Abstract:
A phase-change memory device and a method of fabricating the same are provided. The phase-change memory device includes a semiconductor substrate in which a word line is arranged, a diode line disposed over the word line and extending parallel to the word line, a phase-change line pattern disposed over the diode line, and a projection disposed between the diode line and the phase-change line pattern and protruding from the diode line. The diode line and the projection are formed of a single layer to be in continuity with each other.

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
       [0001]    The present application claims priority under 35 U.S.C. 119(a) to Korean application number 10-2012-0147439, filed on Dec. 17, 2012, in the Korean Intellectual Property Office, which is incorporated herein by reference in its entirety. 
       BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    The inventive concept relates to a resistance memory device, and more particularly, to a phase-change memory device and a method of fabricating the same. 
         [0004]    2. Related Art 
         [0005]    A phase-change memory devices that is one of nonvolatile memory devices includes a phase-change material of which resistance is changed depending on temperature. As the phase-change material, there is typically a chalcogenide material including germanium (Ge), antimony (Sb), and/or tellurium (Te). The phase-change material is changed into an amorphous state or a crystalline state depending on temperature to define a reset state (or logic “1”) or a set state (or logic “0”). 
         [0006]    A memory cell of the phase-change material layer may include a variable resistor configured of a phase-change material and a switching device configured to selectively drive the variable resistor that are connected between a word line and a bit line. 
         [0007]    As the switching device of the phase-change memory device, a diode occupying a small area has been mainly used. 
         [0008]    An early diode is formed by doping impurities into a polysilicon layer patterned using a general photolithography process. 
         [0009]    However, it is a trend to require a diode and a heating electrode having a critical dimension (CD) equal to or less than resolution of exposure equipment. In order to meet these demands, the diode and the heating electrode having the CD equal to or less than the resolution of the equipment are formed by forming a hard mask layer for confining a diode and a heating electrode region using double spacer patterning technology (SPT) and patterning a lower layer using the hard mask layer. 
         [0010]    However, when a heating electrode layer and a diode layer are etched using the hard mask, since a thickness of a film to be etched is very large, leaning occurs and thus the phase-change memory becomes in an unstable state. 
         [0011]    In particular, as illustrated in  FIG. 1 , a phase-change material layer  10  has a positive slope due to the leaning and thus a location in which phase-change is generated in the phase-change material layer  10  is biased downward. In  FIG. 1 , “A” indicates a location in which phase-change is normally generated when the leaning is not generated, and “B” indicates a location in which the phase-change is generated when the leaning is generated. When the phase-change generation location is changed, heat loss is generated to a side of a barrier layer  15  below the phase-change material layer  10 . 
         [0012]    When the phase-change memory device is fabricated, a double SPT process may be performed, and the heating electrode layer and the diode layer may be simultaneously etched using a mask material obtained the double SPT process. Thus, etching failure may occur and long fabrication processing time may be required. 
       SUMMARY 
       [0013]    According to one aspect of an exemplary embodiment of the present invention, there is provided a phase-change memory device. The phase-change memory device may include a semiconductor substrate in which a word line is arranged, a diode line disposed over the word line and extending parallel to the word line, a phase-change line pattern disposed over the diode line, and a projection disposed between the diode line and the phase-change pattern and protruding from the diode line. The diode line and the projection are formed of a single layer to be in continuity with each other. 
         [0014]    According to another aspect of an exemplary embodiment of the present invention, there is provided a phase-change memory device. The phase-change memory device may include a word line, a line-shaped diode disposed over the word line, a pattern-shaped heating electrode formed of the same material as the line-shaped diode, and a phase-change line pattern disposed over the heating electrode to correspond to the heating electrode. 
         [0015]    According to still another aspect of an exemplary embodiment of the present invention, there is provided a method of fabricating a phase-change memory device. The method may include forming a word line over a semiconductor substrate, forming a diode layer over the word line, forming a phase-change layer over the diode layer, patterning the phase-change layer by etching, thereby forming a phase-change line in a line shape extending to a first direction, patterning the diode layer by etching, thereby forming a diode line in the same shape as the phase-change line, filling an insulating layer between the line-shaped phase-change layer and the diode layer, depositing a conductive layer over the insulating layer and the phase-change line, patterning the conductive layer and the phase-change line by etching, thereby respectively forming a bit line and a phase-change line pattern in a line shape extending to a second direction perpendicular to the first direction, and etching the exposed diode layer using a bit line as a mask, thereby forming a line-shaped heating electrode and simultaneously confining a line-shaped diode. 
         [0016]    These and other features, aspects, and embodiments are described below in the section entitled “DETAILED DESCRIPTION”. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    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: 
           [0018]      FIG. 1  is a cross-sectional view illustrating a phase-change location in a phase-change material layer of a general phase-change memory device; 
           [0019]      FIGS. 2 to 9  are perspective views sequentially illustrating a process of fabricating a phase-change memory device according to an exemplary embodiment of the inventive concept; 
           [0020]      FIG. 10  is a cross-sectional view illustrating the phase-change memory device taken along line y-y′ shown in  FIG. 9 ; and 
           [0021]      FIGS. 11 and 12  are views explaining a SPT method according to an exemplary embodiment of the inventive concept. 
       
    
    
     DETAILED DESCRIPTION 
       [0022]    Hereinafter, exemplary embodiments will be described in greater detail with reference to the accompanying drawings. 
         [0023]    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. 
         [0024]    Referring to  FIG. 2 , a word line  110  extending to a first direction is formed on the semiconductor substrate  100  through a conventional method. An insulating layer  115  is formed in a space between word lines  110  to insulate adjacent word lines  110  from each other. A semiconductor layer  125  is formed on the semiconductor substrate including the word line  110 . The semiconductor layer  125  may include a polysilicon layer, an amorphous layer, or a crystalline silicon layer. The semiconductor layer  125  may be an intrinsic semiconductor layer or a semiconductor layer doped with first conductivity type impurities, for example, n-type impurities. Subsequently, impurities are implanted into the exposed semiconductor layer  125  to perform a diode operation. 
         [0025]    When the semiconductor layer  125  is an intrinsic layer, for example, n-type impurities are ion-implanted into a lower region of the semiconductor layer  125  as a target, and p-type impurities are ion-implanted into an upper region of the semiconductor layer  125  as a target. When the semiconductor layer  125  is an n-doped layer, p-type impurities are ion-implanted into the upper region of the semiconductor layer  125  as a target. 
         [0026]    Therefore, the semiconductor layer  125  is divided into a high concentration p-type impurity region, a low concentration p-type impurity region, a low concentration n-type impurity region, and a high concentration n-type impurity region from a top thereof to a bottom thereof. 
         [0027]    A barrier layer  120  may be interposed between the semiconductor layer  125  and the word line  110  and a barrier layer  130  may be also formed on the semiconductor layer  125 . In the exemplary embodiment, for clarity, the barrier layer  120  disposed below the semiconductor layer  125  may be referred to as a lower barrier layer  120  and the barrier layer  130  disposed on the semiconductor layer  125  may be referred to as an upper barrier layer  130 . Each of the upper and lower barrier layers  130  and  120  may include titanium/titanium nitride (Ti/TIN), but the upper and lower barrier layers  130  and  120  are not limited thereto. Various materials serving as a conductive barrier may be used as the upper and lower barrier layers  130  and  120 . A phase-change material layer  135 , a connection layer  140 , and a hard mask layer  150  are sequentially formed on the upper barrier layer  130 . The phase-change material layer  135  may include a chalcogenide material containing Ge, Sb, and/or Te. The connection layer  140  may include the same material as an upper electrode to be formed in a subsequent process. 
         [0028]    Referring to  FIG. 3 , a mask pattern (not shown) is formed on a hard mask layer  150  through a SPT method, and the hard mask layer  150  is etched in the same shape as the mask pattern to form a hard mask layer pattern  150   a.    
         [0029]    As illustrated in  FIG. 11 , in the SPT method, a sacrificial pattern  210  is formed on the layer  200  to be etched, and spacers  220  are formed on both sides of the sacrificial pattern  210  through a conventional spacer forming method. As illustrated in  FIG. 12 , the sacrificial pattern  210  is removed, and the etched pattern  200   a  is formed using the remaining spacers  210  as a mask. Therefore, the hard mask layer pattern  150   a  in the exemplary embodiment may correspond to the etched pattern  200   a  of  FIG. 12 . 
         [0030]    Referring back to  FIG. 3 , the connection layer  140 , the phase-change material layer  135 , and the upper barrier layer  130  below the hard mask layer pattern  150   a  are sequentially patterned using the hard mask layer pattern  150   a  obtained the above-described SPT method. A structure including the connection layer pattern  140   a , phase-change material layer pattern  135   a , and upper barrier layer pattern  130   a  has a line pattern shape extending to the first direction (for example, a direction parallel to the word line). The structure having the line pattern shape (hereinafter, referred to as a phase-change line) may be disposed to correspond to the word line  110  therebelow parallel to the word line. 
         [0031]    Referring to  FIG. 4 , heat-resistance spacers  155  are formed on the sidewalls of the phase-change line extending to the first direction through a conventional method. The heat-resistance spacers  155  may be provided to protect the phase-change material layer pattern  135   a . The heat-resistance spacers  155  are formed on the sidewalls of the phase-change material layer pattern  135   a  to prevent heat from moving to adjacent cells in phase-change. The heat-resistance spacers  155  may include a silicon nitride layer. 
         [0032]    Referring to  FIG. 5 , the underlying semiconductor layer  125  and the lower barrier layer  120  are patterned using the heat-resistance spacers  155  and the hard mask layer pattern  150   a  as a mask to form a diode line  125   a  and a lower barrier layer pattern  120   a . The diode line  125   a  is disposed on the word line  110 , and the hard mask layer pattern  150   a  may be removed in the patterning process to expose the connection layer pattern  140   a.    
         [0033]    As illustrated in  FIG. 6 , an interlayer insulating layer  160  is buried between diode lines  125   a  and the phase-change lines. A surface planarization is performed on the buried interlayer insulating layer  160 . 
         [0034]    Referring to  FIG. 7 , an upper metal layer  165  is formed on the semiconductor substrate including the planarized interlayer insulating layer  160 . The upper metal layer  165  is electrically connected to the exposed connection layer pattern  140   a.    
         [0035]    Referring to  FIG. 8 , a mask pattern (not shown) is formed on the upper metal layer  165  using the SPT method illustrated in  FIGS. 11 and 12 , and the upper metal layer  165  is patterned in the same shape as the mask pattern to define the bit line  165   a . The phase-change line exposed by the bit line  165   a  is removed to define a phase-change line pattern. The phase-change line pattern includes a second connection layer pattern  140   b , a second phase-change material layer pattern  135   b , and a second upper barrier layer pattern  130   b  (see  FIG. 10 ). Phase-change line patterns are separated between cells. 
         [0036]    As illustrated in  FIG. 9 , the semiconductor layer  125   a  exposed by the bit line  165   a  is partially etched. The partial etching process is a process that etches a partial thickness of a total thickness of a film. In the exemplary embodiment, only a portion of the exposed semiconductor layer  125   a  corresponding to the high concentration p-type impurity region is etched to form a semiconductor layer  125   c.    
         [0037]      FIG. 10  is a cross-sectional view illustrating the phase-change memory device taken along line y-y′ of  FIG. 9 . As illustrated in  FIG. 10 , the semiconductor layer  125   c  (hereinafter, referred to as a high concentration p-type layer) corresponding to the patterned high concentration p-type impurity region serves as a heating electrode in the phase-change memory device, a low concentration p-type impurity region  125   b - 3 , a low concentration n-type impurity region  125   b - 2 , and a high concentration n-type impurity region  125   b - 1  together serve as a line-shaped diode  125   b.    
         [0038]    Specifically, as illustrated in  FIG. 10 , since the high concentration p-type layer  125   c  corresponds to a substantial conductive layer, the node separation between cells is done through the partial patterning of the high concentration p-type impurity region. In particular, since a semiconductor layer such as a polysilicon layer has superior heating characteristics, the polysilicon layer may be used as a heating electrode of the phase-change memory device. 
         [0039]    On the other hand, even when the low concentration p-type impurity region  125   b - 3  and the n-type impurity regions  125   b - 2  and  125   b - 1  are not patterned, but remain in a line shape, there is no electrical issue. As known, in the PN junction, current flows from a p-type impurity region to an n-type impurity region when a threshold voltage or more is applied, while current does not flow from the n-type impurity region to the p-type impurity region unless a breakdown voltage or more is applied. Therefore, even when a specific cell operates, a diode operation does not occur in other cells adjacent to the specific cell and disturbance is not caused. Further, since the line-shaped low concentration p-type impurity region, low concentration n-type impurity region, and high concentration n-type impurity region extend parallel to the word line, an electric issue is not caused even when a corresponding word line is selected. 
         [0040]    Therefore, in the exemplary embodiment, since the phase-change material layer and the heating electrode layer (high concentration p-type impurity region) are separately etched in different steps, the pattern leaning and positive slope occurring in etching of a thick film are not caused and a phase-change error may be reduced. 
         [0041]    Further, as in the related art, since the phase-change layer, heating electrode, and diode layer are not collectively etched, a processing time may be considerably reduced. 
         [0042]    The above embodiment of the present invention is illustrative and not limitative. Various alternatives and equivalents are possible. The invention is not limited by the embodiment described herein. Nor is the invention limited to any specific type of semiconductor device. Other additions, subtractions, or modifications are obvious in view of the present disclosure and are intended to fall within the scope of the appended claims.