AUTOMATED OPTICAL LINEWIDTH MEASUREMENT

Optical metrology method and apparatus in which the sheared portions of an optical image are automatically aligned so as to enable the widths of high contrast lines to be measured using optical image shearing. A mechanism splits a line image of an object into two, shears the two images and records the displacement distance, and an imaging system e.g. a television camera generates an electronic signal which represents the intensity profile of the sheared image in a direction perpendicular to the line image and parallel to the direction of shear. The intensity profile of the sheared image is sampled and digitized, and the digital signal is correlated with a digital filter. A mechanism then adjusts the shearing to a position given by an electronic signal, and the two positions taken up by the shearing mechanism are recorded, the difference therebetween is calculated, and then multiplied by a calibration constant, to provide line width information to be displayed on a display device.