JPH05164788A - Signal measuring device - Google Patents

Abstract

PURPOSE:To improve the accuracy of measurement and reduce the load of a detection system for a signal-measuring device which measures a voltage signal at a part to be measured by utilizing electro optical effect. CONSTITUTION:Laser beam which is reflected by a light-reflection electrode 22 impinges on a light modulator 33 through an electrical optical crystal 21, a glass plate 23, a scanner 32, and a beam splitter 31. The light modulator 33 modules laser beam from the beam splitter 31 so that intensity of linear polarization constituents which cross each other may be nearly equal each other. Control signal to the light modulator 33 is a signal which is measured for each measurement point previously and is input to the light modulator 33 from a control device 39.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal measuring device, and more particularly to a signal measuring device for measuring a voltage signal of a portion to be measured by utilizing electro-optic effect.

In manufacturing and using a semiconductor element such as an LSI, whether or not the semiconductor element logically operates as designed,
In addition, it is indispensable to accurately measure the signal waveform inside and outside the semiconductor element in order to determine the presence or absence of a defect.

However, with the recent increase in the speed of semiconductor elements, it has become difficult to perform accurate measurement by the conventional electrical signal waveform detection method using an LSI tester or the like.
Therefore, as an alternative to the electrical signal waveform detection method, an optical signal waveform detection method using the electro-optic effect has been attracting attention as a method capable of measuring a high speed signal (for example, JA. Valdmanis and G. Mourou,
“Subpicosecond electronics sampling: principals a
nd application "IEEE JOURNAL OF Q
UANTUM ELECTRONICS. VOL. QE
-22. pp. 69-78).

Further, the present applicant mounts the LSI to be inspected on the electro-optic crystal, reflects the laser light after entering the electro-optic crystal, and analyzes the polarization state of the reflected light to detect the LSI to be inspected. A measuring device for measuring the waveform of an electric signal at an output terminal has been proposed (Japanese Patent Laid-Open No. 1-28566).

In such a signal measuring device, the position dependence of the birefringence of the electro-optic crystal, the dependence of the optical characteristics of the optical scanning system on the optical scanning position, the incomplete adjustment of the optical system, and the like are not affected as much as possible. It is necessary to measure the voltage of the measuring part.

[0006]

2. Description of the Related Art FIG. 6 is a block diagram showing the essential parts of an example of a signal measuring apparatus proposed by the applicant of the present invention. In the figure, 1 is an electro-optic crystal, for example, a GaAs crystal (plane orientation [100],
A thickness of about 200 μm) is formed in a thin plate shape. A transparent electrode 2 made of an oxide such as indium or tin is formed on one surface of the electro-optical crystal 1.
A contact electrode made of aluminum, gold or the like is formed on the other surface of the. The transparent electrode 2 is grounded.

The input / output pin 5 of the LSI 4 to be measured is electrically connected to the contact electrode 3. This measured LS
When I4 is brought into an operating state and a voltage is taken out from the input / output pin 5 and applied to the contact electrode 3, an electric field is induced in the electro-optic crystal 1. Then, the electro-optic crystal 1 produces birefringence in which the refractive index changes depending on the axial direction due to the Pockels effect according to the strength of the electric field.

Therefore, in the above-mentioned device proposed by the applicant of the present invention, the laser light from the transparent electrode 2 side is passed through the transparent electrode 2 and the electro-optic crystal 1 respectively, and is electrically connected to the target input / output pin 5 for contacts. The electrode 3 is irradiated and reflected, and the reflected laser light is again reflected by the electro-optic crystal 1 and the transparent electrode 2.
Take it out through.

The above reflected laser light is used as the target input / output pin 5
Since the refractive index of the electro-optic crystal 1 is changed according to the voltage, the polarization state is changed according to the voltage. Therefore, the reflected laser light is received by a light receiving portion (not shown) to discriminate the polarization state, whereby the target voltage of the input / output pin 5 of the LSI to be measured can be measured.

[0010]

However, in the signal measuring device proposed by the present applicant, if the adjustment of the optical system is insufficient, a slight deviation of the optical path occurs at each measuring point, and as a result, The amount of detected light may vary, and the measurement accuracy cannot be improved. Further, in the case of a measuring device that performs measurement at a plurality of points on the electro-optical crystal 1, the stress applied to the crystal, crystal defects, and the like cause nonuniformity in the birefringence of the crystal and change the polarization state of the laser light. Also, due to the scanning position dependence of the optical characteristics of the optical scanning system, the detected voltage may be different depending on the measurement point even if the same voltage is applied to each measurement point. is there.

Since the change in the polarization state of the reflected laser light due to the voltage applied to the electro-optic crystal 1 is extremely small,
It is necessary to convert this change into an electric signal by the photodetector, amplify it with a large amplification factor by the amplifier, and input it to the A / D converter. Therefore, if there is the nonuniformity of the birefringence at each measurement point as described above, saturation of the output of the amplifier or A
If the input voltage to the D / D converter exceeds the input range, problems such as undetectability occur, and measurement accuracy deteriorates.

The present invention has been made in view of the above points,
An object of the present invention is to provide a signal measuring device that solves the above problems by providing a modulator on the incident optical path of a polarization analyzer or by providing a light intensity modulator at a predetermined position within the polarization analyzer.

[0013]

FIG. 1 is a block diagram showing the principle of the present invention. As shown in the figure, according to the present invention, the polarization analysis is performed on the change in the polarization state of the light beam that passes through or reflects the electro-optical crystal 12 while the voltage from the measured portion 11 is applied to the measurement point of the electro-optical crystal 12. By detecting with the device 13,
The signal measuring device for measuring the voltage from the part to be measured 11 has an optical modulator 14 and a control means 15.

The optical modulator 14 is provided in the incident optical path of the polarization analyzer 13. Also, the above-mentioned control means 15
Inputs into the optical modulator 14 a control signal measured in advance at each measurement point so that the orthogonal components of the light beams incident on the polarization analyzer 13 through the optical modulator 14 become substantially equal to each other.

Further, according to the present invention, the first and second light intensity modulators, the first and second light intensity modulators are provided in the respective optical paths between the polarization beam splitter constituting the polarization analyzer 13 and the first and second photodetectors. A control signal for correcting the variation of the detected light amounts of the first and second photodetectors, which are separately transmitted through the second light intensity modulator and incident, is set to the first and second lights. It has the 1st and 2nd control means which respectively inputs into an intensity modulator.

[0016]

In the present invention, the polarized light (light beam) extracted from the electro-optic crystal 12 is modulated by the optical modulator 14 so that the linearly polarized light components orthogonal to each other are equalized, and is incident on the polarization analyzer 13. Therefore, even if the crystal birefringence is non-uniform at a plurality of measurement points of the electro-optic crystal 12 or the optical characteristics of the optical scanning system depend on the scanning position, the optical modulator 14 and its modulation characteristics are changed. The light beam from the electro-optic crystal 12 is made incident on the ellipsometer 13 in a state where the nonuniformity is corrected by the control means 15 for controlling.

Further, since the amount of light incident on the first and second photodetectors is adjusted by the above-mentioned first and second light intensity modulators, the adjustment of the optical system is insufficient and each measurement point is not adjusted. It is possible to correct the variation in the detected light amount in the case where a slight deviation occurs.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 shows a block diagram of an embodiment of the present invention. In the figure, the electro-optic crystal 21 corresponds to the electro-optic crystal 12 in FIG. 1, and is, for example, a thin plate made of GaAs crystal as described above. A plurality of light-reflecting electrodes 22 made of aluminum, gold or the like are provided on one surface of the electro-optic crystal 21, and these constitute a plurality of measurement points. In addition, the electro-optic crystal 2
A glass plate 23 is formed on the surface opposite to the surface on which the first light reflection electrode 22 is provided.

The light reflecting electrode 22 is electrically contacted with the input / output pin 27 of the large-scale semiconductor integrated circuit (LSI) 26, which is the part to be measured 11, via the contact pin 24 and the test board 25, respectively. The optical system 28 is the laser light source 2
9, a collimator, an optical element 30 such as a λ / 4 plate, a beam splitter 31, a scanner 32, a light modulator 33, a polarization beam splitter 34, and photodetectors 35 and 36. The polarization beam splitter 34 and the photodetectors 35 and 36 constitute the polarization analyzer 13 described above.

Further, 37 is a differential amplifier, 38 is a signal processing unit, 39 is a control device, 40 is a timing generator, and 41 is an LSI driving device. The control device 39 is a device for causing the timing generator 40 to generate various timing pulses and performing a required measurement operation in synchronization with the timing pulses, and has the control means 15 described above.

In such a configuration, the timing generator 4
A timing pulse from 0 is applied to the LSI drive device 41 to bring the LSI 26 into an operating state and input / output pin 27 thereof.
To output voltage. At the same time, the timing pulse from the timing generator 40 is applied to the laser light source 29 in the optical system 28, and this is intermittently driven to generate a laser light pulse.

This laser light pulse is transmitted by the λ in the optical element 30.
Beam splitter 31 after circularly polarized by / 4 plate
Then, it passes through the scanner 32, the glass plate 23, and the electro-optic crystal 21, respectively, and enters the predetermined light reflection electrode 22 to which the output measured voltage of the measured LSI 26 is applied and is reflected there. The scanner 32 has a known configuration,
It is composed of an optical scanning lens, a galvano mirror, and the like, and the incident laser light is scanned on the light reflection electrode 22 by rotating the galvano mirror.

Here, when the laser light passes through the electro-optic crystal 21, the polarization state of the laser light changes according to the voltage applied from the LSI pin 27 to the light reflection electrode 22 due to the electro-optic effect. The laser light (light pulse) reflected by the light reflecting electrode 21 becomes elliptically polarized light. The reflected laser light travels backward in the incident optical path, and the electro-optic crystal 21 and the glass plate 2
Beam splitter 31 through the scanner 3 and the scanner 32, respectively.
After being incident on the optical modulator 33 and reflected there,
It is incident on the polarization beam splitter 34 through.

The polarization beam splitter 34 decomposes the incident laser light into linearly polarized light components having two axial azimuths orthogonal to each other, and transmits the linearly polarized light component having one axial azimuth through a condenser lens (not shown). Incident on the first photodetector 35,
The linearly polarized light component of the other axis direction is reflected and made incident on the second photodetector 36 through a condenser lens (not shown).

Since the linearly polarized light components incident on the photodetectors 35 and 36 are the light components reflected and transmitted by the polarization beam splitter 34 as described above, their detection signals are signals of opposite phases. On the other hand, the noise due to the fluctuation of the light amount has the same phase. Therefore, by taking the difference between the output detection signals of the two photodetectors 35 and 36 with the differential amplifier 37, noise can be reduced and only the signal component can be taken out.

The output signal of the differential amplifier 37 is the signal processing unit 3
8 is supplied to the A / D converter 42 shown in FIG. 3, where analog-to-digital conversion is performed, and then a digital value is measured, whereby the input / output pin 27 to the measurement point (light reflection electrode 22) is measured. The applied voltage is measured.

Here, the change of the polarization state with respect to the applied voltage of the crystal is converted into the light intensity with respect to the applied voltage of 1 V, which is 0.
Since it is extremely small, about 1%, the signal is greatly amplified by the differential amplifier 37 before being input to the A / D converter 42.
Therefore, if the electro-optic crystal 21 has non-uniform birefringence, the polarization state of the return light deviates from circular polarization regardless of the LSI terminal voltage. If this deviation is large, the output of the differential amplifier 37 The signal may be saturated or the A / D converter 42
The input range will be exceeded and measurement will be disabled or the measurement accuracy will deteriorate.

Therefore, in this embodiment, as shown in FIGS. 2 and 3, an optical modulator 33 is provided on the incident light side of the polarization beam splitter 34 to prevent the above phenomenon.
The optical modulator 33 is an optical modulator that uses an electro-optic crystal that can change the phase difference between two linearly polarized lights by a control voltage. The installation angle of the axis that generates the phase difference is the polarization separation angle of the polarization beam splitter 34. It is installed at an angle of 45 degrees.

The control voltage is generated by amplifying an analog voltage obtained by digital / analog conversion by the D / A converter 43 in the control device 39 by the amplifier 44 as shown in FIG. At this time, the digital value input to the D / A converter 43 is a value that has been measured and registered in advance for each input / output pin 27 of the LSI 26, or a value that has been measured and determined immediately before the measurement, and the polarized beam It is a value that makes the light intensities of the two linearly polarized light components extracted from the splitter 34 match.

Here, it will be described in detail that the light intensity of the two linearly polarized light components extracted from the polarization beam splitter 34 can be matched by the light modulator 33.

The axis for generating the phase difference of the optical modulator 33 is, as described above, with respect to the x-axis of the incident light and the outgoing light (that is, the basic axis of the polarization separation angle of the polarization beam splitter 34) as shown in FIG. It is arranged at an angle of 45 °. Figure 4
The polarization state is calculated using the Jones matrix for the optical system shown in.

The optical modulator 33 in which the direction in which the phase difference is generated is inclined 45 ° from the x-axis is represented by the following Jones matrix.

[0033]

[Equation 1]

Where R (θ) is the rotation matrix, Γ
Is the generated phase difference and is a function of the voltage applied to the optical modulator 33.

If the polarization state of incident light is arbitrary, it is expressed as follows.

[0036]

[Equation 2]

The polarization state of outgoing light is given by the following equation.

[0038]

[Equation 3]

The light intensity of the x component and the y component of the emitted light is given by the following equation.

[0040]

[Equation 4]

Therefore, the phase difference generated by the modulator is

[0042]

[Equation 5]

By setting

[0044]

[Equation 6]

That is, it is possible to equalize the light intensity of the x component and the y component of the emitted light.

As described above, according to this embodiment, by generating the control voltage satisfying the formula shown in the above equation 5 and applying it to the optical modulator 33, and changing its birefringence,
For the incident light of any polarization state, x is output from the optical modulator 33.
It is possible to extract polarized light having a polarization state in which the light intensities of the component and the y component are equal. As a result, all the voltages of the input / output pins 27 are output saturated of the differential amplifier 37 and the A / D converter 4
Since the measurement can be performed without causing an excessive input exceeding the input range of 2, the voltage measurement can be performed with higher accuracy than in the past.

Next, the structure of the second embodiment of the essential part of the present invention will be described with reference to FIG. In the figure, the same components as those in FIG. 3 are designated by the same reference numerals, and the description thereof will be omitted. In this embodiment, as shown in FIG. 5, the optical modulator 33 is deleted, and instead, the first optical modulator 51 and the first polarizer 52 are provided in the optical path between the polarization beam splitter 34 and the photodetector 35. With the provision
A second optical modulator 53 and a second polarizer 54 are provided in the optical path between the polarization beam splitter 34 and the photodetector 36.

Further, in this embodiment, the birefringence of the optical modulator 51 is variably controlled by the D / A converter 55 and the amplifier 56,
The D / A converter 57 and the amplifier 58 variably control the birefringence of the optical modulator 53. These D / A converters 55, 5
7. The amplifiers 56 and 58 are provided in the control device 39 described above. The optical modulators 51 and 53 are composed of electro-optic crystals. The light modulator 51 and the polarizer 52 form a first light intensity modulator, and the light modulator 53 and the polarizer 54 form a second light intensity modulator.

Next, the operation of this embodiment will be described. The linearly polarized light component reflected by the polarization beam splitter 34 is incident on the optical modulator 51, where it is modulated into elliptically polarized light or circularly polarized light according to the control voltage from the amplifier 56, and then incident on the polarizer 52. Then, only the linearly polarized light component having a predetermined axis direction is passed and is incident on the photodetector 35.

On the other hand, the linearly polarized light component transmitted through the polarization beam splitter 35 is incident on the optical modulator 53, where it is modulated into elliptically polarized light or circularly polarized light according to the control voltage from the amplifier 58, and then to the polarizer 54. It is made incident, and only the linearly polarized light component of a predetermined axis direction is passed and made incident on the photodetector 36.

Therefore, the light intensity of the light incident on the photodetectors 35 and 36 is determined by the linearly polarized light component transmitted through the polarizers 52 and 54, which is determined by the amplifiers 56 and 58 and the optical modulator 5.
It depends on the control voltage applied to 1, 53. Therefore,
The digital value measured and registered in advance for each input / output pin 27 of the LSI 26 or the digital value measured and determined immediately before the measurement is set to D / By inputting to the A converters 55 and 57 and extracting a predetermined control voltage from the amplifiers 56 and 58, it is possible to correct the variation in the two detected light amounts due to the deviation of the optical path at each measurement point.

The present invention is not limited to the above-mentioned embodiment, and the optical modulator 33 may be provided in the optical path of the laser light incident on the electro-optic crystal 21, and the incidence of the electro-optic crystal 21. They may be provided in the respective optical paths of the light and the emitted light, and the point is that they may be provided in the incident optical paths of the polarization analyzer.

[0053]

As described above, according to the present invention, the light intensity in the two polarization separation directions of the light incident on the ellipsometer is controlled by the optical modulator and the control means depending on the location of the birefringence of the electro-optic crystal. Since the voltage can be the same regardless of the characteristics, it is possible to measure the voltage more stably and more accurately than before, and to adjust the incident light quantity of the two photodetectors by the two light intensity modulators and the control means. As a result, accurate voltage measurement can be performed irrespective of slight adjustment errors in the optical system, and the characteristics of the measurement points due to inhomogeneity of the birefringence of the electro-optic crystal at each measurement point or incomplete adjustment of the optical system. It has features such that the load on the detection system due to fluctuations can be reduced.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a configuration diagram of a first embodiment of a main part of the present invention.

FIG. 4 is an operation explanatory diagram of the optical modulator of FIG.

FIG. 5 is a configuration diagram of a second embodiment of the main part of the present invention.

FIG. 6 is a main part configuration diagram of an example of a conventional device.

[Explanation of symbols]

 11 measured part 12, 21 electro-optic crystal 13 polarization analyzer 14 optical modulator 15 control means 33, 51, 53 optical modulator 34 polarization beam splitter 35, 36 photodetector 37 differential amplifier 52, 54 polarizer

Claims (5)

[Claims] 1. A change in the polarization state of a light beam transmitted or reflected back and forth through the electro-optic crystal (12) in a state where a voltage from the measured part (11) is applied to the measurement point of the electro-optic crystal (12). In a signal measuring device for measuring the voltage from the measured part (11) by detecting with a polarization analyzer (13), an optical modulator (14) provided in the incident optical path of the polarization analyzer (13). ) And a control signal measured in advance at each measurement point so that the orthogonal components of the light beam incident on the polarization analyzer (13) through the optical modulator (14) become substantially equal to each other. A signal measuring device comprising: a control means (15) for inputting to a modulator (14). 2. The optical modulator (14) sets the phase difference generation direction to 4 from the polarization splitting axis of the polarization analyzer (13).
The signal measuring device according to claim 1, wherein the signal measuring device is an optical modulator tilted by 5 °. 3. A polarization beam splitter (34) for separating the incident light having passed through the optical modulator (14) into two linearly polarized light components orthogonal to each other.
And a first and a second photodetector (35, 36) for respectively detecting two linearly polarized light components extracted from the polarization beam splitter (34). apparatus. 4. A polarization beam splitter () is used for converting a light beam transmitted or reflected through the electro-optical crystal (12) back and forth in a state where a voltage from the measured portion (11) is applied to a measurement point of the electro-optical crystal (12). 34) decomposes into two linearly polarized light components orthogonal to each other, and these two linearly polarized light components are separately detected by the first and second photodetectors (35, 36) to obtain the electric power based on the signals obtained. A signal measuring device for measuring a voltage from the measured part (11) by detecting a change in a polarization state of a light beam from the optical crystal (12), comprising: the polarization beam splitter (34); Second
First and second light intensity modulators (51, 52; 5) provided in respective optical paths between the respective photodetectors (35, 36) of
3, 54) and the first and second light intensity modulators (51, 52; 53, 5)
4) is transmitted through each of the first and second photodetectors (35, 36) separately, and a control signal for correcting the variation of the detected light amount at each measurement point is input to the first and second photodetectors (35, 36). First input to each optical intensity modulator (51, 52; 53, 54)
And a second control means (55, 56; 57, 58). 5. The first and second light intensity modulators (51)
~ 54) are each the polarization beam splitter (34).
Modulator for modulating linearly polarized light component
And a polarizer (52, 54) for transmitting a polarization component transmitted through the optical modulator (51, 53) as linearly polarized light.