Patent Publication Number: US-2021183944-A1

Title: Layout pattern for magnetoresistive random access memory

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a layout pattern for magnetoresistive random access memory (MRAM). 
     2. Description of the Prior Art 
     Magnetoresistance (MR) effect has been known as a kind of effect caused by altering the resistance of a material through variation of outside magnetic field. The physical definition of such effect is defined as a variation in resistance obtained by dividing a difference in resistance under no magnetic interference by the original resistance. Currently, MR effect has been successfully utilized in production of hard disks thereby having important commercial values. Moreover, the characterization of utilizing GMR materials to generate different resistance under different magnetized states could also be used to fabricate MRAM devices, which typically has the advantage of keeping stored data even when the device is not connected to an electrical source. 
     The aforementioned MR effect has also been used in magnetic field sensor areas including but not limited to for example electronic compass components used in global positioning system (GPS) of cellular phones for providing information regarding moving location to users. Currently, various magnetic field sensor technologies such as anisotropic magnetoresistance (AMR) sensors, GMR sensors, magnetic tunneling junction (MTJ) sensors have been widely developed in the market. Nevertheless, most of these products still pose numerous shortcomings such as high chip area, high cost, high power consumption, limited sensibility, and easily affected by temperature variation and how to come up with an improved device to resolve these issues has become an important task in this field. 
     SUMMARY OF THE INVENTION 
     According to an embodiment of the present invention, a layout pattern for magnetoresistive random access memory (MRAM) includes a first magnetic tunneling junction (MTJ) pattern on a substrate, a second MTJ pattern adjacent to the first MTJ pattern, and a third MTJ pattern between the first MTJ pattern and the second MTJ pattern. Preferably, the first MTJ pattern, the second MTJ pattern, and the third MTJ pattern constitute a staggered arrangement. 
     According to an embodiment of the present invention, the third MTJ pattern is disposed along a first direction relative to the first MTJ pattern and the second MTJ pattern is disposed along a second direction relative to the third MTJ pattern. 
     According to an embodiment of the present invention, the second MTJ pattern is disposed along a third direction relative to the first MTJ pattern. 
     According to an embodiment of the present invention, an angle included by the first direction and the third direction is less than 90 degrees. 
     According to an embodiment of the present invention, an angle included by the second direction and the third direction is less than 90 degrees. 
     According to an embodiment of the present invention, the first direction, the second direction, and the third direction together constitute a triangle. 
     According to an embodiment of the present invention, a fourth MTJ pattern is disposed along the second direction relative to the first MTJ pattern. 
     According to an embodiment of the present invention, the fourth MTJ pattern is disposed along the first direction relative to the second MTJ pattern. 
     According to an embodiment of the present invention, the first MTJ pattern, the second MTJ pattern, the third MTJ pattern, and a fourth MTJ pattern together constitute a rhombus. 
     According to an embodiment of the present invention, a distance between the first MTJ pattern and the second MTJ pattern is different from a distance between the third MTJ pattern and the fourth MTJ pattern. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a top view of a semiconductor device according to an embodiment of the present invention. 
         FIG. 2  illustrates cross-sectional views of  FIG. 1  along the sectional lines AA′ and BB′. 
         FIG. 3  illustrates a top view of a semiconductor device according to an embodiment of the present invention. 
         FIG. 4  illustrates cross-sectional views of  FIG. 3  along the sectional lines CC′ and DD′. 
         FIG. 5  illustrates a layout pattern of MTJs within MRAM unit according to an embodiment of the present invention. 
         FIG. 6  illustrates a layout pattern of MTJs within MRAM unit according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-4 ,  FIGS. 1 and 3  illustrate layout top views of a semiconductor device, or more specifically a MRAM device according to an embodiment of the present invention, the top portion of  FIG. 2  illustrates a cross-section of  FIG. 1  along the sectional line AA′, the bottom portion of  FIG. 2  illustrates a cross-section of  FIG. 1  along the sectional line BB′, the top portion of  FIG. 4  illustrates a cross-section of  FIG. 3  along the sectional line CC′, the bottom portion of  FIG. 4  illustrates a cross-section of  FIG. 3  along the sectional line DD′. As shown in  FIGS. 1-4 , the MRAM device preferably includes a substrate  12  made of semiconductor material, in which the semiconductor material could be selected from the group consisting of silicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC), and gallium arsenide (GaAs). A MRAM region  14  and a periphery region (not shown) surrounding the MRAM region  14  are defined on the substrate  12 . 
     Active devices such as metal-oxide semiconductor (MOS) transistors, passive devices, conductive layers, and interlayer dielectric (ILD) layer could also be formed on top of the substrate  12 . More specifically, planar MOS transistors or non-planar (such as FinFETs) MOS transistors could be formed on the substrate  12 , in which the MOS transistors could include transistor elements such as gate structures such as word lines  16 , source/drain regions  20 , spacers, epitaxial layers, and contact etch stop layer (CESL). The ILD layer could be formed on the substrate  12  to cover the MOS transistors, and a plurality of contact plugs  22  could be formed in the ILD layer to electrically connect to the gate structure and/or source/drain regions  20  of MOS transistors. Since the fabrication of planar or non-planar transistors and ILD layer is well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. 
     The semiconductor device also includes metal interconnections  24  disposed on the ILD layer, metal interconnections  26 ,  28 ,  30  disposed on the metal interconnections  24 , MTJ  32  disposed on the metal interconnection  30 , and inter-metal dielectric (IMD) layer (not shown) surrounding the metal interconnections  24 ,  26 ,  28 ,  30 , and the MTJ  32 . In this embodiment, each of the metal interconnections  24 ,  26 ,  28 ,  30  could be fabricated according to a single damascene or dual damascene process and embedded in the IMD layer and/or stop layer while electrically connected to each other. For instance, each of the metal interconnections  24  could include a trench conductor, the metal interconnection  26  could include a via conductor, the metal interconnection  28  could include a trench conductor, and the metal interconnection  30  could include a via conductor. Preferably, the metal interconnection  24  could also be referred to as the first level metal interconnection M 1 , the metal interconnection  26  could also be referred to as the first level via conductor V 1 , the metal interconnection  28  could be referred to as the second level metal interconnection M 2 , and the metal interconnection  30  could be referred to as the second level via conductor V 2 . 
     Moreover, each of the metal interconnections  24 ,  26 ,  28 ,  30  could further includes a barrier layer and a metal layer, in which the barrier layer could be selected from the group consisting of titanium (Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN) and the metal layer could be selected from the group consisting of tungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Since single damascene process and dual damascene process are well known to those skilled in the art, the details of which are not explained herein for the sake of brevity. In this embodiment, the metal layers are preferably made of copper, the IMD layers are preferably made of silicon oxide, and the stop layers are preferably made of nitrogen doped carbide (NDC), silicon nitride, silicon carbon nitride (SiCN), or combination thereof. 
     In this embodiment, the MTJ  32  could include a bottom electrode disposed on the metal interconnection  30 , a MTJ stack disposed on the bottom electrode, and a top electrode disposed on the MTJ stack, in which the MTJ stack preferably includes a pinned layer, a barrier layer, and a free layer. Specifically, each of the bottom electrode and the top electrode are preferably made of conductive material including but not limited to for example Ta, Pt, Cu, Au, Al, or combination thereof. The pinned layer could be made of antiferromagnetic (AFM) material including but not limited to for example ferromanganese (FeMn), platinum manganese (PtMn), iridium manganese (IrMn), nickel oxide (NiO), or combination thereof, in which the pinned layer is formed to fix or limit the direction of magnetic moment of adjacent layers. The free layer could be made of ferromagnetic material including but not limited to for example iron, cobalt, nickel, or alloys thereof such as cobalt-iron-boron (CoFeB), in which the magnetized direction of the free layer could be altered freely depending on the influence of outside magnetic field. 
     It should be noted that even though the MTJ  32  on top portion of  FIG. 2  and the MTJ  32  on bottom portion of  FIG. 2  are both disposed directly on top of the contact plug  22 , according to other embodiment of the present invention, it would also be desirable to move the MTJs  32  freely within the boundary of metal interconnection  28  or second level metal interconnection M 2  according to the staggered arrangement of MTJs  32  shown in  FIG. 1  or  FIG. 3 . For instance, it would be desirable to overlap the MTJ  32  and the contact plug  22  as shown in  FIGS. 2 and 4  or not overlapping the MTJs  32  and contact plugs  22  underneath as shown  FIGS. 1 and 3 , which are all within the scope of the present invention. Moreover, the contact plug  22  directly under the MTJ  32  shown on top portion of  FIG. 2  is preferably connected to a drain region (not shown) while the two contact plugs  22  adjacent two sides of the drain region are connected to a source region. Conversely, the contact plug  22  directly under the MTJ  32  on bottom portion of  FIG. 2  is connected to a source region while the two contact plugs  22  on right side of the source region including the middle contact plug  22  is connected to a drain region and the right contact plug is connected to another source region. 
     Referring to  FIG. 5 ,  FIG. 5  illustrates a layout pattern of adjacent MTJs and metal interconnections within a MRAM unit generated after optical proximity correction (OPC) process according to a conventional art. As shown in  FIG. 5 , the layout pattern of the MRAM unit preferably includes multiple columns such as three columns of pattern combination constituted by MTJ patterns and metal interconnection patterns arranged according to an array, in which each column includes a plurality of MTJ patterns (represented by circular patterns) and a plurality of via patterns (represented by square patterns) under each of the MTJ patterns arranged according to a straight line. For instance, the layout pattern on the left column preferably includes a first MTJ pattern  102 , a second MTJ pattern  104 , a third MTJ pattern  106 , and via patterns  108  all arranged according to a straight line manner on the substrate  12 . Preferably, the first MTJ pattern  102 , the second MTJ pattern  104 , and the third MTJ pattern  106  are arranged from top to bottom to constitute a straight line altogether according to a top view perspective, and the via patterns  108  overlapping each of the first MTJ pattern  102 , the second MTJ pattern  104 , and the third MTJ pattern  106  underneath are also arranged according to a straight line. 
     It should be noted that since the aforementioned embodiment of placing the MTJ patterns and via patterns along a straight line could shorten the distance between adjacent MTJs such as by shortening the distance D 1  between centers of adjacent MTJs and result in contamination, the following embodiments of the present invention preferably adjust the arrangements among MTJ patterns and/or via patterns so that the MTJ patterns would not be too close to each other thereby minimizing the chance of contamination. 
     Referring to  FIG. 6 ,  FIG. 6  illustrates a layout pattern of adjacent MTJs and metal interconnections within a MRAM unit generated after optical proximity correction (OPC) process. As shown in  FIG. 6 , the layout pattern of the MRAM unit preferably includes multiple columns of pattern combination constituted by MTJ patterns (such as the MTJ  32  shown in  FIGS. 1-4 ) and via patterns (such as the metal interconnections  30  directly under the MTJ  32  shown in  FIGS. 1-4 ) arranged according to an array with staggered arrangement. For instance, the layout pattern from the second column to the fourth column from the left preferably includes a first MTJ pattern  122  disposed on the substrate  12 , a second MTJ pattern  126  disposed under or below the first MTJ pattern  122 , a third MTJ pattern  124  disposed between the first MTJ pattern  122  and the second MTJ pattern  126 , a fourth pattern  128  disposed between the first MTJ pattern  122  and the second MTJ pattern  126  and opposite to the third MTJ pattern  124 , and via patterns  130  under and overlapping the first MTJ pattern  122 , the second MTJ pattern  126 , the third MTJ pattern  124 , and the fourth MTJ pattern  128 , in which the first MTJ pattern  122 , the second MTJ pattern  126 , the third MTJ pattern  124 , the fourth MTJ pattern  128 , and the via patterns  130  are arranged according to a staggered arrangement. Similar to the aforementioned embodiment, the MTJ patterns  122 ,  124 ,  126 ,  128  are represented by circular patterns while the via patterns  130  underneath are represented by square patterns. 
     Specifically, the third MTJ pattern  124  is disposed along a first direction  134  relative to the first MTJ pattern  122 , the second MTJ pattern  126  is disposed along a second direction  136  relative to the third MTJ pattern  124 , the second MTJ pattern  126  is disposed along a third direction  138  (such as Y-direction) relative to the first MTJ pattern  122 , and the fourth MTJ pattern  128  is also disposed along the same first direction  134  relative to the second MTJ pattern  126  while the fourth MTJ pattern  128  is also disposed along the second direction  136  relative to the first MTJ pattern  122 , in which the angle included by the first direction  134  and the third direction  138  is less than 90 degrees, the angle included by the second direction  136  and the third direction  138  is less than 90 degrees, and the angle included by the first direction  134  and the second direction  136  could be less than, equal to, or greater than 90 degrees. 
     Viewing from an overall perspective, the positions of the first MTJ pattern  122 , the second MTJ pattern  126 , and the third MTJ pattern  124 , such as the central points of the first MTJ pattern  122 , second MTJ pattern  126 , and third MTJ pattern  124  together constitute a triangle while the central points of the first MTJ pattern  122 , second MTJ pattern  126 , and fourth MTJ pattern  128  also constitute another triangle that is preferably a mirror image of the triangle formed by the first MTJ pattern  122 , second MTJ pattern  126 , and third MTJ pattern  124 . The center points of first MTJ pattern  122 , second MTJ pattern  126 , third MTJ pattern  124 , and fourth MTJ pattern  128  also constitute a rhombus altogether. 
     Viewing from another perspective, the first direction  134  extended from the center or central point of the first MTJ pattern  122  to the center of the third MTJ pattern  124 , the second direction  136  extended from the center of the third MTJ pattern  124  to the center of the second MTJ pattern  126 , and the third direction  138  extended from the center of the first MTJ pattern  122  to the center of the second MTJ pattern  126  preferably constitute a triangle. Similarly, the second direction  136  extended from the center of the first MTJ pattern  122  to the center of the fourth MTJ pattern  128 , the first direction  134  extended from the center of the fourth MTJ pattern  128  to the center of the second MTJ pattern  126 , and the third direction  138  extended from the center of the second MTJ pattern  126  to the center of the first MTJ pattern  122  also constitute another triangle. 
     Moreover, the first direction  134  extended from the center or central point of the first MTJ pattern  122  to the center of the third MTJ pattern  124 , the second direction  136  extended from the center of the third MTJ pattern  124  to the center of the second MTJ pattern  126 , the second direction  136  extended from the center of the first MTJ pattern  122  to the center of the fourth MTJ pattern  128 , and the first direction  134  extended from the center of the fourth MTJ pattern  128  to the center of the second MTJ pattern  126  together constitute a rhombus, in which the distance between the center of the first MTJ pattern  122  and the center of the second MTJ pattern  126  is preferably different from the distance between the center of the third MTJ pattern  124  and the center of the fourth MTJ pattern  128 . 
     It should be noted that the triangle constituted by the aforementioned combination of patterns or the three directions  134 ,  136 ,  138  could include all types of triangles such as equilateral triangle, isosceles triangle, right angle triangle, or any irregular triangle, and the rhombus formed by four directions  134  and  136  is also not limited to the one disclose above. For instance, the distance between the center of the first MTJ pattern  122  and the center of the second MTJ pattern  126  could be less than, equal to, or greater than the distance between the center of the third MTJ pattern  124  and the center of the fourth MTJ pattern  128 . Since all the via patterns  130  overlap the MTJ patterns, the via patterns  130  could also be arranged in the same manner as the MTJ patterns disclosed above and the detailed of which are not explained herein for the sake of brevity. 
     Overall, by positioning the MTJ patterns according to a staggered manner in this embodiment, a shortest distance D 2  measured from the center of the first MTJ pattern  122  to the center of the third MTJ pattern  124  would then correspond to a hypotenuse of a triangle as opposed to a cathetus as disclosed in the embodiment shown in  FIG. 5 . As a result, the shortest distance D 2  between the centers of each of the MTJ patterns would be greater than the shortest distance D 1  between the MTJ patterns disclosed in the embodiment shown in  FIG. 5 . By following this design it would be desirable to increase the distance between adjacent MTJs thereby avoiding contamination. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.