Abstract:
A semiconductor memory device having a cell pattern formed on an interconnection and capable of reducing an interconnection resistance and a fabrication method thereof are provided. The semiconductor device includes a semiconductor substrate in which a cell area, a core area, and a peripheral area are defined and a bottom structure is formed, a conductive line formed on an entire structure of the semiconductor substrate, a memory cell pattern formed on the conductive line in the cell area, and a dummy conductive pattern formed on any one of the conductive line in the core area and the peripheral area.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 U.S.C. 119(a) to Korean application number 10-2011-0108591, filed on Oct. 24, 2011, in the Korean Patent Office, which is incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The inventive concept relates to a method of fabricating a semiconductor memory, and more particularly, to a semiconductor memory device having cell patterns formed on an interconnection and a fabrication method thereof. 
         [0004]    2. Related Art 
         [0005]    In general, fabrication processes for a cell area, a core area and a peripheral area in a memory device are separately performed. However, the cell area, the core area and the peripheral area operate correlatively with each other. Accordingly, a structure of patterns and stacks should be formed to ensure operational and characteristic connections between correlated circuits in the cell area, the core area, and the peripheral area. 
         [0006]      FIG. 1  is a cross-sectional view illustrating a structure of a semiconductor memory device, for example, a phase-change random access device (PCRAM). 
         [0007]    An isolation layer  103  is formed on a semiconductor substrate  101  where a cell area, a core area, and a peripheral area are respectively defined. A switch  105  configured to select a word line is formed on the cell and core areas of the semiconductor substrate  101 . At this time, a circuit pattern is also formed in the peripheral area to match the height of patterns or structures between the cell and core areas and the peripheral area. 
         [0008]    A conductive line  107  is formed on the semiconductor substrate having the switch  105 . The conductive line  107  may be formed using a metal material such as tungsten (W) and serve as a word line in a cell operation. The conductive line  107  in the cell and core areas is electrically connected to the switch  105  which is formed below the conductive line  107 . The conductive line  107  in the peripheral area may contact with the underlying circuit pattern to serve as an interconnection. 
         [0009]    A cell pattern is formed on the conductive line  107  in the cell and core areas. In particular, in the PCRAM device, the cell pattern is coupled to the conductive line  107  through an access element such as a diode. 
         [0010]    The diode as the access element may include a barrier metal layer  109  and an N-type semiconductor layer  111 ; and further include a silicide layer, which could be formed by silicidation to a surface of the N-type semiconductor layer  111 , to reduce a contact resistance. However, the diode is not limited thereto. In addition, a lower electrode  115 , a phase-change material pattern  117 , an upper electrode  119 , and a bit line  121  are formed on the access element  109  and  111  (or  113 ) through general processes well known to one skilled in the art. 
         [0011]      FIG. 2  is a layout of the semiconductor memory device illustrated in  FIG. 1 . 
         [0012]      FIG. 2  illustrates that a plurality of unit memory cells MC are formed in a cell area, a word line contact WC is formed in a core area. Further, a contact for connection between a peripheral circuit and the cell area is formed in the peripheral area. 
         [0013]    The unit memory cell of the memory device should have a size to guarantee an operational characteristic thereof. However, as the semiconductor device is highly integrated, a word line size (or width), that is, a critical dimension of the conductive line  107 , decreases so that the series resistance of the conductive line  107  increases. The increased series resistance of the conduction line  107  cause voltage drop, thereby threatening a sensing margin. 
         [0014]    To solve above-described concerns, the word line selection switch  105  should be designed to provide sufficient driving current on the conductive line  107 . However, a large transistor is required to increase drivability of the switch  105 , resulting in increase of a chip size. 
         [0015]    As another method to solve the concerns, a method of forming a deep trench for the conductive line  107  may be considered. However, the method may be difficult to be applied because of restriction based on integration degree of the semiconductor memory device. 
       SUMMARY 
       [0016]    According to one aspect of an exemplary embodiment, there is a provided a semiconductor device. The semiconductor device may include a semiconductor substrate in which a cell area, a core area, and a peripheral area are defined and a bottom structure is formed, a conductive line formed on an entire structure of the semiconductor substrate, a memory cell pattern formed on the conductive line in the cell area, and a dummy conductive pattern formed on any one of the conductive line in the core area and the peripheral area. 
         [0017]    According to another aspect of an exemplary embodiment, there is a provided a method of fabricating a memory device having a cell pattern formed on an interconnection. The method may include forming a conductive line on an entire structure of a semiconductor substrate in which a cell area, a core area, and a peripheral area are defined, and forming a cell pattern on the conductive line in the cell area and a dummy conductive pattern on the conductive line in the core area and the peripheral area. 
         [0018]    A semiconductor memory device includes a word line in a cell area, and a dummy pattern in a core area and a peripheral area, wherein the word line and the dummy pattern have the same structure and the same height from a semiconductor substrate level. 
         [0019]    These and other features, aspects, and embodiments are described below in the section entitled “DETAILED DESCRIPTION”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]    The above and other aspects, features and other advantages of the subject matter of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
           [0021]      FIG. 1  is a cross-sectional view illustrating a structure of a general semiconductor memory device; 
           [0022]      FIG. 2  is a layout of the semiconductor memory device illustrated in  FIG. 1 ; 
           [0023]      FIG. 3  is a cross-sectional view illustrating a structure of a semiconductor memory device according to an exemplary embodiment of the inventive concept; and 
           [0024]      FIG. 4  is a layout of the semiconductor memory device illustrated in  FIG. 3 . 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    Hereinafter, exemplary embodiments will be described in greater detail with reference to the accompanying drawings. 
         [0026]    Exemplary embodiments are described herein with reference to cross-sectional illustrations that are schematic illustrations of exemplary embodiments (and intermediate structures). As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, exemplary embodiments should not be construed as limited to the particular shapes of regions illustrated herein but may be to include deviations in shapes that result, for example, from manufacturing. In the drawings, lengths and sizes of layers and regions may be exaggerated for clarity. Like reference numerals in the drawings denote like elements. It is also understood that when a layer is referred to as being “on” another layer or substrate, it can be directly on the other or substrate, or intervening layers may also be present. 
         [0027]      FIG. 3  is a cross-sectional view illustrating a structure of a semiconductor memory device according to an exemplary embodiment of the inventive concept. 
         [0028]    A semiconductor memory device according to an exemplary embodiment includes a cell pattern which is formed on a conductive line  207 , preferably, a word line. The semiconductor memory device may include a PCRM, but the semiconductor memory device is not limited thereto. 
         [0029]    The cell pattern is formed on the conductive line  207  in the cell area. Dummy conductive patterns  223  and  225  may be formed on the conductive line  207  in the core area and/or the peripheral area. 
         [0030]    Hereinafter, the structure of the semiconductor memory device will be described below in detail. 
         [0031]    An isolation layer  203  is formed in a semiconductor substrate  201  in which the cell area, the core area and the peripheral area are defined. 
         [0032]    A switch  205  for word line selection is formed on the cell and core areas of the semiconductor substrate  201  including the isolation layer  203 . At this time, a circuit pattern may be also formed in the peripheral area, for matching structures&#39; height of the peripheral area with that of the cell and core areas. 
         [0033]    Subsequently, the conductive line  207 , which are electrically connected to the switch  205 , are formed over an entire surface of the semiconductor substrate in which the switch  205  is formed. The conductive line  207  including a metal material such as tungsten (W) may serve as word lines. 
         [0034]    The cell pattern and the dummy conductive pattern  223  are formed on the conductive line  207  of the cell and core areas, and, simultaneously, the dummy conductive pattern  225  is formed on the conductive line  207  of the peripheral area. That is, while an access element including layers  209  and  211  is formed on the conductive line  207  of the cell area, the dummy conductive patterns  223  and  225  like the access element are also formed in the core area and the peripheral area by forming and patterning the same materials. 
         [0035]    Specifically, layers for the access element are sequentially formed over an entire structure of the semiconductor substrate in which the conductive line  207  are formed, and then the layers are etched for patterning. The access element may function as a diode. As the access element, the diode may have a stacked structure of a barrier metal layer  209  and an N-type semiconductor layer  211 , but the diode is not limited thereto. In addition, a silicide layer  213  may be formed by performing silicidation on an upper surface of the access element formed in the cell area. 
         [0036]    Meanwhile, although  FIG. 3  illustrates that the dummy conductive patterns  223  and  225  are formed on both the core area and the peripheral area, the inventive concept is not limited thereto. That is, the dummy conductive pattern may be selectively formed on the core area or the peripheral area. 
         [0037]    Next, the cell pattern including a lower electrode  215 , a phase-change material layer  217  and an upper electrode  219  may be formed on the access element and a bit line may be formed on the cell pattern. Detailed fabrication methods for the cell pattern and the bit line are well known to one skilled in the art. 
         [0038]    The dummy conductive patterns  223  and  225  are respectively formed on the conductive line  207  of the core area and the conductive line  207  of the peripheral area. The dummy conductive patterns  223  and  225  may have the same structure as the access element. Referring to the example of  FIG. 3 , like the diode including the barrier metal layer  209  and the N-type semiconductor layer  211  functioning as the access element, the dummy conductive patterns  223  and  225  also have a stacked structure of the barrier layer  209  and the N type semiconductor layer  211 . 
         [0039]      FIG. 4  is a layout of the semiconductor memory device illustrated in  FIG. 3 . 
         [0040]    Referring to  FIG. 4 , the dummy conductive patterns  223  and  225  are formed on the core area and the peripheral area. The dummy conductive patterns  223  and  225  are formed on the conductive line  207  to serve as a parallel resistance component against the conductive line  207 . 
         [0041]    The resistance of the conductive line  207  may be less recognized than the original resistance of the conductive line  207  because two similar resistances of the conductive line  207  and the dummy conductive patterns  223  and  225  are recognized in parallel. 
         [0042]    When the conductive line  207  serves as a word line in a recording operation, voltage drop through the word line is reduced. Thus, a voltage applied for operation of the memory device may be reduced; and a sensing margin may be improved as compared with a conventional memory device which operates in the same applying voltage. 
         [0043]    Further, a resistance component of the word line may be reduced without increase in drivability of the switch for controlling the word line so that burden on large transistor&#39;s drivability is reduced, dimension increase may be prevented, and a chip size may be reduced. 
         [0044]    It is not required to form a deep trench for the word line on process; and thus burden on process development may be reduced. A height difference between the cell and core areas and the peripheral area decreases so that the height balance between the cell and core areas and the peripheral area may be improved and a fabrication yield may be increased. 
         [0045]    While certain embodiments have been described above, it will be understood that the embodiments described are by way of example only. Accordingly, the devices and methods described herein should not be limited based on the described embodiments. Rather, the systems and methods described herein should only be limited in light of the claims that follow when taken in conjunction with the above description and accompanying drawings.