JPH09288131A - Method for measuring voltage waveform - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically verify and monitor electric contact between a wiring layer and a probe by determining a voltage origin with voltage difference between both ends of a voltage transducer eliminated while the probe is electrically floated. SOLUTION: A transparent electrode 5 for applying reference voltage to one of main surfaces of an electro-optic crystal (voltage transducer) 4, while a probe 7 is attached to the other surface via a reflection electrode 6. The probe 7 is brought into contact with a wiring layer 17 provided on a substrate 16 such as an Si substrate for measuring a signal 18 to be measured applied to the wiring layer 17. In determining a voltage origin, while the probe 7 is electrically floated before it is brought into contact with the wiring layer 17, electric conductivity of the voltage transducer 4 is used to eliminate voltage difference between both ends of the transducer 4 for determining the voltage origin. Since the voltage origin can be thus determined without using a calibration pad, measurement of an absolute level of a voltage waveform is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage waveform measuring method, and more particularly to a method for automatically measuring a wiring voltage waveform inside a semiconductor large scale integrated circuit device (LSI device) using an electro-optical effect. The present invention relates to a voltage waveform measuring method.

[0002]

2. Description of the Related Art In designing and manufacturing a semiconductor device such as a semiconductor large scale integrated circuit, it is indispensable to accurately grasp the voltage waveform applied to the wiring inside the semiconductor device. The width of the wiring layer is becoming narrower with the improvement of the integration degree, and it is becoming difficult to cope with the conventional method of measuring the voltage waveform by bringing the prober into contact with the fine wiring layer using an optical microscope.

As an alternative to this optical microscope, A
A surface shape measuring device capable of detecting a fine structure such as FM (atomic force microscope) or STM (scanning tunneling electron microscope) is used. As a voltage waveform detecting device, a fine probe is brought into contact with a wiring layer to form a voltage waveform. It is devised to measure.

When the voltage waveform applied to the fine wiring layer is measured by combining such a surface shape measuring device and a voltage waveform detecting device, the surface shape measuring device has an insulating surface to be measured. AFM, which is capable of shape measurement, is considered promising.

Further, since accurate measurement is becoming difficult with the electrical measurement method, it is possible to measure a high-speed signal in a fine measurement region by utilizing the electro-optic effect of the electro-optic crystal. A method has been proposed (if necessary, JA Valdmanis and G. Mou).
rou, IEEE JOURNAL OF QUANT
UM ELECTRONICS, Vol. QE-22,
1986, pp. 69-78).

FIG. 13 is an explanatory view of a conventional voltage signal measuring device using the electro-optic effect, in which a transparent electrode 5 for applying a reference voltage is provided on one main surface of the electro-optic crystal 4. At the same time, a probe 7 is attached to the other surface via the reflective electrode 6, and the probe 7 is brought into contact with a wiring layer 17 provided on a substrate 16 such as a Si substrate to be applied to the wiring layer 17. The signal 18 is measured.

Then, a phase plate 2 is attached to the electro-optic crystal 4.
Laser light is emitted from the laser light source 1 through the beam splitter 3 and the beam splitter 3, and the reflected light from the reflective electrode 6 is detected by the photodetectors 13 and 14 via the polarization beam splitter 11 and the mirror 12, respectively, and the detection output is detected. It is input to the differential amplifier 15 and its differential output X is obtained.

This output X depends on the signal under measurement V applied to the wiring layer 17 and is represented by V = a (X-b). The amplitude of the signal under measurement is determined by the coefficient a and the coefficient b is determined. Determines the position of 0V.

In this case, the measured signal V applied to the wiring layer 17 changes the refractive index of the electro-optical crystal 4 by the Pockels effect, and the polarization state of the laser light passing through the electro-optical crystal 4 changes. Then, the components reflected by the polarization beam splitter 11 and detected by the photodetector 13 and those transmitted by the polarization beam splitter 11 are detected by the photodetector 1.
The fact that the ratio with the component detected in 4 changes is used.

In the voltage waveform measuring device using such an electro-optic crystal, in order to measure the absolute level of the voltage waveform, it is necessary to obtain the voltage origin, that is, the coefficient b which determines 0V. In order to obtain the coefficient b, a method has been proposed in which a calibration pad having a known voltage is prepared and a probe is brought into contact with the pad to obtain the correspondence between the voltage V and the detection signal X.

[0011]

In the conventional method of determining the coefficient b using the calibration pad, the electro-optical effect (Pockels effect) is small, so that the modulation factor of the polarization state of the laser light is 0.1, for example. Since it is as small as about%, the voltage waveform measurement is greatly affected by a small change in the optical axis and a change in the signal processing system, and it becomes necessary to remeasure the coefficients a and b.

However, if the EO probe (electro-optical probe) is moved to the calibration pad each time re-measurement is performed, it not only takes time, but also the optical axis is moved by moving from the calibration pad to the measurement point. There is a possibility that there will be a shift and accurate measurement will not be possible.

Further, even if the coefficients a and b can be accurately measured, it is necessary to bring the probe into accurate contact with the wiring layer and to make it conductive in order to measure the voltage waveform. Since Al or Al alloy is used for the wiring inside the device, it is necessary to break through the natural oxide film on the surface of the wiring layer with a probe to secure electrical contact.

Therefore, it is necessary to make the probe lack a large load as compared with the case of measuring the surface shape. However, as the width of the wiring layer becomes finer, the thickness of the wiring layer also becomes thinner and the wiring layer is not broken. In addition, it is difficult to control the optimum load for ensuring electrical contact, and even if the skill of an experienced operator is relied upon, it takes time to confirm the electrical contact.

Even if electrical contact between the wiring layer and the probe is confirmed, good contact is ensured for a predetermined time due to displacement due to vibration or thermal expansion when the wiring layer width becomes fine. It's getting harder to continue.

Therefore, it is an object of the present invention to determine the voltage origin by a simple method in voltage waveform measurement, and to automatically confirm and monitor the electrical contact between the wiring layer and the probe.

[0017]

FIG. 1 is an explanatory view of the principle configuration of the present invention, and means for solving the problems in the present invention will be described with reference to FIG. See FIG. 1. (1) The present invention is a contact-type voltage waveform measuring method for optically measuring a voltage applied to an object to be measured, and a probe is attached to one surface of a voltage transducer.
It is characterized in that the origin of the voltage is determined by eliminating the voltage difference across the voltage transducer due to the electrical conductivity of the voltage transducer while the probe is electrically floating.

The voltage transducer can be regarded as a parallel connection circuit in which a resistance R and a capacitance C between one surface and another surface on which the probe is attached are parallel to each other in terms of an equivalent circuit. After moving the needle to the voltage measurement point, the parallel connection circuit of R and C was discharged with a time constant RC by electrically floating the probe in the step of, and the voltage difference across the voltage transducer was eliminated by the discharge. Later, signal X
The coefficient b, that is, the voltage origin can be accurately determined by measuring

(2) According to the present invention, in the above (1), the electro-optic crystal having photoconductivity is used as the voltage transducer, and the electro-conductivity of the electro-optic crystal is irradiated by irradiating the electro-optic crystal with light. It is characterized by increasing.

As described above, when the electro-optic crystal having photoconductivity is used as the voltage transducer, the electric conductivity of the electro-optic crystal is increased and R is decreased by irradiating light in the step of, so It is possible to eliminate the voltage across the voltage transducer with a small time constant, that is, in a shorter time.

(3) Further, in the present invention according to the above (1), an electro-optic crystal is used as the voltage transducer,
It is characterized in that a periodic electric signal is applied to the surface of the electro-optic crystal opposite to the surface on which the probe is attached, and the voltage origin is determined by averaging one cycle.

As described above, in the step, when a periodic electric signal having a period faster than the time constant RC is applied to the surface of the electro-optic crystal opposite to the surface on which the probe is attached, the potential difference between both ends of the crystal is increased. Changes in the signal cycle instead of 0V, but by canceling the fluctuation component by taking the average value over one cycle, the average value corresponds to the voltage V = 0. You can decide.

(4) Further, according to the present invention, in the voltage waveform measuring method by the optical sampling method utilizing the Pockels effect of the electro-optic crystal, the probe is attached to one surface of the electro-optic crystal, and A reference electrode for applying a reference voltage is provided on the other surface, and while the AC voltage is applied to the reference electrode, the object to be measured is measured in synchronization with the applied AC voltage by the optical sampling method. It is characterized in that the probe is brought close to the position, the change in the detected waveform amplitude is monitored, and the point where the amplitude change is stable is taken as the electrical contact point.

After the voltage origin is determined in the step, the probe is brought into contact with the object to be measured in the step.
While applying an AC voltage to the reference electrode provided on the other surface of the electro-optic crystal, while performing voltage measurement by the optical sampling method in synchronization with the applied AC voltage, bring the probe closer to the measured object, By monitoring changes in the detected waveform amplitude, reliable electrical contact can be made automatically.

(5) Further, in the present invention, in the above (4), after detecting the electrical contact point, the probe is further pressed against the object to be measured by a predetermined amount which is determined in advance to stabilize the electrical contact. Is characterized by.

As described above, after the detection of the electric contact point, the electric contact can be stabilized by further applying a predetermined amount of load to the probe so that the optimum load is experimentally confirmed in advance. .

(6) Further, in the present invention, in the above (4) or (5), when the signal frequency applied to the object to be measured matches the signal frequency of the AC voltage applied to the reference electrode, detection is performed. The occurrence of frequency matching is detected because the noise level of the signal
It is characterized in that the signal frequency of the AC voltage applied to the reference electrode is changed.

As described above, when the signal frequency applied to the object to be measured matches the signal frequency of the AC voltage applied to the reference electrode, the mutual signals cancel each other, and the noise level of the detected signal is detected. Does not decrease due to the averaging process, so the occurrence of frequency matching can be detected by detecting it, and the electrical contact can be reliably detected by changing the signal frequency of the AC voltage applied to the reference electrode. .

(7) Further, in the present invention according to any one of the above (4) to (6), the waveform of the AC voltage applied to the reference electrode at a predetermined cycle is measured during the voltage waveform measurement of the object to be measured. If the amplitude value obtained at the time of confirming the electrical contact point falls below a predetermined error range, the voltage waveform measurement of the measured object is interrupted.

As described above, during the measurement of the voltage waveform of the object to be measured, the waveform of the AC voltage applied to the reference electrode is measured at a predetermined cycle as the step, and the amplitude obtained at the time of confirming the electrical contact point is measured. By comparing the measured value with the value, it is possible to determine the contact failure and automatically stop the voltage waveform measurement of the measurement target to prevent erroneous measurement.

(8) Further, in the present invention according to any one of (4) to (6), the optical sampling is performed in synchronization with the voltage waveform applied to the object to be measured immediately after confirmation of the electrical contact point. Hold the amplitude value of the detected voltage waveform,
During measurement of the voltage waveform of the measured object, if the amplitude value of the measured voltage waveform falls below the held amplitude value by more than the specified error range, it is possible to interrupt the voltage waveform measurement of the measured object. Characterize.

As described above, in the step (1), immediately after confirmation of the electrical contact point, optical sampling is performed in synchronization with the voltage waveform applied to the object to be measured, the amplitude value of the detected voltage waveform is held, and While measuring the voltage waveform of the measurement target, determine the contact failure by comparing with the measured voltage waveform,
It is possible to prevent erroneous measurement by automatically interrupting the voltage waveform measurement of the measurement target.

(9) Further, in the present invention according to the above (7) or (8), after interrupting the voltage waveform measurement of the object to be measured, an AC voltage is applied again to the reference electrode to confirm the electrical contact point. It is characterized by performing.

In (7) or (8), after the voltage waveform measurement of the object to be measured is interrupted, the electrical contact point is automatically confirmed again by the method of (4) as a part of the step. As a result, even when there is a change in amplitude as in the above (8), it is possible to distinguish between destruction of the object to be measured itself and mere misalignment of the probe, so that there is no erroneous measurement, and at high speed, It is possible to accurately measure the voltage waveform of the measurement target.

(10) Further, the present invention is characterized in that, in the above (7) or (8), the load applied to the probe is further increased after the voltage waveform measurement of the object to be measured is interrupted.

As described above, after the voltage waveform measurement of the object to be measured is interrupted, a simple operation of further increasing the load applied to the probe instead of the step of Can be recovered.

(11) Further, the present invention is a contact-type voltage waveform measuring method for optically measuring a voltage applied to an object to be measured, wherein the probe is attached to one surface of the voltage transducer and A pulse voltage is applied from one end of and the change in the electrical contact state is detected by the change in the waveform of the reflected voltage pulse generated due to the impedance mismatch in the contact portion between the probe and the object to be measured.

As the steps of and, the above (4)
Since it takes a relatively long time when the electrical contact is checked optically as in (1), etc., the electrical contact can be checked by an electrical means to ensure high-speed and reliable electrical contact. Can be confirmed.

(12) Further, in the present invention according to the above (11), the dispersion value of the voltage waveform measured during the arithmetic mean measurement of the voltage waveform of the measurement object is changed to the dispersion value of the voltage waveform previously measured. It is characterized by detecting the change of the electrical contact state by comparing with.

(13) Further, in the present invention according to the above (11), the voltage histogram of the measured voltage waveform is changed to the voltage histogram of the previously measured voltage waveform during the arithmetic mean measurement of the voltage waveform of the object to be measured. It is characterized by detecting the change of the electrical contact state by comparing with.

(14) Further, in the present invention according to the above (11), by comparing the measured voltage waveform with the voltage waveform measured before during the averaging measurement of the voltage waveform of the object to be measured, It is characterized by detecting a change in an electrical contact state.

(15) In the present invention, in the above (14), the difference calculation between the measured voltage waveform and the voltage waveform measured before is performed during the arithmetic mean measurement of the voltage waveform of the object to be measured, and the difference is calculated. It is characterized in that the change in the electrical contact state is detected by the average value of the signal waveform.

(16) Further, in the present invention according to the above (14), a difference operation between the measured voltage waveform and the voltage waveform measured before is performed during the arithmetic mean of the voltage waveform of the object to be measured, and the difference is calculated. It is characterized in that the change in the electrical contact state is detected by the amplitude value of the signal waveform.

As described above, the dispersion value of the measured voltage waveform, the voltage histogram of the measured voltage waveform, the average value of the difference signal waveform between the measured voltage waveform and the voltage waveform measured before that, or the difference signal waveform By using the amplitude value, the maintenance confirmation of the electrical contact state can be performed at high speed and with high accuracy.

(17) Further, the present invention is characterized in that in any one of the above (11) to (16), an electro-optic crystal having a Pockels effect is used as the voltage transducer.

As described above, by using the electro-optic crystal having the Pockels effect as the voltage transducer, the voltage waveform of the object to be measured can be accurately obtained by utilizing the electro-optic effect, that is, the Pockels effect. .

(18) Further, the present invention is characterized in that, in any one of the above (11) to (16), a semiconductor optical switch is used as the voltage transducer.

In this way, as a voltage transducer,
By using a semiconductor optical switch such as a photoconductive element, the voltage waveform of the measured object can be electrically acquired.

[0049]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a schematic configuration of a voltage waveform measuring apparatus used for implementing the present invention will be described with reference to FIG. See FIG. 2. The voltage waveform measuring apparatus used for carrying out the present invention has substantially the same configuration as the conventional voltage waveform measuring apparatus shown in FIG. 13, and applies a reference voltage to one main surface of the electro-optic crystal 4. The transparent electrode 5 is provided, and the probe 7 is attached to the other surface through the reflective electrode 6, and the probe 7 is brought into contact with the wiring layer 17 provided on the substrate 16 such as a Si substrate to form the wiring layer 17. The measured signal 18 being applied is measured.

Actually, in the electro-optic crystal 4, the probe 7 is attached to the wiring layer 17 to be measured by a parallel leaf spring through a hollow pipe for guiding the laser beam attached to the transparent electrode 5 side. It is held vertically.

Then, the phase plate 2 is added to the electro-optic crystal 4.
Laser light is emitted from the laser light source 1 through the beam splitter 3 and the beam splitter 3, and the reflected light from the reflective electrode 6 is detected by the photodetectors 13 and 14 via the polarization beam splitter 11 and the mirror 12, respectively, and the detection output is detected. The transparent electrode 5 is used to obtain the differential output X by inputting it to the differential amplifier 15.
To the ground wire 9 or the low frequency oscillator 10 via the switch 8.
It is different from the conventional voltage waveform measuring device in that it is switchably connected to the device. By opening the switch 8, it is possible to determine the voltage origin, and by connecting it to the ground line 9, the measured object can be measured. That is, the voltage waveform of the signal under measurement 18 applied to the wiring layer 17 can be measured, and the electrical contact can be confirmed by connecting to the low frequency oscillator 10.

The optical system for voltage detection in the above description is an example of the measuring method, and the application of the present invention to other optical system configurations is not hindered.

Next, referring to FIG. 3A, a method of determining the voltage origin according to the first embodiment of the present invention will be described. See FIG. 3A. Both ends of the electro-optic crystal 4, that is, the transparent electrode 5 and the reflective electrode 6.
If the resistance between the probe and the capacitor is R and the capacitance is C, the probe 7 is kept in an electrically floating state before coming into contact with the wiring layer 17 (not shown), and is maintained for a time sufficiently longer than the time constant t = RC. To do.

At this time, even if a potential difference occurs at both ends of the electro-optical crystal due to charge-up during measurement or the like, the electro-optical crystal 4 can be regarded as a parallel circuit of a resistance R and a capacitance C in terms of an equivalent circuit. Therefore, even if the potential of the probe 7 in the initial state is V ₀ in the state where the transparent electrode 5 is connected to the ground wire 9, the probe 7 is electrically floated, and the charge of the capacitance C is changed by the resistance R. After discharging and time t = RC, the potential of the probe 7 becomes V ₀ / e (e is the base of natural logarithm).

Therefore, a time sufficiently longer than t = RC,
For example, the resistance at both ends of the electro-optic crystal is 10 MΩ, and the capacitance is 1
If nF, t = 0.01 seconds, and therefore, the voltage V =
This means that the coefficient b of the signal X with respect to 0 is obtained.

After that, the probe 7 is brought into electrical contact with the wiring layer 17, and the measured signal 18 applied to the wiring layer 17 is applied.
By measuring the voltage waveform of, the absolute value of the voltage of the signal under measurement 18 can be accurately measured.

FIG. 4 is an explanatory diagram of the measurement result in the first embodiment of the present invention, in which the EO measurement value which is the measurement result is the measured signal previously measured by other means. It was confirmed that it corresponds to voltage brilliantly and can perform highly accurate measurement.

Even if a direct current electric signal is applied to the transparent electrode 5, the potential difference between both ends of the electro-optic crystal 4 is 0 V when the time constant RC or more elapses by floating the probe.
, So there is no problem.

Next, referring to FIG. 3B, ZnTe is used as the electro-optic crystal 4 according to the second embodiment of the present invention.
A method of determining the voltage origin when a crystal having photoconductivity such as is used will be described. See FIG. 3B. In the second embodiment, light 19 is applied to the electro-optic crystal 4 such as ZnTe in a state where the probe 7 is electrically floated before contacting the wiring layer 17. Therefore, the resistance R of the electro-optical crystal 4 is greatly reduced by the photocarriers generated by the irradiation of the light 19, and the time constant RC of the discharge is also significantly reduced accordingly, so that the time required for determining the voltage origin is significantly increased. It can be shortened.

Next, a third embodiment of the present invention will be described with reference to FIG. 5A and 5B, in the third embodiment, a signal having a period faster than the time constant RC, for example, a high frequency signal without DC offset is applied from the high frequency signal source 20 to the transparent electrode 5. , The potential difference between both ends of the crystal is not 0V but fluctuates according to the cycle of the high frequency signal, but it is 0V in terms of direct current. Therefore, the measured signal X should be averaged over one cycle to cancel the fluctuation. Thus, the average value is obtained by obtaining the voltage V = 0, that is, the coefficient b of the voltage origin.

As shown by the broken line in the figure, when the voltage waveform of the object to be measured is measured with the direct current applied voltage 21 (V ') applied to the transparent electrode, the voltage origin is measured. It corresponds to the target potential V ′.

As described above, in the embodiments of the first to third embodiments of the present invention, the probe 7 is kept on the measured point without using the special calibration pad, and the voltage origin Since the determination is performed, the time required to determine the voltage origin is shortened, and the determination of the voltage origin and the measured object, that is, the measured signal 18 applied to the wiring layer 17 are continuously performed, so that the reliability is improved. Is improved.

After determining the voltage origin as described above, the voltage waveform of the object to be measured is measured. At that time, it is essential to confirm the electrical contact between the probe and the object to be measured. However, a fourth embodiment of the present invention relating to an automatic confirmation method for optically confirming this electrical contact will be described with reference to FIGS. 6 to 8.

See FIG. 6A. FIG. 6A shows a state in which the low frequency signal 10 is applied to the transparent electrode.
Shows an equivalent circuit when the probe is brought close to the wiring layer
Therefore, electrical contact can be made between the probe and the wiring layer.
If not, between the probe and the wiring layer, the probe-wiring layer
Inter-capacity 22 (C _g) Is capacitively coupled
You.

That is, the wiring layer in the semiconductor device is made of Al.
Alternatively, since it is formed by using an Al alloy, a natural oxide film is formed on the surface, and even if the probe is physically contacted with the wiring layer after the surface shape is measured by using the AFM, the However, they are not necessarily in contact with each other and are capacitively coupled by the capacitance C _g .

Therefore, the low-frequency signal V _a from the low-frequency oscillator 10 is _divided by the capacitance C _g and the capacitance C _c of the electro-optic crystal 4, and the laser light is emitted from the low-frequency oscillator 1
In the voltage waveform measurement in which irradiation is performed in synchronization with the frequency of 0 and optical sampling is performed, the voltage V _c applied to the electro-optic crystal 4 is measured.

This V _c is V _c = V _a × C _g / (C _c +
C _g ), and the capacitance C _g is inversely proportional to the distance between the probe and the wiring layer. Therefore, as the probe approaches the wiring layer, V
_c gradually approaches V _a , and the voltage waveform increases.

See FIG. 6B. In FIG. 6B, the measurement is performed before the probe contacts the wiring layer.
The voltage waveform of a step-like signal applied to the electro-optic crystal 4 made of ZnTe from the low-frequency oscillator 10 via the transparent electrode is shown. Since V _g is a measurement in a state where C _g is small, V _c is V _a It is much smaller and the amplitude at the detection output is also smaller.

See FIG. 6C. FIG. 6C shows the case where the probe is in sufficient electrical contact with the wiring layer.
Shows the equivalent circuit of the probe contact in this case.
The contact resistance 23 (R) is connected in series.
Resistance R is capacitance C_gSmall enough compared to the impedance of
Therefore, V_c≒ V _aAnd the voltage V_aMost of it is electric light
It is applied to the learning crystal 4.

Therefore, the amplitude of the voltage waveform to be measured becomes large and is stabilized, and the amplitude of the voltage waveform does not change even if a load is further applied to the probe. The establishment of contact can be detected.

See FIG. 6 (d). FIG. 6 (d) shows Z from the low frequency oscillator 10 through the transparent electrode, measured with the probe in sufficient contact with the wiring layer.
FIG. 6 shows a voltage waveform of a step-like signal applied to the electro-optic crystal 4 made of nTe, in which a change in amplitude of three times or more of the amplitude before electrical contact shown in FIG. 6B is seen.

FIG. 7 is a flowchart summarizing such a contact detection process. First, the switch 8 in FIG. 2 is connected to the low frequency oscillator 10 side, and the transparent electrode 5 side is connected to the AC from the low frequency oscillator 10. After applying the voltage, the probe 7 is brought into contact with the wiring layer 17 to be measured, and the voltage waveform of the AC voltage is measured by the optical sampling method while increasing the load applied to the probe 7.

When the measured value of this voltage waveform is smaller than the sum of the amplitude immediately before contact, three times the standard deviation σ of the variation (noise) of the measured value, and the margin set empirically in advance, that is, If the measured value <amplitude immediately before contact + 3σ + margin, it is assumed that contact has not been established, and further load is applied to bring the probe closer, and the amplitude is measured again.

If the measured value of the voltage waveform is: measured value> amplitude immediately before contact + 3σ + margin, it is determined that contact has been established, the contact detection flag is turned on, and the switch 8 shown in FIG. Switching to the side, the transparent electrode 5 serving as the reference electrode is grounded, and the measurement of the signal under measurement 18 applied to the wiring layer 17 is started.

In the above description, the measurement value is compared with (amplitude immediately before contact + 3σ + margin), but the amplitude value of the measured voltage waveform is compared with the amplitude value of the voltage waveform measured immediately before. However, establishment of contact may be detected by stabilizing the comparison value.

In order to maintain stable contact, a preset load is further applied after the contact establishment is detected and before the measurement of the voltage waveform of the measured object is started to make contact with the measured object. Must be maintained and strengthened. Since this load amount depends on the vibration amount of the object to be measured and the vibration amount of the environment, it is necessary to determine the optimum load in advance by experiments or the like.

After the contact is established in this manner, the measurement of the voltage waveform of the object to be measured is started. During the measurement of the voltage waveform, it is necessary to monitor whether or not the electrical contact is maintained. Is preferable, and by performing such monitoring, it is possible to prevent erroneous measurement from occurring when electrical contact is lost due to vibration or the like.

The following two methods are suitable as such a monitoring method. First, as the first method, after the contact is established, the transparent electrode is connected to the ground wire to obtain the voltage waveform of the object to be measured. Waveform measurement is performed by irradiating laser light in synchronization.

Then, the amplitude of the voltage waveform obtained at that time is stored and stored as a reference amplitude, and thereafter, the amplitude value of the measured waveform is stored during the measurement period, that is, with respect to the stored value. Then, if the preset margin is determined in consideration of the statistical variation of the measured values in advance, it is judged that there is a possibility of contact abnormality, the measurement is stopped, and the contact establishment detection operation, that is, contact The point detection operation is performed to determine whether the voltage waveform applied to the measurement target is abnormal, that is, whether the measurement target is abnormal or whether the contact is not maintained.

FIG. 8 is a flow chart showing a second method relating to the contact maintenance confirmation method. First, the amplitude value of the voltage waveform of the low frequency signal obtained when the contact is established is stored and stored as the reference amplitude value. After that, the timer (Timer) is started and at the same time, the measurement of the voltage waveform of the measured object is started.

When this timer is smaller than a preset time interval, the waveform measurement is continued, and when it is larger than the preset time interval, the waveform measurement is interrupted and the transparent electrode is set to a lower frequency than the low frequency oscillator. , The amplitude value of the voltage waveform measured at this time, that is, the amplitude value in which the measured amplitude value is stored, that is, the stored value, in consideration of the statistical variation of the measured value in advance. When the set margin is less than the determined setting margin, it is determined that the contact is abnormal, the measurement is stopped, the contact detection request flag is turned on, and the contact point detection operation described in FIG. 7 is performed again.

When the amplitude value exceeds the preset margin with respect to the stored value, it is determined that the contact is maintained, the timer is reset, and the voltage waveform measurement is started again. .

Two of these monitoring methods may be used in combination, and when it is determined that there is a possibility of contact abnormality, a probe is applied instead of the contact point detection operation. The electrical contact may be restored by increasing the load.

As described above, in the fourth embodiment of the present invention, electrical contact between the probe and the object to be measured can be ensured with high reproducibility and high stability, and further, electrical contact can be ensured. The contact maintenance can be easily monitored, and highly reliable voltage waveform measurement can be performed.

Next, referring to FIGS. 9 to 12, the electrical contact between the probe and the object to be measured is electrically confirmed, and the maintenance of the electrical contact is electrically monitored. A fifth embodiment will be described.

That is, although the fourth embodiment using the electro-optical effect has the characteristics of high impedance and high band, it has a drawback that the measurement time is longer than that of the electrical measurement method, and the voltage Frequent contact confirmation during waveform measurement lowers the throughput of the apparatus, so this fifth embodiment proposes a faster electrical measurement method.

FIG. 9 is a diagram showing a schematic configuration of the fifth embodiment of the present invention, and the measuring method itself of the voltage waveform of the signal under measurement applied to the wiring layer 17 is as described above. Similar to the fourth embodiment, the voltage of the wiring layer 17 applied via the probe 7 to the voltage transducer made of the electro-optic crystal 4 is optically measured by irradiating the laser light 24. is there.

Further, the means for detecting the contact establishment of the probe 7 and the contact maintenance monitoring during the voltage waveform measurement are connected to the electro-optic crystal 4 via the relay 25 composed of a high frequency relay, the relay 25 and the directional coupler 27. For example, a pulse generator 28 that applies a steep pulse voltage with a rise time of about 100 ps, and a voltage measuring device 29 that detects a reflected voltage pulse generated due to impedance mismatch at the contact portion between the probe 7 and the wiring layer 17. Further, the reference voltage source 26 applies a reference voltage to the transparent electrode 5 via the relay 25 during the normal voltage waveform measurement.

FIG. 10 shows a flow chart of contact establishment detection and contact maintenance monitoring in the fifth embodiment. First, the probe 7 is used.
After contacting the wiring layer 17 with the wiring layer 17, the relay 25 is switched to the directional coupler 24 side, a pulse voltage is applied from the pulse generator 27 to the transparent electrode 5, and the reflected voltage pulse generated by the impedance mismatch is transmitted to the relay 25. Also, the voltage is measured by the voltage measuring device 29 via the directional coupler 27.

Then, a change in the waveform of the measured reflected voltage pulse, a change in the arrival time of the reflected voltage pulse, or a waveform of the reflected voltage pulse is compared with a predetermined voltage value at a predetermined time to determine the contact state. A change, that is, a contact establishment is detected.

Here, a specific contact detection method will be described with reference to FIG. See FIG. 11A. FIG. 11A shows the probe 7 and the wiring layer 17 to be measured.
It is a diagram for explaining the method of detecting the electrical contact, that is, the method of detecting the electrical contact point,
Since the electro-optic crystal 4 can be regarded as a discrete element having a high resistance and a low capacitance, the probe 7 and the wiring layer 17 in the non-contact state.
The impedance between, rather than as a capacitance C _g,
It is regarded as a resistance R of about 10 MΩ to 1 GΩ, and in the case of a contact state, it is regarded as a resistance of about 1 Ω.

See FIG. 11B. In FIG. 11B, in this state, the pulse generator 2 is connected to the transparent electrode 5 via the directional coupler 27 and the relay 25.
8 shows the result of simulating the waveform of the reflected voltage pulse measured by the voltage measuring device 29 when the pulse voltage is applied from 8 and the resistance R is 10M.
When it is as large as Ω, the rising edge of the reflected voltage pulse is dull, and when the resistance is 1 Ω, the rising edge is steep.

Therefore, by measuring the voltage waveform at an appropriate timing and comparing it with a preset threshold value shown by a broken line in the figure, it is determined whether the value of the contact resistance is suitable for measuring the voltage waveform of the object to be measured. To determine.

As described above, as another determination method, the determination may be performed by utilizing the change in the waveform of the reflected voltage pulse, that is, the change in the steepness of the rising edge, or the arrival of the reflected voltage pulse. The establishment of contact may be determined by the change of time.

Referring again to FIG. 10, after detecting the establishment of contact as described above, the acquired voltage waveform of the reflected voltage pulse is stored / stored, the relay 25 is switched to the reference voltage source 26 side, and the laser beam 24 is irradiated. Then, the measurement of the signal under measurement optically applied to the wiring layer 17 is started, the voltage waveform is measured, and the measured waveform data is stored.

Then, during the averaging measurement of the voltage waveform,
If the waveform measurement conditions do not change, compare the waveform data acquired / stored immediately before with the newly acquired waveform data, and if both waveform data match, good contact is maintained. Then, the voltage waveform measurement is continued. In that case, the stored waveform data is replaced with the latest waveform data.

On the other hand, if the two waveform data do not match, good contact may not have been maintained, or the object to be measured may have been damaged during the measurement. It is necessary to detect contact establishment again, and it is also necessary to detect contact establishment again when the waveform measurement conditions change.

In this way, when the contact establishment is detected again, the relay 25 is switched to the directional coupler 27 side, the pulse voltage is applied again from the pulse generator 28, and the reflected voltage pulse is measured by the voltage measuring device 29. Is acquired as reflected waveform data.

The acquired reflection waveform data is compared with the reflection waveform data acquired / stored in the first contact establishment detecting step, and when both reflection waveform data match, it is judged that the contact is maintained, Again, the relay 25 is switched to the reference voltage source 26 side to restart the measurement.

On the other hand, when the two reflected waveform data do not match, it is determined that the contact is abnormal, the voltage waveform measurement is stopped, and the probe contact operation is started again.

Next, with reference to FIG. 12, a concrete comparison method of waveform data during voltage waveform measurement will be described. See FIG. 12 (a). FIG. 12 (a) shows changes in the acquired voltage waveform of the measured object, and the contact maintenance can be monitored by directly comparing the reflected waveform itself.

12B to 12C, FIG. 12B shows a voltage histogram of the acquired voltage waveform, and FIG. 12C shows the dispersion of the acquired voltage waveform. The contact maintenance can be monitored by using the voltage histogram of such a voltage waveform or the dispersion value of the voltage waveform, and the method using the dispersion value of the voltage waveform is the simplest.

See FIG. 12 (d). FIG. 12 (d) shows a difference waveform obtained by performing a difference calculation between the obtained voltage waveform and the voltage waveform obtained immediately before, its average value, and the integrated value. The contact maintenance can be monitored by using the amplitude value, the average value, or the integral value of such a difference waveform. Among them, the method of using the integral value may use an integrator. It's simple.

In the description of the fifth embodiment, the electro-optic crystal such as ZnTe is used as the voltage transducer for optically measuring the voltage waveform of the object to be measured. A semiconductor optical switch having conductivity may be used, and in this case, it is also possible to measure by electrically detecting a signal generated by the increase in conductivity when the semiconductor optical switch is irradiated with laser light. Is.

In the fifth embodiment of the present invention, since the contact establishment detection and the contact maintenance confirmation are performed by the electric means, the time required is longer than that in the fourth embodiment using the optical means. It can be shortened and the throughput of the voltage waveform measuring device can be improved.

However, when using electrical means, in addition to the usual optical measuring means, electrical measuring means such as a high frequency relay, a directional coupler, a pulse generator, or a voltage measuring device is required. Therefore, there is a problem that the device configuration becomes complicated as compared with the fourth embodiment.

In the description of each of the above embodiments, ZnTe having photoconductivity is used as the electro-optic crystal, but it is not limited to ZnTe.
SO (Bi ₁₂ SiO ₂₀ ) or BGO (Bi ₁₂ Ge)
It is also possible to use an electro-optic crystal such as O ₂₀ ).

[0108]

According to the present invention, when the voltage waveform is measured by utilizing the electro-optic effect, the voltage origin can be determined without using the calibration pad, so that the absolute level of the voltage waveform can be measured. Moreover, since it is possible to automatically establish the electrical contact between the probe and the object to be measured and monitor the contact maintenance during the measurement, it is possible to measure the voltage waveform applied to the internal wiring of the semiconductor large scale integrated circuit device. It can be performed at high speed and accurately.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a principle configuration of the present invention.

FIG. 2 is an explanatory diagram of a voltage waveform measuring device used for implementing the present invention.

FIG. 3 is an explanatory diagram of the first and second embodiments of the present invention.

FIG. 4 is an explanatory diagram of measurement results according to the first embodiment of the present invention.

FIG. 5 is an explanatory diagram of a third embodiment of the present invention.

FIG. 6 is an explanatory diagram of a fourth embodiment of the present invention.

FIG. 7 is an explanatory diagram of a contact detection step according to the fourth embodiment of the present invention.

FIG. 8 is an explanatory diagram of a contact maintenance confirmation step according to the fourth embodiment of the present invention.

FIG. 9 is an explanatory diagram of a schematic configuration of a fifth embodiment of the present invention.

FIG. 10 is an explanatory diagram of a contact confirmation step according to the fifth embodiment of the present invention.

FIG. 11 is an explanatory diagram of a contact confirmation method according to the fifth embodiment of the present invention.

FIG. 12 is an explanatory diagram of a voltage waveform comparison method according to the fifth embodiment of the present invention.

FIG. 13 is an explanatory diagram of a conventional voltage waveform measuring device.

[Explanation of symbols]

 1 Laser Light Source 2 Phase Plate 3 Beam Splitter 4 Electro-Optical Crystal 5 Transparent Electrode 6 Reflective Electrode 7 Probe 8 Switch 9 Ground Wire 10 Low Frequency Oscillator 11 Polarized Beam Splitter 12 Mirror 13 Photodetector 14 Photodetector 15 Differential Amplifier 16 Substrate 17 Wiring layer 18 Signal to be measured 19 Light 20 High frequency signal source 21 Applied potential 22 Probe-wiring layer capacitance 23 Probe contact resistance 24 Laser light 25 Relay 26 Reference voltage source 27 Directional coupler 28 Pulse generator 29 Voltage measurement vessel

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H01L 21/66 G01R 31/28 R (72) Inventor Soichi Hama 4 Ueodachu, Nakahara-ku, Kawasaki-shi, Kanagawa Chome 1-1 1-1 Fujitsu Limited (72) Inventor Kazuyuki Ozaki 4-1-1 Kamiodachu Nakahara-ku, Kawasaki City, Kanagawa Prefecture Fujitsu 1-1

Claims (18)

[Claims] 1. A contact-type voltage waveform measuring method for optically measuring a voltage applied to an object to be measured, wherein the probe is attached to one surface of a voltage transducer and the probe is electrically floated. In this state, the voltage waveform measurement method is characterized in that the voltage origin is determined by eliminating the voltage difference across the voltage transducer due to the electrical conductivity of the voltage transducer. 2. The electro-optic crystal having photoconductivity is used as the voltage transducer, and the electro-conductivity of the electro-optic crystal is enhanced by irradiating the electro-optic crystal with light. Voltage waveform measurement method. 3. An electro-optic crystal is used as the voltage transducer, a periodic electric signal is applied to the surface of the electro-optic crystal opposite to the surface on which the probe is attached, and the voltage origin is determined by averaging one cycle. The voltage waveform measuring method according to claim 1, wherein 4. A voltage waveform measuring method using an optical sampling method utilizing the Pockels effect of an electro-optical crystal, wherein a probe is attached to one surface of the electro-optical crystal and the other surface of the electro-optical crystal is referred to. A reference electrode for applying a voltage is provided, and in the state where an AC voltage is applied to the reference electrode, while performing voltage measurement by an optical sampling method in synchronization with the applied AC voltage, the probe is attached to the object to be measured. A method for measuring a voltage waveform, which is characterized in that a change in the detected waveform amplitude is approached, and a point where the amplitude change is stable is set as an electrical contact point. 5. The electric contact is stabilized by further pressing the probe against the object to be measured by a predetermined amount determined after the detection of the electric contact point.
The described voltage waveform measurement method. 6. When the signal frequency applied to the object to be measured matches the signal frequency of the AC voltage applied to the reference electrode, the noise level of the detected signal does not decrease due to the averaging process, so the frequency matching is achieved. 6. The voltage waveform measuring method according to claim 4 or 5, wherein the occurrence of the occurrence is detected and the signal frequency of the AC voltage applied to the reference electrode is changed. 7. The voltage waveform of the alternating voltage applied to the reference electrode is measured at a predetermined cycle during the voltage waveform measurement of the object to be measured, and the measured amplitude value is obtained at the time of confirming the electrical contact point. 7. The voltage waveform measuring method according to claim 4, wherein the voltage waveform measurement of the object to be measured is interrupted when the amplitude value falls below a predetermined error range. 8. Immediately after confirming the electrical contact point, optical sampling is performed in synchronism with the voltage waveform applied to the measured object, and the amplitude value of the detected voltage waveform is held to obtain the measured value of the measured object. During measurement of the voltage waveform, when the amplitude value of the measured voltage waveform falls below the held amplitude value by more than a predetermined error range, the voltage waveform measurement of the measurement target is interrupted. 7. Any one of claims 4 to 6
The voltage waveform measuring method described in the item. 9. The method according to claim 7, wherein after the voltage waveform measurement of the object to be measured is interrupted, an AC voltage is applied to the reference electrode again to confirm the electrical contact point.
The voltage waveform measuring method described in. 10. The voltage waveform measuring method according to claim 7, wherein the load applied to the probe is further increased after the measurement of the voltage waveform of the object to be measured is interrupted. 11. A contact-type voltage waveform measuring method for optically measuring a voltage applied to an object to be measured, the probe being attached to one surface of a voltage transducer,
A pulse voltage is applied from one end of the voltage transducer, and a change in an electrical contact state is detected by a change in a waveform of a reflected voltage pulse generated by impedance mismatch in a contact portion between the probe and the object to be measured. Voltage waveform measurement method. 12. A change in an electrical contact state by comparing a variance value of a measured voltage waveform with a variance value of a previously measured voltage waveform during the arithmetic mean measurement of the voltage waveform of the measured object. Is detected.
The described voltage waveform measurement method. 13. A change in an electrical contact state by comparing a voltage histogram of a measured voltage waveform with a voltage histogram of a previously measured voltage waveform during the arithmetic mean measurement of the voltage waveform of the measured object. 12. The voltage waveform measuring method according to claim 11, wherein the voltage waveform is detected. 14. A change in electrical contact state is detected by comparing a measured voltage waveform with a previously measured voltage waveform during the averaging measurement of the voltage waveform of the object to be measured. The voltage waveform measuring method according to claim 11. 15. The differential calculation between the measured voltage waveform and the voltage waveform measured before is performed during the averaging of the voltage waveform of the measured object, and the average value of the differential signal waveform is used to determine the electrical contact state. The method for measuring voltage waveform according to claim 14, wherein a change is detected. 16. A difference calculation between a measured voltage waveform and a voltage waveform measured before that is performed during the averaging of the voltage waveform of the object to be measured, and the electrical contact state is determined by the amplitude value of the difference signal waveform. The voltage waveform measuring method according to claim 11, wherein a change is detected. 17. The voltage waveform measuring method according to claim 11, wherein an electro-optic crystal having a Pockels effect is used as the voltage transducer. 18. The voltage waveform measuring method according to claim 11, wherein a semiconductor optical switch is used as the voltage transducer.