Patent Publication Number: US-6982555-B2

Title: Semiconductor device

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a method for separately measuring capacitive components in a semiconductor device and a Test Element Group (TEG) pattern having its function. 
   In the design and development of high-performance LSIs, it is significant to sample (measure) the characteristics of semiconductor elements placed in an LSI with high accuracy, and a technique for sampling (measuring) the same and the optimal design of a TEG are required. 
   In recent years, as semiconductor elements become finer, the influences of noises caused by crosstalk and the degradation of delay characteristics due to a Miller capacitance have become more obvious. Therefore, it has been required to sample capacitive components of individual conductor members, such as interconnects and semiconductor layers, of the characteristics of the semiconductor device with high accuracy. 
   A technique for sampling parasitic capacitances as disclosed in Patent Document 1 (U.S. Pat. No. 6,300,765 B1) has been conventionally known. The objective of this technique is to separately measure interconnect-to-interconnect capacitances C 12  and C 13 . 
     FIG. 7  is a circuit diagram illustrating the structure of a capacitance measuring circuit for measuring parasitic capacitances as disclosed in Patent Document 1. 
   As shown in this figure, a P-type Metal Insulator Semiconductor Field Effect Transistor (PMISFET)  101  and an N-type Metal Insulator Semiconductor Field Effect Transistor)  102  are connected in series to each other, and the drain of each of the PMISFET  101  and the NMISFET  102  is connected via a node N 1  to an interconnect W 1 . The source of the PMISFET  101  is connected to a power supply pad PST for supplying a power supply voltage Vdd, while the source of the NMISFET  102  is connected to a ground pad GND (voltage Vss). The gate of the PMISFET  101  is connected to a charging pad  111 , while the gate of the NMISFET  102  is connected to a discharging pad  112 . Furthermore, there are provided an interconnect W 2  arranged in a layer higher than the interconnect W 1  and crossing the interconnect W 1  when viewed in a plane, and an interconnect W 3  extending substantially parallel to the interconnect W 1  and crossing the interconnect W 2  when viewed in the same plane. The interconnect W 2  is connected to a first pad  113  for measuring current via a node N 2  and an NMISFET  103 , while the interconnect W 3  is connected to a second pad  114  for measuring current via a node N 3  and an NMISFET  104 . The gate of each of the NMISFETs  103  and  104  is connected to a current-monitoring pad  115 . The capacitance measuring circuit is configured so that it can measure currents I 1  and I 2  by bringing the first and second pads  113  and  114  for measuring current into contact with probes of ammeters  121  and  122 , respectively. When the probes of the ammeters  121  and  122  come into contact with the pads  113  and  114  for measuring current, respectively, the sources of the NMISFETs  103  and  104  are fixed at 0V. 
   The interconnect W 2  is connected via an NMISFET  105  to the ground pad GND, while the interconnect W 3  is connected via an NMISFET  106  to the ground pad GND. 
   Here, the capacitance between the interconnects W 1  and W 2  is designated C 12 , the capacitance between the interconnects W 1  and W 3  is designated C 13 , and the capacitance between the interconnects W 2  and W 3  is designated C 23 . In this relation, the capacitance C 12  is a value obtained by dividing a charge induced in the interconnect W 2  when a voltage is applied to the interconnect W 1 , by the applied voltage. The capacitance C 13  is a value obtained by dividing a charge induced in the interconnect W 3  when a voltage is applied to the interconnect W 1 , by the applied voltage. 
     FIG. 8  is a timing diagram illustrating the operation of the capacitance measuring circuit shown in  FIG. 7 . The known capacitance measuring circuit operation will be described with reference to  FIG. 8 . 
   First, the power supply voltage Vdd is fixed at a voltage Vcc, while the ground voltage Vss is fixed at 0V. A charging voltage V 111  and a discharging voltage V 112  are switched between the voltages Vcc and Vss such that both of the PMISFET  101  and the NMISFET  102  are not ON at any timing. However, there exists a timing at which both of the PMISFET  101  and the NMISFET  102  are OFF. Therefore, no flow-through current passing through both of the PMISFET  101  and the NMISFET  102  is produced. 
   Between timings t 0  and t 1 , the discharging voltage V 112  is held at the voltage Vcc so that the NMISFETs  102 ,  105  and  106  are ON. Therefore, the potentials of the nodes N 1 , N 2  and N 3  are fixed at the ground voltage Vss. 
   Between timings t 1  and t 2 , all the MISFETs  101 ,  102 ,  103 ,  104 ,  105 , and  106  are OFF. 
   Between timings t 2  and t 3 , since the PMISFET  101  and the NMISFET  102  are OFF, and the NMISFETs  103  and  104  are ON, it is possible to monitor currents. 
   Between timings t 3  and t 4 , since the PMISFET  101  is ON, a charge from the interconnect W 1  to the interconnects W 2  and W 3  is induced. At this time, currents are monitored using the ammeters  121  and  122 , thereby measuring the capacitances C 12 , C 13  and C 23 . The time between the timings t 3  and t 4  is set at a time enough to induce a charge in the interconnect W 1  and monitor the currents using the ammeters  121  and  122 . 
   Between timings t 4  and t 5 , the PMISFET  101  is OFF. 
   Between timings t 5  and t 6 , since all the MISFETs are OFF, it becomes impossible to monitor the currents. 
   Between timings t 6  and t 7 , the same operations as between the timings t 0  and t 1  are carried out. Thereafter, the above-mentioned operations for the timings t 1  through t 7  are periodically repeated. 
   The value to be observed by a measuring device using this circuit is a mean value between the currents I 1  and I 2  detected over time by the ammeters  121  and  122 , respectively. When the frequency of the gate input waveform is f(=1/T) (T denotes the time from the timing t 0  to the timing t 7 ), the following formulae (1) and (2) hold:
 
 I   1 = C   12 · Vcc·f   (1)
 
 I   2 = C   13 · Vcc·f   (2)
 
   By using the formulae (1) and (2), measured capacitance values C 12  and C 13  are obtained from the following formulae (3) and (4):
 
 C   12 = I   1 /( Vcc·f )  (3)
 
 C   13 = I   2 /( Vcc·f )  (4)
 
   This known technique is characterized in that the desired capacitances C 12  and C 13  can directly be measured without the need for canceling the parasitic capacitance of a transistor. 
   SUMMARY OF THE INVENTION 
   The known technique, however, has the following defects: 
   (1) the capacitance value C 23  between the interconnects W 2  and W 3  as shown in  FIG. 7  cannot be measured using a circuit pattern shown in  FIG. 7 ; 
   (2) even when the circuit pattern shown in  FIG. 7  is used, the charge induced in the interconnect W 1  when a voltage is applied to the interconnect W 2  and the charge induced in the interconnect W 1  when a voltage is applied to the interconnect W 3  cannot be measured; and 
   (3) the number of pads is large for the number of measurable items and typically the area of each of the pads is approximately 100 μm×100 μm, leading to an increase in the area occupied by the semiconductor device. 
   Furthermore, concerning the defect (2), the difference between Cgd(=dQg/dVd, Qg: gate charge, Vd: drain voltage) and Cdg(=dQd/dVg, Qd: drain charge, Vg: gate voltage) in the MIS capacitance cannot be measured. 
   It is an object of the present invention to provide a semiconductor device including a capacitance measuring circuit that can separately measure capacitance components. 
   The semiconductor device of the present invention comprises a capacitance measuring circuit in which, when there exist first through third conductor members, the first and second conductor members are connected via respective switching transistors to a common charging voltage supply part and the second and third conductor members are connected via respective switching transistors to a current sampling part. 
   Thereby, besides parasitic capacitances between the first and second conductor members and parasitic capacitances between the first and third conductor members, parasitic capacitances between the second and third conductor members can also be measured. Only two pads connected to a charging voltage supply part and a current sampling part, respectively become necessary on a semiconductor chip corresponding to the capacitance measuring circuit. Therefore, the number of pads of the whole semiconductor device can be decreased. 
   Furthermore, if all the conductor members are chargeable and dischargeable, then the parasitic capacitance caused between the second conductor member and the first conductor member when the second conductor member is charged or the parasitic capacitance caused between the third conductor member and the first conductor member when the third conductor member is charged, for example, can also be measured. 
   Preferably, there is provided a discharge part, and the conductor member whose parasitic capacitance is not to be measured is discharged while the parasitic capacitance between the other two conductor members is measured. 
   The first through third conductor members may be all interconnects or may be any three-way combination of a source/drain region, a substrate region and a gate electrode of a MISFET. In the latter case, the semiconductor chip has a triple well structure, thereby reducing the influence of noises in the capacitance measurement. 
   If the charging voltage supply part is operated at a power supply voltage lower than that supplied to a control circuit, then the influence of substrate noises leading to problems in the measurement of the capacitances representing analog quantities can be suppressed. 
   There may be provided an oscillator for generating a clock signal having a higher frequency than an external clock signal. This allows the control circuit to generate a waveform. The provision of a frequency divider facilitates external monitoring of the frequency. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device according to a first embodiment. 
       FIG. 2  is a timing diagram illustrating the time variation of gate biases that are output from a control circuit in the capacitance measurement using the capacitance measuring circuit and are applied to gates of MISFETs, respectively. 
       FIG. 3  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device according to a second embodiment. 
       FIG. 4  is a cross sectional view of the semiconductor device according to the second embodiment. 
       FIG. 5  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device according to a third embodiment. 
       FIG. 6  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device according to a fourth embodiment. 
       FIG. 7  is a circuit diagram illustrating the structure of a capacitance measuring circuit for measuring parasitic capacitance disclosed in Patent Document 1. 
       FIG. 8  is a timing diagram illustrating the operation of the known capacitance measuring circuit. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   (Embodiment 1) 
     FIG. 1  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device (LSI) according to a first embodiment. The capacitance measuring circuit located in the semiconductor device of this embodiment is configured to measure the capacitance (parasitic capacitance) between each two of three conductor members forming a target capacitor section (section to be measured in capacitance). 
   As shown in  FIG. 1 , the target capacitor section in the semiconductor device of this embodiment is provided with three conductor members each two opposed with dielectrics interposed therebetween. The three conductor members are an interconnect W 1  (first conductor member), an interconnect W 2  (second or third conductor member) placed in a layer higher than the interconnect W 1  and crossing the interconnect W 1  when viewed in a plane, and an interconnect W 3  (third or second conductor member) extending substantially parallel to the interconnect W 1  and crossing the interconnect W 2  when viewed in the same plane. Capacitances between the interconnects W 1  and W 2  are designated C 12  and C 21 , capacitances between the interconnects W 1  and W 3  are designated C 13  and C 31 , and capacitances between the interconnects W 2  and W 3  are designated C 23  and C 32 . In this relation, the capacitance C 12  is a value obtained by dividing a charge induced in the interconnect W 2  when a voltage is applied to the interconnect W 1 , by the applied voltage. The capacitance C 21  is a value obtained by dividing a charge induced in the interconnect W 1  when a voltage is applied to the interconnect W 2 , by the applied voltage. The capacitance C 13  is a value obtained by dividing a charge induced in the interconnect W 3  when a voltage is applied to the interconnect W 1 , by the applied voltage. The capacitance C 31  is a value obtained by dividing a charge induced in the interconnect W 1  when a voltage is applied to the interconnect W 3 , by the applied voltage. The capacitance C 23  is a value obtained by dividing a charge induced in the interconnect W 3  when a voltage is applied to the interconnect W 2 , by the applied voltage. The capacitance C 32  is a value obtained by dividing a charge induced in the interconnect W 2  when a voltage is applied to the interconnect W 3 , by the applied voltage. 
   In the capacitance measuring circuit, there are placed three PMISFETs  1 ,  2  and  3  (charge-side switching transistors) placed in parallel with one another and three NMISFETs  4 ,  5  and  6  (discharge-side switching transistors) connected in series to the PMISFETs  1 ,  2  and  3 , respectively. The sources of the PMISFETs  1 ,  2  and  3  are commonly connected via a charging voltage supply part to a power supply pad PST for supplying a power supply voltage Vdd, while the sources of the NMISFETs  4 ,  5  and  6  are commonly connected via a discharging part to a ground pad GND (voltage Vss). The drains of the PMISFET  1  and the NMISFET  4  are connected via a node N 1  to the interconnect W 1 . The drains of the PMISFET  2  and the NMISFET  5  are connected via a node N 2  to the interconnect W 2 . The drains of the PMISFET  3  and the NMISFET  6  are connected via a node N 3  to the interconnect W 3 . 
   That is, the interconnect W 1  is connected via the PMISFET  1  to the charging voltage supply part and the power supply pad PST, the interconnect W 2  is connected via the PMISFET  2  to the charging voltage supply part and the power supply pad PST, and the interconnect W 3  is connected via the PMISFET  3  to the charging voltage supply part and the power supply pad PST. 
   Although not shown in  FIG. 1 , the power supply pad PST is also connected to an active region (substrate region) of each of the PMISFETs  1 ,  2  and  3 , and the ground pad GND is also connected to an active region of each of the NMISFETs  4 ,  5 ,  6 ,  7 ,  8 , and  9 , whereby these pads supply potentials to the substrates. 
   The interconnect W 1  is connected via the node N 1  and the NMISFET  7  (third switching transistor for measuring current) through a current sampling part to a current-monitoring pad  41 . The interconnect W 2  is connected via the node N 2  and the NMISFET  8  (first or second switching transistor for measuring current) through the current sampling part to the current-monitoring pad  41 . The interconnect W 3  is connected via the node N 3  and the NMISFET  9  (second or first switching transistor for measuring current) through the current sampling part to the current-monitoring pad  41 . That is, all of the interconnects W 1 , W 2  and W 3  are connected to the current-monitoring pad  41  through the common current-sampling part and are configured so that their currents I can be measured by bringing a probe of an ammeter  45  into contact with the current-monitoring pad  41 . The outlet side of the ammeter  45  is fixed at the ground level (0V). 
   A control circuit  31 , an oscillator  32  for generating a clock signal having a higher frequency than an external clock signal and a frequency divider  33  are connected in parallel to one another between the power supply pad PST (voltage Vdd) and the ground pad GND (voltage Vss). The control circuit  31  operates in synchronization with a high-frequency clock signal Clk generated by the oscillator  32  and applies a bias for ON/OFF switching to each of the gates G 1  through G 9  of the MISFETs  1  through  9 . A high-frequency signal output from the oscillator  32  is input to an input part of the frequency divider  33 , and an output part of the frequency divider  33  is connected to a frequency-monitoring pad  43 . 
   According to the semiconductor device of this embodiment, in the capacitance measuring circuit, the interconnect W 1  that is the first conductor member is connected via the PMISFET  1  that is the charge-side switching transistor to the charging voltage supply part, the interconnect W 2  (or W 3 ) that is the second conductor member and the interconnect W 3  (or W 2 ) that is the third conductor member are connected to the current-sampling part via the NMISFETs  8  and  9  that are the switching transistors for measuring current, respectively, and the interconnect W 2  (or W 3 ) that is the second conductor member is connected to the charging voltage supply part via the PMISFET  2  (or  3 ) that is the charge-side switching transistor. Therefore, it becomes possible to measure the capacitance C 23  between the interconnects W 2  and W 3  (or the capacitance C 32  between the interconnects W 3  and W 2 ) in addition to the capacitance C 12  between the interconnects W 1  and W 2  and the capacitance C 13  between the interconnects W 1  and W 3 . 
   Furthermore, the interconnects W 2  and W 3  are connected to the charging voltage supply part via the PMISFET  2  and  3  that are the charge-side switching transistors, and the interconnect W 1  is connected to the current-sampling part via the NMISFET  7  that is the switching transistor for measuring current. Therefore, as will be described later, it becomes possible to separately measure all the capacitive components among the three interconnects W 1 , W 2  and W 3 , i.e., the capacitances C 12  and C 21  between the interconnects W 1  and W 2 , the capacitances C 13  and C 31  between the interconnects W 1  and W 3  and the capacitances C 23  and C 32  between the interconnects W 2  and W 3 . 
   Moreover, the interconnects W 1 , W 2  and W 3  are connected via the NMISFETs  4 ,  5  and  6  that are the discharge switching transistors, respectively, through the discharge part to the ground pad. Therefore, in a mode for measuring the capacitance between two interconnects, it becomes possible to fix the potential of an interconnect that is not involved in the capacitance measurement, thereby preventing the accuracy of measuring the capacitance from being deteriorated due to the influence of the interconnect that is not involved in the capacitance measurement. 
   The capacitance measuring circuit of this embodiment has the advantages that the inclusion of the oscillator  32  therein allows the control circuit  31  to generate a waveform by applying a clock signal having a higher frequency than an external clock signal to the control circuit  31  and the inclusion of the frequency divider  33  therein simplifies the external monitoring of the frequency. 
     FIG. 2  is a timing diagram illustrating the time variation of gate biases Vg 1  through Vg 9  that are output from the control circuit  31  in the capacitance measurement using the capacitance measuring circuit and are applied to the gates G 1  through G 9  of the MISFETs  1  through  9 . In this figure, T 12  denotes the period during which the capacitance C 12  is monitored, T 13  denotes the period during which the capacitance C 13  is monitored, T 21  denotes the period during which the capacitance C 21  is monitored, T 23  denotes the period during which the capacitance C 23  is monitored, T 31  denotes the period during which the capacitance C 31  is monitored, and T 32  denotes the period during which the capacitance C 32  is monitored. Although not shown in  FIG. 2 , the power supply voltage Vdd is fixed at a voltage Vcc, and the ground voltage Vss is fixed at 0V. 
   Control During the Period T 12    
   First, the NMISFETs  4 ,  5  and  6  are ON at a timing t 10 , because the gate biases Vg 4 , Vg 5  and Vg 6  of the NMISFETs  4 ,  5  and  6  are all at H level. The PMISFETs  1 ,  2  and  3  are OFF, because the gate biases Vg 1 , Vg 2  and Vg 3  of the NMISFETs  1 ,  2  and  3  are all at H level. The NMISFETs  7 ,  8  and  9  are OFF, because the gate biases Vg 7 , Vg 8  and Vg 9  of the NMISFETs  7 ,  8  and  9  are all at L level. Since at this time the NMISFETs  4 ,  5  and  6  are ON and the PMISFET  1 ,  2  and  3  are OFF, charges on the nodes N 1 , N 2  and N 3  are all released into the ground. 
   At a timing t 11 , the gate biases Vg 4  and Vg 5  of the NMISFETs  4  and  5  change to L level so that the NMISFETs  4  and  5  turn OFF. Therefore, the nodes N 1  and N 2  are cut off from the ground pad GND. 
   Next, at a timing t 12 , the gate bias Vg 8  of the NMISFET  8  changes to H level so that the NMISFET  8  turns ON. Therefore, the interconnect W 2  is brought into conduction with the current-monitoring pad  41  via the node N 2 . 
   Next, at a timing t 13 , the gate bias Vg 1  of the PMISFET  1  changes to L level so that the PMISFET  1  turns ON. Therefore, the interconnect W 1  is brought into conduction with the power supply pad PST via the node N 1 , and thus the interconnect W 1  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 13  to the timing t 14  to measure the current I, the capacitance value C 12  between the interconnects W 1  and W 2  can be measured from the current I corresponding to the charge induced in the interconnect W 2  when the voltage Vcc is applied to the interconnect W 1 , on the basis of the following formula (5):
 
 C   12 = I /( Vcc·f )  (5)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes the time from the timing t 10  to the timing t 17 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 13 , t 12 , t 11 , and t 10  are carried out at the timings t 14 , t 15 , t 16 , and t 17 , respectively. Finally, the control state at the timing  17  is returned to the same state as at the timing t 10 . 
   During the period T 12 , the PMISFET  1  and the NMISFET  4  or the NMISFET  7  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  1  and the NMISFET  4  or the NMISFET  7  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 12 , the PMISFETs  2  and  3  are always OFF. Thus, the interconnects W 2  and W 3  are not charged with the voltage Vcc. Moreover, during the period T 12 , the NMISFETs  7  and  9  are always OFF. Thus, the nodes N 1  and N 3  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 1  and W 3  are not observed. Since during the period T 12  the gate bias Vg 6  of the NMISFET  6  is always at H level, the NMISFET  6  is always ON, and the potential of the node N 3  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 3  is not observed. 
   Control During the Period T 13    
   First, at a timing t 20 , each of the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  is at the same voltage level as at the timing t 10  during the period T 12 . 
   At a timing t 21 , the gate biases Vg 4  and Vg 6  of the NMISFETs  4  and  6  change to L level so that the NMISFETs  4  and  6  turn OFF. Therefore, the nodes N 1  and N 3  are cut off from the ground pad GND. 
   Next, at a timing t 22 , the gate bias Vg 9  of the NMISFET  9  changes to H level so that the NMISFET  9  turns ON. Therefore, the interconnect W 3  is brought into conduction with the current-monitoring pad  41  via the node N 3 . 
   Next, at a timing t 23 , the gate bias Vg 1  of the PMISFET  1  changes to L level so that the PMISFET  1  turns ON. Therefore, the interconnect W 1  is brought into conduction with the power supply pad PST via the node N 1 , and thus the interconnect W 1  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 23  to the timing t 24  to measure the current I, the capacitance value C 13  between the interconnects W 1  and W 3  can be measured from the current I corresponding to the charge induced in the interconnect W 3  when the voltage Vcc is applied to the interconnect W 1 , on the basis of the following formula (6):
 
 C   13 = I /( Vcc·f )  (6)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes the time from the timing t 20  to the timing t 27 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 23 , t 22 , t 21 , and t 20  are carried out at the timings t 24 , t 25 , t 26 , and t 27 , respectively. Finally, the control state at the timing  27  is returned to the same state as at the timing t 20 . 
   During the period T 13 , the PMISFET  1  and the NMISFET  4  or the NMISFET  7  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  1  and the NMISFET  4  or the NMISFET  7  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 13 , the PMISFETs  2  and  3  are always OFF. Thus, the interconnects W 2  and W 3  are not charged with the voltage Vcc. Moreover, during the period T 13 , the NMISFETs  7  and  8  are always OFF. Thus, the nodes N 1  and N 2  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 1  and W 2  are not observed. Since during the period T 13  the gate bias Vg 5  of the NMISFET  5  is always at H level, the NMISFET  5  is always ON, and the potential of the node N 2  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 2  is not observed. 
   Control During the Period T 21    
   First, at a timing t 30 , each of the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  is at the same voltage level as at the timing t 10  during the period T 12 . 
   At a timing t 31 , the gate biases Vg 4  and Vg 5  of the NMISFETs  4  and  5  change to L level so that the NMISFETs  4  and  5  turn OFF. Therefore, the nodes N 1  and N 2  are cut off from the ground pad GND. 
   Next, at a timing t 32 , the gate bias Vg 7  of the NMISFET  7  changes to H level so that the NMISFET  7  turns ON. Therefore, the interconnect W 1  is brought into conduction with the current-monitoring pad  41  via the node N 1 . 
   Next, at a timing t 33 , the gate bias Vg 2  of the PMISFET  2  changes to L level so that the PMISFET  2  turns ON. Therefore, the interconnect W 2  is brought into conduction with the power supply pad PST via the node N 2 , and thus the interconnect W 2  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 33  to the timing t 34  to measure the current I, the capacitance value C 21  between the interconnects W 2  and W 1  can be measured from the current I corresponding to the charge induced in the interconnect W 1  when the voltage Vcc is applied to the interconnect W 2 , on the basis of the following formula (7):
 
 C   21 = I /( Vcc·f )  (7)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes a time from the timing t 30  to the timing t 37 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 33 , t 32 , t 31 , and t 30  are carried out at the timings t 34 , t 35 , t 36 , and t 37 , respectively. Finally, the control state at the timing t 37  is returned to the same state as at the timing t 30 . 
   During the period T 21 , the PMISFET  2  and the NMISFET  5  or the NMISFET  8  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  2  and the NMISFET  5  or the NMISFET  8  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 21 , the PMISFETs  1  and  3  are always OFF. Thus, the interconnects W 1  and W 3  are not charged with the voltage Vcc. Moreover, during the period T 21 , the NMISFETs  7  and  9  are always OFF. Thus, the nodes N 1  and N 3  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 1  and W 3  are not observed. Since during the period T 21  the gate bias Vg 6  of the NMISFET  6  is always at H level, the NMISFET  6  is always ON, and the potential of the node N 3  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 3  is not observed. 
   Control During the Period T 23    
   First, at a timing t 40 , each of the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  is at the same voltage level as at the timing t 10  during the period T 12 . 
   At a timing t 41 , the gate biases Vg 5  and Vg 6  of the NMISFETs  5  and  6  change to L level so that the NMISFETs  5  and  6  turn OFF. Therefore, the nodes N 1  and N 3  are cut off from the ground pad GND. 
   Next, at a timing t 42 , the gate bias Vg 9  of the NMISFET  9  changes to H level so that the NMISFET  9  turns ON. Therefore, the interconnect W 3  is brought into conduction with the current-monitoring pad  41  via the node N 3 . 
   Next, at a timing t 43 , the gate bias Vg 2  of the PMISFET  2  changes to L level so that the PMISFET  2  turns ON. Therefore, the interconnect W 2  is brought into conduction with the power supply pad PST via the node N 2 , and thus the interconnect W 2  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 43  to the timing t 44  to measure the current I, the capacitance value C 23  between the interconnects W 2  and W 3  can be measured from the current I corresponding to the charge induced in the interconnect W 3  when the voltage Vcc is applied to the interconnect W 2 , on the basis of the following formula (8):
 
 C   23 = I /( Vcc·f )  (8)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes the time from the timing t 40  to the timing t 47 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 43 , t 42 , t 41 , and t 40  are carried out at the timings t 44 , t 45 , t 46 , and t 47 , respectively. Finally, the control state at the timing t 47  is returned to the same state as at the timing t 40 . 
   During the period T 23 , the PMISFET  2  and the NMISFET  5  or the NMISFET  8  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  2  and the NMISFET  5  or the NMISFET  8  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 23 , the PMISFETs  1  and  3  are always OFF. Thus, the interconnects W 1  and W 3  are not charged with the voltage Vcc. Moreover, during the period T 23 , the NMISFETs  7  and  8  are always OFF. Thus, the nodes N 1  and N 2  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 1  and W 2  are not observed. Since during the period T 23  the gate bias Vg 4  of the NMISFET  4  is always at H level, the NMISFET  4  is always ON, and the potential of the node N 1  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 1  is not observed. 
   Control During the Period T 31    
   First, at a timing t 50 , each of the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  is at the same voltage level as at the timing t 10  during the period T 12 . 
   At a timing t 51 , the gate biases Vg 4  and Vg 6  of the NMISFETs  4  and  6  change to L level so that the NMISFETs  4  and  6  turn OFF. Therefore, the nodes N 1  and N 3  are cut off from the ground pad GND. 
   Next, at a timing t 52 , the gate bias Vg 7  of the NMISFET  7  changes to H level so that the NMISFET  7  turns ON. Therefore, the interconnect W 1  is brought into conduction with the current-monitoring pad  41  via the node N 1 . 
   Next, at a timing t 53 , the gate bias Vg 3  of the PMISFET  3  changes to L level so that the PMISFET  3  turns ON. Therefore, the interconnect W 3  is brought into conduction with the power supply pad PST via the node N 3 , and thus the interconnect W 3  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 53  to the timing t 54  to measure the current I, the capacitance value C 31  between the interconnects W 3  and W 1  can be measured from the current I corresponding to the charge induced in the interconnect W 1  when the voltage Vcc is applied to the interconnect W 3 , on the basis of the following formula (9):
 
 C   31 = I /( Vcc·f )  (9)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes the time from the timing t 50  to the timing t 57 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 53 , t 52 , t 51 , and t 50  are carried out at the timings t 54 , t 55 , t 56 , and t 57 , respectively. Finally, the control state at the timing t 57  is returned to the same state as at the timing t 50 . 
   During the period T 31 , the PMISFET  3  and the NMISFET  6  or the NMISFET  9  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  3  and the NMISFET  6  or the NMISFET  9  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 31 , the PMISFETs  1  and  2  are always OFF. Thus, the interconnects W 1  and W 2  are not charged with the voltage Vcc. Moreover, during the period T 31 , the NMISFETs  8  and  9  are always OFF. Thus, the nodes N 2  and N 3  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 2  and W 3  are not observed. Since during the period T 31  the gate bias Vg 5  of the NMISFET  5  is always at H level, the NMISFET  5  is always ON, and the potential of the node N 2  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 2  is not observed. 
   Control During the Period T 32    
   First, at a timing t 60 , each of the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  is at the same voltage level as at the timing t 10  during the period T 12 . 
   At a timing t 61 , the gate biases Vg 5  and Vg 6  of the NMISFETs  5  and  6  change to L level so that the NMISFETs  5  and  6  turn OFF. Therefore, the nodes N 2  and N 3  are cut off from the ground pad GND. 
   Next, at a timing t 62 , the gate bias Vg 8  of the NMISFET  8  changes to H level so that the NMISFET  8  turns ON. Therefore, the interconnect W 2  is brought into conduction with the current-monitoring pad  41  via the node N 2 . 
   Next, at a timing t 63 , the gate bias Vg 3  of the PMISFET  3  changes to L level so that the PMISFET  3  turns ON. Therefore, the interconnect W 3  is brought into conduction with the power supply pad PST via the node N 3 , and thus the interconnect W 3  is charged. 
   Accordingly, when the probe of the ammeter  45  is brought into contact with the current-monitoring pad  41  during a period from the timing t 63  to the timing t 64  to measure the current I, the capacitance value C 32  between the interconnects W 3  and W 2  can be measured from the current I corresponding to the charge induced in the interconnect W 1  when the voltage Vcc is applied to the interconnect W 3 , on the basis of the following formula (10):
 
 C   32 = I /( Vcc·f )  (10)
 
where f(=1/T) is the frequency of the gate input waveform and T denotes the time from the timing t 60  to the timing t 67 .
 
   Thereafter, gate biases are changed such that the operations opposite to those at the timings t 63 , t 62 , t 61 , and t 60  are carried out at the timings t 64 , t 65 , t 66 , and t 67 , respectively. Finally, the control state at the timing t 67  is returned to the same state as at the timing t 60 . 
   During the period T 32 , the PMISFET  3  and the NMISFET  6  or the NMISFET  9  are not ON simultaneously. Thus, a flow-through current that flows through the PMISFET  3  and the NMISFET  6  or the NMISFET  9  does not flow from the power supply pad PST into the current-monitoring pad  41  and the ground pad GND. During the period T 32 , the PMISFETs  1  and  2  are always OFF. Thus, the interconnects W 1  and W 2  are not charged with the voltage Vcc. Moreover, during the period T 32 , the NMISFETs  7  and  9  are always OFF. Thus, the nodes N 1  and N 3  are not brought into conduction with the current-monitoring pad  41 , and consequently currents from the interconnects W 1  and W 3  are not observed. Since during the period T 32  the gate bias Vg 4  of the NMISFET  4  is always at H level, the NMISFET  4  is always ON, and the potential of the node N 1  is fixed at 0V. Therefore, the capacitance relating to the interconnect W 1  is not observed. 
   According to the capacitance measuring circuit of this embodiment, when there exist three interconnects W 1 , W 2  and W 3 , the capacitances C 21 , C 23 , C 31 , and C 32  can be measured by charging the interconnects W 2  and W 3 , besides the capacitances C 12  and C 13  that can be observed by charging the interconnect W 1 . 
   In addition, only five pads are necessary for this embodiment. Therefore, the number of pads can be significantly decreased as compared with the number of pads, seven, that is required for the known capacitance measuring circuit shown in  FIG. 7 , resulting in the reduced area of the semiconductor device. 
   (Embodiment 2) 
     FIG. 3  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device (LSI) according to a second embodiment. The capacitance measuring circuit located in the semiconductor device of this embodiment is configured to measure the capacitance (parasitic capacitance) between each two of three conductor members forming a target capacitor section. 
   As shown in  FIG. 3 , the target capacitor section in the semiconductor device of this embodiment is also provided with three conductor members each two opposed with dielectrics interposed therebetween. However, unlike the first embodiment, the three conductor members of this embodiment are a source/drain region SD (first conductor member) formed by doping part of a semiconductor substrate with impurities, a substrate region SUB (second conductor member) corresponding to a well and a gate electrode GT (third conductor member). 
   On the other hand, the structure of the capacitance measuring circuit is the same as that of the first embodiment. Capacitances between the source/drain region SD and the substrate region SUB are designated Cdb (corresponding to C 12 ) and Cbd (corresponding to C 21 ), capacitances between the source/drain region SD and the gate electrode GT are designated Cdg (corresponding to C 13 ) and Cgd (corresponding to C 31 ), and capacitances between the substrate region SUB and the gate electrode GT are designated Cbg (corresponding to C 23 ) and Cgb (corresponding to C 32 ). In this relation, the capacitance Cdb is a value obtained by dividing a charge induced in the substrate region SUB when a voltage is applied to the source/drain region SD, by the applied voltage. The capacitance Cbd is a value obtained by dividing a charge induced in the source/drain region SD when a voltage is applied to the substrate region SUB, by the applied voltage. The capacitance Cdg is a value obtained by dividing a charge induced in the gate electrode GT when a voltage is applied to the source/drain region SD, by the applied voltage. The capacitance Cgd is a value obtained by dividing a charge induced in the source/drain region SD when a voltage is applied to the gate electrode GT, by the applied voltage. The capacitance Cbg is a value obtained by dividing a charge induced in the gate electrode GT when a voltage is applied to the substrate region SUB, by the applied voltage. The capacitance Cgb is a value obtained by dividing a charge induced in the substrate region SUB when a voltage is applied to the gate electrode GT, by the applied voltage. 
     FIG. 4  is a cross sectional view of the semiconductor device of this embodiment. As shown in this figure, the semiconductor device of this embodiment has a structure in which the target capacitor section is surrounded by a triple well. 
   This figure shows the cross sectional structure of the target capacitor section and the capacitance measuring circuit that are part of a logic circuit located in the semiconductor device but does not show the other regions such as a memory region and a peripheral circuit region. 
   The semiconductor substrate is partitioned into plural active regions by isolation regions  55  having a shallow trench structure. In the semiconductor substrate, there are provided a P-well  51  occupying most of the semiconductor substrate, a deep N-well  52  the lower side of which is surrounded by the P-well  51 , a P-well  53  the lower side of which is covered by the deep N-well  52 , and an N-well  54  for separating the P-wells  53  and  51  from each other. 
   The NMISFET of the target capacitor section comprises a source/drain region  56  (SD) formed by doping the P-well  53  corresponding to the substrate region SUB with N-type impurities, and a gate electrode  61  (GT). On the other hand, the NMISFET of the capacitance measuring circuit comprises a source/drain region  58  formed by doping the P-well  51  with N-type impurities, and a gate electrode  62 . 
   Also in this embodiment, when the capacitances C 12  and C 21  in the first embodiment are replaced with the capacitances Cdb and Cbd, the capacitances C 13  and C 31  are replaced with the capacitances Cdg and Cgd, and the capacitances C 23  and C 32  are replaced with the capacitances Cbg and Cgb, each of the capacitances Cdb, Cbd, Cdg, Cgd, Cbg, and Cgb can be measured utilizing the control method shown in  FIG. 2  and the formulae (5) through (10). 
   Since this embodiment employs, particularly, the structure of the semiconductor device in which the target capacitor section is surrounded by the triple well, capacitances between each two of members of the MISFET can be measured with high accuracy, while noises from the MISFET in the capacitance measuring circuit operating by a high-frequency clock are cut off. 
   Furthermore, when the voltages of the power supply pad PST, the ground pad GND and the pad  41  for measuring current are changed, the capacitances can be measured in an arbitrary voltage state. In particular, the MIS capacitance has a voltage dependency. The voltage dependencies of the capacitances can be measured by the following formula (11).
 
 C ( v )={ I ( V+δV )− I ( V )}/ f   (11)
 
   (Embodiment 3) 
     FIG. 5  is a circuit diagram illustrating the structure of a capacitance measuring circuit placed in a semiconductor device (LSI) according to a third embodiment. The capacitance measuring circuit located in the semiconductor device of this embodiment is configured to measure the capacitance (parasitic capacitance) between each two of three conductor members forming a target capacitor section. 
   Also in this embodiment, as shown in  FIG. 5 , an interconnect W 1  (first conductor member), an interconnect W 2  (second conductor member) and an interconnect W 3  (third conductor member) are placed as three conductor members in the target capacitor section. The target capacitor section is configured to measure the capacitances C 12  and C 21  between the interconnects W 1  and W 2 , the capacitances C 13  and C 31  between the interconnects W 1  and W 3 , and the capacitances C 23  and C 32  between the interconnects W 2  and W 3 . 
   The structure of the capacitance measuring circuit of this embodiment is characterized in that two MISFETs  7   a  and  7   b  that are equivalent to the NMISFET  7  in the first embodiment are connected in series, two MISFETs  8   a  and  8   b  that are equivalent to the NMISFET  8  are connected in series, and two MISFETs  9   a  and  9   b  that are equivalent to the NMISFET  9  are connected in series. The pairs of MISFETs receive common gate biases Vg 7 , Vg 8  and Vg 9 , respectively. While one of each pair of MISFETs (for example, NMISFET  7   a ,  8   a  or  9   a ) is a current-monitoring MISFET having the same threshold voltage as the NMISFETs  7 ,  8  or  9  in the first embodiment, the other (for example, NMISFETs  7   b ,  8   b  or  9   b ) is a MISFET for suppressing off-leakage current, which has a higher threshold voltage than the NMISFETs  7 ,  8  and  9  in the first embodiment. The other structure is identical with the structure of the measuring circuit shown in  FIG. 1 . 
   Also in the capacitance measuring circuit of this embodiment, the capacitances C 12  and C 21  between the interconnects W 1  and W 2 , the capacitances C 13  and C 31  between the interconnects W 1  and W 3 , and the capacitances C 23  and C 32  between the interconnects W 2  and W 3  can be measured utilizing the control method shown in  FIG. 2  and the formulae (5) through (10). 
   According to the capacitance measuring circuit of this embodiment, as in the first embodiment, the capacitances C 12 , C 21 , C 13 , C 31 , C 23 , and C 32  between each two of the three conductor members can be measured while the number of pads is decreased. 
   In addition, since in the capacitance measuring circuit of this embodiment, a current-monitoring MISFET (for example, NMISFETs  7   a ,  8   a  or  9   a ) and a MISFET for suppressing off-leakage current (for example, NMISFET  7   b ,  8   b  or  9   b ) having a higher threshold voltage than the current-monitoring MISFET are placed in series between each of the nodes N 1 , N 2  and N 3  and the pad  41  for measuring current, this effectively decreases leakage current. 
   Furthermore, since the operations of the current-monitoring MISFET and the MISFET for suppressing off-leakage current are controlled by a common control signal (a gate bias Vg 7 , Vg 8  or Vg 9 ), a redundant control circuit is unnecessary. Therefore, the structure of the control circuit can be simplified. 
   When the capacity to drive the current-monitoring MISFET is less necessary, the number of MISFETs placed in series with that current-monitoring MISFET can be increased, thereby enhancing the effect of decreasing leakage current. 
   The conductor members in the third embodiment are not limited to the interconnects W 1 , W 2  and W 3  but may be a source/drain region, a substrate region and a gate electrode as shown in  FIGS. 3 and 4 . 
   (Embodiment 4) 
     FIG. 6  is a circuit diagram illustrating the structure of a capacitance measuring circuit for measuring the capacitances of capacitors placed in a semiconductor device (LSI) according to a fourth embodiment. The capacitance measuring circuit located in the semiconductor device of this embodiment is configured to measure the capacitance between each two of three conductor members forming a target capacitor section. 
   Also in this embodiment, as shown in  FIG. 6 , an interconnect W 1  (first conductor member), an interconnect W 2  (second conductor member) and an interconnect W 3  (third conductor member) are placed as three conductor members in the target capacitor section. The target capacitor section is configured to measure the capacitances C 12  and C 21  between the interconnects W 1  and W 2 , the capacitances C 13  and C 31  between the interconnects W 1  and W 3 , and the capacitances C 23  and C 32  between the interconnects W 2  and W 3 . 
   The structure of the capacitance measuring circuit of this embodiment is characterized in that there are provided power supply pads PST 1  and PST 2  for individually supplying power supply voltages Vdd 1  (for example, 0.1V) and Vdd 2  (for example, 1.2V) to the capacitance measuring circuit and the interconnects W 1 , W 2  and W 3  of the target capacitor section. The configurations of the other parts are identical with those of the first embodiment. 
   Also in the capacitance measuring circuit of this embodiment, the capacitances C 12  and C 21  between the interconnects W 1  and W 2 , the capacitances C 13  and C 31  between the interconnects W 1  and W 3 , and the capacitances C 23  and C 32  between the interconnects W 2  and W 3  can be measured utilizing the control method shown in  FIG. 2  and the formulae (5) through (10). 
   According to the capacitance measuring circuit of this embodiment, as in the first embodiment, the capacitances C 12 , C 21 , C 13 , C 31 , C 23 , and C 32  between each two of the three conductor members can be measured while the number of pads is decreased. 
   In addition, since in the semiconductor device of this embodiment there are provided power supply pads PST 1  and PST 2  for individually supplying power supply voltages Vdd 1  and Vdd 2  to the capacitance measuring circuit and the interconnects W 1 , W 2  and W 3  of the target capacitor section, the following effects can be delivered. 
   The power supply voltage Vdd 1  supplied to the interconnects W 1 , W 2  and W 3  is not for controlling the operations of the MISFETs. Thus, the voltage Vdd 1  is not required to be much high. The reason is that the gate biases Vg 1  through Vg 9  of the MISFETs  1  through  9  are supplied from the control circuit  31 . If the voltage between the source and drain in each of the MISFETs  1  through  9  is lowered, the operating speed of that MISFET  1  through  9  may be decreased to some extent. In such a case, since the operating frequency is lowered, the function of measuring the capacitances is not degraded. When the voltages applied to the interconnects W 1 , W 2  and W 3  are increased, noises are easily included in the currents I to be measured. Contrarily, when, as in this embodiment, the power supply voltage Vdd 1  is decreased, the occurrence of the noise can be suppressed. 
   On the other hand, the power supply voltage Vdd 2  supplied to a capacitance sampling part such as the control circuit  31  is for controlling the operations of the MISFETs. Thus, in order to keep the operating speeds of the MISFETs high, the voltage Vdd 2  must be high to some extent. Even when the power supply voltage Vdd 2  is made higher, the occurrence of noise has less effect on the operation of each MISFET. In general, noises of the substrate lead to inconveniences for an analog circuit but present no problem for a logic circuit. 
   The conductor members of the fourth embodiment are not limited to the interconnects W 1 , W 2  and W 3  but may be a source/drain region, a substrate region and a gate electrode as shown in  FIGS. 3 and 4 . In the capacitance measuring circuit of the fourth embodiment, each of the NMISFETs  7 ,  8  and  9  may comprise plural MISFETs placed in series as shown in  FIG. 5 . 
   The number of conductor members placed in the target capacitor section, for example, interconnects, may be four or more. Also in this case, if, as shown in  FIGS. 1 ,  3 ,  5 , and  6 , one PMISFET and two NMISFETs are placed for each of the conductor members, then the capacitance between each two of the interconnects can be measured. 
   In each of the embodiments, the semiconductor substrate includes a substrate wholly made of a semiconductor (for example, a semiconductor such as Si, Ge or GaAs), an SOI substrate, and a substrate having a heterojunction (for example, a Si/SiGe-type semiconductor substrate). 
   According to the semiconductor device of the present invention, the capacitances (parasitic capacitances) among three or more conductor members can be measured separately while the number of necessary pads is decreased.