Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Reexamination Certificate
1992-12-03
2001-07-03
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
C356S239100
Reexamination Certificate
active
06255666
ABSTRACT:
FIELD OF THE INVENTION
This invention generally relates to optical apparatus and methods, and relates, more specifically, to an optical inspection apparatus and method for detecting faults in a flat, polished flat panel, such as those commonly used in Liquid Crystal Display (LCD) panels. This apparatus inspects with high resolution at high speed with automatic handling of the flat panel to allow the apparatus to be used effectively in a production inspection environment.
DESCRIPTION OF THE PRIOR ART
Flat panels for LCD panels require a surface that is flat to a high degree of accuracy, and that is free from defects such as scratches and chips. Some optical inspection systems have been used with limited success in inspecting transparent flat panels, but do not provide the accuracy or speed that is needed in a production environment.
Dark field microscopes and scatterometers are inspection apparatus well-known in the art. A dark field microscope can somewhat accurately locate surface defects, but takes too long to inspect to be effectively used in a production environment. A scatterometer is faster than a dark field microscope, but has less accuracy (detects fewer defects). Both the dark field microscope and the scatterometer have low detection sensitivity to shallow defects or defects that have a depth less than the wavelength of the light used, which cause a phase shift in the light beam but do not diffuse (scatter) the light in different directions. An interferometer, which is well-known in the art, is suitable to detecting phase shifts, but takes substantial time and effort to set up, limiting its use to laboratory environments.
The inherent limitations of the prior art inspection systems have limited their use in industrial production environments. Indeed, the most common inspection method used in a production environment is a manual, visual inspection by human inspectors, which hold the flat panel in their hands and move the flat panel in ambient or special light looking for the presence of scratches, chips and other defects. This inspection method is labor intensive, relatively slow, and subject to human errors such as missed defects which the human eye cannot easily distinguish.
Therefore, there existed a need to provide a high speed optical inspection system and method which has a high sensitivity to defects which can be used to inspect transparent flat panels in a production environment. This inspection system includes automatic handling of the flat panels, high speed inspection, and high resolution to detect defects smaller that the spot size of the beam and/or more shallow than the wavelength of light used. The increased speed of this apparatus increases throughput of the production system, and assures that any mistakes or defects introduced by human inspectors is eliminated.
SUMMARY OF THE INVENTION
It is an object of this invention to provide a high-speed optical inspection apparatus and method suitable for production testing of transparent flat panels.
It is another object of this invention to provide a high speed optical inspection apparatus and method which is computer-controlled using an IBM PC-AT computer or equivalent.
It is a further object of this invention to provide a high speed optical inspection apparatus and method with surface inspection which has a high speed optical scanner to provide linear movement of the beam across one axis of the flat panel, and a flat panel actuator to move the flat panel, thereby positioning each portion of the flat panel in the path of the linear movement of the beam, thereby completely inspecting the entire face surface of the flat panel.
It is yet another object of this invention to provide a high speed optical inspection apparatus and method which has an Automatic Flat Panel Handler for automatically loading the flat panels into the apparatus and for automatically unloading the flat panels from the apparatus.
It is a still further object of this invention to provide a high speed optical inspection apparatus and method which detects both phase and amplitude changes of the light beam using multiple detectors to sense changes in the nominal Gaussian distribution of the light beam.
It is yet another object of this invention to provide a high speed optical inspection apparatus and method which has a trigger detector within the path of the scanning light beam to provide a signal to synchronize the controlling computer to the scan of the light beam.
According to the preferred embodiment of the present invention, an optical inspection apparatus for inspecting a transparent flat panel is provided. This inspection apparatus is controlled by an IBM PC-AT computer or equivalent, and has a typical color monitor, printer and keyboard. An Optical Inspection Assembly is provided which comprises a Surface Inspection Assembly. The Surface Inspection Assembly nominally comprises a laser light source which transmits a light beam, a high-speed Optical Scanner, Scanning Optics, a beam splitter, optional Detection Optics, and a Parallel Detector Array within a Detector. In this configuration the light beam in the Surface Inspection Assembly originates in the laser, is transmitted through a filter, and is transmitted to the Optical Scanner, which reflects the light beam off the moving polygonal scanner head, causing the light beam to sweep across the Scanning Optics.
The size of a flat panel can be much greater than the size of a practical lens. Placing the Optical Scanner at a distance from the Scanning Optics less than the focal length of the Scanning Optics causes the light beam to diverge at the Scanning Optics, making the beam sweep a distance larger than the diameter of the lens. The beam is focused at the center of the transparent flat panel media by the Scanning optics. On the opposite side of the flat panel is a strip of a spherical mirror which reflects the divergent beam back through the Scanning Optics to the Optical Scanner. This reflected beam is distinguished from the transmitted beam using a beam splitter between the laser and the Optical Scanner. The reflected beam is then directed to the Parallel Detector Array, which detects defects in the flat panel above a programmable threshold. This array is typically a matrix of photodiodes or Charge-Coupled Devices (CCDs) upon which the light beam is projected. This matrix configuration provides a two dimensional Gaussian response with respect to light intensity (amplitude). Any defect in the flat panel deflects light from the Parallel Detector Array (causing a change in the nominal light level) or shifts its phase (causing a change in the Gaussian distribution), both of which are detected by the processing electronics coupled to the Parallel Detector Array. Thus the processing electronics simply look for changes in the nominal level or distribution of the Gaussian response provided by the Parallel Detector Array in response to a nominal light beam, which changes correspond to surface defects an a transparent flat panel.
In this preferred embodiment, the flat panel is placed on an actuator that positions the flat panel such that the scanning begins at the top of the flat panel and moves down. Once the Optical Scanner beam completes one scan, the panel is raised to the next position, and the scanning continues in like manner until the entire surface of the flat panel has been inspected. The computer controls the movement of the flat panel to assure the entire surface is scanned. If the Surface Inspection Assembly detects a defect greater than its programmed threshold, a fault signal is sent to the computer to indicate the flat panel failed the inspection.
The foregoing and other objects, features and advantages will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.
REFERENCES:
patent: 3900265 (1975-08-01), Merlen et al.
patent: 4265545 (1981-05-01), Slaker
patent: 4376583 (1983-03-01), Alford et al.
patent: 4455086 (1984-06-01), West et al.
patent: 4570074 (1986-02-01), Jette
patent: 4725139 (1988-02-01
Brunfeld Andrei
Laver Ilan
Pekel Ely
Shamir Joseph
Singher Liviu
Allen Stephone B.
Brown & Sharpe Surface Inspection Systems, Inc.
Wolf Greenfield & Sacks P.C.
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