JP3734995B2 - Integrated circuit device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an integrated circuit device including an observation pad for measuring a signal state of an electrode wiring by electro-optic sampling.
[0002]
[Prior art]
In an integrated circuit device equipped with a high-density integrated circuit, wiring for connecting a huge number of built-in elements is multilayered. Therefore, in order to measure the signal waveform in the wiring arranged in the lower layer of the multilayer structure, a via extending to the uppermost layer is formed by connecting to this wiring, and a pad for inspection and measurement is connected to the via. ing. Electron beam probing is used for measurement of the signal waveform in the wiring using the inspection / measurement pad.
However, as the speed of integrated circuits has increased, electron beam probing has insufficient time resolution, and measurement in a state where the integrated circuit operation is normally performed has become difficult.
[0003]
As a measurement technique for solving the above problems, a method using an electro-optic crystal as a sensor for measuring an electric field is known as a means for measuring a high-speed electric signal waveform. This utilizes the property of the electro-optic crystal in which the birefringence changes with an electric field, and is called electro-optic sampling.
Briefly, when laser light is irradiated onto the electro-optic crystal as probe light, the phase difference of the vibration components in the two orthogonal directions of the emitted light, that is, the polarization state, depends on the magnitude of the electric field on the electro-optic crystal. Change. Usually, the polarization change described above can be converted into a change in the intensity of laser light by passing through a polarizing plate set in an appropriate axial direction. Therefore, if the change in the intensity of the laser beam is detected, the change in the electric field with respect to the electro-optic crystal can be detected. Further, when a pulse wave is used for the laser light, it is possible to measure a time-varying electric field, that is, a temporal change of an electric signal with a resolution corresponding to the pulse width. The above is the principle of electro-optic sampling.
[0004]
If the electro-optic crystal is disposed on the wiring electrode of the integrated circuit and used, an electric field generated when a signal flows through the wiring electrode can be detected, and a continuity test of the wiring electrode can be performed. .
Among these, the method shown in FIG. 3 is the most general method, and what is generally called “external probe method” is applied to the test of the integrated circuit having the test pad. In this method, a wiring electrode 303 formed on a circuit board 301 via an insulating film 302 is connected to a via metal 305 formed so as to penetrate through an insulating protective film 304 formed thereon, and The via metal 305 is connected to the test pad 306 formed on the insulating protective film 304 and tested.
[0005]
In the above test, first, the surface of the electro-optic crystal 310 on which the dielectric multilayer mirror 311 is formed is placed close to the insulating protective film 304 on the test pad 306. Then, the leakage electric field 320 from the inspection pad 306 is coupled to the electro-optic crystal 310, and the change in polarization of the laser light 313 reflected from the dielectric multilayer mirror 311 is detected according to the change in electric field strength. By detecting this change in polarization, the wiring electrode 303 that is electrically connected to the inspection pad 306 via the via metal 305 can be tested.
[0006]
By the way, the electro-optic (EO) sampling technique as described above detects an electric field coupled to an electro-optic crystal. Therefore, since the signal voltage of the wiring electrode 303 to be measured shown in FIG. 3 is very small, the electric field from the inspection pad 306 is very weak. When it is very strong, crosstalk 330 is generated by a leakage electric field 320a from a neighboring wiring electrode. If the crosstalk 330 occurs, the inspection of the inspection pad 306 by electro-optic sampling may be affected.
[0007]
[Problems to be solved by the invention]
As described above, when trying to apply the electro-optic sampling technique to the internal node measurement of LSI integrated with high density, it may be difficult to accurately measure the waveform if the signal is very small. .
The present invention has been made to solve the above problems, and provides an integrated circuit device capable of measuring a signal state of an arbitrary wiring electrode of an integrated circuit with high accuracy by using an electro-optic sampling technique. The purpose is to do.
[0008]
[Means for Solving the Problems]
An integrated circuit device of the present invention is connected to an integrated circuit formed on a semiconductor substrate, an insulating protective film formed so as to cover the integrated circuit, and a first wiring electrode constituting the integrated circuit, thereby protecting the insulation. A first observation pad made of metal formed on the film and a second electrode wiring connected to a second electrode wiring having a signal intensity lower than that of the first electrode wiring when the integrated circuit is operated by applying a signal. The second observation pad is formed in a larger area than the first observation pad, and the leakage electric field from the observation pad is coupled to a desired electro-optic crystal to reduce the leakage electric field. In the state measured by electro-optic sampling using an electro-optic crystal, the observation pad corresponds to the signal strength of the signal passing through the electrode wiring connected to the observation pad in a state where the signal is applied to the integrated circuit and operated. Desired electric light Is formed over the area where the electric field which can be detected by electro-optical sampling using crystals are obtained, the signal waveform of the electrode wiring in a state of being operated by applying a signal to the integrated circuit, the electric field generated from the observation pad It is made to measure by detecting by electro-optic sampling.
According to the present invention, the electric field strength at the observation pad corresponds to the signal strength at the electrode wiring .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
In the present embodiment, an integrated circuit device is configured as shown in FIG. In FIG. 1, (a) is a front view and (b) is a plan view. This integrated circuit first includes wiring electrodes 103l, 103m, and 103n formed on a circuit board 101 with an insulating film 102 interposed therebetween. Further, vias 105l, 105m, and 105n are formed through the insulating protective film 104 formed on these wiring electrodes and connected to the wiring electrodes 103l, 103m, and 103n, respectively. On the insulating protective film 104, a square observation pad 106l is formed and connected to the via 105l. Similarly, a square observation pad 106n is formed on the insulating protective film 104 and connected to the via 105n. In the above configuration, in this embodiment, it is assumed that the signal intensity in each wiring electrode is wiring electrode 103l <wiring electrode 103n <wiring electrode 103m.
[0010]
The areas of the observation pads 106l and 106n in FIG. 1 are designed based on FIG. 2 showing the relationship between the area of the observation pads and the measurement sensitivity in electro-optic sampling. As shown in FIG. 2, in the measurement by non-contact type electro-optic sampling, the measurement sensitivity depends on the area of the observation pad, and the measurement sensitivity improves as the area of the observation pad increases. The measurement sensitivity depends on the observation pad area as described above, which is a feature of non-contact type electro-optic sampling that is not found in electron beam probing or contact type electro-optic sampling. The present invention utilizes this phenomenon. Yes.
[0011]
Referring to FIG. 2 in more detail, first, the point 21l is a point that shows a measurement sensitivity at which an electric signal passing through the wiring electrode 103l can be measured with a sufficient signal-to-noise ratio (S / N) by electro-optic sampling. Further, the point 21m is a point indicating a measurement sensitivity at which an electric signal passing through the wiring electrode 103m can be measured with a sufficient signal-to-noise ratio by electro-optic sampling. And the point 21n is a point which shows the measurement sensitivity which can measure the electric signal which passes through the wiring electrode 103n with a sufficient signal-to-noise ratio by electro-optic sampling.
[0012]
As described above, since the signal intensity at each wiring electrode is wiring electrode 103l <wiring electrode 103n <wiring electrode 103m, the measurement sensitivity required for each is wiring electrode 103l> wiring electrode as shown in FIG. 103n> wiring electrode 103m. Since the relationship between the measurement sensitivity and the pad area varies depending on the electro-optic crystal used, in FIG. 2, the vertical axis and the horizontal axis are arbitrarily scaled. For example, when cadmium tellurium is used as an electro-optic crystal, the unit of the horizontal axis is μm ² .
[0013]
Accordingly, the observation pad area corresponding to the sensitivity indicated by the point 21l is indicated by the point 22l, and the area of the observation pad 106l illustrated in FIG. 1 may be the area indicated by the point 22l. Similarly, the observation pad area corresponding to the sensitivity indicated by the point 21n is indicated by the point 22m, and the area of the observation pad 106n shown in FIG. 1 may be the area indicated by the point 22n. Note that since the signal passing through the wiring electrode 103m is very large, the measurement sensitivity may be small, and sufficient measurement sensitivity is obtained with the area of the upper surface of the via 105, so that an observation pad is unnecessary.
[0014]
As described above, if the area of the observation pad is set to be equal to or larger than the area where the measurement sensitivity according to the intensity of the electric signal passing through each wiring electrode is reached, the signal waveform passing through any wiring electrode is set to the intensity of this signal. It can measure with high accuracy.
Incidentally, as shown in FIG. 2, if the area of the observation pad is greater than a certain value, the measurement sensitivity is not improved. Further, if the area of the observation pad is made too large, it will hinder the improvement of the degree of integration of the integrated circuit. Therefore, if the observation pad is, for example, a square whose side is about 30 μm is used as the upper limit, the effect of improving the sensitivity can be sufficiently obtained without hindering the improvement of the integration degree. In the above embodiment, the observation pad having a square planar shape is used. However, the present invention is not limited to this, and other shapes such as a rectangle or a circle may be used.
[0015]
【The invention's effect】
As described above, in the present invention, the integrated circuit formed on the semiconductor substrate, the insulating protective film formed so as to cover the integrated circuit, and the insulating protective film connected to the wiring electrode constituting the integrated circuit An observation pad made of metal formed on the surface, and the observation pad is formed in an area corresponding to the signal strength of the electrode wiring connected to the observation pad in a state in which the signal is applied to the integrated circuit and operated. Then, the signal waveform of the electrode wiring in a state in which the integrated circuit is operated by applying a signal is measured by detecting the electric field generated from the observation pad by electro-optic sampling.
According to the present invention, since the electric field strength at the observation pad corresponds to the signal strength at the electrode wiring, the signal state of any wiring electrode of the integrated circuit can be measured with high accuracy using the electro-optic sampling technique. Effect.
[Brief description of the drawings]
1A and 1B are a cross-sectional view and a plan view showing a partial configuration of an integrated circuit according to the present invention.
FIG. 2 is a correlation diagram showing the relationship between the area of an observation pad and measurement sensitivity in electro-optic sampling.
FIG. 3 is an explanatory view showing a conventional test method using electro-optic sampling.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 101 ... Circuit board, 102 ... Insulating film, 103l, 103m, 103n ... Wiring electrode, 104 ... Insulating protective film, 105l, 105m, 105n ... Via, 106l, 106m, 106n ... Observation pad.

Claims (1)

An integrated circuit formed on a semiconductor substrate;
An insulating protective film formed so as to cover the integrated circuit;
A first observation pad made of a first metal formed on the insulating protective film is connected to a wiring electrode constituting the integrated circuit,
A second observation pad connected to a second electrode wiring whose signal intensity in a state of being operated by applying a signal to the integrated circuit is smaller than the first electrode wiring ;
The second observation pad is formed in a larger area than the first observation pad,
In the state where the leakage electric field from the observation pad is coupled to a desired electro-optic crystal and the leakage electric field is measured by electro-optic sampling using the electro-optic crystal, the observation pad sends a signal to the integrated circuit. Formed more than the area where an electric field that can be detected by electro-optic sampling using a desired electro-optic crystal is obtained according to the signal intensity of the signal passing through the electrode wiring connected to the observation pad in the state of being applied and operated. And
An integrated circuit device, wherein a signal waveform of the electrode wiring in a state in which a signal is applied to the integrated circuit is measured by detecting an electric field generated from the observation pad by electro-optic sampling. .

Images