Abstract:
Disclosed herein is a device that includes: first and second memory mats each including a plurality of bit lines; a sense area arranged between the first and second memory mats; a column selection line provided on the first memory mat; and a compensation capacitance provided on the second memory mat. The sense area includes a plurality of sense amplifiers. Each of the sense amplifiers is connected to an associated one or ones of the bit lines. At least one of the sense amplifiers is selected based on a column selection signal supplied via the column selection line. At least a part of the compensation capacitance is formed in a same wiring layer as the column selection line.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a semiconductor device and more particularly relates to a semiconductor device including a compensation capacitance for power-source voltage. 
         [0003]    2. Description of Related Art 
         [0004]    In a semiconductor device such as a DRAM (Dynamic Random Access Memory), a compensation capacitance for power-source voltage is sometimes provided to stabilize an internal power-source voltage (see Japanese Patent Application Laid-open No. 2010-182392). A gate capacitance of a MOS transistor is generally used as the compensation capacitance for the power-source voltage. 
         [0005]    However, when the gate capacitance is used as the compensation capacitance for the power-source voltage, it is necessary to form a MOS transistor for the compensation capacitance for the power-source voltage on a semiconductor substrate, which causes a problem of increasing the chip size. In addition, if the compensation capacitance for the power-source voltage becomes insufficient at a later stage of designing, it necessitates a change of a device layout on the semiconductor substrate to add an additional MOS transistor for increasing the compensation capacitance for the power-source voltage, which in turn causes a problem of increasing the time for development. 
       SUMMARY 
       [0006]    In one embodiment, there is provided a semiconductor device that includes: a plurality of memory mats arranged in a first direction; a plurality of sense areas each arranged between two of the memory mats, each of the sense areas including a plurality of sense amplifiers selected based on a column selection signal; a column decoder generating the column selection signal; a column selection line extending in the first direction on the memory mats and supplying the column selection signal from the column decoder to the sense areas; and a compensation capacitance provided on one of the memory mats which is located farther than the other of the memory mats from the column decoder. The compensation capacitance includes a first capacitance electrode to which a first power source potential is supplied and a second capacitance electrode to which a second power source potential is supplied, and at least one of the first and second capacitance electrodes is formed in a same wiring layer as the column selection line. 
         [0007]    In another embodiment, there is provided a semiconductor device that includes: first and second memory mats each including a plurality of bit lines; a sense area arranged between the first and second memory mats; a column selection line provided on the first memory mat; and a compensation capacitance provided on the second memory mat. The sense area includes a plurality of sense amplifiers. Each of the sense amplifiers is connected to an associated one or ones of the bit lines. At least one of the sense amplifiers is selected based on a column selection signal supplied via the column selection line. At least a part of the compensation capacitance is formed in a same wiring layer as the column selection line. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is an overall layout diagram indicative of an embodiment of a semiconductor device  10  according to an embodiment of the present invention; 
           [0009]      FIG. 2  is an enlarged diagram indicative of an embodiment of the memory cell area  11  shown in  FIG. 1 ; 
           [0010]      FIG. 3  is a circuit diagram for explaining a method of selecting a sense amplifier; 
           [0011]      FIG. 4A  is a layout diagram indicative of an embodiment of the compensation capacitance for the power-source voltage  21 ; 
           [0012]      FIG. 4B  is an equivalent circuit diagram indicative of an embodiment of the compensation capacitance for the power-source voltage  21 ; 
           [0013]      FIG. 5A  is a layout diagram indicative of an embodiment of the compensation capacitance for the power-source voltage  30 ; 
           [0014]      FIG. 5B  is an equivalent circuit diagram indicative of an embodiment of the compensation capacitance for the power-source voltage  30 ; 
           [0015]      FIG. 6  is a schematic diagram showing an example of stabilizing an operating potential of a sense amplifier by the compensation capacitance for the power-source voltage  30 ; 
           [0016]      FIG. 7  is a diagram indicative of an embodiment of the configuration of the main parts of  FIG. 6  in more detail; 
           [0017]      FIG. 8  is a circuit diagram indicative of an embodiment of the sense area SA; 
           [0018]      FIG. 9  is a diagram indicative of an embodiment of a shape of a compensation capacitance for the power-source voltage according to a modification; 
           [0019]      FIG. 10  is a diagram indicative of an embodiment of a shape of a compensation capacitance for the power-source voltage according to another modification; 
           [0020]      FIG. 11  is a schematic diagram for explaining memory mats of an open bit line architecture; 
           [0021]      FIG. 12  is a schematic diagram for explaining memory mats of a folded bit line architecture; and 
           [0022]      FIG. 13  is a schematic diagram for explaining an example of forming the compensation capacitance for the power-source voltage in a three-dimensional manner. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0023]    Preferred embodiments of the present invention will be explained below in detail with reference to the accompanying drawings. 
         [0024]    Referring now to  FIG. 1 , the semiconductor device  10  according to the present embodiment is a DRAM, which includes four memory cell areas  11 . In each of the memory cell areas  11 , a row decoder  12  is provided while being adjacent to the X direction of the memory cell area  11  and a column decoder  13  is provided while being adjacent to the Y direction of the memory cell area  11 . The row decoder  12  is arranged between two memory cell areas  11  adjacent to each other in the X direction, and the column decoder  13  is arranged between two memory cell areas  11  adjacent to each other in the Y direction. 
         [0025]    Turning to  FIG. 2 , the memory cell area  11  includes a plurality of memory mats MAT arranged in a matrix form. Sub-word driver areas SWD are arranged on both sides of each of the memory mats MAT in the X direction, and sense areas SA are arranged on both sides of the memory mat MAT in the Y direction. However, for memory mats MATa and MATb located at respective edges of the memory cell area  11  in the Y direction, the sense area SA is located only on one side in the Y direction. Therefore, each sense area SA is arranged while being sandwiched by two memory mats MAT adjacent to each other in the Y direction. In this explanation, the memory mat MATa represents a memory mat that is farthest from the column decoder  13 , and the memory mat MATb represents a memory mat closest to the column decoder  13 . The sense areas SA are shown as being hatched in  FIG. 2 . 
         [0026]    Main word lines MWL that are driven by the row decoder  12  are respectively connected to the sub-word drive areas SWD. Each of the main word lines MWL is a signal line for transmitting a main word signal, and is provided while extending in the X direction as shown in  FIG. 2 . The main word signal is a signal for selecting one of a plurality of sub-word drivers included in the sub-word drive areas SWD. The sub-word driver is a circuit for driving a sub-word line SWL provided while extending in the X direction in the memory mat MAT. 
         [0027]    Column selection lines YS driven by the column decoder  13  are respectively connected to the sense areas SA. Each of the column selection lines YS is a signal line for transmitting a column selection signal, which is provided while extending in the Y direction as shown in  FIG. 2 . The column selection signal is a signal for selecting one of a plurality of sense amplifiers included in the sense areas SA. The sense amplifier is a circuit for amplifying a signal on a bit line BL provided while extending in the Y direction in the memory mat MAT. A memory cell MC is located at an intersection of the bit line BL and the sub-word line SWL. 
         [0028]    Turning to  FIG. 3 , the sense areas SA include a plurality of sense amplifiers SAMP, and a pair of bit lines BL is connected to each of the sense amplifiers SAMP. With this configuration, when the sense amplifier SAMP is activated, a potential difference generated between the pair of bit lines BL is amplified. Each of the sense amplifiers SAMP is connected to a local I/O line LIO via a column switch YSW corresponding to the sense amplifier SAMP. The column switch YSW is provided for each of the sense amplifiers SAMP, and a corresponding bit of the column selection signal is supplied to a gate electrode of a MOS transistor constituting the column switch YSW. With this configuration, it is possible to select a desired sense amplifier SAMP based on the column selection signal. 
         [0029]    Referring back to  FIG. 2 , a compensation capacitance area  20  is provided outside the memory cell area  11 . In the example shown in  FIG. 2 , the compensation capacitance area  20  is arranged on the opposite side of the column decoder  13  across the memory cell area  11 . The compensation capacitance area  20  is an area in which a compensation capacitance for stabilizing an internal power-source voltage is arranged. The compensation capacitance for the power-source voltage arranged in the compensation capacitance area  20  is obtained by using a gate capacitance of a MOS transistor, and a plurality of types of MOS transistors are used according to a voltage level of an internal power source to be stabilized. In the example shown in  FIG. 2 , a compensation capacitance  21  for the power-source voltage using MOS transistors having thin gate dielectric films and a compensation capacitance  22  for the power-source voltage using MOS transistors having thick gate dielectric films are used. The compensation capacitance  21  is used for stabilizing an internal power source with a low voltage level, while the compensation capacitance  22  is used for stabilizing an internal power source with a high voltage level. 
         [0030]    In addition to the compensation capacitance area  20 , a compensation capacitance  30  for the power-source voltage is provided on the memory mat MATa that is located farthest from the column decoder  13  in the semiconductor device  10  according to the present embodiment. The compensation capacitance  30  provided on the memory mat MATa is a capacitance obtained by using the same wiring layer as the column selection line YS. The compensation capacitance  30  can be arranged on the memory mat MATa that is located at the far end, because the column selection line YS is a wiring line for connecting the column decoder  13  and the sense amplifier area SA and it does not need to be wired on the memory mat MATa that is located the far end so that there is an empty space on the same wiring layer as the column selection line YS on the memory mat MATa that is located at the far end. 
         [0031]    Turning to  FIGS. 4A and 4B , the compensation capacitance  21  for the power-source voltage is constituted by a gate electrode  21   g  and diffusion regions  21   sd  that constitute a MOS transistor, and a gate dielectric film (not shown) between the gate electrode  21   g  and the diffusion regions  21   sd  functions as a capacitance dielectric film. In the present example, the diffusion regions  21   sd  are connected to a power source line VL 1  via a contact conductor  21   c  and the gate electrode  21   g  is connected to a power source line VL 2  via a contact conductor  21   c . The power source line VL 1  is, for example, a power source line to which a ground potential (VSS) is supplied, and the power source line VL 2  is, for example, a power source line to which an internal power-source voltage is supplied. The compensation capacitance  22  for the power-source voltage also has a similar configuration. 
         [0032]    Turning to  FIGS. 5A and 5B , the compensation capacitance  30  for the power-source voltage is constituted by a power source line VL 1  and a power source line VL 2  formed in a comb shape on a predetermined wiring layer. That is, the compensation capacitance  30  is a planar capacitance formed in a wiring layer, and unlike the compensation capacitance  21 , the compensation capacitance  30  does not occupy a semiconductor substrate. 
         [0033]    Turning to  FIG. 6 , a power generating circuit (power source circuit)  40  for a sense amplifier is arranged near the column decoder  13 , and an operating potential SAP of a sense amplifier is generated by the power source circuit  40 . The operating potential SAP is supplied to each sense area SA via the power source line VL 2 , and a potential of the operating potential SAP is stabilized by the compensation capacitance  30  arranged on the memory mat MATa that is located at the far end. The potential of the operating potential SAP becomes unstable as a distance from the power source circuit  40  increases; however, because the compensation capacitance  30  is arranged at a position farthest from the power source circuit  40 , the operating potential SAP is also supplied to the sense area SA at the far end, in a correct manner. The compensation capacitance area  20  is omitted from  FIG. 6 . 
         [0034]    Turning to  FIG. 7 , the operating potential SAP generated by the power source circuit  40  is commonly supplied to a plurality of sense areas SA via the power source line VL 2 . The power source line VL 2  is formed in a plurality of wiring layers. In  FIG. 7 , a portion denoted by reference character VL 2 (L 1 ) is formed in a first metal wiring layer, a portion denoted by reference character VL 2 (L 2 ) is formed in a second metal wiring layer, and a portion denoted by reference character VL 2 (L 3 ) is formed in a third metal wiring layer. The first metal wiring layer is a metal wiring layer located on the lowermost layer, and the second metal wiring layer and the third metal wiring layer are formed in this order on layers above the first metal wiring layer. 
         [0035]    The power source line VL 2  (L 3 ) formed in the third metal wiring layer is provided while extending in the Y direction to pass an upper portion of the memory mat MAT. On the other hand, the power source line VL 2 (L 2 ) formed on the second metal wiring layer is provided while extending in the X direction to pass an upper portion of the sense area SA. A contact conductor  51  is provided at an intersection of the power source line VL 2 (L 3 ) and the power source line VL 2 (L 2 ), so that the power source lines VL 2 (L 3 ) and VL 2 (L 2 ) are short-circuited via the contact conductor  51 . With this configuration, the power source line VL 2  is formed in a mesh shape. 
         [0036]    Although not shown in  FIG. 7 , other power source lines and signal lines are formed on the second and third metal wiring layers in practice, and the power source lines formed on these wiring layers are designed to have a wide line width. Therefore, there is substantially no empty space on the second and third metal wiring layers on the memory mat MAT. On the other hand, the column selection line YS is arranged on the first metal wiring layer. As shown in  FIG. 7 , the column selection line YS is provided while extending in the Y direction over the other memory mats MAT and MATb except for the memory mat MATa at the far end. The notation “YS(L 1 )” in  FIG. 7  means that the column selection line YS is formed in the first metal wiring layer. Therefore, there is substantially no empty space over the other memory mats MAT and MATb except for the memory mat MATa located at the far end. 
         [0037]    On the other hand, over an upper portion of the memory mat MATa located at the far end, the column selection line YS is not formed in the first metal wiring layer, and therefore there is an empty space in the first metal wiring layer. In the present embodiment, the compensation capacitance  30  for the power-source voltage is formed in the first metal wiring layer by using this empty space. As described above, the compensation capacitance  30  is constituted by the power source lines VL 1  and VL 2  formed in a comb shape, and these power source lines respectively function as capacitance electrodes. Among these power source lines, the power source line VL 2 (L 1 ) is connected to the power source line VL 2 (L 3 ) formed in the third metal wiring layer via a contact conductor  52  formed on a connection area  31 . To the power source line VL 1 (L 1 ) which is the other one of the power source lines, a ground potential is supplied via another connection area (not shown). 
         [0038]    Turning to  FIG. 8 , the sense amplifier SAMP provided in the sense area SA is constituted by a pair of P-channel MOS transistors that are cross-coupled to each other and a pair of N-channel MOS transistors that are cross-coupled to each other, and sources of the P-channel MOS transistors are connected to the power source line VL 2 . A transistor denoted by reference numeral  41  in  FIG. 8  is a driver circuit that supplies the operating potential SAP to the power source line VL 2 , which is included in the power source circuit  40 . 
         [0039]    Because the power source line VL 2  is designed to have a sufficient line width, a line resistance R is relatively small. However, because a voltage fall is more likely to occur with an increasing distance from the power source circuit  40 , the operating potential SAP supplied to a sense area SAa that is located at the far end can be possibly lowered. Nevertheless, in the present embodiment, because the compensation capacitance  30  for the power-source voltage is arranged on the memory met MATa located at the far end, it is possible to stabilize the operating potential SAP supplied to the sense area SAa located at the far end. 
         [0040]    As explained above, in the present embodiment, because the compensation capacitance  30  is arranged on the memory mat MATa located at the far end, it is possible to stabilize the internal power-source voltage. Furthermore, if the number of the compensation capacitances  21  and  22  using the gate capacitances of the MOS transistors can be reduced by providing the compensation capacitance  30 , it is possible to downsize the chip dimension. Alternatively, by leaving an empty space in the first metal wiring layer on the memory mat MATa located at the far end at an early stage of designing and arranging the compensation capacitance  30  in the empty space in the first metal wiring layer when the compensation capacitance for the power-source voltage is insufficient at a later stage of designing, it is possible to increase the compensation capacitance for the power-source voltage in a simple manner without changing the designing such as a mask for diffusion region. 
         [0041]    It is apparent that the present invention is not limited to the above embodiments, but may be modified and changed without departing from the scope and spirit of the invention. 
         [0042]    For example, although the present embodiment described above has explained an example in which the comb-shaped power source lines VL 1  and VL 2  that constitute the compensation capacitance  30  are extended in the Y direction as shown in  FIG. 7 , the comb-shaped power source lines VL 1  and VL 2  can be extended in the X direction as shown in  FIG. 9 . Furthermore, the shape of the power source lines VL 1  and VL 2  is not limited to the comb shape, and can be a shape shown in  FIG. 10 . 
         [0043]    In addition, the configuration of the memory mat MAT is not limited to any specific type, and can be, for example, a so-called open bit line architecture as shown in  FIG. 11  or a so-called folded bit line architecture as shown in  FIG. 12 . In the open bit line architecture shown in  FIG. 11 , two bit lines BL making a pair are respectively arranged in two memory mats MAT that are adjacent to each other in the Y direction; therefore, the sense area SA is provided only on one side in the memory mats MATa and MATb that are located at both ends in the Y direction (see  FIG. 2 ). On the other hand, in the folded bit line architecture shown in  FIG. 12 , two bit lines BL making a pair are arranged in the same memory mat MAT; therefore, the sense area SA is provided only on one side in either one of the memory mats MATa and MATb that are located at both ends in the Y direction. 
         [0044]    This means that there is always an empty space in the metal wiring layer on the memory mat MATa located at the far end in the open bit line architecture, while there sometimes is an empty space or no empty space in the metal wiring layer on the memory mat MATa located at the far end in the folded bit line architecture according to the side of the memory mat MAT where the sense area SA is arranged. Considering this point, it is more preferable to apply the present invention to a semiconductor device of an open bit line architecture. 
         [0045]    In addition, in the embodiment described above, although the two power line sources VL 1  and VL 2  that constitute the compensation capacitance  30  are formed in the same wiring layer, the present invention is not limited thereto. As shown in  FIG. 13 , a three-dimensional capacitor can be configured by forming the power source lines VL 1  and VL 2  in wiring layers different from each other. For example, this configuration can be achieved by forming the power source line VL 1  in the first metal wiring layer as the column selection line YS and forming the power source line VL 2  in the second metal wiring layer. By configuring such a three-dimensional capacitor, it is possible to increase the compensation capacitance for the power-source voltage. However, in this case, it requires empty spaces in two wiring layers and a design change on two wiring layers when changing capacitance of the compensation capacitance for the power-source voltage at the designing stage. Considering these points, it is preferable to form both the power source lines VL 1  and VL 2  in a single wiring layer as described in the above embodiment.