Optical line width measuring apparatus and method

Claim 1

In an apparatus for optically testing the lateral dimensions of a diffraction pattern of material disposed on a substrate, said diffraction pattern comprised of a planar array of spaced strips of material having a strip width a and a periodicity d, said apparatus including means for exposing said diffraction pattern to a beam of monochromatic light to diffract said beam into diffracted beams of various orders, detector means including detectors for measuring the intensity of at least two of the diffracted beams to obtain at least two intensity signals and means responsive to said intensity signals for determining the width a of said strips, wherein the improvement comprises: means for moving said detectors to respective positions in a plane to intercept said diffracted beams, said intercept plane being orthogonal to said diffraction array strips; wherein said detector moving means includes a pair of pivotal arms having a respective one of said detectors connected at one end of each arm, said arms being pivotally connected for rotation about an axis lying in an extension of and parallel to said diffraction array strips; further including means to control the spacing between said detectors to a predetermined value corresponding to the periodicity d; and wherein said detector spacing means includes: a pin on each of said pivotal arms; a guide member including means for positioning said guide member in a direction parallel to the plane of said diffraction array strips and perpendicular to said pivotal arms axis; and a slot in said guide member extending orthogonally to the direction of movement of said guide member and adapted to receive each of said pins to effect pivotal movement of said arms as said guide member is moved, the distance between each pin and the pivotal axis of said arms and the position of said guide member defining thereby the respective positions of said detectors.