JP3192831B2 - Electric measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention has application in semiconductor research and manufacturing. In particular, the present invention relates to a technology for measuring the operation state of a high-speed integrated electronic circuit.

[0002]

2. Description of the Related Art In the field of electronics in recent years, the frequency of a signal reaches 250 GHz, and the current state of high-speed electrical measurement technology is such that means for observing these high-speed electrical waveforms cannot keep up with technological progress. .
Furthermore, as the miniaturization of elements progresses, not only the temporal resolution but also the spatial resolution of the electric measurement device cannot keep up with the current technological advances.

In order to observe high-speed phenomena such as a high-speed operation state of a minute element, a sampling oscilloscope has been conventionally used as a typical example. In recent years, an EO sampling method utilizing the electro-optic effect of an optical crystal has been studied (EO sampling Takeshi Kamiya, Ryo Takahashi Electro-optic sampling using a semiconductor laser as a light source, Applied Physics Vol. 61, No. 1, p. 30, 1992). In the field of lasers,
Since optical pulses in the sub-picosecond region have become relatively easy to obtain, the optical sampling method attempts to use this laser pulse for sampling electrical signals. This method is faster than traditional electronic measurement,
Moreover, the potential at the point to be measured can be directly measured without contacting the circuit to be measured without extracting the signal to the outside. This method can be said to replace the electrical pulse for sampling in the sampling oscilloscope with the optical pulse.

Another method for directly measuring the potential at a point to be measured with high spatial resolution is an electron beam tester (G. Plows Electron-Beam Probing "Semiconducto").
r and Semimetals Vol.28 (Measurement of High-Speed
Signals in Solid State Devices) Chap.6, p.336, Edite
d by RKWillardson and Albert C. Beer, Academic Pre
ss.1990), the electron beam tester is also a powerful means of observing the electric signal inside the IC in IC operation diagnosis and analysis technology.

[0005] As a device 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 spread. Since these devices can obtain a three-dimensional image at an 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. As a method of measuring the potential of an object by applying these methods is described.
M) (AFHou, F. Ho and DMBloom)
Picosecond Electrical Sanpling using a Scanning Fo
rce Microscope "Electronics Letters Vol.28 No.25, p.
2302.1992). In this method, a high-speed electronic circuit is used as an object to be measured in a normal AFM. In this case, a repulsive force or attractive force is generated between the cantilever of the AFM and the object to be measured according to the potential at the point to be measured, and the force causes a minute displacement of the position of the cantilever. The method of Bloom and the like attempts to measure the time change of the potential of the measured point by detecting the minute displacement.

[0006]

However, the time resolution of a sampling oscilloscope is limited by the time that can be measured by the time constant determined by the width of an electric pulse for sampling and the electric resistance and capacitance of the measuring system. is there. Further, since the signal to be measured is taken out of the measuring point by a cable or a waveguide, the signal to be measured is disturbed, and there is a problem in its reliability.

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

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

The time resolution of a scanning tunneling microscope or a scanning atomic force microscope is limited by the response speed of a mechanical cantilever, so that it is difficult to use it for measuring high-speed electric waveforms.

Therefore, a new measuring means is required for accurate evaluation of the electric waveform of a high-speed electronic circuit, particularly, a high-density integrated electronic circuit.

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

[0012]

According to the present invention, there is provided a needle probe which is brought close to an electronic device to be measured at a distance of about an atom, and a detecting means for detecting a current flowing through the needle probe. It is an electric measuring device provided.

Here, a feature of the present invention is that an optically active substance which is non-conductive in the measurement environment is provided between the needle probe and the detecting means, and the optically active substance is brought into a conductive state. Means for irradiating pulsed light having an intensity of, and means for irradiating the optically active substance with pulsed light.
Tunnel current detected by the detecting means by irradiation
Position of the needle probe so that the average value of
Position control means for controlling, and detecting by the detecting means
Using the position control means included in the tunnel current
The signal in a frequency band sufficiently higher than the frequency band
Means for measuring an electric signal of the electronic device under test .

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 conducting in a normal measurement environment, perform the measurement in a dark room.

The optically active substance is a group IV semiconductor, III-
Desirably, either V group semiconductor or II-VI group semiconductor is used.

The pulse light is a repetitive pulse light,
It is preferable that a means for synchronizing the means for measuring with the means for irradiating the pulsed light be provided.

[0017]

In order to measure the temporal change of the electric field of an object to be measured at an ultra-high speed and an ultra-high spatial resolution, a device having a spire arranged in the vicinity of the object to be measured and a current measuring means and an optically active device By irradiating this optically active substance of a terminal connected through a substance with light of a short pulse, light is radiated depending on a voltage between an object to be measured and a terminal having a spire shape. The current that flows only during the period is measured. Thus, the potential of the device under test can be sampled and measured.

That is, a terminal having a spire shape very close to an object to be measured is electrically non-conductive as it is, and has no electrical influence on the object to be measured such as electric resistance and capacitance of the measuring system. It is. Here, when an optical pulse is applied 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.

[0019] between the terminal and the object to be measured having a steeple shape, keep apart a distance of about atoms. As a result, current flows due to tunnel effect or field emission. The present invention
Now, this current is used for probe position control, electrical signal measurement,
For two purposes simultaneously. That is,
The frequency band of the current is divided into two, and the low frequency side is used for position control
Next, the high frequency side is used for measuring the electric signal.

The high-speed electrical measuring apparatus thus configured enables high-speed electrical waveform measurement, which was impossible in the past, and enables monitoring, control, and specification of a measurement point with high-precision spatial resolution. Thus, inexpensive and highly reliable measurement can be realized.

[0021]

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

According to the present invention, the electronic device to be measured has an atomic
A needle probe 2 to close apart distance only, the needle probe 2 flows detection to that current-voltage converter current 1
7 is an electrical measuring device comprising:

Here, a feature of the present invention is that the optically active substance 12 which is in a non-conductive state in the measurement environment between the needle probe 2 and the current / voltage converter 17 is included. comprising a light pulse source 13 as a means for applying a pulse light of the intensity to conductive state, the optical pulse source
13 irradiates the optically active substance 12 with pulsed light,
The average value of the tunnel current detected by the current-voltage converter 17 is
A position for controlling the position of the needle probe 2 so as to be constant.
Control unit 15 and actuator 16 and current-voltage conversion
Position included in the tunnel current detected by the detector 17
Frequency band sufficiently higher than the frequency band used by the control unit 15
The electrical signal of the electronic device under test is measured using the
Amplifier 18, bandpass filter 19 and oscilloscope
It is located with the Corp 10 . Needle probe 2 position
Between Position Control and Measurement of Electrical Signal of Electronic Device Under Test
Will be described later in detail. Optically active substance 12
Is a group IV semiconductor, a group III-V semiconductor, or a group II-VI semiconductor.

The pulse light is a repetitive pulse light,
In FIG. 1A, the optical pulse source 13 and the power supply unit 5 are synchronized by a synchronizing circuit 20. In FIG. 1B, a means for synchronizing the measurement timing of the oscilloscope 10 with the optical pulse source 13 is provided. I have. 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 needle probe 2 is provided on the actuator 16. The measured electronic device 11 is mounted on the actuator 16 '. The position control unit 15 controls the distance between the two actuators 16 and 16 'to a preset value.

In the first embodiment of the present invention, by changing the light pulse applied to the device under test 1 and the alternating voltage applied to the device under test 1, those beat components can be extracted. This is nothing but sampling measurement.If the alternating voltage is high-speed and the signal to be measured is used, if this light pulse is an ultra-high-speed light pulse, the desired measurement can be performed by the above-mentioned sampling measurement. Becomes ADVANTAGE OF THE INVENTION According to this invention, the high-speed sampling measurement which was impossible by the conventional electronic measurement is easily attained, and the industrial value is extremely large.

In the first embodiment of the present invention, a case has been described in which a metal is used as the needle probe 2 and a semiconductor wafer is used as the DUT 1. Similar results were obtained when a metal and / or semimetal, semiconductor, or the like was used as the measurement object 1. In addition, the region where the tunnel current is generated has a very small area, so that a good result was obtained even in the case of an object to be measured having a fine pattern. In addition, even when the width of the light pulse is set to picoseconds or subpicoseconds, a high-speed system which can sufficiently follow the pulse width is obtained. Almost the same effects were obtained when using II-VI group semiconductors. In the first embodiment of the present invention, the case where a semi-insulating semiconductor is used is shown. However, when a p-type or n-type semiconductor is used,
The same effect was obtained although the sensitivity was slightly lowered.

[Reference Experimental Example] The inventor conducted the following experiment in order to explain the above operation. 2 and 3 are diagrams showing the experimental arrangement. FIG. 4 is a diagram illustrating the principle of measurement. 5 to 10 are diagrams showing the results of the experiment. 5 to 10, the horizontal axis represents time, and the vertical axis represents voltage. Experiments were carried out in the air by two experimental setup as shown in FIGS. 2 and 3. In this experiment, the DUT 1 is formed of the optically active substance 12 for convenience, and platinum iridium (hereinafter, referred to as PtIr) is used for the needle probe 2. By irradiating light near the tip of the needle probe 2, The potential is measured by activating the optically active substance 12. This makes it possible to measure the operating characteristics of the present invention the Kazumi施例device equivalently.

The device under test 1 is composed of semi-insulating gallium arsenide (hereinafter referred to as GaAs) and indium phosphide (hereinafter referred to as I).
nP) wafer. Gold (Au) was sputter-deposited on the wafer surface to form an electrode, and a lead wire was bonded with a silver paste. In addition, in order to prevent oxidation and / or contamination of the surface of the DUT 1, the cleavage was performed immediately before the measurement, and the cleavage plane was used as the DUT 1. As a light source, aluminum arsenide gallium having a wavelength of 650 nm (hereinafter referred to as AlGaAs)
-Pulsed light from the LED was used. The LED 3 was impedance-matched to be 50Ω, and the response speed to the input voltage was 45 ns.

First, an experimental example shown in FIG. 2 will be described. An object to be measured 1 of a semiconductor wafer (GaAs or InP) and a needle probe 2 are installed at a small distance in the atmosphere. On the other hand, the LED 3 is driven by the pulse generator 4 and configured to irradiate light near the tip of the needle probe 2 on the DUT 1. A DC bias voltage is applied to the device under test 1 by the power supply unit 5.

On the other hand, the needle probe 2 is driven by the piezo drive element 6, and the needle probe 2 and the DUT 1
The feedback circuit including the preamplifier 7 and the operational amplifiers 8 and 9 detects the tunnel current flowing between them, and controls the minute position. The control system itself is
It is equivalent to that of a conventional scanning tunnel 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 so fast that the pulse signal can be sufficiently observed by the oscilloscope 10 connected to its output.

Next, an experimental example shown in FIG. 3 will be described. Figure 3
The experimental example shown in FIG. 2 shows an experimental arrangement when performing an experiment by applying an alternating electric field instead of applying a DC voltage to the DUT 1 in FIG.

In FIG. 3 , the DUT 1 and the needle probe 2
It is set apart in the atmosphere by a small distance as in FIG. 2 and. The LED 3 is driven by the pulse generator 4,
It is configured to irradiate light near the tip of the needle probe 2 on the DUT 1.

The DUT 1 is driven by the oscillator 25, and the pulse generator 4 and the oscillator 25 at this time are driven.
Can be observed by the frequency counter 31.

The needle probe 2 is driven by a piezo drive element 6, and a feedback circuit composed of a preamplifier 7 and operational amplifiers 8 and 9 detects a tunnel current flowing between the needle probe 2 and the DUT 1, and detects a minute position. Control. The time constant of the control system at this time is the same as 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. The oscillator 25 can apply a DC voltage as an offset.

[0038] In this experimental setup, the DUT 1 DUT of the atomic order of small distance (5~10Å) spaced by consisting needle probe 2 which provided the measuring apparatus 1 and the needle-like probe 2
Irradiates a short pulse light near the portion where the object 1 faces, thereby measuring the current flowing between the object 1 and the needle probe 2 to sample and measure the potential of the object 1 Thus, the operating state of the DUT 1 or the electric field distribution of the DUT 1 can be measured.

[0039] With reference to FIG. 4, a measurement principle. Figure 4
As shown in (a), when the potential VD of the sample DUT and the potential Vt of the terminal tip having the spire shape are VD = Vt, the center of the band gap of the terminal tip having the spire shape coincides with the Fermi level of the sample DUT. Suppose that In such a case, a tunnel current does not normally flow because the number of carriers is small. Also, no field emission occurs. When light is irradiated to the terminal tip having a spire shape in this state, carriers are generated only during the light irradiation, and a tunnel current flows. Further, depending on the shape of the tunnel barrier, a current due to field emission also flows. The magnitude of this current, and FIG. 4 (b)
And (c), it depends on the potential difference between the DUT under test and the terminal tip having the spire 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.

By utilizing this phenomenon, the short pulse laser beam to be irradiated and the repetition frequency thereof are set to a frequency slightly deviated from the frequency of the electric signal of the device under test 1, and the current flowing at this time is measured. Thereby, a sampling operation can be performed. In this case, the electric signal of the DUT 1 is easily measured by a normal measuring device such as a digital oscilloscope 30 as a signal having a frequency difference between the repetition frequency of the light pulse and the electric signal, that is, a beat component. Can be.

In order to maintain the position of the terminal tip, a conventional scanning tunneling microscope (STM) is used.
It is effective to apply feedback so that the average current becomes constant. However, the frequency band of this feedback control system is sufficiently narrowed to make the frequency of the electric signal of the DUT 1, the repetition frequency of the optical pulse, and their beats. By setting the frequency to be sufficiently higher than the frequency band of the feedback control system, it is possible to measure the electric signal of the DUT 1 while maintaining the position of the terminal tip having a spire shape .

Further, by applying a bias voltage to the DUT 1 and / or the terminal tip as the terminal having the spire shape and adjusting the respective bias currents, the potential of the DUT 1 can be adjusted with high accuracy. It is also possible to configure to measure. At this time, a group IV semiconductor such as silicon, a group III-V based semiconductor such as arsenic gallium, a group II-VI based semiconductor such as zinc selenide, or the like can be used as the terminal tip having the spire shape formed of the above semiconductor.

Returning to FIG. 2 , 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. 2 , a power supply 5
The pulse generator 4 outputs a rectangular pulse light from the LED 3 with a DC bias applied by the
Then, the output of the preamplifier 7 was measured using an oscilloscope 10, and the response to the pulse light of the tunnel current generated between the DUT 1 and the needle probe 2 was observed. The 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 has a frequency band of 400 KH.
about z. On the other hand, the frequency band of the scanning tunneling microscope control system is determined by the time constant of the integration circuit, and is set to 300 Hz in this experimental example. Therefore, signals 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
When semi-insulating InP was used as the result (frequency 10
The KHz) shown in Figure 5. FIG. 6 shows the results (frequency 1 KHz) when using semi-insulating GaAs. In FIGS. 5 and 6 , rectangular waves 41 and 43 are driving voltages of the LED 3, and dull waveforms 42 and 44 are tunnel currents. The reason why the waveforms 42 and 44 of the tunnel current are not perfect rectangular waves but rounded is that the pass band 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 portion corresponds to the time when current is flowing. Although the origin of the current appears to be shifted downward due to an extra offset in the preamplifier 7, it changes between 0 nA and 2 nA around the average tunnel current of 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 varied between -5V and + 5V, but in each case a similar result was obtained in which the current flowed only while light was applied. Further, such a response of the tunnel current to light was observed even when the bias voltage was sufficiently smaller than the band gap of the DUT 1 and was almost 0 V.

Next, in the experimental setup of FIG. 3 describes the experimental methods and results for the beat detection of light pulses and an AC bias. In FIG. 3 , 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 a beat frequency Δf component is found in the tunnel current. Tried whether or not. FIG. 7 shows the driving pulse of LED3 (400 KHz).
The waveform 45 of FIG. FIG. 8 shows a waveform 46 of an AC component (400 KHz) of the bias voltage. A DC component of +2 V is superimposed on this as an offset, and +1 V is eventually obtained.
The voltage was applied to the DUT 1 as a sine wave varying between + and 3V. 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 using a digital oscilloscope 30 in a single shot. In order to detect only the beat component Δf, a component near 400 KHz which is a fundamental frequency was removed by the low-pass filter 32. The frequency of the light pulse and the AC bias voltage was measured by the frequency counter 31.

Next, a semi-insulating-type I as the DUT 1 in FIG. 9
The results when nP was used are shown. FIG. 10 shows a semi-insulating Ga.
The result when As was used is shown. FIG. 9 shows 9.54 KHz, 13.96 KHz, and 17.27 KH as Δf described above.
9 (a) to 9 (d) show output waveforms 47 to 50 in the case of z and 20.05 KHz, respectively. In addition, 20 in Figure 10
The output waveform 51 in the case of KHz is shown. In each case, the unevenness corresponding to the beat can be clearly confirmed. The number of irregularities corresponds to each Δf, and it can be seen that the number of irregularities increases as Δf increases. The amplitude is also about 1 nA, which corresponds well to the set average tunnel current of 1 nA.

[0051]

As described above, according to the present invention, high-speed electric waveforms that can not be obtained by the conventional electronic measurement method can be sampled and measured in real time, and extremely excellent in time resolution and spatial resolution can be measured. The industrial value is extremely large, as equipment can be provided. The advantages of this method are listed below, with sub-picosecond time resolution,
STM or AFM as a microscope with spatial resolution of about nm, no crosstalk, non-contact measurement, measurement without extracting signals outside
Functions (control functions, etc.) can be used as they are, so that the state of the sample surface and the positions of the above terminals can be monitored with ultra-high resolution. The absolute value of the signal potential can be measured. And so on.

[Brief description of the drawings]

FIG. 1 is a block diagram of a device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an experimental arrangement.

FIG. 3 is a diagram showing an experimental arrangement.

FIG. 4 is a diagram showing a measurement principle.

FIG. 5 is a view showing experimental results.

FIG. 6 is a view showing experimental results.

FIG. 7 is a view showing an experimental result.

FIG. 8 is a view showing an experimental result.

FIG. 9 is a view showing an experimental result.

FIG. 10 is a view showing an experimental result.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 object to be measured 2 needle probe 3 LED 4 pulse generator 5 power supply unit 6 piezo drive element 7 preamplifier 8, 9 operational amplifier 10 oscilloscope 11 electronic device to be measured 12 optically active substance 13 optical pulse source 14 lens 15 position control unit 16, 16 'actuator 17 current-voltage converter 18 amplifier 19 band-pass filter 20 synchronization 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

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01R 1/06 G01R 31/302 G01R 13/00 G01R 19/00 H01L 21/66

Claims (1)

(57) [Claims] 1. An electronic device under testIt's about the distance of an atom
SeparateNeedle probe to be brought close and this needle probe
The current flowing throughdetectionDodetectionMeasuring instrument with means
The needle probe and the probedetectionBetween the means and its measurement environment
Optically active substance in non-conducting stateIs providedThe optically active substance is illuminated with pulsed light of an intensity that makes it conductive.
Means to shoot, The irradiating means irradiates the optically active substance with pulsed light.
The tunnel current detected by the detection means.
Control the position of the needle probe so that the average value is constant
Position control means, Included in the tunnel current detected by the detection means
Sufficiently higher than the frequency band used by the position control means
The signal of the electronic device under test is generated by
Means for measuring the signal Electric meter characterized by comprising:
Measuring device.