Abstract:
Embodiments of the present invention provide improved three-dimensional memory cells, arrays, devices, and/or the like and associated methods. In one embodiment, a three-dimensional memory cell is provided. The three-dimensional memory cell comprises a first conductive layer; a third conductive layer spaced apart from the first conductive layer; a channel conductive layer connecting the first conductive layer and the third conductive layer to form an opening having internal surfaces; a dielectric layer disposed along the internal surfaces of the opening surrounded by the first conductive layer, the channel conductive layer and the third conductive layer; and a second conductive layer interposed and substantially filling a remaining open portion formed by the dielectric layer. The first conductive layer, the dielectric layer, and the second conductive layer are configured to form a staircase structure.

Description:
TECHNOLOGICAL FIELD 
       [0001]    Embodiments of the present invention relate generally to a semiconductor device, in particular, a three dimensional memory for improved gate capacity. 
       BACKGROUND 
       [0002]    Semiconductor devices are typically classified as either volatile semiconductor devices, which require power to maintain storage of data, or non-volatile semiconductor devices, which can retain data even upon removal of a power source. An example non-volatile semiconductor device is a flash memory device, which generally includes a matrix of memory cells arranged in rows and columns. Each memory cell in the matrix includes a transistor structure having a gate, a drain, a source, and a channel defined between the drain and the source. Each memory cell is located at an intersection between a word line and a bit line, wherein the gate is connected to the word line, the drain is connected to the bit line, and the source is connected to a source line, which in turn is connected to common ground. The gate of a conventional flash memory cell generally comprises a dual-gate structure, including a control gate and a floating gate, wherein the floating gate is suspended between two oxide layers to trap electrons that program the cell. 
         [0003]    Flash memory devices may in turn be classified as NOR or NAND flash memory devices. Of these, NOR flash memory typically offers faster program and read speeds whereby each cell connects to ground at one end and connects to the bit line at the other end. Using conventional manufacturing methods, NOR and NAND flash take a 2D form by which the memory cells are created in a two dimensional array on a silicon substrate. However, the 2D architecture has demonstrated limitations, such as the scaling limitations encountered due to the process and device restrictions. Therefore, a 3D architecture, which stacks cells on top of each other, has been developed with respect to 3D NAND flash offering faster program and erase. Accordingly, there is a need in the art to increase the scalability of performance of read operations and maximize the data capacity properties of 3D NOR devices. 
       BRIEF SUMMARY OF EXEMPLARY EMBODIMENTS 
       [0004]    Embodiments of the present invention provide semiconductor devices, in particular, a gate structure for improved capacity, such as for 3D NOR flash memory. 
         [0005]    In one aspect of the present invention, a three-dimensional memory cell is provided. In one embodiment, the three-dimensional memory cell comprises a first conductive layer and a third conductive layer. The third conductive layer is spaced apart from the first conductive layer. The three-dimensional memory cell further comprises a channel conductive layer. The channel conductive layer connects the first conductive layer and the third conductive layer. The channel conductive layer, first conductive layer, and third conductive layer form an opening having internal surfaces. A dielectric layer is disposed long the internal surfaces of the opening surrounded by the first conductive layer, the channel conductive layer, and the third conductive layer. The three-dimensional memory cell further comprises a second conductive layer interposed and substantially filling a remaining open portion formed by the dielectric layer. The first conductive layer, the dielectric layer, and the second conductive layer are configured to form a staircase structure. 
         [0006]    In another aspect of the present invention, an apparatus for improving gate capacity of a nonvolatile memory device is provided. In one embodiment, the apparatus comprises a three-dimensional memory array. The memory array comprises a plurality of memory strings. Each of the plurality of memory strings comprises (a) a plurality of memory cells and (b) an end connected to a channel line. Each memory cell has (a) a first end connected to a bit line, (b) a second end connected to a source line, and (c) a third end connected to a word line. Each pair of adjacent memory cells shares one of a bit line and a source line. 
         [0007]    In still another aspect of the present invention, a method for fabricating a string of memory cells for a three-dimensional memory array is provided. In one embodiment, the method comprises providing a layered structure, the layered structure comprising a cap layer, one or more third conductive layers, one or more sacrificial layers, one or more first conductive layers, and an insulating layer; forming a hole through a plurality of layers of the layered structure; depositing a channel conductive layer within the hole; removing at least one of the one or more sacrificial layers to providing one or more openings, each opening having internal surfaces; depositing a dielectric layer along the internal surfaces of each opening, resulting in a remaining opening; depositing a second conductive layer within the remaining opening, the second conductive layer substantially filling the remaining opening, wherein the first conductive layer, second conductive layer, third conductive layer, dielectric layer, and insulating layer are configured to form a staircase structure. 
         [0008]    The above summary is provided merely for purposes of summarizing some example embodiments to provide a basic understanding of some aspects of the invention. Accordingly, it will be appreciated that the above-described embodiments are merely examples and should not be construed to narrow the scope or spirit of the invention in any way. It will be appreciated that the scope of the invention encompasses many potential embodiments in addition to those here summarized, some of which will be further described below. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0009]    Having thus described certain example embodiments of the present disclosure in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
           [0010]      FIG. 1A  illustrates a cross section of a string of memory cells of a three dimensional memory according to an embodiment of the invention; 
           [0011]      FIG. 1B  illustrates a staircase view of a string of memory cells, according to an embodiment of the invention; 
           [0012]      FIG. 1C  illustrates a top view of memory cells in a matrix according to an embodiment of the invention; 
           [0013]      FIG. 2A  illustrates an algorithm according to an embodiment of the invention; 
           [0014]      FIG. 2B  illustrates an algorithm according to an embodiment of the invention; 
           [0015]      FIG. 2C-D  illustrates-program algorithms according to an embodiment of the invention; 
           [0016]      FIG. 2E-F  illustrates read algorithms according to an embodiment of the invention; 
           [0017]      FIG. 2G-H  illustrates erase algorithms according to an embodiment of the invention; 
           [0018]      FIGS. 3A-3F  illustrate cross sections of some of the steps of forming a string of memory cells, according to an embodiment of the invention; and 
           [0019]      FIG. 4  is a flowchart illustrating a process for fabricating a string of memory cells according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Some embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention are shown. Indeed, various embodiments of the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. 
         [0021]    As used in the specification and in the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly indicates otherwise. For example, reference to “a gate structure” includes a plurality of such gate structures. 
         [0022]    Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation. All terms, including technical and scientific terms, as used herein, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs unless a term has been otherwise defined. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning as commonly understood by a person having ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure. Such commonly used terms will not be interpreted in an idealized or overly formal sense unless the disclosure herein expressly so defines otherwise. 
         [0023]    As used herein, “a string of memory cells” refers to a component of a semiconductor device, such as a memory device. Non-limiting examples of memory devices include flash memory devices (e.g., a NOR flash memory device). Erasable programmable read-only memory (EPROM) and electrically erasable read-only memory (EEPROM) devices are non-limiting examples of flash memory devices. The string of memory cells of the invention may be a structure portion of a three dimensional memory array and/or device or a sub-assembly of a component or components of such three dimensional memory structures. 
         [0024]    As used herein, a “non-volatile memory device” refers to a semiconductor device which is able to store information even when the supply of electricity is removed. Non-volatile memory includes, without limitation, Mask Read-Only Memory, Programmable Read-Only Memory, Erasable Programmable Read-Only Memory, Electrically Erasable Programmable Read-Only Memory, and Flash Memory, such as NAND and NOR flash memory. 
         [0025]    As used herein, a “substrate” may include any underlying material or materials upon which a device, a circuit, an epitaxial layer, or a semiconductor may be formed. Generally, a substrate may be used to define the layer or layers that underlie a semiconductor device or even forms the base layer of a semiconductor device. The substrate may include one or any combination of silicon, doped silicon, germanium, silicon germanium, semiconductor compounds, or other semiconductor materials. 
         [0026]    The string of memory cells of the three dimensional memory of the invention and methods of manufacturing such devices results in a string of memory cells that improves capacity; thereby, provides improving the scalability of such memory structures, such as for 3D NOR flash memory. In turn, such scaling reduces or eliminates the extent of current leakage that may be experienced by three dimensional memory. The invention provides a string of memory cells of a three dimensional memory (e.g., a nonvolatile memory device such as a 3D NOR flash memory device) and methods of manufacturing such devices that provides scalable high density three dimensional memory configured for random access. 
         [0027]      FIG. 1A  illustrates a cross section of a string of memory cells  100  comprising a common source line, word line, and bit line according to an embodiment of the invention. In the illustrated embodiment, the string of memory cells  100  comprises the memory cells C 1 , C 2 , and C 3 . The string of memory cells  100  comprises a cap layer  5 , one or more third conductive layers  65 , one or more dielectric layers  45 , one or more second conductive layers  60 , one or more first conductive layers  20 , and an insulating layer  10 . The string of memory cells  100  may further comprise a channel conductive layer  40 . 
         [0028]    In various embodiments, the cap layer  5  and/or the insulating layer  10  are configured to enclose the string of memory cells therebetween. For example, in some embodiments, the cap layer  5  may cap one end of the string of memory cells  100  and the insulating layer may isolate the cells of the memory string  100  from the metal routing of the three-dimensional memory assembly/array/device. In various embodiments, the cap layer  5  may be and/or act as a substrate. For example, the cap layer  5  may be made of oxide, silicon, doped silicon, germanium, silicon germanium, semiconductor compounds, or other semiconductor materials. The insulating layer  10  may be an oxide layer, in various embodiments. 
         [0029]    In various embodiments, the first conductive layers  20  may each correspond to a common source line. In various embodiments, the second conductive layers  60  may each correspond to one or more word lines. The second conductive layer  60  may be configured to correspond to (e.g., include) a plurality of word lines up to an order of N word lines. The third conductive layers  65  may each correspond to a bit line. Each memory cell in the matrix includes a transistor structure having a gate, a drain, a source, and a channel defined between the drain and the source. The gate may be connected to the word line, the drain may be connected to the bit line, and the source may be connected to a source line, which in turn may be connected to common ground. Each of the first conductive layers  20 , second conductive layers  60 , and third conductive layers  65  may be made of n+poly, poly-silicon layer, metal, or other conductive material. 
         [0030]    As depicted, the dielectric layer  45  comprises at least one of a block layer, storage layer, or tunnel layer. The dielectric layer  45  may comprise an oxide/nitride/oxide (ONO) layer such that the block layer may correspond to the oxide layer, the storage layer may correspond to the nitride layer, and the tunnel layer may correspond to the oxide layer as described herein. In various embodiments, the dielectric layer  45  is formed by replacement. 
         [0031]    As shown in  FIG. 1A , the string of memory cells comprises several memory cells. For example, there are at least two memory cells (cell C 1  and cell C 2 ) in this string. The cell C 1  comprises a first conductive layer  20 , a dielectric layer  45 , a second conductive layer  60 , and a third conductive layer  65 . The first conductive layer  20  referred as one common source line (e.g., CS 1 ). The second conductive layer  60  may be referred to as a word line. The third conductive layer  65  may be referred to as a bit line. The cell C 2  comprises a third conductive layer  65 , a dielectric layer  45 , a second conductive layer  60 , and a first conductive layer  20 . The first conductive layer  20  referred as one common source line (e.g., CS 1 ). The second conductive layer  60  may be referred to as a word line. The third conductive layer  65  may be referred to as a bit line. The cell C 1  and the cell C 2  shares the same third conductive layer  65  (e.g., have a common bit line). Likewise, the cell C 2  and the cell C 3  shares a same common source line (e.g., CS 1 )  20 . 
         [0032]      FIG. 1B  illustrates a staircase view of a string of memory cells according to an embodiment of the invention. The first conductive layer  20 , the dielectric layer  45 , the second conductive layer  60 , and the third conductive layer  65  are structured in a staircase of a memory cell C 1  Likewise, the memory cell C 2  has similar staircase structure as cell C 1  and shares a same bit line  65 . 
         [0033]      FIG. 1C  illustrates a top view of memory cells in a matrix according to an embodiment of the invention. The memory cells in the matrix comprises a plurality of memory strings  100 . As depicted, the memory cells in the matrix (e.g., a non-volatile memory device) comprises a plurality of word lines (of which WL 1 , WL 2 , WL 3 , and WL 4  are illustrated) that intersect a plurality of bit lines (e.g., BL 1 ). A memory cell is located at each intersecting point of a word line and a bit line. As further depicted, the memory cells in the matrix comprises a plurality of common source lines (of which CS 1  and CS 2  are illustrated) that also intersect a plurality of bit lines (e.g., BL 1 ). The layers as described above, for example, are further depicted in staircase  202  as described herein with reference to  FIG. 1B . 
         [0034]    Thus, a plurality of memory strings  100  may be combined into a three-dimensional memory array. The three-dimensional memory array may be a part of a nonvolatile memory device for improving gate capacity. Each of the memory strings comprises a plurality of memory cells (e.g., C 1 , C 2 , C 3 ). Each memory string is operatively attached to a channel line  150 , as shown in  FIGS. 2A-2H  via the channel conductive layer  40 . Each of the memory cells has a first end/terminal/electrode operatively connected to a bit line. For example, cell C 1  may be attached to a bit line  130  via a bit line end/terminal/electrode comprising at least a portion of the third conductive layer  65 . Each of the memory cells has a second end/terminal/electrode operatively connected to a source line. For example, C 1  may be attached to a common source line  140 ,  142  via a source line end/terminal/electrode comprising at least a portion of the first conductive layer  20 . Additionally, each memory cell has a third end/terminal/electrode operatively connected to a word line. For example, cell C 1  may be attached to word line WL 1  via a word line end/terminal/electrode comprising at least a portion of the second conductive layer  60 . In various embodiments, each pair of adjacent memory cells shares one of a bit line and a source line. For example, cells C 1  and C 2  share the same third conductive layer  65  and therefore share a bit line  130  due to their shared bit line end/terminal/electrode. In another example, cells C 2  and C 3  share the same first conductive layer  20  and therefore share a source line  140 ,  142  due to their shared source line end/terminal/electrode. 
         [0035]      FIG. 2A  illustrates an algorithm according to an embodiment of the invention. As depicted in  FIG. 2A , a multi-dimensional memory array  1000  comprises a plurality of memory strings  110 . In one embodiment, each memory string  110  is structured in the same manner as the memory string  100  shown in  FIGS. 1A-1C . However, the memory strings  110  may each have more of fewer memory cells than the string of memory cells  100  (e.g., each memory string  110  may comprise more of fewer than three memory cells associated therewith). Each memory string  110  comprises a first end  120  structured to connect to a channel line  150  and a second end  115  structured to connect to a bit line  130  in a pre-determined direction (e.g., a vertical direction). The channel line  150  may be connected to the channel conductive layer  40  for each memory string. The channel line  150  is capable of providing an operation voltage to the channel conductive layer  40  for each memory cell of the string of memory cells comprising memory string  110 . 
         [0036]      FIG. 2B  illustrates an algorithm according to an embodiment of the invention. The multi-dimensional memory array  2000  comprises a plurality of memory strings  110 . The plurality of memory strings  110  comprises a first end  120  structured to connect to a channel line  150  and a second end  115  structured to connect to a bit line  130  in a pre-determined direction. Each memory string  110  comprises at least one memory cell. The first terminal  160  of the at least one memory cell is configured to connect to the bit line  130 . 
         [0037]    In some embodiments, a second terminal  170  of the at least one memory cell is configured to connect to a common source line  140 ,  142 . As depicted, the plurality of memory strings  110  is structured in a plane comprising at least one of an x plane, y plane, or z plane. 
         [0038]      FIGS. 2C-2H  illustrate various algorithms according to an embodiment of the invention, such as program, read, and erase algorithms for embodiments of the present invention. The multi-dimensional memory array as depicted may optionally comprise a plurality of memory strings, a first end structured to connect to a channel, and a second end structured to connect to a bit line in a pre-determined direction as described herein with reference to  FIGS. 2A-2B . 
         [0039]    With reference to  FIG. 2C , a program algorithm is illustrated according to an embodiment of the invention. As the legend below the diagram illustrates, memory cell  210  comprises a program cell and memory cell  212  comprises an inhibited cell. In some embodiments, the non-volatile memory device may be operable to perform a program operation based, at least in part, on channel hot electron injection such that a carrier may be injected from the channel to the dielectric (e.g., dielectric layer  45 ). In an example embodiment, at a common source voltage (e.g., VCS 1 =0V, where V is the unit of measure for Voltage) applied to the memory cell  210  (e.g., the program cell) without the application of a voltage bias (Vb), the programing operation may occur at a predetermined word line voltage (e.g., VWL 2 =9.5V) and/or a predetermined bit line voltage (e.g., VBL 1 =4.5V). Alternatively or additionally, the non-volatile memory device may be configured to suppress, via an inhibition operation, the hot electron injection in response to the application of a different voltage bias in some memory cells. The inhibition operation may prevent current leakage and damage to the dielectric (e.g., dielectric  45 ) should the carrier interfere with the structure of the dielectric. For example, at a common source voltage (e.g., VCS 1 =0V) applied to the memory cell  212  (e.g., the inhibited cell) with the application of a voltage bias (e.g., Vb=0 and Vb=3), an inhibition operation may occur at a predetermined word line voltage of, for example, VWL 1 =0˜Vt−1 and VWL 2 =9.5V and/or bit line voltage of, for example, VBL 1 =4.5V. 
         [0040]      FIG. 2D  illustrates a program algorithm according to an embodiment of the invention. In some embodiments, the non-volatile memory device may be operable to perform a program operation based, at least in part, on FN injection (e.g., Fowler-Nordheim electron injection or tunneling injection) such that charge carriers may be injected, for example, via an insulating layer to an electric conductor. In an example embodiment, at a common source voltage (e.g., VCS 1 =0V) applied to the program cell without the application of a voltage bias, the programing operation may occur at a predetermined word line voltage (e.g., VWL 2 =15V) and/or a predetermined bit line voltage (e.g., VBL 1 =0V). Alternatively or additionally, the non-volatile memory device may be configured to suppress, via an inhibition operation, the FN injection in response to the application of a different voltage bias to some memory cells as described herein. The inhibition operation may weaken the electric field corresponding to the tunneling layer. For example, at a common source voltage (e.g., VCS 2 =5V, VCS 1 =0V, and VCS 1 =0V respectively) applied to the memory cell (e.g., the inhibited cell) with the application of a voltage bias (e.g., Vb=0, Vb=0, and Vb=8), an inhibition operation may occur at a predetermined word line voltage of, for example, VWL 2 =15V, VWL 1 =0V, and VWL 2 =15V and/or bit line voltage of, for example, VBL 2 =5, VBL 1 =0V, and VBL 1 =0V. 
         [0041]      FIGS. 2E-F  illustrate a read algorithm according to an embodiment of the invention. In some embodiments, the non-volatile memory device may be operable to perform the read operation such that current may flow through the channel to the bit line when a predetermined voltage is applied to the gate corresponding to the non-volatile memory device. In this regard, the bit line voltage is reduced (e.g., pulled down). In an example embodiment, at a common source voltage (e.g., VCS 1 =0V) applied to the read cell without the application of a voltage bias, the read operation may occur at a predetermined word line voltage (e.g., VWL 2 =5˜7V) and/or a predetermined bit line voltage (e.g., VBL 1 =1V). Alternatively or additionally, the non-volatile memory device may be configured to decrease, via an inhibition operation, the current (e.g., inhibit the read operation) in response to the application of a different voltage bias to some memory cells. For example, at a common source voltage (e.g., VCS 2 =1V, VCS 1 =0V, and VCS 1 =0V respectively) applied to the memory cell (e.g., the inhibited cell) with the application of a voltage bias (e.g., Vb=0, Vb=0, and Vb=−1), an inhibition operation may occur at a predetermined word line voltage (e.g., VWL 2 =5˜7V, VWL 1 =0V, and VWL 2 =5˜7V) and/or bit line voltage (e.g., VBL 1 =1V, VBL 1 =1V, and VBL 1 =1V). 
         [0042]      FIGS. 2G-H  illustrate an erase algorithm according to an embodiment of the invention. In some embodiments, the non-volatile memory device may be configured to perform an erase operation based, at least in part, on FN injection. In this regard, the non-volatile memory device may be configured to set the bias to a predetermined value (e.g., zero) to suppress, via an inhibition operation, the FN injection. For example, at a common source voltage (e.g., VCS=0V) applied to the memory cell (e.g., the inhibited block) and with the application of a voltage bias (e.g., Vb=8), an inhibition operation may occur at a predetermined word line voltage (e.g., VWL=0V) and/or bit line voltage (e.g., VBL=0V). 
         [0043]      FIGS. 3A-3F  illustrate a cross section view of some of the steps of forming a string of memory cells  100  of a three dimensional memory according to an embodiment of the invention.  FIG. 4  provides a flowchart describing the steps illustrated by  FIGS. 3A-3F . Starting at step  310 , shown in  FIG. 3A , a layered structure  300  is provided. The layered structure  300  comprises the cap layer  5 , the one or more third conductive layers  65 , one or more sacrificial layers  15 , the one or more first conductive layers  20 , and the insulating layer  10 . The sacrificial layers may be made of SiN or other appropriate material. For example, the layered structure  300  comprises a cap layer  5 . Adjacent the cap layer  5  is a third conductive layer  65 . Adjacent the third conductive layer  65 , but on the opposite side of the third conductive layer  65  as the cap layer  5 , is a sacrificial layer  15 . Adjacent to the side of the sacrificial layer  15  that is opposite the conductive layer  65  is a first conductive layer  20 . The layered structure continues with a sacrificial layer  15 , a third conductive layer  65 , a sacrificial layer  15 , and a first conductive layer  20 . The layered structure  300  may continue in this manner until terminating in an insulating layer  10  adjacent a first conductive layer  20 . 
         [0044]    Referring to  FIG. 4 , at step  320 , the channel is formed, as shown in  FIG. 3B . For example, a hole  30  may be etched through the layered structure  300 , such that the hole  30  passes through insulating layer  10 , the one or more first conductive layers  20 , the one or more sacrificial layers  15 , and the third conductive layers  65 . In some embodiments, the etching process results in the hole  30  such that the hole  30  would be filled with conductive materials later to act as a vertical channel for each memory cells. In some embodiments, the hole  30  may be perpendicular to the boundary lines of at least one of the layers of the layered structure  300 . 
         [0045]    As shown in  FIG. 4 , step  330  comprises interposing or depositing the channel conductive layer  40  into the hole  30 . For example, as depicted in  FIG. 3C , the channel conductive layer  40  may substantially fill the hole  30 . In at least one embodiment, the channel conductive layer  40  comprises poly-silicon. In some embodiments, the channel conductive layer  40  may be metal, silicon (Si), or another suitable material. 
         [0046]    Returning to  FIG. 4 , at step  340  at least one of the one or more sacrificial layers  15  is removed.  FIG. 3D  illustrates the layered structure  300  after the removal of the sacrificial layers  15 . The sacrificial layer  15 , for example a SiN layer, may be removed by an etching process. The removal of the sacrificial layer(s)  15  results in a plurality of openings  101 . Each opening is bordered along one edge by a first conductive layer  20 , a third conductive layer  65 , and the channel conductive layer  40 . 
         [0047]    With reference to  FIG. 4 , at step  350 , the one or more dielectric layers  45  are disposed. For example, of dielectric layer  45  may be deposited within each of the openings  101 , as shown in  FIG. 3E . For example, a dielectric layer  45  may be deposited along the internal surfaces of the opening  101 . For example, the dielectric layer  45  may be deposited along within the opening  101  such that a portion of the dielectric layer  45  borders a first conductive layer  20 , another portion of the dielectric layer  45  borders the third conductive layer  65 , and another portion of the dielectric layer  45  borders the channel conductive layer  40 . The dielectric layer  45  may be deposited such that a remaining opening  50  results. As depicted, the dielectric layer  45  comprises an ONO layer (e.g., an oxide/nitride/oxide layer or fill-in). The dielectric layer  45  is similar to a lamination structure having multiple layers including a lower oxide film  46 , a nitride film  47 , and an upper oxide film  48 . 
         [0048]    Returning to  FIG. 4 , at step  360 , the second conductive layer  60  is interposed or deposited within the remaining opening  50 . A cross section of the string of memory cells resulting from step  360  is illustrated in  FIG. 1F . The second conductive layer  60  may be interposed within the second opening  50  so as to substantially fill the remaining opening  50   
         [0049]    In an embodiment of the invention, the second conductive layer  60  may function, for example, as a word line or a gate electrode. The word line or gate electrode may be configured for read, erase, or other programmatic functions. 
         [0050]    Following these steps and/or interspersed therebetween, any additional steps known in the art may be used to finalize the fabrication of the string of memory cells. Such steps may include forming a second conductive layer or a control gate layer and may include other additional steps depending upon the design and desired attributes of the gate structure. 
         [0051]    An aspect of the invention provides a string of memory cells, a three dimensional memory array and/or device fabricated according to a method of the invention. 
         [0052]    Many modifications and other embodiments of the inventions set forth herein will come to mind to one skilled in the art to which these inventions pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the inventions are not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe exemplary embodiments in the context of certain exemplary combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative embodiments without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.