JP2003043079A - Probing system and capacitance measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a probing system which can remove the influence of stray a capacitance and carry out high-precision measurement. SOLUTION: This is a probing system equipped with a prober 1 and a capacitance measuring circuit 6. The prober 1 has a sealed box 11, and a signal cable 7 whose one end (its internal conductor 72) as a detecting probe comes in contact with a sample to be measured and is covered with an external conductor 71. The measuring circuit 6 has a voltage follower (an operational amplifier 61) whose non-inversion input terminal is connected to the internal conductor 72 of the signal cable, 7, and whose output terminal is connected to the external conductor 71, a resistor (R3) 67 whose one end is connected to the internal conductor 72, and an operational amplifier 60 whose output terminal is connected to the other end of the resistor (R3) 67 so that the resistor (R3) 67 and the operational amplifier 61 are included in the negative feedback route.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a probing system for measuring electrical characteristics of a sample to be measured, and more particularly to a probing system suitable for measuring a minute capacitance value of the order of several fF with high accuracy.

[0002]

2. Description of the Related Art FIG. 13 is a block diagram of a conventional probing system for measuring electrical characteristics such as capacitance formed on a semiconductor substrate. This probing system
It is roughly divided into a prober 1 and a capacity meter 2. The prober 1 includes a shield box 11 connected to an earth (ground), a stage 13 placed in the shield box 11, a stand 15 surrounding the stage 13 and a manipulator 1 placed on the stand 15.
4 and.

On the stage 13, a sample to be measured 12 forming a capacitance to be measured is placed, and the manipulator 1
A signal cable 3 and a ground cable 4 are fixed to 4. The signal cable 3 and the ground cable 4 are coaxial cables shielded by an outer conductor, and the tips of the inner conductors are exposed, and the inner portion of the inner conductor is exposed as a detection probe and an earth probe, respectively. (Such as the electrodes that it is composed of). The other end of the signal cable 3 is
It is connected to the capacitance meter 2, while the other end of the earth cable 4 is connected to earth. The conductive portion of the stage 13, the conductive portion of the stand 15, the conductive portion of the manipulator 14 and the outer conductors of the cables 3 and 4 are connected to the ground by connecting or contacting the shield box 11, and disturbance noise is generated. Is shielded.

With such connection and configuration, the capacitance meter 2
By measuring the capacitance between the inner conductor and the outer conductor of the signal cable 3 connected to, it becomes possible to measure the capacitance of the sample 12 to be measured. However, as it is, the inner conductor of the signal cable 3 and the outer conductor of the signal cable 3, the shield box 11, the stage 13, the manipulator 14
The stray capacitance formed between the stage 13 and the electrode of the DUT 12 with which the inner conductor of the signal cable 3 is in contact with the stage 15 and the stage 15 is added as an error.

Therefore, the conventional probing system is
For example, the true capacitance value is to be measured by measuring the capacitance in a state where the inner conductors of the signal cable 3 and the ground cable 4 are not in contact with the sample 12 to be measured and subtracting the capacitance value from the actual measurement value.

[0006]

However, the above-mentioned stray capacitance is caused by the bending of the signal cable 3, the temperature change of the dielectric constant of the insulator in the signal cable 3, the positional relationship between the signal cable 3 and the manipulator 14, and the like. Due to various factors such as the temperature-dependent fluctuation of the dielectric constant of the atmosphere in the shield box 11 and the movement of the measurer (for example, several hundred fF).
Because it varies (on the order of femtofarad; 10 ⁻¹⁵ F), the conventional probing system is limited to measuring a capacity of several tens of pF, and several tens of f
It is difficult to measure a minute capacitance of F or less. Then, this invention is made in order to solve the said subject, and it aims at providing the probing system which can remove the influence of a stray capacitance and can perform a highly accurate measurement.

[0007]

In order to achieve the above object, a probing system according to the present invention is a probing system including a prober and a first measurement circuit, wherein the prober is a box covering a sample to be measured. And a signal line having one end that contacts the sample to be measured as a detection probe and a first shield member that covers the signal line, and the other end of the signal line in the first measurement circuit is connected to an input terminal. And a voltage follower in which the first shield member is connected to an output terminal, impedance means whose one end is connected to the signal line, and the other end of the impedance means is connected to the output terminal, and the impedance is Means and the voltage follower means include a first operational amplifier connected to be included in the negative feedback path.

As a result, the first shield member covering the signal line is driven to the output potential of the voltage follower, that is, the output potential of the signal line and having the low output impedance, and is guarded.

Here, the box may be in a state of being electrically connected to the first shield member or grounded. In the case of grounding, the capacitance to the box is also detected. The canceling means may be used in the latter stage in order to eliminate it, but it is preferably electrically connected to the first shield member in order to increase the factor of error occurrence. Similarly, a mounting table for holding the sample to be measured, a manipulator for fixing the signal line and the probe, and the like are provided in the probe, and the conductive portions of the mounting table and the manipulator are also electrically connected to the first shield member. Can be connected to or grounded. In the case of grounding, the capacitance of the pair stand and the pair of manipulators is also detected. The canceling means may be used in the latter stage in order to eliminate it, but it is preferably electrically connected to the first shield member in order to increase the factor of error occurrence. When the box is grounded, it is more preferable that the first shield member is floating with respect to the box in order to prevent the first shield member from being grounded.

As the reference potential probe, the other end of the reference potential line which comes into contact with the sample to be measured is not only grounded but also
You may connect to the power supply etc. which generate | occur | produce the stabilized constant DC voltage. Then, the second shield member that covers the reference potential line is electrically connected to the first shield member, grounded, or placed in a floating state. In this case, the grounding that can minimize the influence of disturbance is the more preferable mode. With this, by adopting a connection mode according to the measurement environment, the characteristics of the sample to be measured, etc., for example, it is possible to perform highly accurate measurement based on a more stable ground potential. Here, the "reference potential" refers to a state in which a potential that is constant over time is held, and also includes a state in which it is grounded.

The sample to be measured may be measured by using a triple coaxial cable having a structure in which the signal line and the reference potential line are covered with a double shield. Then, the outermost shield may be connected to a guard or a ground (ground), or may be floated. This can enhance the shield effect. It is preferable that the outermost shield is grounded and the inner shield is connected to the guard because the external disturbance can be minimized. Further, as the guard potential, the output signal of the voltage follower may not be used as it is, but a compensated signal obtained by performing phase / amplitude compensation of the signal may be used. As a result, by adjusting the phase and amplitude in advance, a guard signal whose phase and amplitude perfectly match the AC voltage applied to the signal line is applied to the external conductor, and the stray capacitance is completely eliminated. Will be canceled.

As a target for applying the guard potential,
The present invention is not limited to the outer conductor of the cable or a device member such as a box, but may be an unnecessary conductive portion in the sample to be measured. For example, when measuring the gate-source capacitance of a MOS transistor, the drain and the semiconductor substrate (bulk portion) may be held at the guard potential.
As a result, unnecessary capacitance between electrodes (capacitance between gate and drain, capacitance between gate and bulk, capacitance between source and bulk)
Is eliminated and pure gate-source capacitance is measured.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a diagram showing a configuration of a probing system according to the present invention.
The same components as the conventional components shown in FIG. 13 are designated by the same reference numerals, and the description thereof will be omitted. The probing system according to the present invention is roughly divided into a prober 1 and a capacity meter 5. Prober 1
The same components as those shown in FIG. 13, that is, the shield box 11, the stage 13, the manipulator 14 are shown.
And a stand 15. The sample to be measured 12 forming the capacitance to be measured is placed on the stage 13, and the signal cable 7 and the reference potential cable 8 are fixed to the manipulator 14.

Then, the shield box 11, the conductive portion of the stage 13, the conductive portion of the stand 15, the conductive portion of the manipulator 14, and the outer conductor 7 of the signal cable 7.
1 and the outer conductor 81 of the reference potential cable 8 (hereinafter, these are collectively referred to as “conductive portion of prober”).
They are electrically connected via the shield box 11 and the like, and have the same potential. As described above, the prober 1 of the present probing system has the individual components in common with the conventional prober 1 shown in FIG. 13, but differs in the connection state. That is, the conductive portion of the conventional prober 1 is shown in FIG.
As shown in FIG. 3, it is connected to the earth (ground) through the shield box 11 and the outer conductor of the signal cable 3, but the conductive portion of the prober 1 of the probing system is as shown in FIG. , Held at a potential determined by the capacitance measuring circuit 6 that is released from ground and applies a voltage to the outer conductor of the signal cable 7 (the same guard potential as the potential of the inner conductor of the signal cable 7 as described later) Has been done.

FIG. 2 is an enlarged view of the sample 12 to be measured shown in FIG. The sample 12 to be measured is a circuit having a stacked structure including an insulating layer formed on a Si substrate, and the measurement electrode 125, the capacitive insulating film 124, the lower electrode 123, the field oxide film 122, and the like from the upper layer to the lower layer. It is composed of a silicon substrate 121. Here, the capacitive insulating film 12
The capacitance formed by the two electrodes 125 and 123 that oppose each other with 4 in between is the measurement target. for that reason,
The inner conductor 82 of the reference potential cable 8 is the measurement electrode 125.
The inner conductor 72 of the signal cable 7 is in contact with the lower electrode 123.

The signal cable 7 (and the reference potential cable 8) has its outer conductor 71 (outer conductor 81) electrically connected to the shield box 11 and only the tip of the inner conductor 72 (inner conductor 82). The inner conductor 72 (inner conductor 82) is shielded by extending to the vicinity of the lower electrode 123 (measuring electrode 125) so as to be exposed. Inner conductor 72 of signal cable 7 (and reference potential cable 8)
The exposed tip of the (inner conductor 82) acts as a detection probe, and the position is adjusted by the manipulator 14 to contact the appropriate position of the lower electrode 123 (measurement electrode 125).

FIG. 3 is a circuit diagram of the capacitance measuring circuit 6 included in the capacitance meter 5 shown in FIG. This capacitance measuring circuit 6
Is a measuring circuit that outputs a voltage corresponding to the capacitance value to the output terminal 62 by applying an AC voltage to the capacitance connected to the inner conductor 72 of the signal cable 7, and also the inner conductor of the signal cable 7. It also functions as a guarding means (voltage source) for applying a voltage of the same potential as the voltage appearing at 72 to the external conductor 71. Specifically, the capacitance measuring circuit 6 includes an AC signal generator 64, two operational amplifiers 60 and 61, three resistors (R1) 65, and a resistor (R2).
66, a resistor (R3) 67, and a signal cable 7. The resistor (R1) 65, the resistor (R2) 66, and the operational amplifier 60 constitute a negative feedback circuit that inverts and amplifies the signal from the AC signal generator 64 and outputs the voltage to the AC output terminal 63. The resistor (R3) 67, the inner conductor 72 of the signal cable 7 and the operational amplifier 61 are connected in series in this order, and the feedback path of the negative feedback circuit (between the output terminal of the operational amplifier 60 and the resistor (R2) 66) is connected. ) Has been inserted.

The operational amplifier 61 functions as a voltage follower (impedance converter) having a voltage gain of 1 by short-circuiting the output terminal and the inverting input terminal. The output terminal of the operational amplifier 61 is connected to the outer conductor 71 of the signal cable 7. As a result, the outer conductor 71 of the signal cable 7 and the conductive portion of the prober 1 connected to the outer conductor 71 are always at the same potential as the inner conductor 72 of the signal cable 7 (guard potential).
Driven by and guarded. That is, stray capacitance is generated between the inner conductor 72 of the signal cable 7 and the outer conductor 71 of the signal cable 7 and the conductive portion of the prober 1, and a measurement error due to a change in the dielectric constant of the medium existing therebetween is generated. Occurrence and instability are avoided.

Next, the relationship between the voltage V01 at the output terminal 62 of the capacitance measuring circuit 6 and the capacitance value Cs of the sample 12 to be measured will be described. First, regarding the relationship between the voltage Vi of the signal generated by the AC signal generator 64 and the voltage V02 at the AC output terminal 63, focusing on the inverting amplifier circuit by the operational amplifier 60, V02 = − (R2 / R1) · Vi ( Equation 1) is obtained. Since the operational amplifier 61 functions as a voltage follower, this voltage V02 is the voltage at the non-inverting input terminal of the operational amplifier 61, that is, the internal conductor 72 of the signal cable 7 and the resistor (R3) 67. It is equal to the potential at the connection point. On the other hand, the output terminal of the operational amplifier 60 is connected to the other end of the resistor (R3) 67. The voltage V02 of the signal line is applied to the capacitance to be measured, and a current based on the voltage V02 flows through the resistor (R3) 67. It is an operational amplifier 6
This is because the input impedance of 1 is extremely high. At this time, the current IR3 flowing through the resistor (R3) 67 is IR3 = jωCs · V02. Now, assuming that the voltage of the output terminal 62 is V01, the relationship of V01 = V02 + R3 · IR3 is established. When IR3 is deleted from these equations, V01 = (1 + jωCs · R3) · V02 (Equation 2). Substituting the above equation 1 into this equation 2, V01 =-((1 + jωCsR3) R2 / R1) Vi (expression 3) is obtained.

As can be seen from Equation 3, the operational amplifier 6
The output voltage V01 of 0 contains an AC component proportional to the electrostatic capacitance Cs of the sample 12 to be measured. What should be noted here is that the operational amplifier 61 is in the state of an emergency short circuit, so that the inner conductor 72 and the outer conductor 71 have the same potential. Therefore, any stray capacitance that is considered to be formed between them is not detected. Similarly, when the outer conductor 71 and the shield box 11 are connected, the stray capacitance that is considered to be formed between the outer conductor 71 and the shield box is not detected. Further, when the stage 13, the stand 15, the manipulator 14, etc. are similarly connected to the external conductor 71, the stray capacitance is not detected similarly. As a result, the output voltage V01 of the operational amplifier 60 does not include any term related to the stray capacitance generated between the inner conductor 72 and the outer conductor 71, so that the capacitance Cs of the sample 12 to be measured is in the fF order. However, the operational amplifier 60 outputs the voltage V01 corresponding to only such a minute electrostatic capacitance Cs.

From this output voltage V01, a voltage proportional to the electrostatic capacitance Cs of the sample 12 to be measured can be obtained. From the value of this voltage, the resistance value R3 of the resistor 67 and the magnitude of the AC signal voltage Vi. , It is possible to obtain the electrostatic capacitance Cs. As described above, the output voltage V of the operational amplifier 60
01 does not include a term relating to the stray capacitance generated between the inner conductor 72 and the outer conductor 71, and the capacitance C of the measured sample 12 is
Since only the term corresponding to s is included, the capacitance Cs can be detected with high accuracy, no matter how small the capacitance Cs is.

Here, the lower electrode 123 which is one of the electrodes forming the sample 12 to be measured in FIGS. 1 to 3 may be a semiconductor wafer. In this case, the probing system of FIG. 1 can be used to judge the quality of the sample 12 to be measured. That is, it is possible to monitor the magnitude of the electrostatic capacitance formed between the lower electrode 123 and the measurement electrode 125, and determine whether the sample to be measured is good or bad depending on whether or not the value of the electrostatic capacitance is a normal value. it can. Also in this case, the output voltage V01 of the operational amplifier 60 does not include a term related to the stray capacitance generated between the inner conductor 72 and the outer conductor 71, and corresponds to the electrostatic capacitance between the DUT and the measurement electrode. Therefore, even if the capacitance is very small, the capacitance value can be measured with high accuracy, and the quality of the sample to be measured can be determined with high accuracy. . Specifically, DRAM memory cell capacitance element, wiring capacitance, MOS
Transistor gate capacitance and overlap capacitance, pn
It becomes possible to measure a minute capacitance of each part in the semiconductor device such as a junction capacitance, which can contribute to the provision of a high-performance and low-cost semiconductor device.

The sample 12 to be measured in FIGS. 1 to 3 can be, for example, the capacitance of a capacitive sensor. One electrode of the capacitive sensor is connected to the non-inverting input terminal of the operational amplifier 61 via the inner conductor 72 of the signal cable 7, and the other electrode (or its equivalent) is connected to the inner conductor 82 of the reference potential cable 8. To ground. The “capacitive sensor” that is the target of such capacitance measurement includes an acceleration sensor, seismograph, pressure sensor, displacement sensor, displacement meter, proximity sensor, touch sensor, ion sensor, humidity sensor, raindrop sensor, snow sensor, Lightning sensor, alignment sensor, contact failure sensor, shape sensor, end point detection sensor, vibration sensor, ultrasonic sensor, angular velocity sensor, liquid amount sensor, gas sensor, infrared sensor, radiation sensor, water level gauge, freeze sensor, moisture meter, vibration It includes all transducers (devices) such as a meter, a charge sensor, and a known capacitive sensor such as a printed circuit board inspection machine that detect various physical quantities by utilizing changes in electrostatic capacitance.

Next, an experimental example when the gate capacitance of the MOS transistor is measured using the above probing system will be shown. FIG. 4 is a diagram showing a connection state and a measurement result when the gate-drain capacitance (CGDO) of the MOS transistor 90 is actually measured. In this MOS transistor 90, the width W of the gate 91 is 50 μm, the length L is 2.0 μm, and the thickness Tox of the insulating oxide film 94 is 15 nm. Here, the gate 91 is brought into contact with the inner conductor 72 of the signal cable 7, and the drain 93 is connected to the reference potential cable 8.
The source 92 and the semiconductor bulk 95 are electrically connected to the outer conductor 71 and the like of the signal cable 7 by being brought into contact with the inner conductor 82. At this time, the inner conductor 82 is connected to the ground (ground). The source 92 and the semiconductor bulk 95 have the guard potential,
That is, it is prevented that the gate 91 and the drain 93 are driven to the same potential, and the capacitance between them is added as an error, and an accurate capacitance value between the gate 91 and the drain 93 (here, 1
7.8 fF) has been obtained.

FIG. 5 is a diagram showing a connection state and a measurement result when the gate-source capacitance (CGSO) of the MOS transistor 90 is actually measured. Here, the gate 91 is brought into contact with the inner conductor 72 of the signal cable 7, and the source 92 is connected.
Is brought into contact with the inner conductor 82 of the reference potential cable 8, and the drain 93 and the semiconductor bulk 95 are electrically connected to the outer conductor 71 and the like of the signal cable 7. At this time, the inner conductor 82 is connected to the ground (ground). The drain 93 and the semiconductor bulk 95 are driven to the guard potential, that is, the same potential as the gate 91 by the measurement in such a connection configuration, and it is avoided that the capacitance between them is added as an error. An accurate capacitance value (here, 16.3 fF) between 91 and the source 92 is obtained.

FIG. 6 is a diagram showing a connection state and a measurement result when the gate-drain and source capacitance (CGDO & CGSO) of the MOS transistor 90 is actually measured.
Here, the gate 91 is connected to the inner conductor 72 of the signal cable 7.
, The source 92 and the drain 93 are electrically connected to the inner conductor 82 of the reference potential cable 8, and the semiconductor bulk 95 is connected to the outer conductor 71 and the like of the signal cable 7. At this time, the inner conductor 82 is connected to the ground.
The semiconductor bulk 9 is measured by the measurement in such a connection form.
5 is driven to the guard potential, that is, the same potential as the gate 91, and it is avoided that the capacitance between them is added as an error, and the gate 91, the source 92, and the drain 93.
An accurate capacitance value (here, 34.4 fF) is obtained.

When the above three measurement results are summarized in a table,
It is as follows.

[Table 1] The “capacitance value per 1 μm” in this table is a value obtained by dividing the value of “measurement result” in the left column by the width W (50 μm) of the gate 91. The capacity parameter value shown in the lower part is the theoretical value.

As can be seen from this table, the "capacity per 1 .mu.m" obtained by actual measurement shows a value extremely close to the theoretical value, although it is on the order of fF by this probing system. The measured value of the gate-drain and source capacitance (CGDO, CGSO) is almost the sum of the measured value of the gate-drain capacitance (CGDO) and the measured value of the gate-source capacitance (CGSO) by individual measurement. equal. From this, it is confirmed that in each measurement, the stray capacitance is effectively canceled by the guard potential.

Next, FIGS. 7 to 9 show three modifications 1 to 3 regarding the connection form in the probing system of the present embodiment shown in FIG. The characteristics of these modified examples are as shown in the following table.

[Table 2] In this table, "Source" means a signal,
"Guard" means a guard potential (connection to the AC output terminal 63 of the capacitance measuring circuit 6), "reference potential" means connection to a predetermined constant potential including ground, and "float". "Means an open state insulated from any of these potentials.

In the probing system according to the first modification shown in FIG. 7, the outer conductor 81 of the reference potential cable 8 is not connected to the shield box 11 and is grounded (for example, shorted to the inner conductor 82) or floated. 1 in that it is placed in a state (not shown), which is different from the embodiment of FIG. 1 in which it is held at the guard potential. FIG. 7 shows a state in which the outer conductor 81 of the reference potential cable 8 is opened without making contact with the shield box 11 (a portion 17 where the reference potential cable 8 penetrates the shield box 11). By adopting such a connection configuration, it is possible to avoid a state in which an AC signal is applied between the inner conductor 82 and the outer conductor 81 of the reference potential cable 8 and to make the reference potential unstable. Can be prevented.

In the probing system according to the second modification shown in FIG. 8, the conductive portion of the prober 1 excluding the outer conductor 71 of the signal cable 7, that is, the outer conductor 81 of the reference potential cable 8, the shield box 11, and the stage. This embodiment is different from the embodiment of FIG. 1 in which the guard potential is held, in that the conductive portion of 13, the conductive portion of the stand 15 and the conductive portion of the manipulator 14 are grounded. In FIG. 8, a portion 18 where the signal cable 7 penetrates the shield box 11
As shown by a and 18b, the outer conductor 71 of the signal cable 7 is opened without making contact with the shield box 11, and the connection point 18 between the shield box 11 and the ground is formed.
As shown in c, it is shown that the shield box 11 is grounded. With this connection configuration, the bulk side of the DUT 12 can be set to the ground potential,
Since the entire sample 12 to be measured is shielded by the ground potential, the shielding effect against the entry of disturbance noise can be increased. In addition, a place where the operator can easily touch (shield box 1
1 and the manipulator 14) are grounded, so that safety against electric shock is secured. By the way, in all other examples of the connection form of the present invention, the bulk side of the measured sample 12 has the guard potential (the same potential as the internal conductor 72 of the signal cable 7).

In the probing system according to the third modification shown in FIG. 9, the inner conductor 82 of the reference potential cable 8 is held at a constant DC potential 19 biased from the ground (for example, in a stabilized DC voltage power supply). 1) in that it is connected to the output terminal). With such a connection configuration, the measurement electrode 125 of the sample to be measured 12 connected to the inner conductor 82 of the reference potential cable 8 is not grounded but is maintained at a constant DC potential and does not include noise or the like. Since the potential is maintained at a stabilized level, more stable capacity measurement can be realized. As can be seen from the above equation 3, the output voltage V01 obtained by the capacitance measuring circuit 6 is the signal V from the AC signal generator 64.
Since it depends on the AC component of i and not on the DC component,
The magnitude of the reference potential of the measured sample 12 (DC potential)
Does not cause a measurement error. In addition, by measuring the change of the capacitance value while changing the bias potential to the sample 12 to be measured, the CV measurement in the MOS or the like becomes possible.

According to the above modification, the signal state flowing through the reference potential cable 8, the effect of the shield covering the sample 12 to be measured, the reference potential of the sample 12 to be measured, etc. are changed. As shown, the common feature is that the outer conductor 71 and the inner conductor 72 of the signal cable 7 are maintained at the same potential, and the stray capacitance between them is canceled. Therefore, these embodiments and modified examples are appropriately selected according to the measurement environment (amount of disturbance noise, frequency of applied AC signal, etc.) and characteristics of the DUT 12 (size of capacitance value, etc.). By using each of them, it is possible to measure highly accurate and stable microcapacity by taking advantage of each merit.

In any probing system, the two cables 7 and 8 were coaxial cables having one outer conductor as a shield, but instead of this, a coaxial cable having a double shield structure. A cable (triaxial cable) may be used. Specifically, for the signal cable 7, the core wire is sourced and the inner shield is
It is conceivable that the Guard and the outer shield are grounded, set to the reference potential or float state, or the reference potential cable 8 is connected to set the core wire to the reference potential, the inner shield to Guard, and the outer shield to the ground or float state. As a result, it becomes possible to enhance the shield effect for the signal flowing through the core wire and to secure the safety against electric shock.

Next, a modified example and an application circuit which replace the capacitance measuring circuit 6 of the present embodiment shown in FIG. 3 will be shown. Figure 10
FIG. 9 is a circuit diagram of a capacitance measuring circuit 20 that can be replaced with the capacitance measuring circuit 6 according to the first modification. This capacitance measuring circuit 2
0 is equivalent to the capacitance measuring circuit 6 shown in FIG. 3 in which the phase amplitude compensating circuit 21a is inserted between the AC output terminal 63 of the operational amplifier 61 and the outer conductor 71 of the signal cable 7. That is, in the capacitance measuring circuit 6 shown in FIG. 3, the output signal of the operational amplifier 61 is directly applied to the outer conductor 71 of the signal cable 7, whereas in the capacitance measuring circuit 20, the output of the operational amplifier 61 is output. The signal is subjected to phase (and amplitude) compensation, and the obtained signal after compensation is applied to the outer conductor 71 of the signal cable 7. This is between the potential of the inner conductor 72 of the signal cable 7 (signal potential) and the potential of the outer conductor 71 (guard potential) due to the characteristics of the operational amplifier 61 itself (not being an ideal operational amplifier) and the influence of peripheral circuits. This is because there is a slight deviation (difference in phase and amplitude) between the two, and the deviation is completely canceled.

FIG. 11 is a circuit diagram including a capacitance measuring core section 41 which can be replaced with the capacitance measuring circuits 6 and 20 according to the second modification. The capacitance measuring circuit 40 is roughly divided into
A core section 41 corresponding to the capacitance measuring circuits 6 and 20 shown in FIGS. 3 and 10, an inverting section 42 for inverting and amplifying a signal voltage V01 at an output terminal 62 of the core section 41 as an input, and an inverting section thereof. The addition unit 43 is configured to add the signal voltage V03 at the output terminal 44 of 42 and the signal voltage V02 at the AC output terminal 63 of the core unit 41 and output the signal of the voltage V04 to the output terminal 45. The core portion 41 is equivalent to the capacitance measuring circuit 6 shown in FIG. 3 in which the phase amplitude compensating circuit 21b is inserted between the output terminal of the AC signal generator 64 and the outer conductor 71 of the signal cable 7. . That is, this core section 41 is common to the first modification shown in FIG. 10 in that a phase amplitude compensating circuit is added to the capacitance measuring circuit 6 of FIG. Is different from the first modified example in that the signal from the AC signal generator 64 is directly used as the input.

The inverting section 42 includes a variable resistor (R4) 50, a resistor (R5) 51, a variable resistor (R6) 52, and a capacitor 53.
And an operational amplifier 54, so that the voltage gain is 1 and the phase of the signal V03 at its output terminal 44 is the same as the signal V02 at the AC output terminal 63 of the core portion 41. , Variable resistance (R4) 50 and variable resistance (R
6) The resistance value of 52 is adjusted. The following relationship is established between the input voltage V01 and the output voltage V03 of the inverting section 42. V03 = -V01 (Formula 4)

The adder 43 is an adder in which three resistors (R7) 55, resistors (R8) 56 and resistors (R9) 57 having the same resistance value are connected to an operational amplifier 58. That is, 2
The voltages V02 and V03 of the two input signals and the output voltage V04 are
The following relationship holds. V04 =-(V02 + V03) (Equation 5) By substituting the above Equation 4 into this Equation 5, V04 = V01-V02 (Equation 6) is obtained. As can be seen from Equation 6, the output terminal 45
Signal voltage V04 of the two output terminals 62 of the core portion 41,
The difference between the signal voltages V01 and V02 at 63, in other words, the change in the output voltage corresponding to the change in the measured capacitance.
Substituting Equation 2 into this Equation 6 and rearranging it, and then substituting Equation 1, Vi (Equation 7) holds. That is, it can be seen that the voltage V04 proportional to the capacitance value Cs is output from the output terminal 45 of the capacitance measuring circuit 40 of the second modified example. Therefore, the unknown capacitance value Cs can be specified by performing various signal processes based on the voltage V04. Also, the above formula 7
Is simpler than the equation 3 showing the output voltage V01 shown in FIG. 3 (the output V04 and the input Vi are proportional).
As can be seen from this, in the capacitance measuring circuit 40, the occurrence of error factors is suppressed as much as possible.

FIG. 12B is a detailed circuit diagram of the phase / amplitude compensation circuit 21b shown in FIG. The phase / amplitude compensation circuit 21b is roughly divided into a phase adjusting unit 24 that shifts the phase of the signal input from the input terminal 22, and an amplitude adjusting unit that voltage-amplifies the output signal and outputs the voltage to the output terminal 23. And 25. Phase adjuster 24
Is an all-pass filter in which the resistor 33, the variable resistor 34, the resistor 35, and the capacitor 36 are connected to the operational amplifier 31. By adjusting the resistance value of the variable resistor 34, the amount of phase shift by the phase adjusting unit 24 can be adjusted.

The amplitude adjusting section 25 is an inverting amplifier circuit in which the resistor 37 and the variable resistor 38 are connected to the operational amplifier 32. By adjusting the resistance value of the variable resistor 38, the amplitude (voltage) amplification factor by the amplitude adjusting unit 25 can be adjusted. On the other hand, this phase amplitude compensation circuit 21b is shown in FIG.
When applied to the capacitance measuring circuit 20 shown in FIG.
To delete. By doing so, as shown in FIG. 12 (a), the phase / amplitude compensation circuit 21a for the capacitance measuring circuit 20 shown in FIG. 10 is capable of adjusting both the amplitude and the phase without phase inversion. Can be obtained. In this way, in the phase amplitude compensation circuits 21a and 21b,
By properly adjusting the three variable resistors 34 and 38,
The deviation of the signal between the non-inverting input terminal and the AC output terminal 63 of the operational amplifier 61 of the capacitance measuring circuit 6, that is, the deviation of the signal potential between the inner conductor 72 and the outer conductor 71 of the signal cable 7 is canceled, and the amplitude and phase are canceled. It is possible to get close to the ideal state of an immergenary short that perfectly matches. Therefore, if the generated signal Vi from the AC signal generator 64 has a frequency of about several kHz to several hundred KHz, the stray capacitance between the inner conductor 72 and the outer conductor 71 of the signal cable 7 is reliably canceled, and Only the capacitance Cs of the measurement sample 12 can be accurately detected.

Although the probing system according to the present invention has been described above based on the embodiment and the modifications, it goes without saying that the present invention is not limited to these. For example, the probing system according to the present embodiment is used for measuring capacitance, but it can be used for measuring inductance. Further, in the present embodiment, the coaxial cables are used as the signal cable 7 and the reference potential cable 8, but instead of this, a single-core cable and a shield material that covers it are combined, or a twisted wire such as a twisted pair is used. May be used.

Further, in the capacitance measurement of the sample 12 to be measured shown in FIG. 2 and the MOS transistor 90 shown in FIG. 4 and the like, even if the electrodes and terminals for contacting the signal cable 7 and the reference potential cable 8 are exchanged, respectively. Good. For example, the inner conductor 72 of the signal cable 7 may be brought into contact with the measurement electrode 125 of the sample to be measured 12, and the inner conductor 82 of the reference potential cable 8 may be brought into contact with the lower electrode 123. Further, in the present embodiment, the signal cable 7 and the reference potential cable 8 are
Are fixed by the manipulator 14 and their internal conductors directly contact the measured sample 12, but may contact the measured sample 12 via the probe needle fixed to the manipulator 14. In this case, the signal cable 7
The reference potential cable 8 is connected to the probe needle via a connector or the like without exposing its internal conductor.
It is desirable that the probe needle itself, like a coaxial cable, has a structure that is covered with a shield member via an insulating material and is guarded except for the tip end portion that comes into contact with the measured sample 12.

In the present embodiment, the sample to be measured 12 is
As impedance means connected in series to the resistor (R
3) 67 was used, but is not limited to such a resistance as long as it has a fixed impedance. For example,
It may be a capacitance, an inductance, an impedance by a combination thereof, or the like. In addition, the probing system of various variations can be constructed by arbitrarily combining the connection form and the capacitance measuring circuit of the probing system according to the present embodiment and the modification. For example, by adopting the probing system of FIG. 7 as the connection mode and the circuit shown in FIG. 11 as the capacitance measuring circuit thereof, the ground potential is stabilized and the capacitance value Cs can be easily calculated from the output voltage. A practical probing system that can identify

It is also possible to adopt a configuration in which various connection forms are selected by a switching circuit. For example, a switching circuit that connects the conductive portion of the prober 1 to the outer conductor 71 of the signal cable 7 or the ground may be provided. Similarly, the resistance (R3) 6 connected in series with the capacitance of the sample 12 to be measured.
As 7, a switching circuit for selecting one of a plurality of resistors having different resistance values may be provided, or a switching circuit for connecting or disconnecting the capacitance measuring circuit 6 and the signal cable 7 may be provided. This makes it possible to measure the capacitance over a wide range and facilitate the phase / amplitude adjustment in the inverting unit 42.

Further, the phase / amplitude compensation circuits 21a and 21b shown in FIG. 12 both have the function of adjusting the phase and the amplitude, but the present invention does not necessarily have the function of adjusting both the phase and the amplitude. Not what you need. That is, if the signals flowing through the outer conductor 71 and the inner conductor 72 of the signal cable 7 can be made to have the same potential, a compensation circuit having a function of adjusting only the phase or only the amplitude may be sufficient. .

[0046]

As is apparent from the above description, according to the probing system of the present invention, the inner conductor and the outer conductor of the signal cable are held at the same electric potential, so that the inner conductor and the outer conductor of the signal cable are kept at the same potential. It is avoided that the stray capacitance is added as a measurement error and that the stray capacitance is affected by a change in temperature or the like. This makes it possible to accurately measure minute capacitance values of the fF order, etc., and
It is possible to perform stable measurement.

Further, it has been confirmed by actual measurement using the probing system of the present invention that a semiconductor sample can be measured with an accuracy of several fF. When the sample to be measured is a semiconductor wafer, various minute capacitances of the semiconductor wafer can be measured with high accuracy according to the present invention. Therefore, despite the simple method, the semiconductor device can be measured with high accuracy. It is possible to measure the electrical characteristics of the above and determine the quality thereof, and it is possible to provide a high performance and low cost semiconductor device.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a probing system according to the present invention.

FIG. 2 is an enlarged view of the measured sample shown in FIG.

FIG. 3 is an example of a circuit diagram of a capacitance measuring circuit included in the capacitance meter of the system.

FIG. 4 is a diagram showing a connection state and a measurement result of an example of actually measuring the gate-drain capacitance (CGDO) of a MOS transistor using the same system.

FIG. 5 is a diagram showing a connection state and a measurement result of an example of actually measuring the gate-source capacitance (CGSO) of the MOS transistor 90 using the system.

FIG. 6 shows a gate-drain-source capacitance (CGDO & CGS) of a MOS transistor 90 using the system.
It is a figure which shows the connection state and the measurement result of the example which measured O).

FIG. 7 is a diagram showing a first modification of the connection form of the probing system.

FIG. 8 is a diagram showing a second modification of the connection form of the probing system.

FIG. 9 is a diagram showing a modified example 3 of the connection form of the probing system.

FIG. 10 is a circuit diagram showing a first modification of the capacitance measuring circuit.

FIG. 11 is a circuit diagram showing a second modification of the capacitance measuring circuit.

FIG. 12A is an example of a detailed circuit diagram of a phase amplitude compensation circuit in the second modification, and FIG. 12B is a detailed circuit diagram of the phase amplitude compensation circuit in the first modification. This is an example.

FIG. 13 is a diagram showing a configuration of a conventional probing system.

[Explanation of symbols]

1 prober 5 capacity meter 6 Capacity measurement circuit 7 signal cable 8 reference potential cable 11 shield box 12 Sample to be measured 13 stages 14 Manipulator 15 Stand 17, 18a-c Contact / connection points 19 DC potential 20 Capacity measuring circuit 21a, 21b Phase amplitude compensation circuit 22 Input terminals 23, 44, 45, 62, 63 Output terminals 24 Phase adjuster 25 Amplitude adjuster 31, 32, 54, 58, 60, 61 Operational amplifier 33, 35, 37, 65-67 Fixed resistance 34, 38 Variable resistance 36, 53 condenser 40 capacitance measurement circuit 41 core 42 Inversion section 43 adder 64 AC signal generator 71 outer conductor 72 Inner conductor 81 outer conductor 82 Inner conductor 90 MOS transistor 91 gate 92 Source 93 drain 94 insulating oxide film 95 Semiconductor bulk 121 Silicon substrate 122 field oxide film 123 Lower electrode 124 Capacitance insulating film 125 measuring electrodes

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2G011 AA22 AB06 AB09 AC33 AD01                       AE03                 2G028 AA01 AA04 BB11 CG07 DH05                       DH09 HM05 HN09 MS05                 4M106 AA01 BA01 BA14 DD03 DD15                       DD30

Claims (11)

[Claims] 1. A probing system including a prober and a first measurement circuit, wherein the prober includes a box for covering the sample to be measured, a signal line whose one end contacts the sample to be measured as a detection probe, and the signal. A first shield member that covers a line, and the first measurement circuit has a voltage follower in which the other end of the signal line is connected to an input terminal and the first shield member is connected to an output terminal, The impedance means having one end connected to the signal line, the other end of the impedance means is connected to an output terminal, and the impedance means and the voltage follower means are connected so as to be included in a negative feedback path. A probing system having an operational amplifier. 2. A probing system including a prober and a second measurement circuit, wherein the prober includes a box that covers the sample to be measured, a signal line whose one end contacts the sample to be measured as a detection probe, and the signal. A first shield member for covering the line, and the second measurement circuit has first and second input terminals that are in an emergency short circuit state, and the other end of the signal line is connected to the first input terminal. A second operational amplifier connected thereto; a guard means for applying a voltage having the same potential as the signal voltage of the signal line to the first shield member; an impedance means having one end connected to the signal line; The other end is connected to the output terminal, and the impedance means and the third operational amplifier are connected so as to be included in the negative feedback path. And a probing system. 3. The probing system according to claim 1, wherein the box is electrically connected to the first shield member or is connected to a reference potential. 4. The prober further has a mounting table for holding a sample to be measured, and the mounting table is electrically connected to the first shield member or connected to a reference potential. The probing system according to any one of claims 1 to 3, which is characterized. 5. The prober further has a reference potential line whose one end contacts a sample to be measured as a reference potential probe, and the other end of the reference potential line is grounded or held at a constant potential. The probing system according to claim 1, wherein the probing system is provided. 6. The prober further includes a second shield member that covers the reference potential line, and the second shield member is electrically connected to the first shield member or connected to a reference potential. 6. The probing system according to claim 5, wherein the probing system is placed in a floating state. 7. The probing system according to claim 1, wherein the first shield member has a coaxial structure of a plurality of layers. 8. An AC signal is input to the first operational amplifier or the third operational amplifier, and the guard means is an AC signal appearing at the output terminal of the AC signal, the voltage follower, or the second operational amplifier. 8. The probing system according to claim 1, wherein at least one of phase compensation and amplitude compensation is applied to the first shield member and the obtained signal is applied to the first shield member. 9. A method for measuring the capacitance of a sample to be measured by a probing system including a prober and a measuring circuit, wherein the sample to be measured placed on the prober is covered with a box and is covered with a first shield member. One end of the wire is brought into contact with the sample to be measured as a detection probe, and in the measurement circuit, the other end of the signal line is connected to the input terminal of the voltage follower, and the first shield member is connected to the output terminal thereof. One end of the impedance means is connected to the signal line and the other end is connected to the output terminal of the first operational amplifier so that the impedance means and the voltage follower means are included in the negative feedback path of the first operational amplifier. And connecting the output terminal of the first operational amplifier to the output terminal of the measurement circuit, and based on the voltage of the output terminal of the measurement circuit. Then, the capacity measuring method is characterized by measuring the capacity of the sample to be measured. 10. A method for measuring the capacitance of a sample to be measured by a probing system including a prober and a measuring circuit, wherein the sample to be measured placed on the prober is covered with a box and a signal is covered with a first shield member. The one end of the wire is brought into contact with the sample to be measured as a detection probe, and in the measurement circuit, the first and second input terminals of the second operational amplifier are brought into the state of an emergency short, and the signal is input to the first input terminal thereof. The other end of the line is connected, a voltage having the same potential as the signal voltage of the signal line is applied to the first shield member by the guard means, one end of the impedance means is connected to the signal line, and the other end is connected to the first line. 3 is connected to the output terminal of the operational amplifier, and the impedance means and the second operational amplifier are connected so as to be included in the negative feedback path of the third operational amplifier. Then, the output terminal of the third operational amplifier is used as the output terminal of the measurement circuit, and the capacitance of the sample to be measured is measured based on the voltage of the output terminal of the measurement circuit. 11. The sample to be measured is a MOS transistor including a semiconductor bulk having a source terminal and a drain terminal formed thereon and a gate terminal facing each other with an oxide film interposed therebetween. At least 1
At least one of the remaining terminals and the semiconductor bulk that are connected to a signal line and are not electrically connected to the signal line.
One of them is connected to a reference potential, and when at least one of the remaining portions which has not been connected until now exists in the terminal and the semiconductor bulk, the (existing) portion is electrically connected to the first shield member. Then, the reference voltage is connected to ground, a predetermined voltage, or a voltage applied while sweeping, and the capacitance of a predetermined portion in the MOS transistor is measured based on the voltage of the output terminal of the measurement circuit. The method for measuring capacitance according to claim 9 or 10, characterized in that.