage, a read voltage, a pass voltage, an erase voltage, an erase verification voltage, or a turn-on voltage. 
     The row decoder  124  may be connected to the memory cell array  121  via a plurality of string select lines SSL, a plurality of word lines WL, and a plurality of ground select lines GSL. The row decoder  124  may select any of the plurality of memory blocks BLK 1  to BLKn of the memory cell array  121  in response to the row address R-ADDR, and may select any of word lines WL of the selected memory block. For example, during a program operation, the row decoder  124  may apply a program voltage and verification voltage to the selected word lines, and may apply a pass voltage to an unselected word line. In addition, the row decoder  124  may select some string select lines from among the string select lines SSL or some ground select lines from among the ground select lines GSL, in response to the row address R_ADDR. 
     The page buffer unit  125  may be operated as a write driver or a detection amplifier according to an operation mode. During a read operation, the page buffer unit  125  may sense a bit line BL of a selected memory cell under control by the control circuit  122 . The sensed data may be stored in a latch provided within the page buffer unit  125 . In addition, the page buffer unit  125  may dump the data stored in the latch to the input/output circuit unit  126  via a data line DL under control by the control circuit  122 . 
     The input/output circuit unit  126  may temporarily store a command CMD, an address ADDR, and data DATA received from the outside of the non-volatile memory device  120  via an input/output line I/O. The input/output circuit unit  126  may temporarily store read data of the non-volatile memory device  120  and output the read data to the outside via the input/output circuit unit  126  at a designated time. 
       FIG.  4    is a perspective view illustrating a first memory block BLK 1  according to some example embodiments of the inventive concepts. In detail,  FIG.  4    representatively illustrates the first memory block BLK 1  from among the plurality of memory blocks BLK 1  to BLKn in  FIG.  3   . The first memory block BLK 1  may include NAND strings or cell strings having a 3D structure or vertical structure, and the first memory block BLK 1  may include structures extending in a plurality of directions X, Y, and Z. Hereinafter, reference is made to  FIGS.  1  and  2   . 
     Referring to  FIG.  4   , the first memory block BLK 1  may be provided in a vertical direction Z with respect to a substrate SUB. The substrate SUB may have a first conductive type (e.g., p-type), and may have a common source line CSL thereon, the common source line CSL being doped with impurities of a second conductive type (e.g., n-type). 
     A plurality of insulating materials IL extending in a second vertical direction Y may be sequentially provided in the vertical direction Z in an area of the substrate SUB between the common source lines CSL. The plurality of insulating materials IL may be provided apart from each other by a certain distance in a first horizontal direction X. The insulating materials IL may include an insulating material, such as silicon oxide. 
     A channel structure P may be provided on the substrate SUB between the common source lines CSL, the channel structure P being sequentially arranged in the second horizontal direction Y and passing through the insulating materials IL in the vertical direction Z. The channel structure P may be connected to the substrate SUB via the insulating materials IL. The channel structure P may include a plurality of materials. For example, the channel structure P may include a surface layer S and an inner layer I. The surface layer S may include a silicon material having a first conductive type and may function as a channel area. In some example embodiments, the channel structure P may be referred to as a vertical channel structure or pillar. The inner layer I may include an insulating material, such as silicon oxide, or an air gap. 
     A charge storage layer CS may be provided along the insulating materials IL, the channel structure P, and an exposed surface of the substrate SUB. The charge storage layer CS may include a gate insulation layer (also referred to as “a tunneling insulation layer”), a charge trap layer, and a blocking insulation layer. For example, the charge storage layer CS may have an oxide-nitride-oxide (ONO) structure. In addition, a gate electrode GE, such as a ground select line GSL, a string select line SSL, and word lines WL 1  to WL 8 , may be provided on an exposed surface of the charge storage layer CS. 
     A drain contact or drain electrode DR may be provided on the channel structure P. For example, the drain electrode DR may include a silicon material doped with impurities having a second conductive type. Bit lines BL 1  to BL 3  may be provided on the drain electrode DR, the bit lines BL 1  to BL 3  extending in the first horizontal direction X and being arranged apart from each other by a certain distance in the second horizontal direction Y. 
     The first memory block BLK 1  may include a first sub-block SB 1  and a second sub-block SB 2  that are stacked in the vertical direction Z. The first sub-block SB 1  may include first to third word lines WL 1  to WL 3 , and the second sub-block SB 2  may include fifth to eighth word lines WL 5  to WL 8 . In  FIG.  4   , each of the sub-blocks includes only three word lines. However, this is for convenience of explanation, and each of the sub-blocks may include more than three word lines. 
     The first memory block BLK 1  may include a dummy block DB between the first sub-block SB 1  and the second sub-block SB 2 . The dummy block DB may include an inter-stack area INT-ST defined in the manufacturing process step of the non-volatile memory device ( 120  in  FIG.  3   ), and dummy cells (DC 1  and DC 2  in  FIG.  5   ) adjacent to the inter-stack area INT-ST. The upper surface of the inter-stack area INT-ST may denote a boundary surface (or a junction portion) of the first stack and the second stack of the first memory block BLK 1  defined in the manufacturing process step. 
     The dummy block DB may include fourth and fifth word lines WL 4  and WL 5 , and the fourth and fifth word lines WL 4  and WL 5  may be referred to as “dummy word lines”. The fourth and fifth word lines WL 4  and WL 5  may include word lines adjacent to the inter-stack area INT-ST. In other words, dummy word lines (e.g., the fourth and fifth word lines WL 4  and WL 5 ) may include word lines adjacent to the junction portion of the first stack and the second stack of the first memory block BLK 1 . In  FIG.  4   , the dummy block DB includes two dummy word lines. However, this is for convenience of explanation, and the dummy block DB may include more than two dummy word lines. 
       FIG.  5    is an equivalent circuit diagram of a non-volatile memory device according to some example embodiments of the inventive concepts. In detail,  FIG.  5    is an equivalent circuit diagram of the first memory block BLK 1  in  FIG.  4   . 
     Referring to  FIG.  5   , the first memory block BLK 1  may include NAND strings NS 11  to NS 33 , word lines WL 1  to WL 8 , bit lines BL 1  to BL 3 , ground select lines GSL 1  to GSL 3 , string select lines SSL 1  to SSL 3 , and the common source line CSL. In  FIG.  5   , each of the cell strings NS 11  to NS 33  includes six memory cells MC 1  to MC 6  and two dummy cells DC 1  and DC 2  that are connected to the eight word lines WL 1  to WL 8 . However, the inventive concepts are not limited thereto. 
     For example, one or more dummy cells may be provided between the string select transistor SST and the sixth memory cell MC 6 , in each of the cell strings. According to some example embodiments, one or more dummy cells may be provided between the ground select transistor GST and the first memory cell MC 1 , in each of the cell strings. 
     The dummy cells DC 1  and DC 2  may have the same structure as the memory cells MC 1  to MC 6 , and may be either unprogrammed (e.g., when programming is inhibited), or programmed differently from the way in which the memory cells MC 1  to MC 6  are programmed For example, when the memory cells MC 1  to MC 6  are programmed to have two or more threshold voltage distributions, the dummy cells DC 1  and DC 2  may be programmed to have one threshold voltage distribution range or a smaller number of threshold voltage distributions than the memory cells MC. 
     Each of the cell strings (e.g., NS 11 ) may include the string select transistor SST, the plurality of memory cells MC 1  to MC 6 , the plurality of dummy cells DC 1  and DC 2 , and the ground select transistor GST, which are connected in series to each other. Each of the plurality of memory cells MC 1  to MC 6  and the plurality of dummy cells DC 1  and DC 2  may be connected to a corresponding one of the word lines WL 1  to WL 8 . The ground select transistor GST may be connected to a corresponding ground select line (e.g., GSL 1 ). The string select transistor SST may be connected to a corresponding string select line (e.g., SSL 1 ), and may be connected to a corresponding one of the bit lines BL 1  to BL 3 . The ground select transistor GST may be connected to the common source line CSL. 
       FIG.  6    is a flowchart of an erase method of a non-volatile memory device, according to some example embodiments of the inventive concepts. In detail,  FIG.  6    is a flowchart of an erase method for a sub-block included in a memory block. Hereinafter, reference is made to  FIGS.  1  to  5   , and redundant descriptions are omitted. 
     Referring to  FIG.  6   , an erase method S 200  for a sub-block may include a plurality of operations S 210  to S 240 . 
     In operation S 210 , the memory controller ( 110  in  FIG.  2   ) may receive, from a host thereof, an erase command for the first sub-block (SB 1  in  FIG.  4   ) or second sub-block (SB 2  in  FIG.  4   ). For example, the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ) may be in a programmed state, and the erase command may include a command to perform an erase operation on any one sub-block from among the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ). Hereinafter, an erase operation for the second sub-block (SB 2  in  FIG.  4   ) is mainly described, for convenience of explanation. However, the inventive concepts are not limited thereto. 
     In operation S 220 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies a block reset condition. 
     The memory controller ( 110  in  FIG.  2   ) may receive, from the control circuit ( 122  in  FIG.  3   ), monitoring information of a threshold voltage of the dummy block (DB of  FIG.  4   ). The memory controller ( 110  in  FIG.  2   ) may compare a voltage level of a threshold voltage (Vth, DC ) of the dummy cells included in the dummy block (DB in  FIG.  4   ) with the voltage level of the first reference voltage V 1 . The voltage level of the first reference voltage V 1  may have a threshold value at which the first memory block (BLK 1  in  FIG.  4   ) may normally perform a read operation, as described with reference to operation S 110  in  FIG.  1   , and may have a reference value for determining whether a block reset operation is necessary or desired. 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) does not satisfy the block reset condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 230 . 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) satisfies the block reset operation. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 240 . 
     In operation S 230 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform an erase operation on the second sub-block (SB 2  in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). 
     For example, an erase body voltage may be applied to the substrate (SUB in  FIG.  4   ), and an erase voltage may be applied to the sixth to eighth word lines (WL 6  to WL 8  in  FIG.  4   ) of the second sub-block (SB 2  in  FIG.  4   ). The erase body voltage may have a voltage level that is relatively greater than that of the erase voltage, and the erase voltage may include a ground voltage. In this case, a voltage for not injecting a hole into the first sub-block (SB 1  in  FIG.  4   ) may be applied to the fourth and fifth word lines WL 5  and WL 6  of the dummy block (DB in  FIG.  4   ), and a voltage may not be applied to the first to third word lines WL 1  to WL 3  of the first sub-block (SB 1  in  FIG.  4   ). 
     In operation S 240 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a block reset operation under control by the memory controller ( 110  in  FIG.  2   ). The block reset operation may denote operations S 120  to S 150  described with reference to  FIG.  1   . 
     Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may turn on the dummy cells included in the dummy block (DB in  FIG.  4   ) by applying a turn-on voltage to word lines included in the dummy cells (S 120  in  FIG.  1   ), and then transfer data programmed in the first sub-block (SB 1  in  FIG.  4   ) to the second memory block (BLK 2  in  FIG.  2   ) (S 130  in  FIG.  1   ). In this case, the second memory block may include a normal memory block including dummy cells in which the voltage level of the threshold voltage (Vth, DC ) is greater than 0 V and less than the voltage level of the first reference voltage V 1 . Subsequently, an erase operation may be performed on the entire first memory block (BLK 1  in  FIG.  4   ) (S 140  in  FIG.  1   ), and dummy cells included in the first memory block (BLK 1  in  FIG.  4   ) may be re-programmed (S 150  in  FIG.  1   ). 
     In other words, even in a case in which the first memory block BLK 1  receives an erase command with respect to the second sub-block (SB 2  in  FIG.  4   ), when the first memory block BLK 1  satisfies the block reset operation, an erase operation may be performed on the entire first memory block BLK 1  including the first sub-block (SB 1  in  FIG.  4   ). In this case, data pre-programmed in the first sub-block (SB 1  in  FIG.  4   ) may be transferred to the second memory block (BLK 2  in  FIG.  2   ), and thus, the data may be recovered. Accordingly, the reliability of the non-volatile memory device ( 120  in  FIG.  2   ) may be improved. 
       FIG.  7    is a flowchart of a program method of a non-volatile memory device, according to some example embodiments of the inventive concepts. In detail,  FIG.  7    is a flowchart of a method of programming memory cells included in the first sub-block SB 1 , in a case in which the second sub-block SB 2  in  FIG.  4    is programmed Hereinafter, reference is made to  FIGS.  3  to  6   , and redundant descriptions are omitted. 
     Referring to  FIG.  7   , a program method S 300  for the first sub-block S 300  may include a plurality of operations S 310  to S 350 . 
     In operation S 310 , the memory controller ( 110  in  FIG.  2   ) may receive, from a host thereof, a program command for memory cells included in the first sub-block (SB 1  in  FIG.  4   ). 
     In operation S 320 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies a block reset condition. 
     The memory controller ( 110  in  FIG.  2   ) may receive, from the control circuit ( 122  in  FIG.  3   ), monitoring information of the threshold voltage (Vth, DC ) of the dummy cells included in the dummy block (DB in  FIG.  4   ). The memory controller ( 110  in  FIG.  2   ) may compare the voltage level of the threshold voltage (Vth, DC ) of the dummy cells with the voltage level of the first reference voltage V 1 . The voltage level of the first reference voltage V 1  may have a threshold value in which the first memory block (BLK 1  in  FIG.  4   ) may normally perform a read operation, as described above with reference to the operation S 110  in  FIG.  1   , and may have a reference value for determining whether a block reset operation is necessary or desired. 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) does not satisfy the block reset condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 330 . When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) satisfies the block reset operation. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 340 . 
     In operation S 330 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a program operation on the first sub-block (SB 1  in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). 
     For example, a block pass voltage may be applied to the sixth to eighth word lines WL 6  to WL 8  in  FIG.  4    of the second sub-block (SB 2  in  FIG.  4   ) and the fourth and fifth word lines WL 5  and WL 6  of the dummy block (DB in  FIG.  4   ). A voltage level of the block pass voltage may be greater than a maximum voltage level from among voltage levels that a threshold voltage of a programmed memory cell may have. Thus, the voltage level of the block pass voltage may be higher than the threshold voltage. Accordingly, a channel may be provided in the second sub-block (SB 2  in  FIG.  4   ) and the dummy block (DB in  FIG.  4   ), regardless of whether the memory cells of the second sub-block (SB 2  in  FIG.  4   ) and the dummy cells of the dummy block (DB in  FIG.  4   ) are programmed The voltage level of the block pass voltage may be equal to or similar to a voltage level of the turn-on voltage. 
     A program voltage may be applied to a select word line of the first sub-block (SB 1  in  FIG.  4   ), and a pass voltage may be applied to non-select word lines. Program loops may be performed by incremental step pulse programming (ISPP), and a voltage level of the program voltage applied to the select word line of the first sub-block (SB 1  in  FIG.  4   ) may gradually increase. The pass voltage applied to the non-select word lines of the first sub-block (SB 1  in  FIG.  4   ) may be equal to or different from the voltage level of the block pass voltage. 
     In operation S 340 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may program the second memory block (BLK 2  in  FIG.  2   ) under control by the memory controller ( 110  in  FIG.  2   ). The second memory block (BLK 2  in  FIG.  2   ) may include a normal memory block including dummy cells in which the voltage level of the threshold voltage is greater than 0 V and less than the voltage level of the first reference voltage V 1 . 
     In operation S 350 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a block reset operation on the first memory block (BLK 1  in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). The block reset operation may denote operations S 120  to S 150  described with reference to  FIG.  1   . 
     Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may apply a turn-on voltage to word lines of the dummy cells included in the dummy block (DB in  FIG.  4   ) (S 120  in  FIG.  1   ), and then transfer data pre-programmed in the second sub-block (SB 2  in  FIG.  4   ) to a sub-block of the second memory block (BLK 2  in  FIG.  2   ) that is unprogrammed, or an n th  memory block (BLKn in  FIG.  2   ). Subsequently, the non-volatile memory device ( 120  in  FIG.  2   ) may perform an erase operation on the entire first memory block (BLK 1  in  FIG.  4   ) (S 140  in  FIG.  1   ) and re-program the dummy cells included in the dummy block (DB in  FIG.  4   ) (S 150  in  FIG.  1   ). 
       FIG.  8    is a flowchart of a program method of a non-volatile memory device, according to some example embodiments of the inventive concepts. In detail,  FIG.  8    is a flowchart of a method of programming memory cells of the second sub-block SB 2 , in a state in which the first sub-block SB 1  in  FIG.  4    is programmed Hereinafter, reference is made to  FIGS.  3  to  6   , and redundant descriptions are omitted. 
     Referring to  FIG.  8   , a program method S 400  for the second sub-block may include a plurality of operations S 410  to S 480 . 
     In operation S 410 , the memory controller ( 110  in  FIG.  2   ) may receive, from a host thereof, a program command for memory cells included in the second sub-block (SB 2  in  FIG.  4   ). 
     In operation S 420 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies a dummy block turn-off condition. The memory controller ( 110  in  FIG.  2   ) may receive, from the control circuit ( 122  in  FIG.  3   ), monitoring information of a threshold voltage of the dummy block (DB of  FIG.  4   ). The memory controller ( 110  in  FIG.  2   ) may compare a voltage level of a threshold voltage (Vth, DC ) of the dummy cells included in the dummy block (DB in  FIG.  4   ) with a voltage level of the second reference voltage V 2 . 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than the voltage level of the second reference voltage V 2 , the dummy cells may not be normally turned off. In other words, the voltage level of the second reference voltage V 2  may have a threshold value in which the dummy cells may electrically block the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ). Accordingly, the voltage level of the second reference voltage V 2  may have a reference value for determining whether an operation may be performed in units of sub-blocks. The voltage level of the second reference voltage V 2  may be a preset value, or may be a value input by a user. The voltage level of the second reference voltage V 2  is described in greater detail later with reference to  FIG.  9   . 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the second reference voltage V 2 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) satisfies the dummy block turn-off condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 430 . When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the second reference voltage V 2 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) does not satisfy the dummy block turn-off condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 450 . 
     In operation S 430 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the second reference voltage V 2 , the non-volatile memory device ( 120  in  FIG.  2   ) may turn off the dummy cells of the dummy block (DB in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). A turn-off voltage may be applied to the dummy word lines (WL 4  and WL 5  in  FIG.  4   ). For example, the turn-off voltage may include a ground voltage. Accordingly, the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ) may be electrically separated from each other. 
     In operation S 440 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a program operation on the second sub-block (SB 2  in  FIG.  4   ). A program voltage may be applied to a select word line of the second sub-block (SB 2  in  FIG.  4   ), and a pass voltage may be applied to a non-select word line. In this case, when the dummy cells of the dummy block (DB in  FIG.  4   ) are turned off in operation S 430 , the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ) may be electrically separated from each other. Accordingly, a ground voltage may be applied to the word lines (WL 1  to WL 3  in  FIG.  4   ) of the first sub-block, or a voltage may not be applied thereto. 
     In operation S 450 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies a block reset condition. When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the second reference voltage V 2 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies the block reset condition. The memory controller ( 110  in  FIG.  2   ) may compare the voltage level of the threshold voltage (Vth, DC ) of the dummy cells with the voltage level of the first reference voltage V 1 . The voltage level of the first reference voltage V 1  may include a threshold value at which the first memory block (BLK 1  in  FIG.  4   ) may normally perform a read operation, as described above with reference to operation S 110  in  FIG.  1   . 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) does not satisfy the block reset condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 460 . When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V and greater than the voltage level of the first reference voltage V 1 , it may be determined that the first memory block (BLK 1  in  FIG.  3   ) satisfies the block reset condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 470 . 
     In operation S 460 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may turn on the dummy block (DB in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). To turn on the dummy block (DB in  FIG.  4   ), a turn-on voltage may be applied to the dummy word lines (WL 4  and WL 5  in  FIG.  4   ). 
     A voltage level of the turn-on voltage may be greater than the voltage level of the threshold voltage (Vth, DC ) of the dummy cells. When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the voltage level of the turn-on voltage may be greater than a voltage level of a voltage applied to the word line of the dummy cells so as to turn on the dummy cells. For example, the voltage level of the turn-on voltage may be greater than a maximum voltage level that is achievable by a read voltage. The read voltage may include a voltage applied to word lines of memory cells included in a sub-block during a read operation. For example, the voltage level of the turn-on voltage may be greater than the voltage level of the first reference voltage V 1 . Accordingly, a channel may be provided in the dummy cell. The first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ) may be electrically connected to each other. 
     In operation S 440 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a program operation on the second sub-block (SB 2  in  FIG.  4   ). A program voltage may be applied to a select word line of the second sub-block (SB 2  in  FIG.  4   ), and a pass voltage may be applied to a non-select word line. In this case, when the dummy block (DB in  FIG.  4   ) is turned on in operation S 450 , the first sub-block (SB 1  in  FIG.  4   ) and the second sub-block (SB 2  in  FIG.  4   ) are electrically connected to each other, and thus, a pass voltage may be applied to the word lines of the first sub-block (SB 1  in  FIG.  4   ). The pass voltage applied to the word lines of the first sub-block (SB 1  in  FIG.  4   ) may be equal to the turn-on voltage applied to a dummy cell, or may have a different voltage level. 
     In operation S 470 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may program data for programming, in the second memory block (BLK 2  in  FIG.  2   ). The second memory block (BLK 2  in  FIG.  2   ) may include a normal memory block including dummy cells in which the voltage level of the threshold voltage (Vth, DC ) is greater than 0 V and less than the voltage level of the first reference voltage V 1 . 
     In operation S 480 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a block reset operation on the first memory block (BLK 1  in  FIG.  4   ) under control by the memory controller ( 110  in  FIG.  2   ). The block reset operation may denote operations S 120  to S 150  described with reference to  FIG.  1   . 
     Accordingly, a turn-on voltage may be applied to the dummy word lines (WL 4  and WL 5  in  FIG.  5   ) included in the dummy block (DB in  FIG.  4   ) (S 120  in  FIG.  1   ). Subsequently, data programmed in the first sub-block (SB 1  in  FIG.  4   ) may be transferred to a sub-block of the second memory block (BLK 2  in  FIG.  2   ) that is unprogrammed, or an n th  memory block (BLKn in  FIG.  2   ) (S 130  in  FIG.  1   ). Thereafter, an erase operation may be performed on the entire first memory block (BLK 1  in  FIG.  4   ) (S 140  in  FIG.  1   ), and the dummy cells included in the dummy block (DB in  FIG.  4   ) may be re-programmed (S 150  in  FIG.  1   ). 
       FIG.  9    is a diagram illustrating a distribution of threshold voltages of memory cells that are programmed, according to some example embodiments of the inventive concepts. In detail,  FIG.  9    is a diagram illustrating a first reference voltage (V 1  in  FIG.  1   ) and a second reference voltage (V 2  in  FIG.  8   ), and is described with reference to  FIGS.  1  to  8   . 
     Referring to  FIG.  9   , the horizontal axis may indicate threshold voltages of memory cells, and the vertical axis may indicate cell counts, i.e., the number of memory cells. Memory cells (MC 1  to MC 6  in  FIG.  5   ) may be classified as SLC, MLC, TLC, or QLC, according to the number of bits stored in the memory cells (MC 1  to MC 6  in  FIG.  5   ). In  FIG.  10   , the memory cells (MC 1  to MC 6  in  FIG.  5   ) are TLCs, for convenience of explanation. However, the inventive concepts are not limited thereto. 
     The memory cells (MC 1  to MC 6  in  FIG.  5   ) may be in an erase state or a state in which one or more bits are programmed The memory cells (MC 1  to MC 6  in  FIG.  5   ) may be programmed as any of first to eighth states S 1  to S 8 , and the first to eighth states S 1  to S 8  may be defined as a range of a threshold voltage V th  of the memory cells (MC 1  to MC 6  in  FIG.  5   ). The first state S 1  may denote an erase state, and the eight state S 8  may denote a state in which a largest amount (e.g., first amount) of data is programmed. 
     The voltage level of the first reference voltage V 1  may be equal to a maximum value Vth8max of a voltage level that the threshold voltage of the memory cell (MC 1  to MC 6  in  FIG.  5   ) may have, when the memory cells (MC 1  to MC 6  in  FIG.  5   ) are programmed to the eighth state S 8 . 
     The voltage level of the second reference voltage V 2  may be equal to a value obtained by subtracting a maximum value Vth8max of a voltage level that the threshold voltage of the memory cell (MC 1  to MC 6  in  FIG.  5   ) may have when the memory cell (MC 1  to MC 6  in  FIG.  5   ) is programmed to the eighth state S  8 , by a voltage level of a channel after a read operation is performed. The second reference voltage V 2  may include a voltage in which negative boosting occurs when a ground voltage is applied to a word line, or may denote a voltage for maintaining a channel potential. The voltage level of the second reference voltage V 2  may be less than the voltage level of the first reference voltage V 1 . 
       FIG.  10    is a flowchart of a data recovery method of a non-volatile memory device when a read error occurs, according to some example embodiments of the inventive concepts. Hereinafter, reference is made to  FIGS.  3  to  6   , and redundant descriptions are omitted. 
     Referring to  FIG.  10   , a data recovery method S 500  of a non-volatile memory device may include a plurality of operations S 510  to S 540 . 
     In operation S 510 , when the non-volatile memory device ( 120  in  FIG.  2   ) performs a read operation based on a read command, an ECC error may occur. The non-volatile memory device ( 120  in  FIG.  2   ) may detect the ECC error. The ECC error may include a case in which data programmed in a memory cell is erroneously read, or a case in which data including an error is not accurately detected or corrected. The ECC error may occur when a read cycle increases. 
     In operation S 520 , the memory controller ( 110  in  FIG.  2   ) may determine whether the first memory block (BLK 1  in  FIG.  4   ) satisfies a block reset condition. The memory controller ( 110  in  FIG.  2   ) may receive, from the control circuit ( 122  in  FIG.  3   ), monitoring information of the threshold voltage (Vth, DC ) of the dummy cells included in the dummy block (DB in  FIG.  4   ). The memory controller ( 110  in  FIG.  2   ) may compare the voltage level of the threshold voltage (Vth, DC ) of the dummy cells with the voltage level of the first reference voltage V 1 . As described above with reference to the operation S 110  in  FIG.  1   , the voltage level of the first reference voltage V 1  may have a threshold value in which the first memory block (BLK 1  in  FIG.  4   ) may normally perform a read operation, and may have a reference value for determining whether a block reset operation is necessary or desired. 
     When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the memory controller ( 110  in  FIG.  2   ) may determine that the first memory block (BLK 1  in  FIG.  4   ) does not satisfy the block reset condition. Thus, the memory controller  110  may determine whether to reset the first memory block BLK 1  based on the first reference voltage V 1 . Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 530 . When the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , it may be determined by the memory controller  110  that the first memory block (BLK 1  in  FIG.  3   ) satisfies the block reset condition. Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may be controlled to perform operation S 540 . 
     In operation S 530 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is greater than 0 V and less than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may transfer data stored in the first memory block (BLK 1  in  FIG.  2   ) to the second memory block (BLK 2  in  FIG.  2   ) under control by the memory controller ( 110  in  FIG.  2   ). The second memory block (BLK 2  in  FIG.  2   ) may include a memory block in which a read cycle is less than a reference value. Accordingly, a read operation may be re-performed on the data transferred to the second memory block (BLK 2  in  FIG.  2   ). 
     In operation S 540 , when the voltage level of the threshold voltage (Vth, DC ) of the dummy cells is less than 0 V or greater than the voltage level of the first reference voltage V 1 , the non-volatile memory device ( 120  in  FIG.  2   ) may perform a block reset operation under control by the memory controller ( 110  in  FIG.  2   ). The block reset operation may denote operations S 120  to S 150  described with reference to  FIG.  1   . 
     Accordingly, the non-volatile memory device ( 120  in  FIG.  2   ) may turn on the dummy cells included in the dummy block (DB in  FIG.  4   ) by applying a turn-on voltage to word lines included in the dummy cells (S 120  in  FIG.  1   ), and then transfer data programmed in the first memory block (BLK 1  in  FIG.  2   ) to the second memory block (BLK 2  in  FIG.  2   ) (S 130  in  FIG.  1   ). In this case, the second memory block may include a normal memory block including dummy cells in which the voltage level of the threshold voltage (Vth, DC ) is greater than 0 V and less than the voltage level of the first reference voltage V 1 . In addition, the second memory block (BLK 2  in  FIG.  2   ) may include a memory block in which a read cycle is less than a reference value. Subsequently, an erase operation may be performed on the entire first memory block (BLK 1  in  FIG.  4   ) (S 140  in  FIG.  1   ), and dummy cells included in the first memory block (BLK 1  in  FIG.  4   ) may be re-programmed (S 150  in  FIG.  1   ). 
       FIG.  11    is a cross-sectional view illustrating a structure of a non-volatile memory device according to some example embodiments of the inventive concepts. In detail,  FIG.  11    is a diagram illustrating a structure of the non-volatile memory device  120  in  FIGS.  2  and  3   . Hereinafter, reference is made to  FIGS.  1  and  2   . 
     Referring to  FIG.  11   , the non-volatile memory device  120  may include a peripheral circuit area PERI and a cell area CELL. Each of the peripheral circuit area PERI and the cell area CELL may include an external pad bonding area PA, a word line bonding area WLBA, and a bit line bonding area BLBA. 
     The non-volatile memory device  120  may have a chip-to-chip (C2C) structure. The C2C structure may be provided by manufacturing an upper chip including the cell area CELL, on a first wafer, manufacturing a lower chip including the peripheral circuit area PERI, on a second wafer that is different from the first wafer, and then connecting the upper chip and the lower chip to each other by a bonding method. For example, the bonding method may denote a method of electrically connecting a bonding metal provided on an uppermost metal layer of the upper chip and a bonding metal provided on an uppermost metal of the lower chip to each other. For example, when the bonding metal includes copper (Cu), the bonding method may include a Cu—Cu bonding method. In another example embodiment, the bonding metal may include not only Cu, but also aluminum (Al) or tungsten (W). 
     The peripheral circuit area PERI may include a first substrate  210 , an interlayer insulation layer  215 , a plurality of circuit elements  220   a,    220   b,  and  220   c,  first metal layers  230   a,    230   b,  and  230   c,  and second metal layers  240   a,    240   b,  and  240   c,  wherein the plurality of circuit elements  220   a,    220   b,  and  220   c  are provided on the first substrate  210 , the first metal layers  230   a,    230   b,  and  230   c  are respectively connected to the plurality of circuit elements  220   a,    220   b,  and  220   c,  and the second metal layers  240   a,    240   b,  and  240   c  are provided on the first metal layers  230   a,    230   b,  and  230   c.  In some example embodiments, the first metal layers  230   a,    230   b,  and  230   c  may include W having a relatively high electrical non-resistivity, and the second metal layers  240   a,    240   b,  and  240   c  may include Cu having a relatively low electrical non-resistivity. 
     In  FIG.  11   , only the first metal layers  230   a,    230   b,  and  230   c  and the second metal layers  240   a,    240   b,  and  240   c  are shown. However, the inventive concepts are not limited thereto, and at least one metal layer may be further provided on the second metal layers  240   a,    240   b,  and  240   c.  At least a portion of the at least one metal layer provided on the second metal layers  240   a,    240   b,  and  240   c  may include Al or the like having a lower electrical non-resistivity than Cu included in the second metal layers  240   a,    240   b,  and  240   c.    
     The interlayer insulation layer  215  may be arranged on the first substrate  210  to cover the plurality of circuit elements  220   a,    220   b,  and  220   c,  the first metal layers  230   a,    230   b,  and  230   c,  and the second metal layers  240   a,    240   b,  and  240   c,  and may include an insulating material, such as silicon oxide and silicon nitride. 
     Lower bonding metals  271   b  and  272   b  may be provided on the second metal layer  240   b  of the word line bonding area WLBA. In the word line bonding area WLBA, the lower bonding metals  271   b  and  272   b  in the peripheral circuit region PERI may be electrically connected to upper bonding metals  371   i b  and  372   b  in the cell region CELL in a bonding manner, and the lower bonding metals  271   b  and  272   b  and the upper bonding metals  371   b  and  372   b  may be formed of aluminum (Al), copper (Cu), tungsten (W), or the like. 
     The cell area CELL may provide at least one memory block. The cell area CELL may include a second substrate  310  and a common source line  320 . Word lines  330  may be stacked on the second substrate  310  in a direction (a Z-axis direction) perpendicular to the upper surface of the second substrate  310 . String select lines and a ground select line may be respectively arranged on and below the word lines  330 , and the plurality of word lines  330  may be arranged between the string select lines and the ground select line. 
     In the bit line bonding area BLBA, a channel structure CH may extend in the direction (the Z-axis direction) perpendicular to the upper surface of the second substrate  310  and pass through the word lines  330 , the string select lines, and the ground select line. The channel structure CH may include a data storage layer, a channel layer, and a buried insulation layer. The channel layer may be electrically connected to a first metal layer  350   c  and a second metal layer  360   c.  For example, the first metal layer  350   c  may include a bit line contact, and the second metal layer  360   c  may include a bit line. The bit line  360   c  may extend in a direction (a Y-axis direction) parallel to the upper surface of the second substrate  310 . 
     An area in which the channel structure CH and the bit line  360   c  are arranged may be defined as the bit line bonding area BLBA. The bit line  360   c  may be electrically connected to the circuit elements  220   c  included in a page buffer  393 . For example, the bit line  360   c  may be connected to the upper bonding metals  371   c  and  372   c  of the peripheral circuit area PERI, and the upper bonding metals  371   c  and  372   c  may be connected to the lower bonding metals  271   c  and  272   c  connected to the circuit elements  220   c  of the page buffer  393 . The page buffer  393  may correspond to the page buffer  393  described with reference to  FIG.  3   . 
     In the word line bonding area WLBA, the word lines  330  may each extend in a second direction (an X-axis direction) that is perpendicular to the first direction (the Y-axis direction) and parallel to the upper surface of the second substrate  310 , and may be connected to a plurality of cell contact plugs  340 . The word lines  330  and the cell contact plugs  340  may be connected to each other through pads provided by at least some of the word lines  330  that extend to have different lengths in the second direction. A first metal layer  350   b  and a second metal layer  360   b  may be sequentially connected on the cell contact plugs  340  connected to the word lines  330 . The cell contact plugs  340  may be connected to the peripheral circuit area PERI in the word line bonding area WLBA through the upper bonding metals  371   i b  and  372   b  of the cell area CELL and the lower bonding metals  271   b  and  272   b  of the peripheral circuit area PERI. 
     The cell contact plugs  340  may be electrically connected to the circuit elements  220   b  included in the row decoder  124 . An operating voltage of the circuit elements  220   b  may be different from an operating voltage of the circuit elements  220   c  included in the page buffer  393 . For example, the operating voltage of the circuit elements  220   b  may be less than the operating voltage of the circuit elements  220   c.  The row decoder  124  may correspond to the row decoder  124  in  FIG.  2   . 
     A common source line contact plug  380  may be arranged in the external pad bonding area PA. The common source line contact plug  380  may include a conductive material (e.g., a metal, a metal compound, polysilicon, etc.) and may be electrically connected to the common source line  320 . A first metal layer  350   a  and a second metal layer  360   a  may be sequentially stacked on the common source line contact plug  380 . An area in which the common source line contact plug  380 , the first metal layer  350   a,  and the second metal layer  360   a  are arranged may be defined as the external pad bonding area PA. 
     The external pad bonding area PA may include input/output pads  205  and  305 . A lower insulation layer  201  covering the lower surface of the first substrate  210  may be provided under the first substrate  210 , and a first input/output pad  205  may be provided on the lower insulation layer  201 . The first input/output pad  205  may be connected to at least one of the plurality of circuit elements  220   a,    220   b,  and  220   c  through a first input/output contact plug  203 , and may be separated from the first substrate  210  by the lower insulation layer  201 . A side insulation layer may be arranged between the first input/output contact plug  203  and the first substrate  210  and electrically separate the first input/output contact plug  203  and the first substrate  210  from each other. 
     An upper insulation layer  301  covering the upper surface of the second substrate  310  may be provided on the second substrate  310 , and a second input/output pad  305  may be arranged on the upper insulation layer  301 . The second input/output pad  305  may be connected to at least one of the plurality of circuit elements  220   a,    220   b,  and  220   c  through a second input/output contact plug  303 . In some example embodiments, the second input/output pad  305  may be electrically connected to the circuit element  220   a.    
     The second substrate  310 , the common source line  320 , and the like may not be arranged in an area in which the second input/output contact plug  303  is arranged. In addition, the second input/output pad  305  may not overlap the word lines  330  in the third direction (the Z-axis direction). The second input/output contact plug  303  may be separated from the second substrate  310  in a direction parallel to the upper surface of the second substrate  310 , and may be connected to the second input/output pad  305  via an interlayer insulation layer  315 . 
     According to some example embodiments, the first input/output pad  205  and the second input/output pad  305  may be selectively provided. For example, the non-volatile memory device  120  may include only the first input/output pad  205  arranged on the first substrate  210 , or may include only the second input/output pad  305  arranged on the second substrate  310 . In some example embodiments, the non-volatile memory device  120  may include both the first input/output pad  205  and the second input/output pad  305 . 
     In each of the external pad bonding area PA and the bit line bonding area BLBA each included in the cell area CELL and the peripheral circuit area PERI, a metal pattern of the uppermost metal layer may be present as a dummy pattern, or the uppermost metal layer may be empty. 
     In the external pad bonding area PA, the non-volatile memory device  120  may have a lower metal pattern  273   a  having the same shape as an upper metal pattern  372   a  of the cell area CELL, in the uppermost metal layer of the peripheral circuit area PERI to correspond to the upper metal pattern  372   a  provided in the uppermost metal layer of the cell area CELL. The lower metal pattern  273   a  provided in the uppermost metal layer of the peripheral circuit area PERI may not be connected to an additional contact in the peripheral circuit area PERI. Similarly, in the external pad bonding area PA, the upper metal pattern  372   a  having the same shape as the lower metal pattern  273   a  of the peripheral circuit area PERI may be provided in the upper metal layer of the cell area CELL to correspond to the lower metal pattern  273   a  provided in the uppermost metal layer of the peripheral circuit area PERI. 
     The lower bonding metals  271   b  and  272   b  may be provided on the second metal layer  240   b  of the word line bonding area WLBA. In the word line bonding area WLBA, the lower bonding metals  271   b  and  272   b  of the peripheral circuit area PERI may be electrically connected to the upper bonding metals  371   b  and  372   b  of the cell area CELL by a bonding method. 
     In addition, in the bit line bonding area BLBA, an upper metal pattern  392  having the same shape as a lower metal pattern  252  of the peripheral circuit area PERI may be provided in the uppermost metal layer of the cell area CELL to correspond to the lower metal pattern  252  provided in the uppermost metal layer of the peripheral circuit area PERI. A contact may not be provided on the upper metal pattern  392  provided in the uppermost metal layer of the cell area CELL. 
       FIG.  12    is a block diagram of a computing system  200  according to some example embodiments of the inventive concepts. 
     Referring to  FIG.  12   , a computing system  200  may include a memory system  210 , a processor  220 , a RAM  230 , an input/output device  240 , and a power device  250 . Although not shown in  FIG.  12   , the computing system  200  may further include ports capable of communicating with a video card, a sound card, a memory card, a universal serial bus (USB) device, or other electronic devices. The computing system  200  may be implemented as a personal computer, or may be implemented as a portable electronic apparatus, such as a laptop computer, a mobile phone, a personal digital assistant (PDA), and a camera. 
     The processor  220  may perform specific operations or tasks. According to some example embodiments, the processor  220  may include a micro-processor and a central processing unit (CPU). The processor  220  may perform communication with the RAM  230 , the input/output device  240 , and the memory system  210  via a bus  260 , such as an address bus, a control bus, and a data bus. According to some example embodiments, the processor  220  may be connected to an expansion bus, such as a peripheral component interconnect (PCI) bus. 
     The memory system  210  may communicate with the processor  220 , the RAM  230 , and the input/output device  240  via the bus  260 . According to a request from the processor  220 , the memory system  210  may store data that is received or provide stored data to the processor  220 , the RAM  230 , or the input/output device  240 . 
     Meanwhile, the memory system  210  may include the memory system  100  described with reference to  FIG.  2   . The memory system  210  may include a memory  211  and a memory controller  212 . The memory  211  may correspond to the non-volatile memory device  120  described with reference to  FIGS.  1  to  10   . In other words, the memory system  210  may include the non-volatile memory device  120  described with reference to  FIGS.  2  to  10   . 
     The memory  211  may be operated under control by the memory controller  212 , according to the operating method according to some example embodiments described with reference to  FIGS.  1  and  6  to  10   . For example, the memory  211  may perform a block reset operation based on a threshold voltage level of dummy cells. The memory controller  212  may determine whether the threshold voltage level of the dummy cells satisfies a condition for performing a block reset operation, and a block reset operation of the memory  211  may be controlled based on the determination. 
     The RAM  230  may store data necessary or desired for operations of the computing system  200 . For example, the RAM  230  may be implemented as DRAM, mobile DRAM, static RAM (SRAM), PRAM, ferroelectric RAM (FRAM), ReRAM (RRAM), and/or magnetic RAM (MRAM). 
     The input/output device  240  may include an input means, such as a keyboard, a keypad, and a mouse, and an output means, such as a printer and a display. The power device  250  may apply an operating voltage necessary or desired for operations of the computing system  200 . 
       FIG.  13    is a block diagram of an SSD system  300  according to some example embodiments of the inventive concepts. 
     Referring to  FIG.  13   , the SSD system  300  may include a host  310  and an SSD  320 . The SSD  320  may exchange a signal (SGL) with the host  310  via a signal connector and receive power (PWR) via a power connector. 
     The SSD  320  may include an SSD controller  321 , an auxiliary power device  322 , and a plurality of memory devices  323 ,  324 , and  325 . The plurality of memory devices  323 ,  324 , and  325  may include a vertically stacked NAND flash memory device. At least one of the plurality of memory devices  323 ,  324 , and  325  may include the non-volatile memory device  120  described with reference to  FIGS.  1  to  10   . For example, at least one of the plurality of memory devices  323 ,  324 , and  325  may perform a block reset operation under control by the SSD controller  321 , according to the operating method according to some example embodiments described with reference to  FIGS.  6  to  10   . 
     Any of the elements and/or functional blocks disclosed above may include or be implemented in processing circuitry such as hardware including logic circuits; a hardware/software combination such as a processor executing software; or a combination thereof. For example, the memory controller  110 , memory controller  212  and SSD controller  321  may be implemented as processing circuitry. The processing circuitry specifically may include, but is not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, application-specific integrated circuit (ASIC), etc. The processing circuitry may include electrical components such as at least one of transistors, resistors, capacitors, etc. The processing circuitry may include electrical components such as logic gates including at least one of AND gates, OR gates, NAND gates, NOT gates, etc. 
     Processor(s), controller(s), and/or processing circuitry may be configured to perform actions or steps by being specifically programmed to perform those action or steps (such as with an FPGA or ASIC) or may be configured to perform actions or steps by executing instructions received from a memory, or a combination thereof. While the inventive concepts have been particularly shown and described with reference to example embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.