JPH08278335A - Measuring device of resistivity - Google Patents

Abstract

PURPOSE: To provide a resistivity measuring circuit capable of expanding a range of resistivity measurement, enhancing the accuracy of the measurement and reducing a cost of a resistivity measuring device. CONSTITUTION: A resistivity measuring circuit comprises a constant current power source circuit 11 that supplies a constant current (i) to a specimen 14 to be measured in the measuring of the resistivity and a voltage measuring circuit 12 that measures an output voltage from the specimen 14. It further comprises a common power source circuit 13 that commonly supplies a DC voltage to the constant current power source circuit 11 and voltage measuring circuit 12. The voltage measuring circuit 12 comprises a differential amplifier 15 which is connected to a measuring terminal of an output voltage Δe from the specimen 14 and a constant voltage circuit 17 that supplies a constant voltage to a power source terminal of the differential amplifier 15. The constant voltage circuit 17 is connected to a terminal of the common power source circuit 13 via a constant current circuit 19.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resistivity measuring circuit for measuring the resistivity of silicon bulk, wafer, etc., sheet resistance, etc. by using the DC 4-probe method, and in particular, widening the range and increasing the measurement range. The present invention relates to a resistivity measuring circuit suitable for improving accuracy and reducing the cost of a measuring device.

[0002]

2. Description of the Related Art When the resistivity of a sample is measured by using a four-probe probe for measurement, the contact resistance between the sample and the four-probe probe for measurement becomes, for example, a megohm base when the resistivity of the sample becomes high. . Therefore, conventionally, a circuit configuration in which the constant current power supply circuit is a floating type has been adopted as the measurement circuit in order to avoid a leakage current from the constant current power supply. Specifically, a circuit configuration in which a battery is used as a power source (FIG. 3) and a circuit configuration in which a capacitor is charged to form a floating circuit for a short time (FIG. 4) have been adopted. Alternatively, there is a circuit configuration in which the output of the voltage measuring circuit is galvanically isolated and the power supply unit thereof is floating.

[0003]

The above-mentioned conventional techniques have the following problems. (1) It is necessary to sufficiently increase the insulation resistance of the floating circuit. This is because the leakage current flowing through the insulation resistance may cause an error. (2) External induction noise (AC power supply) is easily received from the floating circuit, and measurement error due to noise is likely to occur. (3) The floating circuit requires a special member, which makes the device expensive.

These problems will be further described with reference to the drawings. FIG. 3 is an example of a floating constant current power supply system using a battery as a power source, and the portion surrounded by a broken line is a portion showing the floating constant current power supply unit. In FIG. 4, the relay 44 is closed and the capacitor 45 is charged from the power supply 43. During measurement, 44 is opened and the broken line portion is configured as a floating constant current power supply circuit.

FIG. 5 shows an external power source 50 in the circuit of FIG.
It shows how a noise power supply 50 'causes a fault signal to flow into the voltage measurement amplifier 56. The leakage current or the induced current is coupled to the floating power source through the insulation resistance 54 or the floating capacitance 55, and flows through the measurement sample 57 as a current 53.
Occurs as.

This current is the contact resistance 5 of the probe with the sample 57.
9 (r _{1 to} r ₄ ), the current 53 causes a voltage drop due to r ₂ or r ₃ . Therefore, a fault signal is applied to the amplifier 56, which becomes an error voltage with respect to the measured value or induced noise, which causes deterioration of the performance of the measuring instrument. In particular, when the internal resistance of the sample or the above-mentioned contact resistance with the sample is large, this performance deterioration tends to be large and the measurement range is limited.

Further, the floating circuits shown in FIGS. 3 and 4 require an insulating member such as Teflon (registered trademark) and a special member such as a shield box for shielding an inductive noise signal.

It is an object of the present invention to provide a resistivity measuring circuit in which the range of resistivity measurement is expanded, the precision of measurement is improved, and the cost of the resistivity measuring device is reduced.

[0009]

In order to achieve the above object, in the present invention, for example, as shown in FIG. 1, a constant current power supply circuit 11 for supplying a constant current i to a sample 14 to be measured in measuring resistivity, In a resistivity measuring circuit having a voltage measuring circuit 12 for measuring an output voltage from the sample 14, a circuit configuration of a common power source 13 for commonly applying a DC voltage to the constant current power source circuit 11 and the voltage measuring circuit 12 is provided. In addition, the voltage measuring circuit 12 includes a constant voltage circuit 1 in which a differential amplifier 15 is connected to a measuring terminal for the output voltage Δe from the sample 14 and a constant voltage is applied to a power supply terminal of the differential amplifier 15.
7 and the constant voltage circuit 17 are connected to a terminal of the common power source 13 via a constant current circuit 19 in a circuit configuration.

The constant voltage circuit 17 may be a floating power supply circuit. As an example of this case, FIG. 1 shows the constant voltage circuit 17 in a battery display. (Note that the configuration of the differential amplifier to which a constant voltage is applied by the floating power supply circuit, that is, the portion 18 surrounded by the broken line in FIG. 1 is hereinafter referred to as a floating power supply-equipped differential amplifier.) Alternatively, the constant voltage circuit may be, for example, As shown in FIG.
As the power supply terminal, the constant current circuit 22 or 22 'is used.
Has a first power supply terminal S1 and a second power supply terminal S2 connected to the respective terminals of the common power supply via the first power supply terminal S1 and the output terminals a and b of the differential amplifier. A circuit in which resistors R having the same resistance value are respectively connected between them, and resistors R having the same resistance value are respectively connected between the second power supply terminal S2 and the output terminals a and b of the differential amplifier. In addition to the above configuration, a circuit configuration is provided for supplying the respective voltages of the first power supply terminal S1 and the second power supply terminal S2 to the respective power supply terminals c and d of the differential amplifier, and the power supply terminal is provided with an emitter. You may make it provide the structure of the transistor 23 and 23 'which connects a base to each of the 1 power supply terminal S1 and the 2nd power supply terminal S2, and connects a collector to each terminal of the said common power supply, respectively.

[0011]

The resistivity is measured by the 4-probe method as follows. That is, in FIG. 1, the output current i of the constant current power supply circuit 11 is passed through a 4-probe probe to, for example, a silicon sample 14, and a voltage Δe proportional to the sample resistivity is generated at a measurement terminal. Δe is measured by the voltage measuring circuit 12, and thereby the resistivity ρ is calculated by (Equation 1).

[0012]

[Equation 1]

These calculation formulas and measuring methods are known.

In the present invention, the constant current power supply circuit 11 is directly connected to the common power supply 13 as described above. Therefore, as described in the prior art, the leakage current and the induction current which are coupled to the power supply as the power supply floats. There is very little room for current to enter, there is little error in the generation of the measured voltage Δe, and a wide range of output voltages, for example, several V to several tens of V, generated corresponding to a wide range of sample internal resistance and probe contact resistance. The constant current characteristic can be maintained even in the above step, and highly accurate generation of the measurement voltage Δe can be obtained.

As described above, in response to the generation of highly accurate measurement voltage over a wide range of resistance measurement, it is necessary to enable sufficiently high accuracy measurement even in the voltage measurement circuit. In the present invention, the voltage measuring circuit 12 connected to the common power source
Makes this possible. That is, as will be described later and in more detail, the differential amplifier 15 is supplied with a constant voltage, and the differential amplifier 18 with a floating power supply is connected to the common power supply via the constant current circuit 19 having a high internal resistance. Since it operates following a wide range of common-mode input voltages, the floating power supply-equipped differential amplifier 18 can secure a highly accurate and highly stable output. In this case, a voltage proportional to the measurement signal voltage Δe is included between the input terminals of the floating power supply-equipped differential amplifier 18, and the common mode voltage shown in FIG. a voltage generated in relation to the magnitude of the internal resistance and probe of a contact resistance, hereinafter also referred to as common mode voltage) but e _c is included, from the differential output of the floating-powered differential amplifier 18 The common mode voltage is removed and only the output voltage proportional to the measured voltage Δe is obtained. That is, according to the configuration of the voltage measurement circuit 12 of the present invention, a stable output voltage irrelevant to a wide range of common mode voltages can be obtained, and highly accurate voltage measurement can be performed.

If the terminal voltage of a resistor through which a constant current flows is used as the voltage of the constant voltage circuit and the voltage is applied to the power supply terminal of the amplifier via, for example, a transistor, the current flowing through the resistor is constant. As long as a constant voltage can be applied to the amplifier.

Further, according to the present invention, since the member for floating the circuit is not required, the cost of the device can be reduced.

[0018]

1 shows an embodiment of the resistivity measuring circuit of the present invention, and FIG. 2 shows another embodiment of the voltage measuring circuit of the present invention. In the above description, the characteristic configuration of the present invention has been described with reference to FIGS. 1 and 2. Further, among the configurations of the present invention shown in FIG. 1, the constant current power supply circuit 11 seems to be clear without further detailed description. Therefore, a wide range will be described below with reference to the embodiment of the voltage measuring circuit of FIG. It will be described in detail that it becomes possible to operate with a common mode voltage.

In FIG. 2, reference numeral 21 is a general measurement differential operational amplifier. 22, 22 'are constant current circuits, 23,
Reference numeral 23 'is a transistor for supplying a constant voltage to the power supply terminals c and d of the amplifier 21. 23 base voltage e _s2 'of the base voltage e _s1, 23 of the voltage Vbe is typically 0.6V position 23 between the emitter and the base of the' may be considered substantially point c, and the voltage of point d. Therefore the power supply voltage of 21 of the amplifier, that is, the voltage between the c-d is, it may be expressed as Vs = e _s1 -e _s2 ......... (number 2). Here, even if the common mode voltage e _c fluctuates, the amplifier 21 can operate in a wide range of common mode voltages if Vs is constant. This point will be further described below.

The input of 21 is Δe.

[0021]

(Equation 3)

The point b output e _b is e _b = voltage e _s1 of e _c -n · Δe ......... (number 4) s ₁ points _{e s1 = e a + i 1} · R ......... ( 5) or _{e s1 = e b + i 2} · R ......... ( 6) voltage e _s2 of s ₂ points _{e s2 = e b -i 2 '} · R ......... ( 7) or e _s2 = e _a - i ₁ ′ · R (Equation 8) Substituting (Equation 3) and (Equation 4) into (Equation 5) to (Equation 8), e _s1 = e _c + i ₁ · R + n · Δe ………… (Equation 5) _{9) e s1 = e c +} i 2 · R-n · Δe ......... ( number _{10) e s2 = e c -i} 2 '· R-n · Δe ......... ( number 11) e _s2 = e _c - i ₁ ′ · R−n · Δe ... (Equation 12) Substituting (Equation 9) to (Equation 12) into (Equation 2), (Equation 9),
From (Equation 11), Vs = e _s1 −e _s2 = i ₁ · R + i ₂ ′ · R (Equation 13) is obtained, and from (Equation 10) and (Equation 12) Vs = e _s1 −e _s2 = i ₂ · R + i ₁ ′ · R (Equation 14) is obtained. If both sides of (Equation 13) and (Equation 14) are added, 2Vs = i ₁ · R + i ₂ ′ · R + i ₂ · R + i ₁ ′ · R = (i ₁ + i ₂ + i ₁ ′ + i ₂ ′) · R ... Equation 15) is obtained. Ignoring the base currents of 23 and 23 'at s ₁ and s ₂ points, i ₁ + i ₂ = i = i ₁ ′ + i ₂ ′, which is substituted into (Equation 15) and 2Vs = 2i ·
That is, R, that is, Vs = i · R ... (Equation 16) is obtained.

Therefore, Vs is independent of changes in e _c and e _c , and within the voltage output allowable range of the constant current power supplies 22 and 22 ′, the constant voltage Vs maintains the power supply of 21 with respect to changes in the magnitude of e _c. Can be supplied as. In the meantime, 21 maintains the operation as a differential amplifier. Where 21 differential output voltages (e _a
-E _b ) is calculated from (Equation 3) and (Equation 4).

[0024]

[Equation 17]

Then, if the (e _a −e _b ) which has no relation to the common mode voltage e _c is input to the differential input type A / D converter 16 of FIG. 1, Δe can be measured.

[0026]

According to the present invention, the error factor on the measuring circuit can be eliminated, so that highly accurate resistivity measurement can be performed in a wide measuring range of high resistance and low resistance. Further, a member for floating the circuit, that is, a battery, a charging capacitor, an insulating amplifier, a switching relay and the like are not required, which makes the measuring device inexpensive.

[Brief description of drawings]

FIG. 1 is an embodiment diagram of a resistivity measuring circuit of the present invention.

FIG. 2 is a diagram showing another embodiment of the voltage measuring circuit according to the present invention.

FIG. 3 is a diagram illustrating a conventional example of a floating power supply system using a battery.

FIG. 4 is a conventional example diagram of a floating power supply system using a capacitor.

FIG. 5 is a diagram showing an example of inflow of a fault signal in the related art.

[Explanation of symbols]

11 ... Constant current power supply circuit 12 ... Voltage measurement circuit 13 ... Common power supply 14 ... Sample 15 ... Differential amplifier 16 ... Differential input type A / D converter 17 ... Battery display meaning constant voltage circuit or floating power supply 18 ... Floating Differential amplifier with power source 19 ... Constant current circuit 21 ... Differential operational amplifier for measurement 22, 22 '... Constant current circuit 23, 23' ... Transistor 31 ... Constant current circuit 32 ... Battery 36 ... Differential operational amplifier 37 ... Sample 38 ... A / D converter 41 ... Constant current circuit 43 ... Power supply 44 ... Relay 45 ... Capacitor 46 ... Differential operational amplifier 47 ... Sample 48 ... A / D converter 50 ... External power supply 50 '... Noise power supply 51 ... Constant current circuit 53 ... Current (fault signal current) 54 ... Insulation resistance 55 ... Stray capacitance 56 ... Differential operational amplifier 57 ... Sample 58 ... A / D converter 59 ... Probe contact resistance

Claims (3)

[Claims] 1. A resistivity measuring circuit having a constant current power supply circuit for applying a constant current to a sample to be measured in measuring resistivity and a voltage measuring circuit for measuring an output voltage from the sample, comprising: And a circuit configuration of a common power supply for commonly applying a DC voltage to the voltage measurement circuit, wherein the voltage measurement circuit has a differential amplifier connected to an output voltage measurement terminal from the sample, and a power supply for the differential amplifier. A resistivity measuring circuit comprising: a constant voltage circuit for applying a constant voltage to a terminal; and a circuit configuration for connecting the constant voltage circuit to a terminal of the common power source via a constant current circuit. 2. The resistivity measuring circuit according to claim 1,
A resistivity measuring circuit, wherein the constant voltage circuit is a floating power supply circuit. 3. The resistivity measuring circuit according to claim 1, wherein:
The constant voltage circuit has, as its power supply terminals, a first power supply terminal and a second power supply terminal connected to each terminal of the common power supply via the constant current circuit. A resistor having the same resistance value is connected between each output terminal of the differential amplifier and a resistor having the same resistance value is connected to the second terminal.
And a circuit configuration for connecting between each of the output terminals of the differential amplifier and each of the voltages of the first power supply terminal and the second power supply terminal to each power supply terminal of the differential amplifier. As a circuit configuration for giving each, a transistor configuration in which an emitter is connected to the power supply terminal of the differential amplifier, a base is connected to each of the first power supply terminal and the second power supply terminal, and a collector is connected to each terminal of the common power supply. A resistivity measuring circuit comprising: