JPH08129054A - Circuit test equipment for integrated circuits - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a circuit test device for an integrated circuit which has little disturbance to the circuit in the electro-optical sampling method and which is highly sensitive and stable. [Structure] A probe light (laser light) 5 is made incident on an electro-optic crystal element 1 arranged near an integrated circuit (circuit board) 4 to be tested and whose birefringence is changed by an electric field, and the test is performed on the circuit. For measuring the signal electric field corresponding to the electric signal by detecting the change of the polarization state of the probe light accompanying the input of the electric signal for measurement, and evaluating the integrated circuit from the measured signal electric field. A circuit test apparatus, wherein the electro-optic crystal element has the characteristics that the dielectric constant and the refractive index are low, the electro-optic constant is large, the temperature change of the refractive index is small, and the optical damage threshold value is high. It is characterized by being composed of rubidium or potassium arsenate titanate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit testing device for an integrated circuit, and more particularly to a circuit testing device for an integrated circuit which is highly sensitive and stable with little disturbance to the circuit in the electro-optical sampling method. .

[0002]

2. Description of the Related Art As a means for evaluating and testing an integrated circuit in a non-contact manner, there is known a method of using an electro-optical material for a sensor for measuring an electric field. That is, it utilizes the property of the electro-optic material that its birefringence changes depending on the electric field. When the material is irradiated with laser light as probe light, the two irradiated light beams intersect at right angles depending on the magnitude of the electric field. The phase difference of the directional vibration component, that is, the polarization state changes. Usually, this change in polarization can be converted into a change in laser light intensity by passing through a polarizing plate set in an appropriate axial direction. If a pulse wave is used for the laser light, an electric field that changes with time, that is, an electric field change corresponding to the time change of an electric signal input to an integrated circuit can be measured with a resolution equivalent to a pulse width, which is called an electro-optical sampling method. Has been. Among them, as shown in FIG. 2, an element (electro-optical crystal element) made of an electro-optical material is arranged in the vicinity of the circuit to couple a leak electric field from the circuit with the material (coupling),
The method of detecting the change in polarization according to the change in the intensity of the electric field is the most general-purpose method and is generally called the external probe method. That is, the polarization change is detected to measure the signal electric field corresponding to the test electric signal input to the circuit, and the integrated circuit is evaluated from the measured signal electric field.

Particularly, in this external probe method, as shown in FIG.
The electric field in the direction parallel to the circuit board a as shown in (horizontal electric field)
Lithium tantalate (LiTaO ₃ ... LT) and lithium niobate (LiNbO ₃ ) which are complex oxides have been used as materials for detecting with high sensitivity. Then, in the external probe method, the C axis (optical axis) of the crystal element b is set parallel to the lateral electric field generated by the wiring electrode c of the circuit board a, and the laser beam d is irradiated perpendicularly to the C axis. The signal electric field is measured by detecting the polarization change of the reflected light from the reflection film e deposited on the back surface of the crystal element b.

[0004]

However, these materials have the following problems, and there is a problem that needs to be solved.

That is, the conventional crystal applied to the above-mentioned electro-optical crystal element has the following major problems.

First, since the conventionally applied electro-optic crystal has a large relative dielectric constant (about 40), it may affect the circuit operation as a capacitive load or change the characteristic impedance of the wiring. There was a problem of disturbance to the circuit such as causing signal reflection.

In order to reduce the influence of the above disturbance, it is possible to increase the distance between the electro-optical crystal element and the circuit, but on the contrary, it causes a problem that the measurement sensitivity is lowered.

Secondly, the conventionally applied electro-optic crystal has a problem of optical damage in which the birefringence of the material changes with time by irradiation with laser light. In electro-optical sampling, this causes light quantity loss due to fluctuations in the bias point and scattering, which significantly reduces measurement sensitivity and reliability. In general, the sensitivity is improved as the intensity of light applied to the crystal is increased. However, this optical damage limits the upper limit of the light intensity that can be applied and limits the sensitivity. In addition, in practice, since the light intensity per unit area becomes a problem, the beam diameter cannot be made small, and there is also a problem that it hinders high spatial resolution.

Thirdly, the conventionally applied electro-optic crystal has a problem that the temperature dependence of its birefringence is large. In general, an integrated circuit generates a certain amount of heat during its operation, and has a spatial temperature variation within the circuit. When the temperature of the electro-optical crystal element arranged near the integrated circuit changes and the birefringence of the element changes,
Similar to the above-mentioned optical damage, there is a problem that the bias point fluctuates and the measurement signal level fluctuates.

The present invention has been made by paying attention to such a problem, and its problem is that it is applied to a circuit test of an integrated circuit which is highly sensitive and stable with little disturbance to the circuit. An object of the present invention is to provide a circuit test device for an integrated circuit, which is characterized by a crystalline material.

[0011]

That is, the invention according to claim 1 makes probe light incident on an electro-optical crystal element which is arranged in the vicinity of an integrated circuit to be tested and whose birefringence is changed by an electric field. , Inputting a test electric signal to the integrated circuit, and measuring the signal electric field corresponding to the electric signal by detecting the change in the polarization state of the probe light accompanying the input of the electric signal, the measured signal Assuming an integrated circuit circuit tester that evaluates integrated circuits from electric fields,
It is characterized in that the electro-optical crystal element is composed of rubidium titanate phosphate or potassium arsenate titanate.

[0012]

According to the integrated circuit circuit testing apparatus of the first aspect of the present invention, the electro-optical crystal element arranged in the vicinity of the integrated circuit to be tested has a low dielectric constant and a low refractive index and has an electro-optical constant. Is large and has a small change in the refractive index with temperature and a high optical damage threshold, it is composed of rubidium titanate phosphate or potassium arsenate titanate. The influence is reduced, the time resolution determined by the light propagation time is improved, the fluctuation rate of the bias point due to temperature fluctuation is improved, and the sensitivity is improved, and there is no time fluctuation of the measured value due to optical damage. It is possible to collect light into a small spot.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings.

[Embodiment 1] This embodiment relates to a circuit test apparatus to which rubidium titanate phosphate is applied as an electro-optic crystal element. In addition, rubidium titanate phosphate (RT
P) has been widely used as a wavelength conversion element for second harmonic generation, which is a different application from electro-optical sampling.

FIG. 1 is a schematic perspective view showing the setting of the crystal axis direction when RTP is applied as a lateral electric field measuring sensor for electro-optical sampling. 1 in FIG.
Is an electro-optic crystal element made of rubidium titanate (RTP), 2 is a reflective film, 3 is a wiring electrode, 4 is a circuit board, and 5 is laser light as probe light. In order to detect the electric field in the lateral direction with the highest sensitivity and minimize the influence of components in other directions, x
The axis is set to the direction of the transverse electric field to be detected, and the y-axis is set to be the light propagation direction.

[0016]

[Table 1] Table 1 shows a conventional material, lithium tantalate (LT).
And rubidium titanate phosphate according to this embodiment (RT
The material constants of P) are compared from the viewpoint of performance when used as a crystal for electro-optic sampling. Of the constants listed in Table 1, first, the relative permittivity ε is a measure that the crystal influences the circuit as a capacitive load, as already described. The smaller this value is, the larger the disturbance to the circuit. Is small. Next, the refractive index n gives the transit time of light in the crystal, which is one of the factors controlling the time resolution of electro-optic sampling. In general, the speed of light in the medium is 1 / n, and therefore, the smaller the value of the refractive index n, the more suitable the material is for achieving high time resolution. n ₃ ³
r _c / ε is a sensitivity figure of merit. n ₃ ³ r _c gives a degree that is birefringence of the crystal to the electric field changes, the sensitivity becomes higher as this value is larger. On the other hand, ε affects the amount of electric field coupled to the crystal, and the larger this value is, the more the electric field is removed from the crystal and the sensitivity is lowered. Therefore, the ratio of the two becomes a measure of the sensitivity performance.

From the data shown in Table 1, R
It is confirmed that TP is superior to LT in terms of the degree of disturbance, time resolution, and sensitivity, as well as a higher threshold value for optical damage, and stability because it has a small temperature coefficient of natural birefringence. Further, since the light damage threshold value is high, the light can be focused on a small spot, and as a result, high spatial resolution can be achieved.

[0018]

[Table 2] Next, as a more quantitative comparison of RTP and LT with respect to the above sensitivity, an example of the calculated value of the half-wave voltage Vπ is shown below.
Vπ is a voltage (potential of the wiring) required for the phase of light propagating back and forth in the crystal to change by 180 degrees due to an electric field coupled to the crystal, and the sensitivity increases in proportion to the reciprocal of Vπ.

Table 2 shows GaAs in the example shown in FIG.
The calculated value of Vπ when the electro-optic crystal element 1 is close to the wiring (width 5 μm, spacing 10 μm) on the substrate (circuit board) 4 at the distances h = 0 μm and 5 μm is shown. From the data shown in Table 2, the LT has a higher sensitivity when the separation distance is zero (contact state) where each Vπ is the minimum, but the distance of about 5 μm is usually caused because the circuit is disturbed or damaged. Provide a distance. It can be confirmed that the sensitivity is about twice higher than that of RTP at the standard separation distance of 5 μm. Further, this result shows that the amount of change in sensitivity with respect to the change in the separation distance is smaller in RTP, and the dispersion of the measurement values due to the setting error of the separation distance is smaller,
This means that the measurement reproducibility is good.

It goes without saying that the RTP described above can be applied not only as a crystal in the external probe method but also as an electric field sensor of various structures in electro-optical sampling.

[Embodiment 2] This embodiment is substantially the same as the circuit test apparatus according to Embodiment 1 except that potassium arsenate titanate is applied as the electro-optic crystal element. It should be noted that potassium titanate arsenate (KTA) has been widely used as a wavelength conversion element for second harmonic generation and optical parametric oscillation, which are applications other than electro-optical sampling.

Since the data relating to potassium arsenate titanate (KTA) shown in Tables 1 and 2 are the same as the data relating to rubidium titanate phosphate (RTP), the circuit test according to Example 2 was conducted. It can be confirmed that the device also has substantially the same characteristics as the circuit test device according to the first embodiment.

[0023]

According to the invention of claim 1, in the circuit test of the integrated circuit, the influence of the capacitive load is reduced, the time resolution determined by the light propagation time is improved, and the fluctuation of the bias point due to the temperature fluctuation. The efficiency is improved and the sensitivity is improved, and the measured value does not change with time due to optical damage, and it becomes possible to focus light to a small spot. It has the effects of high sensitivity, high time resolution, high spatial resolution, and highly stable circuit testing.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of a circuit testing device according to an embodiment of the present invention.

FIG. 2 is an operation explanatory view of a circuit test device according to a conventional example.

[Explanation of symbols]

 1 Electro-Optical Crystal Element 2 Reflective Film 3 Wiring Electrode 4 Circuit Board 5 Laser Light

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G02F 1/03 501 H01L 21/66 C 7735-4M

Claims (1)

[Claims] 1. A probe light is made incident on an electro-optic crystal element which is arranged in the vicinity of an integrated circuit to be tested and whose birefringence is changed by an electric field, and an electric signal for test is inputted to the integrated circuit. A circuit test device for an integrated circuit, which detects a change in the polarization state of the probe light accompanying the input of the electric signal, measures a signal electric field corresponding to the electric signal, and evaluates the integrated circuit from the measured signal electric field. 2. The circuit testing device for an integrated circuit according to claim 1, wherein the electro-optic crystal element is composed of rubidium titanate phosphate or potassium arsenate titanate.