Alignment correction prior to image sampling in inspection systems

Abstract

A method and apparatus, and variations of each, for inspecting a wafer defining at least one die thereon is disclosed. The present invention first obtains the electronic image equivalent of two die, and then determines the x and y offset between those electronic images. Prior to inspection for defects, those two electronic images are aligned by adjusting the x and y positions of one electronic image of one die with respect to the electronic image of the other die. Once that is accomplished, the those electronic images are compared to detect any defects that may exist on one of the die.

1 . A method for inspecting a wafer defining at least one die thereon, said method comprising the steps of: 
 a. obtaining the electronic image equivalent of two die;    b. determining the x and y offset between the electronic images of said two die of step a.;    c. aligning said electronic images of said two die by adjusting the x and y positions of one electronic image of one die with respect to said electronic image of said other die;    d. comparing said electronic images from step C.;    e. identifying image differences between the two die compared in step d.    
   
   
       2 . An apparatus to inspect a wafer defining at least one die thereon comprising: 
 an x-y stage to transport said die;    a scanner to obtain an electronic image equivalent of said at least one die as said x-y stage transports said die;    a first comparator coupled to said scanner to determine the x and y offset between the electronic images of two die;    an alignment computer to reposition said scanner to adjust the x and y positions of one electronic image of one die with respect to said electronic image of said other die;    a second comparator coupled to said scanner to compare said electronic images of said first and second die following the operation of said alignment computer; and    a defect detector coupled to said second comparator to identify defect differences between said electronic images compared by said second comparator.