JPH02238376A - Probe for measuring electric field - Google Patents

Abstract

PURPOSE:To measure an object operating at a high speed, with high sensitivity, high spatial resolution and excellent reproducibility, by a construction wherein a probe is shaped in a thin disk having a small projecting part and a thin-film electrooptic crystal on a part of which a dielectric reflecting film is formed by coating is fixed on the fore-end face of the projecting part. CONSTITUTION:A probe 5 is formed in the shape of a thin disk which has a small projecting part and is provided with a reflection preventing film 4 on the surface, and an electrooptic crystal 2 on the central part of which a dielectric reflecting film 3 is formed by coating is fixed on the fore-end face of the projecting part located on the other surface parallel to said surface. The probe is supported by a probe supporting jig 7 when high precision in the degree of parallelism and can be brought near sufficiently to a circuit 8 to be measured, while an objective lens for a trigger light is dispensed with. Accordingly, it is possible to bring the film 3 near remarkably to the circuit 8, such as LSI, operating at an ultra-high speed and thereby to measure an electric field with high sensitivity, high spatial resolution and excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Prior Art] A method of using an electro-optic crystal as an electric field measurement probe is known as a means for non-contact evaluation and testing of integrated circuits and devices. That is, when the electro-optic crystal is placed near the circuit under test, an electric signal or electric field from the circuit under test is coupled to the electro-optic crystal, and the crystal is irradiated with pulsed laser light as sampling light, the electric signal or electric field is This method utilizes the principle that the polarization state of the irradiated light changes depending on the size of the irradiated light.

Conventionally, as a probe for this purpose, as shown in Fig. 4, a dielectric reflective film is coated on one end of a thin cylindrical transparent support pole (for example, a quartz pole) with a length of about 10 mm and a diameter of several millimeters. Paste the vapor-deposited electro-optic crystal,
It uses a structure whose tip is polished into a pyramid shape several tens of micrometers square.

However, the conventional structure has the following problems, which need to be solved. [Problems to be solved by the invention] The probe with the structure shown in Figure 4 (.) mainly has the following problems. It has four major problems as described below.

First of all, because the side surface of the support is obliquely polished so that the tip surface of the probe is several tens of micrometers square, the circuit under test is viewed from above the probe through the objective lens, as shown in Figure (b). It is difficult to observe and it is not possible to precisely align the probe with respect to the single path to be measured. The second problem is that in optical measurements based on the above principle, a separate laser beam called a trigger light is irradiated onto the photoelectric conversion element formed on the circuit under test, as shown in FIG. A method is often used in which an electrical signal is generated and applied to a device or integrated circuit, and the response is measured using sampling light. However, when using a probe with this structure, an additional objective lens is required. Therefore, the photoelectric conversion element must be irradiated from an oblique direction. Further, in some cases, an optical system for detecting the irradiation position of the trigger light wA is also required, which makes the optical system as a whole extremely complicated.

The third problem is that the structure makes it difficult to maintain parallelism between the dielectric coating surface of the electro-optic crystal and the circuit to be measured. In order to obtain sufficient measurement sensitivity, it is necessary to shorten the distance between the probe and the circuit under test to a few micrometers, but if the parallelism between the two is poor, the crystal end may come into contact with the circuit under test and destroy the circuit. There is a high possibility that it will. A slight tilt on the side of the circuit under test can be easily corrected by adjusting the tilt on the stage side. However, if the probe support is provided with a tilting mechanism, the direction in which the sampling light is reflected from the dielectric coating surface and returned changes with each adjustment, making detection of the reflected light cumbersome. Therefore, it is desirable to always fix the crystal surface of the probe in a horizontal state, but with a rod-shaped probe structure, it is not easy to support it to fix it horizontally. Furthermore, a fourth problem is that since the overall length of the probe is relatively large, an objective lens with a large magnification cannot be used. In order to improve the spatial resolution of measurements, it is necessary to focus the beam using an objective lens with high magnification, but generally speaking, as the magnification increases, the focal length decreases, making it impossible to widen the gap between the lens and the circuit under test. Therefore, there are problems in that the rod-shaped probe is not suitable for measurements with high spatial resolution.

The present invention solves the above problems, makes it possible to easily irradiate both sampling light and trigger light, easily detect the irradiation position, and without destroying the circuit under test. It has a probe structure that allows the probe to be brought close and can be used even if the working distance between the objective lens and the circuit under test is narrow. The purpose of the present invention is to provide a probe structure that can perform measurements with high spatial resolution and good reproducibility.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides an electric field measurement probe that has a thin disc-shaped substrate made of a transparent material and a thin film electro-optic crystal, and one of the substrates is made of a transparent material. An anti-reflection film is applied to one surface, a micro protrusion is provided in the center of the other surface, the tip surface of the protrusion is made parallel to the surface of the substrate, and the thin film electro-optic film having the same shape is placed on the tip surface of the protrusion. We decided to provide a structure in which a crystal is fixed and a portion of its surface is coated with a dielectric reflective film.

[Function] Making the entire probe into a thin disk shape with small protrusions makes it possible to use a high-magnification objective lens with a short working distance, which reduces the beam diameter of the irradiated light and improves spatial resolution. This results in an improvement in In addition, it is possible to form the disk-shaped substrate and the protrusion at the same time, which makes it possible to accurately achieve parallelism between the electro-optic crystal surface that is attached and fixed to the tip of the protrusion and the substrate surface. . As a result, this probe has a structure that allows it to be fixed with a jig similar to the holder used to fix ordinary disk-shaped lenses and mirrors, and the probe crystal surface can be fixed in an extremely horizontal state. Even if the probe is brought close to the circuit under test during measurement, there is no risk of damage due to contact.

In addition, applying a reflective film to a part of the surface of the electro-optic crystal
Sampling light is directed to the reflective film using only one objective lens,
The trigger light makes it possible to irradiate each photoelectric conversion element formed on the circuit under test through its periphery, and the same objective lens illuminates the irradiation position of these two lights.
This also makes it possible to observe the optical system and simplify the optical system.

[Example] FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

Moreover, FIG. 3 is an explanatory diagram showing an example of use of the present invention. In both figures, 1 is a transparent support, 2 is an electro-optic crystal, 3 is a dielectric reflective film, 4 is an antireflection film, 5 is a probe, 6 is an objective lens, 7 is a jig for supporting the probe, and 8 is a measured object. circuit, 9
is the stage.

The transparent support 1 has a structure in which a protrusion is provided in the center of a thin disk-shaped substrate as a whole, and the material of the support is, for example, synthetic quartz. One surface of the substrate is optically polished and then coated with a dielectric film 4 to prevent reflection of the wavelength of light used. At the center of the other surface, a microprotrusion whose tip surface is parallel to the substrate surface is provided, and at the tip surface of the protrusion, a thin film electro-optic crystal 2 (for example, LiTaO) of the same shape is provided.
3 or a aA s) are pasted together.

In actual measurements, it is important to determine the positional relationship of the optical axis of the crystal and other crystal axis directions with respect to the pattern of the circuit to be measured. Therefore, the shape of the tip surface of the protrusion and the crystal surface is a regular square in order to clearly indicate the optical axis or crystal axis direction of the electro-optic crystal 2, and the optical axis or crystal axis is perpendicular to or at an angle of 45 degrees to one specific side. It is desirable that there be one. FIGS. 2(a) and 2(b) show specific directions of optical axes and crystal axes when L i T a○ or G a As is used as an electro-optic crystal.

A high reflection film 3 made of a dielectric multilayer film for reflecting the laser light used is partially applied to the surface of the electro-optic crystal 2. It is desirable that the reflective film has a diameter sufficiently larger than the beam diameter of the laser beam to be irradiated. Also, as shown in Figure 2,
The optical axis or crystal axis of the electro-optic crystal can also be expressed by making the shape of the reflective film a regular square and making the optical axis or crystal axis perpendicular to 45 degrees to one particular side.

Since this probe has the same disk structure as a normal lens or mirror, it can be easily used with a jig similar to a commonly used lens holder or mirror holder, as shown in the usage example in Figure 3. It can be supported and fixed, and it is easy to replace. It is also possible to set the crystal surface parallel to the stage 9 by fixing it with a similar jig. In actual measurement, as shown in the figure, the sampling light is focused on the reflective film 3 at the tip of the probe by the objective lens 6, and the trigger light is focused through the peripheral part of the reflective film 3 by the same objective lens 6. The light is focused on the circuit under test 8 below the probe. Furthermore, the irradiation position of the laser beam can also be observed using the same objective lens.

[Effects of the Invention] According to the present invention, sampling light and trigger light can be irradiated simultaneously using only one objective lens. Since the irradiation position can be easily detected using the same lens, the optical system can be extremely simplified. Furthermore, since the structure allows the probe to be easily supported, it is possible to bring the probe close to the circuit under test without destroying it, thereby improving measurement sensitivity and reproducibility. Furthermore, since the overall thickness of the probe is thin, a high magnification lens with a short focal length can be used, allowing for high spatial resolution of measurements.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing the direction of the optical axis and crystal axis of an electro-optic crystal in the present invention, and FIG. 3 is an explanatory diagram showing an example of use of the present invention. , FIG. 4 is an explanatory diagram showing a conventional probe structure and an example of its use. (Explanation of symbols) 1...Transparent support 2...Electro-optical component 3.
...Dielectric reflective film 4...Anti-reflection film 5...Probe 6...Objective lens 7...Probe support jig 8...Circuit under test 9...Stage

Claims (1)

[Claims] An electro-optic crystal is fixed to a transparent material, the electro-optic crystal is placed near an electrical circuit to be measured, and light is irradiated to the electro-optic crystal through the material to measure the electric field of the electrical circuit to be measured. The electric field measuring probe for detecting electric field has a thin disk-shaped substrate made of a transparent material and a thin film electro-optic crystal, and one surface of the substrate is coated with an anti-reflection coating, and the other surface is coated with an anti-reflection coating in the center. A microprotrusion is provided, the tip surface of the protrusion is made parallel to the surface of the substrate, the thin film electro-optic crystal having the same shape is fixed to the tip surface of the protrusion, and a part of the surface is coated with a dielectric reflective film. An electric field measurement probe characterized by having a structure.