JPH06281707A - Device for measuring voltage distribution - Google Patents

Abstract

PURPOSE:To provide a device by which the voltage distribution inside an LSI can be measured two-dimensionally with high space resolution, with regard to the evaluation method for an electronic circuit by using the electrooptic effect. CONSTITUTION:A light beam emitted from a specially incoherent light source 6 is passed through a polarized light beam slitter 7 and further are directed to an electrooptic material 8 as a light beam having a uniform polarization direction. The material 8 is placed adjacent to an electronic circuit 5 in which the electronic elements such as transistors, diodes, etc., are integrated and the birefringence change is generated therein due to the voltage distribution inside the circuit 5. The space distribution is extracted by the splitter 7 and its image is formed on the light receiving surface of a photoelectric detector 9 through an image formation optical system 14. After the image obtained by the detector 9 is subjected to processing such as integration, etc., in an image processor 10, it is outputted as the measurement result of voltage distribution in the circuit 5 to an image display 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of electronic measurement, and relates to an apparatus for two-dimensionally measuring the voltage distribution inside an electronic circuit in a non-contact manner.

[0002]

2. Description of the Related Art In recent years, with the development of high-density and highly integrated electronic devices, the ratio of the number of electronic elements in a circuit to the number of external terminals has increased remarkably. Since it is difficult to evaluate such a device from the outside, it is necessary to directly measure each electronic element inside the electronic circuit.
As a method therefor, a method using an electron beam and a method using electro-optic sampling utilizing the electro-optic effect
(For example, Javaldmanis and G. Mourou, "Subpicosecond e
lectrooptic sampling: Principles and applications ",
IEEE J. Quantum Electron., Vol.QE-22, no.1, pp.69-78, J
an. 1986.) is used.

The former is a method of irradiating an electrode inside an electronic circuit with an electron beam and measuring the voltage of the electrode from the energy of secondary electrons emitted from the electrode. In this method, the voltage distribution inside the circuit can be measured by scanning the electron beam. However, there is a problem in that the object to be measured needs to be placed in a vacuum, and in principle the absolute potential cannot be measured.

In the latter, an electro-optic material is inserted into an electric field generated from an electric signal to the outside, and the birefringence in the electro-optic material (LiNbO3, ZnSe, ZnTe, etc.) is changed by the electric field (Pockels effect), and the birefringence thereof is changed. This is a method of detecting the amount of change in refraction with pulsed laser light synchronized with an electric signal. Since this method is in principle non-contact, it does not disturb the measurement object and can perform measurement in the atmosphere. But,
Since the amount of change in birefringence of the electro-optic material is very small, it takes a few seconds to detect the electric signal at a single point inside the device, and it is necessary to use beam scanning technology to measure the voltage of a specific area. It is expected that it will take several tens of minutes to measure the distribution.

A method for planarly detecting an electric signal inside an electronic circuit by using an electro-optical sampling technique is disclosed in Japanese Patent Laid-Open No. 64/1988.
-18073. This method does not mention the type of light source used, but it is impossible to extract spatial information from the inside of a spatially coherent light beam as in the conventional case. Also, as mentioned above,
It is considered that it is very difficult to take a time-divided image by two-dimensional detection using the electro-optic effect, because the amount of modulation of the electro-optic material used conventionally on light is very small.

[0006]

Based on the current situation as described in the preceding paragraph, the present invention is mainly intended to solve the following problems in measuring the waveform of an electric signal inside an electronic circuit.

In voltage measurement using the electro-optic effect,
Two-dimensional measurement of a steady voltage distribution inside an electronic device in a short time by using incoherent continuous light and a material having a large electro-optic effect such as liquid crystal.

The present invention solves the above problems by providing an apparatus for contactlessly measuring the operating characteristics of individual electronic elements in an electronic circuit.

[0009]

A measuring device for an electric signal inside an electronic circuit according to the present invention comprises an electro-optical material (or liquid crystal) installed so as to cover an object to be measured, and continuous light incoherent to the material. It is characterized in that the voltage distribution inside the circuit can be measured in parallel by irradiating with and detecting the spatial information inside the irradiation light. In addition, this device has an advantage that measurement can be performed with a very simple optical system.

[0010]

When spatially coherent light such as laser light undergoes a wavefront change, the spatial information inside the beam spot is retained immediately after the change. However, as the beam propagates, interference occurs inside the spot and the spatial information becomes uniform. On the other hand, when spatially incoherent light is used, two-dimensional spatial information can be extracted from within the light spot even after propagating. The inventors have used spatially incoherent continuous light to
We devised a method to measure the voltage distribution inside an electronic device. The present invention is implemented as follows. When an electro-optical material is installed in the vicinity of an operating electronic circuit in which transistors, diodes, etc. are integrated, the birefringence in the material changes due to the electric field generated from the electronic circuit. At this time, when incoherent light having a uniform polarization component is incident on the material, the polarization state of the incident light changes due to the change of birefringence reflecting the voltage distribution of the electronic circuit. This change in polarization is converted into light intensity, which is received by a two-dimensionally arranged detector (CCD camera or the like) and a spatial distribution image is output. In this way, the voltage distribution inside the electronic device to be measured can be measured two-dimensionally. In particular, when a white light source is used, the wavelength can be appropriately selected by using a wavelength selection filter or the like. If a wavelength as short as possible is selected within a range where the electro-optic material used at this time interacts, measurement can be performed with a spatial resolution corresponding to the wavelength. For example, if a wavelength of 400 nm is selected, it is possible to obtain a spatial resolution on the order of submicrons, and it is possible to measure the voltage distribution with a spatial resolution higher than conventional. Furthermore, when liquid crystal is used instead of the electro-optical material, a two-dimensional image with high contrast can be obtained, and the voltage distribution can be measured in a short time. Liquid crystals are classified into various types according to the arrangement of the molecular axes, and each has a characteristic that the orientation of liquid crystal molecules changes when a voltage is applied. Above all, the twisted nematic (TN) liquid crystal is designed so as to change the phase of incident light when no voltage is applied, and to decrease the amount of change as the voltage is applied.
As an example, FIG. 1 shows the relationship between the applied voltage and the phase change of incident light. From this, it can be seen that a large phase change of about 2π occurs between the applied voltages of 1.5 to 3V. Therefore, as shown in FIG. 2, a transparent reference electrode 1 on the upper surface of the liquid crystal,
A probe head having a structure in which a reflection film 3 for incident light is provided on the lower surface is manufactured. This structure is realized by sandwiching the liquid crystal between two thin transparent substrates (~ 100μm glass etc. with transparent electrodes in advance) or by laminating a film-like liquid crystal on a substrate with transparent electrodes. it can. By using such a probe head made of liquid crystal, it is possible to obtain a contrast image that reflects the voltage distribution of the electronic device, and it is also possible to measure the absolute potential by changing the voltage applied to the reference electrode. Become. As described above, it is possible to obtain a high contrast image with a very simple optical system as compared with the method of scanning the laser light and measuring the voltage distribution.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 3 is a structural diagram showing an embodiment of a voltage measuring device using a spatially incoherent light source according to the present invention.

Monochromatic light emitted from a spatially incoherent light source 6 such as a mercury lamp passes through a polarization beam splitter 7 and becomes a uniform light in the polarization direction. This light is incident on an electro-optical material 8 such as ZnSe, which is installed near the electronic circuit 5 to be measured. A reflection film for the wavelength of the light source 6 is provided on the lower surface of the electro-optical material 8,
Incident light is reflected on this surface. By the way, electro-optical material 8
When a voltage is applied, the birefringence of that portion changes and gives phase modulation to the light propagating in the material. Therefore, the light incident on the electro-optical material 8 is emitted with a change in the polarization direction that reflects the voltage distribution of the electronic circuit 5. This light passes through the polarization beam splitter 7 again, but only the portion where the polarization has changed at that time is reflected. 2 inside this reflected light
The three-dimensional image passes through the image forming optical system 14 and is formed on the light receiving surface of the photoelectric detector 9. A CCD camera, a two-dimensionally arrayed photodiode, or the like is used as the photoelectric detector 9 so that it can be detected as a two-dimensional image. The distribution image thus detected is subjected to processing such as integration in the image processing device 10 and output to the image display device 7. In this way, the spatially incoherent light source 6 is used to
Was able to be measured two-dimensionally.

Next, an embodiment for observing a minute area of an electronic device will be described. The measuring optical system at this time is shown in FIG. In this measurement system, white light such as a tungsten lamp is used as the incoherent light source 6. The light emitted from the light source 6 passes through the wavelength selection filter 12,
Only light of a single wavelength (wavelength of about 0.5 μm) is transmitted. After this single light passes through the polarization beam splitter 7,
The light is focused by the lens 13 and is incident on the probe head 4 using liquid crystal. This probe head 4 has the structure shown in FIG. In general, the response speed of liquid crystal is about microseconds, which is slower than the time change of the electric signal inside the electronic device, but the amount of change in polarization given to the propagating light is large, so that a high-contrast image can be obtained. After that, the incident light is reflected by the lower surface of the probe head 4 and then only the modulated portion is reflected by the polarization beam splitter 7 in the same manner as described above.
After being detected by the photoelectric detector 9 through the display device 4, the display device 11
Is output to. Thus, white light was used as the incoherent light source 6, and the steady voltage distribution of the electronic circuit 5 could be measured with a submicron spatial resolution. Also,
Since the real image inside the electronic device is observed when the wavelength selection filter 12 is removed, there is an advantage that the region to be measured can be freely selected by making it possible to take it in and out.

With this method, it is not necessary to narrow down the laser beam as in the conventional electro-optical sampling, so that measurement can be performed with extremely high spatial resolution. In addition, there is a feature that the voltage distribution inside the electronic circuit can be measured two-dimensionally with a very simple optical system.

[0016]

INDUSTRIAL APPLICABILITY As described above, according to the present invention, a voltage measuring apparatus for injecting a beam of light into an electro-optical material installed in the vicinity of an electronic device to detect the modulation of the beam reflecting a voltage change inside the device is spatially analyzed. By using an incoherent light source and a planar array of photodetectors,
It is possible to measure the voltage distribution inside the electronic device two-dimensionally.

[Brief description of drawings]

FIG. 1 is a graph showing an example of a relationship between an applied voltage of a TN liquid crystal and a phase change with respect to incident light.

FIG. 2 is a structural diagram showing an example of a liquid crystal structure necessary for measuring a voltage distribution of an electronic device according to the present invention.

FIG. 3 is a structural diagram showing an embodiment of a voltage measuring device using a spatially incoherent light source according to the present invention.

FIG. 4 is a structural diagram showing an embodiment of an apparatus for two-dimensionally measuring a voltage distribution using the liquid crystal according to the present invention.

[Explanation of symbols]

 1 Reference electrode (transparent electrode) 2 Liquid crystal 3 Reflective film for incident light 4 Probe head using liquid crystal 5 Electronic circuit to be measured 6 Spatial incoherent light source 7 Polarizing beam splitter 8 Electro-optical material 9 Photoelectric detector 10 Image processing device 11 Image display device 12 Wavelength selection filter 13 Lens 14 Imaging optical system

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Teruyuki Tamaki 5-10-1, Fuchinobe, Sagamihara-shi Nippon Steel Corp. Electronics Company Research Laboratory

Claims (2)

[Claims] 1. A voltage detection device of a type using an electro-optic material whose refractive index changes with voltage, and a continuous light source for generating spatially incoherent light, and an optical device for converting polarization change of light into intensity change. A voltage distribution measuring device comprising: a system; and a photoelectric detector that two-dimensionally detects reflected light of light irradiated on an object to be measured. 2. The voltage distribution measuring device according to claim 1, wherein the electro-optical material is liquid crystal, and the liquid crystal has a shape of a thin film or is sandwiched between thin substrates and has an electrode on an upper portion thereof.