JPH05107274A - Voltage detector - Google Patents

Abstract

PURPOSE:To obtain a voltage detector with higher voltage detection sensitivity by measuring a measuring distance between an object to be measured and a light probe precisely to control in the voltage detector which measures a voltage of an object to be measured in a noncontact manner. CONSTITUTION:A part of light P outputted from a second light source 56 is 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 to make the second reflected light P2. Interference light is generated by the two reflected light beams. The intensity of the interference light is detected by an interference light detection means 60. A measuring distance control means 67 controls a measuring distance (d) short and at a high accuracy between a light probe 40 and the object 42 to be measured based on the resulting detection signal. By varying a wavelength range of the light P corresponding to the measuring distance (d), an absolute measuring distance (d) can be measured based on the intensity of the interference light 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, and may be a circularly polarized beam, 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).
Generally, the shorter the measurement distance, the higher the detection sensitivity can be obtained. 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.

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.

[0008]

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

First, the accuracy in controlling the measurement distance h ₀ depends on the error of the set reference distance and the measurement error of the optical displacement sensor. 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, since the optical displacement sensor 16 cannot directly measure the measurement distance h ₀ between the optical probe and the object to be measured 18, it is necessary to set the reference distance in advance. The operation to control the distance was complicated.

Third, the multifocal lens 4 is specially designed,
It was expensive because it had to be manufactured.

[0012]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and includes a second light source for varying the wavelength width of light that partially passes through the reflecting means and emitting the light. The first reflected light emitted from the second light source, passing through the electro-optical material, and partially reflected by the reflecting means, and the surface of the DUT emitted from the second light source, passing through the electro-optical material and the reflecting means. Second light detecting means for detecting the interference light generated by the second reflected light reflected by the second light, and the measurement distance between the optical probe and the object to be measured based on the detection signal output from the second light detecting means. And a measurement distance control means for controlling the wavelength distance of the light emitted from the second light source in accordance with the measurement distance.

[0013]

The part of the light emitted 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 detected by the second light detection means and output as a detection signal. The measurement distance between the optical probe and the object to be measured is measured and controlled by the measurement distance control means which inputs the detection signal.

By varying the wavelength width of the light in accordance with the measurement distance, the absolute measurement distance can be obtained based on the intensity of the detected interference light.

[0015]

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 one-dot chain 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 measurement and control of the measurement distance d between the optical probe 40 and the object 42 to be measured will be described. A second light source 56, which will be described later, outputs a light P having a wavelength λ ₂ different from the light pulse L having a wavelength λ ₁ emitted from the first pulse light source 30. The light P passes through the half mirror 58 and is reflected by the dichroic mirror 36. Here, the dichroic mirror 36 has a wavelength λ
The light P of ₂ is reflected at a right angle. The reflected light P is condensed by the objective lens 38 on the multilayer film mirror 40c. The multilayer mirror 40c reflects a part of the light P having the wavelength λ ₂ and transmits the rest. Multilayer mirror 40
Light reflected by c (first reflected light) is reflected light P1, is transmitted through the multilayer mirror 40c, is reflected by the surface of the DUT 42, and is again passed through the multilayer mirror 40c (second reflected light). Is reflected light P2. The reflected lights P1 and P2 are reflected by the dichroic mirror 36 and the half mirror 58 and given to the interference light detector 60 which is the second light detecting means. The interference light detector 60 detects the intensity of the interference light generated by the two reflected lights as the interference output I. The interference output I has a constant relationship with the measurement distance d, and s
It is proportional to in ² (2d / λ ₂ ). The processing unit 62 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 and the DUT 42 are supported by supports 68 and 70, respectively.
Further, these two supports 68 and 70 are driven by the optical probe driving section 64 and the DUT driving section 66.
Both drive units 64 and 66 are configured by a motor, a piezo element, or the like. The processing unit 62 uses the calculated measurement distance d.
Based on the above, the optical probe driving section 64 and the DUT driving section 66 are respectively supplied with control signals to drive the optical probe 40 and the DUT 42 to control the measurement distance d. That is, the processing unit 62, the optical probe driving unit 6
4, the measured object drive unit 66 constitutes a measured distance control means 67.

Next, the principle of obtaining the absolute measurement distance by varying the wavelength width from the second light source 56 and outputting the light will be described.

If the spectral width Δλ is finite with respect to the wavelength λ _{2 of the} light source, the relationship between the measurement distance d and the interference output I is shown in FIG. FIG. 2 is a characteristic diagram showing the measurement distance d on the horizontal axis and the interference output I on the vertical axis. The wavelength width of the light output from the second light source 56 is Δλ _N in FIG. 2 (a), Δλ _W in FIG. 2 (b), and Δλ _N <
There is a relationship of Δλ _W. As shown in the figure, interference output I has its amplitude changes at a constant period (λ _2/2). Further, the amplitude of the interference output I tends to decrease as the measurement distance d increases. The decrease in the amplitude is remarkable when the wavelength width is large (Fig. 2 (b)).

Now, consider the case where the measurement distance d is obtained from the interference output I. First, when the wavelength width of light is narrow as shown in FIG. 2A, the amplitude of the interference output I with respect to the measurement distance d decreases little, so that an absolute measurement distance cannot be obtained. On the other hand, when the wavelength width of the light is wide as shown in FIG. 2 (b), the amplitude of the interference output I greatly decreases with respect to the measurement distance d, so that the absolute measurement distance can be easily obtained. Is.

Next, the procedure for measuring the measurement distance d will be described. First, at the stage where the measurement distance d is large, in order to secure the interference output I of a magnitude necessary for detection,
The wavelength width of light is narrowed as shown in FIG. 2 (a), and measurement is performed to obtain the measurement distance d. When the measurement distance d becomes short, even if the wavelength width is widened, it is possible to obtain an interference output I of a sufficient magnitude for detection. Therefore, the wavelength width should be wide as shown in FIG. 2 (b). Measurement is performed to obtain an absolute measurement distance d. That is, the wavelength width of the light of the second light source 56 is changed according to the measurement distance d. This operation is performed by the processing unit 62 applying a control signal to the second light source 56 and causing the second light source 56 to output light having a wavelength width corresponding to the measurement distance d.

By obtaining the absolute measurement distance d as described above, it is possible to prevent the collision and damage of the optical probe 40 and the DUT 42.

Second light source 5 which outputs light of different wavelength widths
Although various configurations of 6 are conceivable, the principle thereof will be described below with reference to examples.

One method is to construct the second light source 56 as shown in FIG. That is, the second light source 5
Reference numeral 6 denotes a light source 56a that outputs light P ₀ having a wide wavelength width.
And a light wavelength width conversion means 56b which receives the light and selects and outputs the light P having a desired wavelength width. Next, two specific examples using this method will be shown.

(1) The light source 56a has a white light source for outputting white light having a wide wavelength width, and the light wavelength width varying means 56b
Has a spectroscope. White light output from the white light source is supplied to the spectroscope, and the width of the exit slit of the spectroscope is adjusted based on the control signal from the processing unit 62 to obtain light having a desired wavelength width from the spectroscope. be able to.

(2) Similarly to the above, the light source 56a has a white light source, and the light wavelength width varying means 56b has a plurality of optical filters having different transmission wavelength widths. The optical filter is sequentially switched based on the control signal from the processing unit 62, and the white light output from the white light source is passed through the switched optical filter, whereby light having a desired wavelength width can be obtained.

The other method uses a principle different from the above-described method, and by applying a predetermined control signal to the second light source 56, the wavelength width of the light output from the second light source 56 is directly measured. It is variable. Specific examples of other methods will be shown below.

As the second light source 56, a semiconductor laser (L
Use D). Since the semiconductor laser lit by DC oscillates in a single longitudinal mode, the wavelength width of the obtained light is narrow. However, it is possible to oscillate the semiconductor laser in multiple modes and widen the wavelength width of light by further superimposing a high frequency input on the semiconductor laser during DC lighting. Therefore, by appropriately controlling the superimposed high frequency input based on the control signal from the processing unit 62, it is possible to obtain light having a desired wavelength width from the semiconductor laser.

As described above, according to this embodiment, the optical probe 4
Since the measurement distance d between 0 and the object to be measured 42 can be directly measured, there is no need to set the reference distance in advance, which is different from the conventional case, and there is an advantage that the operation for controlling the measurement 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, when the measuring distance is short, the absolute measuring distance can be accurately measured, so that the optical probe and the object to be measured can be prevented from colliding or being damaged.

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. Further, unlike the conventional case, an expensive multifocal lens is not required. Therefore, the device can be constructed at low cost.

[0037]

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

First, when measuring and controlling the measurement distance,
Since the interference of light is used, 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.

Second, 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.

Thirdly, when the measurement distance is short, the absolute measurement distance can be accurately measured, so that the optical probe and the object to be measured can be prevented from colliding or being damaged.

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, the multifocal lens and the optical displacement sensor, which are expensive because they have been specially designed and manufactured, are not required, so that the cost can be reduced as compared with the conventional one.

[Brief description of drawings]

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

FIG. 2 is a characteristic diagram showing a relationship between a measurement distance d and an interference output I in the voltage detecting device according to the present embodiment.

FIG. 3 is a block diagram showing a configuration of a second light source in this embodiment.

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 ... Interference light detector (second light detecting means) 67 ... Measuring distance control means d ... Measurement distance P ... Light with variable wavelength width P1 ... First reflected light P2 ... Second reflected light

Claims (2)

[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 having a variable wavelength width that partially passes through the reflection means, and a second light source that emits light and passes through the electro-optic material. First reflected light partially reflected by the reflecting means, 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 DUT.
Second light detecting means for detecting the interference light generated by the reflected light, and measurement for controlling the measuring distance between the optical probe and the object to be measured based on the detection signal output from the second light detecting means. A voltage detection device comprising: a distance control unit, wherein the wavelength width of the light emitted from the second light source is varied in accordance with the measurement distance. 2. The voltage according to claim 1, further comprising correction means for correcting the detection output of the first photodetection means on the basis of the distance signal from the measurement distance control means and correcting the measurement voltage. Detection device.