Abstract:
The invention discloses a power mesh managing method utilized in an integrated circuit. The integrated circuit includes a standard cell and a standard-cell power supplying mesh corresponding to a first direction. The power mesh managing method includes: defining a power supplying network including a first plurality of power meshes growing along the first direction and a second plurality of power meshes growing along a second direction, and defining an assistant connecting network on a third metal layer, wherein the assistant connecting network includes a plurality of assistant connecting lines growing along the second direction, the first plurality of power meshes are formed on a first metal layer, the second plurality of power meshes on a second metal layer, the third metal layer is below the first metal layer, and the second metal layer is above the first metal layer.

Description:
BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The invention relates to a power mesh managing method and related integrated circuit, particularly to a method for managing power mesh of a standard cell and related integrated circuit. 
     (b) Description of the Related Art 
     As the APR (automatic placement and routing) tool not only helps a circuit designer placing circuit elements at the suitable locations in the chip easily but also helps the circuit designer managing the power routing, the APR tool has become one of the indispensable tools for the circuit designer. 
     Generally, the APR tool uses two types of blocks to manage circuit elements. One of them is the standard cell. As the name implies, the standard cell is a type of standardized block having specific size and built-in power managing method for managing some often-used standard circuit elements, such as: flip-flops, logic gates, and the like. Then, the APR tool can neatly arrange a plurality of standard cells in the area of a chip. The other one is the macro block. The macro block is different from the standard cell. The macro block does not have fixed size and is used to manage the circuits having specific functions designed by the circuit designer, such as: SRAM, ADC, and so on. 
     However, the APR tool follows specific routing rules to appropriately arrange the macro block and the standard cell at the suitable locations of the chip and to draw the power network. But, as the APR tool can only perform regular management, the details of the management still needs manual adjustments by the designer. Therefore, the APR tool still needs to be improved. 
     Now please refer to  FIG. 1  which shows a three-dimensional schematic diagram illustrating the standard cell  100  and the standard cell power supplying meshes  110 ,  120  managed by the APR tool according to the prior art. In general, as shown in  FIG. 1 , the standard cell power supplying meshes  110 ,  120  growing along the horizontal direction are placed along each side of the standard cell  100  according to the managing rule of the traditional APR tool. The power supplying mesh  110  conducts the external power V DD  to the standard cell  100  while the power supplying mesh  120  conducts the ground power V SS  to the standard cell  100 . 
     Then, please refer to  FIG. 2  which shows a three-dimensional schematic diagram illustrating the standard cell  100 , the standard-cell power supplying meshes  110 ,  120 , shown in  FIG. 1 , and the power supplying network  200  located above the standard cell  100 . Please note that, for clarity, only three rows of standard cell  100  are shown in  FIG. 2 . But, in practical applications, there can be many more standard cells  100  in the chip. As shown in  FIG. 2 , the lower part is the standard cell and the standard cell power supplying meshes  110 ,  120  in  FIG. 1  while the upper part is the power supplying network  200  managed by the APR tool according to the prior art. As shown in  FIG. 2 , the power supplying network  200  includes the horizontal power supplying mesh  210  and the vertical power supplying mesh  220 . The vertical power supplying mesh  220  and the horizontal power supplying mesh  210  are located in different metal layers. The vertical power supplying mesh  220  is positioned on the layer above the horizontal power supplying mesh  210 . The horizontal power supplying mesh  210  is perpendicular to the vertical power supplying mesh  220  to form a matrix. Besides, the horizontal power supplying mesh  210  includes a plurality of mutually interlaced power lines  211  and ground lines  212 . The vertical power supplying mesh  220  also includes a plurality of mutually interlaced power lines  221  and ground lines  222 . 
     Besides, the power lines  211 ,  221  must couple to the external power (not shown in the figure). The power lines  211 ,  221  couple to the above mentioned standard-cell power supplying mesh  110  through the via hole (“via”) and the via plug  230  for conducting the voltage V DD  that is provided by the external power into the standard cell  100 . On the other hand, the ground lines  212 ,  222  also must couple to the ground voltage V SS . And, the ground lines  212 ,  222  couple to the standard-cell power supplying mesh  120  through the via and the via plug  230  for conducting the ground voltage into the standard cell  100 . Please note that, for clarity, the via  230  between the horizontal power supplying mesh  210  and the standard cell power supplying meshes  110 ,  120  is not shown in  FIG. 2 . In general, the interlacing power lines, that are at the equal potential, of the horizontal power supplying mesh  210  and the vertical power supplying mesh  220  (such as: between  211  and  221  and between  221  and  222 ) couple to each other at the overlapping area through the via and the via plug. The via and the via plug to couple the power supplying meshes at the overlapping area are also not shown in  FIG. 2 , for clarity. 
     Please also note that, in order to conduct the external power V DD /ground voltage V SS  into the standard cell  100 , the resistance between the external power and the standard cell  100  is generally properly designed to obtain better overall circuit performance. The resistance between the external power and the standard cell  100  is directly related to the number of the vias and the via plugs. As is well known to the industry, due to the resistance shunting effect, the more is the number of the vias/via plugs the more is the reduction of the resistance between the external power and the standard cell  100 . Hence, the positions that can be allocated to the vias/via plugs become crucial. As mentioned before, the adjustable range of the resistance becomes larger as there are more allocable positions for the vias/via plugs. Therefore, in general, the routing rules of the APR tool are usually designed to place the vias and the via plugs, at the overlapping areas between the power supplying meshes  210 / 220  and the standard cell power meshes  110 / 120  and at the overlapping areas between the power supplying mesh  210  and the power supplying mesh  220  for coupling. However, such a design will cause some problems. 
     Now, please refer to  FIG. 3  which shows a schematic diagram illustrating the side view of the standard cell power meshes  110 ,  120  and the standard-cell power supplying network  200  located in the upper layer. As shown in  FIG. 3 , since the horizontal power supplying mesh  210  is located in the layer below the vertical power supplying mesh  220 , the horizontal power supplying mesh  210  can be coupled to the standard-cell power supplying meshes  110 / 120  by way of the via/via plug  230  without obstruction. Therefore, the above mentioned routing mechanism will not face too many problems. But, for the vertical power supplying mesh  220 , since the vertical power supplying mesh  220  may be blocked by the horizontal power supplying mesh  210  that may be positioned between the power supplying mesh  220  located in the upper layer and the standard-cell power supplying meshes  110 ,  120 , the power supplying mesh  220  located in the upper layer may not be able to couple to the standard-cell power supplying meshes  110 ,  120  below by way of the vias/via plugs. Therefore, the positions for placing the vias/via plugs become limited. As shown in  FIG. 3 , the via/via plug  230  that is marked by “X” indicates that the via/via plug cannot be placed at that location. That is, the via/via plug  230 , that is supposed to couple the vertical power lines  221 / 222  in the upper layer to the standard cell power meshes  110 / 120  in the lower layer, is blocked by the horizontal power supplying mesh  210  and cannot be provided. 
     Besides, the above mentioned structure has another problem. In addition to the drawback that the horizontal power supplying mesh  210  blocks the connecting route between the vertical power supplying mesh  220  and the power supplying meshes  110 / 120  below. The position and the width for the horizontal power supplying mesh  210  suffer a lot of limitations to complete the above mentioned coupling mechanism. For example, if the horizontal power supplying mesh  210  is too wide and is not positioned suitably, the standard-cell power supplying meshes  110 ,  120  of different electrical properties can be shadowed simultaneously. Then, the standard-cell power supplying meshes  110 ,  120  cannot directly acquire the voltage V DD  and the ground voltage V SS  simultaneously through the horizontal power supplying mesh  210  or the vertical power supplying mesh  220  above. As above mentioned, the position and the width for the horizontal power supplying mesh  210  must be properly designed to avoid the above mentioned problems. However, such an approach reduces the flexibility of the routing and the routing design becomes much more complicated. 
     Therefore, those who are skilled in the art must develop new routing rules and layout methods to solve the above mentioned problems. 
     BRIEF SUMMARY OF THE INVENTION 
     Therefore, one object of the invention is to provide a routing rule of the APR tool and the related integrated circuit layout method for managing a new type of standard-cell power supplying mesh and solving the problems in the prior art. 
     A power mesh managing method applicable in an integrated circuit is provided. The integrated circuit comprises at least a standard cell and a standard-cell power supplying mesh of the standard cell. The standard-cell power supplying mesh corresponding to a first direction couples to the standard cell. The power mesh managing method comprises defining a power supplying network and defining an assistant connecting network on a third metal layer. The power supplying network includes a plurality of first power supplying meshes growing along the first direction and a plurality of second power supplying meshes growing along a second direction. The first power supplying meshes are on a first metal layer and the second power supplying meshes are on a second metal layer. The assistant connecting network includes a plurality of assistant connecting lines growing along the second direction. The second metal layer is above the first metal layer and the third metal layer is below the first metal layer. 
     An integrated circuit comprises a standard cell, a standard-cell power supplying mesh, a power supplying network, and an assistant connecting network. The standard-cell power supplying mesh corresponding to a first direction couples to the standard cell. The power supplying network includes a plurality of first power supplying meshes corresponding to the first direction and a plurality of second power supplying meshes corresponding to a second direction. The assistant connecting network is formed on a third metal layer. The first power supplying meshes are formed on a first metal layer and the second power supplying meshes are formed on a second metal layer. The assistant connecting network includes a plurality of assistant connecting lines corresponding to the second direction. The second metal layer is above the first metal layer and the third metal layer is below the first metal layer. 
     A better circuit routing method can be managed according to the invention and the method can be implemented in the APR tool to design a better circuit layout that avoids blocking the vias/via plugs by the power supplying mesh below and eliminates the limitations of the position and the width for the horizontal power supplying mesh. Not only the routing design flexibility is improved but also the routing design can be done by following the well-defined rules. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a three-dimensional schematic diagram illustrating the standard cell and the standard cell power supplying meshes managed by the APR tool according to the prior art; 
         FIG. 2  shows a three-dimensional schematic diagram illustrating the standard cell, the standard-cell power supplying meshes, and the power supplying mesh located in the layer above the standard cell in  FIG. 1 ; 
         FIG. 3  shows a schematic diagram illustrating a side view of  FIG. 2 ; 
         FIG. 4  shows a schematic diagram illustrating the power supplying network and the assistant connecting network located in the layer above the standard cell according to one embodiment of the invention; 
         FIG. 5  shows a schematic diagram illustrating a side view of  FIG. 4 ; and 
         FIG. 6  shows the flow chart of the steps executed by the APR tool according to one embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Now, please refer to  FIG. 4  which shows a schematic diagram illustrating the power supplying network  200  and the assistant connecting network  400  located in the layer above the standard cell  100  according to one embodiment of the invention. The structure and the functionalities of the standard cell  100  and the standard-cell power supplying meshes  110 ,  120  in  FIG. 4  are the same as those of the standard cell  100  and the standard-cell power supplying meshes  110 ,  120  in  FIG. 1 . Please note that only three rows of standard cell  100  are shown in  FIG. 4 , for clarity. However, there can be more standard cells  100  in the actual chip. 
     Please note that an assistant connecting network  400  is also located, together with the power supplying network  200 , in the layer above the standard cell  100  according to one embodiment of the invention. Similarly, the power supplying network  200  is the same as the power supplying network  200  in  FIG. 2  and includes the horizontal power supplying mesh  210  and the vertical power supplying mesh  220 . The vias/via plugs  231 / 232  couple the horizontal power supplying mesh  210  and the vertical power supplying mesh  220 . In order to clearly mark the electrical property, as shown in  FIG. 4 , the via/via plug  231  is used to couple various power lines (that is, the voltage corresponds to the V DD ). The via/via plug  232  is used to couple various ground lines (that is, the voltage corresponds to the V SS ). 
     As mentioned before, if there is only the power supplying network  200  located in the layer above the standard cell  100 , the horizontal power supplying mesh  210  may block the electrical coupling between the vertical power supplying mesh  220  and the standard-cell power supplying meshes  110 ,  120  (that is, limiting the via positions between the vertical power supplying mesh  220  and the standard-cell power supplying meshes  110 ,  120 ). Positioning the horizontal power supplying mesh  210  is also limited. Therefore, besides the power supplying network  200 , a layer of assistant connecting network  400  is set up between the power supplying network  200  and the standard-cell power supplying meshes  110 ,  120  to assist the electrical coupling between the power supplying network  200  and the standard-cell power supplying meshes  110 ,  120  according to one embodiment of the invention. According to one embodiment of the invention, the assistant connecting network  400  couples to the horizontal power supplying mesh  210  through the vias/via plugs  231 / 232 . The assistant connecting network  400  includes a plurality of assistant connecting lines  410  growing vertically like the vertical power supplying mesh  220 . 
     Thus, the horizontal power supplying mesh  210  can be successfully coupled to the standard-cell power supplying meshes  110 / 120  below by way of the assistant connecting lines  410  of the assistant connecting network  400 . As shown in  FIG. 4 , the assistant connecting lines  410  couple to the standard-cell power supplying meshes  110 / 120  by way of the vias/via plugs  231 / 232 , separately, according to one embodiment of the invention. Since the assistant connecting line  410  growing vertically like the vertical power supplying mesh  220  is vertical to the standard-cell power supplying meshes  110 / 120  growing horizontally and nothing is in between to block each other, the assistant connecting line  410  couples to the standard-cell power supplying meshes  110 / 120  by the via/via plug  231 / 232  smoothly. The assistant connecting line  410  also couples to the horizontal power supplying mesh  210  by the via/via plug  231 / 232 . Therefore, the horizontal power supplying mesh  210  couples to the standard-cell power supplying meshes  110 / 120  for conducting the external power into the standard cell  100 . 
     Since the horizontal power supplying mesh  210  couples to the vertical power supplying mesh  220  and even if the assistant connecting line  410  does not couple to the vertical power supplying mesh  220  directly, the vertical power supplying mesh  220  still couples to the standard-cell power supplying meshes  110 / 120  below through the horizontal power supplying mesh  210  and the assistant connecting line  410 . 
     Or, the assistant connecting line  410  can be coupled to the vertical power supplying mesh  220  by the via/via plug  231 / 232  according to another embodiment of the invention (not shown in the figure). Then, the vertical power supplying mesh  220  couples to the standard-cell power supplying meshes  110 / 120  directly by way of the assistant connecting line  410 . 
     Now, please refer to  FIG. 5  which shows a schematic diagram illustrating a side view of  FIG. 4 . It is clearly shown in  FIG. 5  that the vertical power supplying mesh  220  couples to the standard-cell power supplying meshes  110 / 120  below through the horizontal power supplying mesh  210  and the assistant connecting line  410  by way of the vias/via plugs  231 / 232 . 
     Furthermore, it should be noted that the above mentioned structure can be implemented easily by those who are skilled in the art. Since there are usually more than three metal layers above the standard cell  100  in the advanced process, those who are skilled in the art can select any three metal layers to implement the above mentioned power supplying network  200  and the above mentioned assistant connecting network  400  according to different requirements. For example, as the standard-cell power supplying meshes  110 ,  120  are usually located at the metal layer M 1 , those who are skilled in the art can choose the metal layers M 4 , M 5 , M 6  to implement the power supplying network  200  and the above mentioned assistant connecting network  400 . 
     Please note that, in order to reduce the routing resource used by the newly introduced assistant connecting network  400 , the width for the assistant connecting line  410  is substantially equal to the width of a via plug according to one embodiment of the invention. Thus, such a design releases the space of the lower metal layers. As the space of the lower metal layers is more precious, the released space can be used for routing and coupling in the other portion of the circuit. Therefore, the benefit of implementing the assistant connecting line  410  with less width in the lower metal layers (such as the above mentioned metal layer M 4 ) is to release more space of the lower metal layers. 
     Since both of the horizontal power supplying mesh  210  and the vertical power supplying mesh  220  couple to the standard-cell power supplying meshes  110 ,  120  below by way of the assistant connecting network  400 , the position and the width for the horizontal power supplying mesh  210  do not suffer the same limitation mentioned before. For example, the horizontal power supplying mesh  210  couples to the standard-cell power supplying meshes  110 ,  120  by way of the assistant connecting network  400 . Then, even if the width for the horizontal power supplying mesh  210  is larger to shadow the standard-cell power supplying meshes  110 ,  120  below, such mechanism will not influence the electrical properties of the standard-cell power supplying meshes  110 ,  120  (that is, the standard-cell power supplying meshes  110 ,  120  can acquire the voltage V DD  and the ground potential V SS  from the assistant connecting network  400  above directly through the via). 
     Those who are skilled in the art should be able to implement the descriptions up to now in the APR tool to set up a new routing rule. Please refer to  FIG. 6  which shows the flow chart of the managing method executed by the APR tool according to one embodiment of the invention. The method comprises the following steps: 
     Step  600 : defining a standard cell  100  and related power supplying meshes  110 ,  120 ; 
     Step  610 : defining a power supplying network in the layer above the standard cell  100  where the power supplying network includes a plurality of power supplying mesh structure  210  growing along the vertical direction and a plurality of power supplying mesh structure  220  growing along the horizontal direction and the power supplying mesh structure  210  and the power supplying mesh structure  220  are placed on different metal layers; 
     Step  620 : defining an assistant connecting network  400  between the power supplying meshes  110 ,  120  of the standard cell  100  and the above mentioned power supplying network, where the assistant connecting network  400  includes a plurality of connecting lines  410  growing along the horizontal direction; 
     Step  630 : performing the electrical coupling for the assistant connecting network and the power supplying mesh and performing the electrical coupling for the assistant connecting network and the power supplying network. The coupling step is to form the vias and the via plugs in the vertically intersected overlapping areas of the power supplying network and the assistant connecting network, and in the vertically intersected overlapping areas of the assistant connecting network and the power supplying network. 
     First of all, a common standard cell, the standard-cell power supplying mesh (Step  610 ), and the power supplying network (Step  620 ) are drawn according to the prior art. Then, the assistant connecting network disclosed before is drawn between the power supplying network and the standard-cell power supplying mesh (Step  630 ). Lastly, the standard-cell power supplying mesh, the power supplying network, and the assistant connecting network are coupled by way of the vias (Step  640 ). Those who are skilled in the art should be able to understand the description up to now. Thus, the details of the program codes of the APR tool will not be repeated hereinafter. 
     Please note that, as one additional metal layer is used to manage the assistant connecting network according to one embodiment of the invention, the assistant connecting network is only implemented above the standard cell. The assistant connecting network is not arranged above the more complicated macro block. However, such an example is only one embodiment of the invention and should not be construed as any limitation on the implementation of the invention. 
     Compared to the prior art, a better circuit routing method can be managed according to the invention. The method can be implemented in the APR tool to design a better circuit layout that avoids blocking the vias by the power supplying mesh below. The limitations of the position and the width for the horizontal power supplying mesh can be eliminated. Not only the flexibility of the routing design is improved but also the routing design can be done by following the well-defined rules. 
     Although the description of the invention is by way of above-mentioned examples of embodiments, however, it should not be construed as any limitation on the scope of the invention. Various modifications or changes can be performed by those who are skilled in the art without deviating from the scope of the invention.