JPH02238382A - Positioning method of probe and circuit to be measured - Google Patents

Abstract

PURPOSE:To enable execution of measurement without disturbance and with excellent reproducibility by an electric-field probe positioned with high precision, by conducting optical positioning by using an objective lens having different focal distances with respect to lights of two wavelengths. CONSTITUTION:In a state wherein an electric-field probe 5 is withdrawn, a first- wavelength light sent by a first interference filter through an objective lens 1 is focused on a circuit 6 to be measured, by adjusting the position in the vertical direction of a stage 7 in accordance with a focal distance f1 of the first wavelength light. Next, the probe 5 is inserted into an optical path and a second-wavelength light is made incident by a second interference filter. Then the light is imaged at a different focal distance f2, since the lens 1 has chromatic aberration on the optical axis with respect to lights having different wavelengths. When the second-wavelength light is imaged on a dielectric multilayer film 4 reflecting lights, which is provided in a part of an electrooptic crystal 3 on a transparent substrate 2 of the probe 5, accordingly, the probe 5 and the circuit 6 are positioned precisely at a minute distance of a focal distance difference f1 - f2 from each other, and an electric field generated by the circuit 6 is measured without disturbance and with excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a positioning method for determining the separation distance between a probe and a circuit under test.

? [Prior art] As a means of evaluating and testing integrated circuits and devices, an electro-optic crystal is placed near the circuit under test as an electric field probe, and when the crystal is irradiated with a laser beam pulse with a narrow pulse width, the inside of the circuit under test is detected. A method is known that utilizes the principle that the polarization state of irradiated light changes depending on the magnitude of the electrical signal. In this method, measurement sensitivity largely depends on the distance between the electro-optic crystal and the circuit under test, and generally the narrower the gap, the higher the sensitivity. On the other hand, the disturbance to the circuit becomes larger as the gap becomes narrower. For example, when L i T a O ■, a typical electro-optic crystal, is brought into close contact with wiring in a coplanar structure, the wiring becomes difficult due to the high dielectric constant of the crystal. The characteristic impedance of is reduced by about 50%.

Furthermore, there is an extremely high risk of physically destroying the circuit under test if it is brought into close contact with it. [Problem to be solved by the invention] Therefore, in order to avoid disturbing the circuit as in the prior art and to obtain sufficient measurement sensitivity, it is essential to maintain a separation distance between the two on the order of several micrometers. be. Furthermore, in order to obtain measurement reproducibility and calibration accuracy, separation distance accuracy of within 1 micrometer is required. However, until now, there has been no technology that satisfies these requirements, and this has been a major problem in putting circuit testing methods based on the above principles into practical use.The present invention solves the above problems and The object of the present invention is to obtain a method for positioning the distance between a circuit under test and a probe with high precision in order to measure a device without disturbance and with good reproducibility.

[Means to solve the problem]

In order to achieve the above object, the present invention uses a microscope objective lens having chromatic aberration on the optical axis for light of two wavelengths, and passes light of a first wavelength to a circuit under test through the lens. A wavelength of light is irradiated onto the tips of the electro-optic crystals that make up the probe, and both the first wavelength light and the second wavelength light reflected from the circuit under test and the electro-optic crystal form an image. By slightly moving the circuit under test and the probe to focus, we set the distance between them to a constant value. In particular, the crystal surface of the probe is coated with a dielectric multilayer film selected to transmit light of the first wavelength and reflect light of the second wavelength, and the coating portion It can be used as a marker during probe positioning, and as a reflective film for pulsed laser light when measuring electrical signals.

[Effect]

By performing optical positioning using an objective lens with two wavelengths of light and different focal lengths, it is possible to bring the circuit under test and the probe close to a gap of several micrometers, and the distance accuracy is 1 micrometer. Accuracy within the range achieved is achieved. Being able to set the gap to several micrometers in this way makes it possible to obtain sufficient measurement sensitivity in measuring electrical signals, and being able to set it with high precision makes it possible to obtain good reproducibility. Furthermore, there is no disturbance to the circuit such as destruction of the circuit under test or change in characteristic impedance, which has been a problem in the past. [Example] Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing a positioning procedure. In the figure, 1 is a microscope objective lens, 2 is a transparent substrate, 3 is an electro-optic crystal, and 4 is a dielectric multilayer film, and these transparent substrate 2, electro-optic crystal 3, and dielectric multilayer film 4 constitute a probe 5. ing. 6 is a circuit under test, and 7 is a stage.

The objective lens 1 is designed to intentionally have chromatic aberration on the optical axis for light of two wavelengths, that is, to have a slightly different focal length for light of the first and second wavelengths. Furthermore, although there is a slight chromatic aberration for the light of the third wavelength, which is the laser light for measuring the minute electric field coupled from the circuit under test 6 to the electro-optic crystal 3, the diameter of the condensed beam is It is desirable that it does not change significantly. The probe 5 mainly consists of a thin electro-optic crystal 3 and a transparent substrate 2 supporting it, and a dielectric multilayer film 4 of an appropriate shape is partially applied to the surface of the electro-optic crystal 3. In this dielectric multilayer film, the light of the first wavelength that is irradiated and focused on the circuit under test 6 exhibits a transmission characteristic, making it possible to observe the circuit under test, and also irradiates the probe surface. For the light of the second wavelength that is focused by
The thickness of each layer is set so as to exhibit reflection characteristics and enable observation of the probe surface. Further, this dielectric polygon film must be designed to be a highly reflective film even for light of the third wavelength.

FIG. 2 is an explanatory diagram showing an example of a positioning procedure.

First, light of the first wavelength, e.g., g-line (wavelength 0.4358 micrometers), is irradiated onto the circuit under test 6 using the interference filter ■8, and the stage 7 is moved slightly to bring it into focus. The circuit to be measured 6 is fixed at a position at a distance f. At this time, it is desirable that the probe 5 be retracted upward so as not to come into contact with the circuit under test 6. Next, replace the interference filter ■8 with the interference filter ■9, and use the light of the second wavelength. e-line (wavelength 0.5461 micrometer)
irradiate the dielectric coating portion 4 on the surface of the probe 5,
The tip of the probe 5 is positioned at the focal length f2 while lowering the probe 5 little by little so that the probe 5 is in focus. By the above procedure, the distance h between the circuit under test 6 and the tip of the probe 5 can be uniquely set to the value h=f - f2. Further, by changing the first wavelength or the second wavelength using the interference filters 8 and 9, etc., it is possible to set an arbitrary separation distance according to the chromatic aberration of the objective lens 1.

〔Effect of the invention〕

As described above, the method of positioning the probe and the circuit under test according to the present invention is a method of positioning the probe and the circuit under test in which the probe is brought close to the circuit under test. a step of irradiating light of a first wavelength to the circuit under test and light of a second wavelength to the tip of the probe through a microscope objective lens having a second wavelength, and a second wavelength reflected from the circuit under test; By determining the distance between the circuit under test and the probe, the distance between the circuit under test and the probe having an electro-optic crystal can be set to several micrometers or less than 1 micrometer. This not only makes it possible to measure the electrical signals coupled from the circuit under test to the electro-optic crystal with high sensitivity and good reproducibility, but also solves the problem of disturbance and destruction of the circuit under test. .

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the procedure of the positioning method according to the present invention. 1... Objective lens 2... Transparent substrate 3...
Electro-optic crystal 4... Dielectric multilayer film 5... Probe 6... Target circuit 7... Stage
8...Interference filter 9...Interference filter■ Representative patent attorney Junnosuke Nakamura

Claims (1)

[Claims] (1) In a method of positioning the probe and the circuit under test, in which the probe is brought close to the circuit under test, the light of the first wavelength is irradiating the circuit under test with light and the tip of the probe with light of a second wavelength; and irradiating the light of the first wavelength reflected from the circuit under test and the light of a second wavelength reflected from the tip of the probe. By the step of forming an image,
A method for positioning a probe and a circuit under test, comprising determining a distance between the circuit under test and the probe.