JPH05107275A - Voltage detector - Google Patents

Abstract

PURPOSE:To obtain a voltage detector with a higher voltage detection sensitivity by measuring a measuring distance between the object to be measured and a light probe precisely to control in a voltage detector which measures the voltage of the object to be measured in a noncontact manner. CONSTITUTION:Parts of three light beams P emitted from a second light source 56 are reflected by a reflection means 40c to make the first reflected light P1 and the rest thereof is reflected on the surface of an object 42 to be measured separately to make the second reflected lights P2. Three interference light beams are generated by the two reflected lights. Then intensity of each interference light is detected by an interference light detection means 60. A measuring distance control means 67 and an inclination drive section 69 measure a measuring distance (d) between a light probe 40 and the object 42 to be measured and the inclination of the object 42 to be measured based on a detection signal to control.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage detecting device for measuring a voltage of an object to be measured with an optical probe, and more particularly, by precisely measuring and controlling a measuring distance between the object to be measured and the optical probe. The present invention relates to a voltage detection device having improved voltage detection sensitivity.

[0002]

2. Description of the Related Art A voltage detecting device for contactlessly measuring a voltage of a predetermined portion of an object to be measured such as an integrated circuit is known, for example, in U.S. Pat. No. 4,618,819. This voltage detecting device uses an optical probe using an electro-optical material such as LiTaO ₃ having an electro-optical effect in which the refractive index changes according to the electric field strength.

The voltage detection principle of this voltage detection device will be described below. The tip of the optical probe to which the electro-optic material is attached is positioned in the electric field of the object to be measured, and a linearly polarized beam is irradiated into the optical probe. This light beam is reflected by the end surface of the electro-optical material on the side of the object to be measured, converted into a change in light intensity by the light detecting element, and received by the photodetector. Since the polarization state of the light beam reflected by the electro-optical material changes according to the electric field strength of the electro-optical material by the measured object, by amplifying the output of this detector, the voltage of a predetermined part of the measured object is increased. To be measured. The light beam irradiated into the optical probe here is not limited to a linearly polarized beam, but a circularly polarized beam,
It may be an elliptically polarized beam or the like.

The detection sensitivity of the voltage detection device largely depends on the distance between the optical probe and the object to be measured (hereinafter referred to as the measurement distance), and generally, the shorter the measurement distance, the higher the detection sensitivity. Obtainable. Therefore, in order to increase the detection sensitivity and obtain good reproducibility during measurement, it is necessary to make the measurement distance as short as possible and accurately control the measurement distance.

If the measuring distance control means is not provided, not only the reproducibility of measurement deteriorates, but also the optical probe may collide with the object to be measured and destroy it. On the other hand, if the measurement distance is increased to prevent this destruction, there arises a problem that the detection sensitivity decreases.

In order to solve these problems, for example,
A voltage detection device for accurately controlling the measurement distance is proposed, which is described on pages 4001 to 4009 of the document “J. Apple, Phys. 66 (9), 1989”.

FIG. 4 is a block diagram showing the configuration of this conventional voltage detecting device. Two different wavelengths λ ₁ and λ ₂
The light beam L including the light of
Enters a multiple (double) focus lens 4 having different types of focus.
The multifocal lens 4 has different focal lengths f ₁ and f ₂ for wavelengths λ ₁ and λ ₂ , respectively. Therefore, the light beams L are focused at different focal positions. The light beams L that have passed through the multifocal lens 4 are reflected at their respective focal points and travel toward the half mirror 2. The light beam L reflected here is detected by the television camera 24, visualized on the monitor 26, and analyzed by the video signal analyzer 28. By these imaging and analysis, it is monitored whether the irradiated light beam L is focused on the electro-optical material 10 and the DUT 18. The electro-optic material 10 is fixed to the tip of the probe head 8 supported by the support body 6, and the support body 6 is vertically driven by a piezo drive device 14 controlled by a controller 12 as indicated by an arrow, and the wavelength The light of λ ₂ is adjusted so as to be focused on the electro-optical material 10. The displacement of the support 6 is detected by the optical displacement sensor 16. An object to be measured 18 such as an integrated circuit is installed on a sample stage 22 and is driven up and down by a stage controller 20 to obtain a wavelength λ ₁
Is used to adjust the distance to the surface of the DUT 18 to match the focal length f ₁ .

At this time, the electro-optical material 10 and the object to be measured 18 are
And the measured distance h ₀ between them is the difference in focal length (f ₁ −f ₂ ). Using this measurement distance (f ₁ −f ₂ ) as a reference distance, the movement distance of the electro-optical material 10 is detected by the optical displacement sensor 16, and the measurement distance h ₀ is indirectly determined by increasing or decreasing the movement distance from the reference distance. Can be calculated. Therefore, by driving the support 6, the measurement distance h ₀ can be measured and controlled.

[0009]

However, the above-mentioned conventional voltage detecting device has the following problems.

First, the accuracy in controlling the measurement distance depends on the error of the set reference distance, the measurement error of the optical displacement sensor, and the like. Therefore, the measurement distance cannot be controlled with higher accuracy than these errors. Therefore, since the measurement distance cannot be shortened, higher detection sensitivity cannot be obtained.

Secondly, when it is desired to bring the measurement distance closer to about 1 μm or less, the parallelism between the object to be measured and the optical probe is controlled in order to prevent contact and collision between the optical probe and the object to be measured. Must match. However, conventionally, it is impossible to shorten the measurement distance because the parallelism cannot be measured or controlled.

Thirdly, the optical displacement sensor cannot directly measure the measuring distance between the optical probe and the object to be measured,
Since it is necessary to set the reference distance in advance, the operation of controlling the measurement distance is complicated.

Fourth, the multifocal lens is expensive because it needs to be specially designed and manufactured.

[0014]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and includes a second light source that emits light that partially passes through the reflecting means, and the second light source. The first reflected light that is emitted and passes through the electro-optical material and is partially reflected by the reflecting means, and the second reflected light that is emitted from the second light source and passes through the electro-optical material and the reflecting means and is reflected by the surface of the object to be measured. Second, which detects the interference light generated by the reflected light
And a measurement distance control means for controlling the distance between the optical probe and the object to be measured based on the detection signal output from the second light detection means. One or more lights are emitted, each of these lights is condensed at a different position of the reflecting means, and the interference light generated corresponding to each of these lights is detected by the second light detecting means. Is.

The present invention also provides the above second light source and second light source.
Light detecting means and measuring distance control means, and the light emitted from the second light source irradiates a part or all of the reflecting means, and the second light detecting means observes the interference fringes generated by the interference light. It comprises a two-dimensional photodetector. In this case, the second light source may change the wavelength of light and output it.

Further, the present invention has an inclination control means for controlling the inclination of the object to be measured.

[0017]

A part of the light output from the second light source is reflected by the reflecting means to become the first reflected light, and the rest is reflected at the surface of the object to be measured to become the second reflected light. Interference light is generated by these two reflected lights. This interference light is generated corresponding to each of the three or more lights emitted from the second light source.
Each of these interference lights is detected by the second light detecting means,
It is output as a detection signal. The measurement distance control means inputs this detection signal and measures and controls the distance between the optical probe and the object to be measured. Here, since three or more interference lights are generated, the inclination of the object to be measured with respect to the optical probe is also measured.

Moreover, the interference fringes corresponding to the inclination of the object to be measured are generated by the light applied to a part or all of the reflecting means. Therefore, the inclination of the object to be measured can also be measured by detecting the interference fringes by the second photodetection means including the two-dimensional photodetector. At this time, change the wavelength of the light,
The tilt direction is detected by detecting the interference fringes that move according to the tilt direction of the DUT.

Further, the inclination control means controls the inclination of the measured object based on the measured inclination of the measured object. As a result, the parallelism between the object to be measured and the optical probe is controlled.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the voltage detecting device according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of the voltage detecting device according to this embodiment.

The portion indicated by the alternate long and short dash line is the measurement of the measurement distance,
It is a part that performs control and is a characteristic part of the present invention.

First, the principle of voltage detection will be described. An optical pulse L having a wavelength λ ₁ is emitted from the pulse light source 30.
The polarizer 32 transmits only a specific polarization component of the emitted light pulse L. Let this polarized light pulse be L1.
The transmitted light pulse L1 passes through the half mirror 34 and the dichroic mirror 36. The dichroic mirror 36 is transparent to light of wavelength λ ₁ . The light pulse L1 that has passed through the dichroic mirror 36 passes through the glass support 40a and the electro-optic material 40b supported by the glass support 40a by the objective lens 38, and the multilayer film mirror 40c.
Focused on top. The optical probe 40 includes the glass support 40a, the electro-optic material 40b, and the multilayer mirror 40c. The optical probe 40 is located at a measurement distance d from an object to be measured 42 such as an integrated circuit. The device under test 42 operates by being supplied with power and signals from the device under test control circuit 44. In addition, the DUT control circuit 44
Sends a control signal to the control unit 46, and the control unit 46 receives the control signal and controls the lighting timing of the pulse light source 30. At the same time, the control unit 46 sends a control signal to the measuring unit 52.

The light pulse L1 focused on the multilayer mirror 40c is reflected by the multilayer mirror 40c and again passes through the electro-optic material 40b. Here, the refractive index of the electro-optical material 40b through which the light pulse L1 passes changes according to the voltage change generated on the surface of the DUT 42. Therefore, the polarization component of the optical pulse L1 input to the optical probe 40 is given a change corresponding to the voltage change of the DUT 42, and is output from the optical probe 40 in the direction opposite to the input. The optical pulse L1 output in the opposite direction from the optical probe 40 is reflected by the half mirror 34 and input to the analyzer 48. When the light pulse L1 passes through the analyzer 48, only a specific polarization component of the light pulse L1 is extracted and given to the photodetector 50. This photo detector 50
The light pulse applied to the optical path is L2. The photodetector 50 is
The detection signal corresponding to the intensity of the given light pulse L2 is output to the measuring unit 52. The measuring section 52 detects the voltage of the DUT 42 by amplifying and detecting the detection signal based on the control signal from the control section 46. The display unit 54 is
It receives the data of the detected voltage and displays it.
The light source that emits light of wavelength λ ₁ is not limited to the pulse light source, and may be a continuous light source.

Next, the principle of measuring and controlling the measuring distance d between the optical probe 40 and the object 42 to be measured will be described. From the second light source 56, the first pulsed light source 3
Three light P having a wavelength λ ₂ different from the light pulse L having a wavelength λ ₁ emitted from 0 are output as described later. Each of these lights P passes through the half mirror 58 and is reflected by the dichroic mirror 36. Here, the dichroic mirror 36 is configured to reflect each light P having a wavelength λ _{2 at} a right angle. Each reflected light P is condensed by the objective lens 38 at different positions on the multilayer film mirror 40c as described later. The multilayer mirror 40c reflects a part of each light P having a wavelength λ ₂ and transmits the rest. Each light (first reflected light) partially reflected by the multilayer film mirror 40c is defined as reflected light P1,
The remaining light (second reflected light) that passes through the multilayer film mirror 40c, is reflected by the surface of the DUT 42, and passes through the multilayer film mirror 40c again is referred to as reflected light P2. Each of these reflected lights P
1, P2 are reflected by the dichroic mirror 36 and the half mirror 58, and are given to the interference light detector 60 which is the second light detecting means. The interference light detector 60 detects, as an interference output I, the intensity of the interference light generated by the pair of two reflected lights P1 and P2. Three interference outputs I are detected for the three emitted lights from the second light source 56. Each of these interference outputs I has a fixed relationship with the measurement distance d and is proportional to sin ² (2d / λ ₂ ). Processing unit 6
2 receives the interference output I from the interference light detector 60 and calculates the measurement distance d based on the above relationship.

The optical probe 40 is supported by a support 68, and the support 68 is driven by an optical probe driving section 64. The DUT 42 is supported by a tilt drive unit 69 that changes the tilt with respect to the optical probe 40. The tilt drive unit 69 is composed of, for example, a goniometer and is supported by the support unit 70. The support 70 is driven by the DUT driving unit 66. Both drive units 64 and 66 are configured by a motor, a piezo element, or the like. The processing unit 62, based on the calculated measurement distance d, drives the optical probe driving unit 64 and the DUT driving unit 6.
By giving control signals to 6 respectively, the optical probe 40 and the DUT 42 are driven to control the measurement distance d. That is, the processing unit 62, the optical probe driving unit 64,
And the measured object drive unit 66 controls the measured distance control means 6
7 are configured. The processing unit 62 measures the inclination of the DUT 42 with respect to the optical probe 40, and
A control signal is given to the tilt drive unit 69 to drive it, and control is performed so that the parallelism between the optical probe 40 and the DUT 42 is matched. That is, the processing unit 62, the DUT driving unit 66, and the tilt driving unit 69 constitute tilt control means.

According to the present embodiment as described above, since the measurement distance d between the optical probe 40 and the object 42 to be measured can be directly measured, it is not necessary to set the reference distance in advance, unlike the conventional case, and the measurement can be performed. There is an advantage that the operation of controlling the distance is simple. In addition, since the accuracy of controlling the measurement distance uses the interference of light, it is possible to obtain high accuracy based on the wavelength of light. Therefore, the measuring distance can be made shorter than in the conventional case, so that higher detection sensitivity can be obtained, and moreover, control with excellent reproducibility of the measuring distance can be performed.

Further, the measurement distance d calculated by the processing unit 62
The information regarding the is given to the measuring unit 52. The measuring unit 52 corrects the detection signal obtained from the photodetector 50 based on the above information, and corrects the measurement voltage. DUT 42
Since the detection voltage of is corrected based on the accurate measurement distance thus obtained, it is possible to obtain a more accurate voltage.

Further, since the distance measurement is performed within the field width of the objective lens 38, it is not necessary to attach an optical displacement sensor to the outside as in the conventional case. Furthermore, unlike the prior art, an expensive multifocal lens is unnecessary. Therefore, the device can be constructed at low cost.

Further, in the present embodiment, the second light source 56 shown in FIG. 1 emits three lights to the multilayer film mirror 40c as described above. That is, the second light source 56
Is configured to include three light sources. FIG. 2 is a diagram showing a main part of the optical probe 40. As described above, each of the lights output from the second light source 56 is collected at different positions A ₀ , A _X , and A _Y on the multilayer mirror 40c. Although not shown, part of each of the lights is also applied to different positions on the DUT 42. Interference light is generated as described above corresponding to each of these lights. The intensity of each of these interference lights is
It is detected by an interfering photodetector 60, which is configured to include three photodetectors to detect each of the above lights. As a result, the measurement distances between the three positions A ₀ , A _X , and A _Y on the reflecting means 40c and the respective positions on the DUT 42 corresponding to these positions are measured. As described above, by obtaining the measurement distances at three different positions, the object to be measured 4 with respect to the optical probe 40 is measured.
The inclination of 2 can be measured. In addition, in order to obtain the inclination,
It is necessary to measure the measurement distance at at least three positions.

Based on the tilt thus measured,
The processing unit 62 shown in FIG.
The inclination of 2 is varied to control the parallelism so that the measured distances at the three positions are equal to each other.

Next, a second embodiment of the present invention will be described. In this embodiment, the second light source 5 in FIG.
Only one light of wavelength λ ₂ is emitted from 6. The emitted light is evenly applied to a part or the whole area on the reflection means 40c of the optical probe 40 and is not condensed. Similarly, the object 42 to be measured is also uniformly irradiated with light. As a result, the interference light generated corresponding to the above-described light causes a number of interference fringes corresponding to the size of the inclination of the DUT 42 with respect to the optical probe 40. In order to detect the interference fringes, a two-dimensional photodetector such as a video camera may be used as the interference light detector 60 to observe the interference light as an image.

FIG. 3 shows an example of the state of the interference fringes detected by a video camera or the like. FIG. 3A shows a state in which the inclination is large and the number of interference fringes is large. FIG. 3B shows a state where the inclination is small and the number of interference fringes is small. FIG. 3 (c) shows a state in which the parallelism is perfectly matched and there is no interference fringe. That is, while the state of the interference fringes is being detected, the tilt drive section 69 causes the DUT 42 so that the interference fringes become the state of FIG.
The parallelism of the DUT 42 with respect to the optical probe 40 can be matched by controlling the inclination of the. However, in the case of the second embodiment, unlike the first embodiment, the state in which the position between the reflecting means 40c and the object to be measured 42 is long, and at which position it is short, that is, , The tilt direction cannot be determined. Therefore, it is necessary to tilt the device under test 42 and confirm the direction in which the number of interference fringes decreases to determine the tilt direction, and then control the tilt of the device under test 42 to adjust the parallelism. The drive control of the DUT 42 is performed in the same manner as in the first embodiment described above.

Next, a third embodiment of the present invention will be described. In this embodiment, the wavelength of the light is varied and output from the second light source 56 with the same configuration as the second embodiment. In this case, if the wavelength λ ₂ of the light emitted from the second light source 56 is changed from one wavelength λ _A to another wavelength λ _B longer than this, the interference fringes shown in FIG. A phenomenon occurs in which the distance from the object to be measured 42 moves from the shorter side to the longer side. If this phenomenon is detected, it is possible to easily determine the above-described inclination direction, so that the operation of controlling the inclination of the DUT 42 is further simplified.

As a method of varying the output light wavelength λ ₂ of the second light source 56, there are the following methods, for example. That is, a semiconductor laser (LD) is used as a light source, and the output light wavelength λ ₂ can be varied by increasing or decreasing the injection current supplied to this semiconductor laser. Specifically, when the injection current is increased, the output light wavelength becomes longer, and when the injection current is decreased, the output light wavelength becomes shorter.

Also in the second and third embodiments described above, the inclination state of the object 42 to be measured with respect to the optical probe 40 is detected and controlled, and the parallelism is adjusted so that the optical probe and the object to be measured are caused by this inclination. It is possible to prevent contact and collision with objects. Therefore, the measurement distance can be made close to about 1 μm or less, so that extremely high detection sensitivity can be obtained.

[0037]

As described above, the voltage detecting device of the present invention has the following effects.

Firstly, since the interference of light is used as the accuracy in measuring and controlling the measurement distance, a high accuracy based on the wavelength of light can be obtained. Therefore, the measuring distance can be made shorter than in the conventional case, so that higher detection sensitivity can be obtained, and moreover, control with excellent reproducibility of the measuring distance can be performed.

Secondly, the tilted state of the object to be measured with respect to the optical probe is detected and controlled based on the interference light, and the parallelism is adjusted, so that the contact between the optical probe and the object to be measured caused by the tilt, Collisions can be prevented. Therefore, since the measurement distance can be controlled to about 1 μm or less, extremely high detection sensitivity can be obtained.

Thirdly, since the measurement distance between the optical probe and the object to be measured can be directly measured, it is not necessary to set the reference distance in advance, and the operation for controlling the measurement distance becomes simple.

Fourth, a more accurate voltage can be obtained by correcting the detection voltage of the object to be measured based on the obtained accurate measurement distance.

Fifth, since the multifocal lens and the optical displacement sensor, which are expensive because they are specially designed and manufactured, are unnecessary, the device can be constructed at a lower cost than the conventional one.

[Brief description of drawings]

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

FIG. 2 is a perspective view showing a part of the optical probe in the first embodiment.

FIG. 3 is a state diagram showing interference fringes of interference light in the second embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a conventional voltage detection device.

[Explanation of symbols]

 40 ... Optical probe 40b ... Electro-optical material 40c ... Multilayer film mirror (reflecting means) 42 ... Object to be measured 56 ... Second light source 60 ... Interfering light detector (second light detecting means) 67 ... Measuring distance control means 69 ... Tilt drive part d ... Measuring distance P1 ... First reflected light P2 ... Second reflected light

Claims (4)

[Claims] 1. An optical probe comprising a first light source, an electro-optical material whose refractive index changes in response to a change in the voltage of an object to be measured, and a reflection means for reflecting the light emitted from the first light source. A first light detecting means for detecting the light emitted from the first light source, passing through the electro-optical material, and reflected by the reflecting means, and the measured object based on the reflected light. In a voltage detection device for detecting the voltage of an object, a second light source that emits light that partially passes through the reflecting means, and a second light source that is emitted from the second light source and passes through the electro-optical material and is Partly reflected first reflected light, and second reflected light emitted from the second light source, passing through the electro-optical material and the reflecting means, and reflected by the surface of the object to be measured.
Second light detecting means for detecting the interference light generated by the reflected light, and a measuring distance for controlling the distance between the optical probe and the object to be measured based on the detection signal output from the second light detecting means. Control means, wherein three or more lights are emitted from the second light source, each of the lights is condensed at a different position of the reflecting means, and the lights are generated corresponding to each of the lights. A voltage detecting device, wherein the interference light is detected by the second light detecting means. 2. An optical probe comprising a first light source, an electro-optical material whose refractive index changes in response to a voltage change of an object to be measured, and a reflection means for reflecting the light emitted from the first light source. A first light detecting means for detecting the light emitted from the first light source, passing through the electro-optical material, and reflected by the reflecting means, and the measured object based on the reflected light. In a voltage detection device for detecting the voltage of an object, a second light source that emits light that partially passes through the reflecting means, and a second light source that is emitted from the second light source and passes through the electro-optical material and is Partly reflected first reflected light, and second reflected light emitted from the second light source, passing through the electro-optical material and the reflecting means, and reflected by the surface of the object to be measured.
Second light detecting means for detecting the interference light generated by the reflected light, and a measuring distance for controlling the distance between the optical probe and the object to be measured based on the detection signal output from the second light detecting means. A light emitted from the second light source is applied to a part or all of the reflecting means, and the second light detecting means observes an interference fringe generated by the interference light. A voltage detection device comprising a detector. 3. The voltage detecting device according to claim 2, wherein the second light source variably emits the wavelength of light. 4. The voltage detecting device according to claim 1, further comprising an inclination control means for controlling the inclination of the object to be measured.