HK1068407A - Integrated visual imaging and electronic sensing inspection systems - Google Patents

Description

Integrated vision imaging and electronic inspection system

Technical Field

The present invention relates to the field of automatic testing of active plates for liquid crystal displays.

Background

A typical LCD screen is formed using a liquid crystal material sandwiched between an active plate and a ground plate. Polarizers, chromating filters and spacers may also be included between the disks. During fabrication, many active disks may be formed on a single glass plate. In each area on a glass plate on which an active pad is to be formed, a pixel area, a driving line, a gate line, and a driving element are constituted. Typically, a thin film transistor is used as the driving element.

Due to the relative complexity of the active plate compared to the ground plate, defects in most LCD displays can be traced to some form of defect in the active plate. Due to the significant additional expense of fabricating practical LCD displays from active disks, various techniques have been developed for individually inspecting active disks so that defective active disks can be identified, repaired or discarded at the stage of the fabrication process.

An exemplary portion of an active plate 20 for a monochrome display is schematically shown in fig. 1. As can be seen therein, a plurality of conductive areas 14 are arranged in an XY matrix, each defining a pixel in the final display. Associated with each conductive region is a thin film transistor 16 having an input terminal connected to a respective row line in the matrix, and a control terminal or gate connected to a respective column line. In the particular matrix shown in fig. 1, adjacent row lines are coupled to opposite sides of the matrix, while adjacent column lines are coupled to the top and bottom of the matrix, respectively. A color display is similar, but each pixel of the display comprises 3 pixels on the active disc, each pixel for a different color.

In operation, during each scan of the array, each conductive region is charged to the voltage on a respective array line when the respective thin film transistor is turned on by the voltage on the respective column line. However, while the active plate can be electrically operated without the ground plate and liquid crystal material sandwiched therebetween, no visually perceptible change occurs during operation.

Various techniques are known in the art for inspecting and testing LCD active disks before proceeding with further fabrication of the complete LCD screen. Each of these techniques is well suited for detecting certain defects, but not certain others.

One commonly used inspection technique is to conduct the inspection under visible light using digital camera and computer based image analysis. Since the active plate comprises an array of a large number of pixel areas and thin film transistors, a convenient form of optical inspection is to form a differential image between the repeating patterns of the image. This is commonly referred to as Automated Optical Inspection (AOI). If there is no defect, the difference image is zero. If defective, the difference image is positive or negative. In this way, various defects can be detected, such as short and open circuits and other defects in geometry that can cause malfunction of the display, or unacceptable variations in image brightness across the pixel array. However, other potential defects, such as certain defects that cause one or more transistors to malfunction and/or prevent the conductive regions of the pixel from holding charge until it is updated at the next scan, cannot be detected in this manner.

The visible light system may be transmissive or penetrating (illumination and camera on both sides of the disc), or reflective (illumination and camera on the same side of the disc), with the active disc fixed and the camera on a moving system for step and repeat operation, in particular with the illumination system moving with the camera, to ensure uniform illumination for each camera field of view. Typically, the camera is also equipped with a Z-axis movement system for greater flexibility.

Other known systems for evaluating active plates during the manufacturing process of an LCD include methods for electrically testing the active plate to enable an acceptance/rejection decision to be made based on reasonably accurate predictions of how the plate will perform in the finished LCD display. One such technique utilizes a voltage imaging sensor, as described in U.S. patent No. 4983911, assigned to Photo Dynamics, inc. These systems provide a two-dimensional image of the voltage distribution on the surface of the active plate, thereby enabling the image to be digitized by a suitable camera. Such systems illuminate an active disk with a collimated beam of optical energy of known polarity through an electro-optic modulator located sufficiently close to the disk to be affected by the voltage on the active disk. Thus, the voltage imaging sensor simulates the upper half of an LCD screen and converts the charge (voltage) on the active plate into visible light. Thus, such systems require at least that the electro-optic modulator be located very close to the substrate. This method is capable of detecting defects in operation, such as transistors, but has a higher resolution limit than AOI systems.

The assignee of the present invention Photo Dynamics, inc. Such systems may be of a disk size or smaller, typically operating in a step and repeat mode with the camera. Although reflection mode is generally used, both reflective and transmissive systems are known.

Another well-known testing technique is the electron beam scanning or e-beam scanning technique. In these test systems, the active disk is placed in a vacuum chamber and the disk is scanned with an electron beam and secondary electrons are detected with a flash camera. The camera output relative to the electron beam position provides image data of the disk voltage. Typically, a small portion of the active disk is scanned at any one time, and the entire disk is scanned in a step and repeat fashion. Insufficient secondary electrons indicate disc defects.

Finally, active disk test systems based on charge detection are also known. These systems are based on the concept of turning on each transistor on the active plate, charging the conductive area of the corresponding pixel to a particular voltage, then turning off the transistor, and then turning on the transistor to short the pixel conductive area to ground while measuring the charge returned from the conductive pixel area. Insufficient charge indicates a disc defect. Typically, the transistor conduction period when charging the pixel conductive regions corresponds to the time the transistor is conducting for such a purpose in the finished display, and the time before shorting the pixel conductive regions for charge measurement corresponds to the time between scans in the finished LCD.

Thus, in AOI systems using visible light, the camera is typically spaced sufficiently far from the active disk being inspected, whereas in systems of the voltage imaging sensor type, at least the electro-optical modulator must be brought very close to the active disk in order to obtain a voltage image of effective resolution. In an electron beam system, although a camera for providing a two-dimensional image is not required, a vacuum environment must be provided. Instead, only a light sensor, preferably with a photomultiplier to increase the brightness of the light is required, wherein the XY information of the two-dimensional image is provided by the electron beam scanning control system. Finally, in charge-sensing type devices, a camera is not used at all, and no mechanical transport system is required other than for loading and unloading the active pads under test, as is generally required in some fashion for all other test and inspection systems.

Summary of The Invention

An integrated inspection test system for Liquid Crystal Display (LCD) active pads is disclosed. This integrated inspection test system may combine visual imaging inspection and electronic inspection such as voltage imaging, electron beam inspection, or charge inspection in a single system, wherein the defect information obtained by the visual inspection system is combined with the defect information obtained by the electronic inspection system to generate a defect report. A stationary disc is scanned by one or more cameras and image data from the cameras is processed to detect potential defects. A high resolution electronic detection system inspects the stationary disk and processes the image data from the sensor to detect potential defects. Potential defects from the visual image data and the electronic inspection image data are processed to generate final defect information.

Brief description of the drawings

Fig. 1 shows a portion of a typical active disc for a monochrome display.

FIG. 2 is a block diagram of a control system of a typical integrated inspection test system utilizing a visible light camera and a voltage imaging sensor.

Fig. 3 schematically illustrates a transport system for the exemplary system of fig. 2.

Fig. 4 is a block diagram of a control system of a typical integrated inspection test system utilizing a visible light camera and an electron beam test system.

Fig. 5 schematically illustrates a transport system for the exemplary system of fig. 4.

FIG. 6 is a block diagram of a control system of a typical integrated inspection test system utilizing a visible light camera and a charge test system.

Fig. 7 schematically illustrates a transport system for the exemplary system of fig. 6.

Detailed Description

In the following description, various embodiments of the present invention are disclosed. These different embodiments represent different combinations of inspection and testing techniques in a single inspection and testing system, as opposed to separate systems for each such technique as is known in the art. However, certain design details of the system of the present invention may be substantially the same as these independent systems, or any and obvious modifications of these independent systems are known in the art. And therefore these details will only be described in a general sense. Rather, these and other details, particularly those unique to the present invention, are set forth in sufficient detail to enable one skilled in the art to make and use the invention.

Referring to fig. 2 and 3, there can be seen a block diagram of a control system for a typical integrated inspection test system and a schematic diagram of a transport system for such a system, respectively. Such a system provides visual inspection with a visible light camera 22 and voltage imaging testing by a voltage imaging sensor 24. Preferably, the active disk 20 is delivered and located in the package 26 of the integrated inspection and test system by a robotic system, indicated by the numeral 28. The robotic system may be manually controlled or, preferably, controlled by a controller 30 that controls various other systems of the exemplary embodiment of the present invention. The controller itself will receive various control inputs from the control input device 32 including switches such as a manual control switch, a switch indicating that an active disk is being loaded properly, a switch indicating that another active disk is in the loaded position, etc., and typically also including a keyboard and control display for menu driven or click graphical control, or both as desired.

The loading system used in this embodiment of the present invention, and more particularly the disk positioning device in the inspection system, includes an electrical contact system, generally designated by the numeral 34, for automatically contacting the peripheral region surrounding the active disk 20. Generally, the pad is tested either electrically in situ using shorting bar 18 (FIG. 1) (see U.S. Pat. No. 5081687, the contents of which are incorporated herein by reference) or by contacting the end regions of the row and column lines on the active pad. Such delivery systems and systems for contacting the periphery of an active disk are generally known in the art, including systems produced by Dynamics, inc.

As seen in fig. 2 and 3, the visible light camera 22 and the voltage imaging sensor 24 are both supported on an XY transport system, indicated by the numeral 36, which is controlled by the controller 30 through an XY control system 38. Since manual Z-axis adjustment may be part of the setup step for inspection and testing of a specifically designed active disk, automatic control of the visible light camera along the Z-axis by Z-control 37 and the voltage imaging sensor along the Z-axis by Z-control 39 is optional and not necessary. Preferably, the motion in the XY plane is controlled by any known X and Y linear transport system, although other transport systems capable of sweeping through an area, such as a rectangular area, may be used, such as a rho-theta transport system. However, XY transport systems are preferred because of their more straightforward applicability to step and repeat imaging inspection techniques typically used in active pad inspection.

In addition, the visible light camera is controlled by a camera control 40 controlled by the controller 30 according to functions such as image acquisition, focal length, and the like. Similarly, the function of the voltage imaging sensor is controlled by a control 46 controlled by the controller 30.

Generally, testing procedures for visible light cameras are well known in the art. The output of the visible light camera will be digitized and stored (block 48), with an image processor 50 providing image analysis of the acquired image. Typically, digitization and storage, as well as image processing, are controlled by controller 30 to synchronize with the motion of the transport system and the operation of the camera. Similarly, the voltage imaging sensor 24 will provide an image that is digitized and stored in block 52 and analyzed by the image processor 54, which is also synchronized by the controller 30 as the active disk array is operated on by the array operator 56, which provides control voltages to the array. Generally, displays 58 and 60 will be provided to allow viewing of visible light images and voltage images. Alternatively, a single display may be provided, preferably coupled to be able to display either a visible light image or a voltage image, or even to have the two images side-by-side or proportional and overlapping as desired. Finally, a pass/fail determination is made and a report is provided based on the results of the processing of the two images (box 62).

Referring to fig. 4 and 5, another exemplary embodiment of the present invention can be seen. In this embodiment, a visible light inspection system is combined with an electron beam testing system. The XY control 38 (fig. 4), Z control 37, XY transport system 36, disk contacts 34, camera control 40, visible light camera 22, digitizing and storage circuit 48, display 58, and image processor 50 may be identical or substantially identical to those used in the previous embodiments.

For packaging of the inspection and test system of the present embodiment, a vacuum environment is required for the electron beam and sensor 24'. Thus, package 26' in this embodiment is a vacuum package that can be drawn to the vacuum range characteristics of prior art e-beam test equipment. In addition, as is characteristic of the prior art e-beam test apparatus, a second vacuum lock and disk load chamber 64 is provided. The vacuum chamber 64 is a small and simple chamber that can be opened for loading or unloading active disks and can be conveniently evacuated to a desired vacuum level so that the active disks to be tested can be transferred from the vacuum chamber 64 to the main enclosure 26 ' and the inspected active disks can be transferred from the main enclosure 26 ' to the vacuum latches 64 without opening the main vacuum chamber 26 '. This avoids having to repeat the evacuation of the larger vacuum enclosure 26' and the equipment therein that may slowly release air trapped therein. Although not shown, a second vacuum chamber may be used if desired so that during testing of a disc, the apertures of both latching chambers may be opened, one for releasing the previously tested disc, one for receiving the next disc to be tested, and then both are drawn to the required vacuum, one at the end for receiving the disc being inspected and tested and the other for loading the next disc to be inspected and tested immediately thereafter.

As in the case of using the voltage imaging sensor of fig. 2 and 3, electron beam testing of the active array 20 is performed, with the voltage across the array controlled by the array operator 56 'being controlled by the controller 30'. The electron beam control 46 ' controls the scanning of the electron beam over the active disk surface and provides information about the position of the electron beam, so that the output of the sensor is digitized and stored (box 52 '), and provides scanning information for the display 60 '. The image processor 54 'is used to analyze the image information of the electron beam and provide the results of the inspection and testing, along with the output of the vision image processor 50, to the decision-making module 62' to provide a final inspection test report. The electron beam generator and sensor 24 'may be controlled by the Z-axis control 39' in the Z direction, although previously the Z-axis control may be a manual control or adjustment as part of the initial setup for inspection and testing of specially designed active disks.

Referring to fig. 6 and 7, there can be seen a block diagram for another exemplary integrated inspection test system and a schematic diagram of a transport system for the system, specifically a system that combines inspection with a visible light camera and array testing with charge detection. In this system, only the transport system 36 "for the visible light camera 22 is required, since the tests with charge detection are all electronic. In the embodiment of fig. 6 and 7, the disk loading system may be the same as that used in fig. 2 and 3, with the array 20 being electrically operated by the array operator 56 ", the charge measurement being taken in block 66, and the results being provided to the decision module 62" for providing an inspection test report.

The visible light camera inspection system and the voltage imaging inspection system disclosed herein are disclosed above in the context of a reflective system, but pass-through systems are also known in the art. For example, in a visible light camera pass-through system, the light source and the visible light camera are located on opposite sides of the active disc. Similarly, in a pass-through voltage imaging system, the source and camera of the polarized array of light are located on opposite sides of the active plate (see, for example, U.S. patent No. 4983911 to Photon Dynamics, inc., assigned to the assignee of the present invention). Such a system is not preferred, in part because of the relatively high complexity required of the transport system, and if desired, one or both of the visual image inspection system and the voltage imaging system used by the present invention may be of the pass-through type.

Of course, the control systems disclosed in fig. 2, 4 and 6 are merely exemplary. In general, various functions identified herein may be performed or altered as desired under program control using one or more processors. Further, while the inspection and testing systems disclosed herein are disclosed herein in terms of processing information obtained from the inspection system (visible light) and the applicable electrical testing system individually, the images may be digitized and analyzed by sharing the computer equipment needed for multiple systems. Further, one of the advantages of the present invention is the ability to access both inspection and test information, which has considerable discretionary value for acceptance/elimination, repair/scrap decisions, and process control purposes.

While one of the advantages of the preferred embodiment of the present invention is the savings realized by sharing a single conveyor system with multiple sensors, multiple conveyor systems may be used if desired. This still retains the economy of sharing electronics, packaging and reducing floor space compared to a separate system, and the advantages of reduced handling of the disc and combined inspection and testing results while the disc remains in the system. However, there are certain limitations caused by integrating two transport systems in a single station or component. One of the limitations is the physical limitation that the visible light camera and the voltage imaging sensor or the electron beam source and sensor and the corresponding transport system do not collide with each other. Generally, the voltage imaging sensor and the electron beam sensor should be located close to the surface of the active disk, while the visible light camera 22 is usually located approximately above the surface of the active disk. Therefore, it is possible to easily locate the transport system of the visible-light camera sufficiently above the transport system of the voltage imaging sensor/electron beam sensor, so that the XY transport system can be easily configured without any collision. However, this is possible when Z-axis control is performed on the visible light camera 22, i.e., the camera, especially when in a lower position, may collide with the voltage imaging sensor. In this case, the controller must be programmed to abnormally lift the visible light camera vertically whenever the visible light camera is within a predetermined proximity to the voltage imaging sensor. This limitation is very easily adjusted by a person skilled in the art using software, although it is possible to choose to design the transport system such that, in case of some kind of failure causing a collision, the two transport systems will be temporarily stopped without damaging each other, or one pushes the other away without damaging the other. As another alternative, if the visible light inspection and the voltage imaging inspection/electron beam inspection are not performed simultaneously, the voltage imaging sensor/electron beam sensor may have a parking position on the side of the active disk to be inspected, the visible light camera may have its own parking position on the side of the active disk to be inspected, and the other may scan the active disk alone while the one is in the parking position, thereby preventing any possibility of collision. However, it does have the disadvantage of negating the possibility of performing an examination simultaneously using both examination techniques.

Another limitation is the optical limitation, i.e., the limitation that the field of view of the visible light camera is not obstructed by the voltage imaging sensor/electron beam sensor or any part of its transmission system. This is also easily adjusted by software if it is desired that both systems operate simultaneously, and if not, can be avoided entirely by locating the placement away from the edge of the active disk being inspected, as previously described.

Certain specific embodiments of the present invention have been described herein. However, the disclosed embodiments are merely exemplary, as the invention may be practiced in many ways that are not specifically described herein. Thus, while certain preferred embodiments of the present invention have been disclosed, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims (22)

1. A device for inspecting an active plate of a liquid crystal display, the active plate having a matrix of active elements coupled to row and column lines on a first side and a second side of the active plate, comprising:

in a single inspection station, a holder adapted to hold the active plate and in electrical contact with the row and column lines on a first side of the active plate, a visual image camera in a position to provide visual image data of the active plate in the holder, and an electronic sensor disposed proximate to the first edge of the active plate adapted to detect operation of the active plate;

a processor electrically coupled to the holder so as to electrically couple to and electrically operate the active pads in the holder;

a visual image processor coupled to the visual image camera, receiving visual image data of the active disk in the holder and processing the visual image data to detect defects in the active disk; and

an electronic sensor output processor is electrically coupled to the electronic sensor for processing the electronic sensor output to detect defects in the operation of the active plate.

2. The apparatus of claim 1, wherein the electronic sensor comprises a voltage image sensor.

3. The apparatus of claim 1 wherein the inspection station comprises a first vacuum chamber and the electronic sensor comprises an e-beam sensor.

4. The apparatus of claim 3, wherein the inspection station further comprises a second vacuum chamber coupled to said first vacuum chamber for loading and unloading active disks into and from said holder in said first vacuum chamber.

5. The apparatus of claim 1, wherein the visual image camera is mounted on a visual image transfer system for moving the visual image camera over an area parallel to the active disk in the holder.

6. The apparatus of claim 5, wherein the visual image delivery system comprises visual camera motion in a direction perpendicular to an active disk in a holder.

7. The apparatus of claim 1, wherein the electronic sensor is mounted on an electronic sensor transport system for moving the electronic sensor in an area parallel to an active disk in a holder.

8. The apparatus of claim 1, wherein the visual image camera is mounted on a visual image transfer system for moving the visual image camera over an area parallel to an active plate in a holder, and the electronic sensor is mounted on an electronic sensor transfer system for moving the electronic sensor over an area parallel to an active plate in a holder, the electronic sensor transfer system being located between the active plate in a holder and the visual image transfer system.

9. The apparatus of claim 8, further comprising a controller coupled to the visual image camera, the visual image transfer system, the electronic sensor, and the electronic sensor transfer system to provide simultaneous step and repeat scanning of the active disk by the visual image camera and the electronic sensor without mechanical interference with each other and without interference of the electronic sensor with the visual image of the active disk by the visual image processor.

10. A device for inspecting an active plate of a liquid crystal display, the active plate having a matrix of active elements coupled to row and column lines on a first side and a second side of the active plate, comprising:

a holder in the single inspection station adapted to hold the active plate and in electrical contact with the row and column lines on a first side of the active plate, and a visual image camera providing visual image data of the active plate in the holder;

a processor electrically coupled to the holder so as to electrically couple to the active plate in the holder and to charge and thereafter discharge each transistor in the matrix on the active plate to measure the charge remaining on the active plate to detect an electrical defect in the active plate; and

a visual image processor coupled to the visual image camera, receiving visual image data of the active disk in the holder, and processing the visual image data to detect a visual defect in the active disk.

11. The apparatus of claim 10, the visual image camera mounted on a visual image transfer system for moving the visual image camera in an area parallel to an active disk in a holder.

12. The apparatus of claim 11, wherein the visual image delivery system comprises visual camera motion in a direction perpendicular to an active disk in a holder.

13. A method for inspecting an active pad having a matrix of active elements coupled to row and column lines on a first side and a second side of the active pad, comprising the steps of:

locating an active disk in an inspection station;

electrically contacting the row and column lines on a first side of the active pad to operate the active elements on the pad;

inspecting the active disc with a vision camera to detect visually observable defects; and is

The active disk is inspected using an electronic sensor adapted to detect defects of the active disk in operation.

14. The method of claim 13, wherein inspecting the active plate with the electronic sensor comprises inspecting the active plate with a voltage image sensor.

15. The method of claim 13, wherein positioning the active disk in the inspection station comprises positioning the active disk in a vacuum environment in the inspection station, and inspecting the active disk with the electronic sensor comprises inspecting the active disk with an e-beam sensor.

16. The method of claim 14, further comprising loading and unloading the active disk into and out of the inspection station through the second vacuum environment.

17. The method of claim 13, wherein inspecting the active disk with the vision camera comprises inspecting the active disk with the vision camera by moving the vision camera in a step and repeat manner in a region parallel to the active disk in the holder.

18. The method of claim 17, wherein inspecting the active disk with the vision camera comprises moving the vision camera in a direction perpendicular to the active disk in the holder.

19. The method of claim 13, wherein inspecting the active disk with the electronic sensor comprises inspecting the active disk with the electronic sensor by moving the electronic sensor in a step and repeat manner in a region parallel to the active disk in the holder.

20. The method of claim 13, wherein inspecting the active disk with the vision camera comprises inspecting the active disk with the vision camera by moving the vision camera in a step and repeat manner in a region parallel to the active disk in the holder, and inspecting the active disk with the electronic sensor comprises inspecting the active disk with the electronic sensor by moving the electronic sensor in a step and repeat manner in a region parallel to the active disk in the holder.

21. The method of claim 20, further comprising controlling the visual image camera and the electronic sensor to provide simultaneous scanning of the active disk by the visual image camera and the electronic sensor in a step and repeat manner without mechanically interfering with each other and without the electronic sensor interfering with the visual image of the visual image camera.

22. The method of claim 13, wherein inspecting the active pads with the electronic sensor comprises charging each transistor in the matrix on the active pads and thereafter discharging to detect the charge remaining on the active pads to detect electrical defects in the active pads.