Optics: measuring and testing – Inspection of flaws or impurities – Surface condition
Reexamination Certificate
2001-09-04
2004-11-23
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Surface condition
C356S601000
Reexamination Certificate
active
06822734
ABSTRACT:
FIELD OF INVENTION
The present invention relates to the fabrication and inspection of flat workpieces in general and more particularly to the fabrication and inspection of flat articles such as flat panel display screens (FPDs) for computers, television and other suitable applications.
BACKGROUND OF THE INVENTION
Flat panel visual displays such as liquid crystal displays (LCDS) are becoming increasingly popular for use in computer and television screens. However their cost remains high, in part, due to relatively low manufacturing yields.
There exist various well known techniques for FPD fabrication. Most of these techniques comprise a multi-step photolithographic process in which various thin films and photo-sensitive protective photoresist coatings are applied in turn to a glass substrate. The thin films may be metallic, non-metallic dielectric or the like depending on the particular process step. The photoresist coatings are selectively exposed, typically to UV light, developed and selectively washed away from the substrate. The thin films are etched to selectively remove regions not protected by residual photoresist. Repetition of this process deposits on the substrate a multi-layered matrix structure of metal connectors, thin film transistors, optical filters such as polarizors, and individually controllable liquid crystal cells.
Various steps in the FPD fabrication process are highly sensitive to airborne and other impurities as well as to process defects. Unfiltered air typically contains many millions of airborne particles, such as dust, per cubic meter. Conventional FPD fabrication techniques require that the maximum level of airborne particulate concentration range between 10-100 particles per cubic meter, depending on the sensitivity of the given process step.
Consequently, FPDs are typically fabricated in environments containing highly filtered air thus providing reduced contamination by airborne particles.
FPD fabrication facilities are typically situated in so-called “clean rooms” in which the ambient air is filtered to maintain a level of airborne particulate contamination which is at the upper end of the above-mentioned concentration range, typically at a concentration level of less than 100 airborne particles per cubic meter. This level of particulate contamination is insufficiently low for some fabrication steps. However, it is generally impracticable, because of cost and limitations on human access, to maintain large volumes of air in a clean room at the low levels of airborne particulate concentration required for such extremely contamination-sensitive fabrication steps. Consequently. FPD fabrication equipment performing steps requiring an even lower level of airborne particulate concentration typically includes a self-contained ultra clean micro-environment in which a required low level of airborne particulate concentration is maintained. Other types of FPD fabrication equipment define a micro-environment which may not differ from those of the clean room in terms of its airborne particulate concentration, but which differs in other characteristics.
In a typical FPD fabrication facility, human attendants are permitted into the clean room facilities having maximum concentration levels as low as 100 particles per cubic meter, however the attendants must be suitably dressed in protective clothing. Human attendants, even in suitable dress, typically can not access self-contained micro environments of fabrication equipment during operation thereof. Consequently, fabrication equipment operating is typically fully automated and is operational without human intervention.
It is well known to inspect FPD substrates during and following fabrication. Conventional automated inspection techniques are directed to ascertaining the uniformity of a matrix structure deposited on a glass substrate, determines whether dust has been trapped in intermediate matrix layers on the FPD, and ascertaining the performance of completed FPD panels. In addition non-automated human inspection is used to determine the existence of large scale process defects, generally visible to the human eye, such as chemical residues that have not been fully washed away, streaks, scratches and uneven exposure of the photoresist. The present invention relates to inspections of this latter type, namely large scale process defects.
Conventionally, all inspection of FPD substrates is performed in a clean room but outside the self-contained ultra-clean micro environments of the FPD fabrication equipment. A batch of substrates is typically inspected only after a series of process steps is completed. There is often a considerable time delay between the completion of a fabrication process and inspection. In the event of recurring contamination or recurring process flaws, many conventional automated system for inspecting FPD substrates during fabrication for ascertaining the uniformity of the matrix structure deposited on the glass substrate and determining whether dust has been trapped in intermediate matrix layers thereof, is commercially available from the present assignee, Orbotech Ltd. of Israel, and is designated by catalogue no. LC 3090. Part of this system is described and claimed in U.S. Patent
The existing Orbotech system described above is not normally used for identifying many typical fabrication large scale process defects on FPD substrates because it collects data relating to a matrix structure having dimensions that are orders of magnitude smaller than those of typical process defects. Moreover, because the system scans the substrates, it is physically relatively large, expensive and complex to operate.
Human inspection for process defects is conventionally performed by an operator situated inside the clean room who positions a substrate under a light source to inspect it for undesired residues, streaks, scratches and other relatively large scale anomalies on the substrate. While such inspection can be useful to detect certain large scale fabrication process defects, it takes place outside the self-contained micro environment of contamination-sensitive process equipment and it suffers from the typical high cost and non-standardization associated with non-automated human inspection methods.
Other types of inspection, typified by the disclosure of U.S. Pat. No. 5,771,068, assigned to the present assignee and incorporated herein by reference, are conventionally used to inspect FPDs that are sufficiently completed to enable selective activation of pixels. According to an embodiment described in U.S. Pat. No. 5,771,068, various combinations of pixels are illuminated and a relatively low resolution staring array sensor images the entire substrate as the various combinations are illuminated. The images are analyzed for variations in intensities. This type of inspection is clearly not suitable for inspection FPD substrates in intermediate stages of fabrication.
Additional publications that are believed to be relevant to the art of inspecting for large scale defects and non-conformities on surfaces of articles include U.S. Pat. No. 5,640,237 and Japan Patent Application 11-94753.
SUMMARY OF INVENTION
The present invention seeks to overcome drawbacks of conventional FPD inspection systems and to provide an improved system and method for automated inspection of FPDs and other flat surfaces.
The present invention further seeks to provide an FPD manufacturing system having increased yield.
The present invention still further seeks to provide an automated system for inspecting FPDs which is less expensive and more compact in size than conventional automated scanning FPD inspection systems.
Additionally the present invention seeks to provide a system operative to inspect FPD substrates inside the self-contained ultra-clean micro environment of equipment performing contamination-sensitive FPD fabrication processes.
One aspect of a preferred embodiment of the invention relates to a system and method for the manufacture of FPDs using contamination-sensitive fabrication equipment having a self-contained micro environ
Eidelman Doron
Fisch David
Gross Avi
Noy Amir
Barth Vincent P.
Ladas & Parry
Orbotech Ltd.
Rosenberger Richard A.
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