Patent Publication Number: US-8110878-B2

Title: Semiconductor device having a plurality of shallow wells

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of Application No. 12/901,858 filed Oct. 11, 2010, now U.S. Pat. No. 7,982,271 which is a division of application Ser. No. 12/422,278 filed Apr. 12, 2009 (now U.S. Pat. No. 7,821,076). Also, the disclosure of Japanese Patent Application No. 2008-123634 filed on May 9, 2008 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device and, more particularly, to a technology which is effective when applied to a semiconductor device formed with a well in a three-layer structure, i.e., a so-called triple well structure which has a deep well of a second conductivity type different from a first conductivity type in a substrate of the first conductivity type, and further has a shallow well of the first conductivity type in the deep well. 
     For example, Japanese Unexamined Patent Publication No. 2006-303753 (Patent Document 1) describes a logic circuit and an I/O circuit in a semiconductor integrated circuit device having a so-called triple well structure. In the triple well structure, a deep n-well is formed on a p-type semiconductor substrate, and an n-well for forming a p-type MISFET and a p-well for forming an n-type MISFET are formed thereon. 
     Japanese Unexamined Patent Publication No. Hei 11-97560 (Patent Document 2) discloses a technology which forms, in a nonvolatile semiconductor memory device having a floating gate electrode and a control gate electrode on a semiconductor substrate, an n-well in a p-type semiconductor substrate, forms a p-well in the n-well, forms an antistatic n-type diffusion layer in the p-well, and electrically couples the antistatic diffusion layer and the control gate electrode to prevent the degradation of the reliability of an insulating film due to charging during the processing of an interconnection layer by etching, or prevent a dielectric breakdown therein. 
     Japanese Unexamined Patent Publication No. 2005-340548 (Patent Document 3) discloses a technology which couples a floating interconnection to a clamp diode to transfer charge that has flown to the floating interconnection to the clamp diode, and thereby prevent a short circuit between the floating interconnection and a ground interconnection adjacent thereto. 
     Japanese Unexamined Patent Publication No. 2001-358143 (Patent Document 4) discloses a technology for a semiconductor device including at least one interconnection layer including a plurality of relay pins electrically coupled to a plurality of respective gate electrodes, and an uppermost interconnection layer including a plurality of interconnection patterns which are electrically coupled to the plurality of respective relay pins. According to the technology, the gate electrodes are wired using the uppermost-layer interconnection pattern to transfer electrification charge to a region other than the gate electrodes during the etching of the interconnection layers, and thereby prevent the degradation of gate insulating film. 
     [Patent Document 1] 
     
         
         Japanese Unexamined Patent Publication No. 2006-303753
 
[Patent Document 2]
 
         Japanese Unexamined Patent Publication No. Hei 11-97560
 
[Patent Document 3]
 
         Japanese Unexamined Patent Publication No. 2005-340548
 
[Patent Document 4]
 
         Japanese Unexamined Patent Publication No. 2001-358143 
       
    
     SUMMARY OF THE INVENTION 
     In a SOC (System On Chip) product, a semiconductor device having a triple-well structure is used for the purpose of reducing power consumption during standby or the like. However, the semiconductor device having the triple-well structure has various technological problems described herein below. 
     In general, for signal transfer, electrical coupling is provided as necessary between field effect transistors respectively formed in different triple well regions, and between a field effect transistor formed in a triple well region and a field effect transistor formed in a substrate region. However, a study conducted by the present inventors has revealed that, in a specified circuit, a dielectric breakdown due to a triple well structure occurs in the gate insulating film of a field effect transistor. As an effective method for preventing such a dielectric breakdown, a method can be considered which, e.g., provides electrical coupling between field effect transistors respectively formed in different triple well regions via a level shift circuit. However, the level shift circuit has been originally designed to provide coupling between regions with mutually different power supply voltages. When the level shift circuit is disposed for each signal line between regions each with the same power supply voltage, not only design is complicated, but also the level shift circuit occupies a partial region of a semiconductor device. Accordingly, the semiconductor is increased in size to cause a problem of higher product manufacturing cost or the like. 
     An object of the present invention is to provide a technology which allows improvements in manufacturing yield and product reliability in a semiconductor device having a triple well structure. 
     The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings. 
     As shown below, a brief description will be given of an embodiment of a representative aspect of the invention disclosed in the present application. 
     The embodiment (first method) is a semiconductor device having a deep n-type well formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the substrate, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the deep n-type well, an inverter circuit including an n-channel field effect transistor formed in the first shallow p-type well in the substrate and a p-channel field effect transistor formed in the second shallow n-type well in the substrate, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the deep n-type well. In a region different from the respective regions where the deep n-type well, the first shallow p-type well, and the second shallow n-type well are formed, a shallow p-type well is formed. A p-type diffusion tap formed in the shallow p-type well is wired to a p-type diffusion tap formed in the third shallow p-type well using an interconnection in an n-th layer. The respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the deep n-type well are wired to the respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the substrate using an interconnection in an n-th or higher order layer. 
     Another embodiment (second method) is a semiconductor device having a deep n-type well formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the substrate, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the substrate, and an inverter circuit including an re-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the deep n-type well. In a region different from the respective regions where the deep n-type well, the first shallow p-type well, and the second shallow n-type well are formed, a shallow p-type well is formed. An n-type diffusion layer formed in the shallow p-type well is wired to an n-type diffusion tap formed in the fourth shallow n-type well using an interconnection in an n-th layer. The respective gate electrodes of the re-channel field effect transistor and the p-channel field effect transistor each formed in the deep n-type well are wired to the respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the substrate using an interconnection in an n-th or higher order layer. 
     Still another embodiment (third method) is a semiconductor device having a first deep n-type well and a second deep n-type well each formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the first deep n-type well, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the second deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the first deep n-type well, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the second deep n-type well. An n-type diffusion tap formed in the second shallow n-type well in the first deep n-type well is wired to an n-type diffusion tap formed in the fourth shallow n-type well in the second deep n-type well using an interconnection in an n-th layer. The respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the first deep n-type well are wired to the respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the second deep n-type well using an interconnection in an n-th or higher order layer. 
     Yet another embodiment (fourth method) is a semiconductor device having a first deep n-type well and a second deep n-type well each formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the first deep n-type well, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the second deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the first deep n-type well, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the second deep n-type well. A p-type diffusion tap formed in the first shallow n-type well in the first deep n-type well is wired to a p-type diffusion tap formed in the third shallow n-type well in the second deep n-type well using an interconnection in an n-th layer. The respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the first deep n-type well are wired to the respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the second deep n-type well using an interconnection in an n-th or higher order layer. 
     Still another embodiment (fifth method) is a semiconductor device having a first deep n-type well and a second deep n-type well each formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the first deep n-type well, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the second deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the first deep n-type well, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the second deep n-type well. The semiconductor device further includes a first diode including a sixth shallow p-type well and an n-type diffusion layer, and a second diode including a seventh shallow p-type well and an n-type diffusion layer in mutually different regions other than respective regions where the first and second deep n-type wells are formed. The n-type diffusion layer forming the first diode is wired to an n-type diffusion tap formed in the second shallow n-type well in the first deep n-type well using an interconnection in an n-th layer. The n-type diffusion layer forming the second diode is wired to an n-type diffusion tap formed in the fourth shallow n-type well in the second deep n-type well using the interconnection in the n-th layer. The respective drain electrodes of the re-channel field effect transistor and the p-channel field effect transistor each formed in the first deep n-type well are wired to the respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the second deep n-type well using an interconnection in an n-th or higher order layer. 
     Yet another embodiment (sixth method) is a semiconductor device having a first deep n-type well and a second deep n-type well each formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the first deep n-type well, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the second deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the first deep n-type well, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the second deep n-type well. A fifth shallow p-type well and a sixth shallow p-type well are formed in mutually different regions other than respective regions where the first and second deep n-type wells are formed. The semiconductor device further includes a diode including the sixth shallow p-type well and an n-type diffusion layer. A p-type diffusion tap formed in the fifth shallow p-type well is wired to a p-type diffusion tap formed in the third shallow p-type well in the second deep n-type well using an interconnection in an n-th layer. The n-type diffusion layer forming the diode is wired to an n-type diffusion tap formed in the second shallow n-type well in the first deep n-type well using the interconnection in the n-th layer. The respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the first deep n-type well are wired to the respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the second deep n-type well using an interconnection in an n-th or higher order layer. 
     Still another embodiment (seventh method) is a semiconductor device having a first deep n-type well and a second deep n-type well each formed in a p-type substrate, which includes a first shallow p-type well and a second shallow n-type well which are formed in mutually different regions in the first deep n-type well, a third shallow p-type well and a fourth shallow n-type well which are formed in mutually different regions in the second deep n-type well, an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the first shallow p-type well and the second shallow n-type well in the first deep n-type well, and an inverter circuit including an n-channel field effect transistor and a p-channel field effect transistor which are respectively formed in the third shallow p-type well and the fourth shallow n-type well in the second deep n-type well. A first bidirectional diode and a second bidirectional diode are formed in mutually different regions other than respective regions where the first and second deep n-type wells are formed. A cathode of the first bidirectional diode, an anode of the second bidirectional diode, and an n-type diffusion tap formed in the fourth shallow n-type well are wired using an interconnection in an n-th layer. An anode of the first bidirectional diode, a cathode of the second bidirectional diode, and an n-type diffusion tap formed in the second shallow n-type well are wired using the interconnection in the n-th layer. The respective drain electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the first deep n-type well are wired to the respective gate electrodes of the n-channel field effect transistor and the p-channel field effect transistor each formed in the second deep n-type well using an interconnection in an n-th or higher order layer. 
     The following is a brief description of an effect achievable by the embodiment of the representative aspect of the invention disclosed in the present application. 
     In a semiconductor device having a triple well structure, a dielectric breakdown in the gate insulating film of a field effect transistor formed in a triple well region is prevented to allow improvements in manufacturing yield and product reliability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a structural view of a semiconductor device used by the present inventors for analysis; 
         FIG. 2(   a ) is a circuit diagram showing a first circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1 , and  FIG. 2(   b ) is a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model; 
         FIG. 3(   a ) is a circuit diagram showing a second circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1 , and  FIG. 3(   b ) is a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model; 
         FIG. 4(   a ) is a circuit diagram showing a third circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1 , and  FIG. 4(   b ) is a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model; 
         FIG. 5  is a circuit diagram illustrating a first example of a first method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a first embodiment; 
         FIG. 6  is a principal-portion cross-sectional view of a first circuit illustrating the first example of the first method shown in  FIG. 5  mentioned above; 
         FIG. 7  is a principal-portion plan view of the first circuit illustrating the first example of the first method shown in  FIG. 5  mentioned above; 
         FIG. 8  is a circuit diagram illustrating a second example of the first method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the first embodiment; 
         FIG. 9  is a principal-portion cross-sectional view of the first circuit illustrating the second example of the first method shown in  FIG. 8  mentioned above; 
         FIG. 10  is a principal-portion plan view of the first circuit illustrating the second example of the first method shown in  FIG. 8  mentioned above; 
         FIG. 11  is a circuit diagram illustrating a second method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a second embodiment; 
         FIG. 12  is a principal-portion cross-sectional view of a first circuit illustrating the second method shown in  FIG. 11  mentioned above; 
         FIGS. 13(   a ) and  13 ( b ) are principal-portion plan views of the first circuit illustrating the second method shown in  FIG. 11  mentioned above; 
         FIG. 14  is a circuit diagram illustrating a third method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a third embodiment; 
         FIG. 15  is a principal-portion cross-sectional view of a third circuit illustrating the third method shown in  FIG. 14  mentioned above; 
         FIG. 16  is a principal-portion plan view of the third circuit illustrating the third method shown in  FIG. 14  mentioned above; 
         FIG. 17  is a circuit diagram illustrating a first example of a fourth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a fourth embodiment; 
         FIG. 18  is a principal-portion cross-sectional view of a third circuit illustrating the first example of the fourth method shown in  FIG. 17  mentioned above; 
         FIG. 19  is a principal-portion plan view of the third circuit illustrating the first example of the fourth method shown in  FIG. 17  mentioned above; 
         FIG. 20  is a circuit diagram illustrating a second example of the fourth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the fourth embodiment; 
         FIG. 21  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the fourth method shown in  FIG. 20  mentioned above; 
         FIG. 22  is a principal-portion plan view of the third circuit illustrating the second example of the fourth method shown in  FIG. 20  mentioned above; 
         FIG. 23  is a circuit diagram illustrating a fifth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a fifth embodiment; 
         FIG. 24  is a principal-portion cross-sectional view of the third circuit illustrating the fifth method shown in  FIG. 23  mentioned above; 
         FIG. 25  is a principal-portion plan view of the third circuit illustrating the fifth method shown in  FIG. 23  mentioned above; 
         FIG. 26  is a circuit diagram illustrating a first example of a sixth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a sixth embodiment; 
         FIG. 27  is a principal-portion cross-sectional view of a third circuit illustrating the first example of the sixth method shown in  FIG. 26  mentioned above; 
         FIG. 28  is a principal-portion plan view of the third circuit illustrating the first example of the sixth method shown in  FIG. 26  mentioned above; 
         FIG. 29  is a circuit diagram illustrating a second example of the sixth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the sixth embodiment; 
         FIG. 30  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the sixth method shown in  FIG. 29  mentioned above; 
         FIG. 31  is a circuit diagram illustrating a first example of a seventh method for preventing a dielectric breakdown in the gate insulating film of a MIS according to a seventh embodiment; 
         FIG. 32  is a principal-portion cross-sectional view of a third circuit illustrating the first example of the seventh method shown in  FIG. 31  mentioned above; 
         FIG. 33  is a principal-portion plan view of the third circuit illustrating the first example of the seventh method shown in  FIG. 31  mentioned above; 
         FIG. 34  is a circuit diagram illustrating a second example of the seventh method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the seventh embodiment; 
         FIG. 35  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the seventh method shown in  FIG. 34  mentioned above; and 
         FIG. 36  is a principal-portion plan view of the third circuit illustrating the second example of the seventh method shown in  FIG. 34  mentioned above. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     If necessary for the sake of convenience, each of the following embodiments will be described hereinbelow by dividing it into a plurality of sections or implementations. However, they are by no means irrelevant to each other unless shown particularly explicitly, and are mutually related to each other such that one of the sections or implementations is a variation or a detailed or complementary description of some or all of the others. 
     When the number and the like of elements (including the number, numerical value, amount, and range thereof) are referred to in the following embodiments, they are not limited to specific numbers unless shown particularly explicitly or unless they are obviously limited to specific numbers in principle. The number and the like of the elements may be not less than or not more than specific numbers. It will be easily appreciated that, in the following embodiments, the components thereof (including also elements and steps) are not necessarily indispensable unless shown particularly explicitly or unless the components are considered to be obviously indispensable in principle. Likewise, if the configurations, positional relationship, and the like of the components and the like are referred to in the following embodiments, the configurations and the like are assumed to include those substantially proximate or similar thereto unless shown particularly explicitly or unless obviously they are not in principle. The same shall apply to the foregoing numeric value and the range. 
     In the drawings used in the following embodiments, even plan views may be hatched for clear illustration of the drawings. In the following embodiments, a MISFET (Metal Insulator Semiconductor Field Effect Transistor) representing a field effect transistor will be referred to as a MIS for short, a p-channel MISFET will be referred to as a pMIS for short, and an n-channel MISFET will be referred to as an nMIS for short. In the following embodiments, when a wafer is mentioned, it typically indicates a Si (Silicon) monocrystalline wafer, but it is not limited thereto. It is assumed that the term “wafer” also indicates a SOI (Silicon On Insulator) wafer, an insulating film substrate for forming an integrated circuit thereon, or the like. It is also assumed that the shapes of wafers are not limited to circular or generally circular shapes, and include a square shape, a rectangular shape, and the like. 
     In the following embodiments, the wording “deep well” and “shallow well” are used to describe wells forming a triple well structure. The wording “deep and shallow” is associated with a depth from the principal surface of a substrate in the thickness direction thereof, and wells are to be relatively and generally classified into the two categories of the “deep well” and the “shallow well”. Accordingly, the depths of a plurality of the “deep wells” are not necessarily constant, and may be different from each other. Likewise, the depths of a plurality of the “shallow wells” are not necessarily constant, and may be different from each other. However, the plurality of “deep wells” are constantly formed deeper than the plurality of “shallow wells”. The “shallow well” is formed in a substrate or in the “deep well”, and the plurality of “shallow wells” may also be formed in mutually different regions in the substrate where the “deep well” is not formed, or in mutually different regions in the “deep well”. 
     Throughout the drawings for illustrating the following embodiments, components having the same functions will be provided with the same reference numerals in principle, and a repeated description thereof will be omitted. Hereinbelow, the embodiments of the present invention will be described in detail with reference to the drawings. 
     First, for clearer understanding of the semiconductor devices according to the embodiments of the present invention, a description will be given of the cause of a dielectric breakdown in the gate insulating film of a MIS formed in a triple well region, which has been found by the present inventors. 
     As a result of a study conducted by the present inventors, it has been revealed that, when coupling holes for coupling a lower-layer interconnection and an upper-layer interconnection are formed in an insulating film formed between the lower-layer interconnection and the upper-layer interconnection, a dielectric breakdown occurs in the gate insulating film of a MIS formed in a triple well region. Because the coupling holes have been formed by a dry etching method using plasma discharge, it is presumed that the dielectric breakdown has occurred due to charging resulting from the plasma discharge. It has been further revealed that a deep well forming the triple well region is charged by the plasma discharge, and the dielectric breakdown has occurred in the gate insulating film of a MIS which intervenes a path extending from the deep well to a substrate. In particular, when the deep well occupies a large area of, e.g., 1 mm 2  or more, the occurrence of the dielectric breakdown has been frequently observed. The mechanism of the occurrence of a dielectric breakdown in the gate insulating film of a MIS due to charging resulting from plasma discharge is described in detail in “Plasma Charging Damage in Advanced VLSI Technology” by C. Cheung, 1998 IEDM Short Course and in “Plasma Currents, Voltages and Chargin” by J. McVittle, 1997 2nd International Symposium on Plasma Process-Induced Damage, Tutorial. 
     Referring to  FIGS. 1 to 4 , a specific description will be given of the result of analyzing a dielectric breakdown in the gate insulating film of a MIS formed in a triple well region, which has been obtained by the present inventors.  FIG. 1  is a structural view of a semiconductor device used by the present inventors for analysis.  FIG. 2(   a ) is a circuit diagram showing a first circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1  and  FIG. 2(   b ) is a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model.  FIG. 3(   a ) is a circuit diagram showing a second circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1 , and  FIG. 3(   b ) is a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model.  FIG. 4(   a ) is a circuit diagram showing a third circuit in which a dielectric breakdown occurs in the gate insulating film of a MIS in a circuit portion forming the semiconductor device of  FIG. 1 , and  FIG. 4(   b ) a principal-portion cross-sectional view of circuit elements for illustrating a dielectric breakdown model. 
     As shown in  FIG. 1 , a semiconductor device  1  has first regions (regions surrounded by the double solid frame lines in  FIG. 1 ) where a shallow n-type well and a shallow p-type well are formed in mutually different regions in a substrate, and respective circuit elements are formed in the shallow n-type well and the shallow p-type well, and second regions (regions surrounded by the dotted frame lines in  FIG. 1 ) where a deep n-type well is formed in a substrate, a shallow n-type well and a shallow p-type well are respectively formed in mutually different regions in the deep n-type well, and respective circuit elements are formed in the shallow n-type well and the shallow p-type well. 
     Examples of the first regions mentioned above include an I/O region  2  and a control logic region  3 . Examples of the second regions mentioned above include an analog  1  region  4 , a phase synchronization circuit region  5 , an analog  2  region  6 , an analog  2  control region  7 , and a main logic region  8 . In the main logic region  8 , a CPU (Central Processing Unit)  9 , a DSP (Digital Signal Processor)  10 , a RAM (Random Access Memory)  11 , or the like are mounted by way of example. In the peripheral region of the semiconductor device  1 , a plurality of bonding pads BP are formed. 
     The circuit elements mentioned above are, e.g., MIS transistors, and an example of signal transfer between individual MIS transistors is shown by the bidirectional arrow in the drawing. Signal transfer is performed not only between individual MIS transistors formed in the first regions or between individual MIS transistors formed in the second region, but also between a MIS transistor formed in the first region and a MIS transistor formed in the second transistor or between a MIS transistor formed in the second region and a MIS transistor formed in another second region different from the second region mentioned above. 
     The present inventors have manufactured the above-mentioned semiconductor device  1  having the triple well structure, performed a functional test thereon, and recognized a dielectric breakdown in the gate insulating film of a MIS in a specified circuit. For example, the dielectric breakdown in the gate insulating film of a MIS has been recognized in each of the first circuit ( 1 ) in which the output stage of an inverter circuit formed in the first region is wired to the common gate electrode of an inverter circuit formed in the second region, a second circuit ( 2 ) in which the common gate electrode of the inverter circuit formed in the first region is wired to the output stage of the inverter circuit formed in the second region, and the third circuit ( 3 ) in which the output stage of the inverter circuit formed in the second region is coupled to the common gate electrode of an inverter circuit formed in another second region different from the second region mentioned above. An inverter circuit is a circuit including a pair of a pMIS and an nMIS in which the respective gate electrodes of the pair of a pMIS and an nMIS are coupled, the respective drain electrodes thereof are coupled, the source electrode of the pMIS is coupled to an n-type well formed with the pMIS transistor, and the source electrode of the nMIS is coupled to a p-type well formed with the nMIS. 
     Hereinbelow, a description will be given of a dielectric breakdown model in the gate insulating film of a MIS transistor in each of the foregoing first, second, and third circuits in which the dielectric breakdown has been recognized in the gate insulating film of the MIS transistor. 
     (1) As shown in  FIG. 2(   a ), the first circuit in which the output stage of the inverter circuit formed in the first region is wired to the common gate electrode of the inverter formed in the second region includes an inverter circuit INV formed in a substrate Sub, and an inverter circuit INV 0  formed in a deep n-type well DNW 0 . 
     In the p-type substrate Sub, a shallow n-type well NW and a shallow p-type well PW are formed, while in the shallow n-type well NW, a pMIS  100   p  is further formed. In the shallow p-type well PW, an nMIS  100   n  is further formed. The pMIS  100   p  and the nMIS  100   n  form the inverter circuit INV. In the deep n-type well DNW 0 , a shallow n-type well NW 0  and a shallow p-type well PW 0  are formed. In the shallow n-type well NW 0 , a pMIS  200   p  is further formed, while in the shallow p-type well PW 0 , an nMIS  200   n  is further formed. The pMIS  200   p  and the nMIS  200   n  form the inverter circuit INV 0 . 
     The respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are electrically coupled to the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV. As a result of the functional test conducted by the present inventors, it has been recognized that a dielectric breakdown has occurred in the gate insulating film of the pMIS  200   p  or the nMIS  200   n  forming the inverter circuit INV 0 . 
     Referring to  FIG. 2(   b ), a description will be given of the mechanism of the occurrence of a dielectric breakdown in the gate insulating film of the pMIS  200   p  or the nMIS  200   n  forming the inverter circuit INV 0 . 
     For example, when positive charge flows into the shallow n-type well NW 0  in the deep n-type well DNW 0  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when coupling holes are formed in an interlayer insulating film formed over an interconnection, the positive charge that has flown into the shallow n-type well NW 0  is accumulated in the deep n-type well DNW 0  and in the shallow n-type well NW 0  because the deep n-type well DNW 0  is not electrically coupled to the substrate Sub. 
     On the other hand, since the gate electrode of the nMIS  100   n  formed in the shallow p-type well PW in the substrate Sub is in a floating state, the nMIS  100   n  is brought into a conducting state so that a path is formed which extends from the substrate Sub to the gate electrode of the pMIS  200   p  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  via the shallow p-type well PW, a p-type diffusion tap PD, the nMIS  100   n  (the source electrode Sn thereof, the channel region thereof, and the drain electrode Dn thereof), and the interconnection. As a result, the potential of the gate electrode of the pMIS  200   o  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  becomes equal to the potential (0 V) of the substrate Sub. Therefore, it is presumed that the voltage applied to the gate insulating film of the pMIS  200   p  increases to cause a dielectric breakdown (the path I indicated by the dotted line in  FIG. 2(   b )). 
     For example, when negative charge flows into the shallow p-type well PW 0  in the deep n-type well DNW 0  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when coupling holes are formed in the interlayer insulating film formed over the interconnection, the negative charge that has flown into the shallow p-type well PW 0  is accumulated therein because the shallow p-type well PW 0  is formed in the deep n-type well DNW 0 , and the deep n-type well DNW 0  is not electrically coupled to the substrate Sub. 
     By contrast, even when negative charge flows into the shallow p-type well PW in the substrate Sub, the negative charge that has flown into the shallow p-type well PW is discharged to the substrate Sub since the shallow p-type well PW has the same conductivity type as that of the substrate Sub. As a result, the potential of the gate electrode of the nMIS  200   n  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  becomes equal to the potential (0 V) of the substrate Sub. Therefore, it is presumed that the voltage applied to the gate insulating film of the nMIS  200   n  increases to cause a dielectric breakdown (the path II indicated by the dotted line in  FIG. 2(   b )). 
     (2) As shown in  FIG. 3(   a ), the second circuit in which the common gate electrode of the inverter circuit formed in the first region is wired to the output stage of the inverter circuit formed in the second region includes the inverter circuit INV formed in the substrate Sub, and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . 
     In the p-type substrate Sub, the shallow n-type well NW and the shallow p-type well PW are formed. In the shallow n-type well NW, the pMIS  100   p  is further formed, while in the shallow p-type well PW, the nMIS  100   n  is further formed. The pMIS  100   p  and the nMIS  100   n  form the inverter circuit INV. In the deep n-type well DNW 0 , the shallow n-type well NW 0  and the shallow p-type well PW 0  are formed. In the shallow n-type well NW 0 , the pMIS  200   p  is further formed. In the shallow p-type well PW 0 , the nMIS  200   n  is further formed. The pMIS  200   p  and the nMIS  200   n  form the inverter circuit INV 0 . 
     The respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . As a result of the functional test conducted by the present inventors, it has been recognized that a dielectric breakdown has occurred in the gate insulating film of the pMIS  100   p  or the nMIS  100   n  forming the inverter circuit INV. 
     Referring to  FIG. 3(   b ), a description will be given of the mechanism of the occurrence of a dielectric breakdown in the gate insulating film of the pMIS  100   p  or the nMIS  100   n  forming the inverter circuit INV. 
     For example, when positive charge flows into the shallow n-type well NW 0  in the deep n-type well DNW 0  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when a coupling hole is formed in the interlayer insulating film formed over the interconnection, the positive charge that has flown into the shallow n-type well NW 0  is accumulated in the deep n-type well DNW 0  and in the shallow n-type well NW 0  because the deep n-type well DNW 0  is not electrically coupled to the substrate Sub. Since the gate electrode of the pMIS  200   p  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  is in a floating state, the pMIS  200   p  is brought into a conducting state so that a path is formed which extends from the deep n-type well DNW 0  to the gate electrode of the nMIS  100   n  formed in the shallow p-type well PW in the substrate Sub via the shallow n-type well NW 0 , an n-type diffusion tap ND 0 , the pMIS  200   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), and the interconnection. 
     On the other hand, since the shallow p-type well PW in the substrate Sub has the same conductivity type as that of the substrate Sub, the potential of the shallow p-type well PW becomes equal to the potential (0 V) of the substrate Sub. Therefore, it is presumed that the voltage applied to the gate insulating film of the nMIS  100   n  formed in the shallow p-type well PW in the substrate Sub increases to cause a dielectric breakdown (the path III indicated by the dotted line in  FIG. 3(   b )). 
     For example, when negative charge flows into the shallow p-type well PW 0  formed in the deep n-type well DNW 0  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when coupling holes are formed in the interlayer insulating film formed over an interconnection, the negative charge that has flown into the shallow p-type well PW 0  is accumulated therein because the shallow p-type well PW 0  is formed in the deep n-type well DNW 0 , and the deep n-type well DNW 0  is not electrically coupled to the substrate Sub. 
     By contrast, even when negative charge flows into the shallow p-type well PW in the substrate Sub, the negative charge that has flown into the shallow p-type well PW 0  is discharged to the substrate Sub since the shallow p-type well PW has the same conductivity type as that of the substrate Sub. It is to be noted that, when the inverter circuits each including the pMIS and the nMIS which are respectively formed in the shallow n-type well and the shallow p-type well in the substrate include one in which the respective gate electrodes of the pMIS and the nMIS are wired to each other and in a floating state, a low-resistance conducting state is established between the foregoing shallow n-type well and the foregoing shallow p-type well which are formed in mutually different regions, though the description thereof using the drawings is omitted herein. Accordingly, when such an inverter circuit is present in the substrate Sub shown in  FIGS. 3(   a ) and  3 ( b ), the low-resistance conducting state is established between the shallow n-type well NW and the shallow p-type well PW each formed in the substrate Sub so that the respective potentials of the shallow n-type well NW and the shallow p-type well PW each formed in the substrate Sub become equal to the potential (0 V) of the substrate Sub. As a result, it is presumed that the voltage applied to each of the gate insulating films of the pMIS  100   p  and the nMIS  100   p  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub increases to cause a dielectric breakdown (the line IV indicated by the dotted line in  FIG. 3(   b )). 
     (3) As shown in  FIG. 4(   a ), the third circuit in which the output stage of the inverter circuit formed in the second region is wired to the common gate electrode of the inverter formed in another second region different from the second region mentioned above includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and an inverter circuit INV 1  formed in a deep n-type well DNW 1 . 
     In the deep n-type well DNW 0 , the shallow n-type well NW 0  and the shallow p-type well PW 0  are formed. In the shallow n-type well NW 0 , the pMIS  200   p  is further formed, while in the shallow p-type well PW 0 , the nMIS  200   n  is further formed. The area occupied by the deep n-type well DNW 0  is relatively small, and less than, e.g., 1 mm 2 . The pMIS  200   p  and the nMIS  200   n  form the inverter circuit INV 0 . In the deep n-type well DNW 1 , a shallow n-type well NW 1  and a shallow p-type well PW 1  are formed. In the shallow n-type well NW 1 , a pMIS  300   p  is further formed, while in the shallow p-type well PW 1 , an nMIS  300   n  is further formed. The area occupied by the deep n-type well DNW 1  is relatively large, and is not less than, e.g., 1 mm 2 . The pMIS  300   p  and the nMIS  300   n  form the inverter circuit INV 1 . 
     The respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are electrically coupled to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 . As a result of the functional test conducted by the present inventors, it has been recognized that a dielectric breakdown has occurred in the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 . A dielectric breakdown is likely to occur in the gate insulating film of each of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1  which occupies an area of not less than 1 mm 2 . 
     Referring to  FIG. 4(   b ), a description will be given of the mechanism of the occurrence of a dielectric breakdown in the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 . 
     For example, when positive charge flows into the shallow n-type well NW 1  in the deep n-type well DNW 1  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when coupling holes are formed in the interlayer insulating film formed over the interconnection, the positive charge that has flown into the shallow n-type well NW 1  is accumulated in the deep n-type well DNW 1  and in the shallow n-type well NW 1  because the deep n-type well DNW 1  is not electrically coupled to the substrate Sub. 
     By contrast, when positive charge flows into the shallow n-type well NW 0  in the deep n-type well DNW 0 , the positive charge that has flown in the shallow n-type well NW 0  is accumulated in the deep n-type well DNW 0  and in the shallow n-type well NW 0  because the deep n-type well DNW 0  is not electrically coupled to the substrate Sub. However, since the area occupied by the deep n-type well DNW 0  is smaller than the area occupied by the deep n-type well DNW 1 , the amount of charge accumulated in the deep n-type well DNW 0  is smaller than the amount of charge accumulated in the deep n-type well DNW 1 . Accordingly, the amount of charge charging the gate electrode of the pMIS  300   p  in order to couple the drain electrode of the pMIS  200   p  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  to the gate electrode of the pMIS  300   p  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1  is different from the amount of charge charging the shallow n-type well NW 1  in the deep n-type well DNW 1 . Therefore, it is presumed that the voltage applied to the gate insulating film of the pMIS  300   p  formed in the shallow n-type well NW 1  increases to cause a dielectric breakdown (the path V indicated by the dotted line in  FIG. 4(   b )). 
     For example, when negative charge flows into the shallow p-type well PW 1  in the deep n-type well DNW 1  during manufacturing thereof due to plasma discharge associated with a dry etching method which is implemented when coupling holes are formed in the interlayer insulating film formed over the interconnection, the negative charge that has flown in the shallow p-type well PW 1  is accumulated therein because the shallow p-type well PW 1  is formed in the deep n-type well DNW 1 , and the deep n-type well DNW 1  is not electrically coupled to the substrate Sub. On the other hand, negative charge that has flown in the shallow p-type well PW 0  in the deep n-type well DNW 0  is likewise accumulated in the shallow p-type well PW 0  in the deep n-type well DNW 0 . However, the area occupied by the p-type well PW 0  is smaller than the area occupied by the p-type well PW 1  so that the amount of charge accumulated in the p-type well PW 1  is larger than the amount of charge accumulated in the p-type well PW 0 . For example, because the gate electrode of the pMIS  200   p  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  is in a floating state, the pMIS  200   p  is brought into a conducting state so that a path is formed which extends from the deep n-type well DNW 0  to the gate electrode of the nMIS  300   n  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  via the shallow n-type well NW 0 , the n-type diffusion tap ND 0 , the pMIS  200   n  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), and the interconnection. As a result, it is presumed that the voltage applied to the gate insulating film of the nMIS  300   n  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  increases to cause a dielectric breakdown (the path VI indicated by the dotted line in  FIG. 4(   b )). 
     The present inventors have verified that a dielectric breakdown occurs in the gate insulating film of a MIS not only in the first, second, and third circuits described above, but also in a fourth circuit in which, e.g., the common gate electrode of an inverter circuit formed in a deep n-type well is wired to the drain electrode of a MIS formed in the substrate and in a fifth circuit in which the output stage of an inverter circuit formed in a deep n-type well is wired to the gate electrode of a MIS formed in the deep n-type well. In each of the fourth and fifth circuits, a dielectric breakdown in the gate insulating film of a MIS can be prevented by, e.g., disposing an inverter circuit which does not contribute to a circuit operation in the deep n-type well, wiring a shallow p-type well to the substrate using a lowermost-layer interconnection, wiring the common gate electrode to a shallow n-type well using an uppermost-layer interconnection, and discharging charge accumulated in the deep n-type well. As for a method for preventing a dielectric breakdown in the gate insulating film of a MIS in the fourth and fifth circuits, it is disclosed in Japanese Patent Application No. 2008-6436 (filed by Hiraiwa, et al. on Jan. 16, 2008). 
     According to the result of the analysis described heretofore, in preventing a dielectric breakdown in the gate insulating film of a MIS, it is effective to reduce the voltage applied to the gate insulating film of the MIS to a value of not more than the dielectric breakdown voltage of the gate insulating film of the MIS, or eliminate the potential difference between deep wells formed in mutually different regions. Hereinbelow, a detailed description will be given of the method for preventing a dielectric breakdown in the gate insulating film of a MIS in the embodiments of the present invention. 
     Embodiment 1 
     In the present first embodiment, a description will be given of two examples (first and second examples) of a first method for preventing a dielectric breakdown in the gate insulating film of a MIS in each of the foregoing first circuit ( FIGS. 2(   a ) and  2 ( b ) mentioned above) and the foregoing second circuit ( FIGS. 3(   a ) and  3 ( b ) mentioned above). First, the first example of the first method will be described with reference to  FIGS. 5 to 7 , and then the second example of the first method will be described with reference to  FIGS. 8 to 10 .  FIG. 5  is a circuit diagram illustrating the first example of the first method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present first embodiment.  FIG. 6  is a principal-portion cross-sectional view of the first circuit illustrating the first example of the first method shown in  FIG. 5  mentioned above.  FIG. 7  is a principal-portion plan view of the first circuit illustrating the first example of the first method shown in  FIG. 5  mentioned above.  FIG. 8  is a circuit diagram illustrating the second example of the first method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present first embodiment.  FIG. 9  is a principal-portion cross-sectional view of the first circuit illustrating the second example of the first method shown in  FIG. 8  mentioned above.  FIG. 10  is a principal-portion plan view of the first circuit illustrating the second example of the first method shown in  FIG. 8  mentioned above. 
     First, the first example of the first method will be described. 
     As described above, the first circuit ( FIGS. 2(   a ) and  2 ( b ) mentioned above) includes the inverter circuit INV formed in the substrate Sub, and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . The respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are electrically coupled to the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV. In the gate insulating film of the pMIS  200   p  or the nMIS  200   n  forming the inverter circuit INV 0 , a dielectric breakdown has occurred. 
     On the other hand, as described above, the second circuit ( FIGS. 3(   a ) and  3 ( b ) mentioned above) includes the inverter circuit INV formed in the substrate Sub, and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . The respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  100   p  or the nMIS  100   n  forming the inverter circuit INV, a dielectric breakdown has occurred. 
     As shown in  FIG. 5 , in the first example of the first method according to the present first embodiment, a shallow p-type well PW 100  is formed in the substrate Sub, and a p-type diffusion tap PD 100  for potential fixation is formed in the shallow p-type well PW 100 . The p-type diffusion tap PD 100  is coupled to a p-type diffusion tap PD 0  for potential fixation which is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0 , i.e., the wiring of the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective gate electrodes of the pMIS  200   p  and the nMIS  200   p  which form the inverter circuit INV 0 , and the wiring of the respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are performed using an interconnection in the same layer as that of the interconnection used to wire the p-type diffusion tap PD 100  to the p-type diffusion tap PD 0 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the p-type diffusion tap PD 100  to the p-type diffusion tap PD 0  is performed using an interconnection in a second layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the p-type diffusion tap PD 100  to the p-type diffusion tap PD 0  is performed using an interconnection in a third layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 6 , in the first circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV and the respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ), a parasitic pn diode is formed by the wiring of the p-type diffusion tap PD 100  to the p-type diffusion tap PD 0 . The parasitic pn diode forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 100 , the p-type diffusion tap PD 100 , the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     In the first circuit, in a manufacturing step of forming the coupling holes for coupling the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV formed in the substrate Sub, the gate electrode of the pMIS  200   p  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  is brought into a floating state to bring the pMIS  200   p  into a conducting state. As a result, a discharge path is formed which extends from the deep n-type well DNW 0  to the substrate Sub via the shallow n-type well NW 0 , the n-type diffusion tap ND 0 , the pMIS  200   p  (the source electrode Sp thereof, the channel region thereof, and the drain region Dp thereof), the shallow p-type well PW 0 , the p-type diffusion tap PD 0 , the interconnection, the p-type diffusion tap PD 100 , and the shallow p-type well PW 100 . 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0 . 
     In the second circuit (circuit in which the respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV are wired to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ) also, the same effect as obtained in the first circuit described above can be obtained, though the description thereof is omitted herein. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  100   p  and the nMIS  100   n  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub. 
       FIG. 7  shows a principal-portion plan view of the p-type diffusion tap PD 100  formed in the substrate Sub and the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 . 
     In the shallow p-type well PW 100  in the substrate Sub, the p-type diffusion tap PD 100  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub, coupling holes CNT 1  are formed to reach the p-type diffusion tap PD 100 . Likewise, in the shallow p-type well PW 0  in the deep n-type well DNW 0 , the p-type diffusion tap PD 0  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub (deep n-type well DNW 0 ), the coupling holes CNT 1  are formed to reach the p-type diffusion tap PD 0 . There is also formed an interconnection M 1  in a first layer which is electrically coupled to the p-type diffusion tap PD 100  or the p-type diffusion tap PD 0  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 100  formed in the shallow p-type well PW 100  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 . The p-type diffusion tap PD 100  formed in the shallow p-type well PW 100  in the substrate Sub is electrically coupled to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  using an interconnection M 2  in the second layer. 
     Next, the second example of the first method will be described. 
     In the second example of the first method also, a description is given of the method for preventing a dielectric breakdown in the gate insulating film of the pMIS  200   p  or the nMIS  200   n  forming the inverter circuit INV 0 , which occurs in the first circuit ( FIGS. 2(   a ) and  2 ( b ) mentioned above), and a dielectric breakdown in the gate insulating of the pMIS  100   p  or the nMIS  100   n  forming the inverter circuit INV, which occurs in the second circuit ( FIGS. 3(   a ) and  3 ( b ) mentioned above), in the same manner as in the first example of the first method described above. The first and second examples of the first method are different in that, in the first example, the shallow p-type well PW 100  is formed in the substrate Sub, and the p-type diffusion tap PD 100  which is electrically coupled to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  is formed in the shallow p-type well PW 100 , while in the second example, the p-type diffusion tap PD for potential fixation which is formed in the shallow p-type well PW in the substrate Sub is used also as a p-type diffusion tap for discharging accumulated charge. 
     As shown in  FIG. 8 , in the second example of the first method according to the present first embodiment, the p-type diffusion tap PD for potential fixation is formed in the shallow p-type well PW in the substrate Sub where the nMIS  100   n  is formed, while the p-type diffusion tap PD 0  for potential fixation is formed in the shallow p-type well NW 0  in the deep n-type well DNW 0  where the nMIS  200   n  is formed. The p-type diffusion tap PD is further coupled to the p-type diffusion tap PD 0  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0 , i.e., the wiring of the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 , and the wiring of the respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are performed using the interconnection in the same layer as that of the interconnection used to wire the p-type diffusion tap PD to the p-type diffusion tap PD 0 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the p-type diffusion tap PD to the p-type diffusion tap PD 0  is performed using the interconnection in the second layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the p-type diffusion tap PD to the p-type diffusion tap PD 0  is performed using the interconnection in the third layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 9 , in the first circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV and the respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ), a parasitic pn diode is formed by the wiring of the p-type diffusion tap PD to the p-type diffusion tap PD 0 . The parasitic pn diode forms a discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW, the p-type diffusion tap PD, the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     In the first circuit, in the manufacturing step of forming the coupling holes for coupling the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0 , the respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0  are each brought into a floating state to bring each of the pMIS  200   p  and the nMIS  200   n  into a conducting state. As a result, a discharge path is formed which extends from the deep n-type well DNW 0  to the substrate Sub via the shallow n-type well NW 0 , the n-type diffusion tap ND 0 , the pMIS  200   p  (the source electrode Sp thereof, the channel region thereof, and the drain region Dp thereof), the nMIS  200   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD, and the shallow p-type well WP. 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0 . 
     It is to be noted that a parasitic diode Di is present between the shallow p-type well PW formed in the substrate Sub and the source electrode Sn of the nMIS  100   n  formed in the shallow p-type well PW. However, since the substrate Sub, the shallow p-type well PW, and the p-type diffusion tap DP are all p-type semiconductor regions, it is considered that the discharge path extending from the substrate Sub through the shallow p-type well PW and the p-type diffusion tap DP is more dominant than the parasitic diode Di. 
     In the second circuit (circuit in which the respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV are wired to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ) also, the same effect as obtained in the first circuit described above can be obtained, though the description thereof is omitted herein. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  100   p  and the nMIS  100   n  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub. 
       FIG. 10  shows a principal-portion plan view of the inverter circuit INV 0  formed in the substrate Sub and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . 
     In the shallow p-type well PW in the substrate Sub, the nMIS  100   n  is formed. The nMIS  100   n  includes n-type diffusion layers DIFn forming a source electrode and a drain electrode. On the other hand, in the shallow n-type well NW in the substrate Sub, the pMIS  100   p  is formed. The pMIS  100   p  includes p-type diffusion layers DIFp forming a source electrode and a drain electrode. In the interlayer insulating film (not shown) over the substrate Sub, the coupling holes CNT 1  are formed in contact with the drain electrode (n-type diffusion layer DIFn) of the nMIS  100   n  or with the drain electrode (p-type diffusion layer DIFp) of the pMIS  100   p . Through the coupling holes CNT 1 , the respective drain electrodes of the nMIS  100   n  and the pMIS  100   p  are electrically coupled via the interconnection M 1  in the first layer. 
     In the shallow n-type well NW in the substrate Sub, an n-type diffusion tap ND is formed, while in the shallow p-type well PW, the p-type diffusion tap PD is formed. In the interlayer insulating film (not shown) over the substrate Sub, the coupling holes CNT 1  are formed in contact with the n-type diffusion tap ND or with the source electrode (p-type diffusion layer DIFp) of the pMIS  100   p . Through the coupling holes CNT 1 , the n-type diffusion tap ND and the source electrode of the pMIS  100   p  are electrically coupled via the interconnection in the first layer. The gate electrode of the nMIS  100   n  and the gate electrode of the pMIS  100   p  are formed of a conductive film in the same common layer. Through the coupling holes CNT 1  formed in the interlayer insulating film (not shown) formed over the substrate Sub, the interconnection M 1  in the first layer is electrically coupled to the conductive film. 
     Likewise, in the shallow p-type well PW 0  in the deep n-type well DNW 0 , the nMIS  200   n  is formed. The nMIS  200   n  includes the n-type diffusion layers DIFn forming a source electrode and a drain electrode. On the other hand, in the shallow n-type well NW in the deep n-type well DNW 0 , the pMIS  200   p  is formed. The pMIS  200   p  includes the p-type diffusion layers DIFp forming a source electrode and a drain electrode. In the interlayer insulating film (not shown) over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed in contact with the drain electrode (n-type diffusion layer DIFn) of the nMIS  200   n  or with the drain electrode (p-type diffusion layer DIFp) of the pMIS  200   p . Through the coupling holes CNT 1 , the respective drain electrodes of the nMIS  200   n  and the pMIS  200   p  are electrically coupling via the interconnection M 1  in the first layer. 
     In the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed, while in the shallow p-type well PW 0 , the p-type diffusion tap PD 0  is formed. In the interlayer insulating film (not shown) over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed in contact with the n-type diffusion tap ND 0  or with the source electrode (p-type diffusion layer DIFp) of the pMIS  200   p . Through the coupling holes CNT 1 , the n-type diffusion tap ND 0  and the source electrode of the pMIS  200   p  are electrically coupled via the interconnection M 1  in the first layer. The gate electrode of the nMIS  200   n  and the gate electrode of the pMIS  200   p  are formed of a conductive film in the same common layer. Through the coupling holes CNT 1  formed in the interlayer insulating film (not shown) formed over the substrate Sub, the interconnection M 1  in the first layer is electrically coupled to the conductive film. 
     There are further formed the interconnection M 1  in the first layer which is electrically coupled to the common gate electrode of the pMIS  100   p  and the nMIS  100   n  each formed in the substrate Sub through the coupling holes CNT 1 , and the interconnection M 1  in the first layer which is electrically coupled to each of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  each formed in the deep n-type well DNW 0  through the coupling holes CNT 1 . Additionally, the coupling holes CNT 2  are formed in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnections M 1  in the first layer. Through the coupling holes CNT 2 , the interconnection in the first layer which is electrically coupled to the common gate electrode of the pMIS  100   p  and the nMIS  100   p  is electrically coupled to the interconnection M 1  in the first layer which is electrically coupled to each of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  via the interconnection M 2  in the second layer. 
     To the p-type diffusion tap PD formed in the shallow p-type well PW in the substrate Sub or to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 , the interconnections M 1  in the first layer are electrically coupled through the coupling holes CNT 1 . In the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnections M 1  in the first layer, the coupling holes CNT 2  are formed. Through the coupling holes CNT 2 , the p-type diffusion taps PD and PD 0  are electrically coupled via the interconnection M 2  in the second layer. 
     In the present first embodiment, it is assumed that the p-type diffusion taps PD and PD 100  are wired to the p-type diffusion tap PD 0  using an interconnection in a second or higher order layer. This is because, since an interconnection in a first layer is generally used as a signal interconnection, it is difficult to couple the p-type diffusion taps PD and PD 100  to the p-type diffusion tap PD 0  using the interconnection in the first layer. Therefore, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used to wire the p-type diffusion taps PD and PD 100  to the p-type diffusion tap PD 0 . 
     Thus, according to the present first embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  due to a plasma charge-up phenomenon in, e.g., a dry etching step, the charge can be easily discharged to the substrate Sub. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow n-type well PW 0  in the deep n-type well DNW 0  to form the inverter circuit INV 0 , and a dielectric breakdown in each of the gate insulating films of the pMIS  100   p  and the nMIS  100   n  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub to form the inverter circuit INV. In particular, when, e.g., the shallow p-type well PW formed in the substrate Sub and the shallow p-type well PW 0  formed in the deep n-type well DNW 0  are at the same potential, the first method in the present first embodiment serves as an effective means. 
     Embodiment 2 
     In the present second embodiment, a description will be given of a second method for preventing a dielectric breakdown in the gate insulating film of a MIS in each of the foregoing first circuit ( FIGS. 2(   a ) and  2 ( b ) mentioned above) and the foregoing second circuit ( FIGS. 3(   a ) and  3 ( b ) mentioned above) with reference to  FIGS. 11 to 13 .  FIG. 11  is a circuit diagram illustrating the second method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present second embodiment.  FIG. 12  is a principal-portion cross-sectional view of the first circuit illustrating the second method shown in  FIG. 11  mentioned above.  FIGS. 13(   a ) and  13 ( b ) are principal-portion plan views of the first circuit illustrating the second method shown in  FIG. 11  mentioned above. 
     As described above, the first circuit ( FIGS. 2(   a ) and  2 ( b ) mentioned above) includes the inverter circuit INV formed in the substrate Sub, and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . The respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are electrically coupled to the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV. In the gate insulating film of the pMIS  200   p  or the nMIS  200   n  which form the inverter circuit INV 0 , a dielectric breakdown has occurred. 
     On the other hand, as described above, the second circuit ( FIGS. 3(   a ) and  3 ( b ) mentioned above) includes the inverter circuit INV formed in the substrate Sub, and the inverter circuit INV 0  formed in the deep n-type well DNW 0 . The respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  100   p  or the nMIS  100   n  forming the inverter circuit INV, a dielectric breakdown has occurred. 
     As shown in  FIG. 11 , in the second method according to the present second embodiment, a shallow p-type well PW 200  in the substrate Sub and an n-type diffusion layer in the shallow p-type well PW 200  form a pn diode Di 200 . The cathode of the pn diode Di 200  and the n-type diffusion tap ND 0  for potential fixation which is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  are coupled using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0 , i.e., the wiring of the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective gate electrodes of the pMIS  200   p  and the nMIS  200  which form the inverter circuit INV 0 , and the wiring of the respective gate electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  are performed using an interconnection in the same layer as that of the interconnection used to wire the n-type diffusion layer of the pn diode Di 200  to the n-type diffusion tap ND 0 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the n-type diffusion layer of the pn diode Di 200  to the n-type diffusion tap ND 0  is performed using the interconnection in the second layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the n-type diffusion layer of the pn diode Di 200  to the n-type diffusion tap ND 0  is performed using the interconnection in the third layer, the wiring of the inverter circuit INV formed in the substrate Sub to the inverter circuit INV 0  formed in the deep n-type well DNW 0  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 12 , in the first circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  100   p  and the nMIS  100   n  which form the inverter circuit INV and the respective gate electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ), when the potential of the substrate Sub is higher than the potential of the deep n-type well DNW 0 , the pn diode Di 200  forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 200 , an n-type diffusion layer DIn, the interconnection, the n-type diffusion tap ND 0 , and the shallow n-type well NW 0 . When the potential of the substrate Sub is lower than the potential of the deep n-type well DNW 0 , the pn diode Di 200  is in a reverse direction. For example, in a manufacturing step using plasma discharge such as a dry etching step, optical excitation due to light emission or thermal excitation due to heat increases a leakage current in the reverse direction to form a discharge path. 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0 . 
     In the second circuit (circuit in which the respective gate electrodes of the pMIS  100   p  and the names  100   n  which form the inverter circuit INV are wired to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ) also, the same effect as obtained in the first circuit described above can be obtained, though the description thereof is omitted herein. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  100   p  and the nMIS  100   n  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub. 
       FIGS. 13(   a ) and  13 ( b ) show principal-portion plan views of the pn diode Di 200  formed in the substrate Sub and the n-type diffusion tap ND 0  formed in the deep n-type well DNW 0 .  FIG. 13(   a ) is a principal-portion plan view of the pn diode Di 200  formed of the n-type diffusion layer DIn which is formed in the shallow p-type well PW 200  in the substrate Sub.  FIG. 13(   b ) is a principal-portion plan view of the pn diode Di 200  formed of the n-type diffusion layer DIn which is formed in the shallow p-type well PW 200  in the substrate Sub, and surrounded by a guard ring formed of a p-type diffusion layer DIp. 
     As shown in  FIG. 13(   a ), the n-type diffusion layer DIn is formed in the shallow p-type well PW 200  in the substrate Sub. In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to reach the n-type diffusion layer DIn. Likewise, in the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed. In the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed to reach the n-type diffusion tap ND 0 . There is also formed the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn or the n-type diffusion tap ND 0  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn formed in the shallow p-type well PW 200  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 . The n-type diffusion layer DIn formed in the shallow p-type well PW 200  in the substrate Sub is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  using the interconnection M 2  in the second layer. 
     As shown in  FIG. 13(   b ), the n-type diffusion layer DIn is formed in the shallow p-type well PW 200  which is formed in the substrate Sub, and the p-type diffusion layer DIp is further formed to surround the n-type diffusion layer DIn at a given distance therefrom. In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to reach the n-type diffusion layer DIn or the p-type diffusion layer DIp. In the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed. In the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed to reach the n-type diffusion tap ND 0 . There is also formed the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn, the p-type diffusion layer DIp, or the n-type diffusion tap ND 0  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn formed in the shallow p-type well PW 200  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 . The n-type diffusion layer DIn formed in the shallow p-type well PW 200  in the substrate Sub is electrically coupled the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  using the interconnection M 2  in the second layer. 
     In the present second embodiment, it is assumed that the n-type diffusion tap ND 0  is wired to the cathode of the pn diode Di 200  using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used to wire the n-type diffusion tap ND 0  to the cathode of the pn diode Di 200 . 
     Thus, according to the present second embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 , the charge can be easily discharged to the substrate Sub, in the same manner as in the first embodiment described above. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0  to form the inverter circuit INV 0 , and a dielectric breakdown in each of the gate insulating films of the pMIS  100   p  and the nMIS  100   n  which are respectively formed in the shallow n-type well NW and the shallow p-type well PW in the substrate Sub to form the inverter circuit INV. In particular, in the case where the nMIS  100   n  and the pMIS  100   p  which are respectively formed in the shallow p-type well PW and the shallow n-type well NW in the substrate Sub are formed into a digital circuit, the nMIS  200   n  and the pMIS  200   p  which are respectively formed in the shallow p-type well PW 0  and the shallow n-type well NW 0  in the deep n-type well DNW 0  are formed into an analog circuit, and each of the nMIS  100   n , the pMIS  100   p , the pMIS  200   p , and the nMIS  200   n  has a dedicated power supply or ground, i.e., in the case where the power supply of the shallow n-type well NW formed in the substrate Sub is different from the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0 , and the power supply of the shallow p-type well PW formed in the substrate Sub is different from the power supply of the shallow p-type well PW 0  formed in the deep n-type well DNW 0 , the second method in the present second embodiment serves as an effective means. 
     Embodiment 3 
     In the present third embodiment, a description will be given of a third method for preventing a dielectric breakdown in the gate insulating film of a MIS in the foregoing third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) with reference to  FIGS. 14 to 16 .  FIG. 14  is a circuit diagram illustrating the third method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present third embodiment.  FIG. 15  is a principal-portion cross-sectional view of the third circuit illustrating the third method shown in  FIG. 14  mentioned above.  FIG. 16  is a principal-portion plan view of the third circuit illustrating the third method shown in  FIG. 14  mentioned above. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 14 , in the third method according to the present third embodiment, the n-type diffusion tap ND 0  for potential fixation is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  where the pMIS  200   p  is formed, while an n-type diffusion tap ND 1  for potential fixation is formed in the shallow n-type well NW 1  in the deep n-type well DNW 1 . The n-type diffusion tap ND 0  is further coupled to the n-type diffusion tap ND 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to wire the n-type diffusion tap ND 0  to the n-type diffusion tap ND 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the n-type diffusion tap ND 0  to the n-type diffusion tap ND 1  is performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type diffusion well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the n-type diffusion tap ND 0  to the n-type diffusion tap ND 1  is performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 15 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), the wiring of the n-type diffusion tap ND 0  to the n-type diffusion tap ND 1  forms a discharge path (or a discharge path in a direction reverse to that of the discharge path) extending from the deep n-type well DNW 1  to the deep n-type well DNW 0  via the shallow n-type well NW 1 , the n-type diffusion tap ND 1 , the interconnection, the n-type diffusion tap ND 0 , and the shallow n-type well NW 0 . As a result, the deep n-type well DNW 0  and the deep n-type well DNW 1  which are formed in mutually different regions are at the same potential. 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  in a manufacturing step using plasma discharge such as, e.g., a dry etching step to another well region such as, e.g., the deep n-type well DNW 0 . As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 16  shows a principal-portion plan view of the n-type diffusion tap ND 0  formed in the deep n-type well DNW 0  and the n-type diffusion tap ND 1  formed in the deep n-type well DNW 1 . 
     In the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed to reach the n-type diffusion tap ND 0 . Likewise, in the shallow n-type well NW 1  in the deep n-type well DNW 1 , the n-type diffusion tap ND 1  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 1 ), the coupling holes CNT 1  are formed to reach the n-type diffusion tap ND 1 . There is also formed the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion taps ND 0  and ND 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1 , and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 . The n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1  is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  using the interconnection M 2  in the second layer. 
     In the present third embodiment, it is assumed that the n-type diffusion taps ND 0  and ND 1  are wired using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used to wire the n-type diffusion taps ND 0  and ND 1 . 
     Thus, according to the present third embodiment, even when charge is accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1 , the charge can be discharged to another well region such as the deep n-type well DNW 0  only on the assumption that the potential of the deep n-type well DNW 1  is the same as the potential of the deep n-type well DNW 0 . This allows a reduction in the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are each formed in the deep n-type well DNW 1  to form the inverter circuit INV 1 . In particular, when, e.g., the shallow p-type well PW 0  formed in the deep n-type well DNW 0  is at a minus potential relative to the ground potential, i.e., when the power supply of the shallow n-type well NW 1  formed in the deep n-type well DNW 1  is the same as the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0 , and the power supply of the shallow p-type well PW 1  formed in the deep n-type well DNW 1  is different from the power supply of the shallow p-type well PW 0  formed in the deep n-type well DNW 0 , the third method in the present third embodiment serves as an effective means. 
     Embodiment 4 
     In the present fourth embodiment, a description will be given of two examples (first and second examples) of a fourth method for preventing a dielectric breakdown in the gate insulating film of a MIS in the foregoing third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above). First, the first example of the fourth method will be described with reference to  FIGS. 17 to 19 , and then the second example of the fourth method will be described with reference to  FIGS. 20 to 22 .  FIG. 17  is a circuit diagram illustrating the first example of the fourth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present fourth embodiment.  FIG. 18  is a principal-portion cross-sectional view of the third circuit illustrating the first example of the fourth method shown in  FIG. 17  mentioned above.  FIG. 19  is a principal-portion plan view of the third circuit illustrating the first example of the fourth method shown in  FIG. 17  mentioned above.  FIG. 20  is a circuit diagram illustrating the second example of the fourth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present fourth embodiment.  FIG. 21  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the fourth method shown in  FIG. 20  mentioned above.  FIG. 22  is a principal-portion plan view of the third circuit illustrating the second example of the fourth method shown in  FIG. 20  mentioned above. 
     First, the first example of the fourth method will be described. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 17 , in the first example of the fourth method according to the present fourth embodiment, the p-type diffusion tap PD 0  for potential fixation is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 , while in the shallow p-type well PW 1  in the deep n-type well DNW 1 , a p-type diffusion tap PD 1  for potential fixation is formed. The p-type diffusion tap. PD 0  is coupled to the p-type diffusion tap PD 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to wire the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1  is performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1  is performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 18 , in the third circuit (circuit in which wiring is provided between the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  and the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 ), a parasitic pn diode is formed by the wiring of the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1 . Because the parasitic pn diode is formed, and the respective gate electrodes of the nMIS  300   n  and the pMIS  300   p  which are formed in the deep n-type well DNW 1  are each in a floating state, the nMIS  300   n  and the pMIS  300   p  are each brought into a conducting state. As a result, a discharge path (or a discharge path in a direction reverse to that of the discharge path) is formed which extends from the deep n-type well DNW 1  to the deep n-type well DNW 0  via the shallow n-type well NW 1 , the shallow n-type diffusion tap ND 1 , the pMIS  300   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), the nMIS  300   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  in a manufacturing step using plasma discharge such as, e.g., a dry etching step to another well region such as, e.g., the deep n-type well DNW 0 . As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 19  shows a principal-portion plan view of the p-type diffusion tap PD 0  formed in the deep n-type well DNW 0  and the p-type diffusion tap PD 1  formed in the deep n-type well DNW 1 . 
     In the shallow p-type well PW 0  in the deep n-type well DNW 0 , the p-type diffusion tap PD 0  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 0 ), the coupling holes CNT 1  are formed to reach the p-type diffusion tap PD 0 . Likewise, in the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 1  is formed, while in the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type well DNW 1 ), the coupling holes CNT 1  are formed to reach the p-type diffusion tap PD 1 . There is also formed the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion taps PD 0  and PD 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 . The p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  is electrically coupled to the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  using the interconnection M 2  in the second layer. 
     Next, the second example of the fourth method will be described. 
     In the second example of the fourth method also, a description is given of the method for preventing a dielectric breakdown in the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , which occurs in the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above). The first and second examples of the fourth method are different in that, in the first example, the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  is electrically coupled to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , while in the second example, a shallow p-type well is further formed in the substrate Sub, and a p-type diffusion tap for potential fixation which is formed in the shallow p-type well is electrically coupled to the p-type diffusion taps PD 0  and PD 1  mentioned above. 
     As shown in  FIG. 20 , in the second example of the fourth method according to the present fourth embodiment, a p-type diffusion tap PD 400  for potential fixation is formed in a shallow p-type well PW 400  which is formed in the substrate Sub, and the p-type diffusion tap  400  is further coupled to the p-type diffusion tap PD 0  for potential fixation which is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  and to the p-type diffusion tap PD 1  for potential fixation which is formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  is performed using the interconnection in the same layer as that of the interconnection used to wire the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1  is performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the p-type diffusion tap PD 0  to the p-type diffusion tap PD 1  is performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 21 , in the third circuit (circuit in which wiring is provided between the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  forming the inverter circuit INV 1  and the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  forming the inverter circuit INV 0 ), the respective gate electrodes of the nMIS  300   n  and the pMIS  300   p  which are respectively formed in the shallow p-type well PW 1  and the shallow n-type well NW 1  in the deep n-type well DNW 1  are each in a floating state so that the nMIS  300   n  and the pMIS  300   p  are each brought into a conducting state. As a result, a discharge path is formed which extends from the deep n-type well DNW 1  to the substrate Sub via the shallow n-type well NW 1 , the n-type diffusion tap ND 1 , the pMIS  300   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), the nMIS  300   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD 400 , and the shallow p-type well PW 400 . Likewise, the respective gate electrodes of the nMIS  200   n  and the pMIS  200   p  which are respectively formed in the shallow p-type well PW 0  and the shallow n-type well NW 0  in the deep n-type well DNW 0  are each in a floating state so that the nMIS  200   n  and the pMIS  200   p  are each brought into a conducting state. As a result, a discharge path is formed which extends from the deep n-type well DNW 0  to the substrate Sub via the shallow n-type well NW 0 , the n-type diffusion tap ND 0 , the pMIS  200   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), the nMIS  200   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD 400 , and the shallow p-type well PW 400 . 
     In addition, a discharge path is formed which extends from the substrate Sub to the deep n-type well DNW 1  via the shallow p-type well PW 400 , the p-type diffusion tap PD 400 , the interconnection, the p-type diffusion tap PD 1 , and the shallow p-type well PW 1 . Likewise, a discharge path is formed which extends from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 400 , the p-type diffusion tap PD 400 , the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     The formation of the discharge paths mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  or the change accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  in a manufacturing step using plasma discharge such as, e.g., a dry etching step to the substrate Sub. As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the gate insulating film of the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 22  shows a principal-portion plan view of the p-type diffusion tap PD 0  formed in the deep n-type well DNW 0 , the p-type diffusion tap PD 1  formed in the deep n-type well DNW 1 , and the p-type diffusion tap PD 400  formed in the substrate Sub. 
     In addition to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  and the p-type diffusion tap PD 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  which are shown in  FIG. 19  mentioned above, the p-type diffusion tap PD 400  is formed in the shallow p-type well PW 400  formed in the substrate Sub, similarly to the p-type diffusion taps PD 0  and PD 1 . In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to respectively reach the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , and the p-type diffusion tap PD 400  formed in the shallow p-type well PW 400  in the substrate Sub. There is also formed the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , and the p-type diffusion tap PD 400  formed in the shallow p-type well PW 400  in the substrate Sub through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, the coupling holes CNT 2  are formed to reach the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , to the p-type diffusion tap PD 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , and to the p-type diffusion tap PD 400  formed in the shallow p-type well PW 400  in the substrate Sub. Through the coupling holes CNT 2 , the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , and the p-type diffusion tap PD 400  formed in the shallow p-type well PW 400  in the substrate Sub are electrically coupled using the interconnection M 2  in the second layer. 
     In the present fourth embodiment, it is assumed that the wiring of the p-type diffusion taps PD 0  and PD 1  in the first example and the wiring of the p-type diffusion taps PD 0 , PD 1 , and PD 400  in the second example are performed using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used for the wiring. 
     Thus, according to the present fourth embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 , or in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  due to a plasma charge-up phenomenon in, e.g., a dry etching step, the charge can be easily discharged to the substrate Sub to allow a reduction in the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0 . As a result, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  each formed the deep n-type well DNW 1  to form the inverter circuit INV 1 . In particular, when the shallow p-type well PW 0  formed in the deep n-type well NDW 0  and the shallow p-type well PW 1  formed in the deep n-type well DNW 1  are at the same ground potential, i.e., when the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow n-type well NW 1  formed in the deep n-type well DNW 1 , the fourth method in the present fourth embodiment serves as an effective means. 
     Embodiment 5 
     In the present fifth embodiment, a description will be given of a fifth method for preventing a dielectric breakdown in the gate insulating film of a MIS in the foregoing third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) with reference to  FIGS. 23 to 25 .  FIG. 23  is a circuit diagram illustrating the fifth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present fifth embodiment.  FIG. 24  is a principal-portion cross-sectional view of the third circuit illustrating the fifth method shown in  FIG. 23  mentioned above.  FIG. 25  is a principal-portion plan view of the third circuit illustrating the fifth method shown in  FIG. 23  mentioned above. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 23 , in the fifth method according to the present fifth embodiment, a shallow p-type well PW 500  formed in the substrate Sub and an n-type diffusion layer formed in the shallow p-type well PW 500  form a pn diode Di 500 , and the cathode of the pn diode Di 500  is coupled to the n-type diffusion tap ND 0  for potential fixation which is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  using an interconnection in a second or higher order layer. In addition, a shallow p-type well PW 501  formed in the substrate Sub and an n-type diffusion layer formed in the shallow p-type well PW 501  form a pn diode Di 501 , and the cathode of the pn diode Di 501  is coupled to the n-type diffusion tap ND 1  for potential fixation which is formed in the shallow n-type well NW 1  in the deep n-type well DNW 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to wire the n-type diffusion layer of the pn diode Di 500  to the n-type diffusion tap ND 0 , and the interconnection used to wire the n-type diffusion layer of the pn diode Di 501  to the n-type diffusion tap ND 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the n-type diffusion layer of the pn diode Di 500  to the n-type diffusion tap ND 0 , and the wiring of the n-type diffusion layer of the pn diode Di 501  to the n-type diffusion tap ND 1  are performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the n-type diffusion layer of the pn diode Di 500  to the n-type diffusion tap ND 0 , and the wiring of the n-type diffusion layer of the pn diode Di 501  to the n-type diffusion tap ND 1  are performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 24 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), when the potential of the substrate Sub is higher than the potential of the deep n-type well DNW 0 , the pn diode Di 500  forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 500 , an n-type diffusion layer DIn 0 , the interconnection, the n-type diffusion tap ND 0 , and the shallow n-type well NW 0 . When the potential of the substrate Sub is lower than the potential of the deep n-type well DNW 0 , the pn diode Di 500  is in a reverse direction. For example, in a manufacturing step using plasma discharge such as a dry etching step, optical excitation due to light emission or thermal excitation due to heat increases a leakage current in the reverse direction to form a discharge path. 
     Likewise, when the potential of the substrate Sub is higher than the potential of the deep n-type well DNW 1 , the pn diode Di 501  forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 1  via the shallow p-type well PW 501 , an n-type diffusion layer DIn 1 , the interconnection, the n-type diffusion tap ND 1 , and the shallow n-type well NW 0 . When the potential of the substrate Sub is lower than the potential of the deep n-type well DNW 1 , the pn diode Di 501  is in a reverse direction. For example, in a manufacturing step using plasma discharge such as a dry etching step, optical excitation due to light emission or thermal excitation due to heat increases a leakage current in the reverse direction to form a discharge path. 
     The formation of the discharge paths mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  via the discharge path mentioned above, and likewise allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  via the discharge path mentioned above. As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 25  shows a principal-portion plan view of the pn diode Di 500  formed in the substrate Sub, the n-type diffusion tap ND 0  formed in the shallow p-type well NW 0  in the deep n-type well DNW 0 , the pn diode Di 501  formed in the substrate Sub, and the n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1 . 
     The n-type diffusion layer DIn 0  is formed in the shallow p-type well PW 500  in the substrate Sub, while the n-type diffusion layer DIn 1  is formed in the shallow p-type well PW 501  in the substrate Sub. In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to reach the n-type diffusion layers DIn 0  and DIn 1 . In the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed, while in the shallow n-type well NW 1  in the deep n-type well DNW 1 , the n-type diffusion tap ND 1  is formed. In the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type wells DNW 0  and DNW 1 ), the coupling holes CNT 1  are formed to reach the n-type diffusion taps ND 0  and ND 1 . There is also formed the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion taps ND 0  and ND 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, the coupling holes CNT 2  are formed to reach the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn 0  formed in the shallow p-type well PW 500  in the substrate Sub or to the n-type diffusion layer DIn 1  formed in the shallow p-type well PW 501  in the substrate Sub. Likewise, the coupling holes CNT 2  are formed to reach the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  or to the n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1 . The n-type diffusion layer DIn 0  formed in the shallow p-type well PW 500  in the substrate Sub is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  coupled using the interconnection M 2  in the second layer. Likewise, the n-type diffusion layer DIn 1  formed in the shallow p-type well PW 501  in the substrate Sub is electrically coupled to the n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DNW 1  using the interconnection M 2  in the second layer. 
     In the present fifth embodiment, it is assumed that the wiring of the n-type diffusion tap ND 0  to the cathode of the pn diode Di 500 , and the wiring of the n-type diffusion tap ND 1  to the cathode of the pn diode Di 501  are performed using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used for the wiring. 
     Thus, according to the present fifth embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  or in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1 , the charge can be easily discharged to the substrate Sub to allow a reduction in the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1  to form the inverter circuit INV 1 . In particular, in the case where the semiconductor device has, e.g., an analog leased ground and a back bias in combination, the shallow p-type well PW 0  formed in the deep n-type well DNW 0  and the shallow p-type well PW 1  formed in the deep n-type well DNW 1  are provided with grounds independent of each other, and a power supply given to the shallow n-type well NW 0  formed in the deep n-type well DNW 0  is interrupted for leakage current prevention, i.e., in the case where the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow n-type well NW 1  formed in the deep n-type well DNW 1 , and the power supply of the shallow p-type well PW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow p-type well PW 1  formed in the deep n-type well DNW 1 , the fifth method in the present fifth embodiment serves as an effective means. 
     Embodiment 6 
     In the present sixth embodiment, a description will be given of two examples (first and second examples) of a sixth method for preventing a dielectric breakdown in the gate insulating film of a MIS in the foregoing third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above). First, the first example of the sixth method will be described with reference to  FIGS. 26 to 28 , and then the second example of the sixth method will be described with reference to  FIGS. 29 and 30 .  FIG. 26  is a circuit diagram illustrating the first example of the sixth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present sixth embodiment.  FIG. 27  is a principal-portion cross-sectional view of the third circuit illustrating the first example of the sixth method shown in  FIG. 26  mentioned above.  FIG. 28  is a principal-portion plan view of the third circuit illustrating the first example of the sixth method shown in  FIG. 26  mentioned above.  FIG. 29  is a circuit diagram illustrating the second example of the sixth method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present sixth embodiment.  FIG. 30  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the sixth method shown in  FIG. 29  mentioned above. 
     First, the first example of the sixth method will be described. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 26 , in the first example of the sixth method according to the present sixth embodiment, a shallow p-type well PW 600  formed in the substrate Sub and an n-type diffusion layer formed in the shallow p-type well PW 600  form a pn diode Di 600 . The cathode of the pn diode Di 600  and the n-type diffusion tap ND 0  for potential fixation which is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  are coupled using an interconnection in a second or higher order layer. 
     In the shallow p-type well PW 601  formed in the substrate Sub, a p-type diffusion tap PD 601  for potential fixation is formed. In the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 1  for potential fixation is formed. Further, the p-type diffusion tap PD 600  and the p-type diffusion tap PD 1  are coupled using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to wire the n-type diffusion layer of the pn diode Di 600  to the n-type diffusion tap ND 0 , and the interconnection used to wire the p-type diffusion tap PD 601  to the p-type diffusion tap PD 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the n-type diffusion layer of the pn diode Di 600  to the n-type diffusion tap ND 0  and the wiring of the p-type diffusion tap PD 601  to the p-type diffusion tap PD 1  are performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the n-type diffusion layer of the pn diode Di 600  to the n-type diffusion tap ND 0  and the wiring of the p-type diffusion tap PD 601  to the p-type diffusion tap PD 1  are performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 27 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), when the potential of the substrate Sub is higher than the respective potentials of the deep n-type wells DNW 0  and DNW 1 , the pn diode Di 600  forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 600 , the n-type diffusion layer DIn 0 , the interconnection, the n-type diffusion tap ND 0 , and the shallow n-type well NW 0 . In addition, a pn parasitic diode forms a discharge path extending from the substrate Sub to the deep n-type well DNW 1  via the shallow p-type well PW 601 , the p-type diffusion tap PD 601 , the interconnection, the p-type diffusion tap PD 1 , and the shallow p-type well PW 1 . 
     When the potential of the substrate Sub is lower than the respective potentials of the deep n-type wells DNW 0  and DNW 1 , the pn diode Di 600  is in a reverse direction. For example, in a manufacturing step using plasma discharge such as a dry etching step, optical excitation due to light emission or thermal excitation due to heat increases a leakage current in the reverse direction to form a discharge path. Because the respective gate electrodes of the nMIS  300   n  and the pMIS  300   p  which are respectively formed in the shallow p-type well PW 1  and the shallow n-type well NW 1  in the deep n-type well DNW 1  are each in a floating state, the nMIS  300   n  and the pMIS  300   p  are each brought into a conductive state. As a result, a discharge path is formed which extends from the deep n-type well DNW 1  to the substrate Sub via the shallow n-type well NW 1 , the n-type diffusion tap ND 1 , the pMIS  300   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), the nMIS  300   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD 1 , the p-type diffusion tap PD 601 , and the shallow p-type well PW 601 . 
     The formation of the discharge paths mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  via the discharge path mentioned above, and likewise allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  via the discharge path mentioned above. As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  can be reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 28  shows a principal-portion plan view of the pn diode Di 600  formed in the substrate Sub, the p-type diffusion tap PD 601  formed in the shallow p-type well PW 601  in the substrate Sub, the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , and the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
     The n-type diffusion layer DIn 0  is formed in the shallow p-type well PW 600  formed in the substrate Sub, and the p-type diffusion tap PD 601  is formed in the shallow p-type well PW 601  formed in the substrate Sub. In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to reach the n-type diffusion layer DIn 0  or the p-type diffusion tap PD 601 . The interconnection M 1  in the first layer is formed to be electrically coupled to the n-type diffusion layer DIn 0  or the p-type diffusion tap PD 601  through the coupling holes CNT 1 . In the shallow n-type well NW 0  in the deep n-type well DNW 0 , the n-type diffusion tap ND 0  is formed, while in the shallow p-type well PW 1  in the deep n-type well DNW 1 , the p-type diffusion tap PD 1  is formed. In the interlayer insulating film (not shown) formed on the substrate (the deep n-type wells DNW 0  and DNW 1 ), the coupling holes CNT 1  are formed to reach the n-type diffusion tap ND 0  or the p-type diffusion tap PD 1 . The interconnection M 1  in the first layer is formed to be electrically coupled to the n-type diffusion tap ND 0  or the p-type diffusion tap PD 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn 0  formed in the shallow p-type well PW 600  in the substrate Sub and to the p-type diffusion tap PD 601  formed in the shallow p-type well PW 601  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  and to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 . The n-type diffusion layer DIn 0  formed in the shallow p-type well PW 600  in the substrate Sub is electrically coupled to the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  using the interconnection M 2  in the second layer. Likewise, the p-type diffusion tap PD 601  formed in the shallow p-type well PW 601  in the substrate Sub is electrically coupled to the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DNW 1  using the interconnection M 2  in the second layer. 
     Next, the second example of the sixth method will be described. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 29 , in the second example of the sixth method according to the present sixth embodiment, the p-type diffusion tap PD 600  for potential fixation is formed in the shallow p-type well PW 600  in the substrate Sub, and the p-type diffusion tap PD 0  for potential fixation is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 . Further, the p-type diffusion tap PD 600  and the p-type diffusion tap PD 0  are coupled using an interconnection in a second or higher order layer. 
     In addition, the shallow p-type well PW 601  formed in the substrate Sub and an n-type diffusion layer formed in the shallow p-type well PW 601  form a pn diode Di 601 . The cathode of the pn diode Di 601  is coupled to the n-type diffusion tap ND 1  for potential fixation which is formed in the shallow n-type well NW 1  in the deep n-type well DNW 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  is performed using the interconnection in the same layer as that of the interconnection used to wire the p-type diffusion tap PD 600  to the p-type diffusion tap PD 0 , and the interconnection used to wire the n-type diffusion layer of the pn diode Di 601  to the n-type diffusion tap ND 1 , or an interconnection in a layer higher in order than that. For example, in the case where the wiring of the p-type diffusion tap PD 600  to the p-type diffusion tap PD 0  and the wiring of the n-type diffusion layer of the pn diode Di 601  to the n-type diffusion tap ND 1  are performed using the interconnection in the second layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the wiring of the p-type diffusion tap PD 600  to the p-type diffusion tap PD 0  and the wiring of the n-type diffusion layer of the pn diode Di 601  to the n-type diffusion tap ND 1  are performed using the interconnection in the third layer, the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 30 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), when the potential of the substrate Sub is higher than the respective potentials of the deep n-type wells DNW 0  and DNW 1 , the pn diode Di 600  forms a forward discharge path extending from the substrate Sub to the deep n-type well DNW 1  via the shallow p-type well PW 601 , the n-type diffusion layer DIn 1 , the interconnection, the n-type diffusion tap ND 1 , and the shallow n-type well NW 1 . In addition, a pn parasitic diode forms a discharge path extending from the substrate Sub to the deep n-type well DNW 0  via the shallow p-type well PW 600 , the p-type diffusion tap PD 600 , the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     When the potential of the substrate Sub is lower than the respective potentials of the deep n-type wells DNW 0  and DNW 1 , the pn diode Di 601  is in a reverse direction. For example, in a manufacturing step using plasma discharge such as a dry etching step, optical excitation due to light emission or thermal excitation due to heat increases a leakage current in the reverse direction to form a discharge path. Because the respective gate electrodes of the nMIS  200   n  and the pMIS  200   p  which are respectively formed in the shallow p-type well PW 0  and the shallow n-type well NW 0  in the deep n-type well DNW 0  are each in a floating state, the nMIS  200   n  and the pMIS  200   p  are each brought into a conductive state. As a result, a discharge path is formed which extends from the deep n-type well DNW 0  to the substrate Sub via the shallow n-type well NW 0 , the p-type diffusion tap ND 0 , the pMIS  100   p  (the source electrode Sp thereof, the channel region thereof, and the drain electrode Dp thereof), the nMIS  100   n  (the drain electrode Dn thereof, the channel region thereof, and the source electrode Sn thereof), the interconnection, the p-type diffusion tap PD 600 , and the shallow p-type well PW 600 . 
     The formation of the discharge path mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  via the discharge path mentioned above, and likewise allows discharge of the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  via the discharge path mentioned above. As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
     In the present sixth embodiment, it is assumed that the n-type diffusion tap ND 0  is wired to the cathode of the pn diode Di 600  using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used for the wiring. 
     Thus, according to the present sixth embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 , or in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1 , the charge can be easily discharged to the substrate Sub to allow a reduction in the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1  to form the inverter circuit INV 1 . In particular, in the case where the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1  form a digital circuit, the pMIS  200   p  and the nMIS  200   n  which are respectively formed in the shallow n-type well NW 0  and the shallow p-type well PW 0  in the deep n-type well DNW 0  form an analog circuit, and each of the pMIS  300   p , the nMIS  300   n , the pMIS  200   p , and the nMIS  200   n  has a dedicated power supply or ground, i.e., in the case where the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow n-type well NW 1  formed in the deep n-type well DNW 1 , and the power supply of the shallow p-type well PW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow p-type well PW 1  formed in the deep n-type well DNW 1 , the sixth method in the present sixth embodiment serves as an effective means. 
     Embodiment 7 
     In the present seventh embodiment, a description will be given of two examples (first and second examples) of a seventh method for preventing a dielectric breakdown in the gate insulating film of a MIS in the foregoing third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above). First, the first example of the seventh method will be described with reference to  FIGS. 31 to 33 , and then the second example of the seventh method will be described with reference to  FIGS. 34 to 36 .  FIG. 31  is a circuit diagram illustrating the first example of the seventh method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present seventh embodiment.  FIG. 32  is a principal-portion cross-sectional view of the third circuit illustrating the first example of the seventh method shown in  FIG. 31  mentioned above.  FIG. 33  is a principal-portion plan view of the third circuit illustrating the first example of the seventh method shown in  FIG. 31  mentioned above.  FIG. 34  is a circuit diagram illustrating the second example of the seventh method for preventing a dielectric breakdown in the gate insulating film of a MIS according to the present seventh embodiment.  FIG. 35  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the seventh method shown in  FIG. 34  mentioned above.  FIG. 36  is a principal-portion cross-sectional view of the third circuit illustrating the second example of the seventh method shown in  FIG. 34  mentioned above. 
     First, the first example of the seventh method will be described. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  forming the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 31 , in the first example of the seventh method according to the present seventh embodiment, the n-type diffusion tap ND 0  for potential fixation is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , while the n-type diffusion tap ND 1  for potential fixation is formed in the shallow n-type well NW 1  in the deep n-type well NW 1 . Further, between the n-type diffusion tap ND 0  and the n-type diffusion tap ND 1 , bidirectional diodes Di 700  and Di 701  are formed using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to form the bidirectional diodes Di 700  and Di  701 , or an interconnection in a layer higher in order than that. For example, in the case where the interconnection in the second layer is used to form the bidirectional diodes Di 700  and Di  701 , the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the interconnection in the third layer is used to form the bidirectional diodes Di 700  and Di  701 , the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 32 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DMW 0  is wired to the cathode (the n-type diffusion layer DIn 0  formed in a shallow n-type well NW 700  in the substrate Sub) of the bidirectional diode Di 700  and to the anode (the p-type diffusion layer DIp 1  formed in a shallow n-type well NW 701  in the substrate Sub) of the bidirectional diode Di 701 , and the n-type diffusion tap ND 1  formed in the shallow n-type well NW 1  in the deep n-type well DMW 1  is wired to the anode (a p-type diffusion layer DIp 0  formed in the shallow n-type well NW 700  in the substrate Sub) of the bidirectional diode Di 700  and to the cathode (the n-type diffusion layer DIn 1  formed in the shallow n-type well NW 701  in the substrate Sub) of the bidirectional diode Di 701 . This forms a discharge path extending from the deep n-type well DNW 0  to the deep n-type well DNW 1  via the shallow n-type well NW 0 , the n-type diffusion tap ND 0 , the interconnection, the bidirectional diode Di 701  (the n-type diffusion layer DIn 1 , the shallow n-type well NW 701 , and the p-type diffusion layer DIp 1 ), the interconnection, the n-type diffusion tap ND 1 , and the shallow n-type well NW 1 . This also forms a discharge path extending from the deep n-type well DNW 1  to the deep n-type well DNW 0  via the shallow n-type well NW 1 , the n-type diffusion tap ND 1 , the interconnection, the pn diode Di 700  (the p-type diffusion layer DIp 0 , the shallow n-type well NW 700 , and the n-type diffusion layer DIn 0 ), the interconnection, the n-type diffusion tap ND 0 , and the shallow n-type well NW 0 . 
     The formation of the discharge paths mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  or the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  via the discharge path mentioned above even when a potential difference occurs between the deep n-type well DNW 1  and the deep n-type well DNW 0 . As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 33  shows a principal-portion plan view of the bidirectional diodes Di 700  and Di 701  formed in the substrate Sub, the n-type diffusion tap ND 0  formed in the deep n-type well DNW 0 , and the n-type diffusion tap ND 1  formed in the deep n-type well DNW 1 . 
     In the mutually different regions in the shallow n-type well NW 700  formed in the substrate Sub, the n-type diffusion layer DIn 0  and the p-type diffusion layer DIp 0  are formed (Di 700 ). In the mutually different regions in the shallow n-type well NW 701  formed in the substrate Sub, the n-type diffusion layer DIn 1  and the p-type diffusion layer DIp 1  are formed (Di 701 ). In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to individually reach the n-type diffusion layers DIn 0  and DIn 1  and the p-type diffusion layers DIp 0  and DIp 1 . The n-type diffusion tap ND 0  is formed in the shallow n-type well NW 0  in the deep n-type well DNW 0 , while the n-type diffusion tap ND 1  is formed in the shallow n-type well NW 1  in the deep n-type well DNW 1 . In the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type wells DNW 0  and DNW 1 ), the coupling holes CNT 1  are formed to individually reach the n-type diffusion taps ND 0  and ND 1 , the n-type diffusion layers DIn 0  and DIn 1 , and the p-type diffusion layers DIp 0  and DIp 1 . The interconnection M 1  in the first layer is formed to be electrically coupled to the n-type diffusion taps ND 0  and ND 1 , the n-type diffusion layers DIn 0  and DIn 1 , and the p-type diffusion layers DIp 0  and DIp 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn 0  and the p-type diffusion layer DIp 0  each formed in the shallow n-type well NW 700  in the substrate Sub and to the n-type diffusion layer DIn 1  and the p-type diffusion layer DIp 1  each formed in the shallow n-type well NW 701  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion tap ND 0  and the n-type diffusion tap ND 1  which are respectively formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  and the shallow n-type well NW 1  in the deep n-type well DNW 1 . The p-type diffusion layer DIp 1  (the bidirectional diode Di 701 ) formed in the shallow n-type well NW 701  in the substrate Sub, the n-type diffusion layer DIn 0  (the bidirectional diode Di 700 ) formed in the shallow n-type well NW 700  in the substrate Sub, and the n-type diffusion tap ND 0  formed in the shallow n-type well NW 0  in the deep n-type well DNW 0  are electrically coupled using the interconnection M 2  in the second layer. The p-type diffusion layer DIp 0  (the bidirectional diode Di 700 ) formed in the shallow n-type well NW 700  in the substrate Sub, the n-type diffusion layer DIn 1  (the bidirectional diode Di 701 ) formed in the shallow n-type well NW 701  in the substrate Sub, and the n-type diffusion tap ND 1  in the shallow n-type well NW 1  formed in the deep n-type well DNW 1  are electrically coupled using the interconnection M 2  in the second layer. 
     Next, the second example of the seventh method will be described. 
     As described above, the third circuit ( FIGS. 4(   a ) and  4 ( b ) mentioned above) includes the inverter circuit INV 0  formed in the deep n-type well DNW 0 , and the inverter circuit INV 1  formed in the deep n-type well DNW 1 . The respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1  are electrically coupled to the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0 . In the gate insulating film of the pMIS  300   p  or the nMIS  300   n  which form the inverter circuit INV 1 , a dielectric breakdown has occurred. 
     As shown in  FIG. 34 , in the second example of the seventh method according to the present seventh embodiment, the p-type diffusion tap PD 0  for potential fixation is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 , and the p-type diffusion tap PD 1  for potential fixation is formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 . Further, the bidirectional diodes Di 700  and Di 701  are formed between the p-type diffusion tap PD 0  and the p-type diffusion tap PD 1  using an interconnection in a second or higher order layer. 
     The wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  and the inverter circuit INV 1  formed in the deep n-type well DNW 1 , i.e., the wiring of the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  to the respective gate electrodes of the pMIS  300   p  and the nMIS  300   p  which form the inverter circuit INV 1  is performed using an interconnection in the same layer as that of the interconnection used to form the bidirectional diodes Di 700  and Di  701 , or an interconnection in a layer higher in order than that. For example, in the case where the interconnection in the second layer is used to form the bidirectional diodes Di 700  and Di  701 , the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a second or higher order layer. In the case where the interconnection in the third layer is used to form the bidirectional diodes Di 700  and Di  701 , the wiring of the inverter circuit INV 0  formed in the deep n-type well DNW 0  to the inverter circuit INV 1  formed in the deep n-type well DNW 1  is performed using an interconnection in a third or higher order layer. 
     As shown in  FIG. 35 , in the third circuit (circuit in which wiring is provided between the respective drain electrodes of the pMIS  200   p  and the nMIS  200   n  which form the inverter circuit INV 0  and the respective gate electrodes of the pMIS  300   p  and the nMIS  300   n  which form the inverter circuit INV 1 ), the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DMW 0  is wired to the cathode (the n-type diffusion layer DIn 0  formed in the shallow n-type well NW 700  in the substrate Sub) of the bidirectional diode Di 700  and to the anode (the p-type diffusion layer DIp 1  formed in the shallow n-type well NW 701  in the substrate Sub) of the bidirectional diode Di 701 , and the p-type diffusion tap PD 1  formed in the shallow p-type well PW 1  in the deep n-type well DMW 1  is wired to the cathode (the n-type diffusion layer DIn 1  formed in the shallow n-type well NW 701  in the substrate Sub) of the bidirectional diode Di 701  and to the anode (the p-type diffusion layer DIp 0  formed in the shallow n-type well NW 700  in the substrate Sub) of the bidirectional diode Di 700 . This forms a discharge path extending from the deep n-type well DNW 0  to the deep n-type well DNW 1  via the shallow p-type well PW 0 , the p-type diffusion tap PD 0 , the interconnection, the pn diode Di 701  (the p-type diffusion layer DIp 1 , the shallow n-type well NW 701 , and the n-type diffusion layer DIn 1 ), the interconnection, the p-type diffusion tap PD 1 , and the shallow p-type well PW 1 . This also forms a discharge path extending from the deep n-type well DNW 1  to the deep n-type well DNW 0  via the shallow p-type well PW 1 , the p-type diffusion tap PD 1 , the interconnection, the pn diode Di 700  (the p-type diffusion layer DIp 0 , the shallow n-type well NW 700 , and the n-type diffusion layer DIn 0 ), the interconnection, the p-type diffusion tap PD 0 , and the shallow p-type well PW 0 . 
     The formation of the discharge paths mentioned above allows discharge of the charge accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0  or the charge accumulated in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1  via the discharge path mentioned above even when a potential difference occurs between the deep n-type well DNW 1  and the deep n-type well DNW 0 . As a result, the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0  is reduced. Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . 
       FIG. 36  shows a principal-portion plan view of the bidirectional diodes Di 700  and Di 701  formed in the substrate Sub, the n-type diffusion tap ND 0  formed in the deep n-type well DNW 0 , and the n-type diffusion tap ND 1  formed in the deep n-type well DNW 1 . 
     In the mutually different regions in the shallow n-type well NW 700  formed in the substrate Sub, the n-type diffusion layer DIn 0  and the p-type diffusion layer DIp 0  are formed (Di 700 ). In the mutually different regions in the shallow n-type well NW 701  formed in the substrate Sub, the n-type diffusion layer DIn 1  and the p-type diffusion layer DIp 1  are formed (Di 701 ). In the interlayer insulating film (not shown) formed over the substrate Sub, the coupling holes CNT 1  are formed to individually reach the n-type diffusion layers DIn 0  and DIn 1  and the p-type diffusion layers DIp 0  and DIp 1 . The p-type diffusion tap PD 0  is formed in the shallow p-type well PW 0  in the deep n-type well DNW 0 , while the p-type diffusion tap PD 1  is formed in the shallow p-type well PW 1  in the deep n-type well DNW 1 . In the interlayer insulating film (not shown) formed over the substrate Sub (the deep n-type wells DNW 0  and DNW 1 ), the coupling holes CNT 1  are formed to individually reach the p-type diffusion taps PD 0  and PD 1 , the n-type diffusion layers DIn 0  and DIn 1 , and the p-type diffusion layers DIp 0  and DIp 1 . The interconnection M 1  in the first layer is formed to be electrically coupled to the p-type diffusion taps PD 0  and PD 1 , the n-type diffusion layers DIn 0  and DIn 1 , and the p-type diffusion layers DIp 0  and DIp 1  through the coupling holes CNT 1 . 
     Further, in the interlayer insulating film (not shown) formed over the substrate Sub to cover the interconnection M 1  in the first layer, there are formed the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the n-type diffusion layer DIn 0  and the p-type diffusion layer DIp 0  each formed in the shallow n-type well NW 700  in the substrate Sub and to the n-type diffusion layer DIn and the p-type diffusion layer DIp 1  each formed in the shallow n-type well NW 701  in the substrate Sub, and the coupling holes CNT 2  reaching the interconnection M 1  in the first layer which is electrically coupled to the p-type diffusion tap PD 0  and the p-type diffusion tap PD 1  which are respectively formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  and the shallow p-type well PW 1  in the deep n-type well DNW 1 . The n-type diffusion layer DIn 1  (the bidirectional diode Di 701 ) formed in the shallow n-type well NW 701  in the substrate Sub, the n-type diffusion layer DIn 0  (the bidirectional diode Di 700 ) formed in the shallow n-type well NW 700  in the substrate Sub, and the p-type diffusion tap PD 0  formed in the shallow p-type well PW 0  in the deep n-type well DNW 0  are electrically coupled using the interconnection M 2  in the second layer. The p-type diffusion layer DIp 0  (the bidirectional diode Di 700 ) formed in the shallow n-type well NW 700  in the substrate Sub, the n-type diffusion layer DIn 1  (the bidirectional diode Di 701 ) formed in the shallow n-type well NW 701  in the substrate Sub, and the p-type diffusion tap PD 1  in the shallow p-type well PW 1  formed in the deep n-type well DNW 1  are electrically coupled using the interconnection M 2  in the second layer. 
     In the present seventh embodiment, it is assumed that the wiring of the n-type diffusion tap ND 0  to the cathode of the pn diode Di 700  and to the anode of the pn diode Di 701  and the wiring of the n-type diffusion tap ND 1  to the anode of the pn diode Di 700  and to the cathode of the pn diode Di 701  in the first example, and the wiring of the p-type diffusion tap PD 0  to the cathode of the pn diode  700  and to the anode of the pn diode Di 701  and the wiring of the p-type diffusion tap PD 1  to the anode of the pn diode  700  and to the cathode of the pn diode  701  are each performed using an interconnection in a second or higher order layer. However, in the case where layout using the interconnection in the first layer is possible, the interconnection in the first layer can also be used for the wiring. 
     Thus, according to the present seventh embodiment, even when charge is accumulated in the deep n-type well DNW 0 , the shallow n-type well NW 0 , and the shallow p-type well PW 0 , or in the deep n-type well DNW 1 , the shallow n-type well NW 1 , and the shallow p-type well PW 1 , the charge can be easily discharged to another well region to allow a reduction in the potential difference between the deep n-type well DNW 1  and the deep n-type well DNW 0 . Therefore, it is possible to prevent a dielectric breakdown in each of the gate insulating films of the pMIS  300   p  and the nMIS  300   n  which are respectively formed in the shallow n-type well NW 1  and the shallow p-type well PW 1  in the deep n-type well DNW 1  to form the inverter circuit INV 1 . In particular, in the case where the shallow p-type well PW 0  and the shallow n-type well NW 0  each formed in the deep n-type well DNW 0  form an analog circuit, and have respective particular power supplies or ground potentials, and the shallow p-type well PW 1  and the shallow n-type well N 1  each formed in the deep n-type well DNW 1  form another analog circuit, and have respective particular power supplies or ground potential which are different from the power supplies or the ground potentials applied to the shallow p-type well PW 0  and the shallow n-type well NW 0  each formed in the deep n-type well DNW 0 , i.e., in the case where the power supply of the shallow p-type well PW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow p-type well PW 1  formed in the deep n-type well DNW 1 , and the power supply of the shallow n-type well NW 0  formed in the deep n-type well DNW 0  is different from the power supply of the shallow n-type well NW 1  formed in the deep n-type well DNW 1 , the seventh method in the present seventh embodiment serves as an effective means. 
     While the invention achieved by the present inventors has been described specifically based on the embodiments of the invention, it will be easily appreciated that the present invention is not limited to the embodiments described above, and various changes and modification can be made therein without departing from the gist thereof. 
     The present invention provides a technology which is effective when applied to a semiconductor device having a triple well structure adopted to, e.g., a versatile SOC product.