JP5086591B2 - Capacity measuring device and capacity measuring method - Google Patents

Description

  The present invention relates to a capacitance measuring apparatus and a capacitance measuring method used for quasi-static capacitance measurement of a capacitive element in development of a semiconductor device or a semiconductor process.

  In the development of semiconductor devices and semiconductor processes, capacitance measurement of an object to be measured (DUT: Device Under Test) is performed for evaluation of the semiconductor devices and semiconductor processes. Capacitance measurement of an object to be measured is broadly classified into high-frequency capacitance measurement and low-frequency (quasi-static) capacitance measurement. In capacitance measurement at a low frequency, due to the recent miniaturization of semiconductor processes, the capacitance to be measured is reduced, and a technique capable of performing high-precision measurement is required.

  The step voltage method is a method for measuring the amount of change in charge generated by changing the voltage applied to the object to be measured, and obtaining the capacitance value of the object to be measured from the amount of change in charge charge and the amount of change in applied voltage. For example, Patent Document 1 discloses a technique related to the step voltage method.

  By the way, with the miniaturization of the semiconductor process, particularly in the case of capacitance measurement at low frequency, a large leak current due to the resistance component of the measurement object flows into the ammeter for measuring the charging current flowing through the measurement object. There is a problem that this causes an error in capacity measurement. FIG. 5 shows an example of the influence of this leakage current. When the voltage applied to the object to be measured is changed, a charging current flows through the object to be measured, and the charge charge (the area of the current (I) graph in FIG. 5) changes. When there is no leakage current, the current that flows into the ammeter is only the charging current that flows through the object to be measured, but when there is a leakage current, the leakage current is also in addition to the charging current that flows through the object to be measured. As a result, the amount of change in the charge to be measured cannot be measured correctly. Therefore, there is a demand for a capacitance measuring method capable of correcting the charge corresponding to the leakage current. A conventional example of a capacitance measuring method capable of correcting a leakage current will be shown below.

The relationship among the capacitance C (unit F), charge charge Q (unit C), and applied voltage V (unit V) of the measurement target is expressed by the following equation.
Q = CV (1)

Assuming that the capacitance C of the object to be measured is constant, if the voltage V applied to the object to be measured is changed from a certain voltage V _set1 to a different voltage V _set2 , the charged charge of the object to be measured is also changed from a certain value Q _1. to change to a different value Q _2. That is, the charge charge changes by ΔQ (= Q ₂ −Q ₁ ). This charge charge change amount ΔQ is obtained by integrating the charging current I as in the following equation.
ΔQ = ∫Idt (2)

FIG. 6 is a diagram showing an example in which the change amount ΔQ of the charge when the applied voltage is changed is obtained by rectangular approximation of a section for each period Δt _PLC determined as a predetermined integer multiple of PLC (Power Line Cycle). It is. Δt _PLC is, for example, 20 ms when the frequency of the power supply voltage is 50 Hz, and is 16.67 ms, for example, when the frequency of the power supply voltage is 60 Hz. In this case, the change amount ΔQ of the charge charge is approximately expressed by the following equation.
ΔQ ≒ ΣI _k * Δt _PLC (3)
However, k = 1, 2,..., T _cinteg / Δt _PLC . T _cinteg is the integration time of the charging current.

FIG. 9 is a block diagram when performing measurement by the conventional step voltage method. The output of the variable voltage source 82 is connected to one end of the measurement target (DUT) 81, and the other end of the measurement target 81 is The ammeter 84 is connected to the ground terminal. On the other hand, a voltmeter 83 is connected to the output of the variable voltage source 82. FIG. 7 is a diagram showing a measurement sequence by the conventional step voltage method, and shows a change in applied voltage in one measurement step. First, the value of the applied voltage at the variable voltage source 82 is set to a certain value V _set1 . When predetermined time from the setting of the applied voltage delay1 has elapsed, measurements are taken of the applied voltages V ₁ by voltmeter 83, followed by measurement of the leakage current I _L1 by the current meter 84 is carried out. Thus measurement of the applied voltage V ₁ and the measurement of the leakage current I _L1 would be done in the order is because the voltmeter 83 and current meter 84 share one A / D converter. After measuring the applied voltage V _1, the measurement of the charging current by the ammeter 84 is started, and the set value of the applied voltage is changed to a different value V _set2 . As a result, the applied voltage increases.

The measurement of the charging current by the ammeter 84 is repeated T _cinteg / Δt _PLC at Δt _PLC intervals, and the integrated value is obtained as the charge charge change amount ΔQ _total . When the measurement of the charging current is completed, the voltmeter 83 measures the applied voltage V ₂ , and then the ammeter 84 measures the leakage current I _L2 .

The capacitance value C is obtained using the following equation.
C = ΔQ / ΔV = (ΔQ _total −ΔQ _Leak + Q _correction ) / (V ₂ −V ₁ ) (4)
= {(ΣI _k * Δt _PLC ) −ΔQ _Leak } / (V ₂ −V ₁ ) (5)
Here, ΔQ _Leak is the amount of change in the charge due to the leakage current, and as shown in FIG. 8, the following equation is obtained using the trapezoidal approximation based on the assumption that the charge charge increases linearly with time. Is required.

ΔQ _Leak = 1/2 (I _L1 + I _L2 ) τ + I _L2 (T _{cinteg −τ} ) (6)
Here, τ is a charging time for the object to be measured, and this time is determined as follows.

In this measurement, the ammeter 84 measures the charging current every period Δt _PLC and simultaneously monitors or monitors the state of the ammeter 84. If the output voltage is not equal to the set voltage value, it is determined that charging is in progress. It is considered that the charging is completed when the voltage becomes equal to the set voltage value (hereinafter, this state is referred to as a Vloop state).

The reason why the charging current is measured every period Δt _PLC and the state of the ammeter 84 is monitored is to cancel the influence of the power line noise.

In equation (4), Q _correction is the amount of charge charged in the range resistance parallel capacitor inside the ammeter 84.

When the measurement of the leakage current I _L2 in the ammeter 84 is completed, after waiting for the time determined delay2, it performed a similar measurement by increasing the next step i.e. the voltage setting value.
JP 2002-168893 A

However, in the above conventional capacity measuring method, the ammeter 84 detects whether or not the VLoop state at the time of measuring the charging current, that is, whether or not the output voltage and the set voltage value are equal to each other is detected every Δt _PLC period. The detection accuracy of the timing changed to the state is restricted by the detection resolution. This restriction affected the measurement accuracy of the leakage current, and consequently the measurement accuracy of the capacitance.

  In addition, the conventional capacity measurement method is based on the assumption that the charge amount increases linearly with time. However, the charge amount does not always increase linearly with time. Therefore, in the conventional measurement method using trapezoidal approximation for capacity measurement, a measurement error occurs when the charge amount does not increase linearly with time.

  In view of such circumstances, an object of the present invention is to provide a capacitance measuring apparatus and a capacitance measuring method capable of measuring the capacitance value of a measurement target with high accuracy by increasing the measurement accuracy of leakage current.

  In order to solve the above-described problems, a capacitance measuring device according to the present invention includes a voltage applying unit that applies voltage fluctuation from a first set voltage to a second set voltage to a measurement target, and before and after the voltage fluctuation. Current measuring means for measuring a leakage current flowing through the measurement target and a charging current flowing through the measurement target according to the voltage variation, and a voltage for measuring an applied voltage during a period when the charging current flows through the measurement target due to the voltage variation Based on the current measurement result of the measurement means, the current measurement means and the voltage measurement result of the voltage measurement means, a leakage current value at the time of charging of the measurement target is calculated, and the measurement target is calculated using the leakage current value And a calculation means for calculating a target capacitance value.

  That is, the capacity measuring device of the present invention measures the applied voltage simultaneously with the measurement of the charging current of the measurement target because the leakage current during charging of the measurement target is proportional to the applied voltage. The value is used for calculating the leakage current value at the time of charging the measurement target, and the leakage current value at the time of charging is used for calculating the capacitance value of the measurement target.

  According to the present invention, since it is not necessary to determine the charging time necessary for obtaining the amount of change in the charge due to the leak current using the trapezoidal approximation, the capacitance value of the measurement target can be accurately measured. Further, even when the charge amount of the measurement target does not increase linearly with time, the capacity value of the measurement target can be measured with high accuracy.

  Further, in another aspect of the present invention, the voltage measuring means measures the applied voltage before and after the voltage fluctuation in addition to the measurement of the applied voltage during the period in which the charging current flows through the object to be measured due to the voltage fluctuation. The means is based on the current measurement result of the current measurement means and the measurement result of the voltage measurement means based on the applied voltage during the period in which the charging current flows and the applied voltage before and after voltage fluctuation. The leakage current value at the time of charging may be calculated.

  According to the capacitance measuring apparatus and the capacitance measuring method of the present invention, it is possible to measure the leakage current with high accuracy and accurately measure the capacitance value of the measurement target.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a connection configuration between a capacity measuring apparatus and an object to be measured according to an embodiment of the present invention. As shown in the figure, this capacitance measuring device includes a first measurement unit 2 that operates as a step voltage source that applies a step voltage so as to give a voltage fluctuation to the object 1 to be measured, and the like. The second measurement unit 3 operates as an ammeter that measures the current flowing through the measurement target 1 before and after the fluctuation of the applied voltage. Cx is a capacitance component of the measurement target 1, and Rx is a resistance component of the measurement target 1.

  FIG. 2 is a diagram showing the configuration of the first measurement unit 2 and the second measurement unit 3. The first measurement unit 2 and the second measurement unit 3 are configured by the same hardware. FIG. 2 shows only one configuration of the first measurement unit 2 or the second measurement unit 3.

  The first measurement unit 2 and the second measurement unit 3 include a VDAC (voltage value digital / analog converter) 11, an IDAC (current value digital / analog converter) 12, a V / I error amplifier 13, a power amplifier 14, and a current monitor. The circuit 15 includes a VM buffer amplifier 16, a current monitor amplifier 17, a voltage monitor amplifier 18, a voltage measurement ADC (analog / digital converter) 19, and a control logic unit 21. Apart from this, this capacity measuring device includes at least one current measuring ADC 20 as a shared resource used by each measuring unit.

  The VDAC 11 converts the digital voltage value supplied from the controller 22 through the control logic unit 21 into an analog value and outputs the analog value to the V / I error amplifier 13. The IDAC 12 converts a digital current value supplied from the controller 22 through the control logic unit 21 into an analog value and outputs the analog value to the V / I error amplifier 13.

  The V / I error amplifier 13 takes the difference between the voltage value output from the VDAC 11 and the output of the VM buffer amplifier 16 in the V Loop state, that is, the state where the output voltage and the set voltage value are equal, and the set voltage value is 1 to be measured. The power amplifier 14 is controlled so as to be output to the connection terminal 23. Further, the V / I error amplifier 13 takes the difference between the current value output from the IDAC 12 and the output of the current monitor amplifier 17 in the non-Vloop state, that is, the state where the output voltage and the set voltage value are not equal. Is output to the connection terminal 23 of the object 1 to be measured.

  The power amplifier 14 controls the voltage or current output to the connection terminal 23 of the measurement target 1 based on the output of the V / I error amplifier 13. The current monitor circuit 15 is a circuit that observes the current flowing through the measurement target 1. The current monitor circuit 15 has a function of switching current sensitivity (current range) in accordance with the current flowing through the measurement target 1.

  The VM buffer amplifier 16 observes the voltage at the connection terminal 23 of the measurement target 1. The current monitor amplifier 17 is an amplifier that normalizes the current value measured by the current monitor circuit 15 so that it can be A / D converted. The voltage monitor amplifier 18 is an amplifier that normalizes the voltage value measured by the VM buffer amplifier 16 so that it can be A / D converted.

  One of the ADCs 19 and 20 is a circuit that is provided in each measurement unit and converts an analog voltage value normalized by the voltage monitor amplifier 18 into a digital voltage value. The other ADC 20 is a common circuit used by each measurement unit, is connected via a connection terminal 27 provided in each measurement unit, and is normalized by the current monitor amplifier 17 of each measurement unit. This circuit converts a current value into a digital current value.

  The control logic unit 21 is a logic circuit that processes a control command from the controller 22. In accordance with a control command from the controller 22, the control logic unit 21 performs control such as setting a voltage value for the VDAC 11, setting a current value for the IDAC 12, and transmitting the outputs of the two ADCs 19 and 20 to the controller 22.

  By having the above configuration, the first measurement unit 2 operates as a voltage source having a function of limiting current, a function of setting a voltage value to be applied to the measurement target 1, and a function of measuring an applied voltage. The second measurement unit 3 operates as an ammeter that measures the charging current of the measurement target 1.

  The controller 22 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input / output unit, and the like. The ROM stores a program that is a processing procedure for capacity measurement by the step voltage method and firmware such as various parameter information. The controller 22 is connected through the input / output unit so as to be able to communicate with the control logic unit 21 of each of the first measurement unit 2 and the second measurement unit 3, the man-machine interface 24, the external interface 25, and the like. . In accordance with the firmware stored in the ROM, the CPU executes issuance of control commands and arithmetic processing for measuring the capacity of the measurement target 1 based on the outputs of the first measurement unit 2 and the second measurement unit 3. The measurement result of the capacity is output to the man-machine interface 24, the external interface 25, etc. through the input / output unit.

  The man-machine interface 24 is an interface for performing input / output with a user, and specifically includes a display device such as a display, an input device such as a keyboard, and the like. The external interface 25 is an interface for performing input / output with a device connected to the measurement apparatus via a communication cable. The connected device is a recording device for recording on a recording medium.

Next, the operation of the capacity measuring apparatus of this embodiment will be described.
Since the leakage current of the object 1 to be measured is proportional to the applied voltage, in the capacity measurement by the capacity measuring apparatus of this embodiment, the applied voltage is measured simultaneously with the measurement of the charging current of the object 1 to be measured. The value is used to calculate the leakage current value at the time of charging the object 1 to be measured, and the capacitance value of the object 1 to be measured is calculated by using the leakage current value at the time of charging.

  FIG. 3 is a sequence of capacitance measurement by the capacitance measuring apparatus of the present embodiment, and shows a change in applied voltage in one measurement step. FIG. 4 is a diagram showing continuous measurement steps, applied voltage and charging current for each measurement step.

First, under the control of the controller 22, the first measurement unit 2 sets the value of the applied voltage of the measurement target 1 to a predetermined set value V _set1 . Thereafter, the controller 22 waits for a predetermined time delay1 to elapse, and takes in the current value measured by the second measurement unit 3 as the leak current value _IL1 before the voltage fluctuation, The voltage value measured by the measurement unit 2 is taken in as the applied voltage value V ₁ before voltage fluctuation. As described above, the first measurement unit 2 and the second measurement unit 3 operate independently so that the measurement result of the first measurement unit 2 and the measurement result of the second measurement unit 3 can be simultaneously captured. Thus, the measurement result can be output.

Next, the controller 22 changes the set value of the applied voltage to a different set value V _set2 determined in advance. Due to this voltage fluctuation, a charging current for capacity measurement starts to flow through the object 1 to be measured. At the same time or almost simultaneously with the start of charging of the object 1 to be measured, the controller 22 starts taking in the voltage value measured by the first measurement unit 2 as the value of the applied voltage at the time of charging, and the second measurement. The capturing of the current value measured by the unit 3 as the charging current value is started. Each measurement of the applied voltage and the charging current at the time of charging is continued for a predetermined time T. This time T is a value obtained by adding a margin to the expected time until the applied voltage of the object 1 to be measured reaches V _{set2 with} respect to the voltage variation from V _set1 to V _set2 .

Next, the controller 22 takes in the voltage value measured by the first measurement unit 2 as the value of the applied voltage V ₂ after voltage fluctuation, and also takes the current value measured by the second measurement unit 3 after voltage fluctuation. As a value of the leakage current I _L2 After that, the controller 22 waits for a predetermined time delay2 to elapse, and performs control so that the next step, that is, the voltage setting value is increased and the same measurement is performed.

  The controller 22 takes in the measurement result of the first measurement unit 2 and the measurement result of the second measurement unit 3 as described above, stores them in the RAM, and stores the capacitance value of the measurement target 1 according to the firmware stored in the ROM. An operation for calculating C is executed. The capacitance value C is obtained by the following formula.

C = ΔQ / ΔV = {(I _M −I _Leak ) * T _cinteg + Q _correction } / (V ₂ −V ₁ ) (7)

Here, I _M is the charging current value measured during the T _cinteg time by the second measuring unit 3, I _Leak is the leakage current during charging, T _cinteg is the charging time, and Q _correction is the second measuring unit 3 Is the amount of charge charged in the internal range resistor parallel capacitor. The leakage current I _Leak during charging is obtained from the applied voltage measured simultaneously with the measurement of the charging current, the average value V _avrg is obtained, and the average value V _avrg of the applied voltage is used to obtain the following value.

I _Leak = I _L1 + (I _L2 −I _L1 ) * (V _avrg −V ₁ ) / (V ₂ −V ₁ ) (8)

V ₁ is the measurement voltage of the first measurement unit 2 before voltage fluctuation, V ₂ is the measurement voltage of the first measurement unit 2 after voltage fluctuation, and IL ₁ is measured by the second measurement unit 3 before voltage fluctuation. Leakage current I _L2 is the leakage current measured by the second measurement unit 3 after voltage fluctuation.

It should be noted that in the equations (7) and (8), the measured applied voltage values V ₁ and V ₂ are used for the calculation of the capacitance value C and the leakage current value I _Leak. This is because the measurement resolution of the applied voltage is higher than the resolution. If the voltage setting resolution is sufficiently high, the set voltage values V _set1 and V _set2 may be used.

As described above, according to the capacity measuring apparatus of this embodiment, the leakage current value I _Leak during charging of the measurement target 1 based on the applied voltage during the period when the charge current flows through the measurement target 1 due to voltage fluctuation. Since the capacitance value C of the object 1 to be measured is obtained, it is not necessary to determine the charging time τ necessary for obtaining the charge charge variation ΔQ _Leak due to the leak current using the conventional trapezoidal approximation. In the conventional determination of the charging time τ, the detection resolution at the timing when the state has changed to the VLoop state is limited to the Δt _PLC interval. However, the capacitance measuring apparatus of the present embodiment is not limited by such resolution, and the capacitance value The measurement accuracy of C can be improved.

  In addition, since the conventional capacity measurement method is based on the assumption that the charge amount increases linearly with time, a measurement error of the capacitance value C occurs when the charge amount does not actually increase linearly with time. However, such a measurement error does not occur in the capacity measuring apparatus of the present embodiment.

  It should be noted that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, it is described that only one capacity measuring device is provided in the above-described embodiment.

It is a figure which shows the connection of the capacity | capacitance measuring apparatus concerning embodiment of this invention, and a to-be-measured object. It is a figure which shows the structure of the 1st measurement unit in FIG. 1, and a 2nd measurement unit. It is a capacity | capacitance measurement sequence by the capacity | capacitance measuring apparatus of this embodiment. It is a figure which shows the applied voltage and charging current for every continuous measurement step and each measurement step. It is a figure which shows the influence of the leakage current to the charging current of to-be-measured object. It is a figure which shows the measuring method of the variation | change_quantity of a charge charge. It is a figure which shows the measurement sequence by the conventional step voltage method. It is a figure which shows the change of the leakage current assumed in the measuring method of FIG. It is a block diagram which shows the structure of the capacity | capacitance measuring apparatus by the conventional step voltage method.

Explanation of symbols

1 Target Object 2 First Measurement Unit 3 Second Measurement Unit 11 VDAC
12 IDAC
13 V / I error amplifier 14 Power amplifier 15 Current monitor circuit 16 VM buffer amplifier 17 Current monitor amplifier 18 Voltage monitor amplifier 19, 20 ADC
21 Control logic part 22 Controller

Claims (4)

Voltage application means for applying a voltage variation from the first set voltage to the second set voltage to the object to be measured;
Current measuring means for measuring a charge current during a given period of time through the object to be measured by the leakage current and the voltage variation through the object to be measured Target before and after the voltage fluctuation,
Voltage measurement means for measuring the voltage applied time flowing through the object to be measured the charging current by the voltage fluctuation,
Based on the current measurement result of the leakage current by the current measurement unit and the voltage measurement result of the voltage measurement unit, a leakage current value during the charging period of the measurement target is calculated, and the leakage current value is calculated using the leakage current value. A capacity measuring apparatus comprising: a calculation unit that calculates a capacity value of a measurement target. It said voltage measuring means, in addition to the measurement of the applied voltage period flowing through the object to be measured the charging current by the voltage variation, is measured before and after applying voltage of the voltage fluctuation,
Said calculating means includes a current measurement result obtained by the current measuring means of the leakage current flowing through the object to be measured before and after the voltage variation, the measurement results of the voltage measuring means, the object to be measured the charging current based on the applied voltage before and after applying voltage and the voltage fluctuation of the period to flow, the capacitance measuring device according to claim 1, characterized in that to calculate the value of leakage current during charging of the object to be measured . Applying a voltage variation from the first set voltage to the second set voltage to the object to be measured;
Measuring a leakage current flowing through the measurement object before and after the voltage fluctuation;
Measuring a charging current during a predetermined period flowing through the measurement object by the voltage fluctuation;
Measuring a voltage applied time flowing through the object to be measured the charging current by the voltage fluctuation,
A step of the calculated leak current 及 beauty leakage current value during charging of the object to be measured The measurement results on the basis of the applied voltage, calculates the capacitance value of the object to be measured using the leak current value A capacity measuring method comprising: Monitoring the applied voltage before and after the voltage fluctuation,
Calculating the capacitance value, the leakage current, the on the basis of the respective measurement results before and after the applied voltage of the applied voltage period in which the charging current to be measured flows, and the voltage variation, the measured The capacity measurement method according to claim 3, wherein a leak current value during the charging period of the target is calculated.

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