Patent ID: 6219442
Filing Date: 2001-04-17
Classification: G01N

Abstract:
Apparatus for determining characteristics of a visible pattern on a substrate during an inspection process, wherein said apparatus comprises:a holder holding said substrate stationary during said inspection process, wherein said holder is divided into quadrants for engaging corners of said substrate, with a first quadrant being stationary, with a second quadrant being movable in a first direction in alignment with said first quadrant, with a third quadrant being movable in a second direction, perpendicular to said first direction, in alignment with said first quadrant, and with a fourth quadrant being movable in alignment with said second and third quadrants;a plurality of camera units aimed at said visible pattern, wherein each camera unit within said plurality thereof is aimed at a different field of view in a spaced-apart relationship with fields of view of each other camera unit within said plurality thereof, and wherein each camera unit within said plurality thereof produces an electronic camera output signal indicative of features of a portion of said visible pattern during said inspection process, wherein said plurality of camera units includes four camera units, each of which has a field of view including a corner of a rectangular portion of said visible pattern, wherein a first camera unit is held stationary with said first quadrant, with a field of view of said first camera unit extending along a portion of said substrate held within said first quadrant, wherein a second camera unit is moved with said second quadrant, with a field of view of said second camera unit extending along a portion of said substrate held within said second quadrant, wherein a third camera unit is moved with said third quadrant, with a filed of view of said third camera unit extending along a portion of said substrate held within said third quadrant, and wherein a fourth camera unit is moved with said fourth quadrant, with a field of view of said fourth camera unit extending along a portion of said substrate held within said fourth quadrant; andcomputing means responsive to each said camera output signal during said inspection process for determining whether features of said visible pattern are within pre-determined limits, wherein said computing means is additionally operable during a calibration process, occurring before said inspection process, for determining calibration factors to be applied to said camera output signals during said inspection process, wherein each camera unit within said plurality thereof is held stationary during both said calibration process and said inspection process, wherein said computing means determines angular and linear locations of each camera unit within said plurality thereof during said calibration process from said camera output signals indicative of features in pre-determined locations on said calibration substrate, and wherein said computing means determines an overall size of said visible pattern from said camera output signals from said four camera units.