JP2000180498A - Operational amplifier circuit and method for evaluating semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately, easily measure inner element characteristics of a semiconductor device without measuring a film thickness of a capacity insulating layer by measuring an output voltage of a closed loop operational amplifier circuit having an inverter and a feedback capacitor. SOLUTION: The operational amplifier circuit AMP has an inverter in which CMOS inverters inv1, inv2 and inv3 are connected in series, and an output of the inverter is connected to its input Vf through a feedback capacitor Cf. An input capacitor C1 is connected to the input Vf and an input voltage Vin is connected to the capacitor C1. Further, a balanced resistance element R is connected to a connector of the inverters inv2, inv3 between a power source Vdd and a ground. A ground capacitor CL is connected to the output of the inverter. With the constitution, an oscillation in a feedback system having the capacitor Cf as a feedback circuit is prevented. In order to obtain an infinitesimal leakage current of the capacity insulating layer, the voltage Vin is maintained constantly, and an output Vout is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an operational amplifier circuit for measuring characteristics of internal elements of a semiconductor device, and a method of evaluating a semiconductor device using the same.

[0002]

2. Description of the Related Art Generally, it is not easy to know the characteristics of internal elements of a semiconductor device. For example, in measuring the dielectric constant of a capacitive insulating film, an optical interference film pressure gauge or an ellipsometer is used.
The thickness d of the capacitive insulating film is measured in advance, the capacitance of the reference capacitor is measured, and the dielectric constant εi is obtained from Expression (1). In this case, the actual measurement of the film thickness is indispensable.

(Equation 1)

Furthermore, the Cox measurement of the formula (1) uses a capacitance measuring device, and after measuring a plurality of capacitors, divides the measurement result to obtain an average value. Is limited by

[0004]

SUMMARY OF THE INVENTION The present invention has been made in order to solve such a conventional problem, and the actual measurement of the film thickness and the like inside the semiconductor is unpredictable. It is an object of the present invention to provide an operational amplifier circuit and a method for evaluating a semiconductor device, which are capable of measuring the temperature.

[0005]

According to the first aspect of the present invention, a closed loop operational amplifier circuit comprising an inverter circuit composed of odd-numbered stages of CMOS inverters and a feedback capacitor connected between an output and an input of the inverter circuit. An output terminal for outputting an output voltage of the closed-loop operational amplifier circuit, an input capacitor connected to an input of the closed-loop operational amplifier circuit, and an input capable of externally inputting a known first input voltage to the input capacitor And an operational amplifier circuit having a terminal and capable of measuring characteristics of an internal element based on an output voltage of the closed loop operational amplifier circuit.

Thus, the internal element characteristics of the semiconductor device can be easily and accurately measured without measuring the thickness of the capacitance insulating layer.

According to the second aspect, an odd-numbered series CMOS
A closed loop operational amplifier circuit including an inverter circuit including an inverter, a feedback capacitor connected between an output and an input of the inverter circuit, an output terminal for outputting an output voltage of the closed loop operational amplifier circuit, and the closed loop operational amplifier An input capacitor connected to an input of a circuit; and an input terminal capable of externally inputting a known first input voltage to the input capacitor, wherein the input capacitor is connected to a constant first input voltage input to the input terminal. The amount of change in the second input voltage of the closed loop operational amplifier circuit can be obtained from the change in the output voltage, and the leakage current of the capacitive insulating layer can be obtained from the amount of charge transfer of the capacitive insulating layer of the feedback capacitor and the input capacitor. .

As a result, the circuit scale is small and the simple D
The leak current value of each capacitance insulating layer of 10 ^-15 A or less can be measured with high accuracy by a C (direct current) measuring device.

According to a third aspect of the present invention, there is provided an operational amplifier circuit according to the first aspect, further comprising at least one closed loop operational amplifier circuit having a switch for selectively connecting at least two input capacitors. And
By appropriately arranging this in the semiconductor wafer surface, the distribution of the internal element characteristics of the semiconductor device in the wafer surface can be determined.

According to a fourth aspect of the present invention, there is provided at least one closed-loop operational amplifier circuit having a switch for selectively connecting at least two input capacitors, and switching the switch to switch the feedback capacitor and each of the feedback capacitors. After measuring the leak current of the capacitive insulating layer of the input capacitor by the method of claim 2, the distribution of the leak current in the plane of the wafer can be measured.

As a result, the circuit scale is small and the simple D
With a C (direct current) measuring device, the distribution of the leakage current value of each capacitance insulating layer of 10 ^-15 A or less in the wafer surface can be measured with high accuracy.

According to claim 5, the operational amplifier circuit according to claim 1 or 3, wherein the input capacitor and the feedback capacitor are formed of a capacitive insulating layer having the same dielectric constant. . Here, the same dielectric constant means
It is desirable that it is less than 0.05%, especially 0.01%
Good results are obtained below.

By using this operational amplifier circuit, the relative thickness of each capacitance insulating film inside the semiconductor device can be easily determined without using a highly accurate thickness gauge.

According to the sixth aspect, the input capacitor and the feedback capacitor are formed of a capacitive insulating layer having the same dielectric constant, and the change of the output voltage with respect to the change of the second input voltage of the closed loop operational amplifier circuit. A capacitance ratio between the input capacitor and the feedback capacitor is determined based on the amount, and a relative film thickness of the capacitive insulating layer in a wafer surface can be determined.

According to this, the relative in-plane distribution of the film thickness of the capacitive insulating film of the semiconductor wafer can be easily understood, and the evaluation of the semiconductor device can be easily performed.

According to a seventh aspect of the present invention, in the operational amplifier circuit according to the first or third aspect, the respective capacitive insulating layers of the input capacitor and the feedback capacitor are formed to have the same thickness. It is shown. Here, the same thickness means, for example, that the error distribution is 10% or less in the same 8-inch wafer surface. It is needless to say that the input capacitor and the feedback capacitor set in the same circuit element are very close to each other because they are so close to each other that they have the same thickness. It is called thickness.

By using this operational amplifier circuit, the relative capacitance of each capacitance insulating film inside the semiconductor device can be easily determined without using a high-precision capacitance meter.

According to the eighth aspect, the respective capacitive insulating layers of the input capacitor and the feedback capacitor are formed to have the same thickness, and the capacitance insulating layers of the input capacitor and the feedback capacitor are formed with respect to the variation of the second input voltage of the closed loop operational amplifier circuit. A capacitance ratio between the input capacitor and the feedback capacitor is determined based on a change amount of the output voltage, and a relative dielectric constant of the capacitive insulating layer in a wafer plane can be determined. By doing so, the relative distribution of the capacitance of each capacitance insulating film inside the semiconductor device within the semiconductor wafer surface can be easily measured without using a highly accurate capacitance meter.

According to a ninth aspect of the present invention, the respective capacitive insulating layers of the input capacitor and the feedback capacitor are formed by MOS capacitors of the same size. An amplifier circuit is shown. Here, the same size indicates that the error is 0.05 μm or less with respect to a specified value.

According to a tenth aspect of the present invention, there is provided a closed loop operational amplifier circuit including an inverter circuit including an odd-numbered series of CMOS inverters, a feedback capacitor connected between an output and an input of the inverter circuit, and the closed loop. An output terminal for outputting an output voltage of the operational amplifier circuit, an input capacitor connected to an input of the closed loop operational amplifier circuit, and an input terminal capable of externally inputting a known first input voltage to the input capacitor The respective capacitance insulating layers of the input capacitor and the feedback capacitor are formed by MOS capacitors of the same size, and the capacitances of the input capacitor and the feedback capacitor are determined based on the output voltage with respect to a first input voltage. From the ratio, the relative interface state in the wafer surface of the capacitive insulating layer was determined. Rukoto can be.

By using the operational amplifier circuit and the semiconductor device evaluation method, a relative interface state distribution in a wafer surface of a capacitor having a minute capacitance equal to or higher than the accuracy of the capacitance measuring device can be obtained.

[0022]

FIG. 1 shows an operational amplifier circuit AMP provided inside a semiconductor device for measuring internal element characteristics.
The operational amplifier circuit AMP is a CMOS inverter inv1, i
It has an inverter circuit in which nv2 and inv3 are connected in series, and the physical size of the transistor used in this CMOS inverter is Lp = 1.0 μm and Wp = 6.1.
μm, Ln = 0.8 μm, and Wn = 2.2 μm. The output of this inverter circuit is connected to a 2 pF feedback capacitor Cf.
Connected to the input Vf. An input capacitor C1 of 2 pF is connected to an input Vf of the inverter circuit, and an input voltage Vin is connected to the input capacitor C1. Further, CMOS inverters inv2 and inv
At the connection with v3, a 45 kΩ balanced resistance element R is connected between the power supply Vdd of the operational amplifier circuit AMP and the ground, thereby suppressing the gain of the inverter circuit. Further, a ground capacitor CL is connected between the output of the inverter circuit and the ground to form a low-pass filter. With the above configuration, the capacitor C
Oscillation in a feedback system having f as a feedback path is prevented. The input voltage Vin is supplied from an input terminal (input pin) formed outside the semiconductor device, and the output voltage Vout is output from an output terminal (output pin) formed outside.
Output from

In the measurement for obtaining the minute leakage current of the capacitance insulating layer, the input voltage Vin is kept constant, and the output voltage Vout of the inverter circuit is measured. Now, a charge conservation law is established between the feedback capacitor Cf, the input capacitor C1, the output voltage Vout of the inverter circuit, the input voltage Vf of the inverter circuit, and the input voltage Vin, and the relationship therebetween can be described as in equation (2). Is divided by Cf to obtain Equation (3). Now, since Cf = C1 = 2 pF, Equation (3) is rewritten from Equation (4) to Equation (5).

(Equation 2) Here, as shown in FIG. 4, Vout changes from 3.00 V to 2.0 in 1 hour = 3600 seconds due to the occurrence of a leak current.
It has dropped by 0.38V to 64V. From equation (5) that Vin is constant, ΔVf = the change due to the leak current per hour of the input voltage Vf of the inverter circuit.
Obtain 0.19V.

The movement of the one in charge, from Q = CV, the ΔQ = (C1 + Cf) × ΔVf = (2 × 10 ^{over 12} + 2 × 10 ^{over 12)} × 0.19 = 7.6 × 10 ^{over 12.} Accordingly, the leak current i to be obtained is as follows: i = 7.6 × ¹⁰⁻¹² ÷ 3600 (A) = 2.1 × ¹⁰⁻¹⁵ (A) = 2.1 (fA) Even if the amount of change in the inverter input voltage Vf is less than one-tenth of this example, it is possible to measure with a simple voltmeter.
^-15 (A) Even below, measurement can be easily performed with a simple device as in this embodiment.

As shown in FIG. 3, the leakage current can be measured by measuring the change in the Vout-Vin characteristic when the input voltage Vin is changed. Assuming that the input characteristic when there is no leak is p1 and the input characteristic is p2 after the leak has occurred, both are represented as substantially parallel straight lines. If Vin and Vout before and after the leak are known, the amount of change in the inverter input voltage Vf can be determined from Equation (3), and thereafter, the leak current is obtained in the same manner as described above. Here, the input voltage is changed by directly changing the input voltage supplied from the external input pin, or by applying a plurality of input voltages to the external input pin in advance and switching between them by an internal switch.

According to the equation (3), the ratio between the input voltage and the output voltage is represented by the capacitance ratio between the feedback capacitor and the input capacitor. This indicates that even if there is a small capacitance difference between the feedback capacitor and the input capacitor, which is smaller than the accuracy of the capacitance measuring device, the difference can be determined by the output voltage obtained from the operational amplifier circuit AMP of the present invention. I have. Although not shown here, it was confirmed that a large number of the operational amplifier circuits AMP were formed on the wafer surface and the in-plane distribution of the relative capacitance having a small difference was obtained.

When the film thickness of the feedback capacitor Cf is df, its relative permittivity is εf, and the film thickness of the input capacitor C1 is d1 and its relative permittivity is ε1, equation (3) becomes equation (6).
Can be rewritten as

(Equation 3) As is clear from the equation (6), if the relative film thickness distribution in the semiconductor wafer surface is clear, the relative dielectric constant distribution in the wafer surface can be obtained, while the relative dielectric constant distribution in the wafer surface can be obtained. If a proper dielectric constant distribution is known, a relative film thickness distribution can be obtained.

The feedback capacitor Cf and the input capacitor C1 which constitute the operational amplifier circuit AMP are formed of a large number of the above-mentioned operations of about 100 μm × about 500 μm each formed of an insulating film of a known material having the same thickness and having a thickness error of 10% or less. A semiconductor device including the amplifier circuit AMP was manufactured. Under this condition, since the film thickness is the same, Expression (6) can be rewritten as Expression (7).

(Equation 4) From this, the ratio of the input voltage to the output voltage of each operational amplifier circuit AMP indicates the relative permittivity of these insulating films, and as a result, a large number of operational amplifier circuits AMP formed in the semiconductor device.
As a result, it was confirmed that the relative dielectric constant distribution in the semiconductor device surface was determined.

Further, the feedback capacitor Cf and the input capacitor C1 constituting the operational amplifier circuit AMP are about 100 μm × about 500 μm each formed by an insulating film having the same dielectric constant made of a material having a dielectric constant error of 0.01% or less. A semiconductor device including a large number of the operational amplifier circuits AMP was manufactured. Under this condition, since the dielectric constant is the same, equation (6) can be rewritten as equation (8).

(Equation 5) From this, the ratio of the input voltage to the output voltage of each operational amplifier circuit AMP indicates the relative film thickness of these insulating films. As a result, the operational amplifier circuits AMP formed in a large number on the semiconductor device cause It was confirmed that a typical film thickness distribution of the insulating film was obtained. Furthermore, as a result of additional tests, it was found that the film thickness distribution could be sufficiently obtained up to a dielectric constant error of 0.05%, which was a preferable range.

These calculations are obtained by calculating the ratio between the input voltage Vin and the output voltage Vout. As described above, the voltmeter has higher accuracy than the capacitance meter, and the calculation of the voltage ratio can be easily performed with higher accuracy. Therefore, when the distribution in the wafer surface is directly obtained from the film thickness or the dielectric constant, By comparison, a relative distribution that detected subtle differences was obtained.

The interface level is a capacitance at which electric charges are captured by a physical defect at the MOS interface.
(Electricity). This interface state greatly affects the characteristics of the MOS device. When measuring this interface state distribution, the input capacitor C
1. The feedback capacitor Cf is constituted by a MOS capacitor of the same size (with an accuracy within 0.05 μm with respect to a specified value), and the output voltage Vout is measured. Here, assuming that the fixed charge density in the oxide film is equal, as shown in FIG. 2, since the CV curves of the feedback capacitor and the input capacitor are shifted, the difference in the interface state can be obtained.

When the capacitance values of C1 and Cf change to Ca and Cb due to the interface state, the output voltage Vout can be expressed as in equation (9). Where α = (Ca / C
b). Further, the difference between Ca and Cb is expressed by equation (10). From these and Q = CV, the difference in interface state density is given by equation (11).

(Equation 6) It was confirmed that the difference between the interface states of the two capacitors can be obtained from Equations (10) and (11) by obtaining one reference capacitor capacity Cb. In order to obtain the absolute value of the interface state, it is necessary to separately obtain a known reference capacitor interface state.

[0033]

As described above, a closed loop operational amplifier circuit comprising an inverter circuit composed of odd-numbered series CMOS inverters, a feedback capacitor connected between the output and the input of the inverter circuit, and a closed loop operational amplifier circuit comprising: An output terminal for outputting an output voltage, an input capacitor connected to an input of the closed-loop operational amplifier circuit, and an input terminal capable of externally inputting a known first input voltage to the input capacitor; Since the operational amplifier circuit can measure the characteristics of the internal elements based on the output voltage of the operational amplifier circuit, the internal element characteristics of the semiconductor device can be easily measured with high accuracy without measuring the film thickness of the capacitive insulating layer. Then, the leak current of the capacitive insulating layer is obtained from the amount of charge transfer of the capacitive insulating layer of the feedback capacitor and the input capacitor. Therefore, the circuit scale is small and a DC (direct current) measuring device of 10 ^-15 A or less is used. The leak current value of the capacitive insulating layer can be measured with high accuracy.

Further, at least one closed-loop operational amplifier circuit having a switch for selectively connecting at least two input capacitors is provided on the semiconductor wafer surface of the operational amplifier circuit as appropriate, so that the inside of the semiconductor device is The distribution of the device characteristics in the wafer plane can be understood. In particular, the distribution of the leakage current in the wafer plane can be measured, and the circuit scale is small, and a simple DC (direct current) measuring device of 10 ^-15 A or less can be obtained. The distribution of the leakage current value of each capacitance insulating layer within the wafer surface can be measured with high accuracy.

Further, since the input and feedback capacitors use an operational amplifier circuit composed of capacitive insulating layers having the same dielectric constant, each capacitive insulating film inside the semiconductor device can be used without using a highly accurate film thickness gauge. Can be easily understood. Also, at this time, the capacitance ratio between the input capacitor and the feedback capacitor was determined, and the relative thickness of the capacitive insulating layer in the wafer surface was determined. The distribution is easily understood, and the evaluation of the semiconductor device is facilitated.

In addition, since the operational amplifier circuits in which the respective capacitive insulating layers of the input capacitor and the feedback capacitor are formed to have the same thickness are used, the inside of the semiconductor device can be used without using a highly accurate capacitance meter. The relative capacitance of each capacitance insulating film can be easily understood. Also, at this time, the capacitance ratio between the input capacitor and the feedback capacitor was obtained, and the relative permittivity of the capacitance insulating layer in the wafer plane was obtained. The relative distribution of the capacitance of the capacitor in the plane of the semiconductor wafer can be easily measured.

In addition, an operational amplifier circuit in which the respective capacitance insulating layers of the input capacitor and the feedback capacitor are formed by MOS capacitors of the same size is provided. As shown above, the relative interface state in the wafer surface can be obtained, and the relative interface state distribution in the wafer surface of a capacitor having a small capacitance exceeding the accuracy of the capacitance measuring device can be obtained. Has excellent effects.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a circuit provided inside a semiconductor device according to the present invention.

FIG. 2 is a graph showing a capacity measured according to the example.

FIG. 3 is a graph showing an input / output relationship of the circuit of FIG. 1; .

FIG. 4 is a graph showing the change over time of the output of the circuit of FIG. 1;

[Explanation of symbols]

C1, Cf, CL. . . Capacitors inv1, inv2, inv3. . . CMOS inverter . . Resistance Vin. . . Input voltage Vout. . . Output voltage.

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Kazuhiro Yamamoto 1-8 Fuso-cho, Amagasaki City, Hyogo Sumitomo Metal Industries, Ltd. Electronics Technology Research Laboratory F-term (reference) 2G003 AA07 AA10 AB01 AB05 AB07 AH05 2G032 AA10 AB01 AD01 AD03 AL00 2G036 AA04 AA19 AA21 BA41 BB09 CA10 CA12 9A001 BB02 BB04 BB05 JJ45 KK37 KK54 LL08

Claims (10)

[Claims] 1. A closed loop operational amplifier circuit comprising an inverter circuit composed of odd-numbered series CMOS inverters and a feedback capacitor connected between an output and an input of the inverter circuit; and an output voltage of the closed loop operational amplifier circuit. An input terminal connected to an input of the closed loop operational amplifier circuit; and an input terminal capable of externally inputting a known first input voltage to the input capacitor. An operational amplifier circuit that can measure the characteristics of internal elements based on the output voltage. 2. A closed loop operational amplifier circuit comprising an inverter circuit composed of odd-numbered stages of CMOS inverters and a feedback capacitor connected between an output and an input of the inverter circuit; and outputting an output voltage of the closed loop operational amplifier circuit. An input terminal connected to an input of the closed-loop operational amplifier circuit; and an input terminal capable of inputting a known first input voltage to the input capacitor from outside. The change amount of the second input voltage of the closed loop operational amplifier circuit is obtained from the change of the output voltage with respect to the given first input voltage, and the charge transfer amount of the feedback capacitor and the capacitance insulating layer of the input capacitor is calculated from the change amount. A method for evaluating a semiconductor device in which leakage current of a capacitor insulating layer is obtained. 3. The operational amplifier circuit according to claim 1, further comprising at least one closed-loop operational amplifier circuit having a switch for selectively connecting at least two input capacitors. 4. The circuit of claim 1, further comprising at least one closed-loop operational amplifier circuit having a switch for selectively connecting at least two input capacitors, wherein said switch is switched to capacitively insulate said feedback capacitor and each of said input capacitors. 3. A method of evaluating a semiconductor device, comprising: measuring a leakage current of a layer by the method according to claim 2, and measuring a distribution of the leakage current in a plane of the wafer. 5. The operational amplifier circuit according to claim 1, wherein said input capacitor and said feedback capacitor are formed of a capacitive insulating layer having the same dielectric constant. 6. The input capacitor and the feedback capacitor are each formed of a capacitive insulating layer having the same dielectric constant, and based on a change in the output voltage with respect to a change in a second input voltage of the closed loop operational amplifier circuit, 5. The evaluation method for a semiconductor device according to claim 4, wherein a capacitance ratio between the input capacitor and the feedback capacitor is obtained, and a relative thickness of the capacitance insulating layer in a wafer surface is obtained. 7. The operational amplifier circuit according to claim 1, wherein the capacitance insulating layers of the input capacitor and the feedback capacitor are formed to have the same thickness. 8. A change amount of the output voltage with respect to a change amount of a second input voltage of the closed-loop operational amplifier circuit, wherein respective capacitance insulating layers of the input capacitor and the feedback capacitor are formed to have the same thickness. Based on, to determine the capacitance ratio of the input capacitor and the feedback capacitor,
5. The method for evaluating a semiconductor device according to claim 4, wherein a relative dielectric constant of the capacitance insulating layer in a wafer plane is obtained. 9. The operational amplifier circuit according to claim 1, wherein the respective capacitive insulating layers of the input capacitor and the feedback capacitor are formed by MOS capacitors of the same size. 10. A closed-loop operational amplifier circuit comprising an inverter circuit composed of odd-numbered series CMOS inverters and a feedback capacitor connected between an output and an input of the inverter circuit; and outputting an output voltage of the closed-loop operational amplifier circuit. An input terminal connected to an input of the closed-loop operational amplifier circuit; and an input terminal capable of externally inputting a known first input voltage to the input capacitor. The respective capacitive insulating layers of the feedback capacitor are formed by capacitors of the same size, and based on the output voltage with respect to a first input voltage, the capacitance insulating layer is determined based on a capacitance ratio between the input capacitor and the feedback capacitor. Semiconductor device characterized in that relative interface states in a wafer surface of the semiconductor device are obtained. The method of evaluation.