Method and apparatus for flat patterned media inspection

Abstract

A concurrent low resolution/high resolution parallel scanning system is provided as an improvement in the scanning process of an inspection system for planar objects, such as large flat plates employed in panel displays, whereby lower resolution defect detection efficiently overlaps and parallels higher resolution defect review and classification stages in which defects are automatically defined and resolved. Although the invention is a valid solution for the more general problem of optically inspecting the surface of a flat article for defects, the invention is particularly useful for detecting pattern defects on large glass plates deposited with integrated-circuits for forming LCD flat panel displays.

What is claimed is:  
     
         1 . A method for flat patterned media inspection comprising: 
 detecting for defects of the flat patterned media through an on-the-fly automatic focus imaging means using a relatively lower resolution protocol; while concurrently    reviewing, using a relatively higher resolution protocol, defects which have been noted by said detecting step.    
     
     
         2 . A method for concurrent on-the-fly defect detection, review and classification of phenomena in an object under test comprising the following parallel operations: 
 acquiring and detecting images of the object through a defect detection subsystem having a plurality of defect detection sub-system modules according to a first relatively lower operating resolution; while concurrently    acquiring, reviewing and classifying portions of the images through a defect review sub-system having a plurality of defect review sub-system modules using a relatively higher resolution.    
     
     
         3 . The method according to  claim 2  comprising: 
 constructing a forward flow graph with nodes corresponding to defect candidates and current position of one of the defect review sub-system modules, and with arcs corresponding to feasible motions from the current position for the defect review subsystem module to first selected defect candidates and in between second selected defect candidates;  
 for each arc signifying a module move from one defect candidate to another defect candidate, associating costs to arcs as a function of cost factors, including a cost of missing other defects, distance of necessary motion, and worthiness of a captured defect to obtain a resulting graph;  
 solving the resulting graph for minimum cost path from the current location of the defect review sub-system module to an end of a y-axis window considered; and  
 computing motion data for the defect review sub-system module for controlling motion of the defect review sub-system module.  
 
     
     
         4 . The method according to  claim 2  comprising: 
 beginning at a pre-determined distance from a target candidate location, and during the motion of the defect review sub-system module, capturing a sequence of image data from an imaging element of the defect review sub-system module;  
 using the sequence of image data in combination with a focus quality measure computed over the images to sample a focus quality curve;  
 interpolating the samples of the focus quality curve with a smoothing function to determine a maximizing focus point for a z-stage moving the focusing optics; and  
 directing the z-stage to a the z-axis position which maximizes the said focus quality metric curve to achieve sharpest focus of the target candidate location.  
 
     
     
         5 . The method according to  claim 2  comprising: 
 generating in the defect detection sub-system, a sequence of defect candidates;  
 queuing and scheduling the sequence for imaging by a plurality of the defect resolution sub-system modules;  
 dispatching the defect resolution sub-system modules to perform relatively higher resolution imaging of outstanding defect candidates to create a sequence of defect candidates associated with the relatively higher resolution image data;  
 causing the defect candidates to experience a two stage processing involving: 
 an automatic review process; and  
 an automatic classification process;  
 
 during the automatic review process, comparing the high resolution candidate image with a reference image stored in system memory of known defect status, wherein the comparing comprises compensating for known variations between test and reference including correcting for at least one of the following: 
 imaging instrument sensitivities and sensor pixel sensitivity variations;  
 
 compensating for spatial misalignment at sensor pixel level to result in either the validation of the existence of a legitimate defect at the candidate location or rejection of the defect as a false defect, including an artifact of known limitations of the low resolution DDS sub-system;  
 conveying information on legitimate defects to for automatic classification processing; thereafter 
 during automatic classification processing, using the relatively higher resolution defect image in combination with output of the automatic classification processing to extract relevant features of the defect; and  
 making a final decision on type of the defect through the classification processing.  
 
 
     
     
         6 . An apparatus for flat patterned media inspection comprising: 
 a detection sub-system for detecting defects through an on-the-fly automatic focus imaging means using a relatively lower resolution protocol; and    a review sub-system for reviewing defects noted by said detection sub-system using a relatively higher resolution protocol.    
     
     
         7 . An apparatus for concurrent on-the-fly defect detection, review and classification of phenomena in an object under test comprising: 
 a defect detection sub-system having a plurality of defect detection sub-system modules for acquiring and detecting images of the object according to a first relatively lower operating resolution; and    a defect review sub-system having a plurality of defect review sub-system modules for acquiring, reviewing and classifying portions of the images using a relatively higher resolution.    
     
     
         8 . The apparatus according to  claim 7  wherein the defect detection subsystem is mounted on a first moveable gantry and the defect resolution sub-system is mounted on a second moveable gantry.  
     
     
         9 . The apparatus according to  claim 7  wherein the defect detection subsystem comprises a plurality of detection modules fixedly mounted on a first moveable gantry and the defect resolution sub-system comprises a plurality of resolution sub-system module mounted for motion along on a second moveable gantry.  
     
     
         10 . The apparatus according to  claim 9  wherein motion of first ones of said resolution modules are limited by position of second ones of said resolution modules and further including a controller for: 
 constructing a forward flow graph with nodes corresponding to defect candidates and current position of one of the defect review sub-system modules, and with arcs corresponding to feasible motions from the current position for the defect review sub-system module to first selected defect candidates and in between second selected defect candidates;  
 for each arc signifying a module move from one defect candidate to another defect candidate, associating costs to arcs as a function of cost factors, including a cost of missing other defects, distance of necessary motion, and worthiness of a captured defect to obtain a resulting graph;  
 solving the resulting graph for minimum cost path from the current location of the defect review sub-system module to an end of a y-axis window considered; and  
 computing motion data for the defect review sub-system module for controlling motion of the defect review sub-system module.