JPS63269198A - Inspection of driving circuit substrate for liquid crystal display unit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for inspecting a liquid crystal drive circuit board that integrates a large number of electrical drive elements for driving a liquid crystal display used in a television or the like.

[Conventional technology]

In general, the inspection of a drive circuit board on which electrically driven elements mainly composed of semiconductor elements such as transistors are integrated has been carried out by mechanically scanning the surface of the element to inspect the surface irregularities, and optically, that is, WI This was done by observing the shape using a microscope or the like, and then applying an electrical probe to the element to measure its electrical characteristics.

However, even a small liquid crystal drive circuit board for a 3-inch TV screen drives more than 80,000 pixels individually, so the same number of drive elements are integrated and has the same area as a 3-inch screen. However, the conventional inspection method described above has the following disadvantages.

First, the method of mechanically inspecting surface irregularities is suitable for inspecting straight lines, but is not suitable for inspecting large areas because it requires a long inspection time.

Next, although the method of optically inspecting the shape can be used to inspect a wide area, it cannot be applied to something that has a transparent electric bridge, such as a liquid crystal drive circuit board.

In addition, although the method using an electric stylus has the advantage of being able to measure electrical characteristics, it also has the following drawbacks: 1) It is easy to damage the element because it comes into direct mechanical contact with the element; 2) It produces a very small signal depending on the contact pressure operation becomes unstable. ■Since it is necessary to measure each element one by one, there are drawbacks such as the time required for inspection. To be more specific about the inspection time, in the case of a circuit board having 80,000 elements, even if each element is inspected at 0.1 seconds, it will take 8000 seconds, or more than 2.2 hours.

For this reason, when testing using such conventional methods, samples are inspected, or the display image is visually inspected after the driver circuit board is assembled into the liquid crystal display element to form a completed liquid crystal display. It was designed to determine whether or not images were missing.

The former method cannot ensure complete inspection, and the latter method has the drawback of high inspection costs.

Therefore, another possible testing method is to use an electron beam tester, which is used to analyze the operation of ICs. This method uses an electron beam as a probe to measure the potential distribution of metal wiring inside an IC.

[Problem that the invention seeks to solve]

However, this electron beam tester can connect an external power source to the IC and put the IC into operation state, and then measure the potential distribution or time change in potential of the metal wiring inside the IC. It is not possible to judge whether it is good or bad.

In particular, in the case of a drive circuit board for a liquid crystal display, which is the object of the present invention, when it is not connected to a liquid crystal display element, the pixel electrodes that should be connected to it are floating and isolated without being connected anywhere. Since the potential of this electrode fluctuates irregularly, inspection using an electron beam tester cannot be carried out.

As described above, there is a method for quickly and inexpensively testing the acceptability of a drive circuit board for a liquid crystal display that has a large number of drive elements and includes isolated electrodes with unstable potentials in the circuit.
Since this has not been found so far, it is an object of the present invention to provide a new testing method that can test this type of circuit board in a short time and at low cost.

[Means for solving problems]

In order to achieve such an object, the present invention provides a driving element of a driving circuit board for a liquid crystal display in which a large number of driving elements for individually electrically driving display elements of a liquid crystal display on a pixel basis are integrated. While a predetermined voltage is applied to the surface of the driving element on the substrate, a focused electron beam scans and charges the surface of the drive element, and the secondary electrons generated at this time are detected and imaged. The presence or absence of a defect in each drive element is determined based on the image density.

[Effect]

When a predetermined driving voltage is applied to a driving circuit board for a liquid crystal display and a charge is applied to the surface of a driving element on the board while scanning with a focused electron beam, a charge is applied to the metal wiring on the surface of the driving element. is regulated by the operating potential of the electrode of the drive element connected to the metal wiring, and secondary electrons are generated according to that potential. Therefore, when the secondary electrons are converted into an optical signal and imaged, the generated secondary electrons are The density of the image changes depending on the amount of secondary electrons. The density of this image decreases and becomes white if the potential of the portion scanned by the electron beam is negative, and the density increases and becomes black as the potential becomes more positive.

If the metal wiring is normal, even if it is charged by an electron beam, the potential will be regulated by the potential of the electrode of the connected driving element, so the concentration will correspond to the level of that potential.
If there is a defect in the metal wiring and the connection with the electrode of the drive element is broken, it will be charged by the electron beam and become a negative potential.
At this time, the image density decreases and becomes white. In this way, it is possible to determine whether the metal wiring and the drive element are good or bad from changes in the density of the secondary electron image.

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

FIG. 1 schematically shows the configuration of an inspection device used to carry out the method of the present invention.

In this figure, 10 is a vacuum chamber, and the upper part is
Electron gun that emits an electron beam 11. An electromagnetic electron lens 12 for narrowing the electron beam emitted from the electron gun 11 and a scanning coil 13 for scanning the electron beam narrowed by the electron lens 12 over a predetermined area are provided. Electrons &*1 scanned by scanning coil 13
A sample stage 15' on which a sample to be inspected to be irradiated with light 9 is placed
A scintillation detector 16 configured by combining a scintillator and a photomultiplier, for example, is housed in order to detect secondary electrons generated from the sample on the sample stage 15°. A scanning coil 13 is installed outside the vacuum chamber 10.
A scanning oscillator 14 that generates a scanning signal to be applied to the scanning oscillator 14. An image display device, such as a CRT, for forming an image of the output signal of the scintillation detector 16 and displaying it, and a mechanical sample scanning mechanism 18 for moving the sample 5 in order to change its inspection range are provided.

An example of a drive circuit board for a liquid crystal display, which is a sample to be inspected with this apparatus, is shown in FIGS. 2 and 3.

As shown in FIG. 2, the drive circuit board 15 is a transparent glass insulating substrate l with an area corresponding to a liquid crystal display element (not shown).
Image W made of a transparent conductive tWQ mainly composed of indium oxide divided according to the pixels of the liquid crystal display element on the top: An electrical drive element consisting of an electrode 2 and a thin film FET (field effect transistor) 3 is a matrix. The number of pixels is integrated in the same shape as the number of pixels. In the case of a liquid crystal display for a 3-inch television screen, the number of pixels is 85.800, so 85.800 driving elements are integrated on the substrate 1.

FIG. 3 shows an enlarged cross-sectional structure of one drive element. In FIG. 3, 4 is the gate of the FET 3, and 4° is the gate electrode formed on the gate 4.

8 is the drain of FET3, 8° is the drain electrode formed on the drain 8, and 9 is the source of FET3.

9゛ is a source electrode formed on this source 9;
Further, 5 is an insulating film that provides insulation between each of these elements and between each driving element. A pixel electrode 2 connected to a liquid crystal display element is connected to a drain electrode 8'' of the FET 3.

As shown in FIG. 2, the gate electrode 4° and source electrode 9° of each FET 3 are individually drawn out around the glass substrate l via the gate electrode wiring 6 and source electrode wiring I7, respectively, and are connected to the drive circuit of the display device. Becomes connected.

A liquid crystal display device is completed by bonding a liquid crystal display element to the drive circuit board configured as described above.

In order to reduce the cost of inspection, the present invention inspects the presence or absence of defects in parts before the drive circuit board is assembled into a liquid crystal display.The method of the present invention will be specifically explained below.

When the driving circuit board 15 as shown in FIG. 2 is completed, it is inserted as a sample into the vacuum chamber 10 of the inspection apparatus shown in FIG. 1 for inspection, and placed on the sample stage 15''. The air inside is removed to create a vacuum, and the same voltage as that used in a normal drive state is applied from a power supply device (not shown) to the drive circuit board 15.The FET 3, which is a drive element on the drive circuit board, is brought into a conductive state. In order to do this, the voltages applied to the gate electrode wiring 6 and the source electrode wiring 7 are set to positive voltages.

In this state, the electron beam 19 emitted from the electron gun is focused by the electron lens 12 and irradiated onto the surface of the drive circuit board 15 while scanning, thereby charging the metal wiring on the surface.

As a result, the potential of the pixel electrode 2 of each drive element becomes FT! ,
It changes depending on the operating state of T3, and the corresponding secondary electrons 20 are generated. The secondary electrons are detected by the scintillation detector 1G and converted into an electrical image signal. The image is sent to an image display device 17, such as a CRT, which operates in synchronization with the scanning of %119, and in this display device, the pattern of potential distribution on the substrate surface is displayed in shades of image density.

In this case, the display screen is generally positively charged in the area irradiated by the electron beam 19, and the more positive charges there are, the higher the image density becomes, resulting in a black image; The density becomes lighter, resulting in a white image, and at an intermediate zero potential, a gray image with intermediate density results. The density of this image can be adjusted by adjusting the accelerating voltage of electron &i19.

The apparatus used in the present invention has the same principle as a scanning electron microscope, but since magnification is not the purpose, a magnification of 20 times or less is sufficient, and the apparatus can be simplified.

Determination of the presence or absence of defects in the substrate is performed as follows. First, when inspecting the presence or absence of disconnection in the wiring of each drive element on the substrate, drive the FET so that a positive potential is applied to the source and gate of the FET of the drive element. Select voltage polarity.

At this time, if the wiring of the drive element is normal, the FET 3 is conductive, so even if the drain electrode 8° and therefore the pixel electrode 2 are charged by the electron beam 19, they have a positive potential, and there is almost no emission of secondary electrons. The normal element is N in Figure 4.
It is displayed in black as shown in . In this figure, the black parts are indicated by hunting.

If any one of the gate electrode 4', source electrode 9°, and drain electrode in the driving element has a defect such as disconnection or poor connection, the FET 3 becomes non-conductive, and the pixel electrode 2 becomes isolated. The pixel electrode of an element with such a defect is charged to a negative potential according to the accelerating voltage of the electron beam 19 by the irradiation of electrons &1l19, and the emission of secondary electrons becomes large. The image density decreases and the image appears white.

Next, in order to check whether there is a short circuit between the electrodes of the driving element, a driving voltage is applied to the substrate so that the source 9 is at a positive potential and the gate is at a zero or negative potential, and the electron beam 19 is irradiated. .

At this time, if the drive element is normal, the FET is in a non-conductive state, so the pixel electrode 2 is isolated and charged by the electron beam 19. At this time, the accelerating voltage of the electron beam is set in the range where the secondary electron efficiency is 1 or more (0.8 to 1.
5 kV), the isolated pixel electrode will have a weak positive potential, and the image density will be gray, which is between black and white.

In the case of a drive element with a defect that causes a short circuit between the gate and drain of the FET of the drive element, the drain, and therefore the pixel electrode 2, will have a potential equal to the gate potential, 0 or negative, so that the irradiation with the electron beam 19 will not be possible. Even if there is, the potential does not change, and the image density in this area decreases and becomes white.

Furthermore, in the case of a drive element having a defect that causes a short circuit between the source and drain, the drain electrode, and therefore the pixel electrode 2, have the same potential as the source, so the image in this portion has a high density and is displayed black.

In this way, by changing the polarity of the voltage applied to the drive circuit board to be inspected and irradiating it with an electron beam, a secondary electron image is obtained, and from the change in image density, it is possible to detect short circuits in the wiring of each drive element. It is possible to distinguish and determine the location of a disconnection abnormality.

Since secondary electron emission varies depending on the substance and shape, it is possible to inspect the shape, and by scanning the electron beam 19, inspection can be performed over a wide range. Furthermore, secondary electron emission is also influenced by the potential of the irradiated part. The electron beam tester utilizes this effect.The present invention is different in that isolated electrodes are also charged by irradiation with electrons 1419, and normal elements and abnormal elements can be distinguished from each other by charging the isolated electrodes. This is what I did.

In addition to the embodiments described above, the method of the present invention can be implemented in various ways. In this inspection method, the entire surface of the object to be inspected can be automatically observed by moving the sample table on which the object to be inspected is moved by a scanning mechanism. Furthermore, by combining an image processing device that analyzes the difference in image density between a normal element and an abnormal element, it is possible to extract an abnormal part and automatically output its area, position, shape, etc.

In the above example, the drive circuit board 15 using the FET 3 was used as the test target, but the test target is not limited to this, but is also applicable to drive circuit boards using diodes and other conductive parts on a part of the surface of the test target. The method of the present invention can be applied to substrates on which a large number of small elements, including a large number of small elements, are regularly arranged.

〔Effect of the invention〕

As can be seen from the above description, according to the present invention, when inspecting defects in a large number of arrayed driving elements constituting a driving circuit board for a liquid crystal display device, the substrate is irradiated with a focused electron beam. By using this electron beam as a probe, the shape and electrical characteristics of elements with isolated electrodes can be inspected simultaneously without contact, and by scanning the electron beam, large areas can be inspected at once. Therefore, the inspection time can be significantly shortened, and the inspection speed can be significantly improved. Specifically, when inspecting a substrate for a 3-inch TV liquid crystal display device that has approximately 80,000 driving elements, it is possible to scan 1,000 driving elements in one second in one scan. , for this board, 80
Even if repeated scanning is performed, it only takes 80 seconds, which is one-hundredth of the time required for conventional inspection methods using stylus probes.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing the configuration of an inspection device used in the present invention, FIG. 2 is a perspective view showing an example of a drive circuit board to be inspected by the present invention, and FIG. 3 is a drive element shown in FIG. 2. FIG. 4 is a diagram showing an example of a secondary electron image, and FIG. 5 is a diagram used to explain the operation of the present invention. 10: Vacuum chamber, 11: Electron gun, 12: Electron lens, 13: Scanning coil, 15: Drive circuit board, 15°=sample stage, 16: Scintillation detector, 17: Image table (Figure 1) @ff(KV) Figure 5'$2 Figure S ρ Figure 3 Figure 4

Claims (1)

[Claims] 1) While applying a predetermined voltage to the drive elements of a drive circuit board on which a large number of drive elements for individually electrically driving display elements of a liquid crystal display pixel by pixel are integrated, The surface of each drive element is scanned by a focused electron beam while being charged, the secondary electrons generated at this time are detected, this is converted into an image, and the presence or absence of defects in each of the drive elements is determined based on the density of the image. A method for inspecting a drive circuit board for a liquid crystal display device, characterized in that: