JPH0735772A - Electric measuring apparatus - Google Patents

Abstract

PURPOSE:To measure high speed electric waveforms with high speed time resolution and high accuracy spatial resolution by providing a pulse light applying means for making an optically active substance between a probe and a current measuring means conductive. CONSTITUTION:A light pulse source 13 for applying pulse light which contains an optically active substance 12 which is non-conductive under measurement environments for making the substance 12 conductive is provided between a needle probe 2 and a current-voltage converter 17. The pulse light is repetitive pulse light, the pulse source 13 and a power source 5 are synchronized by a synchronization circuit 20, and light pulses from the pulse source 13 are applied via an optical fiber 22 from a lens 14 to the substance 12. The needle probe 16 is placed on an actuator, and an electric device 11 to be measured is placed on an actuator 16', while a distance between the actuators 16, 16' is controlled to be constant by a position control part 15. By varying the light pulses to the device to be measured and AC voltage applied, desired measurement of high speed electric waveforms is possible with beam components taken out.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention finds use in the research and manufacture of semiconductors. In particular, it relates to a technique for measuring an operating state of a high speed integrated electronic circuit.

[0002]

2. Description of the Related Art In recent years, the frequency of signals handled in the field of electronics has reached 250 GHz, and the means for observing these high-speed electrical waveforms cannot keep up with the technological progress at the present time. .
In addition, the miniaturization of elements has progressed, and not only the temporal resolution but also the spatial resolution of electrical measuring devices cannot keep up with the current technological progress.

In order to observe a high speed phenomenon such as a high speed operation state of a minute element, a sampling oscilloscope has conventionally been a typical one. Further, in recent years, EO sampling method utilizing the electro-optic effect of optical crystals has been studied (EO sampling Takeshi Kamiya, Ryo Takahashi, Electro-Optical Sampling Applied Physics Vol. 61, No. 1, p30, 1992). In the laser field,
Since it has become relatively easy to obtain optical pulses in the sub-picosecond region, it is the optical sampling method that attempts to use these laser pulses for sampling electrical signals. This method is faster than conventional electronic measurement,
Moreover, the potential at the point to be measured can be directly measured on the circuit to be measured without contacting the circuit without extracting the signal to the outside. It can be said that this method replaces the electrical pulse for sampling in the sampling oscilloscope with the optical pulse.

Further, there is an electron beam tester (G.Plows "Electron-Beam Probing" Semiconduct) as another method for directly measuring the potential at a point to be measured with high spatial resolution.
or and Semimetals Vol.28 (Measurement of High-Spee
d Signals in Solid State Devices) Chap.6, p.336, Edit
ed by RKWillardson and Albert C. Beer, AcademicPre
ss.1990), the electron beam tester is also a powerful means for observing electric signals inside the IC in the IC operation diagnosis and analysis technology.

As an apparatus for observing the surface shape of an object to be measured with high precision spatial resolution, a scanning tunneling microscope or a scanning atomic force microscope has recently been rapidly developed and prevailed. Since these devices can obtain a three-dimensional image with ultra-high spatial resolution at the atomic level, they are very suitable for observing the surface shape of a semiconductor integrated circuit or the like. A scanning atomic force microscope (AF) recently proposed by Bloom et al.
M) is used (AFHou, F.Ho and DMBloom
"Picosecond Electrical Sanpling using a Scanning F
orce Microscope "Electronics Letters Vol.28 No.25,
p.2302.1992). In this method, a high-speed electronic circuit is used as a measured object of a normal AFM. In this case, a repulsive force or an attractive force is generated between the cantilever of the AFM and the object to be measured according to the potential of the point to be measured, and the force causes a slight displacement of the position of the cantilever. The method of Bloom et al. Attempts to measure the time change of the potential at the measured point by detecting this minute displacement.

[0006]

However, the time resolution of the sampling oscilloscope has a limit to the measurable speed due to the time constant determined by the width of the electric pulse for sampling and the electric resistance and capacitance of the measurement system. is there. Further, since the signal under measurement is taken out from the measuring point by the cable or the waveguide, the signal under measurement is disturbed and there is a problem in its reliability.

In the EO sampling method, it is difficult to measure the absolute value of the signal, and there is a practical problem regarding the method of monitoring and controlling the probe position with high spatial resolution.

The electron beam tester has a low time resolution, cannot be applied to the evaluation of ICs using high-speed transistors, and has the inconvenience that a high vacuum is required as a measurement environment.

The scanning tunneling microscope or scanning atomic force microscope is difficult to use for measuring a high-speed electric waveform because the time resolution is limited by the response speed of a cantilever which is a mechanical system.

Therefore, there is a need for new measuring means for the accurate evaluation of the electrical waveforms of high-speed electronic circuits, especially those of highly integrated electronic circuits.

The present invention has been made against such a background, and meets a demand for measuring a high-speed electric waveform with a high-speed time resolution and a high-precision spatial resolution at an arbitrary measurement point including the inside of an integrated circuit. Therefore, it is an object of the present invention to provide a highly reliable and high-speed electrical measuring device which can be applied to a finer object to be measured at a higher speed.

[0012]

SUMMARY OF THE INVENTION The present invention is an electrical measuring apparatus comprising a needle-shaped probe which is brought close to an electronic device to be measured, and means for measuring a current flowing through the needle-shaped probe.

Here, the feature of the present invention resides in that an optically active substance which is non-conducting in the measurement environment is included between the needle probe and the means for measuring the current, and the optically active substance is conducted. It is provided with a means for irradiating a pulsed light having an intensity for making the state.

As the optically active substance, a substance which is non-conductive in the measurement environment and exhibits conductivity when irradiated with light is selected. If it is already in the normal measurement environment, the measurement is performed in a dark room.

The optically active substance is a group IV semiconductor, III-
It is desirable to be either a group V semiconductor or a group II-VI semiconductor.

The pulsed light is repetitive pulsed light,
It is desirable to include means for synchronizing the measuring means with the means for irradiating the pulsed light.

[0017]

In order to measure the temporal change of the electric field possessed by the object to be measured at an extremely high speed and with an extremely high spatial resolution, it has a steeple shape arranged in the object to be measured and its vicinity, means for measuring current and optical activity. By irradiating this optically active substance of the terminal connected through the substance with short pulsed light, the light is radiated depending on the voltage between the DUT and the terminal having the pinnacle shape. The current that flows only during the period is measured. Thereby, the potential of the measured object can be sampled and measured.

That is, the terminal having a pinnacle shape which is extremely close to the object to be measured is electrically non-conductive as it is, and there is no electrical influence on the object to be measured such as electric resistance and capacitance of the measuring system. Is. Here, when an optical pulse is irradiated to the optically active substance to which this terminal is connected,
The terminal becomes a conductor and a current flows between the terminal and the object to be measured, so that the potential of the object to be measured can be measured.

The terminal having a steeple shape and the object to be measured may be separated by an atomic distance or may be in contact with each other. When they are separated, a current flows due to a tunnel effect or field emission. When they are in contact with each other, a current flows due to a tunnel effect if a barrier is formed at the interface, and a normal current flows if no barrier is formed. Even when they are in contact, if the resistance of the current path of the terminal is sufficiently high and the capacitance of the optically active region when not conducting is sufficiently small, the influence on the object to be measured can be made sufficiently small. In this case, the magnitude of the detected current is defined by this resistance value and is proportional to the potential of the DUT.

The high-speed electrical measuring device configured as described above enables measurement of high-speed electrical waveforms, which has been impossible in the past, and enables terminal position monitoring, control, and measurement point identification with high precision spatial resolution. Therefore, inexpensive and highly reliable measurement can be realized.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram of a first embodiment device of the present invention.

In the present invention, a needle probe 2 which is brought close to an electronic device to be measured, and a current-voltage converter 17 and an amplifier 1 are provided as means for measuring the current flowing through the needle probe 2.
This is an electrical measuring device equipped with 8, a bandpass filter 19, and an oscilloscope 10.

Here, the feature of the present invention is that the optically active substance 12 which is in a non-conducting state in the measurement environment between the needle-shaped probe 2 and the current-voltage converter 17 is included. The optical pulse source 13 is provided as a means for irradiating the pulsed light with the intensity that brings the light into a conducting state.
The optically active substance 12 is one of a group IV semiconductor, a group III-V semiconductor, and a group II-VI semiconductor.

The pulsed light is repetitive pulsed light,
In FIG. 1A, the optical pulse source 13 and the power supply unit 5 are synchronized by the synchronizing circuit 20, and in FIG. 1B, a means for synchronizing the measurement timing of the oscilloscope 10 with the optical pulse source 13 is provided. There is. The optical pulse generated from the optical pulse source 13 is applied to the optically active substance 12 from the lens 14 via the optical fiber 22.

The actuator 16 is provided with the needle probe 2. The measured electronic device 11 is installed in the actuator 16 '. The distance between the two actuators 16 and 16 'is controlled by the position controller 15 to a preset value.

In the first embodiment of the present invention, the beat components can be extracted by changing the light pulse applied to the DUT 1 and the alternating voltage applied to the DUT 1. This means that it is nothing but sampling measurement, and in the case where the alternating voltage is high speed and the signal to be measured, etc., if the ultrafast optical pulse is used as this light pulse, the desired measurement can be performed by the above sampling measurement. Becomes According to the present invention, high-speed sampling measurement, which has been impossible with conventional electronic measurement, can be easily performed, and its industrial value is extremely large.

In the first embodiment of the present invention, the case where a metal is used as the needle-shaped probe 2 and a semiconductor wafer is used as the DUT 1, but the reverse case, that is, a semiconductor is used as the needle-shaped probe 2, Similar results were obtained when a metal and / or a semimetal, a semiconductor or the like was used as the measured object 1. In addition, the region where the tunnel current is generated has a very small area, so that good results were obtained even in the case of the object to be measured having a fine pattern. In addition, the high speed of the system was sufficiently obtained even when the width of the light pulse was picosecond or subpicosecond. Also, the similar effect was obtained when the II-VI group semiconductor was used. In the first embodiment of the present invention, the case of using a semi-insulating type semiconductor is shown. However, in the case of using a p-type or n-type semiconductor,
A similar effect was obtained with a slight decrease in sensitivity.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram of the second embodiment of the present invention. In the second embodiment of the present invention, the position of the needle-shaped probe 2 is detected as the position of the light of the continuous laser light source 27 reflected on the back surface of the cantilever 21 in the same manner as in a normal scanning atomic force microscope (AFM), and the light position is detected. It is controlled by a position control system including a detector 28. In this case, the position control system and the electrical measurement system can be completely specialized. As in the case of the first embodiment of the present invention shown in FIG.
The configuration of (a) or (b) can be adopted.

[Reference Experimental Example] The inventor conducted the following experiment in order to explain the above operation. 3 and 4 are views showing the experimental arrangement. FIG. 5 is a diagram showing the measurement principle. 6 to 11 are diagrams showing experimental results. 6 to 11, the horizontal axis represents time and the vertical axis represents voltage. The experiment was conducted in the atmosphere by two types of experimental arrangements as shown in FIGS. 3 and 4. In this experiment, for the sake of convenience, the DUT 1 is formed of the optically active substance 12, and platinum iridium (hereinafter referred to as PtIr) is used for the needle-shaped probe 2, and by irradiating the vicinity of the tip of the needle-shaped probe 2 with light. The optically active substance 12 is activated and the potential is measured. As a result, the operating characteristics of the devices of the first and second embodiments of the present invention can be measured equivalently.

The device under test 1 is semi-insulating gallium arsenide (hereinafter referred to as GaAs) and indium phosphide (hereinafter referred to as I).
wafer (referred to as nP). Gold (Au) was sputter-deposited on the surface of the wafer to form an electrode, and a lead wire was bonded with a silver paste. Further, in order to prevent the surface of the DUT 1 from being oxidized and / or contaminated, it was cleaved immediately before the measurement, and the cleaved surface was used as the DUT 1. Aluminum arsenic gallium (hereinafter referred to as AlGaAs) with a wavelength of 650 nm as a light source
-Used pulsed light from the LED. The LED 3 was impedance-matched so as to be 50Ω, and the response speed to the input voltage was 45 ns.

First, the experimental example shown in FIG. 3 will be described. A DUT 1 of a semiconductor wafer (GaAs or InP) and a needle-shaped probe 2 are installed in the atmosphere with a minute distance therebetween. On the other hand, the LED 3 is driven by the pulse generator 4 and is configured to irradiate the vicinity of the tip of the needle probe 2 on the DUT 1 with light. A DC bias voltage is applied to the DUT 1 by the power supply unit 5.

On the other hand, the needle-shaped probe 2 is driven by the piezo driving element 6, and the needle-shaped probe 2 and the DUT 1 are measured.
A feedback circuit including a preamplifier 7 and operational amplifiers 8 and 9 detects a tunnel current flowing between the two, and minute position control is performed. This constitutes a control system similar to that of a scanning tunneling microscope.

At this time, the time constant of the entire feedback circuit is designed to be larger than the time constant of the pulse signal from the pulse generator 4. However, the preamplifier 7 is fast enough to observe the pulse signal by the oscilloscope 10 connected to its output.

Next, the experimental example shown in FIG. 4 will be described. Figure 4
The experimental example shown in FIG. 3 shows an experimental arrangement when an experiment is performed by applying an alternating electric field to the DUT 1 in FIG. 3 instead of applying a DC voltage.

In FIG. 4, the DUT 1 and the needle probe 2 are shown.
Are set apart from each other by a minute distance in the atmosphere as in FIG. The LED 3 is driven by the pulse generator 4,
It is configured such that the vicinity of the tip of the needle-shaped probe 2 on the DUT 1 is irradiated with light.

The device under test 1 is driven by the oscillator 25, and the pulse generator 4 and the oscillator 25 at this time are driven.
The repetition frequency and the difference frequency Δf between them can be observed by the frequency counter 31.

The needle-shaped probe 2 is driven by the piezo driving element 6, and the tunnel current flowing between the needle-shaped probe 2 and the DUT 1 is detected by the feedback circuit including the preamplifier 7 and the operational amplifiers 8 and 9, and the minute position is detected. It is designed to be controlled. The time constant of the control system at this time is the same as that of the experimental example shown in FIG.

The output signal of the preamplifier 7 can be observed by the digital oscilloscope 30 via the low pass filter 32. Further, the oscillator 25 can apply a DC voltage as an offset.

In this experimental arrangement, the object to be measured 1 and the needle-shaped probe 2 of the measuring device composed of the needle-shaped probe 2 which is brought into contact with the object-to-be-measured 1 or is separated by a minute distance (5 to 10 Å) of an atomic scale. By irradiating short pulsed light in the vicinity of the area where the two oppose each other, the electric current generated between the DUT 1 and the needle probe 2 is measured to sample and measure the potential of the DUT 1. The operating state of the device under test 1 or the electric field distribution of the device under test 1 can be measured by.

The principle of measurement will be described with reference to FIG. Figure 5
As shown in (a), when the potential VD of the sample DUT and the potential Vt of the terminal tip having a steeple shape are VD = Vt, the center of the band gap of the terminal tip having a steeple shape and the Fermi level of the sample DUT coincide with each other. Suppose that In such a case, since there are usually few carriers, no tunnel current flows. Also, no field emission occurs. When light is applied to the terminal tip having a steeple shape in this state, carriers are generated and a tunnel current flows only while the light is hit. In addition, a current due to field emission also flows depending on the shape of the tunnel barrier. The magnitude of this current is shown in FIG.
And as shown in (c), it depends on the potential difference between the DUT to be measured and the terminal tip having a steeple shape, that is, VD-Vt. Therefore, the potential of the sample DUT can be known by appropriately setting Vt and observing the current at that time.

Utilizing this phenomenon, the short pulse laser light of the light to be irradiated and its repetition frequency are set to a frequency slightly deviated from the frequency of the electric signal of the DUT 1, and the current flowing at this time is measured. Thus, the sampling operation can be performed. In this case, the electrical signal of the DUT 1 can be easily measured by a normal measuring device such as the digital oscilloscope 30 as a signal having a frequency difference between the repetition frequency of the optical pulse and the electrical signal, that is, a beat component. You can

In order to hold the position of the terminal tip, it is effective to apply feedback so that the average current becomes constant by the same means as in the scanning tunneling microscope (STM). By setting the frequency band of the system sufficiently narrow and setting the frequency of the electric signal of the DUT 1 and the repetition frequency of the optical pulses and their beat frequencies to be sufficiently higher than the frequency band of this feedback control system, the steeple shape is obtained. DUT 1 while holding the position of terminal tip having
The electrical signal of can be measured.

In a scanning atomic force microscope (AFM), the atomic force acting between the DUT 1 and this terminal tip is detected as a displacement of the position of the terminal, similarly to the generally used method. However, it is also effective to give feedback so that it becomes constant.

Further, as the terminal tip having the above-mentioned steeple shape, a bias voltage is applied to the DUT 1 and / or the terminal tip, and the bias current of each is adjusted to adjust the potential of the DUT 1 with high accuracy. It can also be configured to measure. At this time, a group IV semiconductor such as silicon, a group III-V semiconductor such as arsenic gallium, a group II-VI semiconductor such as zinc selenide, or the like can be used as the terminal tip having the steeple shape formed of the above semiconductor.

Returning to FIG. 3, the response of the system to the light pulse was confirmed by this experimental arrangement. The experimental method and results will be described. In FIG. 3, the power source unit 5 is attached to the DUT 1.
The pulse generator 4 outputs a rectangular pulse light from the LED 3 under the condition that the DC bias is applied by the
The cleaved surface was irradiated and the output of the preamplifier 7 was measured using the oscilloscope 10, and the response of the tunnel current generated between the DUT 1 and the needle probe 2 to the pulsed light was observed. The electric potential of the needle probe 2 is 0V. At this time, the feedback circuit controls the average tunnel current to be 1 nA.

This preamplifier 7 converts a tunnel current of 1 nA into a voltage of 10 mV, but the frequency band is 400 KH.
It is about z. On the other hand, the frequency band of the scanning tunneling microscope control system is determined by the time constant of the integrating circuit, and is set to 300 Hz in this experimental example. Therefore, a signal in the frequency range of about 1 KHz to 400 KHz between them can be applied and detected without disturbing the operation of the feedback control system.

Next, various experimental results will be shown. DUT 1
Results when using semi-insulating InP as
KHz) is shown in FIG. FIG. 7 shows the result (frequency 1 KHz) when using semi-insulating GaAs. In FIGS. 6 and 7, rectangular waves 41 and 43 are drive voltages of the LED 3, and blunt waveforms 42 and 44 are tunnel currents. The waveforms 42 and 44 of the tunnel current are not perfect rectangular waves but are blunted because the passband width of the preamplifier 7 is narrow and the time constant is about 10 μs.
This value corresponds well with the time constant obtained from these waveforms.

Since the sign of the tunnel current is inverted,
The downward part corresponds to when the current is flowing. The origin of the current seems to be shifted downward due to the extra offset in the preamplifier 7, but it changes between 0 nA and 2 nA around the average tunnel current 1 nA, which is a plausible behavior.

The results shown here are for the case where the bias voltage from the power supply unit 5 is +2 V DC. The bias voltage was changed between −5 V and +5 V, and in each case, the same result was obtained in that the current flowed only while the light was illuminated. Further, such a response of the tunnel current to light was similarly observed even when the bias voltage was sufficiently smaller than the bandgap of the DUT 1 and was almost 0V.

Next, in the experimental arrangement of FIG. 4, an experimental method and results for detecting the beat of the optical pulse and the AC bias will be described. In FIG. 4, the repetition frequency of the light pulse from the LED 3 driven by the pulse generator 4 is set to 400 KHz, the frequency of the AC component of the bias voltage by the oscillator 25 is set to 400 KHz + Δf, and the beat frequency Δf component is found in the tunnel current. I tried no. Fig. 8 shows LED3 drive pulse (400KHz)
Waveform 45 is shown. Further, FIG. 9 shows a waveform 46 of the AC component (400 KHz) of the bias voltage. The DC component of + 2V is superimposed on this as an offset, and eventually + 1V
It was applied to the DUT 1 as a sine wave varying from 3 V to +3 V. At this time, feedback control is performed so that the average tunnel current becomes 1 nA.

In this state, the output from the preamplifier 7 corresponding to the tunnel current was measured by a single shot using the digital oscilloscope 30. In order to detect only the beat component Δf, the component around 400 KHz which is the fundamental frequency was removed by the low pass filter 32. The frequency of the light pulse and the AC bias voltage were measured by the frequency counter 31.

Next, FIG. 10 shows the result when semi-insulating InP is used as the DUT 1. Figure 11 shows semi-insulated G
The result when aAs is used is shown. FIG. 10 shows Δf described above.
As 9.54 KHz, 13.96 KHz, 17.27
Output waveform 47 to 50 in the case of KHz and 20.05 KHz
Are shown in FIGS. 10 (a) to 10 (d), respectively. In addition, FIG.
Shows the output waveform 51 in the case of 20 KHz. In either case, the unevenness corresponding to the beat can be clearly confirmed. It can be seen that the number of irregularities corresponds to each Δf, and the number of irregularities increases as Δf increases. Also, the amplitude is 1
The average tunneling current is 1
It corresponds well with nA.

[0053]

As described above, according to the present invention, high-speed electrical waveforms, which were not possible by the conventional electronic measurement method, can be sampled and measured in real time, and the measurement with excellent time resolution and spatial resolution can be achieved. The industrial value is extremely high, such as the provision of equipment. The advantages of this method are listed: time resolution of sub-picoseconds, spatial resolution of about nm, no crosstalk, non-contact measurement, measurement without extracting the signal, STM as a microscope, Since the functions (control functions, etc.) of AFM etc. can be used as they are, it is possible to monitor the state of the sample surface and the positions of the above terminals with ultra-high resolution, to measure the absolute value of the signal potential, and to vacuum even in the atmosphere. Above all, it can be measured.

[Brief description of drawings]

FIG. 1 is a block configuration diagram of an apparatus according to a first embodiment of the present invention.

FIG. 2 is a block configuration diagram of a second embodiment device of the present invention.

FIG. 3 is a diagram showing an experimental arrangement.

FIG. 4 is a diagram showing an experimental arrangement.

FIG. 5 is a diagram showing a measurement principle.

FIG. 6 is a diagram showing experimental results.

FIG. 7 is a diagram showing experimental results.

FIG. 8 is a diagram showing experimental results.

FIG. 9 is a diagram showing experimental results.

FIG. 10 is a diagram showing experimental results.

FIG. 11 is a diagram showing experimental results.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 DUT 2 Needle-like probe 3 LED 4 Pulse generator 5 Power supply section 6 Piezo drive element 7 Preamplifier 8, 9 Operational amplifier 10 Oscilloscope 11 Electronic device under test 12 Optical active substance 13 Optical pulse source 14 Lens 15 Position control section 16, 16 'Actuator 17 Current-voltage converter 18 Amplifier 19 Bandpass filter 20 Synchronous circuit 21 Cantilever 22 Optical fiber 25 Oscillator 27 Continuous laser light source 28 Optical position detector 30 Digital oscilloscope 31 Frequency counter 32 Low-pass filter

Claims (3)

[Claims] 1. An electric measuring device comprising a needle-shaped probe which is brought close to an electronic device to be measured, and means for measuring a current flowing through the needle-shaped probe, the needle-shaped probe and the means for measuring the current. An electrical measuring apparatus comprising an optically active substance that is in a non-conducting state in the measurement environment, and means for irradiating with pulsed light of an intensity that brings the optically active substance into a conducting state. 2. The optically active substance is a group IV semiconductor, III
The electrical measuring device according to claim 1, which is one of a -V group semiconductor and a II-VI group semiconductor. 3. The electric measuring device according to claim 1, wherein the pulsed light is repetitive pulsed light, and a means for synchronizing the measuring means with the means for irradiating the pulsed light is provided.