Abstract:
A semiconductor device in a continuous diffusion region formed on a semiconductor substrate and having either a P-type or N-type polarity includes: a first transistor formed within the continuous diffusion region; a second transistor formed within the continuous diffusion region and in an area that is different from an area where the first transistor is formed; a third transistor formed within the continuous diffusion region and in an area between the first and second transistors, and having a gate electrode to which a fixed potential is applied; and a fourth transistor formed within the continuous diffusion region and in an area between the second and third transistors, and having a gate electrode to which a fixed potential is applied.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application, filed under 35 U.S.C. §111(a), of PCT Application No. PCT/JP2007/074091, filed on Dec. 14, 2007, the disclosure of which is herein incorporated in its entirety by reference. 
    
    
     FIELD 
     The present invention relates to a semiconductor device formed on a semiconductor substrate. 
     BACKGROUND 
     In post-65 nm generation microscopic technology for a large-scale integrated circuit designed by a gate array method or a standard cell method used in an information processing device, there is known a technique for increasing the mobility of electron and holes by using a dual-stress called strained silicon in the drain-source portion. Further, in the case where a plurality of circuits are arranged close to one another, an STI (Shallow Trench Isolation) is used for device isolation, in which a trench is formed in a silicon surface by anisotropic etching, and the trench is buried with an insulating film such as an oxide film, followed by flattening. 
     As a prior art relating to the present invention, there is known a CMOS (Complementary Metal Oxide Semiconductor) in which a shield gate is provided between NMOS (Negative channel Metal Oxide Semiconductor) transistors and an active region provided for each PMOS (Positive channel Metal Oxide Semiconductor) transistor (refer to, e.g., Patent Document 1).
     [Patent Document 1] Japanese Laid-Open Patent Publication No. 2006-210453   

     PROBLEMS TO BE SOLVED BY THE INVENTION 
     There is a case where, when a plurality of circuits are arranged close to one another in a continuous diffusion layer, the performance of a transistor deteriorates due to constraint on the shape thereof or device isolation, or the transistor is subject to noise. 
     SUMMARY 
     According to an aspect of the invention, a semiconductor device in a continuous diffusion region formed on a semiconductor substrate and having either a P-type or N-type polarity is provided, the device includes: a first transistor formed within the continuous diffusion region; a second transistor formed within the continuous diffusion region and in an area that is different from an area where the first transistor is formed; a third transistor formed within the continuous diffusion region and in an area between the first and second transistors, and having a gate electrode to which a fixed potential is applied; and a fourth transistor formed within the continuous diffusion region and in an area between the second and third transistors, and having a gate electrode to which a fixed potential is applied. 
     The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention, as claimed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram illustrating the outline of a configuration of a first circuit; 
         FIG. 2  is a circuit diagram illustrating the details of the configuration of the first circuit; 
         FIG. 3  is a plan view illustrating a layout example of a first circuit according to Comparative Example 1; 
         FIG. 4  is a cross-sectional view illustrating a layout example of the first circuit according to Comparative Example 1; 
         FIG. 5  is a plan view illustrating a layout example of the first circuit according to Comparative Example 2; 
         FIG. 6  is a cross-sectional view illustrating a layout example of the first circuit according to Comparative Example 2; 
         FIG. 7  is a circuit diagram illustrating the details of a configuration of the first circuit according to a first embodiment; 
         FIG. 8  is a plan view illustrating a layout example of the first circuit according to the first embodiment; 
         FIG. 9  is a cross-sectional view illustrating a layout example of the first circuit according to the first embodiment; 
         FIG. 10  is a plan view illustrating a layout example of the first circuit according to a second embodiment; 
         FIG. 11  is a cross-sectional view illustrating a layout example of the first circuit according to the second embodiment; 
         FIG. 12  is a circuit diagram illustrating the outline of a configuration of a second circuit; 
         FIG. 13  is a circuit diagram illustrating the details of the configuration of the second circuit; 
         FIG. 14  is a circuit diagram illustrating the details of a configuration of the second circuit according to a third embodiment; and 
         FIG. 15  is a plan view illustrating a layout example of the second circuit according to the third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First, a first circuit exemplified as a circuit for explaining an embodiment of the present invention will be described. The first circuit includes a 2-NAND (2-input negative logical multiplication) circuit and an INV (Inverter: negative) circuit. 
       FIG. 1  is a circuit diagram illustrating the outline of a configuration of the first circuit. The 2-NAND circuit receives as inputs IN 1  and IN 2  and outputs A. The INV circuit receives as an input A and outputs OUT.  FIG. 2  is a circuit diagram illustrating the details of the configuration of the first circuit. The 2-NAND circuit is constituted by PMOS transistors TP 1 , TP 2  and NMOS transistors TN 1 , TN 2 . The INV circuit is constituted by a PMOS transistor TP 3  and a NMOS transistor TN 3 . 
     Next, Comparative Examples 1 and 2 exemplified as layout examples of the first circuit will be described. 
     Comparative Example 1 
     Comparative Example 1 is a case where an STI is used for device isolation.  FIG. 3  is a plan view illustrating a layout example of the first circuit according to Comparative Example 1. In  FIG. 3 , the same reference marks as those in  FIG. 2  denote the same or corresponding parts as those in  FIG. 2 , and the descriptions thereof will be omitted here. Hereinafter, in the plan view of the layout, a region surrounded by a bold line denotes a diffusion layer. A diffusion layer LPa constitutes the diffusion layer of the PMOS transistors TP 1  and TP 2 , and a diffusion layer LNa constitutes the diffusion layer of the NMOS transistors TN 1  and TN 2 . Further, a diffusion layer LPb constitutes the diffusion layer of the PMOS transistor TP 3 , and a diffusion layer LNb constitutes the diffusion layer of the NMOS transistor TN 3 . Hereinafter, in the layout view, a region shaded by diagonal lines denotes a metal, a region shaded by horizontal lines denotes a gate polysilicon which is a gate electrode formed by polycrystalline silicon, and a blackened region denotes a contact serving as a contact point for upper layer wiring. 
     A power supply wiring VDD (high potential) is disposed at the uppermost portion in  FIG. 3 , and a power supply wiring VSS (low potential) is disposed at the lowermost portion. The PMOS transistors are arranged on the VDD side, and the NMOS transistors are arranged on the VSS side. As the PMOS transistors, the PMOS transistors TP 2 , TP 1 , and TP 3  are arranged in this order from the left. As the NMOS transistors, the NMOS transistors TN 2 , TN 1 , and TN 3  are arranged in this order from the left. 
     IN 1  is a gate electrode of the transistors TP 1  and TN 1 , and IN 2  is a gate electrode of the transistors TP 2  and TN 2 . A (SN 1 ) is a drain electrode of the transistors TP 1 , TN 1 , and TP 2  and a gate electrode of the transistors TP 3  and TN 3 . OUT is a drain electrode of the transistors TP 3  and TN 3 . SP 2  is a source electrode of the transistor TP 2 , SP 1  is a source electrode of the transistor TP 1 , and SN 2  is a source electrode of the transistor TN 2 . SP 3  is a source electrode of the transistor TP 3 , and SN 3  is a source electrode of the transistor TN 3 . 
       FIG. 4  is a cross-sectional view illustrating a layout example of the first circuit according to Comparative Example 1. In  FIG. 4 , the same reference marks as those in  FIG. 3  denote the same or corresponding parts as those in  FIG. 3 , and the descriptions thereof will be omitted here.  FIG. 4  is a cross-sectional view taken along X-X′ line of  FIG. 3 . 
     STIs are provided on the left side of the transistors TP 2  and TN 2 , on the right side of the transistors TP 3  and TN 3 , and between the transistors TP 1 , TN 1  and transistors TP 3 , TN 3 , respectively. As diffusion layers, a diffusion layer LPa of the transistors TP 1  and TP 2 , a diffusion layer LNa of the transistors TN 1  and TN 2 , a diffusion layer LPb of the transistor TP 3 , and a diffusion layer LNb of the transistor TN 3  are provided. That is, the diffusion layer of the 2-NAND circuit and diffusion layer of the INV circuit are isolated from each other by the STI. 
     According to Comparative Example 1, the diffusion layers of the 2-NAND circuit and INV circuit are isolated from each other by the STI and, correspondingly, the size of the diffusion layers is reduced, so that the effect of a strained silicon is small. Further, the transistor performance deteriorates due to a compression stress from the STI. 
     Comparative Example 2 
     Comparative Example 2 is a case where a dummy transistor is used for device isolation in place of the STI.  FIG. 5  is a plan view illustrating a layout example of the first circuit according to Comparative Example 2. In  FIG. 5 , the same reference marks as those in  FIG. 3  denote the same or corresponding parts as those in  FIG. 3 , and the descriptions thereof will be omitted here.  FIG. 6  is a cross-sectional view illustrating a layout example of the first circuit according to Comparative Example 2. In  FIG. 6 , the same reference marks as those in  FIG. 5  denote the same or corresponding parts as those in  FIG. 5 , and the descriptions thereof will be omitted here.  FIG. 6  is a cross-sectional view taken along X-X′ line of  FIG. 5 . 
     In Comparative Example 2, the PMOS transistors TP 1  and TP 3  are isolated from each other by a dummy transistor XP, and the NMOS transistors TN 1  and TN 3  are isolated from each other by a dummy transistor XN. A gate electrode EP 0  of the dummy transistor XP is provided between the source electrodes SP 1  and SP 3 , and a gate electrode EN 0  is provided as an enable terminal of the dummy transistor XN between the source electrodes SN 1  and SN 3 . As a result, all the PMOS transistors TP 1 , TP 2 , XP, and TP 3  are formed on one continuous diffusion layer LP 0 , and all the NMOS transistors TN 1 , TN 2 , XN, and TN 3  are formed on one continuous diffusion layer LN 0 . 
     When the gate electrode EP 0  is connected to the VDD, the dummy transistor XP is kept in an OFF state. Further, when the gate electrode EN 0  serving as the enable terminal is connected to the VSS, the dummy transistor XN is kept in an OFF state. 
     According to Comparative Example 2, the problem of Comparative Example 1 can be solved. However, since only transistors having the same characteristics can be constructed in one diffusion layer, the performance of the transistor is constrained. 
     First Embodiment 
     In the present embodiment, a semiconductor device in which two dummy transistors are provided between two devices and thereby different channel widths W can be set for the two devices will be described. 
       FIG. 7  is a circuit diagram illustrating the details of a configuration of the first circuit according to the first embodiment. In  FIG. 7 , the same reference marks as those in  FIG. 2  denote the same or corresponding parts as those in  FIG. 2 , and the descriptions thereof will be omitted here. The circuit of  FIG. 7  is obtained by adding the dummy PMOS transistors XP 1  and XP 2  and dummy NMOS transistors XN 1  and XN 2  to the circuit of  FIG. 2 . 
       FIG. 8  is a plan view illustrating a layout example of the first circuit according to the first embodiment. In  FIG. 8 , the same reference marks as those in  FIG. 5  denote the same or corresponding parts as those in  FIG. 5 , and the descriptions thereof will be omitted here. Further,  FIG. 8  illustrates the layout of the circuit of  FIG. 7 .  FIG. 9  is a cross-sectional view illustrating a layout example of the first circuit according to the first embodiment. In  FIG. 9 , the same reference marks as those in  FIG. 8  denote the same or corresponding parts as those in  FIG. 8 , and the descriptions thereof will be omitted here.  FIG. 9  is a cross-sectional view taken along X-X′ line of  FIG. 8 . 
     In the present embodiment, PMOS transistors TP 1  (first transistor) and TP 3  (second transistor) are isolated from each other by dummy transistors XP 1  (third transistor) and XP 2  (fourth transistor), and NMOS transistors TN 1  (first transistor) and TN 3  (second transistor) are isolated from each other by dummy transistors XN 1  (third transistor) and XN 2  (fourth transistor). 
     A gate electrode EP 1  of the dummy transistor XP 1  is provided between the source electrodes SP 1  and SP 3 , a gate electrode EP 2  of the dummy transistor XP 2  is provided between the gate electrode EP 1  and source electrode SP 3 , and a drain electrode FP of the dummy transistors XP 1  and XP 2  is provided between the gate electrodes EP 1  and EP 2 . Similarly, a gate electrode EN 1  is provided as an enable terminal of the dummy transistor XN 1  between the source electrodes SN 1  and SN 3 , a gate electrode EN 2  is provided as an enable terminal of the dummy transistor XN 2  between the gate electrode EN 1  and source electrode SN 3 , and a drain electrode FN of the dummy transistors XN 1  and XN 2  is provided between the gate electrodes EN 1  and EN 2 . Although there are provided in this example the drain electrode FP which is connected to the VDD so as to make the potentials of the drains of the dummy transistors XP 1  and XP 2  constant and the drain electrode FN which is connected to the VSS so as to make the potentials of the drains of the dummy transistors XN 1  and XN 2  constant, the drain electrodes FP and FN need not always be provided. 
     Thus, all the PMOS transistors TP 1 , TP 2 , XP 1 , XP 2 , and TP 3  are formed on one continuous diffusion layer LP 1 , and all the NMOS transistors TN 1 , TN 2 , XN 1 , XN 2 , and TN 3  are formed on one continuous diffusion layer LN 1 . 
     When the gate electrodes EP 1  and EP 2  are connected to the VDD, the dummy transistors XP 1  and XP 2  are kept in an OFF state. Similarly, when the gate electrodes EN 1  and EN 2  serving as the enable terminals are connected to the VSS, the dummy transistors XN 1  and XN 2  are kept in an OFF state. That is, existence of the dummy transistors XP 1 , XP 2 , XN 1 , and XN 2  does not affect the function of the first circuit. 
     In the present embodiment, the channel width W of the diffusion layer LP 1  is changed between the dummy transistors XP 1  and XP 2 . That is, in the diffusion layer LP 1 , the channel width W of a region LPa (first diffusion region) where the transistors TP 1 , TP 2 , and XP 1  are formed is set to W 1 , and the channel width W of a region LPb (second diffusion region) where the transistors XP 2  and TP 3  are formed is set to W 2 . Similarly, the channel width W of the diffusion layer LN 1  is changed between the XN 1  and XN 2 . That is, in the diffusion layer LN 1 , the channel width W of a region LNa (first diffusion region) where the transistors TN 1 , TN 2 , and XN 1  are formed is set to W 3 , and the channel width W of a region LNb (second diffusion region) where the transistors XN 2  and TN 3  are formed is set to W 4 . 
     By providing the two dummy transistors in one diffusion layer, it is possible to define the boundary of the channel width between the two dummy transistors. Therefore, a fixed channel width can be set for the left side region of the one diffusion layer LP 1  starting from the dummy transistor XP 1  and extending to the left and another fixed channel width can be set for the right side region of the one diffusion layer LP 1  starting from the dummy transistor XP 2  and extending to the right. Similarly, a fixed channel width can be set for the left side region of the one diffusion layer LN 1  starting from the dummy transistor XN 1  and extending to the left and another fixed channel width can be set for the right side region of the one diffusion layer LN 1  starting from the dummy transistor XN 2  and extending to the right. 
     According to the present embodiment, by forming the diffusion layer in a continuous manner across a plurality of circuits, it is possible to eliminate the need to provide the STI which may cause the deterioration of the transistor performance and to enhance the effect of the strained silicon. Further, by providing the two dummy transistors between two devices, it is possible to set different channel widths W for the two devices. Thus, the value of the channel width can be made different region by region in one continuous diffusion layer, allowing design of a transistor having appropriate channel widths for respective circuits. That is, even in the case where there occurs a need to change the value of the channel width in order to optimize transistor characteristics for each region in the continuous diffusion layer, a transistor having optimum channel width can be obtained by forming the dummy transistors in the region at which the channel width is changed. 
     Second Embodiment 
     In the present embodiment, a semiconductor device in which two dummy transistors are provided between two devices and thereby different threshold voltages Vth can be set for the two devices will be described. 
       FIG. 10  is a plan view illustrating a layout example of the first circuit according to the second embodiment. In  FIG. 10 , the same reference marks as those in  FIG. 8  denote the same or corresponding parts as those in  FIG. 8 , and the descriptions thereof will be omitted here. As with  FIG. 8 ,  FIG. 10  illustrates the layout of the circuit of  FIG. 7 .  FIG. 11  is a cross-sectional view illustrating a layout example of the first circuit according to the second embodiment. In  FIG. 11 , the same reference marks as those in  FIG. 10  denote the same or corresponding parts as those in  FIG. 10 , and the descriptions thereof will be omitted here.  FIG. 11  is a cross-sectional view taken along X-X′ line of  FIG. 10 . 
     As in the case of the first embodiment, all the PMOS transistors TP 1 , TP 2 , XP 1 , XP 2 , and TP 3  are formed on one continuous diffusion layer LP 1 , and all the NMOS transistors TN 1 , TN 2 , XN 1 , XN 2 , and TN 3  are formed on one continuous diffusion layer LN 1 . 
     In the present embodiment, the dose amount of a region (first diffusion region) where the transistors TP 1 , TP 2 , and XP 1  are formed and does amount of a region (second diffusion region) where the transistors XP 2  and TP 3  are formed are made different to thereby set the value of the threshold voltage Vth of the PMOS transistors TP 1  and TP 2  to Vthp 1  and the value of the threshold voltage Vth of the PMOS transistors TP 3  to Vthp 2 . The dose amount denotes an electron or ion injection amount per unit area of the silicon substrate. Similarly, the dose amount of a region (first diffusion region) where the NMOS transistors TN 1 , TN 2 , and XN 1  are formed and does amount of a region (second diffusion region) where the transistors XN 2  and TN 3  are formed are made different to thereby set the value of the threshold voltage of the transistors TN 1  and TN 2  to Vthn 1  and the value of the threshold voltage of the transistors TN 3  to Vthn 2 . 
     For example, an ion injection mask for normal threshold voltage is used to conduct ion injection to the region where the transistors XP 2  and TP 3  are formed and region where the transistors XN 2  and TN 3  are formed, while an ion injection mask for high threshold voltage is used to conduct ion injection to the region where the transistors TP 1 , TP 2 , and XP 1  are formed and region where the transistors TN 1 , TN 2 , and XN 1  are formed. As a result, the threshold voltages Vthp 1  and Vthn 1  of the transistors TP 1 , TP 2 , TN 1 , and TN 2  can be made higher than the threshold voltages Vthp 2  and Vthn 2  of the transistors TP 3  and TN 3 . 
     Further, as in the case of the first embodiment, in the diffusion layer LP 1 , the channel width W of the region where the transistors TP 1 , TP 2 , and XP 1  are formed is set to W 1 , and the channel width W of the region where the transistors XP 2  and TP 3  are formed is set to W 2 . Similarly, in the diffusion layer LN 1 , the channel width W of the region where the transistors TN 1 , TN 2 , and XN 1  are formed is set to W 3 , and the channel width W of the region where the transistors XN 2  and TN 3  are formed is set to W 4 . 
     By providing the two dummy transistors in one diffusion layer LP 1 , it is possible to define the boundary of the threshold voltage between the two dummy transistors. Therefore, a fixed threshold voltage can be set for the left side region of the one diffusion layer LP 1  starting from the dummy transistor XP 1  and extending to the left and another fixed threshold voltage can be set for the right side region of the one diffusion layer LP 1  starting from the dummy transistor XP 2  and extending to the right. Similarly, a fixed threshold voltage can be set for the left side region of the one diffusion layer LN 1  starting from the dummy transistor XN 1  and extending to the left and another threshold voltage width can be set for the right side region of the one diffusion layer LN 1  starting from the dummy transistor XN 2  and extending to the right. 
     According to the present embodiment, by forming the diffusion layer in a continuous manner across a plurality of circuits, it is possible to eliminate the need to provide the STI which may cause the deterioration of the transistor performance and to enhance the effect of the strained silicon. Further, the value of the threshold voltage can be made different region by region in one continuous diffusion layer, allowing design of a transistor having appropriate threshold voltage values for respective circuits. 
     Although both the channel width and threshold voltage are made different between the regions which are isolated from each other by the dummy transistors in the present embodiment, only the threshold voltage may be made different between the regions. 
     Third Embodiment 
     In the present embodiment, a semiconductor device in which two dummy transistors are provided between two devices and thereby stable power supply to the two devices can be achieved will be described. 
     First, a second circuit exemplified as a circuit will be described. The second circuit has a first 2-NAND (2-input negative logical multiplication) circuit and a second 2-NAND circuit. 
       FIG. 12  is a circuit diagram illustrating the outline of a configuration of the second circuit. The first 2-NAND circuit receives as inputs IN 1   a  and IN 2   a  and outputs OUTa. The second 2-NAND circuit receives as inputs IN 1   b  and IN 2   b  and outputs OUTb.  FIG. 13  is a circuit diagram illustrating the details of the configuration of the second circuit. The first 2-NAND circuit is constituted by PMOS transistors TP 1   a , TP 2   a  and NMOS transistors TN 1   a , TN 2   a . The second 2-NAND circuit is constituted by PMOS transistors TP 1   b , TP 2   b  and NMOS transistors TN 1   b , TN 2   b.    
       FIG. 14  is a circuit diagram illustrating the details of a configuration of the second circuit according to the third embodiment. In  FIG. 14 , the same reference marks as those in  FIG. 13  denote the same or corresponding parts as those in  FIG. 13 , and the descriptions thereof will be omitted here. The circuit of  FIG. 14  is obtained by adding the dummy PMOS transistors XP 3  and dummy NMOS transistor XN 3  to the circuit of  FIG. 13 . 
       FIG. 15  is a plan view illustrating a layout example of the second circuit according to the third embodiment.  FIG. 15  illustrates the layout of the circuit of  FIG. 14 . As in the case of the first embodiment, a power supply wiring VDD (high potential) is disposed at the uppermost portion in  FIG. 15 , and a power supply wiring VSS (low potential) is disposed at the lowermost portion. The PMOS transistors are arranged on the VDD side, and the NMOS transistors are arranged on the VSS side. As the PMOS transistors, the transistors TP 2   a , TP 1   a , XP 3 , TP 1   b , and TP 2   b  are arranged in this order from the left. As the NMOS transistors, the transistors TN 2   a , TN 1   a , XN 3 , TN 1   b , and TN 2   b  are arranged in this order from the left. 
     In the present embodiment, PMOS transistors TP 1   a  (fifth transistor) and TP 1   b  (sixth transistor) are isolated from each other by dummy transistors XP 3  (seventh transistor), and NMOS transistors TN 1   a  (fifth transistor) and TN 1   b  (sixth transistor) are isolated from each other by dummy transistors XN 3  (seventh transistor). 
     IN 1   a  is a gate electrode of the transistors TP 1   a  and TN 1   a , and IN 2   a  is a gate electrode of the TP 2   a  and TN 2   a . IN % is a gate electrode of the TP 1   b  and TN 1   b , and IN 2   b  is a gate electrode of the TP 2   b  and TN 2   b . OUTa is a drain electrode of the TP 1   a , TP 2   a , and TN 2   a . OUTb is a drain electrode of the TP 1   b , TP 2   b , and TN 2   b . SP 1   a  is a source electrode of the TP 1   a , and SN 1   a  is a source electrode of the TN 1   a . SP 2   a  is a source electrode of the TP 2   a . SP 1   b  is a source electrode of the TP 1   b , and SN 1   b  is a source electrode of the TN 1   b , and SP 2   b  is a source electrode of the TP 2   b.    
     In the present embodiment, the TP 1   a  and TP 1   b  are isolated from each other by a dummy transistor XP 3  and the TN 1   a  and TN 1   b  are isolated from each other by a dummy transistor XN 3 . A gate electrode EP 3  of the XP 3  is provided between the SP 1   a  and SP 1   b , and a gate electrode EN 3  is provided as an enable terminal of the XN 3  between the SN 1   a  and SN 1   b . As a result, all the PMOS transistors TP 2   a , TP 1   a , XP 3 , TP 1   b , and TP 2   b  are formed on one continuous diffusion layer LP 3  (diffusion region), and all the NMOS transistors TN 2   a , TN 1   a , XN 3 , TN 1   b , and TN 2   b  are formed on one continuous diffusion layer LN 3  (diffusion region). 
     When the gate electrode EP 3  is connected to the VSS, the dummy transistor XP 3  is kept in an ON state. Further, the gate electrode EN 3  is connected to the VDD, the dummy transistor XN 3  is kept in an ON state. That is, existence of the dummy transistors XP 3  and XN 3  does not affect the function of the second circuit. 
     In the case where the source electrodes SP 1   a  and SP 1   b  connected to the power supply wiring are disposed close to each other, the dummy transistor XP 3  is provided between the source electrodes SP 1   a  and SP 1   b , thereby reducing power supply noise in the power supply wiring VDD by an electrostatic capacitance of the dummy transistor XP 3  connecting the power supply wirings. Similarly, in the case where the source electrodes SP 1   a  and SP 1   b  connected to the power supply wiring are disposed close to each other, the dummy transistor XN 3  is provided between the source electrodes SN 1   a  and SN 1   b , thereby reducing power supply noise in the power supply wiring VDD by an electrostatic capacitance of the dummy transistor XN 3  connecting the power supply wirings. 
     According to the present embodiment, by forming the diffusion layer in a continuous manner across a plurality of circuits, it is possible to eliminate the need to provide the STI which may cause the deterioration of the transistor performance and to enhance the effect of the strained silicon. Further, by providing the dummy transistors, it is possible to reduce the power supply noise to thereby make the circuit operation stable. 
     According to the embodiments of the present invention, it is possible to improve the performance of a circuit in the case where a plurality of circuits are arranged in a continuous diffusion layer. 
     All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the invention and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a depicting of the superiority and inferiority of the invention. Although the embodiment(s) of the present inventions have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.